Petrography and geochemistry characteristics of the lower Cretaceous Muling Formation from the Laoheishan Basin, Northeast China: implications for provenance and tectonic setting

NASA Astrophysics Data System (ADS)

Song, Yu; Liu, Zhaojun; Meng, Qingtao; Wang, Yimeng; Zheng, Guodong; Xu, Yinbo

2017-06-01

The petrography, mineralogy and geochemistry of sedimentary rocks from the lower Cretaceous Muling Formation (K1ml) in the Laoheishan basin, northeast (NE) China are studied to determine the weathering intensity, provenance and tectonic setting of the source region. Petrographic data indicate the average quartz-feldspar-lithic fragments (QFL) of the sandstone is Q = 63 %, F = 22 %, and L = 15 %. Lithic fragments mainly contain volcanic clasts that derived from surrounding basement. X-ray diffraction (XRD) data reveal abundant clay and detrital minerals (e.g. quartz), as well as minor calcite in the fine-grained sediments. The Hf contents and element concentration ratios such as Al2O3/TiO2, Co/Th, La/Sc, and La/Th are comparable to sediments derived from felsic and intermediate igneous rocks. The strong genetic relationship with the igneous rocks from the northwest and northeast areas provides evidence that the sediments of the Muling Formation (K1ml) in the Laoheishan basin have been derived from this area. The chemical index of alteration (CIA) and index of chemical variability (ICV) reveal an intensive weathering in the source region of the sediments. The multidimensional tectonic discrimination diagrams indicate that the source rocks of K1ml are mainly derived from the collision system. However, they may also comprise sediments derived from the continental rift system. The results are consistent with the geology of the study area.

Recent tectonic stress field, active faults and geothermal fields (hot-water type) in China

NASA Astrophysics Data System (ADS)

Wan, Tianfeng

1984-10-01

It is quite probable that geothermal fields of the hot-water type in China do not develop in the absence of recently active faults. Such active faults are all controlled by tectonic stress fields. Using the data of earthquake fault-plane solutions, active faults, and surface thermal manifestations, a map showing the recent tectonic stress field, and the location of active faults and geothermal fields in China is presented. Data collected from 89 investigated prospects with geothermal manifestations indicate that the locations of geothermal fields are controlled by active faults and the recent tectonic stress field. About 68% of the prospects are controlled by tensional or tensional-shear faults. The angle between these faults and the direction of maximum compressive stress is less than 45°, and both tend to be parallel. About 15% of the prospects are controlled by conjugate faults. Another 14% are controlled by compressive-shear faults where the angle between these faults and the direction maximum compressive stress is greater than 45°.

Tectonic Implications of Paleoproterozoic Deo Khe Granitoids in Northwestern Vietnam

NASA Astrophysics Data System (ADS)

Hoang, T. H. A.; Yu, Y.; Pham, T. H.; Choi, S. H.; Tu, V. L.; Son, L. M.

2015-12-01

An integrated study of petrographic description, zircon U/Pb geochronology, and Hf isotopic analysis was carried out on the medium-grained two-mica Deo Khe Granitoids (DKG) in northwestern Vietnam. U/Pb zircon ages were 1855-1873 Ma, interpreted as the time of magma crystallization. On the basis of Hf isotopic compositions, a single-stage Hf model ages were estimated as 3.3-2.8 Ga. Values of Hf isotopes ɛHf (t) range from -23.6 to -17.5, suggesting that the DKG are products of reworked Archean crustal rocks. A similar sequence of tectonic events including the presence of 2.8-2.9 Ga tonalite-trondhjemite-granodiorite (TTG) gneiss, metamorphic development of TTG gneiss at 1.9-2.0 Ga, and 1.85 Ga magmatic activity were recognized both in Yangtze block and northwestern Vietnam. Therefore we propose that basement rocks in northern Vietnam are similar to those found along southern China.

Tectonic Plates of China

DTIC Science & Technology

1977-04-01

C. Sun and Ta-iang Teng Contractor: University of Southern California Principal Investigator: Professor Ta-liang Teng (213) 746-6124 Contract Number...83 i" I. INTRODUCTION Over the vast Chinese mainland, one of the most interesting and dynamic regions of the world, complex tectonics, coupled with...west Pacific and the Alpine- Himalaya tectonic belts, the multitude of Chinese tectonic com- plexities is evident from its enormous topographic relief

Nature and tectonic implications of uneven sedimentary filling of the South China Sea oceanic basin

NASA Astrophysics Data System (ADS)

Yin, Shaoru; Li, Jiabiao; Ding, Weiwei; Fang, Yinxia

2017-04-01

The IODP Expedition 349 in 2014, for the first time, illustrated significant differences of sediment rate and lithology in the central South China Sea (SCS) oceanic basin. Based on seismic reflection profiles tied to IODP349 drilling data, we investigated characteristics of sedimentary filling of the whole SCS oceanic basin, and examined their implications for tectonics. Results show that sediments fill the SCS oceanic basin mainly in three depositional patterns. Firstly, during the Oligocene to middle Miocene, sediments amassed almost solely and then connected like a band parallel to the continent in a low average sediment rate (<10 m/Myr) in the northern oceanic basin. These sediments were deposited mainly in the form of submarine fans and mass transport deposits. Sediments were predominately supplied by the Red and Pearl Rivers and the Dongsha Islands. The sedimentary characteristics likely reflect the latest early Miocene end of seafloor spreading of the SCS and the first-phase rapid uplift of the Tibetan Plateau. Secondly, during the late Miocene, deposition mainly occurred in the Northwest Sub-basin and extended southeastward with a middle average sediment rate ( 30 m/Myr). Sediments were mostly transported by the Red River and Xisha Trough and deposited in the form of submarine fans. The abnormal increase of sediment rate in the Northwest Sub-basin reflects late Miocene slip reversal of the Red River Fault. Finally, since the Pliocene, sediments gradually propagated northeastward in the Southwestern Sub-basin, and accumulated rapidly in the southeastern and northeastern basin, especially in the northern Manila Trench during the Quaternary, in an average sediment rate about 60-80 m/Myr. These sediments were transported mainly by submarine canyons and settled in the form of submarine fans and canyon-overbank deposition. Sediments came from four major sources, including Taiwan, Dongsha Islands, Mekong River, and northern Palawan. The Pliocene to Quaternary explosion of uneven sedimentary filling in the SCS oceanic basin points to the combined action of local and regional tectonics, including the two-phase rapid uplift of the Tibetan Plateau, the Pliocene to Quaternary increased northwestward movement of the Philippine Sea plate and Dongsha event. This study exhibits hitherto most completed observation of sedimentary filling of the SCS oceanic basin and provides new geophysical evidences for the local and regional important tectonics.

Intracontinental mantle plume and its implications for the Cretaceous tectonic history of East Asia

NASA Astrophysics Data System (ADS)

Ryu, In-Chang; Lee, Changyeol

2017-12-01

A-type granitoids, high-Mg basalts (e.g., picrites), adakitic rocks, basin-and-range-type fault basins, thinning of the North China Craton (NCC), and southwest-to-northeast migration of the adakites and I-type granitoids in southern Korea and southwestern Japan during the Cretaceous are attributed to the passive upwelling of deep asthenospheric mantle or ridge subduction. However, the genesis of these features remains controversial. Furthermore, the lack of ridge subduction during the Cretaceous in recently suggested plate reconstruction models poses a problem because the Cretaceous adakites in southern Korea and southwestern Japan could not have been generated by the subduction of the old Izanagi oceanic plate. Here, we speculate that plume-continent (intracontinental plume-China continent) and subsequent plume-slab (intracontinental plume-subducted Izanagi oceanic plate) interactions generated the various intracontinental magmatic and tectonic activities in eastern China, Korea, and southwestern Japan. We support our proposal using three-dimensional numerical models: 1) An intracontinental mantle plume is dragged into the mantle wedge by corner flow of the mantle wedge, and 2) the resultant channel-like flow of the mantle plume in the mantle wedge apparently migrated from southwest to northeast because of the northeast-to-southwest migration of the East Asian continental blocks with respect to the Izanagi oceanic plate. Our model calculations show that adakites and I-type granitoids can be generated by increased slab-surface temperatures because of the channel-like flow of the mantle plume in the mantle wedge. We also show that the southwest-to-northeast migration of the adakites and I-type granitoids in southern Korea and southwestern Japan can be attributable to the opposite migration of the East Asian continental blocks with respect to the Izanagi oceanic plate. This correlation implies that an intracontinental mantle plume existed in eastern China during the Cretaceous and that the mantle plume was entrained into the mantle wedge as a channel-like flow. An intracontinental mantle plume can explain the adakitic rocks, A-type granitoids, high-Mg basalts, and basin-and-range-type fault basins distributed in eastern China. Thus, the mantle plume and its interaction with the overlying continent and subducting slab through time plausibly explain the Cretaceous tectonic history of East Asia.

Provenance analysis of the Late Paleozoic sedimentary rocks in the Xilinhot Terrane, NE China, and their tectonic implications

NASA Astrophysics Data System (ADS)

Han, Jie; Zhou, Jian-Bo; Wilde, Simon A.; Song, Min-Chun

2017-08-01

The Xilinhot Terrane is located in the eastern segment of the Central Asian Orogenic Belt in NE China, and is a key to a hotly debated issue on the Paleozoic tectonic evolution of this giant progenic belt. To constrain the tectonic evolution of the Xilinhot Terrane in the Late Paleozoic, we undertook zircon U-Pb dating and geochemical analyses of the Zhesi and Benbatu formations in the Suolun and Xi Ujimqin areas in the Xilinhot Terrane. Samples of the Benbatu Formation yield detrital zircon U-Pb ages ranging from 2659 Ma to 316 Ma, with four age populations at: 2659-1826 Ma, 1719-963 Ma, 590-402 Ma, and 396-316 Ma, whereas samples from the Zhesi Formation yield detrital zircon U-Pb ages ranging from 1967 Ma to 250 Ma, with four age populations at: 1967-1278 Ma, 971-693 Ma, 561-403 Ma, and 399-250 Ma. The age groups of both the Benbatu and Zhesi formations in the Xilinhot Terrane are similar to those in other parts of the Central Asian Orogenic Belt (CAOB). This evidence indicates that the Xilinhot Terrane is a microcontinent, and not an accretionary complex as previously thought. Furthermore, the youngest zircon grains in the Benbatu and Zhesi formations yield weighted mean 206Pb/238U ages of 322 ± 12 Ma (MSDW = 0.12, n = 4) and 257 ± 2.8 Ma (MSDW = 1.6, n = 8), respectively. Combined with fossil data, our new data suggest that the Benbatu and Zhesi formations in the Xilinhot Terrane were possibly deposited at ∼322 Ma and ∼257 Ma, respectively. Based on the provenance of the Carboniferous-Permian sandstones came from the blocks of NE China, we speculate that the Xilinhot Terrane is the western part of the Songliao block.

Devonian alkaline magmatic belt along the northern margin of the North China Block: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Zhang, Qi-Qi; Zhang, Shuan-Hong; Zhao, Yue; Liu, Jian-Min

2018-03-01

Some Devonian magmatic rocks have been identified from the northern margin of the North China Block (NCB) in recent years. However, their petrogenesis and tectonic setting are still highly controversial. Here we present new geochronological, Sr-Nd-Hf isotopic and whole-rock chemical data on several newly identified and previously reported Devonian alkaline complexes, including mafic-ultramafic rocks (pyroxenites and gabbros), alkaline rocks (syenites, monzonites) and alkaline granites in the northern NCB. We firstly identified some mafic-ultramafic rocks coeval with monzonite and quartz monzonite in the Sandaogou and Wulanhada alkaline intrusions. New zircon U-Pb dating of 16 samples from the Baicaigou, Gaojiacun, Sandaogou, Wulanhada and Chifeng alkaline intrusions combined with previous geochronological results indicate that the Devonian alkaline rocks emplaced during the early-middle Devonian at around 400-380 Ma and constitute an E-W-trending alkaline magmatic belt that extend ca. 900 km long along the northern margin of the NCB. Whole-rock geochemical and Sr-Nd-Hf isotopic data reveal that the Devonian alkaline rocks were mainly originated from partial melting of a variably enriched lithospheric mantle with different involvement of ancient lower crustal component and fractional crystallization. The Devonian alkaline magmatic belt rocks in the northern NCB are characterized by very weak or no deformations and were most likely related to post-collision extension after arc-continent collision between the Bainaimiao island arc and the northern margin of North China Craton during the latest Silurian. Partial melting of subcontinental lithospheric mantle to produce the Devonian alkaline magmatic rocks suggests that the northern North China Craton has an inhomogeneous, variably enriched subcontinental lithospheric mantle and was characterized by significant vertical crustal growth during the Devonian period.

Mesozoic Deformation and Its Geological Significance in the Southern Margin of the South China Sea

NASA Astrophysics Data System (ADS)

Zhu, Rongwei; Liu, Hailing; Yao, Yongjian; Wang, Yin

2018-05-01

The pre-Eocene history of the region around the present South China Sea is not well known. New multi-channel seismic profiles provide valuable insights into the probable Mesozoic history of this region. Detailed structural and stratigraphic interpretations of the multi-channel seismic profiles, calibrated with relevant drilling and dredging data, show major Mesozoic structural features. A structural restoration was done to remove the Cenozoic tectonic influence and calculate the Mesozoic tectonic compression ratios. The results indicate that two groups of compressive stress with diametrically opposite orientations, S(S)E-N(N)W and N(N)W-S(S)E, were active during the Mesozoic. The compression ratio values gradually decrease from north to south and from west to east in each stress orientation. The phenomena may be related to the opening of the proto-South China Sea (then located in south of the Nansha block) and the rate at which the Nansha block drifted northward in the late Jurassic to late Cretaceous. The Nansha block drifted northward until it collided and sutured with the southern China margin. The opening of the present South China Sea may be related to this suture zone, which was a tectonic zone of weakness.

Cenozoic tectonic subsidence in the Southern Continental Margin, South China Sea

NASA Astrophysics Data System (ADS)

Fang, Penggao; Ding, Weiwei; Fang, Yinxia; Zhao, Zhongxian; Feng, Zhibing

2017-06-01

We analyzed two recently acquired multichannel seismic profiles across the Dangerous Grounds and the Reed Bank area in the South China Sea. Reconstruction of the tectonic subsidence shows that the southern continental margin can be divided into three stages with variable subsidence rate. A delay of tectonic subsidence existed in both areas after a break-up, which was likely related to the major mantle convection during seafloor spreading, that was triggered by the secondary mantle convection below the continental margin, in addition to the variation in lithospheric thickness. Meanwhile, the stage with delayed subsidence rate differed along strikes. In the Reed Bank area, this stage is between 32-23.8 Ma, while in the Dangerous Grounds, it was much later (between 19-15.5 Ma). We believe the propagated rifting in the South China Sea dominated the changes of this delayed subsidence rate stage.

Petrogenesis of the Dalongkai ultramafic-mafic intrusion and its tectonic implication for the Paleotethyan evolution along the Ailaoshan tectonic zone (SW China)

NASA Astrophysics Data System (ADS)

Liu, Huichuan; Wang, Yuejun; Zi, Jian-Wei

2017-06-01

Layered ultramafic-mafic intrusions are usually formed in an arc/back-arc or intra-plate tectonic environment, or genetically related to a mantle plume. In this paper, we report on an ultramafic-mafic intrusion, the Dalongkai intrusion in the Ailaoshan tectonic zone (SW China), whose occurrence is closely associated with arc/back-arc magmatic rocks. The Dalongkai intrusion is composed of plagioclase-lherzolite, hornblende-peridotite, lherzolite and wehrlite at the bottom, cumulate plagioclase-pyroxenite at the middle part, changing to fine-grained gabbro towards the upper part of the intrusion, forming layering structure. Zircons from the plagioclase-pyroxenites and gabbros yielded U-Pb ages of 272.1 ± 1.7 Ma and 266.4 ± 5.8 Ma, respectively. The plagioclase-pyroxenites show cumulate textures, and are characterized by high MgO (25.0-28.0 wt.%; mg# = 80.6-82.3), Cr (1606-2089 ppm) and Ni (893-1203 ppm) contents, interpreted as early cumulate phases. By contrast, the gabbros have relatively lower mg# values (56.3-62.7), and Cr (157-218 ppm) and Ni (73-114 ppm) concentrations, and may represent frozen liquids. The plagioclase-pyroxenites and gabbros share similar chondrite-normalized REE patterns and primitive mantle-normalized trace element profiles which are analogous to those of typical back-arc basin basalts. The εNd(t) values for both rock types range from +2.20 to +4.22. These geochemical and isotopic signatures suggest that the Dalongkai ultramafic-mafic rocks originated from a MORB-like mantle source metasomatized by subduction-related, sediment-derived fluids. Our data, together with other geological evidence, indicate that the emplacement of the Dalongkai ultramafic-mafic intrusion most likely occurred in a back-arc extensional setting associated with subduction of the Ailaoshan Paleotethyan branch ocean during the Middle Permian, thus ruling out the previously speculated linkage to the Emeishan mantle plume, or to an intra-continental rift.

Geochronology and geochemistry of Mesozoic intrusive rocks in the Xing'an Massif of NE China: Implications for the evolution and spatial extent of the Mongol-Okhotsk tectonic regime

NASA Astrophysics Data System (ADS)

Li, Yu; Xu, Wen-Liang; Tang, Jie; Pei, Fu-Ping; Wang, Feng; Sun, Chen-Yang

2018-04-01

This study presents new zircon U-Pb-Hf and whole-rock geochemical data for intrusive rocks in the Xing'an Massif of NE China, with the aim of furthering our understanding of the evolution and spatial influence of the Mongol-Okhotsk tectonic regime. Zircon U-Pb dating indicates that five stages of Mesozoic magmatism are recorded in the Xing'an Massif, namely during the Middle Triassic ( 237 Ma), the Late Triassic ( 225 Ma), the Early Jurassic ( 178 Ma), the Middle Jurassic ( 168 Ma), and the late Early Cretaceous ( 130 Ma). The Middle Triassic-Early Jurassic intrusive rocks in the Xing'an Massif are dominantly granodiorites, monzogranites, and syenogranites that formed from magma generated by partial melting of newly accreted continental crust. Geochemistry of the Middle Triassic-Early Jurassic granitoid suites of the Xing'an Massif indicates their formation at an active continental margin setting, related to the southwards subduction of the Mongol-Okhotsk oceanic plate. The Middle Jurassic monzogranites in the Xing'an Massif are geochemically similar to adakites and have εHf(t) values (+3.8 to +5.8) and Hf two-stage model ages (TDM2; 979-850 Ma) that are indicative of derivation from magma generated by partial melting of thickened juvenile lower crust. The Middle Jurassic monzogranites formed in a compressional setting related to the closure of the Mongol-Okhotsk Ocean. The late Early Cretaceous intrusive rocks in the Xing'an Massif are dominated by A-type granitoids that are associated with bimodal volcanic rocks, suggesting their formation in an extensional environment related to either (i) delamination of a previously thickened region of the crust, associated with the Mongol-Okhotsk tectonic regime; (ii) the subduction of the Paleo-Pacific Plate; or (iii) the combined influence of these two tectonic regimes.

Structural features of northern Tarim basin: Implications for regional tectonics and petroleum traps

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong Jia; Juafu Lu; Dongsheng Cai

1998-01-01

The rhombus-shaped Tarim basin in northwestern China is controlled mainly by two left-lateral strike-slip systems: the northeast-trending Altun fault zone along its southeastern side and the northeast-trending Aheqi fault zone along its northwestern side. In this paper, we discuss the northern Tarim basin`s structural features, which include three main tectonic units: the Kalpin uplift, the Kuqa depression, and the North Tarim uplift along the northern margin of the Tarim basin. Structural mapping in the Kalpin uplift shows that a series of imbricated thrust sheets have been overprinted by strike-slip faulting. The amount of strike-slip displacement is estimated to be 148more » km by restoration of strike-slip structures in the uplift. The Kuqa depression is a Mesozoic-Cenozoic foredeep depression with well-developed flat-ramp structures and fault-related folds. The Baicheng basin, a Quaternary pull-apart basin, developed at the center of the Kuqa depression. Subsurface structures in the North Tarim uplift can be divided into the Mesozoic-Cenozoic and the Paleozoic lithotectonic sequences in seismic profiles. The Paleozoic litho-tectonic sequence exhibits the interference of earlier left-lateral and later right-lateral strike-slip structures. Many normal faults in the Mesozoic-Cenozoic litho-tectonic sequence form the negative flower structures in the North Tarim uplift; these structures commonly directly overlie the positive flower structures in the Paleozoic litho-tectonic sequence. The interference regions of the northwest-trending and northeast-trending folds in the Paleozoic tectonic sequence have been identified to have the best trap structures. Our structural analysis indicates that the Tarim basin is a transpressional foreland basin rejuvenated during the Cenozoic.« less

Crustal dynamics studies in China

NASA Technical Reports Server (NTRS)

Wu, F. T.

1985-01-01

Geodynamics of Mainland China and Taiwan are discussed. The following research was performed: (1) the tectonics along the Tanlu fault in eastern China; (2) tectonics in the Taiwan Strait behind the collision zone in Taiwan; and (3) analysis of faulting in the vicinity of the Altyn Tagn fault. It is found that the existence of the fault is traced back to at least Jurassic with the deposition of conglomerate sandstones in the troungh along the present Tanlu fault branches in the Shantung Province. Taiwan is the product of collision between the Phillipine plate and the Asian plate and Taiwan came into being because of a former island arc.

Cenozoic Tectonic Evolution of Northeast China and Surrounding Areas Reproduced by Slab Subduction Models

NASA Astrophysics Data System (ADS)

Yang, T.; Moresi, L. N.; Zhao, D.; Sandiford, D.

2017-12-01

Northeast China lies at the continental margin of the western Pacific subduction zone where the Pacific Plate subducts beneath the Eurasia Plate along the Kuril-Japan trench during the Cenozoic, after the consumption of the Izanagi Plate. The Izanagi Plate and the Izanagi-Pacific mid-ocean ridge recycled to the mantle beneath Eurasia before the early Cenozoic. Plate reconstructions suggest that (1) age of the incoming Pacific Plate at the trench increases with time; (2) convergence rate between the Pacific and Eurasia Plates increased rapidly from the late Eocene to the early Miocene. Northeast China and surrounding areas suffered widespread extension and magmatism during the Cenozoic, culminating in the opening of the Japan Sea and the rifting of the Baikal Rift Zone. The Japan Sea opened during the early Miocene and kept spreading until the late Miocene, since when compression tectonics gradually prevailed. The Baikal Rift Zone underwent slow extension in the Cenozoic but its extension rate has increased rapidly since the late Miocene. We investigate the Cenozoic tectonic evolution of Northeast China and surrounding areas with geodynamic models. Our study suggests that the rapid aging of the incoming Pacific Plate at the subduction zone leads to the increase of plate convergence and trench motion rates, and explains the observed sequence of regional tectonic events. Our geodynamic model, which reproduces the Cenozoic regional tectonic events, predicts slab morphology and stress state consistent with seismic observations, including over 1000 km of slab stagnant in the transition zone, and the along-dip principal compressional stress direction. Our model requires a value of the 660 km phase transition Clapeyron slope of -2.5 MPa/K to reproduce the stagnant slab and tectonic events in the study region. This suggests that the Pacific slab is hydrated in the transition zone, explaining geochemical characteristics of some regional Cenozoic igneous rocks which were suggested to originate from a hydrous mantle transition zone.

Multiple Emplacement and Exhumation History of the Late Mesozoic Dayunshan-Mufushan Batholith in Southeast China and Its Tectonic Significance: 1. Structural Analysis and Geochronological Constraints

NASA Astrophysics Data System (ADS)

Ji, Wenbin; Faure, Michel; Lin, Wei; Chen, Yan; Chu, Yang; Xue, Zhenhua

2018-01-01

The South China Block (SCB) experienced a polyphase reworking by the Phanerozoic tectonothermal events. To better understand its Late Mesozoic tectonics, an integrated multidisciplinary investigation has been conducted on the Dayunshan-Mufushan composite batholith in the north-central SCB. This batholith consists of two major intrusions that recorded distinct emplacement features. According to our structural analysis, two deformation events in relation to batholith emplacement and subsequent exhumation are identified. The early one (D1) was observed mostly at the southern border of the batholith, characterized by a top-to-the-SW ductile shearing in the early-stage intrusion and along its contact zone. This deformation, chiefly associated with the pluton emplacement at ca. 150 Ma, was probably assisted by farfield compression from the northern Yangtze foreland belt. The second but main event (D2) involved two phases: (1) ductile shearing (D2a) prominently expressed along the Dayunshan detachment fault at the western border of the batholith where the syntectonic late-stage intrusion and minor metasedimentary basement in the footwall suffered mylonitization with top-to-the-NW kinematics; and (2) subsequent brittle faulting (D2b) further exhumed the entire batholith that behaved as rift shoulder with half-graben basins developed on its both sides. Geochronological constraints show that the crustal ductile extension occurred during 132-95 Ma. Such a Cretaceous NW-SE extensional tectonic regime, as indicated by the D2 event, has been recognized in a vast area of East Asia. This tectonism was responsible not only for the destruction of the North China craton but also for the formation of the so-called "southeast China basin and range tectonics."

The ~2.4 Ga granitoids in the Quanji Massif，NW China: Petrogenesis and Implication for the early Paleoproterozoic Tectonics

NASA Astrophysics Data System (ADS)

Gong, S.; Chen, N.; Wang, Q.

2014-12-01

The 2.4-2.2 Ga collision-related magmatism had once been considered to be weak or lacking, and were interpreted to represent the stagnation and deceleration of plate subduction. However, large-scale intermediate to acid intrusions at 2.4-2.2 Ga are widely reported in the Trans-North China Orogen and Tarim Craton, NW China. Here we presented geochronological and geochemical and Nd-Hf isotopic studies of the Hudesheng and Delingha granitoids in the Quanji Massif, which could shed new light on the NW China and global tectonics in the Paleoproterozoic. The two granitoids are exposed in the eastern and central parts of the Quanji Massif, showing similar rock types and including mainly the syenogranitic, monzogranitic and adamellitic gneisses, with ~2.41 Ga low P/T-type amphibolite enclaves. They were formed at 2.37-2.39 Ga and underwent medium P/T-type amphibolite-facies metamorphism at ~1.95-1.90 Ga. Both granitoids have relatively high Si, K contents and FeO*/Mg, 104Ga/Al ratios, and are characterized by a relative enrichment in LILEs and LREEs, but depletion in Ba, Sr, Eu and Nb. These signatures are similar to those of the high-K calc-alkaline I-type granites, and with some geochemical features of A-type granites as well, suggesting that their formation might be related to a post-collisional setting with transition from compression to extension regimes at ~2.4 Ga. The whole-rock Nd and zircon Hf isotopes suggest important crustal growth occurred at ~2.5-2.8 Ga, and the precursor magmas of both granitoids were derived from partial melting of the Neo-Archean juvenile and ancient crustal components. Collectively, the ~2.37-2.39 Ga magmatic activities in the Quanji Massif took place right after arc-related metamorphism and arc-continent collision, thus probably making up part of the arc-related ~2.4-2.2 Ga magmatic activities, including those in the Trans-North China Orogen and Tarim Craton, NW China. This implies that a prolonged strong subduction-accretion-collision process occurred in the North China, consistent with those magmatic events having been discovered recently worldwide. This study is supported by National Natural Science Foundation of China (Grant Nos. 40972042, 41172069 and 41372075)

Understanding the Geological Structures of North China By Analyzing Regional Gravity and Magnetic Data

NASA Astrophysics Data System (ADS)

Shi, L.; Guo, L.; Meng, X.; Yao, C.

2010-12-01

North China is one of the most tectonically important regions in the world to study important continent geodynamics issues such as intraplate earthquakes, volcanism and continent-continent collision. The North China Craton, covering most of North China, bounded by complicated fault systems and orogenic belts, is one of the oldest cratons on the Earth, and is unique in its tectonic reactivation in the Late Mesozoic and Cenozoic. In the past few decades, a variety of geophysical methods were conducted to study geological tectonics and evolution of North China. We analyzed the regional gravity and magnetic data of this region using new data enhancement techniques to understand the regional geological structures. The satellite-derived free-air gravity anomalies with a resolution of 1 arc-minute were assembled from the Scripps Institution of Oceanography, and were then reduced to obtain Complete Bouguer Gravity Anomalies (CBGA). The Magnetic Anomalies (MA) with a resolution of 2 arc-minutes were assembled from the World Digital Magnetic Anomaly Map. The CBGA and the MA were then gridded on a regular grid, the MA were subsequently reduced to the magnetic pole. Then the data were processed with standard techniques to attenuate the high-frequency noise and analyze the regional and residual anomalies. Specially, we calculated the tilt-angle derivatives of the data. We then calculated the directional horizontal derivatives of the tilt-angle derivatives along different directions. This special processing derived clearer geological structures with more details. From the results of the preliminary processing, we analyzed the main deep faults and tectonic units distributed in this region. In the future, the interpretation of the CBGA and the MA with constraints of other geophysical methods will be performed for better understanding the deep structure of this region. Acknowledgment: We acknowledge the financial support of SinoProbe-01-05, the Fundamental Research Funds for the Central Universities (2010ZY26), and the National Natural Science Foundation of China (40904033).

Zircon U-Pb age, Hf isotope and geochemistry of Carboniferous intrusions from the Langshan area, Inner Mongolia: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Liu, Min; Zhang, Da; Xiong, Guangqiang; Zhao, Hongtao; Di, Yongjun; Wang, Zhong; Zhou, Zhiguang

2016-04-01

Late Paleozoic was a critical period for the tectonic evolution of the northern margin of the Alxa-North China craton, but the evolutionary history is not well constrained. The Carboniferous intrusions in the Langshan area in the western part of the northern margin of the Alxa-North China craton are mainly composed of tonalite, quartz diorite, olivine gabbro and pyroxene peridotite. Zircon LA-ICP-MS U-Pb dating indicates that the Langshan Carboniferous intrusions were emplaced at ca. 338-324 Ma. The quartz diorites are characterized by high amounts of compatible trace elements (Cr, Ni and V) and high Mg# values, which may suggest a significant mantle source. The positive Pb and negative Nb-Ta-Ti anomalies, the variable εHf(t) (-6.9 to 2.0) values and the old Hf model ages (1218-1783 Ma) imply some involvement of ancient continental materials in its petrogenesis. The tonalite has relatively high Sr/Y ratios, low Mg#, Yb and Y contents, features of adakite-like rocks, negative εHf(t) values (-9.8 to -0.1) and older Hf model ages (1344-1953 Ma), which suggest significant involvement of ancient crust materials and mantle-derived basaltic component in its petrogenesis. The high Mg# values, high Cr and Ni contents, and low Zr and Hf contents of the mafic-ultramafic rocks show evidence of a mantle source, and the relatively low zircon εHf(t) values (-5.9 to 3.2) might point to an enriched mantle. The trace element characteristics indicate the influence of subducted sediments and slab-derived fluids. In the tectonic discrimination diagrams, all the rocks plot in subduction-related environment, such as volcanic arc and continental arc. Considering the regional geology, we suggest that the Carboniferous intrusions in the Langshan area were likely emplaced during the late stage of the southward subduction of the Paleo-Asian Ocean plate, which formed a continental arc along the northern margin of the Alxa-North China craton.

Geochemistry and geochronology of the blueschist in the Heilongjiang Complex and its implications in the late Paleozoic tectonics of eastern NE China

NASA Astrophysics Data System (ADS)

Ge, Mao-hui; Zhang, Jin-jiang; Liu, Kai; Ling, Yi-yun; Wang, Meng; Wang, Jia-min

2016-09-01

The Paleozoic to early Mesozoic tectonic framework and evolution of Northeast China, especially the Jiamusi block and its related structural belts, are highly debated. In this paper, geochemical, geochronological and isotopic analyses were carried out on the blueschist in the Heilongjiang Complex to address these issues. The Heilongjiang Complex defines the suture belt between the Jiamusi block and the Songliao block in NE China, and the blueschist is a major composition for this complex, coexisting with mafic-ultramafic rocks, greenschist, quartzite and mica schist. The blueschist has a mineral association of sodic amphibole, epidote, chlorite, phengite, albite and quartz with accessory phases of apatite, titanite, zircon and ilmenite. Together with the lithological association, the major and trace element compositions present that the protoliths of the blueschist can be divided into the alkaline and tholeiitic basalts and have OIB affinities, formed in an ocean island setting, indicated by the (La/Yb) N values of 3.57 - 11.54, and the (La/Sm) N values of 0.69 - 3.64. The high and positive εNd (t) values of + 3.7 to + 9.0, and relative enrichment in Nb (vs. Th) and Ta (vs. U) show that both the alkaline and tholeiitic basalts may be derived from the asthenospheric mantle with insignificant crustal contamination. Magmatic zircons from the blueschist in Yilan area yield a 206Pb/238U age of 281 ± 3 Ma, interpreted as its protolithic age. The youngest ages of 200 Ma of the detrital zircons in the associated mica schist from Mudanjiang area place constraints on the timing of metamorphism for the blueschist. These indicate that a big ocean existed between the Jiamusi and Songliao blocks at least since the early Permian, and the blueschist formed since the late Triassic to late Jurassic by the subduction of this ocean. Such an ocean during the Permian - Jurassic is difficult to be interpreted by the tectonic evolution of the Paleo-Asian Ocean.

Lg wave attenuation in southeastern margin of Tibetan Plateau and the Indochina Peninsula and its implications of potential crustal flow

NASA Astrophysics Data System (ADS)

He, X.; Zhao, L. F.; Xie, X. B.; Yao, Z. X.

2017-12-01

Mechanisms that accommodate tectonic deformation in southeastern Tibetan Plateau and the Indochina Peninsula have been under heated debate between two popular end-number models, rigid block extrusion and viscous crustal flow channel, while recent studies suggest that they are not irreconcilable (e.g., Liu et al., 2014). To provide new insights into regional tectonic evolution, we collect 22,242 vertical seismograms and perform the Lg wave attenuation tomography at 58 individual frequencies between 0.05-10.0 Hz to investigate Lg wave attenuation in this region. The resultant broadband Lg wave attenuation model exhibits strong lateral variation that correlates with regional tectonics. A significant low Q belt, originating in the southeast Tibet, striking southeast and connecting to northern South China Sea, is the most conspicuous feature in our Lg Q maps, indicating intense crustal deformation and tectonic activities. For the northwestern part of this belt, two low Q channels joint beneath Songpan-Ganzi block but separate beneath Chuan-Dian block (eastern channel) and northern Sibumasu block (western channel) encountering Chuxiong basin in the central Chuan-Dian. This acute Lg attenuation may be resulted from viscous lower crust, thermal activities, shear heating along strike-slip fault and fractured brittle upper crust. The two channels are also consistent with zones of low seismic velocity and high conductivity between depth of 20 and 40 km (Bai et al., 2010; Bao et al., 2015), indicating possible partial-molten mid and lower crust. Together with evidences from paleo-elevation reconstruction and seismic anisotropy (Li et al., 2015; Wei et al., 2013), gravity-driven flow of viscous partial-molten mid-lower crust, which underlies brittle upper crust, is suggested and the mechanism that ductile flow of thickened lower crust uplifts topography and drags brittle upper crust to move with respect to each other may accommodate regional tectonics. We attribute distinct low Q zones beneath Yinggehai basin to ultra-thick sediment and sever thermal activities, and another obvious low Q zone beneath Sumatra Islands to dozens of volcanos. This work is supported by the Earthquake Experimental Field, CEA (grants 2016 CESE 0203) and the National Natural Science Foundation of China (grants 41374065, 41630210).

Detrital zircons from the Tananao metamorphic complex of Taiwan: Implications for sediment provenance and Mesozoic tectonics

NASA Astrophysics Data System (ADS)

Yui, T. F.; Maki, K.; Lan, C. Y.; Hirata, T.; Chu, H. T.; Kon, Y.; Yokoyama, T. D.; Jahn, B. M.; Ernst, W. G.

2012-05-01

Taiwan formed during the Plio-Pleistocene collision of Eurasia with the outboard Luzon arc. Its pre-Tertiary basement, the Tananao metamorphic complex, consists of the western Tailuko belt and the eastern Yuli belt. These circum-Pacific belts have been correlated with the high-temperature/low-pressure (HT/LP) Ryoke belt and the high-pressure/low-temperature (HP/LT) Sanbagawa belt of Japan, respectively. To test this correlation and to reveal the architecture and plate-tectonic history of the Tananao metamorphic basement, detrital zircons were separated from 7 metasedimentary rock samples for U-Pb dating by LA-ICPMS techniques. Results of the present study, coupled with previous data, show that (1) the Tailuko belt consists of a Late Jurassic to earliest Cretaceous accretionary complex sutured against a Permian-Early Jurassic marble ± metabasaltic terrane, invaded in the north by scattered Late Cretaceous granitic plutons; the latter as well as minor Upper Cretaceous cover strata probably formed in a circum-Pacific forearc; (2) the Yuli belt is a mid- to Late Cretaceous accretionary complex containing HP thrust sheets that were emplaced attending the Late Cenozoic Eurasian plate-Luzon arc collision; (3) these two Late Mesozoic belts are not coeval, and in part were overprinted by low-grade metamorphism during the Plio-Pleistocene collision; (4) accreted clastic sediments of the Tailuko belt contain mainly Phanerozoic detrital zircons, indicating that terrigenous sediments were mainly sourced from western Cathaysia, whereas in contrast, clastic rocks of the Yuli accretionary complex contain a significant amount of Paleoproterozoic and distinctive Neoproterozoic zircons, probably derived from the North China craton and the Yangtze block ± eastern Cathaysia, as a result of continent uplift/exhumation after the Permo-Triassic South China-North China collision; and (5) the Late Jurassic-Late Cretaceous formation of the Tananao basement complex precludes the possibility that the early Yanshanian (Early Jurassic) granitoids in southern China represent a landward arc contemporaneous with the later, outboard Tananao accretionary event.

Apparent Susceptibility Contrast Distribution of Continental Lithosphere in China and Its Surroundings: Implications to Regional Tectonics

NASA Astrophysics Data System (ADS)

Du, J.; Chen, C.; Sun, S.; Zhang, Y.; Liang, Q.

2015-12-01

Lithospheric magnetic field characterizes response of magnetic properties of rocks, which are mainly dependent on mineral and temperature variations. Hence, lithospheric magnetic structure brings important information to understand tectonic and thermal processes in the crust and uppermost mantle. In particular, the reliable global geomagnetic field models with large-scales based on satellite magnetic measurements provide regional view of the lithospheric magnetic structure. Here, with smallest and flattest constraints we use the inversion method based on the single layer model to calculate the spatial distribution of apparent susceptibility of continental lithosphere in China and its surroundings. It should be noted that: (1) magnetic anomaly data we used has removed the effect of global oceanic remanent magnetization, (2) the error of magnetic anomaly data is estimated from statistical analysis among MF7, GRIMM_L120, CHAOS5 and CM5 models, (3) the magnetic layer is bounded by the bottom of sediment and the Moho from CRUST1.0 model and is discretized into ellipsoidal prisms with equal angles in latitude and longitude, and (4) an adaptive subdivision & Gauss-Legendre quadrature with fixed order is adopted to solve the forward problem and IGRF11 is utilized as inducing field model. Since the missing longest wavelength components in the lithospheric magnetic field models and the so-called magnetic annihilators, the Apparent Susceptibility Contrast (ASC) distribution is obtained. The ASC distribution has obvious variations and illustrates the mosaic continent with old blocks, orogenic belts, rework fragments and also earthquake regions/zones. Moreover, the ASC distribution provides new insights and evidences of the destruction of North China Craton and geodynamic processes of Tibetan plateau and Baikal rift etc. This study is supported by China Postdoctoral Science Foundation (Grant No.: 2015M572217) and Natural Science Fund of Hubei Province (Grant No.: 2015CFB361).

Tectonics and distribution of gold deposits in China - An overview

USGS Publications Warehouse

Zhou, T.; Goldfarb, R.J.; Phillips, G.N.

2002-01-01

Gold exploration in China has expanded rapidly during the last two decades since a modern approach to economic development has become a national priority. China currently produces 180 tonnes (t) of gold annually, which is still significantly less than South Africa, USA, and Australia. However, China is now recognized as possessing significant gold resources in a wide range of mineral deposit types. Present estimates of gold resources in China exceed 4,500 t, which comprise 60% in gold-only deposits, more than 25% in base metal-rich skarn, porphyry, and vein deposits, and more than 10% in placer accumulations. The major gold provinces in China formed during the main episodes of Phanerozoic tectonism. Such tectonism involved interaction of China's three major Precambrian cratons, North China, Tarim, and Yangtze (or South China when combined with Cathysia block), with the Angara (or Siberian), Kazakhstan-Kyrgyzstan, and Indian cratons. Resulting collisions included deformation of accreted oceanic sequences between the cratonic blocks. The most important ore-forming orogenies were (1) the late Paleozoic Variscan (405-270 Ma), which led to amalgamation of the Angara, North China and Yangtze cratons, (2) the Indosinian (270-208 Ma), which led to the collision of North China and South China cratons, (3) the Yanshanian (208-90 Ma), which was largely influenced by the subduction of the Izanagi-Pacific plates beneath eastern China, and (4) the Himalayan (<90 Ma) indentation of the Indian continent into Eurasia. No important Precambrian gold systems are recognized in China, mainly because of reworking of exposed Precambrian rocks by these younger orogenies, but there are a few Caledonian (600-405 Ma) gold-bearing system in northern Xinjiang. Most of China's orogenic, epithermal, and Carlinlike gold deposits are in the reworkerd margins of major cratonic blocks and in metasedimentary rock-dominated fold belts adjacent to these margins. Accordingly, the major gold provinces are present along the northern, southeastern and southern margins of the North China craton, along the southwestern and northwestern margins of the Yangtze craton, in the Tianshan and Altayshan orogenic belts in northern Xinjiang, and throughout the southeastern China fold belt. Gold-placer deposits derived from these primary deposits are concentrated in the northernmost part of northeastern China and along the northerwestern margin of the Yangtze craton. The major provinces with significant gold in porphyry-related copper systems and base metal skarns are present in the Yangtze River area along the northeastern and southeastern margin of the Yangtze craton, in the fold belt in southwestern China, and scattered through northern China. Three-quarters of the Chinese gold-only deposits occur within the North China craton margins. Half are located in the uplifted Precambrian metamorphie rocks and most of the remainder are hosted in the Phanerozoic granitoids that intruded the reworked Precambrian terranes. The abundance of granite-hosted gold contrasts the North China craton with other Precambrian cratons, such as those in Western Australia, central Canada, and Zimbabwe, where gold is mainly hosted in the Archean greenstone belts. This difference may be explained by the multiple episodes of Phanerozoic tectonism along the North China craton margins resulting from the collision of the Angara, North China, and South China cratons, and from subduction of the Izanagi-Pacific oceanic plates underneath the eastern China continent.

The initiation and tectonic regimes of the Cenozoic extension in the Bohai Bay Basin, North China revealed by numerical modelling

NASA Astrophysics Data System (ADS)

Li, Lu; Qiu, Nansheng

2017-06-01

In this study the dynamic aspects of the Cenozoic extension in the Bohai Bay Basin are considered in the context of initial thickness of the crust and lithosphere, tectonic force, strain rate and thermal rheology, which are directly or indirectly estimated from a pure shear extensional model. It is accordingly reasonable to expect that, in the Bohai Bay Basin, the thickness variation could be present prior to the initiation of extension. The extensional deformation is localized by a thickness variation of the crust and lithosphere and the heterogeneity of the initial thickness plays an important role in rifting dynamics. The onset of rifting requires a critical tectonic force (initial tectonic force) to be applied, which then immediately begins to decay gradually. Rifting will only occur when the total effective buoyancy force of the subducting slab reaches a critical level, after a certain amount of subduction taking place. The magnitude of the tectonic force decreases with time in the early phase of rifting, which indicates the weakening due to the increase in geothermal gradient. In order to deform the continental lithosphere within the currently accepted maximum magnitude of the force derived from subducted slab roll-back, the following conditions should be satisfied: (1) the thickness of the continental lithosphere is significantly thin and less than 125 km and (2) the lithosphere has a wet and hot rheology, which provides implications for rheological layering in continental lithosphere. Our results are strongly supported by the ;crème brûlée; model, in which the lower crust and mantle are relatively ductile.

Understanding the Tectonic Features in the South China Sea By Analyzing Magnetic Anomalies

NASA Astrophysics Data System (ADS)

Guo, L.; Meng, X.; Shi, L.; Yao, C.

2011-12-01

The South China Sea (SCS) is surrounded by the Eurasia, Pacific and India-Australia plates. It formed during Late Oligocene-Early Miocene, and is one of the largest marginal seas in the Western Pacific. The collision of Indian subcontinent and Eurasian plate in the northwest, back-arc spreading in the centre and subduction beneath the Philippine plate along Manila trench in the east and along Palawan trough in the south had produced the complex tectonic features in the SCS that we can see today. In the past few decades, a variety of geophysical methods were conducted to study geological tectonics and evolution of the SCS. Here, we analyzed the magnetic data of this area using new data enhancement techniques to understand the regional tectonic features. We assembled the magnetic anomalies data with a resolution of two arc-minute from the World Digital Magnetic Anomaly Map, and then gridded the data on a regular grid. Then we used the method of reduction to the pole at low latitude with varying magnetic inclinations to stably reduce the magnetic anomalies. Then we used the preferential continuation method based on Wiener filtering and Green's equivalence principle to separate the reduced-to-pole (RTP) magnetic anomalies, and subsequently analyze the regional and residual anomalies. We also calculated the directional horizontal derivatives and the tilt-angle derivative of the data to derive clearer geological structures with more details. Then we calculated the depth of the magnetic basement surface in the area by 3D interface inversion. From the results of the preliminary processing, we analyzed the main faults, geological structures, magma distribution and tectonic features in the SCS. In the future, the integrated interpretation of the RTP magnetic anomalies, Bouguer gravity anomalies and other geophysical methods will be performed for better understanding the deep structure , the tectonic features and evolution of the South China Sea. Acknowledgment: We acknowledge the financial support of the SinoProbe project (201011039), the Fundamental Research Funds for the Central Universities (2010ZY26, 2011PY0184), and the National Natural Science Foundation of China (40904033, 41074095).

Preliminary publications Book 1 from Project on Mineral Resources, Metallogenesis and Tectonics of Northeast Asia

USGS Publications Warehouse

Ariunbileg, Sodov; Badarch, Gombosuren; Berzin, Nikolai A.; Bulgatov, Alexander N.; Chimed, Noosoi; Deikunenko, Aleksey V.; Dejidmaa, Gunchin; Diggles, Michael F.; Distanov, Elimir G.; Dorjgotov, Dangindorjiin; Gerel, Ochir; Gordienko, Ivan V.; Gotovsuren, Ayurzana; Hwang, Duk-Hwan; Khanchuk, Alexander I.; Koch, Richard D.; Miller, Robert J.; Nokleberg, Warren J.; Obolenskiy, Alexander A.; Ogasawara, Masatsugu; Orolmaa, Demberel; Oxman, Vladimir S.; Parfenov, Leonid M.; Popeko, Ludmila I.; Prokopiev, Andrey V.; Smelov, Alexander P.; Sotnikov, Vitaliy I.; Sudo, Sadahisa; Timofeev, Vladimir F.; Tret'yakov, Felix F.; Vernikovsky, Valery A.; Ye, Mao; Zadgenizov, Alexander P.

1999-01-01

This report consists of preliminary data tables, maps, and interpretative articles compiled in late 1997 and early 1998 for a new project on the Mineral Resources, Metallogenesis, and Tectonics of Northeast Asia (Eastern and Southern Siberia, Mongolia, North-eastern China, South Korea, and Japan).

Mesozoic to Cenozoic tectonic transition process in Zhanhua Sag, Bohai Bay Basin, East China

NASA Astrophysics Data System (ADS)

Cheng, Yanjun; Wu, Zhiping; Lu, Shunan; Li, Xu; Lin, Chengyan; Huang, Zheng; Su, Wen; Jiang, Chao; Wang, Shouye

2018-04-01

The Zhanhua sag is part of the Bohai Bay intracontinental basin system that has developed since the Mesozoic in East China. The timing of this basin system coincides with the final assembly of East Asia and the development of Western Pacific-type plate margin. Here we use 3-D seismic and core log data to investigate the evolution of this basin and discuss its broad tectonic settings. Our new structural study of Zhanhua sag suggests that there are four major tectonic transitions occurred in the Bohai Bay Basin during Mesozoic and Cenozoic: (1) The first tectonic transition was from stable Craton to thrusting during the Triassic, mainly caused by the South China Block's subduction northward beneath the North China Block, which induced the formation of the NW-striking thrust faults. (2) The second tectonic transition was mainly characterized by a change from compression to extension, which can be further divided into two-stages. At the first stage, two episodes of NW-SE shortening occurred in East Asia during Early-Middle Jurassic and Late Jurassic-earliest Cretaceous, respectively. At the second stage, the extension and left-lateral shearing took place during Early Cretaceous while compression occurred during Late Cretaceous. The NW-striking thrust faults changed to normal faults and the NNE-striking left-lateral strike-slip faults started to influence the eastern part of the basin. (3) The third transition occurred when the NW-SE extension and NNE-striking right-lateral shearing started to form during Paleogene, and the peak deformation happen around 40 Ma due to the change of the subduction direction of Pacific Plate relative to Eurasia Plate. The NE-striking normal faults are the main structure, and the pre-existing NNE-striking strike-slip faults changed from left-lateral to right-lateral. (4) The fourth transition saw the regional subsidence during Neogene, which was probably caused by the India-Asia "Hard collision" between 25 and 20 Ma.

Amalgamation of East Eurasia Since Late Paleozoic: Constraints from the Apparent Polar Wander Paths of the Major China Blocks

NASA Astrophysics Data System (ADS)

Wu, L.; Kravchinsky, V. A.; Potter, D. K.

2014-12-01

It has been a longstanding challenge in the last few decades to quantitatively reconstruct the paleogeographic evolution of East Eurasia because of its great tectonic complexities. As the core region, the major China cratons including North China Block, South China Block and Tarim Block hold the key clues for the understanding of the amalgamation history, tectonic activities and biological affinity among the component blocks and terranes in East Eurasia. Compared with the major Gondwana and Laurentia plates, however, the apparent polar wander paths of China are not well constrained due to the outdated paleomagnetic database and relatively loose pole selection process. With the recruitment of the new high-fidelity poles published in the last decade, the rejection of the low quality data and the strict implementation of Voo's grading scheme, we build an updated paleomagnetic database for the three blocks from which three types of apparent polar wander paths (APWP) are computed. Version 1 running mean paths are constructed during the pole selection and compared with those from the previous publications. Version 2 running mean and spline paths with different sliding time windows are computed from the thoroughly examined poles to find the optimal paths with the steady trend, reasonable speed for the polar drift and plate rotation. The spline paths are recommended for the plate reconstructions, however, considering the poor data coverage during certain periods. Our new China APWPs, together with the latest European reference path, the geological, geochronological and biological evidence from the studied Asian plates allow us to reevaluate the paleogeographic and tectonic history of East Eurasia.

Tectonics, topography, and river system transition in East Tibet: Insights from the sedimentary record in Taiwan

NASA Astrophysics Data System (ADS)

Lan, Qing; Yan, Yi; Huang, Chi-Yue; Clift, Peter D.; Li, Xuejie; Chen, Wenhuang; Zhang, Xingchang; Yu, Mengming

2014-09-01

The Cenozoic in East Asia is marked by major changes in tectonics, landscapes, and river systems, although the timing and nature of such changes remains disputed. We investigate the geochemistry and neodymium isotope character of Cenozoic mudstones spanning the breakup unconformity in the Western Foothills of Taiwan in order to constrain erosion and drainage development in southern China during the opening of the South China Sea. The La/Lu, Eu/Eu*, Th/Sc, Th/La, Cr/Th, and ɛNd values in these rocks show an abrupt change between ˜31 and 25 Ma. Generally the higher ɛNd values in sediments deposited prior to 31 Ma indicate erosion from Phanerozoic granitic sources exposed in coastal South China, whereas the lower ɛNd values suggest that the main sources had evolved to inland southern China by ˜25 Ma. The SHRIMP U-Pb ages of zircons from a tuff, together with biostratigraphy data constrain the breakup unconformity to be between ˜39 and 33 Ma, suggesting that the seafloor spreading in the South China Sea commenced before ˜33 Ma. This is significantly older than most of the oceanic crust preserved in the deeper part of the basin. Diachronous westward younging of the breakup unconformities and provenance changes of basins are consistent with seafloor spreading propagating from east to west. Initial spreading of the South China Sea prior to ˜33 Ma corresponds to tectonic adjustment in East Asia, including extrusion of the Indochina block and the rotation and eastward retreat of the subducting Pacific Plate.

Present-day geothermal characteristics of the Ordos Basin, western North China Craton: new findings from deep borehole steady-state temperature measurements

NASA Astrophysics Data System (ADS)

Gao, Peng; Qiu, Qianfeng; Jiang, Guangzheng; Zhang, Chao; Hu, Shengbiao; Lei, Yuhong; Wang, Xiangzeng

2018-03-01

Heat flow and associated thermal regimes are related to the tectonic evolution and geophysical properties of the lithosphere. The Ordos Basin is located in a tectonic transitional zone: areas to the east of the basin are characterized as tectonically active, while regions to the west of the basin are characterized as tectonically stable. It is of general interest to learn the geothermal characteristics of the basin in such tectonic conditions. To clarify the spatial variability of the present-day geothermal field across the basin and its implications, we report 13 terrestrial heat flow points based on the first systematic steady-state deep borehole temperature measurements in the basin. The new data together with existing data show that the geothermal gradients in the basin range from 12.6 to 42.3° C km-1 with a mean of 27.7 ± 5.3° C km-1; the terrestrial heat flow values range from 43.3 to 88.7 mW/m2 with a mean of 64.7 ± 8.9 mW/m2. Such values are higher than those of typical cratonic basins and lower than those of tectonically active areas. By using all these data in the basin and adjacent areas, we plot geothermal gradient and heat flow distribution maps. The maps reveal that the basin is cooling westward and northward. The distribution pattern of the geothermal field is consistent with the lithospheric thickness variation in the basin. This similarity suggests that the geothermal spatial variability of the Ordos Basin is mainly influenced by heat from the deep mantle. In the southeastern basin, we locate a positive geothermal anomaly caused by the convergence of heat flow in basement highs and the high radiogenic heat production. In addition, the high heat flow in the eastern basin is related to the intense uplift during the Cenozoic Era.

Present-day geothermal characteristics of the Ordos Basin, western North China Craton: new findings from deep borehole steady-state temperature measurements

NASA Astrophysics Data System (ADS)

Gao, Peng; Qiu, Qianfeng; Jiang, Guangzheng; Zhang, Chao; Hu, Shengbiao; Lei, Yuhong; Wang, Xiangzeng

2018-07-01

Heat flow and associated thermal regimes are related to the tectonic evolution and geophysical properties of the lithosphere. The Ordos Basin is located in a tectonic transitional zone: areas to the east of the basin are characterized as tectonically active, while regions to the west of the basin are characterized as tectonically stable. It is of general interest to learn the geothermal characteristics of the basin in such tectonic conditions. To clarify the spatial variability of the present-day geothermal field across the basin and its implications, we report 13 terrestrial heat flow points based on the first systematic steady-state deep borehole temperature measurements in the basin. The new data together with existing data show that the geothermal gradients in the basin range from 12.6 to 42.3 °C km-1 with a mean of 27.7 ± 5.3 °C km-1; the terrestrial heat flow values range from 43.3 to 88.7 mW m-2 with a mean of 64.7 ± 8.9 mW m-2. Such values are higher than those of typical cratonic basins and lower than those of tectonically active areas. By using all these data in the basin and adjacent areas, we plot geothermal gradient and heat flow distribution maps. The maps reveal that the basin is cooling westwards and northwards. The distribution pattern of the geothermal field is consistent with the lithospheric thickness variation in the basin. This similarity suggests that the geothermal spatial variability of the Ordos Basin is mainly influenced by heat from the deep mantle. In the southeastern basin, we locate a positive geothermal anomaly caused by the convergence of heat flow in basement highs and the high radiogenic heat production. In addition, the high heat flow in the eastern basin is related to the intense uplift during the Cenozoic Era.

A tectonic model for the Tertiary evolution of strike slip faults and rift basins in SE Asia

NASA Astrophysics Data System (ADS)

Morley, C. K.

2002-04-01

Models for the Tertiary evolution of SE Asia fall into two main types: a pure escape tectonics model with no proto-South China Sea, and subduction of proto-South China Sea oceanic crust beneath Borneo. A related problem is which, if any, of the main strike-slip faults (Mae Ping, Three Pagodas and Aliao Shan-Red River (ASRR)) cross Sundaland to the NW Borneo margin to facilitate continental extrusion? Recent results investigating strike-slip faults, rift basins, and metamorphic core complexes are reviewed and a revised tectonic model for SE Asia proposed. Key points of the new model include: (1) The ASRR shear zone was mainly active in the Eocene-Oligocene in order to link with extension in the South China Sea. The ASRR was less active during the Miocene (tens of kilometres of sinistral displacement), with minor amounts of South China Sea spreading centre extension transferred to the ASRR shear zone. (2) At least three important regions of metamorphic core complex development affected Indochina from the Oligocene-Miocene (Mogok gneiss belt; Doi Inthanon and Doi Suthep; around the ASRR shear zone). Hence, Paleogene crustal thickening, buoyancy-driven crustal collapse, and lower crustal flow are important elements of the Tertiary evolution of Indochina. (3) Subduction of a proto-South China Sea oceanic crust during the Eocene-Early Miocene is necessary to explain the geological evolution of NW Borneo and must be built into any model for the region. (4) The Eocene-Oligocene collision of NE India with Burma activated extrusion tectonics along the Three Pagodas, Mae Ping, Ranong and Klong Marui faults and right lateral motion along the Sumatran subduction zone. (5) The only strike-slip fault link to the NW Borneo margin occurred along the trend of the ASRR fault system, which passes along strike into a right lateral transform system including the Baram line.

Mineral-deposit models for northeast Asia, Chapter 3 in Metallogenesis and tectonics of northeast Asia

USGS Publications Warehouse

Obolenskiy, Alexander A.; Rodionov, Sergei M.; Ariunbileg, Sodov; Dejidmaa, Gunchin; Distanov, Elimir G.; Dorjgotov, Dangindorjiin; Gerel, Ochir; Hwang, Duk-Hwan; Sun, Fengyue; Gotovsuren, Ayurzana; Letunov, Sergei N.; Li, Xujun; Nokleberg, Warren J.; Ogasawara, Masatsugu; Seminsky, Zhan V.; Smelov, Akexander P.; Sotnikov, Vitaly I.; Spiridonov, Alexander A.; Zorina, Lydia V.; Yan, Hongquan

2010-01-01

The major purposes of this chapter are to provide (1) an overview of the regional geology, tectonics, and metallogenesis of Northeast Asia for readers who are unfamiliar with the region, (2) a general scientific introduction to the succeeding chapters of this volume, and (3) an overview of the methodology of metallogenic and tectonic analysis used in this study. We also describe how a high-quality metallogenic and tectonic analysis, including construction of an associated metallogenic-tectonic model will greatly benefit other mineral resource studies, including synthesis of mineral-deposit models; improve prediction of undiscovered mineral deposit as part of a quantitative mineral-resource-assessment studies; assist land-use and mineral-exploration planning; improve interpretations of the origins of host rocks, mineral deposits, and metallogenic belts, and suggest new research. Research on the metallogenesis and tectonics of such major regions as Northeast Asia (eastern Russia, Mongolia, northern China, South Korea, and Japan) and the Circum-North Pacific (the Russian Far East, Alaska, and the Canadian Cordillera) requires a complex methodology including (1) definitions of key terms, (2) compilation of a regional geologic base map that can be interpreted according to modern tectonic concepts and definitions, (3) compilation of a mineral-deposit database that enables a determination of mineral-deposit models and clarification of the relations of deposits to host rocks and tectonic origins, (4) synthesis of a series of mineral-deposit models that characterize the known mineral deposits and inferred undiscovered deposits in the region, (5) compilation of a series of metallogenic-belt belts constructed on the regional geologic base map, and (6) construction of a unified metallogenic and tectonic model. The summary of regional geology and metallogenesis presented here is based on publications of the major international collaborative studies of the metallogenesis and tectonics of Northeast Asia that have been led by the U.S. Geological Survey (USGS). These studies have produced two broad types of publications (1) a series of regional geologic, mineral-deposit, and metallogenic-belt maps, with companion descriptions of the region, and (2) a suite of metallogenic and tectonic analyses of the same region. The study area consists of eastern Russia (most of eastern Siberia and the Russian Far East), Mongolia, northern China, South Korea, Japan, and adjacent offshore areas. The major cooperative agencies are the Russian Academy of Sciences; the Academy of Sciences of the Sakha Republic (Yakutia); VNIIOkeangeologia and Ministry of Natural Resources of the Russian Federation; the Mongolian Academy of Sciences; the Mongolian University of Science and Technology; the Mongolian National University; Jilin University, Changchun, People?s Republic of China, the China Geological Survey; the Korea Institute of Geosciences and Mineral Resources; the Geological Survey of Japan/AIST; the University of Texas, Arlington, and the U.S. Geological Survey (USGS). This study builds on and extends the data and interpretations from a previous project on the Major Mineral Deposits, Metallogenesis, and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera conducted by the USGS, the Russian Academy of Sciences, the Alaska Division of Geological and Geophysical Surveys, and the Geological Survey of Canada. The major products of this project were summarized by Naumova and others (2006) and are described in appendix A.

Introduction to Regional Geology, Tectonics, and Metallogenesis of Northeast Asia

USGS Publications Warehouse

Parfenov, Leonid M.; Badarch, Gombosuren; Berzin, Nikolai A.; Hwang, Duk-Hwan; Khanchuk, Alexander I.; Kuzmin, Mikhail I.; Nokleberg, Warren J.; Obolenskiy, Alexander O.; Ogasawara, Masatsugu; Prokopiev, Andrei V.; Rodionov, Sergey M.; Smelov, Alexander P.; Yan, Hongquan

2007-01-01

This introduction presents an overview of the regional geology, tectonics, and metallogenesis of Northeast Asia. The major purposes are to provide a relatively short summary of these features for readers who are unfamiliar with Northeast Asia; a general scientific introduction for the succeeding chapters of this volume; and an overview of the methodology of metallogenic and tectonic analysis employed for Northeast Asia. The introduction also describes how a high-quality metallogenic and tectonic analysis, including synthesis of an associated metallogenic-tectonic model will greatly benefit refinement of mineral deposit models and deposit genesis; improvement of assessments of undiscovered mineral resources as part of quantitative mineral resource assessment studies; land-use and mineral exploration planning; improvement of interpretations of the origins of host rocks, mineral deposits, and metallogenic belts; and suggestions for new research. The compilation, synthesis, description, and interpretation of metallogenesis and tectonics of major regions, such as Northeast Asia (Eastern Russia, Mongolia, northern China, South Korea, and Japan) and the Circum-North Pacific (Russian Far East, Alaska, and Canadian Cordillera) requires a complex methodology. The methodology includes: (1) definitions of key terms; (2) compilation of a regional geologic base map that can be interpreted according to modern tectonic concepts and definitions; (3) compilation of a mineral deposit database that enables the determination of mineral deposit models, and relations of deposits to host rocks and tectonic origins; (4) synthesis of a series of mineral deposit models that characterize the known mineral deposits and inferred undiscovered deposits of the region; (5) compilation of a series of maps of metallogenic belts constructed on the regional geologic base map; and (6) formulation of a unified metallogenic and tectonic model. The summary of regional geology and metallogenesis in this introduction is based on publications of the major international collaborative studies of the metallogenesis and tectonics of Northeast Asia that were led by the U.S. Geological Survey. These studies have produced two broad types of publications. One type is a series of regional geologic, mineral deposit, and metallogenic belt maps and companion descriptions for the regions. Examples of major publications of this type are Obolenskiy and others (2003a, b, 2004), Parfenov and others (2003, 2004a, b), Nokleberg and others (2004), Rodionov and others (2004), and Naumova and others (2006). The other type is a suite of metallogenic and tectonic analyses of these same regions. Examples of major publications of this type are Rodionov and others (2004), Nokleberg and others (2000, 2004, 2005), and Naumova and others (2006). The Northeast Asia project area consists of eastern Russia (most of Siberia and most of the Russian Far East), Mongolia, Northern China, South Korea, Japan, and adjacent offshore areas. This area is approximately bounded by 30 to 82? N. latitude and 75 to 144? E. longitude. The major participating agencies are the Russian Academy of Sciences, Academy of Sciences of the Sakha Republic (Yakutia), VNIIOkeangeologia and Ministry of Natural Resources of the Russian Federation, Mongolian Academy of Sciences, Mongolian University of Science and Technology, Mongolian National University, Jilin University, Changchun, China, the China Geological Survey, the Korea Institute of Geosciences and Mineral Resources, the Geological Survey of Japan/AIST, University of Texas Arlington, and the U.S. Geological Survey. The Northeast Asia project extends and build on data and interpretations from a previous project on the Major Mineral Deposits, Metallogenesis, and Tectonics of the Russian Far East, Alaska, and the Canadian Cordillera that was conducted by the USGS, the Russian Academy of Sciences, the Alaska Division of Geological and Geophysical Surveys,

Cenozoic plate reconstruction of the South China Sea region

NASA Astrophysics Data System (ADS)

Lee, Tung-Yi; Lawver, Lawrence A.

1994-07-01

Reconstructions of the South China Sea region at 60 Ma, 40 Ma, 30 Ma, 20 Ma, 10 Ma and 5 Ma are presented. We have attempted to place the South China Sea Basin in a regional tectonic framework. The tectonic evolution of the major blocks surrounding the South China Sea were analyzed, as well as the relative motions of the Indian and Australian plates. We have tried to correct the tectonic models available in this region. A 3-D graphics terminal was used to derive rotation poles for the different tectonic blocks and our model was then tested to determine its self-consistency. When the model conflicted with previous interpretations the input data were evaluated for alternative explanations. At least two, and possibly three, stages of extension can be recognized in this region. The earliest one, active in the Late Cretaceous to Eocene, involved NW-SE extension. The second one, active from the Late Eocene to Early Miocene involved north-south extension. The third stage of extension, which probably trended NW-SE, can be dated as post-Oligocene. The first extensional event produced the NE-SW trending proto-South China Sea and a series of sedimentary basins along the South China margin. Following the southeastward extrusion of Indochina, the proto-South China Sea was mostly consumed at the Palawan Trough. Renewed north-south extension in the South China continental margin started the present-day South China Sea spreading in the Oligocene. The southeastward extrusion of Indochina, blocked by Sundaland, resulted in the NW-SE trending opening of the South China Sea Basin in the Early Miocene. Collision of the North Palawan microcontinental block with the West Philippines block stopped the opening of the South China Sea at the end of Early Miocene. Spreading activity switched to the Sulu Sea Basin in the Middle Miocene but collision between the Sulu Ridge and the West Philippines at Mindanao halted the opening of the Sulu Sea at the end of the Middle Miocene. In the Late Miocene, Greater India continued its northward path and seems to have ripped open the Andaman Sea. In the Pliocene, subduction along the northern Manila Trench placed the North Luzon Arc on a collision path with the East Asia continental margin at Taiwan. Our reconstructions, along with detailed geological and geophysical information, may be used as a predictive tool for basin evolution models and block interactions in this region. The development of the South China Sea Basin, the Gulf of Thailand, the Malay Basin and the central Thailand basins are the result of collision-induced extensional forces. The Sulu, Celebes and Sumatra basins were formed as a consequence of prolonged subduction. The opening of the Pearl River Mouth, West Natuna, South China Sea, Sulu, and possibly Celebes, basins were terminated by various plate collisions. During the course of plate reorganizations major boundary faults have changed their slip senses during different stages of evolution.

Cenozoic pulsed compression of Da'an-Dedu Fault Zone in Songliao Basin (NE China) and its implications for earthquake potential: Evidence from seismic data

NASA Astrophysics Data System (ADS)

Yu, Zhongyuan; Zhang, Peizhen; Min, Wei; Wei, Qinghai; Zhao, Bin

2018-01-01

The Da'an-Dedu Fault Zone (DDFZ) is a major tectonic feature cutting through the Songliao Basin from south to north in NE China. Pulsed compression deformation of DDFZ during the Cenozoic implies a complex geodynamic process, and the latest stage of which occurred in the Quaternary directly influences the present seismicity of the interior basin. Although most of the evidence for Quaternary deformation about the Songliao Basin in the past decades was concentrated in marginal faults, all five earthquake swarms with magnitudes over 5.0 along the buried DDFZ with no surface expression during the past 30 years suggest it is a main seismogenic structure with seismic potential, which should deserve more attention of geologists. However, limited by the coverage of the Quaternary sedimentary and absence of strong historic and instrumental earthquakes records (M > 7), the geometric pattern, Quaternary activity and seismic potential of the DDFZ remain poorly understood. Thus, unlike previous geophysical studies focused on crust/mantle velocity structure across the fault and the aim of exploring possible mineral resources in the basin, in this study we have integrated a variety of the latest seismic data and drilling holes from petroleum explorations and shallow-depth seismic reflection profiles, to recognize the Cenozoic pulsed compression deformation of the DDFZ, and to discuss its implication for earthquake potential. The results show that at least four stages of compression deformation have occurred along the DDFZ in the Cenozoic: 65 Ma, 23 Ma, 5.3 Ma, and 1.8 Ma, respectively, although the geodynamic process behind which still in dispute. The results also imply that the tectonic style of the DDFZ fits well with the occurrence of modern seismic swarms. Moderate earthquake potential (M ≤ 7.0) is suggested along the DDFZ.

Petrogenesis and tectonic implications of Early Cretaceous volcanic rocks from Lingshan Island in the Sulu Orogenic Belt

NASA Astrophysics Data System (ADS)

Meng, Yuanku; Santosh, M.; Li, Rihui; Xu, Yang; Hou, Fanghui

2018-07-01

The Dabie-Sulu orogenic belt in eastern China marks the boundary between the Yangtze Block and the North China Block. Here we investigate a suite of volcanic rocks from Lingshan Island in the Sulu belt comprising rhyolite, trachyte, trachyandesite and basaltic trachyandesite. We present petrological, geochemical and zircon Usbnd Pb ages and Hfsbnd O isotope data with a view to gain insights on the petrogenesis and tectonic implications. SHRIMP II analyses of zircon grains from the rhyolite yield 206Pb/238U age of 127.6 ± 1.3 Ma and LA-MC-ICP-MS dating show 126.3 ± 1.2 Ma and 127.3 ± 1.1 Ma, together constraining the eruption time as Early Cretaceous. LA-MC-ICP-MS analyses of zircon grains from the andesitic rocks yield 206Pb/238U ages of 129.0 ± 1.6 Ma, 129.8 ± 1.5 Ma and 130.9 ± 1.0 Ma. Geochemically, the rhyolite shows shoshonitic features with low MgO and Cr, but high Na2O + K2O. The zircon grains from these rocks yield negative εHf(t) values and low δ18O values, and these together with the presence of Neoproterozoic inherited zircons suggest that the magma source involved melting of the Yangtze crust. The andesitic rocks, including basaltic trachyandesite, trachyandesite and trachyte, show a wide range of SiO2, Mg# values, and Cr, enriched in LILE and LREE, depleted in HFSE (Nb, Ta and Ti), and have significantly negative zircon εHf(t) values, suggesting derivation from subcontinental lithosphere mantle that was metasomatized by felsic melts. Our results, integrated with those from previous studies suggest heterogeneous magma involving the mixing of mantle and crustal sources within an extensional setting in the Early Cretaceous.

Geometry and kinematics of Majiatan Fold-and-thrust Belt, Western Ordos Basin: implication for Tectonic Evolution of North-South Tectonic Belt

NASA Astrophysics Data System (ADS)

He, D.

2017-12-01

The Helan-Chuandian North-South Tectonic Belt crossed the central Chinese mainland. It is a boundary of geological, geophysical, and geographic system of Chinese continent tectonics from shallow to deep, and a key zone for tectonic and geomorphologic inversion during Mesozoic to Cenozoic. It is superimposed by the southeastward and northeastward propagation of Qinghai-Tibet Plateau in late Cenozoic. It is thus the critical division for West and East China since Mesozoic. The Majiatan fold-and-thrust belt (MFTB), locating at the central part of HCNSTB and the western margin of Ordos Basin, is formed by the tectonic evolution of the Helan-Liupanshan Mountains. Based on the newly-acquired high-resolution seismic profiles, deep boreholes, and surface geology, the paper discusses the geometry, kinematics, and geodynamic evolution of MFTB. With the Upper Carboniferous coal measures and the pre-Sinian ductile zone as the detachments, MFTB is a multi-level detached thrust system. The thrusting was mainly during latest Jurassic to Late Cretaceous, breaking-forward in the foreland, and resulting in a shortening rate of 25-29%. By structural restoration, this area underwent extension in Middle Proterozoic to Paleozoic, which can be divided into three phases of rifting such as Middle to Late Proterozoic, Cambiran to Ordovician, and Caboniferous to early Permian. It underwent compression since Late Triassic, including such periods as Latest Triassic, Late Jurassic to early Cretaceous, Late Cretaceous to early Paleogene, and Pliocene to Quaternary, with the largest shortening around Late Jurassic to early Cretaceous period (i.e. the mid-Yanshanian movement by the local name). However, trans-extension since Eocene around the Ordos Basin got rise to the formation the Yingchuan, Hetao, and Weihe grabens. It is concluded that MFTB is the leading edge of the intra-continental Helan orogenic belt, and formed by multi-phase breaking-forward thrusting during Late Jurassic to Cretaceous. During Cenozoic, MFTB is moderately modified by the northeastward compression due to the NE propagation of Qinghai-Tibet Plateau, and distinctly superimposed by the Yingchuan half-graben. North-South Tectonic Belt underwent a full cycle from extension during Middle Proterozoic to Paleozoic to compression since late Triassic.

On the Evolution of Terrestrial Planets: Implications of Evolutionary Paths and Evolving Lid-States

NASA Astrophysics Data System (ADS)

Weller, M. B.; Lenardic, A.

2015-12-01

Growing geodynamic and geochemical evidence suggests that plate tectonics may not have operated on the early Earth, with both the timing of its onset and the length of its activity far from certain [e.g., 1, 2, and references therein]. Accordingly, information from current observations and processes have the potential of sampling portions of the Earth that has both formed under and been modified by differing tectonic regimes. Here we use coupled 3D mantle convection and planetary tectonics simulations to explore evolutionary paths and planetary tectonic regimes. Early in the geologic lifetime of a terrestrial planet, high mantle temperatures favour stagnant-lids. As radiogenics decay, an initial stagnant-lid may yield into a high temperature mobile-lid state. The transition from an initial stagnant-lid is a function of yield strength, in addition to both internal and surface temperatures. Each lid-state has specific diagnostics and implications for internal parameters, and consequently planetary evolution. The implication within this framework is that a system with a different thermal evolution has the potential to migrate through tectonic regimes at the same 'thermal time' (e.g. temperature), but very different 'temporal times'. This indicate that multiple modes of convection and surface tectonics can potentially operate on a single planetary body at different times in its evolution, as consequence of changing internal parameters, surface temperatures, and differing thermal histories. We will discuss the implications of terrestrial worlds that can alternate, and be offset between multiple tectonic states over giga-year timescales. [1] O'Neill et. al. (2013b) Geol. Soc. London; [2] Weller et al. (2015) EPSL

Analysis of the geological structure and tectonic evolution of Xingning-Jinghai sag in deep water area, northern South China Sea

NASA Astrophysics Data System (ADS)

Han, Xiaoying; Ren, Jianye; Lin, Zi; Yang, Linlong

2015-04-01

Recent years, oil and gas exploration of the Pearl River Mouth Basin in the northern margin of South China Sea continuously achieved historic breakthroughs. The Xingning-Jinghai sag, which is located in southeast of the Pearl River Mouth Basin, is a deep-water sag with a great exploration potential. Its tectonic evolution is extremely complex. It experienced Mesozoic subduction to Cenozoic intra-continental rifting background, and finally evolved into a deep-water sag of the northern continental margin of South China Sea. The geological characteristics and the tectonic evolution of Xingning-Jinghai sag was closely related to the process of formation and evolution of the passive continental margin of the northern South China Sea. It is confirmed by many geophysical data that compared with adjacent Chaoshan depression, the crustal thickness of Xingning-Jinghai sag was rapidly thinning, and it developed detachment faults with later magmatic intrusion. The development of detachment faults have dynamic significance for the spreading of the South China Sea. Based on the seismic geological interpretation of 2D seismic data in the study area, the characteristics of detachment fault and supra-detachment basin have been proposed in this study. The characteristics of the detachment fault are low angle and high ratio between heave and throw. The geometry of the detachment fault is a typical lisric shape, with the dip of fault decreasing generally from the seismic profile. The detachment basin where sediments are not deposited over a tilting hanging-wall block but onto a tectonically exhumed footwall which is different from the typical half graben basin. Seismic profiles indicate two different structural styles in the east and west part of Xingning-Jinghai sag. In the west of the sag, there developed two large detachment faults, which control their detachment basin systems and the typical H block, and the two detachment faults are dipping landward and seaward, respectively. In the east, affected by the later volcanic activities, Xingning-Jinghai sag deformed complicatedly and developed a series of landward dipping faults, showing the compound graben structure. Combined with the fault activity quantitative calculation, basin subsidence history and other advanced technology, the basin tectonic evolution has been divided into rift stage and post-rift stage. Considering the extension development evolution of Xingning-Jinghai sag and the extension and thinning of lithosphere under the background of spreading of the South China Sea, we argue that the northern margin of the South China lithosphere experienced an intense stretching and thinning stage. At this period, the subsidence of the Xingning-Jinghai sag was controlled by the detachment faults, indicating a rifting stage. With the development of the detachment faults, the thickness of crust was extremely thinned. After the spreading of the South China Sea the whole sag entered into the depression period which was characterized by thermal subsidence.

Early Paleozoic tectonic reactivation of the Shaoxing-Jiangshan fault zone: Structural and geochronological constraints from the Chencai domain, South China

NASA Astrophysics Data System (ADS)

Sun, Hanshen; Li, Jianhua; Zhang, Yueqiao; Dong, Shuwen; Xin, Yujia; Yu, Yingqi

2018-05-01

The Shaoxing-Jiangshan fault zone (SJFZ), as a fundamental Neoproterozoic block boundary that separates the Yangtze Block from the Cathaysia Block, is the key to understanding the evolution of South China from Neoproterozoic block amalgamation to early Paleozoic crustal reworking. New structural observations coupled with geochronological ages from the Chencai domain indicate that intense ductile deformation and metamorphism along the SJFZ occurred at ∼460-420 Ma, in response to the early Paleozoic orogeny in South China. To the east of the SJFZ, the deformation involves widespread generations of NE-striking foliation, intrafolial folds, and local development of sinistral-oblique shear zones. The shearing deformation occurred under amphibolite facies conditions at temperatures of >550 °C (locally even >650 °C). To the west of the SJFZ, the deformation corresponds to sinistral-oblique shearing along NE-striking, steep-dipping zones under greenschist facies conditions at temperatures of 400-500 °C. These deformation styles, as typical mid-crustal expressions of continental reworking, reflect tectonic reactivation of the pre-existing, deeply rooted Neoproterozoic block boundary in the early Paleozoic. We infer that the tectonic reactivation, possibly induced by oblique underthrusting of north Cathaysia, facilitated ductile shearing and burial metamorphic reactions, giving rise to the high-strain zones and high-grade metamorphic rocks. With respect to pre-existing mechanical weakness, our work highlights the role of tectonic reactivation of early structures in localizing later deformation before it propagates into yet undeformed domains.

Crustal structure and continental dynamics of Central China: A receiver function study and implications for ultrahigh-pressure metamorphism

NASA Astrophysics Data System (ADS)

He, Chuansong; Dong, Shuwen; Chen, Xuanhua; Santosh, M.; Li, Qiusheng

2014-01-01

The Qinling-Tongbai-Hong'an-Dabie-Sulu orogenic belt records the tectonic history of Paleozoic convergence between the South China and North China Blocks. In this study, the distribution of crustal thickness and P- and S-wave velocity ratio (Vp/Vs) is obtained by using the H-k stacking technique from the Dabie-Sulu belt in central China. Our results show marked differences in the crustal structure between the Dabie and Sulu segments of the ultrahigh-pressure (UHP) orogen. The lower crust in the Dabie orogenic belt is dominantly of felsic-intermediate composition, whereas the crust beneath the Sulu segment is largely intermediate-mafic. The crust of the Dabie orogenic belt is thicker by ca. 3-5 km as compared to that of the surrounding region with the presence of an ‘orogenic root’. The crustal thickness is nearly uniform in the Dabie orogenic belt with a generally smooth crust-mantle boundary. A symmetrically thickened crust in the absence of any deep-structural features similar to that of the Yangtze block suggests no supportive evidence for the proposed northward subduction of the Yangtze continental block beneath the North China Block. We propose that the collision between the Yangtze and North China Blocks and extrusion caused crustal shortening and thickening, as well as delamination of the lower crust, resulting in asthenospheric upwelling and lower crustal UHP metamorphism along the Dabie Orogen. Our results also reveal the presence of a SE to NW dipping Moho in the North China Block (beneath the Tran-North China Orogen and Eastern Block), suggesting the fossil architecture of the northwestward subduction of the Kula plate.

The electrical structure of lithosphere beneath Northeast China —Preliminary results from SinoProbe-01-04

NASA Astrophysics Data System (ADS)

Hui, F.; Qing, Z.; Gengen, Q.; Fagen, P.; Dawei, B.; Baotun, G.; Jingqi, L.; Changwang, L.; Xiaochang, L.; Meixing, H.; Bingrui, D.

2012-12-01

Being constituted by the Seberia, Northern China fossil plate and Pacific Plate, the tectonics of Northeast China are very complicated. In order to study the electrical structure in these areas, the project SinoProbe-01-04 'Experimental study of 'standard monitoring network' of continental EM parameters in Northeast China' have established a 4°×4°regional MT array covering the whole Northeast China(Fig. 1). To make sure that MT data observed on each standard point representatively, a cross profile with the standard point being center and eight auxiliary measuring points around has been designed in practical work, and the same direction of the physical measuring point should have 20 km space, the observation time should be more than 120 hours in standard point and more than 24 hours in each auxiliary station. Both broadband MT equipment (V5-2000) and long-period MT equipment (LEMI-417M) have been used together in standard point, then the ultra-wideband electromagnetic signals at 320HZ-1/10000Hz can be acquired by combining the field data observed by each equipment. Eleven MT standard network control point with total 99 physical measuring points have been finished in 2010, then those works were repeated again in 2011 to make sure observed result reliable. Based on the observed result, this article preliminary analysis the electrical structure of each major tectonic element in Northeast China, which including the regularity of distribution of regional electrical spindle, the distribution characteristics of vertical conductivity, development status of the low resistivity layer in the crust, and the depth of the high conductivity layer in upper mantle. It has been founded that the electrical features of the major tectonic element in Northeast China are different and appear electrical-heterogeneous in cross direction. Fig.1 MT array observed site

Geothermal studies in China

NASA Astrophysics Data System (ADS)

Ji-Yang, Wang; Mo-Xiang, Chen; Ji-An, Wang; Xiao, Deng; Jun, Wang; Hsien-Chieh, Shen; Liang-Ping, Hsiung; Shu-Zhen, Yan; Zhi-Cheng, Fan; Xiu-Wen, Liu; Ge-Shan, Huang; Wen-Ren, Zhang; Hai-Hui, Shao; Rong-Yan, Zhang

1981-01-01

Geothermal studies have been conducted in China continuously since the end of the 1950's with renewed activity since 1970. Three areas of research are defined: (1) fundamental theoretical research on geothermics, including subsurface temperatures, terrestrial heat flow and geothermal modeling; (2) exploration for geothermal resources and exploitation of geothermal energy; and (3) geothermal studies in mines. Regional geothermal studies have been conducted recently in North China and more than 2000 values of subsurface temperature have been obtained. Temperatures at a depth of 300 m generally range from 20 to 25°C with geothermal gradients from 20 to 40°C/km. These values are regarded as an average for the region with anomalies related to geological factors. To date, 22 reliable heat flow data from 17 sites have been obtained in North China and the data have been categorized according to fault block tectonics. The average heat flow value at 16 sites in the north is 1.3 HFU, varying from 0.7 to 1.8 HFU. It is apparent that the North China fault block is characterized by a relatively high heat flow with wide variations in magnitude compared to the mean value for similar tectonic units in other parts of the world. It is suggested that although the North China fault block can be traced back to the Archaean, the tectonic activity has been strengthening since the Mesozoic resulting in so-called "reactivation of platform" with large-scale faulting and magmatism. Geothermal resources in China are extensive; more than 2000 hot springs have been found and there are other manifestations including geysers, hydrothermal explosions, hydrothermal steam, fumaroles, high-temperature fountains, boiling springs, pools of boiling mud, etc. In addition, there are many Meso-Cenozoic sedimentary basins with widespread aquifers containing geothermal water resources in abundance. The extensive exploration and exploitation of these geothermal resources began early in the 1970's. Since then several experimental power stations using thermal water have been set up in Fengshun (Fungshun),

Estimation of subsurface formation temperature in the Yangtze area, South China: implications for shale gas generation and preservation

NASA Astrophysics Data System (ADS)

Liu, S.; Hao, C.; Li, X.; Xu, M.

2015-12-01

Temperature is one key parameter for hydrocarbon generation and preservation, also playing important role in geothermal energy assessment;however, accurate regional temperature pattern is still challenging, owing to a lack of data coverage and data quality as well. The Yangtze area, located in the South China, is considered as the most favorable target for shale gas resource exploration in China, and attracts more and more attention recently. Here we used the newly acquired steady-state temperature loggings, reliable Drilling Stem Test temperature data available and thermal properties, estimated the subsurface temperature-at-depth for the Yangtze area. Results show that the geothermal gradient ranges between 17 K/m and 74K/m, mainly falling into 20~30K/m, with a mean of 24 K/m; heat flow varies from 25 mW/m2 to 92 mW/m2, with a mean of 65 mW/m2. For the estimated temperature-at-depth, it is about 20~50 ℃ at the depth of 1000m, 50~80℃ for that at 2000m; while the highest temperature can be up to 110℃ at 3000m depth. Generally, the present-day geothermal regime of the Yangtze area is characterized by high in the northeast, low in the middle and localized high again in the southwest, and this pattern is well consistent with the tectono-thermal processes occurred in the area. Due to Cenozoic crustal extension in the northeastern Yangtze area, magmatism is prevailed, accounting for the high heat flow observed. Precambrian basement exists in the middle Yangtze area, such as the Xuefeng and Wuling Mountains, heat flow and subsurface temperature accordingly show relatively low as well. While for the southwestern Yangtze area, especially Yunnan and western Sichuan provinces, localized Cenozoic magmatism and tectonic activities are available, which is attributed to the high geothermal regime there. Considering the Paleozoic intensive tectonic deformation in the Yangtze area, tectonically stable area is prerequisite for shale gas preservation. Geothermal regime analysis presented here, indicates that the middle and northwestern Yangtze areas are favorable for shale gas preservation. In addition, the localized high temperature within the generally low geothermal background is also suggested here as a possible beneficial condition for shale gas generation.

Geochronology and geochemistry of tuff beds from the Shicaohe Formation of Shennongjia Group and tectonic evolution in the northern Yangtze Block, South China

NASA Astrophysics Data System (ADS)

Du, Qiuding; Wang, Zhengjiang; Wang, Jian; Deng, Qi; Yang, Fei

2016-03-01

Meso- to Neoproterozoic magmatic events are widespread in the Yangtze Block. The geochronology and tectonic significance of the Shennongjia Group in the Yangtze Block are still highly controversial. An integrated geochronology and geochemistry approach provides new insights into the geochronological framework, tectonic setting, magmatic events, and basin evolution of the northern Yangtze Block. Our new precise sensitive high-resolution ion microprobe U-Pb data indicate a deposition age of 1180 ± 15 Ma for the Shicaohe Formation subalkaline basaltic tuff that is geochemically similar to modern intracontinental rift volcanic rocks. The integration of available geochemical data together with our new U-Pb ages indicates the Shicaohe Formation subalkaline basaltic tuff formed ca. 1180 in a continental rift-related setting on a passive continental margin. The Shennongjia Group is topped by the Zhengjiaya Formation volcanic sequence, indicating arc-related igneous events at 1103 Ma. The transition of the late Mesoproterozoic tectonic regime from intracontinental extension to convergence occurred between ca. 1180 and 1103 Ma in the northern Yangtze Block. Tectonic evolution in the Neoproterozoic led to accretion along the northern margin of the Yangtze Block. These results provide geochronological evidence, which is of utmost importance for reconfiguration of the chronostratigraphic framework and for promoting research on Mesoproterozoic strata in China, thereby increasing understanding of magmatic events and basin evolutionary history in the northern Yangtze Block.

Inversion of the Erlian Basin (NE China) in the early Late Cretaceous: Implications for the collision of the Okhotomorsk Block with East Asia

NASA Astrophysics Data System (ADS)

Guo, Zhi-Xin; Shi, Yuan-Peng; Yang, Yong-Tai; Jiang, Shuan-Qi; Li, Lin-Bo; Zhao, Zhi-Gang

2018-04-01

A significant transition in tectonic regime from extension to compression occurred throughout East Asia during the mid-Cretaceous and has stimulated much attention. However, the timing and driving mechanisms of the transition remain disputed. The Erlian Basin, a giant late Mesozoic intracontinental petroliferous basin located in the Inner Mongolia, Northeast China, contains important sedimentary and structural records related to the mid-Cretaceous compressional event. The stratigraphical, sedimentological and structural analyses reveal that a NW-SE compressional inversion occurred in the Erlian Basin between the depositions of the Lower Cretaceous Saihan and Upper Cretaceous Erlian formations, causing intense folding of the Saihan Formation and underlying strata, and the northwestward migration of the depocenters of the Erlian Formation. Based on the newly obtained detrital zircon U-Pb data and previously published paleomagnetism- and fossil-based ages, the Saihan and Erlian formations are suggested as latest Aptian-Albian and post-early Cenomanian in age, respectively, implying that the inversion in the Erlian Basin occurred in the early Late Cretaceous (Cenomanian time). Apatite fission-track thermochronological data record an early Late Cretaceous cooling/exhuming event in the basin, corresponding well with the aforementioned sedimentary, structural and chronological analyses. Combining with the tectono-sedimentary evolutions of the neighboring basins of the Erlian Basin, we suggest that the early Late Cretaceous inversional event in the Erlian Basin and the large scale tectonic transition in East Asia shared the common driving mechanism, probably resulting from the Okhotomorsk Block-East Asia collisional event at about 100-89 Ma.

Recognized Multiple Rifts of the Neoproterozoic in the Initiation of the Tarim Craton (NW China) and Their Tectonic Implications

NASA Astrophysics Data System (ADS)

He, B.; Jiao, C.; Huang, T.; Zhou, X.; Cai, Z.; Cao, Z.; Jiang, Z.; Cui, J.; Yu, Z.; Chen, W.

2017-12-01

The Tarim Basin is the largest, oil-bearing and superimposed basin in the northwest of China. The development and tectonic property of the initial Tarim basin have been acutely disputed and remain enigmatic. Urgently need to reveal the origin and formation dynamics of the Tarim Carton and evaluate the potential of the deep energy resources. However, covered by vast desert and huge-thickness sedimentary strata, suffered by multiple tectonic movements, seismic data with low signal- to- noise ratio in the deep are the critical difficulties. We analyse 4 field outcrops, 18 wells, 27 reprocessed seismic reflection profiles with high SNR across the basin and many ancillary ones and aeromagnetic data. We find about 20 normal fault-controlled rift depressions of the Cryogenian and Ediacaran scattered in the Tarim basin, which developed on the Precambrian metamorphic and crystalline basements and covered by the epeiric sea and basin facies sediments of the Lower Cambrian. The structural styles of the rifts are mainly half grabens, symmetrical troughs and horst-grabens. The regional differences exist obviously in spatial and temporal. The WNW-ESE-trending faults occur in the central part and northern of the basin and the NE, and the NEE-trending faults occur in the southern parts, which response with the anomaly of aeromagnetic. Some main faults of the Ediacaran inherited from the Cryogenian and some occurred newly, the more rifting depressions occurred during the Ediacaran. The extensional NNW-SSE-oriented and NNE-SSW-oriented paleostress field occurred simultaneously during rifting, and accompanied with the clockwise shearing. According to the activities of syn-sedimentary faults, magmatic events and sediments, the tectonic properties of the rifts are different depending on their locations in the Tarim craton. The rifting phases mainly occurred from 780 Ma to 615 Ma. The formation of rifts were associated with the opening of the South Tianshan Ocean and the South Altun-West Kunlun Oceans, which located at the north and south margin of the Tarim block, respectively, in response to break-up of the Rodinia supercontinent. The multiple rifts recognized reflect the fine-scale structure of the initiation of the Tarim craton and is the significant for understanding of the plate system and formation dynamics.

Tidal dynamics and mangrove carbon sequestration during the Oligo–Miocene in the South China Sea

PubMed Central

Collins, Daniel S.; Avdis, Alexandros; Allison, Peter A.; Johnson, Howard D.; Hill, Jon; Piggott, Matthew D.; Hassan, Meor H. Amir; Damit, Abdul Razak

2017-01-01

Modern mangroves are among the most carbon-rich biomes on Earth, but their long-term (≥106 years) impact on the global carbon cycle is unknown. The extent, productivity and preservation of mangroves are controlled by the interplay of tectonics, global sea level and sedimentation, including tide, wave and fluvial processes. The impact of these processes on mangrove-bearing successions in the Oligo–Miocene of the South China Sea (SCS) is evaluated herein. Palaeogeographic reconstructions, palaeotidal modelling and facies analysis suggest that elevated tidal range and bed shear stress optimized mangrove development along tide-influenced tropical coastlines. Preservation of mangrove organic carbon (OC) was promoted by high tectonic subsidence and fluvial sediment supply. Lithospheric storage of OC in peripheral SCS basins potentially exceeded 4,000 Gt (equivalent to 2,000 p.p.m. of atmospheric CO2). These results highlight the crucial impact of tectonic and oceanographic processes on mangrove OC sequestration within the global carbon cycle on geological timescales. PMID:28643789

Origin of marginal basins of the NW Pacific and their plate tectonic reconstructions

NASA Astrophysics Data System (ADS)

Xu, Junyuan; Ben-Avraham, Zvi; Kelty, Tom; Yu, Ho-Shing

2014-03-01

Geometry of basins can indicate their tectonic origin whether they are small or large. The basins of Bohai Gulf, South China Sea, East China Sea, Japan Sea, Andaman Sea, Okhotsk Sea and Bering Sea have typical geometry of dextral pull-apart. The Java, Makassar, Celebes and Sulu Seas basins together with grabens in Borneo also comprise a local dextral, transform-margin type basin system similar to the central and southern parts of the Shanxi Basin in geometry. The overall configuration of the Philippine Sea resembles a typical sinistral transpressional "pop-up" structure. These marginal basins except the Philippine Sea basin generally have similar (or compatible) rift history in the Cenozoic, but there do be some differences in the rifting history between major basins or their sub-basins due to local differences in tectonic settings. Rifting kinematics of each of these marginal basins can be explained by dextral pull-apart or transtension. These marginal basins except the Philippine Sea basin constitute a gigantic linked, dextral pull-apart basin system.

The interior of Venus and Tectonic implications

NASA Technical Reports Server (NTRS)

Phillips, R. J.; Malin, M. C.

1983-01-01

It is noted in the present consideration of the Venus lithosphere and its implications for plate tectonics that the major linear elevated regions of Venus, which are associated with Beta Regio and Aphrodite Terra, do not seem to have the shape required for sure interpretation as the divergent plate boundaries of seafloor spreading. Such tectonics instead appear to be confined to the median plains, and may not be resolvable in the Pioneer Venus altimetry data. The ratios of gravity anomalies to topographic heights indicate that surface load compensation occurs at depths greater than about 100 km under the western Aphrodite Terra and 400 km under Beta Regio, with at least some of this compensation probably being maintained by mantle convection. It is also found that the shape of Venus's hypsogram is very different from the ocean mode of the earth's hypsogram, and it is proposed that Venus tectonics resemble intraplate, basin-and-swell tectonics on earth.

