Noble gases fingerprint a metasedimentary fluid source in the Macraes orogenic gold deposit, New Zealand

NASA Astrophysics Data System (ADS)

Goodwin, Nicholas R. J.; Burgess, Ray; Craw, Dave; Teagle, Damon A. H.; Ballentine, Chris J.

2017-02-01

The world-class Macraes orogenic gold deposit (˜10 Moz resource) formed during the late metamorphic uplift of a metasedimentary schist belt in southern New Zealand. Mineralising fluids, metals and metalloids were derived from within the metasedimentary host. Helium and argon extracted from fluid inclusions in sulphide mineral grains (three crush extractions from one sample) have crustal signatures, with no evidence for mantle input (R/Ra = 0.03). Xenon extracted from mineralised quartz samples provides evidence for extensive interaction between fluid and maturing organic material within the metasedimentary host rocks, with 132Xe/36Ar ratios up to 200 times greater than air. Similarly, I/Cl ratios for fluids extracted from mineralised quartz are similar to those of brines from marine sediments that have interacted with organic matter and are ten times higher than typical magmatic/mantle fluids. The Macraes mineralising fluids were compositionally variable, reflecting either mixing of two different crustal fluids in the metasedimentary pile or a single fluid type that has had varying degrees of interaction with the host metasediments. Evidence for additional input of meteoric water is equivocal, but minor meteoric incursion cannot be discounted. The Macraes deposit formed in a metasedimentary belt without associated coeval magmatism, and therefore represents a purely crustal metamorphogenic end member in a spectrum of orogenic hydrothermal processes that can include magmatic and/or mantle fluid input elsewhere in the world. There is no evidence for involvement of minor intercalated metabasic rocks in the Macraes mineralising system. Hydrothermal fluids that formed other, smaller, orogenic deposits in the same metamorphic belt have less pronounced noble gas and halogen evidence for crustal fluid-rock interaction than at Macraes, but these deposits also formed from broadly similar metamorphogenic processes.

Extreme variation of sulfur isotopic compositions in pyrite from the Qiuling sediment-hosted gold deposit, West Qinling orogen, central China: An in situ SIMS study with implications for the source of sulfur

USGS Publications Warehouse

Chen, Lei; Li, Xian-hua; Li, Jian-wei; Hofstra, Albert H.; Liu, Yu; Koenig, Alan E.

2015-01-01

High spatial resolution textural (scanning electron microscope (SEM)), chemical (electron microprobe (EMP)) and laser ablation-inductively coupled plasma-mass spec- trometry (LA-ICP-MS)), and sulfur isotopic (secondary ion mass spectrometry (SIMS)) analyses of pyrite from the Qiuling sediment-hosted gold deposit (232±4 Ma) in the West Qinling orogen, central China were conducted to distinguish pyrite types and gain insights into the source and evolution of sulfur in hydrothermal fluids. The results reveal an enormous variation (−27.1 to +69.6‰) in sulfur isotopic composition of pyrite deposited during three paragenetic stages. Pre-ore framboidal pyrite, which is characterized by low concentra- tions of As, Au, Cu, Co, and Ni, has negative δ34S values of −27.1 to −7.6‰ that are interpreted in terms of bacterial re- duction of marine sulfate during sedimentation and diagenesis of the Paleozoic carbonate and clastic sequences, the predom- inant lithologies in the deposit area, and the most important hosts of many sediment-hosted gold deposits throughout the West Qinling orogen. The ore-stage hydrothermal pyrite con- tains high concentrations of Au, As, Cu, Sb, Tl, and Bi and hasa relatively narrow range of positive δ34S values ranging from +8.1 to +15.2‰. The sulfur isotope data are comparable to those of ore pyrite from many Triassic orogenic gold deposits and Paleozoic sedimentary exhalative (SEDEX) Pb-Zn de- posits in the West Qinling orogen, both being hosted mainly in the Devonian sequence. This similarity indicates that sulfur, responsible for the auriferous pyrite at Qiuling, was largely derived from the metamorphic devolatization of Paleozoic marine sedimentary rocks. Post-ore-stage pyrite, which is sig- nificantly enriched in Co and Ni but depleted in Au and As, has unusually high δ34S values ranging from +37.4 to +69.6 ‰, that are interpreted to result from thermochemical reduc- tion of evaporite sulfates in underlying Cambrian sedimentary

The Kharapeh orogenic gold deposit: Geological, structural, and geochemical controls on epizonal ore formation in West Azerbaijan Province, Northwestern Iran

USGS Publications Warehouse

Niroomand, Shojaeddin; Goldfarb, Richard J.; Moore, Farib; Mohajjel, Mohammad; Marsh, Erin E.

2011-01-01

The Kharapeh gold deposit is located along the northwestern margin of the Sanandaj–Sirjan Zone (SSZ) in the West Azerbaijan province, Iran. It is an epizonal orogenic gold deposit formed within the deformed zone between central Iran and the Arabian plate during the Cretaceous–Tertiary Zagros orogeny. The deposit area is underlain by Cretaceous schist and marble, as well as altered andesite and dacite dikes. Structural analysis indicates that the rocks underwent tight to isoclinal recumbent folding and were subsequently co-axially refolded to upright open folds during a second deformation. Late- to post-tectonic Cenozoic granites and granodiorites occur northeast of the deposit area. Mineralization mainly is recognized within NW-trending extensional structures as veins and breccia zones. Normal faults, intermediate dikes, and quartz veins, oriented subparallel to the axial surface of the Kharapeh antiform, indicate synchronous extension perpendicular to the fold axis during the second folding event. The gold-bearing quartz veins are >1 km in length and average about 6 m in width; breccia zones are 10–50 m in length and ≤1 m in width. Hydrothermal alteration mainly consists of silicification, sulfidation, chloritization, sericitization, and carbonatization. Paragenetic relationships indicate three distinct stages—replacement and silicification, brecciation and fracture filling, and cataclastic brecciation—with the latter two being gold-rich. Fluid inclusion data suggest mineral deposition at temperatures of at least 220–255°C and depths of at least 1.4–1.8 km, from a H2O–CO2±CH4 fluid of relatively high salinity (12–14 wt.% NaCl equiv.), which may reflect metamorphism of passive margin carbonate sequences. Ore fluid δ18O values between about 7‰ and 9‰ suggest no significant meteoric water input, despite gold deposition in a relatively shallow epizonal environment. Similarities to other deposits in the SSZ suggest that the deposit formed as

Multiple sulfur isotopes monitor fluid evolution of an Archean orogenic gold deposit

NASA Astrophysics Data System (ADS)

LaFlamme, Crystal; Sugiono, Dennis; Thébaud, Nicolas; Caruso, Stefano; Fiorentini, Marco; Selvaraja, Vikraman; Jeon, Heejin; Voute, François; Martin, Laure

2018-02-01

The evolution of a gold-bearing hydrothermal fluid from its source to the locus of gold deposition is complex as it experiences rapid changes in thermochemical conditions during ascent through the crust. Although it is well established that orogenic gold deposits are generated during time periods of abundant crustal growth and/or reworking, the source of fluid and the thermochemical processes that control gold precipitation remain poorly understood. In situ analyses of multiple sulfur isotopes offer a new window into the relationship between source reservoirs of Au-bearing fluids and the thermochemical processes that occur along their pathway to the final site of mineralisation. Whereas δ34S is able to track changes in the evolution of the thermodynamic conditions of ore-forming fluids, Δ33S is virtually indelible and can uniquely fingerprint an Archean sedimentary reservoir that has undergone mass independent fractionation of sulfur (MIF-S). We combine these two tracers (δ34S and Δ33S) to characterise a gold-bearing laminated quartz breccia ore zone and its sulfide-bearing alteration halo in the (+6 Moz Au) structurally-controlled Archean Waroonga deposit located in the Eastern Goldfields Superterrane of the Yilgarn Craton, Western Australia. Over 250 analyses of gold-associated sulfides yield a δ34S shift from what is interpreted as an early pre-mineralisation phase, with chalcopyrite-pyrrhotite (δ34S = +0.7‰ to +2.9‰) and arsenopyrite cores (δ34S = ∼-0.5‰), to a syn-mineralisation stage, reflected in Au-bearing arsenopyrite rims (δ34S = -7.6‰ to +1.5‰). This shift coincides with an unchanging Δ33S value (Δ33S = +0.3‰), both temporally throughout the Au-hosting hydrothermal sulfide paragenesis and spatially across the Au ore zone. These results indicate that sulfur is at least partially recycled from MIF-S-bearing Archean sediments. Further, the invariant nature of the observed MIF-S signature demonstrates that sulfur is derived from a

Physical and chemical controls on ore shoots - insights from 3D modeling of an orogenic gold deposit

NASA Astrophysics Data System (ADS)

Vollgger, S. A.; Tomkins, A. G.; Micklethwaite, S.; Cruden, A. R.; Wilson, C. J. L.

2016-12-01

Many ore deposits have irregular grade distributions with localized elongate and well-mineralized rock volumes commonly referred to as ore shoots. The chemical and physical processes that control ore shoot formation are rarely understood, although transient episodes of elevated permeability are thought to be important within the brittle and brittle-ductile crust, due to faulting and fracturing associated with earthquake-aftershock sequences or earthquake swarms. We present data from an orogenic gold deposit in Australia where the bulk of the gold is contained in abundant fine arsenopyrite crystals associated with a fault-vein network within tight upright folds. The deposit-scale fault network is connected to a deeper network of thrust faults (tens of kilometers long). Using 3D implicit modeling of geochemical data, based on radial basis functions, gold grades and gold-arsenic element ratios were interpolated and related to major faults, vein networks and late intrusions. Additionally, downhole bedding measurements were used to model first order (mine-scale) fold structures. The results show that ore shoot plunges are not parallel with mine-scale or regional fold plunges, and that bedding parallel faults related to flexural slip folding play a pivotal role on ore shoot attitudes. 3D fault slip and dilation tendency analysis indicate that fault reactivation and formation of linking faults are associated with large volumes of high-grade ore. We suggest slip events on the large-scale thrust network allowed mineralizing fluids to rapidly migrate over large distances and become supersaturated in elements such as gold, promoting widespread precipitation and high nucleation densities of arsenopyrite upon fluid-rock interaction at trap sites within the deposit.

Mineral potential tracts for orogenic, Carlin-like, and epithermal gold deposits in the Islamic Republic of Mauritania, (phase V, deliverable 69): Chapter H in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Goldfarb, Richard J.; Marsh, Erin; Anderson, Eric D.; Horton, John D.; Finn, Carol A.; Beaudoin, Georges

2015-01-01

A preliminary evaluation of these gold data can be used to develop broad, firstorder tracts defining favorable and permissive areas for gold resources; detailed metamorphic and structural maps are required for more detailed future tract definition. Such a first-order assessment can, nonetheless, broadly identify four tracts of gold resource potential. Three of these are favorable for discovery of new orogenic gold deposits. One tract, although not favorable, is nevertheless permissive for discovery of epithermal gold deposits. Tract 1 is defined by favorable medium metamorphic grade greenstone belts within vast areas of unfavorable high metamorphic grade, Mesoarchean and Paleoproterozoic granite-gneiss basement of the Rgueïbat Shield. Faults >200 km in length following the general strike of the greenstone belts; lineament intersections with both exposed and buried parts of greenstone belts within 500 m of the surface, as defined by aeromagnetic data (Finn and Anderson, 2015); and areas of banded iron formation (BIF) in the belts are particularly favorable areas for hosting gold resources in orogenic gold deposits within and along the margins of the greenstone belts. Tracts 2 and 3, also for orogenic gold, reflect the favorable Proterozoic-Cambrian metamorphic rocks of the Northern and Southern Mauritanides, with >200-km-long faults following the general strike of the range, and areas underlain by ultramafic and BIF rocks being particularly favorable. Outcrops of Triassic-Jurassic igneous rocks along the margins of the Taoudeni Basin define tract 4, which is permissive for epithermal gold deposits. Although extensive data are lacking for the area, carbonate units along the northern side of the Taoudeni Basin could be considered permissive host rocks for Carlin-type mineralization, but the deep-water carbonate lithologies are typically not favorable for such. 

Geological characteristics and ore-forming process of the gold deposits in the western Qinling region, China

NASA Astrophysics Data System (ADS)

Liu, Jiajun; Liu, Chonghao; Carranza, Emmanuel John M.; Li, Yujie; Mao, Zhihao; Wang, Jianping; Wang, Yinhong; Zhang, Jing; Zhai, Degao; Zhang, Huafeng; Shan, Liang; Zhu, Laimin; Lu, Rukui

2015-05-01

The western Qinling, belonging to the western part of the Qinling-Dabie-Sulu orogen between the North China Block and South China Block, is one of the most important gold regions in China. Isotopic dates suggest that the Mesozoic granitoids in the western Qinling region emplaced during the Middle-Late Triassic, and the deposits formed during the Late Triassic. Almost all gold deposits in the western Qinling region are classified as orogenic, Carlin-type, and Carlin-like gold deposits, and they are the products of Qinling Orogenesis caused by the final collision between the North China Block and the South China Block. The early subduction of the Mian-Lue oceanic crust and the latter collision between South Qinling Terrane and the South China Block along the Mian-Lue suture generated lithosphere-scale thermal anomalies to drive orogen-scale hydrothermal systems. The collision-related magmatism also provided heat source for regional ore-forming fluids in the Carlin-like gold deposits. Orogenic gold deposits such as Huachanggou, Liziyuan, and Baguamiao lie between the Shang-Dan and Mian-Lue sutures and are confined to WNW-trending brittle-ductile shear zones in Devonian and Carboniferous greenschist-facies metasedimentary rocks that were highly-deformed and regionally-metamorphosed. These deposits are typical orogenic gold deposits and formed within a Late Triassic age. The deposits show a close relationship between Au and Ag. Ores contain mainly microscopic gold, and minor electrum and visible gold, along with pyrite. The ore-forming fluids were main metamorphic fluids. Intensive tectonic movements caused by orogenesis created fluid-migrating channels for precipitation locations. Although some orogenic gold deposits occur adjacent to granitoids, mineralization is not synchronous with magmatism; that is, the granitoids have no genetic relations to orogenic gold deposits. As ore-forming fluids converged into dilated fractures during the extension stage of orogenesis

The Tintina Gold Belt - A global perspective

USGS Publications Warehouse

Goldfarb, Richard J.; Hart, Craig J.R.; Miller, Marti L.; Miller, Lance D.; Farmer, G. Lang; Groves, David I.; Tucker, Terry L.; Smith, Moira T.

2000-01-01

The so-called Tintina Gold Belt extends for more than 1000 km along the length of the northern North American Cordillera. Middle to Late Cretaceous Au deposits within the belt have various similar characteristics, among which are a spatial and temporal association with magmatism; Bi-W-Te signatures in deposits hosted by granitod stocks and As-Sb signatures where hosted by sedimentary rocks and dyke systems; and δ180 values consistently > 12 per mil for Au-bearing quartz. Nevertheless significant differences in structural styles, levels of deposit emplacement, ore-fluid chemistry, and Au grades suggest that the characteristics represent a broad range of deposit types. Many of these are best classified as orogenic Au deposits in the Yukon-Tanana terrane, as epithermal and porphyry-style Au deposits in the Kuskokwim region, and as Au-bearing, granite-related veins and stockworks, replacements, and skarns, as well as associated polymetallic lodes, in central Yukon. The diverse types of Au deposits and associated plutons of the Tintina Gold Belt collectively define a 45-m.y.-long period of arc magmatism that migrated northwesterly, for about 1000 km, across the active collisional margin of Cretaceous northwestern North America. The initiation of fluid flow and plutonism in Albian time seems to correlate with the onset of oblique subduction and dextral strike-slip on the Denali-Farewell, Tintina-Kaltag, and related fault systems. Initial Au-vein formation and subduction-related magmatism at about 115-110 Ma (e.g., including the Goodpaster and Fortymile districts), within the seaward side of the Yukon-Tanana terrane, correlate with the arrival of the Wrangellia superterrane off the continental margin. Dextral translation of the allochthonous Wrangellia block was associated with the migration of the thermal pulse to the northwest at about 95-90 Ma. Orogenic (or so­ called mesotherrnal) and granitoid-related Au deposits formed across the width of the Yukon

Mineralisation footprints and regional timing of the world-class Siguiri orogenic gold district (Guinea, West Africa)

NASA Astrophysics Data System (ADS)

Lebrun, Erwann; Thébaud, Nicolas; Miller, John; Roberts, Malcolm; Evans, Noreen

2017-04-01

Siguiri is a world-class orogenic gold district hosted in the weakly metamorphosed Upper Birimian to Lower Tarkwa Group sedimentary rocks of the Siguiri Basin (Guinea). The district is characterised by a protracted deformation history associated with four main deformation events: D1S is a N-S compression; D2S is an E-W compression progressively evolving into an early-D3S transpression and then into a late-D3S NNW-SSE transtension and D4S is a NE-SW compression. Field observations, petrography and geochemistry at three key deposits of the Siguiri district (Bidini, Sintroko PB1 and Kosise) suggest a polyphase hydrothermal history that can be subdivided into four hydrothermal events. The first hydrothermal event was associated with the development of barren bedding-parallel and en-echelon V2S quartz-dominated-(pyrite) veins. The second hydrothermal event is characterised by the development of V3A pyrite-ankerite veins late during D3S. Laser ablation-ICP-MS data show that this vein set contains high gold contents of up to 43.3 ppm, in substitution in pyrite crystal lattice, representing a minor first gold mineralisation event. The third and most prominently developed hydrothermal event is late D3S and represents the second and principal gold mineralisation event. This mineralisation event led to two distinct mineralisation textures. The first texture is best exposed in the Kosise deposit and is characterised by gold-bearing quartz-ankerite-arsenopyrite conjugate V3B veins. Although the bulk of the gold is hosted in native gold grains in V3B veins, LA-ICP-MS analyses show that gold also substitutes in the arsenopyrite crystal lattice (up to 55.5 ppm). The second mineralisation texture is best expressed in the Sanu Tinti deposit and consists of disseminated barren pyrite hosted in a polymict conglomerate. The second and third hydrothermal events are both structurally controlled by a series of early-D3S N-S, NE-SW, WNW-ESE and E-W sub-vertical incipient structures

Extension and gold mineralisation in the hanging walls of active convergent continental shear zones

NASA Astrophysics Data System (ADS)

Upton, Phaedra; Craw, Dave

2014-07-01

Orogenic gold-bearing quartz veins form in mountain belts adjacent to convergent tectonic boundaries. The vein systems, hosted in extensional structures within compressively deformed rocks, are a widespread feature of these orogens. In many cases the extensional structures that host gold-bearing veins have been superimposed on, and locally controlled by, compressional structures formed within the convergent orogen. Exploring these observations within the context of a three-dimensional mechanical model allows prediction of mechanisms and locations of extensional zones within convergent orogens. Our models explore the effect of convergence angle and mid-crustal strength on stress states and compare them to the Southern Alps and Taiwan. The dilatation zones coincide with the highest mountains, in the hanging walls of major plate boundary faults, and can extend as deep as the brittle-ductile transition. Extensional deformation is favoured in the topographic divide region of oblique orogens with mid-lower crustal rheology that promotes localisation rather than diffuse deformation. In the near surface, topography influences the stress state to a depth approximately equal to the topographic relief, bringing the rock closer to failure and rotating σ1 to near vertical. The distribution of gold-bearing extensional veins may indicate the general position of the topographic divide within exhumed ancient orogens.

Paleozoic–early Mesozoic gold deposits of the Xinjiang Autonomous Region, northwestern China

USGS Publications Warehouse

Rui, Zongyao; Goldfarb, Richard J.; Qiu, Yumin; Zhou, T.; Chen, R.; Pirajno, Franco; Yun, Grace

2002-01-01

The late Paleozoic–early Mesozoic tectonic evolution of Xinjiang Autonomous Region, northwestern China provided a favorable geological setting for the formation of lode gold deposits along the sutures between a number of the major Eastern Asia cratonic blocks. These sutures are now represented by the Altay Shan, Tian Shan, and Kunlun Shan ranges, with the former two separated by the Junggar basin and the latter two by the immense Tarim basin. In northernmost Xinjiang, final growth of the Altaid orogen, southward from the Angara craton, is now recorded in the remote mid- to late Paleozoic Altay Shan. Accreted Early to Middle Devonian oceanic rock sequences contain typically small, precious-metal bearing Fe–Cu–Zn VMS deposits (e.g. Ashele). Orogenic gold deposits are widespread along the major Irtysh (e.g. Duyolanasayi, Saidi, Taerde, Kabenbulake, Akexike, Shaerbulake) and Tuergen–Hongshanzui (e.g. Hongshanzui) fault systems, as well as in structurally displaced terrane slivers of the western Junggar (e.g. Hatu) and eastern Junggar areas. Geological and geochronological constraints indicate a generally Late Carboniferous to Early Permian episode of gold deposition, which was coeval with the final stages of Altaid magmatism and large-scale, right-lateral translation along older terrane-bounding faults. The Tian Shan, an exceptionally gold-rich mountain range to the west in the Central Asian republics, is only beginning to be recognized for its gold potential in Xinjiang. In this easternmost part to the range, northerly- and southerly-directed subduction/accretion of early to mid-Paleozoic and mid- to late Paleozoic oceanic terranes, respectively, to the Precambrian Yili block (central Tian Shan) was associated with 400 to 250 Ma arc magmatism and Carboniferous through Early Permian gold-forming hydrothermal events. The more significant resulting deposits in the terranes of the southern Tian Shan include the Sawayaerdun orogenic deposit along the Kyrgyzstan

Gold deposit styles and placer gold characterisation in northern and east-central Madagascar

USGS Publications Warehouse

Pitfield, Peter E. J; Styles, Michael T.; Taylor, Cliff D.; Key, Roger M.; Bauer,; Ralison, A

2009-01-01

Microchemical characterisation of bedrock and placer gold grains from six gold districts within the Archaean domains and intervening Neoproterozoic Anaboriana-Manampotsy belt of northern and east-central Madagascar show few opaque inclusions (e.g pyrrhotite, Bi tellurides) but wide range of Ag contents (40wt%). Some districts exhibit multiple source populations of grains. The ‘greenstone belt’ terranes have an orogenic gold signature locally with an intrusion-related to epithermal overprint. Proterozoic metasediments with felsic to ultramafic bodies yield dominantly intrusion-related gold. A high proportion of secondary gold (<0.5wt% Ag) is related to recycling of paleoplacers and erosion of post-Gondwana planation surfaces and indicates that some mesothermal gold systems were already partially to wholly removed by erosion by the PermoTriassic.

Geochemical modeling of orogenic gold deposit using PCANN hybrid method in the Alut, Kurdistan province, Iran

NASA Astrophysics Data System (ADS)

Mohammadzadeh, Mohammadjafar; Nasseri, Aynur

2018-03-01

In this paper stream sediments based geochemical exploration program with the aim of delineating potentially promising areas by a comprehensive stepwise optimization approach from univariate statistics, PCA, ANN, and fusion method PCANN were under taken for an orogenic gold deposit located in the Alut, Kurdistan province, NW of Iran. At first the data were preprocessed and then PCA were applied to determine the maximum variability directions of elements in the area. Subsequently the artificial neural network (ANN) was used for quick estimation of elemental concentration, as well as discriminating anomalous populations and intelligent determination of internal structure among the data. However, both the methods revealed constraints for modeling. To overcome the deficiency and shortcoming of each individual method a new methodology is presented by integration of both "PCA & ANN" referred as PCANN method. For integrating purpose, the detected PCs pertinent to ore mineralization selected and intruded to neural network structure, as a result different MLPs with various algorithms and structures were produced. The resulting PCANN maps suggest that the gold mineralization and its pathfinder elements (Au, Mo, W, Bi, Sb, Cu, Pb, Ag & As) are associated with metamorphic host rocks intruded by granite bodies in the Alut area. In addition, more concealed and distinct Au anomalies with higher intensity were detected, confirming the privileges of the method in evaluating susceptibility of the area in delineating new hidden potential zones. The proposed method demonstrates simpler network architecture, easy computational implementation, faster training speed, as well as no need to consider any primary assumption about the behavior of data and their probability distribution type, with more satisfactory predicting performance for generating gold potential map of the area. Comparing the results of three methods (PCA, ANN and PCANN), representing the higher efficiency and more

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.

Age constraints on Tarkwaian palaeoplacer and lode-gold formation in the Tarkwa-Damang district, SW Ghana

USGS Publications Warehouse

Pigois, J.-P.; Groves, D.I.; Fletcher, I.R.; McNaughton, N.J.; Snee, L.W.

2003-01-01

Two major epigenetic gold-forming events are recorded in the world-class gold province of southwest Ghana. A pre-Tarkwaian event was the source of the world-class Tarkwa palaeoplacers whereas post-Birimian and Tarkwaian deformation, which was related to the Eburnean orogeny, gave rise to the world-class (e.g. Prestea) to giant (e.g. Obuasi) orogenic gold deposits which have made the region famous for more than 2,500 years. A maximum age of 2133 ?? 4 Ma for Tarkwaian sedimentation is provided by 71 of 111 concordant SHRIMP II U Pb dates from detrital zircons in Tarkwaian clastic rocks from Damang and Bippo Bin, northeast of Tarkwa. The overall data distribution broadly overlaps the relatively poorly constrained ages of Birimian volcanism and associated Dixcove-type granitoid emplacement, indicating syntectonic development of the Tarkwaian sedimentary basin. These zircon ages argue against derivation of the palaeoplacer gold from an orogenic gold source related to the compressional phase of an orogeny significantly older than the Eburnean orogeny. Instead, they suggest that the gold source was either orogenic gold lodes related to an earlier compressional phase of a diachronous Eburnean orogeny or ca. 2200-2100 Ma intrusion-related gold lode. The CO2-rich fluid inclusions in associated vein-quartz pebbles are permissive of either source. At the Damang deposit, an epigenetic, orogenic lode-gold system clearly overprinted, and sulphidised low-grade palaeoplacer hematite magnetite gold occurrences in the Banket Series conglomerate within the Tarkwaian sedimentary sequence. Gold mineralisation is demonstrably post-peak metamorphism, as gold-related alteration assemblages overprint metamorphic assemblages in host rocks. In alteration zones surrounding the dominant, subhorizontal auriferous quartz veins, there are rare occurrences of hydrothermal xenotime which give a SHRIMP U Pb age of 2063 ?? 9 Ma for gold mineralisation. The similar structural timing of epigenetic gold

A new indicator mineral methodology based on a generic Bi-Pb-Te-S mineral inclusion signature in detrital gold from porphyry and low/intermediate sulfidation epithermal environments in Yukon Territory, Canada

NASA Astrophysics Data System (ADS)

Chapman, R. J.; Allan, M. M.; Mortensen, J. K.; Wrighton, T. M.; Grimshaw, M. R.

2017-12-01

Porphyry-epithermal and orogenic gold are two of the most important styles of gold-bearing mineralization within orogenic belts. Populations of detrital gold resulting from bulk erosion of such regions may exhibit a compositional continuum wherein Ag, Cu, and Hg in the gold alloy may vary across the full range exhibited by natural gold. This paper describes a new methodology whereby orogenic and porphyry-epithermal gold may be distinguished according to the mineralogy of microscopic inclusions observed within detrital gold particles. A total of 1459 gold grains from hypogene, eluvial, and placer environments around calc-alkaline porphyry deposits in Yukon (Nucleus-Revenue, Casino, Sonora Gulch, and Cyprus-Klaza) have been characterized in terms of their alloy compositions (Au, Ag, Cu, and Hg) and their inclusion mineralogy. Despite differences in the evolution of the different magmatic hydrothermal systems, the gold exhibits a clear Bi-Pb-Te-S mineralogy in the inclusion suite, a signature which is either extremely weak or (most commonly) absent in both Yukon orogenic gold and gold from orogenic settings worldwide. Generic systematic compositional changes in ore mineralogy previously identified across the porphyry-epithermal transition have been identified in the corresponding inclusion suites observed in samples from Yukon. However, the Bi-Te association repeatedly observed in gold from the porphyry mineralization persists into the epithermal environment. Ranges of P-T-X conditions are replicated in the geological environments which define generic styles of mineralization. These parameters influence both gold alloy composition and ore mineralogy, of which inclusion suites are a manifestation. Consequently, we propose that this methodology approach can underpin a widely applicable indicator methodology based on detrital gold.

Flow of ultra-hot Precambrian orogens and the making of crustal layering in Phanerozoic orogenic plateaux

NASA Astrophysics Data System (ADS)

Chardon, Dominique; Gapais, Denis; Cagnard, Florence; Jayananda, Mudlappa; Peucat, Jean-Jacques

2010-05-01

Reassessment of structural / metamorphic properties of ultra-hot Precambrian orogens and shortening of model weak lithospheres support a syn-convergence flow mode on an orogen scale, with a large component of horizontal finite elongation parallel to the orogen. This orogen-scale flow mode combines distributed shortening, gravity-driven flow, lateral escape, and three-dimensional mass redistribution of buried supracrustal rocks, magmas and migmatites in a thick fluid lower crust. This combination preserves a nearly flat surface and Moho. The upper crust maintains a nearly constant thickness by real-time erosion and near-field clastic sedimentation and by ablation at its base by burial of pop-downs into the lower crust. Steady state regime of these orogens is allowed by activation of an attachment layer that maintains kinematic compatibility between the thin and dominantly plastic upper crust and a thick "water bed" of lower crust. Because very thin lithospheres of orogenic plateaux and Precambrian hot orogens have similar thermomechanical structures, bulk orogenic flow comparable to that governing Precambrian hot orogens should actually operate through today's orogenic plateaux as well. Thus, syn-convergence flow fabrics documented on exposed crustal sections of ancient hot orogens that have not undergone collapse may be used to infer the nature of flow fabrics that are imaged by geophysical techniques beneath orogenic plateaux. We provide a detailed geological perspective on syn-convergence crustal flow in relation to magma emplacement and partial melting on a wide oblique crustal transition of the Neoarchean ultra-hot orogen of Southern India. We document sub-horizontal bulk longitudinal flow of the partially molten lower crust over a protracted period of 60 Ma. Bulk flow results from the interplay of (1) pervasive longitudinal transtensional flow of the partially molten crust, (2) longitudinal coaxial flow on flat fabrics in early plutons, (3) distributed, orogen

Geology, distribution, and classification of gold deposits in the western Qinling belt, central China

USGS Publications Warehouse

Mao, J.; Qiu, Yumin; Goldfarb, R.J.; Zhang, Z.; Garwin, S.; Fengshou, R.

2002-01-01

Gold deposits of the western Qinling belt occur within the western part of the Qinling-Dabie-Sulu orogen, which is located between the Precambrian North China and Yangtze cratons and east of the Songpan-Ganzi basin. The early Paleozoic to early Mesozoic orogen can be divided into northern, central, and southern zones, separated by the Shangdan and Lixian-Shanyang thrust fault systems. The northern zone consists of an early Paleozoic arc accreted to the North China craton by ca. 450 Ma. The central zone, which contains numerous orogenic gold deposits, is dominated by clastic rocks formed in a late Paleozoic basin between the converging cratonic blocks. The southern zone is characterized by the easternmost exposure of Triassic sedimentary rocks of the Songpan-Ganzi basin. These Early to Late Triassic turbidities, in part calcareous, of the immense Songpan-Ganzi basin also border the western Qinling belt to the west. Carlinlike gold deposits are abundant (1) along a westward extension of the southern zone defined by a window of early Paleozoic clastic rocks extending into the basin, and (2) within the easternmost margin of the basinal rocks to the south of the extension, and in adjacent cover rocks of the Yangtze craton. Triassic and Early Jurassic synkinematic granitoids are widespread across the western Qinling belt, as well as in the Songpan-Ganzi basin. Orogenic lode gold deposits along brittle-ductile shear zones occur within greenschist-facies, highly deformed, Devonian and younger clastic rocks of the central zone. Mainly coarse-grained gold, along with pyrite, pyrrhotite, arsenopyrite, and minor base metal sulfides, occur in networks of quartz veinlets, brecciated wall rock, and are dissminated in altered wall rock. Isotopic dates suggest that the deposits formed during the Late Triassic to Middle Jurassic as the leading edge of the Yangtze craton was thrust beneath rocks of the western Qinling belt. Many gold-bearing placers are distributed along the river

Testing ore deposit models using in situ U-Pb geochronology of hydrothermal monazite: Paleoproterozoic gold mineralization in northern Australia

NASA Astrophysics Data System (ADS)

Rasmussen, Birger; Sheppard, Stephen; Fletcher, Ian R.

2006-02-01

The inability to establish absolute ages for gold deposition in the Pine Creek orogen of northern Australia has led to conflicting ore deposit models, ranging from intrusion related, which predict that gold mineralization was synchronous with granite magmatism (ca. 1835 1820 Ma), to orogenic, which place ore deposition nearly 100 m.y. later. Here we present ion microprobe U-Pb geochronology for a mineralized quartz reef from Tom's Gully mine, Mount Bundey, Northern Territory, Australia, and nearby granitic rocks and associated contact aureoles. Isotopic dating of zircon and monazite indicates that intrusion and contact metamorphism occurred ca. 1825 Ma, whereas hydrothermal monazite from the auriferous quartz reef gives a mean 207Pb/206Pb age of 1780 ± 10 Ma, interpreted as the time of gold mineralization. Mineralization therefore postdated intrusion by ˜45 m.y. and preceded a postulated ca. 1740 1730 Ma cratonwide orogenic gold event by ˜50 m.y. Hence, neither the intrusion-related model nor the recently proposed orogenic model is applicable. Combined with a reevaluation of age data from the nearby Goodall gold deposit, our data suggest that mineralization coincides with, and may be related to, an episode of regional low-grade metamorphism, deformation, and fluid circulation (Shoobridge event). Our results demonstrate the importance of high-precision in situ geochronology and detailed petrography for deciphering age relationships in ore deposits, and of testing the veracity of models for ore formation.

Geology and origin of epigenetic lode gold deposits, Tintina Gold Province, Alaska and Yukon: Chapter A in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

USGS Publications Warehouse

Goldfarb, Richard J.; Marsh, Erin E.; Hart, Craig J.R.; Mair, John L.; Miller, Marti L.; Johnson, Craig; Gough, Larry P.; Day, Warren C.

2007-01-01

-rich and 18O-rich crustal fluids, most commonly of low salinity. The older group of ores includes the low-grade intrusion-related gold systems at Fort Knox near Fairbanks and those in Yukon, with fluids exsolved from fractionating melts at depths of 3 to 9 kilometers and forming a zoned sequence of auriferous mineralization styles extending outward to the surrounding metasedimentary country rocks. The causative plutons are products of potassic mafic magmas generated in the subcontinental lithospheric mantle that interacted with overlying lower to middle crust to generate the more felsic ore-related intrusions. In addition, the older ores include spatially associated, high-grade, shear-zonerelated orogenic gold deposits formed at the same depths from upward-migrating metamorphic fluids; the Pogo deposit is a relatively deep-seated example of such. The younger gold ores, restricted to southwestern Alaska, formed in unmetamorphosed sedimentary rocks of the Kuskokwim basin within 1 to 2 kilometers of the surface. Most of these deposits formed via fluid exsolution from shallowly emplaced, highly evolved igneous complexes generated mainly as mantle melts. However, the giant Donlin Creek orogenic gold deposit is a product of either metamorphic devolatilization deep in the basin or of a gold-bearing fluid released from a flysch-melt igneous body.

Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution.

PubMed

Fritz, H; Abdelsalam, M; Ali, K A; Bingen, B; Collins, A S; Fowler, A R; Ghebreab, W; Hauzenberger, C A; Johnson, P R; Kusky, T M; Macey, P; Muhongo, S; Stern, R J; Viola, G

2013-10-01

The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to Mozambique and Madagascar in the south, is the world́s largest Neoproterozoic to Cambrian orogenic complex. It comprises a collage of individual oceanic domains and continental fragments between the Archean Sahara-Congo-Kalahari Cratons in the west and Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of orogeny between ∼850 and 550 Ma. The northern part of the orogen, the Arabian-Nubian Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the Mozambique Ocean. The ocean closed during a protracted period of island-arc and microcontinent accretion between ∼850 and 620 Ma. To the south of the Arabian Nubian Shield, the Eastern Granulite-Cabo Delgado Nappe Complex of southern Kenya, Tanzania and Mozambique was an extended crust that formed adjacent to theMozambique Ocean and experienced a ∼650-620 Ma granulite-facies metamorphism. Completion of the nappe assembly around 620 Ma is defined as the East African Orogeny and was related to closure of the Mozambique Ocean. Oceans persisted after 620 Ma between East Antarctica, India, southern parts of the Congo-Tanzania-Bangweulu Cratons and the Zimbabwe-Kalahari Craton. They closed during the ∼600-500 Ma Kuungan or Malagasy Orogeny, a tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were followed by phases of post-orogenic extension. Early ∼600-550 Ma extension is recorded in the Arabian-Nubian Shield and the Eastern Granulite-Cabo Delgado Nappe Complex. Later ∼550-480 Ma extension affected Mozambique and southern Madagascar. Both extension phases, although diachronous,are interpreted as the result of lithospheric delamination. Along the strike of the East African Orogen, different geodynamic settings resulted in the evolution

Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution

NASA Astrophysics Data System (ADS)

Fritz, H.; Abdelsalam, M.; Ali, K. A.; Bingen, B.; Collins, A. S.; Fowler, A. R.; Ghebreab, W.; Hauzenberger, C. A.; Johnson, P. R.; Kusky, T. M.; Macey, P.; Muhongo, S.; Stern, R. J.; Viola, G.

2013-10-01

The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to Mozambique and Madagascar in the south, is the world´s largest Neoproterozoic to Cambrian orogenic complex. It comprises a collage of individual oceanic domains and continental fragments between the Archean Sahara-Congo-Kalahari Cratons in the west and Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of orogeny between ∼850 and 550 Ma. The northern part of the orogen, the Arabian-Nubian Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the Mozambique Ocean. The ocean closed during a protracted period of island-arc and microcontinent accretion between ∼850 and 620 Ma. To the south of the Arabian Nubian Shield, the Eastern Granulite-Cabo Delgado Nappe Complex of southern Kenya, Tanzania and Mozambique was an extended crust that formed adjacent to theMozambique Ocean and experienced a ∼650-620 Ma granulite-facies metamorphism. Completion of the nappe assembly around 620 Ma is defined as the East African Orogeny and was related to closure of the Mozambique Ocean. Oceans persisted after 620 Ma between East Antarctica, India, southern parts of the Congo-Tanzania-Bangweulu Cratons and the Zimbabwe-Kalahari Craton. They closed during the ∼600-500 Ma Kuungan or Malagasy Orogeny, a tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were followed by phases of post-orogenic extension. Early ∼600-550 Ma extension is recorded in the Arabian-Nubian Shield and the Eastern Granulite-Cabo Delgado Nappe Complex. Later ∼550-480 Ma extension affected Mozambique and southern Madagascar. Both extension phases, although diachronous,are interpreted as the result of lithospheric delamination. Along the strike of the East African Orogen, different geodynamic settings resulted in the evolution of

Timing, Controls and Tectonic Context of Gold Mineralisation in the Southern Uplands-Longford-Down Terrane, Caledonides, Scotland and Ireland.

NASA Astrophysics Data System (ADS)

Rice, Samuel; Cuthbert, Simon; Hursthouse, Andrew

2017-04-01

The relationships between regional tectonic, magmatic and metamorphic events and hydrothermal mineralisation in orogenic settings are controversial [1]. The geotectonic development of the Caledonian orogenic belt of the northern British Isles, which hosts some significant gold deposits, is well-constrained and provides an excellent framework for investigating these relationships. Gold mineralisation at two of the best known deposits, Curraghinalt and Cononish, located in the Grampian Terrane, has recently been shown to have occurred between 462.7 and 452.8 Ma, during the Late Ordovician Grampian event of the Caledonian orogeny [2]. In the Southern Uplands-Longford-Down Terrane syn and post-kinnematic intrusions constrain the age of mineralisation to between 418 and 397 Ma. Mineralisation is hosted by late Caledonian transverse D3 structures of Early Devonian age [3]. Fluid inclusion data indicate that the auriferous quartz veins were deposited from a low salinity carbonic mesothermal ( 330°C) fluid of apparently mixed magmatic-metamorphic origin, consistent with a Caledonian orogenic origin [4-6]. Gold mineralisation is associated with contemporaneous minor intrusions at several localities [7-9] exhibiting comparable mineralogy, geochemistry, fluid inclusion types and structural relationships, indicating that coeval regional magmatism may have been a significant factor for all of the deposits. Gold mineralisation in the SULDT occurred during a transition from compression to strike-slip deformation coeval with a regional pulse of orogenic magmatism [10]. The common association between gold deposits in Phanerozoic orogenic settings and intrusions may explain overlapping characteristics between orogenic, intrusion-related and porphyry gold deposits and may reflect the important role of magmatism in conveying the heat to drive hydrothermal systems at shallow crustal levels. Further work will focus on constraining the sources of mineralising fluids and metals. 1

Erosional Reduction of an Orogenic Wedge: Structural Response to Neogene Climate Change within the St. Elias Orogen, Alaska

NASA Astrophysics Data System (ADS)

Berger, A. L.; Spotila, J. A.; Chapman, J. B.; Pavlis, T. L.; Enkelmann, E.; Buscher, J. T.

2007-12-01

The kinematics and architecture of orogenic systems may be heavily influenced by climate, but little research has focused on the long term effects of glacial erosion on orogenesis. Apatite and zircon (U-Th)/He thermochronometry on >75 bedrock samples across the St. Elias orogen, one of the best examples of a glaciated orogenic wedge, is the basis for a new kinematic model and demonstrates an association between glacial denudation and orogenic architecture. The spatial pattern of low temperature cooling indicates that exhumation and deformation are focused within a thin-skinned fold and thrust belt on the windward flank, whereas the leeward flank of the orogen functions as a deformational backstop. A previously unrecognized structure beneath the Bagley ice field must separate these domains with south-side-up motion. We propose this structure is a backthrust making the orogen doubly-vergent. Suggestive of accelerated backthrust motion in response to climate change, cooling rates within the hanging wall block and across the entire windward flank of the orogen accelerated ten-fold coeval with enhanced glaciation. As backthrust motion increased, glacial unroofing also coincided with a regional shift in deformation away from prominent forethrusts including the North American-Yakutat terrane suture (Chugach St. Elias fault) and the seaward deformation front (Pamplona zone). Across the windward flank of the orogen, exhumation, at rates of up to 5 mm/yr, is focused within a narrow zone, where the glacial equilibrium line altitude (ELA) intersects the orogenic wedge. This zone of rapid exhumation, not present prior to the onset of enhanced glaciation, cuts across the structural trend of the orogen and is more narrowly focused than orographic precipitation. Accelerated denudation at the ELA thus appears to have redistributed strain along a series of forethrusts that lie at the zone of heaviest glacial flux, while the backthrust progressively truncates the southward

Geological and geochemical implications of the genesis of the Qolqoleh orogenic gold mineralisation, Kurdistan Province (Iran)

NASA Astrophysics Data System (ADS)

Taghipour, Batoul; Ahmadnejad, Farhad

2015-03-01

The Qolqoleh gold deposit is located in the northwestern part of the Sanandaj-Sirjan Zone (SSZ), within the NE-SW trending Qolqoleh shear zone. Oligocene granitoids, Cretaceous meta-limestones, schists and metavolcanics are the main lithological units. Chondrite-normalised REE patterns of the ore-hosting metavolcanics indicate REE enrichment relative to hanging wall (chlorite-sericite schist) and footwall (meta-limestone) rocks. The pattern also reflects an enrichment in LREE relative to HREE. It seems that the LREE enrichment is related to the circulation of SO42- and CO2-bearing fluids and regional metamorphism in the Qolqoleh shear zone. Both positive and negative Eu anomalies are observed in shear-zone metavolcanics. These anomalies are related to the degree of plagioclase alteration during gold mineralisation and hydrothermal alteration. In progressing from a metavolcanic protomylonite to an ultramylonite, significant changes occurred in the major/trace element and REE concentration. Utilising an Al-Fe-Ti isocon for the ore-hosting metavolcanics shows that Sc, Y, K, U, P, and M-HREE (except Eu) are relatively unchanged; S, As, Ag, Au, Ca, LOI, Rb and LREE are enriched, and Sr, Ba, Eu, Cr, Co and Ni decrease with an increasing degree of deformation. Based on geochemical features and comparison with other well-known shear zones in the world, the study area is best classified as an Isovolume-Gain (IVG) type shear zone and orogenic type gold mineralisation. Based on the number of phases observed at room temperature and their microthermometric behaviour, three fluid inclusion types have been recognised in quartz-sulphide and quartz-calcite veins: Type I monophase aqueous inclusions, Type II two-phase liquid-vapour (L-V) inclusions which are subdivided into two groups based on the homogenisation temperature (Th): a) L-V inclusions with Th from 205 to 255°C and melting temperature of last ice (Tm) from -3 to -9°C. b) L-V inclusions with higher Th from 335 to 385�

Orogen styles in the East African Orogen: A review of the Neoproterozoic to Cambrian tectonic evolution☆

PubMed Central

Fritz, H.; Abdelsalam, M.; Ali, K.A.; Bingen, B.; Collins, A.S.; Fowler, A.R.; Ghebreab, W.; Hauzenberger, C.A.; Johnson, P.R.; Kusky, T.M.; Macey, P.; Muhongo, S.; Stern, R.J.; Viola, G.

2013-01-01

The East African Orogen, extending from southern Israel, Sinai and Jordan in the north to Mozambique and Madagascar in the south, is the world́s largest Neoproterozoic to Cambrian orogenic complex. It comprises a collage of individual oceanic domains and continental fragments between the Archean Sahara–Congo–Kalahari Cratons in the west and Neoproterozoic India in the east. Orogen consolidation was achieved during distinct phases of orogeny between ∼850 and 550 Ma. The northern part of the orogen, the Arabian–Nubian Shield, is predominantly juvenile Neoproterozoic crust that formed in and adjacent to the Mozambique Ocean. The ocean closed during a protracted period of island-arc and microcontinent accretion between ∼850 and 620 Ma. To the south of the Arabian Nubian Shield, the Eastern Granulite–Cabo Delgado Nappe Complex of southern Kenya, Tanzania and Mozambique was an extended crust that formed adjacent to theMozambique Ocean and experienced a ∼650–620 Ma granulite-facies metamorphism. Completion of the nappe assembly around 620 Ma is defined as the East African Orogeny and was related to closure of the Mozambique Ocean. Oceans persisted after 620 Ma between East Antarctica, India, southern parts of the Congo–Tanzania–Bangweulu Cratons and the Zimbabwe–Kalahari Craton. They closed during the ∼600–500 Ma Kuungan or Malagasy Orogeny, a tectonothermal event that affected large portions of southern Tanzania, Zambia, Malawi, Mozambique, Madagascar and Antarctica. The East African and Kuungan Orogenies were followed by phases of post-orogenic extension. Early ∼600–550 Ma extension is recorded in the Arabian–Nubian Shield and the Eastern Granulite–Cabo Delgado Nappe Complex. Later ∼550–480 Ma extension affected Mozambique and southern Madagascar. Both extension phases, although diachronous,are interpreted as the result of lithospheric delamination. Along the strike of the East African Orogen, different geodynamic settings

A Tale of Two Orogens: Comparing Crustal Processes in the Proterozoic Trans-Hudson and Grenville Orogens, Eastern Canada

NASA Astrophysics Data System (ADS)

Darbyshire, F. A.; Bastow, I. D.; Gilligan, A.; Petrescu, L.

2016-12-01

The Precambrian core of North America is an assemblage of Archean cratons and Proterozoic orogenic belts, preserving over 3 billion years of Earth history. Here we focus on two of the largest collisional orogens, using recent and ongoing seismological studies to probe their present-day structure and tectonic history. The 1.8 Ga collision between the Western Churchill and Superior cratons, along with microcontinental and island arc terranes, formed the Trans-Hudson Orogen (THO), a collisional belt similar in scale and shape to the present-day Himalaya-Karakoram-Tibet Orogen (HKTO). In the Mesoproterozoic, a series of collisions reworked the SE margin of the Superior craton and added new material over a period of several hundred Ma, culminating in the Grenvillian orogeny and the assembly of the supercontinent Rodinia. The Grenville Orogen is thought to have been a large, hot, long-lived plateau which subsequently underwent orogenic collapse. While similar in spatial scale, the Trans-Hudson and Grenville Orogens have significantly different tectonic histories, notably in terms of longevity and tectonic evolution. Comparison of these collisional belts with each other, and with the HTKO, provide valuable insights into plate-tectonic history. Recently a number of broadband seismograph installations have allowed a detailed study of present-day crustal structure beneath the THO and the Grenville. Receiver-function and surface wave studies provide information on crustal thickness variations, bulk crustal composition and crustal heterogeneity. The crust beneath the orogens is generally thicker, more mafic and more heterogeneous than that beneath neighbouring Archean and Phanerozoic domains, with significant along-strike variability and Moho complexity. We review and interpret the new crustal structure information in the context of the tectonic processes affecting the two contrasting orogens.

Gold deposits in the Xiaoqinling-Xiong'ershan region, Qinling mountains, central China

USGS Publications Warehouse

Mao, J.; Goldfarb, R.J.; Zhang, Z.; Xu, W.; Qiu, Yumin; Deng, J.

2002-01-01

The gold-rich Xiaoqinling-Xiong'ershan region in eastern Shaanxi and western Henan provinces, central China, lies about 30-50 km inland of the southern margin of the North China craton. More than 100 gold deposits and occurrences are concentrated in the Xiaoqinling (west), Xiaoshan (middle), and Xiong'ershan (east) areas. Late Archean gneiss of the Taihua Group, and Middle Proterozoic metavolcanic rocks of the Xiong'er Group are the main host rocks for the deposits. Mesozoic granitoids (ca. 178-104 Ma) are present in most gold districts, but deposits are typically hosted in the Precambrian basement rocks hundreds of meters to as far as 10 km from the intrusions and related hornfels zones. Deposits in the Xiaoqinling and Xiaoshan areas are best classified as orogenic gold deposits, with ores occurring in a number of distinct belts both in quartz veins and disseminated in altered metamorphic rocks. Alteration assemblages are dominated by quartz, sericite, pyrite, and carbonate minerals. The ore-forming fluids were low salinity, CO2-rich, and characterized by isotopically heavy ??18O. Four deposits (Dongchuang, Wenyu, Yangzhaiyu, and Dahu) in the Xiaoqinling area each contain resources of about 1 Moz Au. Some of the gold deposits in the Xiong'ershan area represent more shallowly emplaced tellurium-enriched orogenic systems, which include resources of approximately 1-1.5 Moz Au at Shanggong and Beiling (or Tantou). Others are epithermal deposits (e.g., Qiyugou and Dianfang) that are hosted in volcanic breccia pipes. Isotopic dates for all gold deposits, although often contradictory, generally cluster between 172-99 Ma and are coeval with emplacement of the post-kinematic granitoids. The gold deposits formed during a period of relaxation of far-field compressional stresses, clearly subsequent to the extensive Paleozoic-early Mesozoic accretion of are terranes and the Yangtze craton onto the southern margin of the North China craton. Hydrothermal and magmatic events

Accretionary orogens through Earth history

USGS Publications Warehouse

Cawood, Peter A.; Kroner, A.; Collins, W.J.; Kusky, T.M.; Mooney, W.D.; Windley, B.F.

2009-01-01

Accretionary orogens form at intraoceanic and continental margin convergent plate boundaries. They include the supra-subduction zone forearc, magmatic arc and back-arc components. Accretionary orogens can be grouped into retreating and advancing types, based on their kinematic framework and resulting geological character. Retreating orogens (e.g. modern western Pacific) are undergoing long-term extension in response to the site of subduction of the lower plate retreating with respect to the overriding plate and are characterized by back-arc basins. Advancing orogens (e.g. Andes) develop in an environment in which the overriding plate is advancing towards the downgoing plate, resulting in the development of foreland fold and thrust belts and crustal thickening. Cratonization of accretionary orogens occurs during continuing plate convergence and requires transient coupling across the plate boundary with strain concentrated in zones of mechanical and thermal weakening such as the magmatic arc and back-arc region. Potential driving mechanisms for coupling include accretion of buoyant lithosphere (terrane accretion), flat-slab subduction, and rapid absolute upper plate motion overriding the downgoing plate. Accretionary orogens have been active throughout Earth history, extending back until at least 3.2 Ga, and potentially earlier, and provide an important constraint on the initiation of horizontal motion of lithospheric plates on Earth. They have been responsible for major growth of the continental lithosphere through the addition of juvenile magmatic products but are also major sites of consumption and reworking of continental crust through time, through sediment subduction and subduction erosion. It is probable that the rates of crustal growth and destruction are roughly equal, implying that net growth since the Archaean is effectively zero. ?? The Geological Society of London 2009.

Application of U-Th-Pb phosphate geochronology to young orogenic gold deposits: New age constraints on the formation of the Grass Valley gold district, Sierra Foothills province, California

USGS Publications Warehouse

Taylor, Ryan D.; Goldfarb, Richard J.; Monecke, Thomas; Fletcher, Ian R.; Cosca, Michael A.; Kelly, Nigel M.

2015-01-01

The Grass Valley orogenic gold district in the Sierra Nevada foothills province, central California, the largest historic gold producer of the North American Cordillera, comprises both steeply dipping east-west (E-W) veins located along lithologic contacts in accreted ca. 300 and 200 Ma oceanic rocks and shallowly dipping north-south (N-S) veins hosted by the Grass Valley granodiorite; the latter have yielded about 70 percent of the 13 million ounces of historic lode gold production in the district. The oceanic host rocks were accreted to the western margin of North America between 200 and 170 Ma, metamorphosed to greenschist and amphibolite facies, and uplifted between 175 and 160 Ma. Large-scale magmatism in the Sierra Nevada occurred between 170-140 Ma and 120-80 Ma, with the Grass Valley granodiorite being emplaced during the older episode of magmatism. Uranium-lead isotopic dating of hydrothermal xenotime yielded the first absolute age of 162±5 Ma for the economically more significant N-S veins. The vein-hosted xenotime, as well as associated monazite, are unequivocally of hydrothermal origin as indicated by textural and chemical characteristics, including grain shape, lack of truncated growth banding, lack of a Eu anomaly, and low U and Th concentrations. Furthermore, the crack-seal texture of the veins, with abundant wallrock slivers, suggests their formation as a result of episodic fluid flow possibly related to reoccurring seismic events, rather than a period of fluid exsolution from an evolving magma. The N-S veins are temporally distinct from a younger 153-151 Ma gold event that was previously reported for the E-W veins. Overlapping U-Pb zircon (159.9±2.2 Ma) and 40Ar/39Ar biotite and hornblende (159.7±0.6 to 161.9±1.4 Ma) ages and geothermobarometric calculations indicate that the Grass Valley granodiorite was emplaced at ca. 160 Ma at elevated temperatures (~800°C) within approximately 3 km of the paleosurface and rapidly cooled to the ambient

Gold-bearing skarns

USGS Publications Warehouse

Theodore, Ted G.; Orris, Greta J.; Hammerstrom, Jane M.; Bliss, James D.

1991-01-01

In recent years, a significant proportion of the mining industry's interest has been centered on discovery of gold deposits; this includes discovery of additional deposits where gold occurs in skarn, such as at Fortitude, Nevada, and at Red Dome, Australia. Under the classification of Au-bearing skarns, we have modeled these and similar gold-rich deposits that have a gold grade of at least 1 g/t and exhibit distinctive skarn mineralogy. Two subtypes, Au-skarns and byproduct Au-skarns, can be recognized on the basis of gold, silver, and base-metal grades, although many other geological factors apparently are still undistinguishable largely because of a lack of detailed studies of the Au-skarns. Median grades and tonnage for 40 Au-skarn deposits are 8.6 g/t Au, 5.0 g/t Ag, and 213,000 t. Median grades and tonnage for 50 byproduct and Au-skarn deposits are 3.7 g/t Au, 37 g/t Ag, and 330,000 t. Gold-bearing skarns are generally calcic exoskarns associated with intense retrograde hydrosilicate alteration. These skarns may contain economic amounts of numerous other commodities (Cu, Fe, Pb, Zn, As, Bi, W, Sb, Co, Cd, and S) as well as gold and silver. Most Au-bearing skarns are found in Paleozoic and Cenozoic orogenic-belt and island-arc settings and are associated with felsic to intermediate intrusive rocks of Paleozoic to Tertiary age. Native gold, electru, pyrite, pyrrhotite, chalcopyrite, arsenopyrite, sphalerite, galena, bismuth minerals, and magnetite or hematite are the most common opaque minerals. Gangue minerals typically include garnet (andradite-grossular), pyroxene (diopside-hedenbergite), wollastonite, chlorite, epidote, quartz, actinolite-tremolite, and (or) calcite.

Metamorphic origin of ore-forming fluids for orogenic gold-bearing quartz vein systems in the North American Cordillera: constraints from a reconnaissance study of δ15N, δD, and δ18O

USGS Publications Warehouse

Jia, Y.; Kerrich, R.; Goldfarb, R.

2003-01-01

The western North American Cordillera hosts a large number of gold-bearing quartz vein systems from the Mother Lode of southern California, through counterparts in British Columbia and southeastern Alaska, to the Klondike district in central Yukon. These vein systems are structurally controlled by major fault zones, which are often reactivated terrane-bounding sutures that formed in orogens built during accretion and subduction of terranes along the continental margin of North America. Mineralization ages span mid-Jurassic to early Tertiary and encompass much of the evolution ofthe Cordilleran orogen. Nitrogen contents and δ15N values of hydrothermal micas from veins are between 130 and 3,500 ppm and 1.7 to 5.5 per mil, respectively. These values are consistent with fluids derived from metamorphic dehydration reactions within the Phanerozoic accretion-subduction complexes, which have δ15N values of 1 to 6 per mil. The δ18O values of gold-bearing vein quartz from different locations in the Cordillera are between 14.6 and 22.2 per mil but are uniform for individual vein systems. The δD values of hydrothermal micas are between -110 and -60 per mil. Ore fluids have calculated δ18O values of 8 to 16 per mil and δD values of -65 to -10 per mil at an estimated temperature of 300δC; δD values of ore fluids do not show any latitudinal control. These results indicate a deep crustal source for the ore-forming fluids, most likely of metamorphic origin. Low δDH2O values of -120 to -130 per mil for a hydrous muscovite from the Sheba vein in the Klondike district reflect secondary exchange between recrystallizing mica and meteoric waters. Collectively, the N, H, and O isotope compositions of ore-related hydrothermal minerals indicate that the formation of these gold-bearing veins involved dilute, aqueous carbonic, and nitrogen-bearing fluids that were generated from metamorphic dehydration reactions at deep crustal levels. These data are not consistent with either mantle

Architecture, kinematics, and exhumation of a convergent orogenic wedge: A thermochronological investigation of tectonic-climatic interactions within the central St. Elias orogen, Alaska

NASA Astrophysics Data System (ADS)

Berger, Aaron L.; Spotila, James A.; Chapman, James B.; Pavlis, Terry L.; Enkelmann, Eva; Ruppert, Natalia A.; Buscher, Jamie T.

2008-06-01

The kinematics and architecture of orogenic systems along the leading edges of accreting terranes may be heavily influenced by climate, but little research has been devoted to the long-term effects of glacial erosion on orogenesis. Here we use low-temperature apatite and zircon (U-Th)/He and fission-track thermochronometry, along with subsidiary structural relationships and seismicity, to develop a new architectural model of the St. Elias orogen in southern Alaska, which is one of the best examples of a glaciated orogenic wedge worldwide. These data illustrate that the orogen consists of a deformational backstop on the leeward flank and a rapidly deforming and eroding, thin-skinned fold and thrust belt on the windward flank. A structure beneath the Bagley ice field separates these distinct deformational domains, which we propose is a backthrust that makes the orogen doubly-vergent. Thermochronometry within the orogenic wedge suggests that denudation and deformation are strongly influenced by glacial erosion. Long-term exhumation, at rates of up to 4 mm/yr, is concentrated within a narrow zone along the windward flank, where glacier equilibrium lines intersect the orogenic wedge. The onset of enhanced glaciation also coincided with a marked acceleration in exhumation across the orogenic wedge, accelerated backthrust motion, and a major shift in deformation away from the North American-Yakutat terrane suture (Chugach St. Elias fault). We propose that accelerated glacial erosion forced the redistribution of strain along the backthrust and an en echelon array of forethrusts that lie beneath the zone of heaviest glaciation, which in turn are systematically truncated by the backthrust. This focusing of deformation matches predictions from analytical models of orogenic wedges and implies a high degree of coupling between climate and tectonics in this glacially-dominated orogen.

Neoproterozoic, Paleozoic, and Mesozoic granitoid magmatism in the Qinling Orogen, China: Constraints on orogenic process

NASA Astrophysics Data System (ADS)

Wang, Xiaoxia; Wang, Tao; Zhang, Chengli

2013-08-01

The Qinling Orogen is one of the main orogenic belts in Asia and is characterized by multi-stage orogenic processes and the development of voluminous magmatic intrusions. The results of zircon U-Pb dating indicate that granitoid magmatism in the Qinling Orogen mainly occurred in four distinct periods: the Neoproterozoic (979-711 Ma), Paleozoic (507-400 Ma), and Early (252-185 Ma) and Late (158-100 Ma) Mesozoic. The Neoproterozoic granitic magmatism in the Qinling Orogen is represented by strongly deformed S-type granites emplaced at 979-911 Ma, weakly deformed I-type granites at 894-815 Ma, and A-type granites at 759-711 Ma. They can be interpreted as the products of respectively syn-collisional, post-collisional and extensional setting, in response to the assembly and breakup of the Rodinia supercontinent. The Paleozoic magmatism can be temporally classified into three stages of 507-470 Ma, 460-422 Ma and ˜415-400 Ma. They were genetically related to the subduction of the Shangdan Ocean and subsequent collision of the southern North China Block and the South Qinling Belt. The 507-470 Ma magmatism is spatially and temporally related to ultrahigh-pressure metamorphism in the studied area. The 460-422 Ma magmatism with an extensive development in the North Qinling Belt is characterized by I-type granitoids and originated from the lower crust with the involvement of mantle-derived magma in a collisional setting. The magmatism with the formation age of ˜415-400 Ma only occurred in the middle part of the North Qinling Belt and is dominated by I-type granitoid intrusions, and probably formed in the late-stage of a collisional setting. Early Mesozoic magmatism in the study area occurred between 252 and 185 Ma, with the cluster in 225-200 Ma. It took place predominantly in the western part of the South Qinling Belt. The 250-240 Ma I-type granitoids are of small volume and show high Sr/Y ratios, and may have been formed in a continental arc setting related to subduction

Late Mesozoic deformations of the Verkhoyansk-Kolyma orogenic belt, Northeast Russia

NASA Astrophysics Data System (ADS)

Fridovsky, Valery

2016-04-01

The Verkhoyansk-Kolyma orogenic belt marks the boundary between the Kolyma-Omolon superterrane (microcontinent) and the submerged eastern margin of the North Asian craton. The orogenic system is remark able for its large number of economically viable gold deposits (Natalka, Pavlik, Rodionovskoe, Drazhnoe, Bazovskoe, Badran, Malo-Tarynskoe, etc.). The Verkhoyansk - Kolyma orogenic belt is subdivided into Kular-Nera and the Polousny-Debin terranes. The Kular-Nera terrane is mainly composed of the Upper Permian, Triassic, and Lower Jurassic black shales that are metamorphosed at lower greenschist facies conditions. The Charky-Indigirka and the Chai-Yureya faults separate the Kular-Nera from the Polousny-Debin terrane that is predominantly composed of the Jurassic flyschoi dturbidites. The deformation structure of the region evolved in association with several late Mesozoic tectonic events that took place in the north-eastern part ofthe Paleo-Pacific. In Late Jurassic-Early Cretaceous several generations of fold and thrust systems were formed due to frontal accretion of the Kolyma-Omolon superterrane to the eastern margin of the North Asian craton.Thrusting and folding was accompanied by granitic magmatism, metamorphic reworking of the Late Paleozoic and the Early Mesozoic sedimentary rocks, and formation of Au-Sn-W mineralization. Three stages of deformation related to frontal accretion can be distinguished. First stage D1 has developed in the north-eastern part of the Verkhoyansk - Kolyma orogenic belt. Early tight and isoclinal folds F1 and assosiated thrusts are characteristic of D1. Major thrusts, linear concentric folds F2 and cleavage were formed during D2. The main ore-controlling structures are thrust faults forming imbricate fan systems. Frontal and oblique ramps and systems of bedding and cross thrusts forming duplexes are common. It is notable that mineralized tectonized zones commonly develop along thrusts at the contacts of rocks of contrasting competence

The conjunction of factors that lead to formation of giant gold provinces and deposits in non-arc settings

USGS Publications Warehouse

Groves, David I.; Goldfarb, Richard J.; Santosh, M.

2016-01-01

In contrast to their province scale similarities, the different giant gold deposit styles show contrasting critical controls at the district to deposit scale. For orogenic gold deposits, the giants appear to have formed by conjunction of a greater number of parameters to those that control smaller deposits, with resultant geometrical and lithostratigraphic complexity as a guide to their location. There are few giant IRGS due to their inferior fluid-flux systems relative to orogenic gold deposits, and those few giants are essentially preservational exceptions. Many Carlin-type deposits are giants due to the exceptional conjunction of both structural and lithological parameters that caused reactive and permeable rocks, enriched in syngenetic gold, to be located below an impermeable cap along antiformal “trends”. Hydrocarbons probably played an important role in concentrating metal. The supergiant Post-Betze deposit has additional ore zones in strain heterogeneities surrounding the pre-gold Goldstrike stock. All unequivocal IOCG deposits are giant or near-giant deposits in terms of gold-equivalent resources, partly due to economic factors for this relatively poorly understood, low Cu-Au grade deposit type. The supergiant Olympic Dam deposit, the most shallowly formed deposit among the larger IOCGs, probably owes its origin to eruption of volatile-rich hybrid magma at surface, with formation of a large maar and intense and widespread brecciation, alteration and Cu-Au-U deposition in a huge rock volume.

Linkages and feedbacks in orogenic systems: An introduction

USGS Publications Warehouse

Thigpen, J. Ryan; Law, Richard D.; Merschat, Arthur J.; Stowell, Harold

2017-01-01

Orogenic processes operate at scales ranging from the lithosphere to grain-scale, and are inexorably linked. For example, in many orogens, fault and shear zone architecture controls distribution of heat advection along faults and also acts as the primary mechanism for redistribution of heat-producing material. This sets up the thermal structure of the orogen, which in turn controls lithospheric rheology, the nature and distribution of deformation and strain localization, and ultimately, through localized mechanical strengthening and weakening, the fundamental shape of the developing orogenic wedge (Fig. 1). Strain localization establishes shear zone and fault geometry, and it is the motion on these structures, in conjunction with climate, that often focuses erosional and exhumational processes. This climatic focusing effect can even drive development of asymmetry at the scale of the entire wedge (Willett et al., 1993).

Gold potential in the Dalradian rocks of NW Northern Ireland: GIS-based prospectivity analysis using Tellus data

NASA Astrophysics Data System (ADS)

Lusty, P. A. J.; McDonnell, P. M.; Gunn, A. G.; Chacksfield, B. C.; Cooper, M.

2009-04-01

Geographic Information Systems (GIS) are essential tools for the management and integration of the large amounts of multivariate spatial data used in mineral exploration. Prospectivity analysis combines these datasets, in the context of a mineral deposit model, to produce a map showing the distribution of potential for a particular type of mineral deposit. In this example Arc-Spatial Data Modeller software has been used to analyse the prospectivity for orogenic vein gold mineralisation in the Dalradian rocks of north-western Northern Ireland. A knowledge-driven (fuzzy logic) approach was used because of the small number of gold deposits within the area. Fuzzy logic is used in situations where information is inexact and the use of classical set theory is inappropriate. Fuzzy logic allows assignment of weightings to exploration data on a continuous scale from 1 (full membership) to 0 (full non-membership). This allows a level of uncertainty or 'fuzziness' to be incorporated into the modelling. The key stages of prospectivity analysis are: (1) analysis of the deposit model to determine key exploration indicators; (2) data processing, interpretation and analysis to extract key indicators; (3) assignment of weightings, zones and styles of influence to key indicators; and (4) calculation of prospectivity. This research is based largely on new geochemical and geophysical data resulting from the Tellus Project in Northern Ireland. The Tellus Project involved geochemical and airborne geophysical surveys over the whole of Northern Ireland carried out between 2004-6 with funding from the Government of Northern Ireland. The study area (3074 km2) is underlain mainly by Neoproterozoic rocks of the Dalradian Supergroup (ca. 590 Ma) which form part of the Caledonide orogenic belt. The Dalradian Supergroup comprises a thick succession of semi-pelites, psammites and pelites, with graphitic pelite horizons that host much of the known gold mineralisation. In the Sperrin Mountains two

Linking magmatism with collision in an accretionary orogen

PubMed Central

Li, Shan; Chung, Sun-Lin; Wilde, Simon A.; Wang, Tao; Xiao, Wen-Jiao; Guo, Qian-Qian

2016-01-01

A compilation of U-Pb age, geochemical and isotopic data for granitoid plutons in the southern Central Asian Orogenic Belt (CAOB), enables evaluation of the interaction between magmatism and orogenesis in the context of Paleo-Asian oceanic closure and continental amalgamation. These constraints, in conjunction with other geological evidence, indicate that following consumption of the ocean, collision-related calc-alkaline granitoid and mafic magmatism occurred from 255 ± 2 Ma to 251 ± 2 Ma along the Solonker-Xar Moron suture zone. The linear or belt distribution of end-Permian magmatism is interpreted to have taken place in a setting of final orogenic contraction and weak crustal thickening, probably as a result of slab break-off. Crustal anatexis slightly post-dated the early phase of collision, producing adakite-like granitoids with some S-type granites during the Early-Middle Triassic (ca. 251–245 Ma). Between 235 and 220 Ma, the local tectonic regime switched from compression to extension, most likely caused by regional lithospheric extension and orogenic collapse. Collision-related magmatism from the southern CAOB is thus a prime example of the minor, yet tell-tale linking of magmatism with orogenic contraction and collision in an archipelago-type accretionary orogen. PMID:27167207

What Can Modern River Profiles Tell Us about Orogenic Processes and Orogen Evolution?

NASA Astrophysics Data System (ADS)

Whipple, K. X.

2008-12-01

Numerous lines of evidence from theory, numerical simulations, and physical experiments suggest that orogen evolution is strongly coupled to atmospheric processes through the interrelationships among climate, topography, and erosion rate. In terms of orogenic processes and orogen evolution, these relationships are most important at the regional scale (mean topographic gradient, mean relief above surrounding plains) largely because crustal deformation is most sensitive to erosional unloading averaged over sufficiently long wavelengths. For this reason, and because above moderate erosion rates (> 0.2 mm/yr) hillslope form becomes decoupled from erosion rate, attention has focused on the river network, and even on particularly large rivers. We now have data that demonstrates a monotonic relationship between erosion rate and the channel steepness index (slope normalized for differences in drainage area) in a variety of field settings. Consequently, study of modern river profiles can yield useful information on recent and on-going patterns of rock uplift. It is not yet possible, however, to quantitatively isolate expected climatic and lithologic influences on this relationship. A combination of field studies and theoretical analyses are beginning to reveal the timescale of landscape response, and thus the topographic memory of past conditions. At orogen scale, river profile response to a change in rock uplift rate is on the order of 1-10 Myr. Because of these long response times, the modern profiles of large rivers and their major tributaries can potentially preserve an interpretable record of rock uplift rates since the Miocene and are insensitive to short-term climatic fluctuations. Only significant increases in rock uplift rate, however, are likely to leave a clear topographic signature. Strategies have been developed to differentiate between temporal and spatial (tectonic, climatic, or lithologic) influences on channel profile form, especially where spatially

Structure and Tectonics of the Saint Elias Orogen

NASA Astrophysics Data System (ADS)

Bruhn, R. L.; Pavlis, T. L.; Plafker, G.; Serpa, L.; Picornell, C.

2001-12-01

The Saint Elias orogen of western Canada and southern Alaska is a complex mountain belt formed by transform faulting and subduction between the Pacific and North American plates, and collision of the Yakutat terrane. The orogen is segmented into three regions of different structural style caused by lateral variations in transpression and processes of terrane accretion. Deformation is strain and displacement partitioned throughout the orogen; transcurrent motion is focused along discrete strike-slip faults, and shortening is distributed among reverse faults and folds with sub-horizontal axes. Plunging folds accommodate horizontal shortening and extension in the western part of the orogen. Segment boundaries extend across the Yakutat terrane where they coincide with the courses of huge piedmont glaciers that flow from the topographic backbone of the range onto the coastal plain. The eastern segment is marked by strike-slip faulting along the Fairweather transform fault and by a narrow belt of reverse faulting where the transpression ratio is 0.4:1 shortening to dextral shear. The transpression ratio is 1.7:1 in the central part of the orogen where a broad thin-skinned fold and thrust belt deforms the Yakutat terrane south of the Chugach-Saint Elias (CSE) suture. Dextral shearing is accommodated by strike-slip faulting beneath the Seward and Bagley glaciers in the hanging wall of the CSE suture, and partly by reverse faulting along a structural belt that cuts across the Yakutat terrane along the western edge of the Malaspina Glacier and links to the Pamplona fold and thrust belt offshore. Deformation along this segment boundary is probably also driven by vertical axis bending of the Yakutat microplate during collision. Subduction & accretion in the western segment of the orogen causes re-folding of previously formed structures when they are emplaced into the upper plate of the Alaska-Aleutian mega-thrust. Second phase folds plunge at moderate to steep angles and

The dilemma of the Jiaodong gold deposits: Are they unique?

USGS Publications Warehouse

Goldfarb, Richard J.; Santosh, M.

2013-01-01

The ca. 126–120 Ma Au deposits of the Jiaodong Peninsula, eastern China, define the country's largest gold province with an overall endowment estimated as >3000 t Au. The vein and disseminated ores are hosted by NE- to NNE-trending brittle normal faults that parallel the margins of ca. 165–150 Ma, deeply emplaced, lower crustal melt granites. The deposits are sited along the faults for many tens of kilometers and the larger orebodies are associated with dilatational jogs. Country rocks to the granites are Precambrian high-grade metamorphic rocks located on both sides of a Triassic suture between the North and South China blocks. During early Mesozoic convergent deformation, the ore-hosting structures developed as ductile thrust faults that were subsequently reactivated during Early Cretaceous “Yanshanian” intracontinental extensional deformation and associated gold formation.Classification of the gold deposits remains problematic. Many features resemble those typical of orogenic Au including the linear structural distribution of the deposits, mineralization style, ore and alteration assemblages, and ore fluid chemistry. However, Phanerozoic orogenic Au deposits are formed by prograde metamorphism of accreted oceanic rocks in Cordilleran-style orogens. The Jiaodong deposits, in contrast, formed within two Precambrian blocks approximately 2 billion years after devolatilization of the country rocks, and thus require a model that involves alternative fluid and metal sources for the ores. A widespread suite of ca. 130–123 Ma granodiorites overlaps temporally with the ores, but shows a poor spatial association with the deposits. Furthermore, the deposit distribution and mineralization style is atypical of ores formed from nearby magmas. The ore concentration requires fluid focusing during some type of sub-crustal thermal event, which could be broadly related to a combination of coeval lithospheric thinning, asthenospheric upwelling, paleo-Pacific plate

Stable Isotopes (O, H, and S) in the Muteh Gold Deposit, Golpaygan Area, Iran

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

Abdollahi, M. J.; Karimpour, M. H.; Kheradmand, A.

2009-06-15

The Muteh gold district with nine gold deposits is located in the Sanandaj-Sirjan metamorphic zone. Gold mineralization occurs in a pre-Permian complex which mainly consists of green schists, meta-volcanics, and gneiss rocks. Shear zones are the host of gold mineralization. Gold paragenesis minerals include pyrite, chalcopyrite, pyrrhotite, and secondary minerals. Pyrites occur as pre-, syn-, and post-metamorphism minerals. To determine the source of the ore-bearing fluids, fifty samples were selected for petrographical and stable isotope studies. The mean values of 12.4 per mille , and -42 per mille for {delta}{sup 18}O and {delta}D isotopes, respectively, and a mean value ofmore » 7.75 per mille of calculated fractionation factors for {delta}{sup 18}O H{sub 2}O, from quartz veins indicate that metamorphic host rocks are the most important source for the fluids and gold mineralization. Three generations of pyrite can be distinguished showing a wide range of {delta}{sup 34}S. Gold mineralization is closely associated with intense hydrothermal alteration along the ductile shear zones. The characteristics of the gold mineralization in the study area are similar to those of orogenic gold deposits elsewhere.« less

Phanerozoic continental growth and gold metallogeny of Asia

USGS Publications Warehouse

Goldfarb, Richard J.; Taylor, Ryan D.; Collins, Gregory S.; Goryachev, Nicolay A.; Orlandini, Omero Felipe

2014-01-01

The Asian continent formed during the past 800 m.y. during late Neoproterozoic through Jurassic closure of the Tethyan ocean basins, followed by late Mesozoic circum-Pacific and Cenozoic Himalayan orogenies. The oldest gold deposits in Asia reflect accretionary events along the margins of the Siberia, Kazakhstan, North China, Tarim–Karakum, South China, and Indochina Precambrian blocks while they were isolated within the Paleotethys and surrounding Panthalassa Oceans. Orogenic gold deposits are associated with large-scale, terrane-bounding fault systems and broad areas of deformation that existed along many of the active margins of the Precambrian blocks. Deposits typically formed during regional transpressional to transtensional events immediately after to as much as 100 m.y. subsequent to the onset of accretion or collision. Major orogenic gold provinces associated with this growth of the Asian continental mass include: (1) the ca. 750 Ma Yenisei Ridge, ca. 500 Ma East Sayan, and ca. 450–350 Ma Patom provinces along the southern margins of the Siberia craton; (2) the 450 Ma Charsk belt of north-central Kazakhstan; (3) the 310–280 Ma Kalba belt of NE Kazakhstan, extending into adjacent NW Xinjiang, along the Siberia–Kazakhstan suture; (4) the ca. 300–280 Ma deposits within the Central Asian southern and middle Tien Shan (e.g., Kumtor, Zarmitan, Muruntau), marking the closure of the Turkestan Ocean between Kazakhstan and the Tarim–Karakum block; (5) the ca. 190–125 Ma Transbaikal deposits along the site of Permian to Late Jurassic diachronous closure of the Mongol–Okhotsk Ocean between Siberia and Mongolia/North China; (6) the probable Late Silurian–Early Devonian Jiagnan belt formed along the margin of Gondwana at the site of collision between the Yangtze and Cathaysia blocks; (7) Triassic deposits of the Paleozoic Qilian Shan and West Qinling orogens along the SW margin of the North China block developed during collision of South China

Gold deposits in metamorphic belts: Overview of current understanding, outstanding problems, future research, and exploration significance

USGS Publications Warehouse

Groves, D.I.; Goldfarb, R.J.; Robert, F.; Hart, C.J.R.

2003-01-01

Metamorphic belts are complex regions where accretion or collision has added to, or thickened, continental crust. Gold-rich deposits can be formed at all stages of orogen evolution, so that evolving metamorphic belts contain diverse gold deposit types that may be juxtaposed or overprint each other. This partly explains the high level of controversy on the origin of some deposit types, particularly those formed or overprinted/remobilized during the major compressional orogeny that shaped the final geometry of the hosting metamorphic belts. These include gold-dominated orogenic and intrusion-related deposits, but also particularly controversial gold deposits with atypical metal associations. There are a number of outstanding problems for all types of gold deposits in metamorphc belts. These include the following: (1) definitive classifications, (2) unequivocal recognition of fluid and metal sources, (3) understanding of fluid migration and focusing at all scales, (4) resolution of the precise role of granitoid magmatism, (5) precise gold-depositional mechanisms, particularly those producing high gold grades, and (6) understanding of the release of CO2-rich fluids from subducting slabs and subcreted oceanic crust and granitoid magmas at different crustal levels. Research needs to be better coordinated and more integrated, such that detailed fluid-inclusion, trace-element, and isotopic studies of both gold deposits and potential source rocks, using cutting-edge technology, are embedded in a firm geological framework at terrane to deposit scales. Ultimately, four-dimensional models need to be developed, involving high-quality, three-dimensional geological data combined with integrated chemical and fluid-flow modeling, to understand the total history of the hydrothermal systems involved. Such research, particularly that which can predict superior targets visible in data sets available to exploration companies before discovery, has obvious spin-offs for global- to deposit

Geodynamic processes and deformation in orogenic belts

NASA Astrophysics Data System (ADS)

Dennis, John G.; Jacoby, Wolfgang R.

1980-03-01

The development of geosynclines and orogenic belts is related to lithosphere convergence. Initial sediment accumulation implying subsidence, and volcanic activity implying extension and rise of geotherms, are in most cases followed by folding and thrusting suggesting compression and by uplift. In terms of recent analogs, sediment accumulation and crustal extension are characteristic of back-arc spreading; subsequent compression would indicate continent—continent collision; and rise of geotherms most likely requires localized thermal flow (convection) in the asthenosphere. These events are here shown to agree with Andrews and Sleep's (1974) numerical model of asthenosphere flow at converging plate margins. Orthogeosynclinal subsidence appears to be a consequence of subcrustal ablation and lithosphere extension and thinning in active marginal basins. Arc and Andean type magmatism mark the reappearance of ablated and transported, relatively low-density subcrustal material. Collision slows and eventually stops the local convection cell, resulting in local heat accumulation and hence high- T, low- P metamorphism and granitization while marginal basin (orthogeosynclinal) deposits are being compressed into Alpine style orogenic structures. Moreover, closing of the marginal basin leads to subsidiary subduction, which in turn may be responsible for some Alpine style structures. Oceanic trench deposits may become incorporated in orogenic zones, as high- P, low- T metamorphic belts (thalassogeosynclines). Dynamic uplift is a fundamental characteristic of orogeny. Most rising and sinking in orogenic zones can be linked to those asthenosphere processes which are a consequence of Andrews-Sleep convection.

Venus orogenic belt environments - Architecture and origin

NASA Astrophysics Data System (ADS)

Head, James W.; Vorder Bruegge, Richard W.; Crumpler, L. S.

1990-08-01

Orogenic belt environments (Danu, Akna, Freyja, and Maxwell Montes) in Western Ishtar Terra, Venus, display a range of architectural elements, including (from the center of Western Ishtar outward) an inboard plateau (Lakshmi Planum), the linear orogenic belts themselves, outboard plateaus, steep scarps bounding Ishtar, adjacent linear foredeeps and outboard rises, and outboard low-lying volcanic plains. The main elements of the architecture are interpreted to be due to the convergence, underthrusting, and possible subduction of lowland plains at the margins of a preexisting tessera plateau of thicker crust.

A Paleozoic Japan-type subduction-accretion system in the Beishan orogenic collage, southern Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Song, Dongfang; Xiao, Wenjiao; Windley, Brian F.; Han, Chunming; Tian, Zhonghua

2015-05-01

Magmatic arcs ascribed to oceanic lithosphere subduction played a dominant role in the construction of the accretionary Central Asian Orogenic Belt (CAOB). The Beishan orogenic collage, situated between the Tianshan Orogen to the west and the Inner Mongolia Orogen to the east, is a key area to understanding the subduction and accretionary processes of the southern CAOB. However, the nature of magmatic arcs in the Beishan and the correlation among different tectonic units along the southern CAOB are highly ambiguous. In order to investigate the subduction-accretion history of the Beishan and put a better spatial and temporal relationship among the tectonic belts along the southern CAOB, we carried out detailed field-based structural geology and LA-ICP-MS zircon U-Pb geochronological as well as geochemical studies along four cross-sections across crucial litho-tectonic units in the central segment of the Beishan, mainly focusing on the metamorphic assemblages and associated plutons and volcanic rocks. The results show that both the plutonic and volcanic rocks have geochemical characteristics similar to those of subduction-related rocks, which favors a volcanic arc setting. Zircons from all the plutonic rocks yield Phanerozoic ages and the plutons have crystallization ages ranging from 464 ± 2 Ma to 398 ± 3 Ma. Two volcanic-sedimentary rocks yield zircons with a wide age range from Phanerozoic to Precambrian with the youngest age peaks at 441 Ma and 446 Ma, estimated to be the time of formation of the volcanic rocks. These new results, combined with published data on ophiolitic mélanges from the central segment of the Beishan, favor a Japan-type subduction-accretion system in the Cambrian to Carboniferous in this part of the Paleo-Asian Ocean. The Xichangjing-Niujuanzi ophiolite probably represents a major suture zone separating different tectonic units across the Beishan orogenic collage, while the Xiaohuangshan-Jijitaizi ophiolitic mélange may represent a

Uniformity in sulfur isotope composition in the orogenic gold deposits from the Dharwar Craton, southern India

NASA Astrophysics Data System (ADS)

Sakthi Saravanan, C.; Mishra, B.

2009-07-01

The sulfur isotope composition of sulfides (mainly pyrite and arsenopyrite) from gold deposits/prospects of the Dharwar Craton such as Hutti, Hira-Buddini, Uti, Kolar (Chigargunta), Ajjanahalli, and Jonnagiri has a narrow range (δ34S = +1.1 to +7.1‰). Such craton-scale uniformity of the above gold camps is noteworthy, in spite of the wide diversity in host rock compositions and their metamorphic conditions, and suggests a magmatic or average crustal source of sulfur for all deposits studied. In addition, our study points towards gold precipitation from reduced ore fluids, with near-homogeneous sulfur isotope compositions.

The Capricorn Orogen Passive source Array (COPA) in Western Australia

NASA Astrophysics Data System (ADS)

Gessner, K.; Yuan, H.; Murdie, R.; Dentith, M. C.; Johnson, S.; Brett, J.

2015-12-01

COPA is the passive source component of a multi-method geophysical program aimed at assessing the mineral deposits potential of the Proterozoic Capricorn Orogen. Previous results from the active source surveys, receiver functions and magnetotelluric studies show reworked orogenic crust in the orogen that contrasts with more simple crust in the neighbouring Archean cratons, suggesting progressive and punctuated collisional processes during the final amalgamation of the Western Australian craton. Previous seismic studies are all based on line deployment or single station analyses; therefore it is essential to develop 3D seismic images to test whether these observations are representative for the whole orogen. With a careful design that takes advantage of previous passive source surveys, the current long-term and short-term deployments span an area of approximately 500 x 500 km. The 36-month total deployment can guarantee enough data recording for 3D structure imaging using body wave tomography, ambient noise surface wave tomography and P- and S-wave receiver function Common Conversion Point (CCP) stacking techniques. A successive instrument loan from the ANSIR national instrument pool, provided 34 broadband seismometers that have been deployed in the western half of the orogen since March 2014. We expect approximately 40-km lateral resolution near the surface for the techniques we propose, which due to low frequency nature of earthquake waves will degrade to about 100 km near the base of the cratonic lithosphere, which is expected at depths between 200 to 250 km. Preliminary results from the first half of the COPA deployment will be presented in the light of the hypotheses that 1) distinct crustal blocks can be detected continuously throughout the orogen (using ambient noise/body wave tomography); 2) distinct lithologies are present in the crust and upper mantle across the orogen (using receiver function CCP images); and 3) crustal and lithosphere deformation along

Tectonic stress evolution in the Pan-African Lufilian Arc and its foreland (Katanga, DRC): orogenic bending, late orogenic extensional collapse and transition to rifting

NASA Astrophysics Data System (ADS)

Kipata, M. L.; Delvaux, D.; Sebagenzi, M. N.; Cailteux, J.; Sintubin, M.

2012-04-01

Between the paroxysm of the Lufilian orogeny at ~ 550 Ma and the late Neogene to Quaternary development of the south-western branch of the East African rift system, the tectonic evolution of the Lufilian Arc and Kundelungu foreland in the Katanga region of the Democratic Republic of Congo remains poorly unknown although it caused important Cu-dominated mineral remobilizations leading to world-class ore deposits. This long period is essentially characterized by brittle tectonic deformations that have been investigated by field studies in open mines spread over the entire arc and foreland. Paleostress tensors were computed for a database of 1450 fault-slip data by interactive stress tensor inversion and data subset separation, and the relative succession of 8 brittle deformation events established. The oldest brittle structures observed are related to the Lufilian brittle compressional climax (stage 1). They have been re-oriented during the orogenic bending that led to the arcuate shape of the belt. Unfolding the stress directions from the first stage allows to reconstruct a consistent NE-SW direction of compression for this stage. Constrictional deformation occurred in the central part of the arc, probably during orogenic bending (Stage 2). After the orogenic bending, a sequence of 3 deformation stages marks the progressive onset of late-orogenic extension: strike-slip deformations (stages 3-4) and late-orogenic arc-parallel extension (stage 5). It is proposed that these 3 stages correspond to orogenic collapse. In early Mesozoic, NW-SE compression was induced by a transpressional inversion, interpreted as induced by far-field stresses generated at the southern active margin of Gondwana (stage 6). Since then, this region was affected by rift-related extension, successively in a NE-SW direction (stage 7, Tanganyika trend) and NW-SE direction (stage 8, Moero trend).

Reworked crustal of early Paleozoic WuYi Orogen revealed by receiver function data

NASA Astrophysics Data System (ADS)

Wei, Y.; Duan, Y.; Tian, X.; Zhao, Y.

2017-12-01

Intraplate orogenic belt, which occurs at the rigid and undeformable plate interiors, is a distinct new type of orogen rather than an interplate or plate marginal orogenic belt, whose deformation occurs exclusively at plate margins. Therefore, intraplate orogenic belts are the most obvious exception to the plate-tectonic paradigm, they are uncommon in Earth's history. The early Paleozoic Wuyi orogen in South China is one of the few examples of intraplate orogen, and is a key to understanding the process of intraplate orogenesis and global early Paleozoic geodynamics. In this study, we select teleseismic records from 45 mobile linear seismic stations deployed in Wuyi Mountain and 58 permanent stations setting in Jiangxi and Fujian provinces, from January 2011 to December 2012, and calculate the crustal thickness and average crustal Vp/Vs ratio using the H-κ stacking method. The main results include the following: 1) the crustal average Poission's ratio shows an increase tendency from land to sea, the interior of Wuyi orogen belt with an low ration less than 0.23, and the coastline with high ration which is up to 0.28, which indicate a very heterogeneous crustal structure and composition in Wuyi orogen and coast belt. 2) the crustal thickness ranges 28-34 km and shows a tendency of thinning from inland to coast in the region of SE China margin, which maight mean the eastern Eurasia lithospheric is extension and thinning induced by the subducted paleo-Pacific slab. To conclusion, we assume that Wuyi orogen experienced upper crustal thickening, lower crust and lithosphere delamination during the early Paleozoic orogeny, and lithosphere extension in Mesozoic. This research is founded by the Natural Science Foundation of China (41174052 and 41604048).

Architecture and mineral deposit settings of the Altaid orogenic collage: a revised model

NASA Astrophysics Data System (ADS)

Yakubchuk, Alexander

2004-09-01

The Altaids are an orogenic collage of Neoproterozoic-Paleozoic rocks located in the center of Eurasia. This collage consists of only three oroclinally bent Neoproterozoic-Early Paleozoic magmatic arcs (Kipchak, Tuva-Mongol, and Mugodzhar-Rudny Altai), separated by sutures of their former backarc basins, which were stitched by new generations of overlapping magmatic arcs. In addition, the Altaids host accreted fragments of the Neoproterozoic to Early Paleozoic oceanic island chains and Neoproterozoic to Cenozoic plume-related magmatic rocks superimposed on the accreted fragments. All these assemblages host important, many world-class, Late Proterozoic to Early Mesozoic gold, copper-molybdenum, lead-zinc, nickel and other deposits of various types. In the Late Proterozoic, during breakup of the supercontinent Rodinia, the Kipchak and Tuva-Mongol magmatic arcs were rifted off Eastern Europe-Siberia and Laurentia to produce oceanic backarc basins. In the Late Ordovician, the Siberian craton began its clockwise rotation with respect to Eastern Europe and this coincides with the beginning of formation of the Mugodzhar-Rudny Altai arc behind the Kipchak arc. These earlier arcs produced mostly Cu-Pb-Zn VMS deposits, although some important intrusion-related orogenic Au deposits formed during arc-arc collision events in the Middle Cambrian and Late Ordovician. The clockwise rotation of Siberia continued through the Paleozoic until the Early Permian producing several episodes of oroclinal bending, strike-slip duplication and reorganization of the magmatic arcs to produce the overlapping Kazakh-Mongol and Zharma-Saur-Valerianov-Beltau-Kurama arcs that welded the extinct Kipchak and Tuva-Mongol arcs. This resulted in amalgamation of the western portion of the Altaid orogenic collage in the Late Paleozoic. Its eastern portion amalgamated only in the early Mesozoic and was overlapped by the Transbaikal magmatic arc, which developed in response to subduction of the oceanic crust

Proterozoic orogens in southern Peninsular India: Contiguities and complexities

NASA Astrophysics Data System (ADS)

Chetty, T. R. K.; Santosh, M.

2013-12-01

The Precambrian terranes of southern Peninsular India have been central to discussions on the history of formation and breakup of supercontinents. Of particular interest are the Proterozoic high grade metamorphic orogens at the southern and eastern margins of the Indian shield, skirting the 3.4 Ga Dharwar craton which not only preserve important records of lower crustal processes and lithospheric geodynamics, but also carry imprints of the tectonic framework related to the assembly of the major Neoproterozoic supercontinents - Rodinia and Gondwana. These Proterozoic orogens are described as Southern Granulite Terrane (SGT) in the southern tip and the Eastern Ghats Mobile Belt (EGMB) in the eastern domains of the peninsula. The contiguity of these orogens is broken for a distance of ˜400 km and disappears in the Bay of Bengal. These orogens expose windows of middle to lower crust with well-preserved rock records displaying multiple tectonothermal events and multiphase exhumation paths.Recent studies in these orogens have led to the recognition of discrete crustal blocks or terranes separated by major shear zone systems, some of which represent collisional sutures. The SGT and EGMB carry several important features such as fold-thrust tectonics, regional granulite facies metamorphism of up to ultrahigh-temperature conditions in some cases, multiple P-T paths, development of lithospheric shear zones, emplacement of ophiolites, presence of alkaline and anorthositic complexes, development of crustal-scale "flower structures", transpressional strains, and reactivation tectonics. A heterogeneous distribution of different metamorphic and magmatic assemblages with distinct spatial and temporal strain variations in shaping the fabric elements in different blocks is identified. Both EGMB and SGT share a common transpressional deformation history during the latest Neoproterozoic characterized by the steepening of the initial low angle crustal scale structures leading to a

Tectonic setting of synorogenic gold deposits of the Pacific Rim

USGS Publications Warehouse

Goldfarb, R.J.; Phillips, G.N.; Nokleberg, W.J.

1998-01-01

batholith have yielded more than 100 million oz of gold. Additional significant ore-forming events during the development of North America's Cordilleran orogen included those in the Klamath Mountains region, California in the Late Jurassic and Early Cretaceous; the Klondike district, Yukon by the Early Cretaceous; the Nome and Fairbanks districts, Alaska, and the Bridge River district, British Columbia in the middle Cretaceous; and the Juneau gold belt, Alaska in the Eocene. Gold-bearing veins deposited during the Late Jurassic and Early Cretaceous terrane collision that formed the present-day Russian Far East have been the source for more than 130 million oz of placer gold. The abundance of gold-bearing quartz-carbonate veins throughout the Gondwanan, North American and Eurasian continental margins suggests the migration and concentration of large fluid volumes during continental growth. Such volumes could be released during orogenic heating of hydrous silicate mineral phases within accreted marine strata. The common temporal association between gold veining and magmatism around the Pacific Rim reflects these thermal episodes. Melting of the lower thickened crust during arc formation, slab rollback and extensional tectonism, and subduction of a slab window beneath the seaward part of the forearc region can all provide the required heat for initation of the ore-forming processes.

Oblique contractional reactivation of inherited heterogeneities: Cause for arcuate orogens

PubMed Central

Sokoutis, D.; Willingshofer, E.; Brun, J.‐P.; Gueydan, F.; Cloetingh, S.

2017-01-01

Abstract We use lithospheric‐scale analog models to study the reactivation of pre‐existing heterogeneities under oblique shortening and its relation to the origin of arcuate orogens. Reactivation of inherited rheological heterogeneities is an important mechanism for localization of deformation in compressional settings and consequent initiation of contractional structures during orogenesis. However, the presence of an inherited heterogeneity in the lithosphere is in itself not sufficient for its reactivation once the continental lithosphere is shortened. The heterogeneity orientation is important in determining if reactivation occurs and to which extent. This study aims at giving insights on this process by means of analog experiments in which a linear lithospheric heterogeneity trends with various angles to the shortening direction. In particular, the key parameter investigated is the orientation (angle α) of a strong domain (SD) with respect to the shortening direction. Experimental results show that angles α ≥ 75° (high obliquity) allow for reactivation along the entire SD and the development of a linear orogen. For α ≤ 60° (low obliquity) the models are characterized by the development of an arcuate orogen, with the SD remaining partially non‐reactivated. These results provide a new mechanism for the origin of some arcuate orogens, in which orocline formation was not driven by indentation or subduction processes, but by oblique shortening of inherited heterogeneities, as exemplified by the Ouachita orogen of the southern U.S. PMID:28670046

Crustal structure and evolution of the Trans-Hudson orogen: Results from seismic reflection profiling

NASA Astrophysics Data System (ADS)

Baird, D. J.; Nelson, K. D.; Knapp, J. H.; Walters, J. J.; Brown, L. D.

1996-04-01

A 400-km-long deep seismic reflection transect across northeastern Montana and northern North Dakota reveals the crustal-scale structural fabric of the Early Proterozoic Trans-Hudson orogen beneath the Williston basin. Comparison with deep seismic reflection data across the Canadian portion of the same orogen ˜700 km to the north reveals first-order similarities in crustal architecture but documents significant along-strike variation in orogenic evolution. Both transects display a broad crustal-scale antiform axial to the orogen. In the north, geologic data suggest that this antiform is cored by an Archean microcontinent. In the south, west dipping reflections on the western flank of the antiform extend from the upper crust to the uppermost mantle and truncate prominent subhorizontal lower crustal reflections of the Archean Wyoming craton. Within the Wyoming craton, the eastern limit of east dipping midcrustal reflections coincides with the subsurface age boundary between the craton and the Early Proterozoic Trans-Hudson orogen as interpreted from potential field and drill core data. On the basis of subsurface geochronologic data from the crystalline basement and by analogy with the Glennie domain within the exposed Trans-Hudson orogen in Canada, we suggest that the southern antiform is cored by an Archean crustal fragment that was caught up in the terminal collision of the Wyoming and Superior cratons during Hudsonian orogeny. The eastern side of the Trans-Hudson orogen is characterized on both seismic transects by predominantly east dipping crustal penetrating reflections. We interpret the easterly dip of these reflections as evidence that the Superior province was thrust westward over the interludes of the orogen during terminal collision. Although juvenile Early Proterozoic terranes characterize the exposed segment of the Trans-Hudson orogen in Canada, limited drill core information within the Dakota segment of the orogen shows a predominance of granulitic

Exhumation at orogenic indentor corners under long-term glacial conditions: Example of the St. Elias orogen, Southern Alaska

NASA Astrophysics Data System (ADS)

Spotila, James A.; Berger, Aaron L.

2010-07-01

Syntaxial bends in convergent plate boundaries, or indentor corners, display some of the most intriguing deformation patterns on Earth and are type localities for "aneurysms" of coupled erosion, thermal weakening, and strain. The St. Elias orogen in Alaska is a small, young convergent system that has been dominated by a glacial climate for much of its history and exhibits two prominent indentor corners that are not well understood. We have added 40 new apatite (U-Th)/He ages to the already extensive dataset for the low-temperature cooling history of this orogen to constrain the pattern of exhumation in these indentor corners. Ages from the western syntaxis show minor variation across the structural hinge, suggesting that the bend has little effect on the pattern of exhumation and that structures, including the Bagley fault, connect smoothly from the orogen core to the subduction zone to the southwest. Rock uplift on the north flank of the range appears to increase steadily towards the eastern syntaxis, which represents the apex in the right-angle bend between a transform fault in the south and the collision zone in the west. Based on age-elevation relationships, zones of relative rock uplift can be defined in which the Mt. Logan massif, or the area just north of the eastern syntaxis, experienced ˜ 4.8 km greater rock uplift than background levels northwest of the western syntaxis. A bulge in relative rock uplift is symmetric about the hinge in the eastern indentor corner. However, rates of denudation in this bulge are not as rapid as the core of the fold and thrust belt and are lower than those implied by detrital cooling ages from beneath the Seward Glacier. This implies that a large bull's eye of ultra-rapid (˜ 5 mm/yr) exhumation does not occur and that the subpopulation of young detrital ages may be sourced from a narrow transpressional zone along the Fairweather fault. Unlike the Himalayan syntaxes, it thus appears that an aneurysm of coupled erosion

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

Compressional intracontinental orogens: Ancient and modern perspectives

NASA Astrophysics Data System (ADS)

Raimondo, Tom; Hand, Martin; Collins, William J.

2014-03-01

Compressional intracontinental orogens are major zones of crustal thickening produced at large distances from active plate boundaries. Consequently, any account of their initiation and subsequent evolution must be framed outside conventional plate tectonics theory, which can only explain the proximal effects of convergent plate-margin interactions. This review considers a range of hypotheses regarding the origins and transmission of compressive stresses in intraplate settings. Both plate-boundary and intraplate stress sources are investigated as potential driving forces, and their relationship to rheological models of the lithosphere is addressed. The controls on strain localisation are then evaluated, focusing on the response of the lithosphere to the weakening effects of structural, thermal and fluid processes. With reference to the characteristic features of intracontinental orogens in central Asia (the Tien Shan) and central Australia (the Petermann and Alice Springs Orogens), it is argued that their formation is largely driven by in-plane stresses generated at plate boundaries, with the lithosphere acting as an effective stress guide. This implies a strong lithospheric mantle rheology, in order to account for far-field stress propagation through the discontinuous upper crust and to enable the support of thick uplifted crustal wedges. Alternative models of intraplate stress generation, primarily involving mantle downwelling, are rejected on the grounds that their predicted temporal and spatial scales for orogenesis are inconsistent with the observed records of deformation. Finally, inherited mechanical weaknesses, thick sedimentary blanketing over a strongly heat-producing crust, and pervasive reaction softening of deep fault networks are identified as important and interrelated controls on the ability of the lithosphere to accommodate rather than transmit stress. These effects ultimately produce orogenic zones with architectural features and evolutionary

A cryptic Gondwana-forming orogen located in Antarctica.

PubMed

Daczko, Nathan R; Halpin, Jacqueline A; Fitzsimons, Ian C W; Whittaker, Joanne M

2018-05-30

The most poorly exposed and least understood Gondwana-forming orogen lies largely hidden beneath ice in East Antarctica. Called the Kuunga orogen, its interpolation between scattered outcrops is speculative with differing and often contradictory trends proposed, and no consensus on the location of any sutures. While some discount a suture altogether, paleomagnetic data from Indo-Antarctica and Australo-Antarctica do require 3000-5000 km relative displacement during Ediacaran-Cambrian Gondwana amalgamation, suggesting that the Kuunga orogen sutured provinces of broadly Indian versus Australian affinity. Here we use compiled data from detrital zircons offshore of East Antarctica that fingerprint two coastal subglacial basement provinces between 60 and 130°E, one of Indian affinity with dominant ca. 980-900 Ma ages (Indo-Antarctica) and one of Australian affinity with dominant ca. 1190-1140 and ca. 1560 Ma ages (Australo-Antarctica). We combine this offshore compilation with existing and new onshore U-Pb geochronology and previous geophysical interpretations to delimit the Indo-Australo-Antarctic boundary at a prominent geophysical lineament which intersects the coast east of Mirny at ~94°E.

Role of mantle dynamics in rebuilding the Tianshan Orogenic Belt in NW China: A seismic tomographic investigation

NASA Astrophysics Data System (ADS)

He, Chuansong; Santosh, M.

2018-05-01

The Tianshan orogenic belt, Junggar terrane and Altai terrane are located at the southwestern part of the Central Asian Orogenic Belt (CAOB). Here, we investigate the velocity structure beneath the Xinjiang region in NW China, which includes the Tarim terrane, Tianshan orogenic belt, Junggar terrane and Altai terrane with a view to evaluate the mantle dynamics based on teleseismic data recorded by 103 seismic stations. Our tomographic results show both high and low velocity perturbations beneath the Tianshan orogenic belt. We suggest that the high velocity perturbations beneath this orogenic belt might represent the northward subducted lithosphere of the Tarim Basin and the southward subducted lithosphere of the Junggar Basin. The low velocity structure beneath the Tianshan orogenic belt might represent asthenosphere upwelling that triggered the extensive magmatism which contributed to rebuilding of the Tianshan orogenic belt.

The giant Carlin gold province: A protracted interplay of orogenic, basinal, and hydrothermal processes above a lithospheric boundary

USGS Publications Warehouse

Emsbo, P.; Groves, D.I.; Hofstra, A.H.; Bierlein, F.P.

2006-01-01

Northern Nevada hosts the only province that contains multiple world-class Carlin-type gold deposits. The first-order control on the uniqueness of this province is its anomalous far back-arc tectonic setting over the rifted North American paleocontinental margin that separates Precambrian from Phanerozoic subcontinental lithospheric mantle. Globally, most other significant gold provinces form in volcanic arcs and accreted terranes proximal to convergent margins. In northern Nevada, periodic reactivation of basement faults along this margin focused and amplified subsequent geological events. Early basement faults localized Devonian synsedimentary extension and normal faulting. These controlled the geometry of the Devonian sedimentary basin architecture and focused the discharge of basinal brines that deposited syngenetic gold along the basin margins. Inversion of these basins and faults during subsequent contraction produced the complex elongate structural culminations that characterize the anomalous mineral deposit "trends." Subsequently, these features localized repeated episodes of shallow magmatic and hydrothermal activity that also deposited some gold. During a pulse of Eocene extension, these faults focused advection of Carlin-type fluids, which had the opportunity to leach gold from gold-enriched sequences and deposit it in reactive miogeoclinal host rocks below the hydrologic seal at the Roberts Mountain thrust contact. Hence, the vast endowment of the Carlin province resulted from the conjunction of spatially superposed events localized by long-lived basement structures in a highly anomalous tectonic setting, rather than by the sole operation of special magmatic or fluid-related processes. An important indicator of the longevity of this basement control is the superposition of different gold deposit types (e.g., Sedex, porphyry, Carlin-type, epithermal, and hot spring deposits) that formed repeatedly between the Devonian and Miocene time along the trends

Late Paleozoic tectonic evolution and concentrated mineralization in Balkhash and West Junggar, western part of the Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Dong, Shuwen; Chen, Xuanhua; Chen, Zhengle

2016-04-01

The Central Asia Orogenic Belt (CAOB) is an important area with significant growth of the crust and metallogeny in the Late Paleozoic. The Balkhash-Junggar tectono-metallogenic belt consists of the Balkhash, the West Junggar, and the East Junggar tectono-metallogenic belts in western part of the Central Asian Orogenic Belt (CAOB). According to the structural geological relationship, the East Junggar, the West Junggar, and the Balkhash belts are considered to be once a continuous E-W-trending tectono-metallogenic belt in Late Carboniferous. The West Junggar belt is featured with NE-trending left-lateral strike-slip faulting tectonic system (WJTS), while the left-lateral strike-slip faults are E-W-trending in the Balkhash belt. The WJTS consists of the Darabut, the Mayile, and the Baerluke faults, and the blocks among them. All these left-lateral strike-slip faults are forming due to the transition of tectonic settings from syn-collisional orogeny to post-collisional extension during the closure of the ocean (the Junggar Sea) in Late Carboniferous, with significant intrusion of batholiths and crust growth occurred in this period. These faults are truncated by the right-lateral strike-slip faults, such as the Chingiz-Junggar fault, and the Central Balkhash fault in Mesozoic. The Balkhash-Junggar tectono-metallogenic belt is important for the occurrence of many well-known super-large and large porphyry Cu-Mo deposits (such as the Kounrad, the Aktogai, the Borly, and the Baogutu deposits), large skarn Cu deposits (in the Sayak ore-filed), large rare metal deposits (such as the East Kounrad, the Zhanet, and the Akshatau deposits), and large gold deposits (such as the Hatu deposit). Zircon U-Pb ages, Re-Os isotopic dating of molybdenites, 40Ar/39Ar thermochronology of hornblendes, muscovites, biotites, and K-feldspars, and zircon and apatite fission track (FT) and (U-Th)/He dating and thermal history modeling, provide a multidisciplinary approach to constrain the whole

Geochemistry of shale and sedimentary pyrite as a proxy for gold fertility in the Selwyn basin area, Yukon

NASA Astrophysics Data System (ADS)

Sack, Patrick J.; Large, Ross R.; Gregory, Daniel D.

2018-01-01

Selwyn basin area strata contain sedimentary pyrite with Au above background levels when analyzed by laser ablation-inductively coupled mass spectrometry. Hyland Group rocks contain framboidal pyrite contents of 670 ppb Au, 1223 ppm As, and 5.3 ppm Te; the mean of all types of sedimentary pyrite in the Hyland Group is 391 ppb Au, 1489 ppm As, and 3.8 ppm Te. These levels are similar to sedimentary pyrite in host lithologies from major orogenic gold districts in New Zealand and Australia. Comparison of whole rock and pyrite data show that rocks deposited in continental slope settings with significant terrigenous input contain pyrite that is consistently enriched in Au, As, Te, Co, and Cu. Although data are limited, whole rock samples of stratigraphic units containing Au-rich pyrite also contain high Au, indicating that most of the Au is within sedimentary pyrite. Based on geologic characteristics and comparison of pyrite chemistry data with whole rock chemistry, Selwyn basin area strata have the necessary ingredients to form orogenic gold deposits: Au-enriched source rocks, metamorphic conditions permissive of forming a metamorphic ore fluid, and abundant structural preparation for channeling fluids and depositing ore.

Collisional Tectonics in the St. Elias Orogen, Alaska Observed by GPS

NASA Astrophysics Data System (ADS)

Elliott, J.; Freymueller, J. T.; Larsen, C. F.

2008-12-01

The rugged topography of the St. Elias orogen of southern Alaska and the adjacent region of Canada is the result of the on-going collision of the Yakutat block with southern Alaska. Nearly 45 mm/yr of NW-SE directed convergence from the collision is currently accommodated within the St. Elias orogen. A key to understanding this complex collisional boundary is knowing the locations of the structures taking up the convergence. GPS provides a snapshot of the present-day strain field and helps to delineate active structures. As part of the St. Elias Erosion/Tectonics Project (STEEP), we re-surveyed 70 campaign GPS sites across the St. Elias orogen during the summer of 2008. Strain rates derived from our GPS data highlight several areas within the St. Elias orogen. The highest strain rates occur across Icy Bay and the western edge of the Malaspina Glacier. Rates there approach -1 microstrain/yr, a value higher than that observed in the Himalaya. Lower, but still significant, strain rates of about -0.2 microstrain/yr extend north from Icy Bay to the region surrounding Mt. St. Elias. The second major focus of compressive strain in the orogen is centered over the Yakataga fold-and-thrust belt. Strain rates there are in the range of -0.40 to -0.50 microstrain/yr. Little significant strain is seen across the Bagley icefield or to the north of that feature. These results suggest that most of the convergence across the St. Elias orogen is currently accommodated on structures located south of the Bagely icefield, specifically in the Icy Bay, upper Malaspina/Mt. St. Elias, and Yakataga fold-and-thrust belt regions. We use block modeling techniques to describe the tectonic elements of the St. Elias orogen and connect them with the tectonic regime in southeast Alaska. Our preliminary results indicate that a single thrust fault through Icy Bay cannot explain the data there; multiple NW and N directed thrust faults through Icy Bay, along the western edge of the Malaspina Glacier

Orogenic structural inheritance and rifted passive margin formation

NASA Astrophysics Data System (ADS)

Salazar Mora, Claudio A.; Huismans, Ritske S.

2016-04-01

Structural inheritance is related to mechanical weaknesses in the lithosphere due to previous tectonic events, e.g. rifting, subduction and collision. The North and South Atlantic rifted passive margins that formed during the breakup of Western Gondwana, are parallel to the older Caledonide and the Brasiliano-Pan-African orogenic belts. In the South Atlantic, 'old' mantle lithospheric fabric resulting from crystallographic preferred orientation of olivine is suggested to play a role during rifted margin formation (Tommasi and Vauchez, 2001). Magnetometric and gravimetric mapping of onshore structures in the Camamu and Almada basins suggest that extensional faults are controlled by two different directions of inherited older Brasiliano structures in the upper lithosphere (Ferreira et al., 2009). In the South Atlantic Campos Basin, 3D seismic data indicate that inherited basement structures provide a first order control on basin structure (Fetter, 2009). Here we investigate the role of structural inheritance on the formation of rifted passive margins with high-resolution 2D thermo-mechanical numerical experiments. The numerical domain is 1200 km long and 600 km deep and represents the lithosphere and the sublithospheric mantle. Model experiments were carried out by creating self-consistent orogenic inheritance where a first phase of orogen formation is followed by extension. We focus in particular on the role of varying amount of orogenic shortening, crustal rheology, contrasting styles of orogen formation on rifted margin style, and the time delay between orogeny and subsequent rifted passive formation. Model results are compared to contrasting structural styles of rifted passive margin formation as observed in the South Atlantic. Ferreira, T.S., Caixeta, J.M., Lima, F.D., 2009. Basement control in Camamu and Almada rift basins. Boletim de Geociências da Petrobrás 17, 69-88. Fetter, M., 2009. The role of basement tectonic reactivation on the structural evolution

Continuation of the New England Orogen, Australia, beneath the Queensland Plateau and Lord Howe rise

USGS Publications Warehouse

Mortimer, N.; Hauff, F.; Calvert, A.T.

2008-01-01

Greywacke, argillite, greyschist and hypabyssal igneous rocks have been obtained from an Ocean Drilling Program core on the Queensland Plateau and from xenoliths in a volcanic breccia dredged from the crest of the Lord Howe Rise. Low to intermediate detrital quartz contents, 260-240 Ma K-Ar ages, and only moderately radiogenic Sr and Nd isotope compositions, suggest a correlation with the New England Orogen of eastern Australia, rather than with Australia's Lachlan Orogen or other adjacent geological provinces. Our results indicate that the New England Orogen terranes continue towards New Zealand at least as far as the southern Lord Howe Rise. The projected offshore boundaries of the major east Australian orogens are now known with more confidence, and do not appear to require any major cross-orogen offsets.

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.

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.

Geologic map of the Weka Dur gold deposit, Badakhshan Province, Afghanistan, modified from the 1967 original map compilation of M.P. Guguev and others

USGS Publications Warehouse

Peters, Stephen G.; Stettner, Will R.; Masonic, Linda M.

2014-01-01

The Weka Dur gold deposit lies in a cluster of other gold deposits in Badakhshan Province (Ragh district), such as the Kadar, Nesheb Dur, and Rishaw gold occurrences. These gold occurrences lie within a zone of late Hercynian folding and are most likely related to fluids that originated from orogenic processes. The Weka Dur deposit is the largest recorded gold occurrence in Afghanistan and is hosted in Proterozoic mica schist and amphibolite that is intruded by diabase dikes and other intrusive rocks. The tabular orebody is 350 meters (m) long and 2 m wide and can be traced downdip for 110 m. Mineralization consists of ochreous, brecciated schists containing high gold concentrations along gently and steeply dipping fissures. The brecciated rocks grade to 46.7 grams per ton (g/t) silver and contain arsenopyrite, galena, chalcopyrite, and scheelite. Trenches and adits were constructed, mapped, and sampled during the 1960s. Calculated resources are 958.3 kilograms of gold, averaging 4.1 g/t gold.

Non-linear feedbacks drive strain partitioning within an active orogen, southern Alaska

NASA Astrophysics Data System (ADS)

Hooks, B.; Koons, P. O.; Upton, P.

2011-12-01

Temperature plays a very important role in the partitioning of deformation within an active orogen. Local variations in the thermal structure of actively uplifting areas can reinforce focused partitioning of strain locally, whereas regional variations can alter deformation patterns on a much broader scale resulting in the re-organization of an entire orogen. Within southern Alaska, the Yakutat micro-terrane has been subducting beneath North America over the previous ~10 Ma. Early deformation related to this event drove uplift of the Alaska Range, as evidenced by stratigraphic and thermochronologic datasets. This was followed by a southerly discontinuous spatial jump in the deformation front to the coastal St. Elias Range. Here we present 3D numerical models that simulate deformation of Earth materials given assigned applied velocity boundary conditions and mechanical and thermal constitutive relationships on a macro- (plate boundary) and meso-scale (<50-km). The goal is to reproduce first-order strain and uplift patterns within this evolving orogen. The macro-scale model undergoes a spatial and temporal reorganization of deformation as strain is progressively shifted to a trench-ward orogenic wedge, the inlet orogen. Subduction related cooling of the fore-arc (i.e. tectonic refrigeration) provides control on the location of the inlet orogen. This control is based upon the creation of a thin sliver of cold, strong material along the mega-thrust interface. The stronger mega-thrust facilitates more efficient transfer of strain, driving the formation of the inlet orogen and determining the location of its frontal toe. This toe is further stabilized by upward displacement of the upper crust over the refrigerated section. This upward motion causes thermal weakening of the upper crust as a tectonic aneurysm with the location controlled by the thermally strengthened lower crust. The net result is an ever weakening upper crust that focuses strain creating dramatic

Pyrite deformation and connections to gold mobility: insight from micro-structural analysis and trace element mapping

NASA Astrophysics Data System (ADS)

Dubosq, Renelle; Rogowitz, Anna; Lawley, Christopher; Schneider, David; Jackson, Simon

2017-04-01

Pyrite is an important and ubiquitous gold-bearing phase in many orogenic gold deposits making the study of its deformation behaviour under metamorphic conditions crucial to the understanding of gold (re)mobilization. However, pyrite deformation mechanisms and their influence on the retention or release of trace elements during deformation and metamorphism remain poorly understood. We propose a syn- to post-peak metamorphic and deformation driven gold upgrading model where gold is remobilized through deformation-induced diffusion pathways in the form of substructures in pyrite. The middle amphibolite facies assemblage (actinolite-biotite-plagioclase-almandine) of the Detour Lake deposit (Canada) makes it an ideal study area due to maximum temperatures reaching 550°C, exceeding the conditions for plastic deformation in pyrite (450°C). The world-class Detour Lake deposit, containing 16.4 Moz of Au at 1 g/t, is a Neoarchean orogenic gold ore body located in the northern Abitibi district within the Superior Province. The mine is situated along the high strain, sub-vertical ductile-brittle Sunday Lake Deformation Zone (SLDZ) parallel to the broadly E-W trending Abitibi greenstone belt. Herein we combine orientation contrast (OC) forescatter imaging, electron backscatter diffraction (EBSD) and 2D laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) trace element pyrite mapping to evaluate the influence of pyrite brittle and plastic deformation on the release of trace elements during syn-metamorphic gold remobilization. Local misorientation patterns in pyrite exhibit parallel bands that can be described by continuous rotation around one of the <100> axes, whereas higher strain areas reveal more heterogeneous misorientation patterns and the development of low-angle grain boundaries with late fractures indicative of dislocation creep and strain hardening. These late fractures are an important micro-structural setting for gold and clusters of precious

Low-Impact Exploration for Gold in the Scottish Caledonides.

NASA Astrophysics Data System (ADS)

Rice, Samuel; Cuthbert, Simon; Hursthouse, Andrew; Broetto, Gabriele

2017-04-01

The Caledonian orogenic belt of the northern British Isles hosts some significant gold deposits. However, gold mineralization in the region is underexplored. Some of the most prospective areas identified by rich alluvial gold anomalies are environmentally and culturally sensitive. Traditional mineral exploration methods can have a range of negative environmental, social and economic impacts. The regional tourism economy is dependent on outdoor activities, landscape quality, wildlife and industrial heritage and has the potential to be disrupted by mineral resource developments. Low-cost, low-impact exploration strategies are therefore, key to sustainably developing the mineral resource potential. Research currently in progress in part of the Scottish Caledonides aims to develop protocols for more sustainable exploration. We are using a range of geoscience techniques to characterize the mineral system, improve exploration targeting and reduce negative impacts. To do this we targeted an area with a large preexisting dataset (e.g. stream sediment geochemistry, geomorphology, structural geology, petrology, geophysics, mine data) that can be synthesized and analyzed in a GIS. Part of the work aims to develop and test a model for gold dispersion in the surface environment that accounts for climatic and anthropogenic influences in order to locate bedrock sources. This multidisciplinary approach aims to reduce the target areas for subsequent exploration activities such as soil sampling, excavation and drilling.

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

Gold deposits and occurrences of the Greater Caucasus, Georgia Republic: Their genesis and prospecting criteria

USGS Publications Warehouse

Kekelia, S.A.; Kekelia, M.A.; Kuloshvili, S.I.; Sadradze, N.G.; Gagnidze, N.E.; Yaroshevich, V.Z.; Asatiani, G.G.; Doebrich, J.L.; Goldfarb, R.J.; Marsh, E.E.

2008-01-01

The south-central part of the Greater Caucasus region, Georgia Republic, represents an extremely prospective region for significant orogenic gold deposits. Gold-bearing quartz veins are concentrated in two extensive WNW-trending belts, the Mestia-Racha and Svaneti districts, within the northern margin of the Southern Slope Zone of the Great Caucasus orogen. This metalliferous region is dominated by Early to Middle Jurassic slates, which are part of a terrane that likely accreted to the continental margin from late Paleozoic to Jurassic. The slates were subsequently intruded by both Middle to Late Jurassic and Neogene granitoids. Quartz veins in the more carbonaceous slate units are most consistently enriched in As, Au, Hg, Sb, and W, and show mineralization styles most consistent with typical orogenic gold deposits. Quartz veins in the Mestia-Racha district were mined in Soviet times for As, Sb, and W, but many of these are now being recognized as gold resource targets. The veins occur in the footwall of a thrust fault between the Southern Slope zone and an earlier accreted terrane, the Main Zone, to the north. Many veins in the district continue along strike for > 1??km and some cut Neogene intrusions, constraining ore formation to the most recent 4 to 5??million years. Gold deposition thus correlates with final collision of the Arabian plate to the south and uplift of the ore-hosting Greater Caucasus. The Zopkhito deposit, previously mined for antimony, contains an estimated 55??t Au at a cutoff grade of 0.5??g/t. The veins are localized in an area where smaller-order structures show a major change in strike from N-S to more E-W trends. A pyrite-arsenopyrite ore stage includes gold concentrated in both sulfide phases; it is overprinted by a later stibnite-dominant stage. Fluid-inclusion studies of ore samples from the Zopkhito deposit indicate minimum trapping temperatures of 300 to 350????C and 200 to 300????C for the two stages, respectively, and minimum

What controls deformation in a bent three-dimensional orogen? An example from the Bolivian Andes

NASA Astrophysics Data System (ADS)

Kaislaniemi, L.; Whipp, D. M., Jr.

2017-12-01

The width of orogens is thought to be affected by both erosional intensity and strength of the rocks. Along-strike variation of the orogen width can be expected to reflect shifts in these factors. An example of such variation can be found around the Bolivian orocline, which is a change in the orientation of the central Andes, in central Bolivia, from N-S south of 18°S to roughly NW-SE in the north. This bend coincides with 50% reduction in the width of the orogen east of the Altiplano, an approximately eight-fold increase in the annual precipitation, and the presence of a basement arch that reduces the thickness of relatively weak Paleozoic sediments upon which the orogen detaches. This has led to uncertainty about whether the growth of the orogen is controlled primarily by climate (erosion) or tectonics (strength of the basal detachment). We study deformation in a segmented orogen using 3D geodynamic models to understand how along-strike variations in rainfall and basal detachment strength affect orogen deformation and growth of the frontal part of the Andean fold-and-thrust belt (FTB). We calculate the visco-plastic deformation in the retro-wedge of an Andean-style orogen using the finite element software DOUAR (Braun et al. 2008) coupled to the surface process model FastScape (Braun & Willett 2013). The model design includes the basement, the Altiplano, and the FTB east of the plateau. A weak basal detachment zone is prescribed. Strain softening allows development of new faults and free evolution of the detachment zone. The effects of varying rock strength and varying precipitation are considered to determine the primary control(s) on the geometry and evolution of curved orogens. Results show that both increased precipitation and stronger detachment zone can explain differences in the width of the FTB, as reflected in the topography. These factors, however, lead to different structural evolution of the orogen: Weak basal detachment zone promotes growth of the

The eastern Central Asian Orogenic Belt: formation and evolution

NASA Astrophysics Data System (ADS)

Xu, Bei; Xu, Wenliang

2017-08-01

The Central Asian Orogenic Belt (CAOB) extends from the northern Eurasian continent in the west via Mongolia, Inner Mongolia and northeast part of China to the Russia Far East in the east. It is characterized by complex trench-arc-basin subduction system, exotic terrane (microcontinents) accretion, massive generation of juvenile crust during the Neoproterozoic-Phanerozoic (e.g., Jahn et al., 2000, 2004; Sengör et al., 1993). A lot of papers about formation and evolution of the CAOB have been published and new field observations and geochemical data for key areas of the CAOB challenge to previous assessments. Several areas previously defined as juvenile are now shown to have mixed crustal compositions. For example, Kröner et al. (2014, in press) estimated that the distribution of various crustal provinces is truly juvenile crustal material ca. 20%, mixed crust ca. 30%, old crust ca. 50%，respectively, in the CAOB, similar to those in other accretionary orogens through Earth history. A two-stage model for the evolution of the CAOB has been suggested based on recent data from the Eastern Tianshan and Beishan (Gao et al., 2011; Su et al., 2011; Chen et al., 2016; Wang et al., 2017), which suggests the process of the formation and evolution of the CAOB includes closure of the Paleo Asian ocean (PAO), formation of orogenic belt before the late Paleozoic and crustal extension and magmatism resulted from plume upon the young orogenic belt after the late Paleozoic. This new model changes previous concept that the CAOB developed through the Paleozoic and is supported by recent researches on the eastern CAOB.

Paleozoic tectonics of the Ouachita Orogen through Nd isotopes

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

Gleason, J.D.; Patchett, P.J.; Dickinson, W.R.

1992-01-01

A combined isotopic and trace-element study of the Late Paleozoic Ouachita Orogenic belt has the following goals: (1) define changing provenance of Ouachita sedimentary systems throughout the Paleozoic; (2) constrain sources feeding into the Ouachita flysch trough during the Late Paleozoic; (3) isolate the geochemical signature of proposed colliding terranes to the south; (4) build a data base to compare with possible Ouachita System equivalents in Mexico. The ultimate aim is to constrain the tectonic setting of the southern margin of North America during the Paleozoic, with particular emphasis on collisional events leading to the final suturing of Pangea. Ndmore » isotopic data identify 3 distinct groups: (1) Ordovician passive margin sequence; (2) Carboniferous proto-flysch (Stanley Fm.), main flysch (Jackfork and Atoka Fms.) and molasse (foreland Atoka Fm.); (3) Mississippian ash-flow tuffs. The authors interpret the Ordovician signature to be essentially all craton-derived, whereas the Carboniferous signature reflects mixed sources from the craton plus orogenic sources to the east and possibly the south, including the evolving Appalachian Orogen. The proposed southern source is revealed by the tuffs to be too old and evolved to be a juvenile island arc terrane. They interpret the tuffs to have been erupted in a continental margin arc-type setting. Surprisingly, the foreland molasse sequence is indistinguishable from the main trough flysch sequence, suggesting the Ouachita trough and the craton were both inundated with sediment of a single homogenized isotopic signature during the Late Carboniferous. The possibility that Carboniferous-type sedimentary dispersal patterns began as early as the Silurian has important implications for the tectonics and paleogeography of the evolving Appalachian-Ouachita Orogenic System.« less

Paleozoic Orogens of Mexico and the Laurentia-Gondwana Connections: an Update

NASA Astrophysics Data System (ADS)

Ortega-Gutierrez, F.

2009-05-01

The present position of Mexico in North America and the fixist tectonic models that prevailed prior to the seventies of the past century, have considered the main Paleozoic tectonic systems of Mexico as natural extensions of the orogens that fringed the eastern and southern sides of the Laurentian craton. Well known examples of pre-Mesozoic orogens in Mexico are the Oaxacan, Acatlan, and Chiapas polymetamorphic terranes, which have been correlated respectively with the Grenville and Appalachian-Ouachitan orogens of eastern North America. Nonetheless, several studies conducted during the last decade in these Mexican orogenic belts, have questioned their Laurentian connections, regarding northwestern Gondwana instead as the most plausible place for their birth and further tectonic evolution. This work pretends to approach the problem by briefly integrating the massive amount of new geological information, commonly generated through powerful dating methods such as LA-ICPM-MS on detrital zircon of sedimentary and metasedimentary units in the Paleozoic crustal blocks, which are widely exposed in southern and southeastern Mexico. The Acatlan Complex bears the closest relationships to the Appalachian orogenic system because it shows thermotectonic evidence for opening and closure of the two main oceans involved in building the Appalachian mountains in eastern Laurentia, whereas two other Paleozoic terranes in NW and SE Mexico, until recently rather geologically unknown, may constitute fundamental links between the Americas for the last-stage suturing and consolidation of western Pangea. The buried basement of the Yucatan platform (400,000 squared km) on the other hand, remains as one of the most relevant problems of tectonostratigraphic correlations across the Americas, because basement clasts from the Chicxulub impact ejecta reveal absolute and Nd-model ages that suggest close Gondwanan affinities. Major changes in the comprehension of the Paleozoic orogens in Mexico

Evidence for large-scale imbrication during Eocene syn-orogenic exhumation of the Hellenic subduction channel (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Grasemann, Bernhard; Huet, Benjamin; Schneider, David; Rice, Hugh; Lemonnier, Nicolas; Tschegg, Cornelius

2017-04-01

In the Cyclades, Miocene post-orogenic back-arc extension overprinted the exhumed syn- orogenic Eocene subduction channel. Whereas the exact geometry and kinematics of the syn-orogenic exhumation are still controversial, but must have involved a floor thrust and an apparent normal fault at the roof, the post-orogenic extension, leading to the exhumation of Cordilleran-type metamorphic core complexes, is well constrained by several major detachment systems. On the island of Milos, which is part of the South Aegean Volcanic Arc, minor outcrops of schist occur. New data indicate that these witnessed Eocene blueschist facies metamorphism at 8.5 kbar and 400°C, but escaped the Miocene extensional overprint, as they lie in the hanging wall of the West Cycladic Detachment System. In contrast, eclogite pebbles in "Green Lahars" on Milos yield metamorphic conditions of 19.5 kbar at 550°C. Both high-pressure units belong to the Cycladic Blueschist Unit and can only have been juxtaposed by thrusting. This indicates that two nappes, the newly defined Cycladic Blueschist Nappe and the overlying Cycladic Eclogite Nappe, both comprising rocks of the Cycladic Blueschist Unit, exist on Milos. These nappes probably also form the other Cycladic islands, separated by a syn-orogenic thrust, which we name the Trans Cycladic Thrust. The Trans Cycladic Thrust, which traces the orientation of the syn-orogenic exhumation channel, is partly offset by the post-orogenic Miocene extensional detachment systems. As a result of the Mid- to Late Miocene clockwise crustal block rotation, the syn-orogenic channel, and hence the Trans Cycladic Thrust, bends through 90° at Milos, changing from a W-E trending to a N-S trending extrusion-related stretching lineation. Restoration of the Miocene block-rotation and extension results in syn-orogenic thrusting kinematics (top-SSW) in the Cycladic Blueschist Nappe and along the Trans Cycladic Thrust and syn-orogenic apparent normal faulting kinematics (top

Lateral thinking: 2-D interpretation of thermochronology in convergent orogenic settings

NASA Astrophysics Data System (ADS)

Batt, Geoffrey E.; Brandon, Mark T.

2002-05-01

Lateral motion of material relative to the regional thermal and kinematic frameworks is important in the interpretation of thermochronology in convergent orogens. Although cooling ages in denuded settings are commonly linked to exhumation, such data are not related to instantaneous behavior but rather to an integration of the exhumation rates experienced between the thermochronological 'closure' at depth and subsequent exposure at the surface. The short spatial wavelength variation of thermal structure and denudation rate typical of orogenic regions thus renders thermochronometers sensitive to lateral motion during exhumation. The significance of this lateral motion varies in proportion with closure temperature, which controls the depth at which isotopic closure occurs, and hence, the range of time and length scales over which such data integrate sample histories. Different chronometers thus vary in the fundamental aspects of the orogenic character to which they are sensitive. Isotopic systems with high closure temperature are more sensitive to exhumation paths and the variation in denudation and thermal structure across a region, while those of lower closure temperature constrain shorter-term behaviour and more local conditions. Discounting lateral motion through an orogenic region and interpreting cooling ages purely in terms of vertical exhumation can produce ambiguous results because variation in the cooling rate can result from either change in kinematics over time or the translation of samples through spatially varying conditions. Resolving this ambiguity requires explicit consideration of the physical and thermal framework experienced by samples during their exhumation. This can be best achieved through numerical simulations coupling kinematic deformation to thermal evolution. Such an approach allows the thermochronological implications of different kinematic scenarios to be tested, and thus provides an important means of assessing the contribution of

Topographic evolution of orogens: The long term perspective

NASA Astrophysics Data System (ADS)

Robl, Jörg; Hergarten, Stefan; Prasicek, Günther

2017-04-01

The landscape of mountain ranges reflects the competition of tectonics and climate, that build up and destroy topography, respectively. While there is a broad consensus on the acting processes, there is a vital debate whether the topography of individual orogens reflects stages of growth, steady-state or decay. This debate is fuelled by the million-year time scales hampering direct observations on landscape evolution in mountain ranges, the superposition of various process patterns and the complex interactions among different processes. In this presentation we focus on orogen-scale landscape evolution based on time-dependent numerical models and explore model time series to constrain the development of mountain range topography during an orogenic cycle. The erosional long term response of rivers and hillslopes to uplift can be mathematically formalised by the stream power and mass diffusion equations, respectively, which enables us to describe the time-dependent evolution of topography in orogens. Based on a simple one-dimensional model consisting of two rivers separated by a watershed we explain the influence of uplift rate and rock erodibility on steady-state channel profiles and show the time-dependent development of the channel - drainage divide system. The effect of dynamic drainage network reorganization adds additional complexity and its effect on topography is explored on the basis of two-dimensional models. Further complexity is introduced by coupling a mechanical model (thin viscous sheet approach) describing continental collision, crustal thickening and topography formation with a stream power-based landscape evolution model. Model time series show the impact of crustal deformation on drainage networks and consequently on the evolution of mountain range topography (Robl et al., in review). All model outcomes, from simple one-dimensional to coupled two dimensional models are presented as movies featuring a high spatial and temporal resolution. Robl, J., S

Limited climate control of the Chugach/St. Elias thrust wedge in southern Alaska demonstrated by orogenic widening during Pliocene to Quaternary climate change

NASA Astrophysics Data System (ADS)

Meigs, Andrew

2014-05-01

Critical taper wedge theory is the gold standard by which climate control of convergent orogenic belts is inferred. The theory predicts (and models reproduce) that an orogenic belt narrows if erosion increases in erosion in the face of a constant tectonic influx. Numerous papers now argue on the basis of thermochronologic data that the Chugach/ St. Elias Range (CSE) of southern Alaska narrowed as a direct response to Quaternary climate change because glaciers dominated erosion of the orogenic belt. The CSE formed in response to collision of a microplate with North America and is notable because glacial erosion has dominated the CSE for the past 5 to 6 Ma. An increase in sediment accumulation rates in the foreland basin over that time suggests that glacial erosion become more efficient. If correct, it is possible that glacial erosion outpaced rock influx thereby inducing a climatically controlled narrowing of the orogenic wedge during the Quaternary. Growth strata preserved within the wedge provide a test of that interpretation because they demonstrate the spatial and temporal pattern of deformation during the Pliocene to Quaternary climate transition. A thrust front established between 6 and 5 Ma jumped towards the foreland by 30 and 15 km at 1.8 and 0.25 Ma, respectively. Distributed deformation within the thrust belt accompanied the thrust front relocations. Continuous exhumation recorded by low-temperature thermochronometers occurred contemporaneously with the shortening, parallel the structural not the topographic grain, and ages become younger towards the foreland as well. Interpreted in terms of critical wedge theory, continuous distributed deformation reflects a sub-critical wedge taper resulting from the combined effects of persistent exhumation and incremental accretion and orogenic widening via thrust front jumps into the undeformed foreland. Taper angle varies according to published cross-sections and ranges from 3 to 9 degrees. If the wedge oscillated

Shear fabrics reveal orogen-parallel deformations, NW Lesser Garhwal Himalaya, Uttarakhand, India

NASA Astrophysics Data System (ADS)

Biswas, T.; Bose, N.; Mukherjee, S.

2017-12-01

Shear deformation along the Himalayan belt is poorly understood unlike that across the orogen. Field observations and structural analysis along Bhagirathi river section along the National Highway 34 reveals NW Lesser Himalaya (Garhwal region, India) suffered both compression and extension parallel to the orogenic belt and thus forms a unique venue of great structural and tectonic interest. Meso-scale ductile- and brittle shear fabrics, such as S-C, C-P, Y-P, Y-S; are emphasized describing such deformations. Extensional shear fabric strikes N43oE and compressional shear fabrics N39.5oE, which are at a low-angle with the orogenic trend. Our study reviews orogen parallel deformation, both extension as well as compression, taking examples from other part of the world (e.g., Central Andes, N Apennines and SW Alps) and from other terrains in the Himalaya. Proposed models are evaluated and compared with the study area. The results shows that the pre-existing remnant structures (e.g., the Delhi-Haridwar ridge) on the under-thrusting Indian shield/plate plays a vital role in modifying thin-skinned tectonics along with migration of the eastward extrusion of the Tibetian plateau (hinterland deformation) into the Himalayan foreland.

Geochemical evidence for Paleozoic crustal growth and tectonic conversion in the Northern Beishan Orogenic Belt, southern Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Yuan, Yu; Zong, Keqing; He, Zhenyu; Klemd, Reiner; Jiang, Hongying; Zhang, Wen; Liu, Yongsheng; Hu, Zhaochu; Zhang, Zeming

2018-03-01

The Beishan Orogenic Belt is located in the central southernmost part of the Central Asian Orogenic Belt (CAOB), which plays a key role in understanding the formation and evolution of the CAOB. Granitoids are the documents of crustal and tectonic evolution in orogenic belts. However, little is known regarding the petrogenesis and geodynamic setting of the widely distributed Paleozoic granitoids in the Northern Beishan Orogenic Belt (NBOB). The present study reveals significant differences concerning the petrogenesis and tectonic setting of early and late Paleozoic granitoids from the NBOB. The early Paleozoic granitoids from the 446-430 Ma Hongliuxia granite complex of the Mazongshan unit and the 466-428 Ma Shibanjing complex of the Hanshan unit show classic I-type granite affinities as revealed by the relative enrichment of LILEs and LREEs, pronounced depletions of Nb, Ta and Ti and the abundant presence of hornblende. Furthermore, they are characterized by strongly variable zircon εHf(t) values between - 16.7 and + 12.8 and evolved plagioclase Sr isotopic compositions of 0.7145-0.7253, indicating the involvement of both juvenile and ancient continental crust in the magma source. Thus, we propose that the early Paleozoic granitoids in the NBOB were generated in a subduction-related continental arc setting. In contrast, the late Paleozoic 330-281 Ma granitoids from the Shuangjingzi complex of the Hanshan unit exhibit positive zircon εHf(t) values between + 5.8 and + 13.2 and relatively depleted plagioclase Sr isotopic compositions of 0.7037-0.7072, indicating that they were mainly formed by remelting of juvenile crust. Thus, an intra-plate extensional setting is proposed to have occurred during formation of the late Paleozoic granitoids. Therefore, between the early and late Paleozoic, the magma sources of the NBOB granitoids converted from the reworking of both juvenile and ancient crusts during a subduction-induced compressional setting to the remelting of

Some aspects of the role of rift inheritance on Alpine-type orogens

NASA Astrophysics Data System (ADS)

Tugend, Julie; Manatschal, Gianreto; Mohn, Geoffroy; Chevrot, Sébastien

2017-04-01

Processes commonly recognized as fundamental for the formation of collisional orogens include oceanic subduction, arc-continent and continent-continent collision. As collisional belts result from the closure of oceanic basins and subsequent inversion of former rifted margins, their formation and evolution may also in theory be closely interlinked with the initial architecture of the former rifted margins. This assumption is indeed more likely to be applicable in the case of Alpine-type orogens, mainly controlled by mechanical processes and mostly devoid of arc-related magmatism. More and more studies from present-day magma-poor rifted margins illustrate the complex evolution of hyperextended domains (i.e. severely thinned continental crust (<10 km) and/or exhumed serpentinized mantle with relatively minor magmatic additions) between unequivocal continental and oceanic domains. In this contribution, we compare the deep structure of the Pyrenean and Alpine belts to discuss some aspects of the relative role of rift-inherited hyperextension and collisional processes in building Alpine-type orogens. The Pyrenees and Western to Central Alps respectively result from the inversion of a Late Jurassic to Mid Cretaceous and an Early to Middle Jurassic rift system eventually floored by hyperextended crust, exhumed mantle and/or proto-oceanic crust. In spite of uncertainties on the initial width of the hyperextended and proto-oceanic domains, the rift-related pre-collisional architecture of the Alps shows many similarities with that proposed for the Pyrenees. Remnants of these domains occur in the internal parts of both orogens, but they are largely affected by orogeny-related deformation and show a HP-LT to HT-MP metamorphic overprint in the Alps as a result of a polyphase deformation history. Yet, recent high-resolution tomographic images across the Pyrenees (PYROPE) and the Alps (CIFALPS) reveal a surprisingly comparable present-day overall crustal and lithospheric structure

Architecture of orogenic belts and convergent zones in Western Ishtar Terra, Venus

NASA Technical Reports Server (NTRS)

Head, James W.; Vorderbruegge, R. W.; Crumpler, L. S.

1989-01-01

Linear mountain belts in Ishtar Terra were recognized from Pioneer-Venus topography, and later Arecibo images showed banded terrain interpreted to represent folds. Subsequent analyses showed that the mountains represented orogenic belts, and that each had somewhat different features and characteristics. Orogenic belts are regions of focused shortening and compressional deformation and thus provide evidence for the nature of such deformation, processes of crustal thickening (brittle, ductile), and processes of crustal loss. Such information is important in understanding the nature of convergent zones on Venus (underthrusting, imbrication, subduction), the implications for rates of crustal recycling, and the nature of environments of melting and petrogenesis. The basic elements of four convergent zones and orogenic belts in western Ishtar Terra are identified and examined, and then assess the architecture of these zones (the manner in which the elements are arrayed), and their relationships. The basic nomenclature of the convergent zones is shown.

Tectonic controls of Mississippi Valley-type lead-zinc mineralization in orogenic forelands

USGS Publications Warehouse

Bradley, D.C.; Leach, D.L.

2003-01-01

Most of the world's Mississippi Valley-type (MVT) zinc-lead deposits occur in orogenic forelands. We examine tectonic aspects of foreland evolution as part of a broader study of why some forelands are rich in MVT deposits, whereas others are barren. The type of orogenic foreland (collisional versus Andean-type versus inversion-type) is not a first-order control, because each has MVT deposits (e.g., Northern Arkansas, Pine Point, and Cevennes, respectively). In some MVT districts (e.g., Tri-State and Central Tennessee), mineralization took place atop an orogenic forebulge, a low-amplitude (a few hundred meters), long-wavelength (100-200 km) swell formed by vertical loading of the foreland plate. In the foreland of the active Banda Arc collision zone, a discontinuous forebulge reveals some of the physiographic and geologic complexities of the forebulge environment, and the importance of sea level in determining whether or not a forebulge will emerge and thus be subject to erosion. In addition to those on extant forebulges, some MVT deposits occur immediately below unconformities that originated at a forebulge, only to be subsequently carried toward the orogen by the plate-tectonic conveyor (e.g., Daniel's Harbour and East Tennessee). Likewise, some deposits are located along syn-collisional, flexure-induced normal and strike-slip faults in collisional forelands (e.g., Northern Arkansas, Daniel's Harbour, and Tri-State districts). These findings reveal the importance of lithospheric flexure, and suggest a conceptual tectonic model that accounts for an important subset of MVT deposits-those in the forelands of collisional orogens. The MVT deposits occur both in flat-lying and in thrust-faulted strata; in the latter group, mineralization postdated thrusting in some instances (e.g., Picos de Europa) but may have predated thrusting in other cases (e.g., East Tennessee).

Devonian post-orogenic extension-related volcano-sedimentary rocks in the northern margin of the Tibetan Plateau, NW China: Implications for the Paleozoic tectonic transition in the North Qaidam Orogen

NASA Astrophysics Data System (ADS)

Qin, Yu; Feng, Qiao; Chen, Gang; Chen, Yan; Zou, Kaizhen; Liu, Qian; Jiao, Qianqian; Zhou, Dingwu; Pan, Lihui; Gao, Jindong

2018-05-01

The Maoniushan Formation in the northern part of the North Qaidam Orogen (NQO), NW China, contains key information on a Paleozoic change in tectonic setting of the NQO from compression to extension. Here, new zircon U-Pb, petrological, and sedimentological data for the lower molasse sequence of the Maoniushan Formation are used to constrain the timing of this tectonic transition. Detrital zircons yield U-Pb ages of 3.3-0.4 Ga with major populations at 0.53-0.4, 1.0-0.56, 2.5-1.0, and 3.3-2.5 Ga. The maximum depositional age of the Maoniushan Formation is well constrained by a youngest detrital zircon age of ∼409 Ma. Comparing these dates with geochronological data for the region indicates that Proterozoic-Paleozoic zircons were derived mainly from the NQO as well as the Oulongbuluk and Qaidam blocks, whereas Archean zircons were probably derived from the Oulongbuluk Block and the Tarim Craton. The ∼924, ∼463, and ∼439 Ma tectonothermal events recorded in this region indicate that the NQO was involved in the early Neoproterozoic assembly of Rodinia and early Paleozoic microcontinental convergence. A regional angular unconformity between Devonian and pre-Devonian strata within the NQO suggests a period of strong mountain building between the Oulongbuluk and Qaidam blocks during the Silurian, whereas an Early Devonian post-orogenic molasse, evidence of extensional collapse, and Middle to Late Devonian bimodal volcanic rocks and Carboniferous marine carbonate rocks clearly reflect long-lived tectonic extension. Based on these results and the regional geology, we suggest that the Devonian volcano-sedimentary rocks within the NQO were formed in a post-orogenic extensional setting similar to that of the East Kunlun Orogen, indicating that a major tectonic transition from compression to extension in these two orogens probably commenced in the Early Devonian.

Earthquake activity along the Himalayan orogenic belt

NASA Astrophysics Data System (ADS)

Bai, L.; Mori, J. J.

2017-12-01

The collision between the Indian and Eurasian plates formed the Himalayas, the largest orogenic belt on the Earth. The entire region accommodates shallow earthquakes, while intermediate-depth earthquakes are concentrated at the eastern and western Himalayan syntaxis. Here we investigate the focal depths, fault plane solutions, and source rupture process for three earthquake sequences, which are located at the western, central and eastern regions of the Himalayan orogenic belt. The Pamir-Hindu Kush region is located at the western Himalayan syntaxis and is characterized by extreme shortening of the upper crust and strong interaction of various layers of the lithosphere. Many shallow earthquakes occur on the Main Pamir Thrust at focal depths shallower than 20 km, while intermediate-deep earthquakes are mostly located below 75 km. Large intermediate-depth earthquakes occur frequently at the western Himalayan syntaxis about every 10 years on average. The 2015 Nepal earthquake is located in the central Himalayas. It is a typical megathrust earthquake that occurred on the shallow portion of the Main Himalayan Thrust (MHT). Many of the aftershocks are located above the MHT and illuminate faulting structures in the hanging wall with dip angles that are steeper than the MHT. These observations provide new constraints on the collision and uplift processes for the Himalaya orogenic belt. The Indo-Burma region is located south of the eastern Himalayan syntaxis, where the strike of the plate boundary suddenly changes from nearly east-west at the Himalayas to nearly north-south at the Burma Arc. The Burma arc subduction zone is a typical oblique plate convergence zone. The eastern boundary is the north-south striking dextral Sagaing fault, which hosts many shallow earthquakes with focal depth less than 25 km. In contrast, intermediate-depth earthquakes along the subduction zone reflect east-west trending reverse faulting.

Lithosphere structure of the west Qinling orogenic belt revealed by deep seismic reflection profile

NASA Astrophysics Data System (ADS)

Wang, H.

2009-12-01

The west Qinling orogen located in the northeastern margin of the Qinghai-Tibet plateau, is transformation zone between the N-S-trending and E-W-trending tectonics in the Chinese continent. Further study of the fine crust structure of the west Qinling orogen and its relationships with surrounding basins have very important significance for understanding tectonic response of the northeastern margin of the plateau about collision convergence of the Indian block and Asian block and learning formation and evolution of the plateau. In 2009, we reprocessed the data of the Tangke-Hezuo deep seismic reflection profiles collected in 2004 across the west Qinling orogen and the northern Songpan block. The new results show the lithosphere fine structure of the west Qinling orogen. Reflection features indicate that an interface at 6.0-7.0s (TWT) divided the crust into the upper and lower crust, whose structural style and deformation are totally different. Integrating geological data, we deduce that the interface at 6.0-7.0s (depth with 18-21 km) was the basement detachment, which made deformation decoupled of the upper and lower crust. The multi-layered reflections in the upper crust reveal the sedimentary covers of the west Qinling orogen, disclose the thickness of the various structure layer and deformation degree, and provide a basis for the prospective evaluation of a multi-metallic mineral and energy exploration. The north dipping strong reflection characteristics of the lower crust in the west Qinling orogen constituted imbricate structure, such imbricate structural features provide seismology evidence for researching the west Qinling thrusting toward the northern Songpan block, and have great significance for studying formation and evolution of the Songpan-Garze structure. Moho reflections are observed around 17.0-17.2s, characterized by nearly horizontal reflections, which implies the west Qinling orogen underwent an intense extension post orogeny caused the lithosphere

Timing of crust formation and recycling in accretionary orogens: Insights learned from the western margin of South America

NASA Astrophysics Data System (ADS)

Bahlburg, Heinrich; Vervoort, Jeffrey D.; Du Frane, S. Andrew; Bock, Barbara; Augustsson, Carita; Reimann, Cornelia

2009-12-01

Accretionary orogens are considered major sites of formation of juvenile continental crust. In the central and southern Andes this is contradicted by two observations: siliciclastic fills of Paleozoic basins in the central Andean segment of the accretionary Terra Australis Orogen consist almost exclusively of shales and mature sandstones; and magmatic rocks connected to the Famatinian (Ordovician) and Late Paleozoic magmatic arcs are predominantly felsic and characterized by significant crustal contamination and strongly unradiogenic Nd isotope compositions. Evidence of juvenile crustal additions is scarce. We present laser ablation (LA)-ICPMS U-Pb ages and LA-MC-ICPMS Hf isotope data of detrital zircons from seven Devonian to Permian turbidite sandstones incorporated into a Late Paleozoic accretionary wedge at the western margin of Gondwana in northern Chile. The combination with Nd whole-rock isotope data permits us to trace the evolution of the South American continental crust through several Proterozoic and Paleozoic orogenic cycles. The analyzed detrital zircon spectra reflect all Proterozoic orogenic cycles representing the step-wise evolution of the accretionary SW Amazonia Orogenic System between 2.0 and 0.9 Ga, followed by the Terra Australis Orogen between 0.9 and 0.25 Ga. The zircon populations are characterized by two prominent maxima reflecting input from Sunsas (Grenville) age magmatic rocks (1.2-0.9 Ga) and from the Ordovician to Silurian Famatinian magmatic arc (0.52-0.42 Ga). Grains of Devonian age are scarce or absent from the analyzed zircon populations. The Hf isotopic compositions of selected dated zircons at the time of their crystallization ( ɛHf ( T) ; T = 3.3-0.25 Ga) vary between - 18 and + 11. All sandstones have a significant juvenile component; between 20 and 50% of the zircons from each sedimentary rock have positive ɛHf ( T) and can be considered juvenile. The majority of the juvenile grains have Hf-depleted mantle model ages (Hf

The main features of the Uralian Paleozoic magmatism and the epioceanic nature of the orogen

NASA Astrophysics Data System (ADS)

Fershtater, G. B.