Carboniferous volcanic rocks associated with back-arc extension in the western Chinese Tianshan, NW China: Insight from temporal-spatial character, petrogenesis and tectonic significance

NASA Astrophysics Data System (ADS)

Su, Wenbo; Cai, Keda; Sun, Min; Wan, Bo; Wang, Xiangsong; Bao, Zihe; Xiao, Wenjiao

2018-06-01

The Yili-Central Tianshan Block, as a Late Paleozoic major continental silver of the Central Asian Orogenic Belt, holds a massive volume of Carboniferous volcanic rocks, occurring as subparallel magmatic belts. However, the petrogenesis and tectonic implications of these volcanic rocks remain enigmatic. This study compiled isotopic age data for mapping their temporal-spatial character, and conducted petrogenetic study of these magmatic belts, aiming to understand their tectonic implications. Our compiled dataset reveals four magmatic belts in the Yili-Central Tianshan Block, including the Keguqinshan-Tulasu belt and the Awulale belt in the north, and the Wusun Mountain belt and the Haerk-Nalati belt in the south. In addition, our new zircon U-Pb dating results define two significant Early Carboniferous eruptive events (ca. 355-350 Ma and 325 Ma) in the Wusun Mountain belt. Volcanic rocks of the early significant eruptive event (ca. 355-350 Ma) in the Wusun Mountain comprise basalt, trachy-andesite, andesite, dacite and rhyolite, which are similar to the typical rock assemblage of a continental arc. Their positive εNd(t) values (+0.3 to +1.5) and relatively high Th/Yb and Nb/Yb ratios suggest the derivation from a mantle source with additions of slab-derived components. The gabbroic dykes and rhyolites of the late volcanic event (ca. 325 Ma) form a bimodal rock association, and they show alkaline features, with relatively low Th/Yb and Th/Nb ratios, and higher positive εNd(t) values (εNd(t) = +3.3-+5.0). It is interpreted that the gabbroic dykes and rhyolites may have been derived from mantle and juvenile crustal sources, respectively. The isotopic and trace elemental variations with time elapse of the Wusun Mountain magmatic belt show an important clue for strengthening depletion of the magma sources. Considering the distinctive temporal-spatial character of the Carboniferous volcanic rocks, two separate subduction systems in the southern and northern margins of the Yili-Central Tianshan Block were suggested to be the causes for extensive emplacements of the igneous products, which may be in an association with synchronous subduction of the South Tianshan and the North Tianshan oceanic plates, respectively. In this tectonic context, the Carboniferous magmatic rocks of the Wusun Mountain may be a tectonic response to the change in magma sources due to back-arc propagation in the western Chinese Tianshan.

Geochronological and sedimentological evidences of Panyangshan foreland basin for tectonic control on the Late Paleozoic plate marginal orogenic belt along the northern margin of the North China Craton

NASA Astrophysics Data System (ADS)

Li, Jialiang; Zhou, Zhiguang; He, Yingfu; Wang, Guosheng; Wu, Chen; Liu, Changfeng; Yao, Guang; Xu, Wentao; Zhao, Xiaoqi; Dai, Pengfei

2017-08-01

There is a wide support that the Inner Mongolia Palaeo-uplift on the northern margin of the North China Craton has undergone an uplifting history. However, when and how did the uplift occurred keeps controversial. Extensive field-based structural, metamorphic, geochemical, geochronological and geophysical investigations on the Inner Mongolia Palaeo-uplift, which suggested that the Inner Mongolia Palaeo-uplift was an uplifted region since the Early Precambrian or range from Late Carboniferous-Early Jurassic. The geochemical characteristics of the Late Paleozoic to Early Mesozoic intrusive rocks indicated that the Inner Mongolia Palaeo-uplift was an Andean-type continental margin that is the extensional tectonic setting. To address the spatial and temporal development of the Inner Mongolia Palaeo-uplift, we have carried out provenance analysis of Permian sedimentary rocks which collected from the Panyangshan basin along the northern margin of the North China Craton. The QFL diagram revealed a dissected arc-recycled orogenic tectonic setting. Moreover, the framework grains are abundant with feldspar (36-50%), indicating the short transport distance and unstable tectonic setting. Detrital zircon U-Pb analysis ascertained possible provenance information: the Precambrian basement ( 2490 and 1840 Ma) and continental arc magmatic action ( 279 and 295 Ma) along the northern margin of the North China Craton. The projection in rose diagrams of the mean palaeocurrent direction, revealing the SSW and SSE palaeoflow direction, also shows the provenance of the Panyangshan basin sources mainly from the Inner Mongolia Palaeo-uplift. The andesite overlying the Naobaogou Formation has yielded U-Pb age of 277.3 ± 1.4 Ma. The additional dioritic porphyry dike intruded the Naobaogou and Laowopu Formations, which has an emplacement age of 236 ± 1 Ma. The above data identify that the basin formed ranges from Early Permian to Middle Triassic (277-236 Ma). Accordingly, the Inner Mongolia Palaeo-uplift also was developed in the Early Permian to Middle Triassic (277-236 Ma), related to the final closure of the Paleo-Asian Ocean. Furthermore, we advocate that the tectonic setting of Inner Mongolia Palaeo-uplift probably belonged to the plate marginal orogenic belt during Early Permian-Middle Triassic.

Geochronological and sedimentological evidences of Panyangshan foreland basin for tectonic control on the Late Paleozoic plate marginal orogenic belt along the northern margin of the North China Craton

NASA Astrophysics Data System (ADS)

Li, Jialiang; Zhou, Zhiguang; He, Yingfu; Wang, Guosheng; Wu, Chen; Liu, Changfeng; Yao, Guang; Xu, Wentao; Zhao, Xiaoqi; Dai, Pengfei

2018-06-01

There is a wide support that the Inner Mongolia Palaeo-uplift on the northern margin of the North China Craton has undergone an uplifting history. However, when and how did the uplift occurred keeps controversial. Extensive field-based structural, metamorphic, geochemical, geochronological and geophysical investigations on the Inner Mongolia Palaeo-uplift, which suggested that the Inner Mongolia Palaeo-uplift was an uplifted region since the Early Precambrian or range from Late Carboniferous-Early Jurassic. The geochemical characteristics of the Late Paleozoic to Early Mesozoic intrusive rocks indicated that the Inner Mongolia Palaeo-uplift was an Andean-type continental margin that is the extensional tectonic setting. To address the spatial and temporal development of the Inner Mongolia Palaeo-uplift, we have carried out provenance analysis of Permian sedimentary rocks which collected from the Panyangshan basin along the northern margin of the North China Craton. The QFL diagram revealed a dissected arc-recycled orogenic tectonic setting. Moreover, the framework grains are abundant with feldspar (36-50%), indicating the short transport distance and unstable tectonic setting. Detrital zircon U-Pb analysis ascertained possible provenance information: the Precambrian basement ( 2490 and 1840 Ma) and continental arc magmatic action ( 279 and 295 Ma) along the northern margin of the North China Craton. The projection in rose diagrams of the mean palaeocurrent direction, revealing the SSW and SSE palaeoflow direction, also shows the provenance of the Panyangshan basin sources mainly from the Inner Mongolia Palaeo-uplift. The andesite overlying the Naobaogou Formation has yielded U-Pb age of 277.3 ± 1.4 Ma. The additional dioritic porphyry dike intruded the Naobaogou and Laowopu Formations, which has an emplacement age of 236 ± 1 Ma. The above data identify that the basin formed ranges from Early Permian to Middle Triassic (277-236 Ma). Accordingly, the Inner Mongolia Palaeo-uplift also was developed in the Early Permian to Middle Triassic (277-236 Ma), related to the final closure of the Paleo-Asian Ocean. Furthermore, we advocate that the tectonic setting of Inner Mongolia Palaeo-uplift probably belonged to the plate marginal orogenic belt during Early Permian-Middle Triassic.

Joint inversion of high resolution S-wave velocity structure underneath North China Basin

NASA Astrophysics Data System (ADS)

Yang, C.; Li, G.; Niu, F.

2017-12-01

North China basin is one of earthquake prone areas in China. Many devastating earthquakes occurred in the last century and before, such as the 1937 M7.0 Heze Earthquake in Shandong province, the 1966 M7.2 Xingtai Earthquake and 1976 Tangshan Earthquake in Hebei province. Knowing the structure of the sediment cover is of great importance to predict strong ground motion caused by earthquakes. Unconsolidated sediments are loose materials, ranging from clay to sand to gravel. Earthquakes can liquefy unconsolidated sediments, thus knowing the distribution and thickness of the unconsolidated sediments has significant implication in seismic hazard analysis of the area. Quantitative estimates of the amount of extension of the North China basin is important to understand the thinning and evolution of the eastern North China craton and the underlying mechanism. In principle, the amount of lithospheric stretching can be estimated from sediment and crustal thickness. Therefore an accurate estimate of the sediment and crustal thickness of the area is also important in understanding regional tectonics. In this study, we jointly invert the Rayleigh wave phase-velocity dispersion and Z/H ratio data to construct a 3-D S-wave velocity model beneath North China area. We use 4-year ambient noise data recorded from 249 temporary stations, and 139 earthquake events to extract Rayleigh wave Z/H ratios. The Z/H ratios obtained from ambient noise data and earthquake data show a good agreement within the overlapped periods. The phase velocity dispersion curve was estimated from the same ambient noise data. The preliminary result shows a relatively low Z/H ratio and low velocity anomaly at the shallow part of sediment basins.

3-D crustal structure beneath the southern Korean Peninsula from local earthquakes

NASA Astrophysics Data System (ADS)

Kim, K. H.; Park, J. H.; Park, Y.; Hao, T.; Kang, S. Y.; Kim, H. J.

2017-12-01

Located at the eastern margin of the Eurasian continent, the geology and tectonic evolution of the Korean Peninsula are closely related to the rest of the Asian continent. Although the widespread deformation of eastern Asia and its relation to the geology and tectonics of the Korean Peninsula have been extensively studied, the answers to many fundamental questions about the peninsula's history remain inconclusive. The three-dimensional subsurface structure beneath the southern Korean Peninsula is poorly known, even though such information could be key in verifying or rejecting several competing models of the tectonic evolution of East Asia. We constructed a three-dimensional velocity model of the upper crust beneath the southern Korean Peninsula using 19,935 P-wave arrivals from 747 earthquakes recorded by high-density local seismic networks maintained by Korea Meteorological Administration and Korea Institute of Geosciences and Mineral Resources. Results show significant lateral and vertical variations: velocity increases from northwest to southeast at shallow depths, and significant velocity variations are observed across the South Korea Tectonic Line between the Okcheon Fold Belt and the Youngnam Massif. Collision between the North China and South China blocks during the Early Cretaceous might have caused extensive deformation and the observed negative velocity anomalies in the region. The results of the tomographic inversion, combined with the findings of previous studies of Bouguer and isostatic gravity anomalies, indicate the presence of high-density material in the upper and middle crust beneath the Gyeongsang Basin in the southeastern Korean Peninsula. Although our results partially support the indentation tectonic model, it is still premature to discard other tectonic evolution models because our study only covers the southern half of the peninsula.

Origin of the Dongsha Event in the South China Sea

NASA Astrophysics Data System (ADS)

Xie, Zhiyuan; Sun, Longtao; Pang, Xiong; Zheng, Jinyun; Sun, Zhen

2017-12-01

Post-rift tectonic activities have been widely observed in the northern continental margin of the South China Sea, especially during the late Miocene. Large numbers of faults became active. Unconformities, uplift of faulted blocks, sequence tilting, erosion along the Dongsha massif and canyon incision were also discriminated at this stage in the Pearl River Mouth basin (PRMB) and the area to the east. This tectonism has been named Dongsha Event. A number of hypotheses have been put forward to explain the mechanism of the Dongsha Event, such as high-velocity lower crustal flow, magmatic underplating, and arc-continent collision. To investigate the tectonic dynamics, sequence contact relationships, fault activities, and magmatism were analyzed along large numbers of seismic profiles that cover the eastern PRMB and Southwest Taiwan Basin. The timing, affected regions, and differences in the intensity of tectonic deformation were assessed, upon which the plate bending model was favored. In order to check the reasonableness of plate bending model, effective elastic thickness and other geodynamic parameters were calculated constrained by uplift area width and regarding the trench as sediment filling. A maximum Te value of 27 km and a minimum value of 4 km were obtained. Integrating with the former stress field calculation, we conclude that the Dongsha Event was mainly affected by subduction and collision of the South China Sea toward the Philippine Sea plate. This event commenced at about 10 Ma and peaked at around 3.6 Ma. Although the high effective elastic thickness required is a problem to be addressed, this research provides by far the most comprehensive evidences to the mechanism of the Dongsha Event.

Origin and tectonic evolution of early Paleozoic arc terranes abutting the northern margin of North China Craton

NASA Astrophysics Data System (ADS)

Zhou, Hao; Pei, Fu-Ping; Zhang, Ying; Zhou, Zhong-Biao; Xu, Wen-Liang; Wang, Zhi-Wei; Cao, Hua-Hua; Yang, Chuan

2017-12-01

The origin and tectonic evolution of the early Paleozoic arc terranes abutting the northern margin of the North China Craton (NCC) are widely debated. This paper presents detrital zircon U-Pb and Hf isotopic data of early Paleozoic strata in the Zhangjiatun arc terrane of central Jilin Province, northeast (NE) China, and compares them with the Bainaimiao and Jiangyu arc terranes abutting the northern margin of the NCC. Detrital zircons from early Paleozoic strata in three arc terranes exhibit comparable age groupings of 539-430, 1250-577, and 2800-1600 Ma. The Paleoproterozoic to Neoarchean ages and Hf isotopic composition of the detrital zircons imply the existence of the Precambrian fragments beneath the arc terranes. Given the evidences from geology, igneous rocks, and detrital zircons, we proposed that the early Paleozoic arc terranes abutting the northern margin of the NCC are a united arc terrane including the exotic Precambrian fragments, and these fragments shared a common evolutionary history from Neoproterozoic to early-middle Paleozoic.

Late Jurassic rhyolites from the Wuchagou region in the central Great Xing'an Range, NE China: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Ji, Zheng; Ge, Wen-Chun; Yang, Hao; Wang, Qing-hai; Zhang, Yan-long; Wang, Zhi-hui; Bi, Jun-Hui

2018-06-01

We report geochronological, whole-rock geochemical, and zircon Hf isotopic data for Late Jurassic rhyolites in the central Great Xing'an Range of northeastern China, to determine their petrogenesis, source, and tectonic setting. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb ages indicate that the rhyolites previously mapped as the lower Permian Dashizhai Formation in the Wuchagou region formed during the Late Jurassic (162-154 Ma). Geochemically, these rhyolites belong to the mid- to high-K calc-alkaline series and show peraluminous characteristics and consistent correlations between major elements and SiO2. They are characterized by enrichments in large ion lithophile elements (LILEs; e.g., Rb and K) and light rare earth elements (LREEs), and depletions in high field strength elements (HFSEs; e.g., Nb, Ta, and Ti) and heavy rare earth elements (HREEs). In situ Hf isotopic analyses of zircons from the rhyolites reveal relatively homogeneous Hf isotopic compositions, with εHf(t) values of +4.84 to +9.44, and two-stage model ages of 606-895 Ma. Based on their eruption ages, geochemical characteristics, and Hf isotopic compositions, we conclude that the magmas that formed the Late Jurassic rhyolites were produced during partial melting of a Neoproterozoic quartz-bearing amphibolite-facies mafic crust. These magmas subsequently underwent extensive fractional crystallization of plagioclase, hornblende, Ti-bearing phases, monazite, and apatite. Combined with previous data, our results demonstrate that the Late Jurassic volcanic rocks in the Great Xing'an Range were formed in a post-collisional extensional setting. The gravitational collapse of the orogenically thickened crust was caused by break-off of the subducted oceanic slab and upwelling of asthenosphere after closure of the Mongol-Okhotsk Ocean.

Neoproterozoic stratigraphic framework of the Tarim Craton in NW China: Implications for rift evolution

NASA Astrophysics Data System (ADS)

Wu, Lin; Guan, Shuwei; Zhang, Shuichang; Yang, Haijun; Jin, Jiuqiang; Zhang, Xiaodan; Zhang, Chunyu

2018-06-01

The Tarim Craton is overlain by thick Neoproterozoic sedimentary successions in rift tectonic setting. This study examines the latest outcrop, seismic, and drilling core data with the objective of investigating the regional stratigraphy to deeply recognize the evolution of rifting in the craton. Cryogenian to Lower Ediacaran successions are mainly composed of clastic rocks with thicknesses of 2000-3000 m, and the Upper Ediacaran successions are composed of carbonate rocks with thicknesses of 500-800 m. The rift basins and stratigraphic zones are divided into northern and southern parts by a central paleo-uplift. The northern rift basin extends through the northern Tarim Craton in an E-W direction with two depocenters (Aksu and Kuruktag). The southern rift basin is oriented NE-SW. There are three or four phases of tillites in the northern zone, while there are two in the southern zone. Given the north-south difference of the stratigraphic framework, the northern rift basin initiated at ca. 740 Ma and the southern rift basin initiated at ca. 780 Ma. During the Cryogenian and Ediacaran, the northern and southern rift basins were separated by the central paleo-uplift, finally connecting with each other in the early Cambrian. Tectonic deformation in the Late Ediacaran led to the formation of a parallel unconformity in the rift basins and an angular unconformity in the central paleo-uplift. The Neoproterozoic rift basins continued to affect the distribution of Lower Cambrian hydrocarbon source rocks. The north-south distribution and evolution of the rift basins in the Tarim Craton have implications for reconstructions of the Rodinia supercontinent.

Implications of ground water chemistry and flow patterns for earthquake studies.

PubMed

Guangcai, Wang; Zuochen, Zhang; Min, Wang; Cravotta, Charles A; Chenglong, Liu

2005-01-01

Ground water can facilitate earthquake development and respond physically and chemically to tectonism. Thus, an understanding of ground water circulation in seismically active regions is important for earthquake prediction. To investigate the roles of ground water in the development and prediction of earthquakes, geological and hydrogeological monitoring was conducted in a seismogenic area in the Yanhuai Basin, China. This study used isotopic and hydrogeochemical methods to characterize ground water samples from six hot springs and two cold springs. The hydrochemical data and associated geological and geophysical data were used to identify possible relations between ground water circulation and seismically active structural features. The data for delta18O, deltaD, tritium, and 14C indicate ground water from hot springs is of meteoric origin with subsurface residence times of 50 to 30,320 years. The reservoir temperature and circulation depths of the hot ground water are 57 degrees C to 160 degrees C and 1600 to 5000 m, respectively, as estimated by quartz and chalcedony geothermometers and the geothermal gradient. Various possible origins of noble gases dissolved in the ground water also were evaluated, indicating mantle and deep crust sources consistent with tectonically active segments. A hard intercalated stratum, where small to moderate earthquakes frequently originate, is present between a deep (10 to 20 km), high-electrical conductivity layer and the zone of active ground water circulation. The ground water anomalies are closely related to the structural peculiarity of each monitoring point. These results could have implications for ground water and seismic studies in other seismogenic areas.

Implications of ground water chemistry and flow patterns for earthquake studies

USGS Publications Warehouse

Guangcai, W.; Zuochen, Z.; Min, W.; Cravotta, C.A.; Chenglong, L.

2005-01-01

Ground water can facilitate earthquake development and respond physically and chemically to tectonism. Thus, an understanding of ground water circulation in seismically active regions is important for earthquake prediction. To investigate the roles of ground water in the development and prediction of earthquakes, geological and hydrogeological monitoring was conducted in a seismogenic area in the Yanhuai Basin, China. This study used isotopic and hydrogeochemical methods to characterize ground water samples from six hot springs and two cold springs. The hydrochemical data and associated geological and geophysical data were used to identify possible relations between ground water circulation and seismically active structural features. The data for ??18O, ??D, tritium, and 14C indicate ground water from hot springs is of meteoric origin with subsurface residence times of 50 to 30,320 years. The reservoir temperature and circulation depths of the hot ground water are 57??C to 160??C and 1600 to 5000 m, respectively, as estimated by quartz and chalcedony geothermometers and the geothermal gradient. Various possible origins of noble gases dissolved in the ground water also were evaluated, indicating mantle and deep crust sources consistent with tectonically active segments. A hard intercalated stratum, where small to moderate earthquakes frequently originate, is present between a deep (10 to 20 km), high-electrical conductivity layer and the zone of active ground water circulation. The ground water anomalies are closely related to the structural peculiarity of each monitoring point. These results could have implications for ground water and seismic studies in other seismogenic areas. Copyright ?? 2005 National Ground Water Association.

Crustal structure of Yunnan province, People's Republic of China, from seismic refraction profiles

USGS Publications Warehouse

Kan, R.-J.; Hu, H.-X.; Zeng, R.-S.; Mooney, W.D.; McEvilly, T.V.

1986-01-01

Seismic refraction, profiles in Yunnan Province, southwestern China, define the crustal structure in an area of active tectonics, on the southern end of the Himalaya-Burma arc. The crustal thickness ranges from 38 to 46 kilometers, and the relatively low mean crustal velocity indicates a crustal composition compatible with normal continental crust and consisting mainly of meta-sedimentary and silicic intrusive rocks, with little mafic or ultramafic component. This composition suggests a crustal evolution involving sedimentary processes on the flank of the Yangtze platform rather than the accretion of oceanic island arcs, as has been proposed. An anomalously low upper-mantle velocity observed on one profile, but not on another at right angles to it may indicate active tectonic processes in the mantle or seismic anisotropy.

Crustal Structure of Yunnan Province, People's Republic of China, from Seismic Refraction Profiles.

PubMed

Kan, R J; Hu, H X; Zeng, R S; Mooney, W D; McEvilly, T V

1986-10-24

Seismic refraction, profiles in Yunnan Province, southwestern China, define the crustal structure in an area of active tectonics on the southern end of the Himalaya-Burma arc. The crustal thickness ranges from 38 to 46 kilometers, and the relatively low mean crustal velocity indicates a crustal composition compatible with normal continental crust and consisting mainly of meta-sedimentary and silicic intrusive rocks, with little mafic or ultramafic component. This composition suggests a crustal evolution involving sedimentary processes on the flank of the Yangtze platform rather than the accretion of oceanic island arcs, as has been proposed. An anomalously low upper-mantle velocity observed on one profile but not on another at right angles to it may indicate active tectonic processes in the mantle or seismic anisotropy.

Study of southern CHAONAN sag lower continental slope basin deposition character in Northern South China Sea

NASA Astrophysics Data System (ADS)

Tang, Y.

2009-12-01

Northern South China Sea Margin locates in Eurasian plate,Indian-Australia plate,Pacific Plates.The South China Sea had underwent a complicated tectonic evolution in Cenozoic.During rifting,the continental shelf and slope forms a series of Cenozoic sedimentary basins,including Qiongdongnan basin,Pearl River Mouth basin,Taixinan basin.These basins fill in thick Cenozoic fluviolacustrine facies,transitional facies,marine facies,abyssal facies sediment,recording the evolution history of South China Sea Margin rifting and ocean basin extending.The studies of tectonics and deposition of depression in the Southern Chaonan Sag of lower continental slope in the Norther South China Sea were dealt with,based on the sequence stratigraphy and depositional facies interpretation of seismic profiles acquired by cruises of“China and Germany Joint Study on Marine Geosciences in the South China Sea”and“The formation,evolution and key issues of important resources in China marginal sea",and combining with ODP 1148 cole and LW33-1-1 well.The free-air gravity anomaly of the break up of the continental and ocean appears comparatively low negative anomaly traps which extended in EW,it is the reflection of passive margin gravitational effect.Bouguer gravity anomaly is comparatively low which is gradient zone extended NE-SW.Magnetic anomaly lies in Magnetic Quiet Zone at the Northern Continental Margin of the South China Sea.The Cenozoic sediments of lower continental slope in Southern Chaonan Sag can be divided into five stratum interface:SB5.5,SB10.5,SB16.5,SB23.8 and Hg,their ages are of Pliocene-Quaternary,late Miocene,middle Miocene,early Miocene,paleogene.The tectonic evolution of low continental slope depressions can be divided into rifting,rifting-depression transitional and depression stages,while their depositional environments change from river to shallow marine and abyssa1,which results in different topography in different stages.The topographic evolvement in the study area includes three stages,that is Eogene,middle stage of lately Oligocene to early Miocene and middle Miocene to Present.Result shows that there are a good association of petroleum source rocks,reservoir rocks and seal rocks and structural traps in the Cenozoic and Mesozoic strata,as well as good conditions for the generation-migration-accumulation-preservation of petroleum in the lower continatal slope of Southern Chaoshan Sag.So the region has good petroleum prospect. Key words:Northern South China Sea;Chaoshan Sag; lower continental slope; deposition.

Multisystem dating of modern river detritus from Tajikistan and China: Implications for crustal evolution and exhumation of the Pamir

USGS Publications Warehouse

Barbara Carappa,; Mustapha, F.S.; Cosca, Michael A.; Gehrels, George E.; Schoenbhohm, L; Sobel, E.; DeCelles.P.,; Russell, Joellen; Goodman, Paul

2014-01-01

The Pamir is the western continuation of Tibet and the site of some of the highest mountains on Earth, yet comparatively little is known about its crustal and tectonic evolution and erosional history. Both Tibet and the Pamir are characterized by similar terranes and sutures that can be correlated along strike, although the details of such correlations remain controversial. The erosional history of the Pamir with respect to Tibet is significantly different as well: Most of Tibet has been characterized by internal drainage and low erosion rates since the early Cenozoic; in contrast, the Pamir is externally drained and topographically more rugged, and it has a strongly asymmetric drainage pattern. Here, we report 700 new U-Pb and Lu-Hf isotope determinations and >300 40Ar/39Ar ages from detrital minerals derived from rivers in China draining the northeastern Pamir and >1000 apatite fission-track (AFT) ages from 12 rivers in Tajikistan and China draining the northeastern, central, and southern Pamir. U-Pb ages from rivers draining the northeastern Pamir are Mesozoic to Proterozoic and show affinity with the Songpan-Ganzi terrane of northern Tibet, whereas rivers draining the central and southern Pamir are mainly Mesozoic and show some affinity with the Qiangtang terrane of central Tibet. The εHf values are juvenile, between 15 and −5, for the northeastern Pamir and juvenile to moderately evolved, between 10 and −40, for the central and southern Pamir. Detrital mica 40Ar/39Ar ages for the northeastern Pamir (eastern drainages) are generally older than ages from the central and southern Pamir (western drainages), indicating younger or lower-magnitude exhumation of the northeastern Pamir compared to the central and southern Pamir. AFT data show strong Miocene–Pliocene signals at the orogen scale, indicating rapid erosion at the regional scale. Despite localized exhumation of the Mustagh-Ata and Kongur-Shan domes, average erosion rates for the northeastern Pamir are up to one order of magnitude lower than erosion rates recorded by the central and southern Pamir. Deeper exhumation of the central and southern Pamir is associated with tectonic exhumation of central Pamir domes. Deeper exhumation coincides with western and asymmetric drainages and with higher precipitation today, suggesting an orographic effect on exhumation. A younging-southward trend of cooling ages may reflect tectonic processes. Overall, cooling ages derived from the Pamir are younger than ages recorded in Tibet, indicating younger and higher magnitudes of erosion in the Pamir.

Age and geochemistry of Neoproterozoic granitoids in the Songnen-Zhangguangcai Range Massif, NE China: Petrogenesis and tectonic implications

NASA Astrophysics Data System (ADS)

Luan, Jin-Peng; Xu, Wen-Liang; Wang, Feng; Wang, Zhi-Wei; Guo, Peng

2017-10-01

This study presents new zircon U-Pb ages and geochemical data for Neoproterozoic granitoids in the Songnen-Zhangguangcai Range Massif (SZRM) of NE China. This dataset provides insights into the Neoproterozoic tectonic setting of the SZRM and the links between this magmatism and the evolution of the Rodinia supercontinent. The zircon U-Pb dating indicates that the Neoproterozoic magmatism within the SZRM can be subdivided into two stages: (1) a ∼917-911 Ma suite of syenogranites and monzogranites, and (2) an ∼841 Ma suite of granodiorites. The 917-911 Ma granitoids contain high concentrations of SiO2 (67.89-71.18 wt.%), K2O (4.24-6.91 wt.%), and Al2O3 (14.89-16.14 wt.%), and low concentrations of TFe2O3 (1.63-3.70 wt.%) and MgO (0.53-0.88 wt.%). They are enriched in the light rare earth elements (LREE) and the large ion lithophile elements (LILE), are depleted in the heavy REE (HREE) and the high field strength elements (HFSE; e.g., Nb, Ta, and Ti), and have slightly positive Eu anomalies, indicating that they are geochemically similar to high-K adakitic rocks. They have zircon εHf (t) values and TDM2 ages from -4.4 to +1.5 and 1915 Ma to 1592 Ma, respectively, suggesting that they were derived from a primary magma generated by the partial melting of ancient thickened lower crustal material. In comparison, the 841 Ma granodiorites contain relatively low concentrations of Al2O3 (14.50-14.58 wt.%) and K2O (3.27-3.29 wt.%), relatively high concentrations of TFe2O3 (3.78-3.81 wt.%) and the HREE, have negative Eu anomalies, and have zircon εHf (t) values and TDM2 ages from -4.7 to +1.0 and 1875 to 1559 Ma, respectively. These granodiorites formed from a primary magma generated by the partial melting of ancient crustal material. The ∼917-911 Ma magmatism within the SZRM is inferred to have formed in an orogenic setting, whereas the ∼841 Ma magmatism formed in an anorogenic setting related to either a post-orogenic tectonic event or the onset of Neoproterozoic continental rifting. It is proposed that the microcontinental massifs within the eastern central Asian orogenic belt of NE China formed during or following the final stage of assembly of Rodinia before rifting away from the Tarim Craton in response to the Rodinia breakup.

A new Triassic shortening-extrusion tectonic model for Central-Eastern Asia: Structural, geochronological and paleomagnetic investigations in the Xilamulun Fault (North China)

NASA Astrophysics Data System (ADS)

Zhao, Pan; Faure, Michel; Chen, Yan; Shi, Guanzhong; Xu, Bei

2015-09-01

At the northern margin of the North China Block (NCB), the Xilamulun Fault (XMF) is a key belt to decipher the tectonic evolution of Central-Eastern Asia, as it records the Paleozoic final closure of the Paleo-Asian Ocean, and localizes a Late Triassic intracontinental deformation. In this study, structural analysis, 40Ar-39Ar dating, and paleomagnetic studies were performed to investigate the kinematics of the XMF and to further discuss its Triassic geodynamic significance in the Central-Eastern Asia framework after the Paleozoic Central Asian Orogenic evolution. The structural analyses reveal two phases of ductile deformation. The first one (D1), which displays N-verging and E-W trending folds, is related to the Early Paleozoic collisional event between the NCB and the Songliao-Hunshandake Block (SHB). The second phase (D2) displays a high-angle foliation and a pervasive sub-horizontal E-W stretching lineation with kinematic criteria indicative of dextral strike-slip shearing. The 40Ar-39Ar dating on mylonitic granite places the main shearing event around 227-209 Ma. This D2 shearing is coeval with that of the dextral strike-slip Bayan Obo-Chifeng Fault (BCF) and the Chicheng-Fengning-Longhua Fault to the south, which together constitute a dextral shearing fault system on the northern margin of the NCB during the Late Triassic. The paleomagnetic study performed on the Middle Permian Guangxingyuan pluton, located between the XMF and BCF, documents a local clockwise rotation of this pluton with respect to the NCB and SHB. Our multidisciplinary study suggests an NNW-SSE shortening and strike-slip shearing dominated tectonic setting on the northern margin of the NCB during the Late Triassic. Combining the contemporaneous dextral strike-slip movements of the XMF and BCF in northern China and the sinistral strike-slip movement of East Gobi Fault (EGF) in southeastern Mongolia with the large-scale tectonic framework, a Late Triassic NNW-SSE shortening-eastward extrusion tectonic model for Central-Eastern Asia is firstly proposed. The NNW-SSE shortening results in the eastward extrusion of the continental wedge bounded by the BCF and EGF, which is accommodated by the different kinematic patterns of the southern (XMF and BCF) and northwestern (EGF) bounding faults. This shortening-extrusion tectonic framework is tentatively interpreted as the result of the far field forces associated with three Late Triassic lithosphere-scale convergences in East Asia: i) northward intracontinental subduction between the NCB and South China Block, ii) collision of the Qiangtang Block with the Qaidam Block, and iii) southward subduction of the Mongol-Okhotsk Ocean beneath the Mongolia Block.

A new Triassic shortening-extrusion tectonic model for Central-EasternAsia: Structural, geochronological and paleomagnetic investigations in the Xilamulun Fault (North China)

NASA Astrophysics Data System (ADS)

Zhao, Pan; Faure, Michel; Chen, Yan; Xu, Bei

2017-04-01

At the northern margin of the North China Block (NCB), the Xilamulun Fault (XMF) is a key belt to decipher the tectonic evolution of Central-Eastern Asia, as it records the Paleozoic final closure of the Paleo-Asian Ocean, and localizes a Late Triassic intracontinental deformation. In this study, structural analysis, 40Ar-39Ar dating, and paleomagnetic studies were performed to investigate the kinematics of the XMF and to further discuss its Triassic geodynamic significance in the Central-Eastern Asia framework after the Paleozoic Central Asian Orogenic evolution. The structural analyses reveal two phases of ductile deformation. The first one (D1), which displays N-verging and E-W trending folds, is related to the Early Paleozoic collisional event between the NCB and the Songliao-Hunshandake Block (SHB). The second phase (D2) displays a high-angle foliation and a pervasive sub-horizontalE-W stretching lineation with kinematic criteria indicative of dextral strike-slip shearing. The 40Ar-39Ar dating on mylonitic granite places the main shearing event around 227-209 Ma. This D2 shearing is coeval with that of the dextral strike-slip Bayan Obo-Chifeng Fault (BCF) and the Chicheng-Fengning-Longhua Fault to the south, which together constitute a dextral shearing fault system on the northern margin of the NCB during the Late Triassic. The paleomagnetic study performed on the Middle Permian Guangxingyuan pluton, located between the XMF and BCF, documents a local clockwise rotation of this pluton with respect to the NCB and SHB. Our multidisciplinary study suggests anNNW-SSE shortening and strike-slip shearing dominated tectonic setting on the northern margin of the NCB during the Late Triassic. Combining the contemporaneous dextral strike-slip movements of the XMF and BCF in northern China and the sinistral strike-slip movement of East Gobi Fault (EGF) in southeastern Mongolia with the large-scale tectonic framework, a Late Triassic NNW-SSE shortening-eastward extrusion tectonic model for Central-Eastern Asia is firstly proposed. The NNW-SSE shortening results in the eastward extrusion of the continental wedge bounded by the BCF and EGF, which is accommodated by the different kinematic patterns of the southern (XMF and BCF) and northwestern (EGF) bounding faults. This shortening-extrusion tectonic framework is tentatively interpreted as the result of the far field forces associated with three Late Triassic lithosphere-scale convergences in East Asia: i)northward intracontinental subduction between the NCB and South China Block, ii)collision of the Qiangtang Block with the Qaidam Block, and iii)southward subduction of the Mongol-Okhotsk Ocean beneath the Mongolia Block.

Venus tectonics - An overview of Magellan observations

NASA Technical Reports Server (NTRS)

Solomon, Sean C.; Smrekar, Suzanne E.; Bindschadler, Duane L.; Grimm, Robert E.; Kaula, William M.; Mcgill, George E.; Phillips, Roger J.; Saunders, R. S.; Schubert, Gerald; Squyres, Steven W.

1992-01-01

Magellan observations of the tectonic characteristics of highland regions on Venus are discussed with reference to competing theories for highland formation and evolution. Complex rigid terrain, or tessera, and the extent to which these elevated blocks of intensely deformed crust may be genetically related to highlands are then considered. Further, the tectonics of plains and lowland regions are examined, including deformation belts and coronae, and possible relations between such features and mantle dynamics. Implications of these observations for the global tectonics of Venus are discussed.

Tectono-climatic implications of Eocene Paratethys regression in the Tajik basin of central Asia

NASA Astrophysics Data System (ADS)

Carrapa, Barbara; DeCelles, Peter G.; Wang, Xin; Clementz, Mark T.; Mancin, Nicoletta; Stoica, Marius; Kraatz, Brian; Meng, Jin; Abdulov, Sherzod; Chen, Fahu

2015-08-01

Plate tectonics and eustatic sea-level changes have fundamental effects on paleoenvironmental conditions and bio-ecological changes. The Paratethys Sea was a large marine seaway that connected the Mediterranean Neotethys Ocean with Central Asia during early Cenozoic time. Withdrawal of the Paratethys from central Asia impacted the distribution and composition of terrestrial faunas in the region and has been largely associated with changes in global sea level and climate such as cooling associated with the Eocene/Oligocene transition (EOT). Whereas the regression has been dated in the Tarim basin (China), the pattern and timing of regression in the Tajik basin, 400 km to the west, remain unresolved, precluding a test of current paleogeographic models. Here we date the Paratethys regression in Tajikistan at ca. 39 million years ago (Ma), which is several million years older than the EOT (at ca. 34 Ma) marking the greenhouse to icehouse climate transition of the Cenozoic. Our data also show a restricted, evaporitic marine environment since the middle-late Eocene and establishment of desert like environments after ca. 39 Ma. The overall stratigraphic record from the Tajik basin and southern Tien Shan points to deposition in a foreland basin setting by ca. 40 Ma in response to active tectonic growth of the Pamir-Tibet Mountains at the same time. Combined with the northwestward younging trend of the regression in the region, the Tajik basin record is consistent with northward growth of the Pamir and suggests significant tectonic control on Paratethys regression and paleoenvironmental changes in Central Asia.

Contemporary Tectonics of China

DTIC Science & Technology

1978-02-01

that it would be of value to the United States to understand seismicity in China because their methods used in predicting large intraplate seismic...ability to discriminate between natural events and nuclear explosions. General Method In order to circumvent the limitations placed on studies of...accurate relative locations. Fault planes maybe determined with this method , thereby removing the ambiguity of the choice of fault plane from a fault plane

Basin-mountain structures and hydrocarbon exploration potential of west Junggar orogen in China

NASA Astrophysics Data System (ADS)

Wu, X.; Qi, X.; Zheng, M.

2015-12-01

Situated in northern Xinjiang, China, in NE-SW trend, West Junggar Orogen is adjacent to Altai fold belt on the north with the Ertix Fault as the boundary, North Tianshan fold belt on the south with the Ebinur Lake Strike-slip Fault as the boundary, and the Junggar Basin on the southeast with Zaire-Genghis Khan-Hala'alat fold belt as the boundary. Covering an area of about 10×104 km2 in China, there are medium and small intermontane basins, Burqin-Fuhai, Tacheng, Hefeng and Hoxtolgay, distributing inside the orogen. Tectonically West Junggar Orogen lies in the middle section of the Palaeo-Asian tectonic domain where the Siberia, Kazakhstan and Tarim Plates converge, and is the only orogen trending NE-SW in the Palaeo-Asian tectonic domain. Since the Paleozoic, the orogen experienced pre-Permian plate tectonic evolution and post-Permian intra-plate basin evolution. Complex tectonic evolution and multi-stage structural superimposition not only give rise to long term controversial over the basin basement property but also complex basin-mountain coupling relations, structures and basin superimposition modes. According to analysis of several kinds of geological and geophysical data, the orogen was dominated by compressive folding and thrust napping from the Siberia plate in the north since the Late Paleozoic. Compressive stress weakened from north to south, corresponding to subdued vertical movement and enhanced horizontal movement of crustal surface from north to south, and finally faded in the overthrust-nappe belt at the northwest margin of the Junggar Basin. The variation in compressive stress is consistent with the surface relief of the orogen, which is high in the north and low in the south. There are two kinds of basin-mountain coupling relationships, i.e. high angle thrusting and overthrusting and napping, and two kinds of basin superimposition modes, i.e. inherited and progressive, and migrating and convulsionary modes. West Junggar orogen has rich oil and gas shows. Tacheng Basin, north faulted fold belt in the Heshituoluogai basin, and Hongyan fault bench zone in north Ulungur Depression in the Junggar Basin are promising areas for hydrocarbon exploration.

Imaging 3D crustal and upper mantle structures of the Northeast China using local and teleseismic data

NASA Astrophysics Data System (ADS)

Huang, J.

2017-12-01

Northeast China is located in the composite part of Paleo Asia ocean and Pacific ocean Domain, it undergone multi-stage tectonism and has complicated geological structure. In this region, two major geologic and geophysical boundaries are distinct, the NNE-trending North South Gravity Lineament (NSGL) and Tanlu fault. With respect to North China Craton (NCC), Northeast China is more closely adjacent to the subduction zone of Pacific slab. Along the eastern boundary of Northeast China, the subducting Pacific plate approaches depths of 600 km, many deep earthquakes occurred here. This region becomes an ideal place to investigate deep structure related to deep subduction, deep earthquakes as well as intraplate volcanism. In this study, we determined high-resolution three dimensional P- and S-wave velocity models of the crust and upper mantle to 800 km depth by jointly inverting arrival times from local events and relative residuals from teleseismic events. Our results show that main velocity anomalies exhibited block feature and are generally oriented in NE to NNE direction, which is consistent with regional tectonic direction. The NSGL is characterized by a high-velocity (high-V) anomaly belt with a width of approximately 100 km, and the high-V anomaly extents to the bottom of upper mantle or mantle transition zone. The songliao basin, which is located between NSGL and Tanlu fault tectonic boundaries, obvious low-velocity anomaly extends to about depth of 200 km(. Under the Great Xing'an Range on the west side of NSGL, the low velocity extend to the lithosphere. Our results also show that most of deep earthquakes all occurred in deep subduction zone with high-velocity anomaly. Further, we also observed that extensive low velocity exists above deep-earthquakes zones, this result suggests that deep subduction of the Pacific slab maybe affect overlying lithosphere, resulting in the state of molten, semi-molten or high water.This research is supported by the National Science Foundation of China (91114204) and National Key R&D Plan (2017YFC0601406)

Geochronological framework of the early Paleozoic Bainaimiao Cu-Mo-Au deposit, NE China, and its tectonic implications

NASA Astrophysics Data System (ADS)

Zhou, Zhen-Hua; Mao, Jing-Wen; Ma, Xing-Hua; Che, He-Wei; Ou'yang, He-Gen; Gao, Xu

2017-08-01

The Bainaimiao Cu-Mo-Au deposit of NE China is an important ore deposit in the middle section of the northern margin of the North China Craton. The early Paleozoic Bainaimiao Group is the main ore-hosting rock. The mineralization at the deposit shows features of porphyry alteration and late-stage orogenesis and transformation. Zircon LA-ICP-MS U-Pb age data indicate that the ages of the Third and Fifth formations of the Bainaimiao Group are 492.7 ± 2.9 Ma (MSWD = 0.53) and 488.9 ± 3.1 Ma (MSWD = 0.92), respectively. The age of quartz diorite that intrudes the Bainaimiao Group is 459.3 ± 6.4 Ma (MSWD = 2.20). Molybdenite samples from massive Cu-Mo-bearing ores and quartz veins in the southern ore belt yield a Re-Os isochron age of 438.2 ± 2.7 Ma (MSWD = 0.16), which is consistent with the Re-Os isochron age of molybdenite in the northern ore belt, implying that the two ore belts belong to the same mineralization system. Muscovite from a post-magmatic Cu-Mo-bearing quartz-calcite vein yields an Ar-Ar isochron age of 422.5 ± 3.9 Ma (MSWD = 0.64) with an initial 40Ar/36Ar ratio of 286 ± 21. The well-defined plateau age of the muscovite is 422.4 ± 2.6 Ma (MSWD = 0.05), which represents the time of the post-magmatic orogenic transformation event. Based on our new age data and previous findings, we propose that the Bainaimiao Cu-Mo-Au deposit formed in an active continental margin setting and experienced four stages of ore mineralization: (1) a Late Cambrian-Middle Ordovician volcanic-sedimentary stage; (2) a Late Ordovician porphyry mineralization stage; (3) a Late Silurian regional metamorphism stage; and (4) an orogenic transformation stage. Subhedral and euhedral Paleoproterozoic (2402-1810 Ma) inherited zircons indicate that the Bainaimiao Group has a tectonic affinity with the North China Craton. The Central Asian Orogenic Belt, which is closely related to the complex closure of the Paleo-Asian Ocean, is favorable for prospecting for Paleozoic porphyry Cu-Mo or Cu-Au mineralization and associated epithermal Au deposits.

Rifting and reactivation of a Cretaceous structural belt at the northern margin of the South China Sea

NASA Astrophysics Data System (ADS)

Nanni, Ugo; Pubellier, Manuel; Chan, Lung Sang; Sewell, Roderick J.

2017-04-01

The Tiu Tang Lung Fault, Hong Kong Special Administrative Region - China, is located on the northern stretched continental margin of the South China Sea. Along this fault, Middle Jurassic volcanic rocks of the Tai Mo Shan Formation are tectonically juxtaposed on Lower Cretaceous sedimentary rocks of the Pat Sin Leng Formation. Both extensional detachments and compressional features are observed and various genetic strain configurations are proposed for the Tiu Tang Lung Fault with implications for understanding the dynamics of the pre-South China Sea rifting during the Cretaceous. We have identified tilted bedding planes in the continental deposits of the Pat Sin Leng Formation which can be related to Early Cretaceous syn-extensional deposition. A mid-Cretaceous penetrative top-to-the-south to top-to-the-west shear fabric is also observed and serves as an indicator of the strain pattern. This deformation is expressed by cleavages, schistosity, S/C fabrics, kink-folds, phacoids and stretched pebbles at both a macroscopic and microscopic scale. Cleavages and bedding are generally sub-parallel to the local shear orientation. The whole sedimentary pile is crosscut by Cenozoic N70 and N150 normal faults. These constraints, together with previous fission track, seismic and structural data, allow us to reinterpret the kinematics of this domain during syn-orogenic to syn-extensional periods. The observed top-to-the-south thrusting event is coeval with NE-SW strike-slip sinistral fault movement. Subsequent N-S extension can be correlated with South China Sea rifting from Eocene to Oligocene. These observations reveal a polyphase history associated with continental margin inversion which witnessed localized extension on previous compressional structures.

Mayer Kangri metamorphic complexes in Central Qiangtang (Tibet, western China): implications for the Triassic-early Jurassic tectonics associated with the Paleo-Tethys Ocean

NASA Astrophysics Data System (ADS)

Wang, Yixuan; Liang, Xiao; Wang, Genhou; Yuan, Guoli; Bons, Paul D.

2018-03-01

The Mesozoic orogeny in Central Qiangtang Metamorphic Belt, northern Tibet, provides important insights into the geological evolution of the Paleo-Tethys Ocean. However, the Triassic-early Jurassic tectonics, particularly those associated with the continental collisionstage, remains poorly constrained. Here we present results from geological mapping, structural analysis, P-T data, and Ar-Ar geochronology of the Mayer Kangri metamorphic complex. Our data reveal an E-W-trending, 2 km wide dome-like structure associated with four successive tectonic events during the Middle Triassic and Early Jurassic. Field observations indicate that amphibolite and phengite schist complexes in this complex are separated from the overlying lower greenschist mélange by normal faulting with an evident dextral shearing component. Open antiform-like S2 foliation of the footwall phengite schist truncates the approximately north-dipping structures of the overlying mélange. Microtextures and mineral chemistry of amphibole reveal three stages of growth: Geothermobarometric estimates yield temperatures and pressures of 524 °C and 0.88 GPa for pargasite cores, 386 °C and 0.34 GPa for actinolite mantles, and 404 °C and 0.76 GPa for winchite rims. Peak blueschist metamorphism in the phengite schist occurred at 0.7-1.1 GPa and 400 °C. Our Ar-Ar dating of amphibole reveals rim-ward decreasing in age bands, including 242.4-241.2 Ma, ≥202.6-196.8, and 192.9-189.8 Ma. The results provide evidence for four distinct phases of Mesozoic tectonic evolution in Central Qiangtang: (1) northward oceanic subduction beneath North Qiangtang ( 244-220 Ma); (2) syn-collisional slab-break off (223-202 Ma); (3) early collisional extension driven by buoyant extrusion flow from depth ( 202.6-197 Ma); and (4) post-collision contraction and reburial (195.6-188.7 Ma).

Geodynamics map of northeast Asia

USGS Publications Warehouse

Parfenov, Leonid M.; Khanchuk, Alexander I.; Badarch, Gombosuren; Miller, Robert J.; Naumova, Vera V.; Nokleberg, Warren J.; Ogasawara, Masatsugu; Prokopiev, Andrei V.; Yan, Hongquan

2013-01-01

This map portrays the geodynamics of Northeast Asia at a scale of 1:5,000,000 using the concepts of plate tectonics and analysis of terranes and overlap assemblages. The map is the result of a detailed compilation and synthesis at 5 million scale and is part of a major international collaborative study of the mineral resources, metallogenesis, and tectonics of northeast Asia conducted from 1997 through 2002 by geologists from earth science agencies and universities in Russia, Mongolia, northeastern China, South Korea, Japan, and the USA.

Early Jurassic mafic dykes from the Xiazhuang ore district (South China): Implications for tectonic evolution and uranium metallogenesis

NASA Astrophysics Data System (ADS)

Wang, Lian-Xun; Ma, Chang-Qian; Lai, Zhong-Xin; Marks, Michael A. W.; Zhang, Chao; Zhong, Yu-Fang

2015-12-01

A comprehensive study on zircon U-Pb age dating, whole-rock geochemistry and Sr-Nd isotope data has been conducted on the mafic rocks of the Xiazhuang uranium ore district and adjacent regions in South China. Based on field work and petrographic features, three rock types (the Kuzhukeng gabbro, the WNW-trending dolerite dykes and the NNE-trending lamprophyre dykes) are distinguished. Early Jurassic SHRIMP and LA-ICPMS ages of zircon for the Kuzhukeng gabbro (198 ± 1 Ma) and WNW-trending dolerite dykes (193 ± 4 Ma) have been obtained, which are 50 Ma older than previously thought (being Cretaceous). These geochronologic data provide new evidence for the rarely identified Early Jurassic magmatisms in South China. Whole-rock geochemical data for the Kuzhukeng gabbro and WNW-trending dolerite dykes are similar, both of which being higher in FeO and TiO2 but lower in SiO2 and K2O than the NNE-trending lamprophyre dykes. Trace element characteristics and Sr-Nd isotope data indicate arc-like signatures similar to the Cretaceous southeast coast basalts of China for the lamprophyre dykes, but an OIB-like geochemical affinity for the high-TiO2 mafic rocks similar to the Permo/Triassic Emeishan flood basalts and the Middle Jurassic Ningyuan alkaline basalts. We propose that the lamprophyre dykes formed in an arc volcanic system driven by the subduction of the paleo-Pacific plate. In contrast, the Kuzhukeng gabbro and associated dolerite dykes record the post-orogenic (Indosinian) extension event in the Tethyan tectonic regime. This further implies that the Indosinian extension may have lasted until the Early Jurassic, and therefore, the subduction of the paleo-Pacific plate in south China was probably later than this period. Most U deposits of the Xiazhuang area are located at the intersection between the WNW-trending dolerite dykes and the NNE-trending faults within the Triassic granites of eastern Guidong complex, South China. Previous metallogenesis studies assumed that intrusion of the WNW-trending mafic dykes induced upward migration of mantle-derived CO2-rich fluids, which leached U from the Triassic granite and subsequently precipitated at the intersection between mafic dykes and NEE-trending faults. Our new age data for the WNW-trending dolerite dykes reveal an age gap with respect to the associated U deposits (85-135 Ma) of at least 50 Ma, arguing against this model. Here, we propose that the role played by the dolerite dykes for U mineralizations is more likely to provide a favorable physicochemical environment promoting the precipitation of U from oxidized fluids. The fluids themselves, however, are probably related to the NNE-trending fault system and associated lamprophyre dykes rather than to the dolerites.

Geochemistry, zircon U-Pb dating and Hf isotopies composition of Paleozoic granitoids in Jinchuan, NW China: Constraints on their petrogenesis, source characteristics and tectonic implication

NASA Astrophysics Data System (ADS)

Zeng, Renyu; Lai, Jianqing; Mao, Xiancheng; Li, Bin; Ju, Peijiao; Tao, Shilong

2016-05-01

Granitoids are widely distributed in Jinchuan at the southwestern margin of the North China plate, which is also an important area of mineral deposits. The research subject of this article are two Paleozoic granitoids, a cataclastic syenogranite and a granodiorite porphyry. This study presents whole rock geochemistry and zircon U-Pb-Hf isotope data for the two granitoids to determine their petrogenesis, source characteristics and tectonic significance. The cataclastic syenogranite is characterized by metaluminous composition with high potassium, and LaN/YbN from 39 to 48. The composition with strong negative Eu anomalies and Zircon saturation temperatures (TZr) from 947 to 1072 °C classify this intrusion as an A-type granite. The granodiorite porphyry is metaluminous with high sodium, sub-alkaline, LaN/YbN ratios from 27 to 32. These I-type intrusions have no Eu anomalies and TZr ranges from 818 to 845 °C. Both the cataclastic syenogranite and granodiorite porphyry show enrichment of LREE and LILE and depletion of HREE and HFSE, except Hf and Zr. Using single zircon LA-ICP-MS U-Pb dating, the emplacement age of the cataclastic syenogranite and granodiorite porphyry are determined at 433.4 ± 3.7 Ma and 361.7 ± 4.6 Ma, respectively. Zircons from the cataclastic syenogranits have uniform negative εHf(t) values (-11 ± 0.5 to -9 ± 0.5), implying the involvement of an old Palaeoproterozoic crustal source in magma genesis. The zircons from the granodiorite porphyry have εHf(t) values that range from -8 ± 1.0 to +10 ± 0.6, suggesting heterogeneous source materials involving both juvenile and ancient crust reworked crustal components. Based on the geological significance of granites at the southwestern margin of the North China plate, the closure of the North Qilian Ocean occurred at ∼444 Ma. Geochemical features suggest that the cataclastic syenogranite and granodiorite porphyry formed in an intraplate extensional and compressional setting, respectively. Hence after a period of extensional post-collisional intraplate evolution, strong compressive forces affected the area.

Mantle convection pattern and subcrustal stress field under Asia

NASA Technical Reports Server (NTRS)

Liu, H.-S.

1978-01-01

Satellite tracking and surface gravity data are used to model the subcrustal stress fields in the terrestrial mantle beneath Asia; the results permit interpretation of the tectonic and seismic systems in China. The east and west China blocks, together with five seismic zones, are identified and related to metallogenic domains on the Chinese mainland. In addition, it is shown that the subcrustal stresses beneath China are arranged perpendicularly to the major fault systems and seismic belts. Stress calculations indicate a notable zone of compression in north China, associated with the Shansi Graben, the Linfen Basin Systems and, possibly, the high seismicity of the region.

Tectonic transition associated with Kazakhstan Orocline in the Late Paleozoic: magmatic archives of western Chinese Tianshan

NASA Astrophysics Data System (ADS)

Cai, Keda

2016-04-01

Kazakhstan accretionary system was a principle component of the Central Asian Orogenic Belt (CAOB) that is one of the largest accretionary orogens on earth. The Kazakhstan composite continent could have been established in the Early Paleozoic by the Kazakhstan accretionary system in the form of progressively amalgamations of diverse tectonic units, such as continental ribbon, accretionary prim, oceanic remnant and arc material. Subsequently, the composite continent was bended to form a spectacular U-shaped architecture that probably occurred in the Late Paleozoic. The western Chinese Tianshan is situated on the south wing of the Kazakhstan Orocline, featured by extensive magmatim, intense deformation and voluminous mineralization. Our new geochronological and geochemical data suggest a noticeable magmatic gap between Late Devonian and Early carboniferous and contrasting magma sources of these magmatic rocks. The significant shifts correspond to the tectonic transition from terrane amalgamation to mountain bending in the Early Paleozoic. This study was financially supported by the Major Basic Research Project of the Ministry of Science and Technology of China (2014CB448000), Xinjiang outstanding youth scientific grant (2013711003) and the Talent Awards to KDC from the China Government under the 1000 Talent Plan.

Post-rift Tectonic History of the Songliao Basin, NE China: Cooling Events and Post-rift Unconformities Driven by Orogenic Pulses From Plate Boundaries

NASA Astrophysics Data System (ADS)

Song, Ying; Stepashko, Andrei; Liu, Keyu; He, Qingkun; Shen, Chuanbo; Shi, Bingjie; Ren, Jianye

2018-03-01

The classic lithosphere-stretching model predicts that the post-rift evolution of extensional basin should be exclusively controlled by decaying thermal subsidence. However, the stratigraphy of the Songliao Basin in northeastern China shows that the post-rift evolution was punctuated by multiple episodes of uplift and exhumation events, commonly attributed to the response to regional tectonic events, including the far-field compression from plate margins. Three prominent tectonostratigraphic post-rift unconformities are recognized in the Late Cretaceous strata of the basin: T11, T03, and T02. The subsequent Cenozoic history is less constrained due to the incomplete record of younger deposits. In this paper, we utilize detrital apatite fission track (AFT) thermochronology to unravel the enigmatic timing and origin of post-rift unconformities. Relating the AFT results to the unconformities and other geological data, we conclude that in the post-rift stage, the basin experienced a multiepisodic tectonic evolution with four distinct cooling and exhumation events. The thermal history and age pattern document the timing of the unconformities in the Cretaceous succession: the T11 unconformity at 88-86 Ma, the T03 unconformity at 79-75 Ma, and the T02 unconformity at 65-50 Ma. A previously unrecognized Oligocene unconformity is also defined by a 32-24 Ma cooling event. Tectonically, all the cooling episodes were regional, controlled by plate boundary stresses. We propose that Pacific dynamics influenced the wider part of eastern Asia during the Late Cretaceous until Cenozoic, whereas the far-field effects of the Neo-Tethys subduction and collision processes became another tectonic driver in the later Cenozoic.

Seismic imaging of Late Cretaceous magmatic system in the northern margin of South China Sea

NASA Astrophysics Data System (ADS)

Xia, S.; Xu, H.; Sun, J.; Zhao, F.; Fan, C.

2017-12-01

The origin and evolution of magmatism in the rifting margins are the fundamentally geological subjects, and remain the focus of intense study. Different from the classical volcanic or nonvolcanic rifting margins, the northern margin of South China Sea (SCS) experienced uniquely regional tectonic processes, and formed plentiful intraplate seamounts mainly at the postrift period. There is considerable controversy over what caused the intensively postrift intraplate volcanism. Here we combine a new crustal structure with previously systematic petrologic and seismic tomographic results to first provide importantly new insights into a mantle plume origin and complex multilevel plumbing system of intraplate seamounts in the northern margin of SCS. Large amounts of active melts from the lower mantle migrated upward and reached the base of the lithosphere. The volatile-rich and overheated magmas continued ascending along the weak zone through the lithosphere and intruded into the lower crust. The intrusion magmas then ascended forward along the faults formed during the rifting, and supplied the magma source for the formation of intraplate seamounts in the northern margin of SCS. It supplies an important implication for the volume and range of late Cenozoic basaltic magmatism deriving from the Hainan mantle plume. Keywords: South China Sea; Late Cretaceous; Magmatic System; Hainan Plume AcknowledgementsThe field work of this study was assisted by the captain and crew of the R/V Shiyan 2. Prof. Xuelin Qiu supplied great helps for the successful implementation of the cruise. This work was partially supported by grants from the National Natural Science Foundation of China (Grant Nos. 91328206 and 41576041).

Deep thermal structure of Southeast Asia constrained by S-velocity data

NASA Astrophysics Data System (ADS)

Yu, Chuanhai; Shi, Xiaobin; Yang, Xiaoqiu; Zhao, Junfeng; Chen, Mei; Tang, Qunshu

2017-12-01

Southeast Asia, located in the southeastern part of the Eurasian Plate, is surrounded by tectonically active margins, exhibiting intense seismicity and volcanism, contains complex geological units with a perplexing evolution history. Because tectonic evolution is closely related to the deep thermal structure, an accurate estimation of the lithosphere thermal structure and thickness is important in extracting information on tectonics and geodynamics. However, there are significant uncertainties in the calculated deep thermal state constrained only by the observed surface heat flow. In this study, in order to obtain a better-constrained deep thermal state, we first calculate the deep thermal structure of Southeast Asia by employing an empirical relation between S-velocity and temperature, and then we estimate the base of the thermal lithosphere from the calculated temperature-depth profiles. The results show that, in general, the temperature is higher than the dry mantle solidus below the top of the seismic low-velocity zone, possibly indicating the presence of partial melt in the asthenosphere, particularly beneath oceanic basins such as the South China Sea. The temperature at a depth of 80 km in rifted and oceanic basins such as the Thailand Rift Basin, Thailand Bay, Andaman Sea, and South China Sea is about 200 °C higher than in plateaus and subduction zones such as the Khorat Plateau, Sumatra Island, and Philippine Trench regions. We suggest that the relatively cold and thick lithosphere block of the Khorat Plateau has not experienced significant internal deformation and might be extruded and rotated as a rigid block in response to the Indo-Eurasia collision. Our results show that the surface heat flow in the South China Sea is mainly dominated by the deep thermal state. There is a thermal anomaly in the Leiqiong area and in the areas adjacent to the northern margin of the South China Sea, indicating the presence of a high-temperature and thin lithosphere in the area of the well-known and controversial Hainan plume. The thermal lithosphere-asthenosphere boundary uplift area along the Xisha and southeastern Vietnam margin, in the western margin of South China Sea, which corresponds to the volcanic belt around this area, might indicate upwelling of hot mantle materials. The temperature values at 100 and 120 km depths through most regions of Southeast Asia are about 1400-1500 and 1550-1600 °C, respectively, which are nearly uniform with a small temperature difference. Our results also show that the lithosphere becomes thinner from the continent blocks toward the oceanic basins, with the smaller thickness values of 65-70 km in the South China Sea. The estimated base of the lithosphere corresponds approximately to the 1400 °C isotherm and shows good correlation with the tectonic setting.

Comparison of Tarim and central Asian FSU basins, I: Phanerozoic paleogeography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heubeck, C.; Shangyou N.

1996-12-31

Large amounts of previously unpublished data on the petroleum geology of the FSU`s Central Asian Republics and of China`s Tarim region have found their way into the western public domain in the past few years. These data provide for the first time the opportunity to merge detailed stratigraphic, tectonic, and paleogeographic studies done during the past decades on both sides of the FSU-Chinese border and to place the results in a plate-tectonic and palinspastically restored reference frame. Major tectonic events affecting the active post-Silurian south-facing margin of Asia between the Caspian Sea and Tarim include (1) the collapse of themore » Kazakhstan arc fragments (ca. 400-300 Ma); (2) collision of YiIi with Tarim (ca. 375 Ma); (3) consolidation of the Turan Platform from pre-existing basement blocks (ca. 280-220 Ma), (4) collision of Tarim/Yili with the Kazakhstan arcs (ca. 260 Ma); (5) stabilization of a south-facing Triassic active margin (ca. 250 - 200 Ma); (6) accretion of Cimmeria (ca. 200 Ma) and associated reactivation events in Turan, Syr-Darja, and Tarim; (7) reactivation and modification of intracontinental structures during the collision of central Asia with India (ca. 55 Ma to present) and with the Arabian platform (ca. 25 Ma). Periodic large-scale flooding of denuded continental platforms (Turan, Tadjik) during sea-level highstands is recorded in the Jurassic, Mid-Late Cretaceous, and the Early Tertiary, resulting in extensive tracts of restricted marine sedimentary systems and marine incursions deep into central Asia (SW Tarim, Kuche Depression, Fergana, Turgay). Mesozoic-Cenozoic source rocks are sensitive to rapid lateral facies changes, and understanding their distribution requires detailed stratigraphic analysis. The attempted synthesis of data from China and the FSU with plate-tectonic concepts allows the transfer and testing of play concepts and hydrocarbons systems across the FSU-Chinese border.« less

Crustal structure of mainland China from deep seismic sounding data

USGS Publications Warehouse

Li, S.; Mooney, W.D.; Fan, J.

2006-01-01

Since 1958, about ninety seismic refraction/wide angle reflection profiles, with a cumulative length of more than sixty thousand kilometers, have been completed in mainland China. We summarize the results in the form of (1) a new contour map of crustal thickness, (2) fourteen representative crustal seismic velocity-depth columns for various tectonic units, and, (3) a Pn velocity map. We found a north-south-trending belt with a strong lateral gradient in crustal thickness in central China. This belt divides China into an eastern region, with a crustal thickness of 30-45??km, and a western region, with a thickness of 45-75??km. The crust in these two regions has experienced different evolutionary processes, and currently lies within distinct tectonic stress fields. Our compilation finds that there is a high-velocity (7.1-7.4??km/s) layer in the lower crust of the stable Tarim basin and Ordos plateau. However, in young orogenic belts, including parts of eastern China, the Tianshan and the Tibetan plateau, this layer is often absent. One exception is southern Tibet, where the presence of a high-velocity layer is related to the northward injection of the cold Indian plate. This high-velocity layer is absent in northern Tibet. In orogenic belts, there usually is a low-velocity layer (LVL) in the crust, but in stable regions this layer seldom exists. The Pn velocities in eastern China generally range from 7.9 to 8.1??km/s and tend to be isotropic. Pn velocities in western China are more variable, ranging from 7.7 to 8.2??km/s, and may display azimuthal anisotropy. ?? 2006.

Reviews and new metallogenic models of mineral deposits in South China: An introduction

NASA Astrophysics Data System (ADS)

Hu, Rui-Zhong; Chen, Wei Terry; Xu, De-Ru; Zhou, Mei-Fu

2017-04-01

In South China, the Yangtze and Cathaysia blocks were welded together along the Jiangnan Fold Belt during Neoproterozoic time (∼830 Ma). Large-scale mineralization in these two blocks occurred from Proterozoic to Cenozoic, making the region one of the most important polymetallic metallogenic provinces in the world. Of particular importance are world-class deposits of iron-oxide copper gold (IOCG), sediment-hosted Mn-P-Al-(Ni, Mo, PGE), syenite-carbonatite-related REE, felsic intrusion-related Sn-W-Mo-Cu-Fe-Pb-Zn, mafic intrusion-related V-Ti-Fe and Cu-Ni-PGE and low-temperature hydrothermal Pb, Zn, Au, and Sb (Fig. 1). In addition, the Ta-Nb, Hg, As, Tl and U deposits in South China are among the world largest of these kinds. Because of these deposits, South China has been a focus of researches for many years. Publications before 2005 were mostly restricted in Chinese. In the past decade, some case studies on some world-class deposits in South China are available in international journals. These recent studies have advanced our understanding of their mode of formation. However, some important issues regarding the timing, tectonic setting and mechanisms of metal concentration still remain poorly understood. This special issue brings together some of the latest information on these topics, including major review papers on specific types of mineralization and several papers dealing with some specific deposits in the region. We anticipate that this issue will generate more interests in the studies of mineral deposits in South China. In this introduction, we outline the tectonic framework and associated deposits.

Isotopic and paleomagnetic constraints on the Mesozoic tectonic evolution of south China

NASA Astrophysics Data System (ADS)

Gilder, Stuart A.; Gill, James; Coe, Robert S.; Zhao, Xixi; Liu, Zhongwei; Wang, Genxian; Yuan, Kuirong; Liu, Wenlong; Kuang, Guodun; Wu, Haoruo

1996-07-01

In order to better constrain the paleogeographic evolution of south China we measured Sm-Nd and Rb-Sr isotopic compositions for 23 Mesozoic granites that crop out throughout the area. Tightly grouped neodymium depleted mantle model ages (1.4 ± 0.3 Ga) suggest the region is underlain by relatively homogeneous Proterozoic crust and fail to define crustal provinces. Neither the isotopic nor geologic data suggest that a Mesozoic suture exists. However, granites possessing anomalously high Sm (>8 ppm) and Nd (>45 ppm) concentrations, relatively high initial epsilon neodymium (-4 to -8), and high but variable initial 87Sr/86Sr (0.759 to 0.713) form a northeast trending zone that coincides with two prominent Mesozoic basins. Southeast of the zone lie the majority of Mesozoic intrusives and Upper Triassic to Lower Cretaceous extensional basins found in south China. Mesozoic paleomagnetic poles are well clustered northwest of the zone. Pre-Cretaceous poles southeast of it are discordant with respect to those from the northwest. The only recognized tectonostratigraphic terrane in south China lies southeast of the zone. The terrane is bordered by a northeast trending sinistral fault that was active in the Mesozoic. Other faults in south China have similar attitudes, ages, and sense of shear. Together, the observations suggest that the Mesozoic tectonic regime in south China consisted of strike-slip activity plus concomitant rifting as terranes or fragments of similar crust were transported north along sinistral faults. The zone, defined by the granites enriched in Nd and Sm, demarcates displaced terranes to the southeast from relatively stable land to the northwest.

The Composition and Mineralogy of Exoplanets, Using the Hypatia Catalogue: Implications for Extrasolar Plate Tectonics and Mantle Convection

NASA Astrophysics Data System (ADS)

Putirka, K. D.; Rarick, J.

2018-05-01

Many exoplanets have pyroxenite mantle mineralogies, which may impede plate tectonics, due higher mantle viscosities and lid yield strengths; majorite-rich transition zones on these may also prevent subducted slabs from reaching lower mantle depths.

Block Tectonics on Venus

NASA Astrophysics Data System (ADS)

Byrne, P. K.; Ghail, R. C.; Şengör, A. M. C.; Klimczak, C.; Solomon, S. C.

2017-11-01

Hey! You know continental China? We think it's an analog to a bunch of places on Venus where the lithosphere is broken into chunks that have jostled into each other. You should come check out this presentation, it'll be great!

Parallel Extension Tectonics (PET): Early Cretaceous tectonic extension of the Eastern Eurasian continent

NASA Astrophysics Data System (ADS)

Liu, Junlai; Ji, Mo; Ni, Jinlong; Guan, Huimei; Shen, Liang

2017-04-01

The present study reports progress of our recent studies on the extensional structures in eastern North China craton and contiguous areas. We focus on characterizing and timing the formation/exhumation of the extensional structures, the Liaonan metamorphic core complex (mcc) and the Dayingzi basin from the Liaodong peninsula, the Queshan mcc, the Wulian mcc and the Zhucheng basin from the Jiaodong peninsula, and the Dashan magmatic dome within the Sulu orogenic belt. Magmatic rocks (either volcanic or plutonic) are ubiquitous in association with the tectonic extension (both syn- and post-kinematic). Evidence for crustal-mantle magma mixing are popular in many syn-kinematic intrusions. Geochemical analysis reveals that basaltic, andesitic to rhyolitic magmas were generated during the tectonic extension. Sr-Nd isotopes of the syn-kinematic magmatic rocks suggest that they were dominantly originated from ancient or juvenile crust partly with mantle signatures. Post-kinematic mafic intrusions with ages from ca. 121 Ma to Cenozoic, however, are of characteristic oceanic island basalts (OIB)-like trace element distribution patterns and relatively depleted radiogenic Sr-Nd isotope compositions. Integrated studies on the extensional structures, geochemical signatures of syn-kinematic magmatic rocks (mostly of granitic) and the tectono-magmatic relationships suggest that extension of the crust and the mantle lithosphere triggered the magmatisms from both the crust and the mantle. The Early Cretaceous tectono-magmatic evolution of the eastern Eurasian continent is governed by the PET in which the tectonic processes is subdivided into two stages, i.e. an early stage of tectonic extension, and a late stage of collapse of the extended lithosphere and transformation of lithospheric mantle. During the early stage, tectonic extension of the lithosphere led to detachment faulting in both the crust and mantle, resulted in the loss of some of the subcontinental roots, gave rise to the exhumation of the mccs, and triggered plutonic emplacement and volcanic eruptions of hybrid magmas. During the late stage, the nature of mantle lithosphere in North China was changed from the ancient SCLM to the juvenile SCLM. Extensional structures in eastern Eurasian continent provide a general architecture of the extensional tectonics of a rifted continent. Progressive extension resulted a sudden collaps of the crust (lithosphere) at ca. 130 to 120 Ma, associated with exhumation of mcc's and giant syn-kinematic magmatism, and post-kinematic magmatism. Parallel extension of both the crust and the mantle resulted in detachment faulting and magmatism, and also contributed to inhomogeneous thinning of the NCC lithosphere. Paleo-Pacific plate subduction and roll-back of the subducting oceanic plate contributed to the PET tectonic processes.

Anisotropy and tectonic deformation in the Ordos basin revealed by an active source seismic experiment

NASA Astrophysics Data System (ADS)

Jun, W. S.; Wang, F.; Xu, T.

2016-12-01

With the purpose of exploring the Ordos block, western North China Craton, two controlled-source deep seismic transects were conducted across this region. The first one is a 650 km long profile oriented N-S; the second is 1530 km and is oriented E-W. The upper mantle P wave-velocity derived from these profiles features a 0.25 km/s difference between them. Being the E-W higher that the N-S. The results obtained from both seismic profiles indicate that the upper mantle beneath the Ordos block presents seismic anisotropy in terms of discrepancy in Pn-wave velocity, such as the apparent seismic velocities observed along the two reference profiles demonstrate. This result is consistent with SKS-wave splitting measurements in the interior of the Ordos block. This indicates that the compressive stress state in Ordos during the Mesozoic became an extensional stress state in the Cenozoic. The high-velocity anomaly in the uppermost mantle under the west-east profile suggests that the lithospheric mantle is still not water-rich. Unlike what happened in the NCC to east of the Taihang Mountains, where the lithosphere experienced its thinning and destruction since the Mesozoic, the lithosphere in the interior of Ordos has suffered less deformation and remained tectonically stable. Keywords: wide-angle seismic profiling, Pn phase, high-velocity anomaly, upper mantle anisotropy, Ordos block, North China Craton. ReferencesChen L., 2009. Lithospheric structure variations between the eastern and central North China Craton from S- and P-receiver function migration. Phys. Earth Planet. Inter. 173, 216-227. Gao S., Rudnick R.L., Xu W.L., et al., 2008. Recycling deep cratonic lithosphere and generation of intraplate magmatism in the North China Craton. Earth Planet. Sci. Lett. 270, 41-53. Xu T., Zhang Z.J., Gao E.G., et al., 2010. Segmentally iterative ray tracing in complex 2D and 3D heterogeneous block models. Bull. Seism. Soc. Am. 100, 841-850. Zhu R.X., Zheng T.Y., 2009. Destruction geodynamics of the North China Craton and its Paleoproterozoic plate tectonics. Chinese Sci. Bull. 54(14), 1950-1961 (in Chinese).

Petrogenesis of Permian A-type granitoids in the Cihai iron ore district, Eastern Tianshan, NW China: Constraints on the timing of iron mineralization and implications for a non-plume tectonic setting

NASA Astrophysics Data System (ADS)

Zheng, Jiahao; Mao, Jingwen; Chai, Fengmei; Yang, Fuquan

2016-09-01

The geochronology and geochemistry of granitoids in the Eastern Tianshan, NW China provide important constraints on the timing of iron mineralization, as well as in understanding evolution history of the southern Central Asian Orogenic Belt (CAOB). Here we present results from a detailed study on granitoid rocks from the Cihai iron ore district in the Beishan region, southern part of the Eastern Tianshan. The granitoid rocks are composed of granodiorite, quartz monzonite, granite, and monzonite. Zircon U-Pb analyses yielded the ages of 294.1 ± 2.2 Ma, 286.5 ± 0.7 Ma, 284.3 ± 3.3 Ma, and 265.6 ± 3.0 Ma, respectively, suggesting they were formed in Early-Middle Permian. Among these granitoid rocks, the ages of quartz monzonite and granite are close to the timing of iron mineralization ( 282 Ma), indicating they may provide a source of iron in the Cihai ore district. Geochemically, the granodiorite, granite, and quartz monzonite samples are characterized by high FeOt/(FeOt + MgO) and Ga/Al ratios (0.84-0.94 and 2.28-3.27, respectively), as well as high zircon saturation temperatures (781-908 °C), similar to those of typical A-type granitoids. Isotopically, they display consistently depleted Hf isotopic compositions (εHf(t) = + 1.18 to + 15.37). Geological, geochemical, and isotopic data suggest that the Cihai A-type granitoids were derived from melting of juvenile lower crust. Some Early Permian A-type granitoids were recently identified in the Tarim and Eastern Tianshan with the ages between 294 and 269 Ma. The A-type granitoids in the Eastern Tianshan formed earlier between 294-284 Ma and exhibit characteristics of A2 type granitoids, whereas the A-type granitoids in the Tarim formed later between 277-269 Ma and show A1 granitoids affinity. We suggest that the Permian Tarim mantle plume does not account for the formation of the A-type granitoids in the Eastern Tianshan area, and the Eastern Tianshan was in a non-plume tectonic setting during Early Permian time. A slab break-off event has been suggested as the possible tectonic mechanism that triggered the formation of Early Permian A-type granitoids in the Eastern Tianshan.

Age, tectonic setting, and metallogenic implication of Phanerozoic granitic magmatism at the eastern margin of the Xing'an-Mongolian Orogenic Belt, NE China

NASA Astrophysics Data System (ADS)

Chen, Cong; Ren, Yunsheng; Zhao, Hualei; Yang, Qun; Shang, Qingqing

2017-08-01

The eastern margin of the Xing'an-Mongolian Orogenic Belt is characterised by widespread Phanerozoic granitic magmatism, some of which is closely related to significant ore mineralisation. This paper presents new geochronological, petrogenetic, and tectonic data for selected intrusions. Zircon U-Pb geochronology for five granitoid plutons indicates they were emplaced during the middle-late Permian (264-255 Ma) and Cretaceous (106-94 Ma), and thus granitic magmatism occurred throughout the Phanerozoic, Permian (268-252 Ma), Early-Middle Triassic (248-240 Ma), Early Jurassic (183 Ma), and Cretaceous (112-94 Ma). The Permian granitoids consist of monzogranite, granodiorite, tonalite, and quartz diorite, characterised by enrichment in Na2O (3.60-4.72 wt.%), depletion in K2O (0.97-2.66 wt.%), and a negative correlation between P2O5 and SiO2. Together with the presence of hornblende, these geochemical features are indicative of an I-type affinity. The Permian granitic magmatism is associated with quartz-vein-type tungsten deposits (252 Ma; unpublished Sm-Nd isochron age), which formed in an active continental margin setting related to subduction of the Palaeo-Asian Ocean. The Cretaceous quartz diorites have an adakitic affinity, having relatively high Sr (374-502 ppm), low Yb (0.51-0.67 ppm) and Y (8.7-10.7 ppm), and high Sr/Y (39.4-46.8) and (La/Yb)N values (16.2-34.7), suggesting that they were related to the partial melting of subducted oceanic crust. In addition, they are associated with porphyry Au-Cu deposits. We conclude that the Cretaceous granitic rocks and associated porphyry Au-Cu mineralisation occurred in an extensional tectonic setting related to the subduction of the Palaeo-Pacific Plate beneath the Eurasian Plate. In addition, the large-scale Early-Middle Triassic syn-collisional granite belt at the eastern margin of the Xing'an-Mongolian Orogenic Belt extends from the middle of Jilin Province to the Wangqing-Hunchun region, constraining the timing of the final collision between the North China Craton and the Jiamusi-Khanka Massif, and suggesting that the Xra Moron River-Changchun Suture likely extends eastward into the eastern Hunchun region. This collision caused the Middle Triassic mesothermal lode gold mineralisation.

Pn tomography of South China Sea, Taiwan Island, Philippine archipelago, and adjacent regions

NASA Astrophysics Data System (ADS)

Li, Xibing; Song, Xiaodong; Li, Jiangtao

2017-02-01

The South China Sea (SCS) and its surrounding areas are geologically highly heterogeneous from the interactions of multiple plates in Southeast Asia (Eurasian plate, Indian-Australian plate, Philippine Sea plate, and Pacific plate). To understand the tectonics at depth, here we combined bulletin and handpicked data to conduct Pn tomography of the region. The results show distinct features that are correlated with the complex geology at surface, suggesting a lithosphere-scale tectonics of the region. Low Pn velocities are found along a belt of the western Pacific transpressional system from the Okinawa Trough and eastern East China Sea, across central and eastern Taiwan orogeny, to the island arcs of the Luzon Strait and the entire Philippine Islands, as well as under the Palawan Island and part of the continental margin north of the Pearl River Basin. High velocities are found under Ryukyu subduction zone, part of the Philippine subduction zone, part of the Eurasian subduction beneath the southwestern Taiwan, and the continent-ocean boundary between the south China and the SCS basin. The Taiwan Strait, the Mainland SE coast, and the main SCS basin sea are relatively uniform with average Pn values. Crustal thicknesses show large variations in the study region but also coherency with tectonic elements. The Pn pattern in Taiwan shows linear trends of surface geology and suggests strongly lithosphere-scale deformation of the young Taiwan orogenic belt marked by the deformation boundary under the Western Foothill and the Western Coastal Plain at depth, and the crustal thickness shows a complex pattern from the transpressional collision. Our observations are consistent with rifting and extension in the northern margin of the SCS but are not consistent with mantle upwelling as a mechanism for the opening and the subsequent closing of the SCS. The Philippine island arc is affected by volcanisms from both the Asian and Philippine Sea subductions in the south but mainly from the Asian subduction in the north and under the Luzon Strait.

Comparison of the tectonics and geophysics of the major structural belts between the northern and southern continental margins of the South China Sea

NASA Astrophysics Data System (ADS)

Xia, Kan-yuan; Huang, Ci-liu; Jiang, Shao-ren; Zhang, Yi-xiang; Su, Da-quan; Xia, Si-gao; Chen, Zhong-rong

1994-07-01

A comparison of the tectonics and geophysics of the major structural belts of the northern and the southern continental margins of South China Sea has been made, on the basis of measured geophysical data obtained by ourselves over a period of 8 years (1984-1991). This confirmed that the northern margin is a divergent one and the southern margin is characterized by clearly convergent features. The main extensional structures of the northern margin are, from north to south: (1) The Littoral Fault Belt, a tectonic boundary between the continental crust and a transitional zone, along the coast of the provinces of Guangdong and Fujian in South China. It is characterised by earthquake activities, high magnetic anomalies and a rapid change in crustal thickness. (2) The Northern and Southern Depression zones (i.e., the Pearl River Mouth Basin), this strikes NE-ENE and is a very large Cenozoic depression which extends from offshore Shantou westwards to Hainan Island. (3) The Central Uplift Zone. This includes the Dongsha Uplift, Shenhu Uplift and may be linked with the Penghu uplift and Taiwan shoals to the east, forming a large NE-striking uplift zone along the northern continental slope. It is characterized by high magnetic anomalies. (4) Southern Boundary Fault Belt of the transitional crust. This has positive gravity anomalies on the land side and negative ones on the sea side. (5) The Magnetic Quiet Zone. This is located south of the southern Boundary Fault Belt and between the continental margin and the Central Basin of the South China Sea. Magnetic anomalies in this belt are of small amplitude and low gradient. We consider the Magnetic Quiet Zone to be a very important tectonic zone. The major structures of southern continental margin southwards are: (1) The Northern Fault Belt of the Nansha Block. This extends along the continental slope north of the Liyue shoal (Reed Bank) and Zhongye reef, and is a tectonic boundary between oceanic crust and the Nansha Block continental crust. (2) The Nansha Block Uplift Zone. Due to the development of reefs and shoals, there are many channels and valleys. Our long-distance multichannel seismic profiles indicated that there are thick Paleogene sediments and thin Neogene sediments all over the central part of the block. (3) The Nansha Trough, a nappe structure formed by the southeastward drifting of Nansha Block and northwestward overthrusting of Palawan-northwest Borneo. (4) Zengmu Shoal Basin, southwest of the Nansha Block; the maximum thickness of Cenozoic strata is over 9 km in this important petroliferous basin.

Detrital zircon provenance of the Late Triassic Songpan-Ganzi complex: Sedimentary record of collision of the North and South China blocks

USGS Publications Warehouse

Weislogel, A.L.; Graham, S.A.; Chang, E.Z.; Wooden, J.L.; Gehrels, G.E.; Yang, H.

2006-01-01

Using detrital zircon geochronology, turbidite deposystems fed from distinct sediment sources can be distinguished within the Songpan-Ganzi complex, a collapsed Middle to Late Triassic turbidite basin of central China. A southern Songpan-Ganzi deposystem initially was sourced solely by erosion of the Qinling-Dabie orogen during early Late Triassic time, then by Qinling-Dabie orogen, North China block, and South China block sources during middle to late Late Triassic time. A northern Songpan-Ganzi system was sourced by erosion of the Qinling-Dabie orogen and the North China block throughout its deposition. These separate deposystems were later tectonically amalgamated to form one complex and then uplifted as the eastern Tibet Plateau. ?? 2006 Geological Society of America.

Geochemical and geochronological constrains on the Chiang Khong volcanic rocks (northwestern Thailand) and its tectonic implications

NASA Astrophysics Data System (ADS)

Qian, Xin; Feng, Qinglai; Chonglakmani, Chongpan; Monjai, Denchok

2013-12-01

Volcanic rocks in northwestern Thailand exposed dominantly in the Chiang Khong area, are commonly considered to be genetically linked to the tectonic evolution of the Paleo-Tethyan Ocean. The volcanic rocks consist mainly of andesitic to rhyolitic rocks and are traditionally mapped as Permian-Triassic sequences. Our zircon U-Pb geochronological results show that two andesitic samples (TL-1-B and TL-31-B), are representative of the Doi Yao volcanic zone, and give a mean weighted age of 241.2±4.6 Ma and 241.7±2.9 Ma, respectively. The rhyolitic sample (TL-32-B1) from the Doi Khun Ta Khuan volcanic zone erupted at 238.3±3.8 Ma. Such ages indicate that Chiang Khong volcanic rocks erputed during the early Middle Triassic period. Seven samples from the Doi Yao and Doi Khun Ta Khuan zones exhibit an affinity to arc volcanics. Three rhyolitic samples from the Chiang Khong area have a geochemical affinity to both arc and syn-collisional volcanic rocks. The Chiang Khong arc volcanic rocks can be geochemically compared with those in the Lampang area in northern Thailand, also consistent with those in Jinghong area of southwestern Yunnan. This indicates that the Chiang Rai arc-volcanic zone might northwardly link to the Lancangjiang volcanic zone in southwestern China.

The distribution and composition characteristics of siliceous rocks from Qinzhou Bay-Hangzhou Bay joint belt, South China: constraint on the tectonic evolution of plates in South China.

PubMed

Li, Hongzhong; Zhai, Mingguo; Zhang, Lianchang; Zhou, Yongzhang; Yang, Zhijun; He, Junguo; Liang, Jin; Zhou, Liuyu

2013-01-01

The Qinzhou Bay-Hangzhou Bay joint belt is a significant tectonic zone between the Yangtze and Cathaysian plates, where plentiful hydrothermal siliceous rocks are generated. Here, the authors studied the distribution of the siliceous rocks in the whole tectonic zone, which indicated that the tensional setting was facilitating the development of siliceous rocks of hydrothermal genesis. According to the geochemical characteristics, the Neopalaeozoic siliceous rocks in the north segment of the Qinzhou Bay-Hangzhou Bay joint belt denoted its limited width. In comparison, the Neopalaeozoic Qinzhou Bay-Hangzhou Bay joint belt was diverse for its ocean basin in the different segments and possibly had subduction only in the south segment. The ocean basin of the north and middle segments was limited in its width without subduction and possibly existed as a rift trough that was unable to resist the terrigenous input. In the north segment of the Qinzhou Bay-Hangzhou Bay joint belt, the strata of hydrothermal siliceous rocks in Dongxiang copper-polymetallic ore deposit exhibited alternative cycles with the marine volcanic rocks, volcanic tuff, and metal sulphide. These sedimentary systems were formed in different circumstances, whose alternative cycles indicated the release of internal energy in several cycles gradually from strong to weak.

Integrated Analysis on Gravity and Magnetic Fields of the Hailar Basin, NE China: Implications for Basement Structure and Deep Tectonics

NASA Astrophysics Data System (ADS)

Sun, Bin; Wang, Liangshu; Dong, Ping; Wu, YongJing; Li, Changbo; Hu, Bo; Wang, Chong

2012-11-01

The Hailar Basin is one of the typical basins among the NE China Basin Groups, which is situated in the east of East Asia Orogene between the Siberia Plate and the North China Plate. Based on the detailed analysis of magnetic, gravity, petrophysical, geothermal and seismological data, we separate the Gravity and Magnetic Anomalies (GMA) into four orders using Wavelet Multi-scale Decomposition (WMD). The apparent depths of causative sources were then assessed by Power Spectrum Analysis (PSA) of each order. Low-order wavelet detail anomalies were used to study the basin's basement structure such as major faults, the basement lithology, uplifts and depressions. High-order ones were used for the inversion of Moho and Curie discontinuities using the Parker method. The results show that the Moho uplifting area of the Hailar Basin is located at the NE part of the basin, the Curie uplifting area is at the NW part, and neither of them is consistent with the basin's sedimentary center. This indicates that the Hailar Basin may differ in basin building pattern from other middle and eastern basins of the basin groups, and the Hailar Basin might be of a passive type. When the Pacific Plate was subducting to NE China, the frontier of the plate lying on the mantle transition zone didn't pass through the Great Khingan Mountains region, so there is not an obvious magma upwelling or lithospheric extension in the Hailar Basin area. Finally, based on the seismological data and results of WMD, a probable 2D crust model is derived from an across-basin profile using the 2D forward modeling of the Bouguer gravity anomaly. The results agree with those from seismic inversion, suggesting WMD is suitable for identifying major crustal density interfaces.

Neogene-Recent Reactivation of Cretaceous-age Faults in Southern Vietnam, with Implications for the Himalayan-Tibetan Orogen

NASA Astrophysics Data System (ADS)

Burberry, C. M.; Elkins, L. J.; Hoang, N.; Anh, L. D.; Dinh, S. Q.

2017-12-01

The tectonic activity and ongoing diffuse volcanic activity of the Central Highlands of Vietnam have, to date, been challenging to explain using accepted plate tectonics principles. The various hypotheses invoked to explain the voluminous magmatism include extrusion related to the Himalayan-Tibetan orogen, extension related to the South China Sea, and plume activity beneath Hainan. We present a combined remote sensing and field study, focused on fault orientation and age relative to lava flows in order to discriminate between these models. Landsat ETM+ and SPOT data were processed to highlight variations in lithology and to remove vegetation, and lineaments were interpreted from these images. The lineament data were compared to existing geologic maps, and to regions of known flow age. Key locations were visited in the field, where fault orientations and relative age were recorded. At many locations, the slip direction could be measured using trend and plunge of mineral lineations. The remote data reveal a complex pattern of lineaments, with prominent N-S, NE-SW and NW-SE directions. Lineaments are observed to cut lava flows with ages of 2.2+/- 0.1 Ma and younger. In the field, NE-SW oriented faults were identified in Jurassic-Cretaceous sedimentary rocks with two phases of movement; a dip-slip phase and a younger, dominantly strike-slip phase. Strike-slip faults were identified in lava flows of approx. 3.2 Ma, also oriented NE-SW. These results indicate that there has been fault activity since the Pliocene, and that this fault activity includes reactivation of dip-slip faults as strike-slip. This is consistent with the movement vector of the southern Indochina Block SE with respect to the Sunda block, and with microplate rotation due to asthenospheric extrusion. These results therefore suggest that ongoing Himalayan-Tibetan collision is still being accommodated, in part, by active lithospheric extrusion of the Indo-China block.

Alluvial fan facies of the Yongchong Basin: Implications for tectonic and paleoclimatic changes during Late Cretaceous in SE China

NASA Astrophysics Data System (ADS)

Chen, Liuqin; Steel, Ronald J.; Guo, Fusheng; Olariu, Cornel; Gong, Chenglin

2017-02-01

Late Cretaceous continental redbeds, the Guifeng Group of the Yongchong Basin in SE China have been investigated to conduct detailed fan facies description and interpretation. Tectonic activities determined the alluvial fan development along the basin margin, but the alluvial facies was linked with paleoclimate changes. The Guifeng Group is divided into the Hekou, Tangbian and Lianhe formations in ascending order. The Hekou conglomerates are typically polymict, moderately sorted with erosional bases, cut-and-fill features, normal grading and sieve deposits, representing dominant stream-flows on alluvial fans during the initial opening stage of the basin infill. The Tangbian Formation, however, is characterized by structureless fine-grained sediments with dispersed coarse clasts, and couplets of conglomerate and sandstone or siltstone and mudstone, recording a change to a playa and ephemeral lake environments with occasional stream flooding, thus indicating a basin expanding stage. The hallmark of the Lianhe Formation is disorganized, poorly sorted conglomerates lack of erosional bases, and a wide particle-size range from clay to boulders together reflect mud-rich debris-flows accumulating on fans, likely related to reactivation of faulting along the northwestern mountain fronts during a post-rift stage. The depositional system changes from stream-flows up through playa with ephemeral streams to debris-flows during the accumulation of the three formations are thus attributed to different source rocks and climatic conditions. Therefore, the fluvial-dominated fans of the Hekou Formation recorded a subhumid paleoclimate (Coniacian-Santonian Age). The dominant semiarid climate during the Campanian Age produced abundant fine-grained sediments in the playa and ephemeral lake environments of the Tangbian Formation. A climatic change towards more humidity during the late stage of the Guifeng Group (Maastrichtian Age) probably yielded high deposition rate of coarse clasts in debris-flow dominated fans of the Lianhe Formation. Thus the Late Cretaceous climate changes are inferred to have influenced and preserved signals in the alluvial stratigraphy of the Yongchong Basin.

Petrogenesis and tectonic implications of the Early Carboniferous to the Late Permian Barleik plutons in the West Junggar (NW China)

NASA Astrophysics Data System (ADS)

Liu, Bo; Han, Bao-Fu; Ren, Rong; Chen, Jia-Fu; Wang, Zeng-Zhen; Zheng, Bo

2017-02-01

The Paleozoic accretionary orogenesis and continental crustal growth in Central Asia are thought to have close relationship with the evolution of the Paleo-Asian Ocean (PAO). The well-exposed plutons in the northern Barleik Mountains of the West Junggar region, NW China, may provide essential insights into the evolution of the Junggar Ocean, a branch of the PAO, and mechanism of continental crustal growth. Our work on the Barleik plutons indicates an early suite of 324-320 Ma diorite and a late suite of 314-259 Ma quartz syenite and granitic porphyry. All the plutons are characterized by high-K calc-alkaline to shoshonitic signatures, varying depletion in Nb, Ta, Sr, P, Eu, and Ti, low initial 87Sr/86Sr ratios (0.70241-0.70585), strongly positive εNd(t) values (+ 5.7-+7.7), and young one-stage Nd model ages (390-761 Ma), suggesting that they resulted from different batches of magma that were produced by fractional crystallization of a metasomatized mantle source with minor crustal contamination. The diorite is coeval with the youngest arc magmatic rocks, indicating a subduction-related origin. By contrast, the quartz syenite and granitic porphyry are geochemically similar to A2-type granites, with high Zr, Ga, and FeOT/[FeOT + MgO], and are coeval with the widespread plutons in the West Junggar. This, together with the occurrence of Late Carboniferous fluvial deposits and the lack of < 320 Ma ophiolitic and subduction-related metamorphic lithologies, definitively indicates a post-collisional setting after the closure of the Junggar Ocean. Slab breakoff accompanied by asthenospheric upwelling and basaltic underplating is a possible geodynamic process that is responsible for the post-collisional magmatism and vertical crustal growth in the region. Thus a tectonic switch from subduction to post-collision started at the end of the Early Carboniferous ( 320 Ma), probably as a result of the final closure of the Junggar Ocean.

Paleomagnetic study of 1765 Ma dyke swarm from the Singhbhum Craton: Implications to the paleogeography of India

NASA Astrophysics Data System (ADS)

Shankar, Ravi; Srinivasa Sarma, D.; Ramesh Babu, N.; Parashuramulu, V.

2018-05-01

We report the first key paleopole as a result of paleomagnetic study on a precisely dated 1765.3 ± 1.0 Ma WNW-ESE trending dyke swarm from Singhbhum Craton. This pole has been used in this study to propose the paleogeographic reconstruction of India with Baltica Craton and North China Craton. Incremental alternating field (AF) and thermal demagnetization, isolated high coercivity components with north to north-westerly declination and shallow negative inclination from 9 sampling sites which are representing different individual dykes. The primary origin of the ChRM is supported by the positive baked contact test. The WNW-ESE trending dykes yield a mean paleomagnetic direction with a declination = 329.2° and an inclination = -22.8° (k = 31.6; α95 = 9.3°). The positive bake contact test proves the primary nature of remanence. The pole position of Singhbhum Craton at 1765 Ma is 45°N, 311°E (dp = 5.2 and dm = 9.9). Paleogeographic reconstruction at ca. 1770 Ma, supported by geological, tectonic and metallogenic evidences indicate that the Baltica Craton and India linkage can be stable for at least ∼370 Ma (∼1770-1400 Ma). There is also reasonable evidence in support of India-North China Craton spatial proximity at ∼1770 Ma.

The Boundary of Tectonic Units of the South China Continent in the Meso-Neoproterozoic - Early Paleozoic: Insights from Integrated Geophysical Study

NASA Astrophysics Data System (ADS)

Guo, L.; Gao, R.; Meng, X.; Zhang, J.; Wang, H.; Liu, Y.