2013-02-01

The 2000 km Uralian Paleozoic orogen is situated on the western flank of the Uralo-Mongolian folded belt. It is characterized by an abundant variety of magmatic rocks and related ore deposits. Uralian Paleozoic magmatism is entirely subduction-related. It is proposed that the Uralian orogen represents a cold mobile belt in which the mantle temperature was 200 to 500 °C cooler than in the adjacent areas; a situation which is similar to the modern West Pacific Triangle Zone including Indonesia, the Philippine Islands, and southern Asia. During the course of the geological evolution of the Uralian orogen, the nature of the magmatism has changed from basic rocks of indisputable mantle origin (460-390 Ma) to mantle-crust gabbro-granitic complexes (370-315 Ma) followed by pure crustal granite magmatism (290-250 Ma). This order in rock type and age reflects the evolution of Paleozoic magmatic complexes from the beginning of subduction to the final stages of the orogen development.

Complex high-strain deformation in the Usagaran Orogen, Tanzania: structural setting of Palaeoproterozoic eclogites

NASA Astrophysics Data System (ADS)

Reddy, S. M.; Collins, A. S.; Mruma, A.

2003-11-01

The Palaeoproterozoic Usagaran Orogen of Tanzania contains the Earth's oldest reported examples of subduction-related eclogite facies rocks. Detailed field mapping of gneisses exposed in the high-grade, eclogite-bearing part of the orogen (the Isimani Suite) indicates a complex deformation and thermal history. Deformation in the Isimani Suite can be broadly subdivided into five events. The first of these (D 1), associated with formation of eclogite facies metamorphism, is strongly overprinted by a pervasive deformation (D 2) at amphibolite facies conditions, which resulted in the accumulation of high strains throughout all of the exposed Isimani rocks. The geometry of foliations and lineations developed during D 2 deformation are variable and have different shear directions that enable five D 2 domains to be identified. Analysis of these domains indicates a geometrical and kinematic pattern that is interpreted to have formed by strain and kinematic partitioning during sinistral transpression. U-Pb SHRIMP zircon ages from a post-D 2 granite and previously published geochronological data from the Usagaran eclogites indicate this deformation took place between 2000 ± 1 Ma and 1877 ± 7 Ma (at 1σ error). Subsequent greenschist facies deformation, localised as shear zones on boundaries separating D 2 domains, have both contractional and extensional geometries that indicate post-1877 Ma reactivation of the Isimani Suite. This reactivation may have taken place during Palaeoproterozoic exhumation of the Usagaran Orogen or may be the result of deformation associated with the Neoproterozoic East African Orogen. U-Th-Pb SHRIMP zircon ages from an Isimani gneiss sample and xenocrysts in a "post-tectonic" granite yield ˜2.7 Ga ages and are similar to published Nd model ages from both the Tanzanian Craton and gneiss exposed east of the Usagaran belt in the East African Orogen. These age data indicate that the Isimani Suite of the Usagaran Orogen reflects reworking of Archaean

Axial Belt Provenance: modern river sands from the core of collision orogens

NASA Astrophysics Data System (ADS)

Resentini, A.; Vezzoli, G.; Paparella, P.; Padoan, M.; Andò, S.; Malusà, M.; Garzanti, E.

2009-04-01

Collision orogens have a complex structure, including diverse rock units assembled in various ways by geodynamic processes. Consequently, orogenic detritus embraces a varied range of signatures, and unravelling provenance of clastic wedges accumulated in adjacent foreland basins, foredeeps, or remnant-ocean basins is an arduous task. Dickinson and Suczek (1979) and Dickinson (1985) recognized the intrinsically composite nature of orogenic detritus, but did not attempt to establish clear conceptual and operational distinctions within their broad "Recycled Orogenic Provenance". In the Alpine and Himalayan belts, the bulk of the detritus is produced by focused erosion of the central backbone of the orogen, characterized by high topography and exhumation rates (Garzanti et al., 2004; Najman, 2006). Detritus derived from such axial nappe pile, including slivers of thinned continental-margin lithosphere metamorphosed at depth during early collisional stages, has diagnostic general features, which allows us to define an "Axial Belt Provenance" (Garzanti et al., 2007). In detail, "Axial Belt" detrital signatures are influenced by metamorphic grade of source rocks and relative abundance of continental versus oceanic protoliths, typifying distinct subprovenances. Metasedimentary cover nappes shed lithic to quartzolithic detritus, including metapelite, metapsammite, and metacarbonate grains of various ranks; only amphibolite-facies metasediments supply abundant heavy minerals (e.g., almandine garnet, staurolite, kyanite, sillimanite, diopsidic clinopyroxene). Continental-basement nappes shed hornblende-rich quartzofeldspathic detritus. Largely retrogressed blueschist to eclogite-facies metaophiolites supply albite, metabasite and foliated antigorite-serpentinite grains, along with abundant heavy minerals (epidote, zoisite, clinozoisite, lawsonite, actinolitic to barroisitic amphiboles, glaucophane, omphacitic clinopyroxene). Increasing metamorphic grade and deeper

Deformation during terrane accretion in the Saint Elias orogen, Alaska

USGS Publications Warehouse

Bruhn, R.L.; Pavlis, T.L.; Plafker, G.; Serpa, L.

2004-01-01

The Saint Elias orogen of southern Alaska and adjacent Canada is a complex belt of mountains formed by collision and accretion of the Yakutat terrane into the transition zone from transform faulting to subduction in the northeast Pacific. The orogen is an active analog for tectonic processes that formed much of the North American Cordillera, and is also an important site to study (1) the relationships between climate and tectonics, and (2) structures that generate large- to great-magnitude earthquakes. The Yakutat terrane is a fragment of the North American plate margin that is partly subducted beneath and partly accreted to the continental margin of southern Alaska. Interaction between the Yakutat terrane and the North American and Pacific plates causes significant differences in the style of deformation within the terrane. Deformation in the eastern part of the terrane is caused by strike-slip faulting along the Fairweather transform fault and by reverse faulting beneath the coastal mountains, but there is little deformation immediately offshore. The central part of the orogen is marked by thrusting of the Yakutat terrane beneath the North American plate along the Chugach-Saint Elias fault and development of a wide, thin-skinned fold-and-thrust belt. Strike-slip faulting in this segment may he localized in the hanging wall of the Chugach-Saint Elias fault, or dissipated by thrust faulting beneath a north-northeast-trending belt of active deformation that cuts obliquely across the eastern end of the fold-and-thrust belt. Superimposed folds with complex shapes and plunging hinge lines accommodate horizontal shortening and extension in the western part of the orogen, where the sedimentary cover of the Yakutat terrane is accreted into the upper plate of the Aleutian subduction zone. These three structural segments are separated by transverse tectonic boundaries that cut across the Yakutat terrane and also coincide with the courses of piedmont glaciers that flow from

Accretionary and collisional orogenesis in the south domain of the western Central Asian Orogenic Belt (CAOB)

NASA Astrophysics Data System (ADS)

Cai, Keda; Long, Xiaoping; Chen, Huayong; Sun, Min; Xiao, Wenjiao

2018-03-01

The Central Asian Orogenic Belt (CAOB) was the result of long-lived multi-stage tectonic evolution, including Proterozoic to Paleozoic accretion and collision, Mesozoic intracontinental modification, and Cenozoic rapid deformation and uplift. The accretionary and collisional orogenesis of its early history generated a huge orogenic collage consisting of diverse tectonic units including island arcs, ophiolites, accretionary prisms, seamounts, oceanic plateaus and micro-continents. These incorporated orogenic components preserved valuable detailed information on orogenic process and continental crust growth, which make the CAOB a key region to understanding of continental evolution, mantle-crust interaction and associated mineralization. The western CAOB refers to the west region in North Xinjiang of China and circum-Balkash of Kazakhstan, with occurrences of the spectacular Kazakhstan orocline and its surrounding mountain belts. Because orogenic fabrics of this part mostly preserve their original features caused by the interactions among the southern Siberian active margin in the north and the Tarim Craton in the south, the western CAOB can be regarded as an ideal region to study the processes of the accretionary and collisional orogenesis and associated mineralization. Since a large number of researchers have been working on this region, research advances bloom strikingly in a short-time period. Therefore, we, in this special issue, focus on these new study advances on the south domain of the western CAOB, including the Kazakhstan collage system, Tianshan orogenic belt and Beishan region, and it is anticipated that this issue can draw more attention from the international research groups to be interested in the studies on orogenesis of the CAOB.

Zircon (U-Th)/He evidence for pre-Eocene orogenic exhumation of eastern North Pyrenean massifs, France

NASA Astrophysics Data System (ADS)

Ternois, Sébastien; Vacherat, Arnaud; Pik, Raphaël; Ford, Mary; Tibari, Bouchaïb

2017-04-01

Orogens and their associated foreland basins are considered as part of a single dynamic system evolving from an early, non equilibrated, growth stage to a late, mature, steady-state stage. Most of our understanding in foreland basins, in particular early convergence-stage deposition, comes from the subducting plate, so that the classic paradigm for foreland basins is the pro-wedge. Models that clearly depict the relationship between erosion of the orogenic wedge and sedimentation into its associated foreland basin only focus on the late post-orogenic phase. Relatively little is known and understood about the very long phase of initiation of orogenesis. In the doubly wedged Pyrenean orogen, where we know and understand relatively little about how the early retro-wedge developed, the record of the onset of orogenic denudation from massifs is quite limited, not only in time but also in space. As part of the OROGEN project funded by TOTAL and the BRGM, this study presents first single-grain zircon (U-Th)/He data from two Palaeozoic massifs of the external Northern Pyrenean Zone, the Agly and Salvezines massifs. It aims at constraining the exhumation history of eastern Pyrenean massifs and understanding what is their significance for early orogenic wedge growth. The Pyrenean orogeny was generated from end Santonian (84 Ma) to Oligocene-Miocene due to convergence of the Iberian and European plates. Aquitaine foreland basin history (Ariège region) indicates that convergence took place in two phases, Campanian to Maastrichian and Eocene, separated by a quiet Paleocene phase. Yet, only Eocene cooling events are recorded by low-temperature thermochronometers in the central Pyrenean massifs (Arize and Trois-Seigneurs). Nine bedrock samples were collected along a WNW-ESE traverse (Salvezines and Saint-Arnac granites, Belesta-Caramany gneisses) and analysed for ZHe dating. Zircon (U-Th)/He data for the Agly and Salvezines massifs, together with forward modelling of data for

Lateral variations in lithospheric and landscape evolution at both ends of the Himalaya-Tibet orogen

NASA Astrophysics Data System (ADS)

Zeitler, P. K.; Schmidt, J. L.; Meltzer, A.

2015-12-01

At the broadest scale, like many orogens the Himalaya encompass a range of orogenic features that are remarkably similar along much of the length of the mountain belt and its neighboring terranes. At one scale of consideration, these similarities appear to be a signal that fundamental processes associated with lithospheric collision have been active. However, the vast size of the Himalaya and Tibet, the different climate regimes experienced by the orogen across time and space, and the along-strike variations in the continental and arc margins that faced one another before collision, make it at once remarkable that any similarities exist, and important to more critically evaluate their nature. The eastern and western Himalayan syntaxes confound any attempt to generalize too much about the Himalaya-Tibet orogen. By area these features occupy at least 25% of the orogenic belt, and compared to the "main" portions of the arc they show clear differences in their lithospheric structures, landscapes, and evolution. The boundary and initial conditions that shaped the eastern and western indentor corners were and are different, as is the nature and timing of erosional exhumation. Some of the most active geologic processes on Earth have recently been in play within the syntaxes, and the evolution of landscapes and fluvial systems, important in developing the sedimentary record of the Himalaya-Tibet system, has been complex and variable in space and time. Southeasternmost Tibet and the Lhasa Block in particular exemplify this complexity both in its complex topographic evolution linked to surface processes and climate, and in lateral variability in lithospheric structure. Taking a system viewpoint, an important question to debate is the degree to which there are features in the Himalaya-Tibet system that are robustly emergent, given the broad boundary conditions of the continental collision plus the suite of local and regional geodynamical processes that have operated during

Seismological Constraints on Lithospheric Evolution in the Appalachian Orogen

NASA Astrophysics Data System (ADS)

Fischer, K. M.; Hopper, E.; Hawman, R. B.; Wagner, L. S.

2017-12-01

Crust and mantle structures beneath the Appalachian orogen, recently resolved by seismic data from the EarthScope SESAME Flexible Array and Transportable Array, provide new constraints on the scale and style of the Appalachian collision and subsequent lithospheric evolution. In the southern Appalachians, imaging with Sp and Ps phases reveals the final (Alleghanian) suture between the crusts of Laurentia and the Gondwanan Suwannee terrane as a low angle (<15°) southward-dipping interface that soles into a flat-lying mid-crustal detachment. The suture location near the top of the crust coincides closely with the northern limit of the Suwannee terrane reconstructed from its lower Paleozoic shelf strata (Boote and Knapp, 2016). The observed suture geometry implies over 300 km of head-on shortening across a plate boundary structure similar in scale to the Himalayan mid-crustal detachment. While the suture and other structures from the Alleghanian collision are preserved in the upper and mid-crust, the lower crust and mantle lithosphere beneath this region have been significantly modified by later processes. Ps receiver functions, wavefield migration and SsPmp modeling reveal that crustal thickness reaches a maximum of 58 km (beneath high elevations in the Blue Ridge terrane) and decreases to 29-35 km (beneath lower elevations in the Carolina and Suwannee terranes). Given metamorphic estimates of unroofing (Duff and Kellogg, 2017) isostatic arguments indicate crustal thicknesses were 15-25 km larger at the end of the orogeny, indicating a thick crustal root across the region. The present-day residual crustal root beneath the Blue Ridge mountains is estimated to have a density contrast with the mantle of only 104±20 kg/m3. This value is comparable to other old orogens but lower than values typical of young or active orogens, indicating a loss of lower crustal buoyancy over time. At mantle depths, the negative shear velocity gradient that marks the transition from

Tectonic evolution of the Black Sea orogene belt and the history of opening of the Black Sea basin

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

Uesuemezsoy, S.

1988-08-01

The Black Sea basin is surrounded by successive orogenic belts of Hercynian, Cimmerian, and Alpine ages. The Rhodope, Thracian, western Pontian, and Transcaucasian (RTPT) blocks of Precambrian age were involved by the circum-Black Sea orogene belts. The Hercynian orogene was documented in the Balkanide, Great Caucasian, Kriastide, southern Pontian, and Transcaucasian belts. The Cimmerian orogene extended north and south of the Black Sea. The southern Cimmerian orogene was represented by the circum-Rhodope and East Thracian-Strandja-Kuere belts. The northern Cimmerian orogene belt extended along the Dobruca-Crimean and southern slope belts. Following the demise of the Black Sea Cimmerian basin, the northernmostmore » oceanic branch extending from Nish-Trajan through the present Black Sea to the intra-Transcaucasian basin, was opened within the Hercynian and Cimmerian consolidated terrain in the Late Jurassic. The other oceanic branch, extending from Izmir-Ankara through circum Kirsehir to various basins, was opened within the Paleotethyan collision belt, considered to be eastern extension of the Pindus basin. The Nish-Trajan sector of the northernmost basin was closed in the middle Cretaceous, and the Moesian platform re-fused to the Getic-Serbo-Macedonian-Rhodope belt. The easternmost extension of the intra-Transcaucasian basin disappeared in the Late Cretaceous. Consequently, the northernmost oceanic branch was reduced to the present Black Sea basin.« less

Lithologically controlled invisible gold, Yukon, Canada

NASA Astrophysics Data System (ADS)

MacKenzie, Doug; Craw, Dave; Finnigan, Craig

2015-02-01

The newly discovered Cretaceous Coffee orogenic gold deposit (>4 Moz resource) consists of an extensive oxidised zone developed on primary sulphidic rock. The primary mineralised rock is characterised by invisible gold in arsenian pyrite that has replaced biotite in selected host rocks. The deposit has a cryptic surface expression and is an example of an extremely subtle exploration target. Hydrothermal emplacement was controlled by extensional fractures, with breccias, but most mineralisation was focused on biotite-bearing granitic gneiss, metasedimentary gneisses, and younger biotite granite. Fine-grained (<0.1 mm) arsenian pyrite replaced biotite along mineral cleavage planes and followed biotite-rich metamorphic and post-metamorphic structural fabrics. Arsenian pyrite also formed overgrowths on earlier coarse-grained (up to 2 mm) barren hydrothermal pyrite. Arsenian pyrite is concentrically zoned on the 1-10-μm scale with respect to As, Sb, and Au contents and typically contains ˜5 wt% As, ˜500 mg/kg Sb, and ˜500 mg/kg Au, in solid solution. Biotite replacement was accompanied by sericitisation, silicification, and ankerite impregnation. Hydrothermal alteration involved dilution and localised depletion of K, Na, and Al in silicified host rocks, but most Ca, Mg, and Fe concentrations remained broadly constant. Magnesium-rich ultramafic host rocks were only weakly mineralised with auriferous arsenian pyrite and have fuchsite and magnesite alteration. Near-surface oxidation has liberated nanoparticulate and microparticulate supergene gold, which remains essentially invisible. Varying degrees of oxidation extend as deep as 250 m below the present subdued topographic surface, well beyond the present vadose zone, and this deep oxidation may have occurred during post-mineralisation uplift and erosion in the Cretaceous. Oxidation has leached some As from the surficial mineralised rocks, decreasing the geochemical signal, which is also obscured by the localised

Microdiamonds from the European Variscan Orogenic Belt

NASA Astrophysics Data System (ADS)

Kotkova, J.; Jakubova, P.; Whitehouse, M.; Fedortchouk, Y.

2014-12-01

Diamond, along with coesite, has been discovered recently in the continental crustal rocks of the European Variscan orogenic belt, namely the Bohemian Massif (BM). In addition to the garnet-phengite gneiss in Germany, western BM, microdiamond occurs in major rock forming minerals - garnet, kyanite - and in zircon in ultrahigh-pressure rocks overprinted under high-pressure granulite facies conditions (c. 16-20 kbar, c. 1000°C) in the northern and eastern BM. Well-preserved 10-30 μm-sized microdiamonds from northern BM exhibit diverse morphologies (SEM data) depending upon the host rock type. Octahedral diamond occurs in felsic garnet-kyanite-feldspar-quartz rock (metasediment), whereas intermediate garnet-clinopyroxene-feldspar-quartz rock contains a cubo-octahedral variety. Diamond morphology can be thus controlled by solid impurities available in the medium of crystallization (K- vs. Ca-bearing fluids or melts), as shown by experiments. Pointed-bottom negatively oriented trigonal etch pits on the octahedral diamond faces developed due to diamond resorption at CO2-dominated environment (less than 50 wt % of H2O, experimental data), possibly by action of a residual fluid. SIMS determined δ13C values range from -22 to -21 ‰ for the felsic rock and from - 26 to - 33 for the intermediate one, corresponding to the typical range of organic carbon δ13C and inconsistent with a significant mantle carbon (δ13C ~ - 5 ‰) input. Diamond-bearing domains in zircon, also analysed by SIMS, yielded a Variscan U-Pb age of c. 340 Ma. The present stage of knowledge allows us to conclude that (i) metamorphic diamonds in the BM occur in lithologies of metasedimentary character, and their carbon source was organic; (ii) crustal-derived CO2-rich fluids with impurities played an important role in diamond formation and dissolution; (iii) diamonds formed during the Variscan orogenic cycle and (iv) diamonds are best preserved in the external domain of the Variscan orogenic belt.

Anatexis of mafic and felsic lower crust: Geochemistry and Nd, Sr and Pb isotopes of late-orogenic granodiorites and leucogranites (Damara orogen, Namibia)

NASA Astrophysics Data System (ADS)

Osterhus, Lennart; Jung, Stefan

2010-05-01

The Damara orogen (Namibia) represents a well-exposed and deeply eroded orogenic mobile belt consisting of the north-south trending Kaoko belt and the northeast-southwest trending intracontinental Damara belt. The latter has been subdivided into a Northern, a Central and a Southern Zone based on stratigraphy, metamorphic grade, structure and geochronology. The late-orogenic granodioritic to leucogranitic Gawib pluton is a cross-cutting, pear-shaped post-tectonic stock within the southern Central Zone which is elsewhere dominated by basement rocks, high-grade metasedimentary rocks of the Tinkas Formation and syn-orogenic granites (Salem-type). The non-foliated granodiorites consist of plagioclase, quartz, microcline, hornblende and biotite whereas the leucogranites consist of microcline, quartz, plagioclase and biotite. Major element variation of the granodiorites show two distinct magma types were some samples have high TiO2, MgO and Fe2O3 and low Al2O3 and others have low TiO2, MgO and Fe2O3 and high Al2O3. Based on high REE, Nb, Zr and Y concentrations some granodiorites can be classified as A-type granitoids. Strontium concentrations are high in the granodiorites (up to 939 ppm) and decrease to < 200 ppm in the leucogranites. Rb/Sr ratios are low (1) in the leucogranites. Granodiorites have moderately radiogenic initial 87Sr/86Sr ratios (0.7088-0.7132), strongly negative initial ɛ Nd values (ca. -12) and comparatively unradiogenic Pb isotope data, the latter obtained on acid-leached feldspar separates. Leucogranites have more radiogenic initial 87Sr/86Sr ratios (0.7223-0.7336) and more negative initial ɛ Nd values (ca. -18). Pb isotopes tend to be less radiogenic than in the granodiorites. The mean crustal residence ages of the granodiorites, expressed as depleted mantle Nd model ages, are ca. 2.0 Ga but the leucogranites tend to have older Nd model ages (2.5 Ga). Therefore, a likely source for the granodiorites and leucogranites is a sequence of mafic to

High-pressure metamorphism in the southern New England Orogen: Implications for long-lived accretionary orogenesis in eastern Australia

NASA Astrophysics Data System (ADS)

Phillips, G.; Offler, R.; Rubatto, D.; Phillips, D.

2015-09-01

New geochemical, metamorphic, and isotopic data are presented from high-pressure metamorphic rocks in the southern New England Orogen (eastern Australia). Conventional and optimal thermobarometry are augmented by U-Pb zircon and 40Ar/39Ar phengite dating to define pressure-temperature-time (P-T-t) histories for the rocks. The P-T-t histories are compared with competing geodynamic models for the Tasmanides, which can be summarized as (i) a retreating orogen model, the Tasmanides formed above a continuous, west dipping, and eastward retreating subduction zone, and (ii) a punctuated orogen model, the Tasmanides formed by several arc accretion, subduction flip, and/or transference events. Whereas both scenarios are potentially supported by the new data, an overlap between the timing of metamorphic recrystallization and key stages of Tasmanides evolution favors a relationship between a single, long-lived subduction zone and the formation, exhumation, and exposure of the high-pressure rocks. By comparison with the retreating orogen model, the following links with the P-T-t histories emerge: (i) exhumation and underplating of oceanic eclogite during the Delamerian Orogeny, (ii) recrystallization of underplated and exhuming high-pressure rocks at amphibolite facies conditions coeval with a period of rollback, and (iii) selective recrystallization of high-pressure rocks at blueschist facies conditions, reflecting metamorphism in a cooled subduction zone. The retreating orogen model can also account for the anomalous location of the Cambrian-Ordovician high-pressure rocks in the Devonian-Carboniferous New England Orogen, where sequential rollback cycles detached and translated parts of the leading edge of the overriding plate to the next, younger orogenic cycle.

Evolving lithospheric flexure and paleotopography of the Pyrenean Orogen from 3D flexural modeling and basin analysis

NASA Astrophysics Data System (ADS)

Curry, M. E.; van der Beek, P.; Huismans, R. S.; Muñoz, J. A.

2017-12-01

The Pyrenees are an asymmetric, doubly-vergent orogen with retro- and pro- foreland basins that preserve a record of deformation since the Mesozoic. The extensive research and exploration efforts on the mountain belt and flanking foreland basins provide an exceptional dataset for investigating geodynamics and surface processes over large spatial and temporal scales in western Europe. We present the results of a numerical modeling study investigating the spatio-temporal variation in lithospheric flexure in response to the developing orogen. We employ a finite element method to model the 3D flexural deformation of the lithosphere beneath the Pyrenean orogen since the onset of convergence in the late Cretaceous. Using subsurface, geophysical, and structural data, we describe the evolving geometry of both the French Aquitaine and Spanish Ebro foreland basins at the present (post-orogenic), the mid-Eocene (peak orogenic), the Paleocene (early orogenic), and the end of the Cretaceous (pre- to early orogenic). The flexural modeling provides insight into how both the rigidity of the lithosphere and the paleotopographic load have varied over the course of orogenesis to shape the basin geometry. We find that the overriding European plate has higher rigidity than the subducting Iberian plate, with modern Effective Elastic Thickness (EET) values of 20 ± 2 and 12 ± 2 km, respectively. Modeling indicates that the modern rigidity of both plates decreases westward towards the Bay of Biscay. The lithospheric rigidity has increased by 50% since the Mesozoic with early Cenozoic EET values of 13 ± 2 and 8 ± 1 km for the European and Iberian plates, respectively. The topographic load began increasing with convergence in the late Cretaceous, reaching modern levels in the central and eastern Pyrenees by the Eocene. In contrast, the topographic load in the western Pyrenees was 70% of the modern value in the Eocene, and experienced topographic growth through the Oligo-Miocene. The

The susceptibility of large river basins to orogenic and climatic drivers

NASA Astrophysics Data System (ADS)

Haedke, Hanna; Wittmann, Hella; von Blanckenburg, Friedhelm

2017-04-01

Large rivers are known to buffer pulses in sediment production driven by changes in climate as sediment is transported through lowlands. Our new dataset of in situ cosmogenic nuclide concentration and chemical composition of 62 sandy bedload samples from the world largest rivers integrates over 25% of Earth's terrestrial surface, distributed over a variety of climatic zones across all continents, and represents the millennial-scale denudation rate of the sediment's source area. We can show that these denudation rates do not respond to climatic forcing, but faithfully record orogenic forcing, when analyzed with respective variables representing orogeny (strain rate, relief, bouguer anomaly, free-air anomaly), and climate (runoff, temperature, precipitation) and basin properties (floodplain response time, drainage area). In contrast to this orogenic forcing of denudation rates, elemental bedload chemistry from the fine-grained portion of the same samples correlates with climate-related variables (precipitation, runoff) and floodplain response times. It is also well-known from previous compilations of river-gauged sediment loads that the short-term basin-integrated sediment export is also climatically controlled. The chemical composition of detrital sediment shows a climate control that can originate in the rivers source area, but this signal is likely overprinted during transfer through the lowlands because we also find correlation with floodplain response times. At the same time, cosmogenic nuclides robustly preserve the orogenic forcing of the source area denudation signal through of the floodplain buffer. Conversely, previous global compilations of cosmogenic nuclides in small river basins show the preservation of climate drivers in their analysis, but these are buffered in large lowland rivers. Hence, we can confirm the assumption that cosmogenic nuclides in large rivers are poorly susceptible to climate changes, but are at the same time highly suited to detect

Cumberland batholith, Trans-Hudson Orogen, Canada: Petrogenesis and implications for Paleoproterozoic crustal and orogenic processes

NASA Astrophysics Data System (ADS)

Whalen, Joseph B.; Wodicka, Natasha; Taylor, Bruce E.; Jackson, Garth D.

2010-06-01

Large volume, plutonic belts, such as the ˜ 221,000 km 2, ca. 1.865-1.845 Ga Cumberland batholith (CB) of the Trans-Hudson Orogen in Canada, are major components of Paleoproterozoic orogenic belts. In many cases, they have been interpreted as continental arc batholiths. The petrogenesis and tectonic context of the CB and implications for crustal growth and recycling are interpreted herein based on a 900 km geochemical-isotopic (Nd-O) transect across it and into granitoid plutons within bounding Archean cratons in central and southern Baffin Island. The mainly granulite grade CB, emplaced over an age span of between 14 and 24 Ma, consists mainly of high-K to shoshonitic monzogranite and granodiorite, but also includes low- and medium-K granitoid rocks. Metaluminous to slightly peraluminous compositions and δ 18O (VSMOW) values (+ 6 to + 10‰) indicate derivation from infracrustal (I-type) sources. ɛ Nd 1.85 Ga signatures (- 12 to - 2) of both mafic and felsic units suggest a dominance of evolved sources. Isotopic signatures in the interior of the CB (- 2 to - 7) are more radiogenic than those within Archean domains in central (- 8 to - 15) and southern (- 5 to - 19) Baffin Island. The isotopic transect is interpreted as 'imaging' an accreted microcontinental block (Meta Incognita) and bounding Archean cratons. The CB includes granites of arc, within-plate (A-type) and post-collisional affinity and volumetrically minor mafic rocks with both arc and non-arc features. (La/Yb) CN and Sr/Y values range from < 1 to 225 and < 1 to 611, respectively. In these respects, some CB granitoid rocks resemble Paleozoic adakitic granites, interpreted as partial melts of greatly thickened crust within post-collisional settings, such as Tibet. Thus, the CB likely encompasses various non-consanguineous magmatic suites generated at deep- to mid-crustal depths. Although CB granitoid rocks undoubtedly had important crustal sources, it is hard to assess the relative contribution of

40Ar/39Ar geochronological constraints on the formation of the Dayingezhuang gold deposit: New implications for timing and duration of hydrothermal activity in the Jiaodong gold province, China

USGS Publications Warehouse

Yang, Li-Qiang; Deng, J.; Goldfarb, Richard J.; Zhang, Jiahua; Gao, Bang-Fei; Wang, Zhong-Liang

2014-01-01

China's largest gold resource is located in the highly endowed northwestern part of the Jiaodong gold province. Most gold deposits in this area are associated with the NE- to NNE-trending shear zones on the margins of the 130–126 Ma Guojialing granite. These deposits collectively formed at ca. 120 ± 5 Ma during rapid uplift of the granite. The Dayingezhuang deposit is a large (> 120 t Au) orogenic gold deposit in the same area, but located along the eastern margin of the Late Jurassic Linglong Metamorphic Core Complex. New 40Ar/39Ar geochronology on hydrothermal sericite and muscovite from the Dayingezhuang deposit indicate the gold event is related to evolution of the core complex at 130 ± 4 Ma and is the earliest important gold event that is well-documented in the province. The Dayingezhuang deposit occurs along the Linglong detachment fault, which defines the eastern edge of the ca. 160–150 Ma Linglong granite–granodiorite massif. The anatectic rocks of the massif were rapidly uplifted, at rates of at least 1 km/m.y. from depths of 25–30 km, to form the metamorphic core complex. The detachment fault, with Precambrian metamorphic basement rocks in the hangingwall and the Linglong granitoids and migmatites in the footwall, is characterized by early mylonitization and a local brittle overprinting in the footwall. Gold is associated with quartz–sericite–pyrite–K-feldspar altered footwall cataclasites at the southernmost area of the brittle deformation along the detachment fault. Our results indicate that there were two successive, yet distinct gold-forming tectonic episodes in northwestern Jiaodong. One event first reactivated the detachment fault along the edge of the Linglong massif between 134 and 126 Ma, and then a second reactivated the shears along the margins of the Guojialing granite. Both events may relate to a component of northwest compression after a middle Early Cretaceous shift from regional NW–SE extension to a NE�

Nature and provenance of the Beishan Complex, southernmost Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Zheng, Rongguo; Li, Jinyi; Xiao, Wenjiao; Zhang, Jin

2018-03-01

The ages and origins of metasedimentary rocks, which were previously mapped as Precambrian, are critical in rebuilding the orogenic process and better understanding the Phanerozoic continental growth in the Central Asian Orogenic Belt (CAOB). The Beishan Complex was widely distributed in the southern Beishan Orogenic Collage, southernmost CAOB, and their ages and tectonic affinities are still in controversy. The Beishan Complex was previously proposed as fragments drifted from the Tarim Craton, Neoproterozoic Block or Phanerozoic accretionary complex. In this study, we employ detrital zircon age spectra to constrain ages and provenances of metasedimentary sequences of the Beishan Complex in the Chuanshanxun area. The metasedimentary rocks here are dominated by zircons with Paleoproterozoic-Mesoproterozoic age ( 1160-2070 Ma), and yield two peak ages at 1454 and 1760 Ma. One sample yielded a middle Permian peak age (269 Ma), which suggests that the metasedimentary sequences were deposited in the late Paleozoic. The granitoid and dioritic dykes, intruding into the metasedimentary sequences, exhibit zircon U-Pb ages of 268 and 261 Ma, respectively, which constrain the minimum deposit age of the metasedimentary sequences. Zircon U-Pb ages of amphibolite (274 and 216 Ma) indicate that they might be affected by multi-stage metamorphic events. The Beishan Complex was not a fragment drifted from the Tarim Block or Dunhuang Block, and none of cratons or blocks surrounding Beishan Orogenic Collage was the sole material source of the Beishan Complex due to obviously different age spectra. Instead, 1.4 Ga marginal accretionary zones of the Columbia supercontinent might have existed in the southern CAOB, and may provide the main source materials for the sedimentary sequences in the Beishan Complex.

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

Taconic plate kinematics as revealed by foredeep stratigraphy, Appalachian Orogen

USGS Publications Warehouse

Bradley, D.C.

1989-01-01

Destruction of the Ordovician passive margin of eastern North America is recorded by an upward deepening succession of carbonates, shales, and flysch. Shelf drowning occurred first at the northern end of the orogen in Newfoundland, then at the southern end of the orogen in Georgia, and finally in Quebec. Diachronism is attributed to oblique collision between an irregular passive margin, that had a deep embayment in Quebec, and at least one east dipping subduction complex. The rate of plate convergence during collision is estimated at 1 to 2 cm/yr, and the minimum width of the ocean that closed is estimated at 500 to 900 km. The drowning isochron map provides a new basis for estimating tectonic transport distances of four of these allochthons (about 165 to 450 km), results not readily obtained by conventional structural analysis. -Author

Mineral potential tracts for orogenic, Carlin-like, and epithermal gold deposits in the Islamic Republic of Mauritania, (phase V, deliverable 68): Chapter H1 in Second projet de renforcement institutionnel du secteur minier de la République Islamique de Mauritanie (PRISM-II)

USGS Publications Warehouse

Goldfarb, Richard J.; Marsh, Erin; Horton, John D.

2012-01-01

This report contains the USGS results of the PRISM-II Mauritania Minerals Project and is presented in cooperation with the Ministry of Petroleum, Energy, and Mines of the Islamic Republic of Mauritania. The Report is composed of separate chapters consisting of multidisciplinary interpretive reports with accompanying plates on the geology, structure, geochronology, geophysics, hydrogeology, geochemistry, remote sensing (Landsat TM and ASTER), and SRTM and ASTER digital elevation models of Mauritania. The syntheses of these multidisciplinary data formed the basis for additional chapters containing interpretive reports on 12 different commodities and deposit types known to occur in Mauritania, accompanied by countrywide mineral resource potential maps of each commodity/deposit type. The commodities and deposit types represented include: (1) Ni, Cu, PGE, and Cr deposits hosted in ultramafic rocks; (2) orogenic, Carlin-like, and epithermal gold deposits; (3) polymetallic Pb-Zn-Cu vein deposits; (4) sediment-hosted Pb-Zn-Ag deposits of the SEDEX and Mississippi Valley-type; (5) sediment-hosted copper deposits; ( 6) volcanogenic massive sulfide deposits; (7) iron oxide copper-gold deposits; (8) uranium deposits; (9) Algoma-, Superior-, and oolitic-type iron deposits; (10) shoreline Ti-Zr placer deposits; (11) incompatible element deposits hosted in pegmatites, alkaline rocks, and carbonatites, and; (12) industrial mineral deposits. Additional chapters include the Mauritanian National Mineral Deposits Database are accompanied by an explanatory text and the Mauritania Minerals Project GIS that contains all of the interpretive layers created by USGS scientists. Raw data not in the public domain may be obtained from the Ministry of Petroleum, Energy, and Mines in Nouakchott, Mauritania.

Association of orogenic activity with the Ordovician radiation of marine life

NASA Technical Reports Server (NTRS)

Miller, A. I.; Mao, S.

1995-01-01

The Ordovician radiation of marine life was among the most substantial pulses of diversification in Earth history and coincided in time with a major increase in the global level of orogenic activity. To investigate a possible causal link between these two patterns, the geographic distributions of 6576 individual appearances of Ordovician vician genera around the world were evaluated with respect to their proximity to probable centers of orogeny (foreland basins). Results indicate that these genera, which belonged to an array of higher taxa that diversified in the Middle and Late Ordovician (trilobites, brachiopods, bivalves, gastropods, monoplacophorans), were far more diverse in, and adjacent to, foreland basins than they were in areas farther removed from orogenic activity (carbonate platforms). This suggests an association of orogeny with diversification at that time.

The effect of flexural isostasy on the response time of orogenic systems

NASA Astrophysics Data System (ADS)

Braun, J.; Margirier, A.; Guerit, L.

2017-12-01

The concept of orogenic steady-state implies that mountain belts can reach a dynamic balance between uplift and erosion in order to maintain a quasi-constant shape. The final morphology of the mountain will be a function of the relative efficiency between uplift and erosion and is therefore likely to be modulated by climate. However, reaching such a steady-state cannot be instantaneous and there must exist a time lag between the onset of convergence and the full development of the mountain topography. Similarly, when an orogenic system is subject to a marked change in convergence rate or in climatic conditions, it takes a certain time for it to adapt to such a change and develop a new steady-state morphology. It is during these transient phases that the nature and efficiency of the interactions between tectonics and climate are most likely to be constrained by observations and understood. The duration of this transient stage remains, however, poorly constrained and understood. As shown by many authors (Whipple and Tucker, 1999, for example) the rate at which tectonic systems evolve to reach steady-state is likely controlled by climate and rock strength, which both determine the efficiency of erosional processes, and the rate of uplift. Here we show that isostasy also plays a very important role in determining the length of the transient phase and that, depending on the level of isostatic adjustment, which in turn depends on the flexural strength of the underlying lithosphere, isostasy can change the time it takes for an orogenic system to reach steady-state by an order of magnitude, i.,e. from a few millions to a few tens of millions of years. This has very important implications. It may explain why many young orogenic systems display an increase in uplift and erosion rate millions of years after the onset of collision and that, in these situations, such an increase does not require a steady change in tectonic and/or climate conditions/forcing. We also show that

A discussion on the tectonic implications of Ediacaran late- to post-orogenic A-type granite in the northeastern Arabian Shield, Saudi Arabia

NASA Astrophysics Data System (ADS)

Robinson, F. A.; Bonin, B.; Pease, V.; Anderson, J. L.

2017-03-01

The transition from late-orogenic to post-orogenic magmatism following major orogenic episodes such as the Neoproterozoic to Cambrian East African Orogen (EAO) is an important, yet not well-understood geological event marking the cessation of subduction-controlled magmatism between buoyant lithospheric fragments. Forming the northern part of the EAO in the Arabian-Nubian Shield are three granitic suites that successively intruded the same northeastern area and post-date the 640 Ma major orogenic episode: (1) 620-600 Ma alkali feldspar (hypersolvous) granite with alkaline/ferroan/A-type geochemistry, (2) 599 Ma granite cumulates (some garnet-bearing) with calc-alkaline/magnesian affinities, and (3) 584-566 Ma alkali feldspar (hypersolvous) granite (aegirine-bearing) with a distinctive peralkaline/ferroan/A-type signature. Combining whole-rock geochemistry from the southern and northern Arabian Shield, suites 1 and 2 are suggested to be products of late-orogenic slab tear/rollback inducing asthenospheric mantle injection and lower crustal melting/fractionation toward A-type/ferroan geochemistry. Suite 3, however, is suggested to be produced by post-orogenic lithospheric delamination, which replaced the older mantle with new asthenospheric (rare earth element-enriched) mantle that ultimately becomes the thermal boundary layer of the new lithosphere. Major shear zones, such as the 620-540 Ma Najd Fault System (NFS), are some of the last tectonic events recorded across the Arabian Shield. Data presented here suggest that the NFS is directly related to the late-orogenic (620-600 Ma) slab tear/rollback in the northeastern Shield as it met with opposing subduction polarity in the southern Shield. Furthermore, this study infers that east and west Gondwana amalgamation interacted with opposing convergence reflected by the NFS.

Synchronous partial melting, deformation, and magmatism: evidence from in an exhumed Proterozoic orogen

NASA Astrophysics Data System (ADS)

Levine, J. S. F.; Mosher, S.

2017-12-01

Older orogenic belts that now expose the middle and lower crust record interaction between partial melting, magmatism, and deformation. A field- and microstructural-based case study from the Wet Mountains of central Colorado, an exhumed section of Proterozoic rock, shows structures associated with anatexis and magmatism, from the grain- to the kilometer-scale, that indicate the interconnection between deformation, partial melting, and magmatism, and allow reconstructions of the processes occurring in hot active orogens. Metamorphic grade, along with the degree of deformation, partial melting, and magmatism increase from northwest to southeast. Deformation synchronous with this high-grade metamorphic event is localized into areas with greater quantities of former melt, and preferential melting occurs within high-strain locations. In the less deformed northwest, partial melting occurs dominantly via muscovite-dehydration melting, with a low abundance of partial melting, and an absence of granitic magmatism. The central Wet Mountains are characterized by biotite dehydration melting, abundant former melt and foliation-parallel inferred melt channels along grain boundaries, and the presence of a nearby granitic pluton. Rocks in the southern portion of the Wet Mountains are characterized by partial melting via both biotite dehydration and granitic wet melting, with widespread partial melting as evidenced by well-preserved former melt microstructures and evidence for back reaction between melt and the host rocks. The southern Wet Mountains has more intense deformation and widespread plutonism than other locations and two generations of dikes and sills. Recognition of textures and fabrics associated with partial melting in older orogens is paramount for interpreting the complex interplay of processes occurring in the cores of orogenic systems.

Fault Dating in the US Rockies and Large Regional Extent of Deformation Pulses Along the Sevier Orogen of North America.

NASA Astrophysics Data System (ADS)

van der Pluijm, B.; Lynch, E. A.; Pana, D.; Yonkee, A.

2017-12-01

Recent Ar dating of clay-rich fault rock in the Canadian Rockies identified multiple orogenic pulses: Late Jurassic (163-146 Ma), Mid-Cretaceous (103-99 Ma), Late Cretaceous (76-72 Ma) and Eocene (54-52 Ma; Pana and van der Pluijm, GSAB 2015). New dating in the US Rockies combined with ages in the most frontal section along an Idaho-Wyoming transect show a remarkably similar age pattern: Meade Thrust, 108-102 Ma; (S)Absaroka Thrust, 73 Ma; Darby-Bear Thrust, 56-50 Ma. These radiometric fault ages in the US Rockies match field and tectono-stratigraphic predictions, analogues to those in the Canadian Rockies. Thus, a remarkably long (>1500km) lateral tract along the North American Sevier orogen is characterized by at least three major orogenic pulses that are structurally contiguous. These orogenic pulses are progressively younger in the direction of easterly thrust fault motion (toward cratonic interior) and are separated by long periods of relative tectonic quiescence. We interpret the extensive regional continuity of deformation pulses and tectonic quiescence along the Sevier Orogen as the result of three plate reorganization events in western North America since the Late Jurassic.

A crustal model of the ultrahigh-pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling

USGS Publications Warehouse

Wang, Chun-Yong; Zeng, Rong-Sheng; Mooney, W.D.; Hacker, B.R.

2000-01-01

We present a new crustal cross section through the east-west trending ultrahigh-pressure (UHP) Dabie Shan orogenic belt, east central China, based on a 400-km-long seismic refraction profile. Data from our profile reveal that the cratonal blocks north and south of the orogen are composed of 35-km-thick crust consisting of three layers (upper, middle, and lower crust) with average seismic velocities of 6.0±0.2 km/s, 6.5±0.1 km/s, and 6.8±0.1 km/s. The crust reaches a maximum thickness of 41.5 km beneath the northern margin of the orogen, and thus the present-day root beneath the orogen is only 6.5 km thick. The upper mantle velocity is 8.0±0.1 km/s. Modeling of shear wave data indicate that Poisson's ratio increases from 0.24±0.02 in the upper crust to 0.27±0.03 in the lower crust. This result is consistent with a dominantly felsic upper crustal composition and a mafic lower crustal composition within the amphibolite or granulite metamorphic facies. Our seismic model indicates that eclogite, which is abundant in surface exposures within the orogen, is not a volumetrically significant component in the middle or lower crust. Much of the Triassic structure associated with the formation of the UHP rocks of the Dabie Shan has been obscured by post-Triassic igneous activity, extension and large-offset strike-slip faulting. Nevertheless, we can identify a high-velocity (6.3 km/s) zone in the upper (<5 km depth) crustal core of the orogen which we interpret as a zone of ultrahigh-pressure rocks, a north dipping suture, and an apparent Moho offset that marks a likely active strike-slip fault.

A comparative analysis of pre-Silurian crustal building blocks of the northern and the southern Appalachian orogen

USGS Publications Warehouse

Hibbard, J.P.; van Staal, C.R.; Rankin, D.W.

2007-01-01

The New York promontory serves as the divide between the northern and southern segments of the Appalachian orogen. Antiquated subdivisions, distinct for each segment, implied that they had lithotectonic histories that were independent of each other. Using new lithotectonic subdivisions we compare first order features of the pre-Silurian orogenic 'building blocks' in order to test the validity of the implication of independent lithotectonic histories for the two segments. Three lithotectonic divisions, termed here the Laurentian, Iapetan, and the peri-Gondwanan realms, characterize the entire orogen. The Laurentian realm, composed of native North American rocks, is remarkably uniform for the length of the orogen. It records the multistage Neoproterozoic-early Paleozoic rift-drift history of the Appalachian passive margin, formation of a Taconic Seaway, and the ultimate demise of both in the Middle Ordovician. The Iapetan realm encompasses mainly oceanic and magmatic arc tracts that once lay within the Iapetus Ocean, between Laurentia and Gondwana. In the northern segment, the realm is divisible on the basis of stratigraphy and faunal provinciality into peri-Laurentian and peri-Gondwanan tracts that were amalgamated in the Late Ordovician. South of New York, stratigraphic and faunal controls decrease markedly; rock associations are not inconsistent with those of the northern Appalachians, although second-order differences exist. Exposed exotic crustal blocks of the peri-Gondwanan realm include Ganderia, Avalonia, and Meguma in the north, and Carolinia in the south. Carolinia most closely resembles Ganderia, both in early evolution and Late Ordovician-Silurian docking to Laurentia. Our comparison indicates that, to a first order, the pre-Silurian Appalachian orogen developed uniformly, starting with complex rifting and a subsequent drift phase to form the Appalachian margin, followed by the consolidation of Iapetan components and ending with accretion of the peri

Transient Landscape Evolution is Characteristic of Post-Orogenic Decay: An Example from the Southern Appalachians, U.S.A.

NASA Astrophysics Data System (ADS)

Gallen, S. F.

2016-12-01

Long-term landscape evolution in post-orogenic settings remains an outstanding question in the geosciences. Despite conventional wisdom that topography in dead orogens will slowly and steadily decay through time, observations from around the globe show that dynamic, unsteady (e.g. transient) landscape evolution is the norm. Unraveling the mechanisms that drive unsteadiness in dead orogens is paramount to understanding the stratigraphic record of offshore basins and the geologic factors that contribute to the high biodiversity common in these settings. Here we address the enigma of unsteady post-orogenic landscape evolution with a study of the geomorphology of southern Appalachians, U.S.A. We focus on the 58,000 km2 Upper Tennessee River Basin that covers portions of the fold-and-thrust belt (Valley and Ridge), foreland basin (Appalachian Plateau), and a deeply exhumed thrust sheet (Blue Ridge) of this dead orogen. Using published millennial-scale erosion rates and quantitative analysis of fluvial topography, we show that this region is in a transient state of adjustment to 400 m of base level fall. Ongoing adjustment to base level drop is observed as a zone of high erosion rates, steep river channels and numerous knickpoints located upstream of and surrounding the contact between the Valley and Ridge and adjacent lithotectonic units. We argue that the association of adjusting landscapes and the Valley and Ridge contact is due to the rapid response time of rivers incising soft Valley and Ridge rocks, relative to the harder metamorphic rocks in the Blue Ridge and resistant capstone in the Appalachian Plateau. We propose that base level fall was triggered by incision through the Appalachian Plateau capstone into underlying weaker rocks that set off a wave of transient adjustment, drainage reorganization and ultimately capture of the paleo-Upper Tennessee Basin. Our results indicate that transient landscape evolution is characteristic of post-orogenic settings, as

Targeting of Gold Deposits in Amazonian Exploration Frontiers using Knowledge- and Data-Driven Spatial Modeling of Geophysical, Geochemical, and Geological Data

NASA Astrophysics Data System (ADS)

Magalhães, Lucíola Alves; Souza Filho, Carlos Roberto

2012-03-01

This paper reports the application of weights-of-evidence, artificial neural networks, and fuzzy logic spatial modeling techniques to generate prospectivity maps for gold mineralization in the neighborhood of the Amapari Au mine, Brazil. The study area comprises one of the last Brazilian mineral exploration frontiers. The Amapari mine is located in the Maroni-Itaicaiúnas Province, which regionally hosts important gold, iron, manganese, chromite, diamond, bauxite, kaolinite, and cassiterite deposits. The Amapari Au mine is characterized as of the orogenic gold deposit type. The highest gold grades are associated with highly deformed rocks and are concentrated in sulfide-rich veins mainly composed of pyrrhotite. The data used for the generation of gold prospectivity models include aerogeophysical and geological maps as well as the gold content of stream sediment samples. The prospectivity maps provided by these three methods showed that the Amapari mine stands out as an area of high potential for gold mineralization. The prospectivity maps also highlight new targets for gold exploration. These new targets were validated by means of detailed maps of gold geochemical anomalies in soil and by fieldwork. The identified target areas exhibit good spatial coincidence with the main soil geochemical anomalies and prospects, thus demonstrating that the delineation of exploration targets by analysis and integration of indirect datasets in a geographic information system (GIS) is consistent with direct prospecting. Considering that work of this nature has never been developed in the Amazonian region, this is an important example of the applicability and functionality of geophysical data and prospectivity analysis in regions where geologic and metallogenetic information is scarce.

Porphyry copper assessment of the Central Asian Orogenic Belt and eastern Tethysides: China, Mongolia, Russia, Pakistan, Kazakhstan, Tajikistan, and India: Chapter X in Global mineral resource assessment

USGS Publications Warehouse

Mihalasky, Mark J.; Ludington, Stephen; Hammarstrom, Jane M.; Alexeiev, Dmitriy V.; Frost, Thomas P.; Light, Thomas D.; Robinson, Gilpin R.; Briggs, Deborah A.; Wallis, John C.; Miller, Robert J.; Bookstrom, Arthur A.; Panteleyev, Andre; Chitalin, Andre; Seltmann, Reimar; Guangsheng, Yan; Changyun, Lian; Jingwen, Mao; Jinyi, Li; Keyan, Xiao; Ruizhao, Qiu; Jianbao, Shao; Gangyi, Shai; Yuliang, Du

2015-01-01

The U.S. Geological Survey collaborated with international colleagues to assess undiscovered resources in porphyry copper deposits in the Central Asian Orogenic Belt and eastern Tethysides. These areas host 20 known porphyry copper deposits, including the world class Oyu Tolgoi deposit in Mongolia that was discovered in the late 1990s. The study area covers major parts of the world’s largest orogenic systems. The Central Asian Orogenic Belt is a collage of amalgamated Precambrian through Mesozoic terranes that extends from the Ural Mountains in the west nearly to the Pacific Coast of Asia in the east and records the evolution and final closure of the Paleo-Asian Ocean in Permian time. The eastern Tethysides, the orogenic belt to the south of the Central Asian Orogenic Belt, records the evolution of another ancient ocean system, the Tethys Ocean. The evolution of these orogenic belts involved magmatism associated with a variety of geologic settings appropriate for formation of porphyry copper deposits, including subduction-related island arcs, continental arcs, and collisional and postconvergent settings. The original settings are difficult to trace because the arcs have been complexly deformed and dismembered by younger tectonic events. Twelve mineral resource assessment tracts were delineated to be permissive for the occurrence of porphyry copper deposits based on mapped and inferred subsurface distributions of igneous rocks of specific age ranges and compositions. These include (1) nine Paleozoic tracts in the Central Asian Orogenic Belt, which range in area from about 60,000 to 800,000 square kilometers (km2); (2) a complex area of about 400,000 km2 on the northern margin of the Tethysides, the Qinling-Dabie tract, which spans central China and areas to the west, encompassing Paleozoic through Triassic igneous rocks that formed in diverse settings; and (3) assemblages of late Paleozoic and Mesozoic rocks that define two other tracts in the Tethysides, the 100

Deformation Partitioning: The Missing Link Between Outcrop-Scale Observations And Orogen-Scale Processes

NASA Astrophysics Data System (ADS)

Attia, S.; Paterson, S. R.; Jiang, D.; Miller, R. B.

2017-12-01

Structural studies of orogenic deformation fields are mostly based on small-scale structures ubiquitous in field exposures, hand samples, and under microscopes. Relating deformation histories derived from such structures to changing lithospheric-scale deformation and boundary conditions is not trivial due to vast scale separation (10-6 107 m) between characteristic lengths of small-scale structures and lithospheric plates. Rheological heterogeneity over the range of orogenic scales will lead to deformation partitioning throughout intervening scales of structural development. Spectacular examples of structures documenting deformation partitioning are widespread within hot (i.e., magma-rich) orogens such as the well-studied central Sierra Nevada and Cascades core of western North America: (1) deformation partitioned into localized, narrow, triclinic shear zones separated by broad domains of distributed pure shear at micro- to 10 km scales; (2) deformation partitioned between plutons and surrounding metamorphic host rocks as shown by pluton-wide magmatic fabrics consistently oriented differently than coeval host rock fabrics; (3) partitioning recorded by different fabric intensities, styles, and orientations established from meter-scale grid mapping to 100 km scale domainal analyses; and (4) variations in the causes of strain and kinematics within fold-dominated domains. These complex, partitioned histories require synthesized mapping, geochronology, and structural data at all scales to evaluate partitioning and in the absence of correct scaling can lead to incorrect interpretations of histories. Forward modeling capable of addressing deformation partitioning in materials containing multiple scales of rheologically heterogeneous elements of varying characteristic lengths provides the ability to upscale the large synthesized datasets described above to plate-scale tectonic processes and boundary conditions. By comparing modeling predictions from the recently developed

Constraints on the development of orogenic style gold mineralisation at Mineral de Talca, Coastal Range, central Chile: evidence from a combined structural, mineralogical, S and Pb isotope and geochronological study

NASA Astrophysics Data System (ADS)

Firth, Emily A.; Holwell, David A.; Oliver, Nicholas H. S.; Mortensen, James K.; Rovardi, Matthew P.; Boyce, Adrian J.

2015-08-01

Mineral de Talca is a rare occurrence of Mesozoic, gold-bearing quartz vein mineralisation situated within the Coastal Range of northern Chile. Quartz veins controlled by NNW-SSE-trending faults are hosted by Devonian-Carboniferous metasediments of greenschist facies and younger, undeformed granitoid and gabbro intrusions. The principal structural control in the area is the easterly dipping, NNW-SSE-trending El Teniente Fault, which most likely developed as an extensional normal fault in the Triassic but was later reactivated as a strike-slip fault during subsequent compression. A dilational zone in the El Teniente Fault appears to have focussed fluid flow, and an array of NW-SE-trending veins is present as splays off the El Teniente Fault. Mineralised quartz veins typically up to a metre thick occur in three main orientations: (1) parallel to and within NNW-SSE-trending, E-dipping faults throughout the area; (2) along NW-SE-trending, NE-dipping structures which may also host andesite dykes; and (3) rarer E-W-trending, subvertical veins. All mineralised quartz veins show evidence of multiple fluid events with anastomosing and crosscutting veins and veinlets, some of which contain up to 3.5 vol.% base metal sulphides. Mineralogically, Au is present in three textural occurrences, identified by 3D CT scanning: (1) with arsenopyrite and pyrite in altered wall rock and along the margins of some of the veins; (2) with Cu-Pb-Zn sulphides within quartz veins; and (3) as nuggets and clusters of native Au within quartz. Fluid inclusion work indicates the presence of CO2-CH4-bearing fluids with homogenisation temperatures of ˜350 °C and aqueous fluids with low-moderate salinities (0.4-15.5 wt% NaCl eq.) with homogenisation temperatures in the range of 161-321 °C. The presence of Au with arsenopyrite and pyrite in structurally controlled quartz veins and in greenschist facies rocks with evidence of CO2-bearing fluids is consistent with an orogenic style classification for

Post-collisional magmatism in the central East African Orogen: The Maevarano Suite of north Madagascar

NASA Astrophysics Data System (ADS)

Goodenough, K. M.; Thomas, R. J.; De Waele, B.; Key, R. M.; Schofield, D. I.; Bauer, W.; Tucker, R. D.; Rafahatelo, J.-M.; Rabarimanana, M.; Ralison, A. V.; Randriamananjara, T.

2010-04-01

Late tectonic, post-collisional granite suites are a feature of many parts of the Late Neoproterozoic to Cambrian East African Orogen (EAO), where they are generally attributed to late extensional collapse of the orogen, accompanied by high heat flow and asthenospheric uprise. The Maevarano Suite comprises voluminous plutons which were emplaced in some of the tectonostratigraphic terranes of northern Madagascar, in the central part of the EAO, following collision and assembly during a major orogeny at ca. 550 Ma. The suite comprises three main magmatic phases: a minor early phase of foliated gabbros, quartz diorites, and granodiorites; a main phase of large batholiths of porphyritic granitoids and charnockites; and a late phase of small-scale plutons and sheets of monzonite, syenite, leucogranite and microgranite. The main phase intrusions tend to be massive, but with variably foliated margins. New U-Pb SHRIMP zircon data show that the whole suite was emplaced between ca. 537 and 522 Ma. Geochemically, all the rocks of the suite are enriched in the LILE, especially K, and the LREE, but are relatively depleted in Nb, Ta and the HREE. These characteristics are typical of post-collisional granitoids in the EAO and many other orogenic belts. It is proposed that the Maevarano Suite magmas were derived by melting of sub-continental lithospheric mantle that had been enriched in the LILE during earlier subduction events. The melting occurred during lithospheric delamination, which was associated with extensional collapse of the East African Orogen.

Early tectonic evolution of the Thomson Orogen in Queensland inferred from constrained magnetic and gravity data

NASA Astrophysics Data System (ADS)

Spampinato, Giovanni P. T.; Betts, Peter G.; Ailleres, Laurent; Armit, Robin J.

2015-05-01

The crustal architecture as well as the kinematic evolution of the Thomson Orogen in Queensland is poorly resolved because the region is concealed under thick Phanerozoic sedimentary basins and the basement geology is known from limited drill holes. Combined potential field and seismic interpretation indicates that the Thomson Orogen is characterized by prominent regional NE- and NW-trending structural grain defined by long wavelength and low amplitude geophysical anomalies. The 'smooth' magnetic signature is interpreted to reflect deeply buried source bodies in the mid- to lower crust. Short wavelength positive magnetic features that correlate with negative gravity anomalies are interpreted to represent shallower granitic intrusions. They appear to be focused along major fault zones that might have controlled the locus for magmatism. The eastern Thomson Orogen is characterized by a prominent NE structural grain and orthogonal faults and fold interference patterns resulting in a series of troughs and highs. The western Thomson Orogen consists of a series of NW-trending structures interpreted to reflect reverse faults. Sedimentation and basin development are interpreted to have initiated in the Neoproterozoic to Early Cambrian during E-W- to ENE-WSW extension, possibly related to the Rodinia break-up. This extensional event was followed by Late Cambrian shortening recorded in the Maneroo Platform and the Diamantina River Domain which possibly correlates with the Delamerian Orogeny. Renewed deposition and volcanism occurred during the Ordovician and may have continued until Late Silurian, resulting in thinned Proterozoic basement crust and extensive basin systems that formed in a distal continental back-arc environment. Our interpretation places the Thomson Orogen to the west of the Neoproterozoic passive margin preserved in the Anakie Inlier. The region is likely to represent the internal extensional architecture during the Rodinia break-up that has been

Structural development of an Archean Orogen, Western Point Lake, Northwest Territories

NASA Astrophysics Data System (ADS)

Kusky, Timothy M.

1991-08-01

The Point Lake orogen in the central Archean Slave Province of northwestern Canada preserves more than 10 km of structural relief through an eroded antiformal thrust stack and deeper anastomosing midcrustal mylonites. Fault restoration along a 25 km long transect requires a minimum of 69 km slip and 53 km horizontal shortening. In the western part of the orogen the basal decollement places mafic plutonic/volcanic rocks over an ancient tonalitic gneiss complex. Ten kilometers to the east in the Keskarrah Bay area, slices of gneiss unroofed on brittle thrusts shed molasse into several submerged basins. Conglomerates and associated thinly bedded sedimentary rocks are interpreted as channel, levee, and overbank facies of this thrust-related sedimentary fan system. The synorogenic erosion surface at the base of the conglomerate truncates premetamorphic or early metamorphic thrust faults formed during foreland propagation, while other thrusts related to hinterland-progressing imbrication displace this unconformity. Tightening of synorogenic depositional troughs resulted in the conglomerates' present localization in synclines to the west of associated thrust faults and steepening of structural dips. Eastern parts of the orogen consist of isoclinally folded graywackes composed largely of Mutti and Ricci-Lucchi turbidite facies B, C, and D, interpreted as submarine fan deposits eroded from a distant volcanic arc. Thrust faults in the metasedimentary terrane include highly disrupted slate horizons with meter-scale duplex structures, and recrystallized calcmylonites exhibiting sheath folds and boudin trains with very large interboudin distances. The sequence of fabric development and the overall geometry of this metasedimentary terrane strongly resembles younger forearc accretionary prisms. Conditions of deformation along the thrusts parallel the regional metamorphic zonation: amphibolite facies in the basal decollement through greenschist facies shear zones to cataclastic

Genesis of the hydrothermal gold deposits in the Canan area, Lepaguare District, Honduras

NASA Astrophysics Data System (ADS)

Mattioli, Michele; Menichetti, Marco; Renzulli, Alberto; Toscani, Lorenzo; Salvioli-Mariani, Emma; Suarez, Pedro; Murroni, Alessandro

2014-04-01

The Canan area (Honduras) is characterized by a gold-bearing ore deposit that is associated with quartz-veined shear zones. Gold mineralization occurs in low-to medium-grade metamorphic host-rocks (graphitic and sericitic schists). Hydrothermal fluids, which are associated with the emplacement of Cretaceous-Tertiary granodioritic intrusions, are responsible for the formation of quartz veins and the hydrothermal alteration of wall-rocks. Three main altered zones have been detected in the wall-rocks as far as 150 cm from the quartz veins. The distal zone (up to 50-cm thick) contains quartz, chlorite and illite. The intermediate zone is the thickest (up to 80 cm) and is marked by quartz, muscovite, sulphides, kaolinite and native elements such as Au and Ag. The proximal zone, which is close to the quartz veins, is rather thin (up to 25 cm) and contains clay minerals, Al-oxides-hydroxides and sulphides. The transition from the distal to the proximal zone is accompanied by the enrichment of SiO2 and the depletion of all other major elements, except for Fe2O3(tot). Precious metals occur in the highest concentrations in the intermediate zone (Au up to 7.6 ppm and Ag up to 11 ppm). We suggest that gold was transported as a reduced sulphur complex and was precipitated from the hydrothermal solution by the reaction of the sulphur complexes with Fe2+ from the alteration of the mafic minerals of the host-rock. Fluid-wall-rock interactions seem to be the main cause of gold mineralization. Genetic relationships with a strike-slip fault system, hydrothermal alteration zones within the metamorphic wall-rocks, and an entire set of geochemical anomalies are consistent with orogenic-type gold deposits of the epizonal class.

Kyanite-bearing migmatites in the central Adirondack Mountains: Implications for late to post-orogenic metamorphism and melting in a collisional orogen

NASA Astrophysics Data System (ADS)

Reeder, J.; Metzger, E. P.; Bickford, M. E.; Leech, M. L.

2016-12-01

Sillimanite-rich felsic migmatites exposed at Ledge Mountain in the Central Adirondack Highlands (AH) represent the only location in the AH where kyanite is found. The texturally young kyanite is overprinted on sillimanite in largely undeformed pegmatitic leucosomes, suggesting a late episode of melting taking place deeper than previously thought, and requiring a counter-clockwise P-T path. A final phase of anatexis ca. 1050 Ma in the Eastern AH is consistent with an influx of fluid or decompression from extension in sillimanite-bearing migmatites. Temperatures both from this study and previous work are consistent with granulite-facies metamorphism; however, the presence of kyanite requires higher pressure conditions corresponding to deeper burial of rocks exposed in the central Adirondacks. The Adirondacks are associated with the Grenville Province of eastern North America, that formed during four orogenic events. The most recent (Grenville) orogeny consisted of two stages: crustal thickening and granulite facies metamorphism during the Ottawan phase (ca 1090-1020) then metamorphism and melting in the kyanite field during the much shorter Rigolet pulse (ca 1005-980 Ma). Preliminary U-Pb SHRIMP zircon ages from Ledge Mountain kyanite-bearing migmatites suggest that melting in the Central AH persisted into the Rigolet phase. On the basis of mineral composition and chemistry and the presence of distinctive quartz-sillimanite nodules, the Ledge Mountain migmatites closely resemble the K-rich phase of the Ottawan-age Lyon Mountain granite (LMG) and may represent LMG that was metamorphosed to sillimanite grade and then overprinted by a higher pressure, lower temperature assemblage. Kyanite-bearing felsic anatectites of Rigolet age have previously been observed only in the western portion of the Grenville Province. Documentation of a counterclockwise P-T path and post-Ottawan melting in the Ledge Mountain migmatites requires re-evaluation of current tectonic models for

Carboniferous rifted arcs leading to an archipelago of multiple arcs in the Beishan-Tianshan orogenic collages (NW China)

NASA Astrophysics Data System (ADS)

Tian, Zhonghua; Xiao, Wenjiao; Windley, Brian F.; Zhang, Ji'en; Zhang, Zhiyong; Song, Dongfang

2017-10-01

The Beishan and East Tianshan Orogenic Collages in the southernmost Central Asian Orogenic Belt (CAOB) record the final stages of evolution of the Paleo-Asian Ocean. These collages and their constituent arcs have an important significance for resolving current controversies regarding their tectonic setting and age, consequent accretionary history of the southern CAOB, and the closure time of the Paleo-Asian Ocean. In this paper, we present our work on the southern Mazongshan arc and the northern Hongyanjing Basin in the Beishan Orogenic Collage (BOC), and our comparison with the Bogda arc and associated basins in the East Tianshan Orogenic Collage. Field relationships indicate that the Pochengshan fault defines the boundary between the arc and basin in the BOC. Volcanic rocks including basalts and rhyolites in the Mazongshan arc have bimodal calc-alkaline characteristics, an enrichment in large ion lithophile elements such as Rb, Ba, and Pb and depletion in high field-strength elements (e.g., Nb and Ta), which were probably developed in a subduction-related tectonic setting. We suggest that these bimodal calc-alkaline volcanic rocks formed in rifted arcs instead of post-orogenic rifts with mantle plume inputs. By making detailed geochemical comparisons between the Mazongshan arc and the Bogda arc to the west, we further propose that they are similar and both formed in arc rifts, and helped generate a Carboniferous archipelago of multiple arcs in the southern Paleo-Asian Ocean. These data and ideas enable us to postulate a new model for the tectonic evolution of the southern CAOB.

The tectonic setting and evolution of the 2.7 Ga Kalgoorlie-Kurnalpi Rift, a world-class Archean gold province

NASA Astrophysics Data System (ADS)

Witt, Walter K.; Cassidy, Kevin F.; Lu, Yong-Jun; Hagemann, Steffen G.

2018-01-01

The Yilgarn Craton results from three major mantle input events (at ca 3.0-2.9, 2.8 and 2.7 Ga) that have interacted with > 3.0 Ga continental crust. Zircon geochronology and Sm-Nd isotopic data subdivide the craton into an older Yilgarn proto-craton and the younger, more primitive Eastern Goldfields Superterrane (EGST). Formation of the Kalgoorlie-Kurnalpi Rift (KKR) within the EGST was associated with the 2.7 Ga event, which exploited weakened crust at the eastern margin of the Yilgarn proto-craton where thick sequences of komatiite and basalt were erupted between ca 2710 and 2690 Ma in the Kalgoorlie Terrane. Calc-alkaline volcanism in the Kurnalpi Terrane began at ca 2730 Ma and continued to ca 2690 Ma, overlapping rifting and plume-related volcanism in the Kalgoorlie Terrane. Deposition of siliciclastic sedimentary rocks within basins at ca 2660 resulted from an intra-orogenic extensional event and coincided with the transition from High-Ca to Low-Ca granite magmatism and peak emplacement of intrusions with a metasomatised mantle source component. Most aspects of the KKR are satisfied by broadly coincident plume-related magmatism in the Kalgoorlie Terrane and westward subduction to the east of the Burtville Terrane. Geochemical characteristics of 2730-2700 Ma calc-alkaline volcanism and 2685-2630 Ma low-SiO2 and alkali-rich intrusions support models for a continental margin subduction zone setting. World-class gold deposits formed in reactivated margins of the KKR, which became flux zones for mantle-derived magmas, hydrothermal fluids and heat during 2675-2620 Ma orogenesis. The orogenic gold mineralisation can be subdivided into proximal intrusion-related and distal-source deposits.

Linking time-Temperature history of the Aquitaine basin with post-orogenic evolution of the Pyrenees : new insights from borehole thermochronology

NASA Astrophysics Data System (ADS)

Fillon, Charlotte; Calassou, Sylvain; Mouthereau, Frédéric; Pik, Raphaël; Bellahsen, Nicolas; Gautheron, Cécile

2017-04-01

Within their sedimentary record, foreland basins document vertical movements of the lithosphere, climatic changes, paleogeograhic evolution but also history of exhumation of the adjacent mountain belt. Comparing vertical movements in a range and in its foreland is key to identify processes involved in growth and destruction of mountain belts. The Aquitaine basin, geomorphologically stable since the early Pyrenean orogenesis has the potential to help understanding the driving mechanisms during the late to post-orogenic phases, but the lack of outcrops makes the studies particularly difficult to achieve. To bring a new point of vue on the processes involved in the Cenozoic exhumation of this range, we present new low-Temperature thermochronology data from boreholes of the Aquitaine basin. With the objectives to study rift-related to post-orogenic processes, numerous low-T thermochronological ages ( 300 across the range) have been published, documenting pre-, syn- , and post-orogenic exhumation in the Pyrenees. Using thermal modeling of a new low-T database in the western Axial Zone, we show that a late Miocene (around 10 Ma) uplift occured in the western Pyrenees, which generalizes the post-orogenic signal already detected in the south central Pyrenees. In previous studies, we linked the post-orogenic exhumation in the Southern Pyrenees to the excavation of the foreland valleys caused by the opening of the endorheic Ebro basin towards the Mediterranean Sea. To the West, the tectonic out-of sequence reactivation of the Gavarnie thrust has been invoked to explain the late Miocene AHe ages in the Bielsa massif. These new data might lead us to re-think the causes for such an exhumation signal during "post-orogenic" times. We thus summarize all evidences for the post-orogenic phase and attempt to provide explanation for it: is exhumation driven by Aquitaine foreland basin evolution? Does it reflect a tectonic reactivation of the Pyrenees? or is the signature of a regional

Petrological and zircon evidence for the Early Cretaceous granulite-facies metamorphism in the Dabie orogen, China

NASA Astrophysics Data System (ADS)

Gao, Xiao-Ying; Zhang, Qiang-Qiang; Zheng, Yong-Fei; Chen, Yi-Xiang

2017-07-01

An integrated study of petrology, mineralogy, geochemistry, and geochronology was carried out for contemporaneous mafic granulite and diorite from the Dabie orogen. The results provide evidence for granulite-facies reworking of the ultrahigh-pressure (UHP) metamorphic rock in the collisional orogen. Most zircons from the granulite are new growth, and their U-Pb ages are clearly categorized into two groups at 122-127 Ma and 188 ± 2 Ma. Although these two groups of zircons show similarly steep HREE patterns and variably negative Eu anomalies, the younger group has much higher U, Th and REE contents and Th/U ratios, much lower εHf(t) values than the older group. This suggests their growth is associated with different types of dehydration reactions. The older zircon domains contain mineral inclusions of garnet + clinopyroxene ± quartz, indicating their growth through metamorphic reactions at high pressures. In contrast, the young zircon domains only contain a few quartz inclusions and the garnet-clinopyroxene-plagioclase-quartz barometry yields pressures of 4.9 to 12.5 kb. In addition, the clinopyroxene-garnet Fe-Mg exchange thermometry gives temperatures of 738-951 °C. Therefore, the young zircon domains would have grown through peritectic reaction at low to medium pressures. The younger granulite-facies metamorphic age is in agreement not only with the adjacent diorite at 125 ± 1 Ma in this study but also the voluminous emplacement of coeval mafic and felsic magmas in the Dabie orogen. Mineral separates from both mafic granulite and its adjacent diorite show uniformly lower δ18O values than normal mantle, similar to those for UHP eclogite-facies metaigneous rocks in the Dabie orogen. In combination with major-trace elements and zircon Lu-Hf isotope compositions, it is inferred that the protolith of mafic granulites shares with the source rock of diorites, both being a kind of mafic metasomatites at the slab-mantle interface in the continental subduction channel

Origin of ore-forming fluids of the Haigou gold deposit in the eastern Central Asian Orogenic belt, NE China: Constraints from H-O-He-Ar isotopes

NASA Astrophysics Data System (ADS)

Zeng, Qingdong; He, Huaiyu; Zhu, Rixiang; Zhang, Song; Wang, Yongbin; Su, Fei

2017-08-01

The Haigou lode deposit contains 40 t of gold at an average grade of 3.5 g/t, and is one of the largest deposits in the Jiapigou gold belt located along the eastern segment of the northern margin of the North China Craton. The deposit comprises 15 gold-bearing quartz veins hosted in a Carboniferous monzonite-monzogranite stock. Cretaceous dikes consisting of diorite, diabase, and granodiorite porphyries are well developed in the deposit. The diorite porphyry dikes (130.4 ± 6.3 Ma) occur together with gold-bearing quartz veins in NNE- and NE-striking faults. Gold-bearing quartz veins crosscut the diorite porphyry dikes, and the veins are in turn crosscut by E-W-striking 124.6 ± 2.2 Ma granodiorite porphyry dikes. The mineralization mainly occurs as auriferous quartz veins with minor amounts of sulfide minerals, including pyrite, galena, chalcopyrite, and molybdenite. Gold occurs as either native gold or calaverite. Common gangue minerals in the deposit include quartz, sericite, and calcite. The deposit is characterized by various types of hydrothermal alteration, including silicification, sericitization, chloritization, potassic alteration, and carbonatization. Three stages of hydrothermal activity have been recognized in the deposit: (1) a barren quartz stage; (2) a polymetallic sulfide (gold) stage; (3) a calcite stage. Fluid inclusions in hydrothermal pyrites have 3He/4He ratios of 0.3 to 3.3 Ra and 40Ar/36Ar ratios of 351 to 1353, indicating mixing of fluids of mantle and crustal origin. Hydrothermal quartz yielded δ18O values of -1.3‰ to +7.2‰ and δD values of fluid inclusions in the quartz vary between -80‰ and -104‰. These stable isotope data also suggest mixing of magmatic and meteoric fluids. Noble gas and stable isotopic data suggest that the ore fluids have a predominant mantle source with a significant crustal component. Based on the spatial association of gold-bearing quartz veins with early Cretaceous intrusions, and the H-O-He-Ar isotopic

Hillslope response to knickpoint migration in the Southern Appalachians: Implications for the evolution of post-orogenic landscapes

USGS Publications Warehouse

Wegmann, S.F.G.; Franke, K.L.; Hughes, S.; Lewis, R.Q.; Lyons, N.; Paris, P.; Ross, K.; Bauer, J.B.; Witt, A.C.

2011-01-01

The southern Appalachians represent a landscape characterized by locally high topographic relief, steep slopes, and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 Ma. The fundamental processes responsible for landscape evolution in a post-orogenic landscape remain enigmatic. The non-glaciated Cullasaja River basin of south-western North Carolina, with uniform lithology, frequent debris flows, and the availability of high-resolution airborne lidar DEMs, is an ideal natural setting to study landscape evolution in a post-orogenic landscape through the lens of hillslope-channel coupling. This investigation is limited to channels with upslope contributing areas >2.7 km2, a conservative estimate of the transition from fluvial to debris-flow dominated channel processes. Values of normalized hypsometry, hypsometric integral, and mean slope vs elevation are used for 14 tributary basins and the Cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration. Results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the Cullasaja basin and adjacent hillslopes. Metrics of topography (relief, slope gradient) and hillslope activity (landslide frequency) exhibit significant downstream increases below the current position of major knickpoints. The transient effect of knickpoint-driven channel incision on basin hillslopes is captured by measuring the relief, mean slope steepness, and mass movement frequency of tributary basins and comparing these results with the distance from major knickpoints along the Cullasaja River. A conceptual model of area-elevation and slope distributions is presented that may be representative of post-orogenic landscape evolution in analogous geologic settings. Importantly, the model explains how knickpoint migration and channel- hillslope coupling is an important factor in tectonically-inactive (i

Seismic anisotropies of the Songshugou peridotites (Qinling orogen, central China) and their seismic implications

NASA Astrophysics Data System (ADS)

Cao, Yi; Jung, Haemyeong; Song, Shuguang

2018-01-01

Though extensively studied, the roles of olivine crystal preferred orientations (CPOs or fabrics) in affecting the seismic anisotropies in the Earth's upper mantle are rather complicated and still not fully known. In this study, we attempted to address this issue by analyzing the seismic anisotropies [e.g., P-wave anisotropy (AVp), S-wave polarization anisotropy (AVs), radial anisotropy (ξ), and Rayleigh wave anisotropy (G)] of the Songshugou peridotites (dunite dominated) in the Qinling orogen in central China, based on our previously reported olivine CPOs. The seismic anisotropy patterns of olivine aggregates in our studied samples are well consistent with the prediction for their olivine CPO types; and the magnitude of seismic anisotropies shows a striking positive correlation with equilibrium pressure and temperature (P-T) conditions. Significant reductions of seismic anisotropies (AVp, max. AVs, and G) are observed in porphyroclastic dunite compared to coarse- and fine-grained dunites, as the results of olivine CPO transition (from A-/D-type in coarse-grained dunite, through AG-type-like in porphyroclastic dunite, to B-type-like in fine-grained dunite) and strength variation (weakening: A-/D-type → AG-type-like; strengthening: AG-type-like → B-type-like) during dynamic recrystallization. The transition of olivine CPOs from A-/D-type to B-/AG-type-like in the forearc mantle may weaken the seismic anisotropies and deviate the fast velocity direction and the fast S-wave polarization direction from trench-perpendicular to trench-oblique direction with the cooling and aging of forearc mantle. Depending on the size and distribution of the peridotite body such as the Songshugou peridotites, B- and AG-type-like olivine CPOs can be an additional (despite minor) local contributor to the orogen-parallel fast velocity direction and fast shear-wave polarization direction in the orogenic crust such as in the Songshugou area in Qinling orogen.

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.

Gold mineralisation throughout about 45 Ma of Archaean orogenesis: protracted flux of gold in the Golden Mile, Yilgarn craton, Western Australia

NASA Astrophysics Data System (ADS)

Bateman, Roger; Hagemann, Steffen

2004-10-01

The Golden Mile deposit was discovered in 1893 and represents today the largest Archaean orogenic lode gold system in the world (50 M oz produced gold). The Golden Mile deposit comprises three major styles of gold mineralisation: Fimiston, Oroya and Charlotte styles. Fimiston-style lodes formed at 250 to 350 °C and 100 to 200 MPa and are controlled by brittle ductile fault zones, their subsidiary fault zone and vein networks including breccias and open-cavity-infill textures and hydrothermally altered wall rock. Fimiston lodes were formed late D1, prior to D2 regional upright folding. Hydrothermal alteration haloes comprise a progression toward the lode of diminishing chlorite, an increase in sericite and in Fe content of carbonates. Lodes contain siderite, pyrite, native gold, 17 different telluride minerals (Au Ag tellurides contain ~25% of total gold), tourmaline, haematite, sericite and V-rich muscovite. Oroya-style lodes formed at similar P T conditions as the Fimiston lodes and are controlled by brittle ductile shear zones, associated dilational jogs that are particularly well developed at the contact between Paringa Basalt and black shale interflow sedimentary rocks and altered wall rock. The orebodies are characterised by micro-breccias and zones of intense shear zone foliation, very high gold grades (up to 100,000 g/t Au) and the common association of tellurides and vanadian mica (green leader). Oroya lodes crosscut Fimiston lodes and are interpreted to have formed slightly later than Fimiston lodes as part of one evolving hydrothermal system spanning D1 and D2 deformation (ca. 2,675 2,660 Ma). Charlotte-style lodes, exemplified by the Mt Charlotte deposit, are controlled by a sheeted vein (stockwork) complex of north-dipping quartz veins and hydrothermally altered wall rock. The Mt Charlotte orebody formed at 120 to 440 °C and 150 to 250 MPa during movement along closely spaced D4 (2,625 Ma) and reactivated D2 faults with the quartz granophyre in the

Controls on mineralisation in the Sierra Foothills gold province, central California, USA: A GIS-based reconnaissance prospectivity analysis

USGS Publications Warehouse

Bierlein, F.P.; Northover, H.J.; Groves, D.I.; Goldfarb, R.J.; Marsh, E.E.

2008-01-01

The assessment of spatial relationships between the location, abundance and size of orogenic-gold deposits in the highly endowed Sierra Foothills gold province in California, via the combination of field studies and a GIS-based analysis, illustrates the power of such an approach to the characterisation of important parameters of mineral systems, and the prediction of districts likely to host economic mineralisation. Regional- to deposit-scale reconnaissance mapping suggests that deposition of gold-bearing quartz veins occurred in second- and third-order, east-over-west thrusts during regional east - west compression and right-lateral transpression. At the district-scale, significant zones of mineralisation correspond with such transpressional reactivation zones and dilational jogs that developed during the Late Jurassic - Early Cretaceous along the misaligned segments of first-order faults throughout the Sierra Nevada Foothills Metamorphic Belt. Field-based observations and interpretation of GIS data (including solid geology, structural elements, deposit locations, magnetics, gravity) also highlight the importance of structural permeability contrasts, rheological gradients, and variations in fault orientation for localising mineralisation. Although this approach confirms empirical findings and produces promising results at the province scale, enhanced geological, structural, geophysical and geochronological data density is required to generate regionally consistent, high-quality input layers that improve predictive targeting at the goldfield to deposit-scale.

An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: From subduction magmatism to cratonization

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

Johnson, Simon P.; Korhonen, Fawna J.; Kirkland, Christopher L.

The in situ chemical differentiation of continental crust ultimately leads to the long-term stability of the continents. This process, more commonly known as ‘cratonization’, is driven by deep crustal melting with the transfer of those melts to shallower regions resulting in a strongly chemically stratified crust, with a refractory, dehydrated lower portion overlain by a complementary enriched upper portion. Since the lower to mid portions of continental crust are rarely exposed, investigation of the cratonization process must be through indirect methods. In this study we use in situ Hf and O isotope compositions of both magmatic and inherited zircons frommore » several felsic magmatic suites in the Capricorn Orogen of Western Australia to highlight the differentiation history (i.e. cratonization) of this portion of late Archean to Proterozoic orogenic crust. The Capricorn Orogen shows a distinct tectonomagmatic history that evolves from an active continental margin through to intracratonic reworking, ultimately leading to thermally stable crust that responds similarly to the bounding Archean Pilbara and Yilgarn Cratons.« less

Generation of post-collisional normal calc-alkaline and adakitic granites in the Tongbai orogen, central China

NASA Astrophysics Data System (ADS)

Zhang, Wen-Xiang; Zhu, Liu-Qin; Wang, Hao; Wu, Yuan-Bao

2018-01-01

Post-collisional granites are generally generated by partial melting of continental crust during orogenic extension. The occurrence of normal calc-alkaline granites following adakitic granites in a collisional orogen is frequently supposed as a sign of tectonic regime transition from compression to extension, which has been debated yet. In this paper, we present a comprehensive study of zircon U-Pb ages, Hf-O isotopes, as well as whole-rock major and trace elements and Sr-Nd isotopes, for Tongbai and Jigongshan post-collisional granitic plutons in the Tongbai orogen. Zircon U-Pb dating yields intrusion ages of ca. 140 and 135 Ma for the Tongbai and Jigongshan plutons, respectively, suggesting they are post-collisional granites. These granites are high-K calc-alkaline series, metaluminous to weakly peraluminous with A/CNK ratios of 0.85-1.08. The Tongbai gneissic granites are normal calc-alkaline granite, having variable SiO2 (61.93-76.74 wt%) and Sr/Y (2.9-38.9) and (La/Yb)N (1.7-30.1) ratios with variably negative Eu anomalies (0.41-0.92). They have relatively high initial Sr isotope ratios of 0.707571 to 0.710317, and low εNd(t) (- 15.74 to - 11.09) and εHf(t) (- 17.6 to - 16.9) values. Their Nd and Hf model ages range from 2.2 to 1.8 Ga and 2.3 to 2.2 Ga. On the contrary, the Jigongshan granites show higher SiO2 (66.56-72.11 wt%) and Sr/Y (30.1-182.0) and (La/Yb)N (27.4-91.4) ratios with insignificant Eu anomalies (0.73-1.00), belonging to adakitic granite. They have Isr = 0.707843-0.708366, εNd(t) = - 19.83 to - 17.59, and εHf(t) = - 26.0 to - 23.5. Their Nd and Hf model ages vary from ca. 2.5 to 2.4 Ga and ca. 2.8 to 2.6 Ga. The Tongbai and Jigongshan granites are characterized by mantle-like zircon δ18O values (5.17-5.46‰). These geochemical features suggest that the Tongbai and Jigongshan granites were derived from partial melting of Paleoproterozoic and Archean continental crust, respectively. Fractional crystallization affected the geochemical

Climate Variability and Surface Processes in Tectonically Active Orogens: Insights From the Southern Central Andes and the Northwest Himalaya

NASA Astrophysics Data System (ADS)

Strecker, M. R.; Bookhagen, B.

2008-12-01

The Southern Central Andes of NW Argentina and the NW Himalaya are important orographic barriers that intercept moisture-bearing winds associated with monsoonal circulation. Changes in both atmospheric circulation systems on decadal to millennial timescales fundamentally influence differences in the amount and location of rainfall in both orogens. In India, the eastern arm of the monsoonal circulation draws moisture from the Bay of Bengal and transports humid air masses along the southern Himalayan front to the northwest. There, at the end of the monsoonal conveyer belt, rainfall is diminished and moisture typically does not reach far into the orogen interior. Similar conditions apply to the NW Argentine Andes, which are located within the precipitation regime of the South American Monsoon. Here, pronounced local relief blocks humid air masses from the Amazon region, resulting in extreme gradients in rainfall that leave the orogen interior dry. However, during negative ENSO years (La Niña) and intensified Indian Summer Monsoon years, moisture penetrates farther into the Andean and Himalayan orogens, respectively. Structurally pre- conditioned valley systems may enhance this process and funnel moisture far into the orogen interior. The greater availability of moisture increases runoff, lateral scouring of mountin streams, and ultimately triggers intensified hillslope processes on decadal to centennial timescales. In both environments, the scenario of intensified present-day surface processes and rates is analogous to protracted episodes of enhanced mass removal from hillslopes via deep-seated landslides during the early Holocene and late Pleistocene. Apparently, these episodes were also associated with transient storage of voluminous conglomerates and lacustrine deposits in narrow intermontane basins. Subsequently, these deposits were incised, partly removed, and the fluvial systems adjusted themselves to the pre-depositional base levels through a readjustment and

An isotopic perspective on growth and differentiation of Proterozoic orogenic crust: From subduction magmatism to cratonization

NASA Astrophysics Data System (ADS)

Johnson, Simon P.; Korhonen, Fawna J.; Kirkland, Christopher L.; Cliff, John B.; Belousova, Elena A.; Sheppard, Stephen

2017-01-01

The in situ chemical differentiation of continental crust ultimately leads to the long-term stability of the continents. This process, more commonly known as 'cratonization', is driven by deep crustal melting with the transfer of those melts to shallower regions resulting in a strongly chemically stratified crust, with a refractory, dehydrated lower portion overlain by a complementary enriched upper portion. Since the lower to mid portions of continental crust are rarely exposed, investigation of the cratonization process must be through indirect methods. In this study we use in situ Hf and O isotope compositions of both magmatic and inherited zircons from several felsic magmatic suites in the Capricorn Orogen of Western Australia to highlight the differentiation history (i.e. cratonization) of this portion of late Archean to Proterozoic orogenic crust. The Capricorn Orogen shows a distinct tectonomagmatic history that evolves from an active continental margin through to intracratonic reworking, ultimately leading to thermally stable crust that responds similarly to the bounding Archean Pilbara and Yilgarn Cratons. The majority of magmatic zircons from the main magmatic cycles have Hf isotopic compositions that are generally more evolved than CHUR, forming vertical arrays that extend to moderately radiogenic compositions. Complimentary O isotope data, also show a significant variation in composition. However, combined, these data define not only the source components from which the magmas were derived, but also a range of physio-chemical processes that operated during magma transport and emplacement. These data also identify a previously unknown crustal reservoir in the Capricorn Orogen.

Subduction and Slab Advance at Orogen Syntaxes: Predicting Exhumation Rates and Thermochronometric Ages with Numerical Modeling

NASA Astrophysics Data System (ADS)

Nettesheim, Matthias; Ehlers, Todd A.; Whipp, David M.

2017-04-01

The change in plate boundary orientation and subducting plate geometry along orogen syntaxes may have major control on the subduction and exhumation dynamics at these locations. Previous work documents that the curvature of subducting plates in 3D at orogen syntaxes forces a buckling and flexural stiffening of the downgoing plate. The geometry of this stiffened plate region, also called indenter, can be observed in various subduction zones around the world (e.g. St. Elias Range, Alaska; Cascadia, USA; Andean syntaxis, South America). The development of a subducting, flexurally stiffened indenter beneath orogen syntaxes influences deformation in the overriding plate and can lead to accelerated and focused rock uplift above its apex. Moreover, the style of deformation in the overriding plate is influenced by the amount of trench or slab advance, which is the amount of overall shortening not accommodated by underthrusting. While many subduction zones exhibit little to no slab advance, the Nazca-South America subduction and especially the early stages of the India-Eurasia collision provide end-member examples. Here, we use a transient, lithospheric-scale, thermomechanical 3D model of an orogen syntaxis to investigate the effects of subducting a flexurally stiffened plate geometry and slab advance on upper plate deformation. A visco-plastic upper-plate rheology is used, along with a buckled, rigid subducting plate. The free surface of the thermomechanical model is coupled to a landscape evolution model that accounts for erosion by fluvial and hillslope processes. The cooling histories of exhumed rocks are used to predict the evolution of low-temperature thermochronometer ages on the surface. With a constant overall shortening for all simulations, the magnitude of slab advance is varied stepwise from no advance, with all shortening accommodated by underthrusting, to full slab advance, i.e. no motion on the megathrust. We show that in models where most shortening is

Orogenic delamination - dynamics, effects, and geological expression

NASA Astrophysics Data System (ADS)

Ueda, Kosuke; Gerya, Taras

2010-05-01

Unbundling of continental lithosphere and removal of its mantle portion have been described by two mutually rather exclusive models, convective thinning and integral delamination. Either disburdens the remaining lithosphere, weakens the remainder, and causes uplift and extension. Increased heat flux is likely to promote high-degree crustal melting, and has been viewed as a source for voluminous granitic intrusions in late or collapsing orogenic settings. Collapse may be driven by any of gravitational potential differences from orogen to foreland, by stress inversion in the unburdened domain, or by suction of a retreating trench. In this study, we investigate prerequisites, mechanism, and development paths for orogeny-related mantle lithosphere removal. Our experiments numerically reproduce delamination which self-consistently results from the dynamics of a decoupling collision zone. In particular, it succeeds without a seed facilitating initial separation of layers. External shortening of a continent - ocean - continent assembly, such as to initiate oceanic subduction, is lifted before the whole oceanic part is consumed, leaving slab pull to govern further convergence. Once buoyant continental crust enters, the collision zone locks, and convergence diminishes. Under favourable conditions, delamination then initiates close to the edge of the mantle wedge and at deep crustal levels. While it initially separates upper crust from lower crust according to the weakness minimum in the lithospheric strength profile, the lower crust is eventually also delaminated from the subducting lithospheric mantle, owing to buoyancy differences. The level of delamination within the lithosphere seems thus first rheology-controlled, then density-controlled. Subduction-coupled delamination is contingent on retreat and decoupling of the subducting slab, which in turn is dependent on effective rheological weakening of the plate contact. Weakening is a function of shear-heating and hereby of

Orogenic inheritance and continental breakup: Wilson Cycle-control on rift and passive margin evolution

NASA Astrophysics Data System (ADS)

Schiffer, C.; Petersen, K. D.

2016-12-01

Rifts often develop along suture zones between previously collided continents, as part of the Wilson cycle. The North Atlantic is such an example, formed where Pangaea broke apart along Caledonian and Variscan sutures. Dipping upper mantle structures in E. Greenland and Scotland, have been interpreted as fossil subduction zones and the seismic signature indicates the presence of eclogite and serpentinite. We speculate that this orogenic material may impose a rheological control upon post-orogenic extension and we use thermo-mechanical modelling to explore such effects. Our model includes the following features: 1) Crustal thickness anomalies, 2) Eclogitised mafic crust emplaced in the mantle lithosphere, and 3) Hydrated mantle peridotite (serpentinite) formed in a pre-rift subduction setting. Our models indicate that the inherited structures control the location and the structural and magmatic evolution of the rift. Rifting of thin initial crust allows for relatively large amounts of serpentinite to be preserved within the uppermost mantle. This facilitates rapid continental breakup and serpentinite exhumation. Magmatism does not occur before continental breakup. Rifts in thicker crust preserve little or no serpentinite and thinning is more focused in the mantle lithosphere, rather than in the crust. Continental breakup is therefore preceded by magmatism. This implies that pre-rift orogenic properties may determine whether magma-poor or magma-rich conjugate margins are formed. Our models show that inherited orogenic eclogite and serpentinite are deformed and partially emplaced either as dipping structures within the lithospheric mantle or at the base of the thinned continental crust. The former is consistent with dipping sub-Moho reflectors often observed in passive margins. The latter provides an alternative interpretation of `lower crustal bodies' which are often regarded as igneous bodies. An additional implication of our models is that serpentinite, often

Estimates of late Cenozoic climate change relevant to Earth surface processes in tectonically active orogens

NASA Astrophysics Data System (ADS)

Mutz, Sebastian G.; Ehlers, Todd A.; Werner, Martin; Lohmann, Gerrit; Stepanek, Christian; Li, Jingmin

2018-04-01

The denudation history of active orogens is often interpreted in the context of modern climate gradients. Here we address the validity of this approach and ask what are the spatial and temporal variations in palaeoclimate for a latitudinally diverse range of active orogens? We do this using high-resolution (T159, ca. 80 × 80 km at the Equator) palaeoclimate simulations from the ECHAM5 global atmospheric general circulation model and a statistical cluster analysis of climate over different orogens (Andes, Himalayas, SE Alaska, Pacific NW USA). Time periods and boundary conditions considered include the Pliocene (PLIO, ˜ 3 Ma), the Last Glacial Maximum (LGM, ˜ 21 ka), mid-Holocene (MH, ˜ 6 ka), and pre-industrial (PI, reference year 1850). The regional simulated climates of each orogen are described by means of cluster analyses based on the variability in precipitation, 2 m air temperature, the intra-annual amplitude of these values, and monsoonal wind speeds where appropriate. Results indicate the largest differences in the PI climate existed for the LGM and PLIO climates in the form of widespread cooling and reduced precipitation in the LGM and warming and enhanced precipitation during the PLIO. The LGM climate shows the largest deviation in annual precipitation from the PI climate and shows enhanced precipitation in the temperate Andes and coastal regions for both SE Alaska and the US Pacific Northwest. Furthermore, LGM precipitation is reduced in the western Himalayas and enhanced in the eastern Himalayas, resulting in a shift of the wettest regional climates eastward along the orogen. The cluster-analysis results also suggest more climatic variability across latitudes east of the Andes in the PLIO climate than in other time slice experiments conducted here. Taken together, these results highlight significant changes in late Cenozoic regional climatology over the last ˜ 3 Myr. Comparison of simulated climate with proxy-based reconstructions for the MH and

Late orogenic processes between Baltica and Siberia cratons during the building of Pangea

NASA Astrophysics Data System (ADS)

Puchkov, V.

2003-04-01

Since the Middle Carboniferous, the territory between the Baltica, Kazakhstania and Siberia plates have been part of the continental crust, the last oceanic crust having by then been subducted. At this time continent-continent collision started and proceeded until the latest epochs of the Paleozoic, forming the Uralide orogen. Two features of this collision standout: 1) The northward movement of the Kazakhstanian block between the Baltica and Siberia plates resulted in a large-scale oroclinal bend of structures in West Siberia, which is well expressed in the magnetic field, as well as in the exposed Kazakhstanian structures, and 2) The orogenic event affected the whole territory between the Baltica and Siberia cratons, including the Kazakhstanian continent. A series of intermontane molasse basins are distributed throughout the orogen and in some places, like Bolshoi Karatau, are affected by Late Paleozoic deformation. Continent-continent collision had ceased by the end of the Permian, and in many places Triassic sediments unconformably overly the orogen. Triassic sedimentary sequences are typically coarse-grained (eventually proluvial), evidencing a new stage of mountain building, though many researchers have attributed this to a superplume event. The reason being the widespread flood basalt eruptions that took place not only between, but also on the cratons under discussion. There is a point of view that the break-up of the supercontinents (e.g., Pangea and Rodinia) was preceded by such a superplume event, passing to formation of linear graben systems and then to oceanic spreading. In the case under discussion, the process was arrested (the West Siberian basin with its grabens is often called a "failed ocean"). There is reason to suspect that the Paleozoic collision that led to formation of the Uralides left an enclosed ocean basin in the North, between the Baltica and Siberia plates. Only in the Early Jurassic, with the advent of the Old Kimmerian collision did

From the plutonic root to the volcanic roof of a continental magmatic arc: a review of the Neoproterozoic Araçuaí orogen, southeastern Brazil

NASA Astrophysics Data System (ADS)

Gonçalves, Leonardo; Alkmim, Fernando F.; Pedrosa-Soares, Antônio; Gonçalves, Cristiane C.; Vieira, Valter

2018-01-01

The Araçuaí-West Congo orogen (AWCO) is one of the various components of the Brasiliano/Pan-African orogenic network generated during the amalgamation of West Gondwana. In the reconstructions of Gondwana, the AWCO, encompassing the Araçuaí orogen of South America and the West Congo belt of Southwestern Africa, appears as a tongue-shaped orogenic zone embraced by the São Francisco-Congo craton. Differing from the vast majority of the known orogens owing to its singular confined setting, the AWCO contains a large amount of orogenic igneous rocks emplaced in all stages of its tectonic evolution. We present new and revised information about the oldest Ediacaran granitic assemblage, the G1 Supersuite, which together with the Rio Doce Group defines the Rio Doce magmatic arc, and then we propose a new tectonic setting for the arc. Field relationships and mineralogical compositions of the G1 Supersuite allow us to characterize three lithofacies associations, Opx-bearing rocks, enclave-rich Tonalite-Granodiorite and enclave-poor Granite-Tonalite, suggesting different crustal levels are exposed in the central part of the Araçuaí orogen. The region is interpreted to represent a tilted crustal section, with deep arc roots now exposed along its western border. Chemically, these plutonic associations consist mostly of magnesian, metaluminous to slightly peraluminous, calc-alkaline to alkali-calcic and medium- to high-K acidic rocks. The dacitic and rhyolitic rocks of the Rio Doce Group are mainly magnesian, peraluminous, calcic to calc-alkaline, and medium- to high-K acidic rocks. Zircon U-Pb data constrain the crystallization of the granitoids between ca. 625 and 574 Ma, while the age of the metamorphosed volcanic rocks is around ca. 585 Ma. Thus, within errors, these rock associations likely belong to the same magmatic event and might represent the subduction-related, pre-collisional, evolution of the Araçuaí orogen. In addition, whole-rock Sm-Nd isotopic compositions

Orogen-transverse tectonic window in the Eastern Himalayan fold belt: A superposed buckling model

NASA Astrophysics Data System (ADS)

Bose, Santanu; Mandal, Nibir; Acharyya, S. K.; Ghosh, Subhajit; Saha, Puspendu

2014-09-01

The Eastern Lesser Himalayan fold-thrust belt is punctuated by a row of orogen-transverse domal tectonic windows. To evaluate their origin, a variety of thrust-stack models have been proposed, assuming that the crustal shortening occurred dominantly by brittle deformations. However, the Rangit Window (RW) in the Darjeeling-Sikkim Himalaya (DSH) shows unequivocal structural imprints of ductile deformations of multiple episodes. Based on new structural maps, coupled with outcrop-scale field observations, we recognize at least four major episodes of folding in the litho-tectonic units of DSH. The last episode has produced regionally orogen-transverse upright folds (F4), the interference of which with the third-generation (F3) orogen-parallel folds has shaped the large-scale structural patterns in DSH. We propose a new genetic model for the RW, invoking the mechanics of superposed buckling in the mechanically stratified litho-tectonic systems. We substantiate this superposed buckling model with results obtained from analogue experiments. The model explains contrasting F3-F4 interferences in the Lesser Himalayan Sequence (LHS). The lower-order (terrain-scale) folds have undergone superposed buckling in Mode 1, producing large-scale domes and basins, whereas the RW occurs as a relatively higher-order dome nested in the first-order Tista Dome. The Gondwana and the Proterozoic rocks within the RW underwent superposed buckling in Modes 3 and 4, leading to Type 2 fold interferences, as evident from their structural patterns.

Large along-strike variations in the onset of Subandean exhumation: Implications for Central Andean orogenic growth

USGS Publications Warehouse

Lease, Richard O.; Ehlers, T.A.; Enkelmann, E.

2016-01-01

Plate tectonics drives mountain building in general, but the space-time pattern and style of deformation is influenced by how climate, geodynamics, and basement structure modify the orogenic wedge. Growth of the Subandean thrust belt, which lies at the boundary between the arid, high-elevation Central Andean Plateau and its humid, low-elevation eastern foreland, figures prominently into debates of orogenic wedge evolution. We integrate new apatite and zircon (U-Th)/He thermochronometer data with previously published apatite fission-track data from samples collected along four Subandean structural cross-sections in Bolivia between 15° and 20°S. We interpret cooling ages vs. structural depth to indicate the onset of Subandean exhumation and signify the forward propagation of deformation. We find that Subandean growth is diachronous south (11 ± 3 Ma) vs. north (6 ± 2 Ma) of the Bolivian orocline and that Subandean exhumation magnitudes vary by more than a factor of two. Similar north-south contrasts are present in foreland deposition, hinterland erosion, and paleoclimate; these observations both corroborate diachronous orogenic growth and illuminate potential propagation mechanisms. Of particular interest is an abrupt shift to cooler, more arid conditions in the Altiplano hinterland that is diachronous in southern Bolivia (16-13 Ma) vs. northern Bolivia (10-7 Ma) and precedes the timing of Subandean propagation in each region. Others have interpreted the paleoclimate shift to reflect either rapid surface uplift due to lithosphere removal or an abrupt change in climate dynamics once orographic threshold elevations were exceeded. These mechanisms are not mutually exclusive and both would drive forward propagation of the orogenic wedge by augmenting the hinterland backstop, either through surface uplift or spatially variable erosion. In summary, we suggest that diachronous Subandean exhumation was driven by piecemeal hinterland uplift, orography, and the outward

Greenstone-hosted lode-gold mineralization at Dungash mine, Eastern Desert, Egypt

NASA Astrophysics Data System (ADS)

Zoheir, Basem; Weihed, Pär

2014-11-01

hydrothermal alteration. The calculated δ34SH2S values for early, transitional, and late sulfide assemblages define three distinct ranges (∼1.5-3.6‰), (∼0.4-1.0‰), and (-3.7‰ to -1.9‰), respectively. The systematic evolution towards lighter δ34S values may be attributed to recrystallization, or to ore fluid buffering under variable physicochemical conditions. The shear zone-related setting, mineralogy and isotopic characteristics of gold mineralization in Dungash mine are comparable with other orogenic gold deposits in the region (e.g., Barramiya deposit), which may suggest a regional setting controlling gold metallogeny of the region. This setting should guide future exploration programs in the central Eastern Desert province.

Linking orogen and peripheral foreland basin: conceptual model and application to the Southalpine-Dinaric (Friuli) orocline

NASA Astrophysics Data System (ADS)

Heberer, Bianca; Neubauer, Franz

2010-05-01

Surface uplift and rock exhumation within an orogen are generally a consequence of convergence, and can often be linked with subsidence in a peripheral foreland. Since vertical loads act on the entire lithosphere, these processes can, therefore, be considered as plate-scale processes. Here, we propose a conceptual model for this linkage for the Friuli orocline and its surrounding units. The Friuli orocline stretches from the ENE-trending Southern Alps to the SE-trending Dinarides. There, two Neogene stages of convergence and associated deformation can be differentiated: (1) a Mid-Late Miocene phase of increased surface uplift and intra-orogenic subsidence of sedimentary basins reflecting intra-orogenic crustal-scale folding. Depocentres are e.g. the flexural Belluno, Ljubljana and Klagenfurt basins. (2) A second stage of convergence during Late Pliocene-Pleistocene times led to overall surface uplift in the orogen and contemporaneous pronounced subsidence in the peripheral foreland basin (Venetian platform and the northern Adriatic Sea). We propose, that the spatially variable extent of subsidence originates in variably strong orogen-basin coupling, i.e. weak coupling during stage 1 vs. strong coupling during stage 2. This interpretation is based on the apatite fission track age pattern, the distribution of intra-orogenic Neogene sediment basins and subsidence analyses in the foreland basin (Barbieri et al., 2007). Available low-temperature thermochronological data for the Southern Alps and the NW Dinarides are sparse, in contrast to a dense network of primarily apatite fission track ages north of the Periadriatic lineament (e.g. summarized by Luth & Willingshofer, 2008). AFT ages adjacent to the eastern Periadriatic Lineament mainly range from 15 to 25 Ma (Hejl, 1997; Fodor et al., 2008). Detrital studies on Oligocene to Miocene sediments from the Venetian foreland basin yielded dominant age groups clustering roughly around 20 and 30 Ma (Stefani et al., 2008

Association of gold with uraninite and pyrobitumen in the metavolcanic rock hosted hydrothermal Au-U mineralisation at Rompas, Peräpohja Schist Belt, northern Finland

NASA Astrophysics Data System (ADS)

Molnár, Ferenc; Oduro, Harry; Cook, Nick D. J.; Pohjolainen, Esa; Takács, Ágnes; O'Brien, Hugh; Pakkanen, Lassi; Johanson, Bo; Wirth, Richard

2016-06-01

The Peräpohja Schist Belt comprises a supracrustal sequence of quartzites, mafic volcanics and volcaniclastics, carbonate rocks, black shales, mica schists and greywackes which were deposited from ca. 2.44 to ~1.91 Ga, during the rifting of the Archaean basement in the eastern part of the Fennoscandian shield. Metamorphism and multiple folding of the basin fill took place during the Svecofennian orogeny (1.9-1.8 Ga) followed by intrusions of late-orogenic (1.84-1.80 Ga) and post-orogenic granitoids (1.79-1.76 Ga). The Rompas Au-U mineralisation is hosted by deformed calcsilicate veins in mafic volcanic rocks and locally contains very high grade (>10,000 g/t Au) gold pockets with strict spatial association of gold minerals to uraninite and pyrobitumen. Chemical ages from the unaltered domains in the structure of uraninite indicate a 1.95-1.90 Ga age for the deposition of the primary, high temperature (e.g. U/Th < 100 in uraninite) hydrothermal uranium mineralisation. These data are in agreement with the results of previous U-Pb dating of uraninite by SIMS. Textural evidence suggests that metamorphic recrystallisation of the uraninite-bearing quartz-dolomite veins into calcsilicate mineral assemblages during the Svecofennian orogeny (1.9-1.8 Ga) was followed by a hydrocarbon-bearing fluid flow event and radiolytic polymerisation of hydrocarbons around grains of uraninite. Gold precipitated during a subsequent hydrothermal process in the fractures of uraninite, as well as in the cracks and on the botryoidal surfaces of uraninite-pyrobitumen nodules. Remobilisation and redeposition of uranium by these hydrothermal events produced secondary uraninite grains with chemical ages between 1.85 and 1.65 Ga. Native gold is associated with galena, altaite, hunchunite, nickeline and rare cobaltite, Pb-bearing maldonite, pyrite, pyrrhotite, chalcopyrite, molybdenite and titanite. Raman spectra show disordered structure of undeformed pyrobitumen nodules in contrast with the well

Controlling factors of spatial and temporal preservation of the geochronological signal in sediments during an orogenic cycle

NASA Astrophysics Data System (ADS)

Rat, Juliette; Mouthereau, Frédéric; Bernet, Matthias; Brichau, Stéphanie; Balvay, Mélanie; Garzanti, Eduardo; Ando, Sergio

2017-04-01

Detrital content of sediments preserved in basins provide constraints on the nature of source rocks, dynamics of sediment transport, and potentially on tectonics and climate changes. U-Pb dating method on detrital zircon is ideally suited for provenance studies due to the ability of U-Pb age data to resist several orogenic cycles. However, with the aim to track sediment source evolution over a single orogenic cycle and determine characteristic time and parameters controlling the geochronological signal preservation throughout the cycle from rifting, mountain building to post-collision evolution, low-temperature thermochronology combined with sediment petrography are more appropriate than the U-Pb dating approach taken alone. To better understanding processes at play in the long-term geochronological signal preservation we focus on the sediment record associated with the Iberia plate tectonic evolution, which is part of the OROGEN research project, co-financed by BRGM, TOTAL & CNRS. The Iberian plate recorded a period of extension in the Late Jurassic, followed during the Early Cretaceous (Aptian-Albian) by a major thinning event documented by thick syn-rift sediments in intraplate basins and plate-scale heating/cooling of the Iberia crust, as argued by published fission track ages. Paleogeographic reconstructions that are based on stratigraphic and lithofacies analyses in northern Iberia (Iberian Range, Pyrenees and Basque-Cantabrians Range), describe a large domain of continental/fluvial and shallow-marine siliciclastic deposition. The related detrital content was then recycled during the subsequent Pyrenean orogenic phase in the Ebro foreland basin, and eventually transfer to the Mediterranean realm during post-orogenic re-excavation of the Ebro basin. In this study, we complete the published time-temperature paths in the mesozoic syn-rift basins by providing new thermo-chronological analyses of well-dated syn-collision and post-collision stratigraphic sections

Geometry, kinematics and tectonic models of the Kazakhstan Orocline, Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Li, Pengfei; Sun, Min; Rosenbaum, Gideon; Yuan, Chao; Safonova, Inna; Cai, Keda; Jiang, Yingde; Zhang, Yunying

2018-03-01

The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens on Earth and is characterized by the occurrence of tight oroclines (Kazakhstan and Tuva-Mongolian oroclines). The origin of these large-scale orogenic curvatures is not quite understood, but is fundamentally important for understanding crustal growth and tectonic evolution of the CAOB. Here we provide an outline of available geological and paleomagnetic data around the Kazakhstan Orocline, with an aim of clarifying the geometry, kinematics and geodynamic origin of the orocline. The Kazakhstan Orocline is evident in a total magmatic image, and can be traced by the continuation of high magnetic anomalies associated with the Devonian Volcanic Belt and the Late Devonian to Carboniferous Balkhash-Yili arc. Paleomagnetic data show ∼112-126° clockwise rotation of the northern limb relative to the southern limb in the Late Devonian to Early Carboniferous, as well as ∼15-28° clockwise rotation of the northern limb and ∼39-40° anticlockwise rotation of the southern limb relative to the hinge of the orocline during the Late Carboniferous to Permian. We argue that the Kazakhstan Orocline experienced two-stage bending with the early stage of bending (Late Devonian to Early Carboniferous; ∼112-126°) driven by slab rollback, and the later stage (Late Carboniferous to Permian; 54-68°) possibly associated with the amalgamation of the Siberian, Tarim and Baltic cratons. This new tectonic model is compatible with the occurrence of rift basins, the spatial migration of magmatic arc, and the development of large-scale strike-slip fault systems during oroclinal bending.

Linkages Between Critical Wedges and Crustal Channels Using 2-D Coupled Thermomechanical Finite Element Models: Implications for Himalayan Orogenic Evolution

NASA Astrophysics Data System (ADS)

Sparks, S. A.; Thigpen, J. R.

2017-12-01

In continental tectonics, questions remain regarding the dominant mechanisms of shortening accommodation during orogen evolution. Two quantitatively-supported models, critical wedge and channel flow, have been applied to the Himalaya and proposed for other large collisional systems. These two models represent fundamentally distinct mechanisms for accommodating shortening in collisional systems and until recently have been viewed as mutually exclusive. While there remains support for these mechanisms being incompatible end-members, in more recent studies it has been proposed that either: (1) both geodynamic mechanisms may operate simultaneously yet in spatially distinct parts of the larger composite orogenic system or (2) both mechanisms are present yet they operate at temporally distinct intervals, wherein the orogen progressively develops through stages dominated by mid-crustal channel flow followed by shallow thrust stacking and duplex development. In both scenarios, the mechanism active at each stage in orogen evolution is presumably dependent upon local to regional scale rheological conditions (as a function of orogen dynamic and thermal evolution) that are likely to be transient in both space and time. However, questions regarding the dynamic, mechanical, and thermal-kinematic relationships of such a system remain. Also, while field observations and deformation records derived from analyses of transects within the Himalaya can be interpreted in such a way to be consistent with a unified model, numerical models that predict the behavior of interactions between the end-member models have - until now - not existed. Here, we present results from 2-D coupled thermomechanical finite-element numerical experiments that examine the necessary conditions for mechanical compatibility between the channel and critical wedge by focusing on the role of rheology. These model results will eventually allow us to make preliminary comparisons between model-derived stress

The pre-orogenic detrital zircon record of the Variscan orogeny: Preliminary results

NASA Astrophysics Data System (ADS)

Stephan, Tobias; Kroner, Uwe

2017-04-01

To test plate-tectonic constellations in consideration of the long-term development of sedimentary transport paths, temporally and spatially highly resolved records of provenance analysis are mandatory. The interpretation of existing studies focus on small-scale areas within an orogen thereby neglecting the differing distribution of provenance data in the entire orogenic system. This study reviews a large data set of compiled geochronological data to document the development of pre-orogenic tectonic units on the example of the Variscan orogeny. Constrained by tectonic and geological models, the temporal distribution of U-Pb detrital zircon ages, used as a proxy for sedimentary provenance, shows that some minima and maxima of zircon abundance are nearly synchronous for thousands of kilometres along the orogeny. Age spectra of Precambrian to Lower Palaeozoic samples were constructed on the basis of 38729 U-Pb ages from 685 samples that were compiled from 102 publications. The age compilation combines thermal ionization mass spectrometry (TIMS), laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS), sensitive high-resolution ion microprobe (SHRIMP), and secondary ion mass spectrometry (SIMS) analyses. The data was re-processed using a common age calculation and concordance filter to ensure comparability. The concordance of each zircon grain was calculated from 206Pb/238U and 207Pb/235U ages to guarantee that only concordant grains, i.e., with <10% normal and <5% reverse discordance, were included in the age compilation. In order to ignore a metamorphic overprint and hence a blur of the younger age spectra, the compilation is constrained to age data older than 400 Ma only. If a precise sample age is not documented by the author, the weighted-mean age of the youngest zircon population (n > 3) is used for the maximum age of deposition. In addition to the location of >600 samples, the precise depositional ages result in a spatially and temporally high

Carbonatitic metasomatism in orogenic dunites from Lijiatun in the Sulu UHP terrane, eastern China

NASA Astrophysics Data System (ADS)

Su, Bin; Chen, Yi; Guo, Shun; Chu, Zhu-Yin; Liu, Jing-Bo; Gao, Yi-Jie

2016-10-01

Among orogenic peridotites, dunites suffer the weakest crustal metasomatism at the slab-mantle interface and are the best lithology to trace the origins of orogenic peridotites and their initial geodynamic processes. Petrological and geochemical investigations of the Lijiatun dunites from the Sulu ultrahigh-pressure (UHP) terrane indicate a complex petrogenetic history involving melt extraction and multistage metasomatism (carbonatitic melt and slab-derived fluid). The Lijiatun dunites consist mainly of olivine (Fo = 92.0-92.6, Ca = 42-115 ppm), porphyroblastic orthopyroxene (En = 91.8-92.8), Cr-spinel (Cr# = 50.4-73.0, TiO2 < 0.2 wt.%) and serpentine. They are characterized by refractory bulk-rock compositions with high MgO (45.31-47.07 wt.%) and Mg# (91.5-91.9), and low Al2O3 (0.48-0.70 wt.%), CaO (0.25-0.44 wt.%) and TiO2 (< 0.03 wt.%) contents. Whole-rock platinum group elements (PGE) are similar to those of cratonic mantle peridotites and Re-Os isotopic data suggest that dunites formed in the early Proterozoic ( 2.2 Ga). These data indicate that the Lijiatun dunites were the residues of 30% partial melting and were derived from the subcontinental lithospheric mantle (SCLM) beneath the North China craton (NCC). Subsequent carbonatitic metasomatism is characterized by the formation of olivine-rich (Fo = 91.6-92.6, Ca = 233-311 ppm), clinopyroxene-bearing (Mg# = 95.9-96.7, Ti/Eu = 104-838) veins cutting orthopyroxene porphyroblasts. Based on the occurrence of dolomite, mass-balance calculation and thermodynamic modeling, carbonatitic metasomatism had occurred within the shallow SCLM (low-P and high-T conditions) before dunites were incorporated into the continental subduction channel. These dunites then suffered weak metasomatism by slab-derived fluids, forming pargasitic amphibole after pyroxene. This work indicates that modification of the SCLM beneath the eastern margin of the NCC had already taken place before the Triassic continental subduction. Orogenic

The Ross Orogen and Lachlan Fold Belt in Marie Byrd Land, Northern Victoria Land and New Zealand: implication for the tectonic setting of the Lachlan Fold Belt in Antarctica

USGS Publications Warehouse

Bradshaw, J.D.

2007-01-01

Correlation of the Cambrian Delamerian Orogen of Australia and Ross Orogen of the Transantarctic Mountains widely accepted but the extension of the adjacent Lachlan Orogen into Antarctica is controversial. Outside the main Ross-Delamerian belt, evidence of this orogeny is preserved at Mt Murphy in Marie Byrd Land and the in Takaka Terrane of New Zealand. In all pre-break- configurations of the SW Pacific, these two areas are far removed from the Ross-Delamerian belt. Evidence from conglomerates in the Takaka Terrane, however, shows that in Late Cambrian times it was adjacent to the Ross Orogen. This indicates major tectonic displacements within Gondwana after the Cambrian and before break-up. The Lachlan Orogen formed in an extensional belt in a supra-subduction zone setting and the Cambrian rocks of Marie Byrd Land and New Zealand are interpreted as parts of a rifted continental ribbon on the outboard side of the Lachlan belt.

The evolution of a Gondwanan collisional orogen: A structural and geochronological appraisal from the Southern Granulite Terrane, South India

NASA Astrophysics Data System (ADS)

Plavsa, Diana; Collins, Alan S.; Foden, John D.; Clark, Chris

2015-05-01

Gondwana amalgamated along a suite of Himalayan-scale collisional orogens, the roots of which lace the continents of Africa, South America, and Antarctica. The Southern Granulite Terrane of India is a generally well-exposed, exhumed, Gondwana-forming orogen that preserves a record of the tectonic evolution of the eastern margin of the East African Orogen during the Ediacaran-Cambrian (circa 600-500 Ma) as central Gondwana formed. The deformation associated with the closure of the Mozambique Ocean and collision of the Indian and East African/Madagascan cratonic domains is believed to have taken place along the southern margin of the Salem Block (the Palghat-Cauvery Shear System, PCSS) in the Southern Granulite Terrane. Investigation of the structural fabrics and the geochronology of the high-grade shear zones within the PCSS system shows that the Moyar-Salem-Attur shear zone to the north of the PCSS system is early Paleoproterozoic in age and associated with dextral strike-slip motion, while the Cauvery shear zone (CSZ) to the south of the PCSS system can be loosely constrained to circa 740-550 Ma and is associated with dip-slip dextral transpression and north side-up motion. To the south of the proposed suture zone (the Cauvery shear zone), the structural fabrics of the Northern Madurai Block suggest four deformational events (D1-D4), some of which are likely to be contemporaneous. The timing of high pressure-ultrahigh temperature metamorphism and deformation (D1-D3) in the Madurai Block (here interpreted as the southern extension of Azania) is constrained to circa 550-500 Ma and interpreted as representing collisional orogeny and subsequent orogenic collapse of the eastern margin of the East African Orogen. The disparity in the nature of the structural fabrics and the timing of the deformation in the Salem and the Madurai Blocks suggest that the two experienced distinct tectonothermal events prior to their amalgamation along the Cauvery shear zone during the

Modes of orogen-parallel stretching and extensional exhumation in response to microplate indentation and roll-back subduction (Tauern Window, Eastern Alps)

NASA Astrophysics Data System (ADS)

Scharf, A.; Handy, M. R.; Favaro, S.; Schmid, S. M.; Bertrand, A.

2013-09-01

The Tauern Window exposes a Paleogene nappe stack consisting of highly metamorphosed oceanic (Alpine Tethys) and continental (distal European margin) thrust sheets. In the eastern part of this window, this nappe stack (Eastern Tauern Subdome, ETD) is bounded by a Neogene system of shear (the Katschberg Shear Zone System, KSZS) that accommodated orogen-parallel stretching, orogen-normal shortening, and exhumation with respect to the structurally overlying Austroalpine units (Adriatic margin). The KSZS comprises a ≤5-km-thick belt of retrograde mylonite, the central segment of which is a southeast-dipping, low-angle extensional shear zone with a brittle overprint (Katschberg Normal Fault, KNF). At the northern and southern ends of this central segment, the KSZS loses its brittle overprint and swings around both corners of the ETD to become subvertical, dextral, and sinistral strike-slip faults. The latter represent stretching faults whose displacements decrease westward to near zero. The kinematic continuity of top-east to top-southeast ductile shearing along the central, low-angle extensional part of the KSZS with strike-slip shearing along its steep ends, combined with maximum tectonic omission of nappes of the ETD in the footwall of the KNF, indicates that north-south shortening, orogen-parallel stretching, and normal faulting were coeval. Stratigraphic and radiometric ages constrain exhumation of the folded nappe complex in the footwall of the KSZS to have begun at 23-21 Ma, leading to rapid cooling between 21 and 16 Ma. This exhumation involved a combination of tectonic unroofing by extensional shearing, upright folding, and erosional denudation. The contribution of tectonic unroofing is greatest along the central segment of the KSZS and decreases westward to the central part of the Tauern Window. The KSZS formed in response to the indentation of wedge-shaped blocks of semi-rigid Austroalpine basement located in front of the South-Alpine indenter that was part

Detrital zircon fission track analysis reveals the thermotectonic history of ice-covered rocks of the Chugach-St. Elias orogen, SE-Alaska

NASA Astrophysics Data System (ADS)

Enkelmann, E.; Garver, J. I.; Pavlis, T. L.; Bruhn, R. L.; Chapman, J. B.

2007-12-01

Investigating the exhumation history of the Chugach-St. Elias orogen (SE Alaska) using low-temperature thermochronometers is challenged by significant ice cover. Assuming exhumation drove cooling, cooling ages increase with elevation in an orogenic belt, and as such the youngest ages occur in valley bottoms. Cooling and exhumation rates are expected to be very high in the Chugach-St. Elias orogen due to efficient glacial erosion and the most intense erosion occurs under the major ice fields. To study the cooling history of rapidly exhuming rocks underneath this ice cover, we analyzed detrital zircon fission track (DZFT) ages of Recent sand samples from modern rivers that drain the central Bagley Ice field and smaller glaciers draining north (Chitina valley) and south (Pacific) of the mountain range. A distinct advantage of DZFT is that it allows one to sample a landscape regardless of accessibility. The youngest ZFT component populations of samples north and south of the Bagley Ice field record a Late Miocene (5-13 Ma) cooling of the orogen. The pattern of cooling ages shows symmetry across the orogen predates the earliest record of the collision of the Yakutat terrane with Alaska. This result contrasts with the asymmetric cooling pattern displayed by low- temperature thermochronological ages (AFT and AHe) of the exposed bedrock within the range. Apatite FT and U- Th/He ages of bedrock samples south of the Bagley Ice field record the syn-collisional (<5 Ma) fast exhumation whereas apatite ages to the north reveal more heterogeneous exhumation and vary widely from Miocene to Eocene. The bedrock samples from throughout the orogenic belt thus display predominantly the effects of the recent climatic situation of the mountain range with very high precipitation on the south, seaward side versus a more arid north side. Our ZFT results from the northern drainages highlight the relative sense and timing of two important fault zones, both accommodate south-side-up exhumation

Seismic anisotropy and mantle creep in young orogens

USGS Publications Warehouse

Meissner, R.; Mooney, W.D.; Artemieva, I.

2002-01-01

Seismic anisotropy provides evidence for the physical state and tectonic evolution of the lithosphere. We discuss the origin of anisotropy at various depths, and relate it to tectonic stress, geotherms and rheology. The anisotropy of the uppermost mantle is controlled by the orthorhombic mineral olivine, and may result from ductile deformation, dynamic recrystallization or annealing. Anisotropy beneath young orogens has been measured for the seismic phase Pn that propagates in the uppermost mantle. This anisotropy is interpreted as being caused by deformation during the most recent thermotectonic event, and thus provides information on the process of mountain building. Whereas tectonic stress and many structural features in the upper crust are usually orientated perpendicular to the structural axis of mountain belts, Pn anisotropy is aligned parallel to the structural axis. We interpret this to indicate mountain-parallel ductile (i.e. creeping) deformation in the uppermost mantle that is a consequence of mountain-perpendicular compressive stresses. The preferred orientation of the fast axes of some anisotropic minerals, such as olivine, is known to be in the creep direction, a consequence of the anisotropy of strength and viscosity of orientated minerals. In order to explain the anisotropy of the mantle beneath young orogens we extend the concept of crustal 'escape' (or 'extrusion') tectonics to the uppermost mantle. We present rheological model calculations to support this hypothesis. Mountain-perpendicular horizontal stress (determined in the upper crust) and mountain-parallel seismic anisotropy (in the uppermost mantle) require a zone of ductile decoupling in the middle or lower crust of young mountain belts. Examples for stress and mountain-parallel Pn anisotropy are given for Tibet, the Alpine chains, and young mountain ranges in the Americas. Finally, we suggest a simple model for initiating mountain parallel creep.

Origin of unusual HREE-Mo-rich carbonatites in the Qinling orogen, China

NASA Astrophysics Data System (ADS)

Song, Wenlei; Xu, Cheng; Smith, Martin P.; Kynicky, Jindrich; Huang, Kangjun; Wei, Chunwan; Zhou, Li; Shu, Qihai

2016-11-01

Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ26Mg values (-1.89 to -1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo.

Origin of unusual HREE-Mo-rich carbonatites in the Qinling orogen, China

PubMed Central

Song, Wenlei; Xu, Cheng; Smith, Martin P.; Kynicky, Jindrich; Huang, Kangjun; Wei, Chunwan; Zhou, Li; Shu, Qihai

2016-01-01

Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ26Mg values (−1.89 to −1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo. PMID:27857170

Origin of unusual HREE-Mo-rich carbonatites in the Qinling orogen, China.

PubMed

Song, Wenlei; Xu, Cheng; Smith, Martin P; Kynicky, Jindrich; Huang, Kangjun; Wei, Chunwan; Zhou, Li; Shu, Qihai

2016-11-18

Carbonatites, usually occurring within intra-continental rift-related settings, have strong light rare earth element (LREE) enrichment; they rarely contain economic heavy REE (HREE). Here, we report the identification of Late Triassic HREE-Mo-rich carbonatites in the northernmost Qinling orogen. The rocks contain abundant primary HREE minerals and molybdenite. Calcite-hosted fluid inclusions, inferred to represent a magmatic-derived aqueous fluid phase, contain significant concentrations of Mo (~17 ppm), reinforcing the inference that these carbonatitic magmas had high Mo concentrations. By contrast, Late Triassic carbonatites in southernmost Qinling have economic LREE concentrations, but are depleted in HREE and Mo. Both of these carbonatite types have low δ 26 Mg values (-1.89 to -1.07‰), similar to sedimentary carbonates, suggesting a recycled sediment contribution for REE enrichment in their mantle sources. We propose that the carbonatites in the Qinling orogen were formed, at least in part, by the melting of a subducted carbonate-bearing slab, and that 10 Ma younger carbonatite magmas in the northernmost Qinling metasomatized the thickened eclogitic lower crust to produce high levels of HREE and Mo.

Geochemical and Sm-Nd isotope-geochemical patterns of metavolcanic rocks, diabase, and metagabbroids on the northeastern flank of the South Mongolian-Khingan orogenic belt

NASA Astrophysics Data System (ADS)

Smirnov, Yu. V.; Sorokin, A. A.

2017-05-01

The first results of geochemical and Sm-Nd isotope-geochemical studies of metavolcanic rocks, metagabbroids, and diabase of the Nora-Sukhotino terrane, the least studied part of the South Mongolian-Khingan orogenic belt in the system of the Central Asian orogenic belt are reported. It is established that the basic rocks composing this terrane include varieties comparable with E-MORB, tholeiitic, and calc-alkaline basalt of island arc, calc-alkaline gabbro-diabase, and gabbroids of island arcs. Most likely, these formations should be correlated with metabasalt and associated Late Ordovician gabbro-amphibolite of the Sukdulkin "block" of the South Mongolian-Khingan orogenic belt, which are similar to tholeiite of intraplate island arcs by their geochemical characteristics.

Ediacaran 2,500-km-long synchronous deep continental subduction in the West Gondwana Orogen

NASA Astrophysics Data System (ADS)

Ganade de Araujo, Carlos E.; Rubatto, Daniela; Hermann, Joerg; Cordani, Umberto G.; Caby, Renaud; Basei, Miguel A. S.

2014-10-01

The deeply eroded West Gondwana Orogen is a major continental collision zone that exposes numerous occurrences of deeply subducted rocks, such as eclogites. The position of these eclogites marks the suture zone between colliding cratons, and the age of metamorphism constrains the transition from subduction-dominated tectonics to continental collision and mountain building. Here we investigate the metamorphic conditions and age of high-pressure and ultrahigh-pressure eclogites from Mali, Togo and NE-Brazil and demonstrate that continental subduction occurred within 20 million years over at least a 2,500-km-long section of the orogen during the Ediacaran. We consider this to be the earliest evidence of large-scale deep-continental subduction and consequent appearance of Himalayan-scale mountains in the geological record. The rise and subsequent erosion of such mountains in the Late Ediacaran is perfectly timed to deliver sediments and nutrients that are thought to have been necessary for the subsequent evolution of sustainable life on Earth.

Relationship Between Earthquake b-Values and Crustal Stresses in a Young Orogenic Belt

NASA Astrophysics Data System (ADS)

Wu, Yih-Min; Chen, Sean Kuanhsiang; Huang, Ting-Chung; Huang, Hsin-Hua; Chao, Wei-An; Koulakov, Ivan

2018-02-01

It has been reported that earthquake b-values decrease linearly with the differential stresses in the continental crust and subduction zones. Here we report a regression-derived relation between earthquake b-values and crustal stresses using the Anderson fault parameter (Aϕ) in a young orogenic belt of Taiwan. This regression relation is well established by using a large and complete earthquake catalog for Taiwan. The data set consists of b-values and Aϕ values derived from relocated earthquakes and focal mechanisms, respectively. Our results show that b-values decrease linearly with the Aϕ values at crustal depths with a high correlation coefficient of -0.9. Thus, b-values could be used as stress indicators for orogenic belts. However, the state of stress is relatively well correlated with the surface geological setting with respect to earthquake b-values in Taiwan. Temporal variations in the b-value could constitute one of the main reasons for the spatial heterogeneity of b-values. We therefore suggest that b-values could be highly sensitive to temporal stress variations.

Raman and micro-thermometric investigation of the fluid inclusions in quartz in a gold-rich formation from Lepaguare mining district (Honduras, Central America).

PubMed

Bersani, D; Salvioli-Mariani, E; Mattioli, M; Menichetti, M; Lottici, P P

2009-08-01

Fluid inclusions in the quartz crystals present in gold-rich veins from central Honduras have been studied by means of micro-thermometry and micro-Raman spectroscopy in order to provide information on the physico-chemical conditions and chemical composition of the mineralizing fluids. The use of a confocal micro-Raman apparatus allowed to obtain information on the fluid composition, in particular on the gas phase, minimizing the contributions of the host matrix to the Raman signal. The samples studied were collected from an area (Lepaguare mining district, Northern-Central Honduras) rich in ore deposits due to the Cenozoic magmatic activity, where the gold and sulphide mineralization is connected with a system of quartz veins (few decimetres thick) occurring in low-grade metamorphic rocks and produced by hydrothermal fluids. The quartz crystals present in the gold-rich veins often contain fluid inclusions. Four types of fluid inclusions have been observed, but their assemblage in the same clusters and fracture systems, as well as their comparable salinity and homogenization data, suggest that they have the same origin. Micro-thermometry and Raman spectroscopy provide a composition of the mineralizing fluids attributable to the system H(2)O-NaCl-KCl-CO(2)-CH(4), with temperature and pressure intervals of 210-413 degrees C and 1050-3850 bar, respectively. These data agree with an epigenetic origin of the gold deposit (depth < 6 km) related to granitoid or granodiorite intrusions associated to orogenic environments.

Window into the Caledonian orogen: Structure of the crust beneath the East Shetland platform, United Kingdom

USGS Publications Warehouse

McBride, J.H.; England, R.W.

1999-01-01

Reprocessing and interpretation of commercial and deep seismic reflection data across the East Shetland platform and its North Sea margin provide a new view of crustal subbasement structure beneath a poorly known region of the British Caledonian orogen. The East Shetland platform, east of the Great Glen strike-slip fault system, is one of the few areas of the offshore British Caledonides that remained relatively insulated from the Mesozoic and later rifting that involved much of the area around the British Isles, thus providing an "acoustic window" into the deep structure of the orogen. Interpretation of the reflection data suggests that the crust beneath the platform retains a significant amount of its original Caledonian and older architecture. The upper to middle crust is typically poorly reflective except for individual prominent dipping reflectors with complex orientations that decrease in dip with depth and merge with a lower crustal layer of high reflectivity. The three-dimensional structural orientation of the reflectors beneath the East Shetland platform is at variance with Caledonian reflector trends observed elsewhere in the Caledonian orogen (e.g., north of the Scottish mainland), emphasizing the unique tectonic character of this part of the orogen. Upper to middle crustal reflectors are interpreted as Caledonian or older thrust surfaces that were possibly reactivated by Devonian extension associated with post-Caledonian orogenic collapse. The appearance of two levels of uneven and diffractive (i.e., corrugated) reflectivity in the lower crust, best developed on east-west-oriented profiles, is characteristic of the East Shetland platform. However, a north-south-oriented profile reveals an interpreted south-vergent folded and imbricated thrust structure in the lower crust that appears to be tied to the two levels of corrugated reflectivity on the east-west profiles. A thrust-belt origin for lower crustal reflectivity would explain its corrugated

Peering into the deep: Illuminating the crustal evolution of the Eucla basement and its relationship to the Albany-Fraser Orogen of southwest Australia.

NASA Astrophysics Data System (ADS)

Hartnady, Michael; Kirkland, Chris; Clark, Chris; Spaggiari, Catherine; Smithies, Hugh

2017-04-01

The Albany-Fraser Orogen is a 1200 km long east to northeasterly trending Palaeoproterozoic to Mesoproterozoic orogenic belt that defines the southern to southeastern margin of the West Australian Craton (WAC). The belt records a long and complex geological history spanning the break-up of Nuna between 2000 and 1700 Ma and amalgamation of Rodinia between 1300 and 1000 Ma. Recent geochronological, geochemical and isotopic work has shown that the Albany-Fraser Orogen formed through a protracted period of reworking of the margin of the Archean Yilgarn Craton (part of the WAC) with various additions of mantle-derived material. The Cretaceous Bight and Cenozoic Eucla Basins partially overlie the northeastern part of the Albany-Fraser Orogen and completely cover 1000 km of crystalline basement (the Eucla basement) that separates the belt from the South Australian Craton. This basement constitutes the glue between the major building blocks of Proterozoic Australia, yet, its geological history is poorly understood. New drill cores penetrating the basement have intersected interlayered granitic and gabbroic rocks that yield U-Pb zircon dates that are dissimilar to any magmatic ages from units within the adjoining Albany-Fraser Orogen, with the exception of the youngest, 1190-1125 Ma magmatic suite. In addition, mantle-like hafnium and neodymium isotopic signatures indicate that the rocks of the Eucla basement are dominated by new juvenile addition, and may represent an allochthonous terrane of oceanic heritage. New ɛHf contour maps for the Albany-Fraser Orogen and Eucla basement highlight this difference. Time-slicing the isotopic dataset reveals a pattern of Palaeoproterozoic juvenile magmatism sub-perpendicular to the present day structural grain in the belt. If this marks the presence of an older lithospheric structure then it demonstrates the power that time-constrained isotopic mapping provides for illuminating lithospheric architecture through time. This may be

Tectonic and kinematics of curved orogenic systems: insights from AMS analysis and paleomagnetism

NASA Astrophysics Data System (ADS)

Cifelli, Francesca; Mattei, Massimo

2016-04-01

During the past few years, paleomagnetism has been considered a unique tool for constraining kinematic models of curved orogenic systems, because of its great potential in quantifying vertical axis rotations and in discriminating between primary and secondary (orocline s.l.) arcs. In fact, based on the spatio-temporal relationships between deformation and vertical axis rotation, curved orogens can be subdivided as primary or secondary (oroclines s.l.), if they formed respectively in a self-similar manner without undergoing important variations in their original curved shape or if their curvature in map-view is the result of a bending about a vertical axis of rotation. In addition to the kinematics of the arc and the timing of its curvature, a crucial factor for understanding the origin of belts curvature is the knowledge of the geodynamic process governing arc formation. In this context, the detailed reconstruction of the rotational history is mainly based on paleomagnetic and structural analyses (fold axes, kinematic indicators), which include the magnetic fabric. In fact, in curved fold and thrust belts, assuming that the magnetic lineation is tectonically originated and formed during layer-parallel shortening (LPS) before vertical axis rotations, the orientation of the magnetic lineation often strictly follows the curvature of the orogeny. This assumption represents a fundamental prerequisite to fully understand the origin of orogenic arcs and to unravel the geodynamic processes responsible for their curvature. We present two case studies: the central Mediterranean arcs and the Alborz Mts in Iran. The Mediterranean area has represented an attractive region to apply paleomagnetic analysis, as it shows a large number of narrow arcs, whose present-day shape has been driven by the space-time evolution of the Mediterranean subduction system, which define a irregular and rather diffuse plate boundary. The Alborz Mts. form a sinuous range over 1,200 km long, defining

Synthesis of gold structures by gold-binding peptide governed by concentration of gold ion and peptide.

PubMed

Kim, Jungok; Kim, Dong-Hun; Lee, Sylvia J; Rheem, Youngwoo; Myung, Nosang V; Hur, Hor-Gil

2016-08-01

Although biological synthesis methods for the production of gold structures by microorganisms, plant extracts, proteins, and peptide have recently been introduced, there have been few reports pertaining to controlling their size and morphology. The gold ion and peptide concentrations affected on the size and uniformity of gold plates by a gold-binding peptide Midas-11. The higher concentration of gold ions produced a larger size of gold structures reached 125.5 μm, but an increased amount of Midas-11 produced a smaller size of gold platelets and increased the yield percentage of polygonal gold particles rather than platelets. The mechanisms governing factors controlling the production of gold structures were primarily related to nucleation and growth. These results indicate that the synthesis of gold architectures can be controlled by newly isolated and substituted peptides under different reaction conditions.

Mass elevation and lee effects markedly lift the elevational distribution of ground beetles in the Himalaya-Tibet orogen

PubMed Central

Schmidt, Joachim; Böhner, Jürgen; Brandl, Roland; Opgenoorth, Lars

2017-01-01

Mass elevation and lee effects markedly influence snow lines and tree lines in high mountain systems. However, their impact on other phenomena or groups of organisms has not yet been quantified. Here we quantitatively studied their influence in the Himalaya–Tibet orogen on the distribution of ground beetles as model organisms, specifically whether the ground beetle distribution increases from the outer to the inner parts of the orogen, against latitudinal effects. We also tested whether July temperature and solar radiation are predictors of the beetle’s elevational distribution ranges. Finally, we discussed the general importance of these effects for the distributional and evolutionary history of the biota of High Asia. We modelled spatially explicit estimates of variables characterizing temperature and solar radiation and correlated the variables with the respective lower elevational range of 118 species of ground beetles from 76 high-alpine locations. Both July temperature and solar radiation significantly positively correlated with the elevational ranges of high-alpine beetles. Against the latitudinal trend, the median elevation of the respective species distributions increased by 800 m from the Himalayan south face north to the Transhimalaya. Our results indicate that an increase in seasonal temperature due to mass elevation and lee effects substantially impact the regional distribution patterns of alpine ground beetles of the Himalaya–Tibet orogen and are likely to affect also other soil biota there and in mountain ranges worldwide. Since these effects must have changed during orogenesis, their potential impact must be considered when biogeographic scenarios based on geological models are derived. As this has not been the practice, we believe that large biases likely exist in many paleoecological and evolutionary studies dealing with the biota from the Himalaya-Tibet orogen and mountain ranges worldwide. PMID:28339461

Magnetic signatures of the orogenic crust of the Patagonian Andes with implication for planetary exploration

NASA Astrophysics Data System (ADS)

Díaz Michelena, Marina; Kilian, Rolf

2015-11-01

The Patagonian Andes represent a good scenario of study because they have outcrops of diverse plutonic rocks representative of an orogenic crust on Earth and other planets. Furthermore, metamorphic surface rocks provide a window into deeper crustal lithologies. In such remote areas, satellite and aerial magnetic surveys could provide important geological information concerning exposed and not exposed rocks, but they integrate the magnetic anomalies in areas of kilometres. For the southernmost Andes long wavelength satellite data show clear positive magnetic anomalies (>+100 nT) for the Patagonian Batholith (PB), similar as parts of the older martian crust. This integrated signal covers regions with different ages and cooling histories during magnetic reversals apart from the variability of the rocks. To investigate the complex interplay of distinct magnetic signatures at short scale, we have analysed local magnetic anomalies across this orogen at representative sites by decimeter-scale magnetic ground surveys. As expected, the investigated sites have positive and negative local anomalies. They are related to surface and subsurface rocks, and their different formation and alternation processes including geomagnetic inversions, distinct Curie depths of the magnetic carriers, intracrustal deformation among other factors. Whole rock chemistry (ranging from 45 to >80 wt.% SiO2 and from 1 to 18 wt.% FeOtot.), magnetic characteristics (susceptibilities, magnetic remanence and Königsberger ratios) as well as the composition and texture of the magnetic carriers have been investigated for representative rocks. Rocks of an ultramafic to granodioritic intrusive suite of the western and central PB contain titanomagnetite as major magnetic carrier. Individual magnetic signatures of these plutonic rocks reflect their single versus multidomain status, complex exolution processes with ilmenite lamella formations and the stoichiometric proportions of Cr, Fe and Ti in the oxides. At

Geology and metallogeny of the Ar Rayn terrane, eastern Arabian shield: Evolution of a Neoproterozoic continental-margin arc during assembly of Gondwana within the East African orogen

USGS Publications Warehouse

Doebrich, J.L.; Al-Jehani, A. M.; Siddiqui, A.A.; Hayes, T.S.; Wooden, J.L.; Johnson, P.R.

2007-01-01

The Neoproterozoic Ar Rayn terrane is exposed along the eastern margin of the Arabian shield. The terrane is bounded on the west by the Ad Dawadimi terrane across the Al Amar fault zone (AAF), and is nonconformably overlain on the east by Phanerozoic sedimentary rocks. The terrane is composed of a magmatic arc complex and syn- to post-orogenic intrusions. The layered rocks of the arc, the Al Amar group (>689 Ma to ???625 Ma), consist of tholeiitic to calc-alkaline basaltic to rhyolitic volcanic and volcaniclastic rocks with subordinate tuffaceous sedimentary rocks and carbonates, and are divided into an eastern and western sequence. Plutonic rocks of the terrane form three distinct lithogeochemical groups: (1) low-Al trondhjemite-tonalite-granodiorite (TTG) of arc affinity (632-616 Ma) in the western part of the terrane, (2) high-Al TTG/adakite of arc affinity (689-617 Ma) in the central and eastern part of the terrane, and (3) syn- to post-orogenic alkali granite (607-583 Ma). West-dipping subduction along a trench east of the terrane is inferred from high-Al TTG/adakite emplaced east of low-Al TTG. The Ar Rayn terrane contains significant resources in epithermal Au-Ag-Zn-Cu-barite, enigmatic stratiform volcanic-hosted Khnaiguiyah-type Zn-Cu-Fe-Mn, and orogenic Au vein deposits, and the potential for significant resources in Fe-oxide Cu-Au (IOCG), and porphyry Cu deposits. Khnaiguiyah-type deposits formed before or during early deformation of the Al Amar group eastern sequence. Epithermal and porphyry deposits formed proximal to volcanic centers in Al Amar group western sequence. IOCG deposits are largely structurally controlled and hosted by group-1 intrusions and Al Amar group volcanic rocks in the western part of the terrane. Orogenic gold veins are largely associated with north-striking faults, particularly in and near the AAF, and are presumably related to amalgamation of the Ar Rayn and Ad Dawadimi terranes. Geologic, structural, and metallogenic

The TANAMI Program

DTIC Science & Technology

2010-06-01

Sternwartstrasse 7, 96049 Bamberg, Germany 3 CRESST/ NASA Goddard Space Flight Center, Greenbelt, ~’iID 20771, USA 4 USRA, 10211 Wincopin Circle, Suite...program and present early results on the 75 sources currently being monitored. 1. Introduction Very Long Baseline Interferometry (VLBI) observations...wavelength studies (e.g., Abdo et al. 2010a, Chang et al. 2010) be - sides probing emission processes along AGN jets (e.g., Muller et al. 2010, Hungwe

Restoration of Late Neoarchean-Early Cambrian tectonics in the Rengali orogen and its environs (eastern India): The Antarctic connection

NASA Astrophysics Data System (ADS)

Bhattacharya, A.; Das, H. H.; Bell, Elizabeth; Bhattacharya, Atreyee; Chatterjee, N.; Saha, L.; Dutt, A.

2016-10-01

Geological mapping and P-T path reconstructions are combined with monazite chemical age and Secondary Ion Mass Spectrometric (SIMS) U-Pb zircon age determinations to identify crustal domains with distinctive evolutionary histories in the Rengali orogen sandwiched between two Grenvillian-age metamorphic belts, i.e. the Eastern Ghats Granulite Belt (EGGB) in the south, and the amphibolite facies Gangpur Schist Belt (GSB) in the north, which in turn forms a collar along the NW/W margins of the Paleo/Mesoarchean Singhbhum Craton (SC) north of the Rengali orogen. Anatectic gneisses in the orogen core exhibit multi-phase Neoarchean/Paleoproterozoic deformation, metamorphic P-T histories and juvenile magma emplacement events. The high-grade belt is inferred to be a septum of the Bastar Craton (BC). The flanking supracrustal belt in the orogen - dominated by quartz-muscovite schists (± staurolite, kyanite, garnet pyrophyllite), inter-bedded with poorly-sorted and polymict meta-conglomerate, and meta-ultramafic/amphibolite bands - evolved along P-T paths characterized by sub-greenschist to amphibolite facies peak P-T conditions in closely-spaced samples. The supracrustal rocks and the anatectic gneisses of contrasting metamorphic P-T histories experienced D1, D2 and D3 fabric-forming events, but the high-angle obliquity between the steeply-plunging D3 folds in the anatectic gneisses and the gently-plunging D3 folds in the supracrustal unit suggests the two lithodemic units were tectonically accreted post-S2. The supracrustal belt is inferred to be a tectonic mélange formed in an accretionary wedge at the tri-junction of the Bastar Craton, the Eastern Ghats Granulite Belt and the Singhbhum Craton; the basin closure synchronous with the assembly of EGGB and the Singhbhum Craton-Gangpur Schist belt composite occurred between 510 and 610 Ma. Based on the available evidence across the facing coastlines of the Greater India landmass and the Australo-Antarctic blocks at 500 Ma

Melting of subducted continental crust: Geochemical evidence from Mesozoic granitoids in the Dabie-Sulu orogenic belt, east-central China

NASA Astrophysics Data System (ADS)

Zhao, Zi-Fu; Liu, Zhi-Bin; Chen, Qi

2017-09-01

Syn-collisional and postcollisional granitoids are common in collisional orogens, and they were primarily produced by partial melting of subducted continental crust. This is exemplified by Mesozoic granitoids from the Dabie-Sulu orogenic belt in east-central China. These granitoids were emplaced in small volumes in the Late Triassic (200-206 Ma) and the Late Jurassic (146-167 Ma) but massively in the Early Cretaceous (111-143 Ma). Nevertheless, all of them exhibit arc-like trace element distribution patterns and are enriched in Sr-Nd-Hf isotope compositions, indicating their origination from the ancient continental crust. They commonly contain relict zircons with Neoproterozoic and Triassic U-Pb ages, respectively, consistent with the protolith and metamorphic ages for ultrahigh-pressure (UHP) metaigneous rocks in the Dabie-Sulu orogenic belt. Some granitoids show low zircon δ18O values, and SIMS in-situ O isotope analysis reveals that the relict zircons with Neoproterozoic and Triassic U-Pb ages also commonly exhibit low δ18O values. Neoproterozoic U-Pb ages and low δ18O values are the two diagnostic features that distinguish the subducted South China Block from the obducted North China Block. Thus, the magma source of these Mesozoic granitoids has a genetic link to the subducted continental crust of the South China Block. On the other hand, these granitoids contain relict zircons with Paleoproterozoic and Archean U-Pb ages, which are present in both the South and North China Blocks. Taken together, the Mesozoic granitoids in the Dabie-Sulu orogenic belt and its hanging wall have their magma sources that are predominated by the continental crust of the South China Block with minor contributions from the continental crust of the North China Block. The Triassic continental collision between the South and North China Blocks brought the continental crust into the thickened orogen, where they underwent the three episodes of partial melting in the Late Triassic, Late

Crustal surface wave velocity structure of the east Albany-Fraser Orogen, Western Australia, from ambient noise recordings

NASA Astrophysics Data System (ADS)

Sippl, C.; Kennett, B. L. N.; Tkalčić, H.; Gessner, K.; Spaggiari, C. V.

2017-09-01

Group and phase velocity maps in the period range 2-20 s for the Proterozoic east Albany-Fraser Orogen, Western Australia, are extracted from ambient seismic noise recorded with the 70-station ALFREX array. This 2 yr temporary installation provided detailed coverage across the orogen and the edge of the Neoarchean Yilgarn Craton, a region where no passive seismic studies of this scale have occurred to date. The surface wave velocities are rather high overall (>3 km s-1 nearly everywhere), as expected for exposed Proterozoic basement rocks. No clear signature of the transition between Yilgarn Craton and Albany-Fraser Orogen is observed, but several strong anomalies corresponding to more local geological features were obtained. A prominent, NE-elongated high-velocity anomaly in the northern part of the array is coincident with a Bouguer gravity high caused by the upper crustal metamorphic rocks of the Fraser Zone. This feature disappears towards longer periods, which hints at an exclusively upper crustal origin for this anomaly. Further east, the limestones of the Cenozoic Eucla Basin are clearly imaged as a pronounced low-velocity zone at short periods, but the prevalence of low velocities to periods of ≥5 s implies that the uppermost basement in this area is likewise slow. At longer periods, slightly above-average surface wave velocities are imaged below the Eucla Basin.