2013-12-01

The South China continent (SCC), located in the transition zone of the Eurasia, India and Pacific plates, formed in the Meso-Neoproterozoic by collision of the Yangtze block and the Cathaysia block. However, the boundaries of the two blocks before the late Paleozoic (from Meso-Neoproterozoic to early Paleozoic) remain debated in the literature due to strong and complex tectonic and magmatic activities since then. The south of Jiangnan archicontinent is covered mostly by the thick strata since the late Paleozoic, the surface of which is widely covered by the vegetation. And the regional tectonic deformation is extremely complicated with few basal outcrops. For decades, a variety of geophysical detections have been performed in the SCC for understanding the deep structure and tectonic evolution, including deep seismic sounding (DSS) profiles, magnetotelluric sounding (MT) profiles, gravity and magnetic surveys and a small amount of deep seismic reflection profiles. However, due to the limitations of resolution and accuracy of the observed geophysical data in the past, especially short of the deep seismic reflection profiles to reveal fine lithosphere structure, different scientists presented various views on the division of tectonic units in the SCC. In quite recent years, the SinoProbe-02 project launched a long profile of geophysical detections across the two blocks in the SCC, including deep seismic reflection, DSS, MT, and broadband seismic observation, the resolution and accuracy of which had been improved greatly. These newly data will benefit better understanding the deep structure and tectonic evolution of the SCC. Here, we assembled high-resolution Bouguer gravity anomalies and aeromagnetic anomalies data in the SCC. The magnetic data were reduced to the pole by used a varying magnetic inclinations algorithm. We then performed anomaly separation and multi-scales lineation structure analysis on the gravity and RTP magnetic data, and then did 3D fusion analysis on them. Seismic reflection profiles focus on fine lithosphere structure vertically along the profile, while gravity and magnetic methods are beneficial to reveal regional tectonic features laterally. The integrate study of seismic, gravity and magnetic data will play the advantages of various methods and constraint and confirm each other. Hence, we did the interpretation of gravity and magnetic data with constraints of the newly seismic reflection profile. Based on the above studies, we traced the boundaries of tectonic units in the SCC from Meso-Neoproterozoic to early Paleozoic, and formed a certain understanding of the tectonic evolution in the SCC before the late Paleozoic. Acknowledgment: We acknowledge the financial support of the SinoProbe-02-01 and SinoProbe-01-05 projects, and the Fundamental Research Funds for the Central Universities.

On the relative significance of lithospheric weakening mechanisms for sustained plate tectonics

NASA Astrophysics Data System (ADS)

Araceli Sanchez-Maes, Sophia

2018-01-01

Plate tectonics requires the bending of strong plates at subduction zones, which is difficult to achieve without a secondary weakening mechanism. Two classes of weakening mechanisms have been proposed for the generation of ongoing plate tectonics, distinguished by whether or not they require water. Here we show that the energy budget of global subduction zones offers a simple yet decisive test on their relative significance. Theoretical studies of mantle convection suggest bending dissipation to occupy only 10-20 % of total dissipation in the mantle, and our results indicate that the hydrous mechanism in the shallow part of plates is essential to satisfy the requirement. Thus, surface oceans are required for the long-term operation of plate tectonics on terrestrial worlds. Establishing this necessary and observable condition for sustained plate tectonics carries important implications for planetary habitability at large.

The pre-Devonian tectonic framework of Xing'an-Mongolia orogenic belt (XMOB) in north China

NASA Astrophysics Data System (ADS)

Xu, Bei; Zhao, Pan; Wang, Yanyang; Liao, Wen; Luo, Zhiwen; Bao, Qingzhong; Zhou, Yongheng

2015-01-01

A new tectonic division of the Xing'an-Mongolia orogenic belt (XMOB) in north China has been presented according to our research and a lot of new data of tectonics, geochronology and geochemistry. Four blocks and four sutures have been recognized in the XMOB, including the Erguna (EB), Xing'an-Airgin Sum (XAB), Songliao-Hunshandake (SHB), and Jiamusi (JB), and Xinlin-Xiguitu (XXS), Xilinhot-Heihe (XHS), Mudanjiang (MS) and Ondor Sum-Yongji sutures (OYS). The framework of the XMOB is characterized by a tectonic collage of the blocks and orogenic belts between them. Different Precambrian basements have been found in the blocks, including the Neoproterozoic metamorphic rocks and plutons in the EB, the Neoproterozoic metamorphic rocks in western and eastern of segments of the XAB, Mesoproterozoic and Neoproterozoic metamorphic rocks in middle segments of the XAB, respectively, the Neoproterozoic metamorphic rocks and Mesoproterozoic volcanic rocks and plutons in the SHB, and Neoproterozoic metamorphic rocks in the JB. The XXS resulted from a northwestward subduction of the XAB beneath the EB during the Cambrian, which was followed by the forming of the XHS and OYS in the northwest and south margins of the SHB in the Silurian, respectively. The MS was caused by a westward subduction of the JB beneath the east margin of the SHB during the middle Devonian. The three Cambrian, Silurian and middle Devonian events indicate that the XMOB belongs to a pre-middle Devonian multiple orogenic belt in the Central Asian Orogenic Belt (CAOB). Forming of the XMOB suggests that the southeast part of the Paleo Asian Ocean closed before the middle Devonian.

Red River barrier and Pleistocene climatic fluctuations shaped the genetic structure of Microhyla fissipes complex (Anura: Microhylidae) in southern China and Indochina

PubMed Central

Yuan, Zhi-Yong; Suwannapoom, Chatmongkon; Yan, Fang; Poyarkov, Nikolay A.; Nguyen, Sang Ngoc; Chen, Hong-man; Chomdej, Siriwadee; Murphy, Robert W.

2016-01-01

South China and Indochina host striking species diversity and endemism. Complex tectonic and climatic evolutions appear to be the main drivers of the biogeographic patterns. In this study, based on the geologic history of this region, we test 2 hypotheses using the evolutionary history of Microhyla fissipes species complex. Using DNA sequence data from both mitochondrial and nuclear genes, we first test the hypothesis that the Red River is a barrier to gene flow and dispersal. Second, we test the hypothesis that Pleistocene climatic cycling affected the genetic structure and population history of these frogs. We detect 2 major genetic splits that associate with the Red River. Time estimation suggests that late Miocene tectonic movement associated with the Red River drove their diversification. Species distribution modeling (SDM) resolves significant ecological differences between sides of the Red River. Thus, ecological divergence also probably promoted and maintained the diversification. Genogeography, historical demography, and SDM associate patterns in southern China with climate changes of the last glacial maximum (LGM), but not Indochina. Differences in geography and climate between the 2 areas best explain the discovery. Responses to the Pleistocene glacial–interglacial cycling vary among species and regions. PMID:29491943

Red River barrier and Pleistocene climatic fluctuations shaped the genetic structure of Microhyla fissipes complex (Anura: Microhylidae) in southern China and Indochina.

PubMed

Yuan, Zhi-Yong; Suwannapoom, Chatmongkon; Yan, Fang; Poyarkov, Nikolay A; Nguyen, Sang Ngoc; Chen, Hong-Man; Chomdej, Siriwadee; Murphy, Robert W; Che, Jing

2016-12-01

South China and Indochina host striking species diversity and endemism. Complex tectonic and climatic evolutions appear to be the main drivers of the biogeographic patterns. In this study, based on the geologic history of this region, we test 2 hypotheses using the evolutionary history of Microhyla fissipes species complex. Using DNA sequence data from both mitochondrial and nuclear genes, we first test the hypothesis that the Red River is a barrier to gene flow and dispersal. Second, we test the hypothesis that Pleistocene climatic cycling affected the genetic structure and population history of these frogs. We detect 2 major genetic splits that associate with the Red River. Time estimation suggests that late Miocene tectonic movement associated with the Red River drove their diversification. Species distribution modeling (SDM) resolves significant ecological differences between sides of the Red River. Thus, ecological divergence also probably promoted and maintained the diversification. Genogeography, historical demography, and SDM associate patterns in southern China with climate changes of the last glacial maximum (LGM), but not Indochina. Differences in geography and climate between the 2 areas best explain the discovery. Responses to the Pleistocene glacial-interglacial cycling vary among species and regions.

The Distribution and Composition Characteristics of Siliceous Rocks from Qinzhou Bay-Hangzhou Bay Joint Belt, South China: Constraint on the Tectonic Evolution of Plates in South China

PubMed Central

Li, Hongzhong; Zhai, Mingguo; Zhang, Lianchang; Zhou, Yongzhang; Yang, Zhijun; He, Junguo; Liang, Jin; Zhou, Liuyu

2013-01-01

The Qinzhou Bay-Hangzhou Bay joint belt is a significant tectonic zone between the Yangtze and Cathaysian plates, where plentiful hydrothermal siliceous rocks are generated. Here, the authors studied the distribution of the siliceous rocks in the whole tectonic zone, which indicated that the tensional setting was facilitating the development of siliceous rocks of hydrothermal genesis. According to the geochemical characteristics, the Neopalaeozoic siliceous rocks in the north segment of the Qinzhou Bay-Hangzhou Bay joint belt denoted its limited width. In comparison, the Neopalaeozoic Qinzhou Bay-Hangzhou Bay joint belt was diverse for its ocean basin in the different segments and possibly had subduction only in the south segment. The ocean basin of the north and middle segments was limited in its width without subduction and possibly existed as a rift trough that was unable to resist the terrigenous input. In the north segment of the Qinzhou Bay-Hangzhou Bay joint belt, the strata of hydrothermal siliceous rocks in Dongxiang copper-polymetallic ore deposit exhibited alternative cycles with the marine volcanic rocks, volcanic tuff, and metal sulphide. These sedimentary systems were formed in different circumstances, whose alternative cycles indicated the release of internal energy in several cycles gradually from strong to weak. PMID:24302882

Formation of tectonic peperites from alkaline magmas intruded into wet sediments in the Beiya area, western Yunnan, China

USGS Publications Warehouse

Xu, Xing-Wang; Cai, Xin-Ping; Zhong, Jia-You; Song, Bao-Chang; Peters, Stephen G.

2007-01-01

Tertiary (3.78 Ma to 3.65 Ma) biotite-K-feldspar porphyritic bodies intrude Tertiary, poorly consolidated lacustrine sedimentary rocks in the Beiya mineral district in southwestern China. The intrusives are characterized by a microcrystalline and vitreous-cryptocrystalline groundmass, by replacement of some tabular K-feldspar phenocrysts with microcrystalline chlorite and calcite, and by Fe-rich rings surrounding biotite phenocrysts. Peculiar structures, such as contemporary contact faults and slickensides, ductile shear zones and flow folds, foliation and lineations, tension fractures, and banded and boudin peperites, are developed along the contact zones of the intrusives. These features are related to the forceful intrusion of the alkaline magmas into the wet Tertiary sediments. The partially consolidated magmas were deformed and flattened by continued forceful magma intrusion that produced boudinaged and banded peperites. These peperites characterized by containing oriented deformation fabrics are classified as tectonic peperites as a new type of peperite, and formation of these tectonic peperites was related to fracturing of magmas caused by forceful intrusion and shear deformation and to contemporary migration and injection of fluidized sediments along fractures that dismembered the porphyritic magma. Emplacement of the magma into the wet sediments in the Beiya area is interpreted to be related to a large pressure difference rather than to the buoyancy force.

Blueschist metamorphism and its tectonic implication of Late Paleozoic-Early Mesozoic metabasites in the mélange zones, central Inner Mongolia, China

NASA Astrophysics Data System (ADS)

Zhang, Jinrui; Wei, Chunjing; Chu, Hang

2015-01-01

Blueschists in central Inner Mongolia are distributed as layers and blocks in mélanges including the southern zone in Ondor Sum area and the northern zone in Manghete and Naomuhunni areas. They have been attributed to the subduction of Early Paleozoic oceanic crust. Blueschists from Ondor Sum and Naomuhunni are characterized by occurrence of sodic amphibole coexisting with epidote, albite, chlorite, calcic amphibole (in Ondor Sum) and muscovite (in Naomuhunni). Blueschists in Manghete contain porphyroblastic albite with inclusions of garnet and epidote in a matrix dominated by calcic-sodic amphibole, epidote, chlorite, albite and muscovite. Phase equilibria modeling for three blueschist samples using pseudosection suggest that the AlM2 contents in sodic amphibole can be used as a good barometer in the limited assemblage involving sodic amphibole + actinolite + epidote + chlorite + albite + quartz under pressures <4-6 kbar, while this barometer is largely influenced by temperature and bulk Fe2O3 contents in the actinolite-absent assemblage sodic amphibole + epidote + chlorite + albite + quartz of higher pressure and the AlM2 contents are not pressure-controlled in the albite-absent assemblage sodic amphibole + epidote + chlorite + quartz under pressures > 7-10 kbar. In the sodic amphibole-bearing assemblages, the NaM4 contents in sodic amphibole mainly decrease as temperature rises, being a potential thermometry. The calculated pseudosections constrain the P-T conditions of blueschists to be 3.2-4.2 kbar/355-415 °C in Ondor Sum, 8.2-9.0 kbar/455 °C-495 °C in Manghete and 6.6-8.1 kbar/420-470 °C in Naomuhunni. These P-T estimates indicate a rather high geothermal gradient of 18-25 °C/km for the blueschist metamorphism, being of intermediate P/T facies series. Available zircon U-Pb age data suggests that the protoliths of blueschists were formed later than Late Paleozoic-Early Mesozoic and metamorphosed soon afterwards. An alternative interpretation for the tectonic implication of blueschists in central Inner Mongolia is that they may be a new type attributed to closure of limited ocean basins and do not represent a tectonic regime occurred in conventional subduction setting.

Introduction to special section: China shale gas and shale oil plays

USGS Publications Warehouse

Jiang, Shu; Zeng, Hongliu; Zhang, Jinchuan; Fishman, Neil; Bai, Baojun; Xiao, Xianming; Zhang, Tongwei; Ellis, Geoffrey S.; Li, Xinjing; Richards-McClung, Bryony; Cai, Dongsheng; Ma, Yongsheng

2015-01-01

Even though China shale gas and shale oil exploration is still in an early stage, limited data are already available. We are pleased to have selected eight high-quality papers from fifteen submitted manuscripts for this timely section on the topic of China shale gas and shale oil plays. These selected papers discuss various subject areas including regional geology, resource potentials, integrated and multidisciplinary characterization of China shale reservoirs (geology, geophysics, geochemistry, and petrophysics) China shale property measurement using new techniques, case studies for marine, lacustrine, and transitional shale deposits in China, and hydraulic fracturing. One paper summarizes the regional geology and different tectonic and depositional settings of the major prospective shale oil and gas plays in China. Four papers concentrate on the geology, geochemistry, reservoir characterization, lithologic heterogeneity, and sweet spot identification in the Silurian Longmaxi marine shale in the Sichuan Basin in southwest China, which is currently the primary focus of shale gas exploration in China. One paper discusses the Ordovician Salgan Shale in the Tarim Basin in northwest China, and two papers focus on the reservoir characterization and hydraulic fracturing of Triassic lacustrine shale in the Ordos Basin in northern China. Each paper discusses a specific area.

Major unconformities/termination of extension events and associated surfaces in the South China Seas: Review and implications for tectonic development

NASA Astrophysics Data System (ADS)

Morley, C. K.

2016-04-01

The distribution of unconformities and end of Cenozoic rifting events in the South China Seas (SCS) reflects both the modes of rift development, and the effects of driving mechanisms. Continental rifting began in the eastern basins during the Paleocene, and propagated westwards to the Vietnam basin margin in the Late Eocene. Continental breakup around 32-28 Ma caused a regional reduction or cessation in extensional activity, particularly affecting basins furthest from the spreading centre. Basins in the slope and deepwater area north of the spreading centre exhibit reduced fault activity until 21-20 Ma. Propagation of oceanic crust westwards between ∼25 and 23 Ma, and termination of seafloor spreading sometime between 20.5 and 16 Ma affected fault activity in the Qiongdongnan, and Nam Con Song basins. In the Phu Khanh Basin and South, in the Dangerous Grounds area, extension continued until about 16 Ma, ending at the Red Unconformity. The end of seafloor spreading around 20.5 Ma reflects loss of extensional driving force as thinned continental crust entered the NW Borneo subduction zone. Controversially, a key component of the driving force maybe attributed to slab-pull. A transitional period of about 5-7 my between the onset of subduction of continental crust, and final jamming of the subduction zone (Deep Regional Unconformity, DRU) is inferred. The last pulse of extension was focussed in the western SCS, and terminated around 10.5 Ma. Detailed understanding of proto South China Seas development remains uncertain and controversial.

Detrital zircons from phanerozoic rocks of the Songliao Block, NE China: Evidence and tectonic implications

NASA Astrophysics Data System (ADS)

Zhou, Jian-Bo; Wilde, Simon A.; Zhang, Xing-Zhou; Liu, Fu-Lai; Liu, Jian-Hui

2012-03-01

Rocks that crop out in the northern part of the Songliao Block are mainly consist of high-grade metamorphic gneiss, Paleozoic strata and Mesozoic granites. They are essentially similar to rocks reported from beneath the Songliao Basin that occupies the majority of the Songliao Block. Four samples of Paleozoic metasedimentary rocks from Tieli in the north-eastern part of the Songliao Block yield detrital zircon U-Pb ages ranging from 2690 to 501 Ma, with four age populations at: 2071-2690 Ma, with a peak at 2585 Ma; 1776-1997 Ma, with a peak at 1890 Ma; 719-991 Ma, with a peak at 800 Ma; and 501-592 Ma, with a peak at 518 Ma. These are similar to age populations in other parts of the Central Asian Orogenic Belt (CAOB), although sediments from the Songliao Block contain more abundant Archean and Proterozoic detrital zircons than the neighboring Jiamusi-Khanka Block to the east and Xing'an Block to the west. This may indicate that rocks of this age comprise a minor component of the Songliao Block. The Pan-African zircon ages from the Songliao Block, taken together with ˜500 Ma magmatic and high-grade metamorphic zircons obtained from the nearby Erguna, Xing'an and Jiamusi-Khanka blocks, indicate that Pan-African events affected all blocks of the CAOB in NE China. This suggests that these blocks not only share a common basement, but that they had a common history. An extensive Late Pan-African (˜500 Ma) orogenic terrane thus occupies much of the CAOB in NE China.

40Ar/39Ar dating of oceanic plagiogranite: Constraints on the initiation of seafloor spreading in the South China Sea

NASA Astrophysics Data System (ADS)

Zhong, Li-Feng; Cai, Guan-Qiang; Koppers, Anthony A. P.; Xu, Yi-Gang; Xu, He-Hua; Gao, Hong-Fang; Xia, Bin

2018-03-01

The Cenozoic opening of the South China Sea was one of the most significant tectonic events in SE Asia, coinciding with complex regional rifting, subduction, terrane collision, and large-scale continental strike-slip faulting. The timing of the initiation of seafloor spreading in the South China Sea remains controversial due to a scarcity of incontrovertible age data. This work provides the first report of an oceanic plagiogranite from the Penglai Seamount, located on the 17°N fossil spreading center of the East Sub-basin of the South China Sea, near the Manila Trench. Pyroxene and whole-rock 40Ar/39Ar dating yields ages of 32.3 ± 0.5 Ma and 28.9 ± 1.9 Ma, respectively. The plagiogranite show trace element and isotopic composition similar to those of mid-oceanic ridge basalts (MORB), with 87Sr/86Sr(t) = 0.70394; εNd(t) = 8.21; 206Pb/204Pb = 17.9930, 207Pb/204Pb = 15.4839, 208Pb/204Pb = 37.8852; εHf(t) = 20.95; and γOs(t) = 15.89. It suggested that the rock formed due to differential cooling between adjacent layers of oceanic crust and asthenospheric shearing at the oceanic spreading ridge, resulting in the development of detachment faults. This triggered the subsequent ingress of seawater along the faults, which transformed into a hydrothermal fluid under the influence of shear and geothermal heating, altering the parent gabbro, and leading to the generation of the daughter plagiogranite by anatexis during the early Oligocene. This new geochronology also demonstrates that the initial opening of the South China Sea occurred before 32 Ma, thereby constraining the Cenozoic tectonic evolution of Southeast Asia.

Whole Planet Coupling from Climate to Core: Implications for the Evolution of Rocky Planets and their Prospects for Habitability

NASA Astrophysics Data System (ADS)

Foley, B. J.; Driscoll, P. E.

2015-12-01

Many factors have conspired to make Earth a home to complex life. Earth has abundant water due to a combination of factors, including orbital distance and the climate regulating feedbacks of the long-term carbon cycle. Earth has plate tectonics, which is crucial for maintaining long-term carbon cycling and may have been an important energy source for the origin of life in seafloor hydrothermal systems. Earth also has a strong magnetic field that shields the atmosphere from the solar wind and the surface from high-energy particles. Synthesizing recent work on these topics shows that water, a temperate climate, plate tectonics, and a strong magnetic field are linked together through a series of negative feedbacks that stabilize the system over geologic timescales. Although the physical mechanism behind plate tectonics on Earth is still poorly understood, climate is thought to be important. In particular, temperate surface temperatures are likely necessary for plate tectonics because they allow for liquid water that may be capable of significantly lowering lithospheric strength, increase convective stresses in the lithosphere, and enhance the effectiveness of "damage" processes such as grainsize reduction. Likewise, plate tectonics is probably crucial for maintaining a temperate climate on Earth through its role in facilitating the long-term carbon cycle, which regulates atmospheric CO2 levels. Therefore, the coupling between plate tectonics and climate is a feedback that is likely of first order importance for the evolution of rocky planets. Finally, plate tectonics is thought to be important for driving the geodynamo. Plate tectonics efficiently cools the mantle, leading to vigorous thermo-chemical convection in the outer core and dynamo action; without plate tectonics inefficient mantle cooling beneath a stagnant lid may prevent a long-lived magnetic field. As the magnetic field shields a planet's atmosphere from the solar wind, the magnetic field may be important for preserving hydrogen, and therefore water, on the surface. Thus whole planet coupling between the magnetic field, atmosphere, mantle, and core is possible. We lay out the basic physics governing whole planet coupling, and discuss the implications this coupling has for the evolution of rocky planets and their prospects for hosting life.

Age and tectonic implications of Paleoproterozoic Deo Khe Granitoids within the Phan Si Pan Zone, Vietnam

NASA Astrophysics Data System (ADS)

Anh, Hoang Thi Hong; Hieu, Pham Trung; Tu, Vu Le; Son, La Mai; Choi, Sung Hi; Yu, Yongjae

2015-11-01

We report the first U-Pb zircon ages of 1855-1873 Ma for the Deo Khe Granitoids (DKG) in the Phan Si Pan Zone (PSPZ) of northern Vietnam. The DKG are medium-grained two-mica granitoids predominantly composed of quartz, K-feldspar, and muscovite. Trace element analyses indicate that the DKG are enriched in large ion lithophile elements but depleted in high field strength elements. Zircons from the granitoids have negative εHf(t) values ranging from -23.6 to -17.5. The magmatic zircons from the DKG have single-stage Hf model ages (TDM1) that range from 3.3 to 2.8 Ga and their εHf(t) data all plot well below the evolution trend of 2800 Ma average juvenile mantle. Observed Hf model ages are contemporaneous with the emplacement of 2.90-2.84 Ga tonalite-trondhjemite-granodiorite (TTG) gneiss observed in a nearby Ca Vinh Complex, suggesting that PSPZ in northern Vietnam is a product of partial melting of Archean crust. A sequence of similar tectonic events including initial emplacement of TTG protolith at 2.8-2.9 Ga, metamorphic development of TTG gneiss at 1.9-2.0 Ga, and magmatic activity at 1.8-2.0 Ga are now recognized both in northern Vietnam and Yangtze block which we interpret to indicate basement rocks in northern Vietnam are similar to those found along southern China.

Petrogenesis, detrital zircon SHRIMP U-Pb geochronology, and tectonic implications of the Upper Paleoproterozoic Seosan iron formation, western Gyeonggi Massif, Korea

NASA Astrophysics Data System (ADS)

Kim, Chang Seong; Jang, Yirang; Samuel, Vinod O.; Kwon, Sanghoon; Park, Jung-Woo; Yi, Keewook; Choi, Seon-Gyu

2018-05-01

This study involves investigations on the Upper Paleoproterozoic iron formation (viz., Seosan iron formation) from the Seosan Group, Gyeonggi Massif of the southwestern Korean Peninsula. It occurs as thin banded layers within meta-arkosic sandstone, formed by alternating processes of chemical (hydrothermal) and detrital depositions under a shallow marine environment. It mainly consists of alternating layers of iron oxides, mostly hematite, and quartz. Minor amounts of magnetite surrounded by muscovite, clinopyroxene and amphibole indicate hydrothermal alteration since its formation. Meta-arkosic sandstone is composed of recrystallized or porphyroclastic quartz and microcline, with small amounts of hematite and pyrite clusters. The Seosan iron formation has high contents of total Fe2O3 and SiO2 with positive Eu anomalies similar to those of other Precambrian banded iron formations, and its formation is clearly related to hydrothermal alteration since its deposition. Detrital zircon SHRIMP U-Pb geochronology data from a meta-arkosic sandstone (SN-1) and an iron formation (SN-2) show mainly two age groups of ca. 2.5 Ga and ca. 1.9-1.75 Ga. This together with intrusion age of the granite gneiss (ca. 1.70-1.65 Ga) clearly indicate that the iron formations were deposited during the Upper Paleoproterozoic. The dominant Paleoproterozoic detrital zircon bimodal age peaks preserved in the Seosan iron formation compare well with those from the South China Craton sedimentary basins, reflecting global tectonic events related to the Columbia supercontinent in East Asia.

Strain transformation between tectonic extrusion and crustal thickening in the growth of the Tibetan Plateau

NASA Astrophysics Data System (ADS)

Liu, M.; Li, Y.; Sun, Y.; Shen, X.

2017-12-01

The Indo-Eurasian continental collision since 50 Ma has thickened the crust to raise the Himalayan-Tibetan Plateau and driven lateral extrusion of Asian lithospheric blocks to affect Cenozoic tectonics in central and east Asia. The relative roles of crustal thickening and tectonic extrusion, and the strain partitioning between them over time and space, remain controversial. We have analyzed the strain rates using GPS velocities, and correlated the results with vertical motion derived from precise leveling. We found that tectonic extrusion largely transforms to crustal thickening near the margins of the Tibetan Plateau. Near the NW margin of the Tibetan Plateau, the shear stain transforms to compressive strain, consistent with neotectonic studies that indicate crustal shortening and uplift. Around the SE margin, shear stain largely terminates in the southern Yunnan province of China. The present-day crustal motion in SE Tibetan Plateau can be well explained by gravitational spreading without invoking plate-edge push as envisioned in the tectonic extrusion model. Using data collected from local seismic arrays, we derived receiver functions to image the lithospheric structures across the Tibetan Plateau and the Alashan block to its north and the Ordos block to its east. Our results indicate that the mantle lithosphere of these bounding Asian blocks has not been reworked by Tibetan tectonics; instead they have acted as restrictive walls to the growing Tibetan Plateau. Our finite element modeling shows that crustal deformation along the margins of the Tibetan Plateau are consistent with the notion that the east- and southeastward extrusion of the Tibetan lithosphere is largely confined to the Tibetan Plateau because of the restrictive bounding blocks of the Asian lithosphere. Thus the tectonic impact of the Indo-Eurasian collision on the Cenozoic Asian tectonics may not be as extensive as previously thought.

Tectonically Induced Anomalies Without Large Earthquake Occurrences

NASA Astrophysics Data System (ADS)

Shi, Zheming; Wang, Guangcai; Liu, Chenglong; Che, Yongtai

2017-06-01

In this study, we documented a case involving large-scale macroscopic anomalies in the Xichang area, southwestern Sichuan Province, China, from May to June of 2002, after which no major earthquake occurred. During our field survey in 2002, we found that the timing of the high-frequency occurrence of groundwater anomalies was in good agreement with those of animal anomalies. Spatially, the groundwater and animal anomalies were distributed along the Anninghe-Zemuhe fault zone. Furthermore, the groundwater level was elevated in the northwest part of the Zemuhe fault and depressed in the southeast part of the Zemuhe fault zone, with a border somewhere between Puge and Ningnan Counties. Combined with microscopic groundwater, geodetic and seismic activity data, we infer that the anomalies in the Xichang area were the result of increasing tectonic activity in the Sichuan-Yunnan block. In addition, groundwater data may be used as a good indicator of tectonic activity. This case tells us that there is no direct relationship between an earthquake and these anomalies. In most cases, the vast majority of the anomalies, including microscopic and macroscopic anomalies, are caused by tectonic activity. That is, these anomalies could occur under the effects of tectonic activity, but they do not necessarily relate to the occurrence of earthquakes.

Using earthquake-triggered landslides as a hillslope-scale shear strength test: Insights into rock strength properties at geomorphically relevant spatial scales in high-relief, tectonically active settings

NASA Astrophysics Data System (ADS)

Gallen, Sean; Clark, Marin; Godt, Jonathan; Lowe, Katherine

2016-04-01

The material strength of rock is known to be a fundamental property in setting landscape form and geomorphic process rates as it acts to modulate feedbacks between earth surface processes, tectonics, and climate. Despite the long recognition of its importance in landscape evolution, a quantitative understanding of the role of rock strength in affecting geomorphic processes lags our knowledge of the influence of tectonics and climate. This gap stems largely from the fact that it remains challenging to quantify rock strength at the hillslope scale. Rock strength is strongly scale dependent because the number, size, spacing, and aperture of fractures sets the upper limit on rock strength, making it difficult to extrapolate laboratory measurements to landscape-scale interpretations. Here we present a method to determine near-surface rock strength at the hillslope-scale, relying on earthquake-triggered landslides as a regional-scale "shear strength" test. We define near-surface strength as the average strength of rock sample by the landslides, which is typically < 10 m. Based on a Newmark sliding block model, which approximates slope stability during an earthquake assuming a material with frictional and cohesive strength, we developed a coseismic landslide model that is capable of reproducing statistical characteristics of the distribution of earthquake-triggered landslides. We present results from two well-documented case-studies of earthquakes that caused widespread mass-wasting; the 2008 Mw 7.9 Wenchuan Earthquake, Sichuan Province, China and the 1994 Mw. 6.8 Northridge Earthquake, CA, USA. We show how this model can be used to determine near-surface rock strength and reproduce mapped landslide patterns provided the spatial distribution of local hillslope gradient, earthquake peak ground acceleration (PGA), and coseismic landsliding are well constrained. Results suggest that near-surface rock strength in these tectonically active settings is much lower than that obtained using typical laboratory shear strength measurements on intact rock samples. Furthermore, the near-surface material strength is similar between the study areas despite differences in tectonic, climatic, and lithologic conditions. Variations in near-surface strength within each setting appear to be more strongly associated with factors contributing to the weakening rock through chemical or physical weathering, such as mean annual precipitation and distance to active faults (a proxy for rock shattering intensity), rather than intrinsic lithologic properties. We hypothesize that the shattering of rock through long-term permanent strain accumulation and by repeated earthquakes is an important mechanism that can explain low rock strength values among the different study sites and the spatial pattern of rock strength within each location. These findings emphasize the potential role of factors other than lithology in controlling the spatial distribution of near-surface rock strength in high-relief, tectonically active settings, which has important implications for understanding the evolution of landscapes, interpreting tectonic and climatic signals from topography, critical zone processes, and natural hazard assessment.

Tectonic stress pattern in the Chinese Mainland from the inversion of focal mechanism data

NASA Astrophysics Data System (ADS)

Wei, Ju; Weifeng, Sun; Xiaojing, Ma

2017-04-01

The tectonic stress pattern in the Chinese Mainland and kinematic models have been subjected to much debate. In the past several decades, several tectonic stress maps have been figured out; however, they generally suffer a poor time control. In the present study, 421 focal mechanism data up to January 2010 were compiled from the Global/Harvard CMT catalogue, and 396 of them were grouped into 23 distinct regions in function of geographic proximity. Reduced stress tensors were obtained from formal stress inversion for each region. The results indicated that, in the Chinese Mainland, the directions of maximum principal stress were ˜NE-SW-trending in the northeastern region, ˜NEE-SWW-trending in the North China region, ˜N-S-trending in western Xinjiang, southern Tibet and the southern Yunnan region, ˜NNE-SSW-trending in the northern Tibet and Qinghai region, ˜NW-SE-trending in Gansu region, and ˜E-W-trending in the western Sichuan region. The average tectonic stress regime was strike-slip faulting (SS) in the eastern Chinese Mainland and northern Tibet region, normal faulting (NF) in the southern Tibet, western Xinjiang and Yunnan region, and thrust faulting (TF) in most regions of Xinjiang, Qinghai and Gansu. The results of the present study combined with GPS velocities in the Chinese Mainland supported and could provide new insights into previous tectonic models (e.g., the extrusion model). From the perspective of tectonics, the mutual actions among the Eurasian plate, Pacific plate and Indian plate caused the present-day tectonic stress field in the Chinese Mainland.

The tectonics of Venus: An overview

NASA Technical Reports Server (NTRS)

Solomon, Sean C.

1992-01-01

While the Pioneer Venus altimeter, Earth-based radar observatories, and the Venera 15-16 orbital imaging radars provided views of large-scale tectonic features on Venus at ever-increasing resolution, the radar images from Magellan constitute an improvement in resolution of at least an order of magnitude over the best previously available. A summary of early Magellan observations of tectonic features on Venus was published, but data available at that time were restricted to the first month of mapping and represented only about 15 percent of the surface of the planet. Magellan images and altimetry are now available for more than 95 percent of the Venus surface. Thus a more global perspective may be taken on the styles and distribution of lithospheric deformation on Venus and their implications for the tectonic history of the planet.

Late paleozoic base and precious metal deposits, East Tianshan, Xinjiang, China: Characteristics and geodynamic setting

USGS Publications Warehouse

Mao, J.; Goldfarb, R.J.; Wang, Y.; Hart, C.J.; Wang, Z.; Yang, J.

2005-01-01

The East Tianshan is a remote Gobi area located in eastern Xinjiang, northwestern China. In the past several years, a number of gold, porphyry copper, and Fe(-Cu) and Cu-Ag-Pb-Zn skarn deposits have been discovered there and are attracting exploration interest. The East Tianshan is located between the Junggar block to the north and early Paleozoic terranes of the Middle Tianshan to the south. It is part of a Hercynian orogen with three distinct E-W-trending tectonic belts: the Devonian-Early Carboniferous Tousuquan-Dananhu island arc on the north and the Carboniferous Aqishan - Yamansu rift basin to the south, which are separated by rocks of the Kanggurtag shear zone. The porphyry deposits, dated at 322 Ma, are related to the late evolutionary stages of a subduction-related oceanic or continental margin arc. In contrast, the skarn, gold, and magmatic Ni-Cu deposits are associated with post-collisional tectonics at ca. 290-270 Ma. These Late Carboniferous - Early Permian deposits are associated with large-scale emplacement and eruption of magmas possibly caused by lithosphere delamination and rifting within the East Tianshan.

An Andean-type retro-arc foreland system beneath northwest South China revealed by SINOPROBE profiling

NASA Astrophysics Data System (ADS)

Li, Jianhua; Dong, Shuwen; Cawood, Peter A.; Zhao, Guochun; Johnston, Stephen T.; Zhang, Yueqiao; Xin, Yujia

2018-05-01

In the Mesozoic, South China was situated along the convergent margin between the Asian and Pacific plates, providing an excellent laboratory to understand the interactions between deformation, sedimentation and magmatism in a retroarc environment. The crustal architecture of northwest South China is displayed along the ∼600-km-long SINOPROBE deep seismic reflection profiles and reveals from east to west: (1) highly folded and truncated reflectors in the upper crust of the Yangtze Fold Zone, which correspond to thin- and thick-skinned thrust systems, and document large-scale intraplate structural imbrication and shortening; (2) a crustal-scale flat-ramp-flat structure, termed the Main Yangtze decollement, which forms a weak, viscous layer to accommodate strain decoupling and material transport in the thin- and thick-skinned systems; and (3) nearly flat-lying reflectors in the Sichuan Basin, which support interpretation of the basin as a weakly deformed depocentre. The Yangtze Fold Zone and the Sichuan Basin represent a retro-arc foreland basin system that is >800 km away from the continental-margin magmatic arc. We suggest that tectonic processes across the arc and retro-arc systems, including arc magma flare-up, basin sedimentation, retroarc thrust propagation, lithosphere underthrusting, root foundering, and extension-related magmatism were interrelated and governed mass transfer. Age data and geological relations link the tectonic processes to evolving geodynamics of the subducting Paleo-Pacific plate.

Depositional architecture and evolution of inner shelf to shelf edge delta systems since the Late Oliocene and their respone to the tectonic and sea level change, Pear River Mouth Basin, northern South China Sea

NASA Astrophysics Data System (ADS)

Lin, Changsong; Zhang, Zhongtao; liu, Jingyan; Jiang, Jing

2016-04-01

The Pear River Mouth Basin is located in the northern continent margin of the South China Sea. Since the Late Oligocene, the long-term active fluvial systems (Paleo-Zhujiang) from the western basin margin bebouched into the northern continental margin of the South China Sea and formed widespread deltaic deposits in various depositional geomorphologies and tectonic settings. Based of integral analysys of abundant seismic, well logging and drilling core data, Depositional architecture and evolution of these delta systems and their respone to the tectonic and sea level change are documented in the study. There are two basic types of the delta systems which have been recognized: inner shelf delta deposited in shallow water enviroments and the outer shelf or shelf-edge delta systems occurred in deep water settings. The paleowater depths of these delta systems are around 30 to 80m (inner shelf delta) and 400-1000m (shelf-edge delta) estimated from the thickness (decompaction) of the delta front sequences. The study shows that the inner shelf delta systems are characterized by relatively thin delta forests (20-40m), numereous stacked distributary channel fills, relative coarse river mouth bar deposits and thin distal delta front or distal bar and prodelta deposits. In contrast, the outer shelf or shelf edge delta systems are characteristic of thick (300-800m) and steep (4-60) of deltaic clinoforms, which commonly display in 3D seismic profiles as "S" shape reflection. Large scale soft-sediment deformation structures, slump or debris flow deposits consisting mainly of soft-sediment deformed beds, blocks of sandstones and siltstones or mudstones widely developed in the delta front deposits. The shelf edge delta systems are typically associated with sandy turbidite fan deposits along the prodelta slopes, which may shift basinwards as the progradation of the delta systems. The delta systems underwent several regional cycles of evolution from inner shelf deltas to shelf edge deltas since the Late Oligocene in the study area, and this is consistent with relative sea level changes constrained by interplay of tectonic subsidence or global sea level change and sediment supply. The shelf-edge delta sandy deposits and the associated prodelta turbidite fan systems are the most important oil/gas bearing reservoirs in the continental slope area.

Petrogenesis of Jurassic granitoids at the northeastern margin of the North China Craton: New geochemical and geochronological constraints on subduction of the Paleo-Pacific Plate

NASA Astrophysics Data System (ADS)

Liu, Jin; Zhang, Jian; Liu, Zhenghong; Yin, Changqing; Zhao, Chen; Peng, Youbo

2018-06-01

At the junction between the North China Craton (NCC) and the Central Asian Orogenic Belt (CAOB), northern Liaoning province, NE China, there are widespread Jurassic igneous rocks. The tectonic setting and petrogenesis of these rocks are unresolved. Zircon U-Pb dating, whole-rock geochemistry, and Hf isotopic compositions of Jurassic granitoids were investigated to constrain their ages and petrogenesis in order to understand the tectonic evolution of the Paleo-Pacific Ocean along the northeastern margin of the NCC. Geochronological data indicate that magmatism occurred between the early and late Jurassic (180-156 Ma). Despite the wide range in ages of the intrusions, Jurassic granitoids were likely derived from a similar or common source, as inferred from their geochemical and Hf isotopic characteristics. Compared to the island arc andesite-dacite-rhyolite series, the Jurassic granitoids are characterized by higher SiO2, Al2O3, and Sr contents, and lower MgO, FeOT, Y, and Yb contents, indicating that the primary magmas show typical characteristics of adakitic magmas derived from partial melting of thickened lower crust. These findings, combined with their εHf(t) values (+1.4 to +5.4) and two-stage model ages (1515-1165 Ma), indicate the primary magmas originated from partial melting of juvenile crustal material accreted during the Mesoproterozoic. They are enriched in large-ion lithophile elements (e.g., Rb, K, Th, Ba, and U) and light rare-earth elements (REE), and depleted in high-field-strength elements (e.g., Nb, Ta, Ti, and P) and heavy REE. Based on these findings and previous studies, we suggest that the Jurassic adakitic granitoids (180-156 Ma) were formed in an active continental margin and compressive tectonic setting, related to subduction of the Paleo-Pacific Plate.

Mapping Electrical Structures in the Jarud Basin, Northeast China through Magnetotelluric Sounding

NASA Astrophysics Data System (ADS)

Zhao, W.

2015-12-01

In recent years, China Geological Survey (CGS) has launched 3D geological mapping programs from regional to local scales. The project Deep geological survey at the periphery of the Songliao Basin funded by CGS was implemented from 2012 to 2014. Its main goals are to reveal the tectonic framework of the Jarud Basin (JB) as well as to identify the strata distribution of Permian Linxi Formation by integrating new electromagnetic data with existing geophysical and geological data since black mudstones in the Linxi Formation have shown the potential of shale gas. The study area covered dominantly with Cretaceous-Jurassic igneous rocks with exception of the southeast part is situated in Jarud Banner and Ar Horqin Banner, Inner Mongolia, China. It tectonically lies in the southern Great Khingan Range, western margin of the Songliao Basin, and north of Xar Moron Fault. Over the period of 2012 to 2014, a magnetotelluric survey was carried out at the JB. A total of 926 MT sites with nominal spacing 1 km was acquired in the effective frequency range of 0.01 Hz ~ 300 Hz on six NW and five NE profiles, covering area that exceeds 10, 000 km2. After dimensionality analysis and static shift removal, the nonlinear conjugate algorithm was used to conduct 2D inversion for TM and TE modes. The resistivity models underwent examination using sensitivity tests. The optimal resistivity models revealed numerous large faults, some of which constitute the boundaries of the JB, and modified the tectonic framework. Integrated with well logging and geological mapping data, the strata of Linxi Formation were identified and classified into three depressions: Depressions Arituguri, Gadasu and Wufen. Attention should be paid to Depression Gadasu with area of around 500 km2 since it contains reasonably thick conductive sediments exceeding 4 km in depth which are inferred to be black mudstones pertaining to shale gas.

The Tectonic Boundary Between Eastern Subbaisin and South-West Subbasin of the South China Sea Revealed from the Normalized Magnetic Source Strength

NASA Astrophysics Data System (ADS)

Guo, L.; Meng, X.

2014-12-01

The South China Sea (SCS), surrounded by the Eurasia, Pacific and India-Australia plates, is one of the largest marginal seas in the Western Pacific. It was formed by the interaction of the three plates and the seafloor spreading during Late Oligocene time to Early Miocene time. The boundary between Eastern Subbaisin and South-west Subbasin of the SCS has long been debated in the literature. Refining the boundary is one of the crucial tasks for correctly understanding the seafloor spreading model of the SCS. Due to few drills on the deep ocean basin of the SCS, magnetic data become important information for refining the boundary. However, the interpretation of magnetic data in the SCS suffers from the remanent magnetization of ocean crust as well as igneous rock and seamounts. The conventional reduction-to-pole anomalies at low latitudes usually neglect the remanent magnetization, making the interpretation incorrect. Here, we assembled high-resolution total magnetic intensity (TMI) data around the ocean basin of the SCS, and then did a special transformation of the TMI anomalies with a varying magnetic inclinations algorithm to obtain the normalized source strength (NSS). The NSS has advantage of insensitivity to remanent magnetization, benefitting correct interpretation. The NSS presents discriminative features from east to west in the ocean basin. The boundary of the discriminative features is clear and just ranges from the northeastern edge of the Zhongsha Islands running in the southeast direction to the northeastern edge of the Reed Bank. These imply that magnetic structure and tectonic features in the crust are discriminative between both sides of this boundary. It can be deduced that this boundary is the tectonic boundary between Eastern Subbaisin and South-west Subbasin. We acknowledge the financial support of the National Natural Science Foundation of China (41374093) and the SinoProbe-01-05 project.

Geophysical anomalies associated with Imjin River Belt (IRB) in the middle Korean Peninsula revealed by geomagnetic depth sounding and seismological data

NASA Astrophysics Data System (ADS)

Yang, J.; Choi, H.; Noh, M.; Im, C.

2012-12-01

Imjin River Belt (IRB), located in the middle of the Korean Peninsula, has been one of long-standing geological issues because it is a very important tectonic link to understand a tectonic evolution of north-eastern Asia including China, Korea and Japan. Although the IRB has been considered as an extension of collision belt between the North China Block (NCB) and South China Block (SCB), there is little geophysical observation or study on this issue. In recent, we compiled a new induction arrow map for the Korean Peninsula, on the basis of long-period magneto-telluric (MT) data and the geomagnetic depth sounding data performed since the late 1990's. This newly compiled map has finer spatial resolution expecially in the middle area of the peninsula, which helps us to present the geophysical evidence that the IRB is the continuation or extension of the collision belt to the peninsula. The overall pattern of induction arrows in the peninsula appears to indicate a northwest-southeast direction, which is well-known 'sea effect' by the surrounding seas. However, the results of observations in the middle of the peninsula distinctly show an anomalous pattern around the IRB, which can not be explained only by the surrounding seas. This anomalous pattern may be attributed to enhanced conductivity associated with tectonic events that Imjin River Belt has experienced. The 3-D electromagnetic modeling results, considering both surrounding seas and enhanced conductivity of the IRB, explain well the anomalous observations around the IRB. Furthermore, recent seismological study demonstrates that focal mechanism around the IRB is mainly normal faulting event, which may be interpreted as the reactivation of paleo structures that are related to the post collisional lithospheric delamination. All the geophysical evidences convince us that the IRB is an extension of the collision belt between the NCB and SCB to the peninsula.

An early extensional event of the South China Block during the Late Mesozoic recorded by the emplacement of the Late Jurassic syntectonic Hengshan Composite Granitic Massif (Hunan, SE China)

NASA Astrophysics Data System (ADS)

Wei, Wei; Chen, Yan; Faure, Michel; Martelet, Guillaume; Lin, Wei; Wang, Qingchen; Yan, Quanren; Hou, Quanlin

2016-03-01

Continental scaled extension is the major Late Mesozoic (Jurassic and Cretaceous) tectonic event in East Asia, characterized by faulting, magmatic intrusions and half-grabens in an area with a length of > 5000 km and a width of > 1000 km. Numerous studies have been conducted on this topic in the South China Block (SCB), However, the space and time ranges of the compressional or extensional regimes of the SCB during the Jurassic are still unclear, partly due to the lack of structural data. The emplacement fabrics of granitic plutons can help determine the regional tectonic background. In this study, a multidisciplinary approach, including Anisotropy of Magnetic Susceptibility (AMS), macro and microstructural analyses, quartz c-axis preferred orientation, gravity modeling and monazite EPMA dating, was conducted on the Hengshan composite granitic massif in SCB that consists of the Triassic Nanyue biotite granitic pluton and the Late Jurassic Baishifeng two-mica granitic pluton. The magnetic fabrics are characterized by a consistent NW-SE oriented lineation and weakly inclined foliation. A dominant high temperature deformation with a top-to-the-NW shear sense is identified for both plutons. The deformation increasing from the center of the Baishifeng pluton to its western border is associated to the development of the West Hengshan Boundary Fault (WHBF). The gravity modeling shows a ;saw tooth-shaped; NE-SW oriented structure of the Baishifeng pluton, which may be considered as NE-SW oriented tension-gashes formed due to the NW-SE extension. All results show that the Triassic Nanyue pluton was deformed under post-solidus conditions by the WHBF coeval with the emplacement of the Late Jurassic Baishifeng pluton. All these observations comply with the NW-SE extensional tectonics coeval with the emplacement of the Baishifeng pluton, which argues that the NW-SE crustal stretching started since the Late Jurassic, at least in this part of the SCB.

Geologic Map of the Snegurochka Planitia Quadrangle (V-1): Implications for Tectonic and Volcanic History of the North Polar Region of Venus

NASA Technical Reports Server (NTRS)

Hurwitz, D. M.; Head, J. W.

2009-01-01

Geologic mapping of Snegurochka Planitia (V-1) reveals a complex stratigraphy of tectonic and volcanic features that can provide insight into the geologic history of Venus and Archean Earth [1,2], including 1) episodes of both localized crustal uplift and mantle downwelling, 2) shifts from local to regional volcanic activity, and 3) a shift back to local volcanic activity. We present our progress in mapping the spatial and stratigraphic relationships of material units and our initial interpretations of the tectonic and volcanic history of the region surrounding the north pole of Venus

Arc magmatism and mineralization in North Luzon and its relationship to subduction at the East Luzon and North Manila Trenches

NASA Astrophysics Data System (ADS)

Wolfe, John A.

The Tertiary tectonics of North Luzon are complicated by an early thermotectonic regime in the Eocene (40-50 Ma) and the second from 30 to 17 Ma in the Oligocene resulting from subduction in the East Luzon Trench. The second stage coincided with the opening of the South China Sea on the west side of the Philippines. Portions of the western Philippines were translated south from China by the opening of the South China Sea. This includes Mindoro Island, Palawan and the Reed Bank area. No one has presented any evidence that any oceanic crust existed between early Luzon and China prior to opening of the South China Sea. After spreading of the South China Sea ceased, China began to extrude eastward and coupled with the oceanic crust of the South China Sea initiated subduction in the North Manila trench under Luzon at about 17 Ma. Commencing at approximately 15 Ma a graben formed east of the Manila Trench, centered in Baguio City. It contained the volcanic arc which began to develop as the Agno batholith intruded the graben. The graben extends for at least 75 km on the southwest flank of the Cordillera with relayed extensions into the Cordillera. Porphyry copper mineralization developed within the graben from 10 to 8 Ma interrupted by the explosion of a caldera or volcano tectonic depression extending south of Baguio. This graben contains 22 porphyry copper bodies, some of them uneconomic. Described by Gervasio as a "crackle zone", the same zone was described by Fernandez and Damasco as the area most favorable for gold exploration. The second period of mineralization was imposed on the district from 4 to 3 Ma. Gold mineralization in the Baguio district constituted a third phase of mineralization in the Pleistocene. Absence of commercial mineralization in the Cordillera and Sierra Madre correlated with the Paleogene is one of the criteria for distinguishing between the subduction related to the South China Sea and that related to the Philippine Sea on the east. One of the important conclusions of this paper is that the Oligocene phase of subduction on the East Luzon Trench coincided with the opening of the South China Sea and both of these activities ceased when spreading on the South China Sea ceased. The period of mineralization in the graben at Baguio relates to the Manila Trench on the west side of Luzon with igneous activity commencing about 15 Ma.

Reworking of Paleoproterozoic crust and its implications for the assembly of Rodinia: Evidence from Neoproterozoic (ca. 0.8~0.9 Ga) granitoids in NE China

NASA Astrophysics Data System (ADS)

Wang, F.

2015-12-01

NE China, located between the North China Craton and the Siberian Craton, is considered to represent the eastern section of Central Asian Orogenic Belt (CAOB), and thought to be a collage of several ancient microcontinental massifs. Geochronological and geochemical data on Neoproterozoic granitoids in Songnen-Zhangguangcai Range Massif are presented in order to shed light on the genesis and the genetic link to the tectonic evolution of Rodinia. LA-ICPMS zircon U-Pb ages of 915±4 Ma, 841±5 Ma, and 917±4 Ma, were obtained for two granodiorites and one monzogranite, respectively. These granitoids have SiO2 = 67.89-71.18 wt.%, MgO = 0.53-0.88 wt.%, and Na2O+K2O = 6.48-9.61 wt.%, and are chemically a calc-alkaline series. They are characterized by enrichment in light rare earth elements and large ion lithophile elements, and depletion in heavy rare earth elements and high field strength elements such as Nb, Ta, and Ti, consistent with the chemistry of igneous rocks from an active continental margin setting. The zircons with different ages (ca. 915~917 and 841 Ma) from these granitoids share similar characteristics in Hf isotopic composition. In situ Hf analyses of zircons show that ɛHf (t) values and two-stage model ages of -4.7 ~ +1.5 and 1.7~1.9 Ga, respectively. It is evidence that these Neoproterozoic granitoids were derived from the reworking of the Paleoproterozoic continental crust. The above findings, combined with the regional geologic information, imply that these granitoids formed under an active continental margin setting related to the assembly of Rodinia in the early stage of Neoproterozoic. Meanwhile, similar magmatic events history also suggests that the Songnen-Zhangguangcai Range Massif have an affinity to the Siberia Craton. This research was financially supported by research grants from the Natural Science Foundation of China (Grants 41330206 and 41402043).

The Wenchuan, China M8.0 Earthquake: A Lesson and Implication for Seismic Hazard Mitigation

NASA Astrophysics Data System (ADS)

Wang, Z.

2008-12-01

The Wenchuan, China M8.0 earthquake caused great damage and huge casualty. 69,197 people were killed, 374,176 people were injured, and 18,341 people are still missing. The estimated direct economic loss is about 126 billion U.S. dollar. The Wenchuan earthquake again demonstrated that earthquake does not kill people, but the built environments and induced hazards, landslides in particular, do. Therefore, it is critical to strengthen the built environments, such buildings and bridges, and to mitigate the induced hazards in order to avoid such disaster. As a part of the so-called North-South Seismic Zone in China, the Wenchuan earthquake occurred along the Longmen Shan thrust belt which forms a boundary between the Qinghai-Tibet Plateau and the Sichuan basin, and there is a long history (~4,000 years) of seismicity in the area. The historical records show that the area experienced high intensity (i.e., greater than IX) in the past several thousand years. In other words, the area is well-known to have high seismic hazard because of its tectonic setting and seismicity. However, only intensity VII (0.1 to 0.15g PGA) has been considered for seismic design for the built environments in the area. This was one of the main reasons that so many building collapses, particularly the school buildings, during the Wenchuan earthquake. It is clear that the seismic design (i.e., the design ground motion or intensity) is not adequate in the Wenchuan earthquake stricken area. A lesson can be learned from the Wenchuan earthquake on the seismic hazard and risk assessment. A lesson can also be learned from this earthquake on seismic hazard mitigation and/or seismic risk reduction.

Descriptive models of major uranium deposits in China - Some results of the Workshop on Uranium Resource Assessment sponsored by the International Atomic Energy Agency, Vienna, Austria, in cooperation with China National Nuclear Corporation, Beijing, and the U.S. Geological Survey, Denver, Colorado, and Reston, Virginia

USGS Publications Warehouse

Finch, W.I.; Feng, S.; Zuyi, C.; McCammon, R.B.

1993-01-01

Four major types of uranium deposits occur in China: granite, volcanic, sandstone, and carbonaceous-siliceous-pelitic rock. These types are major sources of uranium in many parts of the world and account for about 95 percent of Chinese production. Descriptive models for each of these types record the diagnostic regional and local geologic features of the deposits that are important to genetic studies, exploration, and resource assessment. A fifth type of uranium deposit, metasomatite, is also modeled because of its high potential for production. These five types of uranium deposits occur irregularly in five tectonic provinces distributed from the northwest through central to southern China. ?? 1993 Oxford University Press.

China Naval Modernization: Implications for U.S. Navy Capabilities - Background and Issues for Congress

DTIC Science & Technology

2010-08-05

interest,” meaning an issue comparable in importance to China’s interest in Taiwan and Tibet; • asserting or defending China’s interpretation of...Continental Shelf in the East China Sea: Meaning and Implications,” China Brief, July 9, 2009: 9-11; Peter Dutton and John Garofano, “China Undermines...which recently has been defined as a ‘core interest’—the same phrase Chinese use to refer to Tibet, Taiwan and Xinjiang. In the process, China is in

China Naval Modernization: Implications for U.S. Navy Capabilities?Background and Issues for Congress

DTIC Science & Technology

2010-07-23

China’s Claims to an Extended Continental Shelf in the East China Sea: Meaning and Implications,” China Brief, July 9, 2009: 9-11; Peter Dutton and John...interest’—the same phrase Chinese use to refer to Tibet, Taiwan and Xinjiang. In the process, China is in effect dismissing the international concept of...in Table 1, China was projected to have a total of 30 relatively modern attack submarines— meaning Shang, Kilo, Yuan, and Song class boats—in

China Naval Modernization: Implications for U.S. Navy Capabilities-Background and Issues for Congress

DTIC Science & Technology

2010-07-26

China’s Claims to an Extended Continental Shelf in the East China Sea: Meaning and Implications,” China Brief, July 9, 2009: 9-11; Peter Dutton...interest’—the same phrase Chinese use to refer to Tibet, Taiwan and Xinjiang. In the process, China is in effect dismissing the international concept...Table 1, China was projected to have a total of 30 relatively modern attack submarines— meaning Shang, Kilo, Yuan, and Song class boats—in commission

Rheological decoupling at the Moho and implication to Venusian tectonics.

PubMed

Azuma, Shintaro; Katayama, Ikuo; Nakakuki, Tomoeki

2014-03-18

Plate tectonics is largely responsible for material and heat circulation in Earth, but for unknown reasons it does not exist on Venus. The strength of planetary materials is a key control on plate tectonics because physical properties, such as temperature, pressure, stress, and chemical composition, result in strong rheological layering and convection in planetary interiors. Our deformation experiments show that crustal plagioclase is much weaker than mantle olivine at conditions corresponding to the Moho in Venus. Consequently, this strength contrast may produce a mechanical decoupling between the Venusian crust and interior mantle convection. One-dimensional numerical modeling using our experimental data confirms that this large strength contrast at the Moho impedes the surface motion of the Venusian crust and, as such, is an important factor in explaining the absence of plate tectonics on Venus.

Rheological decoupling at the Moho and implication to Venusian tectonics

PubMed Central

Azuma, Shintaro; Katayama, Ikuo; Nakakuki, Tomoeki

2014-01-01

Plate tectonics is largely responsible for material and heat circulation in Earth, but for unknown reasons it does not exist on Venus. The strength of planetary materials is a key control on plate tectonics because physical properties, such as temperature, pressure, stress, and chemical composition, result in strong rheological layering and convection in planetary interiors. Our deformation experiments show that crustal plagioclase is much weaker than mantle olivine at conditions corresponding to the Moho in Venus. Consequently, this strength contrast may produce a mechanical decoupling between the Venusian crust and interior mantle convection. One-dimensional numerical modeling using our experimental data confirms that this large strength contrast at the Moho impedes the surface motion of the Venusian crust and, as such, is an important factor in explaining the absence of plate tectonics on Venus. PMID:24638113

The structure and stratigraphy of deepwater Sarawak, Malaysia: Implications for tectonic evolution

NASA Astrophysics Data System (ADS)

Madon, Mazlan; Kim, Cheng Ly; Wong, Robert

2013-10-01

The structural-stratigraphic history of the North Luconia Province, Sarawak deepwater area, is related to the tectonic history of the South China Sea. The Sarawak Basin initiated as a foreland basin as a result of the collision of the Luconia continental block with Sarawak (Sarawak Orogeny). The foreland basin was later overridden by and buried under the prograding Oligocene-Recent shelf-slope system. The basin had evolved through a deep foreland basin ('flysch') phase during late Eocene-Oligocene times, followed by post-Oligocene ('molasse') phase of shallow marine shelf progradation to present day. Seismic interpretation reveals a regional Early Miocene Unconformity (EMU) separating pre-Oligocene to Miocene rifted basement from overlying undeformed Upper Miocene-Pliocene bathyal sediments. Seismic, well data and subsidence analysis indicate that the EMU was caused by relative uplift and predominantly submarine erosion between ˜19 and 17 Ma ago. The subsidence history suggests a rift-like subsidence pattern, probably with a foreland basin overprint during the last 10 Ma. Modelling results indicate that the EMU represents a major hiatus in the sedimentation history, with an estimated 500-2600 m of missing section, equivalent to a time gap of 8-10 Ma. The EMU is known to extend over the entire NW Borneo margin and is probably related to the Sabah Orogeny which marks the cessation of sea-floor spreading in the South China Sea and collision of Dangerous Grounds block with Sabah. Gravity modelling indicates a thinned continental crust underneath the Sarawak shelf and slope and supports the seismic and well data interpretation. There is a probable presence of an overthrust wedge beneath the Sarawak shelf, which could be interpreted as a sliver of the Rajang Group accretionary prism. Alternatively, magmatic underplating beneath the Sarawak shelf could equally explain the free-air gravity anomaly. The Sarawak basin was part of a remnant ocean basin that was closed by oblique collision along the NW Borneo margin. The closure started in the Late Eocene in Sarawak and moved progressively northeastwards into Sabah until the Middle Miocene. The present-day NW Sabah margin may be a useful analogue for the Oligocene-Miocene Sarawak foreland basin.

New seismic observation on the lithosphere and slab subduction beneath the Indo-Myanmar block: Implications for continent oblique subduction and transition to oceanic slab subduction

NASA Astrophysics Data System (ADS)

Jiang, M.; He, Y.; Zheng, T.; Mon, C. T.; Thant, M.; Hou, G.; Ai, Y.; Chen, Q. F.; Sein, K.

2017-12-01

The Indo-Myanmar block locates to the southern and southeastern of the Eastern Himalayan Syntax (EHS) and marks a torsional boundary of the collision between the Indian and Eurasian plates. There are two fundamental questions concerned on the tectonics of Indo-Myanmar block since the Cenozoic time. One is whether and how the oblique subduction is active in the deep; the other is where and how the transition from oceanic subduction and continental subduction operates. However, the two problems are still under heated debate mainly because the image of deep structure beneath this region is still blurring. Since June, 2016, we have executed the China-Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO) and deployed the first portable seismic array in Myanmar in cooperation with Myanmar Geosciences Society (MGS). This array contains 70 stations with a dense-deployed main profile across the Indo-Myanmar Range, Central Basin and Shan State Plateau along latitude of 22° and a 2-D network covering the Indo-Myanmar Range and the western part of the Central Basin. Based on the seismic data collected by the new array, we conducted the studies on the lithospheric structure using the routine surface wave tomography and receiver function CCP stacking. The preliminary results of surface wave tomography displayed a remarkable high seismic velocity fabric in the uppermost of mantle beneath the Indo-Myanmar Range and Central Basin, which was interpreted as the subducted slab eastward. Particularly, we found a low velocity bulk within the high-velocity slab, which was likely to be a slab window due to the slab tearing. The preliminary results of receiver function CCP stacking showed the obvious variations of the lithospheric structures from the Indo-Myanmar Range to the Central Basin and Shan State Plateau. The lithospheric structure beneath the Indo-Myanmar Range is more complex than that beneath the Central Basin and Shan State Plateau. Our resultant high-resolution images will provide important constrains for establishing the tectonic framework of Indian plate eastward subduction. This study is supported by the National Natural Science Foundation of China (grants 41490612, 41274002).

Provenance and tectonic setting of siliciclastic rocks associated with the Neoproterozoic Dahongliutan BIF: Implications for the Precambrian crustal evolution of the Western Kunlun orogenic belt, NW China

NASA Astrophysics Data System (ADS)

Hu, Jun; Wang, He; Wang, Min

2017-10-01

The Late Neoproterozoic Dahongliutan BIF is associated with siliciclastic rocks in the Tianshuihai terrane of the Western Kunlun orogenic belt (WKO), NW China. The sedimentary rocks have various weathering indices (e.g., CIA = 57-87, PIA = 61-96 and Th/U = 4.85-12.45), indicative of varying degrees of weathering in the source area. The rocks have trace element ratios, such as Th/Sc = 0.60-1.21 and Co/Th = 0.29-1.67, and light rare earth element (LREE) enriched chondrite-normalized REE patterns, suggesting that they were mainly sourced from intermediate and felsic rocks. Available U-Pb ages of detrital zircon from these rocks reveal that the detrital sources may have been igneous and metamorphic rocks from the WKO and the Tarim Block. Our study suggests that the Dahongliutan BIF and hosting siliciclastic rocks may have deposited in a setting transitional from a passive to active continental margin, probably related to the Late Neoproterozoic-Early Cambrian seafloor spreading and subduction of the Proto-Tethys Ocean. U-Pb dating of 163 detrital zircons defines five major age populations at 2561-2329 Ma, 2076-1644 Ma, 1164-899 Ma, 869-722 Ma and 696-593 Ma. These age groups broadly correspond to the major stages of supercontinent assembly and breakup events widely accepted for Columbia, Rodinia and Gondwana. Some zircons have TDM2 model ages of 3.9-1.8 Ga and negative εHf(t) values, suggesting that the Archean to Paleoproterozoic (as old as Eoarchean) crustal materials were episodically reworked and incorporated into the late magmatic process in the WKO. Some Neoproterozoic zircons have TDM2 model ages of 1.47-1.07 Ga and 1.81-1.53 Ga and positive εHf(t) values, indicating juvenile crustal growth during the Mesoproterozoic. Our new results, combined with published data, imply that both the Tianshuihai terrane in the WKO and the Tarim Block share the same Precambrian tectonic evolution history.

Transformation from Paleo-Asian Ocean closure to Paleo-Pacific subduction: New constraints from granitoids in the eastern Jilin-Heilongjiang Belt, NE China

NASA Astrophysics Data System (ADS)

Ma, Xing-Hua; Zhu, Wen-Ping; Zhou, Zhen-Hua; Qiao, Shi-Lei

2017-08-01

The eastern Jilin-Heilongjiang Belt (EJHB) of NE China is a unique orogen that underwent two stages of evolution within the tectonic regimes of the Paleo-Asian and Paleo-Pacific oceans. 158 available zircon U-Pb ages, including 26 ages obtained during the present study and 132 ages from the literature, were compiled and analyzed for the Mesozoic and Cenozoic granitoids from the EJHB and the adjacent Russian Sikhote-Alin Orogenic Belt (SAOB), to examine the temporal-spatial distribution of the granitoids and to constrain the tectonic evolution of the East Asian continental margin. Five stages of granitic magmatism can be identified: Early Triassic (251-240 Ma), Late Triassic (228-215 Ma), latest Triassic to Middle Jurassic (213-158 Ma), Early Cretaceous (131-105 Ma), and Late Cretaceous to Paleocene (95-56 Ma). The Early Triassic granitoids are restricted to the Yanbian region along the Changchun-Yanji Suture, and show geochemical characteristics of magmas from a thickened lower crust source, probably due to the final collision of the combined NE China blocks with the North China Craton. The Late Triassic granitoids, with features of A-type granites, represent post-collisional magmatic activities that were related to post-orogenic extension, marking the end of the tectonic evolution of the Paleo-Asian Ocean. The latest Triassic to Paleocene granitoids with calc-alkaline characteristics were NE-trending emplaced along the EJHB and SAOB and young towards the coastal region, and represent continental marginal arc magmas that were associated with the northwestwards subduction of the Paleo-Pacific Plate. Two periods of magmatic quiescence (158-131 and 105-95 Ma) correspond to changes in the subduction direction of the Paleo-Pacific Plate from oblique relative to the continental margin to subparallel. Taking all this into account, we conclude that: (1) the final closure of the Paleo-Asian Ocean occurred along the Changchun-Yanji Suture during the Early Triassic; (2) the onset of the subduction of the Paleo-Pacific Plate beneath the East Asian continental margin probably took place during the latest Triassic (ca. 215 Ma); (3) changes in the drifting direction of the Paleo-Pacific Plate were responsible for the intermittent magmatic activities; and (4) roll-back of the subducted plate resulted in the oceanwards migration of the magmatic arc and large-scale back-arc extension throughout NE China during the Early Cretaceous.

Staff - Marwan A. Wartes | Alaska Division of Geological & Geophysical

Science.gov Websites

programs, offering expertise in sedimentary geology and tectonics. My background is primarily in outcrop : Archives of coupled structural and sedimentary processes (GSA/AAPG) FIELD TRIP LEADERSHIP 2017, Field trip China: Journal of Sedimentary Research, v. 75, no. 2, p. 268-279. Carroll, A.R., and Wartes, M.A., 2003

Olivine fabrics and tectonic evolution of fore-arc mantles: A natural perspective from the Songshugou dunite and harzburgite in the Qinling orogenic belt, central China

NASA Astrophysics Data System (ADS)

Cao, Yi; Jung, Haemyeong; Song, Shuguang

2017-03-01

To advance our understanding of the deformation characteristics, rheological behaviors, and tectonic evolution of the fore-arc lithospheric mantle, we analyzed mineral fabrics for a large spinel-bearing ultramafic massif in the Songshugou area in the Qinling orogenic belt, central China. In the spinel-poor coarse-grained dunite, stronger A/D-type and weaker C-type-like fabrics were found, whereas the spinel-rich coarse-grained dunite displayed a comparatively stronger B-type-like fabric. These olivine fabrics are high-T fabrics influenced by the presence of melt, in which B and C-type-like fabrics are inferred to be produced by melt-assisted grain boundary sliding during synkinematic high-T melt-rock reactions. In contrast, the spinel-poor porphyroclastic and fine-grained dunites present weak AG and B-type-like fabrics, respectively. Their olivine fabrics (low-T fabrics) are inferred to transform from A/D-type fabric in their coarse-grained counterparts possibly through mylonitization process assisted by low-T fluid-rock reactions, during which strain was accommodated by the fluid-enhanced dislocation slip and/or fluid-assisted grain boundary sliding processes. Combined with the tectonic results of our previous work, the high-T olivine fabrics are probably related to a young and warm fore-arc mantle where intense partial melting and high-T boninitic melt-rock reactions prevalently occurred, whereas the low-T olivine fabrics likely reflect the evolving tectonic settings through the cooling fore-arc mantle to a continental lower crust in a collisional orogeny where low-T fluid-rock reactions were pervasively activated. These low-T olivine fabrics imply that though cold, the fore-arc lithospheric mantle may be locally weak (˜20-30 MPa), allowing ductile deformation to occur at a geologically significant strain rate.

Comparison of Tarim and central Asian FSU basins, I: Phanerozoic paleogeography

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heubeck, C.; Shangyou N.

1996-01-01

Large amounts of previously unpublished data on the petroleum geology of the FSU's Central Asian Republics and of China's Tarim region have found their way into the western public domain in the past few years. These data provide for the first time the opportunity to merge detailed stratigraphic, tectonic, and paleogeographic studies done during the past decades on both sides of the FSU-Chinese border and to place the results in a plate-tectonic and palinspastically restored reference frame. Major tectonic events affecting the active post-Silurian south-facing margin of Asia between the Caspian Sea and Tarim include (1) the collapse of themore » Kazakhstan arc fragments (ca. 400-300 Ma); (2) collision of YiIi with Tarim (ca. 375 Ma); (3) consolidation of the Turan Platform from pre-existing basement blocks (ca. 280-220 Ma), (4) collision of Tarim/Yili with the Kazakhstan arcs (ca. 260 Ma); (5) stabilization of a south-facing Triassic active margin (ca. 250 - 200 Ma); (6) accretion of Cimmeria (ca. 200 Ma) and associated reactivation events in Turan, Syr-Darja, and Tarim; (7) reactivation and modification of intracontinental structures during the collision of central Asia with India (ca. 55 Ma to present) and with the Arabian platform (ca. 25 Ma). Periodic large-scale flooding of denuded continental platforms (Turan, Tadjik) during sea-level highstands is recorded in the Jurassic, Mid-Late Cretaceous, and the Early Tertiary, resulting in extensive tracts of restricted marine sedimentary systems and marine incursions deep into central Asia (SW Tarim, Kuche Depression, Fergana, Turgay). Mesozoic-Cenozoic source rocks are sensitive to rapid lateral facies changes, and understanding their distribution requires detailed stratigraphic analysis. The attempted synthesis of data from China and the FSU with plate-tectonic concepts allows the transfer and testing of play concepts and hydrocarbons systems across the FSU-Chinese border.« less

Active tectonics and earthquake potential of the Myanmar region

NASA Astrophysics Data System (ADS)

Wang, Yu; Sieh, Kerry; Tun, Soe Thura; Lai, Kuang-Yin; Myint, Than

2014-04-01

This paper describes geomorphologic evidence for the principal neotectonic features of Myanmar and its immediate surroundings. We combine this evidence with published structural, geodetic, and seismic data to present an overview of the active tectonic architecture of the region and its seismic potential. Three tectonic systems accommodate oblique collision of the Indian plate with Southeast Asia and extrusion of Asian territory around the eastern syntaxis of the Himalayan mountain range. Subduction and collision associated with the Sunda megathrust beneath and within the Indoburman range and Naga Hills accommodate most of the shortening across the transpressional plate boundary. The Sagaing fault system is the predominant locus of dextral motion associated with the northward translation of India. Left-lateral faults of the northern Shan Plateau, northern Laos, Thailand, and southern China facilitate extrusion of rocks around the eastern syntaxis of the Himalaya. All of these systems have produced major earthquakes within recorded history and continue to present major seismic hazards in the region.

Paleozoic intrusive rocks from the Dunhuang tectonic belt, NW China: Constraints on the tectonic evolution of the southernmost Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Zhao, Yan; Sun, Yong; Diwu, Chunrong; Zhu, Tao; Ao, Wenhao; Zhang, Hong; Yan, Jianghao

2017-05-01

The Dunhuang tectonic belt (DTB) is of great importance for understanding the tectonic evolution of the southernmost Central Asian Orogenic Belt (CAOB). In this study, the temporal-spatial distribution, petrogenesis and tectonic setting of the Paleozoic representative intrusive rocks from the DTB were systematically investigated to discuss crustal evolution history and tectonic regime of the DTB during Paleozoic. Our results reveal that the Paleozoic magmatism within the DTB can be broadly divided into two distinct episodes of early Paleozoic and late Paleozoic. The early Paleozoic intrusive rocks, represented by a suite metaluminous-slight peraluminous and medium- to high-K calc-alkaline I-type granitoids crystallized at Silurian (ca. 430-410 Ma), are predominantly distributed along the northern part of the DTB. They were probably produced with mineral assemblage of eclogite or garnet + amphibole + rutile in the residue, and were derived from magma mixing source of depleted mantle materials with various proportions of Archean-Mesoproterozoic continental crust. The late Paleozoic intrusive rocks can be further subdivided into two stages of late Devonian stage (ca. 370-360 Ma) and middle Carboniferous stage (ca. 335-315 Ma). The former stage is predominated by metaluminous to slight peraluminous and low-K tholeiite to high-K calc-alkaline I-type granitic rocks distributed in the central part of the DTB. They were also generated with mineral assemblage of amphibolite- to eclogite-facies in the residue, and originated from magma source of depleted mantle materials mixed with different degrees of old continental crust. The later stage is represented by adakite and alkali-rich granite exposed in the southern part of the DTB. The alkali-rich granites studied in this paper were possibly produced with mineral assemblage of granulite-facies in the residue and were generated by partial melting of thickened lower continental crust. Zircon Hf isotopes and field distribution of those Paleozoic intrusive rocks reveal that both the Silurian and the late Devonian magmatic activities predominantly represent crustal growth processes in the DTB, accompanied by different degrees of reworking of pre-existing continental crust. However, the middle Carboniferous (ca. 335-315 Ma) magmatic activity reflects a crustal reworking process. The Silurian and late Devonian intrusive rocks were most likely formed in the arc-related subduction zones, whereas, the middle Carboniferous intrusive rocks were possibly formed in a transitional tectonic setting from compression to extension, representing the final stage of Paleozoic orogeny in the DTB. These Paleozoic magmatic rocks further suggest that the DTB has reactivated from a stable block to an orogen and undergone two episodes (the early Paleozoic and the late Paleozoic) of orogeny during Paleozoic. It represents a Paleozoic accretionary orogen of the southernmost margin of the CAOB between the Tarim Craton and North China Craton, and tectonically extends northward to the Beishan orogen and westward to the eastern South Tianshan Belt.

Higher Education Tuition and Fees in China: Implications and Impacts on Affordability and Educational Equity

ERIC Educational Resources Information Center

Dong, Haiying; Wan, Xuehong

2012-01-01

Students in China are being shouldered with more financial responsibility for their higher education. This shift impacts individuals across the economic spectrum in different ways. This paper assesses recent trends in China's higher education tuition and fees, and the implications on educational equity. Results document substantial increases in…

Late tectonic uplift of an inverted oceanic basin in South East Asia: the case of Palawan Island (western Philippines)

NASA Astrophysics Data System (ADS)

Meresse, F.; Savva, D.; Pubellier, M.; Steuer, S.; Franke, D.; Cordey, F.; Muller, C.; Sapin, F.; Mouly, B.; Auxiètre, J.-L.

2012-04-01

The elongated island of Palawan, bounded by two marginal basins, the South China Sea to the North and the Sulu Sea to the South is composed of remnants of an inverted basin (Proto-South China Sea) thrusted onto the margin of a continental terrane which rifted away from the Chinese-Vietnamese margin. Based on field observations coupled with seismic and drill-holes data, our study focuses on the structural architecture of the island in order to decipher the geodynamic evolution of the southern margin of the South China Sea. Structurally, the Palawan Island consists of: (i) the Palawan wedge, which extends towards the South China Sea is composed of deformed slope to deep ocean deposits of Cretaceous (north Palawan) to Tertiary (central and south Palawan) ages. This accretionnary wedge is characterized by small wavelength folds of mainly NE-SW trend. Offshore, the unconformable Middle-Late Miocene Tabon limestones unit postdates the last stages of the Palawan wedge growth/setting; (ii) On top of this wedge lie thrust slices of ophiolite bodies comprising ribbon cherts of Albian age as indicated by radiolarians.; these bodies are likely to be relicts of the now-subducted Proto South China Sea; (iii) The central and southern parts of the Palawan island are characterized by a large wavelength antiform of NE-SW trend. This structure is sealed by the slightly tilted Early Pliocene marls unit; (iv) The island also presents necking zones bordered by N-S trending transform faults. This area witnessed the geodynamic evolution of the South East Asia which consists of a succession of opening/closure of oceanic basins and block accretions. The Palawan Island therefore results of the closing of the Proto-South China Sea which once formed both the Palawan accretionary wedge and the overlying ophiolite tectonic slices. During a later compressive event, the rifted continental margin which composes the basement of the Island was inverted, inducing the uplift and the large scale folding of the Palawan Island. In a final stage, the strain relaxing results in the formation of the necking zones, probably reactivating the inherited transform faults of the Proto-South China Sea. Keywords: Palawan Island; South China Sea; oceanic basin; inverted margin; Ophiolite.

Petrogenesis of early Jurassic basalts in southern Jiangxi Province, South China: Implications for the thermal state of the Mesozoic mantle beneath South China

NASA Astrophysics Data System (ADS)

Cen, Tao; Li, Wu-xian; Wang, Xuan-ce; Pang, Chong-jin; Li, Zheng-xiang; Xing, Guang-fu; Zhao, Xi-lin; Tao, Jihua

2016-07-01

Early Jurassic bimodal volcanic and intrusive rocks in southern South China show distinct associations and distribution patterns in comparison with those of the Middle Jurassic and Cretaceous rocks in the area. It is widely accepted that these rocks formed in an extensional setting, although the timing of the onset and the tectonic driver for extension are debated. Here, we present systematic LA-ICP-MS zircon U-Pb ages, whole-rock geochemistry and Sr-Nd isotope data for bimodal volcanic rocks from the Changpu Formation in the Changpu-Baimianshi and Dongkeng-Linjiang basins in southern Jiangxi Province, South China. Zircon U-Pb ages indicate that the bimodal volcanic rocks erupted at ca. 190 Ma, contemporaneous with the Fankeng basalts ( 183 Ma). A compilation of geochronological results demonstrates that basin-scale basaltic eruptions occurred during the Early Jurassic within a relatively short interval (< 5 Ma). These Early Jurassic basalts have tholeiitic compositions and OIB-like trace element distribution patterns. Geochemical analyses show that the basalts were derived from depleted asthenospheric mantle, dominated by a volatile-free peridotite source. The calculated primary melt compositions suggest that the basalts formed at 1.9-2.1 GPa, with melting temperatures of 1378 °C-1405 °C and a mantle potential temperature (TP) ranging from 1383 °C to 1407 °C. The temperature range is somewhat hotter than normal mid-ocean-basalt (MORB) mantle but similar to an intra-plate continental mantle setting, such as the Basin and Range Province in western North America. This study provides an important constraint on the Early Jurassic mantle thermal state beneath South China. Reference: Raczek, I., Stoll, B., Hofmann, A.W., Jochum, K.P. 2001. High-precision trace element data for the USGS reference materials BCR-1, BCR-2, BHVO-1, BHVO-2, AGV-1, AGV-2, DTS-1, DTS-2, GSP-1 and GSP-2 by ID-TIMS and MIC-SSMS. Geostandards Newsletter 25(1), 77-86.

Geochemistry and Geochronology of the Heilongjiang Complex and Its Implications in the Late Paleozoic Tectonics of Eastern NE China

NASA Astrophysics Data System (ADS)

GE, M.; Zhang, J.; Liu, K.; Ling, Y.; Wang, M.; Wang, J.

2016-12-01

The Paleozoic to early Mesozoic tectonic framework of Northeast China, especially the Jiamusi block and its related structural belts, are highly debated. In this contribution, geochemical, geochronological and isotopic analyses were carried out on the basalts in the Heilongjiang complex to address these issues. The Heilongjiang complex defines the suture belt between the Jiamusi block and the Songliao block in Northeast China, and the blueschist is a major composition for this complex, coexisting with ultramafic rocks, amphibolite, greenschist, quartzite and mica schist. The blueschist has a mineral association of sodic amphibole, epidote, chlorite, phengite, albite and quartz with accessory phases of apatite, titanite, zircon and ilmenite. Together with the lithological association, the geochemical results present that the protoliths of the blueschist can be divided into the alkaline and tholeiitic basalts and have OIB affinities, formed in an ocean island setting, indicated by the (La/Yb) N values of 3.57 - 11.54, and the (La/Sm) N values of 0.69 - 3.64. The high and positive ɛNd (t) values of + 3.7 to +9.0, and relative enrichment in Nb and Ta show that both the alkaline and tholeiitic basalts may be derived from the asthenospheric mantle. Magmatic zircons from the blueschist in Yilan area yield a 206Pb/238U age of 281 - 288 Ma, interpreted as its protolithic age. The amphibolite from Xiachengzi area has a zircon U-Pb age of 248 ± 4 Ma, interpreted as its protolith age and has N-MORB affinities, supported by (La/Yb)N ratios of 0.60-0.89 and (La/Sm)N of 0.62-0.84, and high ɛNd (t) values ranging from + 7.8 to + 9.5, deriving from a depleted mantle source. A new 40Ar/39Ar amphibole plateau age of 195 ± 3 Ma and a youngest age of 200 Ma of the detrital zircons from Heilongjiang complex are reported to constrain the metamorphic age of the Heilongjiang complex. In addition, a huge north-south trending granitic belt generated from 174 Ma - 200 Ma has been identified in the Zhangguangcai Range and was proposed to be related to an arc setting. Therefore, combined with previous studies, we provide that a big ocean existed between the Jiamusi and Songliao blocks at least since the early Permian, and the Heilongjiang complex was formed since early Jurassic by the subduction of this ocean, following a collision after 141 Ma.

Arctic-Asian Mobile Belt - Global Structure in the North, Central, and East Asia

NASA Astrophysics Data System (ADS)

Shokalsky, Sergey; Petrov, Oleg; Pospelov, Igor; Kashubin, Sergey; Sobolev, Nikolay; Petrov, Evgeny

2014-05-01

Over the last decade under the international project of five countries, the geological surveys of Russia, China, Kazakhstan, Mongolia, and the Republic of Korea, with the participation of national academies of sciences in these countries compiled a set of digital maps at 1:2.5 M scale. It includes geological, tectonic, metallogenic maps and map of energy resources with databases for North, Central, and East Asia, area of more than 30 million km2. Map compilation was supervised by the Subcommission for Northern Eurasia and Subcommission for Tectonic Maps of the Commission for the Geological Map of the World under the auspices of UNESCO (CGMW). The set of maps was displayed at the 33rd IGC (Oslo, 2008) and 34th IGC (Brisbane, 2012). One of the largest accretion collages of orogenic belts of different ages on the planet (from the Neoproterozoic to Early Mesozoic) is clearly shown in the tectonic map compiled under the joint project. Extended polychronous mobile belt is bounded in the west by the East European Craton, in the east, by the Siberian Craton, in the south, by a chain of Gondwana cratonic blocks - North China, Tarim, Tajik. In the north it can be traced as a broad band within the Circumpolar Region, where it is limited by the North American Craton. The central part of the accretionary belt is hidden under the Meso-Cenozoic sediments of Western Siberia. Analysis of vast geological material shows that the Arctic-Asian mobile belt was formed on place of an extensive paleo-ocean, which closed with a successive rejuvenation of suture ophiolite zones from the marginal to axial zone and along strike to the north and east of the South Siberian segment towards Paleopacific. Arctic-Asian mobile belt is characterized by a complex combination of accretionary and riftogenic tectonic-magmatic processes. At its early stages, accretionary tectonics with a wide development of volcanic belts dominated; at the late ones (in the Late Paleozoic, Mesozoic, and Cenozoic) stretching, rifting and postrift subsidence were widely shown with the formation of oil and gas sedimentary basins with a thick sedimentary cover (West Siberian, Turan, Caspian, Middle Amur, Songliao), large igneous provinces (South Urals, West and East Siberian, Central Kazakhstan, Trans-Baikal, etc.) and rift systems (Mongol-Transbaikal, Baikal, etc.). The aim of further research under the existing joint projects should be identifying and tracing the boundaries of the Arctic-Asian mobile belt, study and correlation of geological complexes-indicators of major tectonic events, reconstruction of the history of the accretionary belt with superimposed oil and gas bearing sedimentary basins as a tectonic structure of the global level.

Spatial and temporal distribution of Mesozoic adakitic rocks along the Tan-Lu fault, Eastern China: Constraints on the initiation of lithospheric thinning

NASA Astrophysics Data System (ADS)

Gu, Hai-Ou; Xiao, Yilin; Santosh, M.; Li, Wang-Ye; Yang, Xiaoyong; Pack, Andreas; Hou, Zhenhui

2013-09-01

The Mesozoic tectonics in East China is characterized by significant lithospheric thinning of the North China Craton, large-scale strike-slip movement along the Tan-Lu fault, and regional magmatism with associated metallogeny. Here we address the possible connections between these three events through a systematic investigation of the geochemistry, zircon geochronology and whole rock oxygen isotopes of the Mesozoic magmatic rocks distributed along the Tan-Lu fault in the Shandong province. The characteristic spatial and temporal distributions of high-Mg adakitic rocks along the Tan-Lu fault with emplacement ages of 134-128 Ma suggest a strong structural control for the emplacement of these intrusions, with magma generation possibly associated with the subduction of the Pacific plate in the early Cretaceous. The low-Mg adakitic rocks (127-120 Ma) in the Su-Lu orogenic belt were formed later than the high-Mg adakitic rocks, whereas in the Dabie orogenic belt, most of the low-Mg adakitic rocks (143-129 Ma) were generated earlier than the high-Mg adakitic rocks. Based on available data, we suggest that the large scale strike-slip tectonics of the Tan-Lu fault in the Mesozoic initiated cratonic destruction at the south-eastern margin of the North China Craton, significantly affecting the lower continental crust within areas near the fault. This process resulted in crustal fragments sinking into the asthenosphere and reacting with peridotites, which increased the Mg# of the adakitic melts, generating the high-Mg adakitic rocks. The gravitationally unstable lower continental crust below the Tan-Lu fault in the Su-Lu orogenic belt triggered larger volume delamination of the lower continental crust or foundering of the root.

The ambient noise and earthquake surface wave tomography of the North China Craton

NASA Astrophysics Data System (ADS)

Pan, J.; Obrebski, M. J.; Wu, Q.; Li, Y.

2010-12-01

The North China Craton (NCC) is unique for its unusual Phanerozoic tectonic activity. The NCC was internally tectonically stable until Jurassic when its southern margin collided with the Yangzte Craton. Subsequently, the eastern and central part of the NCC underwent distinctive evolutions during the Late Mesozoic and Cenozoic. In contrast to the Erdos block located in the western part of NCC and that seems to have preserved the typical features of a stable craton, the eastern NCC has experienced significant lithospheric thinning as evidenced by widespread magmatism activity and normal faulting, among other manifestations. The eastern part of the NCC is also one of the most seismically active intracontinental regions in the world. Here we focus on the region that comprises the North China Basin and the Yanshan-Taihang Mountains, two major tectonic units located to the east and in the center of the NCC, respectively. We combine ambient noise data and ballistic surface wave data recorded by the dense temporary seismic array deployed in the North China to obtain phase velocity maps at periods ranging from 5s to 60s. 1587 and 3667 ray paths were obtained from earthquake surface waves and ambient noise correlations, respectively. The phase velocity distribution was reconstructed with grid size 0.25x0.25 degrees and 0.5x0.5 degrees from ambient noise tomography and earthquake surface wave tomography. For periods shorter than 15s, the phase velocity variations are well correlated with the principal geological units in the NCC, with low-speed anomalies corresponding to the major sedimentary basins and high-speed anomalies coinciding with the main mountain ranges. Within the period range from 20s to 30s, the phase velocity variations seem to be related to the local variations of the crustal thickness. For the periods above 30s, the strength of the phase velocity variations decreases with increasing periods, which may imply that the uppermost mantle is much more homogeneous than the crust. In contrast with typical phase velocities documented worldwide in continental cratons, the phase velocities we measured within the NCC are low. Their range is actually similar to that of the typical phase velocities observed in rift regions around the globe (eg, Rio Grande rift), indicating that the lithosphere of the central and eastern NCC has apparently been eroded and modified.

The relationship between gold ore and geotectonic in West Qinling: Evidence from magnetotelluric soundings

NASA Astrophysics Data System (ADS)

Xu, Daili; Huang, Wei; Zhang, Letian

2017-03-01

The West Qinling belt is the westward extensioin of the Qinling-Dabie-Sulu orogen in central China. It links the Kunlun and Qilian orogens to the west and the Songpan-Ganze belt to the south, making it an important tectonics syntaxis in China. According to the collection and analysis of the data of West Qinling Mountains gold deposit metallogenic chronology, the gold deposits in this area can be divided into five groups by time: 225-245 Ma, 220-190 Ma, 170 Ma±, 135-110 Ma, 75-45 Ma. The formation time is related to the geological process at that time. The relationship between the formation of gold deposit and geological structure can be explored by the research on the present geological structures. According to the regional tectonic evolution and magmatic activity, the gold deposits are divided into four metallogenic epoches: from the end of the Indo-Chinese epoch to the early Yanshanian (245-225 Ma), is one of the initial stages of gold mineralization; the early and the middle Yanshanian (220-190 Ma, 170 Ma±), is the main forming time of the gold mineralization in the West Qinling; the late Yanshanian (135-110 Ma), is the superimposed mineralization stage; at last, the effect of Himalayan hydrothermal activity to the gold deposits. Under the support of three projects naemed " the research on the conductivity of the lithosphere of the Central Orogenic in China ", " the MT array observation of the intersection area of COC(Central Orogen in China) and the North-South seismic belt ", " the experiment research of MT standard network observation in the area of Qinghai-Tibetan Plateau and the North-China " (Sinoprobe-01-02), we collected massive magnetotellurics data for futher study of the present geological strusctures to discess the relationship between gold deposites and geotectonic in West Qinling.

Shell Tectonics: A Mechanical Model for Strike-slip Displacement on Europa

NASA Technical Reports Server (NTRS)

Rhoden, Alyssa Rose; Wurman, Gilead; Huff, Eric M.; Manga, Michael; Hurford, Terry A.

2012-01-01

We introduce a new mechanical model for producing tidally-driven strike-slip displacement along preexisting faults on Europa, which we call shell tectonics. This model differs from previous models of strike-slip on icy satellites by incorporating a Coulomb failure criterion, approximating a viscoelastic rheology, determining the slip direction based on the gradient of the tidal shear stress rather than its sign, and quantitatively determining the net offset over many orbits. This model allows us to predict the direction of net displacement along faults and determine relative accumulation rate of displacement. To test the shell tectonics model, we generate global predictions of slip direction and compare them with the observed global pattern of strike-slip displacement on Europa in which left-lateral faults dominate far north of the equator, right-lateral faults dominate in the far south, and near-equatorial regions display a mixture of both types of faults. The shell tectonics model reproduces this global pattern. Incorporating a small obliquity into calculations of tidal stresses, which are used as inputs to the shell tectonics model, can also explain regional differences in strike-slip fault populations. We also discuss implications for fault azimuths, fault depth, and Europa's tectonic history.

Timing of tectonic evolution of the East Kunlun Orogen, Northern Tibet Plateau

NASA Astrophysics Data System (ADS)

Dong, Yunpeng

2017-04-01

The East Kunlun Orogen, located at the northern Tibet Plateau, represents the western segment of the Central China Orogenic Belt which was formed by amalgamation of the North China blocks and South China blocks. It is a key to understanding the formation of Eastern Asian continent as well as the evolution of the Pangea supercontinent. Based on detailed geological mapping, geochemical and geochronological investigations, the orogen is divided into three main tectonic belts, from north to south, including the Northern Qimantagh, Central Kunlun and Southern Kunlun Belts by the Qimantagh suture, Central Kunlun suture and South Kunlun fault. The Qimantagh suture is marked by the Early Paleozoic ophiolites outcropped in the Yangziquan, Wutumeiren, and Tatuo areas, which consist mainly of peridotites, gabbros, diabases and basalts. Besides, the ophiolite in the Wutumeiren is characterized by occurring anorthosite while the ophiolite in the Tatuo occurring chert. The basalts and diabases from both Yaziquan and Tatuo areas display depletion of Nb, Ta, P and Ti, and enrichment of LILE, suggesting a subduction related tectonic setting. LA-ICP-MS zircon U-Pb age of 421 Ma for the diabase represents the formation age of the Yaziquan ophiolite, while the U-Pb ages of 490 Ma and 505 Ma for gabbro and anorthosite, respectively, constrain the formation age of the Tatuo ophiolite. The basaltic rocks in the Wutumeiren area display flat distribution of HFSEs (such as Nb, Ta, K, La, Ce, Pr, Nd, Zr, Sm, Eu, Ti, Dy, Y, Yb and Lu) and slightly enrichment in LREEs, while the peridotites showing depletion in MREEs. The LA-ICP-MS zircon U-Pb age of 431 Ma for the gabbro represents the formation age of the Wutumeiren ophiolite. Together with regional geology, we suggest herewith a back-arc basin tectonic setting during ca. 505-421 Ma at least for the Qimantagh suture. The Central Kunlun suture is represented by the ophiolite in the Wutuo area, which is characterized by depletion of Nb, Ta, P and Ti, and enrichment of LILEs, LREEs, K, Pb, Sr and Nd, accounting for a subduction relation setting. The gabbro yields a LA-ICP-MS zircon U-Pb age of 243 Ma, representing the formation age of the ophiolite. Taking into account of evidence from the Early Paleozoic ophiolites in the Buqinshan ( Bian Qiantao et al., 2001, 2007; Li Zuochen et al., 2013; Li Ruibao et al., 2014; Liu Zhanqing et al., 2011) and the Derni areas (Chen Liang et al., 2001, 2003), the Central Kunlun ocean might be existed from Early Paleozoic to Middle Triassic time. The Northern Qimantagh tectonic belt, to the north of the Qimantagh suture, exposes a large volume of Early Paleozoic granitic plutons and volcanic rocks. Geochemistry of the granites suggests an arc setting. LA-ICP-MS zircon U-Pb ages ranging from ca. 440 to 402 Ma constrain the time of the subduction and arc setting. The Central Kunlun tectonic belt is characterized by occurring of Paleo-Proterozoic basement which was intruded by large amounts of Triassic granitoids. The basement represented by the Jinshuikou Group including gneisses, amphibolites and marbles, yields a protolith formation age of 2.2 Ga which was overprinted by Neoproterozoic tectono-thermal event. The plutonic intrusions display LA-ICP-MS zircon ages mainly of 260-200 Ma with minor ages of 470-400 Ma, revealing a long-lived subduction from Early Paleozoic to Late Triassic. Taken into together all above evidence, trench-arc-back arc basin tectonics were suggested here accounting for the tectonic evolution of the East Kunlun Orogeny during Early Paleozoic to Triassic time.

Two contrasting late Paleozoic magmatic episodes in the northwestern Chinese Tianshan Belt, NW China: Implication for tectonic transition from plate convergence to intra-plate adjustment during accretionary orogenesis

NASA Astrophysics Data System (ADS)

Wang, Xiangsong; Cai, Keda; Sun, Min; Xiao, Wenjiao; Xia, Xiaoping; Wan, Bo; Bao, Zihe; Wang, Yannan

2018-03-01

Late Carboniferous to Early Permian is a critical period for the final amalgamation of the Central Asian Orogenic Belt (CAOB). However, as most of the accreted terranes of the CAOB are unclear in tectonic nature and origin, the timing and processes of their mutual amalgamation have been poorly constrained. To understand assembly of the West Junggar Terrane with the Yili Block, a suite of the late Paleozoic magmatic rocks, including ignimbrite, rhyolite and granite, in northwestern Chinese Tianshan Belt were studied for their petrogenesis and tectonic implications. Our new results of secondary ion mass spectrometry (SIMS) zircon U-Pb dating reveal two separate magmatic episodes, ca. 300 Ma volcanism (ignimbrite and rhyolite) and ca. 288 Ma plutonsim (biotite granite). Geochemically, for the ca. 300 Ma volcanism, the ignimbrites have low SiO2 (65.8-71.5 wt.%) and Mg# (6-13) values, and exhibit arc affinity with significantly enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE) such as Nb, Ta and Ti. The whole-rock εNd(t) and zircon εHf(t) values range from +6.9 to +7.0 and +9.9 to +14.1 respectively, indicating a juvenile basaltic lower crustal origin. Rhyolites have slightly high SiO2 (72.7-74.0 wt.%) and K2O (3.86-4.53 wt.%) contents, high zircon δ18O (11.67-13.23‰) values, and low whole-rock εNd(t) (+2.9 to +3.8) and zircon εHf(t) (+2.8 to +10.0) values, which may suggest sediment involvements during magma generation. In contrast, for the ca. 288 Ma plutonism, the biotite granites have obviously higher SiO2 (74.7-75.5 wt.%) contents and whole-rock εNd(t) (+7.7 to +8.8), zircon εHf(t) (+9.8 to +12.7), and lower zircon δ18O (5.99-6.84‰) values, than those of the ca. 300 Ma volcanic rocks, which are consistent with signatures of juvenile magma source. According to our estimates of zircon saturation temperatures, together with their contrasting genesis, we attribute the formation of ca. 300 Ma high temperature (815-938 °C) volcanism to oceanic slab break-off during assembly of the West Junggar Terrane with the Yili Block, and relate the generation of ca. 288 Ma low temperature (723-735 °C) plutonism to subsequent strike-slipping of North Tianshan Fault that facilitated introduction of water-fluxes triggering hydrous partial melting of juvenile lower crust. The sequential magmatic episodes in the northwestern Chinese Tianshan Belt may provide a crucial clue to a tectonic transition from plate convergence to intra-plate adjustment during the formation of the Kazakhstan Orocline in the late Paleozoic.