The Moho discontinuity beneath Taiwan orogenic zone inferred from receiver function analysis

NASA Astrophysics Data System (ADS)

Chang, H.; Chen, C.; Liang, W.

2013-12-01

We determine the depth variations of the Moho discontinuity beneath Taiwan from receiver function analysis. Taiwan is a young (~6.5 Ma) orogenic zone as a consequence of oblique collision between the Philippine Sea Plate and the Eurasian Plate. In northeastern Taiwan, the Philippine Sea Plate subducts northwestward under the Eurasian Plate along the Ryukyu Trench; in southern Taiwan, the Eurasian Plate subducts eastward beneath the Philippine Sea Plate along the Manila Trench. Recent tomographic models of Taiwan reveal P-wave velocity variations of the lithospheric structure that provide important constraints on the orogenic processes in this region. However, the depth variations of the Moho discontinuity, a key observation for better understanding crustal deformation, remain elusive. In this study, we aim to delineate the Moho depth variations by analyzing seismic converted phases indicative of the presence of discontinuity structure. We analyze waveform data from teleseismic events recorded at the Broadband Array in Taiwan for Seismology (BATS). Preliminary results of receiver functions beneath BATS stations in eastern Taiwan show that more than one converted phase (P-to-S) are likely present in crustal depths, suggesting possible multiple crustal layering, which may complicate the detection of the Moho. We further carry out synthetic experiments to explore possible crustal structures that reconcile our observations.

Gold Rush!

ERIC Educational Resources Information Center

Brahier, Daniel J.

1997-01-01

Describes a mathematical investigation of gold--how it is weighed, stored, used, and valued. For grades 3-4, children estimate the value of treasure chests filled with gold coins and explore the size and weight of gold bars. Children in grades 5-6 explore how gold is mined and used, and how the value of gold changes over time. (PVD)

Subduction and exhumation of a continental margin in the Scandinavian Caledonides: Insights from ultrahigh pressure metamorphism, late orogenic basins and 3D numerical modelling

NASA Astrophysics Data System (ADS)

Cuthbert, Simon

2017-04-01

The Scandinavian Caledonides (SC) represents a plate collision zone of Himalayan style and scale. Three fundamental characteristics of this orogen are: (1) early foreland-directed, tectonic transport and stacking of nappes; (2) late, wholesale reversal of tectonic transport; (3) ultrahigh pressure metamorphism of felsic crust derived from the underthrusting plate at several levels in the orogenic wedge and below the main thrust surface, indicating subduction of continental crust into the mantle. The significance of this for crustal evolution is the profound remodeling of continental crust, direct geochemical interaction of such crust and the mantle and the opening of accommodation space trapping large volumes of clastic detritus within the orogen. The orogenic wedge of the SC was derived from the upper crust of the Baltica continental margin (a hyper-extended passive margin), plus terranes derived from an assemblage of outboard arcs and intra-oceanic basins and, at the highest structural level, elements of the Laurentian margin. Nappe emplacement was driven by Scandian ( 430Ma) collision of Baltica with Laurentia, but emerging Middle Ordovician ages for diamond-facies metamorphism for the most outboard (or rifted) elements of Baltica suggest prior collision with an arc or microcontinent. Nappes derived from Baltica continental crust were subducted, in some cases to depths sufficient to form diamond. These then detached from the upper part of the down-going plate along major thrust faults, at which time they ceased to descend and possibly rose along the subduction channel. Subduction of the remaining continental margin continued below these nappes, possibly driven by slab-pull of the previously subducted Iapetus oceanic lithosphere and metamorphic densification of subducted felsic continental margin. 3D numerical modelling based upon a Caledonide-like plate scenario shows that if a continental corner or promontory enters the subduction zone, the continental margin

Gold

USGS Publications Warehouse

Kirkemo, Harold; Newman, William L.; Ashley, Roger P.

1998-01-01

Through the ages, men and women have cherished gold, and many have had a compelling desire to amass great quantities of it -- so compelling a desire, in fact, that the frantic need to seek and hoard gold has been aptly named "gold fever." Gold was among the first metals to be mined because it commonly occurs in its native form -- that is, not combined with other elements -- because it is beautiful and imperishable, and because exquisite objects can be made from it.

Gold in minerals and the composition of native gold

USGS Publications Warehouse

Jones, Robert Sprague; Fleischer, Michael

1969-01-01

Gold occurs in nature mainly as the metal and as various alloys. It forms complete series of solid solutions with silver, copper, nickel, palladium, and platinum. In association with the platinum metals, gold occurs as free gold as well as in solid solution. The native elements contain the most gold, followed by the sulfide minerals. Several gold tellurides are known, but no gold selenides have been reported, and only one sulfide, the telluride-sulfide mineral nagyagite, is known. The nonmetallic minerals carry the least gold, and the light-colored minerals generally contain less gold than the dark minerals. Some conclusions in the literature are conflicting in regard to the relation of fineness of native gold to its position laterally and vertically within a lode, the nature of the country rocks, and the location and size of nuggets in a streambed, as well as to the variation of fineness within an individual nugget.

Disclosing the Paleoarchean to Ediacaran history of the São Francisco craton basement: The Porteirinha domain (northern Araçuaí orogen, Brazil)

NASA Astrophysics Data System (ADS)

Silva, Luiz Carlos da; Pedrosa-Soares, Antonio Carlos; Armstrong, Richard; Pinto, Claiton Piva; Magalhães, Joana Tiago Reis; Pinheiro, Marco Aurélio Piacentini; Santos, Gabriella Galliac

2016-07-01

This geochronological and isotopic study focuses on one of the Archean-Paleoproterozoic basement domains of the São Francisco craton reworked in the Araçuaí orogen, the Porteirinha domain, Brazil. It also includes a thorough compilation of the U-Pb geochronological data related to the adjacent Archean and Rhyacian terranes from the São Francisco craton and Araçuaí orogen. The main target of this study is the TTG gneisses of the Porteirinha complex (Sample 1). The gneiss dated at 3371 ± 6 Ma unraveled a polycyclic evolution characterized by two metamorphic overprinting episodes, dated at 3146 ± 24 Ma (M1) and ca. 600 Ma (M2). The former (M1) is so far the most reliable evidence of the oldest metamorphic episode ever dated in Brazil. The latter (M2), in turn, is endemic in most of the exposed eastern cratonic margin within the Araçuaí orogen. Whole-rock Sm-Nd analysis from the gneiss provided a slightly negative εNd(t3370) = - 0.78 value, and a depleted mantle model (TDM) age of 3.5 Ga, indicating derivation mainly from the melting of a ca. 3.5 Ga tholeiitic source. Sample 2, a K-rich leuco-orthogneiss from the Rio Itacambiriçu Complex, was dated at 2657 ± 25 Ma and also presents a ca. 600 Ma M2 overprinting M2 age. The other two analyses were obtained from Rhyacian granitoids. Sample 3 is syn-collisional, peraluminous leucogranite from the Tingui granitic complex, showing a crystallization age of 2140 ± 14 Ma and strong post-crystallization Pb*-loss, also ascribed to the Ediacaran overprinting. Accordingly, it is interpreted as a correlative of the late Rhyacian (ca. 2150-2050 Ma) collisional stage of the Mantiqueira orogenic system/belt (ca. 2220-2000 Ma), overprinted by the Ediacaran collage. Sample 4 is a Rhyacian post-orogenic (post-collisional), mixed-source, peralkaline, A1-type suite, with a crystallization age of 2050 ± 10 Ma, presenting an important post-crystallization Pb*-loss related to Ediacaran collision. The focused region records some

The Yatela gold deposit in Mali, West Africa: The final product of a long-lived history of hydrothermal alteration and weathering

NASA Astrophysics Data System (ADS)

Masurel, Quentin; Miller, John; Hein, Kim A. A.; Hanssen, Eric; Thébaud, Nicolas; Ulrich, Stanislav; Kaisin, Jean; Tessougue, Samuel

2016-01-01

The Yatela gold deposit is located in the Kédougou-Kénieba inlier (KKI), a window of ca. 2200-2050 Ma rocks that are exposed in eastern Senegal and western Mali. The geology of the KKI differs from other Paleoproterozoic granite-greenstone belts and sedimentary basins by the abundance of carbonate rocks. The Yatela deposit occurs within 8 km of the regional-scale Senegal-Mali Shear Zone. Country rocks in the Yatela region have been subjected to polycyclic deformation and regional greenschist-facies metamorphism. A syn-kinematic diorite stock has intruded the metasedimentary sequences in the open pit and is associated with a hornblende-hornfels contact aureole. Field relationships and micro-textural data indicate that the primary gold mineralisation is shear-hosted. The similar relative timing and structural setting between the Yatela primary gold mineralisation and other world-class deposits in the region (e.g., Loulo, Lawrence et al., 2013a; Massawa, Treloar et al., 2014; Sadiola Hill, Masurel et al., in press) suggest that regional orogenic gold mineralisation occurred during a period of transcurrent tectonics, after the cessation of regional compressional deformation. The primary gold mineralisation at Yatela, however, is low-grade and sub-economic. It is hosted by marbles and, to a lesser extent, diorite. The primary ore is pyrite-rich, with abundant chalcopyrite, minor arsenopyrite and accessory Zn-Pb-Sb-Fe-Ag-Co-Ni-bearing mineral species. Post-Birimian surficial dissolution of hydrothermally altered and mineralised host marbles resulted in the creation of troughs, which were draped and infilled with a ferruginous dissolution residue enriched in gold. This auriferous residuum formed the economic resource mined at Yatela until decommissioning in 2013. The Yatela gold deposit is unique with respect to mineralisation types encountered in West Africa because an auriferous residuum of economic interest (>1 Moz) derives from an underlying sub-economic Birimian

Ambient tremors in a collisional orogenic belt

USGS Publications Warehouse

Chuang, Lindsay Yuling; Chen, Kate Huihsuan; Wech, Aaron G.; Byrne, Timothy; Peng, Wei

2014-01-01

Deep-seated tectonic tremors have been regarded as an observation tied to interconnected fluids at depth, which have been well documented in worldwide subduction zones and transform faults but not in a collisional mountain belt. In this study we explore the general features of collisional tremors in Taiwan and discuss the possible generation mechanism. In the 4 year data, we find 231 ambient tremor episodes with durations ranging from 5 to 30 min. In addition to a coseismic slip-induced stress change from nearby major earthquake, increased tremor rate is also highly correlated with the active, normal faulting earthquake swarms at the shallower depth. Both the tremor and earthquake swarm activities are confined in a small, area where the high attenuation, high thermal anomaly, the boundary between high and low resistivity, and localized veins on the surfaces distributed, suggesting the involvement of fluids from metamorphic dehydration within the orogen.

On protolith-, metamorphic overprint, microstructure and rheology of mineral assemblages in orogenic peridotites of the central Scandinavian Caledonides

NASA Astrophysics Data System (ADS)

Gilio, Mattia; Clos, Frediano; Van Roermund, Herman L. M.

2013-04-01

The Scandinavian Caledonides (SC) are a deeply eroded Alpine-type orogenic belt formed by closure of the Iapetus ocean and collision between Baltica and Laurentia (500-380 Ma). The SC consists of a stack of Nappe Complexes (from bottom to top called Lower, Middle, Upper and Uppermost Allochthons) thrusted to the east over the Baltic Shield (Brueckner and Van Roermund, 2004; Gee et al., 2008). Fossil lithospheric mantle fragments, called orogenic peridotites, have been found within the (upper part of) middle, upper and uppermost Allochthons, as well as in the reworked basement gneisses (a.o Western Gneiss Complex (WGC)) along the Norwegian west coast. They occur as isolated lenses that contain diverse mineral parageneses and/or bulk rock compositions. Crustal incorporation of orogenic peridotite is classically interpreted to be the result of plate collisional processes related to orogeny (Brueckner and Medaris, 2000). The WGC and parts of the upper part of the Middle Allochthon (a.o. Seve Nappe Complex (SNC) in N Jämtland/S Västerbotten, central Sweden), are well known for the occurrence of high (HP) and ultrahigh pressure (UHP) metamorphic terranes (of Caledonian age). The (U)HPM evidence clearly demonstrates the deep metamorphic origin of these rocks interpreted to be caused by continental subduction and/or collision. Other metamorphic rocks (of Caledonian age) exposed in allochthonous nappes are solely characterised by greenschist-, amphibolite- and/or MP granulite "facies" mineral assemblages that can be interpreted, in the absence of retrogression, to have formed in less deeply subducted (and/or metamorphic) environments. This duality in metamorphic "facies" allows for a discrimination (at least theoretically) between "deep" versus "shallow" rooted nappes (in central parts of the Scandinavian Caledonides). Conform this reasoning, this duality should also be present within the Caledonian mineral assemblages (= metamorphic overprint) of orogenic peridotites (in

Post-orogenic evolution of mountain ranges and associated foreland basins: Initial investigation of the central Pyrenees

NASA Astrophysics Data System (ADS)

Bernard, Thomas; Sinclair, Hugh; Ford, Mary; Naylor, Mark

2017-04-01

Mountain topography, including surrounding foreland basins, results from the long-term competition between tectonic and surface processes linked to climate. Numerous studies on young active mountain ranges such as the Southern Alps, New Zealand and Taiwan, have investigated the interaction between tectonics, climate and erosion on the topographic landscape. However most of the mountain ranges in the world are in various stages of post-orogenic decay, such as the European Alps, Urals, Caledonides, Appalachians and Pyrenees. The landscape evolution of these decaying mountains, which involve relatively inactive tectonics, should appear simple with progressive and relatively uniform erosion resulting in a general lowering of both elevation and topographic relief. However, in a number of examples, post-orogenic systems suggest a complex dynamism and interactions with their associated foreland basins in term of spatio-temporal variations in erosion and sedimentary flux. The complexity and transition to post-orogenesis is a function of multiple processes. Underpinning the transition to a post-orogenic state is the competition between erosion and crustal thickening; the balance of these processes determines the timing and magnitude of isostatic rebound and hence subsidence versus uplift of the foreland basin. It is expected that any change in the parameters controlling the balance of erosion versus crustal thickening will impact the topographic evolution and sediment flux from the mountain range and foreland basin to the surrounding continental margin. This study will focus on the causes and origins of the processes that define post-orogenesis. This will involve analyses of low-temperature thermochronological and topographic data, geodynamical modelling and sedimentological analyses (grainsize distribution). The Pyrenees and its associated northern retro-foreland basin, the Aquitaine basin, will form the natural laboratory for the project as it is one of the best

Derivatized gold clusters and antibody-gold cluster conjugates

DOEpatents

Hainfeld, James F.; Furuya, Frederic R.

1994-11-01

Antibody- or antibody fragment-gold cluster conjugates are shown wherein the conjugate size can be as small as 5.0 nm. Methods and reagents are disclosed in which antibodies, Fab' or F(ab').sub.2 fragments thereof are covalently bound to a stable cluster of gold atoms. The gold clusters may contain 6, 8, 9, 11, 13, 55 or 67 gold atoms in their inner core. The clusters may also contain radioactive gold. The antibody-cluster conjugates are useful in electron microscopy applications as well as in clinical applications that include imaging, diagnosis and therapy.

Tectonothermal evolution of the Triassic flysch in the Bayan Har Orogen, Tibetan plateau

NASA Astrophysics Data System (ADS)

Wang, Hejing; Rahn, Meinert; Zhou, Jian

2018-01-01

The Bayan Har Orogen comprises a major part of the "Qingzang-Dianxi fold region" in western China. It preserves important information of the tectono-thermal evolution covering the time span from the closure of the Paleo-Tethys Ocean up to the formation of the Himalayas. Low temperature metamorphic indicators, such as mineral assemblages, illite "crystallinity" (IC), chlorite "crystallinity" (CC), illite polytype, b-cell dimension of K-white micas, geothermometry of selected minerals were analyzed. The values of Kübler index (KI) of the Triassic flysch in the Bayan Har Orogen range from 0.23-1.63°Δ2θ while Árkai index (ÁI) in a range of 0.21-0.60°Δ2θ. Iso-thermal zones mapped with KI describe a pair of anchizones and an anchiregion within the Bayan Har Orogen: the "Giant Yushu Anchizone" in the southwest (extending > 750 km long and 100 km wide), the "Zaling-Eling-Lakes Anchizone" in the center (about 150 km long and 40 km wide) and the "Xing-Tong-Zhe Anchiregion" in the northeast (covering an area of roughly 60,000 km2). They are separated by diagenetic zones. Peak metamorphic conditions are estimated around 280-330 °C and a low to intermediate (N. New Hampshire) pressure type. A slight change with increasing then decreasing pressure was observed from SW to NE. The relationship between anchimetamorphic pattern of Triassic flysch and large-scale folds and faults indicates syn- to post structural metamorphism. Compression at the end of the Triassic, induced by the interaction of the Tarim, North China and Indian blocks caused the closure of the Paleo-Tethys Ocean and led to the folding of the Triassic flysch within the Paleo-Tethys Ocean basin. Anchimetamorphism may have been caused by crustal thickening of > 10 km due to an accretionary wedge setting and a temperature increase in those rocks due to burial. Such a regional metamorphic pattern would provide important information for reconstruction of palaeotectonic-palaeogeograph and the evolutionary history

Origin and structure of major orogen-scale exhumed strike-slip

NASA Astrophysics Data System (ADS)

Cao, Shuyun; Neubauer, Franz

2016-04-01

The formation of major exhumed strike-slip faults represents one of the most important dynamic processes affecting the evolution of the Earth's lithosphere and surface. Detailed models of the potential initiation and properties and architecture of orogen-scale exhumed strike-slip faults and how these relate to exhumation are rare. In this study, we deal with key properties controlling the development of major exhumed strike-slip fault systems, which are equivalent to the deep crustal sections of active across fault zones. We also propose two dominant processes for the initiation of orogen-scale exhumed strike-slip faults: (1) pluton-controlled and (2) metamorphic core complex-controlled strike-slip faults. In these tectonic settings, the initiation of faults occurs by rheological weakening along hot-to-cool contacts and guides the overall displacement and ultimate exhumation. These processes result in a specific thermal and structural architecture of such faults. These types of strike-slip dominated fault zones are often subparallel to mountain ranges and expose a wide variety of mylonitic, cataclastic and non-cohesive fault rocks, which were formed at different structural levels of the crust during various stages of faulting. The high variety of distinctive fault rocks is a potential evidence for recognition of these types of strike-slip faults. Exhumation of mylonitic rocks is, therefore, a common feature of such reverse oblique-slip strike-slip faults, implying major transtensive and/or transpressive processes accompanying pure strike-slip motion during exhumation. Some orogen-scale strike-slip faults nucleate and initiate along rheologically weak zones, e.g. at granite intrusions, zones of low-strength minerals, thermally weakened crust due to ascending fluids, and lateral borders of hot metamorphic core complexes. A further mechanism is the juxtaposition of mechanically strong mantle lithosphere to hot asthenosphere in continental transform faults (e.g., San

Age and provenance constraints on seismically-determined crustal layers beneath the Paleozoic southern Central Asian Orogen, Inner Mongolia, China

NASA Astrophysics Data System (ADS)

Jian, Ping; Kröner, Alfred; Shi, Yuruo; Zhang, Wei; Liu, Yaran; Windley, Brian F.; Jahn, Bor-ming; Zhang, Liqao; Liu, Dunyi

2016-06-01

We present 110 ages and 51 in-situ δ18O values for zircon xenocrysts from a post-99 Ma intraplate basaltic rock suite hosted in a subduction-accretion complex of the southern Central Asian Orogenic Belt in order to constrain a seismic profile across the Paleozoic Southern Orogen of Inner Mongolia and the northern margin of the North China Craton. Two zircon populations are recognized, namely a Phanerozoic group of 70 zircons comprising granitoid-derived (ca. 431-99 Ma; n = 31; peak at 256 Ma), meta-granitoid-derived (ca. 449-113 Ma; n = 24; peak at 251 Ma) and gabbro-derived (436-242 Ma; n = 15; peaks at 264 and 244 Ma) grains. Each textural type is characterized by a distinct zircon oxygen isotope composition and is thus endowed with a genetic connotation. The Precambrian population (2605-741 Ma; n = 40) exhibits a prominent age peak at 2520 Ma (granulite-facies metamorphism) and four small peaks at ca. 1900, 1600, and 800 Ma. Our new data, together with literature zircon ages, significantly constrain models of three seismically-determined deep crustal layers beneath the fossil subduction zone-forearc along the active northern margin of the North China Craton, namely: (1) an upper arc crust of early to mid-Paleozoic age, intruded by a major Permian-Triassic composite granitoid-gabbroic pluton (8-20 km depth); (2) a middle crust, predominantly consisting of mid-Meso- to Neoproterozoic felsic and mafic gneisses; and (3) a lower crust composed predominantly of late Archean granulite-facies rocks. We conclude that the Paleozoic orogenic crust is limited to the upper crustal level, and the middle to lower crust has a North China Craton affinity. Furthermore, integrating our data with surface geological, petrological and geochronological constraints, we present a new conceptual model of orogenic uplift, lithospheric delamination and crustal underthrusting for this key ocean-continent convergent margin.

Late Cenozoic Climate Change and its Implications on the Denudation of Orogen Syntaxes

NASA Astrophysics Data System (ADS)

Mutz, Sebastian; Ehlers, Todd

2017-04-01

The denudation history of active orogens is often interpreted in the context of modern climate gradients. Despite the influence of climatic conditions on erosion rates, information about paleoclimate evolution is often not available and thus not considered when denudation histories are interpreted. In this study, we analyze output from paleoclimate simulations conducted with ECHAM5-wiso at T159 (ca. 80x80km) resolution. Specifically, we analyze simulations of pre-industrial (PI, pre-1850), Mid-Holocene (MH, ca. 6ka), Last Glacial Maximum (LGM, ca. 21ka) and Pliocene (PLIO, ca. 3ka) climates and focus on a selection of orogen syntaxes as study regions (e.g. Himalaya, SE Alaska, Cascadia, and Central Andes). For the selected region, we carry out a cluster analysis using a hybrid of hierarchical and k-means clustering procedures using mean annual temperature (MAT), temperature amplitude, mean annual precipitation (MAP), precipitation amplitude and u-wind and v-wind in different months to provide a general overview of paleoclimates in the study regions. Additionally, we quantify differences between paleoclimates by applying two-group linear discrimination analyses to the simulation output for a similar selection of variables. Results indicate the largest differences to the PI climate are observed for the LGM and PLIO climates in the form of widespread cooling and reduced precipitation in the LGM and warming and enhanced precipitation during the PLIO. These global trends can be observed for most locations in the investigated areas, but the strength varies regionally and the trends in precipitation are less uniform than trends in temperatures. The LGM climate shows the largest deviation in annual precipitation from the PI climate, and shows enhanced precipitation in the temperate Andes, and coastal regions for both SE Alaska and the US Pacific Northwest Pacific. Furthermore, LGM precipitation is reduced in the western Himalayas and enhanced in the eastern Himalayas

Lawsonite Blueschists in Recycled Mélange Involved in K-Rich Orogenic Magmatism

NASA Astrophysics Data System (ADS)

Wang, Y.; Prelevic, D.; Foley, S. F.; Buhre, S.; Galer, S. J. G.

2014-12-01

The origin of K-rich orogenic magmatism in the Alpine-Himalayan belt and its relationship to the large-scale elevations in several massifs of the orogen is controversial, particularly the significance of the widespread presence of a geochemical signal typical for recycled continental crust. Two competing scenarios invoke direct melting of continental crust during deep intercontinental subduction and removal of heavily metasomatised mantle lithosphere by delamination into the convecting mantle. Here we investigate the coupling of high Th/La ratio with crustal isotopic signatures in K-rich orogenic lavas that does not occur in volcanic rocks from other collisional environments to distinguish between these two models. High-pressure experimental results on a phyllite representing upper crustal composition and a detailed mineral and geochemical study of blueschists from Tavşanlı mélange, Turkey, indicate that this geochemical fingerprint originates by melting of subducted mélange. Melting of crust at the top of the subducted continental lithosphere cannot produce observed fingerprint, whereas lawsonites, especially those with terrigenous sediment origin from blueschists with high Th/La can. Lawsonites that grow in various components of a subduction mélange inherit the geochemical characteristics of either oceanic or continental protoliths. It is currently uncertain whether those carrying the high Th/La signature originate by direct melting of continental blocks in the mélange or by the introduction of supercritical fluids from lawsonite blueschist of continental origin that infiltrate oceanic sediment blocks. Either way, the high Th/La is later released into subsequently formed melts. This confirms the supposition that lawsonite is the main progenitor of the high Th/La and Sm/La ratio. However, lawsonite must break down completely to impart this unique feature to subsequent magmas. The source regions of the potassic volcanic rocks consist of blueschist facies m

Simultaneous miocene extension and shortening in the himalayan orogen.

PubMed

Hodges, K V; Parrish, R R; Housh, T B; Lux, D R; Burchfiel, B C; Royden, L H; Chen, Z

1992-11-27

The South Tibetan detachment system separates the high-grade metamorphic core of the Himalayan orogen from its weakly metamorphosed suprastructure. It is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front. Geochronologic data from the Rongbuk Valley, north of Qomolangma (Mount Everest) in southern Tibet, demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago, an interval characterized by large-scale crustal thickening at lower structural levels. These data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of Himalayan tectonics in Miocene time.

Derivatized gold clusters and antibody-gold cluster conjugates

DOEpatents

Hainfeld, J.F.; Furuya, F.R.

1994-11-01

Antibody- or antibody fragment-gold cluster conjugates are shown wherein the conjugate size can be as small as 5.0 nm. Methods and reagents are disclosed in which antibodies, Fab' or F(ab')[sub 2] fragments are covalently bound to a stable cluster of gold atoms. The gold clusters may contain 6, 8, 9, 11, 13, 55 or 67 gold atoms in their inner core. The clusters may also contain radioactive gold. The antibody-cluster conjugates are useful in electron microscopy applications as well as in clinical applications that include imaging, diagnosis and therapy. 7 figs.

Not All That Glitters is Gold: Gold Imitations in History.

PubMed

Karpenko, Vladimír

2007-07-01

When gold became considered as a precious metal for decorative purposes and later for coinage, attempts at producing imitations soon began to appear. There were two motives behind this activity: to make a metal that could pass as gold, and to quite openly imitate this precious metal for people who could not afford true gold. Imitation gold was produced by metallurgists, and later also by alchemists. This paper is about gold imitations that did not contain any precious metal. Gold-like alloys of silver are thus excluded. An attempt is further undertaken to classify into separate groups the various gold imitations that have appeared in different cultures throughout time, with an emphasis on brass as a typical imitation of gold.

Phage based green chemistry for gold ion reduction and gold retrieval.

PubMed

Setyawati, Magdiel I; Xie, Jianping; Leong, David T

2014-01-22

The gold mining industry has taken its toll on the environment, triggering the development of more environmentally benign processes to alleviate the waste load release. Here, we demonstrate the use of bacteriophages (phages) for biosorption and bioreduction of gold ions from aqueous solution, which potentially can be applied to remediate gold ions from gold mining waste effluent. Phage has shown a remarkably efficient sorption of gold ions with a maximum gold adsorption capacity of 571 mg gold/g dry weight phage. The product of this phage mediated process is gold nanocrystals with the size of 30-630 nm. Biosorption and bioreduction processes are mediated by the ionic and covalent interaction between gold ions and the reducing groups on the phage protein coat. The strategy offers a simple, ecofriendly and feasible option to recover of gold ions to form readily recoverable products of gold nanoparticles within 24 h.

31 CFR 100.4 - Gold coin and gold certificates in general.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 31 Money and Finance: Treasury 1 2011-07-01 2011-07-01 false Gold coin and gold certificates in... MONETARY OFFICES, DEPARTMENT OF THE TREASURY EXCHANGE OF PAPER CURRENCY AND COIN In General § 100.4 Gold coin and gold certificates in general. Gold coins, and gold certificates of the type issued before...

31 CFR 100.4 - Gold coin and gold certificates in general.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 31 Money and Finance: Treasury 1 2013-07-01 2013-07-01 false Gold coin and gold certificates in... MONETARY OFFICES, DEPARTMENT OF THE TREASURY EXCHANGE OF PAPER CURRENCY AND COIN In General § 100.4 Gold coin and gold certificates in general. Gold coins, and gold certificates of the type issued before...

31 CFR 100.4 - Gold coin and gold certificates in general.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 31 Money and Finance: Treasury 1 2012-07-01 2012-07-01 false Gold coin and gold certificates in... MONETARY OFFICES, DEPARTMENT OF THE TREASURY EXCHANGE OF PAPER CURRENCY AND COIN In General § 100.4 Gold coin and gold certificates in general. Gold coins, and gold certificates of the type issued before...

31 CFR 100.4 - Gold coin and gold certificates in general.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 31 Money and Finance: Treasury 1 2014-07-01 2014-07-01 false Gold coin and gold certificates in... MONETARY OFFICES, DEPARTMENT OF THE TREASURY EXCHANGE OF PAPER CURRENCY AND COIN In General § 100.4 Gold coin and gold certificates in general. Gold coins, and gold certificates of the type issued before...

Role of Neogene Exhumation and Sedimentation on Critical-Wedge Kinematics in the Zagros Orogenic Belt, Northeastern Iraq, Kurdistan

NASA Astrophysics Data System (ADS)

Koshnaw, R. I.; Horton, B. K.; Stockli, D. F.; Barber, D. E.; Tamar-Agha, M. Y.; Kendall, J. J.

2014-12-01

The Zagros orogenic belt and foreland basin formed during the Cenozoic Arabia-Eurasia collision, but the precise histories of shortening and sediment accumulation remain ambiguous, especially at the NW extent of the fold-thrust belt in Iraqi Kurdistan. This region is characterized by well-preserved successions of Cenozoic clastic foreland-basin fill and deformed Paleozoic-Mesozoic hinterland bedrock. The study area provides an excellent opportunity to investigate the linkage between orogenic wedge behavior and surface processes of erosion and deposition. The aim of this research is to test whether the Zagros orogenic wedge advanced steadily under critical to supercritical wedge conditions involving in-sequence thrusting with minimal erosion or propagated intermittently under subcritical condition involving out-of-sequence deformation with intense erosion. These endmember modes of mountain building can be assessed by integrating geo/thermochronologic and basin analyses techniques, including apatite (U-Th)/He thermochronology, detrital zircon U-Pb geochronology, stratigraphic synthesis, and seismic interpretations. Preliminary apatite (U-Th)/He data indicate activation of the Main Zagros Fault (MZF) at ~10 Ma with frontal thrusts initiating at ~8 Ma. However, thermochronometric results from the intervening Mountain Front Flexure (MFF), located between the MZF and the frontal thrusts, suggest rapid exhumation at ~6 Ma. These results suggest that the MFF, represented by the thrust-cored Qaradagh anticline, represents a major episode of out-of-sequence deformation. Detrital zircon U-Pb analyses from the Neogene foreland-basin deposits show continuous sediment derivation from sources to the NNE in Iraq and western Iran, suggesting that out-of-sequence thrusting did not significantly alter sedimentary provenance. Rather, intense hinterland erosion and recycling of older foreland-basin fill dominated sediment delivery to the basin. The irregular distribution of

Orogenic, Ophiolitic, and Abyssal Peridotites

NASA Astrophysics Data System (ADS)

Bodinier, J.-L.; Godard, M.

2003-12-01

"Tectonically emplaced" mantle rocks include subcontinental, suboceanic, and subarc mantle rocks that were tectonically exhumed from the upper mantle and occur:(i) as dispersed ultramafic bodies, a few meters to kilometers in size, in suture zones and mountain belts (i.e., the "alpine," or "orogenic" peridotite massifs - De Roever (1957), Thayer (1960), Den Tex (1969));(ii) as the lower ultramafic section of large (tens of kilometers) ophiolite or island arc complexes, obducted on continental margins (e.g., the Oman Ophiolite and the Kohistan Arc Complex - Coleman (1971), Boudier and Coleman (1981), Burg et al. (1998));(iii) exhumed above the sea level in ocean basins (e.g., Zabargad Island in the Red Sea, St. Paul's islets in the Atlantic and Macquarie Island in the southwestern Pacific - Tilley (1947), Melson et al. (1967), Varne and Rubenach (1972), Bonatti et al. (1981)).The "abyssal peridotites" are samples from the oceanic mantle that were dredged on the ocean floor, or recovered from drill cores (e.g., Bonatti et al., 1974; Prinz et al., 1976; Hamlyn and Bonatti, 1980).Altogether, tectonically emplaced and abyssal mantle rocks provide insights into upper mantle compositions and processes that are complementary to the information conveyed by mantle xenoliths (See Chapter 2.05). They provide coverage to vast regions of the Earth's upper mantle that are sparsely sampled by mantle xenoliths, particularly in the ocean basins and beneath passive continental margins, back-arc basins, and oceanic island arcs.Compared with mantle xenoliths, a disadvantage of some tectonically emplaced mantle rocks for representing mantle compositions is that their original geodynamic setting is not exactly known and their significance is sometimes a subject of speculation. For instance, the provenance of orogenic lherzolite massifs (subcontinental lithosphere versus upwelling asthenosphere) is still debated (Menzies and Dupuy, 1991, and references herein), as is the original setting

31 CFR 100.4 - Gold coin and gold certificates in general.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 31 Money and Finance: Treasury 1 2010-07-01 2010-07-01 false Gold coin and gold certificates in... EXCHANGE OF PAPER CURRENCY AND COIN In General § 100.4 Gold coin and gold certificates in general. Gold coins, and gold certificates of the type issued before January 30, 1934, are exchangeable, as provided...

Geology of the Byrd Glacier Discontinuity (Ross Orogen): New survey data from the Britannia Range, Antarctica

USGS Publications Warehouse

Carosi, R.; Giacomini, F.; Talarico, F.; Stump, E.

2007-01-01

Field activities in the Britannia Range (Transantarctic Mountains, Antarctica) highlighted new geological features around the so-called Byrd Glacier discontinuity. Recent field surveys revealed the occurrence of significant amounts of medium- to high-grade metamorphic rocks, intruded by abundant coarse-grained porphyritic granitoids. Most of the granitoids are deformed, with foliation parallel to the regional foliation in the metamorphics. Two main episodes of deformation are observed. Tight to isoclinal folds and penetrative axial plane foliation are related to the D1 phase, open folds to the D2. The main foliation (D1) trends nearly E-W in agreement with the trend in the southern portion of the Byrd Glacier. In most outcrops, granitic dykes are folded and stretched by the D2 deformation, which shows similar characteristics with the D2 deformation south of the Byrd Glacier. This suggests the occurrence in the Ross orogen of an orogen-normal structure south and north of the Byrd Glacier.

Gold and gold working in Late Bronze Age Northern Greece.

PubMed

Vavelidis, M; Andreou, S

2008-04-01

Numerous objects of gold displaying an impressive variety of types and manufacturing techniques are known from the Late Bronze Age (LBA) contexts of Mycenaean Greece, but very little is known about the origin and processing of gold during the second millennium B.C: . Ancient literature and recent research indicate that northern Greece is probably the richest gold-bearing region in Greece, and yet, very little evidence exists regarding the exploitation of its deposits and the production as well as use of gold in the area during prehistory. The unusual find of a group of small stone crucibles at the prehistoric settlement of Thessaloniki Toumba, one with visible traces of gold melting, proves local production and offers a rare opportunity to examine the process of on-site gold working. Furthermore, the comparison of the chemical composition of prehistoric artefacts from two settlements with those of gold deposits in their immediate areas supports the local extraction of gold and opens up the prospect for some of the Mycenaean gold to have originated in northern Greece. The scarcity of gold items in northern Greek LBA contexts may not represent the actual amount of gold produced and consumed, but could be a result of the local social attitudes towards the circulation and deposition of artefacts from precious metals.

Gold and gold working in Late Bronze Age Northern Greece

NASA Astrophysics Data System (ADS)

Vavelidis, M.; Andreou, S.

2008-04-01

Numerous objects of gold displaying an impressive variety of types and manufacturing techniques are known from the Late Bronze Age (LBA) contexts of Mycenaean Greece, but very little is known about the origin and processing of gold during the second millennium b.c. Ancient literature and recent research indicate that northern Greece is probably the richest gold-bearing region in Greece, and yet, very little evidence exists regarding the exploitation of its deposits and the production as well as use of gold in the area during prehistory. The unusual find of a group of small stone crucibles at the prehistoric settlement of Thessaloniki Toumba, one with visible traces of gold melting, proves local production and offers a rare opportunity to examine the process of on-site gold working. Furthermore, the comparison of the chemical composition of prehistoric artefacts from two settlements with those of gold deposits in their immediate areas supports the local extraction of gold and opens up the prospect for some of the Mycenaean gold to have originated in northern Greece. The scarcity of gold items in northern Greek LBA contexts may not represent the actual amount of gold produced and consumed, but could be a result of the local social attitudes towards the circulation and deposition of artefacts from precious metals.

Crustal structure of the alaska range orogen and denali fault along the richardson highway

USGS Publications Warehouse

Fisher, M.A.; Pellerin, L.; Nokleberg, W.J.; Ratchkovski, N.A.; Glen, J.M.G.

2007-01-01

A suite of geophysical data obtained along the Richardson Highway crosses the eastern Alaska Range and Denali fault and reveals the crustal structure of the orogen. Strong seismic reflections from within the orogen north of the Denali fault dip as steeply as 25?? north and extend downward to depths between 20 and 25 km. These reflections reveal what is probably a shear zone that transects most of the crust and is part of a crustal-scale duplex structure that probably formed during the Late Cretaceous. These structures, however, appear to be relict because over the past 20 years, they have produced little or no seismicity despite the nearby Mw = 7.9 Denali fault earthquake that struck in 2002. The Denali fault is nonreflective, but we interpret modeled magnetotelluric (MT), gravity, and magnetic data to propose that the fault dips steeply to vertically. Modeling of MT data shows that aftershocks of the 2002 Denali fault earthquake occurred above a rock body that has low electrical resistivity (>10 ohm-m), which might signify the presence of fluids in the middle and lower crust. Copyright ?? 2007 The Geological Society of America.

The Tyrrhenian stage geodinamic evolution of Apenninic-Maghrebian orogen (Southern Apennines and Sicily)

NASA Astrophysics Data System (ADS)

Lentini, F.; Carbone, S.; Barreca, G.

2009-04-01

In the Central Mediterranean region the foreland domains are represented by two continental blocks, the Apulian Block to the north and the Pelagian Block to the south, respectively belonging to the Adria and to the Africa plates. They are separated since Permo-Triassic times by the oceanic crust of the Ionian Sea. The Apenninic-Maghrebian orogen is located between two oceanic crusts: the old Ionian crust, at present time subducting beneath the Calabrian Arc, and the new crust of the opening Tyrrhenian Sea. The orogenic belt is represented by a multilayer allochthonous edifice, composed of the Calabride Chain (CC) tectonically overlying the Apenninic-Maghrebian Chain (AMC), which in turn overthrust onto the Upper Miocene and Pliocene top-levels of a deep seated thrust system, originating by the deformation of the innermost carbonates of the Pelagian/Apulian blocks (External Thrust System: ETS). The AMC tectonic units derive from the orogenic transport during Oligo-Miocene times of sedimentary sequences deposited in palaeogeographical domains located between the Europe and the Afro-Adriatic plates. These units are composed of Meso-Cenozoic shallow-water carbonate successions detached from a continental type crust sector, the Panormide/Apenninic Block, recognizable by means of seismic lines shot in the Tyrrhenian offshore of Southern Apennines and Northern Sicily. The Meso-Cenozoic basinal units, that compose the AMC, can be distinguished into two main groups of sequences, originally located on oceanic crusts separated by the Panormide/Apenninic Block: the external ones (Ionides) related to an original basin belonging to branches of the Ionian Palaeobasin involved in the orogenesis, and the internal ones ascribed to the Alpine Tethys (Sicilide Units). The terrigenous deposits of the basinal sequences belonging to the Ionides are represented by Tertiary foreland/foredeep deposits, whose relationships with the substratum are occasionally preserved, although large

Kinematics of post-orogenic extension and exhumation of the Taku Schist, NE Peninsular Malaysia

NASA Astrophysics Data System (ADS)

Md Ali, M. A.; Willingshofer, E.; Matenco, L.; Francois, T.; Daanen, T. P.; Ng, T. F.; Taib, N. I.; Shuib, M. K.

2016-09-01

Recent studies imply that the formation and evolution of many SE Asian basins was driven by extensional detachments or systems of low-angle normal faults that created significant crustal exhumation in their footwalls. In this context, the architecture of the Triassic Indosinian orogen presently exposed in Peninsular Malaysia is compatible with significant extension post-dating the orogenic event. In this study we performed a kinematic analysis based on fieldwork and microstructural observations in the Taku Schist, Kemahang granite and the surrounding Gua Musang sediments of northern Peninsular Malaysia in order to shed light on processes related to the build-up and subsequent demise of the Indosinian orogen. The first three phases of deformation were related to an overall period of E-W oriented contraction and burial metamorphism. These phases of deformation are characterized by isoclinal folding with flat lying axial plane cleavages (D1), asymmetrical folding, top-to-the-W-SW shearing (D2) and upright folding (D3). All are in general agreement with observations of the previously inferred Permo-Triassic Indosinian orogeny. During these times, the Taku Schist, a sequence of Paleozoic clastic sediments with mafic intercalations was metamorphosed to amphibolite facies. These rocks are most likely equivalent to the ones exposed in the Bentong-Raub suture zone. Structural relations suggest that the Triassic Kemahang pluton is syn-kinematic, which provides important constraints for the timing of these contractional events. We demonstrate that the overall shortening was followed by a hitherto undescribed extension in NW-SE direction resulting in the formation of a large-scale detachment, the Taku detachment, in northern Peninsular Malaysia. Extension probably reactivated the former subduction plane as a detachment and exhumed previously buried and metamorphosed rocks of similar lithological composition to the neighboring Bentong-Raub suture zone. Such a mechanism is

Isolating active orogenic wedge deformation in the southern Subandes of Bolivia

NASA Astrophysics Data System (ADS)

Weiss, Jonathan R.; Brooks, Benjamin A.; Foster, James H.; Bevis, Michael; Echalar, Arturo; Caccamise, Dana; Heck, Jacob; Kendrick, Eric; Ahlgren, Kevin; Raleigh, David; Smalley, Robert; Vergani, Gustavo

2016-08-01

A new GPS-derived surface velocity field for the central Andean backarc permits an assessment of orogenic wedge deformation across the southern Subandes of Bolivia, where recent studies suggest that great earthquakes (>Mw 8) are possible. We find that the backarc is not isolated from the main plate boundary seismic cycle. Rather, signals from subduction zone earthquakes contaminate the velocity field at distances greater than 800 km from the Chile trench. Two new wedge-crossing velocity profiles, corrected for seasonal and earthquake affects, reveal distinct regions that reflect (1) locking of the main plate boundary across the high Andes, (2) the location of and loading rate at the back of orogenic wedge, and (3) an east flank velocity gradient indicative of décollement locking beneath the Subandes. Modeling of the Subandean portions of the profiles indicates along-strike variations in the décollement locked width (WL) and wedge loading rate; the northern wedge décollement has a WL of ~100 km while accumulating slip at a rate of ~14 mm/yr, whereas the southern wedge has a WL of ~61 km and a slip rate of ~7 mm/yr. When compared to Quaternary estimates of geologic shortening and evidence for Holocene internal wedge deformation, the new GPS-derived wedge loading rates may indicate that the southern wedge is experiencing a phase of thickening via reactivation of preexisting internal structures. In contrast, we suspect that the northern wedge is undergoing an accretion or widening phase primarily via slip on relatively young thrust-front faults.

Collisional Tectonics of the Saint Elias Orogen, Alaska, Observed by GPS

NASA Astrophysics Data System (ADS)

Elliott, J. L.; Freymueller, J. T.; Larsen, C. F.

2005-12-01

The Saint Elias orogen of south central Alaska and the adjacent area of Canada is the highest coastal mountain range on earth, with peaks that exceed 6000 meters in elevation. It is located in the complex transition zone between transform motion along the Queen Charlotte-Fairweather fault system and subduction along the Aleutian Megathrust. The Yakutat terrane lies in the gap between the end of the Megathrust and the end of the transform system. Roughly 4 cm/yr of convergence is accommodated within the continental crust, onshore and possibly offshore, as the Yakutat terrane collides with southern Alaska. This collision provides the driving force behind the stunning topographic relief of the orogen. As part of the STEEP project designed to unravel the tectonic complexities of this region, we made GPS measurements at 47 sites in south central Alaska during the summer of 2005. Here we present results from 13 campaign GPS sites that had prior measurements. The span of measurements at these campaign sites range from one to twelve years. All of the sites show northwestward motion and uplift. The highest amounts of uplift occur at several coastal sites near Icy Bay where average rates surpass 24 mm/yr. Further north, sites along the Bagley Icefield display an average uplift rate of about 20 mm/yr. A significant portion of this uplift is caused by the melting of regional icefields and the redistribution of mass in large glacier systems such as the Bering Glacier. We also examine the impact of the Denali Fault earthquake on the rates of motion in this area.

Magnitude of crustal shortening and structural framework of the easternmost Himalayan orogen, northern Indo-Burma Ranges of northeastern India

NASA Astrophysics Data System (ADS)

Haproff, P. J.; Yin, A.

2016-12-01

Along-strike variation in crustal shortening throughout the Himalayan orogen has been attributed to (1) diachronous, eastward-increasing convergence, or (2) localized controls including pre-collisional stratigraphic configuration and climate. In this study, we present new geologic maps and balanced cross-sections across the easternmost segment of the Himalayan orogen, the N-S-trending N. Indo-Burma Ranges of northeastern India. First order structures are NE-dipping, km-wide ductile thrust shear zones with mylonitic fabrics indicating top-to-the SW motion. Major structures include the Mayodia klippe and Hunli window, generated during folding of the SW-directed Tidding thrust and duplexing of Lesser Himalayan rocks (LHS) at depth. Reconstruction of two balanced cross-sections yields minimum shortening estimates of 70% (48 km) and 71% (133 km), respectively. The widths of the orogen for each transect are 21 km and 54 km, respectively. Our percent strain values are comparable to that of western Arunachal Himalaya, reflecting eastward-increasing strain due to counterclockwise rotation of India during convergence or along-strike variation in India's subduction angle. However, shortening magnitudes much less than that of the Sikkim (641 km), Bhutan (414-615 km), and western Arunachal Himalaya (515-775 km) could signal eastward increasing shortening of a unique Himalayan stratigraphic framework, evidenced by few GHC rocks, absence of Tethyan strata, and an extensive subduction mélange and forearc complex.

Geology and geochemistry of Carlin-type gold deposits in China

USGS Publications Warehouse

Rui-Zhong, H.; Wen-Chao, S.; Xian-Wu, B.; Guang-Zhi, T.; Hofstra, A.H.

2002-01-01

mineral assemblages, residence of gold, geochemical signatures, paragenetic sequence, and fluid inclusions are remarkably similar, which indicates that the deposits formed from low salinity, moderately acidic, CO2 and H2S-rich in the crust similar processes at relatively shallow levels in the crust (<5 km). However, the deposits in China are associated with large Hg, Sb, As, U, and Tl deposits, which may reflect higher background abundances of these elements. Stable isotopic data suggest meteoric water evolved to become ore fluids through interactions with sedimentary rocks, although contributions of volatiles or metals from deeper levels are present in some deposits in Nevada. In both countries, the deposits appear to have formed in an area of high paleothermal gradients after a change in stress regime during the later phases of orogenic activity.

LOCALIZATION OF GOLD IN MOUSE BRAIN IN RELATION TO GOLD THIOGLUCOSE OBESITY

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

Debons, A.F.; Silver, L.; Cronkite, E.P.

1962-04-01

Administration of gold thioglucose led to the development of hyperphagia and obesity in mice; this confirmed findings by previous investigators. By employing neutron activation analysis and radioautography, it was observed that this syndrome was associated with focal accumulation of gold in the hypothalamus. Animals treated with gold thiomalate failed to show any hypothalamic Iocalization of gold radioautographically or any evidence of the syndrome of hyperphagla and obesity. In additlon, other foci of gold locallzation were found in gold thioglucose-treated but not in the gold thiomalate-treated animals. Gamma spectroscopy studies made possible quantitative measurements of the gold content ln the brainsmore » of both treated groups. Gold thioglucose-treated as well as gold thiomalate-treated animals had appreciable quantities of gold in the brain proper. Phosphorus-32 generated by neutron activation of the sulfur moiety of gold thioglucose proved to be insigniflcant in its contribution to the radioautographic flndings. Implication of the above findings for the glucostatic theory of appetite regulation is discussed. (auth)« less

Evaluation of the Orogenic Belt Hypothesis for the Formation of Thaumasia, Mars

NASA Astrophysics Data System (ADS)

Nahm, A. L.; Schultz, R. A.

2008-12-01

The Thaumasia Highlands (TH) and Solis Planum are two of the best-known examples of compressional tectonics on Mars. The TH is a region of high topography located in the southern portion of the Tharsis Province, Mars. Solis Planum is located in eastern Thaumasia. Two hypotheses for the formation of this region have been suggested: sliding on a weak horizon or thrusting analogous to orogenic wedges on Earth. Both hypotheses require a shallowly dipping to sub-horizontal weak horizon below Thaumasia. Wrinkle ridges in Solis Planum are also inferred to sole into a décollement. If Thaumasia formed by thrusting related to sliding on a décollement, then certain conditions must be met as in critical taper wedge mechanics (CTWM) theory. If the angle between the surface slope and the basal décollement is less than predicted by the critical taper equation, the 'subcritical' wedge will deform internally until critical taper is achieved. Once the critical taper has been achieved, internal deformation ceases and the wedge will slide along its base. Formation of orogenic belts on Earth (such as the Central Mountains in Taiwan) can be described using CTWM. This method is applied here to the Thaumasia region on Mars. The surface slope (alpha) was measured in three locations: Syria Planum-Thaumasia margin, Solis Planum, and the TH. Topographic slopes were compared to the results from the critical taper equation. Because the dip of the basal décollement (beta) cannot be measured directly as on Earth, the dip angle was varied at 0 - 10 degrees; these values span the range of likely values based on terrestrial wedges. Pore fluid pressure (lambda) was varied between 0 (dry) and 0.9 (overpressured); these values span the full range of this important unknown parameter. Material properties, such as the coefficients of internal friction and of the basal décollement, were varied using reasonable values. Preliminary results show that for both reasonable (such as lambda = 0, mu b = 0

The late cretaceous Donlin Creek gold deposit, Southwestern Alaska: Controls on epizonal ore formation

USGS Publications Warehouse

Goldfarb, R.J.; Ayuso, R.; Miller, M.L.; Ebert, S.W.; Marsh, E.E.; Petsel, S.A.; Miller, L.D.; Bradley, D.; Johnson, Chad; McClelland, W.

2004-01-01

-10 per mil, with the sulfur derived from diagenetic pyrite and organic matter within ihe flysch basin. A smaller group of ??34S measurements, which shows values as depleted as -27 per mil, suggests a different local sulfur reservoir in the basin for the later hydrothermal episode dominated by stibnite. Initial ENd of -8.7 to -3.1 and 87Sr/86Sr measurements of 0.706 to 0.709 for the ore-hosting dikes also indicate a crustal reservoir for some of the Late Cretaceous magmatism. Overlapping lead isotope data for these intrusive rocks and for sulfide minerals suggest a crustal contribution for the lead in both. Copper- and gold-bearing stockwork veinlets in hornfels occur at Dome, a prospect located at the northern end of the Donlin Creek deposit. These stockworks are cut by the younger auriferous gold veins that define the main Donlin Creek gold mineralization. Highly saline, gas-rich, heterogeneously trapped fluids deposited the stockworks at temperatures approximately 100??C hotter than those of the main gold-forming event at Donlin Creek. The genetic relationship of the Dome prospect to the main Donlin Creek gold resource is equivocal. The epizonal Donlin Creek deposit shows affinities to the gold systems interpreted by various workers as orogenic or intrusion related; it shows important differences from typical epithermal and Carlin-like deposits. The ore-forming fluids were derived by either broad-scale metamorphic devolatilization above rising mantle melts or exsolution from a magma that was dominated by a significant flysch melt component. ??2004 by Economic Geology.

The shear zone-related gold mineralization at the Turmalina deposit, Quadrilátero Ferrífero, Brazil: structural evolution and the two stages of mineralization

NASA Astrophysics Data System (ADS)

Fabricio-Silva, Wendell; Rosière, Carlos Alberto; Bühn, Bernhard

2018-05-01

Turmalina is an important orogenic gold deposit located in the NW region of the Quadrilátero Ferrífero. The deposit is hosted in an Archean greenstone belt composed of ortho-amphibolites and pelites with interleaved tuffs metamorphosed under amphibolite facies conditions and intruded by a granite stock. The orebodies are controlled by WNW-ESE-trending shear zones, associated with hydrothermal alteration. Three deformation events are recognized in the Turmalina gold deposit: D1 and D2 are the result of a progressive Archean deformation under ductile conditions between 2749 ± 7 and 2664 ± 35 Ma; D3 is characterized by a transpressional event under ductile-brittle conditions with the age still unclear. The three generations of garnet observed show that Grt1 blastesis is pre- to syn-D1 and Grt2 growth during the late to post-deformation stages of the D2 event. The initial temperature (Grt1 core) is around 548-600 °C, whereas during late D2, the temperatures reached 633 °C (metamorphic peak-Grt2 rim), likely as a result of granite intrusion. The Grt3 resulted from re-equilibration under retrograde conditions. Two gold-bearing sulfide stages were identified: pyrrhotite-arsenopyrite ± löllingite ± chalcopyrite ± gold stage I precipitated below a metamorphic peak temperature of 598 ± 19 °C associated with S1 foliation (D1), and pyrrhotite-pyrite-arsenopyrite ± chalcopyrite ± gold stage II is located commonly along V3 quartz-carbonate veinlets with a temperature range between 442 ± 9 and 510 ± 30 °C. We suggest that the granite intrusion imposed an additional thermal effect that promoted further dehydration of country rocks. The Au derived mainly from a metamorphic fluid source but potentially mixed with magmatic fluids from the granite.

Mechanisms of gold bioaccumulation by filamentous cyanobacteria from gold(III)-chloride complex.

PubMed

Lengke, Maggy F; Ravel, Bruce; Fleet, Michael E; Wanger, Gregory; Gordon, Robert A; Southam, Gordon

2006-10-15

The mechanisms of gold bioaccumulation by cyanobacteria (Plectonema boryanum UTEX 485) from gold(III)-chloride solutions have been studied at three gold concentrations (0.8,1.7, and 7.6 mM) at 25 degrees C, using both fixed-time laboratory and real-time synchrotron radiation absorption spectroscopy (XAS) experiments. Interaction of cyanobacteria with aqueous gold(III)-chloride initially promoted the precipitation of nanoparticles of amorphous gold(I)-sulfide at the cell walls, and finally deposited metallic gold in the form of octahedral (111) platelets (approximately 10 nm to 6 microm) near cell surfaces and in solutions. The XAS results confirm that the reduction mechanism of gold(III)-chloride to metallic gold by cyanobacteria involves the formation of an intermediate Au(I) species, gold(I)-sulfide.

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

Gold deposits of the northern margin of the North China craton: Multiple late Paleozoic-Mesozoic mineralizing events

USGS Publications Warehouse

Hart, C.J.R.; Goldfarb, R.J.; Qiu, Yumin; Snee, L.; Miller, L.D.; Miller, M.L.

2002-01-01

(+ 7 to -17???), even within individual deposits, indicate various local country-rock sources for sulfur. Fluid inclusions from all districts show variable homogenization temperatures between 240 and 400 ??C, and are consistently characterized by low salinity, H2O-CO2 ?? CH4, N2 solutions. Although the data are largely consistent with that from orogenic gold veins, intrusion-related veins and epithermal veins are also recognized. The multiple episodes of mineralization are coincident with episodic tectonic reactivations and associated magmatism along the northern margin of the North China craton. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/ 10.1007/s00126-001-0239-2.

Unfolding the arc: The use of pre-orogenic constraints to assess the evolution of the Variscan belt in Western Europe

NASA Astrophysics Data System (ADS)

Casas, Josep M.; Brendan Murphy, J.

2018-06-01

We present a pre-orogenic, early Paleozoic, palinspastic reconstruction of the northern Gondwana margin that was subsequently involved in the Late Paleozoic Variscan orogeny in central and Western Europe. Our reconstruction is based on two pre-orogenic data sets, the age and distribution of Cambrian-Ordovician magmatism and the detrital zircon age signature of late Neoproterozoic-early Paleozoic clastic rocks. We obtain this reconstruction by unfolding the Ibero-Armorican arc and by restoring the movement of the large-scale dextral strike-slip faults that transect the different tectono-stratigraphic units. Our results favour an irregular shape for this part of the northern Gondwana margin with a N-S central segment linking two E-W oriented segments. The proposed reconstruction and the structural restoration of the main features of Variscan deformation is in accordance with some aspects of previously proposed structural models, such as the curved geometry of the Gondwanan margin required by the indentor model for continental collision, the role played by the large strike-slip faults in dispersing formerly juxtaposed units, and the regional-scale oroclinal folding of part of this margin during late Carboniferous-Early Permian times. The combined use of the pre-orogenic geological constraints and palinspastic restoration is a useful approach that may provide a foundation for continual refinement of reconstructions as more data become available.

Timing of sediment-hosted Cu-Ag mineralization in the Trans-Hudson orogen at Janice Lake, Wollaston Domain, Saskatchewan, Canada

NASA Astrophysics Data System (ADS)

Perelló, José; Valencia, Víctor A.; Cornejo, Paula; Clifford, John; Wilson, Alan J.; Collins, Greg

2018-04-01

The Janice Lake Cu-Ag mineralization in the Wollaston Domain of northern Saskatchewan is hosted by a metasedimentary sequence in the upper part of the Wollaston Supergroup of the Trans-Hudson orogen. The Wollaston Supergroup was deposited between 2070 and 1865 Ma in a foreland basin setting constructed over Archean basement of the Hearne craton. The Trans-Hudson orogen underwent final collision and peak metamorphism at 1810 Ma, during consolidation of Laurentia and its amalgamation with the Columbia supercontinent. Titanite is a common constituent of the post-peak metamorphic assemblages of Trans-Hudson lithotectonic units and accompanied disseminated sediment-hosted Cu sulfide mineralization at Janice Lake. Titanite crystals, intergrown with chalcocite over a strike-length of 2 km of Cu-bearing stratigraphy, were dated by the ID-TIMS and LA-ICP-MS U-Pb methods, returning an age range from 1780 to 1760 Ma and a weighted average age of 1775 ± 10 Ma. The titanite ages effectively date the associated chalcocite-dominated sediment-hosted Cu-Ag mineralization and its formation during initial post-orogenic uplift and cooling, 30 myr after peak metamorphism. The age-range and tectonic setting of the Janice Lake mineralization confirms that sediment-hosted Cu mineralization was an integral part of the metallogenic endowment of Columbia and that its emplacement coincided with the continental-scale Trans-Hudson orogeny rather than with diagenesis and extensional basin development 100 myr earlier.

Hydrothermal alteration, ore fluid characteristics, and gold depositional processes along a trondhjemite-komatiite contact at Tarmoola, Western Australia

USGS Publications Warehouse

Duuring, P.; Hagemann, S.G.; Cassidy, K.F.; Johnson, C.A.

2004-01-01

Tarmoola is a structurally controlled Archean orogenic gold deposit hosted in greenschist facies metamorphosed komatiite and trondhjemite in the Leonora district of the Eastern Goldfields province, Yilgarn craton. High-grade (>1 g/t Au) orebodies are located in komatiite wall rock adjacent to the eastern and northeastern margins of the asymmetrical, north-south-striking, Tarmoola trondhjemite intrusion. Gold-bearing veins post-date trondhjemite emplacement (ca. 2700 Ma), quartz diorite dikes (ca. 2667 Ma), and regional greenschist facies metamorphism. Textures and crosscutting relationships in gold-bearing veins indicate two stages of hydrothermal fluid infiltration associated with a single gold-related hydrothermal event: a volumetrically dominant, but gold-poor, stage I fluid and a gold-rich stage II fluid. Gold-bearing veins contain stage I milky quartz and pyrite that are overprinted by stage II quartz-ankerite-muscovite-chalcopyrite-sphalerite-galena-gold-tellurides ?? albite ?? chlorite ?? fuchsite ?? epidote ?? scheelite. Stage I hydrothermal alteration assemblages are different in trondhjemite and komatiite due to contrasting reactions between a common ore fluid and disparate wall-rock chemistry. Stage II fluid-wall rock interaction was minor compared to stage I and is indicated by the overprinting of stage I mineral assemblages by stage II microveins. Wall-rock alteration proximal to veins in trondhjemite is characterized by replacement of igneous plagioclase, amphibole, biotite, and metamorphic chlorite by hydrothermal quartz, muscovite, ankerite, calcite, pyrite, chalcopyrite, sphalerite, galena, tellurides, and gold, whereas in proximal alteration in komatiite, metamorphic chlorite and talc are replaced by ankerite, quartz, muscovite, albite, chlorite, fuchsite, pyrite, chalcopyrite, sphalerite, galena, tellurides, and gold. The stage II fluid was enriched in H2O, CO2, Si, Ca, K, Na, S, Au, Ag, Cu, Pb, W, Bi, As, Mo, Zn, and Te. Based on fluid inclusion

Geochemistry, 40Ar/39Ar geochronology, and geodynamic implications of Early Cretaceous basalts from the western Qinling orogenic belt, China

NASA Astrophysics Data System (ADS)

Zhang, Feifei; Wang, Yuejun; Cawood, Peter A.; Dong, Yunpeng

2018-01-01

The Qinling-Dabie orogenic belt was formed by the collision of the North and South China Cratons during the Early Mesozoic and subsequently developed into an intracontinental tectonic process during late Mesozoic. Field investigations identified the presence of late Mesozoic basalts in the Duofutun and Hongqiang areas in the western Qinling orogenic belt. The petrogenesis of these basalts provides an important constraint on the late Mesozoic geodynamics of the orogen. The representative basaltic samples yield the 40Ar/39Ar plateau age of about 112 Ma. These samples belong to the alkaline series and have SiO2 ranging from 44.98 wt.% to 48.19 wt.%, Na2O + K2O from 3.44 wt% to 5.44 wt%, and MgO from 7.25 wt.% to 12.19 wt.%. They demonstrate the right-sloping chondrite-normalized REE patterns with negligible Eu anomalies (1.00-1.10) and PM-normalized patterns enriched in light rare earth element, large ion lithophile element and high field strength element, similar to those of OIB rocks. These samples additionally show an OIB-like Sr-Nd isotopic signature with εNd(t) values ranging from +6.13 to +10.15 and initial 87Sr/86Sr ratios from 0.7028 to 0.7039, respectively. These samples are geochemically subdivided into two groups. Group 1 is characterized by low Al2O3 and high TiO2 and P2O5 contents, as well as high La/Yb ratios (>20), being the product of the high-pressure garnet fractionation from the OIB-derived magma. Group 2 shows higher Al2O3 but lower P2O5 contents and La/Yb ratios (<20) than Group 1, originating from asthenospheric mantle with input of delaminated lithospheric component. In combination with available data, it is proposed for the petrogenetic model of the Early Cretaceous thickened lithospheric delamination in response to the asthenospheric upwelling along the western Qinling orogenic belt.

Gold and gold-iron oxide magnetic glyconanoparticles: synthesis, characterization and magnetic properties.

PubMed

de la Fuente, Jesús M; Alcántara, David; Eaton, Peter; Crespo, Patricia; Rojas, Teresa C; Fernandez, Asunción; Hernando, Antonio; Penadés, Soledad

2006-07-06

The preparation, characterization and the magnetic properties of gold and gold-iron oxide glyconanoparticles (GNPs) are described. Glyconanoparticles were prepared in a single step procedure in the presence of aqueous solution of thiol functionalized neoglycoconjugates and either gold salts or both gold and iron salts. Neoglycoconjugates of lactose and maltose disaccharides with different linkers were used. Iron-free gold or gold-iron oxide GNPs with controlled gold-iron ratios were obtained. The average core-size diameters are in the range of 1.5-2.5 nm. The GNPs are fully characterized by (1)H NMR spectrometry, transmission electron microscopy (TEM), and UV-vis and X-ray absorption (XAS) spectroscopies. Inductive plasma-atomic emission spectrometry (ICP) and elemental analysis gave the average number of neoglycoconjugates per cluster. The magnetic properties were measured in a SQUID magnetometer. The most remarkable results was the observation of a permanent magnetism up to room temperature in the iron-free gold GNPs, that was not present in the corresponding gold-iron oxide GNPs.

The Western Chugach-St. Elias Orogen, Alaska: Strain Partitioning and the Effect of Glacial Erosion

NASA Astrophysics Data System (ADS)

Berger, A. L.; Spotila, J. A.

2006-12-01

The ongoing collision between the Yakutat terrane and the North American plate in southeastern Alaska's St. Elias orogen is a modern analog for the tectonic processes which produced, and shaped, much of the Cordillera. With convergence rates comparable to that of the Himalaya (>4 cm/yr), a young and dynamic zone of thin-skinned interplate deformation has constructed the highest coastal relief on Earth, and given rise to the second and third highest peaks in North America (5,959 and 5,489 m). The orogen receives upwards of 4 m precipitation annually, has been heavily glaciated for the last 5 Ma, and contains some of the fastest short-term erosion rates known. Over the last few years, evidence has steadily mounted that within such tectonic settings, climate and tectonics exist as a coupled system (i.e. Taiwan and Nanga Parbat). Our ongoing research, aimed at quantifying spatial patterns in exhumation rate as well as the location of active structures within the western half of the St. Elias orogen, bolsters this new paradigm. Bedrock ([U-Th]/He) cooling ages in apatite show that exhumation is currently focused on the windward side of the orogen. Time- averaged, long-term, exhumation rates near the coast are generally ~2-3 mm/yr, versus <0.5 mm/yr on the leeward side of the range. However, the rapid exhumation rates along the windward flank are not spatially uniform with the highest rates measured thus far >~5.5 mm/yr (0.4 Ma cooling age) situated near the Bering and Steller Glaciers. This locus of exhumation could reflect a redistribution of strain by focused erosion beneath these large outlet glaciers. Yet, the structural mechanism of this focused strain is still speculative. Pairs of helium ages spanning the foot-wall and hanging-wall of the Chugach-St. Elias thrust, the suture between the North American plate and colliding Yakutat terrane, imply that the thrust became inactive at some time between 2 and 5 Ma. Because of the coincidence in timing between this

Partial melting of amphibolites in the Eastern Segment of the Sveconorwegian orogen, southern Sweden.

NASA Astrophysics Data System (ADS)

Brophy, E.; Hansen, E. C.; Möller, C.; Huffman, M.

2017-12-01

Mafic migmatites with amphibolitic melanosome and tonalitic leucosome are a common feature in continental collision orogenic zones. However, the anatexis of mafic rocks has received much less attention than anatexis in felsic, intermediate or pelitic compositions. We examined mafic migmatites along a traverse within the Eastern Segment of the 1.14-0.9 Ga Sveconorwegian orogen, between Forsheda and Fegen southern Sweden. This traverse occurs in the center of a >150 km metamorphic transition from sub-greenschist facies in the east to high-pressure granulite and eclogite facies in the west (Möller and Andersson, unpublished metamorphic map). The Eastern Segment is a parautochthonous belt made up of rocks of the Fennoscandian shield that were deformed and metamorphosed during the Sveconorwegian orogeny. Within the traverse amphibolite bodies occur within migmatitic felsic to intermediate orthogneisses. The first appearance of tonalitic leucosome in amphibolite was observed towards the eastern edge of the traverse and continued to occur sporadically westward ranging in abundance (by outcrop area) from 0 to 25 %. The mineral assemblage in amphibolite is hbl + plag ( An30) + qtz + bt ± grt ± ilm ± ttn ± py ± SO2-rich scp. No examples of peritectic pyroxene associated with leucosome were found. The lack of peritectic pyroxene suggests that a water-rich phase was present at the onset of anatexis. The highly variable amount of leucosome further suggests that the amount of melt generated was determined by the amount of water available. Together these suggest that partial was driven by the local influx of a water-rich fluid. In the higher grade portions further west migmatitic amphibolite with tonalitic leucosome occurs in two varieties: one with peritectic pyroxene and relatively small amounts of leucosome, interpreted as forming by water-undersaturated dehydration melting, and another without peritectic pyroxene and with larger amounts of leucosome which is interpreted

Origin of the transition voltage in gold-vacuum-gold atomic junctions.

PubMed

Wu, Kunlin; Bai, Meilin; Sanvito, Stefano; Hou, Shimin

2013-01-18

The origin and the distance dependence of the transition voltage of gold-vacuum-gold junctions are investigated by employing first-principles quantum transport simulations. Our calculations show that atomic protrusions always exist on the electrode surface of gold-vacuum-gold junctions fabricated using the mechanically controllable break junction (MCBJ) method. The transition voltage of these gold-vacuum-gold junctions with atomically sharp electrodes is determined by the local density of states (LDOS) of the apex gold atom on the electrode surface rather than by the vacuum barrier shape. More specifically, the absolute value of the transition voltage roughly equals the rising edge of the LDOS peak contributed by the 6p atomic orbitals of the gold atoms protruding from the electrode surface, whose local Fermi level is shifted downwards when a bias voltage is applied. Since the LDOS of the apex gold atom depends strongly on the exact shape of the electrode, the transition voltage is sensitive to the variation of the atomic configuration of the junction. For asymmetric junctions, the transition voltage may also change significantly depending on the bias polarity. Considering that the occurrence of the transition voltage requires the electrode distance to be larger than a critical value, the interaction between the two electrodes is actually rather weak. Consequently, the LDOS of the apex gold atom is mainly determined by its local atomic configuration and the transition voltage only depends weakly on the electrode distance as observed in the MCBJ experiments.

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.

Extreme mass flux from the glaciated, collisional St. Elias Orogen: Preliminary results from IODP Expedition 341 (Invited)

NASA Astrophysics Data System (ADS)

Gulick, S. P.; Jaeger, J. M.

2013-12-01

Integrated Ocean Drilling Program Expedition 341 drilled a cross-margin transect to investigate the linkages between global climate change, modification of the dynamics of surficial processes, and subsequent tectonic responses. The Gulf of Alaska (GoA) borders the St. Elias orogen, the highest coastal mountain range on Earth. Exp. 341 drilled five sites within a regional seismic reflection grid that spans from the distal Surveyor Fan to the continental shelf. More than 3000 m of high-quality core coupled with seismic reflection profiles collected with nested vertical resolution allows us to address the major objectives of drilling in the GoA. These objectives were to: 1) document the tectonic response of an active orogenic system to late Miocene to recent climate change; 2) establish the timing of advance/retreat phases of the northern Cordilleran ice sheet to test its relation to dynamics of other global ice sheets; 3) implement an expanded source-to-sink study of the interactions between glacial, tectonic, and oceanographic processes responsible for creation of one of the thickest Neogene high-latitude continental margin sequences; 4) understand the dynamics of productivity, nutrients, freshwater input to the ocean, and ocean circulation in the northeast Pacific and their role in the global carbon cycle, and 5) document the spatial and temporal behavior of the geomagnetic field at extremely high temporal resolution in an under-sampled region of the globe. The Exp. 341 cross-margin transect discovered transitions in sediment accumulation rates from >100 m/Ma at the distal site to > 1000 m/Ma in the proximal fan, slope and on the continental shelf that provide a telescoping view of strata formation from the Miocene to the Holocene. Complete recovery and development of spliced sedimentary records of the Pleistocene through Holocene were achieved at the distal, proximal, and slope Sites U1417, U1418, and U1419, respectively, because of exceptional piston core

Sand fairway mapping as a tool for tectonic restoration in orogenic belts

NASA Astrophysics Data System (ADS)

Butler, Rob

2016-04-01

geomorphology. The stratigraphic records are preserved in many parts of the Alpine-Mediterranean region. Examples are drawn from the Eo-Oligocene of the western Alps and the early Miocene of the Maghreb-Apennine system to illustrate how turbidite sedimentology, linked to studies of basin structure, can inform understanding of tectonic processes on regional and local scales. In both examples, sediment was delivered across deforming basin arrays containing contractional structures, sourced from beyond the immediate orogenic segments. The depositional systems show that multiple structures were active in parallel, rather than develop in any particular sequence. Both systems show that significant deformation occurs, emerging to the syn-orogenic surface ahead of the main orogenic wedge. The cycling of uplift and subsidence of "massifs" can be significantly more complex that the histories resolved from thermochronological data alone.

Is It Real Gold?

ERIC Educational Resources Information Center

Harris, Harold H.

1999-01-01

Features acid tests for determining whether jewelry is "real" gold or simply gold-plated. Describes the carat system of denoting gold content and explains how alloys are used to create various shades of gold jewelry. Addresses the question of whether gold jewelry can turn a wearer's skin green by considering various oxidation reactions.…

Moho depth model for the Central Asian Orogenic Belt from satellite gravity gradients

NASA Astrophysics Data System (ADS)

Guy, Alexandra; Holzrichter, Nils; Ebbing, Jörg

2017-09-01

The main purpose of this study is to construct a new 3-D model of the Central Asian Orogenic Belt (CAOB) crust, which can be used as a starting point for future lithospheric studies. The CAOB is a Paleozoic accretionary orogen surrounded by the Siberian Craton to the north and the North China and Tarim Cratons to the south. This area is of great interest due to its enigmatic and still not completely understood geodynamic evolution. First, we estimate an initial crustal thickness by inversion of the vertical gravity component of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) and DTU10 models. Second, 3-D forward modeling of the GOCE gravity gradients is performed, which determines the topography of the Moho, the geometry, and the density distribution of the deeper parts of the CAOB and its surroundings, taking into account the lateral and vertical density variations of the crust. The model is constrained by seismic refraction, reflection, and receiver function studies and geological studies. In addition, we discuss the isostatic implications of the differences between the seismic Moho and the resulting 3-D gravity Moho, complemented by the analysis of the lithostatic load distribution at the upper mantle level. Finally, the correlation between the contrasting tectonic domains and the thickness of the crust reveals the inheritance of Paleozoic and Mesozoic geodynamics, particularly the magmatic provinces and the orocline which preserve their crustal features.

Common Pb isotope mapping of UHP metamorphic zones in Dabie orogen, Central China: Implication for Pb isotopic structure of subducted continental crust

NASA Astrophysics Data System (ADS)

Shen, Ji; Wang, Ying; Li, Shu-Guang

2014-10-01

We report Pb isotopic compositions for feldspars separated from 57 orthogneisses and 2 paragneisses from three exhumed UHPM slices representing the North Dabie zone, the Central Dabie zone and the South Dabie zone of the Dabie orogen, central-east China. The feldspars from the gneisses were recrystallized during Triassic continental subduction and UHP metamorphism. Precursors of the orthogneisses are products of Neoproterozoic bimodal magmatic events, those in north Dabie zone emplaced into the lower crust and those in central and south Dabie zones into middle or upper crust, respectively. On a 207Pb/204Pb vs. 206Pb/204Pb diagram, almost all orthogneisses data lie to the left of the 0.23 Ga paleogeochron and plot along the model mantle evolution curve with the major portion of the data plotting below it. On a 208Pb/204Pb vs. 206Pb/204Pb diagram the most of data of north Dabie zone extend in elongate arrays along the lower crustal curve and others extend between the lower crustal curve to near the mantle evolution curve for the plumbotectonics model. This pattern demonstrates that the Pb isotopic evolution of the feldspars essentially ended at 0.23 Ga and the orthogneiss protoliths were principally dominated by reworking of ancient lower crust with some addition of juvenile mantle in the Neoproterozoic rifting tectonic zone. According to geological evolution history of the locally Dabie orogen, a four-stage Pb isotope evolution model including a long time evolution between 2.0 and 0.8 Ga with a lower crust type U/Pb ratio (μ = 5-6) suggests that magmatic emplacement levels of the protoliths of the orthogneisses in the Dabie orogen at 0.8 Ga also play an important role in the Pb evolution of the exhumed UHPM slices, corresponding to their respective Pb characters at ca. 0.8-0.23 Ga. For example, north Dabie zone requires low μ values (3.4-9.6), while central and south Dabie zones require high μ values (10.9-17.2). On the other hand, Pb isotopic mixing between

Gold paragenesis and chemistry at Batu Hijau, Indoneisa: implications for gold-rich porphyry copper deposits

NASA Astrophysics Data System (ADS)

Arif, J.; Baker, T.

2004-10-01

Gold is an important by-product in many porphyry-type deposits but the distribution and chemistry of gold in such systems remains poorly understood. Here we report the results of petrographic, electron microprobe, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and flotation test studies of gold and associated copper sulfides within a paragenetic framework from the world-class Batu Hijau (914 mt @ 0.53% Cu, 0.40 g/t Au) porphyry copper gold deposit, Indonesia. Unlike many other porphyry copper gold deposits, early copper minerals (bornite digenite chalcocite) are well preserved at Batu Hijau and the chalcopyrite pyrite overprint is less developed. Hence, it provides an excellent opportunity to study the entire gold paragenesis of the porphyry system. In 105 polished thin sections, 699 native gold grains were identified. Almost all of the native gold grains occurred either within quartz veins, attached to sulfide, or as free gold along quartz or silicate grain boundaries. The native gold grains are dominantly round in shape and mostly 1 12 μm in size. The majority of gold was deposited during the formation of early ‘A’ veins and is dominantly associated with bornite rather than chalcopyrite. The petrographic and LA-ICP-MS study results indicate that in bornite-rich ores gold mostly occurs within copper sulfide grains as invisible gold (i.e., within the sulfide structure) or as native gold grains. In chalcopyrite-rich ores gold mostly occurs as native gold grains with lesser invisible gold. Petrographic observations also indicate a higher proportion of free gold (native gold not attached to any sulfide) in chalcopyrite-rich ores compared to bornite rich ores. The pattern of free gold distribution appears to correlate with the flotation test data, where the average gold recovery value from chalcopyrite-rich ores is consistently lower than bornite-rich ores. Our data suggest that porphyry copper-gold deposits with chalcopyrite-rich ores

Enhancement of gold recovery using bioleaching from gold concentrate

NASA Astrophysics Data System (ADS)

Choi, S. H.; Cho, K. H.; Kim, B. J.; Choi, N. C.; Park, C. Y.

2012-04-01

The gold in refractory ores is encapsulated as fine particles (sometimes at a molecular level) in the crystal structure of the sulfide (typically pyrite with or without arsenopyrite) matrix. This makes it impossible to extract a significant amount of refractory gold by cyanidation since the cyanide solution cannot penetrate the pyrite/arsenopyrite crystals and dissolve gold particles, even after fine grinding. To effectively extract gold from these ores, an oxidative pretreatment is necessary to break down the sulfide matrix. The most popular methods of pretreatment include nitric acid oxidation, roasting, pressure oxidation and biological oxidation by microorganisms. This study investigated the bioleaching efficiency of Au concentrate under batch experimental conditions (adaptation cycles and chemical composition adaptation) using the indigenous acidophilic bacteria collected from gold mine leachate in Sunsin gold mine, Korea. We conducted the batch experiments at two different chemical composition (CuSO4 and ZnSO4), two different adaptation cycles 1'st (3 weeks) and 2'nd (6 weeks). The results showed that the pH in the bacteria inoculating sample decreased than initial condition and Eh increased. In the chemical composition adaptation case, the leached accumulation content of Fe and Pb was exhibited in CuSO4 adaptation bacteria sample more than in ZnSO4 adaptation bacteria samples, possibly due to pre-adaptation effect on chalcopyrite (CuFeS2) in gold concentrate. And after 21 days on the CuSO4 adaptation cycles case, content of Fe and Pb was appeared at 1'st adaptation bacteria sample(Fe - 1.82 and Pb - 25.81 times per control sample) lower than at 2'nd adaptation bacteria sample(Fe - 2.87 and Pb - 62.05 times per control sample). This study indicates that adaptation chemical composition and adaptation cycles can play an important role in bioleaching of gold concentrate in eco-/economic metallurgy process.

Effects of Burning Conditions to the Formation of Gold Layer Photograph and Gold Layer Hologram

NASA Astrophysics Data System (ADS)

Kuge, Ken'ichi; Takahashi, Ataru; Harada, Takahito; Doi, Keiji; Sakai, Tomoko

Burning stage from gold nanoparticles to gold layer in the formation process of gold-layer photograph using gold deposition development was investigated. The gelatin layer holding gold nanoparticles is carbonized at about 400°C and burned out until about 500°C. Because gold nanoparticles would be compressed only to vertical direction and then melt to form the gold layer, the gold-layer photograph still holds the high resolution. Gold nanoparaticles do not melt completely even at 900°C, and form continuous clusters of several hundred nm.

The Pico do Itapeva Formation: A record of gravitational flow deposits in an Ediacaran intracontinental basin, southern Brasília Orogen, SE Brazil

NASA Astrophysics Data System (ADS)

Caputo Neto, V.; Ribeiro, A.; Nepomuceno, F. O.; Dussin, I. A.; Trouw, R. A. J.

2018-07-01

The Pico do Itapeva Formation is a key metasedimentary unit to the understanding of the extensional events that occurred between the late stage of the southern Brasília Orogen collision and the main collision in the central Ribeira Orogen. The formation crops out in a 20 km long NE-trending narrow belt in the Mantiqueira mountain range in eastern São Paulo State, Brazil. It is located in the interference zone of the southern Brasília and the central Ribeira orogens and records deformation and greenschist facies metamorphism (biotite zone) related to the Brasiliano orogeny. The Pico do Itapeva Formation rests unconformably on a metaigneous substratum of the Socorro-Guaxupé Nappe/Embu Terrane and, on the southern side, is truncated by a steep SE-dipping dextral reverse shear zone. It consists of a coarsening- and thickening-upward succession, with minimum thickness of 800 m, composed of lutite, arkose and conglomerate. These rocks constitute three distinct lithofacies associations: LAI- arkose, arkose-lutite composite beds, lutite and fine conglomerate beds; LAII- arkose, pebbly arkose and scarce lutite and; LAIII- conglomerate and pebbly arkose. Most of the beds are massive; graded beds, dish and convolute structures occur locally. Bed thickness varies from thin to very thick and amalgamated bodies constitute up to 30m thick strata. Three mappable units at scale 1:20,000 were recognized based on different proportions of the three lithofacies associations. The deposits are interpreted as the record of mass flows and associated processes in a fan delta setting developed in an intermontane rift basin. U-Pb LA-ICP-MS detrital zircon ages suggest the maximum depositional age at ca. 611 Ma and the basin evolution is interpreted in the range between 611 and 580 Ma during an inter-orogenic stage between the Brasília and Ribeira orogenies.

Influence of gold content on copper oxidation from silver-gold-copper alloys

NASA Astrophysics Data System (ADS)

Swinbourne, D. R.; Barbante, G. G.; Strahan, A.

1996-10-01

In the final stages of the smelting of copper anode slimes, a silver alloy, known as “doré,” is produced. Oxidation refining is used to remove copper since this element interferes with subsequent electroparting of the small amounts of gold and platinum group metals in the doré. The gold content of doré can be greatly increased by gold scrap additions and this may affect the minimum achievable copper content of doré. In this work, silver-gold-copper alloys were oxidized by injecting pure oxygen at 1100 °C in the absence of any slag cover. For the gold contents expected in practice, the equilibrium copper content of the doré did not increase significantly as the gold content increased. However, at the other extreme of composition, the equilibrium copper content was a very strong function of the silver content of the gold bullion. The activity coefficient of copper in silver-gold alloys was calculated and compared to those predicted from a ternary subregular solution model of the system Ag-Au-Cu. Satisfactory agreement was found.

Enrichment of Gold in Antimony Matte by Direct Smelting of Refractory Gold Concentrate

NASA Astrophysics Data System (ADS)

Yang, Tianzu; Xie, Boyi; Liu, Weifeng; Zhang, Duchao; Chen, Lin

2018-04-01

Conventional cyanidation technology achieves low gold recovery when used to process refractory gold concentrate. Based on the geochemical characteristics of gold deposit mineralization, a new method is proposed herein for gold enrichment in antimony matte by smelting of refractory gold concentrate. The effects of the FeO/SiO2 and CaO/SiO2 ratios, smelting temperature, and smelting time on the gold recovery were investigated in detail. The optimum conditions were determined to be FeO/SiO2 ratio of 1.2, CaO/SiO2 ratio of 0.4, smelting temperature of 1200°C, and smelting time of 45 min. The gold content in antimony matte and smelting slag was 96.68 and 1.13 g/t, respectively. The gold, antimony, and arsenic recovery was 97.72%, 26.89%, and 6.56%, respectively, with most of the antimony and arsenic volatilized into dust. Mineral liberation analyzer results showed that the antimony matte mainly consisted of FeS and FeO, with three phases, viz. FeAs, SbAs, and AuSb, embedded between them, indicating that gold was easily enriched with antimony and arsenic during smelting of refractory gold concentrate.

Enrichment of Gold in Antimony Matte by Direct Smelting of Refractory Gold Concentrate

NASA Astrophysics Data System (ADS)

Yang, Tianzu; Xie, Boyi; Liu, Weifeng; Zhang, Duchao; Chen, Lin

2018-06-01

Conventional cyanidation technology achieves low gold recovery when used to process refractory gold concentrate. Based on the geochemical characteristics of gold deposit mineralization, a new method is proposed herein for gold enrichment in antimony matte by smelting of refractory gold concentrate. The effects of the FeO/SiO2 and CaO/SiO2 ratios, smelting temperature, and smelting time on the gold recovery were investigated in detail. The optimum conditions were determined to be FeO/SiO2 ratio of 1.2, CaO/SiO2 ratio of 0.4, smelting temperature of 1200°C, and smelting time of 45 min. The gold content in antimony matte and smelting slag was 96.68 and 1.13 g/t, respectively. The gold, antimony, and arsenic recovery was 97.72%, 26.89%, and 6.56%, respectively, with most of the antimony and arsenic volatilized into dust. Mineral liberation analyzer results showed that the antimony matte mainly consisted of FeS and FeO, with three phases, viz. FeAs, SbAs, and AuSb, embedded between them, indicating that gold was easily enriched with antimony and arsenic during smelting of refractory gold concentrate.

Timing and nature of Holocene glacier advances at the northwestern end of the Himalayan-Tibetan orogen

NASA Astrophysics Data System (ADS)

Saha, Sourav; Owen, Lewis A.; Orr, Elizabeth N.; Caffee, Marc W.

2018-05-01

Holocene glacial chronostratigraphies are developed for four glaciated valleys at the northwestern end of the Himalayan-Tibetan orogen using geomorphic mapping and cosmogenic 10Be surface exposure dating. The study areas include the Hamtah valley in the Lahul Himalaya, and the Karzok, Lato and upper Stok valleys in Zanskar. Five local glacial stages are dated to ∼10.4, ∼6.1-3.3, ∼2.1-0.9, ∼0.7-0.4, and ∼0.3-0.2 ka based on 49 new moraine boulder ages. Large age dispersions are evident for each of the local glacial stages. This is especially the case for ∼6.1-3.3 and ∼2.1-0.9 ka, which is likely a result of prior and/or incomplete exposures in very young moraine boulders. An additional compilation of 187 published 10Be moraine boulder ages help define seven Himalayan Holocene regional glacial stages (HHs) for the northwestern end of the Himalayan-Tibetan orogen. These HHs date to ∼10.9-9.3, ∼8.2-7.4, ∼6.9-4.3, ∼4.5-2.8, ∼2.7-1.8, ∼1.8-0.9, and <1 ka. Early Holocene glacier advances were generally more extensive and had larger equilibrium-line altitude depressions (ΔELA = ∼425 ± 229 m) than glacier advances during the mid-Holocene (ΔELA = ∼141 ± 106) and late Holocene (ΔELA = ∼124 ± 121 m). The early Holocene glacier advances likely correspond to orbitally-forced northerly migration of the Intertropical Convergence Zone and enhanced summer monsoon. The timing of the majority of HHs during mid- and late Holocene corresponds well with the North Atlantic cooling that is likely teleconnected via mid-latitude westerlies, particularly during ∼8 ka and after ∼5 ka. These chronostratigraphies suggest that Holocene glaciation in the northwestern part of the Himalayan-Tibetan orogen is largely influenced by long-term orbital forcing amplified by large-scale migration of the Earth's thermal equator and the associated hemispheric oceanic-atmospheric systems.

Orogenic inheritance in Death Valley region, western US Basin and Range: implications for Neogene crustal extension.

NASA Astrophysics Data System (ADS)

Lima, R. D.; Hayman, N. W.; Prior, M. G.; Stockli, D. F.; Kelly, E. D.

2016-12-01

Deformation and temperature evolution during orogenic stages may influence later fabric development, thus controlling large-scale extensional processes that can occur millions of years later. Here, we describe pressure-temperature and fabric evolution from the Death Valley (DV) region and show how inherited fabrics, formed in late orogenic stages during Late Cretaceous time, influenced later Neogene age Basin and Range (BR) extension. The DV region is one of the most extended and thinned regions in the western US BR province, and the two of the ranges that bound the eastern valley expose basement rocks exhumed during the Neogene extension. In the Funeral range, it has been established that older (Precambrian) basement underwent Mesozoic age syn-deformational metamorphism during the Sevier-Laramide orogeny. In contrast, the Black Mountains record widespread tectonic stretching and magmatism of Miocene age on Precambrian basement, and have, overall, been lacking previous evidence of Mesozoic metamorphism and fabric development. In the Funeral Range Late Cretaceous migmatitic fabrics were overprinted by zones of high-strain fabrics formed due to melt-consuming reaction that define an overall P-T cooling path likely during late- to post-orogenesis. These fabrics form interconnected layers of quartz + biotite aggregates, in which individual quartz grains lack evidence of intracrystalline plastic deformation and show consistently random [c]-axis microfabrics. This suggests coupled reaction-diffusion processes that favored diffusion-assisted creep. New geochronometric results of melt products in the Black Mountains show evidence of partial melting of Late Cretaceous age. Contrasting with the neighboring Funeral Range, overprinting by extensional fabrics of Miocene age is widespread, and consists of high-strain, anastomosing foliation composed of retrograde products from preexisting, higher-temperature fabrics. These include interconnected fine-grained chlorite + quartz

Cainozoic Orogenic Magmatism In The Western-central Mediterranean Area: Implications For The Subduction-modified Mantle Sources

NASA Astrophysics Data System (ADS)

Beccaluva, L.; Bianchini, G.; Coltorti, M.; Siena, F.; Verde, M.

In this contribution new REE and Sr-Nd isotopic data carried out on Cainozoic subduction-related volcanic rocks from the western-central Mediterranean are dis- cussed within a general review of the Cainozoic orogenic magmatism of the area. These volcanic events are related to subduction processes which occurred along the Paleo-European margin at least since Eocene and migrated (trough passive sinking and slab roll-back) southeastward up to the present in the peri-Tyrrhenian margin of Italy. Orogenic rocks from Provence (34-20 Ma) are characterised by 87Sr/86Sr be- tween 0.70453 and 0.70579, and 143Nd/144Nd between 0.51292 and 0.51265, which are consistent with mantle sources modified by subduction fluids released by altered oceanic crust. Sr-Nd isotopic composition of orogenic rocks from Sardinia (32-13 Ma), show a more complex picture: some compositions with relatively low 87Sr/86Sr (<0.706) and high 143Nd/144Nd (>0.5125), are compatible with the subduction of pure oceanic crust, while compositions with very high 87Sr/86Sr (up to 0.7113) and low 143Nd/144Nd (down to 0.51219) require additional components of continental crust affinity in the mantle wedge (partial fusion of subducted terrigenous sediments?). As concerns the Aeolian volcanics (< 1.3 Ma), compositions are compatible with man- tle sources solely enriched by fluid components from subducted oceanic crust. How- ever, it is interesting to note that shoshonites from the younger series of Stromboli display distinctly higher 87Sr/86Sr (up to 0.7075) and lower 143Nd/144Nd composi- tion (down to 0.51242), thus requiring once again recycle of continental crust materials in their mantle sources. The influence of such continental crust-derived components appear to be even more important in the mantle sources of the Campania volcanics, where extreme Sr-Nd isotopic compositions are recorded (87Sr/86Sr up to 0.7097; 143Nd/144Nd down to 0.5122).

Petrogenesis of postcollisional magmatism at Scheelite Dome, Yukon, Canada: Evidence for a lithospheric mantle source for magmas associated with intrusion-related gold systems

USGS Publications Warehouse

Mair, John L.; Farmer, G. Lang; Groves, David I.; Hart, Craig J.R.; Goldfarb, Richard J.

2011-01-01

are attributes of the ancient North American cratonic margin that appear to be essential prerequisites to this style of postcollisional magmatism and associated gold-rich fluid exsolution. This type of magmatic hydrothermal activity occurs in a very specific tectonic setting that typically sets intrusion-related gold deposits apart from orogenic gold deposits, which are synorogenic in timing and have no consistent direct relationship to such diverse and contemporaneous lithospheric mantle-derived magmas, although they too are commonly sited adjacent to lithospheric boundaries.

Gold Leaching Characteristics and Intensification of a High S and As-Bearing Gold Concentrate

NASA Astrophysics Data System (ADS)

Yang, Yong-bin; Liu, Xiao-liang; Jiang, Tao; Li, Qian; Xu, Bin; Zhang, Yan

Some high sulfur and arsenic-bearing gold concentrate has a gold leaching rate less than 80% by oxidation roasting-pickling-cyanidation process. The characteristics and intensification of gold leaching were studied systemically. By combining chemical composition and phase analysis, the low gold leaching rate was found to lie in the capsulation of gold by iron-containing phases including iron oxides, arsenopyrite and pyrite. 96.66% of gold in the industrial leaching residue was capsulated and 95.88% of the capsulated turned out to be in the iron-containing phases. The results of laboratory pickling-cyanidation experiments on the calcine and industrial leaching residue presented further demonstration for the fact that gold capsulated in the iron-containing phases was hard to be leached. However, the gold cyanide leaching rate of calcine could be raised over 95% by a reduction roasting-pickling pretreatment which played such a significant role in exposing the capsulated gold that gold leaching was intensified remarkably.

40 Ma of hydrothermal W mineralization during the Variscan orogenic evolution of the French Massif Central revealed by U-Pb dating of wolframite

NASA Astrophysics Data System (ADS)

Harlaux, Matthieu; Romer, Rolf L.; Mercadier, Julien; Morlot, Christophe; Marignac, Christian; Cuney, Michel

2018-01-01

We present U-Pb thermal ionization mass spectrometer (TIMS) ages of wolframite from several granite-related hydrothermal W±Sn deposits in the French Massif Central (FMC) located in the internal zone of the Variscan belt. The studied wolframite samples are characterized by variable U and Pb contents (typically <10 ppm) and show significant variations in their radiogenic Pb isotopic compositions. The obtained U-Pb ages define three distinct geochronological groups related to three contrasting geodynamic settings: (i) Visean to Namurian mineralization (333-327 Ma) coeval with syn-orogenic compression and emplacement of large peraluminous leucogranites (ca. 335-325 Ma), (ii) Namurian to Westphalian mineralization (317-315 Ma) synchronous with the onset of late-orogenic extension and emplacement of syn-tectonic granites (ca. 315-310 Ma) and (iii) Stephanian to Permian mineralization (298-274 Ma) formed during post-orogenic extension contemporaneous with the Permian volcanism in the entire Variscan belt. The youngest ages (276-274 Ma) likely reflect the reopening of the U-Pb isotopic system after wolframite crystallization and may correspond to late hydrothermal alteration (e.g. ferberitization). Our results demonstrate that W(±Sn) mineralization in the FMC formed during at least three distinct hydrothermal events in different tectono-metamorphic settings over a time range of 40 Ma.

Tectonic processes during oblique collision: Insights from the St. Elias orogen, northern North American Cordillera

USGS Publications Warehouse

Pavlis, T.L.; Picornell, C.; Serpa, L.; Bruhn, R.L.; Plafker, G.

2004-01-01

Oblique convergence in the St. Elias orogen of southern Alaska and northwestern Canada has constructed the world's highest coastal mountain range and is the principal driver constructing all of the high topography in northern North America. The orogen originated when the Yakutat terrane was excised from the Cordilleran margin and was transported along margin-parallel strike-slip faults into the subduction-transform transition at the eastern end of the Aleutian trench. We examine the last 3 m.y. of this collision through an analysis of Euler poles for motion of the Yakutat microplate with respect to North America and the Pacific. This analysis indicates a Yakutat-Pacific pole near the present southern triple junction of the microplate and' predicts convergence to dextral-oblique convergence across the offshore Transition fault, onland structures adjacent to the Yakutat foreland, or both, with plate speeds increasing from 10 to 30 mm/yr from southeast to northwest. Reconstructions based on these poles show that NNW transport of the collided block into the NE trending subduction zone forced contraction of EW line elements as the collided block was driven into the subduction-transform transition. This suggests the collided block was constricted as it was driven into the transition. Constriction provides an explanation for observed vertical axis refolding of both earlier formed fold-thrust systems and the collisional suture at the top of the fold-thrust stack. We also suggest that this motion was partially accommodated by lateral extrusion of the western portion of the orogen toward the Aleutian trench. Important questions remain regarding which structures accommodated parts of this motion. The Transition fault may have accommodated much of the Yakutat-Pacific convergence on the basis of our analysis and previous interpretations of GPS-based geodetic data. Nonetheless, it is locally overlapped by up to 800 m of undeformed sediment, yet elsewhere shows evidence of young

Gold in placer deposits

USGS Publications Warehouse

Yeend, Warren; Shawe, Daniel R.; Wier, Kenneth L.

1989-01-01

Man most likely first obtained gold from placer deposits, more than 6,000 years ago. Placers account for more than two-thirds of the total world gold supply, and roughly half of that mined in the States of California, Alaska, Montana, and Idaho.Placer deposits result from weathering and release of gold from lode deposits, transportation of the gold, and concentration of the gold dominantly in stream gravels. Unless preserved by burial, a placer subsequently may be eroded, and either dispersed or reconcentrated.California has produced more than 40 million troy ounces of gold from placers, both modern and fossil (Tertiary). The source of the great bulk of the gold is numerous quartz veins and mineralized zones of the Mother Lode and related systems in the western Sierra Nevada region. The gold-bearing lodes were emplaced in Carboniferous and Jurassic metamorphic rocks intruded by small bodies of Jurassic and Cretaceous igneous rocks. Mineralization occurred probably in Late Cretaceous time. Significant amounts of placer gold also were mined along the Salmon and Trinity Rivers in northern California. Source of the gold is lode deposits in Paleozoic and Mesozoic metamorphic rocks that were intruded by Mesozoic igneous rocks.Alaska has produced roughly 21 million ounces of gold from placer deposits. Most (about 13 million ounces) has come from the interior region, including 7,600,000 ounces from the Fairbanks district and 1,300,000 ounces from the Iditarod district. Lode sources are believed to be mostly quartz veins in Precambrian or Paleozoic metamorphic rocks intruded by small igneous bodies near Fairbanks, and shear zones in Tertiary(?) quartz monzonite stocks at Iditarod. The Seward Peninsula has produced more than 6 million ounces of placer gold, including about 4,000,000 ounces from the Nome district. Most of the gold was derived from raised beach deposits. Source of the gold probably is Tertiary-mineralized faults and joints in metamorphic rocks of late

Modeling the Evolution of Localized Strain in Orogenic Wedges: From Short-term Deformation to Long-term Tectonic States

NASA Astrophysics Data System (ADS)

Weiss, J. R.; Ito, G.; Brooks, B. A.; Olive, J. A. L.; Foster, J. H.; Howell, S. M.

2015-12-01

Some of the most destructive earthquakes on Earth are associated with active orogenic wedges. Despite a sound understanding of the basic mechanics that govern whole wedge structure over geologic time scales and a growing body of studies that have characterized the deformation associated with historic to recent earthquakes, first order questions remain about the linkage of the two sets of processes at the intermediate seismotectonic timescales. Numerical models have the power to test the effects of specific mechanical conditions on the evolution of observables at active orogenic wedges. Here we use a two-dimensional, continuum mechanics-based, finite difference method with a visco-elasto-plastic rheology coupled with surface processes to investigate the spatiotemporal distribution of deformation during wedge growth. The model simulates the contraction of a crustal layer overlying a weak base (décollement) against a rigid backstop and the spontaneous nucleation and evolution of fault zones due to cohesive, Mohr-Coulomb failure with strain weakening. Consistent with critical wedge theory, the average slope across the wedge is controlled by the relative frictional strengths of the wedge and décollement. Initial calculations predict changes in wedge deformation on short geologic timescales (103-105yrs) that involve episodes of widening as new, foreland-verging thrusts nucleate near the surface beyond the wedge toe and propagate down-dip to intersect the décollement. All the while, the wedge thickens via slip on older, internal fault zones. The aim of this study is to identify the parameters controlling the timescales of 1) episodic widening versus thickening and 2) nucleation and life-span of individual fault zones. These are initial steps needed to link earthquake observations to the long-term tectonic states inferred at various orogenic belts around the world.

Seismological structure of the 1.8 Ga Trans-Hudson Orogen of North America

NASA Astrophysics Data System (ADS)

Gilligan, Amy; Bastow, Ian D.; Darbyshire, Fiona A.

2016-06-01

Precambrian tectonic processes are debated: what was the nature and scale of orogenic events on the younger, hotter, and more ductile Earth? Northern Hudson Bay records the Paleoproterozoic collision between the Western Churchill and Superior plates—the ˜1.8 Ga Trans-Hudson Orogeny (THO)—and is an ideal locality to study Precambrian tectonic structure. Integrated field, geochronological, and thermobarometric studies suggest that the THO was comparable to the present-day Himalayan-Karakoram-Tibet Orogen (HKTO). However, detailed understanding of the deep crustal architecture of the THO, and how it compares to that of the evolving HKTO, is lacking. The joint inversion of receiver functions and surface wave data provides new Moho depth estimates and shear velocity models for the crust and uppermost mantle of the THO. Most of the Archean crust is relatively thin (˜39 km) and structurally simple, with a sharp Moho; upper-crustal wave speed variations are attributed to postformation events. However, the Quebec-Baffin segment of the THO has a deeper Moho (˜45 km) and a more complex crustal structure. Observations show some similarity to recent models, computed using the same methods, of the HKTO crust. Based on Moho character, present-day crustal thickness, and metamorphic grade, we support the view that southern Baffin Island experienced thickening during the THO of a similar magnitude and width to present-day Tibet. Fast seismic velocities at >10 km below southern Baffin Island may be the result of partial eclogitization of the lower crust during the THO, as is currently thought to be happening in Tibet.

A synthesis of mineralization styles and geodynamic settings of the Paleozoic and Mesozoic metallic ore deposits in the Altay Mountains, NW China

NASA Astrophysics Data System (ADS)

Yang, Fuquan; Geng, Xinxia; Wang, Rui; Zhang, Zhixin; Guo, Xuji

2018-06-01

The Altay Mountains within the Xinjiang region of northwestern China hosts major metallic ore deposits. Here we review the geological characteristics, metallogenic features and tectonic settings of these deposits. The metallic ore deposits in the Altay Mountains occur mainly within four regions: North Altay, Central Altay, South Altay and Erqis. We recognize seven types of metallic ore deposits in the Altay Mountains: VMS, submarine volcanogenic iron, magmatic, skarn, pegmatite, hydrothermal vein (Cu-Zn, Fe) and orogenic gold. Among these types, the VMS, pegmatite, orogenic gold and skarn deposits are the most common. Most of the rare metal pegmatite deposits are distributed in Central Altay, with only a few in South Altay. The VMS, submarine volcanogenic type iron and skarn-type deposits are distributed in South Altay, whereas the orogenic-type gold deposits are distributed in the Erqis Fault belt. The hydrothermal vein-type deposits occur in the Erqis Fault belt and Chonghu'er Basin in South Altay. Magmatic-type deposits are mostly in the Erqis Fault belt and Central Altay. Based on isotopic age data, the VMS, submarine volcanogenic-type Fe and skarn-type Cu, Pb, Zn, Fe mineralization occurred during Early-Middle Devonian (∼410-377 Ma), orogenic-type Au, magmatic-type Cu-Ni, and a small number of skarn-type Fe, hydrothermal vein-type Cu-Zn, pegmatite-type rare-metal deposits in Early-Middle Permian (293-261 Ma), pegmatite-type rare-metal deposits, few skarn-type Fe deposit in Early-Middle Triassic (248-232 Ma), and dominantly represented by pegmatite-type rare-metal deposits in Late Triassic-Early Jurassic (223-180 Ma). The metallic ore deposits in the Altay Mountains formed in various tectonic settings, such as the Early-Middle Devonian continental arc and oceanic island arc, Early-Middle Permian post-collisional extensional setting, and Triassic-Early Jurassic intracontinental setting.

Coal-oil gold agglomeration assisted flotation to recover gold from refractory ore

NASA Astrophysics Data System (ADS)

Otsuki, A.; Yue, C.

2017-07-01

This study aimed to investigate the applicability of coal-oil gold agglomeration (CGA) assisted flotation to recover gold from a refractory ore. The ore with the grade of 2-5 g/t was tested with the CGA-flotation process in six different size fractions from 38 to 300 urn using different collector types and dosages. In addition, the flotation without CGA was performed under the same condition for comparison. The results showed that the higher gold grade and recovery were achieved by applying the CGA-flotation, compared with the flotation without CGA. More than 20-60 times grade increase from the head grade was obtained with CGA-flotation. The elemental analysis of gold and sulphur explained their relationship with gold recovery. The results well indicated the applicability of CGA to upgrade the refractory gold ore.

Discovery of Latest Cretaceous OIB-type alkaline gabbros in the Eastern Pontides Orogenic Belt, NE Turkey: Evidence for tectonic emplacement of seamounts

NASA Astrophysics Data System (ADS)

Eyuboglu, Yener; Dudas, Francis O.; Chatterjee, Nilanjan; Liu, Ze; Yılmaz-Değerli, Sedanur

2018-06-01

The Meso-Cenozoic geodynamic evolution of the Eastern Pontides Orogenic Belt, a mountain chain extending parallel to the southeastern margin of the Black Sea, has been controversial for the last forty years. Here we present data for a newly discovered alkaline gabbro body and its surrounding basaltic rocks in the northern part of the Eastern Pontides Orogenic Belt. We also provide a comprehensive assessment of the Late Mesozoic-Cenozoic geodynamic evolution of the Eastern Mediterranean region. The gabbroic body is bounded by reverse faults along its northern and southern borders and is surrounded by vesicular, pillow-fragment breccias and pillow basalts. Mineral compositions suggest that crystallization of the gabbros began at about 1170 °C, and the lowest preserved crystallization T is near 1000 °C. Estimated pressure at the beginning of crystallization is 5.7-7.4 kb. The 40Ar/39Ar dating of kaersutite and plagioclase and Usbnd Pb dating of titanite indicated that the Hayrat gabbro crystallized at 67 Ma (Late Maastrichtian). Whole rock major-trace-rare earth element and Sr-Nd-Pb isotope data indicate that the gabbros and basalts have different origins. The gabbros are alkaline and exhibit the geochemical features of OIB, whereas the basalts are tholeiitic and reveal depletions of HFSE that are similar to those of arc rocks. The gabbros are strongly fractionated, and derive from an enriched, lithospheric mantle source, with partial melting occurring in a garnet-stable environment. The basalts are less fractionated, and probably derive from a shallower source in which spinel peridotite was the predominant lithology. Considering all new and old geological, geochemical, geochronological and geophysical data from the Black Sea Basin and the Eastern Pontides-Lesser Caucasus-Alborz Orogenic Belt, we suggest that the alkaline Hayrat gabbro formed in an oceanic intraplate setting, and was accreted to the forearc region of the Eastern Pontides Orogenic Belt during

Cenozoic landforms and post-orogenic landscape evolution of the Balkanide orogen: Evidence for alternatives to the tectonic denudation narrative in southern Bulgaria

NASA Astrophysics Data System (ADS)

Gunnell, Y.; Calvet, M.; Meyer, B.; Pinna-Jamme, R.; Bour, I.; Gautheron, C.; Carter, A.; Dimitrov, D.

2017-01-01

Continental denudation is the mass transfer of rock from source areas to sedimentary depocentres, and is typically the result of Earth surface processes. However, a process known as tectonic denudation is also understood to expose deep-seated rocks in short periods of geological time by displacing large masses of continental crust along shallow-angle faults, and without requiring major contributions from surface erosion. Some parts of the world, such as the Basin and Range in the USA or the Aegean province in Europe, have been showcased for their Cenozoic tectonic denudation features, commonly described as metamorphic core-complexes or as supradetachment faults. Based on 22 new apatite fission-track (AFT) and 21 helium (AHe) cooling ages among rock samples collected widely from plateau summits and their adjacent valley floors, and elaborating on inconsistencies between the regional stratigraphic, topographic and denudational records, this study frames a revised perspective on the prevailing tectonic denudation narrative for southern Bulgaria. We conclude that conspicuous landforms in this region, such as erosion surfaces on basement-cored mountain ranges, are not primarily the result of Paleogene to Neogene core-complex formation. They result instead from "ordinary" erosion-driven, subaerial denudation. Rock cooling, each time suggesting at least 2 km of crustal denudation, has exposed shallow Paleogene granitic plutons and documents a 3-stage wave of erosional denudation which progressed from north to south during the Middle Eocene, Oligocene, Early to Middle Miocene, and Late Miocene. Denudation initially prevailed during the Paleogene under a syn-orogenic compressional regime involving piggyback extensional basins (Phase 1), but subsequently migrated southward in response to post-orogenic upper-plate extension driven by trench rollback of the Hellenic subduction slab (Phase 2). Rare insight given by the denudation pattern indicates that trench rollback

Basement thrust sheets in the Clearwater orogenic zone, central Idaho and western Montana

NASA Astrophysics Data System (ADS)

Skipp, Betty

1987-03-01

The Clearwater orogenic zone in central Idaho and western Montana contains at least two major northeast-directed Cordilleran thrust plates of Early Proterozoic metasedimentary and metaigneous rocks that overrode previously folded Middle Proterozoic rocks of the Belt basin in Cretaceous time. The northeastward migration of the resultant thickened wedge of crustal material combined with Cretaceous subduction along the western continental margin produced a younger northern Bitterroot lobe of the Idaho batholith relative to an older southern Atlanta lobe. Eocene extensional unroofing and erosion of the Bitterroot lobe has exposed the roots of the thick Cordilleran thrust sheets.

Magnetotelluric Imaging of the Lithosphere Across the Variscan Orogen (Iberian Autochthonous Domain, NW Iberia)

NASA Astrophysics Data System (ADS)

Alves Ribeiro, J.; Monteiro-Santos, F. A.; Pereira, M. F.; Díez Fernández, R.; Dias da Silva, Í.; Nascimento, C.; Silva, J. B.

2017-12-01

A new magnetotelluric (MT) survey comprising 17 MT soundings throughout a 30 km long N30°W transect in the Iberian autochthons domain of NW Iberia (Central Iberian Zone) is presented. The 2-D inversion model shows the resistivity structure of the continental crust up to 10 km depth, heretofore unavailable for this region of the Variscan Orogen. The MT model reveals a wavy structure separating a conductive upper layer underlain by a resistive layer, thus picturing the two main tectonic blocks of a large-scale D2 extensional shear zone (i.e., Pinhel shear zone). The upper layer represents a lower grade metamorphic domain that includes graphite-rich rocks. The lower layer consists of high-grade metamorphic rocks that experienced partial melting and are associated with granites (more resistive) emplaced during crustal thinning. The wavy structure is the result of superimposed crustal shortening responsible for the development of large-scale D3 folds (e.g., Marofa synform), later deflected and refolded by a D4 strike-slip shear zone (i.e., Juzbado-Penalva do Castelo shear zone). The later contribution to the final structure of the crust is marked by the intrusion of postkinematic granitic rocks and the propagation of steeply dipping brittle fault zones. Our study demonstrates that MT imaging is a powerful tool to understand complex crustal structures of ancient orogens in order to design future prospecting surveys for mineral deposits of economic interest.

Mineral textural evolution and PT-path of relict eclogite-facies rocks in the Paleoproterozoic Nagssugtoqidian Orogen, South-East Greenland

NASA Astrophysics Data System (ADS)

Müller, Sascha; Dziggel, Annika; Kolb, Jochen; Sindern, Sven

2018-01-01

The Nagssugtoqidian Orogen in South-East Greenland is a deeply eroded, Paleoproterozoic collision orogen. It consists of a variety of Archean and Paleoproterozoic rocks, most notably TTG gneiss, a variety of supracrustal rocks and basic dykes. This study aims at providing new insight into the geodynamic processes and subduction depth of this orogen by investigating the metamorphic evolution of garnet pyroxenite, retrogressed eclogite and amphibolite-facies rocks that are exposed within the Kuummiut Terrane of the Nagssugtoqidian Orogen. The garnet-pyroxenite has a dominant mineral assemblage of garnet, orthopyroxene, clinopyroxene and hornblende, while garnet-amphibolite and garnet-kyanite schist are made up of garnet, hornblende, plagioclase and quartz, and garnet, kyanite, biotite and quartz, respectively. Relicts of, and pseudomorphs after, eclogite-facies mineral assemblages are frequently found within basic metavolcanic rocks and Paleoproterozoic discordant basic dykes. In the retrogressed eclogite, the retrograde mineral reactions ceased prior to completion, resulting in the formation of two domains. A clinopyroxene domain consists of diopside-plagioclase symplectites, which are interpreted to have grown at the expense of omphacite. The symplectites are surrounded and partly replaced by hornblende and plagioclase. Omphacite (XJd 25-42) is preserved in a Na-rich sample, where it occurs in the core of large clinopyroxene and as inclusion in garnet and hornblende. In a garnet domain, garnet is variably replaced by an inner corona of plagioclase and an outer corona of amphibole +/- orthopyroxene and clinopyroxene. The degree of retrogression as well as the type of the retrograde assemblage in both domains appears to be dependent on fluid activity. Large garnet grains preserve Ca-rich cores, interpreted as prograde in origin, while Mg-rich garnet rims formed during eclogite-facies metamorphism and later re-equilibration. Pseudosection modelling combined with

Preparation of conductive gold nanowires in confined environment of gold-filled polymer nanotubes.

PubMed

Mitschang, Fabian; Langner, Markus; Vieker, Henning; Beyer, André; Greiner, Andreas

2015-02-01

Continuous conductive gold nanofibers are prepared via the "tubes by fiber templates" process. First, poly(l-lactide) (PLLA)-stabilized gold nanoparticles (AuNP) with over 60 wt% gold are synthesized and characterized, including gel permeation chromatography coupled with a diode array detector. Subsequent electrospinning of these AuNP with template PLLA results in composite nanofibers featuring a high gold content of 57 wt%. Highly homogeneous gold nanowires are obtained after chemical vapor deposition of 345 nm of poly(p-xylylene) (PPX) onto the composite fibers followed by pyrolysis of the polymers at 1050 °C. The corresponding heat-induced transition from continuous gold-loaded polymer tubes to smooth gold nanofibers is studied by transmission electron microscopy and helium ion microscopy using both secondary electrons and Rutherford backscattered ions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Distribution and composition of gold in porphyry gold systems: example from the Biely Vrch deposit, Slovakia

NASA Astrophysics Data System (ADS)

Koděra, Peter; Kozák, Jaroslav; Brčeková, Jana; Chovan, Martin; Lexa, Jaroslav; Jánošík, Michal; Biroň, Adrián; Uhlík, Peter; Bakos, František

2018-03-01

The Biely Vrch deposit in the Western Carpathians is assigned to the shallow, sulfide-poor porphyry gold deposit type and has an exceptionally low Cu/Au ratio. According to 3-D geochemical models, there is a limited spatial correlation between Au and Cu due to the primary introduction of gold by a salt melt and Cu by low-density vapor. Despite a rough spatial correlation of gold grades with quartz stockwork intensity, gold is hosted mostly by altered rock, exclusively in native form. Three main gold mineral assemblages were recognized here. In the deepest parts of the system, the K- and Ca-Na silicate gold assemblage is associated with minerals of high-temperature alteration (plagioclase, K-feldspar, actinolite), with gold grades and fineness depending on depth and potassium content of the host rock: K-silicate alteration hosts the lowest fineness gold ( 914), whereas Ca-Na silicate alteration has the highest ( 983). The intermediate argillic gold assemblage is the most widespread, with gold hosted mainly by chlorite, illite, smectite, and interstratified illite-chlorite-smectite minerals. The gold fineness is mostly variable (875-990) and inherited from the former gold mineral assemblages. The latest advanced argillic gold assemblage has its gold mostly in kaolinite. The extremely high fineness ( 994) results from gold remobilization by late-stage aqueous magmatic-hydrothermal fluids. Uncommon bonanza-grade appears where the earlier gold mineral assemblages were further enriched by this remobilized gold. Primary precipitation of gold occurred during ascent and cooling of salt melts at 450 to 309 °C, mostly during retrograde quartz solubility.

The eye of the field geologist and the mind of the tectonician: one view of dynamic crustal rheology in convergent orogens

NASA Astrophysics Data System (ADS)

Brown, M.

2004-05-01

Orogens record evidence of interaction between converging plates. However, the response of continental crust to tectonic and gravitational loads is dependent on rheology, which is influenced by composition, architecture, thermal profile and strain rate. Crustal rocks undergo melting in deeper parts of orogens. Greywackes and metapelites are the most fertile protoliths, generating 20-50 and 30 vol. % melt respectively at 1 GPa and 1173K; geophysical data suggest >6 but <20 vol. % interconnected melt in deep crust of active orogens. In numerical models of orogens, the transition from coupled doubly-vergent wedge structure to plateau formation and full basal decoupling requires a viscosity drop of 4 orders of magnitude, inferred to be melt weakening. Deformation experiments on granite indicate a dramatic drop in strength (to 100-200 MPa) as the melt wetting transition is approached at 7 vol. % melt, and a more gradual decrease to <1 MPa prior to the drop at the solid-to-liquid transition (RCMP). Important properties of melting systems are viscosity of the melt, rheology of the crystalline framework of grains and permeability of this framework to flow. Permeability is due to an intergranular network of connected pores, compositional layering/fabric and networks of deformation bands; melt distribution is heterogeneous on multiple length scales. The microstructure of anatectic rocks and the magnitude of weakening accompanying melting suggest a limited role for intracrystalline plasticity with increasing vol. % melt and dominance of melt-assisted diffusion creep or diffusion accommodated granular flow. The intrinsic weakness of melt-bearing intervals in the crust makes them ideal detachment horizons. Observations from metasedimentary migmatitic granulites show preservation of (i) early fabrics, suggesting that the strain field emergent under subsolidus conditions controlled initial distribution of melt produced by suprasolidus mica breakdown, and (ii) layering in melt

Silver, gold, and alloyed silver-gold nanoparticles: characterization and comparative cell-biologic action

NASA Astrophysics Data System (ADS)

Mahl, Dirk; Diendorf, Jörg; Ristig, Simon; Greulich, Christina; Li, Zi-An; Farle, Michael; Köller, Manfred; Epple, Matthias

2012-10-01

Silver, gold, and silver-gold-alloy nanoparticles were prepared by citrate reduction modified by the addition of tannin during the synthesis, leading to a reduction in particle size by a factor of three. Nanoparticles can be prepared by this easy water-based synthesis and subsequently functionalized by the addition of either tris(3-sulfonatophenyl)phosphine or poly( N-vinylpyrrolidone). The resulting nanoparticles of silver (diameter 15-25 nm), gold (5-6 nm), and silver-gold (50:50; 10-12 nm) were easily dispersable in water and also in cell culture media (RPMI + 10 % fetal calf serum), as shown by nanoparticle tracking analysis and differential centrifugal sedimentation. High-resolution transmission electron microscopy showed a polycrystalline nature of all nanoparticles. EDX on single silver-gold nanoparticles indicated that the concentration of gold is higher inside a nanoparticle. The biologic action of the nanoparticles toward human mesenchymal stem cells (hMSC) was different: Silver nanoparticles showed a significant concentration-dependent influence on the viability of hMSC. Gold nanoparticles showed only a small effect on the viability of hMSC after 7 days. Surprisingly, silver-gold nanoparticles had no significant influence on the viability of hMSC despite the silver content. Silver nanoparticles and silver-gold nanoparticles in the concentration range of 5-20 μg mL-1 induced the activation of hMSC as indicated by the release of IL-8. In contrast, gold nanoparticles led to a reduction of the release of IL-6 and IL-8.

Age constraints on felsic intrusions, metamorphism and gold mineralisation in the Palaeoproterozoic Rio Itapicuru greenstone belt, NE Bahia State, Brazil

USGS Publications Warehouse

Mello, E.F.; Xavier, R.P.; McNaughton, N.J.; Hagemann, S.G.; Fletcher, I.; Snee, L.

2006-01-01

U-Pb sensitive high resolution ion microprobe mass spectrometer (SHRIMP) ages of zircon, monazite and xenotime crystals from felsic intrusive rocks from the Rio Itapicuru greenstone belt show two development stages between 2,152 and 2,130 Ma, and between 2,130 and 2,080 Ma. The older intrusions yielded ages of 2,152??6 Ma in monazite crystals and 2,155??9 Ma in zircon crystals derived from the Trilhado granodiorite, and ages of 2,130??7 Ma and 2,128??8 Ma in zircon crystals derived from the Teofila??ndia tonalite. The emplacement age of the syntectonic Ambro??sio dome as indicated by a 2,080??2-Ma xenotime age for a granite dyke probably marks the end of the felsic magmatism. This age shows good agreement with the Ar-Ar plateau age of 2,080??5 Ma obtained in hornblendes from an amphibolite and with a U-Pb SHRIMP age of 2,076??10 Ma in detrital zircon crystals from a quartzite, interpreted as the age of the peak of the metamorphism. The predominance of inherited zircons in the syntectonic Ambro??sio dome suggests that the basement of the supracrustal rocks was composed of Archaean continental crust with components of 2,937??16, 3,111??13 and 3,162??13 Ma. Ar-Ar plateau ages of 2,050??4 Ma and 2,054??2 Ma on hydrothermal muscovite samples from the Fazenda Brasileiro gold deposit are interpreted as minimum ages for gold mineralisation and close to the true age of gold deposition. The Ar-Ar data indicate that the mineralisation must have occurred less than 30 million years after the peak of the metamorphism, or episodically between 2,080 Ma and 2,050 Ma, during uplift and exhumation of the orogen. ?? Springer-Verlag 2006.

Mercury pollution from the artisanal mining in Yani gold district, Northern Bolivia

NASA Astrophysics Data System (ADS)

Alfonso, Pura; Freixas, Anna; Bascompta, Marc; María Aranibar, Ana; Villegas, Karla; María García-Noguero, Eva; Higueras, Pablo; Cielito Saraiva, Angela

2016-04-01

Artisanal gold mining is the main economic activity in the Yani district, Northern Bolivia. In this area abundant orogenic gold deposits constituted by quartz veins hosted in paleozoic turbiditic series that contain either free gold or associated with pyrite. Gold is recovered in processing plants by gravimetric methods using shaking tables in several communities of this district. Previously, miners ground the mineral in ball mills together with mercury. The present study aims to evaluate the effect of mercury used in the gold recovering process to the environment and human health in the Yani district. The assessment was based on the analysis of human hair, sediments and water from the river nearby the processing plant and drinking water from the fountain that supplies these communities. 47 samples of hair from miners and other people from the Yani and Señor de Mayo communities were obtained in 2014 and 52 samples in 2015. All were analysed to evaluate the mercury exposure in these places. The results from the 2014 sampling show a wide range of Hg concentration in hair, especially in Señor de Mayo, with values up to 136 μg/g THg. However, in 2015 among the 43 residents in Señor de Mayo, 29 (67%) exhibit concentrations higher than 2 μg/g THg, with an average value of 5.36 μg/g THg. On the other hand, in Yani only 40% have concentrations above 2 μg/g THg, with an average value of 2.34 μg/g THg. The content in Hg in most of the hair samples exhibit values above the tolerable limits established by the US Environmental Protection Agency (1 μg/g Hg) and the World Health Organisation (WHO, 2 μg/g Hg). These high Hg concentrations are found not only in miners but also in the other members of the community, in spite of low fish consumption in this area. Part of the hair was analysed before and after cleaning. Usually in the second case the content of Hg is reduced, but still show high Hg levels, then probably the atmosphere is polluted with Hg and population is

Geosphere - Cryosphere Interactions in the Saint Elias orogen, Alaska and Yukon (Invited)

NASA Astrophysics Data System (ADS)

Bruhn, R. L.; Sauber, J. M.; Forster, R. R.; Cotton, M. M.

2009-12-01

North America's largest alpine and piedmont glaciers occur in the Saint Elias orogen, where microplate collision together with the transition from transform faulting to subduction along the North American plate boundary, create extreme topographic relief, unusually high annual precipitation by orographic lift, and crustal displacements induced by both tectonic and glacio-isostatic deformation. Lithosphere-scale structure dominates the spatial pattern of glaciation; the piedmont Bering and Agassiz-Malaspina glaciers lay along deeply eroded troughs where reverse faults rise from the underlying Aleutian megathrust. The alpine Seward and Bagley Ice Valley glaciers flow along an early Tertiary plate boundary that has been reactivated by reverse faulting, and also by dextral shearing at the NW end of the Fairweather transform fault. Folding above a crustal-scale fault ramp near Icy Bay localizes orographic uplift of air masses, creating alpine glaciers that spill off the highlands into large ice falls, and rapidly dissect evolving structure by erosion. The rate and orientation of ice surface velocities, and the location of crevassing and folding partly reflect changes in basal topography of the glaciers caused by differential erosion of strata, and juxtaposition of variably oriented structures across faults. The effects of basal topography on ice flow are investigated using remote sensing measurements and analog models of glacier flow over uneven topography. Deformation of the ice in turn affects englacial hydrology and sub-ice fluvial systems, potentially impacting ice mass balance, on-set of surging, and loci of glacier quakes. The glaciers impact tectonics by localizing uplift and exhumation within the orogen, and modulating tectonic stress fields as ice masses wax and wane. This is particularly evident in crustal seismicity rates at annual to decadal time scales, while stratigraphy of coastal terraces record both earthquake deformation and glacial isostasy over

GOLD PLATING PROCESS

DOEpatents

Seegmiller, R.

1957-08-01

An improved bath is reported for plating gold on other metals. The composition of the plating bath is as follows: Gold cyanide from about 15 to about 50 grams, potassium cyanide from about 70 to about 125 grams, and sulfonated castor oil from about 0.1 to about 10 cc. The gold plate produced from this bath is smooth, semi-hard, and nonporous.

Detrital zircon age and isotopic constraints on the provenance of turbidites from the southernmost part of the Beishan orogen, NW China

NASA Astrophysics Data System (ADS)

Guo, Q. Q.; Chung, S. L.; Lee, H. Y.; Xiao, W.; Hou, Q.; Li, S.

2017-12-01

The Altaids in Central and East Asia is one of the largest accretionary orogenic collages in the world. The Beishan orogen, linked the Tianshan and Xingmeng orogens, occupy a key position to trace the terminal processes of the Altaids. It comprises an assemblage of magmatic arcs and ophiolitic mélanges. The Permian clastic turbidites, situated between the Huaniushan arc and the Shibanshan arc, are the youngest reported deep-marine clasts in the Beishan orogen. They are separated into the Liuyuan turbidites (NT) to the north and the Heishankou turbidites (ST) to the south by the Liuyuan complex. Detrital zircon grains from the NT yielded a wide range, from 254-3111 Ma, with two age clusters at 273 Ma and 424 Ma, indicating they provenance from the Huaniushan arc to the north. Those from the ST yielded ages from 260-2209 Ma, with age clusters at 270 Ma, 295 Ma, 420 Ma and 878 Ma, indicating the provenance from the Shibanshan arc to the south. The youngest three grains from the NT yield a weighted mean age of 260 Ma and those from the ST an age of 255 Ma, indicating an End-Permian maximum depositional age. The Precambrian zircons of the NT have diverse ɛHf(t) values (-12.6 to +10.4), while those of the ST from -6 to -2.6, indicating distinguishing histories of their provenances. The NT have more positive ɛNd(t) values than the ST, suggesting more juvenile or less evolved crustal components in the source. Two contrasting provenances, together with data in the literature, define the latest suture in the Beishan region at 240-250 Ma. The younger peak of U-Pb analysis results of detrital zircons from the northern part of the final suture zone in the southern Altaids is younging eastward from 288 Ma to 247 Ma, which may characterize the closure of the Paleo-Asian Ocean from west to east in about 40 Ma. This identification of the latest suture in the southern Altaids provides new constraints on the Paleo-Asian Ocean - specifically the nature and timing of the end of the

Sand petrology and focused erosion in collision orogens: the Brahmaputra case

NASA Astrophysics Data System (ADS)

Garzanti, Eduardo; Vezzoli, Giovanni; Andò, Sergio; France-Lanord, Christian; Singh, Sunil K.; Foster, Gavin

2004-03-01

The high-relief and tectonically active Himalayan range, characterized by markedly varying climate but relatively homogeneous geology along strike, is a unique natural laboratory in which to investigate several of the factors controlling the composition of orogenic sediments. Coupling of surface and tectonic processes is most evident in the eastern Namche Barwa syntaxis, where the Tsangpo-Siang-Brahmaputra River, draining a large elevated area in south Tibet, plunges down the deepest gorge on Earth. Here composition of river sands changes drastically from lithic to quartzofeldspathic. After confluence with the Lohit River, draining the Transhimalayan-equivalent Mishmi arc batholiths, sediment composition remains remarkably constant across Assam, indicating subordinate contributions from Himalayan tributaries. Independent calculations based on petrographical, mineralogical, and geochemical data indicate that the syntaxis, representing only ∼4% of total basin area, contributes 35±6% to the total Brahmaputra sediment flux, and ∼20% of total detritus reaching the Bay of Bengal. Such huge anomalies in erosion patterns have major effects on composition of orogenic sediments, which are recorded as far as the Bengal Fan. In the Brahmaputra basin, in spite of very fast erosion and detrital evacuation, chemical weathering is not negligible. Sand-sized carbonate grains are dissolved partially in mountain reaches and completely in monsoon-drenched Assam plains, where clinopyroxenes are selectively altered. Plagioclase, instead, is preferentially weathered only in detritus from the Shillong Plateau, which is markedly enriched in microcline. Most difficult to assess is the effect of hydraulic sorting in Bangladesh, where quartz, garnet and epidote tend to be sequestered in the bedload and trapped on the coastal plain, whereas cleavable feldspars and amphiboles are concentrated in the suspended load and eventually deposited in the deep sea. High-resolution petrographic and

Paleozoic tectonics in the eastern part of Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Liu, Yongjiang; Li, Weimin; Feng, Zhiqiang; Neubauer, Franz

2017-04-01

The Central Asian Orogenic Belt (CAOB) is the largest accretionary orogen in the world, which is responsible for considerable Phanerozoic juvenile crustal growth. The NE China and its adjacent areas compose the eastern segment of the CAOB, which is a key area for providing important evidence of the CAOB evolution and understanding the NE Asian tectonics. The eastern segment of the CAOB is composed tectonically of four micro-blocks and four sutures, i.e. Erguna block (EB), Xing'an block (XB), Songliao-Xilinhot block (SXB), Jiamusi block (JB), Xinlin-Xiguitu suture (XXS), Heihe-Hegenshan suture (HHS), Mudanjiang-Yilan suture (MYS) and Solonker-Xar Moron-Changchun-Yanji suture (SXCYS). The EB and XB were amalgamated by westward subduction, oceanic island accretions and final collision in ca. 500 Ma. The XB and SXB were amalgamated by subduction-related Early Paleozoic marginal arc, Late Paleozoic marginal arc and final collision in the late Early Carboniferous to early Late Carboniferous. The JB probably had been attached to the SXB in the Early Paleozoic, but broken apart from the SXB in the Triassic and collided back in the Jurassic. The closure of Paleo-Asian Ocean had experienced a long continue/episodic subduction-accretion processes on margins of the NCC to the south and the SXB to the north from the Early to Late Paleozoic. The final closure happened along the SXCYS, from west Solonker, Sonid Youqi, Kedanshan (Keshenketengqi), Xar Moron River through Songliao Basin via Kailu, Tongliao, Horqin Zuoyizhongqi, Changchun, to the east Panshi, Huadian, Dunhua, Yanji, with a scissors style closure in time from the Late Permian-Early Triassic in the west to the Late Permian-Middle Triassic in the east. The amalgamated blocks should compose a united micro-continent, named as Jiamusi-Mongolia Block (JMB) after Early Carboniferous, which bounded by Mongo-Okhotsk suture to the northwest, Solonker-Xar Moron-Changchun suture to the south and the eastern margin of JB to the

Accessing The Fourth Dimension In Orogenic Reconstruction Using Granitoid Thermobarometry

NASA Astrophysics Data System (ADS)

Alexander, E.; Wielicki, M. M.; Harrison, M.; Lovera, O. M.; DePaolo, D.

2016-12-01

Tectonic models for the Tibetan-Himalayan orogen predict very different crustal thickness histories, providing a possible test of these various hypotheses. However, reconstructing the evolution of the Tibetan-Himalayan crust is a four-dimensional problem. Knowing the 2D distribution of U-Pb zircon dated samples permits insights into changes in magmatic style, but understanding of N-S thickening history requires depth information. In S. Tibet, voluminous granitoids emplaced between 200-20 Ma provides a spatiotemporal window into the tectonic evolution of the Tibetan crust. A thermoisotopic model utilizing systematic N-S ɛNd variations as a crustal thickness proxy indicates that, at the time of collision, the crust beneath the Indus-Tsangpo suture was relatively thin ( 20 km), increasing to >45 km 100 km to the N. Given evidence of little post-50 Ma upper-crustal shortening, the Tibetan crust appears to have reached its present 85 km thickness via 20 km of tectonic accretion, 15 km of juvenile magma input, as well as the underthrusted Indian crust. Since zircon ɛHf correlates well with whole rock ɛNd, using it together with in situ δ18O, Ti-thermometry and trace element analyses, has provided a refined picture of the relative roles of assimilation and recharge in granitoid formation. To understand the spatiotemporal progression of thickening, we utilize two thermobarometers to reconstruct crystallization depths: Al-in-hornblende and Ti-in-quartz. While Al-in-hornblende has been more widely tested on igneous systems, our data show that it may be sensitive to closure effects during high T storage and hydrothermal alteration. In contrast, Ti-in-quartz preserves magmatic Ti signatures, and quartz's exclusive structure and resistance to alteration provides a more robust proxy for emplacement conditions. Using these thermobarometers in conjunction with Ti-in-zircon thermometry can establish emplacement depth of syn-collisional Lhasa block granites providing the missing

Signature of Cenozoic orogenic movements in combustion metamorphic rocks: mineralogy and geochronology (example of the Salair-Kuznetsk Basin transition)

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

Novikov, I.S.; Sokol, E.V.; Travin, A.V.

Cenozoic combustion metamorphic (CM) complexes produced by fossil natural coal fires are widespread at range-basin junctions worldwide. Large-scale fires accompany the initial orogenic phases as fresh coal-bearing strata become drawn into the aeration zone as a result of crustal deformation. In combustion metamorphism, the protolith melts to different degrees either into ferrous basic paralava or in glassy clinker. The melt rocks have a phase composition favorable for Ar-40/Ar-39 dating of ignition coeval with the onset of each episode in Late Cenozoic orogenic events. We suggest an algorithm providing correct Ar-40/Ar-39 age determination of CM rocks followed by well-grounded geological interpretationmore » and test the new approach on melt rocks from the Kuznetsk Coal Basin. Paralava samples were dated by Ar-40/Ar-39 incremental heating and the isotope ratios were corrected for Ca-, Cl-, and K-derived Ar isotopic interferences. The interpretation of age-spectrum results was checked against internal and external criteria. The former were plateau and isochrone ages and the latter included the so-called 'couple criterion' and conventional relative ages inferred from geological and stratigraphic evidence. As a result, we distinguished two groups of dates for combustion metamorphic events bracketed between 1.2 {+-} 0.4 and 0.2 {+-} 0.3 Ma. The older ages represent rocks in the western edge of the Prokopievsk-Kiselevsk block of the Salair zone and the younger dates correspond to those in its eastern edge. The reported dates record the time when the fault boundaries of the blocks were rejuvenated during recent activity and the block accreted to the Salair orogenic area as a submontane step. The suggested approach to the choice of objects, classification of rocks, and interpretation of Ar-40/Ar-39 spectra is universal and can be practiced in any area of combustion metamorphism.« less

A Mesozoic orogenic cycle from post-collision to subduction in the southwestern Korean Peninsula: New structural, geochemical, and chronological evidence

NASA Astrophysics Data System (ADS)

Park, Seung-Ik; Kwon, Sanghoon; Kim, Sung Won; Hong, Paul S.; Santosh, M.

2018-05-01

The Early to Middle Mesozoic basins, distributed sporadically over the Korean Peninsula, preserve important records of the tectonic history of some of the major orogenic belts in East Asia. Here we present a comprehensive study of the structural, geochemical, geochronological, and paleontological features of a volcano-sedimentary package, belonging to the Oseosan Volcanic Complex of the Early to Middle Mesozoic Chungnam Basin, within the Mesozoic subduction-collision orogen in the southwestern Korean Peninsula. The zircon U-Pb data from rhyolitic volcanic rocks of the complex suggest Early to Middle Jurassic emplacement age of ca. 178-172 Ma, harmonious with plant fossil taxa found from the overlying tuffaceous sedimentary rock. The geochemical data for the rhyolitic volcanic rocks are indicative of volcanic arc setting, implying that the Chungnam Basin has experienced an intra-arc subsidence during the basin-expanding stage by subduction of the Paleo-Pacific (Izanagi) Plate. The Jurassic arc-related Oseosan Volcanic Complex was structurally stacked by the older Late Triassic to Early Jurassic post-collisional basin-fill of the Nampo Group by the Jangsan fault during basin inversion. The Late Jurassic to Early Cretaceous K-feldspar and illite K-Ar ages marked the timing of inversion tectonics, contemporaneous with the magmatic quiescence in the southern Korean Peninsula, likely due to flat-lying or low-angle subduction. The basin evolution history preserved in the Mesozoic Chungnam Basin reflects a Mesozoic orogenic cycle from post-collision to subduction in the southwestern Korean Peninsula. This, in turn, provides a better understanding of the spatial and temporal changes in Mesozoic tectonic environments along the East Asian continental margin.

Gold Fever! Seattle Outfits the Klondike Gold Rush. Teaching with Historic Places.

ERIC Educational Resources Information Center

Blackburn, Marc K.

This lesson is based on the National Register of Historic Places registration file, "Pioneer Square Historic District," and other sources about Seattle (Washington) and the Klondike Gold Rush. The lesson helps students understand how Seattle exemplified the prosperity of the Klondike Gold Rush after 1897 when news of a gold strike in…

Pan-African granulites of central Dronning Maud Land and Mozambique: A comparison within the East-African-Antarctic orogen

USGS Publications Warehouse

Engvik, A.K.; Elevevold, S.; Jacobs, J.; Tveten, E.; de Azevedo, S.; Njange, F.

2007-01-01

Granulite-facies metamorphism is extensively reported in Late Neoproterozoic/Early Palaeozoic time during formation of the East-African-Antarctic orogen (EAAO). Metamorphic data acquired from the Pan-African orogen of central Dronning Maud Land (cDML) are compared with data from northern Mozambique. The metamorphic rocks of cDML are characterised by Opx±Grt-bearing gneisses and Sil+Kfs-bearing metapelites which indicate medium-P granulite-facies metamorphism. Peak conditions, which are estimated to 800-900ºC at pressures up to 1.0 GPa, were followed by near-isothermal decompression during late Pan-African extension and exhumation. Granulite-facies lithologies are widespread in northern Mozambique, and Grt+Cpx-bearing assemblages show that high-P granulite-facies conditions with PT reaching 1.55 GPa and 900ºC were reached during the Pan-African orogeny. Garnet is replaced by symplectites of Pl+Opx+Mag indicating isothermal decompression, and the subsequent formation of Pl+amphibole-coronas suggests cooling into amphibolite facies. It is concluded that high-T metamorphism was pervasive in EAAO in Late Neoproterozoic/Early Paleozoic time, strongly overprinting evidences of earlier metamorphic assemblages.

Mammalian sensitivity to elemental gold (Au?)

USGS Publications Warehouse

Eisler, R.

2004-01-01

There is increasing documentation of allergic contact dermatitis and other effects from gold jewelry, gold dental restorations, and gold implants. These effects were especially pronounced among females wearing body-piercing gold objects. One estimate of the prevalence of gold allergy worldwide is 13%, as judged by patch tests with monovalent organogold salts. Eczema of the head and neck was the most common response of individuals hypersensitive to gold, and sensitivity can last for at least several years. Ingestion of beverages containing flake gold can result in allergic-type reactions similar to those seen in gold-allergic individuals exposed to gold through dermal contact and other routes. Studies with small laboratory mammals and injected doses of colloidal gold showed increased body temperatures, accumulations in reticular cells, and dose enhancement in tumor therapy; gold implants were associated with tissue injuries. It is proposed that Au? toxicity to mammals is associated, in part, with formation of the more reactive Au+ and Au3+ species.

Basement thrust sheets in the Clearwater orogenic zone, central Idaho and western Montana ( USA).

USGS Publications Warehouse

Skipp, B.

1987-01-01

The Clearwater orogenic zone in central Idaho and W Montana contains at least 2 major NE-directed Cordilleran thrust plates of Early Proterozoic metasedimentary and metaigneous rocks that overrode previously folded Middle Proterozoic rocks of the Belt basin in Cretaceous time. The northeastward migration of the resultant thickened wedge of crustal material combined with Cretaceous subduction along the W continental margin produced a younger N Bitterroot lobe of the Idaho batholith relative to an older S Atlanta lobe. Eocene extensional unroofing and erosion of the Bitterroot lobe has exposed the roots of the thick Cordilleran thrust sheets.-Author

What happens along the flank and corner of a continental indenter? Insights from the easternmost Himalayan orogen and constraints on the models of the India-Asia collision

NASA Astrophysics Data System (ADS)

Haproff, P. J.; Yin, A.; Zuza, A. V.

2017-12-01

Investigations of continental collisions often focus on thrust belts oriented perpendicular to the plate-convergence direction and exclude belts that bound the flanks of a continental indenter despite being crucial to understanding the collisional process. Research of the Himalayan orogen, for example, has mostly centered on the east-trending thrust belt between the eastern and western syntaxes, resulting in inadequate examination of the north-trending Indo-Burma Ranges located along the eastern margin of India. To better understand the development of the entire Himalayan orogenic system, we conducted field mapping across the Northern Indo-Burma Range (NIBR), situated at the intersection of the eastern Himalaya and Indo-Burma Ranges. Our research shows that major lithologic units and thrust faults of the Himalaya extend to the NIBR, suggesting a shared geologic evolution. The structural framework of the NIBR consists of a southwest-directed thrust belt cored by a hinterland-dipping duplex, like the Himalaya. However, the Northern Indo-Burma orogen is distinct based on (1) the absence of the Tethyan Himalayan Sequence and southern Gangdese batholith, (2) the absence of the South Tibetan detachment, (3) crustal shortening greater than 80%, (4) an incredibly narrow orogen width of 7-33 km, (5) exposure of an ophiolitic mélange complex as a klippe, (6) and right-slip shear along the active range-bounding thrust fault. Furthermore, lithospheric deformation along the flank and northeast corner of India is characterized by right-slip transpression partitioned between the thrust belt and right-slip faults. Such a regime is interpreted to accommodate both contraction and clockwise rotation of Tibetan lithosphere around India, consistent with existing continuum deformation and rotation models.

Deformation processes in orogenic wedges: New methods and application to Northwestern Washington State

NASA Astrophysics Data System (ADS)

Thissen, Christopher J.

Permanent deformation records aspects of how material moves through a tectonic environment. The methods required to measure deformation vary based on rock type, deformation process, and the geological question of interest. In this thesis we develop two new methods for measuring permanent deformation in rocks. The first method uses the autocorrelation function to measure the anisotropy present in two-dimensional photomicrographs and three-dimensional X-ray tomograms of rocks. The method returns very precise estimates for the deformation parameters and works best for materials where the deformation is recorded as a shape change of distinct fabric elements, such as grains. Our method also includes error estimates. Image analysis techniques can focus the method on specific fabric elements, such as quartz grains. The second method develops a statistical technique for measuring the symmetry in a distribution of crystal orientations, called a lattice-preferred orientation (LPO). We show that in many cases the symmetry of the LPO directly constrains the symmetry of the deformation, such axial flattening vs. pure shear vs. simple shear. In addition to quantifying the symmetry, the method uses the full crystal orientation to estimate symmetry rather than pole figures. Pole figure symmetry can often be misleading. This method works best for crystal orientations measured in samples deformed by dislocation creep, but otherwise can be used on any mineral without requiring information about slip systems. In Chapter 4 we show how deformation measurements can be used to inform regional tectonic and orogenic models in the Pacific Northwestern United States. A suite of measurements from the Olympic Mountains shows that uplift and deformation of the range is consistent with an orogenic wedge model driven by subduction of the Juan de Fuca plate, and not northward forearc migration of the Oregon block. The deformation measurements also show that deformation within the Olympic Mountains

Gold grade distribution within an epithermal quartz vein system, Kestanelik, NW Turkey: implications for gold exploration

NASA Astrophysics Data System (ADS)

Gulyuz, Nilay; Shipton, Zoe; Gulyuz, Erhan; Lord, Richard; Kaymakci, Nuretdin; Kuscu, İlkay

2017-04-01

Vein-hosted gold deposits contribute a large part to the global gold production. Discovery of these deposits mainly include drilling of hundreds of holes, collecting thousands of soil and rock samples and some geophysical surveys which are expensive and time consuming. Understanding the structures hosting the veins and the variations in gold concentrations within the veins is crucial to constrain a more economic exploration program. The main aim of this study is to investigate the gold grade distribution in the mineralized quartz veins of a well exposed epithermal gold deposit hosted by Paleozoic schist and Eocene quartz-feldspar-hornblende porphyry in Lapseki, NW Turkey. We have constructed 3D architecture of the vein surfaces by mapping their outcrop geometries using a highly sensitive Trimble GPS, collecting detailed field data, well-logs and geochemistry data from 396 drill holes (255 diamond cut and 141 reverse circulation holes). Modelling was performed in MOVE Structural Modelling and Analysis software granted by Midland Valley's Academic Software Initiative, and GIS application softwares Global Mapper and Esri-ArcGIS. We envisaged that while fluid entering the conduit ascents, a sudden thickness increase in the conduit would lead to a drop in the fluid pressure causing boiling (the most dominant gold precipitation mechanism) and associated gold precipitation. Regression analysis was performed between the orthogonal thickness values and gold grades of each vein, and statistical analyses were performed to see if the gold is concentrated at specific structural positions along dip. Gold grades in the alteration zones were compared to those in the adjacent veins to understand the degree of mineralization in alteration zones. A possible correlation was also examined between the host rock type and the gold grades in the veins. These studies indicated that gold grades are elevated in the adjacent alteration zones where high gold grades exist in the veins. Schist

Mineral resource of the month: gold

USGS Publications Warehouse

George, Micheal W.

2009-01-01

The article presents information on the valuable mineral called gold. It states that early civilizations valued gold because of its scarcity, durability and characteristics yellow color. By the late 20th century, gold was used as an industrial metal because of its unique physicochemical properties. The U.S. has several productive deposits of gold, including placer, gold-quartz lode, epithermal and Carlin-type gold deposits.

Occurrences of dendritic gold at the McLaughlin Mine hot-spring gold deposit

NASA Astrophysics Data System (ADS)

Sherlock, R. L.; Lehrman, N. J.

1995-06-01

Two styles of gold dendrites are variably developed at the McLaughlin Mine. The most abundant occurrence is hosted by amber-coloured hydrocarbon-rich opal. Silica likely precipitated from a boiling hydrothermal fluid and complexed with immiscible hydrocarbons forming an amorphous hydrocarbon-silica phase. This phase likely scavenged particulate gold by electrostatic attraction to the hydrocarbon-silica phase. The dendritic nature of the gold is secondary and is the result of dewatering of the amorphous hydrocarbon-silica phase and crystallization of gold into syneresis fractures. The second style of dendritic gold is hosted within vein swarms that focused large volumes of fluid flow. The dendrites occur along with hydrocarbon-rich silica at the upper contact of the vein margins which isolated the dendrites allowing sufficient time for them to grow. In a manner similar to the amber-coloured opal, the dendrites may have formed by scavenging particulate gold by electrostatic attraction to the hydrocarbon-silica phase.

Modeling of gold production in Malaysia

NASA Astrophysics Data System (ADS)

Muda, Nora; Ainuddeen, Nasihah Rasyiqah; Ismail, Hamizun; Umor, Mohd Rozi

2013-04-01

This study was conducted to identify the main factors that contribute to the gold production and hence determine the factors that affect to the development of the mining industry in Malaysia. An econometric approach was used by performing the cointegration analysis among the factors to determine the existence of long term relationship between the gold prices, the number of gold mines, the number of workers in gold mines and the gold production. The study continued with the Granger analysis to determine the relationship between factors and gold production. Results have found that there are long term relationship between price, gold production and number of employees. Granger causality analysis shows that there is only one way relationship between the number of employees with gold production in Malaysia and the number of gold mines in Malaysia.

Late Paleozoic closure of the Ob-Zaisan Ocean along the Irtysh/Chara shear zone and implications for arc amalgamation and oroclinal bending in the western Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Li, Pengfei; Sun, Min; Rosenbaum, Gideon

2016-04-01

The Irtysh/Chara Shear Zone is one of the largest strike-slip systems in the Central Asian Orogenic Belt (CAOB). It records collisional processes of the peri-Siberian orogenic system with the West Junggar-Kazakhstan-Tianshan orogenic system following the closure of the Ob-Zaisan Ocean, but the exact timing of these events remains enigmatic. We conducted detailed structural analysis along the Irtysh Shear Zone (NW China), which together with new geochronological data allows us to reconstruct the tectonic evolution during the final closure of the Ob-Zaisan Ocean. Our results showed that subduction-accretion processes lasted at least until the Late Carboniferous in the Chinese Altai and the East/West Junggar. The subsequent arc amalgamation is characterized by a cycle of crustal thickening, orogenic collapse and transpressional thickening. On a larger scale, the West Junggar- Kazakhstan -Tianshan orogenic system defines a U-shape oroclinal structure (e.g. Xiao et al., 2010). A major phase of oroclinal bending that involved ~110° rotation may have occurred during the Late Devonian to Early Carboniferous (Levashova et al., 2012). Previous authors have linked oroclinal bending with the late Paleozoic amalgamation of the western CAOB, and proposed that a quasi-linear West Junggar- Kazakhstan -Tianshan orogenic system was buckled during the convergence of the Siberian and Tarim cratons following the closure of the Ob-Zaisan Ocean (in the north) and the South Tianshan Ocean (in the south) (e.g. Abrajevitch et al., 2008). This model, however, is not supported by our new data that constrain the closure of the Ob-Zaisan Ocean to the Late Carboniferous. Alternatively, we propose that oroclinal bending may have involved two phases of bending, with the ~110° rotation in the Late Devonian to Early Carboniferous possibly associated with trench retreat. Further tightening may have occurred in response to the convergence of the Siberian and Tarim cratons during the Late

A Non-Diazo Approach to α-Oxo Gold Carbenes via Gold-Catalyzed Alkyne Oxidation

PubMed Central

2015-01-01

For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, α-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C–H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds are the principle and most reliable strategy to access them. Unfortunately, the substrates contain a highly energetic diazo moiety and are potentially explosive. Moreover, chemists need to use energetic reagents to prepare them, putting further constrains on operational safety. In this Account, we show that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate α-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous α-diazo carbonyl compounds as precursors in the realm of gold carbene chemistry. For the past several years, we have demonstrated that alkynes can indeed effectively serve as precursors to versatile α-oxo gold carbenes. In our initial study, we showed that a tethered sulfoxide can be a suitable oxidant, which in some cases leads to the formation of α-oxo gold carbene intermediates. The

A non-diazo approach to α-oxo gold carbenes via gold-catalyzed alkyne oxidation.