Ordovician magmatism in the Lévézou massif (French Massif Central): tectonic and geodynamic implications

NASA Astrophysics Data System (ADS)

Lotout, Caroline; Pitra, Pavel; Poujol, Marc; Van Den Driessche, Jean

2017-03-01

New U-Pb dating on zircon yielded ca. 470 Ma ages for the granitoids from the Lévézou massif in the southern French Massif Central. These new ages do not support the previous interpretation of these granitoids as syn-tectonic intrusions emplaced during the Late Devonian-Early Carboniferous thrusting. The geochemical and isotopic nature of this magmatism is linked to a major magmatic Ordovician event recorded throughout the European Variscan belt and related to extreme thinning of continental margins during a rifting event or a back-arc extension. The comparable isotopic signatures of these granitoids on each side of the eclogite-bearing leptyno-amphibolitic complex in the Lévézou massif, together with the fact that they were emplaced at the same time, strongly suggest that these granitoids were originally part of a single unit, tectonically duplicated by either isoclinal folding or thrusting during the Variscan tectonics.

Archean sedimentation and tectonics in southern Africa

NASA Technical Reports Server (NTRS)

Kidd, W. S. F.

1984-01-01

Sequences in the Barberton Mountain Land greenstone belt (southern Africa) were examined to determine the nature of the sedimentary rocks, their tectonic implications, and their bearing on the present large-scale structural condition of the belt. Also assessed was whether there was evidence for a significant component of shallow-water-deposited sedimentary rocks in the parent materials of the Limpopo belt. The nature of a largehigh strain zone on the southern margin of the central Limpopo belt was examined.

GPS and seismological constraints on active tectonics and arc-continent collision in Papua New Guinea: Implications for mechanics of microplate rotations in a plate boundary zone

NASA Astrophysics Data System (ADS)

Wallace, Laura M.; Stevens, Colleen; Silver, Eli; McCaffrey, Rob; Loratung, Wesley; Hasiata, Suvenia; Stanaway, Richard; Curley, Robert; Rosa, Robert; Taugaloidi, Jones

2004-05-01

The island of New Guinea is located within the deforming zone between the Pacific and Australian plates that converge obliquely at ˜110 mm/yr. New Guinea has been fragmented into a complex array of microplates, some of which rotate rapidly about nearby vertical axes. We present velocities from a network of 38 Global Positioning System (GPS) sites spanning much of the nation of Papua New Guinea (PNG). The GPS-derived velocities are used to explain the kinematics of major tectonic blocks in the region and the nature of strain accumulation on major faults in PNG. We simultaneously invert GPS velocities, earthquake slip vectors on faults, and transform orientations in the Woodlark Basin for the poles of rotation of the tectonic blocks and the degree of elastic strain accumulation on faults in the region. The data are best explained by six distinct tectonic blocks: the Australian, Pacific, South Bismarck, North Bismarck, and Woodlark plates and a previously unrecognized New Guinea Highlands Block. Significant portions of the Ramu-Markham Fault appear to be locked, which has implications for seismic hazard determination in the Markham Valley region. We also propose that rapid clockwise rotation of the South Bismarck plate is controlled by edge forces initiated by the collision between the Finisterre arc and the New Guinea Highlands.

The Neogene tectonic evolution and climatic change of the Tianshui Basin, NE Tibetan Plateau

NASA Astrophysics Data System (ADS)

Peng, T.; Li, J.; Song, C.; Zhao, Z.; Zhang, J.; Wang, X.; Hui, Z.

2013-12-01

The Tianshui Basin, located at the conjunction of NE Tibetan Plateau and Chinese Loess Plateau, has received intensive attention recently. Fine-grained Miocene sediment was identified as loess in its north part and this pushes the onset of Asian aridification into 22 Ma. However, our sedimentological, biomarker, pollen, diatom and mammalian fossils evidence propose that these sediments were suggested to be mudflat/distal fan and floodplain deposit instead of eolian deposit. So detailed tectonic background and climate reconstruction may illustrate the controversy and shed light on the tectonic, climate and ecology interactions. Here we report our integrated studies on the tectonic evolution, climate change and paleoecology reconstruction in the Tianshui basin. Based on the magnetostratigraphy and fossil mammal ages, sedimentological and detrital fission-track thermochronologic (DFT) analysis reveals four episodic tectonic uplift events occurred at ~20 Ma, ~14 Ma, ~9.2-7.4 Ma and ~3.6 Ma along the basin and its adjacent mountains. The timing of these activities at Western Qinling have been documented at many segments of the Tibetan Plateau, so most likely they were the remote response to the ongoing India-Asia collision. Pollen, mammalian fossils and biomarker data permit us to illustrate the paleoenvironment in the Tianshui Basin. During the period of ~17-10 Ma, the climate was generally warm-humid revealed by the broad-leaved forest and low Average Chain Length (ACL) values, when the Paltybelodon and Gomphotherium were roaming near an extensive aquatic setting. In addition, the observed Middle Miocene Climatic Optimum and Middle Miocene Climatic Transition events may be a terrestrial response to global climate changes. During the interval of ~10-6 Ma, the climate was relatively arid characterized by the rapid development of steppe and appearance of the Hipparion fauna, consistent with the biomarker proxy. Although the NE Tibetan Plateau experienced a phase of active uplift around ~8 Ma, we mainly ascribe this arid interval to global change known as the C4 grass expansion, because the subsequent early Pliocene turned back to humid-warm climate again. Since ~4 Ma, it became obviously drier than the previous two arid intervals via the biomarker perspective. This dramatic dry trend may be related to the Tibetan Plateau uplift and/or global cooling, highlighting the importance and complexity of tectonic-climate interaction. Acknowledgements: This work was co-supported by the "Strategic Priority Research Program" of the CAS (XDB03020402), the (973) National Basic Research Program of China (2013CB956400) and the National Natural Science Foundation of China (41021091, 41101012).

Detrital zircon U-Pb geochronology and stratigraphy of the Cretaceous Sanjiang Basin in NE China: Provenance record of an abrupt tectonic switch in the mode and nature of the NE Asian continental margin evolution

NASA Astrophysics Data System (ADS)

Zhang, Feng-Qi; Chen, Han-Lin; Batt, Geoffrey E.; Dilek, Yildirim; A, Min-Na; Sun, Ming-Dao; Yang, Shu-Feng; Meng, Qi-An; Zhao, Xue-Qin

2015-12-01

The age spectra obtained from 505 spots of detrital zircon U-Pb ages of five representative sandstone samples from the Sanjiang Basin in NE China point to a significant change in its provenance during the Coniacian-Santonian. The predominant detrital source for the Sanjiang Basin during the early Cretaceous was the Zhangguangcai Range magmatic belt and Jiamusi Block along its western and southern periphery, whereas it changed in the late Cretaceous to its eastern periphery. The timing of these inferred changes in the detrital source regions and drainage patterns nearly coincide with the age of a regional unconformity in and across the basin. The time interval of non-deposition and unconformity development was coeval with a transitional period between an extensional tectonic regime in the early Cretaceous and a contractional deformation episode in the late Cretaceous. The Sanjiang Basin evolved during this time window from a backarc to a foreland basin. The migration of the coastal orogenic belt and the fold and thrust belt development farther inland during the late Cretaceous marked the onset of regional-scale shortening and surface uplift in the upper plate of a flat (or very shallow-dipping) subduction zone. The stratigraphic record, the detrital source and geochronology of the basinal strata, and the internal structure of the Sanjiang Basin present, therefore, an important record of a tectonic switch in the nature of continental margin evolution of Northeast Asia during the late Mesozoic.

Education for Sustainable Development in Ethnic Autonomous Areas of China: A Comparison of Two Curriculum Initiatives and Their Educational Implications

ERIC Educational Resources Information Center

Khoo, Yishin

2015-01-01

This paper examines the educational implications of two curriculum initiatives in China that have produced curricular materials promoting education for sustainable development (ESD) in minority-populated ethnic autonomous areas in China. The two curriculum projects present distinctive discourses, conceptions, models, frameworks and scopes of ESD…

Temporal–Spatial Surface Seasonal Mass Changes and Vertical Crustal Deformation in South China Block from GPS and GRACE Measurements

PubMed Central

He, Meilin; Shen, Wenbin; Chen, Ruizhi; Ding, Hao; Guo, Guangyi

2017-01-01

The solid Earth deforms elastically in response to variations of surface atmosphere, hydrology, and ice/glacier mass loads. Continuous geodetic observations by Global Positioning System (CGPS) stations and Gravity Recovery and Climate Experiment (GRACE) record such deformations to estimate seasonal and secular mass changes. In this paper, we present the seasonal variation of the surface mass changes and the crustal vertical deformation in the South China Block (SCB) identified by GPS and GRACE observations with records spanning from 1999 to 2016. We used 33 CGPS stations to construct a time series of coordinate changes, which are decomposed by empirical orthogonal functions (EOFs) in SCB. The average weighted root-mean-square (WRMS) reduction is 38% when we subtract GRACE-modeled vertical displacements from GPS time series. The first common mode shows clear seasonal changes, indicating seasonal surface mass re-distribution in and around the South China Block. The correlation between GRACE and GPS time series is analyzed which provides a reference for further improvement of the seasonal variation of CGPS time series. The results of the GRACE observations inversion are the surface deformations caused by the surface mass change load at a rate of about −0.4 to −0.8 mm/year, which is used to improve the long-term trend of non-tectonic loads of the GPS vertical velocity field to further explain the crustal tectonic movement in the SCB and surroundings. PMID:29301236

Mechanism of Earth Fissures in Beijing,China

NASA Astrophysics Data System (ADS)

Zhang, Y.; Gong, H.; Gu, Z.; Wang, R.; Jia, S.; Li, X.

2013-12-01

Earth fissure is one of the natural hazards that can occur due to different mechanisms. The Beijing city, located in the north of North China Plain, China, has undergone extensive fissuring for the last twenty years. These fissures have caused serious damages to homes, farmlands and infrastructures. The previous investigation shows the distribution and direction of the major earth fissures mostly paralleled to the active fault, such as Huangzhuang-Gaoliying Fault. Hence, tectonic movements were thought to be the major cause of the fissuring in this region. But the subsidence caused by overdraft and other geological, hydrological and mechanical factors may also play important roles in forming earth fissure. The purpose of the work was to further explores the reason for the cause of the earth fissures and their mechanism of formations using field investigations, geophysical surveys, geotechnical tests and numerical analysis. The results indicated that over-extraction groundwater and differential subsidence are the major causes of the fissuring. The active faulting and fault zone provided or created an ideal condition for stress to accumulate. The earth fissures occur at times when the accumulated stress exceed the strength of soil or coupled with other process by which the strength of soil material is reduced. Survey and simulated results reveal the complex pattern of earth fissure including tensile deformation, vertical offset and rotation. The potential locations for future damage were also evaluated. Keywords: Earth Fissure; Mechanism; Beijing; Subsidence; tectonic movement; Geophysical survey

Thinned crustal structure and tectonic boundary of the Nansha Block, southern South China Sea

NASA Astrophysics Data System (ADS)

Dong, Miao; Wu, Shi-Guo; Zhang, Jian

2016-12-01

The southern South China Sea margin consists of the thinned crustal Nansha Block and a compressional collision zone. The Nansha Block's deep structure and tectonic evolution contains critical information about the South China Sea's rifting. Multiple geophysical data sets, including regional magnetic, gravity and reflection seismic data, reveal the deep structure and rifting processes. Curie point depth (CPD), estimated from magnetic anomalies using a windowed wavenumber-domain algorithm, enables us to image thermal structures. To derive a 3D Moho topography and crustal thickness model, we apply Oldenburg algorithm to the gravity anomaly, which was extracted from the observed free air gravity anomaly data after removing the gravity effect of density variations of sediments, and temperature and pressure variations of the lithospheric mantle. We found that the Moho depth (20 km) is shallower than the CPD (24 km) in the Northwest Borneo Trough, possibly caused by thinned crust, low heat flow and a low vertical geothermal gradient. The Nansha Block's northern boundary is a narrow continent-ocean transition zone constrained by magnetic anomalies, reflection seismic data, gravity anomalies and an interpretation of Moho depth (about 13 km). The block extends southward beneath a gravity-driven deformed sediment wedge caused by uplift on land after a collision, with a contribution from deep crustal flow. Its southwestern boundary is close to the Lupar Line defined by a significant negative reduction to the pole (RTP) of magnetic anomaly and short-length-scale variation in crustal thickness, increasing from 18 to 26 km.

New Energy Villages in Taiwan and China

NASA Astrophysics Data System (ADS)

Lee, C. S.; Wang, S. C.

2015-12-01

Taiwan locates in the active tectonic subdution and collision belts, therefore, the geothermal gradient is very high and have found 128 sites of high geothermal areas; 20% of them have the temperature between 75 - 200 degree C in which they can be directly used for the electricity generation; 50% of them are in 50 - 74 degree C and the rest 30% are below 50 degree C. These areas need the deep drillings to get into higher temperature for power energy. The first 20% high temperature areas are mostly located in the coastal or mountain regions. The government is interesting to develop these areas as the "New Energy Villages" so that they can not only become self-energy sufficient sites, but also to protect themself from being the loss of electricity and water during the typhoon and earthquake hazards. The multiple usages of hot water (such as the first power generation and then the hot spring utilization) have its merits. China, in the other hand, is not within the present-day active tectonic zone. However, the recent Sino Probe Experiments (Deep Exploration in China) have mapped the Cetaceous plate boundaries in the coast of China. The heat is still possibly migrating to near the surface through the existing structures. For example, the Feng Shun Geothermal Power Station in north of Guangzhou, Guangdong Province, used the 96 degree C hot water from a well of 800 m producing a small amount of 300 KW power since 1984. The Guangdong Province is located in the edge of Mesozoic South China Plate. Further in land, the Huang Mountain, one of the world heritage sites, is located at the boundary of another Mesozoic Yangtze River Plate. There is not a geothermal power plant; however, a number of hot springs are in a booming tour business at the foot hill of the mountain. The electricity has to come from a long way of net working. If China develops the local, small, but sufficient power plants by using the modern geothermal exploration and drilling techniques. The "New Energy Villages" will be benefit to the energy and environment need.

Surface Wave Dispersion Measurements and Tomography from Ambient Seismic Noise Correlation in China

DTIC Science & Technology

2010-03-15

R.A. Jamieson, M.H. Nguyen, et al., Himalayan tectonics explained by extrusion of a low-viscosity crustal channel coupled to focused surface...9 8. Crustal thickness map obtained in this study...not in the margin areas, consistent with the crustal channel flow model. 2. INTRODUCTION The overall objective of this project is to obtain

Anisotropic Rayleigh-wave Phase-velocity Maps in Northern Vietnam

NASA Astrophysics Data System (ADS)

Zhao, L.; Legendre, C. P.; Huang, W.; Huang, B.

2013-12-01

Northern Vietnam is the location of both the Song Ma Complex, the suture between the Indochina and South China Blocks, and the southern end of the giant Red River Shear Zone. Lithospheric structure provides important clues to the evolutions of the tectonic boundary zone and the interaction between the Indochina and South China Blocks. During 2006-2008, an array of 24 broadband stations were deployed in northern Vietnam in a collaborative project between the Institute of Geophysics of the Vietnam Academy of Science and Technology and the Institute of Earth Sciences of Academic Sinica in Taiwan. In this study, we use Rayleigh waveforms recorded at those stations from globally distributed earthquakes to construct the regional isotropic and azimuthally anisotropic phase velocity maps. Rayleigh-wave dispersion curves in the period range of 10-200 sec are obtained manually by the two-station method using vertical-component broadband waveforms. The dispersion curves along the densely distributed crossing paths are inverted via the LSQR algorithm for the isotropic and azimuthally anisotropic phase-velocity maps at a number of periods. Results will be compared with previous studies in this region based on body-wave traveltimes, SKS splitting observations and receiver functions, and with the tectonic features observed in the region.

Education System Reform in China after 1978: Some Practical Implications

ERIC Educational Resources Information Center

Sun, Miantao

2010-01-01

Purpose: This paper aims to provide an overview of education system reform in China since 1978, and its practical implications. Design/methodology/approach: Data were collected from literature review and interview. An overview of education system reform and its practical implications was found through data analysis. Findings: There has been two…

Late Cenozoic Deformation in the Western Tarim Basin, NW China

NASA Astrophysics Data System (ADS)

Thompson, J. A.; Burbank, D. W.; Chen, J.; Li, T.

2009-12-01

The Tian Shan in NW China is one of the most active regions of intracontinental deformation in the world, accommodating a large fraction (~40%) of the shortening from the Indo-Eurasian collision. The western Tarim Basin, situated between the southern Tian Shan and Pamir Mountains, manifests this deformation through a series of east-west trending fault-related folds that have formed during the late Cenozoic. Previous studies in this region have focused on the kinematics, style, and timing of detachment folds related to folding within the foreland basin of the southern Tian Shan. In contrast, this study focuses on the deformation caused by fault-propagation folding resulting from the northward movement of the Pamir. The rates of deformation are calculated using a combination of optically stimulated luminescence (OSL) ages, structural mapping and differential GPS surveys of fault scarps and deformed terrace surfaces crossing active folds. OSL dating provides the time since the sediment was last exposed to daylight, i.e., time since burial. Consequently, OSL is useful for dating the abandonment of terrace surfaces due to tectonic (fold growth) or climatic events. OSL quartz samples were collected from silt lenses within gravel topping the terraces. Most of the quartz OSL signals are weak, thus several grain sizes (silt (4-11 µm, 8-15 µm) and sand (90-125 µm)) were analyzed and different integrations of the shine-down curves were explored to calculate equivalent doses. The implications for different equivalent doses and ages on the calculation of rates of deformation are also addressed.

Updating the Geologic Barcodes for South China: Discovery of Late Archean Banded Iron Formations in the Yangtze Craton.

PubMed

Ye, Hui; Wu, Chang-Zhi; Yang, Tao; Santosh, M; Yao, Xi-Zhu; Gao, Bing-Fei; Wang, Xiao-Lei; Li, Weiqiang

2017-11-08

Banded iron formations (BIFs) in Archean cratons provide important "geologic barcodes" for the global correlation of Precambrian sedimentary records. Here we report the first finding of late Archean BIFs from the Yangtze Craton, one of largest Precambrian blocks in East Asia with an evolutionary history of over 3.3 Ga. The Yingshan iron deposit at the northeastern margin of the Yangtze Craton, displays typical features of BIF, including: (i) alternating Si-rich and Fe-rich bands at sub-mm to meter scales; (ii) high SiO 2  + Fe 2 O 3total contents (average 90.6 wt.%) and Fe/Ti ratios (average 489); (iii) relative enrichment of heavy rare earth elements and positive Eu anomalies (average 1.42); (iv) and sedimentary Fe isotope compositions (δ 56 Fe IRMM-014 as low as -0.36‰). The depositional age of the BIF is constrained at ~2464 ± 24 Ma based on U-Pb dating of zircon grains from a migmatite sample of a volcanic protolith that conformably overlied the Yingshan BIF. The BIF was intruded by Neoproterozoic (805.9 ± 4.7 Ma) granitoids that are unique in the Yangtze Craton but absent in the North China Craton to the north. The discovery of the Yingshan BIF provides new constraints for the tectonic evolution of the Yangtze Craton and has important implications in the reconstruction of Pre-Nuna/Columbia supercontinent configurations.

Mantle seismic anisotropy beneath NE China and implications for the lithospheric delamination hypothesis beneath the southern Great Xing'an range

NASA Astrophysics Data System (ADS)

Chen, Haichao; Niu, Fenglin; Obayashi, Masayuki; Grand, Stephen P.; Kawakatsu, Hitoshi; John Chen, Y.; Ning, Jieyuan; Tanaka, Satoru

2017-08-01

We measured shear wave splitting from SKS data recorded by the transcontinental NECESSArray in NE China to constrain lithosphere deformation and sublithospheric flows beneath the area. We selected several hundreds of high quality SKS/SKKS waveforms from 32 teleseismic earthquakes occurring between 09/01/2009 and 08/31/2011 recorded by 125 broadband stations. These stations cover a variety of tectonic terranes, including the Songliao basin, the Changbaishan mountain range and Zhangguancai range in the east, the Great Xing'an range in the west and the Yanshan orogenic belt in the southwest. We assumed each station is underlaid by a single anisotropic layer and employed a signal-to-noise ratio (SNR) weighted multi-event stacking method to estimate the two splitting parameters (the fast polarization direction φ, and delay time, δt) that gives the best fit to all the SKS/SKKS waveforms recorded at each station. Overall, the measured fast polarization direction lies more or less along the NW-SE direction, which significantly differs from the absolute plate motion direction, but is roughly consistent with the regional extension direction. This suggests that lithosphere deformation is likely the general cause of the observed seismic anisotropy. The most complicated anisotropic structure is observed beneath the southern Great Xing'an range and southwest Songliao basin. The observed large variations in splitting parameters and the seismic tomographic images of the area are consistent with ongoing lithospheric delamination beneath this region.

Satellite Detection of the Convection Generated Stresses in Earth

NASA Technical Reports Server (NTRS)

Liu, Han-Shou; Kolenkiewicz, Ronald; Li, Jin-Ling; Chen, Jiz-Hong

2003-01-01

We review research developments on satellite detection of the convection generated stresses in the Earth for seismic hazard assessment and Earth resource survey. Particular emphasis is laid upon recent progress and results of stress calculations from which the origin and evolution of the tectonic features on Earth's surface can be scientifically addressed. An important aspect of the recent research development in tectonic stresses relative to earthquakes is the implications for earthquake forecasting and prediction. We have demonstrated that earthquakes occur on the ring of fire around the Pacific in response to the tectonic stresses induced by mantle convection. We propose a systematic global assessment of the seismic hazard based on variations of tectonic stresses in the Earth as observed by satellites. This space geodynamic approach for assessing the seismic hazard is unique in that it can pinpoint the triggering stresses for large earthquakes without ambiguities of geological structures, fault geometries, and other tectonic properties. Also, it is distinct from the probabilistic seismic hazard assessment models in the literature, which are based only on extrapolations of available earthquake data.

The contraction/expansion history of Charon with implications for its planetary-scale tectonic belt

NASA Astrophysics Data System (ADS)

Malamud, Uri; Perets, Hagai B.; Schubert, Gerald

2017-06-01

The New Horizons mission to the Kuiper belt has recently revealed intriguing features on the surface of Charon, including a network of chasmata, cutting across or around a series of high topography features, conjoining to form a belt. It is proposed that this tectonic belt is a consequence of contraction/expansion episodes in the moon's evolution associated particularly with compaction, differentiation and geochemical reactions of the interior. The proposed scenario involves no need for solidification of a vast subsurface ocean and/or a warm initial state. This scenario is based on a new, detailed thermo-physical evolution model of Charon that includes multiple processes. According to the model, Charon experiences two contraction/expansion episodes in its history that may provide the proper environment for the formation of the tectonic belt. This outcome remains qualitatively the same, for several different initial conditions and parameter variations. The precise orientation of Charon's tectonic belt, and the cryovolcanic features observed south of the tectonic belt may have involved a planetary-scale impact, that occurred only after the belt had already formed.

China Naval Modernization: Implications for U.S. Navy Capabilities - Background and Issues for Congress

DTIC Science & Technology

2010-08-26

waters.17 Chinese officials in early 2010 began describing this claim as a “core national interest,” meaning an issue comparable in importance to...China’s Claims to an Extended Continental Shelf in the East China Sea: Meaning and Implications,” China Brief, July 9, 2009: 9-11; Peter Dutton and...apparent than in China’s attitude over the South China Sea, which recently has been defined as a ‘core interest’—the same phrase Chinese use to refer

A Stepwise Iterative Procedure to Constrain Stress Drop, Regional Attenuation Models, and Site Effects

DTIC Science & Technology

2010-09-01

Source parameter estimates for 8 crustal pairs near I.NTS using all regional data (left) and restricting the data by magnitude/distance (right). A... tectonic implications of aftershocks of the Mw 7.6 Bhuj earthquake of 26 January 2001, Bull. Seismol. Soc.Am., 94: 818-827. Bodin, P., L...Seismol. Soc. Am.,94:1658-1669. Brune, J. N. (1970). Tectonic stress and the spectra of seismic shear waves from earthquakes, J. Geophys. Res., 75

Late Tharsis tectonic activity and implications for Early Mars

NASA Astrophysics Data System (ADS)

Bouley, S.; Baratoux, D.; Paulien, N.; Missenard, Y.; Saint-Bezar, B.

2017-12-01

Constraining the timing of Tharsis volcanism is critical to understanding the planet's evolution including its climate, surface environment and mantle dynamics. The tectonic history of the Tharsis bulge was previously documented from the distribution and ages of related tectonic features [1]. Here we revisit the ages of 7493 Tharsis-related tectonic features based on their relationship with stratigraphic units defined in the new geological map [2]. Conversely to previous tectonic mapping [1], which suggested that Tharsis growth was nearly achieved during the Noachian, we find a protracted growth of Tharsis during the Hesperian. Faulting at Tempe Terra, Claritas and Coracis Fossae and Thaumasia Planum confirms that tectonic deformation started during the Noachian. Accumulated tectonic deformation was maximum in the Early Hesperian for compressional strain (Solis, Lunae and Ascuris Planum) and extended over time from Noachian to Amazonian for extensional strain (Noctis Labyrinthus and Fossae, Sinai Planum and Tractus, Ulysses and Fortuna fossae, Alba Patera). This new scenario is consistent with a protracted growth of Tharsis dome during the Hesperian and with the timing a large Tharsis-driven true polar wander post-dating the incision of Late Noachian/Hesperian valley networks[3]. References:[1] Anderson et al. JGR-Planets 106, E9, 20,563-20,585 (2001).[2] Tanaka, K.L. et al. Geologic map of Mars (2014). [3] Bouley et al. Nature doi:10.1038 (2016)

Geochronology and geochemistry of basaltic rocks from the Sartuohai ophiolitic mélange, NW China: Implications for a Devonian mantle plume within the Junggar Ocean

NASA Astrophysics Data System (ADS)

Yang, Gaoxue; Li, Yongjun; Santosh, M.; Yang, Baokai; Yan, Jing; Zhang, Bing; Tong, Lili

2012-10-01

The West Junggar domain in NW China is a distinct tectonic unit of the Central Asian Orogenic Belt (CAOB). It is composed of Paleozoic ophiolitic mélanges, arcs and accretionary complexes. The Sartuohai ophiolitic mélange in the eastern West Junggar forms the northeastern part of the Darbut ophiolitic mélange, which contains serpentinized harzburgite, pyroxenite, dunite, cumulate, pillow lava, abyssal radiolarian chert and podiform chromite, overlain by the Early Carboniferous volcano-sedimentary rocks. In this paper we report new geochronological and geochemical data from basaltic and gabbroic blocks embedded within the Sartuohai ophiolitic mélange, to assess the possible presence of a Devonian mantle plume in the West Junggar, and evaluate the petrogenesis and implications for understanding of the Paleozoic continental accretion of CAOB. Zircon U-Pb analyses from the alkali basalt and gabbro by laser ablation inductively coupled plasma mass spectrometry yielded weighted mean ages of 375 ± 2 Ma and 368 ± 11 Ma. Geochemically, the Sartuohai ophiolitic mélange includes at least two distinct magmatic units: (1) a Late Devonian fragmented ophiolite, which were produced by ca. 2-10% spinel lherzolite partial melting in arc-related setting, and (2) contemporary alkali lavas, which were derived from 5% to 10% garnet + minor spinel lherzolite partial melting in an oceanic plateau or a seamount. Based on detailed zircon U-Pb dating and geochemical data for basalts and gabbros from the Sartuohai ophiolitic mélange, in combination with previous work, indicate a complex evolution by subduction-accretion processes from the Devonian to the Carboniferous. Furthermore, the alkali basalts from the Sartuohai ophiolitic mélange might be correlated to a Devonian mantle plume-related magmatism within the Junggar Ocean. If the plume model as proposed here is correct, it would suggest that mantle plume activity significantly contributed to the crustal growth in the CAOB.

Seismic Evidence for a Geosuture between the Yangtze and Cathaysia Blocks, South China

PubMed Central

He, Chuansong; Dong, Shuwen; Santosh, M.; Chen, Xuanhua

2013-01-01

South China, composed of the Yangtze and Cathaysia Blocks and the intervening Jiangnan orogenic belt, has been central to the debate on the tectonic evolution of East Asia. Here we investigate the crustal structure and composition of South China from seismic data employing the H-k stacking technique. Our results show that the composition and seismic structure of the crust in the Jiangnan orogenic belt are identical to those of the Cathaysia Block. Our data reveal a distinct contrast in the crustal structure and composition between the two flanks of the Jiujiang-Shitai buried fault. We propose that the Jiujiang-Shitai buried fault defines a geosuture between the Yangtze and Cathaysia Blocks, and that the felsic lower crust of the Cathaysia Block and the Jiangnan orogenic belt may represent fragments derived from the Gondwana supercontinent. PMID:23857499

Opening of the South China Sea and Upwelling of the Hainan Plume

NASA Astrophysics Data System (ADS)

Yu, Mengming; Yan, Yi; Huang, Chi-Yue; Zhang, Xinchang; Tian, Zhixian; Chen, Wen-Huang; Santosh, M.

2018-03-01

Opening of the South China Sea and upwelling of the Hainan Plume are among the most challenging issues related to the tectonic evolution of East Asia. However, when and how the Hainan Plume affected the opening of the South China Sea remains unclear. Here we investigate the geochemical and isotopic features of the 25 Ma mid-ocean ridge basalt (MORB) in the Kenting Mélange, southern Taiwan, 16 Ma MORB drilled by the IODP Expedition 349, and 9 Ma ocean island basalt-type dredged seamount basalt. The 25 Ma MORBs reveal a less metasomatic depleted MORB mantle-like source. In contrast, the Miocene samples record progressive mantle enrichment and possibly signal the contribution of the Hainan Plume. We speculate that MORBs of the South China Sea which could have recorded plume-ridge source mixing perhaps appear since 23.8 Ma. On the contrary, the Paleocene-Eocene ocean island basalt-type intraplate volcanism of the South China continental margin is correlated to decompression melting of a passively upwelling fertile asthenosphere due to continental rifting.

Developing an Education and Public Outreach (EPO) program for Caltech's Tectonics Observatory

NASA Astrophysics Data System (ADS)

Kovalenko, L.; Jain, K.; Maloney, J.

2012-12-01

The Caltech Tectonics Observatory (TO) is an interdisciplinary center, focused on geological processes occurring at the boundaries of Earth's tectonic plates (http://www.tectonics.caltech.edu). Over the past four years, the TO has made a major effort to develop an Education and Public Outreach (EPO) program. Our goals are to (1) inspire students to learn Earth Sciences, particularly tectonic processes, (2) inform and educate the general public about science in the context of TO discoveries, and (3) provide opportunities for graduate students, postdocs, and faculty to do outreach in the local K-12 schools and community colleges. Our work toward these goals includes hosting local high school teachers and students each summer for six weeks of research experience (as part of Caltech's "Summer Research Connection"); organizing and hosting an NAGT conference aimed at Geoscience teachers at community colleges; participating in teacher training workshops (organized by the local school district); hosting tours for K-12 students from local schools as well as from China; and bringing hands-on activities into local elementary, middle, and high school classrooms. We also lead local school students and teachers on geology field trips through nearby canyons; develop education modules for undergraduate classes (as part of MARGINS program); write educational web articles on TO research (http://www.tectonics.caltech.edu/outreach/highlights/), and regularly give presentations to the general public. This year, we started providing content expertise for the development of video games to teach Earth Science, being created by GameDesk Institute. And we have just formed a scientist/educator partnership with a 6th grade teacher, to help in the school district's pilot program to incorporate new national science standards (NSTA's Next Generation Science Standards, current draft), as well as use Project-Based Learning. This presentation gives an overview of these activities.

Seismic Reflection Characteristic and Structure Unit Division of Nanwei Uplift in the Nansha Waters, South China Sea

NASA Astrophysics Data System (ADS)

Guo, L.; Zhan, W.; Yao, Y.

2016-12-01

Nanwei uplift is located in the continent-ocean transition zone at the southern margin of the South China Sea (SCS). It has the structural characteristics in typical passive margin models. Attributed to squeezing action, the anticline and faulted anticline structure were well developed since Oligocene. The development of organic reef and marine mudstone deposit indicated the drifting and subsidence stage. In this area, the structural evolution is not only related to the dynamic systems of rifting, basin spreading and expansion ending, but also to the collisions between different plates. Meanwhile, a large number of continental margin rifting basins with rich oil and gas resources developed in Nanwei uplift. It is meaningful to analyze the characteristics of seismic reflection waves. Also, two main structural unit were divided for studying the special structures and stratigraphic features in this paper. Two high-resolution single-channel seismic Line Nan-1 and Line Nan-2 in the Nansha Waters, acquired by the trial vessel "Shiyan 2" of the South China Sea Institute of Oceanology in 2013, is interpreted and analyzed in this study. The profiles show that there are a lot of normal fault half-garben systems and depressions in NE direction. Five seismic interfaces have been distinguished, named T0,T3,T4,T5 and Tg respectively. It corresponds to different regional unconformities in different geological age which indicated the characteristics of regional tectonics. On the basis of tectonic shape and previous geophysical data, it is believed that the Nanwei uplift zone is mainly composed of two structural units, the southern subsidence belt and northern buried volcanic uplift belt. The general range of zoning is also discussed in this paper. It is considered that the buried volcanic uplift belt mainly involved the marginal area along the southern ocean basin from 63-72 km wide in SE direction, the neighboring subsidence belt in rifting stage is parallel to the buried volcanic uplift belt with 57.5-128 km wide. In addition, the epicenter distributions of sporadic and larger than 4 magnitude earthquakes suggest that the entire Nanwei uplift is still a relatively stable tectonic activity zone, the crustal stability is good.

Formation of Cretaceous Cordilleran and post-orogenic granites and their microgranular enclaves from the Dalat zone, southern Vietnam: Tectonic implications for the evolution of Southeast Asia

NASA Astrophysics Data System (ADS)

Shellnutt, J. Gregory; Lan, Ching-Ying; Van Long, Trinh; Usuki, Tadashi; Yang, Huai-Jen; Mertzman, Stanley A.; Iizuka, Yoshi; Chung, Sun-Lin; Wang, Kuo-Lung; Hsu, Wen-Yu

2013-12-01

Cordilleran-type batholiths are useful in understanding the duration, cyclicity and tectonic evolution of continental margins. The Dalat zone of southern Vietnam preserves evidence of Late Mesozoic convergent zone magmatism superimposed on Precambrian rocks of the Indochina Block. The Dinhquan, Deoca and Ankroet plutons and their enclaves indicate that the Dalat zone transitioned from an active continental margin producing Cordilleran-type batholiths to highly extended crust producing within-plate plutons. The Deoca and Dinhquan plutons are compositionally similar to Cordilleran I-type granitic rocks and yield mean zircon U/Pb ages between 118 ± 1.4 Ma and 115 ± 1.2 Ma. Their Sr-Nd whole rock isotopes (ISr = 0.7044 to 0.7062; εNd(T) = - 2.4 to + 0.2) and zircon Hf isotopes (εHf(T) = + 8.2 ± 1.2 and + 6.4 ± 0.9) indicate that they were derived by mixing between a mantle component and an enriched component (i.e. GLOSS). The Ankroet pluton is chemically similar to post-orogenic/within-plate granitic rocks and has a zircon U/Pb age of 87 ± 1.6 Ma. Geobarometric calculations indicate that amphibole within the Ankroet pluton crystallized at a depth of ~ 6 kbar which is consistent with the somewhat more depleted Sr-Nd isotope (ISr = 0.7017 to 0.7111; εNd(T) = - 2.8 to + 0.6) and variable εHf(T) compositions suggesting a stronger influence of crustal material in the parental magma. The compositional change of the Dalat zone granitic rocks during the middle to late Cretaceous indicates that the tectonic regime evolved from a continental arc environment to one of post-orogenic extension. The appearance of sporadic post-90 Ma magmatism in the Dalat zone and along the eastern margin of Eurasian indicates that there was no subsequent orogenic event and the region was likely one of highly extended crust that facilitated the opening of the South China Sea during the latter half of the Cenozoic.

Late Paleozoic tectonic evolution of the Central Asian Orogenic Belt: Constraints from multiple arc-basin systems in Altai-Junggar area, NW China

NASA Astrophysics Data System (ADS)

Li, D.

2015-12-01

In this study, we report results from integrated geological, geophysical and geochemical investigations on the Wulungu Depression of the Junggar Basin to understand the Late Paleozoic continental growth of the Junggar area and its amalgamation history with the Altai terrane, within the broad tectonic evolution of the Altai-Junggar area. Based on seismic and borehole data, the Wulungu Depression can be divided into two NW-trending tectonic units by southward thrust faults. The Suosuoquan Sag is composed of gray basaltic andesite, andesite, tuff, tuffaceous sandstone and tuffite, and the overlying Early Carboniferous volcano-sedimentary sequence with lava gushes and marine sediments from a proximal juvenile provenance, compared to the andesite in the Hongyan High. The SIMS Zircon U-Pb ages for andesites from Late Paleozoic strata indicate that these volcanics in Suosuoquan Sag and Hongyan High erupted at 376.3Ma and 313.4Ma, respectively. Most of the intermediate-mafic volcanic rocks exhibit calc-alkaline affinity, low initial 87Sr/86Sr and positive ɛNd(t) and ɛHf(t) values. Furthermore, these rocks have high Th/Yb and low Ce/Pb and La/Yb ratios as well as variable Ba/Th and Ba/La ratios. These features imply that the rocks were derived from partial melting of a mantle wedge metasomatized by subduction-related components in an island arc setting. The basin filling pattern and the distribution of island arc-type volcanics and their zircon Hf model ages with the eruptive time suggest that the Wulungu Depression represents an island arc-basin system with the development of a Carboniferous retro-arc basin. The gravity and magnetic anomaly data suggest that Altai-Junggar area incorporates three arc-basin belts from north to south: the Karamaili-Luliang-Darbut, Yemaquan-Wulungu, and Dulate-Fuhai-Saur. The recognition of the Wulungu arc-basin system demonstrates that the northern Junggar area is built by amalgamation of multiple Paleozoic linear arcs and accretionary complexes and has important implications for continental crustal growth in Altai-Junggar in particular, and the world's largest Phanerozoic accretionary orogen-the CAOB-in general.

Plate Tectonics and Taiwan Orogeny based on TAIGER Experiments

NASA Astrophysics Data System (ADS)

Wu, F. T.; Kuochen, H.; McIntosh, K. D.

2014-12-01

Plate tectonics framework is usually complex in a collision zone, where continental lithosphere is involved. In the young Taiwan orogeny, with geologic understanding and large new geodetic and subsurface datasets now available an environment has been created for testing tectonic hypotheses regarding collision and orogeny. Against the background of the commonly accepted view of Taiwan as a southward propagating, self-similar 2-D orogen, a fully 3-D structure is envisaged. Along the whole length of the island the convergence of the Eurasian plate (EUP) the Philippine Sea plate (PSP) takes shape with different plate configurations. In northern Taiwan the convergence occurs with simultaneous collision of the oceanic PSP with continental EUP and the northward subduction of the PSP; in the south, EUP, in the guise of the South China Sea rifted Eurasian continent, subducts toward the east; in central Taiwan collision of oceanic PSP with continental EUP dominates. When relocated seismicity and focal mechanisms are superposed on subsurface P and Vp/Vs velocity images the configurations and the kinematics of the PSP and EUP collision and subduction become clear. While in northern Taiwan the subduction/collision explains well the high peaks and their dwindling (accompanied by crustal thinning) toward the north. In the south, mountains rise above the east-dipping EUP subduction zone as the Eurasian continental shelf veers toward the southwest, divergent from the trend of the Luzon Arc - calling into question the frequently cited arc-continent collision model of Taiwan orogeny. High velocity anomaly and Benioff seismicity coexist in the south. Going north toward Central Taiwan the high velocity anomaly persists for another 150 km or so, but it becomes seismically quiescent. Above the quiescent section the PSP and EUP collide to build the main part of the Central Range and its parallel neighbor the eastern Coastal Range. Key implications regarding orogeny include: 1) Significant petrological changes may accompany the crustal thickening, e.g., eclogitization, and delamination, 2) Rather than the detachment the exhumation of the metamorphic core of the Central Range is the main engine of the orogeny, and 3) The lithosphere has a complex rheological structure, indicated, in part, by the spatial distribution of seismicity.

Tectonic evolution and hydrocarbon accumulation in the Yabulai Basin, western China

NASA Astrophysics Data System (ADS)

Zheng, Min; Wu, Xiaozhi

2014-05-01

The Yabulai petroliferous basin is located at the north of Hexi Corridor, western China, striking NEE and covering an area of 1.5×104 km2. It is bounded on the south by Beidashan Mountain to the Chaoshui Basin, on the east by Bayanwulashan Mountain to the Bayanhaote Basin, and on the northwest by Yabulai Mountain to the Yingen-Ejinaqi Basin. It is a Meso-cenozoic compressive depression residual basin. In view of regional geotectonics, the Yabulai basin sits in the middle-southern transition belt of Arershan massif in North China Craton. Driven by Indosinian movement at the late Triassic, two near EW normal faults were developed under the regional extensional stress along the northern fringe of Beidashan Mountain and the southern fringe of Yabulai Mountain front in the Arershan massif, forming the embryonic form of the Yabulai rift lake basin. Since Yanshan period, the Yabulai basin evolved in two major stages: Jurassic rift lake basin and Cretaceous rift lake basin. During early Yanshan period, EW striking Yabulai tensional rift was formed. Its major controlling fault was Beidashan normal fault, and the depocenter was at the south of this basin. During middle Yanshan period, collision orogenesis led to sharp uplift at the north of this basin where the middle-lower Jurassic formations were intensely eroded. During late Yanshan period, the Alashan massif and its northern area covered in an extensional tectonic environment, and EW striking normal faults were generated at the Yabulai Mountain front. Such faults moved violently and subsided quickly to form a new EW striking extensional rift basin with the depocenter at the south of Yabulai Mountain. During Himalayan period, the Alashan massif remained at a SN horizontal compressional tectonic environment; under the compressional and strike slip actions, a NW striking and south dipping thrusting nappe structure was formed in the south of the Yabulai basin, which broke the Beidashan normal fault to provide the echelon fault system and finally present the current structural framework of "east uplift and west depression, south faulted and north overlapping". The Yabulai basin presented as a strike-slip pull-apart basin in Mesozoic and a compressional thrusting depression basin in Cenozoic. Particularly, the Mesozoic tectonic units were distributed at a big included angle with the long axis of the basin, while the Cenozoic tectonic units were developed in a basically consistent direction with the long axis. The sags are segmented. Major subsiding sags are located in the south, where Mesozoic Jurassic-Cretaceous systems are developed, with the thickest sedimentary rocks up to 5300m. Jurassic is the best developed system in this basin. Middle Jurassic provides the principal hydrocarbon-bearing assemblage in this basin, with Xinhe Fm. and Qingtujing Fm. dark mudstone and coal as the source rocks, Xinhe Fm. and Qingtujing Fm. sandstones as the reservoir formation, and Xinhe Fm. mudstones as the cap rocks. However, the early burial and late uplifting damaged the structural framework of the basin, thus leading to the early violent compaction and tightness of Jurassic sandstone reservoir and late hydrocarbon maturity. So, tectonic development period was unmatched to hydrocarbon expulsion period of source rocks. The hydrocarbons generated were mainly accumulated near the source rocks and entrapped in reservoir. Tight oil should be the major exploration target, which has been proved by recent practices.

Recent advances on the tectonic and magmatic evolution of the Greater Tibetan Plateau: A special issue in honor of Prof. Guitang Pan

NASA Astrophysics Data System (ADS)

Zhu, Di-Cheng; Chung, Sun-Lin; Niu, Yaoling

2016-02-01

The Greater Tibetan Plateau, also known in China as the Qinghai-Tibet Plateau or the Qingzang Plateau, is a tectonic amalgamation of numbers of continental collision events from the northwest in the early Paleozoic to the southwest in the Cenozoic (cf. Dewey et al., 1988; Pan et al., 2012; Yin and Harrison, 2000). These collision events resulted in orogenic belts that record the prolonged albeit complex histories of opening and closing of Tethyan ocean basins and associated tectonic and magmatic responses (cf. Chung et al., 2005; Pan et al., 2012; Song et al., 2014; Yin and Harrison, 2000; Zhu et al., 2013, 2015). Although many aspects related to these events have been recently synthesized with elegance by Pan et al. (2012) and Zhu et al. (2013) using data and observations made available since 2000, many scientific questions, such as the duration of oceanic basins, the collisional and accretionary processes of different terranes, the processes responsible for crustal growth, and the mechanisms for economic mineralization, remain underdeveloped and require further investigations with additional data.

Is the Ordos Basin floored by a trapped oceanic plateau?

NASA Astrophysics Data System (ADS)

Kusky, Tim; Mooney, Walter

2015-11-01

The Ordos Basin in China has about 10 km of Neoarchean to Quaternary sediments covering an enigmatic basement of uncertain origin. The basement is tectonically stable, has a thick mantle root, low heat flow, few earthquakes, and has been slowly subsiding for billions of years. The basement has geophysical signatures that indicate it is dominantly intermediate to mafic in composition, and is similar to some other cratons world-wide, and also to several major oceanic plateaus. It was accreted to the amalgamated Eastern Block and Central Orogenic belt of the North China Craton (NCC) in the Paleoproterozoic, then involved in several Proterozoic tectonic events including being over-thrust by an accretionary orogen, and intruded by Andean arc-related magmas, and then involved in a continent-continent collision during amalgamation with the Columbia Supercontinent. Thus, the basement rocks are deformed, metamorphosed to granulite facies, and determining their initial origin is difficult. We suggest that the data is consistent with an origin as an oceanic plateau that accreted to the NCC and, later experienced different episodes of differentiation associated with later subduction and collisions. Formation of cratonic lithosphere by accretion of oceanic plateaus may be one mechanism to create stable cratons. Other cratons that apparently formed by partial melting of underplated and imbricated oceanic slabs are stable in some cases, but also re-activated and ;de-cratonized; in some cases in Asia, where they have been affected by younger subduction, hydration, slab roll-back, and melt-peridotite reactions. This suggests that the initial mode of craton formation may be a factor in the preservation of stable cratons, and de-cratonization is not only influenced by younger tectonic activity.

A Triassic-Jurassic westward scissor-like subduction history of the Mudanjiang Ocean and amalgamation of the Jiamusi Block in NE China: Constraints from whole-rock geochemistry and zircon U-Pb and Lu-Hf isotopes of the Lesser Xing'an-Zhangguangcai Range granitoids

NASA Astrophysics Data System (ADS)

Ge, Mao-Hui; Zhang, Jin-Jiang; Li, Long; Liu, Kai

2018-03-01

NE China recorded the key tectonic evolution history of the Eurasian Plate from the Paleozoic-Mesozoic collisional formation of the Central Asian Orogenic Belt to the Mesozoic subduction of the Paleo-Pacific Ocean. To better understand this tectonic transition, it is crucial to constrain the time and pattern of the initial subduction of the Paleo-Pacific Ocean. Recently, some researchers proposed that the Mudanjiang Ocean existed between the Songnen and Jiamusi blocks was part of the Paleo-Pacific Ocean. Here, through geochemical and geochronological studies on the widespread granitoids in the Lesser Xing'an-Zhangguangcai Range in the eastern Songnen Block, we verify that these magmatic rocks show volcanic arc affinity with increased mantle contribution from east to the west of the range, likely related to a flattening subduction of the Mudanjiang Ocean. In addition, a universal westward younging trend for over 70 Myr can be observed for the granitoids throughout the Lesser Xing'an-Zhangguangcai Range, indicating a long-lasting subduction of the Mudanjiang Ocean. More interestingly, the oldest ages of the granitoids in the east display a northward younging trend from 275 Ma to 218 Ma, suggesting that the subduction of the Mudanjiang Ocean had been initiated at latest by 275 Ma in the south and then progressively expanded to the north. Based on these observations, we proposed a new tectonic evolution model for the Mudanjiang Ocean, i.e., a Triassic-Jurassic westward scissor-like subduction and closure, to contribute to the understanding of the early subduction of the Paleo-Pacific Ocean.

Multiple Emplacement and Exhumation History of the Late Mesozoic Dayunshan-Mufushan Batholith in Southeast China and Its Tectonic Significance: 2. Magnetic Fabrics and Gravity Survey

NASA Astrophysics Data System (ADS)

Ji, Wenbin; Chen, Yan; Chen, Ke; Wei, Wei; Faure, Michel; Lin, Wei

2018-01-01

The Late Mesozoic magmatic province is a prominent feature of the South China Block (SCB). However, the tectonic regimes associated with the magmatism are still elusive. A combined anisotropy of magnetic susceptibility and gravity study has been carried out to determine the fabric patterns and shape at depth of the Dayunshan-Mufushan composite batholith in the north-central SCB. This is a companion paper to Part 1 that presented the structural and geochronological data of this batholith. The magnetic fabrics in the batholith interior predominantly reflect magma flow structures. Two distinct patterns of the magnetic lineations are defined, around NNE-SSW and WNW-ESE trends for the early-stage and late-stage intrusions of the batholith, respectively. The gravity survey reveals that the early-stage intrusion has a main feeder zone located below its northern part, while several linear feeder zones trending NNE-SSW are inferred for the late-stage intrusion. Integrating all results, a two-stage construction of the batholith with distinct tectonic regimes has been established. It is concluded that the early-stage intrusion experienced a southward magma transport during its emplacement, partially assisted by far-field compression from the north at ca. 150 Ma. Conversely, the emplacement and exhumation of the late-stage intrusion was accommodated by a NW-SE crustal stretching involving a lateral magma expansion above the multiple feeder zones (likely corresponding to extensional fractures) and ductile shearing during 132-95 Ma localized mainly along the Dayunshan detachment fault. Finally, we discuss the geodynamic linkage between the paleo-Pacific subduction and the Late Mesozoic tectonomagmatism in the SCB.

Compression-extension transition of continental crust in a subduction zone: A parametric numerical modeling study with implications on Mesozoic-Cenozoic tectonic evolution of the Cathaysia Block

PubMed Central

Chan, Lung Sang; Gao, Jian-Feng

2017-01-01

The Cathaysia Block is located in southeastern part of South China, which situates in the west Pacific subduction zone. It is thought to have undergone a compression-extension transition of the continental crust during Mesozoic-Cenozoic during the subduction of Pacific Plate beneath Eurasia-Pacific Plate, resulting in extensive magmatism, extensional basins and reactivation of fault systems. Although some mechanisms such as the trench roll-back have been generally proposed for the compression-extension transition, the timing and progress of the transition under a convergence setting remain ambiguous due to lack of suitable geological records and overprinting by later tectonic events. In this study, a numerical thermo-dynamical program was employed to evaluate how variable slab angles, thermal gradients of the lithospheres and convergence velocities would give rise to the change of crustal stress in a convergent subduction zone. Model results show that higher slab dip angle, lower convergence velocity and higher lithospheric thermal gradient facilitate the subduction process. The modeling results reveal the continental crust stress is dominated by horizontal compression during the early stage of the subduction, which could revert to a horizontal extension in the back-arc region, combing with the roll-back of the subducting slab and development of mantle upwelling. The parameters facilitating the subduction process also favor the compression-extension transition in the upper plate of the subduction zone. Such results corroborate the geology of the Cathaysia Block: the initiation of the extensional regime in the Cathaysia Block occurring was probably triggered by roll-back of the slowly subducting slab. PMID:28182640

Carboniferous - Early Permian magmatic evolution of the Bogda Range (Xinjiang, NW China): Implications for the Late Paleozoic accretionary tectonics of the SW Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Wali, Guzalnur; Wang, Bo; Cluzel, Dominique; Zhong, Linglin

2018-03-01

The Late Paleozoic magmatic evolution of the Bogda Range (Chinese North Tianshan) is important for understanding the accretionary history of the Central Asian Orogenic Belt. We investigated the Carboniferous and Lower Permian volcanic and sedimentary sequences of the Daheyan section, southern Bogda Range, and present new zircon U-Pb ages and whole-rock geochemical data for the volcanic rocks. One Carboniferous rhyolite is dated at 298 ± 8 Ma; a Permian basalt yielded many Proterozoic zircon xenocrysts, and its maximum age (∼297 Ma) is constrained by the detrital zircon ages of the sandstone that stratigraphically underlies it. These volcanic rocks belong to calc-alkaline series. We further synthesize previous geochronological, geochemical and isotopic data of magmatic and sedimentary rocks in the Bogda Range. The available data indicate that the magmatism occurred continuously from 350 Ma to 280 Ma. A comprehensive analysis allows us to propose that: (1) the Carboniferous to Early Permian magmatic rocks of the Bogda Range generally show consistent arc-type features; (2) increasing mantle input through time suggests intra-arc extension in a supra-subduction zone; (3) the localized occurrence of Early Permian alkaline pillow basalts and deep water sediments close to the major shear zone advocate a transtensional crustal thinning during the transition from Carboniferous convergence to Early Permian transcurrent tectonics; (4) occurrence of a large number of Proterozoic zircon xenocrysts in the Late Paleozoic magmatic rocks, and Proterozoic detrital zircons in the coeval clastic sediments suggest a continental or transitional basement of the Bogda Arc; (5) subduction in the Bogda area terminated prior to the deposition of Middle Permian terrestrial sediments.

Marine Terrace Deposits along the Mediterranean Coast on the Southeastern Turkey and Their Implications for Tectonic Uplift and Sea Level Change

NASA Astrophysics Data System (ADS)

Tari, U.; Tüysüz, O.; Blackwell, B. A. B.; Genç, Ş. C.; Florentin, J. A.; Mahmud, Z.; Li, G. L.; Blickstein, J. I. B.; Skinner, A. R.

2016-12-01

Tectonic movements among the African, Arabian and Anatolian Plates have deformed the eastern Mediterranean. These movements caused transtensional opening of the NE-trending Antakya Graben since the late Pliocene. Tectonic uplift coupled with Quaternary sealevel fluctuations has produced several stacked marine terraces along the Mediterranean coasts on the graben. Here, marine terrace deposits that sit on both flanks of the graben at elevations between 3 and 175 m were dated using electron spin resonance (ESR) method in order to calculate uplift rates. The ESR ages range from 12 ka in late MIS 2 to 457 ka in MIS 9-11, but most of the terraces contain molluscs reworked from several earlier deposits due to successive tectonic movements and sealevel fluctuations. By dating in situ fossils, along the basal contacts of the marine terraces, uplift rates were calculated on both sides of the Antakya Graben. Results indicate that these deposits were mainly uplifted by local active faults rather than regional movements.

Sedimentary petrography of the Early Proterozoic Pretoria Group, Transvaal Sequence, South Africa: implications for tectonic setting

NASA Astrophysics Data System (ADS)

Schreiber, U. M.; Eriksson, P. G.; van der Neut, M.; Snyman, C. P.

1992-11-01

Sandstone petrography, geochemistry and petrotectonic assemblages of the predominantly clastic sedimentary rocks of the Early Proterozoic Pretoria Group, Transvaal Sequence, point to relatively stable cratonic conditions at the beginning of sedimentation, interrupted by minor rifting events. Basement uplift and a second period of rifting occurred towards the end of Pretoria Group deposition, which was followed by the intrusion of mafic sill swarms and the emplacement of the Bushveld Complex in the Kaapvaal Craton at about 2050 Ma, the latter indicating increased extensional tectonism, and incipient continental rifting. An overall intracratonic lacustrine tectonic setting for the Pretoria Group is supported by periods of subaerial volcanic activity and palaeosol formation, rapid sedimentary facies changes, significant arkosic sandstones, the presence of non-glacial varves and a highly variable mudrock geochemistry.

Global implications of China's healthcare reform.

PubMed

Yan, Fei; Tang, Shenglan; Zhang, Jian

2016-01-01

The ongoing healthcare reform in China has a powerful spillover effect beyond the health sector and the borders of China. A successful completion of the Chinese reform will offer a new model for social justice development, shift the global economy toward sustainability and create a new hub for science and technology in medical and health science. However, reforming the healthcare system in the most populated country is a daunting task. China will not live up to its promise, and all the potentials may end with hype not hope if coherent national strategies are not constructed and state-of-the-art navigation is not achieved with staggering domestic and global challenges. The cost of failure will be immensely high, socioeconomic costs for Chinese and an opportunity cost for the world as a whole. A full appreciation of the global implications of China's healthcare reform is crucial in keeping China receptive toward good practices evidence-approved elsewhere and open minded to fulfill its international obligations. More critically, the appreciation yields constructive engagements from global community toward a joint development and global prosperity. The current report provides a multiple disciplinary assessment on the global implications of the healthcare reform in China. Copyright © 2014 John Wiley & Sons, Ltd.

Secular cooling of Earth as a source of intraplate stress

NASA Technical Reports Server (NTRS)

Solomon, Sean C.

1987-01-01

The once popular idea that changes in planetary volume play an important role in terrestrial orogeny and tectonics was generally discarded with the acceptance of plate tectonics. It is nonetheless likely that the Earth has been steadily cooling over the past 3-4 billion years, and the global contraction that accompanied such cooling would have led to a secular decrease in the radius of curvature of the plates. The implications of this global cooling and contraction are explored here for the intraplate stress field and the evolution of continental plates.

The feature of the focal mechanism solutions and tectonic stress field around the focus of Zaduo earthquake (Ms 6.3) in eastern Tibet

NASA Astrophysics Data System (ADS)

Yang, Y.; Zeng, Z.; Shuang, X.; Li, X.

2017-12-01

On 17th October, 2016, an earthquake of Ms6.3 occurred in Zaduo County, Qinghai Province (32.9°N, 95.0°E), 159 km away from the epicenter of Yushu Ms7.3 earthquake in 2011. The earthquake is located in the eastern Tibet Plateau and the north region of Eastern Himalayan Syntaxis. Using the broadband seismic waveform data form regional networks, we determined the focal mechanism solutions (FMSs) of 83 earthquakes (M>3.5) occurred in Zaduo and its adjacent areas from 2009 to 2017. We also collected another 63 published FMSs and then inversed the current tectonic stress field in study region using the damped linear inversion method. The results show that the Zaduo earthquake is a normal oblique earthquake. The FMSs in our study region are mainly in strike-slip and normal fault patterns. The strike-slip earthquakes are mainly distributed in Yushu-Ganzi, Zaduo and Yanshiping fault zones, and the normal faulting events occurred in Nu Jiang fault zone and Nierong County and its vicinity, the south and southwest of the study areas. The tectonic stress field results indicate that the stress distribution in the north and east of the study region changes homogeneously and slowly. From west to east, the σ1 gradually changes from NNE to NE direction, and the σ3 varies from NWW to NW direction. Both the maximum (σ1) and minimum (σ3) principal stress axes in the study area are nearly horizontal, except in the Nu Jiang fault zone and its vicinity, the south of the study area, which is in a normal faulting stress regime (σ1 is vertical and σ3 is horizontal). The localized normal faulting stress field in the south area, which is almost limited in a semicircle, indicates that a high pressure and low viscosity body with low S-wave velocity and high conductivity might exists beneath the anomaly area. And there may be another semicircle abnormal area beyond the south of the study region. Waveform data for this study are provided by Data Management Centre of China National Seismic Network at Institute of Geophysics (SEISDMC, doi:10.11998/SeisDmc/SN), China Earthquake Networks Center and GS, QH, SC, XZ Seismic Networks, China Earthquake Administration. This work was supported by the National Nature Science Foundation of China under Grant No.41230206.

Fluvial incision by the Qingyijiang River on the northern fringe of Mt. Huangshan, eastern China: Responses to weakening of the East Asian summer monsoon

NASA Astrophysics Data System (ADS)

Hu, Chunsheng; Liu, Shaochen; Hu, Chenqi; Xu, Guanglai; Zhou, Yingqiu

2017-12-01

This paper focuses on climatic and tectonic controls to determine their relative importance to the Quaternary fluvial incision by the Qingyijiang River, eastern China. The Qingyijiang, which is one of longest tributaries of the lower Yangtze River, drains the northern piedmont of Mt. Huangshan. A field survey focused on three natural sections of the Qingyijiang in the Jingxian basin, where a well-preserved sequence of one alluvial platform (P) and three fluvial terraces (T3, T2, and T1) is presented. The heights of the platform and the terraces above river level are 65, 40, 20, and 7 m respectively. In this study, electron spin resonance (ESR), optical stimulated luminescence (OSL), and palaeomagnetic dating were applied to reconstruct the fluvial incision history of the Qingyijiang and evaluate the possible influence of tectonic uplift and/or climate change on the fluvial incision. The main results show that (1) the ages of P, T3, T2, and T1 were determined to be ∼ 1300, ∼ 900, ∼ 600, and ∼ 1.5 ka respectively, corresponding to four incision events in the Qingyijiang; (2) the East Asian summer monsoon (EASM) experienced four significant weakening events at 1300, 900, 600, and ∼ 1.5 ka, according to previous research. Correspondingly, we propose that four significant increased periods of regional precipitation occurred at 1300, 900, 600, and ∼ 1.5 ka in the study area because of the negative correlation between the intensity of the EASM and regional precipitation from 1960 to 2012; and (3) fluvial incision by the Qingyijiang arose as a result of the weakening of the EASM in combination with tectonic uplift, determined by matching fluvial incision history of the Qingyijiang with tectonic movement and EASM change. In addition, the weakening of the EASM climatically triggered fluvial incision by the Qingyijiang. This study supports the conclusion that major fluvial incision has been climatically triggered; however, it also suggests that the mechanism of river incision may be regionally distinctive in different climatic zones.

Tectonic Deformation Pattern along the Longmen Shan Fault Zone in Eastern Tibet: Insights from Focal Mechanisms of the Wenchuan and Lushan Earthquake Sequences, Southwestern China

NASA Astrophysics Data System (ADS)

Yi, G.; Vallage, A.; Klinger, Y.; Long, F.; Wang, S.

2017-12-01

760 ML≥3.5 aftershocks of the 2008 Wenchuan earthquake, the 2013 Lushan mainshock and its 87 ML≥3.5 aftershocks were selected to obtain focal mechanism solutions from CAP waveform inversion method (Zhu and Helmberger, 1996), along with strain rosette (Amelung and King, 1997) and Areal strain (As) (Vallage et al., 2014), we aimed to analyze the tectonic deformation pattern along the Longmen Shan (LMS) fault zone, southwestern China. The As values show that 93% compressional earthquakes for the Lushan sequence are of pure thrust for the southern segment of the LMS fault zone, while only 50% compressional and nearly 40% of strike-slip and oblique-thrust events for the Wenchuan sequence reflect the strike-slip component increase on the central-northern segment of the LMS fault zone, meaning many different faults responsible for the Wenchuan aftershock activity. The strain rosettes with purely NW-trending compressional white lobe for the entire 87 aftershocks and 4 different classes of magnitudes are very similar to that of the Lushan mainshock. We infer that the geological structures for the southern segment are of thrust faulting under NW compressional deformation. The strain rosettes exhibit self-similarity in terms of orientation and shape for all classes, reflecting that the deformation pattern of the southern segment is independent with earthquake size, and suggesting that each class is representative of the overall deformation for the southern segment. We obtained EW-oriented pure compressional strain rosette of the entire 760 aftershocks and NW-oriented white lobe with small NE-oriented black lobe of the Wenchuan mainshock, and this difference may reflect different tectonic deformation pattern during the co-seismic and post-seismic stages. The deformation segmentation along the Wenchuan coseismic surface rupture is also evidenced from the different orientation of strain rosettes, i.e., NW for the southern area, NE for the central and NNW for the northern parts. The above inferences indicate a very complicated tectonic deformation pattern related to the complex geological structure. The segment of the northern aftershock area without ruptures behaves an oblique compressional deformation.

China-U.S. Relations: Current Issues and Implications for U.S. Policy

DTIC Science & Technology

2009-07-10

Trade Representative (USTR) filed a case against China in the WTO in December 2008 charging that the PRC’s “Famous Chinese” brand program amounted to...Association of America, Inc. has charged that China may be blocking the import of American films , creating more opportunities for pirated versions...Relations: Current Issues and Implications for U.S. Policy Congressional Research Service 10 consumers. In 2007, the USTR filed several cases in

Field geology, geochronology and geochemistry of mafic-ultramafic rocks from Alxa, China: Implications for Late Permian accretionary tectonics in the southern Altaids

NASA Astrophysics Data System (ADS)

Jianyun, Feng; Wenjiao, Xiao

2013-04-01

The termination of orogenesis for the southern Altaids has been controversial. Systematical investigations of field geology, geochronology and geochemistry on mafic-ultramafic rocks from the northern Alxa of the southern Altaids were conducted to address the termination controversy. The newly discriminated mafic-ultramafic rocks belt is located at Bijiertai, Honggueryulin, and Qinggele areas, stretching from west to east for about 100 km in length. All of the three rock associations contact tectonically with the adjacent metamorphic and deformed Precambrian rocks as tectonic blocks or lenses, and are composed of peridotite, pyroxenite, gabbro, and serpentinite, most of which have subjected to pronounced alteration, i.e., serpentinization and chloritization. Geochemically, the rocks are characterized by a uniform trend of compositional distribution, e.g., with low SiO2-contents (42.51-52.21 wt.%) and alkalinity (Na2O+K2O) (0.01-5.45 wt.%, mostly less than 0.8 wt.%), and enriched in MgO (7.37-43.36 wt.%), with Mg# = 52.75-91.87. As the rocks have had strong alteration and have a wide range of loss-on-ignition (LOI: 0.44-14.07 wt.%), the rocks may be subjected to considerable alteration by either sea-water or metamorphic fluid. The REE and trace element patterns for the rocks show a relatively fractionated trend with LILE enrichment and HFSE depletion, similar to that of T-MORB between N-MORB and E-MORB, indicating that the parental melt resulted from the partial melting of oceanic lithospheric mantle overprinted by fluid alteration of island-arc subsequently. The ultramafic rocks are relics derived from the magma after large degree of partial melting of the oceanic lithospheric mantle with overprinted by island-arc processes under the influence of mid-ocean-ridge magmatism. LA - ICP MS U - Pb zircon ages of gabbros from the three spots are 274 ± 3 Ma (MSWD = 0.35), 306 ± 3 Ma (MSWD = 0.49), 262 ± 5 Ma (MSWD = 1.2), respectively, representing the formation ages of the mafic-ultramafic rocks. Therefore, considering the other data published previously, we suggest that the mafic-ultramafic rocks are products of a south-dipping subduction, most probably a ridge subduction for the Paleo-Asian Ocean beneath the Alxa block in the Late Carboniferous to Late Permian before the Paleo-Asian Ocean completely closed. This shed light on the controversial tectonic history of the southern Altaids and support that the termination of the orogenesis was in the end Permian to Triassic.

Tectonic affinities of the accreted basalts in southern Taiwan

NASA Astrophysics Data System (ADS)

Chen, Hsin-Yu; Yang, Huai-Jen; Liu, Yung-Hsin; Huang, Kuo-Fang; Takazawa, Eiichi

2018-06-01

Tectonic affinities of accreted basalts provide constraints on mass transport in convergent boundaries, improving our understandings on the evolution of regional geology. In this study, nineteen accreted basalts from the southernmost tip of Taiwan Island, which is on the convergent boundary between the Eurasian and Philippine Sea Plates, were analyzed for element concentrations as well as Sr, Nd, Hf, and Pb isotope ratios to investigate their tectonic affinities. All the samples contain > 3% LOI, reflecting post-magmatic alteration. LOI and Nb variation diagrams together with comparisons to oceanic basalt compositions indicated that the concentrations of most major elements and Rb, Sr, and Ba were modified by post-magmatic processes to varying extents, while P2O5, REE and HFSE remained immobile. Although some samples show Pb loss, most samples have Pb concentrations not affected by post-magmatic processes. Isotope ratios of Pb, Nd and Hf, generally reflect the mantle source characteristics. The εNd-εHf relationship and trace element abundance ratios indicated that the LREE-depleted samples were mostly scraped off the subducting South China Sea floor, reflecting the volumetric dominance of N-MORB on ocean floors. The overriding Philippine Sea Plate contributed both N-MORB and E-MORB to the accretionary prism. The tectonic affinities of the LREE-enriched samples, however, could not be unambiguously determined for the large geochemical variability of OIB from both subducting and overlying slabs. Based on our results, it is proposed that the tectonic affinity of the basalts in an accretionary prism can indicate the subduction polarity of the associated convergent boundary, providing a constraint for regional geology evolution.

Deformation at longyao ground fissure and its surroundings, north China plain, revealed by ALOS PALSAR PS-InSAR

NASA Astrophysics Data System (ADS)

Yang, Chengsheng; Lu, Zhong; Zhang, Qin; Zhao, Chaoying; Peng, Jianbing; Ji, Lingyun

2018-05-01

The Longyao ground fissure (LGF) is the longest and most active among more than 1000 ground fissures on the North China Plain. There have been many studies on the formation mechanism of the LGF, due to its scientific importance and its potential for damage to the environment. These studies have been based on both regional tectonic analysis and numerical simulations. In order to provide a better understanding of the formation mechanism, the deformation of the crack and its surrounding environment should be taken into consideration. In this paper, PS-InSAR technology was employed to assess the ground deformation of LGF and its surrounding area, using L-band ALOS-1 PALSAR images from 2007 to 2011. The characteristics of ground deformation, relationships between fissure activity and surrounding faults and groundwater exploitation were analyzed. This study shows that the north side of Longyao fault (LF) is uplifting while the south side is subsiding. This provides the tectonic conditions responsible for the activity of the ground fissure. Local groundwater exploitation also plays an important role in the development of ground fissures. InSAR observations were modeled to infer the loading depth (-2.8 km) and the slip rate (31.1 mm/yr) of LF.

An Introduction to Education in the People's Republic of China and U.S.-China Educational Exchanges.

ERIC Educational Resources Information Center

Perrolle, Pierre M.; Reed, Linda A.

Information is presented on China's higher education system, China's current educational exchanges, and the U.S.-China educational exchange process. China's higher education system is considered in terms of historical themes and implications for the present, the number and types of institutions, graduate education, operation of the higher…

Amphibolite of the Xinghuadukou group from the Xinlin-Xiguitu belt, NE China: new evidence for the NE branch of the Paleo-Asian Ocean

NASA Astrophysics Data System (ADS)

Hou, Wenzhu

2017-04-01

The tectonic evolution of the Paleo-Asian Ocean (PAO) witnessed the cycling of two supercontinents, Rodinia and Pangea, in Earth's geological history. This long-lasting paleo-ocean was initiated by the breakup of the supercontinent Rodinia during the Early Neoproterozoic (1,2) and terminated by the final collage of the supercontinent Pangea from Central to Eastern (current coordinates) Asia, likely lasting to the Late Permian or Early Triassic (3,4). Numerous continental and island arcs, seamounts, mid-ocean ridges and micro-blocks were amalgamated responding to the subduction and consumption of the oceanic crust of the PAO, to form the most complex and long-living Phanerozoic accretionary orogenic belt, the Central Asian Orogenic Belt (CAOB) (5,6). Trapped by the collision and amalgamation of the eastern segment of CAOB, several rock suites of oceanic affinity were reported along the Xinlin-Xiguitu belt that connects the Erguna block to the northwest and the Xing'an block to the southeast in NE China, including the Toudaoqiao blueschist (7), Jifeng ophiolite (although the forming environment remains debatable, see 8 and 9), and Xinlin ophiolite (10,11). All these suites have been proposed to be the relics of the NE branch of the PAO. However, along the northeastern extension of this belt, outcropped the Xinghuadukou group that was previously thought Paleoproterozoic in age yet has been reconsidered to be Cambrian (12), the relationship of which and this belt remains unclear. In this study, a suite of amphibolite was collected from the Xinghuadukou group outcropped in the easternmost Xinlin-Xiguitu belt in NE China and conducted geochemical analysis to discuss their forming environment and tectonic implications. Samples display low SiO2 (45%-49%wt), low K2O (0.55%-1.07%wt) compositions, low in A/CNK, but high in A/NK and FeOt/MgO ratios. REE compositions are relative low (ΣREE=52-122ppm) showing a flat chondrite normative pattern with slight enrichment in LREE ((La/Ya)N=1.5-2.4) and no Eu anomaly (Eu/Eu*=0.9-1.0). The LILE fractionation is indistinctive ((Sr/Y)N=1.1-1.8). Samples show an evident E-MORB affinity. Along with the previous studies, it can be concluded: 1) the protolith of the amphibolite of the Xinghuadukou group is a suite of tholeiitic basalt that formed in the oceanic islands environment; 2) with all the oceanic suites reported in Xinlin-Xiguitu belt, a branch of the Eastern PAO can be well defined, which likely existed from the Late Neoproterozoic to Late Cambrian, so called the Xinlin-Xiguitu Ocean. Acknowledgements: This study was financially supported by the National Natural Science Foundation of China (Projects 41190075, 41190070, 41230207, 41390441), the Hong Kong Research Grants Council General Research Fund (HKU7063/13P and 17301915), and the HKU Seed Funding Programme for Basic Research (201311159126). References: 1. N. L. Dobretsov et al., Gondwana Res. 6(2), 143-159 (2003). 2. J. Tang et al., Precambrian Res. 224, 597-611 (2013). 3. J. Y. Li, J. Asian Earth Sci. 26(3), 207-224 (2006). 4. P. R. Eizenhöfer et al., Tectonics 33(4), 441-463 (2014). 5. B. F. Windley et al., J. Geol. Soc. 164(1), 31-47 (2007). 6. W. Xiao et al., Annu. Rev. Earth Planet. Sci. 43, 477-507 (2015). 7. J. B. Zhou et al., J. Asian Earth Sci. 97, 197-210 (2015). 8. Z. Feng et al., Int. J. Earth Sci. 105(2), 491-505 (2016). 9. D. H. Ni, Int. J. Earth Sci. (2016). doi:10.1007/s00531-016-1412-2 10. R. S. Li, Heilongjiang Geology, 2(1), 21-32 (1991). 11. W. Yan et al., Earth Sci. - J. Chin. Uni. Geo. 8 (2014). 12. L. Miao et al., Chin. Sci. Bull. 52(8), 1112-1124 (2007).

New Insight Into the Crustal Structure of the Continental Margin offshore NW Sabah/Borneo

NASA Astrophysics Data System (ADS)

Barckhausen, U.; Franke, D.; Behain, D.; Meyer, H.

2002-12-01

The continental margin offshore NW Sabah/Borneo (Malaysia) has been investigated with reflection and refraction seismics, magnetics, and gravity during the recent cruise BGR01-POPSCOMS. A total of 4000 km of geophysical profiles has been acquired, thereof 2900 km with reflection seismics. The focus of investigations was on the deep water areas. The margin looks like a typical accretionary margin and was presumably formed during the subduction of a proto South China Sea. Presently, no horizontal movements between the two plates are being observed. Like in major parts of the South China Sea, the area seaward of the Sabah Trough consists of extended continental lithosphere which is characterised by a pattern of rotated fault blocks and half grabens and a carbonate platform of Early Oligocene to Early Miocene age. We found evidence that the continental crust also underlies the Sabah Trough and the adjacent continental slope, a fact that raises many questions about the tectonic history and development of this margin. The tectonic pattern of the Dangerous Grounds' extended continental crust can be traced a long way landward of the Sabah Trough beneath the sedimentary succession of the upper plate. The magnetic anomalies which are dominated by the magnetic signatures of relatively young volcanic features also continue under the continental slope. The sedimentary rocks of the upper plate, in contrast, seem to generate hardly any magnetic anomalies. Based on the new data we propose the following scenario for the development of the NW Sabah continental margin: Seafloor spreading in the present South China Sea started at about 30 Ma in the Late Oligocene. The spreading process separated the Dangerous Grounds area from the SE Asian continent and ceased in late Early Miocene when the oceanic crust of the proto South China Sea was fully subducted in eastward direction along the Borneo-Palawan Trough. During Lower and/or Middle Miocene, Borneo rotated counterclockwise and was thrusted onto the edge of the rifted continental block of the Dangerous Grounds. The subducted oceanic crust of the proto South China Sea must today be located below the Eastern part of Sabah and not along the present NW Sabah Trough.

Phase equilibria modelling and zircon dating for Precambrian metapelites from Xinghuadukou Group in Lvlin Forest of Erguna Massif, NE China

NASA Astrophysics Data System (ADS)

Xu, Jiulei; Zheng, Changqing; Tajcmanova, Lucie; Zhong, Xin; Xu, Xuechun; Han, Xiaomeng; Wang, Zhaoyuan

2017-04-01

Xinghuadukou Group, the basement metamorphic complex of Erguna Massif in NE China, is considered to be Mesoproterozoic with Sm-Nd age of 1157±32 Ma. However, the new zircon data from these metamorphic supracrustal rocks in Lvlin Forest show that they formed in Neoproterozoic with the age of 800 Ma. Old zircon age with 2.5 Ga, 2.0 Ga and 1.8 Ga, indicate that the Erguna Massif had an affinity to both Columbia and Rodinia continents. Furthermore, we also present 500 Ma metamorphic age in micashists and 500 Ma age of adjacent granitoids that might have thermally influenced its surrounding. No detailed studies have been undertaken on the metamorphic evolution of the Xinghuadukou Complex. The typical paragneissic mineral assemblage of garnet sillimanite mica schist is Grt+Sil+Bt+Mus+Qtz±Kfs. (Zhou et al., 2011) proposed that the Xinghuadukou Complex appears to have undergone similar granulite facies metamorphic conditions based on the similarity of mineral assemblages to the Mashan Complex in the Jiamusi Massif, NE China. However, the new phase equilibria modelling result shows that these rocks are high amphibolite facies product with 650℃. We can easily find K-feldspar formed by partial melting due to the consuming of muscovite. Also the remaining muscovite is directly connected with a fluid channel in thin sections which indicate that the remaining muscovite formed from retrograde with the existence of fluid. The zoned garnet has low MgO and high CaO content in rims and high MgO and low CaO content in core. It seems that this garnet has high pressure and low temperature (HP-LT) in rims and low pressure and high temperature (LP-HT) in core which would point to an anti-clockwise metamorphic evolution. Zhou, J.B., Wilde, S.A., Zhang, X.Z., Zhao, G.C., Liu, F.L., Qiao, D.W., Ren, S.M. and Liu, J.H., 2011b. A> 1300km late Pan-African metamorphic belt in NE China: new evidence from the Xing'an block and its tectonic implications. Tectonophysics, 509(3): 280-292.

Paleoclimatic and paleomagnetic constraints on the Paleozoic reconstructions of south China, north China and Tarim

NASA Astrophysics Data System (ADS)

Shangyou, Nie

1991-10-01

Paleomagnetic and paleoclimatic data provide the most useful latitudinal constraints for plate reconstructions. Distributions through the Paleozoic of five types of climatically sensitive sediments (coals, evaporites, reefs, dolomites and limestones) for south China, north China and Tarim are shown on 15 maps that include 1578 reliable data points. These paleoclimatic data agree reasonably well with available paleomagnetic directions, although significant divergence between the two exists for the Early Paleozoic. These data indicate the following: (1) South China was in low latitudes during the entire Paleozoic, with a subtropical position in the Cambrian. (2) North China also remained near the equator in the Early and Late Paleozoic, except for the Ordovian and the Late Permian when extensive evaporites suggest slightly higher latitudinal positions, while its Middle Paleozoic position is uncertain due to the missing stratigraphie record. (3) In south China, local tectonics appears to have played a dominant role in determining paleogeography and therefore marine sedimentation, especially after the Late Ordovician-Early Silurian, because the areal coverage of marine sediments through time is distinctly different from what would be expected from published global sea-level curves. (4) Paleoclimatic and paleomagnetic data are compatible with biogeographic data which suggest that south China was part of eastern Gondwana in the Early Paleozoic, but was widely separated from Gondwana in the Late Paleozoic, and the split between the two probably happened in the Devonian, giving rise to a major break-up unconformity in central south China.

Use of SPOT and ERS-1 SAR data to study the tectonic and climatic history of arid regions

NASA Technical Reports Server (NTRS)

Farr, Tom G.; Peltzer, Gilles F.

1993-01-01

In order to separate the effects of the different tectonic and climatic processes on the shapes of desert piedmonts, a modified conic equation was fitted to digital topographic data for individual alluvial fans in Death Valley (California, U.S.). The topographic data were obtained from a SPOT panchromatic stereo pair and from the airborne interferometric SAR (Synthetic Aperture Radar) (TOPSAR). The conic fit allows parameters for the epex position, slope, and radial curvature to be compared with unit age, uplift rate, and climatic conditions. Preliminary results indicate that slope flattens with age and radial curvature is concave up, but decreases with age. Work is continuing on correlation of fit residuals and apex position with fan unit age. This information will help in the determination of tectonic uplift rates and the climatic history of the western U.S. ERS-1 SAR images were used to study an area of western China where a large strike slip fault crosses a series of alluvial fans and stream valleys. Previous analysis of SPOT panchromatic images of the area shows that offsets fans and streams can be recognized. Measurement of the rate of motion of this fault will help in the overall model of deformation of the Asian tectonic plate in response to the collision of the Indian plate.

Geochronology and geochemistry of early Paleozoic igneous rocks of the Lesser Xing'an Range, NE China: Implications for the tectonic evolution of the eastern Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Wang, Zhi-wei; Xu, Wen-liang; Pei, Fu-ping; Wang, Feng; Guo, Peng

2016-09-01

This paper presents new zircon U-Pb, Hf isotope, and whole-rock major and trace element data for early Paleozoic igneous rocks of the Lesser Xing'an Range, NE China, in order to constrain the early Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt (CAOB). Zircon U-Pb dating indicates that early Paleozoic magmatic events within the northern Songnen-Zhangguangcai Range Massif (SZM) can be subdivided into four stages: Middle Cambrian ( 505 Ma), Late Cambrian ( 490 Ma), Early-Middle Ordovician ( 470 Ma), and Late Ordovician (460-450 Ma). The Middle Cambrian monzogranites are K-rich, weakly to strongly peraluminous, and characterized by pronounced heavy rare earth element (HREE) depletions, high Sr/Y ratios, low Y concentrations, low primary zircon εHf(t) values (- 6.79 to - 1.09), and ancient two-stage model (TDM2) ages (1901-1534 Ma). These results indicate derivation from partial melting of thickened ancient crustal materials that formed during the amalgamation of the northern SZM and the northern Jiamusi Massif (JM). The Late Cambrian monzonite, quartz monzonite, and monzogranite units are chemically similar to A-type granites, and contain zircons with εHf(t) values of - 2.59 to + 1.78 and TDM2 ages of 1625-1348 Ma. We infer that these rocks formed from primary magmas generated by partial melting of Mesoproterozoic accreted lower crustal materials in a post-collisional extensional environment. The Early-Middle Ordovician quartz monzodiorite, quartz monzonite, monzogranite, and rhyolite units are calc-alkaline, relatively enriched in light REEs (LREEs) and large ion lithophile elements (LILEs; e.g., Rb, Th, and U), depleted in HREEs and high field strength elements (HFSEs; e.g., Nb, Ta, and Ti), and contain zircons with εHf(t) values of - 7.33 to + 4.98, indicative of formation in an active continental margin setting. The Late Ordovician alkali-feldspar granite and rhyolite units have A-type granite affinities that suggest they formed in an extensional environment. A comparison of early Paleozoic magmatic events and Hf isotopic model ages between the northern SZM and the JM indicates that these two massifs have similar histories of Mesoproterozoic and early Paleozoic crustal accretion and reworking, although the SZM contains much older crustal materials than the JM.

Tertiary fission-track ages from the Bagua syncline (northern Peru): Stratigraphic and tectonic implications

NASA Astrophysics Data System (ADS)

Naeser, C. W.; Crochet, J.-Y.; Jaillard, E.; Laubacher, G.; Mourier, T.; Sigé, B.

The results of five zircon fission-track ages of volcanic tuffs intercalated within the continental deposits of the Bagua syncline (northern Peru) are reported. These 2500-meter-thick deposits overlie mid-Campanian to lower Maastrichtian fine-grained red beds (Fundo El Triunfo Formation). The disconformable fluvial conglomerates of the Rentema Formation are associated with a 54 Ma tuff (upper Paleocene-lower Eocene?) and would reflect the Inca-1 tectonic phase. The Sambimera Formation (Eocene to mid-Miocene) is a coarsening-upward sequence (from lacustrine to fluvial) that contains three volcanic tuffs of 31, 29, and 12 Ma, respectively. A probable stratigraphic gap, upper Eocene-lower Oligocene, would be related to the late Eocene Inca-2 phase. Neither deformation nor sedimentary discontinuity has been recognized so far. However, the lacustrine to fluvial transition could relate to the late Oligocene Aymara tectonic phase. The unconformable fanglomerates and fluvial deposits of the San Antonio Formation contain in their upper part a 9 Ma tuff (mid-to upper Miocene), and thier base records a major tectonic event (Quechua-2 phase?). The unconformable fanglomerates of the Tambopara Formation date the folding of the Bagua syncline, which could be ascribed to the latest Miocene Quechua-3 tectonics. These formations are correlative with comparable deposits in the sub-Andean basins, suggesting that these eastern areas underwent strong tectonic subsidence of the foreland basin type since mid-Miocene times.

Tertiary fission-track ages from the Bagua syncline (northern Peru): Stratigraphic and tectonic implications

USGS Publications Warehouse

Naeser, C.W.; Crochet, J.-Y.; Jaillard, E.; Laubacher, G.; Mourier, T.; Sige, B.

1991-01-01

The results of five zircon fission-track ages of volcanic tuffs intercalated within the continental deposits of the Bagua syncline (northern Peru) are reported. These 2500-meter-thick deposits overlie mid-Campanian to lower Maastrichtian fine-grained red beds (Fundo El Triunfo Formation). The disconformable fluvial conglomerates of the Rentema Formation are associated with a 54 Ma tuff (upper Paleocene-lower Eocene?) and would reflect the Inca-1 tectonic phase. The Sambimera Formation (Eocene to mid-Miocene) is a coarsening-upward sequence (from lacustrine to fluvial) that contains three volcanic tuffs of 31, 29, and 12 Ma, respectively. A probable stratigraphic gap, upper Eocene-lower Oligocene, would be related to the late Eocene Inca-2 phase. Neither deformation nor sedimentary discontinuity has been recognized so far. However, the lacustrine to fluvial transition could relate to the late Oligocene Aymara tectonic phase. The unconformable fanglomerates and fluvial deposits of the San Antonio Formation contain in their upper part a 9 Ma tuff (mid-to upper Miocene), and thier base records a major tectonic event (Quechua-2 phase?). The unconformable fanglomerates of the Tambopara Formation date the folding of the Bagua syncline, which could be ascribed to the latest Miocene Quechua-3 tectonics. These formations are correlative with comparable deposits in the sub-Andean basins, suggesting that these eastern areas underwent strong tectonic subsidence of the foreland basin type since mid-Miocene times. ?? 1991.

Première caractérisation palynologique du Trias moyen dans le Haut Atlas ; implications pour l'initiation du rifting téthysien au Maroc

NASA Astrophysics Data System (ADS)

El Arabi, El Hassane; Diez, José Bienvenido; Broutin, Jean; Essamoud, Rachid

2006-07-01

The Middle Anisian has been palynologically characterized for the first time, at the whole Moroccan scale, in the High Atlas of Marrakech. The stratigraphic, tectonic and paleogeographic implications of this discovery are analysed. To cite this article: E.H. El Arabi et al., C. R. Geoscience 338 (2006).

Exhumation history of the Anqing Orefield in the Lower Yangtze River Metallogenic Belt: Evidence from apatite fission-track thermochronology

NASA Astrophysics Data System (ADS)

Li, X.; Yang, X.

2017-12-01

The Lower Yangtze River Metallogenic Belt (LYRMB) is one of the most important Cu-Au-Fe polymetallic belts in China. These deposits along the Yangtze River region have been related to the Yanshanian intrusive rocks in the Mesozoic. The Anqing orefield is located in the northwestern Anqing, southwestern Anhui Province, eastern China, along the Lower Yangtze River Belt. Here, we report new apatite fission-track (AFT) thermochronology of the granitoids ( 130 Ma for zircon U-Pb age) associated with the Anqing orefields to reveal the exhumation history of the Anqing orefields in LYRMB, eastern China. AFT ages from 54.4±2.1 to 63.9±3.4 Ma with mean measured track lengths between 12.4±1.8 and 13.1±1.4 μm, were obtained for the granitoids sampled from the ore fields in the Anqing orefield, and AFT age of 36.3±1.3 Ma with mean track length of 12.3±2.3μm for the granitoids adjacent to the south Tan-Lu fault. A long, slow exhumation ( 60-15 Ma), and a short, rapid tectonic exhumation (15-0 Ma) have been identified in the study region based on the AFT data and modeling results for the samples from the ore fields. The results show that the granitoids underwent roughly similar cooling, and inferred exhumation pattern. Assuming a steady-state paleogeothermal gradient of 35ºC/km founded on geological setting, the exhumations of 570 m and 1140 m, were achieved in the Anqing orefield, during 60-15 Ma and 15-0 Ma, respectively. Further, the AFT age of the granitoids adjacent to the south Tan-Lu fault is less than the AFT ages of the granitoids associated with the ore fields, possibly owing to the activation of the Tan-Lu fault in the Cenozoic. The exhumation history of the Anqing orefields may be closely response to the Pacific Plate subduction in the Cenozoic, which could be implications for the preservation potential of ore bodies in the Anqing orefield. This work is supported by the National Natural Science Foundation of China (41372227), and the DREAM project of MOST China (2016YFC0600406).

China's "Great Leap" toward Madison Avenue.

ERIC Educational Resources Information Center

Anderson, Michael H.

1981-01-01

Examines the expanding use of advertising in China. Discusses the impact of transnational corporations in communication and other areas on the development of China, and the implications that the introduction of advertising has for China's role as one of the models for developing countries. (JMF)

Reconstructing multiple arc-basin systems in the Altai-Junggar area (NW China): Implications for the architecture and evolution of the western Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Li, Di; He, Dengfa; Tang, Yong

2016-05-01

The Altai-Junggar area in northwestern China is a critical region to gain insights on the tectonic framework and geological evolution of the western Central Asian Orogenic Belt (CAOB). In this study, we report results from integrated geological, geochemical and geophysical investigations on the Wulungu Depression of the Junggar Basin to determine the basement nature of the basin and understand its amalgamation history with the Chinese Altai, within the broad tectonic evolution of the Altai-Junggar area. Based on borehole and seismic data, the Wulungu Depression is subdivided into two NW-trending tectonic units (Suosuoquan Sag and Hongyan High) by southward-vergent thrust faults. The Suosuoquan Sag consists of the Middle-Late Devonian basaltic andesite, andesite, dacite, tuff, tuffaceous sandstone and tuffite, and the overlying Early Carboniferous volcano-sedimentary sequence with lava flows and shallow marine sediments from a proximal juvenile provenance (zircon εHf(t) = 6.0-14.9), compared to the Late Carboniferous andesite and rhyolite in the Hongyan High. Zircon SIMS U-Pb ages for dacites and andesites indicate that these volcanics in the Suosuoquan Sag and Hongyan High erupted at 376.3 Ma and 313.4 Ma, respectively. The Middle-Late Devonian basaltic andesites from well LC1 are calc-alkaline and exhibit primitive magma-like MgO contents (7.9-8.6%) and Mg# values (66-68), with low initial 87Sr/86Sr (0.703269-0.704808) and positive εNd(t) values (6.6-7.6), and relatively high Zr abundance (98.2-116.0 ppm) and Zr/Y ratios (5.1-5.4), enrichment in LREEs and LILEs (e.g., Th and U) and depletion in Nb, Ta and Ti, suggesting that they were probably derived from a metasomatized depleted mantle in a retro-arc extensional setting. The well LC1 andesitic tuffs, well L8 dacites, well WL1 dacitic tuffs and well L5 andesites belong to calc-alkaline and metaluminous to peraluminous (A/CNK = 0.8-1.7) series, and display low Mg# values (35-46) and variably positive εNd(t) (4.5-8.5) and εHf(t) (10.2-16.8) values, as well as young isotopic model ages. These Devonian-Carboniferous intermediate-felsic volcanics are interpreted as the products of partial melting of a juvenile lower crust with some contributions from mantle components in an evolved island arc setting from immature to mature island arc. The basin filling pattern and the distribution of arc volcanics and their zircon Hf model ages with the eruptive time suggest that the Wulungu Depression represents an island arc-basin system with the development of a Carboniferous retro-arc basin. In combination with previous work, we propose that the northern Junggar area comprises three arc-basin belts from south to north: the Darbut-Luliang-Karamaili, Wulungu-Yemaquan, and Saur-Fuhai-Dulate. Such tectonic subdivisions are consistent with the regional gravity and magnetic anomaly data. The recognition of the Wulungu arc-basin system demonstrates that the Junggar Basin is likely underlain by juvenile continental crust rather than ancient Precambrian basement, and also implies that the CAOB was built by amalgamation of multiple linear arcs and accretionary complexes.

Research on Formation Mechanisms of Hot Dry Rock Resources in China

NASA Astrophysics Data System (ADS)

Wang, G.; Xi, Y.

2017-12-01

As an important geothermal resource, hot dry rock(HDR) reserves have been studied in many countries. HDR resources in China have huge capacity and have become one of the most important resources for the potential replacement of fossil fuels. However, HDR resources are difficult to develop and utilise. Technologies for use with HDR, such as high-temperature drilling, reservoir characterisation, reservoir fracturing, microseismic monitoring and high-temperature power stations, originate from the field of oil and drilling. Addressing how to take advantage of these developed technologies is a key factor in the development of HDR reserves. Based on the thermal crustal structure in China, HDR resources can be divided into four types: high radioactive heat production, sedimentary basin, modern volcano and the inner-plate active tectonic belt. The prospective regions of HDR resources are located in South Tibet, West Yunnan, the southeast coast of China, Bohai Rim, Songliao Basin and Guanzhong Basin. The related essential technologies are relatively mature, and the prospect of HDR power generation is promising. Therefore, analysing the formation mechanisms of HDR resources and promoting the transformation of technological achievements, large-scale development and the utilisation of HDR resources can be achieved in China.

The Ms4.4 2016 Yuncheng, Shanxi, China, Seismic Sequence: Source Characterizations and Tectonic Implications

NASA Astrophysics Data System (ADS)

Xie, Z.; Riaz, M. S.; Zheng, Y.; Xiong, X.

2017-12-01

On 12 March 2016 at 11:14 (Beijing time) , a moderate earthquake with magnitude Ms4.4 struck Yuncheng County, Shanxi Province, Central China. Seismic activity continued with numerous aftershocks, and another event with little smaller magnitude of Ms4.0 occurred on 27 March 2016 at 3:58 as well as a lot of aftershocks followed. Seismic waves from the earthquakes were recorded by a dense local broadband seismic network in Shanxi and its surrounding provinces, enabling detailed the source characterizations of this earthquake sequence. The hypocenters of the Yuncheng earthquake sequence determined by the TomoDD method displayed that the events occurred in the middle of Yuncheng Basin which locates between Weihe Basin and Fenhe Basin, one of renowned active seismic belts in mainland China. The relocation of the aftershocks presented a NNW-SSE orientated distribution, and the earlier aftershocks tended to fault at shallow depths, concentrating at 5 km. After the Ms4.0 event, the aftershocks extended to the SSE direction with deeper focal depths. The focal mechanisms of the mainshock and the biggest aftershock obtained by the CAP (Cut And Paste) method indicated consistent right-lateral strike-slip faults. Since the magnitude was relatively small, no surface rupture associated with this shock sequence had been observed, and no known faults exited around the epicenter, indicating that the causative fault was ambiguous just based on the focal mechanism. According to the aftershocks distribution and the recent GPS results, the ruptured fault was apt to the nodal plane striking at 194°, dipping 79° and rake 151° for Ms4.4 mainshock and 199°/73°/141°, representing strike/dip/rake, for Ms4.0 aftershock. This earthquake sequence was regarded as an adjustment of stress accumulation in the pull-apart Yuncheng Basin, implying that the energy around the boundary faults of the basin has accumulated continuously.

The Structure Difference in the Southern Margin of the Dangerous Grounds: Implications for the Final Evolution of the South China Sea

NASA Astrophysics Data System (ADS)

Xi, P.; Shen, C.; Zhao, Z.; Xie, X.; Mei, L.; Gong, J.; Huang, X.