PubMed

Zhang, Liming

2014-03-18

For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, α-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C-H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds are the principle and most reliable strategy to access them. Unfortunately, the substrates contain a highly energetic diazo moiety and are potentially explosive. Moreover, chemists need to use energetic reagents to prepare them, putting further constrains on operational safety. In this Account, we show that the unique access to the gold carbene species in homogeneous gold catalysis offers an opportunity to generate α-oxo gold carbenes if both nucleophile and electrophile are oxygen. Hence, this approach would enable readily available and safer alkynes to replace hazardous α-diazo carbonyl compounds as precursors in the realm of gold carbene chemistry. For the past several years, we have demonstrated that alkynes can indeed effectively serve as precursors to versatile α-oxo gold carbenes. In our initial study, we showed that a tethered sulfoxide can be a suitable oxidant, which in some cases leads to the formation of α-oxo gold carbene intermediates. The

Constraining a Precambrian Wilson Cycle lifespan: An example from the ca. 1.8 Ga Nagssugtoqidian Orogen, Southeastern Greenland

NASA Astrophysics Data System (ADS)

Nicoli, Gautier; Thomassot, Emilie; Schannor, Mathias; Vezinet, Adrien; Jovovic, Ivan

2018-01-01

In the Phanerozoic, plate tectonic processes involve the fragmentation of the continental mass, extension and spreading of oceanic domains, subduction of the oceanic lithosphere and lateral shortening that culminate with continental collision (i.e. Wilson cycle). Unlike modern orogenic settings and despite the collection of evidence in the geological record, we lack information to identify such a sequence of events in the Precambrian. This is why it is particularly difficult to track plate tectonics back to 2.0 Ga and beyond. In this study, we aim to show that a multidisciplinary approach on a selected set of samples from a given orogeny can be used to place constraints on crustal evolution within a P-T-t-d-X space. We combine field geology, petrological observations, thermodynamic modelling (Theriak-Domino) and radiogenic (U-Pb, Lu-Hf) and stable isotopes (δ18O) to quantify the duration of the different steps of a Wilson cycle. For the purpose of this study, we focus on the Proterozoic Nagssugtoqidian Orogenic Belt (NOB), in the Tasiilaq area, South-East Greenland. Our study reveals that the Nagssugtoqidian Orogen was the result of a complete three stages juvenile crust production (Xjuv) - recycling/reworking sequence: (I) During the 2.60-2.95 Ga period, the Neoarchean Skjoldungen Orogen remobilised basement lithologies formed at TDM 2.91 Ga with progressive increase of the discharge of reworked material (Xjuv from 75% to 50%; δ18O: 4-8.5‰). (II) After a period of crustal stabilization (2.35-2.60 Ga), discrete juvenile material inputs (δ18O: 5-6‰) at TDM 2.35 Ga argue for the formation of an oceanic lithosphere and seafloor spreading over a period of 0.2 Ga (Xjuv from < 25% to 70%). Lateral shortening is set to have started at ca. 2.05 Ga with the accretion of volcanic/magmatic arcs (i.e. Ammassalik Intrusive Complex) and by subduction of small oceanic domains (M1: 520 ± 60 °C at 6.6 ± 1.4 kbar). (III) Continental collision between the North Atlantic

Surface-stabilized gold nanocatalysts

DOEpatents

Dai, Sheng [Knoxville, TN; Yan, Wenfu [Oak Ridge, TN

2009-12-08

A surface-stabilized gold nanocatalyst includes a solid support having stabilizing surfaces for supporting gold nanoparticles, and a plurality of gold nanoparticles having an average particle size of less than 8 nm disposed on the stabilizing surfaces. The surface-stabilized gold nanocatalyst provides enhanced stability, such as at high temperature under oxygen containing environments. In one embodiment, the solid support is a multi-layer support comprising at least a first layer having a second layer providing the stabilizing surfaces disposed thereon, the first and second layer being chemically distinct.

Integrating a high-force optical trap with gold nanoposts and a robust gold-DNA bond.

PubMed

Paik, D Hern; Seol, Yeonee; Halsey, Wayne A; Perkins, Thomas T

2009-08-01

Gold-thiol chemistry is widely used in nanotechnology but has not been exploited in optical-trapping experiments due to laser-induced ablation of gold. We circumvented this problem by using an array of gold nanoposts (r = 50-250 nm, h approximately 20 nm) that allowed for quantitative optical-trapping assays without direct irradiation of the gold. DNA was covalently attached to the gold via dithiol phosphoramidite (DTPA). By using three DTPAs, the gold-DNA bond was not cleaved in the presence of excess thiolated compounds. This chemical robustness allowed us to reduce nonspecific sticking by passivating the unreacted gold with methoxy-(polyethylene glycol)-thiol. We routinely achieved single beads anchored to the nanoposts by single DNA molecules. We measured DNA's elasticity and its overstretching transition, demonstrating moderate- and high-force optical-trapping assays using gold-thiol chemistry. Force spectroscopy measurements were consistent with the rupture of the strepavidin-biotin bond between the bead and the DNA. This implied that the DNA remained anchored to the surface due to the strong gold-thiol bond. Consistent with this conclusion, we repeatedly reattached the trapped bead to the same individual DNA molecule. Thus, surface conjugation of biomolecules onto an array of gold nanostructures by chemically and mechanically robust bonds provides a unique way to carry out spatially controlled, repeatable measurements of single molecules.

Lithologic controls on landscape dynamics and aquatic species evolution in post-orogenic mountains

NASA Astrophysics Data System (ADS)

Gallen, Sean F.

2018-07-01

Determining factors that modify Earth's topography is essential for understanding continental mass and nutrient fluxes, and the evolution and diversity of species. Contrary to the paradigm of slow, steady topographic decay after orogenesis ceases, nearly all ancient mountain belts exhibit evidence of unsteady landscape evolution at large spatial scales. External forcing from uplift from dynamic mantle processes or climate change is commonly invoked to explain the unexpected dynamics of dead orogens, yet direct evidence supporting such inferences is generally lacking. Here I use quantitative analysis of fluvial topography in the southern Appalachian Mountains to show that the exhumation of rocks of variable erosional resistance exerts a fundamental, autogenic control on the evolution of post-orogenic landscapes that continually reshapes river networks. I characterize the spatial pattern of erodibility associated with individual rock-types, and use inverse modeling of river profiles to document a ∼150 m base level fall event at 9 ± 3 Ma in the Upper Tennessee drainage basin. This analysis, combined with existing geological and biological data, demonstrates that base level fall was triggered by capture of the Upper Tennessee River basin by the Lower Tennessee River basin in the Late Miocene. I demonstrate that rock-type triggered changes in river network topology gave rise to the modern Tennessee River system and enhanced erosion rates, changed sediment flux and dispersal patterns, and altered bio-evolutionary pathways in the southeastern U.S.A., a biodiversity hotspot. These findings suggest that variability observed in the stratigraphic, geomorphic, and biologic archives of tectonically quiescent regions does not require external drivers, such as geodynamic or climate forcing, as is typically the interpretation. Rather, my findings lead to a new model of inherently unsteady evolution of ancient mountain landscapes due to the geologic legacy of plate tectonics.

Getting the Gold Treatment

NASA Technical Reports Server (NTRS)

2002-01-01

Epner Technology, Inc., worked with Goddard Space Center to apply gold coating to the Vegetation Canopy Lidar (VCL) mirror. This partnership resulted in new commercial applications for Epner's LaserGold(R) process in the automotive industry. Previously, the company did not have equipment large enough to handle the plating of the stainless steel panels cost effectively. Seeing a chance to renew this effort, Epner Technology and Goddard entered into an agreement by which NASA would fund the facility needed to do the gold-plating, and Epner Technology would cover all other costs as part of their internal research and development. The VCL mirror project proceeded successfully, fulfilling Goddard's needs and leaving Epner Technology with a new facility to provide LaserGold for the automotive industry. The new capability means increased power savings and improvements in both quality and production time for BMW Manufacturing Corporation of Spartanburg, South Carolina, and Cadillac of Detroit, Michigan, as well as other manufacturers who have implemented Epner Technology's LaserGold process. LaserGold(R) is a registered trademark of Epner Technology, Inc.

A porphyrin complex of Gold(I): (Phosphine)gold(I) azides as cation precursors

PubMed Central

Partyka, David V.; Robilotto, Thomas J.; Zeller, Matthias; Hunter, Allen D.; Gray, Thomas G.

2008-01-01

A silver- and Brönsted acid-free protocol for generating the (tricyclohexylphosphine)gold(I) cation from the corresponding azide complexes is disclosed. The gold(I) cations so liberated are trapped by complexation with octaethylporphyrin. The first structurally authenticated gold(I) porphyrin complex crystallizes with formula C72H112Au2F12N4P2Sb2, space group C2/c, a = 21.388 (4), b = 19.679 (4), c = 19.231 (3) Å; β = 111.030 (3)°. Solution spectroscopic studies indicate that the di-gold complex fragments on dissolution in organic solvents. Approximate density-functional theory calculations find an electrostatic origin for the binding of two gold(I) centers to the unprotonated nitrogen atoms, despite greater orbital density on the porphyrin meso carbons. PMID:18780788

A novel 'Gold on Gold' biosensing scheme for an on-fiber immunoassay

NASA Astrophysics Data System (ADS)

Punjabi, N.; Satija, J.; Mukherji, S.

2015-05-01

In this paper, we propose a novel „gold on gold‟ biosensing scheme for absorbance based fiber-optic biosensor. First, a self-assembled monolayer of gold nanoparticles is formed at the sensing region of the fiber-optic probe by incubating an amino-silanized probe in a colloidal gold solution. Thereafter, the receptor moieties, i.e. Human immunoglobulin G (HIgG) were immobilized by using standard alkanethiol and classic carbodiimide coupling chemistry. Finally, biosensing experiments were performed with different concentrations of gold nanoparticle-tagged analyte, i.e. Goat anti- Human immunoglobulin G (Nanogold-GaHIgG). The sensor response was observed to be more than five-fold compared to the control bioassay, in which the sensor matrix was devoid of gold nanoparticle film. Also, the response was found to be ~10 times higher compared to the FITC-tagged scheme and ~14.5 times better compared to untagged scheme. This novel scheme also demonstrated the potential in improving the limit of detection for the fiber-optic biosensors.

Lateral Moho variations and the geometry of Main Himalayan Thrust beneath Nepal Himalayan orogen revealed by teleseismic receiver functions

NASA Astrophysics Data System (ADS)

He, Ping; Lei, Jianshe; Yuan, Xiaohui; Xu, Xiwei; Xu, Qiang; Liu, Zhikun; Mi, Qi; Zhou, Lianqing

2018-05-01

The lateral Moho variations and the geometry of the Main Himalayan Thrust under the Nepal Himalayan orogen are investigated to determine a new crustal model using a large number of high-quality receiver functions recorded by the HIMNT and HiCLIMB portable seismic networks. Our new model shows an evident and complicated lateral Moho depth variation of 8-16 km in the east-west direction, which is related to the surface tectonic features. These results suggest a non-uniformed crustal deformation, resulted from the splitting and/or tearing of the Indian plate during the northward subduction. Our migrated receiver function images illustrate a discernible ramp structure of the Main Himalayan Thrust with an abrupt downward bending close to the hypocenter of the 2015 Gorkha Mw 7.8 earthquake. The distribution of the aftershocks coincides with the present decollement structure. Integrating previous magnetotelluric soundings and tomographic results, our results suggest that the ramp-shaped structure within the Main Himalayan Thrust could enhance stress concentration leading to the nucleation of the large earthquake. Our new crustal model provides new clues to the formation of the Himalayan orogen.

Crustal recycling through intraplate magmatism: Evidence from the Trans-North China Orogen

NASA Astrophysics Data System (ADS)

He, Xiao-Fang; Santosh, M.

2014-12-01

The North China Craton (NCC) preserves the history of crustal growth and craton formation during the early Precambrian followed by extensive lithospheric thinning and craton destruction in the Mesozoic. Here we present evidence for magma mixing and mingling associated with the Mesozoic tectonic processes from the Central NCC, along the Trans-North China Orogen, a paleo suture along which the Eastern and Western Blocks were amalgamated at end of Paleoproterozoic. Our investigations focus on two granitoids - the Chiwawu and the Mapeng plutons. Typical signatures for the interaction of mafic and felsic magmas are observed in these plutons such as: (1) the presence of diorite enclaves; (2) flow structures; (3) schlierens; (4) varying degrees of hybridization; and (5) macro-, and micro-textures. Porphyritic feldspar crystals show numerous mineral inclusions as well as rapakivi and anti-rapakivi textures. We present bulk chemistry, zircon U-Pb geochronology and REE data, and Lu-Hf isotopes on the granitoids, diorite enclaves, and surrounding basement rocks to constrain the timing of intraplate magmatism and processes of interaction between felsic and mafic magmas. Our LA-ICP-MS zircon U-Pb data show that the pophyritic granodiorite was emplaced at 129.7 ± 1.0 Ma. The diorite enclaves within this granodiorite show identical ages (128.2 ± 1.5 Ma). The basement TTG (tonalite-trondhjemite-granodiorite) gneisses formed at ca. 2.5 Ga coinciding with the major period of crustal accretion in the NCC. The 1.85 Ga age from zircons in the gabbro with positive Hf isotope signature may be related to mantle magmatism during post-collisional extension following the assembly of the Western and Eastern Blocks of the NCC along the Trans-North China Orogen. Our Hf isotope data indicate that the Neoarchean-Paleoproterozoic basement rocks were derived from complex sources of both juvenile magmas and reworked ancient crust, whereas the magma source for the Mesozoic units are dominantly

Petrogenesis of granitoids and associated xenoliths in the early Paleozoic Baoxu and Enping plutons, South China: Implications for the evolution of the Wuyi-Yunkai intracontinental orogen

NASA Astrophysics Data System (ADS)

Yu, Yang; Huang, Xiao-Long; Sun, Min; He, Peng-Li

2018-05-01

The early Paleozoic Wuyi-Yunkai orogen was associated with extensive felsic magmatic activities and the orogenic core was mainly distributed in the Yunkai and Wugong domains located in the western Cathaysia block and in the Wuyi domain located in the central part of the Cathaysia block. In order to investigate the evolution of the Wuyi-Yunkai orogen, elemental and Sr-Nd isotopic analyses were performed for granites from the Baoxu pluton in the Yunkai domain and from the Enping pluton in the central part of the Cathaysia block. The Baoxu pluton consists of biotite granite with abundant xenoliths of gneissic granite, granodiorite and diorite, and the Enping pluton is mainly composed of massive granodiorite. Biotite granites (441 ± 5 Ma) and gneissic granite xenolith (443 ± 4 Ma) of the Baoxu pluton are all weakly peraluminous (A/CNK = 1.05-1.10). They show high Sr/Y and La/Yb ratios and have negative bulk-rock εNd(t) values (-7.0 to -4.4), which are similar to coeval gneissic S-type granites in the Yunkai domain and were probably derived from dehydration melting of a sedimentary source with garnet residue in the source. Granodiorites (429 ± 3 Ma) from Enping and granodiorite xenolith (442 ± 4 Ma) from Baoxu are metaluminous and have REE patterns with enriched light REE and flat middle to heavy REE, possibly generated by the dehydration melting of an igneous basement at middle to lower crustal level. Diorite xenolith from Baoxu is ultrapotassic (K2O = 4.9 wt%), has high contents of MgO (7.0 wt%), Cr (379 ppm) and Ni (171 ppm) and shows pronounced negative Nb, Ta and Ti anomalies. This xenolith also has negative εNd(t) value (-3.6) and low Rb/Ba and high Ba/Sr ratios, and is thus interpreted to be derived from an enriched lithospheric mantle with the breakdown of phlogopite. Early Paleozoic I- and S-type granites in the Wuyi-Yunkai orogen mostly have negative εNd(t) values and do not have juvenile components, consistent with genesis by an intracontinental

Analysis of gold(I/III)-complexes by HPLC-ICP-MS demonstrates gold(III) stability in surface waters.

PubMed

Ta, Christine; Reith, Frank; Brugger, Joël; Pring, Allan; Lenehan, Claire E

2014-05-20

Understanding the form in which gold is transported in surface- and groundwaters underpins our understanding of gold dispersion and (bio)geochemical cycling. Yet, to date, there are no direct techniques capable of identifying the oxidation state and complexation of gold in natural waters. We present a reversed phase ion-pairing HPLC-ICP-MS method for the separation and determination of aqueous gold(III)-chloro-hydroxyl, gold(III)-bromo-hydroxyl, gold(I)-thiosulfate, and gold(I)-cyanide complexes. Detection limits for the gold species range from 0.05 to 0.30 μg L(-1). The [Au(CN)2](-) gold cyanide complex was detected in five of six waters from tailings and adjacent monitoring bores of working gold mines. Contrary to thermodynamic predictions, evidence was obtained for the existence of Au(III)-complexes in circumneutral, hypersaline waters of a natural lake overlying a gold deposit in Western Australia. This first direct evidence for the existence and stability of Au(III)-complexes in natural surface waters suggests that Au(III)-complexes may be important for the transport and biogeochemical cycling of gold in surface environments. Overall, these results show that near-μg L(-1) enrichments of Au in environmental waters result from metastable ligands (e.g., CN(-)) as well as kinetically controlled redox processes leading to the stability of highly soluble Au(III)-complexes.

Contrasting zircon morphology and UPb systematics in peralkaline and metaluminous post-orogenic granite complexes of the Arabian Shield, Kingdom of Saudi Arabia

USGS Publications Warehouse

Aleinikof, J.N.; Stoeser, D.B.

1989-01-01

Uzircon ages are reported for seven metaluminous-to-peralkaline post-orogenic granites from the Late Proterozoic Arabian Shield of Saudi Arabia. Zircons from the metaluminous rocks are prismatic, with length-to-width ratios of ??? 2-4: 1 and small pyramidal terminations. In contrast, zircons from three of the four peralkaline complexes either lack well-developed prismatic faces (are pseudo-octahedral) or are anhedral. Some zircons from the peralkaline granites contain inherited radiogenic Pb and have very high common Pb contents (206Pb/204Pb < 150), making the UPb method poorly suited for determining the age of these rocks. Zircons in the metaluminous granites do not contain inheritance and yield well-defined concordia intercepts. The span of ages of the seven complexes (670-470 Ma) indicates that post-orogenic granitic magmatism was not a singular event in the Arabian Shield but rather occurred as multiple intrusive episodes from the Late Proterozoic to the Middle Ordovician. ?? 1989.

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

Structural controls on Carlin-type gold mineralization in the gold bar district, Eureka County, Nevada

USGS Publications Warehouse

Yigit, O.; Nelson, E.P.; Hitzman, M.W.; Hofstra, A.H.

2003-01-01

The Gold Bar district in the southern Roberts Mountains, 48 km northwest of Eureka, Nevada, contains one main deposit (Gold Bar), five satellite deposits, and other resources. Approximately 0.5 Moz of gold have been recovered from a resource of 1,639,000 oz of gold in Carlin-type gold deposits in lower plate, miogeoclinal carbonate rocks below the Roberts Mountains thrust. Host rocks are unit 2 of the Upper Member of the Devonian Denay Formation and the Bartine Member of the McColley Canyon Formation. Spatial and temporal relations between structures and gold mineralization indicate that both pre-Tertiary and Tertiary structures were important controls on gold mineralization. Gold mineralization occurs primarily along high-angle Tertiary normal faults, some of which are reactivated reverse faults of Paleozoic or Mesozoic age. Most deposits are localized at the intersection of northwest- and northeast-striking faults. Alteration includes decalcification, and to a lesser extent, silicification along high-angle faults. Jasperoid (pervasive silicification), which formed along most faults and in some strata-bound zones, accounts for a small portion of the ore in every deposit. In the Gold Canyon deposit, a high-grade jasperoid pipe formed along a Tertiary normal fault which was localized along a zone of overturned fault-propagation folds and thrust faults of Paleozoic or Mesozoic age.

The Neoacadian orogenic core of the souther Appalachians: a Geo-traverse through the migmatitic inner Piedmont from the Brushy Mountains to Lincolnton, North Carolina

USGS Publications Warehouse

Merschat, Arthur J.; Hatcher, Robert D.; Byars, Heather E.; Gilliam, William G.; Eppes, Martha Cary; Bartholomew, Mervin J.

2012-01-01

The Inner Piedmont extends from North Carolina to Alabama and comprises the Neoacadian (360–345 Ma) orogenic core of the southern Appalachian orogen. Bordered to west by the Blue Ridge and the exotic Carolina superterrane to the east, the Inner Piedmont is cored by an extensive region of migmatitic, sillimanite-grade rocks. It is a composite of the peri-Laurentian Tugaloo terrane and mixed Laurentian and peri-Gondwanan affinity Cat Square terrane, which are exposed in several gentle-dipping thrust sheets (nappes). The Cat Square terrane consists of Late Silurian to Early Devonian pelitic schist and metagraywacke intruded by several Devonian to Mississippian peraluminous granitoids, and juxtaposed against the Tugaloo terrane by the Brindle Creek fault. This field trip through the North Carolina Inner Piedmont will examine the lithostratigraphies of the Tugaloo and Cat Square terranes, deformation associated with Brindle Creek fault, Devonian-Mississippian granitoids and charnockite of the Cat Square terrane, pervasive amphibolite-grade Devonian-Mississippian (Neoacadian) deformation and metamorphism throughout the Inner Piedmont, and existence of large crystalline thrust sheets in the Inner Piedmont. Consistent with field observations, geochronology and other data, we have hypothesized that the Carolina superterrane collided obliquely with Laurentia near the Pennsylvania embayment during the Devonian, overrode the Cat Square terrane and Laurentian margin, and squeezed the Inner Piedmont out to the west and southwest as an orogenic channel buttressed against the footwall of the Brevard fault zone.

Gold grade variation and particle microchemistry in exploration pits of the Batouri gold district, SE Cameroon

NASA Astrophysics Data System (ADS)

Vishiti, A.; Suh, C. E.; Lehmann, B.; Egbe, J. A.; Shemang, E. M.

2015-11-01

The Batouri area hosts lode-gold mineralization under several-m-thick lateritic cover. Pitting to bed rock on a geochemical Au anomaly defined from previous reconnaissance soil sampling identified five horizons ranging from saprock at the base to laterite at the top. Analysis of bulk samples from each horizon by fire assay shows that most of the horizons are barren although 119 ppb and 48 ppb Au values were obtained from one laterite horizon and one saprolite horizon, respectively, from two separate pits. All the horizons were panned and particulate gold was also recovered only from these two horizons. The gold grains from both horizons are morphologically and compositionally indistinguishable with rare quartz, pyrite and galena inclusions. The grains have irregular, sub-rounded, bean to elongated shapes and they show a remarkable core-rim zonation. Electron microprobe analysis of the grains recorded high gold content in the rims (86.3-100 wt%) and along fissures within the grains (95.1-100 wt%). The cores are relatively Ag rich (11.8-14 wt% Ag) while the rims (0.63-13.7 wt% Ag, most of the values fall within the lower limit of this range) and fissures (0.03-5.02 wt% Ag) are poor in Ag. The low Ag concentration in the rims and along fissures is attributed to preferential leaching of Ag; a process recognized in gold grains and platiniferous alloys from alluvia. The core composition of the grains is similar to that of primary gold composition in the bedrock. These results show that gold in the soil is relic particulate gold derived from the primary source with no evidence of secondary gold precipitation in the weathering cycle. In all the pits no horizon was systematically enriched in gold suggesting there has been no chemical remobilization of gold in this environment. Rather the dispersion of gold here is in the particulate form. Therefore combining particulate gold features with assay data is relevant to exploration in such tropical environments.

Alterations in nanoparticle protein corona by biological surfactants: impact of bile salts on β-lactoglobulin-coated gold nanoparticles.

PubMed

Winuprasith, Thunnalin; Chantarak, Sirinya; Suphantharika, Manop; He, Lili; McClements, David Julian

2014-07-15

The impact of biological surfactants (bile salts) on the protein (β-lactoglobulin) corona surrounding gold nanoparticles (200 nm) was studied using a variety of analytical techniques at pH 7: dynamic light scattering (DLS); particle electrophoresis (ζ-potential); UV-visible (UV) spectroscopy; transmission electron microscopy (TEM); and surface-enhanced Raman scattering (SERS). The bile salts adsorbed to the protein-coated nanoparticle surfaces and altered their interfacial composition, charge, and structure. SERS spectra of protein-coated nanoparticles after bile salt addition contained bands from both protein and bile salts, indicating that the protein was not fully displaced by the bile salts. UV, DLS and TEM techniques also indicated that the protein coating was not fully displaced from the nanoparticle surfaces. The impact of bile salts could be described by an orogenic mechanism: mixed interfaces were formed that consisted of islands of aggregated proteins surrounded by a sea of bile salts. This knowledge is useful for understanding the interactions of bile salts with protein-coated colloidal particles, which may be important for controlling the fate of colloidal delivery systems in the human gastrointestinal tract, or the gastrointestinal fate of ingested inorganic nanoparticles. Copyright © 2014 Elsevier Inc. All rights reserved.

Thermal stability of supported gold nanoparticles

NASA Astrophysics Data System (ADS)

Turba, Timothy Fredrick

Nanoparticle gold is of interest for a wide array of applications including catalysis, gas sensing, and light absorption for color filters and optical switches. Many of these applications are dependent upon the particles having sizes <5nm. In this paper, the thermal stability of nanoparticle gold is evaluated. Unsupported gold nanoparticles can grow (and in some cases double their size) even at room temperature. An important approach to stabilizing gold nanoparticles is through an interaction with a suitable substrate support material. Semiconductor substrates such as GaN are important supports for gold nanoparticles for applications such as sensors, but GaN does not provide a significant stabilizing effect at high temperatures. This paper covers a number of different substrate materials and in particular shows that for some substrates, such as SiO2, gold nanoparticles can be stable at temperatures up to 500°C, which is significantly above the Tammann temperature for bulk gold (395°C). In this dissertation, gold nanoparticles are shown to have complete stability on aluminum-supported silica nanosprings at 550°C in air. This stability window is one of the highest reported for nanoparticle gold and potentially enables a number of applications for this highly active catalyst. X-ray photoelectron spectroscopy measurements were performed before and after heating to 550°C to determine the nature of the interaction between gold and SiO2. A 1.2 eV drop in gold 4f binding energy after heating signified a shift to anionic gold particles (i.e., Au delta-) indicative of strong bonds to oxygen vacancies with neighboring Sidelta+ atoms. Heating in hydrogen at 550°C resulted in a binding energy decrease of 0.4 eV due to an increased fraction of particles with decreased coordination numbers (i.e., more atoms at edges and corners). Lastly, heating gold nanoparticles in an atmosphere of 10% relative humidity at 550°C resulted in apparent encapsulation of the gold.

Imprints of a Pan-African transpressional orogen superimposed on an inferred Grenvillian accretionary belt in central East Antarctica

NASA Astrophysics Data System (ADS)

Ferraccioli, Fausto; Seddon, Samuel; Finn, Carol; Bell, Robin; Wu, Guochao; Jordan, Tom

2017-04-01

The Gamburtsev Subglacial Mountains in interior East Antarctica are underlain by 50-60 km thick crust imaged by gravity and seismic models (Ferraccioli et al., 2011; An et al., 2015). In contrast, the composite Archean to Mesoproterozoic Mawson craton that occupies the Wilkes and Terre Adelie sector of East Antarctica typically features only 40-45 km thick crust (Aitken et al., 2014). Over 200 km thick and seismically fast lithosphere underlies the Gamburtsev Province, as typically observed over Precambrian lithosphere that has not been substantially reworked during Phanerozoic subduction or collision. Satellite and airborne magnetic data indicate that the Gamburtev Province is sandwiched in between distinct Precambrian lithospheric blocks including the Ruker, Princess Elizabeth Land, Vostok, Nimrod (Goodge and Finn, 2010), South Pole and Recovery provinces. Ferraccioli et al., (2011) proposed that a segment of a stalled orogen (i.e. an orogen where widespread orogenic collapse and root delamination has not occurred) is preserved in the Gamburtsev Province and further hypothesised that its origin relates to widespread accretionary and subsequent collisional events at ca 1 Ga, linked to the assembly of the Rodinia supercontinent. However, recent passive seismic interpretations (An et al., 2015) indicate that crustal thickening may relate instead to Pan-African age assembly of Greater India, East Antarctica and Australia within Gondwana (at ca 550 Ma). Here we interpret a set of enhanced magnetic and gravity images, depth to magnetic and gravity sources and preliminary 2D and 3D forward and inverse models to characterise in detail the crustal architecture of the Gamburtsev Province. Enhanced aeromagnetic images reveal a system of subglacial faults that segment the Gamburtsev Province into three distinct geophysical domains, the northern, central and southern domains. Apparent offsets in high-frequency magnetic anomalies within the central domain are interpreted here

Native gold in Hawaiian alkalic magma

USGS Publications Warehouse

Sisson, T.W.

2003-01-01

Native gold found in fresh basanite glass from the early submarine phase of Kilauea volcano, Hawaii, may be the first documented case of the transport of gold as a distinct precious metal phase in a mantle-derived magma. The gold-bearing glass is a grain in bedded volcanic glass sandstone (Japan Marine Science and Technology Center (JAMSTEC) sample S508-R3) collected by the submersible Shinkai 6500 at 3879 m depth off Kilauea's south flank. Extensive outcrops there expose debris-flow breccias and sandstones containing submarine-erupted alkalic rock fragments and glasses from early Kilauea. Precipitation of an immiscible gold liquid resulted from resorption of magmatic sulfides during crystallization-differentiation, with consequent liberation of sulfide-hosted gold. Elevated whole-rock gold concentrations (to 36 ppb) for fresh lavas and clasts from early Kilauea further show that some magmas erupted at the beginning stages of Hawaiian shield volcanoes were distinctly gold rich, most likely owing to limited residual sulfide in their mantle source. Alkalic magmas at other ocean islands may also be gold rich, and oceanic hot-spot provinces may contain underappreciated gold resources.

Shoshonites and Associated Calc-Alkaline Rocks from the Eastern Sayan, Central Asian Orogenic Belt: Geochemistry and Tectonic Setting

NASA Astrophysics Data System (ADS)

Vernikovskaya, A. E.; Romanov, M. I.; Kadilnikov, P. I.; Matushkin, N. Y.; Romanova, I.

2017-12-01

The Central Asian Orogenic Belt (CAOB) is one of the largest accretionary orogens in the world, which formation started in the Neoproterozoic giving rise to numerous assemblages of island arcs, ophiolites, continental fragments and sedimentary basins. The Eastern Sayan, located at the southwestern margin of the Siberian craton, is the key area in understanding the initiation of orogenic processes in the CAOB. Widely distributed mafic igneous rocks (dolerites, gabbro etc.) in the Eastern Sayan were previously considered as part of the Nersa igneous complex of the Neoproterozoic age, whereas tectonic setting of these rocks remained highly debatable. New geochemical and mineralogical data from igneous mafic rocks within the Eastern Sayan show presence of rocks with shoshonitic and high- and low-K calc-alkaline affinities and allowed us to refine the tectonic context of their formation in the southwestern margin of the Siberian craton.All studied intrusive and volcanic rocks in the Eastern Sayan showing OIB-like geochemical signatures. The high-K rocks contain orthoclase, olivine, diopside, augite, anorthite, various amphiboles, including edenite, cataphorite, Mg-cataphorite, anthophyllite-gedrite, Mg-Fe hornblende, biotites of the siderophyllite-eastonite-annite series, as well as zircon, baddeleyite, apatite, magnetite, ilmenite and Cr-spinel. The high-K rock type is characterised by high K2O contents (up to 9.2 wt. %), K2O/Na2O ratios over 90, lowered TiO2 and MgO and moderate FeO contents and negative P and Sr anomalies. In contrast, low-K rocks, characterised by moderate and increased TiO2 and MgO contents, contain augite, pigeonite, olivine, andesine and accessory minerals, such as rutile, titanite, ilmenite and apatite. Both rock types vary considerably in Nb and Ta concentrations, from OIB-like to E-MORB. Such geochemical signatures of calc-alkaline and shoshonitic igneous rocks are indicative of an active continental margin setting. Presence of the active

Detailed energy distributions in laser-produced plasmas of solid gold and foam gold planar targets

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

Dong, Yunsong; Department of Engineering Physics, Tsinghua University, Beijing 100084; Zhang, Lu

Foam gold was proposed to increase the laser to x-ray conversion efficiency due to its important applications. To understand the mechanism of x-ray enhancement, the detailed energy distributions and plasma profiles for laser-irradiated solid gold and foam gold targets were studied comparatively by hydrodynamic simulations using the code Multi-1D. It is confirmed that the radiation heat wave is subsonic for the normal solid gold target, while supersonic for the foam gold target. The shock wave, which is behind the supersonic radiation heat wave for the foam gold target, generates a plasma temperature gradient with high temperature near the shock wavemore » front to produce an additional net outward radiation for enhancement of the x-ray emission. Much larger inward plasma velocity is also driven by the shock wave as an initial plasma velocity for the laser deposition and electron thermal conduct zone, which decreases the expanding plasma kinetic energy loss and helps to increase the x-ray radiation.« less

41 CFR 101-45.002 - Gold.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 41 Public Contracts and Property Management 2 2014-07-01 2012-07-01 true Gold. 101-45.002 Section... PERSONAL PROPERTY § 101-45.002 Gold. (a) Gold will be sold in accordance with this section and part 102-38 of the Federal Management Regulation. (b) Sales of gold shall be processed to— (1) Use the sealed bid...

41 CFR 101-45.002 - Gold.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 41 Public Contracts and Property Management 2 2012-07-01 2012-07-01 false Gold. 101-45.002 Section... PERSONAL PROPERTY § 101-45.002 Gold. (a) Gold will be sold in accordance with this section and part 102-38 of the Federal Management Regulation. (b) Sales of gold shall be processed to— (1) Use the sealed bid...

41 CFR 101-45.002 - Gold.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 41 Public Contracts and Property Management 2 2011-07-01 2007-07-01 true Gold. 101-45.002 Section... PERSONAL PROPERTY § 101-45.002 Gold. (a) Gold will be sold in accordance with this section and part 102-38 of the Federal Management Regulation. (b) Sales of gold shall be processed to— (1) Use the sealed bid...

41 CFR 101-45.002 - Gold.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 41 Public Contracts and Property Management 2 2013-07-01 2012-07-01 true Gold. 101-45.002 Section... PERSONAL PROPERTY § 101-45.002 Gold. (a) Gold will be sold in accordance with this section and part 102-38 of the Federal Management Regulation. (b) Sales of gold shall be processed to— (1) Use the sealed bid...

41 CFR 101-45.002 - Gold.

Code of Federal Regulations, 2010 CFR

2010-07-01

... 41 Public Contracts and Property Management 2 2010-07-01 2010-07-01 true Gold. 101-45.002 Section... PERSONAL PROPERTY § 101-45.002 Gold. (a) Gold will be sold in accordance with this section and part 102-38 of the Federal Management Regulation. (b) Sales of gold shall be processed to— (1) Use the sealed bid...

Crustal structure of the Dabie orogenic belt (eastern China) inferred from gravity and magnetic data

NASA Astrophysics Data System (ADS)

Yang, Yu-shan; Li, Yuan-yuan

2018-01-01

In order to better characterize the crustal structure of the Dabie orogen and its tectonic history, we present a crustal structure along a 500 km long profile across the Dabie orogenic belt using various data processing and interpretation of the gravity and magnetic data. Source depth estimations from the spectral analysis by continuous wavelet transform (CWT) provide better constraints for constructing the initial density model. The calculated gravity effects from the initial model show great discrepancy with the observed data, especially at the center of the profile. More practical factors are then incorporated into the gravity modeling. First, we add a high density body right beneath the high pressure metamorphic (HPM) and ultrahigh pressure metamorphic (UHPM) belt considering the exposed HPM and UHPM rocks in the mid of our profile. Then, the anomalous bodies A, B, and C inferred from the CWT-based spectral analysis results are fixed in the model geometry. In the final crustal density structure, two anomalous bodies B and C with high density and low magnetization could possibly be attributed to metasomatised mantle materials by SiO2-rich melt derived from the foundering subducted mafic lower crust. Under the extensional environment in the early Cretaceous, the upwelling metasomatised mantle was partially melted to produce the parental magma of the post-collisional mafic-ultramafic intrusive rocks. As for the low density body A with strong magnetization located in the lower crust right beneath the HP and UHP metamorphic belt, it is more likely to be composed of serpentinized mantle peridotite (SMP). This serpentinized mantle peridotite body (SMPB) represents the emplacement of mantle-derived peridotites in the crust, accompanying the exhumation of the UHP metamorphic rocks.

Gold metal liquid-like droplets.

PubMed

Smirnov, Evgeny; Scanlon, Micheál D; Momotenko, Dmitry; Vrubel, Heron; Méndez, Manuel A; Brevet, Pierre-Francois; Girault, Hubert H

2014-09-23

Simple methods to self-assemble coatings and films encompassing nanoparticles are highly desirable in many practical scenarios, yet scarcely any examples of simple, robust approaches to coat macroscopic droplets with continuous, thick (multilayer), reflective and stable liquid nanoparticle films exist. Here, we introduce a facile and rapid one-step route to form films of reflective liquid-like gold that encase macroscopic droplets, and we denote these as gold metal liquid-like droplets (MeLLDs). The present approach takes advantage of the inherent self-assembly of gold nanoparticles at liquid-liquid interfaces and the increase in rates of nanoparticle aggregate trapping at the interface during emulsification. The ease of displacement of the stabilizing citrate ligands by appropriate redox active molecules that act as a lubricating molecular glue is key. Specifically, the heterogeneous interaction of citrate stabilized aqueous gold nanoparticles with the lipophilic electron donor tetrathiafulvalene under emulsified conditions produces gold MeLLDs. This methodology relies exclusively on electrochemical reactions, i.e., the oxidation of tetrathiafulvalene to its radical cation by the gold nanoparticle, and electrostatic interactions between the radical cation and nanoparticles. The gold MeLLDs are reversibly deformable upon compression and decompression and kinetically stable for extended periods of time in excess of a year.

Gold Coating

NASA Technical Reports Server (NTRS)

1997-01-01

Epner Technology Inc. responded to a need from Goddard Space Flight Center for the ultimate in electroplated reflectivity needed for the Mars Global Surveyor Mars Orbiter Laser Altimeter (MOLA). Made of beryllium, the MOLA mirror was coated by Epner Technology Laser Gold process, specially improved for the project. Improved Laser Gold- coated reflectors have found use in an epitaxial reactor built for a large semiconductor manufacturer as well as the waveguide in Braun-Thermoscan tympanic thermometer and lasing cavities in various surgical instruments.

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

Biorecovery of gold

USGS Publications Warehouse

Eisler, R.

2003-01-01

Recovery of ionic and metallic gold (Au) from a wide variety of solutions by selected species of bacteria, yeasts, fungi, algae, and higher plants is documented. Gold accumulations were up to 7.0 g/kg dry weight (DW) in various species of bacteria, 25.0 g/kg DW in freshwater algae, 84.0 g/kg DW in peat, and 100.0 g/kg DW in dried fungus mixed with keratinous material. Mechanisms of accumulation include oxidation, dissolution, reduction, leaching, and sorption. Uptake patterns are significantly modified by the physicochemical milieu. Crab exoskeletons accumulate up to 4.9 g Au/kg DW; however, gold accumulations in various tissues of living teleosts, decapod crustaceans, and bivalve molluscs are negligible.

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

Petrogenesis of the Yaochong granite and Mo deposit, Western Dabie orogen, eastern-central China: Constraints from zircon U-Pb and molybdenite Re-Os ages, whole-rock geochemistry and Sr-Nd-Pb-Hf isotopes

NASA Astrophysics Data System (ADS)

Chen, Wei; Xu, Zhaowen; Qiu, Wenhong; Li, Chao; Yu, Yang; Wang, Hao; Su, Yang

2015-05-01

The Dabie orogen is among the most famous continent-continent collisional orogenic belts in the world, and is characterized by intensive post-collisional extension, magmatism and Mo mineralization. However, the genetic links between the mineralization and the geodynamic evolution of the orogen remain unresolved. In this paper, the Yaochong Mo deposit and its associated granitic stocks were investigated to elucidate this issue. Our new zircon U-Pb ages yielded an Early Cretaceous age (133.3 ± 1.3 Ma) for the Yaochong granite, and our molybdenite Re-Os dating gave a similar age (135 ± 1 Ma) for the Mo deposit. The Yaochong stock is characterized by high silica and alkali but low Mg, Fe and Ca. It is enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs: Rb, K, Th and U), but strongly depleted in heavy REEs, and high field strength elements (HFSEs: Nb, Ta, Ti and Y). The Yaochong granite has initial 87Sr/86Sr ratios of 0.7087-0.7096, and Pb isotopic ratios of (206Pb/204Pb)i = 16.599-16.704, (207Pb/204Pb)i = 15.170-15.618 and (208Pb/204Pb)i = 36.376-38.248. The granite has εNd(t) of -18.0 to -16.3 and εHf(t) values of -26.5 to -20.0. All these data indicate that the Yaochong granite is a high-K calc-alkaline fractionated I-type granite, and may have originated from partial melting of the thickened Yangtze continental crust. The Mo ores also show low radiogenic Pb isotopes similar to the Yaochong stock. Medium Re content in molybdenite (21.8-74.8 ppm) also suggests that the ore-forming materials were derived from the thickened lower crust with possibly minor mixing with the mantle. Similar to the Eastern Dabie orogen, the thickened crust beneath the Western Dabie orogen may also have experienced tectonic collapse, which may have exerted fundamental geodynamic controls on the two-stage Mo mineralization in the region.

The Hulan Group: Its role in the evolution of the Central Asian Orogenic Belt of NE China

NASA Astrophysics Data System (ADS)

Wu, Fu-Yuan; Zhao, Guo-Chun; Sun, De-You; Wilde, Simon A.; Yang, Jin-Hui

2007-05-01

The Hulan Group of central Jilin Province, northeastern (NE) China, consists of felsic volcanic and sedimentary rocks that underwent sub-greenschist to amphibolite facies metamorphism and multiple phases of deformation during formation of the Central Asian Orogenic Belt. Young Nd model ages of ˜1100 Ma obtained in this study do not support earlier models that the Hulan Group was either rifted from the North China Craton to the south or from the Jiamusi Block to the north, since both these blocks have much older Nd model ages. Detrital zircon U-Pb ages from a meta-sedimentary rock of the Hulan Group define a maximum age of deposition of 287 ± 6 Ma, not Early Palaeozoic as previously believed. Rb-Sr mineral isochron data indicate that metamorphism of the Hulan Group occurred at ˜250 Ma. This conclusion is further supported by an age of 248 ± 4 Ma for the Dayushan granite, which intruded the Hulan Group. These new isotopic data, together with evaluation of the regional geology, indicate that final oceanic closure in the Chinese segment of the Central Asian Orogenic Belt took place in the Late Permian. The Hulan area is located along the Solonker-Xra Moron-Changchun suture that extends from Inner Mongolia across to central Jilin Province. It is this zone that marks the final ocean closure, resulting in the amalgamation of the North China and Siberian cratons.

The IGY Gold History Preservation Program

NASA Astrophysics Data System (ADS)

Thompson, B. J.; Cliver, E. W.; Gentile, L. C.; Sigsbee, K. M.; Doel, R. E.

2006-05-01

An important part of the 2007 International Year activities will be preserving the history and memory of IGY 1957. The "IGY Gold" History initiative has several goals: 1) identifying and recognizing planners of and participants in the first IGY, 2) preserving memoirs, articles, photographs, and all items of historical significance for the IGY, 3) making these items available to historians, researchers, etc., 4) serving as a contact service for these activities, 5) spreading awareness of the history of geophysics, and 6) planning special events and "reunions." The IGY "Gold" Club identifies participants from the first IGY (gold symbolizing the 50th anniversary). "Gold club" participants will be rewarded with a special "IGY Gold Anniversary" certificate of recognition and a special commemorative "IGY Gold" lapel pin. Many IGY participants from around the globe have received IGY Gold Club awards, and many have submitted valuable historical material about the IGY activities. This is a joint program of the IHY, eGY, IPY, IYPE and IUGG.

The St. Elias orogen as an early stage in the development of indentor corners: Initial results from the STEEP project

NASA Astrophysics Data System (ADS)

Pavlis, T. L.; Bruhn, R. L.; Koons, P.; Berger, A.; Spotila, J.; Barker, A.; Chapman, J.; Doser, D.; Pavlis, G.

2006-12-01

The actively deforming St. Elias orogen of southern Alaska is developed at the transition between the Aleutian trench and the Queen Charlottes transform, and has produced a "one sided" indentor corner as the collided block has been carried obliquely into the subduction-transform transition. A distinctive feature generated within this evolving corner is a 90o bend in the suture at the western edge of the orogen that is associated with a refolding of earlier thin-skinned fold-thrust systems in the collided block. The refolding is recognizable in the area between the bent suture and a major glacial valley, the Bering Glacier, but is absent to the east. Bruhn et al. (2004, GSAB) used this observation to infer an active structure along the Bering Glacier, and speculated that the refolding may be active. New data collected as part of the St. Elias Erosion and tectonics Project (STEEP) provides support for this hypothesis from two observations: 1) clear evidence that many of the hundreds of surface ruptures in this region represent fault-scarps-- probably representing fold-related, bedding- plane slip during refolding; and 2) extremely young (locally <500Ka) U-Th-He apatite cooling ages just west of the Bering Glacier are consistent with the hypothesis of an active structure along the glacial valley. However, young cooling ages to the east of the Bering Glacier as well as geomorphology suggest that at least one of the fold-thrust belt structures is also active, indicating that the interplay of active faults is complex. Additional support for active deformation along the Bering Glacier comes from the spatial distribution of seismicity between the Bering Glacier and Bagley icefield and these observations should be further constrained as data are obtained from the new STEEP broadband seismic network in the area. Analog (sand) and numerical models suggest that this type of feature can originate as the indentor is driven into the corner through a variable vertical axis

The Hatu gold anomaly, Xinjiang-Uygur Autonomous Region, China - testing the hypothesis of aeolian transport of gold

USGS Publications Warehouse

Smith, D.B.; Theobald, P.K.; Shiquan, S.; Tianxiang, R.; Zhihui, H.

1993-01-01

In 1987, a cooperative project between the U.S. Geological Survey and the Institute of Geophysical and Geochemical Exploration was initiated to evaluate the origin of the Hatu gold anomaly. The anomaly is located in the Hatu mining district in the northwest corner of Xinjiang-Uygur Autonomous Region in northwest China. The climate is semiarid to arid and wind erosion predominates. A regional soil survey of the Hatu district, based on samples collected on a 200 by 500 m grid and composited prior to chemical analysis to a density of one sample per square km, delineated a series of south-southeast-trending Au anomalies. Anomalous Au values range from 5 ppb to more than 700 ppb. The Hatu anomaly, the most prominent of these anomalies, is more than 30 km long and about 5 km wide. The mining town of Hatu and the economic gold deposits of Qiqu 1 and Qiqu 2 are at the northern end of this anomaly. The axis of the Hatu anomaly cuts across mapped structure and stratigraphy in the district, but is parallel to the prevailing wind direction. This observation led to the hypothesis that the Hatu anomaly is the result of acolian dispersion of gold from the vicinity of Qiqu 1 and Qiqu 2. The alternative interpretation, that the anomalies reflected additional primary gold occurrences, was not consistent with existing information on the known occurrences and the geology. The investigation led to the identification of three types of gold in heavy-mineral concentrates derived from stream sediments that were collected along the axis of the Hatu anomaly: (1) free gold, (2) gold in pyrite, and (3) gold included in quartz. Gold in quartz was only observed within 2 km of Qiqu 1. The size of the gold particles and the number of gold particles in these samples did not decrease with distance from Qiqu 1 as would be expected from aeolian or fluvial dispersion from a point source. Instead, both the size and amount of gold increased significantly at a distance of 3.5 km from Qiqu 1 and this

The extractive metallurgy of gold

NASA Astrophysics Data System (ADS)

Kongolo, K.; Mwema, M. D.

1998-12-01

Mössbauer spectroscopy has been successfully used in investigation of the gold compounds present in ores and the gold species which occur during the process metallurgy of this metal. This paper is a survey of the basic recovery methods and techniques used in extractive metallurgy of gold. Process fundamentals on mineral processing, ore leaching, zinc dust cementation, adsorption on activated carbon, electrowinning and refining are examined. The recovery of gold as a by-product of the copper industry is also described. Alternative processing methods are indicated in order to shed light on new interesting research topics where Mössbauer spectroscopy could be applied.

Structural, mineralogical and geochemical constraints on the atypical komatiite-hosted Turret deposit in the Agnew-Mt. White district, Western Australia

NASA Astrophysics Data System (ADS)

Voute, F.; Thébaud, N.

2015-08-01

In the Norseman-Wiluna belt, Yilgarn Craton, the Agnew-Mt. White district is the host of many gold deposits. Located in the hinge of the regional Lawlers anticline, the Turret gold deposit is structurally controlled by the Table Hill shear zone that transects the Agnew Ultramafic unit. Geochemistry, coupled with petrographic data, allowed the delineation of the paragenetic sequence associated with gold mineralisation and include (1) a pervasive talc-carbonate alteration assemblage, (2) a pre-mineralisation stage associated with pervasive arsenopyrite + chalcopyrite + pyrrhotite + pyrite alteration, followed by (3) a late deformation event along a dilatational segment of the main Table Hill shear zone, leading to the formation of a breccia hosting a Cu-Bi-Mo-Au (± Ag ± Zn ± Te ± W) metal assemblage. The presence of Au-Ag-Cu alloys, native bismuth, chalcopyrite and other Bi-Te-S phases in the mineralisation stage suggest that gold may have been scavenged from the hydrothermal fluids by composite Bi-Te-Cu-Au-Ag-S liquids or melts. Using this mineral paragenetic sequence, together with mineralogical re-equilibration textures observed, we show that the gold deposition at Turret occurred over a temperature range approximately between c. 350 and 270 °C. This temperature range, together with the structural control and typical mesothermal alteration pattern including carbonate-chlorite alteration, shows that the Turret deposit shares common characteristics with the orogenic gold deposit class. However, the metal association of Cu, Au, Bi, and Mo, the quartz-poor, and high copper-sulphide content (up to 15 %) are characteristics that depart from the typical orogenic gold deposit mineralogy. Through comparison with similar deposits in the Yilgarn Craton and worldwide, we propose that the Turret deposit represents an example of a porphyry-derived Au-Cu-Bi-Mo deposit.

Magma-assisted strain localization in an orogen-parallel transcurrent shear zone of southern Brazil

NASA Astrophysics Data System (ADS)

Tommasi, AndréA.; Vauchez, Alain; Femandes, Luis A. D.; Porcher, Carla C.

1994-04-01

In a lithospheric-scale, orogen-parallel transcurrent shear zone of the Pan-African Dom Feliciano belt of southern Brazil, two successive generations of magmas, an early calc-alkaline and a late peraluminous, have been emplaced during deformation. Microstructures show that these granitoids experienced a progressive deformation from magmatic to solid state under decreasing temperature conditions. Magmatic deformation is indicated by the coexistence of aligned K-feldspar, plagioclase, micas, and/or tourmaline with undeformed quartz. Submagmatic deformation is characterized by strain features, such as fractures, lattice bending, or replacement reactions affecting only the early crystallized phases. High-temperature solid-state deformation is characterized by extensive grain boundary migration in quartz, myrmekitic K-feldspar replacement, and dynamic recrystallization of both K-feldspar and plagioclase. Decreasing temperature during solid-state deformation is inferred from changes in quartz crystallographic fabrics, decrease in grain size of recrystallized feldspars, and lower Ti amount in recrystallized biotites. Final low-temperature deformation is characterized by feldspar replacement by micas. The geochemical evolution of the synkinematic magmatism, from calc-alkaline metaluminous granodiorites with intermediate 87Sr/86Sr initial ratio to peraluminous granites with very high 87Sr/86Sr initial ratio, suggests an early lower crustal source or a mixed mantle/crustal source, followed by a middle to upper crustal source for the melts. Shearing in lithospheric faults may induce partial melting in the lower crust by shear heating in the upper mantle, but, whatever the process initiating partial melting, lithospheric transcurrent shear zones may collect melt at different depths. Because they enhance the vertical permeability of the crust, these zones may then act as heat conductors (by advection), promoting an upward propagation of partial melting in the crust

Nature vs. nurture: gold perpetuates "stemness".

PubMed

Paul, Willi; Sharma, Chandra P; Deb, Kaushik Dilip

2011-01-01

Adult tissues contain quiescent reservoirs of multipotent somatic stem cells and pluripotent embryonic-like stem cells (ELSCs). Credited with regenerative properties gold is used across both -contemporary and -ancient medicines. Here, we show that gold exerted these effects by enhancing the pool of pluripotent ELSC while improving their stemness. We used hESCs as an in-vitro model to understand if gold could enhance self-renewal and pluripotency. Swarna-bhasma (SB), an ancient Indian gold microparticulate (41.1 nm), preparation, reduced spontaneous-differentiation, improved self-renewal, pluripotency and proliferation of hESCs. Colloidal gold-nanoparticles (GNP) (15.59 nm) were tested to confirm that the observations were attributable to nanoparticulate-gold. SB and GNP exposure: maintained -stemness, -karyotypic stability, enhanced pluripotency till day-12, increased average colony-sizes, and reduced the number of autonomously-derived differentiated FGFR1 positive fibroblast-niche-cells/colony. Particulate-gold induced upregulation of FGFR1 and IGF2 expression, and decrease in IGF1 secretion indicates IGF1/2 mediated support for enhanced pluripotency and self-renewal in hESCs.

Juvenile crustal recycling in an accretionary orogen: Insights from contrasting Early Permian granites from central Inner Mongolia, North China

NASA Astrophysics Data System (ADS)

Yuan, Lingling; Zhang, Xiaohui; Xue, Fuhong; Liu, Fulin

2016-11-01

Coeval high-K calc-alkaline to alkaline granites constitute important components of post-collisional to post-orogenic igneous suites in most orogenic belts of various ages on Earth and their genesis harbors a key to ascertaining critical geodynamic controls on continental crustal formation and differentiation. This zircon U-Pb dating and geochemical study documents three contrasting Early Permian granites from Erenhot of central Inner Mongolia, eastern Central Asian Orogenic Belt (CAOB) and reveals concurrent high-K calc-alkaline to alkaline granite association derived from successive partial melting of distinct protoliths. The ca. 280 Ma Gancihuduge (GCG) pluton shows a calc-alkaline I-type character, with initial 87Sr/86Sr ratios of 0.7035 to 0.7039, εNd(t) of + 1.87 to + 4.70, zircon εHf(t) of + 8.0 to + 13.2 and δ18O from 7.4 to 8.7‰. The ca. 276 Ma Cailiwusu (CLS) pluton is magnesian and peraluminous, with initial 87Sr/86Sr ratios of 0.7036 to 0.7040, εNd(t) of + 1.9 to + 2.4, zircon εHf(t) of + 6.5 to + 12.1 and δ18O from 9.7 to 10.9‰. These features are consistent with partial melts of mixed sources composed of newly underplated meta-basaltic to -andesitic protoliths and variable supracrustal components, with distinctively higher proportion of the latter in the CLS pluton. By contrast, the ca. 279 Ma Kunduleng (KDL) suite exhibits an A-type magmatic affinity, with typical enrichment in alkalis, Ga, Zr, Nb and Y, εNd(t) of + 2.39 to + 3.55, zircon εHf(t) from + 8.3 to + 12.3 and δ18O values from 6.8 to 7.5‰. These features suggest that they stem from high-temperature fusion of dehydrated K-rich mafic to intermediate protoliths. Besides presenting a snapshot into a stratified crustal architecture in δ18O, these contrasting granites could not only serve as a temporal marker for monitoring post-collisional extension in the aftermath of a retreating subduction zone, but also present spatial magmatic proxy for tracing crustal formation and

Phanerozoic burial and unroofing history of the western Slave craton and Wopmay orogen from apatite (U-Th)/He thermochronometry

NASA Astrophysics Data System (ADS)

Ault, Alexis K.; Flowers, Rebecca M.; Bowring, Samuel A.

2009-06-01

Low temperature thermochronometry of cratonic regions can illuminate relationships among burial and unroofing patterns, surface subsidence and uplift, and lithosphere-asthenosphere interactions. The Slave craton, initially stabilized by the development of a thick lithospheric mantle root in late Archean time, is an excellent location in which to examine these connections. Although the Slave craton currently lacks Phanerozoic cover, Phanerozoic sedimentary xenoliths entrained in ca. 610 to 45 Ma kimberlites indicate that the region underwent a more dynamic history of burial and unroofing than widely recognized. We report new apatite (U-Th)/He thermochronometry data along a southeast to northwest transect from the interior of the Slave craton into the adjacent Paleoproterozoic Wopmay orogen to resolve the region's depositional and denudational history. Six samples from the western Slave craton and three samples from Wopmay orogen yield mean dates from 296 ± 41 Ma to 212 ± 39 Ma. Individual apatite dates are broadly uniform over a wide span of apatite [eU], and this pattern can be used to more tightly restrict the spectrum of viable temperature-time paths that can explain the dataset. When coupled with geologic and stratigraphic information, temperature-time simulations of the thermochronometry results suggest complete He loss from the apatites at minimum peak temperatures of ~ 88 °C in Devonian-Pennsylvanian time, cooling to near-surface conditions by the Early Cretaceous, followed by reheating to ≤ 72 °C during Cretaceous-Early Tertiary time. Consideration of modern and ancient geotherm constraints implies ≥ 3.3 km of burial during the first Phanerozoic heating phase, with an ancillary phase of reburial in late Mesozoic-Cenozoic time. The uniformity of the apatite (U-Th)/He dates indicates that the rocks encompassed by our > 250 km-long sample transect experienced similar Phanerozoic thermal histories. Despite the distinctly different lithospheric

Lichenoid dermatitis after consumption of gold-containing liquor.

PubMed

Russell, M A; Langley, M; Truett, A P; King, L E; Boyd, A S

1997-05-01

Medicinal gold has a well-known side effect profile that includes mucocutaneous eruptions. We describe three patients with a pruritic dermatitis that began after consumption of a gold-containing alcoholic beverage. Blood and urine gold levels, chemistry panels, hepatitis screens, skin biopsies, and patch tests were performed. The gold-containing liquor was analyzed for the presence and quantity of gold. The liquor consumed by all of the patients was a cinnamon schnapps with free-floating gold-colored flakes. Gold is present in the liquid portion of this liquor and in the solid flakes. Elevated levels of gold in the urine and blood were present in one patient 3 months after last drinking this beverage. Another patient had a positive patch test to gold sodium thiosulfate. All patients experienced improvement of their dermatitis after they stopped drinking the gold-containing liquor.

The geology of the Morro Velho gold deposit in the Archean Rio das Velhas greenstone belt, Quadrilátero Ferrífero, Brazil

USGS Publications Warehouse

Vial, Diogenes Scipioni; DeWitt, Ed; Lobato, Lydia Maria; Thorman, Charles H.

2007-01-01

The Morro Velho gold deposit, Quadrilátero Ferrífero region, Minas Gerais, Brazil, is hosted by rocks at the base of the Archean Rio das Velhas greenstone belt. The deposit occurs within a thick carbonaceous phyllite package, containing intercalations of felsic and intermediate volcaniclastic rocks and dolomites. Considering the temporal and spatial association of the deposit with the Rio das Velhas orogeny, and location in close proximity to a major NNW-trending fault zone, it can be classified as an orogenic gold deposit. Hydrothermal activity was characterized by intense enrichment in alteration zones of carbonates, sulfides, chlorite, white mica±biotite, albite and quartz, as described in other Archean lode-type gold ores. Two types of ore occur in the deposit: dark gray quartz veins and sulfide-rich gold orebodies. The sulfide-rich orebodies range from disseminated concentrations of sulfide minerals to massive sulfide bodies. The sulfide assemblage comprises (by volume), on average, 74% pyrrhotite, 17% arsenopyrite, 8% pyrite and 1% chalcopyrite. The orebodies have a long axis parallel to the local stretching lineation, with continuity down the plunge of fold axis for at least 4.8 km. The group of rocks hosting the Morro Velho gold mineralization is locally referred to as lapa seca. These were isoclinally folded and metamorphosed prior to gold mineralization. The lapa seca and the orebodies it hosts are distributed in five main tight folds related to F1 (the best examples are the X, Main and South orebodies, in level 25), which are disrupted by NE- to E-striking shear zones. Textural features indicate that the sulfide mineralization postdated regional peak metamorphism, and that the massive sulfide ore has subsequently been neither metamorphosed nor deformed. Lead isotope ratios indicate a model age of 2.82 ± 0.05 Ga for both sulfide and gold mineralization. The lapa seca are interpreted as the results of a pre-gold alteration process and may be

Antibody-gold cluster conjugates

DOEpatents

Hainfeld, J.F.

1988-06-28

Antibody- or antibody fragment-gold cluster conjugates are shown wherein the conjugate size can be about 5.0 nm. Methods and reagents are disclosed in which antibodies or Fab' fragments thereof are covalently bound to a stable cluster of gold atoms. 2 figs.

Gold Nanoparticles Cytotoxicity

NASA Astrophysics Data System (ADS)

Mironava, Tatsiana

Over the last two decades gold nanoparticles (AuNPs) have been used for many scientific applications and have attracted attention due to the specific chemical, electronic and optical size dependent properties that make them very promising agents in many fields such as medicine, imagine techniques and electronics. More specifically, biocompatible gold nanoparticles have a huge potential for use as the contrast augmentation agent in X-ray Computed Tomography and Photo Acoustic Tomography for early tumor diagnostic as well these nanoparticles are extensively researched for enhancing the targeted cancer treatment effectiveness such as photo-thermal and radiotherapy. In most biomedical applications biocompatible gold nanoparticles are labeled with specific tumor or other pathology targeting antibodies and used for site specific drug delivery. However, even though gold nanoparticles poses very high level of anti cancer properties, the question of their cytotoxicity ones they are released in normal tissue has to be researched. Moreover, the huge amount of industrially produced gold nanoparticles raises the question of these particles being a health hazard, since the penetration is fairly easy for the "nano" size substances. This study focuses on the effect of AuNPs on a human skin tissue, since it is fall in both categories -- the side effects for biomedical applications and industrial workers and users' exposure during production and handling. Therefore, in the present project, gold nanoparticles stabilized with the biocompatible agent citric acid were generated and characterized by Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). The cytotoxic effect of AuNPs release to healthy skin tissue was modeled on 3 different cell types: human keratinocytes, human dermal fibroblasts, and human adipose derived stromal (ADS) cells. The AuNPs localization inside the cell was found to be cell type dependent. Overall cytotoxicity was found to be dependent

Dating native gold by noble gas analyses

NASA Technical Reports Server (NTRS)

Niedermann, S.; Eugster, O.; Hofmann, B.; Thalmann, CH.; Reimold, W. U.

1993-01-01

Our recent work on He, Ne, and Ar in Alpine gold samples has demonstrated that gold is extremely retentive for He and could thus, in principle, be used for U/Th-He-4 dating. For vein-type gold from Brusson, Northern Italy, we derived a U/Th-He-4 age of 36 Ma, in agreement with the K-Ar formation age of associated muscovites and biotites. However, in placer gold from the Napf area, Central Switzerland, we observed large excesses of both He-4 and radiogenic Ar-40 (Ar-40 sub rad, defined as Ar-40-295.5-Ar-.36). The gas release systematics indicate two distinct noble gas components, one of which is released below about 800 C and the other one at the melting point of gold (1064 C). We now present results of He and Xe measurements in a 1 g placer gold sample from the river Kruempelgraben, as well as He and Ar data for Brusson vein-type gold and for gold from the Lily Gold Mine, South Africa. We calculate reasonable U/Th-He-4 as well as U-Xe ages based on those gases which are released at approximately 800 C. Probably the low-temperature components represent in-situ-produced radiogenic He and fission Xe, whereas the gases evolving when gold melts have been trapped during gold formation. Therefore, only the low-temperature components are relevant for dating purposes.

Transition From Archean Plume-Arc Orogens to Phanerozoic Style Convergent Margin Orogens, and Changing Mantle Lithosphere

NASA Astrophysics Data System (ADS)

Kerrich, R.; Jia, Y.; Wyman, D.

2001-12-01

Mantle plume activity was more intense in the Archean and komatiite-basalt volcanic sequences are a major component of many Archean greenstone belts. Tholeiitic basalts compositionally resemble Phanerozoic and Recent ocean plateau basalts, such as those of Ontong Java and Iceland. However, komatiite-basalt sequences are tectonically imbricated with bimodal arc lavas and associated trench turbidites. Interfingering of komatiite flows with boninite series flows, and primitive to evolved arc basalts has recently been identified in the 2.7 Ga Abitibi greenstone belt, demonstrating spatially and temporally associated plume and arc magmatism. These observations are consistent with an intra-oceanic arc migrating and capturing an ocean plateau, where the plateau jams the arc and imbricated plateau-arc crust forms a greenstone belt orogen. Melting of shallowly subducted plateau basalt crust (high Ba, Th, LREE) accounts for the areally extensive and voluminous syntectonic tonalite batholiths. In contrast, the adakite-Mg-andesite-Niobium enriched basalt association found in Archean greenstone belts and Cenozoic arcs are melts of LREE depleted MORB slab. Buoyant residue from anomalously hot mantle plume melting at > 100km rises to couple with the composite plume-arc crust to form the distinctively thick and refractory Archean continental lithospheric mantle. New geochemical data for structurally hosted ultramafic units along the N. American Cordillera, from S. California to the Yukon, show that these are obducted slices of sub-arc lithospheric mantle. Negatively fractionated HREE with high Al2O3/TiO2 ratios signify prior melt extraction, and variably enriched Th and LREE with negative Nb anomalies a subduction component in a convergent margin. A secular decrease of mantle plume activity and temperature results in plume-arc dominated geodynamics in the Archean with shallow subduction and thick CLM, whereas Phanerozoic convergent margins are dominated by arc-continent, arc

Geophysical data reveal the crustal structure of the Alaska Range orogen within the aftershock zone of the Mw 7.9 Denali fault earthquake

USGS Publications Warehouse

Fisher, M.A.; Ratchkovski, N.A.; Nokleberg, W.J.; Pellerin, L.; Glen, J.M.G.

2004-01-01

Geophysical information, including deep-crustal seismic reflection, magnetotelluric (MT), gravity, and magnetic data, cross the aftershock zone of the 3 November 2002 Mw 7.9 Denali fault earthquake. These data and aftershock seismicity, jointly interpreted, reveal the crustal structure of the right-lateral-slip Denali fault and the eastern Alaska Range orogen, as well as the relationship between this structure and seismicity. North of the Denali fault, strong seismic reflections from within the Alaska Range orogen show features that dip as steeply as 25?? north and extend downward to depths between 20 and 25 km. These reflections reveal crustal structures, probably ductile shear zones, that most likely formed during the Late Cretaceous, but these structures appear to be inactive, having produced little seismicity during the past 20 years. Furthermore, seismic reflections mainly dip north, whereas alignments in aftershock hypocenters dip south. The Denali fault is nonreflective, but modeling of MT, gravity, and magnetic data suggests that the Denali fault dips steeply to vertically. However, in an alternative structural model, the Denali fault is defined by one of the reflection bands that dips to the north and flattens into the middle crust of the Alaska Range orogen. Modeling of MT data indicates a rock body, having low electrical resistivity (>10 ??-m), that lies mainly at depths greater than 10 km, directly beneath aftershocks of the Denali fault earthquake. The maximum depth of aftershocks along the Denali fault is 10 km. This shallow depth may arise from a higher-than-normal geothermal gradient. Alternatively, the low electrical resistivity of deep rocks along the Denali fault may be associated with fluids that have weakened the lower crust and helped determine the depth extent of the after-shock zone.

Fungal Biorecovery of Gold From E-waste.

PubMed

Bindschedler, Saskia; Vu Bouquet, Thi Quynh Trang; Job, Daniel; Joseph, Edith; Junier, Pilar

2017-01-01

Waste electric and electronic devices (e-waste) represent a source of valuable raw materials of great interest, and in the case of metals, e-waste might become a prized alternative source. Regarding gold, natural ores are difficult to mine due to their refractory nature and the richest ores have almost all been exploited. Additionally, some gold mining areas are present in geopolitically unstable regions. Finally, the gold mining industry produces toxic compounds, such as cyanides. As a result, the gold present in e-waste represents a nonnegligible resource (urban mining). Extraction methods of gold from natural ores (pyro- and hydrometallurgy) have been adapted to this particular type of matrix. However, to propose novel approaches with a lower environmental footprint, biotechnological methods using microorganisms are being developed (biometallurgy). These processes use the extensive metabolic potential of microbes (algae, bacteria, and fungi) to mobilize and immobilize gold from urban and industrial sources. In this review, we focus on the use of fungi for gold biomining. Fungi interact with gold by mobilizing it through mechanical attack as well as through biochemical leaching by the production of cyanides. Moreover, fungi are also able to release Au through the degradation of cyanide from aurocyanide complexes. Finally, fungi immobilize gold through biosorption, bioaccumulation, and biomineralization, in particular, as gold nanoparticles. Overall, the diversity of mechanisms of gold recycling using fungi combined with their filamentous lifestyle, which allows them to thrive in heterogeneous and solid environments such as e-waste, makes fungi an important bioresource to be harnessed for the biorecovery of gold. Copyright © 2017 Elsevier Inc. All rights reserved.

Immobilization of gold nanoparticles on cell culture surfaces for safe and enhanced gold nanoparticle-mediated laser transfection.

PubMed

Kalies, Stefan; Heinemann, Dag; Schomaker, Markus; Gentemann, Lara; Meyer, Heiko; Ripken, Tammo

2014-01-01

In comparison to standard transfection methods, gold nanoparticle-mediated laser transfection has proven to be a versatile alternative. This is based on its minor influence on cell viability and its high efficiency, especially for the delivery of small molecules like small interfering RNA. However, in order to transfer it to routine usage, a safety aspect is of major concern: The avoidance of nanoparticle uptake by the cells is desired. The immobilization of the gold nanoparticles on cell culture surfaces can address this issue. In this study, we achieved this by silanization of the appropriate surfaces and the binding of gold nanoparticles to them. Comparable perforation efficiencies to the previous approaches of gold nanoparticle-mediated laser transfection with free gold nanoparticles are demonstrated. The uptake of the immobilized particles by the cells is unlikely. Consequently, these investigations offer the possibility of bringing gold nanoparticle-mediated laser transfection closer to routine usage.

Enhanced chemiluminescence-based detection on gold substrate after electrografting of diazonium precursor-coated gold nanoparticles.

PubMed

Houmed Adabo, Ali; Zeggari, Rabah; Mohamed Saïd, Nasser; Bazzi, Rana; Elie-Caille, Céline; Marquette, Christophe; Martini, Matteo; Tillement, Olivier; Perriat, Pascal; Chaix, Carole; Boireau, Wilfrid; Roux, Stéphane

2016-04-01

Since it was demonstrated that nanostructured surfaces are more efficient for the detection based on the specific capture of analytes, there is a real need to develop strategies for grafting nanoparticles onto flat surfaces. Among the different routes for the functionalization of a surface, the reduction of diazonium salts appears very attractive for the covalent immobilization of nanoparticles because this method does not require a pre-treatment of the surface. For achieving this goal, gold nanoparticles coated by precursor of diazonium salts were synthesized by reduction of gold salt in presence of mercaptoaniline. These mercaptoaniline-coated gold nanoparticles (Au@MA) were successfully immobilized onto various conducting substrates (indium tin oxide (ITO), glassy carbon (GC) and gold electrodes with flat terraces) after addition of sodium nitrite at fixed potential. When applied onto the gold electrodes, such a grafting strategy led to an obvious enhancement of the luminescence of luminol used for the biodetection. Copyright © 2016 Elsevier Inc. All rights reserved.

Gold(I) Carbenoids: On‐Demand Access to Gold(I) Carbenes in Solution

PubMed Central

Sarria Toro, Juan M.; García‐Morales, Cristina; Raducan, Mihai; Smirnova, Ekaterina S.

2017-01-01

Abstract Chloromethylgold(I) complexes of phosphine, phosphite, and N‐heterocyclic carbene ligands are easily synthesized by reaction of trimethylsilyldiazomethane with the corresponding gold chloride precursors. Activation of these gold(I) carbenoids with a variety of chloride scavengers promotes reactivity typical of metallocarbenes in solution, namely homocoupling to ethylene, olefin cyclopropanation, and Buchner ring expansion of benzene. PMID:28090747

Two cryptic anatectic events within a syn-collisional granitoid from the Araçuaí orogen (southeastern Brazil): Evidence from the polymetamorphic Carlos Chagas batholith

NASA Astrophysics Data System (ADS)

Melo, M. G.; Stevens, G.; Lana, C.; Pedrosa-Soares, A. C.; Frei, D.; Alkmim, F. F.; Alkmin, L. A.

2017-04-01

From the earliest (ca. 630 Ma) pre-collisional plutons to the latest (ca. 480 Ma) post-collisional intrusions, the Araçuaí orogen (SE Brazil) records an outstanding succession of granite production events in space and time. The Carlos Chagas batholith (CCB) is the largest ( 14,000 km2) granitic body ascribed to the collisional plutonism (G2 supersuite) in the back-arc region of the Araçuaí orogen, to the east of the Rio Doce magmatic arc. A wide range of monazite and zircon ages (> 725 Ma to ca. 490 Ma) have been found in CCB granites, recording a rich history of crustal recycling and inheritance, magmatic crystallization and anatexis. The CCB includes a dominant granite richer in garnet than in biotite, in which three mineral assemblages can be identified: 1) Qz + Pl + Kfs + Bt + Grt + Ilm ± Rt; 2) Qz + Pl + Kfs + Bt + Grt + Ilm + Sil; and 3) Qz + Pl + Kfs + Bt + Grt + Ilm + Sil + Spl. Rocks which contain mineral assemblage 2 and 3 all contain two generations of garnet. Textural evidence for the presence of former melt, recognized in all studied CCB samples, includes: silicate melt inclusions in poikiloblastic garnet, pseudomorphed thin films of melt surrounding both generations of garnet, pseudomorphed melt pools adjacent to garnet and biotite, and plagioclase and quartz with cuspate-lobate shapes occurring among matrix grains. Both generations of garnet crystals (Grt1 and Grt2) are unzoned in terms of major element concentration, contain small rounded inclusions of Ti-rich biotite and, in addition, the Grt2 crystals also contain inclusions of remnant sillimanite needles. Microstructural evidence, in combination with mineral chemistry, indicates that the garnet crystals grew during two distinct metamorphic-anatectic events, as the peritectic products of fluid-absent melting reactions which consumed biotite, quartz and plagioclase, in the case of Grt1, and which consumed biotite, quartz, plagioclase and sillimanite in the case of Grt2. P-T pseudosections

Synthesis of camptothecin-loaded gold nanomaterials

NASA Astrophysics Data System (ADS)

Xing, Zhimin; Liu, Zhiguo; Zu, Yuangang; Fu, Yujie; Zhao, Chunjian; Zhao, Xiuhua; Meng, Ronghua; Tan, Shengnan

2010-04-01

Camptothecin-loaded gold nanomaterials have been synthesized by the sodium borohydride reduction method under a strong basic condition. The obtained gold nanomaterials have been characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM) and UV-vis absorption spectroscopy. The camptothecin-loaded gold colloidal solution was very stable and can be stored for more than two months at room temperature without obvious changes. The color of the colloidal solution can change from wine red to purple and blue during the acidifying process. It was revealed that the release of camptothecin and the aggregation of gold nanoparticles can be controlled by tuning the solution pH. The present study implied that the gold nanomaterials can be used as the potential carrier for CPT delivery.

Concentration of gold in natural waters

USGS Publications Warehouse

McHugh, J.B.

1988-01-01

The purpose of this paper is to investigate the amount of gold present in natural waters. One hundred and thirty-two natural water samples were collected from various sources and analyzed for gold by the latest techniques. Background values for gold in natural waters range from <0.001 to 0.005 ppb, and anomalous values range from 0.010 to 2.8 ppb. Waters collected from mineralized areas have a mean gold value of 0.101 ppb, whereas waters collected from unmineralized areas have a mean of 0.002 ppb. Some of the high gold values reported in the earlier literature were probably due to interferences by high salt content in the sample and/or lack of proper filter procedures. ?? 1988.