2015-12-01

We interpret two multi-channel seismic reflection profiles, more than 900 km across the entire Dangerous Grounds, locating in east and west of the southern margin of the South China Sea respectively. Eight Cenozoic sequence boundaries are determined as well as three tectono-stratigraphic units. Detailed analysis of extensional features and unconformities revealed the tectonic in the east and west. Early extension (syn-rifting sequence) occurred in the two profiles during continental rifting, which lasted from Palaeocene to Early Oligocene, and resulted in formation of half-grabens and rotated fault-blocks. Late extension (drift-rifting sequence) has the significant difference in the both profiles. The eastern Dangerous Grounds entered rifting-depression stage and some compressional deformation occurred in the Reed Bank basin at about the beginning of Early Miocene, probably resulting from the collision of the Dangerous Grounds and the Sabah-Cagayan Arc. The western Dangerous Grounds was still in rifting until the end of Early Miocene, forming the MMU or DRU which is strongly erosional and represents a major break in sedimentation and/or erosion in partial area. Denudation fold and inverted fault can be distinguished blow the MMU, indicating the cessation of the South China Sea accompanied the NW compression, while the boundary corresponding the MMU is nearly a plano-conformity in the east. The thermal sag (post-rifting sequence) is characterized by non-faulted draping strata in the whole area. The different structure in east and west may be related to the final evolution of the SCS. When the proto-SCS closed in a scissor fashion plus the clockwise rotation of Borneo, the initial collision (c.20Ma) appeared in east part building the NW foreland basin system from Palawan Trough to Reed Bank in a short-live process, while the west part was drifting southwards until c.15Ma to form the even more remarkable foreland system from Borneo Trough to deep-water Sarawak.

Petrogenesis and tectonic implications of the Neoarchean North Liaoning tonalitic-trondhjemitic gneisses of the North China Craton, North China

NASA Astrophysics Data System (ADS)

Wang, Maojiang; Liu, Shuwen; Wang, Wei; Wang, Kang; Yan, Ming; Guo, Boran; Bai, Xiang; Guo, Rongrong

2016-12-01

Tonalitic-trondhjemitic-granodioritic (TTG) gneisses are dominant lithological assemblages in Archean high grade metamorphic terranes in the world. These TTG gneisses preserve important information in formation and evolution of Archean continental crust. Tangtu-Majuanzi microblock in North Liaoning Province (NLP) is one of the major Neoarchean metamorphic basement terranes in the northeastern margin of the North China Craton (NCC). The Tangtu-Majuanzi microblock is composed mainly of Neoarchean tonalitic-trondhjemitic (TT) gneisses, subordinate granodioritic to monzogranitic association (GMA) and minor supracrustal rocks. The tonalitic-trondhjemitic gneisses are divided into high MgO Group (HMG) and low MgO Group (LMG) based on their chemical compositions. Detailed petrogenetic investigations suggest that the magmatic precursors of the HMG samples were derived from partial melting of subducted slabs and contaminated by the overlying mantle wedge during its ascent; whereas, magmatic precursors of the LMG samples were derived from the juvenile lower crust. LA-ICPMS zircon U-Pb isotopic dating analyses reveal that the magmatic precursors of the HMG samples were formed at 2553-2531 Ma. An older HMG tonalitic gneiss sample was discovered at Sandaoguan in the southmost of the studied area, with its magmatic precursor emplaced at 2680 Ma. The magmatic precursors of the LMG samples emplaced at 2595-2583 Ma. Combined with previous credible chronological data, our newly obtained zircon U-Pb dating and Lu-Hf isotopic data indicate that three episodes of magmatism at ∼2700-2680 Ma, ∼2600-2570 Ma and ∼2550-2510 Ma occurred in the Tangtu-Majuanzi microblock, and the TT gneisses in this microblock were subjected to generally amphibolite-facies metamorphism at ∼2520-2470 Ma. Based on the above Neoarchean crust-mantle thermal-dynamic processes, we propose that the Neoarchean magmatism and metamorphism in the Tangtu-Majuanzi microblock of North Liaoning Province occurred in an active continental margin.

The tectonic evolution of the Irtysh tectonic belt: New zircon U-Pb ages of arc-related and collisional granitoids in the Kalaxiangar tectonic belt, NW China

NASA Astrophysics Data System (ADS)

Hong, Tao; Klemd, Reiner; Gao, Jun; Xiang, Peng; Xu, Xing-Wang; You, Jun; Wang, Xin-Shui; Wu, Chu; Li, Hao; Ke, Qiang

2017-02-01

Precise geochronological constraints of the Irtysh tectonic belt situated between the Saur Island Arc and the Altay Terrane are crucial to a better understanding of the tectonic evolution of the Central Asian Orogenic Belt (CAOB). Recently, we discovered repeatedly deformed arc-related and collisional granitoids in the Kalaxiangar tectonic belt (KTB), which is located in the eastern part of the Irtysh tectonic belt. In this study, we report new whole-rock geochemical, zircon U-Pb and Hf isotopic data of the arc-related and collisional granitoids. Our data reveal that 1) arc-related granodioritic porphyries formed at ca. 382-374 Ma. Recrystallized zircon grains from a (ultra-)mylonitic granodiorite of the Laoshankou zone in the southern KTB display a U-Pb age of ca. 360 Ma; 2) syn-collisional granodioritic porphyries, which distribute along faults and parallel to the cleavage, were emplaced at ca. 367-356 Ma, with εHf(t) values varying from + 7.8 to + 14.2 and Hf model ages from 873 to 459 Ma; 3) a post-collisional A-type granodioritic porphyry, which crosscuts the NW-NNW trending schistosity of the metasedimentary country rocks at a low angle, has an age of ca. 324-320 Ma, while the εHf(t) values range from + 7.6 to + 14.4 with Hf model ages from 850 to 416 Ma; 4) post-collisional strike-slip A-type granite dykes, exposed along strike-slip faults, gave ages between 287 and 279 Ma, whereas the εHf(t) values range from + 4.9 to + 12.7 and the Hf model ages from 995 to 500 Ma; and 5) A-type biotite granite dykes, which intruded along conjugate tension joints, have ages of 274-271 Ma, and εHf(t) values from + 1.5 to + 13.2 with Hf model ages from 1196 to 454 Ma. Consequently, we propose that the collision between the Saur Island Arc and the Altay Terrane occurred in the Early Carboniferous (ca. 367-356 Ma) and the subsequent post-collisional tectonic process continued to the Late Carboniferous (ca. 324-320 Ma). It is further suggested that the Irtysh tectonic belt underwent large-scale strike-slip deformation during the mid-Permian between 287 and 279 Ma. The termination of the Irtysh tectonic belt orogeny is thought to have also occurred during the mid-Permian between 274 and 271 Ma.

Searching for Hysteresis in Models of Mantle Convection with Grain-Damage

NASA Astrophysics Data System (ADS)

Lamichhane, R.; Foley, B. J.

2017-12-01

The mode of surface tectonics on terrestrial planets is determined by whether mantle convective forces are capable of forming weak zones of localized deformation in the lithosphere, which act as plate boundaries. If plate boundaries can form then a plate tectonic mode develops, and if not convection will be in the stagnant lid regime. Episodic subduction or sluggish lid convection are also possible in between the nominal plate tectonic and stagnant lid regimes. Plate boundary formation is largely a function of the state of the mantle, e.g. mantle temperature or surface temperature, and how these conditions influence both mantle convection and the mantle rheology's propensity for forming weak, localized plate boundaries. However, a planet's tectonic mode also influences whether plate boundaries can form, as the driving forces for plate boundary formation (e.g. stress and viscous dissipation) are different in a plate tectonic versus stagnant lid regime. As a result, tectonic mode can display hysteresis, where convection under otherwise identical conditions can reach different final states as a result of the initial regime of convection. Previous work has explored this effect in pseudoplastic models, finding that it is more difficult to initiate plate tectonics starting from a stagnant lid state than it is to sustain plate tectonics when already in a mobile lid regime, because convective stresses in the lithosphere are lower in a stagnant lid regime than in a plate tectonic regime. However, whether and to what extent such hysteresis is displayed when alternative rheological models for lithospheric shear localization are used is unknown. In particular, grainsize reduction is commonly hypothesized to be a primary cause of shear localization and plate boundary formation. We use new models of mantle convection with grain-size evolution to determine how the initial mode of surface tectonics influences the final convective regime reached when convection reaches statistical steady-state. Scaling analysis is performed to quantify how subduction initiation from a stagnant lid differs from sustaining subduction in a mobile lid. The implications of our results for the evolution of the mode of surface tectonics on terrestrial planets will also be discussed.

Pit chains on Enceladus signal the recent tectonic dissection of the ancient cratered terrains

NASA Astrophysics Data System (ADS)

Martin, Emily S.; Kattenhorn, Simon A.; Collins, Geoffrey C.; Michaud, Robert L.; Pappalardo, Robert T.; Wyrick, Danielle Y.

2017-09-01

Enceladus is the first outer solar system body on which pit chains have been positively identified. We map the global distribution of pit chains and show that pit chains are among the youngest tectonic features on Enceladus's surface, concentrated in the cratered plains centered on Enceladus's Saturnian and anti-Saturnian hemispheres. Pit chains on Enceladus are interpreted as the surface expressions of subsurface dilational fractures underlying a cover of unconsolidated material, which we infer to be a geologically young cover of loose regolith that mantles the surface of Enceladus. A widespread layer of regolith may act to insulate the surface, which has implications for the thermal state of Enceladus's ice shell. The widespread distribution of pit chains across the cratered plains indicates that this ancient surface has recently been tectonically active.

Ancient plate kinematics derived from the deformation pattern of continental crust: Paleo- and Neo-Tethys opening coeval with prolonged Gondwana-Laurussia convergence

NASA Astrophysics Data System (ADS)

Kroner, Uwe; Roscher, Marco; Romer, Rolf L.

2016-06-01

The formation and destruction of supercontinents requires prolonged convergent tectonics between particular plates, followed by intra-continental extension during subsequent breakup stages. A specific feature of the Late Paleozoic supercontinent Pangea is the prolonged and diachronous formation of the collisional belts of the Rheic suture zone coeval with recurrent continental breakup and subsequent formation of the mid-ocean ridge systems of the Paleo- and Neo-Tethys oceans at the Devonian and Permian margins of the Gondwana plate, respectively. To decide whether these processes are causally related or not, it is necessary to accurately reconstruct the plate motion of Gondwana relative to Laurussia. Here we propose that the strain pattern preserved in the continental crust can be used for the reconstruction of ancient plate kinematics. We present Euler pole locations for the three fundamental stages of the Late Paleozoic assembly of Pangea and closure of the Rheic Ocean: (I) Early Devonian (ca. 400 Ma) collisional tectonics affected Gondwana at the Armorican Spur north of western Africa and at the promontory of the South China block/Australia of eastern Gondwana, resulting in the Variscan and the Qinling orogenies, respectively. The Euler pole of the rotational axis between Gondwana and Laurussia is positioned east of Gondwana close to Australia. (II) Continued subduction of the western Rheic Ocean initiates the clockwise rotation of Gondwana that is responsible for the separation of the South China block from Gondwana and the opening of Paleo-Tethys during the Late Devonian. The position of the rotational axis north of Africa reveals a shift of the Euler pole to the west. (III) The terminal closure of the Rheic Ocean resulted in the final tectonics of the Alleghanides, the Mauritanides and the Ouachita-Sonora-Marathon belt, occurred after the cessation of the Variscan orogeny in Central Europe, and is coeval with the formation of the Central European Extensional Province and the opening of Neo-Tethys at ca. 300 Ma. The Euler pole for the final closure of the Rheic Ocean is positioned near Oslo (Laurussia). Thus, the concomitant formation of convergent and divergent plate boundaries during the assembly of Pangea is due to the relocation of the particular rotational axis. From a geodynamic point of view, coupled collisional (western Pangea) and extensional tectonics (eastern Pangea) due to plate tectonic reorganization is fully explained by slab pull and ridge push forces.

Tectonic and climatic control on evolution of rift lakes in the Central Kenya Rift, East Africa

NASA Astrophysics Data System (ADS)

Bergner, A. G. N.; Strecker, M. R.; Trauth, M. H.; Deino, A.; Gasse, F.; Blisniuk, P.; Dühnforth, M.

2009-12-01

The long-term histories of the neighboring Nakuru-Elmenteita and Naivasha lake basins in the Central Kenya Rift illustrate the relative importance of tectonic versus climatic effects on rift-lake evolution and the formation of disparate sedimentary environments. Although modern climate conditions in the Central Kenya Rift are very similar for these basins, hydrology and hydrochemistry of present-day lakes Nakuru, Elmenteita and Naivasha contrast dramatically due to tectonically controlled differences in basin geometries, catchment size, and fluvial processes. In this study, we use eighteen 14C and 40Ar/ 39Ar dated fluvio-lacustrine sedimentary sections to unravel the spatiotemporal evolution of the lake basins in response to tectonic and climatic influences. We reconstruct paleoclimatic and ecological trends recorded in these basins based on fossil diatom assemblages and geologic field mapping. Our study shows a tendency towards increasing alkalinity and shrinkage of water bodies in both lake basins during the last million years. Ongoing volcano-tectonic segmentation of the lake basins, as well as reorganization of upstream drainage networks have led to contrasting hydrologic regimes with adjacent alkaline and freshwater conditions. During extreme wet periods in the past, such as during the early Holocene climate optimum, lake levels were high and all basins evolved toward freshwater systems. During drier periods some of these lakes revert back to alkaline conditions, while others maintain freshwater characteristics. Our results have important implications for the use and interpretation of lake sediment as climate archives in tectonically active regions and emphasize the need to deconvolve lacustrine records with respect to tectonics versus climatic forcing mechanisms.

Crustal and uppermost mantle structures of the South China from joint analysis of receiver functions and Rayleigh wave dispersions

NASA Astrophysics Data System (ADS)

Guo, Zhi; Gao, Xing; Li, Tong; Wang, Wei

2018-05-01

We use P-wave receiver function H-k stacking and joint inversion of receiver functions and Rayleigh wave dispersions to investigate crustal and uppermost mantle structure beneath the South China. The obtained results reveal prominent crustal structure variations in the study area, Moho depth increases from ∼30 km in the Cathaysia Block to more than ∼60 km in the eastern Tibetan Plateau. A Moho undulation and Vp/Vs ratio variations can be observed from the Cathaysia Block to Yangtze Craton. These observations consistent with the crustal structures predict by the flat slab subduction model. We interpret these lateral crustal structure variations reflect the tectonic evolution of the Yangtze Craton and Cathaysia Block prior the Mesozoic and the post-orogenic magmatism due to the breaking up of the subducted flat slab and subsequent slab rollback in the South China. The observed variations of the crustal structures not only reveal the lateral crustal inhomogeneity, but also provide constraints on the geodynamic evolution of the South China.

Paired Magmatic-Metallogenic Belts in Myanmar - an Andean Analogue?

NASA Astrophysics Data System (ADS)

Gardiner, Nicholas; Robb, Laurence; Searle, Michael; Morley, Christopher

2015-04-01

Myanmar (Burma) is richly endowed in precious and base metals, having one of the most diverse collections of natural resources in SE Asia. Its geological history is dominated by the staged closing of Tethys and the suturing of Gondwana-derived continental fragments onto the South China craton during the Mesozoic-Cenozoic. The country is located at a crucial geologic juncture where the main convergent Tethyan collision zone swings south around the Namche Barwa Eastern Himalayan syntaxis. However, despite recent work, the geological and geodynamic history of Myanmar remains enigmatic. Plate margin processes, magmatism, metasomatism and the genesis of mineral deposits are intricately linked, and there has long been recognized a relationship between the distribution of certain mineral deposit types, and the tectonic settings which favour their genesis. A better knowledge of the regional tectonic evolution of a potential exploration jurisdiction is therefore crucial to understanding its minerals prospectivity. This strong association between tectonics and mineralization can equally be applied in reverse. By mapping out the spatial, and temporal, distribution of presumed co-genetic mineral deposits, coupled with an understanding of their collective metallogenetic origin, a better appreciation of the tectonic evolution of a terrane may be elucidated. Identification and categorization of metallotects within a geodynamically-evolving terrane thus provides a complimentary tool to other methodologies (e.g. geochemical, geochronological, structural, geophysical, stratigraphical), for determining the tectonic history and inferred geodynamic setting of that terrane through time. Myanmar is one such study area where this approach can be undertaken. Here are found two near-parallel magmatic belts, which together contain a significant proportion of that country's mineral wealth of tin, tungsten, copper, gold and silver. Although only a few 100 km's apart, these belts exhibit a contrasting minerals endowment. The Mogok-Mandalay-Mergui (MMM) Belt hosts crustal-melt S-type granites with significant tin-tungsten mineralization, and contains the historically major tungsten deposit of Mawchi. The Wuntho-Popa Arc comprises I-type granites and granodiorites with porphyry-type copper-gold and epithermal gold mineralization, and includes the world-class Monywa copper mine. Recent U-Pb radiometric age dating has shown the potential for the two belts to be both active from the Late Cretaceous to Eocene. The spatial juxtaposition of these two sub-parallel belts, the implication of contemporary magmatism, and their distinct but consistent metallogenic endowment bears strong similarities to the metallogenic belts of the South American Cordillera. Here we investigate whether they together represent the magmatic and metallogenic expression of an Andean-type setting in Myanmar during the subduction of Neo-Tethys. In this analogue the Wuntho-Popa Arc represents a proximal I-type magmatic belt sited immediately above the eastwards-verging Neo-Tethys subduction zone. Exhibiting porphyry-type copper-gold and epithermal gold mineralization, this would therefore be the Myanmar equivalent of the Andean coastal copper belts. Conversely, the parallel MMM Belt, comprised of more distal crustal-melt S-type tin granites, would have an analogue in the Bolivian tin belt.

Assets for Children: Experiences in Asia and Implications for China

ERIC Educational Resources Information Center

Zou, Li; Sherraden, Michael

2010-01-01

A growing number of national and local governments view child development accounts (CDAs) as an innovative policy tool for social and economic development. This article reviews the global landscape of CDAs, presents three CDA policy cases from Asia, analyzes main themes and discusses potential implications for China. (Contains 1 table.)

Komatiite genesis in the Archaean mantle, with implications for the tectonics of Archaean greenstone belts

NASA Technical Reports Server (NTRS)

Elthon, D.

1986-01-01

The presence of ultramafic lavas (komatiites) associated with Archean greenstone belts has been suggested to indicate very high increments (50-80%) of partial melting of the Archean mantle. Such extensive melting of the Earth's mantle during the Archean might have profound effects on the early tectonic and chemical evolution of the planet, although problems associated with keeping the komatiite liquid in equilibrium with the residual mantle at such high increments of melting has cast doubt upon aspects of extensive melting. Two important aspects of the origin of komatiites are discussed below.

Recent developments in understanding the tectonic evolution of the Southern California offshore area: Implications for earthquake-hazard analysis

USGS Publications Warehouse

Fisher, M.A.; Langenheim, V.E.; Nicholson, C.; Ryan, H.F.; Sliter, R.W.

2009-01-01

During late Mesozoic and Cenozoic time, three main tectonic episodes affected the Southern California offshore area. Each episode imposed its unique structural imprint such that early-formed structures controlled or at least influenced the location and development of later ones. This cascaded structural inheritance greatly complicates analysis of the extent, orientation, and activity of modern faults. These fault attributes play key roles in estimates of earthquake magnitude and recurrence interval. Hence, understanding the earthquake hazard posed by offshore and coastal faults requires an understanding of the history of structural inheritance and modifi-cation. In this report we review recent (mainly since 1987) findings about the tectonic development of the Southern California offshore area and use analog models of fault deformation as guides to comprehend the bewildering variety of offshore structures that developed over time. This report also provides a background in regional tectonics for other chapters in this section that deal with the threat from offshore geologic hazards in Southern California. ?? 2009 The Geological Society of America.

Cenozoic sedimentation in the Mumbai Offshore Basin: Implications for tectonic evolution of the western continental margin of India

NASA Astrophysics Data System (ADS)

Nair, Nisha; Pandey, Dhananjai K.

2018-02-01

Interpretation of multichannel seismic reflection data along the Mumbai Offshore Basin (MOB) revealed the tectonic processes that led to the development of sedimentary basins during Cenozoic evolution. Structural interpretation along three selected MCS profiles from MOB revealed seven major sedimentary sequences (∼3.0 s TWT, thick) and the associated complex fault patterns. These stratigraphic sequences are interpreted to host detritus of syn- to post rift events during rift-drift process. The acoustic basement appeared to be faulted with interspaced intrusive bodies. The sections also depicted the presence of slumping of sediments, subsidence, marginal basins, rollover anticlines, mud diapirs etc accompanied by normal to thrust faults related to recent tectonics. Presence of upthrusts in the slope region marks the locations of local compression during collision. Forward gravity modeling constrained with results from seismic and drill results, revealed that the crustal structure beneath the MOB has undergone an extensional type tectonics intruded with intrusive bodies. Results from the seismo-gravity modeling in association with litholog data from drilled wells from the western continental margin of India (WCMI) are presented here.

Magnesium Isotopic Compositions of Continental Basalts From Various Tectonic Settings

NASA Astrophysics Data System (ADS)

Yang, W.; Li, S.; Tian, H.; Ke, S.

2016-12-01

Recycled sedimentary carbonate through subduction is the main light Mg isotopic reservoir in Earth's deep interior, thus Mg isotopic variation of mantle-derived melts provides a fresh perspective on investigating deep carbon cycling. Here we investigate Mg isotopic compositions of continental basalts from various tectonic settings: (1) The Cenozoic basalts from eastern China, coinciding with the stagnant Pacific slab in the mantle transition zone revealed by seismic tomography; (2) The Cenozoic basalts from Tengchong area, southwestern China, which comprises a crucial part of the collision zone between the Indian and Eurasian plates; (3) The Permian basalts from Emeishan large igneous province, related to a mantle plume. The Cenozoic basalts from both eastern China and Tengchong area exhibit light Mg isotopic compositions (δ26Mg = -0.60 to -0.30‰ and -0.51 to -0.33‰), suggesting recycled sedimentary carbonates in their mantle sources. This is supported by their low Fe/Mn, high CaO/Al2O3, low Hf/Hf* and low Ti/Ti* ratios, which are typical features of carbonated peridotite-derived melt. The Tengchong basalts also show high 87Sr/86Sr, high radiogenic Pb and upper crustal-like trace element pattern, indicating contribution of recycled continental crustal materials. By contrast, all Emeishan basalts display a mantle-like Mg isotopic composition, with δ26Mg ranging from -0.35 to -0.19‰. Since the Emeishan basalts derived from a mantle plume, their mantle-like Mg isotopic composition may indicate limited sedimentary carbonated recycled into the lower mantle. This is consistent with a recent experimental study which concluded that direct recycling of carbon into the lower mantle may have been highly restricted throughout most of the Earth's history.

Recent Multidisciplinary Research Initiatives and IODP Drilling in the South China Sea

NASA Astrophysics Data System (ADS)

Lin, J.; Li, C. F.; Wang, P.; Kulhanek, D. K.

2016-12-01

The South China Sea (SCS) is the largest low-latitude marginal sea in the world. Its formation and evolution are linked to the complex continental-oceanic tectonic interaction of the Eurasian, Pacific, and Indo-Australian plates. Despite its relatively small size and short history, the SCS has undergone nearly a complete Wilson cycle from continental break-up to seafloor spreading to subduction, serving as a natural laboratory for studying the linkages between tectonic, volcanic, and oceanic processes. The last several years have witnessed significant progress in investigation of the SCS through comprehensive research programs using multidisciplinary approaches and enhanced international collaboration. The International Ocean Discovery Program (IODP) Expedition 349 drilled and cored five sites in the SCS in 2014. The expedition successfully obtained the first basaltic rock samples of the SCS relict spreading center, discovered large and frequent deep-sea turbidity events, and sampled multiple seamount volcaniclastic layers. In addition, high-resolution near-seafloor magnetic surveys were conducted in the SCS with survey lines passing near some of the IODP drilling sites. Together the IODP drilling and deep-tow magnetic survey results confirmed, for the first time, that the entire SCS basin might have stopped seafloor spreading at similar ages in early Miocene, providing important constraints on marginal sea geodynamic models. In 2007, IODP Expeditions 367 and 368 will drill the northern margin of the SCS to investigate the mechanisms of rifting to spreading processes. Meanwhile, major progress in studying the SCS processes has also been made through comprehensive multidisciplinary programs, for example, the eight-year-long "South China Sea Deep" initiative, which also supports and encourages strong international collaboration. This presentation will highlight the recent multidisciplinary research initiatives in investigation of the SCS and the important role of international collaboration.

Coseismic landslides reveal near-surface rock strength in a high-relief tectonically active setting

USGS Publications Warehouse

Gallen, Sean F.; Clark, Marin K.; Godt, Jonathan W.

2014-01-01

We present quantitative estimates of near-surface rock strength relevant to landscape evolution and landslide hazard assessment for 15 geologic map units of the Longmen Shan, China. Strength estimates are derived from a novel method that inverts earthquake peak ground acceleration models and coseismic landslide inventories to obtain material proper- ties and landslide thickness. Aggregate rock strength is determined by prescribing a friction angle of 30° and solving for effective cohesion. Effective cohesion ranges are from 70 kPa to 107 kPa for 15 geologic map units, and are approximately an order of magnitude less than typical laboratory measurements, probably because laboratory tests on hand-sized specimens do not incorporate the effects of heterogeneity and fracturing that likely control near-surface strength at the hillslope scale. We find that strength among the geologic map units studied varies by less than a factor of two. However, increased weakening of units with proximity to the range front, where precipitation and active fault density are the greatest, suggests that cli- matic and tectonic factors overwhelm lithologic differences in rock strength in this high-relief tectonically active setting.

Linking the southern West Junggar terrane to the Yili Block: Insights from the oldest accretionary complexes in West Junggar, NW China

NASA Astrophysics Data System (ADS)

Ren, Rong; Han, Bao-Fu; Guan, Shu-Wei; Liu, Bo; Wang, Zeng-Zhen

2018-06-01

West Junggar is known to tectonically correlate with East Kazakhstan; however, the tectonic link of the southern West Junggar terrane to adjacent regions still remains uncertain. Here, we examined the oldest accretionary complexes, thus constraining its tectonic evolution and link during the Early-Middle Paleozoic. They have contrasting lithologic, geochemical, and geochronological features and thus, provenances and tectonic settings. The Laba Unit was derived from the Late Ordovician-Early Devonian continental arc system (peaking at 450-420 Ma) with Precambrian substrate, which formed as early as the Early Devonian and metamorphosed during the Permian; however, the Kekeshayi Unit was accumulated in an intra-oceanic arc setting, and includes the pre-Late Silurian and Late Silurian subunits with or without Precambrian sources. Integrated with the regional data, the southern West Junggar terrane revealed a tectonic link to the northern Yili Block during the Late Silurian to Early Devonian, as suggested by the comparable Precambrian zircon age spectra between the southern West Junggar terrane and the micro-continents in the southern Kazakhstan Orocline, the proximal accumulation of the Laba Unit in the continental arc atop the Yili Block, and the sudden appearance of Precambrian zircons in the Kekeshayi Unit during the Late Silurian. This link rejects the proposals of the southern West Junggar terrane as an extension of the northern Kazakhstan Orocline and the Middle Paleozoic amalgamation of West Junggar. A new linking model is thus proposed, in which the southern West Junggar terrane first evolved individually, and then collided with the Yili Block to constitute the Kazakhstan continent during the Late Silurian. The independent and contrasting intra-oceanic and continental arcs also support the Paleozoic archipelago-type evolution of the Central Asian Orogenic Belt.

The mantle lithosphere and the Wilson Cycle

NASA Astrophysics Data System (ADS)

Heron, Philip; Pysklywec, Russell; Stephenson, Randell

2017-04-01

In the view of the conventional theory of plate tectonics (e.g., the Wilson Cycle), crustal inheritance is often considered important in tectonic evolution. However, the role of the mantle lithosphere is usually overlooked due to its difficulty to image and uncertainty in rheological makeup. Deep seismic imaging has shown potential scarring in continental mantle lithosphere to be ubiquitous. Recent studies have interpreted mantle lithosphere heterogeneities to be pre-existing structures, and as such linked to the Wilson Cycle and inheritance. In our study, we analyze intraplate deformation driven by mantle lithosphere heterogeneities from ancient Wilson Cycle processes and compare this to crustal inheritance deformation. We present 2-D numerical experiments of continental convergence to generate intraplate deformation, exploring the limits of continental rheology to understand the dominant lithosphere layer across a broad range of geological settings. By implementing a "jelly sandwich" rheology, characteristic of stable continental lithosphere, we find that during compression the strength of the mantle lithosphere is integral in controlling deformation from a structural anomaly. We posit that if the continental mantle is the strongest layer within the lithosphere, then such inheritance may have important implications for the Wilson Cycle. Furthermore, our models show that deformation driven by mantle lithosphere scarring can produce tectonic patterns related to intraplate orogenesis originating from crustal sources, highlighting the need for a more formal discussion of the role of the mantle lithosphere in plate tectonics. We outline the difficulty in unravelling the causes of tectonic deformation, alongside discussing the role of deep lithosphere processes in plate tectonics.

Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution

NASA Astrophysics Data System (ADS)

Foley, Bradford J.; Driscoll, Peter E.

2016-05-01

Earth's climate, mantle, and core interact over geologic time scales. Climate influences whether plate tectonics can take place on a planet, with cool climates being favorable for plate tectonics because they enhance stresses in the lithosphere, suppress plate boundary annealing, and promote hydration and weakening of the lithosphere. Plate tectonics plays a vital role in the long-term carbon cycle, which helps to maintain a temperate climate. Plate tectonics provides long-term cooling of the core, which is vital for generating a magnetic field, and the magnetic field is capable of shielding atmospheric volatiles from the solar wind. Coupling between climate, mantle, and core can potentially explain the divergent evolution of Earth and Venus. As Venus lies too close to the sun for liquid water to exist, there is no long-term carbon cycle and thus an extremely hot climate. Therefore, plate tectonics cannot operate and a long-lived core dynamo cannot be sustained due to insufficient core cooling. On planets within the habitable zone where liquid water is possible, a wide range of evolutionary scenarios can take place depending on initial atmospheric composition, bulk volatile content, or the timing of when plate tectonics initiates, among other factors. Many of these evolutionary trajectories would render the planet uninhabitable. However, there is still significant uncertainty over the nature of the coupling between climate, mantle, and core. Future work is needed to constrain potential evolutionary scenarios and the likelihood of an Earth-like evolution.

Sea level and shoreline reconstructions for the Red Sea: isostatic and tectonic considerations and implications for hominin migration out of Africa

NASA Astrophysics Data System (ADS)

Lambeck, Kurt; Purcell, Anthony; Flemming, Nicholas. C.; Vita-Finzi, Claudio; Alsharekh, Abdullah M.; Bailey, Geoffrey N.

2011-12-01

The history of sea level within the Red Sea basin impinges on several areas of research. For archaeology and prehistory, past sea levels of the southern sector define possible pathways of human dispersal out of Africa. For tectonics, the interglacial sea levels provide estimates of rates for vertical tectonics. For global sea level studies, the Red Sea sediments contain a significant record of changing water chemistry with implications on the mass exchange between oceans and ice sheets during glacial cycles. And, because of its geometry and location, the Red Sea provides a test laboratory for models of glacio-hydro-isostasy. The Red Sea margins contain incomplete records of sea level for the Late Holocene, for the Last Glacial Maximum, for the Last Interglacial and for earlier interglacials. These are usually interpreted in terms of tectonics and ocean volume changes but it is shown here that the glacio-hydro-isostatic process is an additional important component with characteristic spatial variability. Through an iterative analysis of the Holocene and interglacial evidence a separation of the tectonic, isostatic and eustatic contributions is possible and we present a predictive model for palaeo-shorelines and water depths for a time interval encompassing the period proposed for migrations of modern humans out of Africa. Principal conclusions include the following. (i) Late Holocene sea level signals evolve along the length of the Red Sea, with characteristic mid-Holocene highstands not developing in the central part. (ii) Last Interglacial sea level signals are also location dependent and, in the absence of tectonics, are not predicted to occur more than 1-2 m above present sea level. (iii) For both periods, Red Sea levels at 'expected far-field' elevations are not necessarily indicative of tectonic stability and the evidence points to a long-wavelength tectonic uplift component along both the African and Arabian northern and central sides of the Red Sea. (iv) The observational evidence is consistent with tectonic and isostatic processes both operating over the past 300,000 years without requiring changes in the time averaged (over a few thousand years) tectonic rates. (v) Recent bathymetric data for the Bab al Mandab region have been compiled to confirm the location and depth of the sill controlling flow in and out of the Red Sea. Throughout the last 400,000 years the Red Sea has remained open to the Gulf of Aden with cross sectional areas at times of glacial maxima about 2% of that today. (vi) The minimum channel widths connecting the Red Sea to the Gulf of Aden at times of lowstand occur south of the Hanish Sill. The channels are less than 4 km wide and remain narrow for as long as local sea levels are below -50 m. This occurs for a number of sustained periods during the last two glacial cycles and earlier. (vii) Periods suitable for crossing between Africa and Arabia without requiring seaworthy boats or seafaring skills occurred periodically throughout the Pleistocene, particularly at times of favourable environmental climatic conditions that occurred during times of sea level lowstand.

Ages of the Xinghuadukou Group in the Erguna Block, NE China

NASA Astrophysics Data System (ADS)

Liu, X.; Hou, W.

2016-12-01

The Xinghuadukou group is outcropped in the Erguna block (EB) of NE China, which is an important component of the eastern segment of the Central Asian Orogenic Belt (CAOB). This group was previously classified as Paleoproterozoic in age. However, recent studies reported Paleozoic ages from the meta-volcanic rocks, Paleoproterozoic to Neoarchean detrital zircon ages from the meta-sedimentary rocks and Neoproterozoic ages from the granitoids. The tectonic affinity of the EB is still debated. In order to clarify the aforementioned issues, 19 samples were collected from the Xinghuadukou group from the Mohe region in NE China. All samples underwent gneiss facies metamorphism, including two-mica granitic gneiss and quartz biotite gneiss. Based on the protolith discrimination diagram of Si—(al+fm)-(c+alk) system, 7 samples originated from sedimentary rocks and the other 12 of igneous origin. The orthogneiss samples were plotted as diorite, granodiorite and granite respectively in TAS, showing felsic character (SiO2 57% - 74%). One orthogneiss and one paragneiss samples were chosen to conduct the LA-ICP-MS U-Pb zircon age analysis. Apart from one zircon with the age of 742 Ma shows evident metamorphic rim, all zircons from the orthogneiss show euhedral to subhedral prismatic shape and typical concentric or oscillatory structure indicating the igneous origin. The concordant age of 2478±26 Ma was generated, indicating the existence of the near Archean basement of the EB. The detrital zircons from the paragneiss produced age populations cluster at 0.6, 0.8, 1.9, 2.6 and 2.7 Ga, lacking of the Grenville event age. The youngest zircon age is 395 Ma, taken as the maximum depositional age of the sedimentary protolith. According to the new data obtained, it is suggested that the Xinghuadukou group comprises the early Paleoproterozoic granite-gneiss, which proves the granitic basement of the Erguna block. The sedimentary rocks formed overlying the basement during the early Paleozoic and underwent metamorphism afterward. Compared with the detrital zircon ages profile of S. Siberia, NCC, Tarim, Mongolia and NE Gondwana, the EB is suggested most likely affiliated with NE Gondwana. Therefore, this study prefers a tectonic scenario that the EB drifted from the NE Gondwana and joined the CAOB tectonic domain during the Paleozoic.

Basement and crustal structure of the Davis Sea region (East Antarctica): implications for tectonic setting and continent to oceanic boundary definition

USGS Publications Warehouse

Guseva, Y.B.; Leitchenkov, G.L.; Gandyukhin, V.V.; Ivanov, S.V.

2007-01-01

This study is based on about 8400 km of MCS, magnetic and gravity data as well as 20 sonobuoys collected by the Russian Antarctic Expedition during 2003 and 2004 in the Davis Sea and adjacent areas between 80°E and 102°E. Major tectonic provinces and features are identified and mapped in the study region including: 1) A marginal rift with a the extended continental crust ranging 130 to more than 200 km in width; 2) The marginal volcanic plateau of the Bruce Bank consisting of the Early Cretaceous igneous rocks; 3) The Early Cretaceous and Late Cretaceous−Paleogene oceanic basins; and 4) The Early Cretaceous igneous province of the Kerguelen Plateau. Four major horizons identified in the sedimentary cover of the Davis Sea region are attributed to main tectonic events and/or paleoenvironmental changes.

Biogeographical Consequences of Cenozoic Tectonic Events within East Asian Margins: A Case Study of Hynobius Biogeography

PubMed Central

Li, Jun; Fu, Cuizhang; Lei, Guangchun

2011-01-01

Few studies have explored the role of Cenozoic tectonic evolution in shaping patterns and processes of extant animal distributions within East Asian margins. We select Hynobius salamanders (Amphibia: Hynobiidae) as a model to examine biogeographical consequences of Cenozoic tectonic events within East Asian margins. First, we use GenBank molecular data to reconstruct phylogenetic interrelationships of Hynobius by Bayesian and maximum likelihood analyses. Second, we estimate the divergence time using the Bayesian relaxed clock approach and infer dispersal/vicariance histories under the ‘dispersal–extinction–cladogenesis’ model. Finally, we test whether evolutionary history and biogeographical processes of Hynobius should coincide with the predictions of two major hypotheses (the ‘vicariance’/‘out of southwestern Japan’ hypothesis). The resulting phylogeny confirmed Hynobius as a monophyletic group, which could be divided into nine major clades associated with six geographical areas. Our results show that: (1) the most recent common ancestor of Hynobius was distributed in southwestern Japan and Hokkaido Island, (2) a sister taxon relationship between Hynobius retardatus and all remaining species was the results of a vicariance event between Hokkaido Island and southwestern Japan in the Middle Eocene, (3) ancestral Hynobius in southwestern Japan dispersed into the Taiwan Island, central China, ‘Korean Peninsula and northeastern China’ as well as northeastern Honshu during the Late Eocene–Late Miocene. Our findings suggest that Cenozoic tectonic evolution plays an important role in shaping disjunctive distributions of extant Hynobius within East Asian margins. PMID:21738684

Morphotectonic study of the Brahmaputra basin using geoinformatics

NASA Astrophysics Data System (ADS)

Nath Sarma, Jogendra; Acharjee, Shukla; murgante, Beniamino

2013-04-01

The Brahmaputra River basin occupies an area of 580,000 km2 lying in Tibet (China), Bhutan, India and Bangladesh. It is bounded on the north by the Nyen-Chen-Tanghla mountains, on the east by the Salween River basin and Patkari range of hills, on the south by Nepal Himalayas and the Naga Hills and on the west by the Ganga sub-basin. Brahmaputra river originates at an elevation of about 5150 m in south-west Tibet and flows for about 2900 km through Tibet (China), India and Bangladesh to join the Ganga.. The Brahmaputra River basin is investigated to examine the influence of active structures by applying an integrated study on geomorphology, morphotectonics, Digital Elevation Model (DEM) using topographic map, satellite data, SRTM, and seismic data. The indices for morphotectonic analysis, viz. basin elongation ratio (Re) indicated tectonically active, transverse topographic symmetry (T = 0.018-0.664) indicated asymmetric nature, asymmetric factor (AF=33) suggested tilt, valley floor width to valley height ratio (Vf = 0.0013-2.945) indicated active incision and mountain-front sinuosity (Smf = 1.11-1.68) values indicated active tectonics in the area. A great or major earthquake in the modern times, in this region may create havoc with huge loss of life and property due to high population density and rapidly developing infrastructure. Keywords: .Morphotectonic, Brahmaputra river, earthquake

Spatial variation of present-day stress field and tectonic regime in Tunisia and surroundings from formal inversion of focal mechanisms: Geodynamic implications for central Mediterranean

NASA Astrophysics Data System (ADS)

Soumaya, Abdelkader; Ben Ayed, Noureddine; Delvaux, Damien; Ghanmi, Mohamed

2015-06-01

We compiled 123 focal mechanisms from various sources for Tunisia and adjacent regions up to Sicily, to image the current stress field in the Maghrebides chain (from Tunisia to Sicily) and its foreland. Stress inversion of all the available data provides a first-order stress field with a N150°E horizontal compression (SHmax) and a transpressional tectonic regime, but the obtained stress tensor poorly fit to the data set. We separated them into regional subsets (boxes) in function of their geographical proximity, kinematic regime, homogeneity of kinematic orientations, and tectonic setting. Their respective inversion evidences second- and third-order spatial variations in tectonic regime and horizontal stress directions. The stress field gradually changes from compression in the Maghrebides thrust belt to transpression and strike slip in the Atlassic and Pelagian foreland, respectively, where preexisting NW-SE to E-W deep faults system are reactivated. This spatial variation of the sismotectonic stress field and tectonic regime is consistent with the neotectonic stress field determined by others from fault slip data. The major Slab Transfer Edge Propagator faults (i.e., North-South Axis-Hammamet relay and Malte Escarpment), which laterally delimit the subducting slabs, play an active role in second- and third-order lateral variations of the tectonic regime and stress field orientations over the Tunisian/Sicilian domain. The past and current tectonic deformations and kinematics of the central Mediterranean are subordinately guided by the plate convergence (i.e., Africa-Eurasia), controlled or influenced by lateral slab migration/segmentation and by deep dynamics such as lithosphere-mantle interaction.

On the evolution of the geothermal regime of the North China Basin

NASA Astrophysics Data System (ADS)

Wang, Ji-yang; Chen, Mo-xiang; Wang, Ji-an; Deng, Xiao

1985-12-01

Recent heat flow and regional geothermal studies indicate that the North China Basin is characterized by relatively high heat flow compared with most stable areas in other parts of the world, but lower heat flow than most active tectonic areas. Measured heat flow values range from 61 to 74 mW m -2. The temperature at a depth of 2000 m is generally in the range 75 to 85°C, but sometimes is 90°C or higher. The geothermal gradient in Cenozoic sediments is in the range 30 to 40°C/km for most of the area. The calculated temperature at the Moho is 560 and 640°C for surface heat flow values of 63 and 71 mW m -2, respectively. These thermal data are consistent with other geophysical observations for the North China Basin. Relatively high heat flow in this area is related to Late Cretaceous-Paleogene rifting as described in this paper.

Oligocene-miocene mammalian fossils from Hongyazi Basin and its bearing on tectonics of Danghe Nanshan in northern Tibetan plateau.

PubMed

Li, Qiang; Wang, Xiaoming; Xie, Guangpu; Yin, An

2013-01-01

A shortage of Cenozoic vertebrate fossils in the Tibetan Plateau has been an obstacle in our understanding of biological evolution in response to changes in tectonism, topography, and environment. This is especially true for Paleogene records, so far known by only two sites along the northern rim of the Plateau. We report a Hongyazi Basin in northern Tibetan Plateau that produces at least three mammalian faunas that span Oligocene through late Miocene. Located at the foothills of the Danghe Nanshan and presently connected to the northern margin of the Suganhu Basin through the Greater Haltang River, the intermountain basin is controlled by the tectonics of the Danghe Nanshan to the north and Chahan'ebotu Mountain to the south, making the basin sediments well suited for inferring the evolutionary history of these two mountain ranges. At the bottom of the local section, the Oligocene Haltang Fauna is best compared to the early Oligocene Desmatolagus-Karakoromys decessus assemblage in the Dingdanggou Fauna in Tabenbuluk Basin. The Middle Miocene Ebotu Fauna from the middle Hongyazi section shares many taxa with the late Middle Miocene Tunggur mammal assemblage in Inner Mongolia, such as Heterosminthus orientalis, Megacricetodon sinensis, Democricetodon lindsayi, and Alloptox gobiensis. Toward the top of the section, the Hongyazi Fauna includes late Miocene elements typical of Hipparion faunas of North China. All three faunas are of typical North China-Central Asian characteristics, suggesting a lack of geographic barriers for faunal differentiation through the late Miocene. Sedimentary packages producing these faunas are arrayed from north to south in progressively younger strata, consistent with a compressive regime to accommodate shortening between Danghe Nanshan and Chahan'ebotu Mountain by thrust faults and folds. With additional constraints from vertebrate fossils along the northern flanks of the Danghe Nanshan, an eastward propagation of the Danghe Nanshan is postulated.

Oligocene-Miocene Mammalian Fossils from Hongyazi Basin and Its Bearing on Tectonics of Danghe Nanshan in Northern Tibetan Plateau

PubMed Central

Li, Qiang; Wang, Xiaoming; Xie, Guangpu; Yin, An

2013-01-01

A shortage of Cenozoic vertebrate fossils in the Tibetan Plateau has been an obstacle in our understanding of biological evolution in response to changes in tectonism, topography, and environment. This is especially true for Paleogene records, so far known by only two sites along the northern rim of the Plateau. We report a Hongyazi Basin in northern Tibetan Plateau that produces at least three mammalian faunas that span Oligocene through late Miocene. Located at the foothills of the Danghe Nanshan and presently connected to the northern margin of the Suganhu Basin through the Greater Haltang River, the intermountain basin is controlled by the tectonics of the Danghe Nanshan to the north and Chahan’ebotu Mountain to the south, making the basin sediments well suited for inferring the evolutionary history of these two mountain ranges. At the bottom of the local section, the Oligocene Haltang Fauna is best compared to the early Oligocene Desmatolagus-Karakoromys decessus assemblage in the Dingdanggou Fauna in Tabenbuluk Basin. The Middle Miocene Ebotu Fauna from the middle Hongyazi section shares many taxa with the late Middle Miocene Tunggur mammal assemblage in Inner Mongolia, such as Heterosminthus orientalis, Megacricetodon sinensis, Democricetodon lindsayi, and Alloptox gobiensis. Toward the top of the section, the Hongyazi Fauna includes late Miocene elements typical of Hipparion faunas of North China. All three faunas are of typical North China-Central Asian characteristics, suggesting a lack of geographic barriers for faunal differentiation through the late Miocene. Sedimentary packages producing these faunas are arrayed from north to south in progressively younger strata, consistent with a compressive regime to accommodate shortening between Danghe Nanshan and Chahan’ebotu Mountain by thrust faults and folds. With additional constraints from vertebrate fossils along the northern flanks of the Danghe Nanshan, an eastward propagation of the Danghe Nanshan is postulated. PMID:24376585

Chronology, geochemistry and Sr-Nd isotope studies of Jurassic intrusions in the Diyanqinamu porphyry Mo mine, central Inner Mongolia, China

NASA Astrophysics Data System (ADS)

Sun, Hairui; Huang, Zhilong; Li, Wenbo; Leng, Chengbiao; Ma, Deyun; Zhang, Xingchun

2014-07-01

Available cores of porphyritic granite and aplitic granite from the Diyanqinamu porphyry Mo deposit in the north central Great Xing’an Range presented an opportunity to examine and analyze Mesozoic igneous rocks far from the Paleo-Pacific subduction zone. The Diyanqinamu granites are highly fractionated I-type, distinguished from the M-, A- or S-type granite by: high SiO2, and Rb; low Zr, Nb, Y, and Ce; low Fe2O3total/MgO and (K2O + Na2O)/CaO ratios; low alumina saturation index (<1.1); low initial ISr ratios (0.70137-0.70451); positive εNd(t) values (2.37-3.77); and negative correlation between P2O5 and SiO2. The aplitic granites were generated by fractional crystallization of the porphyritic granite, as evidenced by: spatial proximity; consistent zircon U-Pb ages (156 Ma) within error; correlations between other oxides and SiO2 in Haker diagrams; low Ba, Sr, Nb, P, Ti, Eu; linear relationship in both (La/Yb)N vs. La and Sr vs. Ba diagrams; and, decreasing LREE and ∑REE with increasing SiO2. The Diyanqinamu granites have young depleted-mantle two-stage model ages (avg. TDM2 = 660 Ma) similar to those of most Mesozoic voluminous felsic magmas in northeastern China, and were likely sourced from pre-existent crustal components both “old” and juvenile that had been juxtaposed during the tectonic evolution of the Paleo-Asian Ocean. These granites project in the transitional field from syn-collision to post-collision tectonic settings on tectonic discrimination diagrams, implying emplacement in an extensional environment. Extensional volcanism and basin formation in the Great Xing’an Range region in Late Jurassic is coeval with the Diyanqinamu granites, demonstrating that post-orogenic lithospheric extension related to the closure of the Mongol-Okhotsk Ocean was the main driving force for Late Jurassic magmatism in this region.

Mongolian Oil Shale, hosted in Mesozoic Sedimentary Basins

NASA Astrophysics Data System (ADS)

Bat-Orshikh, E.; Lee, I.; Norov, B.; Batsaikhan, M.

2016-12-01

Mongolia contains several Mesozoic sedimentary basins, which filled >2000 m thick non-marine successions. Late Triassic-Middle Jurassic foreland basins were formed under compression tectonic conditions, whereas Late Jurassic-Early Cretaceous rift valleys were formed through extension tectonics. Also, large areas of China were affected by these tectonic events. The sedimentary basins in China host prolific petroleum and oil shale resources. Similarly, Mongolian basins contain hundreds meter thick oil shale as well as oil fields. However, petroleum system and oil shale geology of Mongolia remain not well known due to lack of survey. Mongolian oil shale deposits and occurrences, hosted in Middle Jurassic and Lower Cretaceous units, are classified into thirteen oil shale-bearing basins, of which oil shale resources were estimated to be 787 Bt. Jurassic oil shale has been identified in central Mongolia, while Lower Cretaceous oil shale is distributed in eastern Mongolia. Lithologically, Jurassic and Cretaceous oil shale-bearing units (up to 700 m thick) are similar, composed mainly of alternating beds of oil shale, dolomotic marl, siltstone and sandstone, representing lacustrine facies. Both Jurassic and Cretaceous oil shales are characterized by Type I kerogen with high TOC contents, up to 35.6% and low sulfur contents ranging from 0.1% to 1.5%. Moreover, S2 values of oil shales are up to 146 kg/t. The numbers indicate that the oil shales are high quality, oil prone source rocks. The Tmax values of samples range from 410 to 447, suggesting immature to early oil window maturity levels. PI values are consistent with this interpretation, ranging from 0.01 to 0.03. According to bulk geochemistry data, Jurassic and Cretaceous oil shales are identical, high quality petroleum source rocks. However, previous studies indicate that known oil fields in Eastern Mongolia were originated from Lower Cretaceous oil shales. Thus, further detailed studies on Jurassic oil shale and its petroleum potential are required.

Preliminary northeast Asia geodynamics map

USGS Publications Warehouse

Parfenov, Leonid M.; Khanchuk, Alexander I.; Badarch, Gombosuren; Miller, Robert J.; Naumova, Vera V.; Nokleberg, Warren J.; Ogasawara, Masatsugu; Prokopiev, Andrei V.; Yan, Hongquan

2003-01-01

This map portrays the geodynamics of Northeast Asia at a scale of 1:5,000,000 using the concepts of plate tectonics and analysis of terranes and overlap assemblages. The map is the result of a detailed compilation and synthesis at 5 million scale and is part of a major international collaborative study of the Mineral Resources, Metallogenesis, and Tectonics of Northeast Asia conducted from 1997 through 2002 by geologists from earth science agencies and universities in Russia, Mongolia, Northeastern China, South Korea, Japan, and the USA. This map is the result of extensive geologic mapping and associated tectonic studies in Northeast Asia in the last few decades and is the first collaborative compilation of the geology of the region at a scale of 1:5,000,000 by geologists from Russia, Mongolia, Northeastern China, South Korea, Japan, and the USA. The map was compiled by a large group of international geologists using the below concepts and definitions during collaborative workshops over a six-year period. The map is a major new compilation and re-interpretation of pre-existing geologic maps of the region. The map is designed to be used for several purposes, including regional tectonic analyses, mineral resource and metallogenic analysis, petroleum resource analysis, neotectonic analysis, and analysis of seismic hazards and volcanic hazards. The map consists of two sheets. Sheet 1 displays the map at a scale of 1:5,000,000, explanation. Sheet 2 displays the introduction, list of map units, and source references. Detailed descriptions of map units and stratigraphic columns are being published separately. This map is one of a series of publications on the mineral resources, metallogenesis, and geodynamics,of Northeast Asia. Companion studies and other articles and maps , and various detailed reports are: (1) a compilation of major mineral deposit models (Rodionov and Nokleberg, 2000; Rodionov and others, 2000; Obolenskiy and others, in press a); (2) a series of metallogenic belt maps (Obolenskiy and others, 2001; in press b); (3) a lode mineral deposits and placer districts location map for Northeast Asia (Ariunbileg and others, in press b); (4) descriptions of metallogenic belts (Rodionov and others, in press); and (5) a database on significant metalliferous and selected nonmetalliferous lode deposits, and selected placer districts (Ariunbileg and others, in press a).

The Research of Tectonic Framework and the Fault Activity in Large Detachment Basin System on Northern Margin of South China Sea

NASA Astrophysics Data System (ADS)

Pan, L., Sr.; Ren, J.

2017-12-01

The South China Sea (SCS) is one of the largest marginal sea on southeast Asia continental margin, developed Paleogene extension-rifting continental margin system which is rare in the world and preserving many deformed characterizes of this kind system. With the investigation of the SCS, guiding by the development of tectonics and geo-physics, especially the development of tectonics and the high quality seismic data based on the development of geo-physics, people gradually accept that the northern margin of the SCS has some detachment basin characterizes. After researching the northern margin of the SCS, we come up with lithosphere profiles across the shelf, slope and deep sea basin in the northeast of the SCS to confirm the tectonic style of ocean-continental transition and the property of the detachment fault. Furthermore, we describe the outline of large detachment basins at northern SCS. Based on the large number of high-quality 2D and 3D deep seismic profile(TWT,10s), drilling and logging data, combined with domestic and international relevant researches, using basin dynamics and tectono-stratigraphy theory, techniques and methods of geology and geophysics, qualitative and quantitative, we describe the formation of the detachment basin and calculate the fault activity rate, stretching factor and settlement. According to the research, we propose that there is a giant and complete detachment basin system in the northern SCS and suggest three conclusions. First of all, the detachment basin system can be divided into three domains: proximal domain covering the Yangjiang Sag, Shenhu uplift and part of Shunde Sag, necking zone covering part of the Shunde Sag and Heshan Sag, distal domain covering most part of Heshan Sag. Second, the difference of the stretching factor is observed along the three domains of the detachment basin system. The factor of the proximal domain is the minimum among them. On the other side, the distal domain is the maximum among them. This phenomenon can be concluded as the factor is gradually increasing from the continent to the ocean. Third, the development of detachment basin is episodic which can be divided into two stages approximately: the rifting and thermal subsidence.

Towards a Holistic Model for the Tectonic Evolution of the North China Craton

NASA Astrophysics Data System (ADS)

Kusky, T. M.; Polat, A.; Windley, B. F.; Wang, J.; Deng, H.

2016-12-01

The North China Craton (NCC) consists of distinctly different tectonic elements assembled during the late Archean - early Proterozoic. We propose a new tectonic evolution of the NCC. The Eastern Block (EB) consists of small microblocks that resemble a collage of accreted arc-rocks from a sutured archipelago similar to the SW Pacific, accreted between 2.6 and 2.7 Ga. An Atlantic-type margin developed on the western side of the EB by 2.5 Ga, and a >1,300 km long arc/accretionary prism collided with this passive margin at 2.5 Ga, obducting ophiolites and ophiolitic mélanges, and forming a foreland basin. This was followed by arc-polarity reversal, and injection of mantle wedge-derived melts. By 2.43 Ga, the ocean behind the accreted arc closed through the collision of an oceanic plateau. Rifting of the amalgamated craton followed at 2.4-2.35 Ga, with a failed rift arm preserved in the center of the craton, and two that successfully made an ocean along the northern margin. By 2.3 Ga an arc built on older cratonic material collided with this passive margin which soon converted to an Andean-type margin. Andean margin tectonics affected much of the craton from 2.3-1.9 Ga, forming a broad E-W swath of continental margin magmas, and retro-arc sedimentary basins including a superimposed basin over the passive margin on the northern margin. From 1.88-1.79 Ga the craton experienced a craton-wide granulite facies metamorphism and basement reactivation event with high-pressure granulites and eclogites in the north, and medium-pressure granulites across the craton. Early Proterozoic granulites and anatectic melts were generated by high-grade metamorphism and partial melting at mid-crustal levels beneath a collisionally-thickened plateau. This collision of the NCC on its northern margin was with the Columbia (Nuna) Continent. The NCC broke out in the period 1753-1673 Ma, as indicated by the formation of a suite of anorthosite, mangerite, charnockite, and alkali-feldspar granites in an ENE-striking belt across the northern margin of the craton, followed by the development of rifts and graben, intrusion of mafic dike swarms, and formation of shelf sediments on the northern passive margin of the craton, which signaled the beginning of a long period of quiescence for the NCC until the Paleozoic.

Subduction Related Crustal and Mantle Deformations and Their Implications for Plate Dynamics

NASA Astrophysics Data System (ADS)

Okeler, Ahmet

Ocean-continent convergence and subsequent continental collision are responsible for continental growth, mountain building, and severe tectonic events including volcanic eruptions and earthquake activity. They are also key driving forces behind the extensive thermal and compositional heterogeneities at crustal and mantle depths. Active subduction along the Calabrian Arc in southern Italy and the Hellenic Arc are examples of such collisional tectonics. The first part of this thesis examines the subduction related deformations within the crust beneath the southern Apennines. By modeling regional surface wave recordings of the largest temporary deployment in the southern Apennines, a lower-crustal/upper-mantle low-velocity volume extending down to 50 km beneath the mountain chain is identified. The magnitude (˜ 0.4 km/s slower) and anisotropic nature (˜ 10%) of the anomaly suggest the presence of hot and partially molten emplacement that may extend into the upper-crust towards Mt. Vulture, a once active volcano. Since the Apulian basement units are deformed during the compressional and consequent extensional events, our observations favor the "thick-skin" tectonic growth model for the region. In the deeper mantle, active processes are thermodynamically imprinted on the depth and strength of the phase transitions. This thesis examines more than 15000 SS precursors and provides the present-day reflectivity structure and topography associated with these phase transitions. Through case studies I present ample evidence for both slab penetration into the lower mantle (beneath the Hellenic Arc, Kurile Island and South America) and slab stagnation at the bottom of the Mantle Transition Zone (beneath the Tyrrhenian Sea and eastern China). Key findings include (1) thermal anomalies (˜ 200 K) at the base of the MTZ, which represent the deep source for Cenozoic European Rift Zone, Mount Etna and Mount Cameroon volcanism, (2) significant depressions (by 20-40 km) at the bottom of the Mantle Transition Zone beneath subducting slabs, (3) a strong 520-km reflector near subducting slabs, (4) a weak and elevated (15-25 km) 410-km reflector within active deformation zones, (5) strong lower mantle reflectors (˜ 900 km) while slabs penetrate into the lower mantle, and (6) consistency between the topography of a 300-km reflector and an exothermic phase transformation.

Plate tectonic reconstruction of the northeast Eurasian margin and Alaska since 50 Ma using subducted slab constraints

NASA Astrophysics Data System (ADS)

Wu, J. E.; Suppe, J.; Chen, Y. W.

2016-12-01

Seismic tomographic studies have revealed a swath of flat slab anomalies in the mantle transition zone at 410 to 660 km depths under Japan, Korea and NE China that continue northwards at deeper depths under the Russian Far East. These slab anomalies are remarkable because they appear to be continuous from their western edge far inland (>2000 km) under the NE Eurasian margin to the present-day NW Pacific subduction zones, which suggests they are Pacific slabs that were subducted in the Cenozoic. Other studies have proposed that some of these slabs were subducted at an ancient subduction zone during the Mesozoic or earlier. Here we discuss the fate of these slabs and their implications for the plate tectonic reconstruction of the NW Pacific margin along NE Asia and Alaska. We present both new and recently published slab mapping (Wu et al., 2016; JGR Solid Earth) including 30 major and minor slabs mapped in 3D from MITP08 global seismic tomography. We unfolded our mapped slabs to a spherical Earth model to estimate their pre-subduction size, shape and locations. The slab constraints were input into GPlates software to constrain a new regional NW Pacific plate tectonic reconstruction in the Cenozoic. Mapped slabs included the Marianas, Izu-Bonin, Japan and Kuril slabs, the Philippine Sea slabs and Aleutian slabs under the Bering Sea. Our mapped western Pacific slabs between the southernmost Izu-Bonin trench and the western Aleutians had unfolded E-W lengths of 3400 to 4900 km. Our plate model shows that these slabs are best reconstructed as Pacific slabs that were subducted in the Cenozoic and account for fast Pacific subduction along the NE Eurasian margin since plate reorganization at 50 Ma. Our mapped northern Kuril slab edge near the western Aleutians and a southern edge at the southernmost Izu-Bonin trench are roughly east-west and consistent with the orientations of Pacific absolute motions since 50 Ma. We interpret these long E-W slab edges as STEP fault-type transforms (i.e. lithospheric tears that progressively formed during subduction). We further discuss our plate model against the opening of the NW Pacific marginal basins in the Cenozoic, including the Japan Sea, Kuril Basin and Okhotsk Sea.

Devonian volcanic rocks of the southern Chinese Altai, NW China: Petrogenesis and implication for a propagating slab-window magmatism induced by ridge subduction during accretionary orogenesis

NASA Astrophysics Data System (ADS)

Ma, Xiaomei; Cai, Keda; Zhao, Taiping; Bao, Zihe; Wang, Xiangsong; Chen, Ming; Buslov, M. M.

2018-07-01

Ridge-trench interaction is a common tectonic process of the present-day Pacific Rim accretionary orogenic belts, and this process may facilitate "slab-window" magmatism that can produce significant thermal anomalies and geochemically unusual magmatic events. However, ridge-trench interaction has rarely been well-documented in the ancient geologic record, leading to grossly underestimation of this process in tectonic syntheses of plate margins. The Chinese Altai was inferred to have undergone ridge subduction in the Devonian and a slab-window model is proposed to interpret its high-temperature metamorphism and geochemically unique magmatic rocks, which can serve as an excellent and unique place to refine the tectonic evolution associated with ridge subduction in an ancient accretionary orogeny. For this purpose, we carried out geochemical and geochronological studies on Devonian basaltic rocks in this region. Secondary ion mass spectrometry (SIMS) zircon U-Pb dating results yield an age of 376.2 ± 2.4 Ma, suggesting an eruption at the time of Late Devonian. Geochemically, the samples in this study have variable SiO2 (43.3-58.3 wt%), low K2O (0.02-0.07 wt%) and total alkaline contents (2.16-5.41 wt%), as well as Fe2O3T/MgO ratios, showing typical tholeiitic affinity. On the other hand, the basaltic rocks display MORB-like REE patterns ((La/Yb)N = 0.90-2.57) and (Ga/Yb)N = 0.97-1.28), and have moderate positive εNd(t) values (+4.4 to +5.4), which collectively suggest a derivation from a mixing source comprising MORB-like mantle of a mature back-arc basin and subordinate arc mantle wedge. These basaltic rocks are characterized by Low La/Yb (1.26-3.69), Dy/Yb (1.51-1.77) and Sm/Yb (0.83-1.32) ratios, consistent with magmas derived from low degree (∼10%) partial melting of the spinel lherzolite source at a quite shallow mantle depth. Considering the distinctive petrogenesis of the basaltic rocks in this region, the Late Devonian basalts in the southern Chinese Altai is suggested to have witnessed the propagating process of slab-window magmatism that was induced by ridge subduction in a nascent rifting stage of a back-arc basin.

Magnetostratigraphy of the Fenghuoshan Group in the Hoh Xil Basin and its tectonic implications for India-Eurasia collision and Tibetan Plateau deformation

NASA Astrophysics Data System (ADS)

Jin, Chunsheng; Liu, Qingsong; Liang, Wentian; Roberts, Andrew P.; Sun, Jimin; Hu, Pengxiang; Zhao, Xiangyu; Su, Youliang; Jiang, Zhaoxia; Liu, Zhifeng; Duan, Zongqi; Yang, Huihui; Yuan, Sihua

2018-03-01

Early Cenozoic plate collision of India and Eurasia was a significant geological event, which resulted in Tibetan Plateau (TP) uplift and altered regional and global atmospheric circulations. However, the timing of initial collision is debated. It also remains unclear whether the TP was deformed either progressively northward, or synchronously as a whole. As the largest basin in the hinterland of the TP, evolution of the Hoh Xil Basin (HXB) and its structural relationship with development of the Tanggula Thrust System (TTS) have important implications for unraveling the formation mechanism and deformation history of the TP. In this study, we present results from a long sedimentary sequence from the HXB that dates the Fenghuoshan Group to ∼72-51 Ma based on magnetostratigraphy and radiometric ages of a volcanic tuff layer within the group. Three depositional phases reflect different stages of tectonic movement on the TTS, which was initialized at 71.9 Ma prior to the India-Eurasia collision. An abrupt sediment accumulation rate increase from 53.9 Ma is a likely response to tectonic deformation in the plateau hinterland, and indicates that initial India-Eurasia collision occurred at no later than that time. This remote HXB tectonosedimentary response implies that compressional deformation caused by India-Eurasia collision likely propagated to the central TP shortly after the collision, which supports the synchronous deformation model for TP.

Basin-mountain structures and hydrocarbon exploration potential of west Junggar orogen in China

NASA Astrophysics Data System (ADS)

Wu, Xiaozhi; He, Dengfa; Qi, Xuefeng

2016-04-01

Situated in northern Xinjiang, China, in NE-SW trend, West Junggar Orogen is adjacent to Altai fold belt on the north with the Ertix Fault as the boundary, North Tianshan fold belt on the south with the Ebinur Lake Strike-slip Fault as the boundary, and the Junggar Basin on the southeast with Zaire-Genghis Khan-Hala'alat fold belt as the boundary. Covering an area of about 10×104 km2 in China, there are medium and small intermontane basins, Burqin-Fuhai, Tacheng, Hefeng and Hoxtolgay, distributing inside the orogen. Tectonically West Junggar Orogen lies in the middle section of the Palaeo-Asian tectonic domain where the Siberia, Kazakhstan and Tarim Plates converge, and is the only orogen trending NE-SW in the Palaeo-Asian tectonic domain. Since the Paleozoic, the orogen experienced pre-Permian plate tectonic evolution and post-Permian intra-plate basin evolution. Complex tectonic evolution and multi-stage structural superimposition not only give rise to long term controversial over the basin basement property but also complex basin-mountain coupling relations, structures and basin superimposition modes. According to analysis of several kinds of geological and geophysical data, the orogen was dominated by compressive folding and thrust napping from the Siberia plate in the north since the Late Paleozoic. Compressive stress weakened from north to south, corresponding to subdued vertical movement and enhanced horizontal movement of crustal surface from north to south, and finally faded in the overthrust-nappe belt at the northwest margin of the Junggar Basin. The variation in compressive stress is consistent with the surface relief of the orogen, which is high in the north and low in the south. There are two kinds of basin-mountain coupling relationships, i.e. high angle thrusting and overthrusting and napping, and two kinds of basin superimposition modes, i.e. inherited and progressive, and migrating and convulsionary modes. West Junggar orogen has rich oil and gas shows, and oil and gas fields have also been discovered in the Zaysan Basin in adjacent Kazakhstan and in adjacent Junggar, Tuha and Santanghu Basins. Drilling data, geochemical analysis of outcrop data, and the disection of ancient Bulongguoer oil reservoir at the south margin of the Hefeng Basin show there developed two sets of good transitional source rocks, the lower Hujierste Formation in the Middle Devonian (D2h1) and the Hebukehe Formation in the Upper Devonian and Lower Carboniferous (D3-C1h) in this area, which, 10 to 300 m thick, mainly distribute in the shoal water zone along Tacheng-Ertai Late Paleozoic island arc belt. Reservoirs were mainly formed in the Jurassic and then adjusted in two periods, one from the end of the Jurassic to middle Cretaceous and the other in early Paleogene. Those early oil reservoirs might be destroyed in areas such as Bulongguoer with poor preservation conditions, but in an area with good geologic and preserving conditions, oil and gas might accumulate again to form new reservoirs. Therefore, a potential Middle Devonian-Lower Carboniferous petroleum system may exist in Tacheng-Ertai island arc belt, which may become a new domain for exploration, north faulted fold belt in the Heshituoluogai basin, and Hongyan fault bench zone in north Ulungur Depression in the Junggar Basin are promising areas for hydrocarbon exploration.

Gravitational field models for study of Earth mantle dynamics

NASA Technical Reports Server (NTRS)

1979-01-01

The tectonic forces or stresses due to the small scale mantle flow under the South American plate are detected and determined by utilizing the harmonics of the geopotential field model. The high degree harmonics are assumed to describe the small scale mantle convection patterns. The input data used in the derivation of this model is made up of 840,000 optical, electronic, and laser observations and 1,656 5 deg x 5 deg mean free air anomalies. Although there remain some statistically questionable aspects of the high degree harmonics, it seems appropriate now to explore their implications for the tectonic forces or stress field under the crust.

An exhumed Late Paleozoic canyon in the rocky mountains

USGS Publications Warehouse

Soreghan, G.S.; Sweet, D.E.; Marra, K.R.; Eble, C.F.; Soreghan, M.J.; Elmore, R.D.; Kaplan, S.A.; Blum, M.D.

2007-01-01

Landscapes are thought to be youthful, particularly those of active orogenic belts. Unaweep Canyon in the Colorado Rocky Mountains, a large gorge drained by two opposite-flowing creeks, is an exception. Its origin has long been enigmatic, but new data indicate that it is an exhumed late Paleozoic landform. Its survival within a region of profound late Paleozoic orogenesis demands a reassessment of tectonic models for the Ancestral Rocky Mountains, and its form and genesis have significant implications for understanding late Paleozoic equatorial climate. This discovery highlights the utility of paleogeomorphology as a tectonic and climatic indicator. ?? 2007 by The University of Chicago. All rights reserved.

Continental origin of the Gubaoquan eclogite and implications for evolution of the Beishan Orogen, Central Asian Orogenic Belt, NW China

NASA Astrophysics Data System (ADS)

Saktura, Wanchese M.; Buckman, Solomon; Nutman, Allen P.; Belousova, Elena A.; Yan, Zhen; Aitchison, Jonathan C.

2017-12-01

The Gubaoquan eclogite occurs in the Paleozoic Beishan Orogen of NW China. Previously it has been interpreted as a fragment of subducted oceanic crust that was emplaced as a mélange within continental rocks. Contrary to this, we demonstrate that the Gubaoquan eclogite protolith was a Neoproterozoic basic dyke/sill which intruded into Proterozoic continental rocks. The SHRIMP Usbnd Pb zircon dating of the metamorphic rims of the Gubaoquan eclogite yields an age 466 ± 27 Ma. Subdued heavy rare earth element abundances and lack of negative Eu anomalies of the metamorphic zircon domains confirm that this age represents eclogite facies metamorphism. The host augen orthogneiss has a Usbnd Pb zircon age of 920 ± 14 Ma, representing the timing of crystallization of the granitic protolith. A leucogranitic vein which intrudes the eclogite has a Usbnd Pb zircon age of 424 ± 8.6 Ma. This granitic vein marks the end of high-grade metamorphism in this area. The overcomplication of tectonic history of the Beishan Orogen is partially caused by inconsistent classifications and nomenclature of the same rock units and arbitrary subdivisions of Precambrian blocks as individual microcontinents. In an attempt to resolve this, we propose a simpler model that involves the partial subduction of the northern passive margin of the Dunhuang Block beneath the active continental margin developing on the Mazongshan-Hanshan Block to the north. Ocean closure and continental collision during the Late Ordovician resulted in continental thickening and eclogite facies metamorphism recorded by the mafic dykes/sills (now the Gubaoquan eclogite). In the light of the new data, the tectonothermal evolution of the Beishan Orogen is reviewed and integrated with the evolution of the Central Asian Orogenic Belt.

Subsidence transition during the post-rift stage of the Dongpu Sag, Bohai Bay Basin, NE China: A new geodynamic model

NASA Astrophysics Data System (ADS)

Xu, Han; Wang, Xin-Wen; Yan, Dan-Ping; Qiu, Liang

2018-06-01

The Dongpu Sag, located in the Bohai Bay Basin, NE China, is a Cenozoic continental rift basin. The post-rift evolution of the Dongpu Sag is associated with the development of petroleum reservoirs and has implications for Neogene-Quaternary basin evolution along the eastern margin of Eurasia. To determine the nature and origin of post-rift subsidence in the Dongpu Sag, we apply backstripping, modified strain-rate inversion, and revised finite extension modelling techniques, using data from 14 real and synthetic wells that are intersected by three seismic lines. Our results reveal discrepancies by subsidence based on backstripping of well data (the observed subsidence) minus that predicted by modified strain-rate inversion and revised finite extension modelling (the predicted subsidence). During the Miocene, the observed subsidence was smaller than the predicted subsidence, leaving negative discrepancies referred to here as "insufficient subsidence" ranging from -343 to -96 m. In contrast, during the Pliocene-Quaternary the observed subsidence was greater than the predicted subsidence by +123 to +407 m, which left positive discrepancies referred to as "over-sufficient subsidence". Therefore, we infer a transition from insufficient to over-sufficient subsidence during the post-rift stage. Normal faulting that started at ca. 5.3 Ma is estimated to have produced only ∼20% of the over-sufficient subsidence. Therefore, the remaining over-sufficient subsidence, as well as the preceding insufficient subsidence and the transition between the two, were likely controlled by lithosphere processes. We propose a new tectonic model in which variations in the conditions (e.g. rate, direction, and angle) associated with subduction of the Pacific plate resulted in a change of heat flow decreasing from a linear to a curvilinear pattern, leading to a transition from insufficient to over-sufficient subsidence.

U-Pb SHRIMP geochronology of zircon in garnet peridotite from the Sulu UHP terrane, China: Implications for mantle metasomatism and subduction-zone UHP metamorphism

USGS Publications Warehouse

Zhang, R.Y.; Yang, J.S.; Wooden, J.L.; Liou, J.G.; Li, T.F.

2005-01-01

We studied the Zhimafang ultrahigh-pressure metamorphic (UHP) peridotite from pre-pilot drill hole PP-1 of Chinese Continental Scientific Drilling project in the Sulu UHP terrane, eastern China. The peridotite occurs as lens within quartofeldspathic gneiss, and has an assemblage of Ol + Opx + Cpx + Phl + Ti-clinohumite (Ti-Chu) + Grt (or chromite) ?? magnesite (Mgs). Zircons were separated from cores at depths of 152 m (C24, garnet lhezolite), 160 m (C27, strongly retrograded phlogopite-rich peridotite) and 225 m (C50, banded peridotite), and were dated by SHRIMP mass spectrometer. Isometric zircons without inherited cores contain inclusions of olivine (Fo91-92), enstatite (En91-92), Ti-clinohumite, diopside, phlogopite and apatite. The enstatite inclusions have low Al2O3 contents of only 0.04-0.13 wt.%, indicating a UHP metamorphic origin. The weighted mean 206Pb/238U zircon age for garnet lherzolite (C24) is 221 ?? 3 Ma, and a discordia lower intercept age for peridotite (C50) is 220 ?? 2 Ma. These ages are within error and represent the time of subduction-zone UHP metamorphism. A younger lower intercept age of 212 ?? 3 Ma for a foliated wehrlite (C27) was probably caused by Pb loss during retrograde metamorphism. The source of zirconium may be partially attributed to melt/fluid metasomatism within the mantle wedge. Geochronological and geochemical data confirm that the mantle-derived Zhimafang garnet peridotites (probably the most representative type of Sulu garnet peridotites) were tectonically inserted into a subducting crustal slab and subjected to in situ Triassic subduction-zone UHP metamorphism. ?? 2005 Elsevier B.V. All rights reserved.

Lifespan of mountain ranges scaled by feedbacks between landsliding and erosion by rivers.

PubMed

Egholm, David L; Knudsen, Mads F; Sandiford, Mike

2013-06-27

An important challenge in geomorphology is the reconciliation of the high fluvial incision rates observed in tectonically active mountain ranges with the long-term preservation of significant mountain-range relief in ancient, tectonically inactive orogenic belts. River bedrock erosion and sediment transport are widely recognized to be the principal controls on the lifespan of mountain ranges. But the factors controlling the rate of erosion and the reasons why they seem to vary significantly as a function of tectonic activity remain controversial. Here we use computational simulations to show that the key to understanding variations in the rate of erosion between tectonically active and inactive mountain ranges may relate to a bidirectional coupling between bedrock river incision and landslides. Whereas fluvial incision steepens surrounding hillslopes and increases landslide frequency, landsliding affects fluvial erosion rates in two fundamentally distinct ways. On the one hand, large landslides overwhelm the river transport capacity and cause upstream build up of sediment that protects the river bed from further erosion. On the other hand, in delivering abrasive agents to the streams, landslides help accelerate fluvial erosion. Our models illustrate how this coupling has fundamentally different implications for rates of fluvial incision in active and inactive mountain ranges. The coupling therefore provides a plausible physical explanation for the preservation of significant mountain-range relief in old orogenic belts, up to several hundred million years after tectonic activity has effectively ceased.

Proto-South China Sea plate tectonics using subducted slab constraints from tomography

NASA Astrophysics Data System (ADS)

Wu, J.; Suppe, J.

2017-12-01

The geology of the South China Sea and surrounding margins is intimately tied to the subduction of its predecessor, the proto-South China Sea. However, published plate reconstructions have shown highly variable sizes and locations for the proto-South China Sea. Despite these differences, most studies agree that the proto-South China Sea was subducted southwards under north Borneo in the Cenozoic. Here we present new details on proto-South China Sea paleogeography using mapped and unfolded slabs from seismic tomography following Wu et al. (2016). We show that most of the proto-South China Sea lithosphere lies directly under the South China Sea and is represented by an extensive (>1000 km N-S) swath of detached, sub-horizontal slab at 450 to 700 km depth, here called the `northern Proto-South China Sea'. Furthermore, slab unfolding shows that prior to subduction at the Manila Trench, the eastern limit of the South China Sea, lay directly above the edge of the `northern Proto-South China Sea', both extending 400 to 500 km to the east of the present Manila trench. These observations show that the South China Sea opened directly above a northward-subducting `northern Proto-South China Sea', which runs counter to most proto-South China Sea plate models. We present a slab-constrained plate reconstruction that shows the proto-South China Sea was consumed by double-sided subduction to both the north and south, as follows: [1] The `northern proto-South China Sea' subducted in the Oligocene-Miocene under the Dangerous Grounds and southward expanding South China Sea by in-place 'self subduction' similar to the western Mediterranean basins. [2] Limited southward subduction of the proto-South China Sea under Borneo occurred pre-Oligocene, represented by the 'southern Proto-South China Sea' slab at 800 to 900 km depths. Our plate reconstruction implies the southern South China Sea was an active margin during South China Sea opening and had a south-facing arc and a north-dipping proto-South China Sea slab. A southern South China Sea arc was likely underthrusted under northern Borneo after 15 Ma. Our model also predicts the formation of a mantle wedge under the South China Sea during seafloor spreading. This suggests that South China Sea opening was accompanied by a more vigorous asthenospheric circulation than previously recognized.

Drainage basin and topographic analysis of a tropical landscape: Insights into surface and tectonic processes in northern Borneo

NASA Astrophysics Data System (ADS)

Mathew, Manoj Joseph; Menier, David; Siddiqui, Numair; Ramkumar, Mu.; Santosh, M.; Kumar, Shashi; Hassaan, Muhammad

2016-07-01

We investigated the recent landscape development of Borneo through geomorphic analysis of two large drainage basins (Rajang and Baram basins). The extraction of morphometric parameters utilizing digital terrain data in a GIS environment, focusing on hydrography (stream length-gradient index, ratio of valley floor width to valley height, and transverse topographic symmetry factor) and topography (local relief and relief anomaly), was carried out in order to elucidate processes governing drainage and landscape evolution. Anomalously high and low values of stream length-gradient indices of main tributary streams associated with faults and multiple knick-points along the channel profiles are linked to deformation events. The development of deeply incised V-shaped valleys show enhanced incision capability of streams in response to steepening of hillslope gradients following tectonic inputs. Deflection of streams and probable dynamic reorganization of the drainage system through stream capture processes as feedbacks to tectonic uplift and orographic effect are observed. Local relief and relief anomaly maps highlight the presence of preserved elevation-accordant relict portions of landscapes characterized by low amplitude relief, nested between ridgelines in regions of complex folding. Our results reveal dynamic geomorphic adjustment of the landscape due to perturbations in tectonic and climatic boundary conditions. The implication is that the landscape of north Borneo experienced a tectonic phase of rapid uplift after 5 Ma and undergoes active folding of the Rajang Group thrust belts in the present-day. Active shortening combined with high rates of denudation in Sarawak, demonstrates transience emphasized by the drainage system attempting to adjust to tectonic and climatic forcing.

The Rankings of Marketing Programs in China.

ERIC Educational Resources Information Center

Siu, Wai-sum

1996-01-01

Nineteen marketing faculty and administrators in China ranked 10 universities offering business administration education and indicated their criteria. Results of the rankings and evaluative criteria are presented, and implications for marketing education in China discussed. It was found that most respondents were more concerned about input…

Status Concern and Relative Deprivation in China: Measures, Empirical Evidence and Economic and Policy Implications

PubMed Central

Xi, CHEN

2017-01-01

Status concern and feelings of relative deprivation affect individual behaviour and well-being. Traditional norms and the alarming inequality in China have made relative deprivation increasingly intense for the Chinese population. This article reviews empirical literature on China that attempts to test the relative deprivation hypothesis, and also reviews the origins and pathways of relative deprivation, compares its economic measures in the literature and summarises the scientific findings. Drawing from solid empirical evidence, the author discusses the important policy implications on redistribution, official regulations and grassroots sanctions, and relative poverty alleviation. PMID:29033479

Status Concern and Relative Deprivation in China: Measures, Empirical Evidence and Economic and Policy Implications.

PubMed

Xi, Chen

2016-02-01

Status concern and feelings of relative deprivation affect individual behaviour and well-being. Traditional norms and the alarming inequality in China have made relative deprivation increasingly intense for the Chinese population. This article reviews empirical literature on China that attempts to test the relative deprivation hypothesis, and also reviews the origins and pathways of relative deprivation, compares its economic measures in the literature and summarises the scientific findings. Drawing from solid empirical evidence, the author discusses the important policy implications on redistribution, official regulations and grassroots sanctions, and relative poverty alleviation.

Nature, diversity of deposit types and metallogenic relations of South China

USGS Publications Warehouse

Zaw, K.; Peters, S.G.; Cromie, P.; Burrett, C.; Hou, Z.

2007-01-01

The South China Region is rich in mineral resources and has a wide diversity of deposit types. The region has undergone multiple tectonic and magmatic events and related metallogenic processes throughout the earth history. These tectonic and metallogenic processes were responsible for the formation of the diverse styles of base and precious metal deposits in South China making it one of the resource-rich regions in the world. During the Proterozoic, the South China Craton was characterised by rifting of continental margin before eruption of submarine volcanics and development of platform carbonate rocks, and the formation of VHMS, stratabound copper and MVT deposits. The Phanerozoic metallogeny of South China was related to opening and closing of the Tethyan Ocean involving multiple orogenies by subduction, back-arc rifting, arc-continent collision and post-collisional extension during the Indosinian (Triassic), Yanshanian (Jurassic to Cretaceous) and Himalayan (Tertiary) Orogenies. The Late Palaeozoic was a productive metallogenic period for South China resulting from break-up and rifting of Gondwana. Significant stratabound base and precious metal deposits were formed during the Devonian and Carboniferous (e.g., Fankou and Dabaoshan deposits). These Late Palaeozoic SEDEX-style deposits have been often overprinted by skarn systems associated with Yanshanian magmatism (e.g., Chengmenshan, Dongguashan and Qixiashan). A number of Late Palaeozoic to Early Mesozoic VHMS deposits also developed in the Sanjiang fold belt in the western part of South China (e.g., Laochang and Gacun). South China has significant sedimentary rock-hosted Carlin-like deposits, which occur in the Devonian- to Triassic-aged accretionary wedge or rift basins at the margin of the South China Craton. They are present in a region at the junction of Yunnan, Guizhou, and Guangxi Provinces called the 'Southern Golden Triangle', and are also present in NW Sichuan, Gansu and Shaanxi, in an area known as the 'Northern Golden Triangle' of China. These deposits are mostly epigenetic hydrothermal micron-disseminated gold deposits with associated As, Hg, Sb + Tl mineralisation similar to Carlin-type deposits in USA. The important deposits in the Southern Golden Triangle are Jinfeng (Lannigou), Zimudang, Getang, Yata and Banqi in Guizhou Province, and the Jinya and Gaolong deposits in Guangxi District. The most important deposits in the Northern Golden Triangle are the Dongbeizhai and Qiaoqiaoshang deposits. Many porphyry-related polymetallic copper-lead-zinc and gold skarn deposits occur in South China. These deposits are related to Indosinian (Triassic) and Yanshanian (Jurassic to Cretaceous) magmatism associated with collision of the South China and North China Cratons and westward subduction of the Palaeo-Pacific Plate. Most of these deposits are distributed along the Lower to Middle Yangtze River metallogenic belt. The most significant deposits are Tonglushan, Jilongshan, Fengshandong, Shitouzui and Jiguanzui. Au-(Ag-Mo)-rich porphyry-related Cu-Fe skarn deposits are also present (Chengmenshan and Wushan in Jiangxi Province and Xinqiao, Mashan-Tianmashan, Shizishan and Huangshilaoshan in Anhui Province). The South China fold belt extending from Fujian to Zhejiang Provinces is characterised by well-developed Yanshanian intrusive to subvolcanic rocks associated with porphyry to epithermal type mineralisation and mesothermal vein deposits. The largest porphyry copper deposit in China, Dexing, occurs in Jiangxi Province and is hosted by Yanshanian granodiorite. The high-sulphidation epithermal system occurs at the Zijinshan district in Fujian Province and epithermal to mesothermal vein-type deposits are also found in the Zhejiang Province (e.g., Zhilingtou). Part of Shandong Province is located at the northern margin of the South China Craton and the province has unique world class granite-hosted orogenic gold deposits. Occurrences of Pt-Pd-Ni-Cu-Co are found in Permian

Comment on "Timing and nature of the Xinlin-Xiguitu Ocean: constraints from ophiolitic gabbros in the northern Great Xing'an Range, eastern Central Asian Orogenic Belt" by Feng et al. (2016)

NASA Astrophysics Data System (ADS)

Ni, Dong-Hong

2017-09-01

We disagree the transitional supra-subduction zone model of Feng et al. (Int J Earth Sci (Geol Rundsch) 105:491-505, 2016) for the tectonic setting of Jifeng ophiolite suite in NE China. Existence of the komatiite in the Jifeng ophiolite indicates an oceanic plateau environment for this ophiolite suite within the so-called Xinlin-Xiguitu ocean.

Glacio-Seismotectonics: Ice Sheets, Crustal Deformation and Seismicity

NASA Technical Reports Server (NTRS)

Sauber, Jeanne; Stewart, Iain S.; Rose, James

2000-01-01

The last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity. This growth has been driven largely by the emergence of postglacial rebound models (PGM) constrained by new field observations that incorporate increasingly realistic rheological, mechanical, and glacial parameters. In this paper, we highlight some of these recent field-based investigations and new PGMs, and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation. The emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern Canada and Fennoscandia. However, many of these models neglect important parameters, such as topography, lateral variations in lithospheric strength and tectonic strain built up during glaciation. In glaciated mountainous terrains, glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism. Such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields.

Comment on: "Morphotectonic records of neotectonic activity in the vicinity of North Almora Thrust Zone, Central Kumaun Himalaya", by Kothyari et al. 2017, Geomorphology (285), 272-286

NASA Astrophysics Data System (ADS)

Rana, Naresh; Sharma, Shubhra

2018-01-01

The recent paper by Kothyari et al. (2017) suggests that the North Almora Thrust (NAT) and a few subsidiary faults in the central Lesser Himalaya were active during the late Quaternary and Holocene. Considering that in the Indian Summer Monsoon (ISM) dominated and tectonically active central Himalaya, the landscape owes their genesis to a coupling between the tectonics and climate. The present study would have been a good contribution toward improving our understanding on this important topic. Unfortunately, the inferences drawn by the authors are based on inadequate/vague field observations, supported by misquoted references, which reflects their poor understanding of the geomorphic processes. For example, authors implicate tectonics in the landform evolution without providing an argument to negate the role of climate (ISM). In view of this, the above contribution does not add anything substantial in improving our existing knowledge of climate-tectonic interaction in landform evolution. On the contrary, if the above publication is not questioned for its scientific merit, it may create enormous confusion and proliferation of wrong scientific data and inferences.

The fate of water within Earth and super-Earths and implications for plate tectonics

PubMed Central

2017-01-01

The Earth is likely to have acquired most of its water during accretion. Internal heat of planetesimals by short-lived radioisotopes would have caused some water loss, but impacts into planetesimals were insufficiently energetic to produce further drying. Water is thought to be critical for the development of plate tectonics, because it lowers viscosities in the asthenosphere, enabling subduction. The following issue persists: if water is necessary for plate tectonics, but subduction itself hydrates the upper mantle, how is the upper mantle initially hydrated? The giant impacts of late accretion created magma lakes and oceans, which degassed during solidification to produce a heavy atmosphere. However, some water would have remained in the mantle, trapped within crystallographic defects in nominally anhydrous minerals. In this paper, we present models demonstrating that processes associated with magma ocean solidification and overturn may segregate sufficient quantities of water within the upper mantle to induce partial melting and produce a damp asthenosphere, thereby facilitating plate tectonics and, in turn, the habitability of Earth-like extrasolar planets. This article is part of the themed issue ‘The origin, history and role of water in the evolution of the inner Solar System’. PMID:28416729

The fate of water within Earth and super-Earths and implications for plate tectonics.

PubMed

Tikoo, Sonia M; Elkins-Tanton, Linda T

2017-05-28

The Earth is likely to have acquired most of its water during accretion. Internal heat of planetesimals by short-lived radioisotopes would have caused some water loss, but impacts into planetesimals were insufficiently energetic to produce further drying. Water is thought to be critical for the development of plate tectonics, because it lowers viscosities in the asthenosphere, enabling subduction. The following issue persists: if water is necessary for plate tectonics, but subduction itself hydrates the upper mantle, how is the upper mantle initially hydrated? The giant impacts of late accretion created magma lakes and oceans, which degassed during solidification to produce a heavy atmosphere. However, some water would have remained in the mantle, trapped within crystallographic defects in nominally anhydrous minerals. In this paper, we present models demonstrating that processes associated with magma ocean solidification and overturn may segregate sufficient quantities of water within the upper mantle to induce partial melting and produce a damp asthenosphere, thereby facilitating plate tectonics and, in turn, the habitability of Earth-like extrasolar planets.This article is part of the themed issue 'The origin, history and role of water in the evolution of the inner Solar System'. © 2017 The Authors.

Tectonic control of complex slope failures in the Ameka River Valley (Lower Gibe Area, central Ethiopia): Implications for landslide formation

NASA Astrophysics Data System (ADS)

Kycl, Petr; Rapprich, Vladislav; Verner, Kryštof; Novotný, Jan; Hroch, Tomáš; Mišurec, Jan; Eshetu, Habtamu; Tadesse Haile, Ezra; Alemayehu, Leta; Goslar, Tomasz

2017-07-01

Even though major faults represent important landslide controlling factors, the role the tectonic setting in actively spreading rifts plays in the development of large complex landslides is seldom discussed. The Ameka complex landslide area is located on the eastern scarp of the Gibe Gorge, approximately 45 km to the west of the Main Ethiopian Rift and 175 km to the southwest of Addis Ababa. Investigation of the complex landslide failures required a combination of satellite and airborne data-based geomorphology, geological field survey complemented with structural analysis, radiocarbon geochronology and vertical electric sounding. The obtained observations confirmed the multiphase evolution of the landslide area. We have documented that, apart from climatic and lithological conditions, the main triggering factor of the Ameka complex landslide is the tectonic development of this area. The E-W extension along the NNE-SSW trending Main Ethiopian Rift is associated with the formation of numerous parallel normal faults, such as the Gibe Gorge fault and the almost perpendicular scissor faults. The geometry of the slid blocks of coherent lithology have inherited the original tectonic framework, which suggests the crucial role tectonics play in the fragmentation of the compact rock-masses, and the origin and development of the Ameka complex landslide area. Similarly, the main scarps were also parallel to the principal tectonic features. The local tectonic framework is dominated by faults of the same orientation as the regional structures of the Main Ethiopian Rift. Such parallel tectonic frameworks display clear links between the extension of the Main Ethiopian Rift and the tectonic development of the landslide area. The Ameka complex landslide developed in several episodes over thousands of years. According to the radiocarbon data, the last of the larger displaced blocks (representing only 2% of the total area) most likely slid down in the seventh century AD. The main scarps, namely the high scarps in the western part, are unstable over the long term and toppling and falling-type slope movements can be expected here in the future.

Holocene vertical tectonic movements of the Taipei Basin, northern Taiwan and its implications

NASA Astrophysics Data System (ADS)

Chen, B.; Hsieh, M.; Lai, T.; Liew, P.

2007-12-01

Many geological data of the Taipei Basin, although, have been published by various studies in past decades, however, vertical tectonic movement rate of the Basin was not well understood so far. This study, therefore, used radiocarbon dates, obtained from fifteen boreholes in the Basin, to calculate the Holocene vertical tectonic movement rate. In addition to the derived tectonic movement rate, this study also discussed the causes of the tectonic patterns of the Taipei Basin. The Taipei Basin, located in the northern Taiwan, was a half graben subsided and extended along the western boundary, the Shangiao Normal Fault, of the Basin. The Holocene vertical tectonic movement rate of the Basin were calculated based on 94 radiocarbon dates in fifteen boreholes, the elevations of the radiocarbon dating samples, and the eustatic sea-level curve of the past 15 ka. The results showed the rate in the western part of the Basin, was -2.2 -- -0.9 mm/yr (negative value indicates subsiding, and positive value indicates uplifting). In the central part of the Basin, the rate was ca. -1 -- 1 mm/yr while in the eastern part of the Basin, the rate was 0.1 -- 1.6 mm/yr. Along the Shiangiao Fault, the rate of the hanging-wall was ca. -1.6 -- -0.4 mm/yr and the rate of the footwall was ca. 0 mm/yr. According to the results of this study, the present territory of the Taipei Basin was not actually consistent with the tectonic subsiding region. The vertical tectonic movement pattern demonstrated subsidence in the western part and uplift in the eastern part of the Taipei Basin. The subsidence of the western part was controlled by the extension of the Shangiao Faul. The uplift of the eastern part might be ascribed to the roll-over of the Fault. Another possibility is that the uplift of the east was controlled by the same behavior as the Western Foothills.Consequently, the deposition of the eastern part of the Basin, wass mainly related to the accommodations due to sea-level rise but not tectonic subsidence.

Changes in Early Adolescents' Sense of Responsibility to Their Parents in the United States and China: Implications for Academic Functioning

ERIC Educational Resources Information Center

Pomerantz, Eva M.; Qin, Lili; Wang, Qian; Chen, Huichang

2011-01-01

This research examined American and Chinese children's sense of responsibility to their parents during early adolescence, with a focus on its implications for children's academic functioning. Four times over the seventh and eighth grades, 825 children (mean age = 12.73 years) in the United States and China reported on their sense of responsibility…

China Naval Modernization: Implications for U.S. Navy Capabilities - Background and Issues for Congress

DTIC Science & Technology

2014-02-28

established method for countering an opponent’s military capability. A September 30, 2011, press report, for example, quotes Lieutenant General Herbert ...to address it. We are unable to provide additional details.”... 122 Spencer Ackerman, “How To Kill...China Naval Modernization: Implications for U.S. Navy Capabilities Congressional Research Service 105 As early as Feb. 17 [2011], Lt. Gen. Herbert

The Sea Dragon Network: Implications of the International Expansion of China’s Maritime Shipping Industry.

DTIC Science & Technology

1998-06-01

SFT enhance Beijing’s regional ability to advance China’s economic, political, and security interests. The analysis suggests China’s foreign policy...trades in China’s favor. The analysis also suggests China’s dependencies on regional MSI and SFT networks increase Beijing’s sense of economic... analysis suggests China’s foreign policy and overseas investment in strategic resources increase levels of SFT and transportation requirements for

International experiences of promoting generics use and its implications to China.

PubMed

Sun, Jing

2013-05-01

To summarize international experiences in promoting use of generics and to extract essence for China's reference. This is a commentary of two systematic reviews about policies to promote use of generics and its implications to China. Price, reimbursement, and generic substitution policies in European countries, and approaches in low and middle income countries in promoting market competition, appropriate intellectual property right protection strategy, and necessary demand side incentives, are all meaningful for China to contain soaring pharmaceutical expenditures, and to maintain the achievements and outcomes of the national health system reform. Effective promotion of generics use must be practice based on the real situation. Tailor-made and comprehensive measures are needed to address both demand and supply sides barriers before achieving tangible cost containment effect without unexpected side effects. © 2013 Wiley Publishing Asia Pty Ltd and Chinese Cochrane Center, West China Hospital of Sichuan University.

Paleomagnetic Results of Permo-Carboniferous Volcanic-sedimentary Strata in Mid-eastern Inner Mongolia, China: Implications for Tectonic Evolution of the Eastern CAOB

NASA Astrophysics Data System (ADS)

Zhang, D.; Huang, B.; Zhao, J.; Bai, Q.; Zhang, Y.; Zhou, T.

2015-12-01

There has been hotly debating over the closure time of the eastern Paleo-Asian Ocean and the tectonic evolution of the eastern CAOB (Central Asian Orogenic Belt) for decades. To better puzzle out this controversy, we carried out a detailed paleomagnetic study on the Permo-Carboniferous volcanic-sedimentary strata in mid-eastern Inner Mongolia, northeast of China. More than 820 samples were collected from 81 sites and titanium-poor magnetite and hematite are proved as the principal magnetic carriers. (1)In Kingan Block, 9 sites of volcanic rocks from Dashizhai Formation (P1) were calculated to get a mean magnetic direction Dg/Ig = 285.5°/77.4°, kg = 68.2, α95 = 6.8° before and Ds/Is = 206.5°/48.2°, ks = 100.8, α95 = 5.5°, N = 9 after bedding correction, which suggests a paleolatitude of 34.5°±5°N. Both the positive fold test and reversal test suggest a pre-folding magnetization and thus may indicate a primary remanence. (2)Three volcanic sections of Baoligaomiao Formation (C3-P1) from Uliastai Passive Margin were sampled and a mean magnetic direction derived from 16 sites is Dg/Ig = 30.1°/31.8°, kg = 16.3, α95 = 9.8° before and Ds/Is = 65.6°/58.1°, ks = 39.8, α95 = 6.1°, N = 16 after bedding correction. The corresponding paleomagnetic pole Plat. /Plong = 43.1° N/186.7°E, A95=8° suggests a paleolatitude of 38.7°±6.3°N. A primary remanence is confirmed by positive fold test. (3) In the northern margin of NCB (North China Block), a ChRM is successfully isolated from 6 sites of basaltic rocks in Elitu Formation (P2) as Dg/Ig = 351.1°/67.2°, kg = 2.1, α95 = 71.8° before and Ds/Is = 351.1°/29.1°, ks = 32.7, α95 = 71.8°, N = 16 after bedding correction, and thus yielded a paleomagnetic pole as Plat. /Plong = 63.1° N/313.5°E, A95=9.5°, which suggests a paleolatitude of 17.2°±7.2°N. A positive fold test and reversal test indicate that the remanence should be primary. The paleomagetic pole of Kingan Block and Uliastai Passive Margin are located at a common small circle and thus indicates they may share a similar paleolatitude, the huge longitudinal difference should be ascribed to relative rotation afterwards . To the contrary, the paleolatitude of the northern margin of NCB and southern Mongolia is much lower than that of Kingan and Uliastai, which may suggest a remain-opening paleogeography of the Paleo-Asian Ocean by middle Permian.

Old Rock on Young Rock.

ERIC Educational Resources Information Center

Simmons, Henry

1983-01-01

In determining how the Appalachian Mountains were formed, various workings of tectonic processes at continental margins are also being illuminated. The research has important implications for understanding specific processes which shaped the earth and for unraveling the record of plate movements now preserved only in present and former continental…

Timing and implications for the late Mesozoic geodynamic settings of eastern North China Craton: Evidences from K-Ar dating age and sedimentary-structural characteristics records of Lingshan Island, Shandong Province

NASA Astrophysics Data System (ADS)

Li, Jie; Jin, Aiwen; Hou, Guiting

2017-12-01

The Lingshan Island in Shandong Province in the eastern North China Craton, well known for the Late Mesozoic multi-scale slide-slump structures is related to paleo-earthquake. Terrigenous clastic rocks, volcanic clastic rocks and volcanic lavas are extensively exposed in the Lingshan Island and its adjacent regions of the Shandong Province, which led to fierce debates on their ages, sedimentary characteristics and tectono-sedimentary evolution. In this contribution, we present the characteristics of the Late Mesozoic stratigraphy in the Lingshan Island. Whole-rock K-Ar dating of dyke at Beilaishi and rhyolites at Laohuzui of the Lingshan Island yielded ages of 159 Ma and 106-92 Ma which coincides with the Laiyang Period rifting and the Qingshan Period rifting in the Jiaolai Basin, respectively. On the basis of the analysis to the Late Mesozoic sedimentary environment of `flysch' and `molasse'-like formations as well as tectonic stress fields reconstruction, four episodes of the tectono-sedimentary evolution were established in the Lingshan Island and its adjacent regions in the eastern North China Craton. They consist of two episodes of extensional events for the syn-rift, and two episodes of compression events for the inversion of the post-rift. The entire episodes can be summarized as follows: (1) the first syn-rift NW-SE extension in Laiyang Period can be identified by the `flysch' formation (Unit 1) and by emplacement of the NE-trending dyke in the Laiyang Group. This syn-rift episode can be related to the NW-SE post-orogenic extension resulted from the gravity collapse of the thickened lithosphere along the Sulu Orogen. (2) The first post-rift NW-SE inversion, which was caused by the NW-directed subduction of Izanaqi Plate, can be well documented by the `X' type conjugate joints as well as slide slump folds in Unit 1. (3) The second syn-rift NW-SE extension in Qingshan Period is characterized by rhyolite rocks (Unit 2). This syn-rift episode can be considered to be associated with lithospheric delamination of the thickened lithosphere in the eastern North China Craton. And finally, (4) the second post-rift NW-SE inversion which resulted from the subduction of the Pacific Plate under the eastern North China Craton in the NW direction at the end of the Qingshan Period is recorded by `molasse'-like formation (Unit 3).

Venus as a laboratory for studying planetary surface, interior, and atmospheric evolution

NASA Astrophysics Data System (ADS)

Smrekar, S. E.; Hensley, S.; Helbert, J.

2013-12-01

As Earth's twin, Venus offers a laboratory for understanding what makes our home planet unique in our solar system. The Decadal Survey points to the role of Venus in answering questions such as the supply of water and its role in atmospheric evolution, its availability to support life, and the role of geology and dynamics in controlling volatiles and climate. On Earth, the mechanism of plate tectonics drives the deformation and volcanism that allows volatiles to escape from the interior to the atmosphere and be recycled into the interior. Magellan revealed that Venus lacks plate tectonics. The number and distribution of impact craters lead to the idea Venus resurfaced very rapidly, and inspired numerous models of lithospheric foundering and episodic plate tectonics. However we have no evidence that Venus ever experienced a plate tectonic regime. How is surface deformation affected if no volatiles are recycled into the interior? Although Venus is considered a ';stagnant' lid planet (lacking plate motion) today, we have evidence for recent volcanism. The VIRTIS instrument on Venus Express mapped the southern hemisphere at 1.02 microns, revealing areas likely to be unweathered, recent volcanic flows. Additionally, numerous studies have shown that the crater population is consistent with ongoing, regional resurfacing. How does deformation and volcanism occur in the absence of plates? At what rate is the planet resurfacing and thus outgassing? Does lithospheric recycling occur with plate tectonics? In the 25 years since Magellan, the design of Synthetic Aperture Radar has advanced tremendously, allowing order of magnitude improvements in altimetry and imaging. With these advanced tools, we can explore Venus' past and current tectonic states. Tesserae are highly deformed plateaus, thought to be possible remnants of Venus' earlier tectonic state. How did they form? Are they low in silica, like Earth's continents, indicating the presence of abundant water? Does the plains volcanism cover an earlier tectonic surface, or perhaps cover ancient impact basins? Was there an abrupt transition in tectonic style, perhaps due to degassing of the crust or a more gradual shift? What is the nature of Venus' modern tectonics? Is the lithosphere still deforming? Is there recent or active volcanism? Is volcanism confined to hotspots, areas above mantle plumes? Has plains volcanism ceased? What are the implications for volatile history? These questions can be addressed via a combination of high resolution altimetry, imaging, and surface emissivity mapping.

Wet Tectonics: A New Planetary Synthesis

NASA Astrophysics Data System (ADS)

Grimm, K. A.

2005-12-01

Most geoscientists (and geoscience textbooks) describe plate tectonics as a `solid-Earth' phenomenon, with fluids playing an important role in discrete geodynamic processes. As a community of diverse research specialists, the critical role of water is being widely elucidated, however these diverse studies do not address the fundamental origin and operation of the global plate tectonic phenomenon, and its expressions in planetary geodynamics and geomorphology. The Wet Tectonics hypothesis extends well beyond the plate tectonics paradigm, to constitute a new synthesis of diverse geoscience specializations and self-organizing complexity into a simple, internally consistent and explicitly testable model. The Wet Tectonics hypothesis asserts that Earth's plate tectonic system arose from and is the explicit and dynamic result of water interacting with the hot silicate mantle. The tectosphere is defined as an interactive functional (rather than structural, compositional or rheological) entity, a planetary-scale dynamic system of plate formation, plate motion, and rock/volatile recycling. Earth's tectosphere extends from the base of the asthenosphere to the top of the crust, arising and evolving as a dynamic pattern of organization that creates, orders and perpetuates itself. Earth's tectosphere is energetically-open, materially ajar (steady-state operation may not require sub-asthenospheric inputs; shifts between distinct tectonic modes may result from changes in coupling between the tectosphere and subasthenospheric reservoirs) and chemically-closed (i.e. the tectosphere recycles its own wastes). Water is a fundamental requirement in all of the constituent processes of Earth's tectosphere, including seafloor spreading, slab cooling/subsidence, plate motion, asthenosphere rheology, and subduction (where crustal and volatile recycling occur). As a working hypothesis, we suggest that the dynamic and persistent hydrosphere and tectosphere on planet Earth are fully interdependent and co-evolving phenomena. The concept of autocatalytic hypercycles has been adapted from molecular biology to resolve the apparent paradox of circular causality amongst the coupled phenomena of liquid water oceans and `plate tectonics'. This new planetary synthesis presents fundamental implications for geological, geophysical, Earth system and planetary sciences, as well as novel hypotheses concerning plate drive (gravity sliding ± slab pull), origin of plate tectonics (Hadean, >=4.4Ga), biogeochemical cycling (balanced global fluxes of water into and out of the tectosphere; is the asthenosphere continuously rehydrated via lateral advection) and planetary geomorphology (simple contrasts between Mars, Earth and Venus).

Ca. 890 Ma magmatism in the northwest Yangtze block, South China: SIMS U-Pb dating, in-situ Hf-O isotopes, and tectonic implications

NASA Astrophysics Data System (ADS)

Zhou, Jiu-Long; Li, Xian-Hua; Tang, Guo-Qiang; Gao, Bing-Yu; Bao, Zhi-An; Ling, Xiao-Xiao; Wu, Li-Guang; Lu, Kai; Zhu, Yu-Sheng; Liao, Xin

2018-01-01

Early Neoproterozoic tectonics of the Yangtze block remains poorly understood because very limited igneous records are available from the time interval of ∼1000-870 Ma. In this paper, our new SIMS U-Pb dating results demonstrate that the Liushudian mafic intrusion and Pinghe alkaline complex in the northwest Yangtze block were emplaced at 888 ± 6 Ma and 891 ± 7 Ma, respectively, representing the products of a ∼890 Ma igneous event. Gabbros from the Liushudian intrusion have rather depleted zircon ɛHf(t) (mean = 10.4) and normal mantle-like zircon δ18O (mean = 5.97‰). Their parental magma was thus probably derived from asthenospheric mantle. Geochemically, these mafic rocks have an affinity to continental flood tholeiitic basalts rather than ocean island basalts, as previously thought. In contrast, an ijolite sample from the Pinghe complex has less depleted zircon ɛHf(t) (mean = 5.7) and anomalously high zircon and apatite δ18O (mean = 13.76‰ and 13.80‰, respectively). Such a characteristic δ18O signal, among the highest yet known for igneous zircons, could be either inherited from a magma source in metasomatized lithospheric mantle or acquired by assimilation of high-δ18O supracrustal materials (e.g., limestone, chert) during magma evolution. An intra-plate extensional environment is suggested for the ∼890 Ma igneous event in the northwest Yangtze block, although it is as yet unclear whether this igneous event is related to a mantle plume or not. It could be concluded that magmatism on the western periphery of the Yangtze block was not shut down between ∼1000 and ∼870 Ma, and the ∼890 Ma intra-plate igneous event may mark either the onset of Neoproterozoic continental rifting or the ending of Late Mesoproterozoic to Early Neoproterozoic lithospheric extension.

Observational Constraints on Lithospheric Rheology and Their Implications for Lithospheric Dynamics and Plate Tectonics

NASA Astrophysics Data System (ADS)

Zhong, S.; Watts, A. B.

2014-12-01

Lithospheric rheology and strength are important for understanding crust and lithosphere dynamics, and the conditions for plate tectonics. Laboratory studies suggest that lithospheric rheology is controlled by frictional sliding, semi-brittle, low-temperature plasticity, and high-temperature creep deformation mechanisms as pressure and temperature increase from shallow to large depths. Although rheological equations for these deformation mechanisms have been determined in laboratory settings, it is necessary to validate them using field observations. Here we present an overview of lithospheric rheology constrained by observations of seismic structure and load-induced flexure. Together with mantle dynamic modeling, rheological equations for high-temperature creep derived from laboratory studies (Hirth and Kohlstedt, 2003; Karato and Jung, 2003) satisfactorily explain the seismic structure of the Pacific upper mantle (Hunen et al., 2005) and Hawaiian swell topography (Asaadi et al., 2011). In a recent study that compared modeled surface flexure and stress induced by volcano loads in the Hawaiian Islands region with the observed flexure and seismicity, Zhong and Watts (2013) showed that the coefficient of friction is between 0.25 and 0.7, and is consistent with laboratory studies and also in-situ borehole measurements. However, this study indicated that the rheological equation for the low-temperature plasticity from laboratory studies (e.g., Mei et al., 2010) significantly over-predicts lithospheric strength and viscosity. Zhong and Watts (2013) also showed that the maximum lithospheric stress beneath Hawaiian volcano loads is about 100-200 MPa, which may be viewed as the largest lithospheric stress in the Earth's lithosphere. We show that the relatively weak lithospheric strength in the low-temperature plasticity regime is consistent with seismic observation of reactivated mantle lithosphere in the western US and the eastern North China. We discuss here the causes of this weakening in the context of the potential effects on laboratory studies of reduced grain size and Peierls stress on the low-temperature deformation regime.

The distribution, geochronology and geochemistry of early Paleozoic granitoid plutons in the North Altun orogenic belt, NW China: Implications for the petrogenesis and tectonic evolution

NASA Astrophysics Data System (ADS)

Meng, Ling-Tong; Chen, Bai-Lin; Zhao, Ni-Na; Wu, Yu; Zhang, Wen-Gao; He, Jiang-Tao; Wang, Bin; Han, Mei-Mei

2017-01-01

Abundant early Paleozoic granitoid plutons are widely distributed in the North Altun orogenic belt. These rocks provide clues to the tectonic evolution of the North Altun orogenic belt and adjacent areas. In this paper, we report an integrated study of petrological features, U-Pb zircon dating, in situ zircon Hf isotope and whole-rock geochemical compositions for the Abei, 4337 Highland and Kaladawan Plutons from north to south in the North Altun orogenic belt. The dating yielded magma crystallization ages of 514 Ma for the Abei Pluton, 494 Ma for the 4337 Highland Pluton and 480-460 Ma for the Kaladawan Pluton, suggesting that they are all products of oceanic slab subduction because of the age constraint. The Abei monzogranites derived from the recycle of Paleoproterozoic continental crust under low-pressure and high-temperature conditions are products of subduction initiation. The 4337 Highland granodiorites have some adakitic geochemical signatures and are sourced from partial melting of thickened mafic lower continental crust. The Kaladawan quartz diorites are produced by partial melting of mantle wedge according to the positive εHf(t) values, and the Kaladawan monzogranite-syenogranite are derived from partial melting of Neoproterozoic continental crust mixing the juvenile underplated mafic material from the depleted mantle. These results, together with existing data, provide significant information about the evolution history of oceanic crust subduction during the 520-460 Ma. The initiation of subduction occurred during 520-500 Ma with formation of Abei Pluton; subsequent transition from steep-angle to flat-slab subduction at ca.500 Ma due to the arrival of buoyant oceanic plateaus, which induces the formation of 4337 Highland Pluton. With ongoing subduction, the steep-angle subduction system is reestablished to cause the formation of 480-460 Ma Kaladawan Pluton. Meanwhile, it is this model that account for the temporal-spatial distribution of these early Paleozoic magmatic rocks in the North Altun orogenic belt.

Structure and sediment budget of Yinggehai-Song Hong basin, South China Sea: Implications for Cenozoic tectonics and river basin reorganization in Southeast Asia

NASA Astrophysics Data System (ADS)

Lei, Chao; Ren, Jianye; Sternai, Pietro; Fox, Matthew; Willett, Sean; Xie, Xinong; Clift, Peter D.; Liao, Jihua; Wang, Zhengfeng

2015-08-01

The temporal link between offshore stratigraphy and onshore topography is of key importance for understanding the long-term surface evolution of continental margins. Here we present a grid of regional, high-quality reflection seismic and well data to characterize the basin structure. We identify fast subsidence of the basin basement and a lack of brittle faulting of the offshore Red River fault in the Yinggehai-Song Hong basin since 5.5 Ma, despite dextral strike-slip movement on the onshore Red River fault. We calculate the upper-crustal, whole-crustal, and whole-lithospheric stretching factors for the Yinggehai-Song Hong basin, which show that the overall extension observed in the upper crust is substantially less than that observed for the whole crust or whole lithosphere. We suggest that fast basement subsidence after 5.5 Ma may arise from crustal to lithospheric stretching by the regional dynamic lower crustal/mantle flow originated by collision between India-Eurasia and Indian oceanic subduction below the Eurasian margin. In addition, we present a basin wide sediment budget in the Yinggehai-Song Hong basin to reconstruct the sedimentary flux from the Red River drainage constrained by high-resolution age and seismic stratigraphic data. The sediment accumulation rates show a sharp increase at 5.5 Ma, which suggests enhanced onshore erosion rates despite a slowing of tectonic processes. This high sediment supply filled the accommodation space produced by the fast subsidence since 5.5 Ma. Our data further highlight two prominent sharp decreases of the sediment accumulation at 23.3 Ma and 12.5 Ma, which could reflect a loss of drainage area following headwater capture from the Paleo-Red River. However, the low accumulation rate at 12.5 Ma also correlates with drier and therefore less erosive climatic conditions.

Geochronology and geochemistry of late Paleozoic-early Mesozoic igneous rocks of the Erguna Massif, NE China: Implications for the early evolution of the Mongol-Okhotsk tectonic regime

NASA Astrophysics Data System (ADS)

Li, Yu; Xu, Wen-Liang; Wang, Feng; Tang, Jie; Zhao, Shuo; Guo, Peng

2017-08-01

We undertook geochemical and geochronological studies on late Paleozoic-early Mesozoic igneous rocks from the Erguna Massif with the aim of constraining the early evolution of the Mongol-Okhotsk tectonic regime. Zircon crystals from nine representative samples are euhedral-subhedral, display oscillatory growth zoning, and have Th/U values of 0.14-6.48, indicating a magmatic origin. U-Pb dating of zircon using SIMS and LA-ICP-MS indicates that these igneous rocks formed during the Late Devonian (∼365 Ma), late Carboniferous (∼303 Ma), late Permian (∼256 Ma), and Early-Middle Triassic (246-238 Ma). The Late Devonian rhyolites, together with coeval A-type granites, formed in an extensional environment related to the northwestwards subduction of the Heihe-Nenjiang oceanic plate. Their positive εHf(t) values (+8.4 to +14.4) and Hf two-stage model ages (TDM2 = 444-827 Ma) indicate they were derived from a newly accreted continental crustal source. The late Carboniferous granodiorites are geochemically similar to adakites, and their εHf(t) values (+10.4 to +12.3) and Hf two-stage model ages (TDM2 = 500-607 Ma) suggest they were sourced from thickened juvenile lower crustal material, this thickening may be related to the amalgamation of the Erguna-Xing'an and Songnen-Zhangguangcai Range massifs. Rocks of the late Permian to Middle Triassic suite comprise high-K calc-alkaline monzonites, quartz monzonites, granodiorites, and monzogranites. These rocks are relatively enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements. They were emplaced, together with coeval porphyry-type ore deposits, along an active continental margin where the Mongol-Okhotsk oceanic plate was subducting beneath the Erguna Massif.

Internet and Information Control: The Case of China.

ERIC Educational Resources Information Center

Xiaoming, Hao; Zhang, Kewen; Yu, Huang

1996-01-01

Examines the potential impact of computer-mediated communication (CMC) on government controls of information in China. Examines the current development of CMC in China; challenges posed by new media technologies to government information control; and the current policy of the Chinese government towards on-line communication and its implications.…

Age and geochemistry of the intrusive rocks from the Shaquanzi-Hongyuan Pb-Zn mineral district: Implications for the Late Carboniferous tectonic setting and Pb-Zn mineralization in the Eastern Tianshan, NW China

NASA Astrophysics Data System (ADS)

Lu, Wan-Jian; Chen, Hua-Yong; Zhang, Li; Han, Jin-Sheng; Xiao, Bing; Li, Deng-Feng; Zhang, Wei-Feng; Wang, Cheng-Ming; Zhao, Lian-Dang; Jiang, Hong-Jun

2017-12-01

The Central Tianshan Terrane (CTT) in the Eastern Tianshan (Xinjiang, NW China) is an important Pb-Zn metallogenic belt and played a pivotal role in crustal evolution and collisional tectonics of the southern Central Asian Orogenic Belt. The Shaquanzi gabbro and Hongyuan granodiorite are located in the northern margin of the CTT and associated with Pb-Zn mineralization. Zircon U-Pb dating yielded weighted mean ages of 307.2 ± 1.5 Ma and 301.2 ± 1.5 Ma for the Shaquanzi gabbro and the Hongyuan granodiorite, respectively. These rocks are medium-K calc-alkaline series and enriched in large ion lithophile elements (LILEs; e.g., K, Rb, Ba) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), displaying typical arc affinities. The Shaquanzi gabbro shows low Nb/Ta (11.0-14.2), a high Mg# range (56-59), positive zircon εHf(t) (+ 3.30 - + 7.26) and whole rock εNd(t) (+ 0.70 - + 1.38) values, and low ISr ratios (0.704858-0.705137), which indicate that the protolith was probably derived from the sub-continental lithospheric mantle that had been metasomatized by subduction-related fluids. The Hongyuan granodiorite contains hornblende but lack of Al-rich minerals and has low ISr ratios (0.704769-0.706211 < 0.707), suggesting an I-type origin. Moreover, the Hongyuan granodiorite has positive εHf(t) (+ 1.12 - + 5.57) and εNd(t) (+ 0.38 - + 1.86) values, with high Mg# (52), variable Nb/Ta ratios (12.6-12.9), low contents of Ni, Cr and Co and Pb isotopes (206Pb/204Pb = 17.461-18.299, 207Pb/204Pb = 15.541-15.581, 208Pb/204Pb = 37.456-38.129), suggesting the Hongyuan granodiorite was generated by partial melting of juvenile crust sources mixed with some mantle-derived materials. Combined published works with our new geochronological, geological, geochemical and isotopic data, we propose that the CTT may have evolved from a continental arc to a syn-collisional setting during the period of ca. 307-301 Ma. The continuing southward subduction of the Junggar oceanic slab beneath the CTT in the Late Carboniferous resulted in extensive arc-related volcanic rocks emplacement that had indirect links to the Pb-Zn mineralization (e.g., reworked/upgraded).

Petrogenesis of Cretaceous (133-84 Ma) intermediate dykes and host granites in southeastern China: Implications for lithospheric extension, continental crustal growth, and geodynamics of Palaeo-Pacific subduction

NASA Astrophysics Data System (ADS)

Yang, Jinbao; Zhao, Zhidan; Hou, Qingye; Niu, Yaoling; Mo, Xuanxue; Sheng, Dan; Wang, Lili

2018-01-01

This paper presents U-Pb zircon geochronology, petrology, and major and trace element, Sr-Nd and zircon Hf isotopic geochemistry of Cretaceous granites and intermediate dykes in the Quanzhou and Xiamen regions of southeastern China. These data are used to investigate igneous petrogenesis and Cretaceous tectonic evolution, and interpret the geodynamics of Palaeo-Pacific slab subduction. Granites in Quanzhou and Xiamen range in age from 133 Ma to 87 Ma, have high SiO2 and K2O contents, low abundances in P2O5, and an A/CNK index that ranges from 0.97 to 1.09, indicating that they are high-K calc-alkaline metaluminous I-type rocks. Slightly negative ɛ Nd (t) values (- 1.2 to - 4.4), young Nd model ages (0.87 Ga to 1.20 Ga) and positive ɛ Hf (t) values (- 0.5 to + 9.9) of zircon grains indicate that the granites were derived from magmas that melted amphibolite in the middle-lower crust, and which may have assimilated country rocks during emplacement in shallow chambers. The intermediate dykes have no genetic link to the granites and magma mixing was negligible. Eight dyke samples have low SiO2 and high MgO, Ni and Cr contents. Negative ε Nd (t) values (- 1.5 to - 2.7) and positive ε Hf (t) values (2.7 to 7.6) suggest that the dykes were derived from residual basic lower crust after mafic-crystal accumulation. Two samples of adakite-like dykes are characterised by high Sr/Y ratios (89 to 100) and high SiO2, low K2O, Ni, Cr contents. In combination with slightly negative ε Nd (t) values (- 1.7 to - 1.8) and positive ε Hf (t) values (2.9 to 4.3), the adakite-like dykes were derived from cumulate basic lower crust which had a mixed source between depleted mantle- and crust-derived melts. Based on our data, combined with previously published work, we suggest that extension-induced middle-lower crustal melting and underplating of mantle-derived basaltic melts were the principal driving mechanisms for Cretaceous granitic magmatism in coastal Fujian Province. Extension was related to subduction retreat whereas steep slab subduction caused underplating of mantle-derived basaltic melts. These processes were coupled and mainly responsible for the tectonic transition during the Cretaceous from compression to extension in the coastal belt of the Cathaysia Plate.

Elucidating tectonic events and processes from variably tectonized conglomerate clast detrital geochronology: examples from the Hongliuhe Formation in the southern Central Asian Orogenic Belt, NW China

NASA Astrophysics Data System (ADS)

Cleven, Nathan; Lin, Shoufa; Davis, Donald; Xiao, Wenjiao; Guilmette, Carl

2017-04-01

This work expands upon detrital zircon geochronology with a sampling and analysis strategy dating granitoid conglomerate clasts that exhibit differing degrees of internal ductile deformation. As deformation textures within clastic material reflect the variation and history of tectonization in the source region of a deposit, we outline a dating methodology that can provide details of the provenance's tectonomagmatic history from deformation-relative age distributions. The method involves bulk samples of solely granitoid clasts, as they are representative of the magmatic framework within the provenance. The clasts are classified and sorted into three subsets: undeformed, slightly deformed, and deformed. LA-ICPMS U-Pb geochronology is performed on zircon separates of each subset. Our case study, involving the Permian Hongliuhe Formation in the southern Central Asian Orogenic Belt, analyzes each of the three clast subsets, as well as sandstone detrital samples, at three stratigraphic levels to yield a profile of the unroofed provenance. The age spectra of the clast samples exhibit different, wider distributions than sandstone samples, considered an effect of proximity to the respective provenance. Comparisons of clast data to sandstone data, as well as comparisons between stratigraphic levels, yield indications of key tectonic processes, in addition to the typical characteristics provided by detrital geochronology. The clast data indicates a minimal lag time, implying rapid exhumation rates, whereas sandstone data alone would indicate a 90 m.y. lag time. Early Paleozoic arc building episodes appear as Ordovician peaks in sandstone data, and Silurian-Devonian peaks in clast data, indicating a younging of magmatism towards the proximal provenance. A magmatic hiatus starts in the Devonian, correlating with the latest age of deformed clasts, interpreted as timing of collisional tectonics. Provenance interpretation using the correlations seen between the clast and sandstone data proves to be more detailed and more robust than that determined from sandstone samples alone. The variably tectonized clast detrital geochronology method offers a regional reconnaissance tool that can address the practical limits of studying regional granitoid distributions.

The Evolution History of South China Sea: a Synthesis of Recent Geophysical, Geological, and Geochemical Results

NASA Astrophysics Data System (ADS)

Xue, M.; Li, L.; Chen, L.

2016-12-01

South China Sea (SCS) is located in the continental margin of Eurasia plate, where different geological blocks/tectonic plates interact. The dynamic mechanism of the formation of South China Sea (SCS) has been debated for decades. In this study, we first synthesize our geophysical results obtained in South China Sea, including an updated 3D velocity model from surface tomography using surrounding land stations and regional earthquakes, and shear wave splitting results obtained at surrounding land stations and OBS, using local, regional, and teleseismic earthquakes. The observed splitting results in South China Sea are complex: the fast polarization direction beneath the central basin is approximately NE-SW, nearly parallel to the extinct ridge in the central basin of SCS; however, the fast axis within the slab is trench-parallel outside the ridge subduction region. In 3D velocity models, subducting slabs are observed as dipping high velocity anomalies, and discontinuous low velocities are observed above the subduction slab, as well as in the basin. How the splitting observations are connected with the velocity models? How observations are linked to one another? How are the observations in central basin linked with surrounding region? We are aiming to link these observations themselves as well as with newly published results from geophysics, geochemistry, and geology in this region. Such a synthesis will improve our understanding about the evolution of South China Sea and facilitate new ideas.

Commentary: The Feasibility of Subduction and Implications for Plate Tectonics on Jupiter's Moon Europa

NASA Astrophysics Data System (ADS)

Kattenhorn, Simon A.

2018-03-01

A new modeling-based study by Johnson et al. (2017, https://doi.org/10.1002/2017JE005370) lends support to the hypothesis that portions of Europa's surface may have been removed by the process of subduction, as suggested by Kattenhorn and Prockter (2014, https://doi.org/10.1038/NGEO2245). Using a simple 1-D model that tracks the thermal and density structure of a descending ice plate, Johnson et al. show that ice plates with 10% porosity and overall salt contents of 5%, which differ in salt content by 2.5% from the surrounding reference ice shell, are nonbuoyant and thus likely to sink through the underlying, convecting portion of the ice shell. The feasibility of subduction in an ice shell is critical to the existence of icy plate tectonics, which is hypothesized to exist at least locally on Europa, potentially making it the only other Solar System body other than Earth with a surface modified by plate tectonics.

Determination of Cenozoic sedimentary structures using integrated geophysical surveys: A case study in the Barkol Basin, Xinjiang, China

NASA Astrophysics Data System (ADS)

Sun, Kai; Chen, Chao; Du, Jinsong; Wang, Limin; Lei, Binhua

2018-01-01

Thickness estimation of sedimentary basin is a complex geological problem, especially in an orogenic environment. Intense and multiple tectonic movements and climate changes result in inhomogeneity of sedimentary layers and basement configurations, which making sedimentary structure modelling difficult. In this study, integrated geophysical methods, including gravity, magnetotelluric (MT) sounding and electrical resistivity tomography (ERT), were used to estimate basement relief to understand the geological structure and evolution of the eastern Barkol Basin in China. This basin formed with the uplift of the eastern Tianshan during the Cenozoic. Gravity anomaly map revealed the framework of the entire area, and ERT as well as MT sections reflected the geoelectric features of the Cenozoic two-layer distribution. Therefore, gravity data, constrained by MT, ERT and boreholes, were utilized to estimate the spatial distribution of the Quaternary layer. The gravity effect of the Quaternary layer related to the Tertiary layer was later subtracted to obtain the residual anomaly for inversion. For the Tertiary layer, the study area was divided into several parts because of lateral difference of density contrasts. Gravity data were interpreted to determine the density contrast constrained by the MT results. The basement relief can be verified by geological investigation, including the uplift process and regional tectonic setting. The agreement between geophysical survey and prior information from geology emphasizes the importance of integrated geophysical survey as a complementary means of geological studies in this region.

Submarine landslides on the north continental slope of the South China Sea

NASA Astrophysics Data System (ADS)

Wang, Weiwei; Wang, Dawei; Wu, Shiguo; Völker, David; Zeng, Hongliu; Cai, Guanqiang; Li, Qingping

2018-02-01

Recent and paleo-submarine landslides are widely distributed within strata in deep-water areas along continental slopes, uplifts, and carbonate platforms on the north continental margin of the South China Sea (SCS). In this paper, high-resolution 3D seismic data and multibeam data based on seismic sedimentology and geomorphology are employed to assist in identifying submarine landslides. In addition, deposition models are proposed that are based on specific geological structures and features, and which illustrate the local stress field over entire submarine landslides in deep-water areas of the SCS. The SCS is one of the largest fluvial sediment sinks in enclosed or semi-enclosed marginal seas worldwide. It therefore provides a set of preconditions for the formation of submarine landslides, including rapid sediment accumulation, formation of gas hydrates, and fluid overpressure. A new concept involving temporal and spatial analyses is tested to construct a relationship between submarine landslides and different time scale trigger mechanisms, and three mechanisms are discussed in the context of spatial scale and temporal frequency: evolution of slope gradient and overpressure, global environmental changes, and tectonic events. Submarine landslides that are triggered by tectonic events are the largest but occur less frequently, while submarine landslides triggered by the combination of slope gradient and over-pressure evolution are the smallest but most frequently occurring events. In summary, analysis shows that the formation of submarine landslides is a complex process involving the operation of different factors on various time scales.

Hydrogeochemical characteristics and genesis of the high-temperature geothermal system in the Tashkorgan basin of the Pamir syntax, western China

NASA Astrophysics Data System (ADS)

Li, Yiman; Pang, Zhonghe; Yang, Fengtian; Yuan, Lijuan; Tang, Pinghui

2017-11-01

High-temperature geothermal systems in China, such as those found in Tenchong and Tibet, are common. A similar system without obvious manifestations found in the Tashkorgan basin in the western Xinjiang Autonomous Region, however, was not expected. The results from borehole measurements and predictions with geothermometers, such as quartz, Na-K and Na-K-Mg, indicate that the reservoir temperature is approximately 250-260 °C. Geothermal water is high in Total Dissolved Solids (>2.5 g/L) and SiO2 content (>273 mg/L), and the water type is Cl·SO4-Na, likely resulting from water-rock interactions in the granodiorite reservoirs. Based on isotope analysis, it appears to be recharged by local precipitation and river water. Evidence from the relationships between major ions and the Cl and molar Na/Cl ratio suggests mixing between deep geothermal water and shallow cold groundwater during the upwelling process. Mixing ratios calculated by the relationship between Cl and SiO2 show that the proportion from cold end-members are 96-99% and 40-90% for riparian zone springs and geothermal water from boreholes, respectively. Active regional tectonic and Neo-tectonic movements in the Pamir syntax as well as radioactive elements in the granodiorite reservoir of the Himalayan stage provide basis for the high heat flow background (150-350 mW/m2). NNW trending fault systems intersecting with overlying NE faults provide circulation conduits with high permeability for geothermal water.

Crustal structure, geophysical models and contemporary tectonism of the Colorado Plateau

NASA Technical Reports Server (NTRS)

Keller, G. R.; Braile, L. W.; Morgan, P.

1979-01-01

A regional analysis of the crust and upper mantle of the Colorado Plateau is presented, using existing geophysical and geological data combined with new surface wave dispersion and groundwater geothermometry data; the tectonic implications of these models are also investigated. Surface wave and seismic refraction data indicate that the crust of the interior of the Colorado Plateau is 44 + or - 3 km thick, and its crustal structure is typical of stable continental areas. Pn velocities, however, appear to be lower (7.8 km/s) than would be expected in a stable region, while silica geothermometry indicates that the average heat flow for the plateau is 55 mW per sq m (1.3 HFU).

Tectonics of the Maryland Piedmont along the Potomac River; insight since 1960 and potential transfer to the Pennsylvania Piedmont

USGS Publications Warehouse

Southworth, C. Scott; Wise, Donald U.; Fleeger, Gary M.

2010-01-01

This is a summary of a half century of research in the Mary land Piedmont and how it may or may not have implications for the Piedmont of Pennsylvania. Much of the field mapping and all of the isotopic analyses of rocks and minerals of the Maryland Piedmont have been conducted since the 1960 Field Conference of Pennsylvania Geologists “Some tectonic and structural problems of the Appalachian Piedmont along the Susquehanna River”. The Piedmont rocks of Maryland and Pennsylvania occur in a critical place within the central Appalachian Pennsylvania embayment (Thomas, 1977), which likely contributed to the distribution of lithologies and structures.

Shallow moonquakes - Depth, distribution and implications as to the present state of the lunar interior

NASA Technical Reports Server (NTRS)

Nakamura, Y.; Latham, G. V.; Dorman, H. J.; Ibrahim, A.-B. K.; Koyama, J.; Horvath, P.

1979-01-01

The observed seismic amplitudes of HFT (high-frequency teleseismic) events do not vary with distance as expected for surface sources, but are consistent with sources in the upper mantle of the moon. Thus, the upper mantle of the moon is the only zone where tectonic stresses deriving from differential thermal contraction and expansion of the lunar interior are presently high enough to cause moonquakes. The distribution of shallow moonquake epicenters suggests a possible correlation with impact basins, implying a lasting tectonic influence of impact basins long after their formation. The finite depths now assigned to these shallow moonquakes necessitate further revision to the seismic structural model of the lunar interior.

China Naval Modernization: Implications for U.S. Navy Capabilities -- Background and Issues for Congress

DTIC Science & Technology

2005-11-18

2005, p. 23; Edward Cody, “China Builds A Smaller, Stronger Military,” Washington Post, April 12, 2005, p. 1; Bryan Bender, “China Bolsters Its Forces...testimony, p. 1; 2003 CFR task force report, pp. 24-25, 31-32, 62-63; Edward Cody, “China Builds A Smaller, Stronger Military,” April 12, 2005, p. 1; David...encircle” China, the report said. See also Edward Cody, “China Builds A Smaller, Stronger Military,” Washington Post, April 12, 2005, p. 1. 84 For

A review of structural patterns and melting processes in the Archean craton of West Greenland: Evidence for crustal growth at convergent plate margins as opposed to non-uniformitarian models

NASA Astrophysics Data System (ADS)

Polat, Ali; Wang, Lu; Appel, Peter W. U.

2015-11-01

The Archean craton of West Greenland consists of many fault-bounded Eoarchean to Neoarchean tectonic terranes (crustal blocks). These tectonic terranes are composed mainly of tonalite-trondhjemite-granodiorite (TTG) gneisses, granitic gneisses, metavolcanic-dominated supracrustal belts, layered anorthositic complexes, and late- to post-tectonic granites. Rock assemblages and geochemical signatures in these terranes suggest that they represent fragments of dismembered oceanic island arcs, consisting mainly of TTG plutons, tholeiitic to calc-alkaline basalts, boninites, picrites, and cumulate layers of ultramafic rocks, gabbros, leucogabbros and anorthosites, with minor sedimentary rocks. The structural characteristics of the terrane boundaries are consistent with the assembly of these island arcs through modern style of horizontal tectonics, suggesting that the Archean craton of West Greenland grew at convergent plate margins. Several supracrustal belts that occur at or near the terrane boundaries are interpreted as relict accretionary prisms. The terranes display fold and thrust structures and contain numerous 10 cm to 20 m wide bifurcating, ductile shear zones that are characterized by a variety of structures including transposed and redistributed isoclinal folds. Geometrically these structures are similar to those occurring on regional scales, suggesting that the Archean craton of West Greenland can be interpreted as a continental scale accretionary complex, such as the Paleozoic Altaids. Melting of metavolcanic rocks during tectonic thickening in the arcs played an important role in the generation of TTGs. Non-uniformitarian models proposed for the origin of Archean terranes have no analogs in the geologic record and are inconsistent with structural, lithological, petrological and geochemical data collected from Archean terranes over the last four decades. The style of deformation and generation of felsic rocks on outcrop scales in the Archean craton of West Greenland and the Mesozoic Sulu orogenic belt of eastern China are similar, consistent with the formation of Archean continental crust by subduction zone processes.

Lineament Azimuths on Europa: Implications for Evolution of the Europan Ice Shell

NASA Astrophysics Data System (ADS)

Kachingwe, M.; Rhoden, A.; Lekic, V.; Hurford, T., Jr.; Henning, W. G.

2016-12-01

Tectonic activity on Europa has been linked to tidal stress caused by its eccentric orbit, finite obliquity, and possibly non-synchronous rotation of the icy shell. Cycloids and other lineaments are thought to form in response to tidal normal stress while strike-slip motion along preexisting faults has been attributed to tidal shear stress. Tectonic features can thus provide constraints on the rotational parameters that govern tidal stress and insight into the tidal-tectonic processes operating on ice-covered ocean bodies. Past lineament azimuth predictions based on stress models accounting for either spin pole precession or longitude translation yielded distributions that varied with location on Europa (e.g. Hurford, 2005; Fig. 16 of Rhoden and Hurford, 2013). Until now, these predicted azimuths have only been tested on a few spatially restricted regions. Additionally, these predictions were made using a thin shell approximation, which neglects the viscoelastic response of Europa's ice shell. Here, we present new measurements of lineament azimuths across geographically diverse regions of Europa, focusing on locations where lineament azimuths have never before been measured but which have been imaged at better than 250 km/pixel resolution. We focus on lineaments that do not exhibit substantial curvature, and we quantify deviations in azimuth observed along each lineament. We quantitatively compare the observed distributions against published predictions as well as new predictions made with a viscoelastic tidal stress model. These results have implications for Europa's interior and the evolution of tidal stress over time.

Seismic Refraction & Wide-angle Reflection Experiment on the Northern Margin of North China Craton -Data Acquisition and Preliminary Processing Result

NASA Astrophysics Data System (ADS)

Li, W.; Gao, R.; Keller, G. R.; Hou, H.; Li, Q.; Cox, C. M.; Chang, J. C.; Zhang, J.; Guan, Y.

2010-12-01

The evolution history of Central Asian Orogen Belt (CAOB) is still the main tectonic problems in northeastern Asia. The Siberia Craton (NC), North China Craton (NCC) and several blocks collided, and the resulting tectonic collage formed as the Paleo-Asian Ocean disappeared. Concerning the northern margin of North China Craton, many different geological questions remain unanswered, such as: the intracontinental orogenic process in the Yanshan orogen and the nature and location of the suture between the southern NC and the northern NCC. In Dec 2009, a 400 km long seismic refraction and wide-angle reflection profile was completed jointly by Institute of Geology, CAGS and University of Oklahoma. The survey line extended from the west end of the Yanshan orogen, across a granitoid belt to the Solonker suture zone. The recording of seismic waves from 8 explosions (500~1500 kg each) was conducted in four deployments of 300 Reftek125 (Texan) seismic recorders, with an average spacing of 1 km. For the calculations, we used the Rayinvr, Vmed and Zplot programs for ray tracing, model modification and phase picking. The initial result show that: 1)the depth of low velocity sediment cover ranges from 0.6 to 2.7 km (velocity: 2.8~5.6 km/s); 2)the depth of basement is 5.6~10 km (the depth of basement under the granitoid belt deepens to 10 km and velocity increases to 6.2 km/s); 3)the upper crust extends to a depth of 15.5~21 km and has the P-wave velocities between 5.6 and 6.4 km/s; 4)the thickness of the lower crust ranges from 22~28 km(velocity: 6.4~6.9 km/s); and 5)the depth of Moho varies from 39.5 km under the granitoid belt to 49 km under the Yanshan orogen. Based on these results, we can preliminarily deduce that: 1) the concave depression of the Moho observed represents the root of the Yanshan orogen, and it may prove that the orogen is dominated by thick-skinned tectonics; 2) the shape of velocity variations under the granitoid belt is suggestive of a magma conduit. It may be connected with subduction-collision magmatism between the southern NC and the northern NCC along the Solonker suture zone. Supported by Sinoprobe-02 and US NSF PIRE grant (0730154)

S-N profile of Receive function image across Qiangtang, Northern Tibet

NASA Astrophysics Data System (ADS)

He, R.; Gao, R.; Deng, G.; Li, W.; Hou, H.; Lu, Z.; Xiong, X.

2010-12-01

Huge thicken Triassic and Jurassic sediments widely outcorp within Qiangtang, tens of oilstones outcorped within Qiangtang showed that Qiangtang have a good advantage in exploring oil and gas. So, the basement beneath Qiangtang and its structures have become the key for us to look for oil and gas accumulations. Within tectonic settings of Qiangtang, the center uplift of Qiangtang (abbr. CUQT) and its developments have become the great barrier to understand the basement and its structures within the basin. Because of complicated structure relief and blueschist and ophiolite outcorps within the CUQT, there was the paradox for lots of geologist to understand how the CUQT developed. One was that it formed under the extension environment. On the contrary, CUQT was ever paleo-Tethys suture zone, because CUQT had the belt of blueschists and ophiolite. So, different opinions to CUQT resulted in the different viewpoints in the basin beneath Qiangtang terrane. Surveying deep structure beneath the CUQT was the key to understand the basement under Qiangtang. In past two years, we have deployed 40 portable broadband seismic stations along E88°to across the whole Qiangtang from Bangong-Nujiang Suture, southern side of Qiangtang terrane, to northern margin of Qiangtang terrane. The temporary network collected a lot of farm waveform data, which is helpful to know about the more finest deep structure beneath the CUQT and its two sides basin. We used P-to-S receiver functions methods to get deep structure image beneath the profile. The preliminary results showed: (1) Within the crust, the velocity structure beneath southern Qiangtang basin is higher than beneath northern Qiangtang basin. (2) Sedimental layer within southern Qiangtang basin is thichen than within northern Qiangtang basin. Combined with other geophysical information, CUQT is an important lithosphere-level boundary fault belts, and southern Qiangtang basin have great difference with northern Qiangtang basin, in velocity structure, basement depth, although during Qiangtang terrane had been strongly reconstructed laterly, especiall in Cenozoic uplift of the Tibetan plateau. The above-mentioned evidences showed that Qiangtang terrance in present-day tectonic study should be divided by CUQT into two parts which includes south Qiangtang terrane in sourthern side and north Qiangtang terrrane in northern side. Because CUQT and Qiangtang terrane were traditionally named, tectonic settings within the Tibetan plateau had to be remarked renewedly . This project was financially supported together by Natural Science Foundations of China (40774051, 40974060), the basic outlay of scientific research work from Ministry of Science and Technology, China in 2009 ( J0915 ), China National Probing Project (SinoProbe-02).

Elite International Baccalaureate Diploma Programme Schools and Inter-Cultural Understanding in China

ERIC Educational Resources Information Center

Wright, Ewan; Lee, Moosung

2014-01-01

The number of International Baccalaureate Diploma Programme (IBDP) schools has increased rapidly in China in recent years. However, access to schools offering the IBDP remains restricted to a relatively elite minority of China's population due to enrolment barriers for Chinese nationals and relatively high school fees. An implication is that…

Reassessing China's Higher Education Development: A Focus on Academic Culture

ERIC Educational Resources Information Center

Yang, Rui

2015-01-01

During the past three and a half decades, China has been progressing in higher education in a surprisingly dramatic manner, evidenced especially by scientific publications and sheer numbers of graduates. Such a fact has national, regional and global implications. China's higher education development and its future directions are now placed highly…

Marriage in the People's Republic of China: Analysis of a New Law.

ERIC Educational Resources Information Center

Engel, John W.

1984-01-01

Analyzes those articles of China's marriage law that deal with marriage contracts. Articles relevant to arranged marriage, marriage by purchase and dowry customs, concubinage or polygamy, marriage restrictions, rituals, and residence customs are analyzed in terms of their contexts in traditional and modern China. Implications are discussed.…

Petrogenesis of the NE Gondwanan uppermost Ediacaran-Lower Cretaceous siliciclastic sequence of Jordan: Provenance, tectonic, and climatic implications

NASA Astrophysics Data System (ADS)

Amireh, Belal S.

2018-04-01

Detrital framework modes of the NE Gondwanan uppermost Ediacaran-Lower Cretaceous siliciclastic sequence of Jordan are determined employing the routine polarized light microscope. The lower part of this sequence constitutes a segment of the vast lower Paleozoic siliciclastic sheet flanking the northern Gondwana margin that was deposited over a regional unconformity truncating the outskirts of the East African orogen in the aftermath of the Neoproterozoic amalgamation of Gondwana. The research aims to evaluate the factors governing the detrital light mineral composition of this sandstone. The provenance terranes of the Arabian craton controlled by plate tectonics appear to be the primary factor in most of the formations, which could be either directly inferred employing Dickinson's compositional triangles or implied utilizing the petrographic data achieved and the available tectonic and geological data. The Arabian-Nubian Shield constitutes invariably the craton interior or the transitional provenance terrane within the NE Gondwana continental block that consistently supplied sandy detritus through northward-flowing braided rivers to all the lower Paleozoic formations. On the other hand, the Lower Cretaceous Series received siliciclastic debris, through braided-meandering rivers having same northward dispersal direction, additionally from the lower Paleozoic and lower-middle Mesozoic platform strata in the Arabian Craton. The formations making about 50% of the siliciclastic sequence represent a success for Dickinson's plate tectonics-provenance approach in attributing the detrital framework components primarily to the plate tectonic setting of the provenance terranes. However, even under this success, the varying effects of the other secondary sedimentological and paleoclimatological factors are important and could be crucial. The inapplicability of this approach to infer the appropriate provenance terranes of the remaining formations could be ascribed either to the special influence of local intracratonic syn-rift rhyolitic extrusions, where their plate tectonic setting is not represented by the standard plate tectonics-provenance diagrams, or to the rather unusual effect of the Late Ordovician glacial event.

Provenance evolution in the northern South China Sea and its implication of paleo-drainage systems from Eocene to Miocene

NASA Astrophysics Data System (ADS)

Cui, Y.; Shao, L.; Qiao, P.

2017-12-01

Geochemistry analysis and detrital zircon U-Pb geochronology aim to fully investigate the "source to sink" patterns of northern South China Sea (SCS) from Eocene to Miocene. Evolutional history of the surrounding drainage system has been highly focused on, in comparison to sedimentary characteristics of the SCS basins. Rapid local provenances were prevailed while large-scale fluvial transport remained to evolve during Eocene. Since early Oligocene, sediments from the South China were more abundantly delivered to the northeastern Pearl River Mouth Basin in addition to Dongsha volcanism supplement. Aside from intrabasinal provenances, long-distance transport started to play significant role in Zhu1 Depression, possibly reaching western and southern Baiyun Sag, partially. Western Qiongdongnan Basin might accept sediments from central Vietnam with its eastern area more affected from Hainan Island and Southern Uplift. In the late Oligocene, due to drastic sea-level changes and rapid exhumation, mafic to altramafic sediments were transported in abundance to Central Depression from Kontum Massif, while multiple provenances casted integrated influence on eastern sedimentary sequences. Southern Baiyun Sag was also affected by an increased supplement from the west Shenhu Uplift or even central Vietnam. Overall pattern did not change greatly since early Miocene, but long-distance transport has become dominant in the northern SCS. Under controlled by regional tectonic cycles, Pearl River gradually evolved into the present scale and exerted its influence on basinal provenances by several stages. Zhu1 Depression was partially delivered sediments from its tributaries in early Oligocene while northern Zhu2 Depression has not been provided abundant materials until late Oligocene. Meanwhile, although detailed transportation routine remains uncertain and controversial, an impressive paleo-channel spanning the whole Qiongdongnan Basin was presumed to supply huge amount of mafic to ultramafic sediments from central Vietnam drainage systems to the further eastern regions, which even reaching Baiyun Sag since the late Oligocene or even earlier. This unique channel was later likely to be replaced by the adjacent provenance of Hainan Island after early Miocene.

Stress Interactions Between the 1976 Magnitude 7.8 Tangshan Earthquake and Adjacent Fault Systems in Northern China

NASA Astrophysics Data System (ADS)

Zhang, Z.; Lin, J.; Chen, Y. J.

2004-12-01

The 28 July 1976 ML = 7.8 Tangshan earthquake struck a highly populated metropolitan center in northern China and was one of the most devastating earthquakes in modern history. Its occurrence has significantly changed the Coulomb stresses on a complex network of strike-slip, normal, and thrust faults in the region, potentially heightened the odds of future earthquakes on some of these fault segments. We have conducted a detailed analysis of the 3D stress effects of the Tangshan earthquake on its neighboring faults, the relationship between stress transfer and aftershock locations, and the implications for future seismic hazard in the region. Available seismic and geodetic data, although limited, indicate that the Tangshan main shock sequence is composed of complex rupture on 2-3 fault segments. The dominant rupture mode is right-lateral strike-slip on two adjoining sub-segments that strike N5¡aE and N35¡aE, respectively. We calculated that the Tangshan main shock sequence has increased the Coulomb failure stress by more than 1 bar in the vicinity of the Lunanxian district to the east, where the largest aftershock (ML = 7.1) occurred 15 hours after the Tangshan main event. The second largest aftershock (ML = 6.8) occurred on the Ninghe fault to the southwest of the main rupture, in a transitional region between the calculated Coulomb stress increase and decrease. The majority of the ML > 5.0 aftershocks also occurred in areas of calculated Coulomb stress increase. Our analyses further indicate that the Coulomb stress on portions of other fault segments, including the Leting and Lulong fault to the east and Yejito fault to the north, may also have been increased. Thus it is critical to obtain estimates of earthquake repeat times on these and other tectonic faults and to acquire continuous GPS and space geodetic measurements. Investigation of stress interaction and earthquake triggering in northern China is not only highly societal relevant but also important for advancing our understanding of the fundamental characteristics of earthquakes in regions of diffuse continental deformation.

Plate Tectonics on Earth-like Planets: Implications for Habitability

NASA Astrophysics Data System (ADS)

Noack, L.; Breuer, D.

2011-12-01

Plate tectonics has been suggested to be essential for life (see e.g. [1]) due to the replenishment of nutrients and its role in the stabilization of the atmosphere temperature through the carbon-silicate cycle. Whether plate tectonics can prevail on a planet should depend on several factors, e.g. planetary mass, age of the planet, water content (at the surface and in the interior), surface temperature, mantle rheology, density variations in the mantle due to partial melting, and life itself by promoting erosion processes and perhaps even the production of continental rock [2]. In the present study, we have investigated how planetary mass, internal heating, surface temperature and water content in the mantle would factor for the probability of plate tectonics to occur on a planet. We allow the viscosity to be a function of pressure [3], an effect mostly neglected in previous discussions of plate tectonics on exoplanets [4, 5]. With the pressure-dependence of viscosity allowed for, the lower mantle may become too viscous in massive planets for convection to occur. When varying the planetary mass between 0.1 and 10 Earth masses, we find a maximum for the likelihood of plate tectonics to occur for planetary masses around a few Earth masses. For these masses the convective stresses acting at the base of the lithosphere are strongest and may become larger than the lithosphere yield strength. The optimum planetary mass varies slightly depending on the parameter values used (e.g. wet or dry rheology; initial mantle temperature). However, the peak in likelihood of plate tectonics remains roughly in the range of one to five Earth masses for reasonable parameter choices. Internal heating has a similar effect on the occurrence of plate tectonics as the planetary mass, i.e. there is a peak in the probability of plate tectonics depending on the internal heating rate. This result suggests that a planet may evolve as a consequence of radioactive decay into and out of the plate tectonics regime. References [1] Parnell, J. (2004): Plate tectonics, surface mineralogy, and the early evolution of life. Int. J. Astrobio. 3(2): 131-137. [2] Rosing, M.T.; D.K. Bird, N.H. Sleep, W. Glassley, and F. Albar (2006): The rise of continents - An essay on the geologic consequences of photosynthesis. Palaeogeography, Palaeoclimatology, Palaeoecology 232 (2006) 99-11. [3] Stamenkovic, V.; D. Breuer and T. Spohn (2011): Thermal and transport properties of mantle rock at high pressure: Applications to super-Earths. Submitted to Icarus. [4] Valencia, D., R.J. O'Connell and D.D. Sasselov (2007): Inevitability of plate tectonics on super-Earths. Astrophys. J. Let. 670(1): 45-48. [5] O'Neill, C. and A. Lenardic (2007). Geological consequences of super-sized Earths. GRL 34: 1-41.

The crustal structures from Wuyi-Yunkai orogen to Taiwan orogen: the onshore-offshore wide-angle seismic experiment of TAIGER and ATSEE projects

NASA Astrophysics Data System (ADS)

Kuochen, H.; Kuo, N. Y. W.; Wang, C. Y.; Jin, X.; Cai, H. T.; Lin, J. Y.; Wu, F. T.; Yen, H. Y.; Huang, B. S.; Liang, W. T.; Okaya, D. A.; Brown, L. D.

2015-12-01

The crustal structure is key information for understanding the tectonic framework and geological evolution in the southeastern China and its adjacent area. In this study, we integrated the data sets from the TAIGER and ATSEE projects to resolve onshore-offshore deep crustal seismic profiles from the Wuyi-Yunkai orogen to the Taiwan orogen in southeastern China. Totally, there are three seismic profiles resolved and the longest profile is 850 km. Unlike 2D and 3D first arrival travel-time tomography from previous studies, we used both refracted and reflected phases (Pg, Pn, PcP, and PmP) to model the crustal structures and the crustal reflectors. 40 shots, 2 earthquakes, and about 1,950 stations were used and 15,319 arrivals were picked among three transects. As a result, the complex crustal evolution since Paleozoic era are shown, which involved the closed Paleozoic rifted basin in central Fujian, the Cenozoic extension due to South China sea opening beneath the coastline of southern Fujian, and the on-going collision of the Taiwan orogen.

THE LITHOSPHERIC MAGNETIC FIELD ALONG THE NISHAN-GUYANG PROFILE, CHINA 6 datesYuan Jiehao1; Gu Zuowen1; Chen Bin1; Xu Rugang2; Wang Lie2; Wang Can1 1. Institute of Geophysics, China Earthquake Administration(IGP CEA), yjh810405@163.com 2. Anhui Earthquake Administration

NASA Astrophysics Data System (ADS)

Yuan, J.

2014-12-01

In order to research the lithospheric magnetic field and the magnetization structure, the geomagnetic field was surveyed along the Nishan-Guyang profile with 900 km long in the Neimenggu and Shanxi provinces in China. The distance between the adjacent geomagnetic sites is about 7 km along the profile. The geomagnetic data were analyzed, and the lithospheric magnetic field was obtained. Using the upward continuation method, the geomagnetic anomalies in different depths were obtained: the basement anomaly, the upper crust anomaly and the superficial anomaly. Basing on these geomagnetic anomalies, the magnetization structure was obtained by using the software of the ModelVision 11.0. The preliminary results show: (1) The geomagnetic anomalies have good relationship with the local geological structure. (2) The magnetization structure is related to the depth variation of the Curie interface, the values of the magnetic susceptibility, the seismic activity and the tectonic block.

Inhomogeneous Crustal Structure of the Rifting in the Okinawa Trough, a Backarc Basin West of Kyushu, Japan, Deduced from Seismic Reflection and Refraction Data

NASA Astrophysics Data System (ADS)

Nishizawa, A.; Kaneda, K.; Oikawa, M.; Horiuchi, D.; Fujioka, Y.; Okada, C.

2017-12-01

Several depressions found under the thick sediments in the East China Sea shelf have been considered as failed rift basins. Their formation age becomes progressively younger from NW to SE and the youngest rift basin is the Okinawa Trough, an active backarc basin of the Ryukyu (Nansei-Shoto) arc-trench system, to the southwest of Kyusyu, Japan. Its rifting is in progress and related hydrothermal activity is present in the trough. The knowledge of the crustal structure of the trough is fundamental to understand the current active tectonics and predict the future of the trough. We, Japan Coast Guard, have conducted extensive seismic reflection and refraction surveys in the Ryukyu region since 2008 and compiled the seismic structures of the Okinawa Trough. We will show the crustal structures along seven along-trough and ten across-trough seismic survey lines. The P-wave velocity models beneath the Okinawa Trough generally show a thinned continental/island arc crust consisting of upper, middle, and lower crusts. Moho depths below the trough were estimated mainly from Moho reflection (PmP) travel times. The crustal thickness of the trough is thinner than those of the East China Sea shelf and of the Ryukyu Islands. The depth of the Moho below the trough decreases from over 30 km in the north to about 13 km in the south, indicating a difference in degree of the rifting process. The position of the shallowest Moho along the across-trough lines in the northern trough does not necessarily correspond to the center of the trough defined as the deepest water depth, but it corresponds to the transition area between the East China Sea shelf and the Okinawa Trough. An M7.1 earthquake occurred at the transition area on Nov. 14, 2015 (JST) and many aftershocks were observed along the transition. This seismic activity demonstrated that the area is under rifting tectonics in the present.

Thermal and exhumation history of the central Tianshan (NW China): Constraints by U-Pb geochronology and Ar-Ar and (U-Th)/He thermochronology

NASA Astrophysics Data System (ADS)

Yin, J.; Chen, W.; Hodges, K. V.; Xiao, W.; Van Soest, M. C.; Cai, K.; Zhang, B.; Mercer, C. M.; Yuan, C.

2015-12-01

Geochronology and thermochronology using multiple mineral-isotopic chronometers reveals the thermo-tectonic history of the central Tianshan (NW China) from emplacement to exhumation. Granites from the central Tianshan, which are associated with the southward subduction of the northern Tianshan Ocean, have been dated at 362-354 Ma using the LA-ICP-MS Zircon U-Pb method. A younger diorite sample (282 ± 1 Ma, Zircon U-Pb method by LA-ICP-MS) from northern Tianshan formed during the final closure of the Northern Tianshan Ocean when the Junggar Block collided with the Yili-Central Tianshan Block. 40Ar/39Ar step-wise heating plateau dates (biotite Ar/Ar: 312-293 Ma; Plagioclase Ar/Ar: 270-229 Ma) from the Central Tianshan show rapid post-magmatic cooling during the Late Carboniferous-Early Permian followed by a more modest rate of cooling from the middle Permian to the middle Jurassic. The northern Tianshan diorite (biotite Ar/Ar: 240 ± 1 Ma) also reveals a middle Jurassic cooling. Apatite (U-Th )/He dates from the central Tianshan samples range from ca. 130 Ma to ca. 116 Ma. The Apatite (U-Th )/He date for the northern Tianshan sample is ca. 27 Ma. Previous studies also reported Apatite (U-Th)/He ages of ca. 44 Ma-11 Ma in the Baluntai area of the southern Central Tianshan[1]. Two episodes of cooling are distinguished by thermal history modelling: (1) Mesozoic cooling occurred as the result of the exhumation and tectonic reactivation of the central Tianshan; and (2) The Tianshan orogenic belt has been rapidly exhumed since the Middle Cenozoic. References [1] Lü, H.H., Chang, Y., Wang, W., Zhou, Z.Y., 2013. Rapid exhumation of the Tianshan Mountains since the early Miocene: Evidence from combined apatite fission track and (U-Th)/He thermochronology. Science China: Earth Sciences, 43(12): 1964-1974 (in Chinese).

Phylogeny and biogeography of South Chinese brown frogs (Ranidae, Anura).

PubMed

Zhou, Yu; Wang, Sirui; Zhu, Hedan; Li, Pipeng; Yang, Baotian; Ma, Jianzhang

2017-01-01

Few studies have explored the role of Cenozoic tectonic evolution in shaping the patterns and processes of extant animal distributions in and around East Asia. In this study, we selected South Chinese brown frogs as a model to examine the phylogenetic and biogeographical consequences of Miocene tectonic events within South China and its margins. We used mitochondrial and nuclear molecular data to reconstruct phylogenetic interrelationships among Chinese brown frogs using Bayesian and maximum likelihood analyses. The phylogeny results show that there are four main clades of Chinese brown frogs. Excepting the three commonly known Chinese brown frog species groups, R. maoershanensis forms an independent clade nearest to the R. japonica group. Phylogeny and P-distance analyses confirmed R. maoershanensis as a valid species. Among South Chinese brown frogs, there are four subclades associated with four geographical areas: (I) R. maoershanensis; (II) R. japonica; (III) R. chaochiaoensis; and (IV) other species of the R. longicrus species group. Divergence times, estimated using mitochondrial sequences, place the vicariance events among the four subclades in the middle to late Miocene epoch. Our results suggest that (1) South Chinese brown frogs originated due to a vicariance event separating them from the R. chensinensis species group at the time of the Geological movement (~18 million years ago, Ma) in southern Tibet and the Himalayan region; (2) the separation and speciation of R. maoershanensis from the R. japonica group occurred due to the dry climate at approximately 16 Ma; (3) South Chinese brown frogs migrated from South China to Japan at the time (~10.8 Ma) that the global sea-level fell and the East China Sea Shelf Basin was swamp facies, when a land gallery may have formed across the sea to connect the two areas; and (4) R. chaochiaoensis separated from other species of the R. longicrus species group during the uplift of the Tibetan Plateau at approximately 9.5 Ma.

North Qinling Terrain as a provenance of Kuanping Group: LA-ICP-MS U-Pb Geochronology of detrital zircons

NASA Astrophysics Data System (ADS)

Hu, B.; Li, S.; Zhai, M.; Wu, J.; Jia, X.

2017-12-01

Though some Neoproterozoic S-type granites in the North Qinling Terrain (NQT), China indicate the collision between the NQT and an unknown block, there are still controversial. The LA-ICP-MS U-Pb ages of detrital zircons of meta-sandstones from the Kuanping Group in Luonan area, NQT, provide sedimentology evidence to prove that the NQT and an unknown block from Rodinia supercontinent have been collided during Meso-Neoproterozoic. The U-Pb ages of detrital zircons from the Kuanping Group show that the main age peaks are at 2.58 Ga, 2.46 Ga, 2.0 Ga, 1.78 Ga, 1.6 Ga, 1.45 Ga and 1.27 Ga. The youngest age of 880 Ma indicates that the sedimentary age of the Kuanping Group is less than 880 Ma. The provenances, which provide 1.45 - 0.88 Ga sediments may come from NQT, which magmatic and metamorphic rocks during this period outcropped. Whereas provenances providing 2.6- 1.6 Ga sediments may come from an unknown block. This indicates that the Kuangping Group received both NQT and the unknown block materials. Therefore, the NQT and the unknown block may have collided before 880 Ma. 889 - 848 Ma A-type granites distributing the NQT was considered forming under a post-collisional tectonics. According the youngest detrital zircon ages of 880 Ma, it is inferred that the Kuanping Basin may also form in the same tectonic environments. Neoproterozoic Kuanping basin and 889 - 848 Ma A-type granites may be a result which NQT broken off a block of Rodinia supercontinent. Acknowledgments: This research is supported by National Key Research and Development Plan of China (2016YFC0601002), Special Fund for Basic Scientific Research of Central Colleges, Chang'an University (310827172201, 0009-2014G1271067) and National Nature Science Foundation of China (41402042).

Petrogenesis and tectonic setting of the Devonian Xiqin A-type granite in the northeastern Cathaysia Block, SE China

NASA Astrophysics Data System (ADS)

Cai, Da-wei; Tang, Yong; Zhang, Hui; Lv, Zheng-Hang; Liu, Yun-long

2017-06-01

Most Silurian-Devonian granites in South China are S- or I-type granites, which are suggested to be petrogenetically related to the Wuyi-Yunkai orogeny. In this paper, we present the detailed LA-ICP-MS zircon U-Pb dating, major and trace element geochemical, and Nd-Hf isotopic data for Xiqin A-type granites in the northeastern Cathaysia Block, SE China. Zircon U-Pb dating results show that the Xiqin granites were emplaced at about 410 Ma, indicating that they were generated at the end of Wuyi-Yunkai orogeny. These granites are high in K2O + Na2O (6.31-8.79 wt%), high field strength elements (Zr + Nb + Ce + Y = 427-699 ppm), rare earth elements (total REE = 221-361 ppm) as well as high Ga/Al ratios (10,000 Ga/Al = 2.50-3.10), and show characteristics typical of A-type granites. εHf(t) values of the Xiqin granites mainly vary from -0.4 to -3.1 and yield Mesoproterozoic T2DM(Hf) (mainly ranging from 1.29 to 1.45 Ga). The εNd(t) values are from -1.23 to -2.11 and T2DM(Nd) vary from 1.25 to 1.32 Ga. These isotopic data suggest that the Xiqin granites were generated by partial melting of metavolcanic rocks with minor metasedimentary rocks in the lower crust. Our data on the Xiqin granites, coupled with previous studies of Silurian-Devonian magmatism, suggest that the tectonic regime had changed to a strongly post-collisional extension environment in the Wuyi-Yunkai orogen at least since 410 Ma, and that delamination, which accounts for the change in stress from the compression to extension and asthenospheric upwelling during the early Paleozoic, plays a significant role in the generation of Xiqin A-type granites.

Beneath the scaly clay and clay breccia of Karangsambung area

NASA Astrophysics Data System (ADS)

Arisbaya, Ilham; Handayani, Lina

2018-02-01

Karangsambung area, Central Java-Indonesia, records tectonic evolution of the western part of Sundaland margin. The area is thought to have undergone a long tectonic evolution from palaeosubduction, collision with the continental fragments of Gondwana, to the formation of the recent subduction zone. An interesting phenomenon in this area is the presence of the Late Cretaceous ophiolitic blocks with an east northeast (ENE) trending-direction surrounded by the east trend of Eocene - Oligocene sedimentary melange formation. There was also an ENE trending Dakah volcanic rocks unit found in this area, with approximately equivalent age with the sedimentary mélange formation. There are two main interpretations regarding this volcanic unit, as an olistostrome and as an insitu shallow subduction magmatic product. Detailed mechanism of the emplacement of the Late Cretaceous ophiolite and the genesis of the volcanic rocks unit and their implications to the regional tectonic model is still open for discussion. Geophysical research in this key area may help to reveal the geometry, relationship among rocks units, and tectonic evolution. Unfortunately, geophysical studies in this area are still lacking. Previous geophysical work in Karangsambung still leaves uncertainty, especially in depth control and spatial resolution issue. Here we describe the results of previous works in Karangsambung as basic knowledge for the upcoming geophysical study.

Andean tectonics: Implications for Satellite Geodesy

NASA Technical Reports Server (NTRS)

Allenby, R. J.

1984-01-01

Current knowledge and theories of large scale Andean tectonics as they relate to site planning for the NASA Crustal Dynamics Program's proposed high precision geodetic measurements of relative motions between the Nazca and South American plates are summarized. The Nazca Plate and its eastern margin, the Peru-Chile Trench, is considered a prototype plate marked by rapid motion, strong seismicity and well defined boundaries. Tectonic activity across the Andes results from the Nazca Plate subducting under the South American plate in a series of discrete platelets with different widths and dip angles. This in turn, is reflected in the tectonic complexity of the Andes which are a multitutde of orogenic belts superimposed on each other since the Precambrian. Sites for Crustal Dynamics Program measurements are being located to investigate both interplate and extraplate motions. Observing operations have already been initiated at Arequipa, Peru and Easter Island, Santiago and Cerro Tololo, Chile. Sites under consideration include Iquique, Chile; Oruro and Santa Cruz, Bolivia; Cuzco, Lima, Huancayo and Bayovar, Peru; and Quito and the Galapagos Islands, Ecuador. Based on scientific considerations, Santa Cruz, Huancayo (or Lima), Quito and the Galapagos Islands should be replaced by Isla San Felix, Chile; Brazilia or Petrolina, Brazil; and Guayaquil, Ecuador. If resources permit, additional important sites would be Buenaventura and Villavicencio or Puerto La Concordia, Colombia; and Mendoza and Cordoba, Argentina.

Comment on "Geochemistry of the Early Miocene volcanic succession of Northland, New Zealand, and implications for the evolution of subduction in the Southwest Pacific" by M.A. Booden, I.E.M. Smith, P.M. Black and J.L. Mauk

NASA Astrophysics Data System (ADS)

Schellart, W. P.

2012-01-01

In a recent paper Booden et al. (2011) present new geochemical and petrological data of Early Miocene volcanics from the Northland region (Northland volcanic belt) in New Zealand, and interpret these data to support a particular regional tectonic model. This tectonic model involves Early Miocene westward subduction of Cretaceous Pacific oceanic lithosphere below the Northland volcanic belt and the authors interpret the volcanic belt as a continental magmatic arc. Although the new data are not in disagreement with such a tectonic model, they provide more support for an alternative interpretation that involves a northeast-dipping subduction zone. Furthermore, geometric and plate kinematic data show that the west-dipping subduction model is unviable, geological and geophysical data contradict the model, while geodynamic arguments indicate that the model is implausible. Here it will be shown that a subduction model, involving a northeast-dipping southwestward retreating slab (made of the Late Cretaceous-Paleocene South Loyalty backarc basin lithosphere) that subsequently detaches, is in agreement with the local geology, geophysics and geochemistry, is geometrically, kinematically and geodynamically viable, and fits within the regional Southwest Pacific tectonic framework.

High precision U-PB geochronology and implications for the tectonic evolution of the Superior Province

NASA Technical Reports Server (NTRS)

Davis, D. W.; Corfu, F.; Krogh, T. E.

1986-01-01

The underlying mechanisms of Archean tectonics and the degree to which modern plate tectonic models are applicable early in Earth's history continue to be a subject of considerable debate. A precise knowledge of the timing of geological events is of the utmost importance in studying this problem. The high precision U-Pb method has been applied in recent years to rock units in many areas of the Superior Province. Most of these data have precisions of about + or - 2-3 Ma. The resulting detailed chronologies of local igneous development and the regional age relationships furnish tight constraints on any Archean tectonic model. Superior province terrains can be classified into 3 types: (1) low grade areas dominated by meta-volcanic rocks (greenstone belts); (2) high grade, largely metaplutonic areas with abundant orthogneiss and foliated to massive I-type granitoid bodies; and (3) high grade areas with abundant metasediments, paragneiss and S-type plutons. Most of the U-Pb age determinations have been done on type 1 terrains with very few having been done in type 3 terrains. A compilation of over 120 ages indicates that the major part of igneous activity took place in the period 2760-2670 Ma, known as the Kenoran event. This event was ubiquitous throughout the Superior Province.

Implications of China's Open-Door Policy for Families: A Family Impact Analysis

ERIC Educational Resources Information Center

Quach, Andrew S.; Anderson, Elaine A.

2008-01-01

China's open-door policy (ODP) was created in 1978 as a response to the severe economic depression affecting the country after the Cultural Revolution. The policy was designed to restore China's financial status and lift the nation out of destitution. By all accounts, the ODP has been successful in improving the country's monetary condition.…

Cross-Border Educational Collaboration between Taiwan and China: The Implications for Educational Governance

ERIC Educational Resources Information Center

Chan, Sheng-Ju

2011-01-01

Taiwan has undertaken a series of cross-border collaboration with China for the past two decades. This paper aims to investigate the Taiwanese approach and policies of educational collaboration with China in a globalized context, where international competitiveness has become a great concern for most countries. It also examines how the Taiwanese…

Internationalisation of Higher Education in the Era of Globalisation: What Have Been Its Implications in China and Japan?

ERIC Educational Resources Information Center

Huang, Futao

2007-01-01

This article describes the internationalisation of higher education in the era of globalisation in China and Japan. It presents the following issues: the relationship between internationalisation and globalisation; major characteristics of the internationalisation of higher education; a comparison between China and Japan; and the results of…

Genetic features of petroleum systems in rift basins of eastern China

USGS Publications Warehouse

Qiang, J.; McCabe, P.J.

1998-01-01

Most oil-bearing basins in eastern China are Mesozoic-Cenozoic continental rifts which have played a habitat for oil and gas in China. Investigation of the petroleum systems may give a better understanding of the oil and gas habitats in these basins. Of the essential elements of the petroleum system, the source rock is the most important in rift basins. However, rift tectonic evolution controls all the essential elements and processes nevessary for a petroleum system. A four stage evolution model is suggested for the controls in the rift basin. A rift basin may consist of sub-basins, depressions, sub-depressions, and major, moderate, and minor uplifts. A depression or sub-depression has its own depocentre (mainly occupied by source rock) and all kinds of lacustrine sediments, and thus has all the essential elements of a petroleum system. However, only those depressions or sub-depressions which are rich in organic matter and deeply buried to generate oil and gas form petroleum systems. Immature oil, another characteristic, complicates the petroleum system in the rift basins. Three types of oil and gas habitats are described as a result of this analysis of the petroleum systems of the 26 largest oil and gas fields discovered in eastern China rift basins: uplifts between oil source centres are the most prospective areas for oil and gas accumulations, slopes connecting oil source centres and uplifts are the second, and the third type is subtle traps in the soil source centre.Most oil-bearing basins in eastern China are Mesozoic-Cenozoic continental rifts which have played a habitat for oil and gas in China. Investigation of the petroleum systems may give a better understanding of the oil and gas habitats in these basins. Of the essential elements of the petroleum system, the source rock is the most important in rift basins. However, rift tectonic evolution controls all the essential elements and processes necessary for a petroleum system. A four stage evolution model is suggested for the controls in the rift basin. A rift basin may consist of sub-basins, depressions, sub-depressions, and major, moderate, and minor uplifts. A depression or sub-depression has its own depocentre (mainly occupied by source rock) and all kinds of lacustrine sediments, and thus has all the essential elements of a petroleum system. However, only those depressions or sub-depressions which are rich in organic matter and deeply buried to generate oil and gas form petroleum systems. Immature oil, another characteristic, complicates the petroleum system in the rift basins. Three types of oil and gas habitats are described as a result of this analysis of the petroleum systems of the 26 largest oil and gas fields discovered in eastern China rift basins: uplifts between oil source centres are the most prospective areas for oil and gas accumulations, slopes connecting oil source centres and uplifts are the second, and the third type is subtle traps in the oil source centre.

Adjoint tomography of crust and upper-mantle structure beneath Continental China

NASA Astrophysics Data System (ADS)

Chen, M.; Niu, F.; Liu, Q.; Tromp, J.

2013-12-01

Four years of regional earthquake recordings from 1,869 seismic stations are used for high-resolution and high-fidelity seismic imaging of the crust and upper-mantle structure beneath Continental China. This unprecedented high-density dataset is comprised of seismograms recorded by the China Earthquake Administration Array (CEArray), NorthEast China Extended SeiSmic Array (NECESSArray), INDEPTH-IV Array, F-net and other global and regional seismic networks, and involves 1,326,384 frequency-dependent phase measurements. Adjoint tomography is applied to this unprecedented dataset, aiming to resolve detailed 3D maps of compressional and shear wavespeeds, and radial anisotropy. Contrary to traditional ray-theory based tomography, adjoint tomography takes into account full 3D wave propagation effects and off-ray-path sensitivity. In our implementation, it utilizes a spectral-element method for precise wave propagation simulations. The tomographic method starts with a 3D initial model that combines smooth radially anisotropic mantle model S362ANI and 3D crustal model Crust2.0. Traveltime and amplitude misfits are minimized iteratively based on a conjugate gradient method, harnessing 3D finite-frequency kernels computed for each updated 3D model. After 17 iterations, our inversion reveals strong correlations of 3D wavespeed heterogeneities in the crust and upper mantle with surface tectonic units, such as the Himalaya Block, the Tibetan Plateau, the Tarim Basin, the Ordos Block, and the South China Block. Narrow slab features emerge from the smooth initial model above the transition zone beneath the Japan, Ryukyu, Philippine, Izu-Bonin, Mariana and Andaman arcs. 3D wavespeed variations appear comparable to or much sharper than in high-frequency P-and S-wave models from previous studies. Moreover our results include new information, such as 3D variations of radial anisotropy and the Vp/Vs ratio, which are expected to shed new light to the composition, thermal state, flow or fabric structure in the crust and upper mantle, as well as the related dynamical processes. We intend to use these seismic images to answer important tectonic questions, namely, 1) what controls the strength of the lithosphere; 2) how does lithosphere deform during the formation of orogens, basins and plateaus; 3) how pervasive is lithospheric delamination or partial removal beneath orogens and plateaus; 3) whether or not (and how) are slab segmentation and penetration into the lower mantle linked to upwellings associated with widespread magmatism in East Asia.

Preliminary publications book 2 from project on mineral resources, metallogenesis, and tectonics of northeast Asia

USGS Publications Warehouse

Nokleberg, Warren J.; Miller, Robert J.; Naumova, Vera V.; Khanchuk, Alexander I.; Parfenov, Leonid M.; Kuzmin, Mikhail I.; Bounaeva, Tatiana M.; Obolenskiy, Alexander A.; Rodionov, Sergey M.; Seminskiy, Zhan V.; Diggles, Michael F.

2003-01-01

This is the Web version of a CD-ROM publication. This report consists of summary major compilations and syntheses accomplished in the six-year project through April 2003 for the study on the Mineral Resources, Metallogenesis, and Tectonics of Northeast Asia (Eastern and Southern Siberia, Mongolia, Northeastern China, South Korea, and Japan). The major scientific goals and benefits of the project are to: (1) provide a comprehensive international data base on the mineral resources of the region that is the first, extensive knowledge available in English; (2) provide major new interpretations of the origin and crustal evolution of mineralizing systems and their host rocks, thereby enabling enhanced, broad-scale tectonic reconstructions and interpretations; and (3) promote trade and scientific and technical exchanges between the North America and Northeast Asia. Data from the project are providing sound scientific data and interpretations for commercial firms, governmental agencies, universities, and individuals that are developing new ventures and studies in the project area, and for land-use planning studies that deal with both mineral potential issues. Northeast Asia has vast potential for known and undiscovered mineral deposits; however, little information existed in English in the West until publication of products from this project. Consequently, data and interpretations from the project are providing basic knowledge for major scientific, commercial, national, and international endeavors by other interested individuals and groups.

The Jianchuan Basin, Yunnan: Implications on the Evolution of SE Tibet During the Eocene

NASA Astrophysics Data System (ADS)

Gourbet, L.; Mahéo, G.; Leloup, P. H.; Jean-Louis, P.; Sorrel, P.; Eymard, I.; Antoine, P. O.; Sterb, M.; Wang, G.; Cao, K.; Chevalier, M. L.; Lu, H.

2015-12-01

The Jianchuan basin, Yunnan Province, China, is the widest continental Cenozoic sedimentary basin in the southeastern Tibetan plateau. It is located ~10 km east of the Red River fault zone. Climatic simulations and palaeoenvironment studies suggest that SE Asia has experienced a variable intensity monsoon system for 40 Ma. Because sediments can record deformation, climate and environment changes, the Jianchuan basin provides the opportunity to assess the relative role of climate and tectonics on the Tibetan plateau formation. Sediments consist of floodplain siltites, massive fluvial sandstone, few carbonate levels, coal and volcanosedimentary deposits. U/Pb dating of zircons from dykes, volcanodetrital deposits and lava flows respectively cutting and interbedded within the sediments was performed by in-situ LA-ICPMS. All ages range from 38 to 35 Ma. Such absolute dating is confirmed by palaeontological evidence. Dental remains of Zaisanamynodonwere found in coal deposits. This giant Rhino lived in Asia during the Ergilian (late Eocene). Our data allow us to propose a revised stratigraphy for the Jianchuan basin: contrary to what was suggested by previous studies, i.e. a continuous sedimentation from the Paleocene to the Miocene, nearly no sedimentation occurred after 34 Ma. Combined with a sedimentological analysis, the data indicate that during the late Eocene, the Jianchuan area was covered by a large (>15 km) braided river system that coexisted with local transient lakes, in a moderate-slope and semi-arid environment. This major sedimentation event was followed by a period of more humid conditions that may be related to an intensification of the monsoon. The end of the sedimentation seems to be contemporaneous with the Ailao Shan-Red River fault activation. The new stratigraphy has also implications for regional studies that need robust age constraints, for example for reconstructing palaeoelevation or provenance of sediments.

Seismic investigation of an ocean-continent transition zone in the northern South China Sea

NASA Astrophysics Data System (ADS)

Zhu, J.; Qiu, X.; Xu, H.; Zhan, W.; Sun, Z.

2011-12-01

Rifted continental margins and basins are mainly formed by the lithospheric extension. Thined lithosphere of passive continental margins results in decompression melt of magma and created oceanic crust and thined ocean-continent transition (OCT) zone. Two refraction profiles used ocean bottom seismometers deployed in the broad continental shelf and three multi-channel seismic reflection lines in the northern South China Sea, acquired by the ship "Shiyan 2" of the South China Sea Institute of Oceanology, Chinese Academy of Sciences in 2010, are processed and interpreted in this study. Seismic reflection lines cut through the Dongsha rise, Zhu-1 and Zhu-2 depression within a Tertiary basin, Pear River Mouth basin (called as Zhujiangkou basin). These tectonic features are clear imaged in the seismic reflection records. Numerous normal faults, cutted through the basement and related to the stretch of the northern South China Sea margin, are imaged and interpreted. Reflection characteristics of the ocean-continent transition (OCT) zone are summaried and outlined. The COT zone is mainly divided into the northern syn-rift subsidence zone, central volcano or buried volcano uplift zone and tilt faulted block near the South Chia Sea basin. Compared to the previous seismic reflection data and refraction velocity models, the segmentation range of the OCT zone is outlined, from width of about 225 km in the northeastern South China Sea , of 160 km in the central to of 110 km in the north-central South China Sea. Based on the epicenter distribution of sporadic and large than 6 magnitude earthquakes, it suggests the OCT zone in the northern South China Sea at present is still an active seismic zone.

Zinc, nickel and cadmium in carambolas marketed in Guangzhou and Hong Kong, China: implication for human health.

PubMed

Li, J T; Liao, B; Lan, C Y; Qiu, J W; Shu, W S

2007-12-15

Carambola (Averrhoa carambola L.) is a popular juicy fruit throughout the tropical and subtropical world. This study was designed to quantify the levels of zinc (Zn), nickel (Ni) and cadmium (Cd) in carambolas marketed in southern China, and further to evaluate the potential health risk of human consumption of carambola. Zinc concentrations, ranging from 1.471 to 2.875 mg/kg (on fresh weight basis), were below the maximum permissible concentration for Zn in fruit of China (5 mg/kg). However, Ni concentrations (0.134-0.676 mg/kg) were considerably higher than the related recommendation values. Furthermore, Cd concentrations in 51% of the carambolas purchased from Guangzhou exceeded the maximum permissible concentration for Cd in fruit of China (0.03 mg/kg). Our results implicated that the consumption of 0.385 kg carambola contaminated by Cd per day would cause the tolerable daily intake (TDI) of Cd by the consumer to be exceeded. In addition, the remarkably high Ni concentrations in carambolas should also be of concern. The status of heavy metal contamination of carambola products marketed in the other regions and their implications for human health should be identified urgently by in-depth studies.

Rare earth element patterns in Archean high-grade metasediments and their tectonic significance

NASA Technical Reports Server (NTRS)

Taylor, Stuart Ross; Rudnick, Roberta L.; Mclennan, Scott M.; Eriksson, Kenneth A.

1986-01-01

REE data on metasedimentary rocks from two different types of high-grade Archean terrains are presented and analyzed. The value of REEs as indicators of crustal evolution is explained; the three geologic settings (in North America, Southern Africa, and Australia) from which the samples were obtained are described; and the data are presented in extensive tables and graphs and discussed in terms of metamorphic effects, the role of accessory phases, provenance, and tectonic implications (recycling, the previous extent of high-grade terrains, and a model of Archean crustal growth). The diversity of REE patterns in shallow-shelf metasediments is attributed to local provenance, while the Eu-depleted post-Archean patterns are associated with K-rich plutons from small, stable early Archean terrains.

Integrated magnetostratigraphy and lithostratigraphy of five cores in Yangtze delta, China : significance of sedimentary evolution

NASA Astrophysics Data System (ADS)

Peng, Jie; Yang, XiaoQiang; Qiang, XiaoKe; Liu, YeBo; Zhou, QiXian

2017-04-01

The sedimentary history and characteristics of the Yangtze delta help us understand the tectonic evolution and geological formation process in the Eastern coastal area of China since the Cenozoic Era. Previous chronology of sediments in this area are not detailed or precise. Furthermore, when the delta area reached the maximum is still debatable. Palaeomagnetic polarity reversal and excursions, AMS14C dating, optically stimulated luminescence (OSL) dating, and the hard clay marker layer analysis were integrated to establish the chronostratigraphic framework of five drilling cores from the south Yangtze delta. Results from the bottom part of core CSB6 suggested Gauss normal polarity chron, an age of more than about 2600 ka. The other four cores showed initial deposition time between 200-60 ka B.P., significantly later than CSB6. We infer the reason is that CSB6 locating in the Changxin-Fenghua Fracture. Combined with data from referenced magnetostratigraphic cores in the Yangtze River Delta, we suggest that tectonic movement resulted in a much longer depositional age in some parts of the Yangtze River Delta and influenced the sedimentary characteristics of thick (North) to thin (South) and thick (East) to thin (West). In conclusion, a relatively wide range of deposition in the Yangtze River Delta occurred since about 200 ka B.P. The deposition of fine particles (clay-silt), which was controlled by slow tectonic subsidence and sea-level changes, expanded to the whole delta region after about 60 ka B.P. We propose that this time scale maybe used for further study on the evolution of the Yangtze delta's paleoclimate and paleoenvironment. References [1]Peng J,Yang X Q,Qiang X K,et al.Magnetostratigraphy characteristics of several cores around the Qiantang River mouth and its significance.Chinese J.Geophys.(in Chinese),2016,59(8):2949-2964. [2]Li C X, Chen Q Q, Zhang J Q,et al. Stratigraphy and paleoenvironmental changes in the Yangtze Delta during the Late Quaternary[J].Journal of Asian Earth Sciences, 2000, 18(2000):453-469. [3]Brad S.Singer. A Quaternary geomagnetic instability time scale[J]. Quaternary Geochronology, 2014,21:29-54.

Modeling and Simulation of the Gonghe geothermal field (Qinghai, China) Constrained by Geophysical

NASA Astrophysics Data System (ADS)

Zeng, Z.; Wang, K.; Zhao, X.; Huai, N.; He, R.

2017-12-01

The Gonghe geothermal field in Qinghai is important because of its variety of geothermal resource types. Now, the Gonghe geothermal field has been a demonstration area of geothermal development and utilization in China. It has been the topic of numerous geophysical investigations conducted to determine the depth to and the nature of the heat source, and to image the channel of heat flow. This work focuses on the causes of geothermal fields used numerical simulation method constrained by geophysical data. At first, by analyzing and inverting an magnetotelluric (MT) measurements profile across this area we obtain the deep resistivity distribution. Using the gravity anomaly inversion constrained by the resistivity profile, the density of the basins and the underlying rocks can be calculated. Combined with the measured parameters of rock thermal conductivity, the 2D geothermal conceptual model of Gonghe area is constructed. Then, the unstructured finite element method is used to simulate the heat conduction equation and the geothermal field. Results of this model were calibrated with temperature data for the observation well. A good match was achieved between the measured values and the model's predicted values. At last, geothermal gradient and heat flow distribution of this model are calculated(fig.1.). According to the results of geophysical exploration, there is a low resistance and low density region (d5) below the geothermal field. We recognize that this anomaly is generated by tectonic motion, and this tectonic movement creates a mantle-derived heat upstream channel. So that the anomalous basement heat flow values are higher than in other regions. The model's predicted values simulated using that boundary condition has a good match with the measured values. The simulated heat flow values show that the mantle-derived heat flow migrates through the boundary of the low-resistance low-density anomaly area to the Gonghe geothermal field, with only a small fraction moving to other regions. Therefore, the mantle-derived heat flow across the tectonic channel to the cohesive continuous supply heat for Gonghe geothermal field, is the main the main causes of abundant geothermal resources.

The People’s Liberation Army and China in Transition

DTIC Science & Technology

2003-08-01

and long- range land-attack cruise missiles. China currently has just one FBM, the Xia, which may not be opera - ble. Its successor class, the Type...prospects for U.S.- China relations and military-to-military cooperation, and the implications of these developments for U.S. defense planning...A R T I THE PEOPLE’S LIBERATION ARMY AND CHINA IN TRANSITION edited by Stephen J. Flanagan and Michael E. Marti, with contributions from: Richard

Walking a Tightrope: Vietnam’s Security Challenge in the South China Sea and Implications for U.S. PACOM

DTIC Science & Technology

2013-11-01

Islands and back up to Taiwan . In the words of analyst Robert Kaplan, “geography propels China forward into the South China Sea.” 3 The bilateral...vigorously began to defend its historical claims to the Paracels and Spratlys, with the Philippines, Malaysia, Taiwan , and Brunei also laying claim to the...approach. 4 Background on the South China Sea dispute provided in Patrick M. Cronin, Peter A. Dutton

Economics and Maritime Strategy: Implications for the 21st Century

DTIC Science & Technology

2006-11-01

nothing to help Thailand. China got credit for not devaluing its currency and offered FTAs to Thailand and subsequently to ASEAN as a whole. (The value and...growth at 6.2 percent; I have augmented it by 1 percent a year to allow for some real currency appreciation; similarly for India. I have also...for some (1 percent a year from 2000) real appreciation of the currencies of China and India, relative to the U.S. dollar. One implication of the

Weathering on a stagnant lid planet: Prospects for habitability?

NASA Astrophysics Data System (ADS)

Foley, B. J.

2016-12-01

Plate tectonics plays a major role in the operation of the long term carbon cycle on Earth, which in turn buffers Earth's climate by regulating atmospheric CO2 levels. As a result, plate tectonics has long been considered to be essential for maintaining habitable conditions over geologic timescales. In particular, plate tectonics returns carbon to the mantle through subduction, allowing for long-lived CO2 degassing to the atmosphere, and plate tectonics sustains a large supply of fresh, weatherable rock at the surface through continual uplift, orogeny, and seafloor spreading. Without a large supply of fresh rock weathering can become supply-limited, where no climate regulating weathering feedback occurs. However, another mechanism for supplying fresh rock to the surface is through volcanism. Volcanism occurs on rocky planets, at least for some portion of their history, regardless of their mode of surface tectonics. In this presentation I assess whether a stagnant lid planet can avoid supply-limited weathering, and thus buffer its climate through the weathering feedback, when the supply of fresh rock is provided solely by volcanism. A simple analysis shows that the amount of CO2 in the mantle is critical for determining whether volcanic degassing overwhelms the supply of rock produced by eruptions, leading to supply-limited weathering and a hot climate, or not. Models of the coupled evolution of climate, mantle temperature, and volcanic rate are then used to determine how long a habitable climate could be maintained on a stagnant lid planet, and how different initial conditions influence this timescale. The results have important implications for the prospects for habitability of stagnant lid planets.

Tectonic implications of facies patterns, Lower Permian Dry Mountain trough, east-central Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gallegos, D.M.; Snyder, W.S.; Spinosa, C.

1991-02-01

Paleozoic tectonism is indicated by a study of a west-east facies analysis transect across the northern portion of the Lower Permian Dry Mountain trough (DMT). In an attempt to characterize the Early Permian basin-filling sequences, three broadly recognizable facies packages have been identified across the DMT: the western margin facies and the central basin facies of the DMT and an eastern shelf facies. In the western margin facies of the basin, pulses of tectonic activity are recorded at McCloud Spring in the Sulphur Springs Range. Here, shallow open-marine carbonate overlies eroded Vinini Formation and, in turn, is unconformably overlain bymore » basinal marine carbonate. An unconformity also marks the contact with the overriding prograding coarse clastic facies. These abrupt transitions suggest the sediments were deposited in a tectonically active area where they preservation of Waltherian sequences is unlikely to occur. Similarly abrupt transitions are evident in the western part of the central basin facies. At Portuguese Springs n the Diamond Range, a thin basal marine conglomerate delineates Lower Permian sedimentation over the Pennsylvanian Ely Formation. Coarsening-upward basinal carbonate strata of pelagic, hemipelagic, and turbidite components overlie the basal conglomerate. this progression of sediments is unconformably overlain by a subaerial sequence of coarse clastic deposits. Within the eastern part of the central basin facies in the Maverick Spring Range, the Lower Permian sediments are open-marine siltstone, wackestone, packstone, and grainstone. The sediments are assigned to a gradually sloping ramp, indicating the effects of tectonism on this margin of the basin were subdued.« less

The Concept of "English Learning Power" and Its Implication for the Design of English Curricula for Primary and Middle Schools in China

ERIC Educational Resources Information Center

Dai, Zhongxin

2015-01-01

In the research on "New Characteristics of Future Basic Education in China," Dina Pei formulates a "three-powered" model to theorize about the characteristics of future basic education in China. The three powers refer to the "Policy-making Power" of the local educational administration, the "Leading Power"…

Swinging Open or Slamming Shut? The Implications of China's Open-Door Policy for Women, Educational Choice and Work

ERIC Educational Resources Information Center

Turner, Yvonne

2006-01-01

This paper explores the link between international tertiary education and evolving attitudes about women and work in China. The paper reviews literature about gender and education in China, commenting on the late-twentieth-century post-reform environment. It goes on to present illustrative primary research material from two studies carried out…

China: The Impact of Climate Change to 2030. Geopolitical Implications

DTIC Science & Technology

2009-06-01

China ranks lower in resilience to climate change than Brazil , Turkey, and Mexico, but higher than India. • China can adapt its administrative...Southeast Asia at risk . 1 The panel had expertise in political science, comparative world...address energy demand primarily through domestically produced coal and imported oil , leading to a severe rise in China’s contribution to global

Field geology, geochronology and geochemistry of mafic-ultramafic rocks from Alxa, China: Implications for Late Permian accretionary tectonics in the southern Altaids

NASA Astrophysics Data System (ADS)

Feng, Jianyun; Xiao, Wenjiao; Windley, Brian; Han, Chunming; Wan, Bo; Zhang, Ji'en; Ao, Songjian; Zhang, Zhiyong; Lin, Lina

2013-12-01

The time of termination of orogenesis for the southern Altaids has been controversial. Systematic investigations of field geology, geochronology and geochemistry on newly discriminated mafic-ultramafic rocks from northern Alxa in the southern Altaids were conducted to address the termination problem. The mafic-ultramafic rocks are located in the Bijiertai, Honggueryulin, and Qinggele areas, stretching from west to east for about 100 km. All rocks occur high-grade gneisses as tectonic lenses that are composed of peridotite, pyroxenite, gabbro, and serpentinite, most of which have undergone pronounced alteration, i.e., serpentinization and chloritization. Geochemically, the rocks are characterized by uniform compositional trends, i.e., with low SiO2-contents (42.51-52.21 wt.%) and alkalinity (Na2O + K2O) (0.01-5.45 wt.%, mostly less than 0.8 wt.%), and enrichments in MgO (7.37-43.36 wt.%), with Mg# = 52.75-91.87. As the rocks have been strongly altered and have a wide range of loss-on-ignition (LOI: 0.44-14.07 wt.%) values, they may have been subjected to considerable alteration by either seawater or metamorphic fluids. The REE and trace element patterns show a relatively fractionated trend with LILE enrichment and HFSE depletion, similar to that of T-MORB between N-MORB and E-MORB, indicating that the parental melt resulted from the partial melting of oceanic lithospheric mantle overprinted by fluid alteration of island-arc origin. The ultramafic rocks are relics derived from the magma after a large degree of partial melting of oceanic lithospheric mantle with superposed island arc processes under the influence of mid-ocean-ridge magmatism. LA-ICP MS U-Pb zircon ages of gabbros from three spots are 274 ± 3 Ma (MSWD = 0.35), 306 ± 3 Ma (MSWD = 0.49), 262 ± 5 Ma (MSWD = 1.2), respectively, representing the formation ages of the mafic-ultramafic rocks. Therefore, considering other previously published data, we suggest that the mafic-ultramafic rocks were products of south-dipping subduction, most probably with a slab window caused by ridge subduction, of the Paleo-Asian Ocean plate beneath the Alxa block in the Late Carboniferous to Late Permian before the Ocean completely closed. This sheds light on the controversial tectonic history of the southern Altaids and supports the concept that the termination of orogenesis was in the end-Permian to Triassic.

Mantle structure and tectonic history of SE Asia

NASA Astrophysics Data System (ADS)

Hall, Robert; Spakman, Wim

2015-09-01

Seismic travel-time tomography of the mantle under SE Asia reveals patterns of subduction-related seismic P-wave velocity anomalies that are of great value in helping to understand the region's tectonic development. We discuss tomography and tectonic interpretations of an area centred on Indonesia and including Malaysia, parts of the Philippines, New Guinea and northern Australia. We begin with an explanation of seismic tomography and causes of velocity anomalies in the mantle, and discuss assessment of model quality for tomographic models created from P-wave travel times. We then introduce the global P-wave velocity anomaly model UU-P07 and the tectonic model used in this paper and give an overview of previous interpretations of mantle structure. The slab-related velocity anomalies we identify in the upper and lower mantle based on the UU-P07 model are interpreted in terms of the tectonic model and illustrated with figures and movies. Finally, we discuss where tomographic and tectonic models for SE Asia converge or diverge, and identify the most important conclusions concerning the history of the region. The tomographic images of the mantle record subduction beneath the SE Asian region to depths of approximately 1600 km. In the upper mantle anomalies mainly record subduction during the last 10 to 25 Ma, depending on the region considered. We interpret a vertical slab tear crossing the entire upper mantle north of west Sumatra where there is a strong lateral kink in slab morphology, slab holes between c.200-400 km below East Java and Sumbawa, and offer a new three-slab explanation for subduction in the North Sulawesi region. There is a different structure in the lower mantle compared to the upper mantle and the deep structure changes from west to east. What was imaged in earlier models as a broad and deep anomaly below SE Asia has a clear internal structure and we argue that many features can be identified as older subduction zones. We identify remnants of slabs that detached in the Early Miocene such as the Sula slab, now found in the lower mantle north of Lombok, and the Proto-South China Sea slab now at depths below 700 km curving from northern Borneo to the Philippines. Based on our tectonic model we interpret virtually all features seen in upper mantle and lower mantle to depths of at least 1200 km to be the result of Cenozoic subduction.

Application of combined 81Kr and 4He chronometers to the dating of old groundwater in a tectonically active region of the North China Plain

NASA Astrophysics Data System (ADS)

Matsumoto, Takuya; Chen, Zongyu; Wei, Wen; Yang, Guo-Min; Hu, Shui-Ming; Zhang, Xiangyang

2018-07-01

Groundwater dating by radio-krypton (81Kr; half-life of about 229,000 years) was applied to the sedimentary basin aquifer of the North China Plain (NCP). Krypton gas extracted from deep groundwater in the Coastal Plain was analyzed for 81Kr/Kr ratios by Atom Trap Trace Analysis, which yielded normalized ratios of 0.05 to 0.20, corresponding to groundwater residence times of 0.5-1 million years. Helium isotope compositions were determined on groundwater samples collected from the Central Plain and the Coastal Plain along a flow path of about 200 km. Helium dissolved in the groundwater samples are a mixture of atmospheric, crustal radiogenic and mantle derived sources. Mantle derived 3He contributes up to 30% of the total, and the area of occurrence coincides with zones of previous magmatic/tectonic activities. By contrast, >90% of 4He is derived from crustal reservoirs and correlates with 81Kr ages. The absolute groundwater ages (81Kr) and radiogenic 4He concentrations permit us to calibrate the 4He flux into the aquifer as well as the vertical diffusion rate of 4He to utilize the radiogenic 4He in groundwater as a quantitative age tracer. Previously, groundwater showed 14C activities near the limit of detection (30-40 k yr), in contrast Kr and radiogenic 4He data reveal progressively older ages from the recharge area to the Coastal Plain, from <20,000 yr to 0.5 to 1 Ma along the flow path of the NCP aquifers.

The distribution, diversity, and conservation status of Cycas in China.

PubMed

Zheng, Ying; Liu, Jian; Feng, Xiuyan; Gong, Xun

2017-05-01

As ancient gymnosperm and woody plants, cycads have survived through dramatic tectonic activities, climate fluctuation, and environmental variations making them of great significance in studying the origin and evolution of flora biodiversity. However, they are among the most threatened plant groups in the world. The principal aim of this review is to outline the distribution, diversity, and conservation status of Cycas in China and provide suggestions for conservation practices. In this review, we describe the taxonomy, distribution, and conservation status of Cycas in China. By comparing Chinese Cycas species with its relatives worldwide, we then discuss the current genetic diversity, genetic differentiation of Cycas, and try to disentangle the potential effects of Quaternary climate changes and topographical events on Cycas . We review conservation practices from both researchers and practitioners for these rare and endangered species. High genetic diversity at the species level and strong genetic differentiation within Cycas have been observed. Most Cycas species in southwest China have experienced population retreats in contrast to the coastal Cycas 's expansion during the Quaternary glaciation. Additionally, human activities and habitat fragmentation have pushed these endangered taxa to the brink of extinction. Although numerous efforts have been made to mitigate threats to Cycas survival, implementation and compliance monitoring in protection zones are currently inadequate. We outline six proposals to strengthen conservation measures for Cycas in China and anticipate that these measures will provide guidelines for further research on population genetics as well as conservation biology of not only cycads but also other endangered species worldwide.

A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

NASA Technical Reports Server (NTRS)

Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

1999-01-01

Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While magnetic anomaly data represent the main focus of this study recently derived satellite gravity data are playing a major role in Arctic studies.

Gondwana dispersion and Asian accretion: Tectonic and palaeogeographic evolution of eastern Tethys

NASA Astrophysics Data System (ADS)

Metcalfe, I.

2013-04-01

Present-day Asia comprises a heterogeneous collage of continental blocks, derived from the Indian-west Australian margin of eastern Gondwana, and subduction related volcanic arcs assembled by the closure of multiple Tethyan and back-arc ocean basins now represented by suture zones containing ophiolites, accretionary complexes and remnants of ocean island arcs. The Phanerozoic evolution of the region is the result of more than 400 million years of continental dispersion from Gondwana and plate tectonic convergence, collision and accretion. This involved successive dispersion of continental blocks, the northwards translation of these, and their amalgamation and accretion to form present-day Asia. Separation and northwards migration of the various continental terranes/blocks from Gondwana occurred in three phases linked with the successive opening and closure of three intervening Tethyan oceans, the Palaeo-Tethys (Devonian-Triassic), Meso-Tethys (late Early Permian-Late Cretaceous) and Ceno-Tethys (Late Triassic-Late Cretaceous). The first group of continental blocks dispersed from Gondwana in the Devonian, opening the Palaeo-Tethys behind them, and included the North China, Tarim, South China and Indochina blocks (including West Sumatra and West Burma). Remnants of the main Palaeo-Tethys ocean are now preserved within the Longmu Co-Shuanghu, Changning-Menglian, Chiang Mai/Inthanon and Bentong-Raub Suture Zones. During northwards subduction of the Palaeo-Tethys, the Sukhothai Arc was constructed on the margin of South China-Indochina and separated from those terranes by a short-lived back-arc basin now represented by the Jinghong, Nan-Uttaradit and Sra Kaeo Sutures. Concurrently, a second continental sliver or collage of blocks (Cimmerian continent) rifted and separated from northern Gondwana and the Meso-Tethys opened in the late Early Permian between these separating blocks and Gondwana. The eastern Cimmerian continent, including the South Qiangtang block and Sibumasu Terrane (including the Baoshan and Tengchong blocks of Yunnan) collided with the Sukhothai Arc and South China/Indochina in the Triassic, closing the Palaeo-Tethys. A third collage of continental blocks, including the Lhasa block, South West Borneo and East Java-West Sulawesi (now identified as the missing "Banda" and "Argoland" blocks) separated from NW Australia in the Late Triassic-Late Jurassic by opening of the Ceno-Tethys and accreted to SE Sundaland by subduction of the Meso-Tethys in the Cretaceous.

China Naval Modernization: Implications for U.S. Navy Capabilities-Background and Issues for Congress

DTIC Science & Technology

2010-06-10

the deployment of U.S. forces to the theater and blunting the operations of those forces that do deploy forward. North Korea and Iran , as part of...primarily capabilities needed for defeating China, not Iran , North Korea or Hizbollah,” said Roger Cliff, a China military specialist at Rand. “So even...global rival to a regional problem more akin to North Korea and Iran . John J. Tkacik, a former State Department China specialist, said the changes

China’s Gender Imbalance and Its Implications on China-Japan and China-Taiwan Security Relations

DTIC Science & Technology

2011-12-01

188. 32 Ibid., 189. 10 jobs that are dangerous and/or labor-intensive.33 The practice of hypergyny ( marrying someone of a higher socioeconomic...clean and sober.44 Wilson and Daly found that young unmarried males abuse alcohol and drugs more than married males, older males, or females.45...females and a great majority of these men will remain single and be unable to marry . Some 70 percent of all violent crime offenders in China are single

The U.S.-Brazil-China trade and transportation triangle : implications for the southwest region.

DOT National Transportation Integrated Search

2009-03-01

The advent of globalization and more integrated international trade has placed increased demands : on transportation infrastructure. This report assesses the impacts of triangular trade between and among : the United States, Brazil and China with an ...

A chironomid-based record of temperature variability during the past 4000 years in northern China and its possible societal implications

NASA Astrophysics Data System (ADS)

Wang, Haipeng; Chen, Jianhui; Zhang, Shengda; Zhang, David D.; Wang, Zongli; Xu, Qinghai; Chen, Shengqian; Wang, Shijin; Kang, Shichang; Chen, Fahu

2018-03-01

Long-term, high-resolution temperature records which combine an unambiguous proxy and precise dating are rare in China. In addition, the societal implications of past temperature change on a regional scale have not been sufficiently assessed. Here, based on the modern relationship between chironomids and temperature, we use fossil chironomid assemblages in a precisely dated sediment core from Gonghai Lake to explore temperature variability during the past 4000 years in northern China. Subsequently, we address the possible regional societal implications of temperature change through a statistical analysis of the occurrence of wars. Our results show the following. (1) The mean annual temperature (TANN) was relatively high during 4000-2700 cal yr BP, decreased gradually during 2700-1270 cal yr BP and then fluctuated during the last 1270 years. (2) A cold event in the Period of Disunity, the Sui-Tang Warm Period (STWP), the Medieval Warm Period (MWP) and the Little Ice Age (LIA) can all be recognized in the paleotemperature record, as well as in many other temperature reconstructions in China. This suggests that our chironomid-inferred temperature record for the Gonghai Lake region is representative. (3) Local wars in Shanxi Province, documented in the historical literature during the past 2700 years, are statistically significantly correlated with changes in temperature, and the relationship is a good example of the potential societal implications of temperature change on a regional scale.

The null hypothesis: steady rates of erosion, weathering and sediment accumulation during Late Cenozoic mountain uplift and glaciation

NASA Astrophysics Data System (ADS)

Willenbring, J. K.; Jerolmack, D. J.

2015-12-01

At the largest time and space scales, the pace of erosion and chemical weathering is determined by tectonic uplift rates. Deviations from this equilibrium condition arise from the transient response of landscape denudation to climatic and tectonic perturbations, and may be long lived. We posit that the constraint of mass balance, however, makes it unlikely that such disequilibrium persists at the global scale over millions of years, as has been proposed for late Cenozoic erosion. To support this contention, we synthesize existing data for weathering fluxes, global sedimentation rates, sediment yields and tectonic motions. The records show a remarkable constancy in the pace of Earth-surface evolution over the last 10 million years. These findings provide strong support for the null hypothesis; that global rates of landscape change have remained constant over the last ten million years, despite global climate change and massive mountain building events. Two important implications are: (1) global climate change may not change global denudation rates, because the nature and sign of landscape responses are varied; and (2) tectonic and climatic perturbations are accommodated in the long term by changes in landscape form. This work undermines the hypothesis that increased weathering due to late Cenozoic mountain building or climate change was the primary agent for a decrease in global temperatures.

Neoproterozoic Evolution and Najd‒Related Transpressive Shear Deformations Along Nugrus Shear Zone, South Eastern Desert, Egypt (Implications from Field‒Structural Data and AMS‒Technique)

NASA Astrophysics Data System (ADS)

Hagag, W.; Moustafa, R.; Hamimi, Z.

2018-01-01

The tectonometamorphic evolution of Nugrus Shear Zone (NSZ) in the south Eastern Desert of Egypt was reevaluated through an integrated study including field-structural work and magnetofabric analysis using Anisotropy of Magnetic Susceptibility (AMS) technique, complemented by detailed microstructural investigation. Several lines of evidence indicate that the Neoproterozoic juvenile crust within this high strain zone suffered an impressive tectonic event of left-lateral transpressional regime, transposed the majority of the earlier formed structures into a NNW to NW-directed wrench corridor depicts the northwestern extension of the Najd Shear System (NSS) along the Eastern Desert of Egypt. The core of the southern Hafafit dome underwent a high metamorphic event ( M 1) developed during the end of the main collisional orogeny in the Arabian-Nubian Shield (ANS). The subsequent M 2 metamorphic event was retrogressive and depicts the tectonic evolution and exhumation of the Nugrus-Hafafit area including the Hafafit gneissic domes, during the origination of the left-lateral transpressive wrench corridor of the NSS. The early tectonic fabric within the NSZ and associated highly deformed rocks was successfully detected by the integration of AMS-technique and microstructural observations. Such fabric grain was checked through a field-structural work. The outcomes of the present contribution advocate a complex tectonic evolution with successive and overlapped deformation events for the NSZ.

Cretaceous-Eocene provenance connections between the Palawan Continental Terrane and the northern South China Sea margin

NASA Astrophysics Data System (ADS)

Shao, Lei; Cao, Licheng; Qiao, Peijun; Zhang, Xiangtao; Li, Qianyu; van Hinsbergen, Douwe J. J.

2017-11-01

The plate kinematic history of the South China Sea opening is key to reconstructing how the Mesozoic configuration of Panthalassa and Tethyan subduction systems evolved into today's complex Southeast Asian tectonic collage. The South China Sea is currently flanked by the Palawan Continental Terrane in the south and South China in the north and the two blocks have long been assumed to be conjugate margins. However, the paleogeographic history of the Palawan Continental Terrane remains an issue of uncertainty and controversy, especially regarding the questions of where and when it was separated from South China. Here we employ detrital zircon U-Pb geochronology and heavy mineral analysis on Cretaceous and Eocene strata from the northern South China Sea and Palawan to constrain the Late Mesozoic-Early Cenozoic provenance and paleogeographic evolution of the region testing possible connection between the Palawan Continental Terrane and the northern South China Sea margin. In addition to a revision of the regional stratigraphic framework using the youngest zircon U-Pb ages, these analyses show that while the Upper Cretaceous strata from the Palawan Continental Terrane are characterized by a dominance of zircon with crystallization ages clustering around the Cretaceous, the Eocene strata feature a large range of zircon ages and a new mineral group of rutile, anatase, and monazite. On the one hand, this change of sediment compositions seems to exclude the possibility of a latest Cretaceous drift of the Palawan Continental Terrane in response to the Proto-South China Sea opening as previously inferred. On the other hand, the zircon age signatures of the Cretaceous-Eocene strata from the Palawan Continental Terrane are largely comparable to those of contemporary samples from the northeastern South China Sea region, suggesting a possible conjugate relationship between the Palawan Continental Terrane and the eastern Pearl River Mouth Basin. Thus, the Palawan Continental Terrane is interpreted to have been attached to the South China margin from the Cretaceous until the Oligocene oceanization of the South China Sea. In our preferred paleogeographic scenario, the sediment provenance in the northeastern South China Sea region changed from dominantly nearby Cretaceous continental arcs of the South China margin to more distal southeastern South China in the Eocene.

Fluvial archives, a valuable record of vertical crustal deformation

NASA Astrophysics Data System (ADS)

Demoulin, A.; Mather, A.; Whittaker, A.

2017-06-01

The study of drainage network response to uplift is important not only for understanding river system dynamics and associated channel properties and fluvial landforms, but also for identifying the nature of crustal deformation and its history. In recent decades, geomorphic analysis of rivers has proved powerful in elucidating the tectonic evolution of actively uplifting and eroding orogens. Here, we review the main recent developments that have improved and expanded qualitative and quantitative information about vertical tectonic motions (the effects of horizontal deformation are not addressed). Channel long profiles have received considerable attention in the literature, and we briefly introduce basic aspects of the behaviour of bedrock rivers from field and numerical modelling perspectives, before describing the various metrics that have been proposed to identify the information on crustal deformation contained within their steady-state characteristics. Then, we review the literature dealing with the transient response of rivers to tectonic perturbation, through the production of knickpoints propagating through the drainage network. Inverse modelling of river profiles for uplift in time and space is also shown to be very effective in reconstructing regional tectonic histories. Finally, we present a synthetic morphometric approach for deducing the tectonic record of fluvial landscapes. As well as the erosional imprint of tectonic forcing, sedimentary deposits, such as fluvial terrace staircases, are also considered as a classical component of tectonic geomorphology. We show that these studies have recently benefited from rapid advances in dating techniques, allowing more reliable reconstruction of incision histories and estimation of incision rates. The combination of progress in the understanding of transient river profiles and larger, more rigorous data sets of terrace ages has led to improved understanding of river erosion and the implications for terrace profile correlation, i.e., extrapolation of local data to entire profiles. Finally, planform changes in fluvial systems are considered at the channel scale in alluvial rivers and regional level in terms of drainage reorganisation. Examples are given of how numerical modelling can efficiently combine with topographic data to shed new light on the (dis)equilibrium state of drainage systems across regional drainage divides.

Family Planning Education and Health Care Delivery in the People's Republic of China: Implications for Educational Alternatives

ERIC Educational Resources Information Center

Hawkins, John N.

1976-01-01

Explores the process recently employed in China (post-1966) to transfer skills and information related to family planning via a network of alternative educational institutions lodged in the health care delivery system. (Author/RK)

Collision of the Tacheng block with the Mayile-Barleik-Tangbale accretionary complex in Western Junggar, NW China: Implication for Early-Middle Paleozoic architecture of the western Altaids

NASA Astrophysics Data System (ADS)

Zhang, Ji'en; Xiao, Wenjiao; Luo, Jun; Chen, Yichao; Windley, Brian F.; Song, Dongfang; Han, Chunming; Safonova, Inna

2018-06-01

Western Junggar in NW China, located to the southeast of the Boshchekul-Chingiz (BC) Range and to the north of the Chu-Balkhash-Yili microcontinent (CBY), played a key role in the architectural development of the western Altaids. However, the mutual tectonic relationships have been poorly constrained. In this paper, we present detailed mapping, field structural geology, and geochemical data from the Barleik-Mayile-Tangbale Complex (BMTC) in Western Junggar. The Complex is divisible into Zones I, II and III, which are mainly composed of Cambrian-Silurian rocks. Zone I contains pillow lava, siliceous shale, chert, coral-bearing limestone, sandstone and purple mudstone. Zone II consists of basaltic lava, siliceous shale, chert, sandstone and mudstone. Zone III is characterized by basalt, chert, sandstone and mudstone. These rocks represent imbricated ocean plate stratigraphy, which have been either tectonically juxtaposed by thrusting or form a mélange with a block-in-matrix structure. All these relationships suggest that the BMTC is an Early-Middle Paleozoic accretionary complex in the eastern extension of the BC Range. These Early Paleozoic oceanic rocks were thrust onto Silurian sediments forming imbricate thrust stacks that are unconformably overlain by Devonian limestone, conglomerate and sandstone containing fossils of brachiopoda, crinoidea, bryozoa, and plant stems and leaves. The tectonic vergence of overturned folds in cherts, drag-related curved cleavages and σ-type structures on the main thrust surface suggests top-to-the-NW transport. Moreover, the positive εNd(t) values of volcanic rocks from the Tacan-1 drill-core, and the positive εHf(t) values and post-Cambrian ages of detrital zircons from Silurian and Devonian strata to the south of the Tacheng block indicate that its basement is a depleted and juvenile lithosphere. And there was a radial outward transition from coral-bearing shallow marine (shelf) to deep ocean (pelagic) environments, and from OIB/E-MORB to N-MORB lava geochemistry away from the Tacheng block. Comparisons with published data suggest that these positive isotopic values, stratigraphic, structural and geochemical relationships can be best understood as an analogue of the relationships between the Ontong Java oceanic plateau and the Pacific oceanic crust. Therefore we propose that the basement of the Tacheng block was an Early Paleozoic oceanic plateau. The southern part of the Tacheng block was an accretionary complex and the northern part was an oceanic basin in the Early Paleozoic, the configuration of which is similar to that of the present Ontong Java oceanic plateau situated on the Pacific oceanic crust, and its accretion into the Solomon accretionary complex. The presence of Ordovician SSZ-type ophiolites, early Paleozoic blueschist and Silurian SSZ-type intrusions in the BMTC, and Early-Middle Paleozoic continental arc-related intrusive rocks in the northern margin of the CBY provide further corroboration of a former subduction zone between the southern West Junggar and the northern margin of the CBY. Furthermore, consideration of the fact that the Kokchetav-North Tianshan range was collaged to the southern margin of the CBY in the Ordovician-Devonian indicates that both ranges were amalgamated synchronously with the CBY constructing the Early-Middle Paleozoic architecture of western Altaids.

Nubia-Arabia-Eurasia plate motions and the dynamics of Mediterranean and Middle East tectonics

NASA Astrophysics Data System (ADS)

Reilinger, Robert; McClusky, Simon

2011-09-01

We use geodetic and plate tectonic observations to constrain the tectonic evolution of the Nubia-Arabia-Eurasia plate system. Two phases of slowing of Nubia-Eurasia convergence, each of which resulted in an ˜50 per cent decrease in the rate of convergence, coincided with the initiation of Nubia-Arabia continental rifting along the Red Sea and Somalia-Arabia rifting along the Gulf of Aden at 24 ± 4 Ma, and the initiation of oceanic rifting along the full extent of the Gulf of Aden at 11 ± 2 Ma. In addition, both the northern and southern Red Sea (Nubia-Arabia plate boundary) underwent changes in the configuration of extension at 11 ± 2 Ma, including the transfer of extension from the Suez Rift to the Gulf of Aqaba/Dead Sea fault system in the north, and from the central Red Sea Basin (Bab al Mandab) to the Afar volcanic zone in the south. While Nubia-Eurasia convergence slowed, the rate of Arabia-Eurasia convergence remained constant within the resolution of our observations, and is indistinguishable from the present-day global positioning system rate. The timing of the initial slowing of Nubia-Eurasia convergence (24 ± 4 Ma) corresponds to the initiation of extensional tectonics in the Mediterranean Basin, and the second phase of slowing to changes in the character of Mediterranean extension reported at ˜11 Ma. These observations are consistent with the hypothesis that changes in Nubia-Eurasia convergence, and associated Nubia-Arabia divergence, are the fundamental cause of both Mediterranean and Middle East post-Late Oligocene tectonics. We speculate about the implications of these kinematic relationships for the dynamics of Nubia-Arabia-Eurasia plate interactions, and favour the interpretation that slowing of Nubia-Eurasia convergence, and the resulting tectonic changes in the Mediterranean Basin and Middle East, resulted from a decrease in slab pull from the Arabia-subducted lithosphere across the Nubia-Arabia, evolving plate boundary.

An unrecognized major collision of the Okhotomorsk Block with East Asia during the Late Cretaceous, constraints on the plate reorganization of the Northwest Pacific

NASA Astrophysics Data System (ADS)

Yang, Yong-Tai

2013-11-01

Interactions at plate boundaries induce stresses that constitute critical controls on the structural evolution of intraplate regions. However, the traditional tectonic model for the East Asian margin during the Mesozoic, invoking successive episodes of paleo-Pacific oceanic subduction, does not provide an adequate context for important Late Cretaceous dynamics across East Asia, including: continental-scale orogenic processes, significant sinistral strike-slip faulting, and several others. The integration of numerous documented field relations requires a new tectonic model, as proposed here. The Okhotomorsk continental block, currently residing below the Okhotsk Sea in Northeast Asia, was located in the interior of the Izanagi Plate before the Late Cretaceous. It moved northwestward with the Izanagi Plate and collided with the South China Block at about 100 Ma. The indentation of the Okhotomorsk Block within East Asia resulted in the formation of a sinistral strike-slip fault system in South China, formation of a dextral strike-slip fault system in North China, and regional northwest-southeast shortening and orogenic uplift in East Asia. Northeast-striking mountain belts over 500 km wide extended from Southeast China to Southwest Japan and South Korea. The peak metamorphism at about 89 Ma of the Sanbagawa high-pressure metamorphic belt in Southwest Japan was probably related to the continental subduction of the Okhotomorsk Block beneath the East Asian margin. Subsequently, the north-northwestward change of motion direction of the Izanagi Plate led to the northward movement of the Okhotomorsk Block along the East Asian margin, forming a significant sinistral continental transform boundary similar to the San Andreas fault system in California. Sanbagawa metamorphic rocks in Southwest Japan were rapidly exhumed through the several-kilometer wide ductile shear zone at the lower crust and upper mantle level. Accretionary complexes successively accumulated along the East Asian margin during the Jurassic-Early Cretaceous were subdivided into narrow and subparallel belts by the upper crustal strike-slip fault system. The departure of the Okhotomorsk Block from the northeast-striking Asian margin resulted in the occurrence of an extensional setting and formation of a wide magmatic belt to the west of the margin. In the Campanian, the block collided with the Siberian margin, in Northeast Asia. At about 77 Ma, a new oceanic subduction occurred to the south of the Okhotomorsk Block, ending its long-distance northward motion. Based on the new tectonic model, the abundant Late Archean to Early Proterozoic detrital zircons in the Cretaceous sandstones in Kamchatka, Southwest Japan, and Taiwan are interpreted to have been sourced from the Okhotomorsk Block basement which possibly formed during the Late Archean and Early Proterozoic. The new model suggests a rapidly northward-moving Okhotomorsk Block at an average speed of 22.5 cm/yr during 89-77 Ma. It is hypothesized that the Okhotomorsk-East Asia collision during 100-89 Ma slowed down the northwestward motion of the Izanagi Plate, while slab pull forces produced from the subducting Izanagi Plate beneath the Siberian margin redirected the plate from northwestward to north-northwestward motion at about 90-89 Ma.

Experiment to evaluate feasibility of utilizing Skylab-EREP remote sensing data for tectonic analysis of the Bighorn Mountains region, Wyoming-Montana

NASA Technical Reports Server (NTRS)

Hoppin, R. A. (Principal Investigator)

1974-01-01

The author has identified the following significant results. S-190A color transparencies from SL-2 of the Big Horn basin region provide the best format to date for geologic study of that region; red beds are quite mappable and resistant key beds sharply outlined. An S-190B color frame from SL-3 of the Pryor-Bighorn mountains provides no indication that the Nye-Bowler lineament extends east of East Pryor Mountain. This has important implications regarding the role of this and other lineaments (which also appear to be of restricted length) in the tectonics of the region. Extensions of these lineaments for great distances does not seem warranted on the basis of surface evidence.

Geological Evolution of the Ganiki Planitia Quadrangle (V14) on Venus

NASA Technical Reports Server (NTRS)

Grosfils, E. B.; Drury, D. E.; Hurwitz, D. M.; Kastl, B.; Long, s. M.; Richards, J. W.; Venechuk, E. M.

2005-01-01

The Ganiki Planitia quadrangle (25-50degN, 180-210degE) is located north of Atla Regio, south of Vinmara Planitia, and southeast of Atalanta Planitia. The region contains a diverse array of volcanic-, tectonic- and impact-derived features, and the objectives for the ongoing mapping effort are fivefold: 1) explore the formation and evolution of radiating dike swarms within the region, 2) use the diverse array of volcanic deposits to further test the neutral buoyancy hypothesis proposed to explain the origin of reservoir-derived features, 3&4) unravel the volcanic and tectonic evolution in this area, and 5) explore the implications of 1-4 for resurfacing mechanisms. Here we summarize our onging analysis of the material unit stratigraphy in the quadrangle, data central to meeting the aforementioned objectives successfully.

Tectonic and magmatic processes of the post-spreading ridge in the Southwest Sub-basin, South China Sea

NASA Astrophysics Data System (ADS)

Li, J.; Zhang, J.; Ruan, A.; Niu, X.; Ding, W.

2016-12-01

We report here a 3D ocean bottom seismometer experiment on the fossil spreading ridge in the Southwest Sub-basin of the South China Sea. An extreme asymmetric crustal structure across the axis is revealed and caused by lower crust thinning and upper mantle uplifting located on NW side of the ridge. Such crustal extension proposed a low-angle oceanic detachment fault throughout the whole crust on the last or post spreading stages. A low-velocity (7.6-7.9 km/s) on the uplifting upper mantle is possibly induced by both mantle serpentinization and/or decompression melting through the detachment fault. Velocity models also demonstrate that a post-spreading volcano erupted on the axis is mainly formed by an extrusive process with an extrusive/intrusive ratio of 1.92. Very low velocity of upper crust (3.1-4.8 km/s) of the volcano is attributed to the composition of volcaniclastic rocks and high-porosity basalts, which have been observed in the borehole and dredged samples on the seamounts nearby. KEY WORDS post-spreading ridge; wide-angle seismic refraction; crustal structure; South China Sea; Southwest Sub-basin

Trade and the Future of China's Black Carbon Emissions

NASA Astrophysics Data System (ADS)

Persad, G.; Oppenheimer, M.; Naik, V.

2016-12-01

Emissions of black carbon aerosols in China have increased by over 200% during the last 50 years, with negative implications both for human health and for regional and global climate. The Representative Concentration Pathway (RCP) emissions scenarios all assume that China's future black carbon emissions will decrease. However, this decline partially depends on the assumption that the evolution of future pollutant emissions in developing nations will match the observed historical relationship between air quality and income in developed nations. Recent research has demonstrated that a substantial portion of China's current black carbon emissions are driven by the production of goods exported for consumption elsewhere. This constitutes an external demand for black carbon-emitting activity in China that is much smaller in the developed nations on which the historical air quality/income relationship is based. We here show using integrated assessment model output, general circulation modeling, and emissions and economic data that (1) China must achieve a faster technological and regulatory evolution than did developed countries in order achieve the same air quality/income trajectory; (2) China's uniquely large share of export-related black carbon-emitting activities and their potential growth are a plausible explanation for this disparity; and (3) the climate and health implications of these export-related black carbon emissions, if unmitigated, are of interest from a policy perspective. Together these results indicate that the production of goods for export will steepen the mitigation curve for China relative to developed nations, if China is to achieve the future black carbon emissions reductions assumed in the RCPs.

Continentward-Dipping Normal Faults, Boudinage and Ductile Shear at Rifted Passive Margins

NASA Astrophysics Data System (ADS)

Clerc, C. N.; Ringenbach, J. C.; Jolivet, L.; Ballard, J. F.

2017-12-01

Deep structures resulting from the rifting of the continental crust are now well imaged by seismic profiles. We present a series of recent industrial profiles that allow the identification of various rift-related geological processes such as crustal boudinage, ductile shear of the base of the crust and low-angle detachment faulting. Along both magma-rich and magma-poor rifted margins, we observe clear indications of ductile deformation of the deep continental crust. Large-scale shallow dipping shear zones are identified with a top-to-the-continent sense of shear. This sense of shear is consistent with the activity of the Continentward-Dipping Normal Faults (CDNF) that accommodate the extension in the upper crust. This pattern is responsible for an oceanward migration of the deformation and of the associated syn-tectonic deposits (sediments and/or volcanics). We discuss the origin of the Continentward-Dipping Normal Faults (CDNF) and investigate their implications and the effect of sediment thermal blanketing on crustal rheology. In some cases, low-angle shear zones define an anastomosed pattern that delineates boudin-like structures that seem to control the position and dip of upper crustal normal faults. We present some of the most striking examples from several locations (Uruguay, West Africa, South China Sea…), and discuss their rifting histories that differ from the classical models of oceanward-dipping normal faults.

Delineation of the New Madrid seismic zone using Landsat MSS data with insurance and tax implications of future fault movement

NASA Astrophysics Data System (ADS)

Wiley, M. A.; Rupert, G. B.; Christy, J. J.; Cochrane, C. L.; Buffington, N. L., Jr.

Landsat MSS imagery was used to delineate the New Madrid seismic zone, near the common borders of Arkansas, Missouri, Tennessee, and Kentucky, which has produced earthquakes wth Modified Mercalli intensities larger than 10. Intepretation of the Landsat image, in conjunction with published data, provides means for combining geomorphic and geophysical data to yield new insights into the tectonics of the area. The paper discusses the value of this technique for constructing and maintaining disaster contingency plans, with particular attention given to insurance and tax implications.

Block Tectonic Motion on Venus

NASA Astrophysics Data System (ADS)

Byrne, P. K.; Ghail, R.; Sengor, A. M. C.; Klimczak, C.; Solomon, S. C.

2017-12-01

Despite close similarities in mass and bulk composition to Earth, Venus apparently shows no evidence for Earth-like plate tectonics, except perhaps for limited plume-induced subduction. We use Magellan radar data to survey numerous examples of low-lying areas infilled with plains lavas and delimited by networks of narrow belts of substantial tectonic deformation; such sites include those at Lavinia and Llorona Planitiæ and to the north of Helen Planitia. This deformation is locally extensional or shortening in style but very often also includes structures that denote substantial lateral motion. Cross-cutting relations suggest that this motion occurred both before and after the lavas were emplaced. Together, these observations imply that many of the belt-bounded areas have acted as relatively rigid blocks that experienced considerable horizontal movement relative to each other, in a manner similar to blocks that constitute parts of the Terran continental lithosphere. On Earth, continental deformation is enabled by the low strength of the lower crust and/or upper mantle. On Venus, the shallow brittle-ductile transition (BDT), a result of the planet's elevated surface temperature, likely acts in a similar way to decouple the upper and lower crust. Subcrustal lid rejuvenation, a recently proposed mechanism for renewal of the mantle portion of Venus' stagnant lithospheric lid through thinning and recycling, could drive the horizontal movement of these rigid blocks. It may be, then, that the blocks move as continental blocks do on Earth, with mantle motion transferred to the surface and manifest as narrow zones of tectonic deformation akin to, for example, the Tian Shan and Altin Tagh ranges that bound the Tarim Basin in northwestern China. The shallow BDT on Venus precludes the blocks from subducting, and so their fate is to shorten, lengthen, or retain their geometry at the expense of adjacent blocks. We suggest that this behavior is analogous to plate-tectonic-driven continental deformation on Earth, and that this activity has operated in the regions documented on Venus since the time of emplacement of the local plains material.

Earthquake Potential in Myanmar

NASA Astrophysics Data System (ADS)

Aung, Hla Hla

Myanmar region is generally believed to be an area of high earthquake potential from the point of view of seismic activity which has been low compared to the surrounding regions like Indonesia, China, and Pakistan. Geoscientists and seismologists predicted earthquakes to occur in the area north of the Sumatra-Andaman Islands, i.e. the southwest and west part of Myanmar. Myanmar tectonic setting relative to East and SE Asia is rather peculiar and unique with different plate tectonic models but similar to the setting of western part of North America. Myanmar crustal blocks are caught within two lithospheric plates of India and Indochina experiencing oblique subduction with major dextral strike-slip faulting of the Sagaing fault. Seismic tomography and thermal structure of India plate along the Sunda subduction zone vary from south to north. Strong partitioning in central Andaman basin where crustal fragmentation and northward dispersion of Burma plate by back-arc spreading mechanism has been operating since Neogene. Northward motion of Burma plate relative to SE Asia would dock against the major continent further north and might have caused the accumulation of strain which in turn will be released as earthquakes in the future.

Application of random seismic inversion method based on tectonic model in thin sand body research

NASA Astrophysics Data System (ADS)

Dianju, W.; Jianghai, L.; Qingkai, F.

2017-12-01

The oil and gas exploitation at Songliao Basin, Northeast China have already progressed to the period with high water production. The previous detailed reservoir description that based on seismic image, sediment core, borehole logging has great limitations in small scale structural interpretation and thin sand body characterization. Thus, precise guidance for petroleum exploration is badly in need of a more advanced method. To do so, we derived the method of random seismic inversion constrained by tectonic model.It can effectively improve the depicting ability of thin sand bodies, combining numerical simulation techniques, which can credibly reducing the blindness of reservoir analysis from the whole to the local and from the macroscopic to the microscopic. At the same time, this can reduce the limitations of the study under the constraints of different geological conditions of the reservoir, accomplish probably the exact estimation for the effective reservoir. Based on the research, this paper has optimized the regional effective reservoir evaluation and the productive location adjustment of applicability, combined with the practical exploration and development in Aonan oil field.

The characteristics of heat flow in the Shenhu gas hydrate drilling area, northern South China Sea

NASA Astrophysics Data System (ADS)

Xu, Xing; Wan, Zhifeng; Wang, Xianqing; Sun, Yuefeng; Xia, Bin

2016-12-01

Marine heat flow is of great significance for the formation and occurrence of seabed oil, gas and gas hydrate resources. Geothermal gradient is an important parameter in determining the thickness of the hydrate stability zone. The northern slope of the South China Sea is rich in gas hydrate resources. Several borehole drilling attempts were successful in finding hydrates in the Shenhu area, while others were not. The failures demand further study on the distribution regularities of heat flow and its controlling effects on hydrate occurrence. In this study, forty-eight heat flow measurements are analyzed in the Shenhu gas hydrate drilling area, located in the northern South China Sea, together with their relationship to topography, sedimentary environment and tectonic setting. Canyons are well developed in the study area, caused mainly by the development of faults, faster sediment supply and slumping of the Pearl River Estuary since the late Miocene in the northern South China Sea. The heat flow values in grooves, occurring always in fault zones, are higher than those of ridges. Additionally, the heat flow values gradually increase from the inner fan, to the middle fan, to the external fan subfacies. The locations with low heat flow such as ridges, locations away from faults and the middle fan subfacies, are more conducive to gas hydrate occurrence.

Ecological and physical barriers shape genetic structure of the Alpine porcini (Boletus reticuloceps).

PubMed

Feng, Bang; Liu, Jian Wei; Xu, Jianping; Zhao, Kuan; Ge, Zai Wei; Yang, Zhu L

2017-04-01

The Alpine porcini, Boletus reticuloceps, is an ectomycorrhizal mushroom distributed in subalpine areas of Southwest China, central China, and Taiwan Island. This distribution pattern makes it an ideal organism to infer how ectomycorrhizal fungi have reacted to historical tectonic and climatic changes, and to illustrate the mechanism for the disjunction of organisms between Southwest China and Taiwan. In this study, we explored the phylogeographic pattern of B. reticuloceps by microsatellite genotyping, DNA sequencing, ecological factor analysis, and species distribution modeling. Three genetic groups from the East Himalayas (EH), northern Hengduan Mountains (NHM), and southern Hengduan Mountains (SHM), were identified. The earlier divergent SHM group is found under Abies in moister environments, whereas the EH and NHM groups, which are physically separated by the Mekong-Salween Divide, are found mainly under Picea in drier environments. Samples from Taiwan showed a close relationship with the SHM group. High mountains did not form dispersal barriers among populations in each of the EH, NHM, and SHM groups, probably due to the relatively weak host specificity of B. reticuloceps. Our study indicated that ecological heterogeneity could have contributed to the divergence between the SHM and the NHM-EH groups, while physical barriers could have led to the divergence of the NHM and the EH groups. Dispersal into Taiwan via Central China during the Quaternary glaciations is likely to have shaped its disjunct distribution.

Changes in Early Adolescents' Sense of Responsibility to their Parents in the United States and China: Implications for Academic Functioning

PubMed Central

Pomerantz, Eva M.; Qin, Lili; Wang, Qian; Chen, Huichang

2011-01-01

This research examined American and Chinese children's sense of responsibility to their parents during early adolescence, with a focus on its implications for children's academic functioning. Four times over the seventh and eighth grades, 825 children (mean age = 12.73 years) in the United States and China reported on their sense of responsibility to their parents. Information on children's academic functioning was also collected from children as well as school records. Although children's sense of responsibility to their parents declined over the seventh and eighth grades in the United States, this was not the case in China. In both countries, children's sense of responsibility was predictive of enhanced academic functioning among children over time. PMID:21466541

Molecular Tectonic Model of Virus Structural Transitions: the Putative Cell Entry States of Poliovirus

PubMed Central

Belnap, David M.; Filman, David J.; Trus, Benes L.; Cheng, Naiqian; Booy, Frank P.; Conway, James F.; Curry, Stephen; Hiremath, Chaitanya N.; Tsang, Simon K.; Steven, Alasdair C.; Hogle, James M.

2000-01-01

Upon interacting with its receptor, poliovirus undergoes conformational changes that are implicated in cell entry, including the externalization of the viral protein VP4 and the N terminus of VP1. We have determined the structures of native virions and of two putative cell entry intermediates, the 135S and 80S particles, at ∼22-Å resolution by cryo-electron microscopy. The 135S and 80S particles are both ∼4% larger than the virion. Pseudoatomic models were constructed by adjusting the beta-barrel domains of the three capsid proteins VP1, VP2, and VP3 from their known positions in the virion to fit the 135S and 80S reconstructions. Domain movements of up to 9 Å were detected, analogous to the shifting of tectonic plates. These movements create gaps between adjacent subunits. The gaps at the sites where VP1, VP2, and VP3 subunits meet are plausible candidates for the emergence of VP4 and the N terminus of VP1. The implications of these observations are discussed for models in which the externalized components form a transmembrane pore through which viral RNA enters the infected cell. PMID:10627545

Molecular tectonic model of virus structural transitions: the putative cell entry states of poliovirus.

PubMed

Belnap, D M; Filman, D J; Trus, B L; Cheng, N; Booy, F P; Conway, J F; Curry, S; Hiremath, C N; Tsang, S K; Steven, A C; Hogle, J M

2000-02-01

Upon interacting with its receptor, poliovirus undergoes conformational changes that are implicated in cell entry, including the externalization of the viral protein VP4 and the N terminus of VP1. We have determined the structures of native virions and of two putative cell entry intermediates, the 135S and 80S particles, at approximately 22-A resolution by cryo-electron microscopy. The 135S and 80S particles are both approximately 4% larger than the virion. Pseudoatomic models were constructed by adjusting the beta-barrel domains of the three capsid proteins VP1, VP2, and VP3 from their known positions in the virion to fit the 135S and 80S reconstructions. Domain movements of up to 9 A were detected, analogous to the shifting of tectonic plates. These movements create gaps between adjacent subunits. The gaps at the sites where VP1, VP2, and VP3 subunits meet are plausible candidates for the emergence of VP4 and the N terminus of VP1. The implications of these observations are discussed for models in which the externalized components form a transmembrane pore through which viral RNA enters the infected cell.

Geochronology and geochemistry of late Carboniferous-middle Permian I- and A-type granites and gabbro-diorites in the eastern Jiamusi Massif, NE China: Implications for petrogenesis and tectonic setting

NASA Astrophysics Data System (ADS)

Bi, Jun-Hui; Ge, Wen-Chun; Yang, Hao; Wang, Zhi-Hui; Xu, Wen-Liang; Yang, Jin-Hui; Xing, De-He; Chen, Hui-Jun

2016-12-01

Late Carboniferous-middle Permian magmatism in the Jiamusi Massif of northeast China, in the eastern segment of the Central Asian Orogenic Belt (CAOB), provides critical evidence regarding the tectonic history and geodynamic processes in the region. The gabbro-diorites of the Longtouqiao pluton and two groups of coeval granite in the study area comprise a bimodal magmatic suite. Precise LA-ICP-MS U-Pb zircon ages indicate that the granitoids and gabbro-diorites were emplaced in the late Carboniferous-middle Permian (302-267 Ma). Group I granites have high SiO2 (70.75-77.04 wt.%) and K2O (3.65-5.89 wt.%) contents, are enriched in LILEs (e.g., Rb, Th, and U) relative to HFSEs and LREEs, and have negative Nb, Ta, P, and Ti anomalies, which collectively indicate affinities with subduction-related magmas. Group II granites are weakly peraluminous (A/CNK = 1.03-1.07) and are characterized by enrichment in alkalis (Na2O + K2O = 8.22-8.90 wt.%), low MgO (0.04-0.09 wt.%) and P2O5 (0.01-0.04 wt.%) contents, high Zr and Nb contents, high 10,000 × Ga/Al ratios, and they are geochemically similar to aluminous A-type granites. All the magmatic zircons in these granitoids have great variations of εHf(t) (+ 7.89 to - 5.60) and two-stage Hf model ages (TDM2) of 0.8-1.7 Ga, which suggest that the precursor magmas originated from a heterogeneous source that involved juvenile components derived from a depleted mantle source during magma generation. The aluminous A-type granite magmas were probably derived by high-temperature partial melting of a felsic crustal source, whereas the other granite magmas probably resulted from partial melting of a mafic lower crust. The gabbro-diorites of the Longtouqiao pluton are depleted in Nb, Ta, P, and Ti, and show flat distributions of most LILEs and HFSEs, except for large positive anomalies in Ba, K, and Pb. These features reflect a limited degree of crustal contamination associated with the subduction-related magmatic processes. These data, together with previously reported data and the nature of various rock types along the eastern part of the Jiamusi Massif, suggest that the intrusive rocks were formed in a geodynamic regime that changed from compression to extension during the westwards subduction of the Paleo-Pacific oceanic lithosphere, probably as a result of slab break-off of the subducting plate.

China-U.S. Relations: Current Issues and Implications for U.S. Policy

DTIC Science & Technology

2008-12-09

cooperatively with China while encouraging Beijing to become a “responsible stakeholder” in the global system. U.S. Treasury Secretary Henry Paulson in...in Beijing in August 2008. Other concerns about China appear driven by security calculations, where U.S. officials question the motivations behind...China’s expanding military budget. One congressionally mandated DOD report concluded Beijing is greatly understating its military expenditures and is

Bridging the Strait: Implications for Japan and the United States Following a Peaceful Reunification of China and Taiwan

DTIC Science & Technology

2007-12-01

8 C . CHINA AND JAPAN ....................................................................................10 D. JAPAN AND THE UNITED STATES... C . Bush, Untying the Knot: Making Peace in the Taiwan Strait. (Washington, D.C.: The Brookings Institute, 2005), 36. 8 Richard Stubbs, Rethinking...Asia’s Economic Miracle , (Houndsmill, England: Plagrave McMillan, 2005), 31-32. 3 Under the “one China, two systems” policy, Taipei would accept that

Disparity and convergence: Chinese provincial government health expenditures.

PubMed

Pan, Jay; Wang, Peng; Qin, Xuezheng; Zhang, Shufang

2013-01-01

The huge regional disparity in government health expenditures (GHE) is a major policy concern in China. This paper addresses whether provincial GHE converges in China from 1997 to 2009 using the economic convergence framework based on neoclassical economic growth theory. Our empirical investigation provides compelling evidence of long-term convergence in provincial GHE within China, but not in short-term. Policy implications of these empirical results are discussed.

Disparity and Convergence: Chinese Provincial Government Health Expenditures

PubMed Central

Pan, Jay; Wang, Peng; Qin, Xuezheng; Zhang, Shufang

2013-01-01

The huge regional disparity in government health expenditures (GHE) is a major policy concern in China. This paper addresses whether provincial GHE converges in China from 1997 to 2009 using the economic convergence framework based on neoclassical economic growth theory. Our empirical investigation provides compelling evidence of long-term convergence in provincial GHE within China, but not in short-term. Policy implications of these empirical results are discussed. PMID:23977049

Chinese Policy Toward South Asia: Implications and Prospects for Nepal

DTIC Science & Technology

2013-03-01

China-India Relations,” Hult International Business School, (July, 2012), http://www.e-ir.info/2012/07/07/an-analysis-of- contemporary-us-china...increasing activities in the Indian Ocean have been global concerns 2 because China and India are emerging as the twenty-first century economic...rapidly developing their hard power capabilities commensurate with their rising statures in global affairs. India is Nepal’s main trading partner

China’s Growing Energy Demand: Implications for the United States

DTIC Science & Technology

2015-06-01

but less oil, natural gas, and nuclear power . By 2013, China consumed 25 percent more energy than the United States, including burning more than three...1 Energy Information Administration, International Energy Outlook 2013 (July 2013), www.eia.gov/ forecasts /archive/ieo13/. 3 output in China...natural gas (other than through pipelines), or the power generated from nuclear energy or renewable sources limits their markets to geographically

Luminescence ages for alluvial-fan deposits in Southern Death Valley: Implications for climate-driven sedimentation along a tectonically active mountain front

USGS Publications Warehouse

Sohn, M.F.; Mahan, S.A.; Knott, J.R.; Bowman, D.D.

2007-01-01

Controversy exists over whether alluvial-fan sedimentation along tectonically active mountain fronts is driven by climatic changes or tectonics. Knowing the age of sedimentation is the key to understanding the relationship between sedimentation and its cause. Alluvial-fan deposits in Death Valley and throughout the arid southwestern United States have long been the subjects of study, but their ages have generally eluded researchers until recently. Most mapping efforts have recognized at least four major relative-age groupings (Q1 (oldest), Q2, Q3, and Q4 (youngest)), using observed changes in surface soils and morphology, relation to the drainage net, and development of desert pavement. Obtaining numerical age determinations for these morphologic stages has proven challenging. We report the first optically stimulated luminescence (OSL) ages for three of these four stages deposited within alluvial-fans along the tectonically active Black Mountains of Death Valley. Deposits showing distinct, remnant bar and swale topography (Q3b) have OSL ages from 7 to 4 ka., whereas those with moderate to poorly developed desert pavement and located farther above the active channel (Q3a) have OSL ages from 17 to 11 ka. Geomorphically older deposits with well-developed desert pavement (Q2d) have OSL ages ???25 ka. Using this OSL-based chronology, we note that alluvial-fan deposition along this tectonically active mountain front corresponds to both wet-to-dry and dry-to-wet climate changes recorded globally and regionally. These findings underscore the influence of climate change on alluvial fan deposition in arid and semi-arid regions. ?? 2007 Elsevier Ltd and INQUA.

Clinopyroxene composition of volcanics from the Manipur Ophiolite, Northeastern India: implications to geodynamic setting

NASA Astrophysics Data System (ADS)

Ovung, Thungyani N.; Ray, Jyotisankar; Ghosh, Biswajit; Koeberl, Christian; Topa, Dan; Paul, Madhuparna

2017-08-01

The volcanic section of the Manipur Ophiolite (MO), representing the crustal portion of the Neo-Tethyan oceanic lithosphere occurs as basalt, basaltic trachyandesite, and dacite in the Gamnom-Phangrei sector, Manipur, at 25°01'N-25°09'N and 94°24'E-94°27'E. They associate with cherts and ultramafics. The clinopyroxene compositions of basalt and basaltic trachyandesite, obtained through electron microprobe analyzer, were used as a petrogenetic indicator to identify the parent magma-types and their tectonic settings. Based on the variable content of major oxides, they are classified as high- and low-Ti clinopyroxenes. High Ti and Al contents with relatively lower silica saturation are observed in the former group and vice versa in the latter. The TiDCpx/rock values in low- and high-Ti clinopyroxene are comparable with island-arc basaltic andesite and MORB, respectively, which confirms that the clinopyroxene composition is primarily related to the host magma-type and its tectonic setting. Clinopyroxene thermometry (ranging 1150-605 °C) suggests progressive differentiation of the parent magmas. Several bivariate and tectonic discrimination diagrams depict MORB (non-orogenic setting) and island-arc boninitic magma affinities (orogenic setting) for the high- and low-Ti clinopyroxenes, respectively. The coexistence of both MORB and island-arc boninitic magma-types in the volcanic section of Manipur Ophiolite as characterized by their varying Ti, Al, and Si contents may indicate either juxtaposition of rocks formed in diverse tectonic settings (i.e., due to transformation of tectonic setting from mid-ocean ridge to supra-subduction zone) or, a change in magma composition in a subduction zone setting. However, field relationships coupled with the mineral-chemical signatures implies a supra-subduction zone setting for the evolution of the crustal section of MO.

LWD lithostratigraphy, physical properties and correlations across tectonic domains at the NanTroSEIZE drilling transect, Nankai Trough subduction zone, Japan

NASA Astrophysics Data System (ADS)

Tudge, J.; Webb, S. I.; Tobin, H. J.

2013-12-01

Since 2007 the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) has drilled a total of 15 sites across the Nankai Trough subduction zone, including two sites on the incoming sediments of the Philippine Sea plate (PSP). Logging-while-drilling (LWD) data was acquired at 11 of these sites encompassing the forearc Kumano Basin, upper accretionary prism, toe region and input sites. Each of these tectonic domains is investigated for changes in physical properties and LWD characteristics, and this work fully integrates a large data set acquired over multiple years and IODP expeditions, most recently Expedition 338. Using the available logging-while-drilling data, primarily consisting of gamma ray, resistivity and sonic velocity, a log-based lithostratigraphy is developed at each site and integrated with the core, across the entire NanTroSEIZE transect. In addition to simple LWD characterization, the use of Iterative Non-hierarchical Cluster Analysis (INCA) on the sites with the full suite of LWD data clearly differentiates the unaltered forearc and slope basin sediments from the deformed sediments of the accretionary prism, suggesting the LWD is susceptible to the subtle changes in the physical properties between the tectonic domains. This differentiation is used to guide the development of tectonic-domain specific physical properties relationships. One of the most important physical property relationships between is the p-wave velocity and porosity. To fully characterize the character and properties of each tectonic domain we develop new velocity-porosity relationships for each domain found across the NanTroSEIZE transect. This allows the porosity of each domain to be characterized on the seismic scale and the resulting implications for porosity and pore pressure estimates across the plate interface fault zone.

Tectonic Implications of Intermediate-depth Earthquakes Beneath the Northeast Caribbean

NASA Astrophysics Data System (ADS)

Mejia, H.; Pulliam, J.; Huerfano, V.; Polanco Rivera, E.

2016-12-01

The Caribbean-North American plate boundary transitions from normal subduction beneath the Lesser Antilles to oblique subduction at Hispaniola before becoming exclusively transform at Cuba. In the Greater Antilles, large earthquakes occur all along the plate boundary at shallow depths but intermediate-depth earthquakes (50-200 km focal depth) occur almost uniquely beneath eastern Hispaniola. Previous studies have suggested that regional tectonics may be dominated by, for example, opposing subducting slabs, tearing of the subducting North American slab, or "slab push" by the NA slab. In addition, the Bahamas Platform, located north of Hispaniola, is likely causing compressive stresses and clockwise rotation of the island. A careful examination of focal mechanisms of intermediate-depth earthquakes could clarify regional tectonics but seismic stations in the region have historically been sparse, so constraints on earthquake depths and focal mechanisms have been poor. In response, fifteen broadband sensors were deployed in the Dominican Republic in 2014, increasing the number of stations to twenty-two. To determine the roles earthquakes play in regional tectonics, a event catalog was created joining data from our stations and other regional stations for which event depths are greater than 50 km and magnitudes are greater than 3.5. All events have been relocated and focal mechanisms are presented for as many events as possible. Multiple probable fault planes are computed for each event. Compressive (P) and tensional (T) axes, from fault planes, are plotted in 3-dimensions with density distribution contours determined of each axis. Examining relationships between axes distributions and events helps constrain tectonic stresses at intermediate-depths beneath eastern Hispaniola. A majority of events show primary compressive axes oriented in a north-south direction, likely produced by collision with the Bahamas Platform.

Clinopyroxene composition of volcanics from the Manipur Ophiolite, Northeastern India: implications to geodynamic setting

NASA Astrophysics Data System (ADS)

Ovung, Thungyani N.; Ray, Jyotisankar; Ghosh, Biswajit; Koeberl, Christian; Topa, Dan; Paul, Madhuparna

2018-06-01

The volcanic section of the Manipur Ophiolite (MO), representing the crustal portion of the Neo-Tethyan oceanic lithosphere occurs as basalt, basaltic trachyandesite, and dacite in the Gamnom-Phangrei sector, Manipur, at 25°01'N-25°09'N and 94°24'E-94°27'E. They associate with cherts and ultramafics. The clinopyroxene compositions of basalt and basaltic trachyandesite, obtained through electron microprobe analyzer, were used as a petrogenetic indicator to identify the parent magma-types and their tectonic settings. Based on the variable content of major oxides, they are classified as high- and low-Ti clinopyroxenes. High Ti and Al contents with relatively lower silica saturation are observed in the former group and vice versa in the latter. The TiDCpx/rock values in low- and high-Ti clinopyroxene are comparable with island-arc basaltic andesite and MORB, respectively, which confirms that the clinopyroxene composition is primarily related to the host magma-type and its tectonic setting. Clinopyroxene thermometry (ranging 1150-605 °C) suggests progressive differentiation of the parent magmas. Several bivariate and tectonic discrimination diagrams depict MORB (non-orogenic setting) and island-arc boninitic magma affinities (orogenic setting) for the high- and low-Ti clinopyroxenes, respectively. The coexistence of both MORB and island-arc boninitic magma-types in the volcanic section of Manipur Ophiolite as characterized by their varying Ti, Al, and Si contents may indicate either juxtaposition of rocks formed in diverse tectonic settings (i.e., due to transformation of tectonic setting from mid-ocean ridge to supra-subduction zone) or, a change in magma composition in a subduction zone setting. However, field relationships coupled with the mineral-chemical signatures implies a supra-subduction zone setting for the evolution of the crustal section of MO.

Crustal structure of China from deep seismic sounding profiles

USGS Publications Warehouse

Li, S.; Mooney, W.D.

1998-01-01

More than 36,000 km of Deep Seismic Sounding (DSS) profiles have been collected in China since 1958. However, the results of these profiles are not well known in the West due to the language barrier. In this paper, we summarize the crustal structure of China with a new contour map of crustal thickness, nine representative crustal columns, and maps showing profile locations, average crustal velocity, and Pn velocity. The most remarkable aspect of the crustal structure of China is the well known 70+ km thickness of the crust of the Tibetan Plateau. The thick (45-70 km) crust of western China is separated from the thinner (30-45 km) crust of eastern China by the north-south trending seismic belt (105??E). The average crustal velocity of China ranges from 6.15 to 6.45 km/s, indicating a felsic-to-intermediate bulk crustal composition. Upper mantle (Pn) velocities are 8.0 ?? 0.2 km/s, equal to the global continental average. We interpret these results in terms of the most recent thermo-tectonic events that have modified the crust. In much of eastern China, Cenoxoic crustal extension has produced a thin crust with a low average crustal velocity, similar to western Europe and the Basin and Range Province, western USA. In western China, Mesozoic and Cenoxoic arc-continent and continent-continent collisions have led to crustal growth and thickening. Inferences on the process of crustal thickening are provided by the deep crustal velocity structure as determined by DSS profiles and other seismological studies. A high velocity (7.0-7.4 km/s) lower-crustal layer has been reported in western China only beneath the southernmost Tibetan Plateau. We identity this high-velocity layer as the cold lower crust of the subducting Indian plate. As the Indian crust is injected northward into the Tibetan lower crust, it heats and assimilates by partial melting, a process that results in a reduction in the seismic velocity of the lower crust in the central and northern Tibetan Plateau. ?? 1998 Elsevier Science B.V. All rights reserved.

Comparative analysis of geodynamic activity of the Caucasian and Eastern Mediterranean segments of the Alpine-Himalayan convergence zone

NASA Astrophysics Data System (ADS)

Chelidze, Tamaz; Eppelbaum, Lev

2013-04-01

The Alpine-Himalayan convergence zone (AHCZ) underwent recent transverse shortening under the effect of collisional compression. The process was accompanied by rotation of separate microplates. The Caucasian and Eastern Mediterranean regions are segments of the of the AHCZ and are characterized by intensive endogenous and exogenous geodynamic processes, which manifest themselves in occurrence of powerful (with magnitude of 8-9) earthquakes accompanied by development of secondary catastrophic processes. Large landslides, rock falls, avalanches, mud flows, etc. cause human deaths and great material losses. The development of the aforesaid endogenous processes is set forth by peculiarities of the deep structure of the region and an impact of deep geological processes. The Caucasus is divided into several main tectonic terranes: platform (sub-platform, quasi-platform) and fold-thrust units. Existing data enable to perform a division of the Caucasian region into two large-scale geological provinces: southern Tethyan and northern Tethyan located to the south of and to the north of the Lesser Caucasian ophiolite suture, respectively. The recent investigations show that the assessments of the seismic hazard in these regions are not quite correct - for example in the West Caucasus the seismic hazard can be significantly underestimated, which affects the corresponding risk assessments. Integrated analysis of gravity, magnetic, seismic and thermal data enables to refine the assessment of the seismic hazard of the region, taking into account real rates of the geodynamic movements. Important role play the last rheological constructions. According to Reilinger et al. (2006) tectonic scheme, the West flanking of the Arabian Plate manifests strike-slip motion, when the East Caucasian block is converging and shortening. The Eastern Mediterranean is a tectonically complex region located in the midst of the progressive Afro-Eurasian collision. The recent increasing geotectonic activity in this region highlights the need for combined analysis of seismo-neotectonic signatures. For this purpose, this article presents the key features of the tectonic zonation of the Eastern Mediterranean. Map of derivatives of the gravity field retracked from the Geosat satellite and novel map of the Moho discontinuity illustrate the most important tectonic features of the region. The Post-Jurassic map of the deformation of surface leveling reflects the modern tectonic stage of Eastern Mediterranean evolution. The developed tectono-geophysical zonation map integrates the potential geophysical field analysis and seismic section utilization, as well as tectonic-structural, paleogeographical and facial analyses. Tectonically the map agrees with the earlier model of continental accretion (Ben-Avraham and Ginzburg, 1990). Overlaying the seismicity map of the Eastern Mediterranean tectonic region (for the period between 1900 and 2012) on the tectonic zonation chart reveals the key features of the seismo-neotectonic pattern of the Eastern Mediterranean. The results have important implications for tectonic-seismological analysis in this region (Eppelbaum and Katz, 2012). A difference in the geotectonic patterns makes interesting comparison of geodynamic activity and seismic hazard of the Caucasian and Eastern Mediterranean segments of the AHCZ.

Terrace sequence along the Yushanguxi River in the southern piedmont of Tian Shan and its relationship to climate and tectonics in northwestern China

NASA Astrophysics Data System (ADS)

Wu, Chuanyong; Zheng, Wenjun; Zhang, Zhuqi; Jia, Qichao; Yu, Jingxing; Zhang, Huiping; Han, Guihong; Yao, Yuan

2018-07-01

Controversies persist regarding the formation of terraces under the control of tectonic factors or climatic changes. This work focuses on the Yushanguxi River in the southern piedmont of Tian Shan, which is an intense tectonic uplift area where the terraces are very developed and the river has deeply downcut. Nine main terraces are distinguished (labelled T1 to Th, from youngest to oldest) based on the interpretation of a high-resolution remote sensing image, field investigations and detailed surveying with differential GPS. The results of the determination of 10Be exposure and 14C show abandoned ages of 2.1 ka for T1, 4.1 ka for T2, 4.2 ka for T3, 8.2 ka for T4, 18.1 ka for T5, 18.8 ka for T6, 102.1 ka for T7, 100.6 ka for T81, 113.9 ka for T82, 144.6 ka for Th1, 210.7 ka for Th2, and 284.3 ka for Th3. Since 18 ka, the incision rate began to increase from 0.6 mm a-1 to 12 mm a-1, which is obviously higher than the fault slip rate of 0.7 mm a-1. We suggest that the rapid downcutting along the Yushanguxi River during the Holocene has mainly been caused by frequent climate fluctuations.

Paleoseismic observations along the Langshan range-front fault, Hetao Basin, China: Tectonic and seismic implications

NASA Astrophysics Data System (ADS)

Dong, Shaopeng; Zhang, Peizhen; Zheng, Wenjun; Yu, Zhongyuan; Lei, Qiyun; Yang, Huili; Liu, Jinfeng; Gong, Huilin

2018-04-01

The Langshan range-front fault (LRF) is an active Holocene normal fault that borders Langshan Mountain and the Hetao Basin, northwest of the Ordos Plateau, China. In this study, paleoseismic trenching was undertaken at three sites (North-South): Dongshen village (TC1), Qingshan (TC2), and Wulanhashao (TC3). The paleoevents ED1, ED2, ED3 from TC1 were constrained to 6.0 ± 1.3, 9.6 ± 2.0, and 19.7 ± 4.2 ka, respectively. The single paleoevent (EQ1) from TC2 was constrained to about 6.7 ± 0.1 ka, and the paleoevents EW1, EW2, and EW3 from TC3 were constrained to 2.3 ± 0.4, 6.0 ± 1.0, and before 7.0 ka, respectively. With reference to previous research, the Holocene earthquake sequence of the LRF can be established as 2.30-2.43 (E1), 3.06-4.41 (E2), 6.71-6.80 (E3), 7.60-9.81 (E4), and 19.70 ± 4.20 (E5) ka BP. Events E1, E3, and E4 might have been caused by events with magnitudes of Mw 7.6-7.8 that ruptured the entire LRF. Event E2 might have been smaller magnitude, about M7.0, and ruptured only a portion of the fault. The vertical slip rate of the LRF at the Qingshan site is inferred as 0.9 or 1.4-1.6 mm/year in the last 6.8 ka. The slip rate at Wulanhashao is considered to have been close to, but not <0.66 mm/year since 15 ka BP. We deem the LRF is an unsegmented active fault. Although the possibility of missing events in Late Pleistocene can not be dismissed, we argue the Holocene paleoearthquake history is complete, indicating an average recurrence interval of 2500 years.

Calibrating the Cretaceous normal superchron with high-precision U-Pb zircon geochronology from Songliao Basin, NE China

NASA Astrophysics Data System (ADS)

Wang, T.; Ramezani, J.; Wang, C.

2017-12-01

The Cretaceous Normal Superchron (CNS) or C34n is defined as the prolonged period of normal geomagnetic polarity, which lasted for approximately 38 Myr from the Aptian to the beginning of the Campanian. Along with the Kiaman Reverse Superchron (Carboniferous-Permian), they constitute the two longest periods of stability in the Earth's magnetic field. Polarity reversals are geologically abrupt events of global extent that form the basis of the Geomagnetic Polarity Timescale. In addition, a causal relationship between the end of a superchron and global environmental change has been hypothesized by some workers. Thus, the precise timing of the onset and termination of CNS has important implications for the correlation of global tectonic, paleoclimatic and paleobiotic events, and may help us better understand the causes and consequences of superchrons. At present, the exact age and duration of CNS are poorly understood, in part due to the relative scarcity of relevant paleomagnetic and radioisotopic data. The end of CNS or the C34n/C33r chron boundary is also considered a suitable proxy for the Santonian-Campanian stage boundary in the absence of diagnostic fossils of global distribution for the latter. The early Campanian ( 84 Ma to 76 Ma) is characterized by a steady cooling of the (greenhouse) climate, preceded by an abrupt (possibly 5-6°C) drop in the global temperatures at the Santonain-Campanian boundary, based on the oxygen isotope record of benthic foraminifera. The peak of dinosaur diversity throughout vast swaths of the continents was reached during the Campanian, as well. Here we present a new age constraint for the termination of CNS based on ash bed geochronology from a near-continuous, subsurface, Cretaceous lacustrine record recovered from the Songliao Basin in Northeast China. This extraordinary record allows integration of high-precision U-Pb geochronology, magnetostratigraphy and cyclostratigraphy that enables a multi-chronometer approach to the calibration of the CNS.

High-pressure granulites in the Fuping Complex of the central North China Craton: Metamorphic P-T-t evolution and tectonic implications

NASA Astrophysics Data System (ADS)

Qian, Jiahui; Yin, Changqing; Zhang, Jian; Ma, Li; Wang, Luojuan

2018-04-01

Mafic granulites in the Fuping Complex occur as lenses or boudins within high-grade TTG (Trondhjemite-Tonalite-Granodiorite) gneisses. Petrographic observations reveal four generations of mineral assemblage in the granulites: an inclusion assemblage of hornblende + plagioclase + ilmenite + quartz within garnet core; an inferred peak assemblage composed of garnet ± hornblende + plagioclase + clinopyroxene + rutile/ilmenite + quartz; a decompression assemblage characterized by symplectites of clinopyroxene ± orthopyroxene + plagioclase, coronae of plagioclase ± clinopyroxene ± hornblende around embayed garnet porphyroblasts or a two-pyroxene association; and a late amphibolite-facies retrogressive assemblage. Two representative samples were used for pseudosection modeling in NCFMASHTO model system to determine their metamorphic evolution. The results show that these granulites experienced a high-pressure stage of metamorphism with peak P-T conditions of 12-13 kbar and 760-800 °C (Pmax) and a post-peak history under P-T conditions of ∼9.0 kbar and 805-835 °C (Tmax), indicating a nearly isothermal decompression process (ITD) with a slight heating. Metamorphic evolution from the Pmax to the Tmax is predicted to be dominated by garnet breakdown through continuous metamorphic reactions of garnet + quartz ± diopside = hornblende + plagioclase + liquid and garnet + quartz + hornblende = plagioclase + diopside + liquid + orthopyroxene. Further metamorphic evolution after the Tmax is dominated by cooling, suggesting that high-pressure (HP) granulites may also exist in the Fuping Complex. Metamorphic zircons in the Fuping HP mafic granulites have left inclined REE patterns, Ti contents of 1.68-6.88 ppm and crystallization temperatures of 602-712 °C. SIMS zircon U-Pb dating on these zircons yields 207Pb/206Pb ages of 1891 ± 14 Ma and 1849 ± 6 Ma, interpreted to represent the cooling stage of metamorphism. The P-T-t evolution of the Fuping HP mafic granulites records well the protracted Paleoproterozoic orogenic event occurred in the central North China Craton.

Occurrence of 1 ka-old corals on an uplifted reef terrace in west Luzon, Philippines: Implications for a prehistoric extreme wave event in the South China Sea region

NASA Astrophysics Data System (ADS)

Ramos, Noelynna T.; Maxwell, Kathrine V.; Tsutsumi, Hiroyuki; Chou, Yu-Chen; Duan, Fucai; Shen, Chuan-Chou; Satake, Kenji

2017-12-01

Recent 230Th dating of fossil corals in west Luzon has provided new insights on the emergence of late Quaternary marine terraces that fringe west Luzon Island facing the Manila Trench. Apart from regional sea level changes, accumulated uplift from aseismic and seismic processes may have influenced the emergence of sea level indicators such as coral terraces and notches. Varied elevations of middle-to-late Holocene coral terraces along the west Luzon coasts reveal the differential uplift that is probably associated with the movement of local onland faults or upper-plate structures across the Manila Trench forearc basin. In Badoc Island, offshore west of Luzon mainland, we found notably young fossil corals, dated at 945.1 ± 4.6 years BP and 903.1 ± 3.9 years BP, on top of a 5-m-high reef platform. To constrain the mechanism of emergence or emplacement of these fossil corals, we use field geomorphic data and wave inundation models to constrain an extreme wave event that affected west Luzon about 1000 years ago. Our preliminary tectonic and tsunami models show that a megathrust rupture will likely lead to subsidence of a large part of the west Luzon coast, while permanent coastal uplift is attributed to an offshore upper-plate rupture in the northern Manila Trench forearc region. The modeled source fault ruptures and tsunami lead to a maximum wave height of more than 3 m and inundation distance as far as 2 km along the coasts of western and northern Luzon. While emplacement of coral boulders by an unusually strong typhoon is also likely, modeled storm surge heights along west Luzon do not exceed 2 m even with Typhoon Haiyan characteristics. Whether tsunami or unusually strong typhoon, the occurrence of a prehistoric extreme wave event in west Luzon remains an important issue in future studies of coastal hazards in the South China Sea region.

Metamorphic P-T evolution of the Gotsu blueschists from the Suo metamorphic belt in SW Japan: Implications for tectonic correlation with the Heilongjiang Complex, NE China

NASA Astrophysics Data System (ADS)

Kabir, Md. Fazle; Takasu, Akira; Li, Weimin

2018-05-01

In the Gotsu area of the c. 200 Ma high-P/T Suo metamorphic belt in the Inner Zone of southwest Japan, blueschists occur as lenses or layers within pelitic schists. Prograde, peak, and retrograde stages are distinguished in the blueschists, and the prograde and the peak metamorphic conditions are determined using pseudosection modelling in the NCKFMASHO system. The prograde metamorphic stage is defined by inclusions in porphyroblastic epidote and glaucophane, such as phengite, chlorite, albite, epidote and glaucophane/winchite, and the estimated metamorphic conditions are <325 °C and < 4-5 kbar at the boundary between the glaucophane schist facies and the greenschist facies. The peak metamorphic stage is well-defined by the schistosity-forming minerals, i.e. epidote, glaucophanic amphibole, phengite, and chlorite, suggesting the glaucophane schist facies conditions of 475-500 °C and 14-16 kbar. Actinolite/magnesiohornblende, chlorite, and albite replacing the peak stage minerals suggest the retrograde metamorphism into the greenschist facies. The metamorphic facies series of the Suo belt is defined by pumpellyite-actinolite facies to epidote-blueschist facies, and it has a relatively lower-P/T compared with the c. 300 Ma Renge belt in the Inner Zone of southwest Japan, which is defined by a sequence of lawsonite-blueschist facies to glaucophane-eclogite facies. The P- {M}_{{H}_2O} pseudosection and water isopleth show that the rocks were dehydrated during the initial stage of the exhumation and remained in water-saturated conditions. Similarities of the detrital zircon and peak metamorphic ages of the blueschists from the Suo metamorphic belt in southwest Japan and the Heilongjiang Complex in northeast China suggest that both metamorphic belts were probably formed in the same Paleo-Pacific subduction system in the Late Triassic to Jurassic period.

Return to Clark Air Force Base: Establishing Permanent Military Bases in the Philippines as part of the United States Grand Strategy in the South China Sea

DTIC Science & Technology

2016-02-16

Unknotting tangled Lines in the South China Sea Dispute” in Territorial Disputes in the South China Sea ed. Billo, Andrew and Jung 1-12 Hayton...in Territorial Disputes in the South China Sea ed. Billo, Andrew and Jung 99-127 Johnston, Alastair, “How New and Assertive Is China’s New...2015) Sutter, Robert, “China’s Rise: Implications for U.S. Leadership in Asia,” East-West Center, Washington, Policy Studies 21. (2006) Thayer, Carl

Increased Economic Relations Between China and Zambia in the Last Decade: Implications on Zambia’s Existing Bilateral Relations with the United States

DTIC Science & Technology

2013-12-13

Pacific region, but also the world at large. China and the U.S. have agreed to a new model of relations, based on practical cooperation and...as a significant model to determine whether the increase in China and Zambia relations lead to a change in the nature of bilateral relations between...a model in countries with similar features and given the circumstances. The last decade has seen China step up its economic activities on the

International Project - Atlas of Geological Maps of Central Asia and Adjacent Territories 1:2 500 000 Scale - the Status and the Development Prospects

NASA Astrophysics Data System (ADS)

Leonov, Y.; Petrov, O. V.; Dong, S.; Morozov, A.; Shokalsky, S.; Pospelov, I.; Erinchek, Y.; Milshteyn, E.

2011-12-01

This project is launched by geological surveys of Russia, China, Mongolia, Kazakhstan and the Republic of Korea with participation of National Academies of Sciences under the aegis of the Commission for the Geological Map of the World since 2004. The project goal is the compilation and subsequent monitoring of the set of digital geological maps for the large part of the Asian continent (20 million km2). Each country finances its own part of the project while all the issues concerning methods and technologies are discussed collectively during annual meetings and joint filed excursions. At the 33d IGC, were shown 4 digital maps of the Atlas at 1: 2,5M - geological, tectonic, metallogenic and energy resources. Geological and energy resources maps were compiled and published by the Chinese part while tectonic and metallogenic maps by Russian side (VSEGEI, Saint-Petersburg). The geological map was also used as the base for the compilation of the other maps of the Atlas. On the tectonic map colours indicate several stages of the continental crust consolidation within fold belts, their tectonic reworking and rifting. The map also shows rock complexes-indicators of geodynamic settings. In the platform areas, the colour reflects the time of beginning of the sedimentary cover formation while its shades reflect the thickness of the sediments. The metallogenic map of the Atlas depicts 1380 objects of metallogenic zoning (from super-provinces to ore clusters) and is accompanied with a database (more than 5000 ore deposits). The map of energy resources with the database contains information on the of coal- and oil-and-gas-bearing basins and main coal and hydrocarbon deposits. In 2009 the study area was extended to the North, East and South in order to embrace bigger territory with ore-bearing Mesozoic-Cenozoic volcanic belts of the Asian continent's Pacific margin. According to nearest plans, discussed with the head of Rosnedra Dr. Anatoliy Ledovskikh and the director of the geological survey of China Dr. Wang Min, in two last years we are going to put into practice the following directions: 1. Study of deep processes and metallogeny of the northern passive and eastern active continental margins of Asia with using of new isotopic data along geotransects and the reprocessing of 3-component seismic data and 3D modeling of the region deep structure. 2. Correlation of the tectonic evolution of the Tibetan Plateau and Baikal rift system in Cenozoic, which is of great importance for understanding the geodynamic evolution of the Central Asia and seismic predictions. 3. Comparison of Siberian and Emeishan major volcanic provinces, accompanied with unique ore deposits. Last VSEGEI isotopic studies revealed the significant role of assimilation of metasedimentary upper crust rocks by mantle magma in the formation of unique Norilsk copper-nickel deposits. The results of the next stage of joint studies under the project will be presented at the 34th IGC, at which a scientific symposium "Geological and Metallogenic Responses to Deep Processes in Eastern Asia and Continental Margins" is to be held.

The influence of topographic stresses on faulting, emphasizing the 2008 Wenchuan, China earthquake rupture

NASA Astrophysics Data System (ADS)

Styron, R. H.; Hetland, E. A.; Zhang, G.

2013-12-01

The weight of large mountains produces stresses in the crust that locally may be on the order of tectonic stresses (10-100 MPa). These stresses have a significant and spatially-variable deviatoric component that may be resolved as strong normal and shear stresses on range-bounding faults. In areas of high relief, the shear stress on faults can be comparable to inferred stress drops in earthquakes, and fault-normal stresses may be greater than 50 MPa, and thus may potentially influence fault rupture. Additionally, these stresses may be used to make inferences about the orientation and magnitude of tectonic stresses, for example by indicating a minimum stress needed to be overcome by tectonic stress. We are studying these effects in several tectonic environments, such as the Longmen Shan (China), the Denali fault (Alaska, USA) and the Wasatch Fault Zone (Utah, USA). We calculate the full topographic stress tensor field in the crust in a study region by convolution of topography with Green's functions approximating stresses from a point load on the surface of an elastic halfspace, using the solution proposed by Liu and Zoback [1992]. The Green's functions are constructed from Boussinesq's solutions for a vertical point load on an elastic halfspace, as well as Cerruti's solutions for a horizontal surface point load, accounting for irregular surface boundary and topographic spreading forces. The stress tensor field is then projected onto points embedded in the halfspace representing the faults, and the fault normal and shear stresses at each point are calculated. Our primary focus has been on the 2008 Wenchuan earthquake, as this event occurred at the base of one of Earth's highest and steepest topographic fronts and had a complex and well-studied coseismic slip distribution, making it an ideal case study to evaluate topographic influence on faulting. We calculate the topographic stresses on the Beichuan and Pengguan faults, and compare the results to the coseismic slip distribution, considering several published fault models. These models differ primarily in slip magnitude and planar vs. listric fault geometry at depth. Preliminary results indicate that topographic stresses are generally resistive to tectonic deformation, especially above ~10 km depth, where the faults are steep in all models. Down-dip topographic shear stresses on the fault are normal sense where the faults dip steeply, and reach 20 MPa on the fault beneath the Pengguan massif. Reverse-sense shear up to ~15 MPa is present on gently-dipping thrust flats at depth on listric fault models. Strike-slip shear stresses are sinistral on the steep, upper portions of faults but may be dextral on thrust flats. Topographic normal stress on the faults reaches ~80 MPa on thrust ramps and may be higher on flats. Coseismic slip magnitude is negatively correlated with topographic normal and down-dip shear stresses. The spatial patterns of topographic stresses and slip suggest that topographic stresses have significantly suppressed slip in certain areas: slip maxima occur in areas of locally lower topographic stresses, while areas of higher down-dip shear and normal stress show less slip than adjacent regions.

Evolution of the Sibişel Shear Zone (South Carpathians): A study of its type locality near Răşinari (Romania) and tectonic implications

NASA Astrophysics Data System (ADS)

Ducea, Mihai N.; Negulescu, Elena; Profeta, Lucia; Sǎbǎu, Gavril; Jianu, Denisa; Petrescu, Lucian; Hoffman, Derek

2016-09-01

The Sibişel Shear Zone is a 1-3 km wide, ductile shear zone located in the South Carpathian Mountains, Romania. In the Rășinari area, the ductile shear zone juxtaposes amphibolite facies rocks of the Lotru Metamorphic Suite against greenschist facies rocks of the Râuşorul Cisnădioarei Formation. The first represents the eroded remnants of Peri-Gondwanan arcs formed between the Neoproterozoic-Silurian (650-430 Ma), regionally metamorphosed to amphibolite facies during the Variscan orogeny (350-320 Ma). The second is composed of metasedimentary and metavolcanic Neoproterozoic-Ordovician (700-497 Ma) assemblages of mafic to intermediate bulk composition also resembling an island arc metamorphosed during the Ordovician (prior to 463 Ma). Between these lie the epidote amphibolite facies mylonitic and ultramylonitic rocks of the Sibișel Formation, a tectonic mélange dominated by mafic actinolite schists attenuated into a high strain ductile shear zone. Mineral Rb-Sr isochrons document the time of juxtaposition of the three domains during the Permian to Early Triassic ( 290-240 Ma). Ductile shear sense indicators suggest a right lateral transpressive mechanism of juxtaposition; the Sibişel shear zone is a remnant Permo-Triassic suture between two Early Paleozoic Gondwanan terranes. A zircon and apatite U-Th/He age transect across the shear zone yields Alpine ages (54-90 Ma apatite and 98-122 Ma zircon); these data demonstrate that the exposed rocks were not subjected to Alpine ductile deformation. Our results have significant implications for the assembly of Gondwanan terranes and their docking to Baltica during Pangea's formation. Arc terranes free of Variscan metamorphism existed until the Early Triassic, emphasizing the complex tectonics of terrane amalgamation during the closure of Paleotethys.

China-Asean Relations: Perspectives, Prospects and Implications for U.S. Interests

DTIC Science & Technology

2006-10-01

sever ties with) the Communist Party of Malaysia (CPM) and the insurgence movement. Indeed, during the early years of the Mahathir administration...rhetoric about the so-called China threat. Indeed, 30 Prime Minister Mahathir had become the most vocal defender of China, from security issues to human...Initially the brain-child of Malaysian Prime Minister Mahathir , the East Asia Summit was formally held in Kuala Lumpur in December 2005, but with the

Geochemical constraints on genesis of Paleoproterozoic A-type granite in the south margin of North China Craton

NASA Astrophysics Data System (ADS)

Xue, Shuo; Xu, Yang; Ling, Ming-Xing; Kang, Qing-Qing; Jiang, Xiao-Yan; Sun, Sai-Jun; Wu, Kai; Zhang, Zhe-Kun; Luo, Ze-Bin; Liu, Yu-Long; Sun, Weidong

2018-04-01

Paleoproterozoic A-type granites are widely outcropped in the North China Craton (NCC), particularly in the Trans-North China Orogen. However, their genesis and tectonic significance remain obscure. Here we report systematic studies on geochronology and geochemical characteristics of A-type granite in Huayangchuan, south margin of the NCC. The samples are enriched in total alkali (K2O + Na2O > 8.97 wt%), and depleted in MgO (0.84-0.93 wt%), CaO (1.28-1.90 wt%) and P2O5 (0.18-0.20 wt%), with high FeOT/MgO (5.69-6.67). They are characterized by high Zr + Y + Nb + Ce values (1293-1392 ppm) and 10,000 × Ga/Al ratios (3.14-3.35), which are typical characteristics of A-type granite. The Huayangchuan A-type granite can be further classified as A1-type subgroup based on particular geochemical features, e.g., low Y/Nb (0.87-1.00) and Yb/Ta (0.88-1.10). High precision zircon U-Pb dating of the A-type granite by secondary ion mass spectrometry (SIMS) yields Paleoproterozoic 207Pb/206Pb ages of 1829.5 ± 2.5 Ma. The low zircon ɛHf(t) values (-6.97 to -10.45), along with zircon Hf model age of 2.7-2.9 Ga, indicate that the Huayangchuan A-type granite was derived from partial melting of the ancient continental crust with contribution of enriched mantle components. The low zircon δ18O composition (4.00 to 6.78‰) indicates that the zircons were crystallized from low δ18O magmas, which derived from the crust metasomatized by low δ18O mantle fluids or melts. The E-W trend A1-type granitic plutons in the NCC are generally outcropped in a rift tectonic regime, which is consistent with the development of the mantle plume in the Xiong'er district. The large volume of basaltic magmas, generated by mantle plume head, underplated the lower continental crust and formed the Huayangchuan A-type granite.

Origin of sapphirine- and garnet-bearing clinopyroxenite xenoliths entrained in the Jiande basalts, SE China

NASA Astrophysics Data System (ADS)

Xiao, Yan; Zhang, Hong-Fu; Liang, Zi; Su, Ben-Xun; Zhu, Bin; Sakyi, Patrick Asamoah

2018-04-01

We present petrological and geochemical data of sapphirine- and garnet-bearing clinopyroxenite xenoliths entrained in the Jiande Cenozoic basalts, SE China, to investigate their igneous and metamorphic history, and reconstruct of the thermal-tectonic evolution of the lithospheric mantle. These xenoliths have an unusual mineral association consisting of clinopyroxene + garnet/kelyphite + spinel (±sapphirine). Clinopyroxene has high Mg# (89-93) and displays convex-upward REE pattern. Garnet, partially to completely kelyphitized, is rich in pyrope end-member. It usually includes relics of spinel, suggesting that garnet was formed at the expense of spinel. The spinel has high MgO (20.8-22.9 wt%) and Al2O3 (64.8-67.9 wt%) contents. Sapphirine, forming a rim on spinel, has homogeneous SiO2 (14.5-14.9 wt%), Al2O3 (60.9-61.7 wt%) and MgO (19.7-20.1 wt%) contents, interpreted to be of metamorphic origin. The subsolidus reaction for the formation of sapphirine is as follows: spinel + garnet = sapphirine + clinopyroxene + orthopyroxene. Thus, the earliest mineral assemblage recorded in these xenoliths was spinel + clinopyroxene. The clinopyroxene in the Jiande clinopyroxenite xenoliths has Li abundances (1.04-1.63 ppm) similar to high-P mafic cumulate but much lower than those in crustal eclogite. In addition, the clinopyroxene and garnet do not show positive Eu anomalies. Therefore, the protolith of these three clinopyroxenite xenoliths was most likely a pyroxenite, originating as clinopyroxene + spinel cumulates from mafic melts percolating through the mantle. Many reaction textures such as formation of garnet and sapphirine were developed during decompression possibly coupled with cooling and melt percolation. During this process, the earlier composition of clinopyroxene and spinel also changed. The latest P-T conditions recorded in these xenoliths were at pressure of 8-10 kbar and temperatures of 1069-1094 °C. These observations imply that these rocks have been tectonically uplifted to shallower levels. The uplift process may have been related to lithospheric thinning process accompanied by lithosphere extension and upwelling of the asthenosphere in eastern China.

Revisiting Mesozoic felsic intrusions in eastern South China: spatial and temporal variations and tectonic significance

NASA Astrophysics Data System (ADS)

Zhu, Kong-Yang; Li, Zheng-Xiang; Xia, Qun-Ke; Xu, Xi-Sheng; Wilde, Simon A.; Chen, Han-Lin

2017-12-01

Whole-rock and mineral geochemical data are used to place new constraints on the petrogenesis and tectonic setting of Mesozoic granitoids (including syenites) in eastern South China. In the Early Mesozoic, granitoids of variable compositions were intruded in the Cathaysia Block which by this time had developed a thickened and highly differentiated Paleoproterozoic crust through the influence of subduction. Late Triassic ( 225 Ma) syenites are significantly different from Jurassic-Cretaceous syenites in South China and from most trachytes (GEOROC database) in terms of their high Th/U, La/Nb and Gd/Yb ratios. Their low Rb contents, coupled with their high K/Rb and Nb/Ta, and low 87Sr/86Sr and 206Pb/204Pb ratios suggest a source that had undergone granulite-facies metamorphism at the base of thickened (> 45 km thick) continental crust where garnet and rutile are stable. The Late Triassic alkaline intrusions thus appear not to be related to continental rifting. Compared with the Late Triassic syenites, contemporaneous syenogranites have higher Ga/Al and Rb/K ratios and ISr values. Their Ga/Al ratios are positively correlated with ISr values, and their higher Ga/Al ratios likewise do not appear to be related to a rift setting but reflect the composition of the source. New Pb isotopic data from Cretaceous magmatic rocks reveal that 120-100 Ma I-type granitoids in Zhejiang Province were likely derived from mixing of three components: contemporaneous basaltic magma, an enriched crustal component and a depleted crustal component. Pb isotopes of both the I-type granitoids and the basalts become more radiogenic towards the coast, where the ca. 100 Ma intrusions dominate. Furthermore, zircon-melt partition of Ce and hornblende oxygen barometries indicate that the Early Cretaceous intrusions also became more oxidized towards the coast. In addition, the ca. 100 Ma granitoids have higher Gd/Yb and lower Fe/Mg ratios than those of the 120-110 Ma suite, implying crustal thickening resulting from 120 to 100 Ma basaltic underplating in the region.

Carboniferous Proto-type Basin Evolution of Junggar Basin in Northwest China: Implications for the Growth Models of Central Asia Orogenic Belt

NASA Astrophysics Data System (ADS)

He, D.

2016-12-01

The Junggar Basin locates in the central part of Paleo-Asian Ocean tectonic domain, and records the dynamic processes of the Central Asian Orogenic Belt from subduction-accretion-collision to later intracontinental deformations. Carboniferous is the key period from subduction to closure in the tectonic evolution of Paleo-Asian Ocean. Based on the borehole, outcrop, seismic and gravity and magnetic anomaly data, the paper made analysis of the Carboniferous basin evolution.Geo-chronological results for the borehole volcanic rocks suggest that the Junggar Basin and adjacent area had five periods of volcanic activities, including two periods in the Early Carboniferous (359-347Ma 347-331Ma and 331-324Ma) and three periods in the Late Carboniferous (323-307Ma and 307-300Ma). Regional unconformities divided the Carboniferous into two tectono-stratigraphic sequences: Lower Carboniferous and Upper Carboniferous. The former is characterized by compressional structures and involves massive calc-alkaline basalts, andesites, dacites and rhyolites, whereas the later is mainly controlled by extensional faults and dominated by intermediate-mafic volcanic rocks, with bimodal volcanic rocks in parts. The paper determined four Carboniferous arc-basin belts in the Junggar Basin and adjacent area from north to south: the Saur-Fuhai-Dulate, Heshituoluogai-Wulungu-Yemaquan, Darbut-Luliang-Karamaili, and Zhongguai-Mosuowan-Baijiahai-Qitai, and identified multi-type basins, such as fore-arc basin, retro-arc basin, intra-arc rift basin, foreland basin and passive continental margin basin,etc.. The Carboniferous proto-type basin evolution of the Junggar Basin can be divided into three phases such as, the early to middle Early Carboniferous subduction-related compressional phase, the late Early Carboniferous to middle Late Carboniferous subduction-related extensional phase and the late Late Carboniferous intra-continental fault-sag phase. The study discloses that the Junggar Basin is likely underlain by juvenile continental crust rather than unified Precambrian basement, and also implies that the Junggar Basin and adjacent area, even the entire CAOB, were built by successively northward amalgamation of multiple linear arc-basin systems characterized by southward accretion.

Seismic Structure of Mantle Transition Zone beneath Northwest Pacific Subduction Zone and its Dynamic Implication

NASA Astrophysics Data System (ADS)

Li, J.; Guo, G.; WANG, X.; Chen, Q.

2017-12-01

The northwest Pacific subduction region is an ideal location to study the interaction between the subducting slab and upper mantle discontinuities. Various and complex geometry of the Pacific subducting slab can be well traced downward from the Kuril, Japan and Izu-Bonin trench using seismicity and tomography images (Fukao and Obayashi, 2013). Due to the sparse distribution of seismic stations in the sea, investigation of the deep mantle structure beneath the broad sea regions is very limited. In this study, we applied the well- developed multiple-ScS reverberations method (Wang et al., 2017) to analyze waveforms recorded by the Chinese Regional Seismic Network, the densely distributed temporary seismic array stations installed in east Asia. A map of the topography of the upper mantle discontinuities beneath the broad oceanic regions in northwest Pacific subduction zone is imaged. We also applied the receiver function analysis to waveforms recorded by stations in northeast China and obtain the detailed topography map beneath east Asia continental regions. We then combine the two kinds of topography of upper mantle discontinuities beneath oceanic and continental regions respectively, which are obtained from totally different methods. A careful image matching and spatial correlation is made in the overlapping study regions to calibrate results with different resolution. This is the first time to show systematically a complete view of the topography of the 410-km and 660-km discontinuities beneath the east Asia "Big mantle wedge" (Zhao and Ohtani, 2009) covering the broad oceanic and continental regions in the Northwestern Pacific Subduction zone. Topography pattern of the 660 and 410 is obtained and discussed. Especially we discovered a broad depression of the 410-km discontinuity covering more than 1000 km in lateral, which seems abnormal in the cold subducting tectonic environment. Based on plate tectonic reconstruction studies and HTHP mineral experiments, we argue that the east-retreat trench motion of the subducting Pacific slab might play an important role in the observed broad depression of the 410-km discontinuity.

Geochronology and geochemistry of the Borohoro pluton in the northern Yili Block, NW China: Implication for the tectonic evolution of the northern West Tianshan orogen

NASA Astrophysics Data System (ADS)

Wang, Meng; Zhang, Jinjiang; Zhang, Bo; Liu, Kai; Chen, Youxin; Zheng, Yanrong

2018-03-01

The closure of the North Tianshan Ocean between the Junggar Terrane and the Yili Block is a longtime debated issue in literature, because of the different understanding of the Carboniferous volcanic rocks in the northern margin of the Yili Block. This study presents new geochronological and whole-rock geochemical data for the granitic rocks from the Borohoro pluton to provide constraints on the tectonic regime for the northern West Tianshan during the Carboniferous. LA-ICP-MS U-Pb dating results reveal two magmatic phases for the Borohoro pluton. The former magmatic activity in the Early Carboniferous formed the fine-grained granodiorite (332 Ma). The later magmatic activity occurred during the Late Carboniferous (305-300 Ma), forming a diversity of granitic rocks, involving quartz diorite, granodiorite and granite. Geochemical and mineralogical studies reveal that the studied granitic rocks from the Borohoro pluton all belong to metaluminous to weakly peraluminous, calc-alkaline I-type granites. They are characterized by enrichment in LILEs relative to HFSEs, and depletion of Nb, Ti and P, typical of continental arc-type granites. The intermediate SiO2, high Al2O3, and relatively low Fe2O3T, MgO and TiO2 contents reflect that these granitic rocks are mainly crust-derived. But the high Mg# values for most samples and the occurrence of microgranular mafic enclaves indicate that their magma sources were mixed by mantle-derived components. Especially, the Late Carboniferous rocks define an elegant mixing trend in both the Rb-Rb/V and the 1/V-Rb/V diagrams, consistent with mixing between magmas from subcontinental lithospheric mantle and mafic lower crust. Taking into consideration of the facts that all the Devonian to Carboniferous granitoids belong to calc-alkaline I-type granites, and granitoids of A-type didn't appear until the Early Permian, we suggest that the subduction of the North Tianshan Ocean continued to the Late Carboniferous, generating the granitic rocks of the Borohoro pluton.

Elemental and Sr-Nd isotopic geochemistry of Cretaceous to Early Paleogene granites and volcanic rocks in the Sikhote-Alin Orogenic Belt (Russian Far East): implications for the regional tectonic evolution

NASA Astrophysics Data System (ADS)

Zhao, Pan; Jahn, Bor-ming; Xu, Bei

2017-09-01

The Sikhote-Alin Orogenic Belt in Russian Far East is an important Late Mesozoic to Early Cenozoic accretionary orogen related to the subduction of the Paleo-Pacific Plate. This belt was generated by successive accretion of terranes made of accretionary prisms, turbidite basins and island arcs to the continental margin of northeastern Asia (represented by the Bureya-Jiamusi-Khanka Block) from Jurassic to Late Cretaceous. In order to study the tectonic and crustal evolution of this orogenic belt, we carried out zircon U-Pb dating, and whole-rock elemental and Sr-Nd isotopic analyses on granites and volcanic rocks from the Primorye region of southern Sikhote-Alin. Zircon dating revealed three episodes of granitoid emplacement: Permian, Early Cretaceous and Late Cretaceous to Early Paleogene. Felsic volcanic rocks (mainly rhyolite, dacite and ignimbrite) that overlay all tectonostratigraphic terranes were erupted during 80-57 Ma, postdating the accretionary process in the Sikhote-Alin belt. The Cretaceous-Paleogene magmatism represents the most intense tectonothermal event in the Sikhote-Alin belt. Whole-rock major and trace elemental data show arc-like affinity for granitoids and volcanic rocks, indicating that they were likely generated in a supra-subduction setting. Their initial 87Sr/86Sr ratios range from 0.7048 to 0.7114, and εNd(t) values vary from +1.7 to -3.8 (mostly < 0). Thus, the elemental and Sr-Nd isotopic data suggest that the felsic magmas were generated by partial melting of source rocks comprising mantle-derived juvenile component and recycled crustal component. In addition to the occurrence in the Sikhote-Alin orogenic belt, Cretaceous to Early Paleogene magmatic rocks are also widespread in NE China, southern Korean peninsula, Japanese islands and other areas of Russian Far East, particularly along the coastal regions of the Okhotsk and Bering Seas. These rocks constitute an extended magmatic belt along the continental margin of NE Asia. The generation of this belt was ascribed to subduction of the Paleo-Pacific Plate.

Petrogenesis and tectonic implications of the Early Paleozoic granites in the western segment of the North Qilian orogenic belt, China

NASA Astrophysics Data System (ADS)

Wang, Nan; Wu, Cai-Lai; Lei, Min; Chen, Hong-Jie

2018-07-01

Early Paleozoic granitic magmatism in the North Qilian orogenic belt records a complete Wilson cycle and provides critical geological clues for unraveling the regional tectonic history. In this study, we report the results of zircon U-Pb ages, Hf isotopic analysis and systematic whole-rock geochemical data for the Late Ordovician Hongliuhe granite and Early Silurian Qingshan monzogranite in the western segment of the North Qilian orogenic belt to constrain their emplacement ages, petrogenesis, and regional evolution history. U-Pb dating reveals that the Hongliuhe granite was emplaced around 453-452 Ma, and the Qingshan monzogranite was emplaced about 440-438 Ma. A geochemical study shows that the two granites belong to the calc-alkaline to high-K calc-alkaline series. The Hongliuhe granite shows adakitic and peraluminous features, while the Qingshan monzogranite belongs to metaluminous to weak peraluminous granites. Zircons in the Hongliuhe granite show εHf(t) values ranging from -15.1 to +11.7 with two-stage Hf model ages (tDM2) of 687-2398 Ma, whereas zircons in the Qingshan monzogranite show εHf(t) values ranging from +5.7 to +11.0 with two-stage Hf model ages from 814 to 1057 Ma. The geochemical characteristics indicate that the Hongliuhe granite was a transitional I/S-type granite and was generated from a thickened lower crust with the addition of minor Paleo- to Mesoproterozoic crustal materials, which left a rutile + garnet + pyroxene ± plagioclase residue. The Qingshan monzogranite formed from the partial melting of mafic crust with minor mantle-derived materials, and the fractionation of Ti-bearing phases, apatite and pyroxene occurred during the magma's evolution, which left an amphibole and plagioclase residue. We infer that the Hongliuhe granite formed during the northward subduction of the North Qilian Ocean, while the Qingshan monzogranite was generated during the post-collision stage between the Qilian and Alxa blocks. This observation indicates that syn-collision stage of the North Qilian orogenic belt began before 453 Ma, and that the extension regime began prior to 444 Ma.

Phylogeographic heterogeneity of the brown macroalga Sargassum horneri (Fucaceae) in the northwestern Pacific in relation to late Pleistocene glaciation and tectonic configurations.

PubMed

Hu, Zi-Min; Uwai, Shinya; Yu, Shen-Hui; Komatsu, Teruhisa; Ajisaka, Tetsuro; Duan, De-Lin

2011-09-01

Pleistocene glacial oscillations and associated tectonic processes are believed to have influenced the historical abundances and distribution of organisms in the Asia Northwest Pacific (ANP). Accumulating evidence indicates that factors shaping tempospatial population dynamics and distribution patterns of marine taxa vary with biogeographical latitude, pelagic behaviour and oceanographic regimes. To detect what kinds of historical and contemporary factors affected genetic connectivity, phylogeographic profiles of littoral macroalga Sargassum horneri in the ANP were analysed based on mitochondrial (Cox3) and chloroplast (rbcL) data sets. Five distinct clades were recovered. A strong signature of biogeographical structure was revealed (Φ(CT) = 0.487, P < 0.0001) derived from remarkable differentiation in clade distribution, as clade I is restricted to Chinese marginal seas (Yellow-Bohai Sea, East China Sea and South China Sea), whereas clades II-V are discontinuously scattered around the main Islands of Japan. Furthermore, two secondary contact regions were identified along the south Japan-Pacific coastline. This significant differentiation between the two basins may reflect historical glacial isolation in the northwestern Pacific, which is congruent with the estimates of clade divergence and demographic expansion during the late Quaternary low sea levels. Analysis of molecular variance and the population-pair statistic F(ST) also revealed significant genetic structural differences between Chinese marginal seas and the Japanese basin. This exceptional phylogeographic architecture in S. horneri, initially shaped by historical geographic isolation during the late Pleistocene ice age and physical biogeographical barriers, can be complicated by oceanographic regimes (ocean surface currents) and relocating behaviour such as oceanic drifting. © 2011 Blackwell Publishing Ltd.

Rayleigh Wave and Shear Wave Tomography of Northeastern China: Results Coconstrained by Multiple Datasets

NASA Astrophysics Data System (ADS)

Zhou, T.; Chen, J.; Han, J.; Tian, Y.; Wu, M.; Yang, Y.; Ning, J.

2014-12-01

We investigate crustal and upper mantle phase velocity structures beneath NorthEastern China (NEC, 40°-54°N, 112°-135°E), a tectonically active region with continental volcanicity divided by active faults. Rayleigh wave phase velocity is obtained respectively by Ambient Noise Method (ANM, Lin et al., GJI, 2009), Two Station Method (TSM, Meier et al., GJI, 2004) and Two Plane Wave Method (TPWM, Yang and Forsyth, JGR, 2005), assuring good frequency coverage. Two-year' events with magnitude Ms>5.5 and epicentral distance Δ>30°recorded by NECESSArray and some permanent stations of CEA are together used in TPWM and TSM, while 1 s continuous seismic observations in the same period are employed in ANM. The period of Rayleigh wave phase velocity spans from 6 s to 150 s, i.e., from 6 s to 30 s (ANM); 30 s to 100 s (TPWM) and 30 s to 150 s (TSM). Shear wave velocity structure of the research region is obtained by Weighted Least Squares Inversion, in which the weight is adopted as function of data quality. Our results not only display close relation with tectonics of this region, such as mountains, sedimentary basins, faults, but also reveal variation feature of crustal thickness. Moreover, our results clearly show that all volcanos in this region have their roots — low velocity zones, among them the roots of Changbai, Jingbohu, Wudalianchi are obviously connected, while the biggest one of Daxinganling is separated. This feature might be result of an early intense eruption in western NEC and a late weak one in eastern NEC.

Three-dimensional Crustal Structure beneath the Tibetan Plateau Revealed by Multi-scale Gravity Analysis

NASA Astrophysics Data System (ADS)

Xu, C.; Luo, Z.; Sun, R.; Li, Q.

2017-12-01

The Tibetan Plateau, the largest and highest plateau on Earth, was uplifted, shorten and thicken by the collision and continuous convergence of the Indian and Eurasian plates since 50 million years ago, the Eocene epoch. Fine three-dimensional crustal structure of the Tibetan Plateau is helpful in understanding the tectonic development. At present, the ordinary method used for revealing crustal structure is seismic method, which is inhibited by poor seismic station coverage, especially in the central and western plateau primarily due to the rugged terrain. Fortunately, with the implementation of satellite gravity missions, gravity field models have demonstrated unprecedented global-scale accuracy and spatial resolution, which can subsequently be employed to study the crustal structure of the entire Tibetan Plateau. This study inverts three-dimensional crustal density and Moho topography of the Tibetan Plateau from gravity data using multi-scale gravity analysis. The inverted results are in agreement with those provided by the previous works. Besides, they can reveal rich tectonic development of the Tibetan Plateau: (1) The low-density channel flow can be observed from the inverted crustal density; (2) The Moho depth in the west is deeper than that in the east, and the deepest Moho, which is approximately 77 km, is located beneath the western Qiangtang Block; (3) The Moho fold, the directions of which are in agreement with the results of surface movement velocities estimated from Global Positioning System, exists clearly on the Moho topography.This study is supported by the National Natural Science Foundation of China (Grant No. 41504015), the China Postdoctoral Science Foundation (Grant No. 2015M572146), and the Surveying and Mapping Basic Research Programme of the National Administration of Surveying, Mapping and Geoinformation (Grant No. 15-01-08).

The distribution and tectonic framework of Late Paleozoic volcanoes in the Junggar basin and its adjacent area, NW China

NASA Astrophysics Data System (ADS)

Mao, X.; Li, J. H.

2012-04-01

We analyse the distribution and characteristics of 145 late Paleozoic volcanoes in north Xinjiang, NW China, including 32 volcanoes on the edge of the Junggar basin. These volcanoes are clustered and can be divided into calderas, volcanic domes, and volcanic necks. There are also 85 volcanoes inside the Junggar basin, which are dominantly distributed in the Ke-Bai fractured zone of the northwestern margin of Junggar Basin, 4 depressions (Dongdaohaizi Depression, Dishuiquan Depression, Sannan Depression and Wucaiwan Depression) and 7 uplifts (Baijiahai uplift, Beisantai uplift, Dibei uplift, Dinan uplift, Sangequan uplift, Shixi uplift and Xiayan uplift). The volcanoes inside the basin are principally controlled by Hercynian Fault Systems, along NE and nearly EW trending faults and most developed in the interjunctions of the faults. The long modification by late-stage weathering and leaching made the volcanoes difficult to identify. Remaining volcanic landforms, changing trends of the volcanic lithofacies and the typical volcanic rock, such as the crypto- explosive breccia, are the typical marks of the late Paleozoic volcanoes in the field; and the concealed volcanic edifices are identified by the techniques of seismic identification, such as seismic slicing, analysis of the attribute and tectonic trend plane. The ages of the volcanic rocks are focused on from 340 Ma to 320Ma and from 300 Ma to 295 Ma, corresponding to the subducting periods of West Junggar and East Junggar. From early Carboniferous to late Carboniferous, the volcanic activities in Junggar Basin and its adjacent areas show a variation trend from undersea to continental, from deep water to shallow water and from continental margin to intracontinental.

South China Sea Tectonics and Magnetics: Constraints from IODP Expedition 349 and Deep-tow Magnetic Surveys

NASA Astrophysics Data System (ADS)

Lin, J.; Li, C. F.; Kulhanek, D. K.; Zhao, X.; Liu, Q.; Xu, X.; Sun, Z.; Zhu, J.

2014-12-01

The South China Sea (SCS) is the largest low-latitude marginal sea in the world. Its formation and evolution are linked to the complex continental-oceanic tectonic interaction of the Eurasian, Pacific, and Indo-Australian plates. Despite its relatively small size and short history, the SCS has undergone nearly a complete Wilson cycle from continental break-up to seafloor spreading to subduction. In January-March 2014, Expedition 349 of the International Ocean Discovery Program (IODP) drilled five sites in the deep basin of the SCS. Three sites (U1431, U1433, and U1434) cored into oceanic basement near the fossil spreading center on the East and Southwest Subbasins, whereas Sites U1432 and U1435 are located near the northern continent/ocean boundary of the East Subbasin. Shipboard biostratigraphy based on microfossils preserved in sediment directly above or within basement suggests that the preliminary cessation age of spreading in both the East and Southwest Subbasins is around early Miocene (16-20 Ma); however, post-cruise radiometric dating is being conducted to directly date the basement basalt in these subbasins. Prior to the IODP drilling, high-resolution near-seafloor magnetic surveys were conducted in 2012 and 2013 in the SCS with survey lines passing near the five IODP drilling sites. The deep-tow surveys revealed detailed patterns of the SCS magnetic anomalies with amplitude and spatial resolutions several times better than that of traditional sea surface measurements. Preliminary results reveal several episodes of magnetic reversal events that were not recognized by sea surface measurements. Together the IODP drilling and deep-tow magnetic surveys provide critical constraints for investigating the processes of seafloor spreading in the SCS and evolution of a mid-ocean ridge from active spreading to termination.

Application of the Geo-Anomaly Unit Concept in Quantitative Delineation and Assessment of Gold Ore Targets in Western Shandong Uplift Terrain, Eastern China

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen Yongqing, E-mail: ydonglai@mail.cgs.gov.cn; Zhao Pengda; Chen Jianguo

2001-03-15

A number of large and giant ore deposits have been discovered within the relatively small areas of lithospheric structure anomalies, including various boundary zones of tectonic plates. The regions have become the well-known intercontinental ore-forming belts, such as the circum-Pacific gold-copper, copper-molybdenum, and tungsten-tin metallogenic belts. These belts are typical geological anomalous areas. An investigation into the hydrothermal ore deposits in different regions in the former Soviet Union illustrated that the geologic structures of ore fields of almost all major commercial deposits have distinct features compared with the neighboring areas. These areas with distinct features are defined as geo-anomalies. Amore » geo-anomaly refers to such a geologic body or a combination of bodies that their composition, texture-structure, and genesis are significantly different from those of their surroundings. A geo-anomaly unit (GU) is an area containing distinct features that can be delineated with integrated ore-forming information using computer techniques on the basis of the geo-anomaly concept. Herein, the GU concept is illustrated by a case study of delineating the gold ore targets in the western Shandong uplift terrain, eastern China. It includes: (1) analyses of gold ore-forming factors; (2) compilation of normalized regional geochemical map and extraction of geochemical anomalies; (3) compilation of gravitational and aeromagnetic tectonic skeleton map and extraction of gravitational and aeromagnetic anomalies; (4) extraction of circular and linear anomalies from remote-sensing Landsat TM images; (5) establishment of a geo-anomaly conceptual model associated with known gold mineralization; (6) establishment of gold ore-forming favorability by computing techniques; and (7) delineation and assessment of ore-forming units. The units with high favorability are suggested as ore targets.« less

The mechanism of post-rift fault activities in Baiyun sag, Pearl River Mouth basin

NASA Astrophysics Data System (ADS)

Sun, Zhen; Xu, Ziying; Sun, Longtao; Pang, Xiong; Yan, Chengzhi; Li, Yuanping; Zhao, Zhongxian; Wang, Zhangwen; Zhang, Cuimei

2014-08-01

Post-rift fault activities were often observed in deepwater basins, which have great contributions to oil and gas migration and accumulation. The main causes for post-rift fault activities include tectonic events, mud or salt diapirs, and gravitational collapse. In the South China Sea continental margin, post-rift fault activities are widely distributed, especially in Baiyun sag, one of the largest deepwater sag with its main body located beneath present continental slope. During the post-rift stage, large population of faults kept active for a long time from 32 Ma (T70) till 5.5 Ma (T10). Seismic interpretation, fault analysis and analogue modeling experiments indicate that the post-rift fault activities in Baiyun sag between 32 Ma (T70) and 13.8 Ma (T30) was mainly controlled by gravity pointing to the Main Baiyun sag, which caused the faults extensive on the side facing Main Baiyun sag and the back side compressive. Around 32 Ma (T70), the breakup of the continental margin and the spreading of the South China Sea shed a combined effect of weak compression toward Baiyun sag. The gravity during post-rift stage might be caused by discrepant subsidence and sedimentation between strongly thinned sag center and wing areas. This is supported by positive relationship between sedimentation rate and fault growth index. After 13.8 Ma (T30), fault activity shows negative relationship with sedimentation rate. Compressive uplift and erosion in seismic profiles as well as negative tectonic subsiding rates suggest that the fault activity from 13.8 Ma (T30) to 5.5 Ma (T10) might be controlled by the subductive compression from the Philippine plate in the east.

Aeolian dust supply from the Yellow River floodplain to the Pleistocene loess deposits of the Mangshan Plateau, central China: Evidence from zircon U-Pb age spectra

NASA Astrophysics Data System (ADS)

Shang, Yuan; Prins, Maarten A.; Beets, Christiaan J.; Kaakinen, Anu; Lahaye, Yann; Dijkstra, Noortje; Rits, Daniël S.; Wang, Bin; Zheng, Hongbo; van Balen, Ronald T.

2018-02-01

The thick loess-palaeosol sequences in the Mangshan Loess Plateau (MLP; central China) along the south bank of the lower reach of the Yellow River provide high-resolution records of Quaternary climate change. In addition, substantial increases in grain-size and accumulation rate have been inferred in the upper part of the loess sequence, above palaeosol layer S2. This study investigates the sources of the long-term dust supply to the MLP and explores the mechanism behind the sudden increase in sediment delivery and coarsening of the loess deposits since S2 (∼240 ka) by using end member modelling of the loess grain-size dataset and single-grain zircon U-Pb dating. Our results indicate that the lower Yellow River floodplain, directly north of the MLP, served as a major dust supply for the plateau at least since the deposition of loess unit L9 and indirectly suggest that the integration of the Yellow River and the disappearance of the Sanmen palaeolake took place before L9 (∼900 ka). The sudden change in sedimentology of the Mangshan sequence above palaeosol unit S2 may result from an increased fluvial sediment flux being transported to the lower reaches of the Yellow River because of tectonic movements (initiated) in the Weihe Basin around 240 ka. Furthermore, sediment coarsening can be explained by the gradual southward migration of the lower Yellow River floodplain towards the MLP since the deposition of palaeosol S2. The migration is evidenced by the formation of an impressive scarp, and is likely caused by tectonic tilting of the floodplain area.

Strength and Elastic thickness of the lithosphere and implication on ductile crustal flow in Europe

NASA Astrophysics Data System (ADS)

Tesauro, M.; Kaban, M. K.; Cloetingh, S. A. P. L.

2012-04-01

The strength and effective elastic thickness (Te) of the lithosphere control its response to tectonic and surface processes. We present the first global strength and effective elastic thickness maps, which are determined using physical properties from recent crustal and lithospheric models. We estimated the lithospheric temperature from inversion of a tomography model and we extrapolated the results to the surface using crustal isotherms for different tectonic provinces based on characteristic values of radiogenic heat production. We assumed different rheologies of the upper and lower crust for continental areas, on the base of the geological features distribution. The results obtained allow us to compare for the first time the lithospheric characteristics of the different tectonic areas. The Te estimated from the strength is compared with the Te obtained by flexural loading and spectral studies. Lithospheric strength is primarily controlled by the crust in young (Phanerozoic) geological provinces characterized by low Te (~25 km), high topography (>1000 m) and active seismicity. In contrast, the old (Achaean and Proterozoic) cratons of the continental plates show strength primarily in the lithospheric mantle, high Te (over 100 km), low topography (<1000 m) and very low seismicity. Using high resolution crustal thickness and density data provided by the EuCRUST-07 model we compute for the European continent the associated lateral pressure gradients (LPG), which can drive horizontal ductile flow in the crust. Incorporation of these data in channel flow models allows us to use potential gravity theory to assess horizontal mass transfer and stress transmission within the European crust. We explore implications of the channel flow concept for a possible range of crustal strength, using end-member 'hard' and 'soft' crustal rheologies to estimate strain rates at the bottom of the ductile crustal layers. The models show that the effects of channel flow superimposed on the direct effects of plate tectonic forces might result in additional significant horizontal and vertical movements associated with zones of compression or extension. Large values of the LPG are predicted perpendicular to the axes of European mountain belts, such as the Alps, Pyrenees-Cantabrian Mountains, Dinarides-Hellenic arc and Carpathians. In general, the crustal flow is directed away from orogens towards adjacent weaker areas. Predicted pressure and strain rate gradients suggest that gravity driven flow may play an essential role in European intraplate tectonics. These results are also important for quantifying the thickness of the low viscosity zones in the lowermost part of the crustal layers.

Museums and Nationalism in Contemporary China

ERIC Educational Resources Information Center

Vickers, Edward

2007-01-01

This article examines the representation of Chinese identity in museums in the People's Republic of China, comparing this briefly with the portrayal of local and national identities in Hong Kong and Taiwan. In particular, the article looks at the implications for museums of the shift in emphasis within state ideology from socialism to…

Chinese Student Life.

ERIC Educational Resources Information Center

Braswell, James; Boone, Jerry N.

1991-01-01

Places life of university students in China in context of Tiananmen Square and Cultural Revolution, with implications of serving them as students in the United States. Presents basic facts of student life in China. Although the emphasis is on college life, some attention is paid to earlier student experiences as well. (Author/NB)

Ecological Education in Rural China: Rediscovering Traditional Knowledge

ERIC Educational Resources Information Center

Liu, Yan

2008-01-01

This article has implications for the ecological sustainability crisis now looming in China and what this portends for the practice of education. Chemical agriculture, although improving agricultural production, harms ecological systems in rural communities. The author presents research on a group of intellectuals and social activists in 1…

Deep conductivity characteristics and preliminary acquaintance of the Lushan earthquake, east edge of Tibetan Plateau, China

NASA Astrophysics Data System (ADS)

Zhou, J.; Wang, X.; Wang, Y.; Min, G.

2013-12-01

1. Introduction The Longmenshan foreland basin developed as a flexural foredeep at western Yangtze Platfrom during the Late Triassic Indosinian orogeny with strong tectonic activity. 2008 Wenchuan earthquake (Mw7.9) happened along the middle segment of the Longmenshan overthrusting belt. 2013 Lushan earthquake (Mw6.6) occurred along the south segment of Longmenshan tectonic zone which belongs to seismic gap during the Wenchuan earthquake. The recent researches ( Yan Zhan etc., 2013; Zhuqi Zhang etc., 2013; Xiwei Xu etc., 2013) indicate that the Lushan earthquake may closely related to the activity of Longmenshan ';s piedmont fault zone while the seismogenic fault and other issues are still controversial. In order to provide an electromagnetic basis in deep earthquake area structure, we detect magnetotelluric(MT) sounding in Lushan earthquake zone to obtain the electrical structure characteristics of Longmenshan's south segment. 2. Data acquisition and processing To research the deep electrical structure of earthquake zone assigning a MT profile through the epicenter which transects the Sichuan platform concave, Longmenshan tectonic belt and Songpan-Ganzi fold system. To analysis the MT data, we carried out the impedance tensor decompositionincluding the swift rotation and bahr method which based on the phase deviation. Ultimately, NLCG method was adopted to inverse MT data. 3. Conclusion The result of MT data discloses deep electrical structure feature of the southern section of Longmenshan overthrusting belt: the burial depth of conductive layer in the upper crust of Songpan-Ganzi plot is larger than that of middle-northern part; there is no conductive zone in Longmenshan high resistance body which connect with the high conductivity layer in the crust of the western section of Songpan-Ganzi plot; there exists a relatively large range of conductive zone in the basin to Longmenshan tectonic belt, which is mostly related to the piedmont of concealed fault zone and resistive intermediate belt at the edge of western basin. Be different form Wenchuan earthquake, Lushan earthquake located in the south of Longmenshan tectonic zone which have a strong connection with the piedmont fault. MT research reveals the difference of the deep electrical structure between the south of Longmenshan tectonic belt and the middle-north belt, from which we can infer that the seismogenic environment are not the same. The epicenter of Lushan earthquake occurred in the east edge of Longmenshan tectonic belt which close to Longmenshan ';s piedmont fault combine with the MT inversion infer that Lushan earthquake has a stronger relationship with Longmenshan ';s piedmont fault. Because of the short term of our work, now further work is ongoing.

Changes in early adolescents' sense of responsibility to their parents in the United States and China: implications for academic functioning.

PubMed

Pomerantz, Eva M; Qin, Lili; Wang, Qian; Chen, Huichang

2011-01-01

This research examined American and Chinese children's sense of responsibility to their parents during early adolescence, with a focus on its implications for children's academic functioning. Four times over the seventh and eighth grades, 825 children (mean age = 12.73 years) in the United States and China reported on their sense of responsibility to their parents. Information on children's academic functioning was also collected from children as well as school records. Although children's sense of responsibility to their parents declined over the seventh and eighth grades in the United States, this was not the case in China. In both countries, children's sense of responsibility was predictive of enhanced academic functioning among children over time. © 2011 The Authors. Child Development © 2011 Society for Research in Child Development, Inc.

Landscapes of human evolution: models and methods of tectonic geomorphology and the reconstruction of hominin landscapes.

PubMed

Bailey, Geoffrey N; Reynolds, Sally C; King, Geoffrey C P

2011-03-01

This paper examines the relationship between complex and tectonically active landscapes and patterns of human evolution. We show how active tectonics can produce dynamic landscapes with geomorphological and topographic features that may be critical to long-term patterns of hominin land use, but which are not typically addressed in landscape reconstructions based on existing geological and paleoenvironmental principles. We describe methods of representing topography at a range of scales using measures of roughness based on digital elevation data, and combine the resulting maps with satellite imagery and ground observations to reconstruct features of the wider landscape as they existed at the time of hominin occupation and activity. We apply these methods to sites in South Africa, where relatively stable topography facilitates reconstruction. We demonstrate the presence of previously unrecognized tectonic effects and their implications for the interpretation of hominin habitats and land use. In parts of the East African Rift, reconstruction is more difficult because of dramatic changes since the time of hominin occupation, while fossils are often found in places where activity has now almost ceased. However, we show that original, dynamic landscape features can be assessed by analogy with parts of the Rift that are currently active and indicate how this approach can complement other sources of information to add new insights and pose new questions for future investigation of hominin land use and habitats. Copyright © 2010 Elsevier Ltd. All rights reserved.

Time variability in Cenozoic reconstructions of mantle heat flow: plate tectonic cycles and implications for Earth's thermal evolution.

PubMed

Loyd, S J; Becker, T W; Conrad, C P; Lithgow-Bertelloni, C; Corsetti, F A

2007-09-04

The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by approximately 0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past.

One Dimensional Backstripping Results from IODP Expedition 318, Site U1356: Tectonic Implications for the Wilkes Land Margin of Antarctica

NASA Astrophysics Data System (ADS)

Hayden, T. G.; Kominz, M. A.; González, J. J.; Escutia, C.; Brinkhuis, H.; Scientific Party of IODP Expedition 318

2011-12-01

The Wilkes Land margin of Antarctica is the conjugate margin of the Great Australian Bight, which underwent extension, thinning and rifting from ~160 Ma until breakup at ~83 Ma. Both Wilkes Land and the Great Australian Bight are considered passive margins, and were thought to be tectonically inactive since breakup at 83 Ma. We have backstripped the U1356 Core recovered from the continental rise off Wilkes Land, Antarctica by IODP Expedition 318. Backstripping input included lithological and sedimentary analysis, paleo-environmental indicators, combined paleomagnetic and biostratigraphic chronologies, and physical properties measurements. Tectonic subsidence shows a major event between 50 and 33.6 Ma, a time represented by a hiatus in the U1356 core. The magnitude of subsidence requires it to be tectonic in origin, and the timing matches with a reorganization of plate motions that represents the transition from slow spreading to fast spreading between Antarctica and Australia, which occurred at approximately 43 Ma. Coupled with a regional seismic framework, and using other Expedition 318 site analyses, the Wilkes Land margin is shown to be far more complex then the simple passive margin currently assumed. We explore several possible mechanisms for the subsidence and erosion observed; including thermal uplift due to continental insulation of the asthenosphere and it's interaction with a recently rifted margin, asthenospheric convection, transtensional or transpressional basin development and loading, and edge-driven asthenospheric convection.

An integrated study of geochemistry and mineralogy of the Upper Tukau Formation, Borneo Island (East Malaysia): Sediment provenance, depositional setting and tectonic implications

NASA Astrophysics Data System (ADS)

Nagarajan, Ramasamy; Roy, Priyadarsi D.; Kessler, Franz L.; Jong, John; Dayong, Vivian; Jonathan, M. P.

2017-08-01

An integrated study using bulk chemical composition, mineralogy and mineral chemistry of sedimentary rocks from the Tukau Formation of Borneo Island (Sarawak, Malaysia) is presented in order to understand the depositional and tectonic settings during the Neogene. Sedimentary rocks are chemically classified as shale, wacke, arkose, litharenite and quartz arenite and consist of quartz, illite, feldspar, rutile and anatase, zircon, tourmaline, chromite and monazite. All of them are highly matured and were derived from a moderate to intensively weathered source. Bulk and mineral chemistries suggest that these rocks were recycled from sedimentary to metasedimentary source regions with some input from granitoids and mafic-ultramafic rocks. The chondrite normalized REE signature indicates the presence of felsic rocks in the source region. Zircon geochronology shows that the samples were of Cretaceous and Triassic age. Comparable ages of zircon from the Tukau Formation sedimentary rocks, granitoids of the Schwaner Mountains (southern Borneo) and Tin Belt of the Malaysia Peninsular suggest that the principal provenance for the Rajang Group were further uplifted and eroded during the Neogene. Additionally, presence of chromian spinels and their chemistry indicate a minor influence of mafic and ultramafic rocks present in the Rajang Group. From a tectonic standpoint, the Tukau Formation sedimentary rocks were deposited in a passive margin with passive collisional and rift settings. Our key geochemical observation on tectonic setting is comparable to the regional geological setting of northwestern Borneo as described in the literature.

Euramerican tonsteins: overview, magmatic origin, and depositional-tectonic implications

USGS Publications Warehouse

Lyons, P.C.; Spears, D.A.; Outerbridge, W.F.; Congdon, R.D.; Evans, H.T.

1994-01-01

Carboniferous tonsteins (kaolinized volcanic-ash beds) of wide geographic distribution are known in both Europe and North America. Relict volcanic minerals common in these Euramerican tonsteins are volcanic quartz (including beta-quartz paramorphs), zircon and ilmenite; less common are magnetite, fayalite, rutile, monazite, xenotime, apatite and sanidine. Data for two relatively thick (3-13 cm) and widespread (>400 km) European tonsteins (Erda and Sub-Worsley Four-foot) indicate an increase in detrital quartz near the top of the beds which indicates mixing with normal clastic sediments, including the introduction of heavy detrital minerals (e.g., tourmaline and garnet). These thick tonsteins show multiple horizontal bedding, normal graded bedding, disturbed bedding, and centimeter-scale scour surfaces. The Fire Clay tonstein in North America represents from one to five separate volcanic air-fall ash deposits as determined by normal graded bedding and mineralogical analysis. These features indicate several episodes of volcanic-ash deposition and very localized subsequent erosion and bioturbation. Electron microprobe data from glass inclusions in volcanic quartz in Euramerican tonsteins indicate a rhyolitic origin for these tonsteins and reveal chemical "fingerprints" valuable for intra- and inter-basinal correlations. However, the tectonic framework for European and North American tonsteins was quite different. In Europe, volcanic-ash beds were associated with Variscan collisional tectonics, whereas in North America, volcanic ash was associated with Ouachita tectonic activity, explosive volcanism from the Yucatan block, collision between the South American and North American plates, and the formation of Pangea. ?? 1994.

Facies Analysis of the Tandoǧdu Travertines, Van, Eastern Anatolia, Turkey: implications for the active tectonic deformation behind the formation and evolution of the travertines

NASA Astrophysics Data System (ADS)

Yesilova, Cetin; Yesilova, Pelin; Aclan, Mustafa; Gülyüz, Nilay

2017-04-01

In this study, stratigraphic and sedimentologic characteristics of Tandoǧdu travertines exposing at the 13 km southwest of Başkale, Van were examined. In this respect, we shed light on their formation conditions and depositional environment by determining their morphological characteristics and analyzing their facies distribution. In addition, kinematic studies were conducted by collecting structural data from the structures hosting the travertines. Tandoǧdu travertines having bed type and ridge type travertines have 5 distinct lithofacies based on the studies conducted. These are: (1) crystalline crust facies, (2) coated bubble facies, (3) paper-thin raft type facies, (4) lithoclast - breccia facies and (5) paleosoil facies. According to the examination of their morphologies and lithofacies; lithofacies were developed depending on the temperature of fluids forming the travertines. Distal from the source field of the hydrothermal fluids, paper-thin raft type facies were developed in shallow pools. Proximal to the source field of the hydrothermal fluids, crystalline crust facies and coated bubble facies were deposited. Existence of breccia facies indicates the effects of active tectonism during the formation of travertines. Hot hydrothermal pools on the ridge type travertines prove the still active tectonic activities. On-going studies aim to date growth of the travertines by U-Th dating method which will also shed some light on the tectonic scenario behind the evolution of the travertines.

High-P metamorphic rocks from the Himalaya and their tectonic implication ? a review

NASA Astrophysics Data System (ADS)

Jan, M. Qasim

The suture zones bordering the Indian subcontinent on the E, N and W are characterized in several places by the occurrence of ophiolitic complexes and tectonic melanges. High-P metamorphic rocks have recently been discovered in the melanges in Burma, Naga Hills, southern Tibet, eastern and western Ladakh, Kohistan (Jijal, Allai, Shangla) and Khost (Afghanistan). The development of these rocks has an important bearing on the plate tectonics of the Himalaya. The High-P metamorphic rocks belong to prehnite-pumpellyite, blueschist and high-P greenschist facies but extensive garnet-granulites have developed at 35 km depth in Jijal. In the Indus-Zangbo suture zone (IZS) the high-P metamorphism is complemented to the N by low- or medium-P metamorphism and calc-alkaline magmatism in Tibet, Ladakh as well as Kohistan. High-P metamorphism in Jijal has been dated at 104 Ma, in Shangla at 70-100 Ma and in western Ladakh during mid-Cretaceous. Elsewhere, the timing of the high-P metamorphism is not known but a Cretaceous age is inferred. Since collision along the IZS occurred during Eocene, the high-P metamorphism is therefore related to the northwards subduction of the neo-Tethyan lithosphere under Tibet or late Mesozoic magmatic arcs. The timing of high-P metamorphism coincides with the breakup of India from Gondwanaland and its rapid northwards movement, whereas the tectonic melanges may principally have formed during Eocene collision and obduction.

Formation and tectonic evolution of the Cretaceous Jurassic Muslim Bagh ophiolitic complex, Pakistan: Implications for the composite tectonic setting of ophiolites

NASA Astrophysics Data System (ADS)

Khan, Mehrab; Kerr, Andrew C.; Mahmood, Khalid

2007-10-01

The Muslim Bagh ophiolitic complex Balochistan, Pakistan is comprised of an upper and lower nappe and represents one of a number of ophiolites in this region which mark the boundary between the Indian and Eurasian plates. These ophiolites were obducted onto the Indian continental margin around the Late Cretaceous, prior to the main collision between the Indian and Eurasian plates. The upper nappe contains mantle sequence rocks with numerous isolated gabbro plutons which we show are fed by dolerite dykes. Each pluton has a transitional dunite-rich zone at its base, and new geochemical data suggest a similar mantle source region for both the plutons and dykes. In contrast, the lower nappe consists of pillow basalts, deep-marine sediments and a mélange of ophiolitic rocks. The rocks of the upper nappe have a geochemical signature consistent with formation in an island arc environment whereas the basalts of the lower nappe contain no subduction component and are most likely to have formed at a mid-ocean ridge. The basalts and sediments of the lower nappe have been intruded by oceanic alkaline igneous rocks during the northward drift of the Indian plate. The two nappes of the Muslim Bagh ophiolitic complex are thus distinctively different in terms of their age, lithology and tectonic setting. The recognition of composite ophiolites such as this has an important bearing on the identification and interpretation of ophiolites where the plate tectonic setting is less well resolved.

Time variability in Cenozoic reconstructions of mantle heat flow: Plate tectonic cycles and implications for Earth's thermal evolution

PubMed Central

Loyd, S. J.; Becker, T. W.; Conrad, C. P.; Lithgow-Bertelloni, C.; Corsetti, F. A.

2007-01-01

The thermal evolution of Earth is governed by the rate of secular cooling and the amount of radiogenic heating. If mantle heat sources are known, surface heat flow at different times may be used to deduce the efficiency of convective cooling and ultimately the temporal character of plate tectonics. We estimate global heat flow from 65 Ma to the present using seafloor age reconstructions and a modified half-space cooling model, and we find that heat flow has decreased by ∼0.15% every million years during the Cenozoic. By examining geometric trends in plate reconstructions since 120 Ma, we show that the reduction in heat flow is due to a decrease in the area of ridge-proximal oceanic crust. Even accounting for uncertainties in plate reconstructions, the rate of heat flow decrease is an order of magnitude faster than estimates based on smooth, parameterized cooling models. This implies that heat flow experiences short-term fluctuations associated with plate tectonic cyclicity. Continental separation does not appear to directly control convective wavelengths, but rather indirectly affects how oceanic plate systems adjust to accommodate global heat transport. Given that today's heat flow may be unusually low, secular cooling rates estimated from present-day values will tend to underestimate the average cooling rate. Thus, a mechanism that causes less efficient tectonic heat transport at higher temperatures may be required to prevent an unreasonably hot mantle in the recent past. PMID:17720806

Identifying mantle lithosphere inheritance in controlling intraplate orogenesis

NASA Astrophysics Data System (ADS)

Heron, Philip J.; Pysklywec, Russell N.; Stephenson, Randell

2016-09-01

Crustal inheritance is often considered important in the tectonic evolution of the Wilson Cycle. However, the role of the mantle lithosphere is usually overlooked due to its difficulty to image and uncertainty in rheological makeup. Recently, increased resolution in lithosphere imaging has shown potential scarring in continental mantle lithosphere to be ubiquitous. In our study, we analyze intraplate deformation driven by mantle lithosphere heterogeneities from ancient Wilson Cycle processes and compare this to crustal inheritance deformation. We present 2-D numerical experiments of continental convergence to generate intraplate deformation, exploring the limits of continental rheology to understand the dominant lithosphere layer across a broad range of geological settings. By implementing a "jelly sandwich" rheology, common in stable continental lithosphere, we find that during compression the strength of the mantle lithosphere is integral in generating deformation from a structural anomaly. We posit that if the continental mantle is the strongest layer within the lithosphere, then such inheritance may have important implications for the Wilson Cycle. Furthermore, our models show that deformation driven by mantle lithosphere scarring can produce tectonic patterns related to intraplate orogenesis originating from crustal sources, highlighting the need for a more formal discussion of the role of the mantle lithosphere in plate tectonics.

Spatial and Alignment Analyses for a Field of Small Volcanic Vents South of Pavonis Mons and Implications for the Tharsis Province, Mars

NASA Technical Reports Server (NTRS)

Bleacher, Jacob E.; Glaze, Lori S.; Greeley, Ronald; Hauber, Ernst; Baloga, Stephen; Sakimoto, Susan E. H.; Williams, David A.; Glotch, Timothy D.

2009-01-01

A field of small volcanic vents south of Pavonis Mons was mapped with each vent assigned a two-dimensional data point. Nearest neighbor and two-point azimuth analyses were applied to the resulting location data. Nearest neighbor results show that vents within this field are spatially random in a Poisson sense, suggesting that the vents formed independently of each other without sharing a centralized magma source at shallow depth. Two-point azimuth results show that the vents display north-trending alignment relationships between one another. This trend corresponds to the trends of faults and fractures of the Noachian-aged Claritas Fossae, which might extend into our study area buried beneath more recently emplaced lava flows. However, individual elongate vent summit structures do not consistently display the same trend. The development of the volcanic field appears to display tectonic control from buried Noachian-aged structural patterns on small, ascending magma bodies while the surface orientations of the linear vents might reflect different, younger tectonic patterns. These results suggest a complex interaction between magma ascension through the crust, and multiple, older, buried Tharsis-related tectonic structures.

Channel morphometry, sediment transport, and implications for tectonic activity and surficial ages of Titan basins

USGS Publications Warehouse

Cartwright, R.; Clayton, J.A.; Kirk, R.L.

2011-01-01

Fluvial features on Titan and drainage basins on Earth are remarkably similar despite differences in gravity and surface composition. We determined network bifurcation (Rb) ratios for five Titan and three terrestrial analog basins. Tectonically-modified Earth basins have Rb values greater than the expected range (3.0-5.0) for dendritic networks; comparisons with Rb values determined for Titan basins, in conjunction with similarities in network patterns, suggest that portions of Titan's north polar region are modified by tectonic forces. Sufficient elevation data existed to calculate bed slope and potential fluvial sediment transport rates in at least one Titan basin, indicating that 75mm water ice grains (observed at the Huygens landing site) should be readily entrained given sufficient flow depths of liquid hydrocarbons. Volumetric sediment transport estimates suggest that ???6700-10,000 Titan years (???2.0-3.0??105 Earth years) are required to erode this basin to its minimum relief (assuming constant 1m and 1.5m flows); these lowering rates increase to ???27,000-41,000 Titan years (???8.0-12.0??105 Earth years) when flows in the north polar region are restricted to summer months. ?? 2011 Elsevier Inc.

Channel morphometry, sediment transport, and implications for tectonic activity and surficial ages of Titan basins

USGS Publications Warehouse

Cartwright, Richard; Clayton, Jordan A.; Kirk, Randolph L.

2011-01-01

Fluvial features on Titan and drainage basins on Earth are remarkably similar despite differences in gravity and surface composition. We determined network bifurcation (Rb) ratios for five Titan and three terrestrial analog basins. Tectonically-modified Earth basins have Rb values greater than the expected range (3.0–5.0) for dendritic networks; comparisons with Rb values determined for Titanbasins, in conjunction with similarities in network patterns, suggest that portions of Titan's north polar region are modified by tectonic forces. Sufficient elevation data existed to calculate bed slope and potential fluvial sedimenttransport rates in at least one Titanbasin, indicating that 75 mm water ice grains (observed at the Huygens landing site) should be readily entrained given sufficient flow depths of liquid hydrocarbons. Volumetric sedimenttransport estimates suggest that ~6700–10,000 Titan years (~2.0–3.0 x 105 Earth years) are required to erode this basin to its minimum relief (assuming constant 1 m and 1.5 m flows); these lowering rates increase to ~27,000–41,000 Titan years (~8.0–12.0 x 105 Earth years) when flows in the north polar region are restricted to summer months.

Possible detachment zone in Precambrian rocks of Kanjamalai Hills, Cauvery Suture Zone, Southern India: Implications to accretionary tectonics

NASA Astrophysics Data System (ADS)

Mohanty, D. P.; Chetty, T. R. K.

2014-07-01

Existence of a possible detachment zone at Elampillai region, NW margin of Kanjamalai Hills, located in the northern part of Cauvery Suture Zone (CSZ), Southern India, is reported here for the first time. Detailed structural mapping provides anatomy of the zone, which are rarely preserved in Precambrian high grade terranes. The detachment surface separates two distinct rock units of contrasting lithological and structural characters: the upper and lower units. The detachment zone is characterized by a variety of fold styles with the predominance of tight isoclinal folds with varied plunge directions, limb rotations and the hinge line variations often leading to lift-off fold like geometries and deformed sheath folds. Presence of parasitic folding and associated penetrative strains seem to be controlled by differences in mechanical stratigraphy, relative thicknesses of the competent and incompetent units, and the structural relief of the underlying basement. Our present study in conjunction with other available geological, geochemical and geochronological data from the region indicates that the structures of the detachment zone are genetically related to thrust tectonics forming a part of subduction-accretion-collision tectonic history of the Neoproterozoic Gondwana suture.

A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

NASA Technical Reports Server (NTRS)

Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

1999-01-01

Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies. These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While Magnetic anomaly data represent the main focus of this study recently derived satellite gravity data (Laxon and McAdoo, 1998) are playing a major role in Arctic studies.

Analysis of very-high-resolution Galileo images of Europa: Implications for small-scale structure and surface evolution

NASA Astrophysics Data System (ADS)

Leonard, E. J.; Pappalardo, R. T.; Yin, A.; Prockter, L. M.; Patthoff, D. A.

2014-12-01

The Galileo Solid State Imager (SSI) recorded nine very high-resolution frames (8 at 12 m/pixel and 1 at 6 m/pixel) during the E12 flyby of Europa in Dec. 1997. To understand the implications for the small-scale structure and evolution of Europa, we mosaicked these frames (observations 12ESMOTTLE01 and 02, incidence ≈18°, emission ≈77°) into their regional context (part of observation 11ESREGMAP01, 220 m/pixel, incidence ≈74°, emission ≈23°), despite their very different viewing and lighting conditions. We created a map of geological units based on morphology, structure, and albedo along with stereoscopic images where the frames overlapped. The highly diverse units range from: high albedo sub-parallel ridge and grooved terrain; to variegated-albedo hummocky terrain; to low albedo and relatively smooth terrain. We classified and analyzed the diverse units solely based on the high-resolution image mosaic, prior to comparison to the context image, to obtain an in-depth look at possible surface evolution and underlying formational processes. We infer that some of these units represent different stages and forms of resurfacing, including cryovolcanic and tectonic resurfacing. However, significant morphological variation among units in the region indicates that there are different degrees of resurfacing at work. We have created candidate morphological sequences that provide insight into the conversion of ridged plains to chaotic terrain—generally, a process of subduing formerly sharp features through tectonic modification and/or cryovolcanism. When the map of the high-resolution area is compared to the regional context, features that appear to be one unit at regional resolution are comprised of several distinct units at high resolution, and features that appear to be smooth in the context image are found to show distinct textures. Moreover, in the context image, transitions from ridged units to disrupted units appear to be gradual; however the high-resolution image reveals them to be abrupt, suggesting tectonic control of these boundaries. These discrepancies could have important implications for a future landed exploration.

From tectonics to tractors: New insight into Earth's changing surface

NASA Astrophysics Data System (ADS)

Larsen, I. J.

2017-12-01

Weathering and erosion of rock and the transport of sediment continually modify Earth's surface. The transformation and transfer of material by both natural and anthropogenic processes drives global cycles and influences the habitability of our planet. By quantitatively linking erosional and depositional landforms to the processes that form them, we better understand how Earth's surface will evolve in the future, and gain the ability to look into the past to recognize how planetary surfaces evolved when environments were drastically different than today. Many of the recent advances in our understanding of the processes that influence landscape evolution have been driven by the development and application of tools such as cosmogenic nuclides, computational models, and digital topographic data. Here I present results gleaned from applying these tools to a diverse set of landscapes, where erosion is driven by factors ranging from tectonics to tractors, to provide insight into the mechanics, chemistry, and history of Earth's changing surface. I will first examine the landslide response of hillslopes in the Himalaya to spatial gradients in tectonic forcing to assess the paradigm of threshold hillslopes. Second, I will present soil production and chemical weathering rates measured in the Southern Alps of New Zealand to determine the relationship between physical erosion and chemical weathering in one of Earth's most rapidly uplifting landscapes, and discuss the implications for proposed links between mountain uplift and global climate. Third, I will discuss results from numerical flood simulations used to explore the interplay between outburst flood hydraulics and canyon incision in the Channeled Scablands of eastern Washington, and explore the implications for reconstructing discharge in flood-carved canyons on Earth and Mars. Finally, I will present new work that couples high resolution spectral and topographic data to estimate the spatial extent of agriculturally-induced topsoil loss in the Midwestern U.S., and discuss the economic and carbon cycle implications. These findings - in some cases unanticipated and exciting - highlight opportunities that stem from using a multi-faceted approach to gain new insights into the physical and chemical processes that modify Earth's changing surface.

Slip distribution and tectonic implication of the 1999 Chi-Chi, Taiwan, earthquake

USGS Publications Warehouse

Ji, C.; Helmberger, D.V.; Song, T.-R.A.; Ma, K.-F.; Wald, D.J.

2001-01-01

We report on the fault complexity of the large (Mw = 7.6) Chi-Chi earthquake obtained by inverting densely and well-distributed static measurements consisting of 119 GPS and 23 doubly integrated strong motion records. We show that the slip of the Chi-Chi earthquake was concentrated on the surface of a "wedge shaped" block. The inferred geometric complexity explains the difference between the strike of the fault plane determined by long period seismic data and surface break observations. When combined with other geophysical and geological observations, the result provides a unique snapshot of tectonic deformation taking place in the form of very large (>10m) displacements of a massive wedge-shaped crustal block which may relate to the changeover from over-thrusting to subducting motion between the Philippine Sea and the Eurasian plates.

Earthquake Related Variation of Total Electron Content in Ionosphere over Chinese Mainland Derived from Observations of a Nationwide GNSS Network

NASA Astrophysics Data System (ADS)

Gan, Weijun

2016-07-01

Crustal Movement Observation Network of China (CMONOC) is a key national scientific infrastructure project carried out during 1997-2012 with 2 phases. The network is composed of 260 continuously observed GNSS stations (CORS) and 2081 campaign mode GNSS stations, with the main purpose to monitor the crustal movement, perceptible water vapor (PWV), total electron content (TEC), and many other tectonic and environmental elements around mainland China, by mainly using the Global Navigation Satellite System (GNSS) technology. Here, based on the GNSS data of 260 CORS of COMNOC for about 5 years, we investigated the characteristics of TEC in ionosphere over Chinese Mainland and discussed if there was any abnormal change of TEC before and after a big earthquake. our preliminary results show that it is hard to see any convincing precursor of TEC before a big earthquake. However, the huge energy released by a big earthquake can obviously disturb the TEC over meizoseismal area.

Seismic evidence for multiple-stage exhumation of high/ultrahigh pressure metamorphic rocks in the eastern Dabie orogenic belt

NASA Astrophysics Data System (ADS)

Luo, Yinhe; Zhao, Kaifeng; Tang, Chi-Chia; Xu, Yixian

2018-05-01

The Dabie-Sulu orogenic belt in China contains one of the largest exposures of high and ultrahigh pressure (HP and UHP) metamorphic rocks in the world. The origin of HP/UHP metamorphic rocks and their exhumation to the surface in this belt have attracted great interest in the geologic community because the study of exhumation history of HP/UHP rocks helps to understand the process of continental-continental collision and the tectonic evolution of post-collision. However, the exhumation mechanism of the HP-UHP rocks to the surface is still contentious. In this study, by deploying 28 broadband seismic stations in the eastern Dabie orogenic belt and combining seismic data from 40 stations of the China National Seismic Network (CNSN), we image the high-resolution crustal isotropic shear velocity and radial anisotropy structure using ambient noise tomography. Our high-resolution 3D models provide new information about the exhumation mechanism of HP/UHP rocks and the origin of two dome structures.

Application of telluric-telluric profiling combined with magnetotelluric and self-potential methods to geothermal exploration in the Fujian Province, China

NASA Astrophysics Data System (ADS)

Pham, Van-Ngoc; Boyer, Danièle; Yuan, Xue Cheng; Liu, Shao Cheng

1995-05-01

In the Fujian Province, southeastern China, most of the hot springs emerge in fluviatile valleys and the geothermal resources are mainly medium and low temperature ones by mixing of hot water with cold superficial groundwater. The occurrence of the thermal waters is controlled by deep tectonic fractures in the bedrock where higher-temperature geothermal reservoirs of economic interest are present. The objective of this study is to detect the deeper active hydrothermal zone under a thick sedimentary cover by geoelectrical methods. In the Gui-An site, the combination of telluric-telluric profiling and magnetotelluric methods turns out very efficient to delineate more accurately the width of the deep conductive fracture zone. Moreover, the self-potential method allows us to localize the most active geothermal zone by electrofiltration processes above a convective cell of hot water which flows up from a deep source. The combined results constitute a possible guide for deep geothermal exploration currently encountered in several geothermal regions over the world.

A New Model of the Early Paleozoic Tectonics and Evolutionary History in the Northern Qinling, China

NASA Astrophysics Data System (ADS)

Dong, Yunpeng; Zhang, Guowei; Yang, Zhao; Qu, Hongjun; Liu, Xiaoming

2010-05-01

The Qinling Orogenic Belt extends from the Qinling Mountains in the west to the Dabie Mountains in the east. It lies between the North China and South China Blocks, and is bounded on the north by the Lushan fault and on the south by the Mianlue-Bashan-Xiangguang fault (Zhang et al., 2000). The Qinling Orogenic Belt itself is divided into the North and South Qinling Terranes by the Shangdan suture zone. Although the Shangdan zone is thought to represent the major suture separating the two blocks, there still exists debate about the timing and mechanism of convergence between these two blocks. For instance, some authors suggested an Early Paleozoic collision between the North China Block and South China Block (Ren et al., 1991; Kroner et al., 1993; Zhai et al., 1998). Others postulated left-lateral strike-slip faulting along the Shangdan suture at ca. 315 Ma and inferred a pre-Devonian collision between the two blocks (Mattauer et al., 1985; Xu et al., 1988). Geochemistry of fine-grained sediments in the Qinling Mountains was used to argue for a Silurian-Devonian collision (Gao et al., 1995). A Late Triassic collision has also been proposed (Sengor, 1985; Hsu et al., 1987; Wang et al., 1989), based on the formation of ultrahigh-pressure metamorphic rocks in the easternmost part of the Qinling Orogenic Belt at ~230 Ma (e.g., Li et al., 1993; Ames et al., 1996). Paleomagnetic data favor a Late Triassic-Middle Jurassic amalgamation of the North China and South China Blocks (Zhao and Coe, 1987; Enkin et al., 1992). It is clear that most authors thought that the Qinling Mountains are a collisional orogen, even they have different methods about the timing of the orogeny. Based on new detailed investigations, we propose a new model of the Early Paleozoic Tectonics and Evolutionary History between the North China and South China Blocks along the Shangdan Suture. The Shangdan suture is marked by a great number of ophiolites, island-arc volcanic rocks and other related rock assemblages. Our new geological and geochemical data revealed a lot of ophiolitic mélanges along the Shangdan suture, such as the Guojiagou, Ziyu, Xiaowangjian, Yanwan, Tangzang, Guanzizhen and Wushan areas from east to west. The ophiolite assemblage in Guojiagou, Ziyu area consists mainly of some blocks of E-MORB type and IAB-type basalts, while the pillow lavas from Xiaowangjian are IAB-type basalts. The basalts from the ophiolite assemblages in Yanwan, Tangzang and Wushan areas possess E-MORB geochemical compositions. The zircons of gabbro from Yanwan ophiolite mélange yield an U-Pb age of 516±3.8 Ma, which represents the formation age of the Yanwan ophiolite. Meanwhile, the basalts in the Guanzizhen ophiolite mélange show N-MORB type geochemical signature, and the zircons from gabbro yield a U-Pb age of 471±1.4 Ma, which constraints the formation age of the mature oceanic crust. Additionally, there also exists a U-Pb age of 523±26 Ma (Lu et al.,2003) and Cambrian-Ordovician radiolarites from the interlayed silicarites within the volcanic rock in the Guojiagou ophiolite mélange (Cui et al., 1995). All these geochemical and geochronological evidences indicate that there existed an oceanic basin and its subduction, which separated the Northern China Block from the Southern China Block during 523 -471 Ma. Accordant with this ocean and its subduction, there had been existed an active continental margin, island-arc setting on the north side of the Shangdan ophiolite mélange which were marked by a series of moderate-basic intrude igneous mass along the Sifangtai-Lajimiao area (Li et al., 1993) and the Fushui area (Dong et al., 1997). In addition to, there also exist a great number of subduction-collisional granites intruding into island-arc basement along the active continental margin. Zircons from the Fushui intrusion yield a U-Pb age of 514±1.3 Ma (Chen et al., 2004), which constraints the time of the subduction. Above all, more and more data suggest that there exists a back-arc basin on the northern side of the island-arc terrain. To the east, it is presented by the Erlangping group in Xixia area, which consists mainly of clastic sediments, carbonatites and basic volcanic rocks. The geochemistry of the basalts show that they were formed in a back-arc basin setting (Sun et al.,1996), and the radiolarites from the interlayed silicalites show the Orovician-Silurian age (Wang et al., 1995). Our new investigation reveals some new tectonic assemblages exposed in the Yinggerzui area, Qinghusi area to the west. The detailed geochemical studies indicate that they were formed in a back-arc basin. All above evidences suggest that there had existed an Early Paleozoic subduction system, which consists of a subduction trench, island-Arc and back-arc basin along the northern Qinling zone. It is also indicated that the Paleo-ocean had been evolved into a complete evolutionary process including initial spreading (E-MORB ophiolite), maturated extension (N-MORB ophiolite) and subduction (Island-arc volcanic rocks). However, it is notable that there are large scale of Devonian clastic sediments distributing on the south of the Shangdan suture, and the pre-Mesozoic rocks in the South Qinling without any metamorphism or just underwent the low-greenschist facies metamorphism in some places, which are very different from the North Qinling Terrane consisting mainly of Precambrian rocks and evolving into an amphibolite facies metamorphism at ~1.0 Ga and greenschist facies metamorphism at ~400 Ma (Liu et al., 1993; Zhang et al., 1994). Accordingly, it is prefer that there only occurred a subduction of the Shangdan oceanic crust from south to north along the Shangdan suture on the south of the Northern Qinling Terrane. However, the Piaochi and the Anjiping granites possessing the sym-collisional type granite geochemistry and formation age of 450-486 (Chen et al., 1991; zhang et al., 1996) indicate that there occurred a collisional event between the North Qinling Island-arc Terrane and the Northern China Block caused by closing of the Early Paleozoic back-arc basin. Additionally, the studies of the metamorphism show that there are two zones of high / ultra-high pressure metamorphic rocks outcropping along the both side of the Northern Qingling island-arc terrane. On the north, it is characterized by eclogite and coesite outcropping in the Guanpo area, and the metamorphic zircon U-Pb age of 507±38 Ma and 509±12 Ma by means of SHRIM (Yang et al., 2002). Meanwhile, there also exist some high pressure basic granulite (Liu et al., 1995) and felsic granulite (Liu et al., 1996) distributing in the Xigou fault on the south margin of the Northern Qingling island-arc terrane. Zircon U-Pb ages of 485±3.3 Ma by means of LA－ICP－MS method (Chen et al., 2004) and 518±12 Ma by means of SHRIM (Liu et al., 2003) constrain the time of the metamorphism. All these metamorphic data suggest the Northern Qingling island-arc terrane had been evolved into a deep subduction event during 485-518 Ma. Based on all above evidences, we infer a new model about the tectonics and evolutionary history of the Norhtern Qinling Terrane. It is emphasized that the Early Paleozoic tectonics between the North China and Southern China Blocks had existed an ocean, island-arc and back-arc basin, and evolved into four stages of evolutionary stages: 1) initial spreading along the Shangdan zone during 516-523 Ma; 2) maturated ocean along the Shangdan zone during 516-471 Ma; 3) subduction along the south side of the Northern Qinling Terrane and formation of the Back-arc basin along the north side of the Northern Qinling Terrane during518-514; 4) closing of the back-arc basin, collision between the Northern Qingling island-arc terrane and the Northern China Block, and deep subduction of the Northern Qingling island-arc terrane during 518-485Ma. This work was supported by NSFC (40772140 & 40972140)

Heat flow pattern in the gas hydrate drilling areas of northern south china sea and the implication for further study

NASA Astrophysics Data System (ADS)

Wang, Lifeng; Sha, Zhibin

2015-04-01

Numerous seismic reflection profiles have been acquired by China Geological Survey (CGS) in the Northern Slope of South China Sea (SCS), clearly indicating widespread occurrence of free gases and/or gas hydrates in the sediments. In the year 2007 and 2013 respectively the gas hydrate samples are successfully recovered during two offshore drilling exploratory programs. Results of geothermal data during previous field studies along the north continental margin, however, show that the gas hydrate sites are associated with high geothermal background in contrast to the other offshore ones where the gas hydrates are more likely to be found in the low geothermal regional backgrounds. There is a common interesting heat flow pattern during the two drilling expeditions that the gas hydrate occurrences coincide with the presences of comparatively low geothermal anomalies against the high thermal background which is mainly caused by concentrated fluid upward movements into the stability zone (GHSZ) detected by the surface heat flow measurements over the studied fields. The key point for understanding the coupling between the presences of the gas hydrates and heat flow pattern at regional scale is to know the cause of high heat flows and the origin of forming gases at depth. We propose that these high heat flows are attributed to elevated shallow fault-fissure system due to the tectonic activities. A remarkable series of vertical faults and fissures are common on the upper continental slope and the forming gases are thought to have migrated with hot advective fluid flows towards seafloor mainly via fault-fissure system from underlying source rocks which are deeper levels than those of the GHSZ. The present study is based on an extensive dataset on hydrate distribution and associated temperature field measurements collected in the vicinity of studied areas during a series of field expeditions organized within the framework of national widely collaborative projects. Those observations bring new insights to our growing understanding of the stability of this dynamic hydrate reservoir in the continental margin shallow subsurface, and alert us that occurrence patterns may be more complex than previously thought. So the future aim of this program is to better understand the factors constraining the distribution of hydrate deposits, and the processes involved in gas hydrate formation.

Sr-Nd-Pb isotope systematics of the Permian volcanic rocks in the northern margin of the Alxa Block (the Shalazhashan Belt) and comparisons with the nearby regions: Implications for a Permian rift setting?

NASA Astrophysics Data System (ADS)

Shi, Guanzhong; Wang, Hua; Liu, Entao; Huang, Chuanyan; Zhao, Jianxin; Song, Guangzeng; Liang, Chao

2018-04-01

The petrogenesis of the Permian magmatic rocks in the Shalazhashan Belt is helpful for us to understand the tectonic evolution of the Central Asian Orogenic Belt (CAOB) in the northern margin of the Alxa Block. The Permian volcanic rocks in the Shalazhashan Belt include basalts, trachyandesites and trachydacites. Our study shows that two basalt samples have negative εNd(t) values (-5.4 to -1.5) and higher radiogenic Pb values, which are relevant to the ancient subcontinental lithospheric mantle. One basalt sample has positive εNd(t) value (+10) representing mafic juvenile crust and is derived from depleted asthenosphere. The trachyandesites are dated at 284 ± 3 Ma with εNd(t) = +2.7 to +8.0; ISr = 0.7052 to 0.7057, and they are generated by different degrees of mixing between mafic magmas and crustal melts. The trachydacites have high εNd(t) values and slightly higher ISr contents, suggesting the derivation from juvenile sources with crustal contamination. The isotopic comparisons of the Permian magmatic rocks of the Shalazhashan Belt, the Nuru-Langshan Belt (representing the northern margin of the Alxa Block), the Solonker Belt (Mandula area) and the northern margin of the North China Craton (Bayan Obo area) indicate that the radiogenic isotopic compositions have an increasingly evolved trend from the south (the northern margins of the Alxa Block and the North China Craton) to the north (the Shalazhashan Belt and the Solonker Belt). Three end-member components are involved to generate the Permian magmatic rocks: the ancient subcontinental lithospheric mantle, the mafic juvenile crust or newly underplated mafic rocks that were originated from depleted asthenosphere, and the ancient crust. The rocks correlative with the mafic juvenile crust or newly underplated mafic rocks are predominantly distributed along the Shalazhashan Belt and the Solonker Belt, and the rocks derived from ancient, enriched subcontinental lithospheric mantle are mainly distributed along the northern margins of the Alxa Block and the North China Craton. The magmatic rock types, isotopic features and their temporal, spatial distributions suggest an extensional regime probably related to rifting.

The development and evolution of landform based on neotectonic movement: The Sancha river catchment in the southwestern China

NASA Astrophysics Data System (ADS)

Zhong, Lingmin; Xu, Mo; Yang, Yanna; Wang, Xingbing

2018-02-01

Neotectonics has changed the coupled process of endogenic and exogenic geological dynamics, which mold the modern landform. Geomorphologic analysis is essential for identifying and understanding the tectonic activity and indicates the responsive mechanism of the landform to tectonic activity. At first, this research reconstructed the twisted Shanpen period planation surface, computed the valley floor width-to-height ratio of Sancha river and extracted the cross sections marking the river terraces to analyze the characteristics of the neotectonics. And then, the relation between neotectonic movement and landform development was analyzed by dividing the landform types. At last, the spatial variation of landform evolution was analyzed by extracting the Hypsometric Integral of sub-catchments. The Sancha river catchment's neotectonic movement presents the tilt-lift of earth's crust from NW to SE, which is characterized by the posthumous activity of Yanshan tectonic deformation. The spatial distribution of river terraces indicates that Sancha river catchment has experienced at least four intermittent uplifts and the fault blocks at both the sides of Liuzhi-Zhijin basement fault have differentially uplifted since the late Pleistocene. As the resurgence of Liuzhi-Zhijin basement fault, the Sancha river catchment was broken into two relative independent landform units. The spatial variations of the landform types near the Sancha river and the sub-catchments' landform evolution are characterized by periodic replacement. The styles of geological structure have controlled the development of landform far away from the Sancha River and influenced the landform evolution. The posthumous activities of the secondary structure have resulted in the spatial variation of sub-catchments' landform evolution, which presents periodic replacement with local exceptions. The present study suggests that spatial variations of the development and evolution of modern landform of Sancha River catchment owe their genesis to the interplay between the hydrodynamic force and tectonic activity in the neotectonic period. Likewise, the application of geomorphic indicators also provides a new way to assess the regional crustal stability.

Tectono-sedimentary features in the Yap subduction zone, Western Pacific: constraints from latest integrated geophysical survey

NASA Astrophysics Data System (ADS)

Dong, D.; Zhang, G.; Bai, Y.; Fan, J.; Zhang, Z.

2017-12-01

The Yap subduction zone, western Pacific, is a typical structure related to the ridge subduction, but comparative shortage of the geophysical data makes the structural details unknown in this area. In this study, we present the latest and high-quality multi-beam swath bathymetry and multi-channel seismic data acquired synchronously in the year 2015 across the Yap subduction zone. Multichannel seismic and multi-beam data are mainly applied to investigate the topography of major tectonic units and stratigraphic structure in the Yap subduction zone and discuss the tectonic characteristics controlled by ridge subduction. It suggests that, Parece Vela Basin, as the regional sedimentary center, developed sedimentary layers nearly 800 meters thick. On the contrast, the horizontal sedimentary layers were not obviously identified in the Yap trench, where subduction erosion occurred. Caroline ridge changed the tectonic characteristics of subduction zone, and influenced magmatism of the Yap arc because of the special topography. The seismic profile clearly reveals landslide deposits at the upper slope break of the forearc, north of the Yap Island, which was identified as the fault notch denoting a lithological boundary in previous work. Detailed topography and geological structure of horst and graben in the north of Yap are depicted, and topographic high of Caroline ridge is supposed to bring greater bending and tension and the subsequent horst and graben belt. Multichannel seismic evidence has been provided for interpreting the expansion of Sorol Trough and its inferred age. A modified model for the Yap subduction zone evolution is proposed, incorporating three major tectonic events: proto-Yap Arc rupture in the Oligocene, collision of the Caroline Ridge and the Yap Trench in the Late Oligocene or Middle Miocene, and onset of the Sorol Trough rifting in the Late Miocene. Acknowledge: This study was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDA11030102), the National Natural Science Foundation of China (No. 41476042, 41506055 )

Developing an Education and Public Outreach (EPO) program for the Caltech Tectonics Observatory

NASA Astrophysics Data System (ADS)

Kovalenko, L.; Nadin, E.; Avouac, J.

2008-12-01

The Caltech Tectonics Observatory (TO) is an interdisciplinary center, focused on geological processes occurring at the boundaries of Earth's tectonic plates. The timescales of these processes span from a few tens of seconds (the typical duration of an earthquake) to tens of millions of years (the time it takes to build mountains). Over the past four years, the TO has brought together 15 Caltech faculty from different fields, several visiting scientists from around the globe, and a few tens of graduate students and postdoctoral students, collaborating on scientific projects. A major objective of the TO now is to develop an Education and Public Outreach (EPO) program. Our goals are to (1) stimulate the interest of students and the general public in Earth Sciences, particularly in the study of tectonic processes, (2) inform and educate the general public about TO discoveries and advancements, and (3) make available the data and techniques developed by the TO for use in classrooms of all levels. To this effect, we have been developing our website for accessibility by the general public and writing educational web articles on TO research. A recent well-visited example is "The science behind the recent 2008 earthquake in China." We distribute animations that illustrate the mechanisms of earthquakes and tsunamis, and the various techniques used by TO scientists in their scientific investigations. The TO website also provides access to geodetic data collected by TO instruments and to the source models of recent large earthquakes as analyzed by TO scientists. The TO hosts tours of its facilities for local elementary school students and is working on developing education modules for high school and undergraduate classes. We are now working on a plan to offer short courses over the summer for undergraduate and graduate students in other institutions, in order to train them to analyze a variety of data and use techniques developed by TO scientists.

China-U.S. Relations: Current Issues and Implications for U.S. Policy

DTIC Science & Technology

2008-10-09

United States willing to work cooperatively with China while encouraging Beijing to become a “responsible stakeholder” in the global system. U.S. Treasury...Secretary Henry Paulson in December 2006 established a U.S.-China Strategic Economic Dialogue with Beijing , the most senior regular dialogue yet held...beyond. Beijing’s response has led some Tibetan activists to add their voices to other calls urging a boycott of the Summer Olympics in Beijing in

China Naval Modernization: Implications for U.S. Navy Capabilities - Background and Issues for Congress

DTIC Science & Technology

2010-04-09

blunting the operations of those forces that do deploy forward. North Korea and Iran , as part of their defiance of international norms, are actively...section ‘Deter and Defeat Aggression in Anti-Access Environments,’ those are primarily capabilities needed for defeating China, not Iran , North Korea or... North Korea and Iran . John J. Tkacik, a former State Department China specialist, said the changes were probably ordered by the White House. "By

China, The Environmental Dragon: The Environmental Security Implications of China’s Rise to Great-Power Status

DTIC Science & Technology

2000-09-01

to endanger their ecosystem.”109 China has a national accrediting body for ISO 14000 environmental management system certification. A handful of...adopt the standard in order to make their job of enforcement and improvement of environmental management easier. A requirement by China’s accreditation ...body that all certification bodies register with it (it has yet to accredit any international organizations) has led to the development of a two-tier

U.S. National Security Implications of Chinese Involvement in Latin America

DTIC Science & Technology

2005-06-01

businessmen from both nations in attendance.𔃺 s 18buiese fro bot nain in attendance.I ! Mexico . Chinese trade with Mexico is significant and has been...corresponding imports from China increased by 476 percent.10 9 In 2004, bilateral trade between China and Mexico was more than $7 billion...representing a 44 percent increase over 2003.110 By contrast to other Latin American countries, however, Mexico has a trade deficit with China that is

Food distribution as a guarantee for nutrition and health: China's experience.

PubMed

Wang, V L

1976-01-01

In China, agriculture, health, education, and welfare are intricately woven as part of the development and its relationship to health programs, the strategy of food rationing and the "private plot" to improve nutrition and health, and the balance of food and population in the Chinese society. China's nutritional experience contributes significantly to understanding the role of "energy food" in the struggle against protein malnutrition and hunger. The author has outlined the implications for the developing countries.

China’s Participation in Anti-Piracy Operations off the Horn of Africa: Drivers and Implications

DTIC Science & Technology

2009-07-01

stakeholder” in resolving global issues , China may be opening the door for other cooperative efforts in the future. China’s naval cooperation in anti...cooperate on global issues of mutual interest. This is particularly important, panelists noted, because the U.S. will increasingly need China’s...to continue to “challenge China to participate as a responsible stakeholder” on global issues , and to provide positive feedback when it does so

Tectonic implications of the Indian Run Formation; a newly recognized sedimentary melange in the northern Virginia Piedmont

USGS Publications Warehouse

Drake, Avery Ala

1985-01-01

Sedimentary melange in the northeastern part of Fairfax County, Virginia, contains both mesoscopic and mappable fragments of Accotink Schist, Lake Barcroft Metasandstone, metagabbro, and ultramafic rocks as well as smaller fragments of other rock types. This melange was originally mapped as the Sykesville Formation, a major precursory sedimentary melange in northern Virginia and Maryland. The fragments of Accotink Schist and Lake Barcroft Metasandstone within the Sykesville were considered to be rip-ups of these units over which the Sykesville slid when finally emplaced. More recent study has shown that fragments of Accotink and Lake Barcroft are restricted to a certain area of sedimentary melange originally defined as Sykesville, and this part of the melange is now considered to be a separate mappable unit, here named the Indian Run Formation. The Indian Run underlies the sequence Accotink Schist and Lake Barcroft Metasandstone which is here formally named the Annandale Group. The Indian Run is intruded by the Occoquan Granite of Cambrian age, so it is of Cambrian or Late Proterozoic age. The Sykesville Formation (restricted) is a much more extensive unit than the Indian Run Formation and is characterized by its contained olistoliths of the Peters Creek Schist, the unit that tectonically overlies it. The Sykesville and Peters Creek constitute a precursory melange-allochthon pair which is here termed a 'tectonic motif.' The Indian Run-Annandale pair then forms a tectonically lower motif, and the overlying pair, the Yorkshire Formation-Piney Branch Complex, forms a tectonically higher motif. The Chopawamsic Formation and underlying sedimentary melange in the area south of Fairfax County may form a tectonic motif beneath the Indian Run-Annandale tectonic motif. Thus, three and perhaps four repetitions of precursory melange-allochthon pairs occur in northern Virginia. Other percursory melanges and motifs may occur in the Maryland Piedmont to the north. The tectonic setting of the motif formation and assemblage is uncertain at this time. A model involving the obduction of several separate sheets onto the ancestral North American continental margin is appealing in that it involves the closing and destruction of a marginal basin, a relatively simple concept. This model fails, however, to supply a source for the sediment necessary to form the precursory melanges. A trench-slope origin would supply the vast amount of needed sediment by accretion. The precursory melangeallochthon motifs would then be stacked near the base of the trench slope. This model is appealing and requires a rather complicated assemblage of continental, arc, and oceanic fragments, such as those that occur on many modern continental margins.

The Silurian Hoedongri Formation in the Taebaeksan Basin of Korea Revisited: its Significance in the Tectonic Reconstruction of East Asia

NASA Astrophysics Data System (ADS)

Chae, S.; Hong, J.; Jung, S.; Ree, J.

2011-12-01

The Silurian Hoedongri Formation of the Taebaeksan Basin of South Korea has been used as a key unit to the correlation of tectonic provinces of East Asia since the South China craton (or Yangtz block) contains Silurian-Devonian sequences as well as Cambrian-Ordovician ones in the Paleozoic basins while the North China craton (or Sino-Korea block) is devoid of Silurian-Devonian sequences. In the Biryongdong area near the type locality of the Hoedongri Formation, it has been reported that the gray limestone of the Hoedongri Formation unconformably overlies brownish gray limestone of the Ordovician Haengmae Formation. However, our detailed examination on the Biryongdong section reveals that both of the brownish gray and gray limestones are mylonitic marbles with the boundary between the two units being a healed fault breccia zone (~ 12 m thick). The main difference of the two units is that repeated cycles of plastic deformation and fracturing occurred in the underlying brownish gray marble ('Haengmae') while the gray marble ('Hoedongri') deformed mainly by intracrystalline plasticity. The mylonitic foliation strikes NW with a low to moderate dip angle (20-60°) to NE. The ridge-in-groove type lineation on foliation surface trends NNW. The shape-preferred foliation of elongated calcite grains are oblique to the mylonitic foliation defined by layers with a grain-size variation, indicating a top-to-the-SSE shear sense. The mylonitic marble consists of elongated remnant grains (80-120 μm) with deformation twins and dynamically recrystallized matrix grains (10-40 μm). Grain boundaries and twin boundaries are lobate or wavy, indicating dynamic boundary migration. Some layers of the gray mylonitic marble are composed entirely of larger (80-120 μm) elongated calcite grains. In the brownish gray mylonitic marble unit, layers of brittle fracturing overprinting mylonitic foliation occur. In some of these layers, fragments (several cm - tens of cm) of the mylonitic marble are angular to subangular with coarse calcite fillings between the fragments. In other layers, mylonitic marble fragments are elongated with matrix foliation wrapping around them. These features suggest repeated cycles of plastic deformation and fracturing. Tectonic significance of this shear zone (at least 90 m thick) is not clear at present, and the regional extent and absolute age constraint of the shear zone should be clarified.

Lacustrine fan delta deposition alongside intrabasinal structural highs in rift basins: an example from the Early Cretaceous Jiuquan Basin, Northwestern China

NASA Astrophysics Data System (ADS)

Zhang, Chengcheng; Muirhead, James D.; Wang, Hua; Chen, Si; Liao, Yuantao; Lu, Zongsheng; Wei, Jun

2018-01-01

Development of fan deltas alongside intrabasinal structural highs has been overlooked compared to those forming on basin margins. However, these fan deltas may provide important clues regarding the tectonic and climatic controls on deposition during rift development. This paper documents fan delta deposition alongside an intrabasinal structural high within the Early Cretaceous Xiagou Formation of the Jiuquan Basin, China, using subsurface geological and geophysical data. Deposits observed in drill core support fan delta deposition occurring almost exclusively through subaerial and subaqueous gravity flows. Subsurface mapping reveals a consistent decrease in the areal extent of fan deltas from lowstand to highstand system tracts, suggesting that deposition alongside the structural high is sensitive to lake-level changes. The temporal and spatial distribution of the fan deltas display retrogradational stacking patterns, where fan deltas exhibit a decreasing lateral extent up-sequence until fan delta deposition terminated and was replaced by deposition of fine-grained lacustrine deposits. The retrogradational stacking patterns observed alongside the intrabasinal structural high are not observed in fan deltas along the basin margin in the lower parts of the Xiagou Formation. Subsidence profiles also show differential subsidence across the basin during the earliest stages of this formation, likely resulting from border fault movements. These data suggest that non-uniform stacking patterns in the lower parts of the Xiagou Formation reflect basin-scale tectonic movements as the dominant control on synrift deposition patterns. However, later stages of Xiagou Formation deposition were characterized by uniform subsidence across the basin, and uniform retrogradational stacking patterns for fan deltas alongside the intrabasinal structural high and border fault. These observations suggest that basin-scale tectonic movements played a relatively limited role in controlling sediment deposition, and imply a potential change to regional-scale processes affecting fan delta deposition during later synrift stages. Climate change is favored here as the region-scale control on the uniform retrogradational fan delta stacking patterns. This assertion is supported by pollen assemblages, isotope signatures, and organic geochemical analyses, which collectively suggest a change from a humid to semi-arid environment during later synrift stages. We suggest that variations in stacking patterns between different fan delta systems can provide insights into the basin- and regional-scale processes that control rift basin deposition.

A review of the tectonic evolution of the Northern Pacific and adjacent Cordilleran Orogen

NASA Astrophysics Data System (ADS)

Jakob, Johannes; Gaina, Carmen; Johnston, Stephen T.

2014-05-01

Numerous plate kinematic models for the North Pacific realm have been developed since the advent of plate tectonics in the early seventies (e.g Atwater (1970), Mammerickx and Sharman (1988)). Although published kinematic models are consistent with the broad scale features of the North Pacific, the link between plate motions and the evolution of the North American Cordillera remains poorly understood. Part of the problem lies in conflicting interpretations of geological versus paleomagnetic data sets, with the result being a lack of consensus regarding: the paleolocation of key geological units; the paleogeography of terrane formation and amalgamation; the motion, boundaries and even existence of oceanic plates; and the character (e.g. trend of subduction) and position of plate boundaries within the northern Pacific basin. Remnants of the Farallon and Kula plates, and some short-lived microplates, demonstrate the complicated tectonic evolution of the oceanic realm west of the North American margin (e.g. Rea and Dixon (1983); McCrory and Wilson (2013); Shephard et al. (2013)). The creation and destruction of major tectonic plates and microplates has presumably left a record in the Cordilleran orogen of western North America. However, working backward from the geological relationships to plate reconstructions remains difficult. Here we investigate the relationship between the plate motions of the Pacific Ocean and the terrane movements in the North American Cordillera by revising the marine magnetic and gravity anomalies of the northern Pacific. In particular, we reevaluate plate boundaries at times of major changes in plate geometry of the Pacific, Kula, Chinook and Farallon plates from C34n onward. Our focus is also on the plate geometries of the Resurrection, Eshamy and Siletz-Crescent plates during the time between anomaly C26 and C12, and the links between plate interactions and on-shore tectonic events recorded in the geological record of Vancouver Island, including the accretion of the Pacific Rim and Crescent terranes to Wrangellia between C25 and C18. References: Atwater, T. (1970). Implications of plate tectonics for the Cenozoic tectonic evolution of western North America. Geological Society of America Bulletin, 81, 3513-3536. McCrory, P. a., & Wilson, D. S. (2013). A kinematic model for the formation of the Siletz-Crescent forearc terrane by capture of coherent fragments of the Farallon and Resurrection plates. Tectonics, 32, 1-19. doi:10.1002/tect.20045 Rea, D. K., & Dixon, J. M. (1983). Late Cretaceous and Paleogene tectonic evolution of the North Pacific Ocean. Earth and Planetary Science Letters, 65, 145-166. Shephard, G. E., Müller, R. D., & Seton, M. (2013). The tectonic evolution of the Arctic since Pangea breakup: Integrating constraints from surface geology and geophysics with mantle structure. Earth-Science Reviews, 124, 148-183. doi:10.1016/j.earscirev.2013.05.012 Mammerickx, J., & Sharman, G. F. (1988). Tectonic evolution of the North Pacific during the Cretaceous quiet period. Journal of Geophysical Research, 93(B4), 3009-3024. doi:10.1029/JB093iB04p03009

Dilution of 10Be in detrital quartz by earthquake-induced landslides: Implications for determining denudation rates and potential to provide insights into landslide sediment dynamics

NASA Astrophysics Data System (ADS)

West, A. Joshua; Hetzel, Ralf; Li, Gen; Jin, Zhangdong; Zhang, Fei; Hilton, Robert G.; Densmore, Alexander L.

2014-06-01

The concentration of 10Be in detrital quartz (10Beqtz) from river sediments is now widely used to quantify catchment-wide denudation rates but may also be sensitive to inputs from bedrock landslides that deliver sediment with low 10Beqtz. Major landslide-triggering events can provide large amounts of low-concentration material to rivers in mountain catchments, but changes in river sediment 10Beqtz due to such events have not yet been measured directly. Here we examine the impact of widespread landslides triggered by the 2008 Wenchuan earthquake on 10Beqtz in sediment samples from the Min Jiang river basin, in Sichuan, China. Landslide deposit material associated with the Wenchuan earthquake has consistently lower 10Beqtz than in river sediment prior to the earthquake. River sediment 10Beqtz decreased significantly following the earthquake downstream of areas of high coseismic landslide occurrence (i.e., with greater than ∼0.3% of the upstream catchment area affected by landslides), because of input of the 10Be-depleted landslide material, but showed no systematic changes where landslide occurrence was low. Changes in river sediment 10Beqtz concentration were largest in small first-order catchments but were still significant in large river basins with areas of 104-105 km. Spatial and temporal variability in river sediment 10Beqtz has important implications for inferring representative denudation rates in tectonically active, landslide-dominated environments, even in large basins. Although the dilution of 10Beqtz in river sediment by landslide inputs may complicate interpretation of denudation rates, it also may provide a possible opportunity to track the transport of landslide sediment. The associated uncertainties are large, but in the Wenchuan case, calculations based on 10Be mixing proportions suggest that river sediment fluxes in the 2-3 years following the earthquake increased by a similar order of magnitude in the 0.25-1 mm and the <0.25 mm size fractions, as determined from 10Beqtz mixing calculations and hydrological gauging, respectively. Such information could provide new insight into sediment transfer, with implications for secondary sediment-related hazards and for understanding the removal of mass from mountains.

Channel flow and localized fault bounded slice tectonics (LFBST): Insights from petrological, structural, geochronological and geospeedometric studies in the Sikkim Himalaya, NE India

NASA Astrophysics Data System (ADS)

Chakraborty, Sumit; Mukhopadhyay, Dilip K.; Chowdhury, Priyadarshi; Rubatto, Daniela; Anczkiewicz, Robert; Trepmann, Claudia; Gaidies, Fred; Sorcar, Nilanjana; Dasgupta, Somnath

2017-06-01

One of the enduring debates in the study of the Himalayan orogen (and continental collision zones in general) is whether the salient observed features are explained (a) by localized deformation along discrete, narrow fault zones/ductile shear zones separating individual blocks or slices (e.g. critical taper or wedge tectonic models), or (b) by distributed deformation dominated by wide zones of visco-plastic flow in the solid or a partially molten state (e.g. channel flow models). A balanced cross-section from Sikkim in the eastern Himalaya that is based on structural data and is drawn to satisfy petrological and geophysical constraints as well, is used in combination with information from petrology, geochronology, geospeedometry and microstructural data to address this question. We discuss that any tectonic model needs to be thermally, rheologically, geometrically and temporally viable in order to qualify as a suitable description of a system; models such as channel flow and critical taper are considered in this context. It is shown that channel flow models may operate with or without an erosional porthole (channel with tunnel and funnel mode vs. channels with only the tunnel mode) and that the predicted features differ significantly between the two. Subsequently, we consider a large body of data from Sikkim to show that a channel flow type model (in the tunneling without funneling mode), such as the ones of Faccenda et al. (2008), describes features formed at high temperatures very well, while features formed at lower temperatures are more consistent with the operation of localized, fault-bounded, slice tectonics, (LFBST, be it in the form of critical taper, wedge tectonics, or something else). Thus, the two modes are not competing, but collaborating, processes and both affect a given rock unit at different points of time during burial, metamorphism and exhumation. A transitional stage separates the two end-member styles of tectonic evolution. The proposed models bear similarities to those suggested by Mallet (1875) and Auden (1935) and mechanisms proposed by Beaumont and Jamieson (2010). We conclude by discussing some of the implications of such a model for motion on the major Himalayan faults, and by considering which features of any given rock are likely to record signatures of a particular style of tectonic evolution. Some directions for future research are suggested in the end.

Tectonics of Europa

NASA Astrophysics Data System (ADS)

Kattenhorn, S. A.; Hurford, T. A.

2007-12-01

This review of Europan tectonics previews a chapter of the forthcoming text "Europa". After the Voyager flyby of the icy moon Europa in 1979, models were developed that attributed pervasive surface fracturing to the effects of tidal forcing due to the gravitational pull of Jupiter. The late 1990s Galileo mission returned high resolution coverage of the surface, allowing a diverse range of tectonic features to be identified. Subsequent description, interpretation, and modeling of these features has resulted in significant developments in five key themes: (1) What drives the tectonics? (2) What are the formation mechanisms of the various types of tectonic features? (3) What are the implications for a subsurface ocean? (4) What is the nature and thickness of the ice shell? (5) Is Europa currently tectonically active? We highlight key developments pertaining to these fundamental issues, focusing on the following elements: (1) Many fracture patterns can be correlated with theoretical stress fields induced by diurnal tidal forcing and long-term effects of nonsynchronous rotation of the ice shell; however, these driving mechanisms alone cannot explain all fracturing. The tectonic fabric has likely been affected by additional contributing effects: tidal despinning, orbital evolution, interior differentiation, polar wander, finite obliquity, stresses due to shell thickening, endogenic forcing by convection and diapirism, and secondary effects driven by strike-slip faulting and plate flexure. (2) Due to the prevalence of global tension, a low lithostatic gradient, and the inherent weakness of ice, tectonic features likely have predominantly extensional primary formation mechanisms (e.g. surface fractures, ridges, and normal faults). There has been no categorical documentation of fracture development by compressive shearing. Even so, the constantly changing nature of the tidal stress field results in shearing reactivation of cracks being important for the morphologic and mechanical development of tectonic features. Hence, strike-slip faults are relatively common. Also, frictional shearing and heating has likely contributed to the construction of edifices along crack margins (i.e., ridges). If Europa has not recently expanded, crustal convergence (although elusive in Galileo images) is required to balance out new surface material created at spreading bands and may be accommodated locally along ridges or convergence bands. (3) Chains of concatenated curved cracks called cycloids provide convincing evidence of a subsurface ocean in that they must be the result of diurnal forcing of sufficient tidal amplitude to break the ice during a large portion of the Europan orbit, suggesting a tidally responding ocean beneath the ice shell. (4) Fracture mechanics reveals that the brittle portion of the ice shell is likely no more than a few km thick, but convection driven diapirism and crater morphologies necessitate a thicker shell overall (up to about 30 km). It is not known if fractures are able to penetrate this entire shell thickness. The brittle layer acts as a stagnant lid to plastic deformation in the ductile portion of the ice shell, resulting in localized brittle deformation. (5) Tectonic resurfacing has dominated the <70 my of visible geologic history. No evidence exists that Europa is currently tectonically active; however, this may be more a failing of the current state of the science rather than a lack of probability. A tectonically based answer to this question lies in a thorough analysis of geologically young surface fractures but would benefit from far more extensive coverage of the surface via a return mission to Europa.

The Concept of Greater China in Higher Education: Adoptions, Dynamics and Implications

ERIC Educational Resources Information Center

Lo, William Yat Wai

2016-01-01

Interpreting modernisation and globalisation in East Asia as processes of Westernisation creates confusion and discomfort among some academics from the region. To illustrate why such discomfort occurs, this article explores the changes in the higher education systems of Hong Kong, Taiwan and mainland China in terms of their "Chineseness"…

Research into Sexism in Language Testing & Its Implications to Language Testing in China

ERIC Educational Resources Information Center

Tao, Baiqiang

2007-01-01

This paper reviews foreign and domestic sexism research and practice in language testing and reveals that China lags behind in this sociolinguistics perspective in both theoretical study and practice. The paper indicates that sexism is represented in the listening comprehension section in National Matriculation English Test (NMET) after a case…

Household Context and Subjective Well-Being among the Oldest Old in China

ERIC Educational Resources Information Center

Chen, Feinian; Short, Susan E.

2008-01-01

This article investigates the importance of household context to subjective well-being among the oldest old (aged 80 years and older) in China. Using data from the Chinese Longitudinal Healthy Longevity Survey, the authors find that living arrangements have strong implications for elderly emotional health. First, living alone is associated with…

School Mapping Restructure in Rural China: Achievements, Problems and Implications

ERIC Educational Resources Information Center

Zhao, Dan; Parolin, Bruno

2012-01-01

This study considers the experience of school mapping restructure (SMR) in areas of rural China. It aims to understand what happened after SMR implementation. Through a combination of instruments such as questionnaires, interviews and document analysis, the study finds that SMR has impacted positively on the development of education in terms of…

New data from fringing-reef cores for the mid-Holocene higher sea level in Hainan Island, northern South China Sea

NASA Astrophysics Data System (ADS)

Yao, Yantao; Zhan, Wenhuan; Sun, Jie

2017-04-01

Most previous research on sea level indicators (including beachrock, abrasion platforms, notches and coral reefs) from coast of northern South China Sea suggested a higher sea level in the mid-Holocene. Microatolls, considered to be one of the most reliable indicators, led to an estimation of 2 to 3 m or even more higher sea levels in the mid-Holocene at southwest Leizhou Peninsula. Volcanic activities, however, occurred at several stages during the Quaternary at southern Leizhou Peninsula and northern Hainan Island, indicating a tectonically unstable local crust. Comprehensive comparison of microatolls between the volcanic and the non-volcanic coasts implied obvious uplift of the volcanic coast, where elevation of microatolls was higher than those on the non-volcanic coast. In addition, microatolls from the non-volcanic coast universally demonstrated a mid-Holocene higher sea level of less than 1 m. Similar studies to date at some tectonically stable locations, distant from the major glaciation centers (the far-field), provided evidence that the mid-Holocene sea level was not as high as that estimated before. On the longest and also the widest fringing reef of Hainan Island, 10 cores were drilled in a transect approximately perpendicular to coastline. Upper and lower unconformities for the layer of Holocene marine sediments witnessed the Holocene transgression and regression, respectively. U-series and AMS14C ages of in-situ surface corals and deposits from the unconformities, compiled with sedimentary characteristics, announced a highest sea level of 1.18 m in 5.30 cal ka BP. The rapid sea level rise mainly occurred in 6.25 5.75 cal ka BP at a rate up to 11.4 mm/a. From 5.30 cal ka BP to 4.50 cal ka BP, it can be regarded as a relative sea level stand, for most surface fossil microatolls on reef flat lived in this period. Since then there might be a sudden and fast sea level fall in 4.50 4.14 cal ka BP, resulting in fast exposure of the initial reef flat and then fast covering of sand dunes or beachrocks. As a result, fossil microtalls on the initial reef flat were well preserved, which were very important to indicating the mid-Holocene higher sea level. Acknowledgement: This research was supported by the National Program on Key Basic Research Project of China (2013CB956104)、National Natural Science Foundation of China (41376063) and the Chinese-Polish collaborated project ERES.

Landslide risk mapping and modeling in China

NASA Astrophysics Data System (ADS)

Li, W.; Hong, Y.

2015-12-01

Under circumstances of global climate change, tectonic stress and human effect, landslides are among the most frequent and severely widespread natural hazards on Earth, as demonstrated in the World Atlas of Natural Hazards (McGuire et al., 2004). Every year, landslide activities cause serious economic loss as well as casualties (Róbert et al., 2005). How landslides can be monitored and predicted is an urgent research topic of the international landslide research community. Particularly, there is a lack of high quality and updated landslide risk maps and guidelines that can be employed to better mitigate and prevent landslide disasters in many emerging regions, including China (Hong, 2007). Since the 1950s, landslide events have been recorded in the statistical yearbooks, newspapers, and monographs in China. As disasters have been increasingly concerned by the government and the public, information about landslide events is becoming available from online news reports (Liu et al., 2012).This study presents multi-scale landslide risk mapping and modeling in China. At the national scale, based on historical data and practical experiences, we carry out landslide susceptibility and risk mapping by adopting a statistical approach and pattern recognition methods to construct empirical models. Over the identified landslide hot-spot areas, we further evaluate the slope-stability for each individual site (Sidle and Hirotaka, 2006), with the ultimate goal to set up a space-time multi-scale coupling system of Landslide risk mapping and modeling for landslide hazard monitoring and early warning.

A comparison of the South China Sea and Canada Basin: two small marginal ocean basins with hyper-extended margins and central zones of sea-floor spreading.

NASA Astrophysics Data System (ADS)

Li, L.

2015-12-01

Both the South China Sea and Canada Basin preserve oceanic spreading centres and adjacent passive continental margins characterized by broad COT zones with hyper-extended continental crust. We have investigated the nature of strain accommodation in the regions immediately adjacent to the oceanic spreading centres in these two basins using 2-D backstripping subsidence reconstructions, coupled with forward modelling constrained by estimates of upper crustal extensional faulting. Modelling is better constrained in the South China Sea but our results for the Beaufort Sea are analogous. Depth-dependent extension is required to explain the great depth of both basins because only modest upper crustal faulting is observed. A weak lower crust in the presence of high heat flow is suggested for both basins. Extension in the COT may continue even after sea-floor spreading has ceased. The analogous results for the two basins considered are discussed in terms of (1) constraining the timing and distribution of crustal thinning along the respective continental margins, (2) defining the processes leading to hyper-extension of continental crust in the respective tectonic settings and (3) illuminating the processes that control hyper-extension in these basins and more generally.

China Naval Modernization: Implications for U.S. Navy Capabilities-Background and Issues for Congress

DTIC Science & Technology

2009-09-23

China Sea, a Chinese reserve vessel squadron has been established,” foreign ministry spokesman Qin Gang told a regular briefing. ... No details were...Bill Gertz, “China Sub Secretly Stalked U.S. Fleet,” Washington Times, November 13, 2006: 13; Philip Creed, “Navy Confirms Chinese Sub Spotted Near...Fallon Confirms Chinese Stalked Carrier,” NavyTimes.com, November 14, 2006; Bill Gertz, “Admiral Says Sub Risked A Shootout,” Washington Times, November