Partial melting of deeply subducted eclogite from the Sulu orogen in China

PubMed Central

Wang, Lu; Kusky, Timothy M.; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin

2014-01-01

We report partial melting of an ultrahigh pressure eclogite in the Mesozoic Sulu orogen, China. Eclogitic migmatite shows successive stages of initial intragranular and grain boundary melt droplets, which grow into a three-dimensional interconnected intergranular network, then segregate and accumulate in pressure shadow areas and then merge to form melt channels and dikes that transport magma to higher in the lithosphere. Here we show, using zircon U–Pb dating and petrological analyses, that partial melting occurred at 228–219 Myr ago, shortly after peak metamorphism at 230 Myr ago. The melts and residues are complimentarily enriched and depleted in light rare earth element (LREE) compared with the original rock. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behaviour of subducted lithosphere and its rapid exhumation, controlling the flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust. PMID:25517619

Gold and its relationship to neurological/glandular conditions.

PubMed

Richards, Douglas G; McMillin, David L; Mein, Eric A; Nelson, Carl D

2002-01-01

Despite increasing sales of gold supplements, and claims of benefits for neurological and glandular conditions, gold has received little attention in modern medical literature except as a drug for rheumatoid arthritis. Historically, however, gold had a reputation as a "nervine," a therapy for nervous disorders. A review of the historical literature shows gold in use during the 19th century for conditions including depression, epilepsy, migraine, and glandular problems such as amenorrhea and impotence. The most notable use of gold was in a treatment for alcoholism developed by Keeley (1897). In the modern medical literature, gold-containing medicines for rheumatoid arthritis are known to have occasional neurotoxic adverse effects. There are also a few studies suggesting a role for gold as a naturally occurring trace element in the reproductive glands. One small recent study demonstrated a possible positive effect of gold on cognitive ability. There is a need for more experimental and clinical research of the neuropharmacology and neurochemistry of gold, and for the exploration of gold's possible role as a trace element.

Gold - Old Drug with New Potentials.

PubMed

Faa, Gavino; Gerosa, Clara; Fanni, Daniela; Lachowicz, Joanna I; Nurchi, Valeria M

2018-01-01

Research into gold-based drugs for a range of human diseases has seen a revival in recent years. This article reviews the most important applications of gold products in different fields of human pathology. Au(I) and Au(III) compounds have been re-introduced in clinical practice for targeting the cellular components involved in the onset and progression of viral and parasitic diseases, rheumatoid arthritis and cancer. After some brief historical notes, this article takes into account the applications of gold compounds against Mycobacterium tuberculosis, and also in tuberculosis and in rheumatoid arthritis treatment. The use of gold containing drugs in the cure of cancer are then considered, with special emphasis to the use of nanoparticles and to the photo-thermal cancer therapy. The use of colloidal gold in diagnostics, introduced in the last decade is widely discussed. As a last point a survey on the adverse effects and on the toxicity of the various gold derivatives in use in medicine is presented. In this review, we described the surprisingly broad spectrum of possible uses of gold in diagnostics and in therapeutic approaches to multiple human diseases, ranging from degenerative to infectious diseases, and to cancer. In particular, gold nanoparticles appear as attractive elements in modern clinical medicine, combining high therapeutic properties, high selectivity in targeting cancer cells and low toxicity. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

From erosion to earthquakes: A geomorphic model for intraplate seismicity in post-orogenic settings

NASA Astrophysics Data System (ADS)

Gallen, S. F.; Thigpen, J. R.

2017-12-01

Intraplate seismicity does not conform to plate tectonics theory and its driving mechanisms remain uncertain, yet it is recognized as a relevant seismic hazard to populated regions, such as eastern North America. A variety of models, mostly geodynamic or tectonic in origin, have been proposed to explain this enigma, but conclusive supporting evidence remains elusive. In order to identify high hazard areas and derive predictive models, it is imperative to identify the underlying processes responsible for intraplate seismicity. Here we conduct an interdisciplinary study of the Eastern Tennessee Seismic Zone (ETSZ), the second most seismically active region east of the Rocky Mountains in the North American continent, to clarify the potential mechanisms driving intraplate seismicity in post-orogenic and passive margin settings. Previous studies document that the Upper Tennessee drainage basin, which lies directly above the ETSZ, is in a transient state of adjustment to 150 m of base level fall that was provoked by river capture in the Late Miocene. Using quantitative geomorphology, we demonstrate that base level fall enhanced erosion rates in a 75 km wide 400 km long corridor of highly erodible rocks in the late Paleozoic (Alleghanian orogen) fold-thrust belt. The total volume of rock preferentially removed above the ETSZ since 9 Ma is 3,600 ± 150 km3. Stress modeling indicates spatially focused erosion has of reduced clamping stresses on ancient basement normal faults beneath the Appalachian fold-thrust belt on the order of 3.5 MPa, with a time-averaged unclamping rate of 0.4 Pa yr-1. Under the assumption that the crust is critically stressed, we argue that the preferential erosion of less competent rock units reduced clamping stresses on relict faults such to induce seismic activity in the ambient stress field. This model for surface process-induced intraplate seismicity is generally transferable to other continental settings where complex geology and landscape

Gold ink coating of thermocouple sheaths

DOEpatents

Ruhl, H. Kenneth

1992-01-01

A method is provided for applying a gold ink coating to a thermocouple sheath which includes the steps of electropolishing and oxidizing the surface of the thermocouple sheath, then dipping the sheath into liquid gold ink, and finally heat curing the coating. The gold coating applied in this manner is highly reflective and does not degrade when used for an extended period of time in an environment having a temperature over 1000.degree. F. Depending on the application, a portion of the gold coating covering the tip of the thermocouple sheath is removed by abrasion.

Directed assembly of gold nanowires on silicon via reorganization and simultaneous fusion of randomly distributed gold nanoparticles.

PubMed

Reinhardt, Hendrik M; Bücker, Kerstin; Hampp, Norbert A

2015-05-04

Laser-induced reorganization and simultaneous fusion of nanoparticles is introduced as a versatile concept for pattern formation on surfaces. The process takes advantage of a phenomenon called laser-induced periodic surface structures (LIPSS) which originates from periodically alternating photonic fringe patterns in the near-field of solids. Associated photonic fringe patterns are shown to reorganize randomly distributed gold nanoparticles on a silicon wafer into periodic gold nanostructures. Concomitant melting due to optical heating facilitates the formation of continuous structures such as periodic gold nanowire arrays. Generated patterns can be converted into secondary structures using directed assembly or self-organization. This includes for example the rotation of gold nanowire arrays by arbitrary angles or their fragmentation into arrays of aligned gold nanoparticles.

Diazonium-derived aryl films on gold nanoparticles: evidence for a carbon-gold covalent bond.

PubMed

Laurentius, Lars; Stoyanov, Stanislav R; Gusarov, Sergey; Kovalenko, Andriy; Du, Rongbing; Lopinski, Gregory P; McDermott, Mark T

2011-05-24

Tailoring the surface chemistry of metallic nanoparticles is generally a key step for their use in a wide range of applications. There are few examples of organic films covalently bound to metal nanoparticles. We demonstrate here that aryl films are formed on gold nanoparticles from the spontaneous reduction of diazonium salts. The structure and the bonding of the film is probed with surface-enhanced Raman scattering (SERS). Extinction spectroscopy and SERS show that a nitrobenzene film forms on gold nanoparticles from the corresponding diazonium salt. Comparison of the SERS spectrum with spectra computed from density functional theory models reveals a band characteristic of a Au-C stretch. The observation of this stretch is direct evidence of a covalent bond. A similar band is observed in high-resolution electron energy loss spectra of nitrobenzene layers on planar gold. The bonding of these types of films through a covalent interaction on gold is consistent with their enhanced stability observed in other studies. These findings provide motivation for the use of diazonium-derived films on gold and other metals in applications where high stability and/or strong adsorbate-substrate coupling are required.

New insights into the extraction of invisible gold in a low-grade high-sulfur Carlin-type gold concentrate by bio-pretreatment

NASA Astrophysics Data System (ADS)

Qiu, Xiao-bin; Wen, Jian-kang; Huang, Song-tao; Yang, Hong-ying; Liu, Mei-lin; Wu, Biao

2017-10-01

To extract gold from a low-grade (13.43 g/t) and high-sulfur (39.94wt% sulfide sulfur) Carlin-type gold concentrate from the Nibao deposit, Guizhou, a bio-pretreatment followed by carbon-in-pulp (CIP) cyanide leaching process was used. Various methods were used to detect the low-grade gold in the concentrate; however, only time-of-flight secondary-ion mass spectrometry (TOF-SIMS) was successful. With bio-pretreatment, the gold recovery rate increased by approximately 70.16% compared with that obtained by direct cyanide leaching of the concentrate. Various attempts were made to increase the final gold recovery rate. However, approximately 20wt% of the gold was non-extractable. To determine the nature of this non-extractable gold, mineralogy liberation analysis (MLA), formation of secondary product during the bio-pretreatment, and the preg-robbing capacity of the carbonaceous matter in the ore were investigated. The results indicated that at least four factors affected the gold recovery rate: gold occurrence, tight junctions of gold-bearing pyrite with gangue minerals, jarosite coating of the ore, and the carbonaceous matter content.

The importance of intracrustal magmatic heat advection in large hot orogens: the Ediacaran-Cambrian ultrahigh-temperature domain of southern Madagascar.

NASA Astrophysics Data System (ADS)

Holder, R. M.; Hacker, B. R.

2016-12-01

Ultrahigh temperature metamorphism (UHTM) represents the thermal extremes of crustal metamorphism and is integral to our understanding of orogenic systems and continental evolution. The relative importance of advective and radiogenic heating in UHTM is often unclear, however, due to retrogression of UHT mineral assemblages and lack of robust chronology. We report the first observation of osumilite, pseudosections, feldspar thermometry, and monazite LASS U-Th-Pb chronology from the Ediacaran-Cambrian Anosyen domain of southern Madagascar to evaluate P-T-time paths and assess the relative importance of advective and radiogenic heating. Pseudosections of an osumilite-bearing assemblage, a garnet-orthopyroxene gneiss, and a garnet-spinel leucogneiss indicate peak conditions of 930-1010 C, 4-6 kbar; 900-950 C, 6-7 kbar; and 970-1000 C, 4.5-5.5 kbar, respectively. Feldspar thermometry indicates T > 915 ± 30 C. These conditions were reached along a low-P prograde path, as implied by cordierite and sillimanite inclusions in garnet. Monazite and zircon U/Th-Pb dating indicates that prograde metamorphism began 625 Ma and lasted 60 Myr. The timing of peak metamorphism is constrained to a 16 ± 2.5 Myr period between 566 ± 2 and 550 ± 1.5 Ma, by monazite inclusions in pseudomorphs after osumilite and monazite from a leucosome in the same outcrop. Peak T was achieved immediately following emplacement of voluminous charnockites (emplaced 1000-1100 C) and related magmas of the Anosyen Batholith. Crystallization of pegmatite dikes, leucosomes, and smaller plutons during cooling lasted from 550 to 510 Ma. This broad thermal history is also recorded by metamorphic monazite Eu/Eu*, which indicate progressive melt generation and extraction prior to 550 Ma followed by melt accumulation and crystallization after 550 Ma. Although the duration of prograde metamorphism is consistent with radiogenic heating models of large hot orogens, peak T was 100-200 C higher in southern Madagascar

Late Triassic granitic rocks of the Central Qiangtang Orogenic Belt, northern Tibet: tracing crustal thickening through post-collisional silicic magmatism

NASA Astrophysics Data System (ADS)

Wu, H.; Chen, J.

2017-12-01

The Central Qiangtang Orogenic Belt (CQOB) was formed through Triassic continental collision between the Southern and Northern Qiangtang terranes. Numerous granitic intrusions occur along the CQOB, forming a Late Triassic granitic belt that stretches 1000 km from west to east. This Central Qiangtang granitic belt was believed to constitute most of the CQOB. Therefore, the CQOB thus provides a typical composite orogen for the study of relationships between granitoid magmatism and orogenic processes. Recently, many studies have been carried out, and the close relationship of the magmatic belt with the evolutionary history of the CQOB is well established. Late Triassic intrusive rocks are widely exposed in the Riwanchaka area of Central Qiangtang, northern Tibet. In this study, new U-Pb zircon ages reveal that Late Triassic magmatism in Riwanchaka took place at ca 225-205 Ma, coeval with exhumation of the metamorphic rocks in Central Qiangtang. Our new and previously published data enable us to correlate the subduction-related volcanic arc rocks in the Riwanchaka area to a post-collisional extension setting related to slab break-off during northward subduction of the Paleo-Tethys Ocean seafloor. Geochemical characteristics suggested that the samples from CQOB can be divided into low-Sr/Y granitoids (LSG) and high-Sr/Y granitoids (HSG). The LSG are normal calc-alkaline I-type granitoids, characterized by varying major and trace element contents indicative of partial melting of ancient mafic lower crust. The HSG are characterized by high Sr/Y ratios and (La/Yb)N (chondrite-normalized) ratios. These signatures indicate that the HSG were derived by partial melting of garnet-bearing thickened lower crust. The crustal structure and evolution of the CQOB are considered on the basis of available data and variations in Sr/Y, La/Yb, and Hf isotopic ratios. Temporal geochemical and Hf isotopic changes, diagnostic of crustal thickening, indicate that the CQOB was greatly

The gold rush 1925-35.

PubMed Central

Keers, R Y

1980-01-01

Although from the time of Koch onwards there had been desultory experiments with a variety of gold preparations in the management of pulmonary tuberculosis, gold as a recognised and accepted treatment did not emerge until 1925. In that year Holger Mollgaard of Copenhagen introduced sanocrysin, a double thiosulphate of gold and sodium, with which he had conducted an extensive series of animal experiments. The results of these were considered to justify its use in clinical practice and two physicians, Secher and Faber, undeterred by its toxicity, reported enthusiastically in its favour. Other Danish physicians followed but, alarmed by violent reactions, modified the dosage, an example followed by British workers. Encouraging results continued to be reported although each series contained a significant proportion of failures, and toxicity remained high. The first properly planned and fully controlled clinical trial took place in the United States and produced a report which was wholly adverse and which sounded the death knell of gold therapy throughout America. Until 1934-35 gold was used extensively in Europe but thereafter there was a sudden and largely universal cessation of interest and within a few years gold, introduced with such éclat and carrying so many high hopes, had vanished from the therapy of tuberculosis even though, at that point, no better alternative was available. PMID:6791290

Sensitive flotation-spectrophotometric determination of gold, based on the gold(I)-iodide-methylene blue system.

PubMed

Marczenko, Z; Jankowski, K

1985-04-01

The gold(I)-iodide-Methylene Blue (MB) system is suitable for flotation separation and spectrophotometric determination of gold. Under the optimum conditions [(MB(+))(AuI(2)(-))].3[(MB(+))(I(3)(-))] is formed, and floated with cyclohexane. The product is dissolved in methanol and its absorbance measured. The molar absorptivity is 3.4 x 10(5)1.mole(-1).cm(-1) at 655 nm. The proposed method is more than three times as sensitive as the Rhodamine B method. Pt, Pd, Ag and Hg interfere seriously, and Ir, Rh, Bi and Cd to a smaller extent. Preliminary separation of gold by precipitation with tellurium as a collector is recommended. The method has been applied to determination of gold traces (about 1 x 10(-4)%) in a copper sample.

Bats, cyanide, and gold mining

USGS Publications Warehouse

Clark, Donald R.

1991-01-01

Although the boom days of prospectors and gold nuggets are long gone, modern technology enables gold to continue to be extracted from ore. Unfortunately, the extraction method has often been disastrous for bats and other wildlife, an issue I first became aware of in early 1989. Phone calls from Drs. Merlin Tuttle and Elizabeth Pierson, a BCI member and bat researcher from Berkeley, California, alerted me that bats were dying from apparent cyanide poisoning at gold mines in the western United States.

Metamorphic evolution and geochronology of the Dunhuang orogenic belt in the Hongliuxia area, northwestern China

NASA Astrophysics Data System (ADS)

Wang, Hao Y. C.; Wang, Juan; Wang, Guo-Dong; Lu, Jun-Sheng; Chen, Hong-Xu; Peng, Tao; Zhang, Hui C. G.; Zhang, Qian W. L.; Xiao, Wen-Jiao; Hou, Quan-Lin; Yan, Quan-Ren; Zhang, Qing; Wu, Chun-Ming

2017-03-01

Garnet-bearing mafic granulites and amphibolites from the Hongliuxia area of the southern Dunhuang orogenic belt, northwestern China, commonly occur as lenses or boudinages enclosed within metapelite or marble, which represent the block-in-matrix feature typical of orogenic mélange. Three to four generations of metamorphic mineral assemblages are preserved in these rocks. In the high-pressure amphibolites, prograde mineral assemblages (M1) occur as inclusions (hornblende + plagioclase + quartz ± chlorite ± epidote ± ilmenite) preserved within garnet porphyroblasts, and formed at 550-590 °C and 7.7-9.2 kbar based on geothermobarometry. The metamorphic peak mineral assemblages (M2) are composed of garnet + hornblende + plagioclase + quartz + clinopyroxene, as well as titanite + zircon + rutile + apatite as accessory minerals in the matrix, and are estimated to have formed at 640-720 °C and 14.1-16.0 kbar. The first retrograde assemblages (M3) are characterized by "white-eye socket" symplectites (hornblende + plagioclase + quartz ± biotite ± epidote ± magnetite) rimming garnet porphyroblasts, which formed at the expense of the garnet rims and adjacent matrix minerals during the decompression stage under P-T conditions of 610-630 °C and 5.6-11.8 kbar. The second retrograde assemblages (M4) are intergrowths of actinolite and worm-like quartz produced by the breakdown of the matrix hornblendes, and formed under P-T conditions of ∼490 °C and ∼2.8 kbar. For the high-pressure mafic granulites, the prograde assemblages (M1) are represented by plagioclase + quartz preserved within the garnet porphyroblasts. The metamorphic peak assemblages (M2) are garnet + matrix minerals (clinopyroxene + plagioclase + quartz + hornblende + rutile + zircon) and were estimated to have formed at ∼680 °C and ∼15.4 kbar. The retrograde assemblages (M3) are characterized by fine-grained patches of hornblende + plagioclase + quartz rimming the garnet porphyroblasts, as well as

Precipitation of lamellar gold nanocrystals in molten polymers

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

Palomba, M.; Carotenuto, G., E-mail: giancaro@unina.it

Non-aggregated lamellar gold crystals with regular shape (triangles, squares, pentagons, etc.) have been produced by thermal decomposition of gold chloride (AuCl) molecules in molten amorphous polymers (polystyrene and poly(methyl methacrylate)). Such covalent inorganic gold salt is high soluble into non-polar polymers and it thermally decomposes at temperatures compatible with the polymer thermal stability, producing gold atoms and chlorine radicals. At the end of the gold precipitation process, the polymer matrix resulted chemically modified because of the partial cross-linking process due to the gold atom formation reaction.

Establishment of gold-quartz standard GQS-1

USGS Publications Warehouse

Millard, Hugh T.; Marinenko, John; McLane, John E.

1969-01-01

A homogeneous gold-quartz standard, GQS-1, was prepared from a heterogeneous gold-bearing quartz by chemical treatment. The concentration of gold in GQS-1 was determined by both instrumental neutron activation analysis and radioisotope dilution analysis to be 2.61?0.10 parts per million. Analysis of 10 samples of the standard by both instrumental neutron activation analysis and radioisotope dilution analysis failed to reveal heterogeneity within the standard. The precision of the analytical methods, expressed as standard error, was approximately 0.1 part per million. The analytical data were also used to estimate the average size of gold particles. The chemical treatment apparently reduced the average diameter of the gold particles by at least an order of magnitude and increased the concentration of gold grains by a factor of at least 4,000.

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

Gel Electrophoresis of Gold-DNA Nanoconjugates

DOE PAGES

Pellegrino, T.; Sperling, R. A.; Alivisatos, A. P.; ...

2007-01-01

Gold-DNA conjugates were investigated in detail by a comprehensive gel electrophoresis study based on 1200 gels. A controlled number of single-stranded DNA of different length was attached specifically via thiol-Au bonds to phosphine-stabilized colloidal gold nanoparticles. Alternatively, the surface of the gold particles was saturated with single stranded DNA of different length either specifically via thiol-Au bonds or by nonspecific adsorption. From the experimentally determined electrophoretic mobilities, estimates for the effective diameters of the gold-DNA conjugates were derived by applying two different data treatment approaches. The first method is based on making a calibration curve for the relation between effectivemore » diameters and mobilities with gold nanoparticles of known diameter. The second method is based on Ferguson analysis which uses gold nanoparticles of known diameter as reference database. Our study shows that effective diameters derived from gel electrophoresis measurements are affected with a high error bar as the determined values strongly depend on the method of evaluation, though relative changes in size upon binding of molecules can be detected with high precision. Furthermore, in this study, the specific attachment of DNA via gold-thiol bonds to Au nanoparticles is compared to nonspecific adsorption of DNA. Also, the maximum number of DNA molecules that can be bound per particle was determined.« less

Plastic deformation in nanoscale gold single crystals and open-celled nanoporous gold

NASA Astrophysics Data System (ADS)

Lee, Dongyun; Wei, Xiaoding; Zhao, Manhong; Chen, Xi; Jun, Seong C.; Hone, James; Kysar, Jeffrey W.

2007-01-01

The results of two sets of experiments to measure the elastic-plastic behaviour of gold at the nanometre length scale are reported. One set of experiments was on free-standing nanoscale single crystals of gold, and the other was on free-standing nanoscale specimens of open-celled nanoporous gold. Both types of specimens were fabricated from commercially available leaf which was either pure Au or a Au/Ag alloy following by dealloying of the Ag. Mechanical testing specimens of a 'dog-bone' shape were fabricated from the leaf using standard lithographic procedures after the leaf had been glued onto a silicon wafer. The thickness of the gauge portion of the specimens was about 100 nm, the width between 250 nm and 300 nm and the length 7 µm. The specimens were mechanically loaded with a nanoindenter (MTS) at the approximate midpoint of the gauge length. The resulting force-displacement curve of the single crystal gold was serrated and it was evident that slip localization occurred on individual slip systems; however, the early stages of the plastic deformation occurred in a non-localized manner. The results of detailed finite element analyses of the specimen suggest that the critical resolved shear stress of the gold single crystal was as high as 135 MPa which would lead to a maximum uniaxial stress of about 500 MPa after several per cent strain. The behaviour of the nanoporous gold was substantially different. It exhibited an apparent elastic behaviour until the point where it failed in an apparently brittle manner, although it is assumed that plastic deformation occurred in the ligaments prior to failure. The average elastic stiffness of three specimens was measured to be Enp = 8.8 GPa and the stress at ultimate failure averaged 190 MPa for the three specimens tested. Scaling arguments suggest that the stress in the individual ligaments could approach the theoretical shear strength. Presented at the IUTAM Symposium on Plasticity at the Micron Scale, Technical

Biophysical characterization of gold nanoparticles-loaded liposomes.

PubMed

Mady, Mohsen Mahmoud; Fathy, Mohamed Mahmoud; Youssef, Tareq; Khalil, Wafaa Mohamed

2012-10-01

Gold nanoparticles were prepared and loaded into the bilayer of dipalmitoylphosphatidylcholine (DPPC) liposomes, named as gold-loaded liposomes. Biophysical characterization of gold-loaded liposomes was studied by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy as well as turbidity and rheological measurements. FTIR measurements showed that gold nanoparticles made significant changes in the frequency of the CH(2) stretching bands, revealing that gold nanoparticles increased the number of gauche conformers and create a conformational change within the acyl chains of phospholipids. The transmission electron micrographs (TEM) revealed that gold nanoparticles were loaded in the liposomal bilayer. The zeta potential of DPPC liposomes had a more negative value after incorporating of Au NPs into liposomal membranes. Turbidity studies revealed that the loading of gold nanoparticles into DPPC liposomes results in shifting the temperature of the main phase transition to a lower value. The membrane fluidity of DPPC bilayer was increased by loading the gold nanoparticles as shown from rheological measurements. Knowledge gained in this study may open the door to pursuing liposomes as a viable strategy for Au NPs delivery in many diagnostic and therapeutic applications. Copyright © 2011 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Functionalization of gold nanoparticles as antidiabetic nanomaterial

NASA Astrophysics Data System (ADS)

Venkatachalam, M.; Govindaraju, K.; Mohamed Sadiq, A.; Tamilselvan, S.; Ganesh Kumar, V.; Singaravelu, G.

2013-12-01

In the present investigation, functionalization of gold nanoparticles synthesized using propanoic acid 2-(3-acetoxy-4,4,14-trimethylandrost-8-en-17-yl) (PAT) an active biocomponent isolated from Cassia auriculata is studied in detail. On reaction of PAT with aqueous HAuCl4, rapid formation of stable gold nanoparticles was achieved. Formation of gold nanoparticles was confirmed by UV-vis spectroscopy, XRD, GC-MS, FTIR, TEM and SEM with EDAX. Gold nanoparticles mostly were monodisperse, spherical in shape and ranged in size 12-41 nm. Gold nanoparticles synthesised using PAT was administered to alloxan (150 mg/kg body weight) induced diabetic male albino rats at different doses (0.25, 0.5, 0.75 and 1.0 mg/kg body weight) for 28 days. Plasma glucose level, cholesterol and triglyceride were significantly (p < 0.001) reduced in experimental animals treated with gold nanoparticles at dosage of 0.5 mg/kg body weight and plasma insulin increased significantly. The newly genre green gold nanoparticles exhibit remarkable protein tyrosine phosphatase 1B inhibitory activity.

Gold and Iron-Gold Nanoparticles for Intracellular Tracking and in Vivo Medical Applicatons

NASA Astrophysics Data System (ADS)

Fu, Wei

2005-03-01

We have fabricated Au and Fe-Au nanoparticles for potential use in ex vivo experiments such as intracellular tracking, as well as a variety of in vivo medical applications. In order to improve their targeting potential, circulation time and flexibility, gold NPs were surface modified using a hetero-bifunctional poly(ethylene glycol) (PEG, MW 1,500) spacers. A coumarin-PEG-gold NP complex was formed and cell viability studies and optical fluorescence experiments were carried out demonstrating the use of these surface-modified gold NPs for drug delivery, gene therapy and cell trafficking experiments. Fe-Au nanoparticles were also fabricated and show significant contrast enhancement in MRI studies through a substantial reduction of the T2 relaxation time.

[Biosynthesis of gold nanoparticles by Azospirillum brasilense].

PubMed

Kupriashina, M A; Vetchinkina, E P; Burov, A M; Ponomareva, E G; Nikitina, V E

2014-01-01

Plant-associated nitrogen-fixing soil bacteria Azospirillum brasilense were shown to reduce the gold of chloroauric acid to elemental gold, resulting in formation of gold nanoparicles. Extracellular phenoloxidizing enzymes (laccases and Mn peroxidases) were shown to participate in reduction of Au+3 (HAuCl4) to Au(0). Transmission electron microscopy revealed accumulation of colloidal gold nanoparticles of diverse shape in the culture liquid of A. brasilense strains Sp245 and Sp7. The size of the electron-dense nanospheres was 5 to 50 nm, and the size of nanoprisms varied from 5 to 300 nm. The tentative mechanism responsible for formation of gold nanoparticles is discussed.

Facile preparation of gold nanocages and hollow gold nanospheres via solvent thermal treatment and their surface plasmon resonance and photothermal properties.

PubMed

Wang, Haifei; Han, Jing; Lu, Wensheng; Zhang, Jianping; Li, Jinru; Jiang, Long

2015-02-15

Although template etching method is one of the most common ways of preparation of hollow gold nanostructures, this approach still requires further improvements to avoid the collapse of gold shells after the cores were removed. In this work, an improved template etching method, with which hollow gold nanostructure is fabricated by etching Polystyrene (PS) cores from PS@Au core-shell nanospheres with solvent thermal treatment in N,N-Dimethylformamide (DMF), is demonstrated. When PS cores were removed by a thermal treatment process, gold nanoshells reconstruct and the collapse of the nanoshells is avoided. Gold nanocages and hollow gold nanospheres are easily obtained from the various structures of PS@Au core-shell nanospheres. These hollow nanostructures represent special near infrared (NIR) optical property and photothermal property. Compared with hollow gold nanospheres, the gold nanocages show higher temperature increase at the same particle concentration. Copyright © 2014 Elsevier Inc. All rights reserved.

Site-specific biomolecule labeling with gold clusters.

PubMed

Ackerson, Christopher J; Powell, Richard D; Hainfeld, James F

2010-01-01

Site-specific labeling of biomolecules in vitro with gold clusters can enhance the information content of electron cryomicroscopy experiments. This chapter provides a practical overview of well-established techniques for forming biomolecule/gold cluster conjugates. Three bioconjugation chemistries are covered: linker-mediated bioconjugation, direct gold-biomolecule bonding, and coordination-mediated bonding of nickel(II) nitrilotriacetic acid (NTA)-derivatized gold clusters to polyhistidine (His)-tagged proteins. Copyright © 2010 Elsevier Inc. All rights reserved.

Protein targets for anticancer gold compounds: mechanistic inferences.

PubMed

Gabbiani, Chiara; Messori, Luigi

2011-12-01

Gold compounds form an interesting class of antiproliferative agents of potential pharmacological use in cancer treatment. Indeed, a number of gold compounds, either gold(III) or gold(I), were recently described and characterised that manifested remarkable cytotoxic properties in vitro against cultured cancer cells; for some of them encouraging in vivo results were also reported toward a few relevant animal models of cancer. The molecular mechanisms through which gold compounds exert their biological effects are still largely unknown and the subject of intense investigations. Recent studies point out that the modes of action of cytotoxic gold compounds are essentially DNA-independent and cisplatin-unrelated, relying -most likely- on gold interactions with a variety of protein targets. Notably, a few cellular proteins playing relevant functional roles were proposed to represent effective targets for cytotoxic gold compounds but these hypotheses need adequate validation. The state of the art of this research area and the perspectives for future studies are herein critically analysed and discussed.

Molecular Simulations of The Formation of Gold-Molecule-Gold Junctions

NASA Astrophysics Data System (ADS)

Wang, Huachuan

2013-03-01

We perform classical molecular simulations by combining grand canonical Monte Carlo (GCMC) sampling with molecular dynamics (MD) simulation to explore the dynamic gold nanojunctions in a Alkenedithiol (ADT) solvent. With the aid of a simple driving-spring model, which can reasonably represent the long-range elasticity of the gold electrode, the spring forces are obtained during the dynamic stretching procedure. A specific multi-time-scale double reversible reference system propagator (double-RESPA) algorithm has been designed for the metal-organic complex in MD simulations to identify the detailed metal-molecule bonding geometry at metal-molecule-metal interface. We investigate the variations of bonding sites of ADT molecules on gold nanojunctions at Au (111) surface at a constant chemical potential. Simulation results show that an Au-ADT-Au interface is formed on Au nanojunctions, bond-breaking intersection is at 1-1 bond of the monatomic chain of the cross-section, instead of at the Au-S bond. Breaking force is around 1.5 nN. These are consistent with the experimental measurements.

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

Gold deposits of the Carolina Slate Belt, southeastern United States--Age and origin of the major gold producers

USGS Publications Warehouse

Foley, Nora K.; Ayuso, Robert A.

2012-01-01

Gold- and iron sulfide-bearing deposits of the southeastern United States have distinctive mineralogical and geochemical features that provide a basis for constructing models of ore genesis for exploration and assessment of gold resources. The largest (historic) deposits, in approximate million ounces of gold (Moz Au), include those in the Haile (~ 4.2 Moz Au), Ridgeway (~1.5 Moz Au), Brewer (~0.25 Moz Au), and Barite Hill (0.6 Moz Au) mines. Host rocks are Late Proterozoic to early Paleozoic (~553 million years old) metaigneous and metasedimentary rocks of the Carolina Slate Belt that share a geologic affinity with the classic Avalonian tectonic zone. The inferred syngenetic and epithermal-subvolcanic quartz-porphyry settings occur stratigraphically between sequences of metavolcanic rocks of the Persimmon Fork and Uwharrie Formations and overlying volcanic and epiclastic rocks of the Tillery and Richtex Formations (and regional equivalents). The Carolina Slate Belt is highly prospective for many types of gold ore hosted within quartz-sericite-pyrite altered volcanic rocks, juvenile metasedimentary rocks, and in associated shear zones. For example, sheared and deformed auriferous volcanogenic massive sulfide deposits at Barite Hill, South Carolina, and in the Gold Hill trend, North Carolina, are hosted primarily by laminated mudstone and felsic volcanic to volcaniclastic rocks. The high-sulfidation epithermal style of gold mineralization at Brewer and low-sulfidation gold ores of the Champion pit at Haile occur in breccias associated with subvolcanic quartz porphyry and within crystal-rich tuffs, ash flows, and subvolcanic rhyolite. The Ridgeway and Haile deposits are primarily epithermal replacements and feeder zones within (now) metamorphosed crystal-rich tuffs, volcaniclastic sediments, and siltstones originally deposited in a marine volcanic-arc basinal setting. Recent discoveries in the region include (1) extensions of known deposits, such as at Haile where

Mantle Recycling of Crustal Materials through Study of Ultrahigh-Pressure Minerals in Collisional Orogens, Ophiolites, and Xenoliths

NASA Astrophysics Data System (ADS)

Liou, J. G.; Tsujimori, T.; Yang, J.; Zhang, R. Y.; Ernst, W. G.

2014-12-01

Newly recognized ultrahigh-pressure (UHP) mineral occurrences including diamonds in ultrahigh-temperature (UHT) felsic granulites of orogenic belts, in chromitites associated with ophiolitic complexes, and in mafic/ultramafic xenoliths suggest the recycling of crustal materials through profound subduction, mantle upwelling, and return to the Earth's surface. Recycling is supported by unambiguously crust-derived mineral inclusions in deep-seated zircons, chromites, and diamonds from collision-type orogens, from eclogitic xenoliths, and from ultramafic bodies of several Alpine-Himalayan and Polar Ural ophiolites; some such phases contain low-atomic number elements typified by crustal isotopic signatures. Ophiolite-type diamonds in placer deposits and as inclusions in chromitites together with numerous highly reduced minerals and alloys appear to have formed near the mantle transition zone. In addition to ringwoodite and stishovite, a wide variety of nanometric minerals have been identified as inclusions employing state-of-the-art analysis. Reconstitution of now-exsolved precursor UHP phases and recognition of subtle decompression microstructures produced during exhumation reflect earlier UHP conditions. Some podiform chromitites and associated peridotites contain rare minerals of undoubted crustal origin, including Zrn, corundum, Fls, Grt, Ky, Sil, Qtz, and Rtl; the zircons possess much older U-Pb ages than the formation age of the host ophiolites. These UHP mineral-bearing chromitites had a deep-seated evolution prior to extensional mantle upwelling and its partial melting at shallow depths to form the overlying ophiolite complexes. These new findings plus stable isotopic and inclusion characteristics of diamonds provide compelling evidence for profound underflow of both oceanic and continental lithosphere, recycling of biogenic carbon into the lower mantle, and ascent to the Earth's surface through deep mantle ascent.

Evolving Mantle Sources in Postcollisional Early Permian-Triassic Magmatic Rocks in the Heart of Tianshan Orogen (Western China)

NASA Astrophysics Data System (ADS)

Tang, Gong-Jian; Cawood, Peter A.; Wyman, Derek A.; Wang, Qiang; Zhao, Zhen-Hua

2017-11-01

Magmatism postdating the initiation of continental collision provides insight into the late stage evolution of orogenic belts including the composition of the contemporaneous underlying subcontinental mantle. The Awulale Mountains, in the heart of the Tianshan Orogen, display three types of postcollisional mafic magmatic rocks. (1) A medium to high K calc-alkaline mafic volcanic suite (˜280 Ma), which display low La/Yb ratios (2.2-11.8) and a wide range of ɛNd(t) values from +1.9 to +7.4. This suite of rocks was derived from melting of depleted metasomatized asthenospheric mantle followed by upper crustal contamination. (2) Mafic shoshonitic basalts (˜272 Ma), characterized by high La/Yb ratios (14.4-20.5) and more enriched isotope compositions (ɛNd(t) = +0.2 - +0.8). These rocks are considered to have been generated by melting of lithospheric mantle enriched by melts from the Tarim continental crust that was subducted beneath the Tianshan during final collisional suturing. (3) Mafic dikes (˜240 Ma), with geochemical and isotope compositions similiar to the ˜280 Ma basaltic rocks. This succession of postcollision mafic rock types suggests there were two stages of magma generation involving the sampling of different mantle sources. The first stage, which occurred in the early Permian, involved a shift from depleted asthenospheric sources to enriched lithospheric mantle. It was most likely triggered by the subduction of Tarim continental crust and thickening of the Tianshan lithospheric mantle. During the second stage, in the middle Triassic, there was a reversion to more asthenospheric sources, related to postcollision lithospheric thinning.

Gold in the hills: patterns of placer gold accumulation under dynamic tectonic and climatic conditions

NASA Astrophysics Data System (ADS)

Roy, Sam; Upton, Phaedra; Craw, Dave

2018-01-01

Formation of placer accumulations in fluvial environments requires 103-106 or even greater times concentration of heavy minerals. For this to occur, regular sediment supply from erosion of adjacent topography is required, the river should remain within a single course for an extended period of time and the material must be reworked such that a high proportion of the sediment is removed while a high proportion of the heavy minerals remains. We use numerical modeling, constrained by observations of circum-Pacific placer gold deposits, to explore processes occurring in evolving river systems in dynamic tectonic environments. A fluvial erosion/transport model is used to determine the mobility of placer gold under variable uplift rate, storm intensity, and rock mass strength conditions. Gold concentration is calculated from hydraulic and bedload grain size conditions. Model results suggest that optimal gold concentration occurs in river channels that frequently approach a threshold between detachment-limited and transport-limited hydraulic conditions. Such a condition enables the accumulation of gold particles within the framework of a residual gravel lag. An increase in transport capacity, which can be triggered by faster uplift rates, more resistant bedrock, or higher intensity storm events, will strip all bedload from the channel. Conversely, a reduction in transport capacity, triggered by a reduction in uplift rate, bedrock resistance, or storm intensity, will lead to a greater accumulation of a majority of sediments and a net decrease in gold concentration. For our model parameter range, the optimal conditions for placer gold concentration are met by 103 times difference in strength between bedrock and fault, uplift rates between 1 and 5 mm a-1, and moderate storm intensities. Fault damage networks are shown to be a critical factor for high Au concentrations and should be a target for exploration.

Growth process and anticancer properties of gold nanorods.

PubMed

Zhang, Junyan; Wang, Mian; Webster, Thomas J

2017-09-01

Gold nanoparticles have been of great interest because of their unique optical properties, facile synthesis and conjugation. Among various shapes of gold nanoparticles, gold nanorods have been widely studied. They can be conjugated with different molecules for biomedical applications, such as tumor imaging and therapy. However, few researchers have studied the antitumor properties of bare gold nanorods. In this study, unfunctionalized gold nanorods were synthesized and tested on breast tumor cells. Results showed that the aspect ratio of gold nanorods could be easily influenced by both reaction time and the amount of silver nitrate in the growth solution. A new growth process is proposed here based on the UV-Vis spectra and TEM images of gold nanorods at different reaction times. More importantly, cell studies showed that within a certain concentration range, the gold nanorods can selectively kill tumor cells while having limited or little influence on healthy mammalian (dermal fibroblast) cells. Thus, this study shows promise for the use of bare gold nanorods for further study alone or in combination with photothermal treatment. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2616-2621, 2017. © 2017 Wiley Periodicals, Inc.

Tailoring surface plasmon resonance and dipole cavity plasmon modes of scattering cross section spectra on the single solid-gold/gold-shell nanorod

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

Chou Chau, Yuan-Fong, E-mail: chou.fong@ubd.edu.bn; Lim, Chee Ming; Kumara, N. T. R. N.

Tunable surface plasmon resonance (SPR) and dipole cavity plasmon modes of the scattering cross section (SCS) spectra on the single solid-gold/gold-shell nanorod have been numerically investigated by using the finite element method. Various effects, such as the influence of SCS spectra under x- and y-polarizations on the surface of the single solid-gold/gold-shell nanorod, are discussed in detail. With the single gold-shell nanorod, one can independently tune the relative SCS spectrum width by controlling the rod length and rod diameter, and the surface scattering by varying the shell thickness and polarization direction, as well as the dipole peak energy. These behaviorsmore » are consistent with the properties of localized SPRs and offer a way to optically control and produce selected emission wavelengths from the single solid-gold/gold-shell nanorod. The electric field and magnetic distributions provide us a qualitative idea of the geometrical properties of the single solid-gold/gold-shell nanorod on plasmon resonance.« less

Tailoring surface plasmon resonance and dipole cavity plasmon modes of scattering cross section spectra on the single solid-gold/gold-shell nanorod

NASA Astrophysics Data System (ADS)

Chou Chau, Yuan-Fong; Lim, Chee Ming; Lee, Chuanyo; Huang, Hung Ji; Lin, Chun-Ting; Kumara, N. T. R. N.; Yoong, Voo Nyuk; Chiang, Hai-Pang

2016-09-01

Tunable surface plasmon resonance (SPR) and dipole cavity plasmon modes of the scattering cross section (SCS) spectra on the single solid-gold/gold-shell nanorod have been numerically investigated by using the finite element method. Various effects, such as the influence of SCS spectra under x- and y-polarizations on the surface of the single solid-gold/gold-shell nanorod, are discussed in detail. With the single gold-shell nanorod, one can independently tune the relative SCS spectrum width by controlling the rod length and rod diameter, and the surface scattering by varying the shell thickness and polarization direction, as well as the dipole peak energy. These behaviors are consistent with the properties of localized SPRs and offer a way to optically control and produce selected emission wavelengths from the single solid-gold/gold-shell nanorod. The electric field and magnetic distributions provide us a qualitative idea of the geometrical properties of the single solid-gold/gold-shell nanorod on plasmon resonance.

Gold leaf counter electrodes for dye-sensitized solar cells

NASA Astrophysics Data System (ADS)

Shimada, Kazuhiro; Toyoda, Takeshi

2018-03-01

In this study, a gold leaf 100 nm thin film is used as the counter electrode in dye-sensitized solar cells. The traditional method of hammering gold foil to obtain a thin gold leaf, which requires only small amounts of gold, was employed. The gold leaf was then attached to the substrate using an adhesive to produce the gold electrode. The proposed approach for fabricating counter electrodes is demonstrated to be facile and cost-effective, as opposed to existing techniques. Compared with electrodes prepared with gold foil and sputtered gold, the gold leaf counter electrode demonstrates higher catalytic activity with a cobalt-complex electrolyte and higher cell efficiency. The origin of the improved performance was investigated by surface morphology examination (scanning electron microscopy), various electrochemical analyses (cyclic voltammetry, linear sweep voltammetry, and electrochemical impedance spectroscopy), and crystalline analysis (X-ray diffractometry).

Hydrofluorination of Alkynes Catalysed by Gold Bifluorides.

PubMed

Nahra, Fady; Patrick, Scott R; Bello, Davide; Brill, Marcel; Obled, Alan; Cordes, David B; Slawin, Alexandra M Z; O'Hagan, David; Nolan, Steven P

2015-01-01

We report the synthesis of nine new N -heterocyclic carbene gold bifluoride complexes starting from the corresponding N -heterocyclic carbene gold hydroxides. A new methodology to access N,N' -bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) fluoride starting from N,N' -bis(2,6-diisopropylphenyl)imidazol-2-ylidene gold(I) hydroxide and readily available potassium bifluoride is also reported. These gold bifluorides were shown to be efficient catalysts in the hydrofluorination of symmetrical and unsymmetrical alkynes, thus affording fluorinated stilbene analogues and fluorovinyl thioethers in good to excellent yields with high stereo- and regioselectivity. The method is exploited further to access a fluorinated combretastatin analogue selectively in two steps starting from commercially available reagents.

Gold, currencies and market efficiency

NASA Astrophysics Data System (ADS)

Kristoufek, Ladislav; Vosvrda, Miloslav

2016-05-01

Gold and currency markets form a unique pair with specific interactions and dynamics. We focus on the efficiency ranking of gold markets with respect to the currency of purchase. By utilizing the Efficiency Index (EI) based on fractal dimension, approximate entropy and long-term memory on a wide portfolio of 142 gold price series for different currencies, we construct the efficiency ranking based on the extended EI methodology we provide. Rather unexpected results are uncovered as the gold prices in major currencies lay among the least efficient ones whereas very minor currencies are among the most efficient ones. We argue that such counterintuitive results can be partly attributed to a unique period of examination (2011-2014) characteristic by quantitative easing and rather unorthodox monetary policies together with the investigated illegal collusion of major foreign exchange market participants, as well as some other factors discussed in some detail.

Magmatism in the Shapinggou district of the Dabie orogen, China: Implications for the formation of porphyry Mo deposits in a collisional orogenic belt

NASA Astrophysics Data System (ADS)

Ren, Zhi; Zhou, Taofa; Hollings, Pete; White, Noel C.

2018-05-01

The Shapinggou molybdenum deposit is located in the Qinling-Dabie Orogen, which hosts the world's largest molybdenum belt. The igneous rocks at Shapinggou can be divided into two stages (136-127 Ma and 118-114 Ma), the early suite of felsic (136-127 Ma, SiO2 = 58.0 to 72.9 wt%) and mafic rocks (133-128 Ma, SiO2 = 45.2 to 57.0 wt%), and a later suite comprising syenite (117 Ma, SiO2 = 64.2 to 65.0 wt%), quartz syenite porphyry (116 Ma, 62.5 to 70.0 wt%), granite porphyry (112 Ma, SiO2 = 75.5 to 77.6 wt%) and diorite porphyry (111 Ma, SiO2 = 56.6 to 59.7 wt%). The early-stage felsic rocks display high SiO2, Al2O3, Na2O, K2O, Sr, LREE contents, and Sr/Y, (La/Yb)N ratios, initial Sr isotope ratios of 0.7076 to 0.7089, but low MgO, FeOT, Y, Yb contents and negative εNd(t) values, consistent with partial melting of the lower continental crust. The early-stage mafic rocks exhibit low SiO2, high MgO, Ni and Cr contents, consistent with an upper mantle source, but trace element and isotope data suggest a role for crustal contamination. The late-stage syenite and quartz syenite porphyry show high abundances of Na2O, K2O, Al2O3, HFSEs (e.g., Th, U, Zr, Hf) and significant negative Eu anomalies. The late-stage granite porphyry displays high SiO2 contents, and depletions in Ba, Sr, Eu and Ti. The geochemical features of the late-stage intrusions are similar to A-type granites. Crystal fractionation of plagioclase, K-feldspar, biotite/ muscovite, amphibole/ garnet and Fe-Ti oxides controlled the evolution of the magma. The geochemical and isotopic data suggest that the rocks at Shapinggou were likely derived from a mixed source of lithospheric mantle, subducted continental crust of the Yangtze Block (Kongling Group) and partial melts of the Dabie Complex. Early stage rocks represent melts of the source with a lower proportion of Dabie Complex materials, whereas late stage rocks were derived from a source with a higher proportion Dabie Complex component. The geochemical and

Gold-Decorated Supraspheres of Block Copolymer Micelles

NASA Astrophysics Data System (ADS)

Kim, M. P.; Kang, D. J.; Kannon, A. G.; Jung, D.-W.; Yi, G. R.; Kim, B. J.

2012-02-01

Gold-decorated supraspheres displaying various surface morphologies were prepared by infiltration of gold precursor into polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) supraspheres under acidic condition. The supraspheres were fabricated by emulsifying PS-b-P2VP polymer solution into surfactant solution. Selective swelling of P2VP in the suprasphere by gold precursor under acidic condition resulted in the formation of gold-decorated supraspheres with various surface structures. As evidenced by TEM and SEM images, dot pattern was formed in the case of smaller supraspheres than 800 nm; whereas fingerprint-like pattern was observed in larger supraspheres than 800 nm. Gold nanoparticles were located inside P2VP domains near the surface of prepared supraspheres as confirmed by TEM. The optical property of the supraspheres was characterized using UV-vis absorption spectroscopy and the maximum absorption peak at around 580 nm was observed, which means that gold nanoparticles densely packed into P2VP domain on the suprasphere. Our approach to prepare gold-decorated supraspheres can be extended to other metallic particles such as iron oxide or platinum nanoparticles, and those precursors can be also selectively incorporated into the P2VP domain.

Gold/silver/gold trilayer films on nanostructured polycarbonate substrates for direct and label-free nanoplasmonic biosensing.

PubMed

López-Muñoz, Gerardo A; Estévez, M-Carmen; Vázquez-García, Marc; Berenguel-Alonso, Miguel; Alonso-Chamarro, Julián; Homs-Corbera, Antoni; Lechuga, Laura M

2018-05-01

Ultrasmooth gold/silver/gold trilayer nanostructured plasmonic sensors were obtained using commercial Blu-ray optical discs as nanoslits-based flexible polymer substrates. A thin gold film was used as an adhesion and nucleation layer to improve the chemical stability and reduce the surface roughness of the overlying silver film, without increasing ohmic plasmon losses. The structures were physically and optically characterized and compared with nanostructures of single gold layer. Ultrasmooth and chemically stable trilayer nanostructures with a surface roughness <0.5 nm were obtained following a simple and reproducible fabrication process. They showed a figure of merit (FOM) value up to 69.2 RIU -1 which is significantly higher (more than 95%) than the gold monolayer counterpart. Their potential for biosensing was demonstrated by employing the trilayer sensor for the direct and refractometric (label-free) detection of C-reactive protein (CRP) biomarker in undiluted urine achieving a Limit of Detection (LOD) in the pM order. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electrochemical Assay of Gold-Plating Solutions

NASA Technical Reports Server (NTRS)

Chiodo, R.

1982-01-01

Gold content of plating solution is assayed by simple method that required only ordinary electrochemical laboratory equipment and materials. Technique involves electrodeposition of gold from solution onto electrode, the weight gain of which is measured. Suitable fast assay methods are economically and practically necessary in electronics and decorative-plating industries. If gold content in plating bath is too low, poor plating may result, with consequent economic loss to user.

[Theragnostic approaches using gold nanorods and near infrared light].

PubMed

Niidome, Takuro; Shiotani, Atsushi; Akiyama, Yasuyuki; Ohga, Akira; Nose, Keisuke; Pissuwan, Dakrong; Niidome, Yasuro

2010-12-01

Gold nanoparticles have unique optical properties such as surface-plasmon and photothermal effects. Such properties have resulted in gold nanoparticles having several clinical applications. Gold nanorods (which are rod-shaped gold nanoparticles) show a surface plasmon band in the near-infrared region. They have therefore been proposed as contrast agents for bioimaging, or as heating devices for photothermal therapy. Polyethylene glycol-modified gold nanorods systemically administrated into mice can be detected with integrating sphere, and the stability of the gold nanorods in blood flow evaluated. After intravenous injection of gold nanorods followed by near-infrared laser irradiation, significant tumor damage triggered by the photothermal effect was observed. To deliver gold nanorods to the target tissue, thermosensitive polymer gel-coated gold nanorods were prepared. After intravenous injection of the gel-modified gold nanorods and irradiation of the tumor, a larger amount of gold was detected in the irradiated tumor than in the non-irradiated tumor. This effect is due to the hydrophobic interaction between the cellular membrane or the extracellular matrix and the gel surfaces induced by the photothermal effect. Furthermore, the photothermal effect enhanced the permeability of the stratum corneum of the skin. As a result of treatment of the skin with ovalbumin and gold nanorods followed by near-infrared light irradiation, a significant amount of protein was detected in the skin. The gold nanorods therefore showed several functions as a photothermal nanodevice for bioimaging, thermal therapy, and a drug delivery system.

Cross-correlations and influence in world gold markets

NASA Astrophysics Data System (ADS)

Lin, Min; Wang, Gang-Jin; Xie, Chi; Stanley, H. Eugene

2018-01-01

Using the detrended cross-correlation analysis (DCCA) coefficient and the detrended partial cross-correlation analysis (DPCCA) coefficient, we investigate cross-correlations and net cross-correlations among five major world gold markets (London, New York, Shanghai, Tokyo, and Mumbai) at different time scales. We propose multiscale influence measures for examining the influence of individual markets on other markets and on the entire system. We find (i) that the cross-correlations, net cross-correlations, and net influences among the five gold markets vary across time scales, (ii) that the cross-market correlation between London and New York at each time scale is intense and inherent, meaning that the influence of other gold markets on the London-New York market is negligible, (iii) that the remaining cross-market correlations (i.e., those other than London-New York) are greatly affected by other gold markets, and (iv) that the London gold market significantly affects the other four gold markets and dominates the world-wide gold market. Our multiscale findings give market participants and market regulators new information on cross-market linkages in the world-wide gold market.

Gold nanoprobes for theranostics

PubMed Central

Panchapakesan, Balaji; Book-Newell, Brittany; Sethu, Palaniappan; Rao, Madhusudhana; Irudayaraj, Joseph

2011-01-01

Gold nanoprobes have become attractive diagnostic and therapeutic agents in medicine and life sciences research owing to their reproducible synthesis with atomic level precision, unique physical and chemical properties, versatility of their morphologies, flexibility in functionalization, ease of targeting, efficiency in drug delivery and opportunities for multimodal therapy. This review highlights some of the recent advances and the potential for gold nanoprobes in theranostics. PMID:22122586

Reconstruction of multiple P-T-t stages from retrogressed mafic rocks: Subduction versus collision in the Southern Brasília orogen (SE Brazil)

NASA Astrophysics Data System (ADS)

Tedeschi, Mahyra; Lanari, Pierre; Rubatto, Daniela; Pedrosa-Soares, Antônio; Hermann, Jörg; Dussin, Ivo; Pinheiro, Marco Aurélio P.; Bouvier, Anne-Sophie; Baumgartner, Lukas

2017-12-01

The identification of markers of subduction zones in orogenic belts requires the estimation of paleo-geothermal gradients through pressure-temperature-time (P-T-t) estimates in mafic rocks that potentially derive from former oceanic units once. However, such markers are rare in supracrustal sequences specially in deeply eroded and weathered Precambrian orogens, and reconstructing their metamorphic history is challenging because they are commonly retrogressed and only preserve a few mineral relicts of high-pressure metamorphism. Metamorphosed mafic rocks from Pouso Alegre region of the Neoproterozoic Southern Brasília Orogen outcrop as rare lenses within continental gneisses. They have previously been classified as retrograde eclogites, based on the presence of garnet and the characteristic symplectitic texture replacing omphacite. These rocks were interpreted to mark the suture zone between the Paranapanema and São Francisco cratons. To test the possible record of eclogitic conditions in the Pouso Alegre mafic rocks, samples including the surrounding felsic rocks have been investigated using quantitative compositional mapping, forward thermodynamic modeling and in-situ dating of accessory minerals to refine their P-T-t history. In the metamorphosed mafic rocks, the peak pressure assemblage of garnet and omphacite (Jd20, reconstructed composition) formed at 690 ± 35 °C and 13.5 ± 3.0 kbar, whereas local retrogression into symplectite or corona occurred at 595 ± 25 °C and 4.8 ± 1.5 kbar. The two reactions were coupled and thus took place at the same time. A zircon U-Pb age of 603 ± 7 Ma was obtained for metamorphic rims and linked to the retrogression stage. Monazite and metamorphic zircon U-Th-Pb ages for the surrounding rocks are at ca. 630 Ma and linked to peak pressure conditions similar to the one recorded by the mafic rocks. The low maximal pressure of 14 kbar and the high geothermal gradient do not necessarily support subduction process

The effect of 3 torque delivery systems on gold screw preload at the gold cylinder-abutment screw joint.

PubMed

Tan, Keson B; Nicholls, Jack I

2002-01-01

This study measured the gold screw preload at the gold cylinder-abutment screw joint interface obtained by 3 torque delivery systems. Using a precalibrated, strain-gauged standard abutment as the load cell, 3 torque delivery systems tested were shown to have significant differences in gold screw preload when a gold cylinder was attached. Mean preloads measured were 291.2 N for hand torque drivers set at 10 Ncm, 340.3 N for electronic torque controllers at low setting/10 Ncm, 384.4 N for electronic torque controllers at high setting/10 Ncm; and 140.8 N for hand-tightening with a prosthetic slot screwdriver. Significant differences in screw preload were also found between operators using a hand torque driver. Hand-tightening delivered insufficient preload and cannot be recommended for final gold screw tightening. Different electronic torque controller units set at 10 Ncm induced mean gold screw preloads that ranged from 264.1 N to as high as 501.2 N. Electronic torque controllers should be regularly recalibrated to ensure optimal output.

Preparation, characterization, and optical properties of gold, silver, and gold-silver alloy nanoshells having silica cores.

PubMed

Kim, Jun-Hyun; Bryan, William W; Lee, T Randall

2008-10-07

This report describes the structural and optical properties of a series of spherical shell/core nanoparticles in which the shell is comprised of a thin layer of gold, silver, or gold-silver alloy, and the core is comprised of a monodispersed silica nanoparticle. The silica core particles were prepared using the Stöber method, functionalized with terminal amine groups, and then seeded with small gold nanoparticles (approximately 2 nm in diameter). The gold-seeded silica particles were coated with a layer of gold, silver, or gold-silver alloy via solution-phase reduction of an appropriate metal ion or mixture of metal ions. The size, morphology, and elemental composition of the composite nanoparticles were characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermal gravimetric analysis (TGA), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The optical properties of the nanoparticles were analyzed by UV-vis spectroscopy, which showed strong absorptions ranging from 400 nm into the near-IR region, where the position of the plasmon band reflected not only the thickness of the metal shell, but also the nature of the metal comprising the shell. Importantly, the results demonstrate a new strategy for tuning the position of the plasmon resonance without having to vary the core diameter or the shell thickness.

Structure and reactivity of a mononuclear gold(II) complex

NASA Astrophysics Data System (ADS)

Preiß, Sebastian; Förster, Christoph; Otto, Sven; Bauer, Matthias; Müller, Patrick; Hinderberger, Dariush; Hashemi Haeri, Haleh; Carella, Luca; Heinze, Katja

2017-12-01

Mononuclear gold(II) complexes are very rare labile species. Transient gold(II) species have been suggested in homogeneous catalysis and in medical applications, but their geometric and electronic structures have remained essentially unexplored: even fundamental data, such as the ionic radius of gold(II), are unknown. Now, an unprecedentedly stable neutral gold(II) complex of a porphyrin derivative has been isolated, and its structural and spectroscopic features determined. The gold atom adopts a 2+2 coordination mode in between those of gold(III) (four-coordinate square planar) and gold(I) (two-coordinate linear), owing to a second-order Jahn-Teller distortion enabled by the relativistically lowered 6s orbital of gold. The reactivity of this gold(II) complex towards dioxygen, nitrosobenzene and acids is discussed. This study provides insight on the ionic radius of gold(II), and allows it to be placed within the homologous series of nd9 Cu/Ag/Au divalent ions and the 5d8/9/10 Pt/Au/Hg 'relativistic' triad in the periodic table.

Synthesis, characterization, cytotoxic and antitubercular activities of new gold(I) and gold(III) complexes containing ligands derived from carbohydrates.

PubMed

Chaves, Joana Darc Souza; Damasceno, Jaqueline Lopes; Paula, Marcela Cristina Ferreira; de Oliveira, Pollyanna Francielli; Azevedo, Gustavo Chevitarese; Matos, Renato Camargo; Lourenço, Maria Cristina S; Tavares, Denise Crispim; Silva, Heveline; Fontes, Ana Paula Soares; de Almeida, Mauro Vieira

2015-10-01

Novel gold(I) and gold(III) complexes containing derivatives of D-galactose, D-ribose and D-glucono-1,5-lactone as ligands were synthesized and characterized by IR, (1)H, and (13)C NMR, high resolution mass spectra and cyclic voltammetry. The compounds were evaluated in vitro for their cytotoxicity against three types of tumor cells: cervical carcinoma (HeLa) breast adenocarcinoma (MCF-7) and glioblastoma (MO59J) and one non-tumor cell line: human lung fibroblasts (GM07492A). Their antitubercular activity was evaluated as well expressed as the minimum inhibitory concentration (MIC90) in μg/mL. In general, the gold(I) complexes were more active than gold(III) complexes, for example, the gold(I) complex (1) was about 8.8 times and 7.6 times more cytotoxic than gold(III) complex (8) in MO59J and MCF-7 cells, respectively. Ribose and alkyl phosphine derivative complexes were more active than galactose and aryl phosphine complexes. The presence of a thiazolidine ring did not improve the cytotoxicity. The study of the cytotoxic activity revealed effective antitumor activities for the gold(I) complexes, being more active than cisplatin in all the tested tumor cell lines. Gold(I) compounds (1), (2), (3), (4) and (6) exhibited relevant antitubercular activity even when compared with first line drugs such as rifampicin.

Colloidal-gold electrosensor measuring device

DOEpatents

Wegner, S.; Harpold, M.A.; McCaffrey, T.M.; Morris, S.E.; Wojciechowski, M.; Zhao, J.; Henkens, R.W.; Naser, N.; O`Daly, J.P.

1995-11-21

The present invention provides a new device for use in measuring lead levels in biological and environmental samples. Using square wave coulometry and colloidal gold particles impregnated on carbon electrodes, the present invention provides a rapid, reliable, portable and inexpensive means of detecting low lead levels. The colloidal gold modified electrodes have microelectrode array characteristics and produce significantly higher stripping detection signals for lead than are produced at bulk gold electrode surfaces. The method is effective in determining levels of lead down to at least 5 {micro}g/dL in blood samples as small as 10 {micro}L. 9 figs.

Colloidal-gold electrosensor measuring device

DOEpatents

Wegner, Steven; Harpold, Michael A.; McCaffrey, Terence M.; Morris, Susan E.; Wojciechowski, Marek; Zhao, Junguo; Henkens, Robert W.; Naser, Najih; O'Daly, John P.

1995-01-01

The present invention provides a new device for use in measuring lead levels in biological and environmental samples. Using square wave coulometry and colloidal gold particles impregnated on carbon electrodes, the present invention provides a rapid, reliable, portable and inexpensive means of detecting low lead levels. The colloidal gold modified electrodes have microelectrode array characteristics and produce significantly higher stripping detection signals for lead than are produced at bulk gold electrode surfaces. The method is effective in determining levels of lead down to at least 5 .mu.g/dL in blood samples as small as 10 .mu.L.

Redbed-type gold mineralisation, Kupferschiefer, south-west Poland

NASA Astrophysics Data System (ADS)

Piestrzyński, Adam; Pieczonka, Jadwiga; Głuszek, Adam

2002-06-01

A new type of gold mineralisation containing minor amounts of platinum and palladium has been found proximal to the secondary redox interface located below the Cu-Ag Kupferschiefer orebody of the Polkowice-Sieroszowice mine in the south-western part of the Lubin-Sieroszowice district, Poland. This deposit can be classified as redbed-type gold. Our study shows that gold, platinum and palladium occur in secondary red-coloured sections of the basal Zechstein sedimentary rocks and in the uppermost Weissliegendes sandstone. Noble metal mineralisation occurs within an average interval of 0.22 m, which lies directly below the copper ores. The average grade of the horizon is 2.25 ppm Au, 0.138 ppm Pt and 0.082 ppm Pd with a metal content of several tens of tonnes of gold. A transition zone has been recognised between the gold-bearing horizon and the copper deposit. This transition zone is characterised by the presence of low grades of copper (<0.2 wt%) and elevated gold contents (>0.5 ppm). Native gold accompanied by electrum, mercury-bearing gold, haematite, covellite, chalcocite, bornite and chalcopyrite has been identified in the gold-bearing horizon. In some sections, Pd-arsenides, tetra-auricupride, Co-arsenides, clausthalite, tennantite, digenite, yarrowite, spionkopite and galena have also been noted.

Mercury contamination from historical gold mining in California

USGS Publications Warehouse

Alpers, Charles N.; Hunerlach, Michael P.; May, Jason T.; Hothem, Roger L.

2005-01-01

Mercury contamination from historical gold mines represents a potential risk to human health and the environment. This fact sheet provides background information on the use of mercury in historical gold mining and processing operations in California, with emphasis on historical hydraulic mining areas. It also describes results of recent USGS projects that address the potential risks associated with mercury contamination. Miners used mercury (quicksilver) to recover gold throughout the western United States. Gold deposits were either hardrock (lode, gold-quartz veins) or placer (alluvial, unconsolidated gravels). Underground methods (adits and shafts) were used to mine hardrock gold deposits. Hydraulic, drift, or dredging methods were used to mine the placer gold deposits. Mercury was used to enhance gold recovery in all the various types of mining operations; historical records indicate that more mercury was used and lost at hydraulic mines than at other types of mines. On the basis of USGS studies and other recent work, a better understanding is emerging of mercury distribution, ongoing transport, transformation processes, and the extent of biological uptake in areas affected by historical gold mining. This information has been used extensively by federal, state, and local agencies responsible for resource management and public health in California.

Increased cellular uptake of peptide-modified PEGylated gold nanoparticles.

PubMed

He, Bo; Yang, Dan; Qin, Mengmeng; Zhang, Yuan; He, Bing; Dai, Wenbing; Wang, Xueqing; Zhang, Qiang; Zhang, Hua; Yin, Changcheng

2017-12-09

Gold nanoparticles are promising drug delivery vehicles for nucleic acids, small molecules, and proteins, allowing various modifications on the particle surface. However, the instability and low bioavailability of gold nanoparticles compromise their clinical application. Here, we functionalized gold nanoparticles with CPP fragments (CALNNPFVYLI, CALRRRRRRRR) through sulfhydryl PEG to increase their stability and bioavailability. The resulting gold nanoparticles were characterized with transmission electron microscopy (TEM), dynamic light scattering (DLS), UV-visible spectrometry and X-ray photoelectron spectroscopy (XPS), and the stability in biological solutions was evaluated. Comparing to PEGylated gold nanoparticles, CPP (CALNNPFVYLI, CALRRRRRRRR)-modified gold nanoparticles showed 46 folds increase in cellular uptake in A549 and B16 cell lines, as evidenced by the inductively coupled plasma atomic emission spectroscopy (ICP-AES). The interactions between gold nanoparticles and liposomes indicated CPP-modified gold nanoparticles bind to cell membrane more effectively than PEGylated gold nanoparticles. Surface plasmon resonance (SPR) was used to measure interactions between nanoparticles and the membrane. TEM and uptake inhibitor experiments indicated that the cellular entry of gold nanoparticles was mediated by clathrin and macropinocytosis. Other energy independent endocytosis pathways were also identified. Our work revealed a new strategy to modify gold nanoparticles with CPP and illustrated the cellular uptake pathway of CPP-modified gold nanoparticles. Copyright © 2017 Elsevier Inc. All rights reserved.

The Niassa Gold Belt, northern Mozambique - A segment of a continental-scale Pan-African gold-bearing structure?

NASA Astrophysics Data System (ADS)

Bjerkgard, T.; Stein, H. J.; Bingen, B.; Henderson, I. H. C.; Sandstad, J. S.; Moniz, A.

2009-01-01

The Niassa Gold Belt, in northernmost Mozambique, is hosted in the Txitonga Group, a Neoproterozoic rift sequence overlying Paleoproterozoic crust of the Congo-Tanzania Craton and deformed during the Pan-African Orogeny. The Txitonga Group is made up of greenschist-facies greywacke and schist and is characterized by bimodal, mainly mafic, magmatism. A zircon U-Pb age for a felsic volcanite dates deposition of the sequence at 714 ± 17 Ma. Gold is mined artisanally from alluvial deposits and primary chalcopyrite-pyrite-bearing quartz veins containing up to 19 ppm Au have been analyzed. In the Cagurué and M'Papa gold fields, dominantly N-S trending quartz veins, hosted in metagabbro and schist, are regarded as tension gashes related to regional strike-slip NE-SW-trending Pan-African shear zones. These gold deposits have been classified as mesozonal and metamorphic in origin. Re-Os isotopic data on sulfides suggest two periods of gold deposition for the Cagurué Gold Field. A coarse-crystalline pyrite-chalcopyrite assemblage yields an imprecise Pan-African age of 483 ± 72 Ma, dating deposition of the quartz veins. Remobilization of early-formed sulfides, particularly chalcopyrite, took place at 112 ± 14 Ma, during Lower Cretaceous Gondwana dispersal. The ˜483 Ma assemblage yields a chondritic initial 187Os/ 188Os ratio of 0.123 ± 0.058. This implies a juvenile source for the ore fluids, possibly involving the hosting Neoproterozoic metagabbro. The Niassa Gold Belt is situated at the eastern end of a SW-NE trending continental-scale lineament defined by the Mwembeshi Shear Zone and the southern end of a NW-SE trending lineament defined by the Rukwa Shear Zone. We offer a review of gold deposits in Zambia and Tanzania associated with these polyphase lineaments and speculate on their interrelation.

Pulling monatomic gold wires with single molecules: an Ab initio simulation.

PubMed

Krüger, Daniel; Fuchs, Harald; Rousseau, Roger; Marx, Dominik; Parrinello, Michele

2002-10-28

Car-Parrinello molecular dynamics simulations demonstrate that pulling a single thiolate molecule anchored on a stepped gold surface does not preferentially break the sulfur-gold chemical bond. Instead, it is found that this process leads to the formation of a monoatomic gold nanowire, followed by breaking a gold-gold bond with a rupture force of about 1.2 nN. The simulations also indicate that previous single-molecule thiolate-gold and gold-gold rupture experiments both probe the same phenomenon, namely, the breaking of a gold-gold bond within a gold nanowire.

Subchronic inhalation toxicity of gold nanoparticles

PubMed Central

2011-01-01

Background Gold nanoparticles are widely used in consumer products, including cosmetics, food packaging, beverages, toothpaste, automobiles, and lubricants. With this increase in consumer products containing gold nanoparticles, the potential for worker exposure to gold nanoparticles will also increase. Only a few studies have produced data on the in vivo toxicology of gold nanoparticles, meaning that the absorption, distribution, metabolism, and excretion (ADME) of gold nanoparticles remain unclear. Results The toxicity of gold nanoparticles was studied in Sprague Dawley rats by inhalation. Seven-week-old rats, weighing approximately 200 g (males) and 145 g (females), were divided into 4 groups (10 rats in each group): fresh-air control, low-dose (2.36 × 104 particle/cm3, 0.04 μg/m3), middle-dose (2.36 × 105 particle/cm3, 0.38 μg/m3), and high-dose (1.85 × 106 particle/cm3, 20.02 μg/m3). The animals were exposed to gold nanoparticles (average diameter 4-5 nm) for 6 hours/day, 5 days/week, for 90-days in a whole-body inhalation chamber. In addition to mortality and clinical observations, body weight, food consumption, and lung function were recorded weekly. At the end of the study, the rats were subjected to a full necropsy, blood samples were collected for hematology and clinical chemistry tests, and organ weights were measured. Cellular differential counts and cytotoxicity measurements, such as albumin, lactate dehydrogenase (LDH), and total protein were also monitored in a cellular bronchoalveolar lavage (BAL) fluid. Among lung function test measurements, tidal volume and minute volume showed a tendency to decrease comparing control and dose groups during the 90-days of exposure. Although no statistically significant differences were found in cellular differential counts, histopathologic examination showed minimal alveoli, an inflammatory infiltrate with a mixed cell type, and increased macrophages in the high-dose rats. Tissue distribution of gold

Gold-Collar Workers. ERIC Digest.

ERIC Educational Resources Information Center

Wonacott, Michael E.

The gold-collar worker has problem-solving abilities, creativity, talent, and intelligence; performs non-repetitive and complex work difficult to evaluate; and prefers self management. Gold-collar information technology workers learn continually from experience; recognize the synergy of teams; can demonstrate leadership; and are strategic thinkers…

Nanoporous Gold for Enzyme Immobilization.

PubMed

Stine, Keith J; Jefferson, Kenise; Shulga, Olga V

2017-01-01

Nanoporous gold (NPG) is a material of emerging interest for immobilization of biomolecules, especially enzymes. The material provides a high surface area form of gold that is suitable for physisorption or for covalent modification by self-assembled monolayers. The material can be used as a high surface area electrode and with immobilized enzymes can be used for amperometric detection schemes. NPG can be prepared in a variety of formats from alloys containing between 20 and 50 % atomic composition of gold and less noble element(s) by dealloying procedures. Materials resembling NPG can be prepared by hydrothermal and electrodeposition methods. Related high surface area gold structures have been prepared using templating approaches. Covalent enzyme immobilization can be achieved by first forming a self-assembled monolayer on NPG bearing a terminal reactive functional group followed by conjugation to the enzyme through amide linkages to lysine residues. Enzymes can also be entrapped by physisorption or immobilized by electrostatic interactions.

Detection of squamous carcinoma cells using gold nanoparticles

NASA Astrophysics Data System (ADS)

Dai, Wei-Yun; Lee, Sze-tsen; Hsu, Yih-Chih

2015-03-01

The goal of this study is to use gold nanoparticle as a diagnostic agent to detect human squamous carcinoma cells. Gold nanoparticles were synthesized and the gold nanoparticle size was 34.3 ± 6.2 nm. Based on the over-expression of epidermal growth factor receptor (EGFR) biomarkers in squamous carcinoma cells, we hypothesized that EGFR could be a feasible biomarker with a target moiety for detection. We further modified polyclonal antibodies of EGFR on the surface of gold nanoparticles. We found selected squamous carcinoma cells can be selectively detected using EGFR antibody-modified gold nanoparticles via receptor-mediated endocytosis. Cell death was also examined to determine the survival status of squamous carcinoma cells with respect to gold nanoparticle treatment and EGFR polyclonal antibody modification.

Precipitation of gold by the reaction of aqueous gold(III)-chloride with cyanobacteria at 25-80{degrees}C, studied by x-ray absorption spectroscopy.

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

Lengke, M. F.; Ravel, B.; Fleet, M. E.

2007-10-01

The mechanisms of gold precipitation by the interaction of cyanobacteria (Plectonema boryanum UTEX 485) and gold(III) chloride aqueous solutions (7.6 mmol/L final gold) have been studied at 25, 60, and 80 C, using both laboratory and real-time synchrotron radiation absorption spectroscopy experiments. Addition of aqueous gold(III) chloride to the cyanobacterial culture initially promoted the precipitation of amorphous gold(I) sulfide at the cell walls and finally caused the formation of octahedral (111) platelets (<1 to 6 {micro}m) of gold metal near cell surfaces and in solutions. X-ray absorption spectroscopy results confirmed that the reduction mechanism of gold(III) chloride to elemental goldmore » by cyanobacteria involves the formation of an intermediate Au(I) species, gold(I) sulfide, with sulfur originating from cyanobacterial proteins, presumably cysteine or methionine. Although the bioreduction of gold(III) chloride to gold(I) sulfide was relatively rapid at all temperatures, the reaction rate increased with the increase in temperature. At the completion of the experiments, elemental gold was the major species present at all temperatures.« less

Antifungal activity of gold nanoparticles prepared by solvothermal method

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

Ahmad, Tokeer, E-mail: tahmad3@jmi.ac.in; Wani, Irshad A.; Lone, Irfan H.

2013-01-15

Graphical abstract: Gold nanoparticles (7 and 15 nm) of very high surface area (329 and 269 m{sup 2}/g) have been successfully synthesized through solvothermal method by using tin chloride and sodium borohydride as reducing agents. As-prepared gold nanoparticles shows very excellent antifungal activity against Candida isolates and activity increases with decrease in the particle size. Display Omitted Highlights: ► Effect of reducing agents on the morphology of gold nanoparticles. ► Highly uniform and monodisperse gold nanoparticles (7 nm). ► Highest surface area of gold nanoparticles (329 m{sup 2/}g). ► Excellent antifungal activity of gold nanoparticles against Candida strains. -- Abstract:more » Gold nanoparticles have been successfully synthesized by solvothermal method using SnCl{sub 2} and NaBH{sub 4} as reducing agents. X-ray diffraction studies show highly crystalline and monophasic nature of the gold nanoparticles with face centred cubic structure. The transmission electron microscopic studies show the formation of nearly spherical gold nanoparticles of average size of 15 nm using SnCl{sub 2}, however, NaBH{sub 4} produced highly uniform, monodispersed and spherical gold nanoparticles of average grain size of 7 nm. A high surface area of 329 m{sup 2}/g for 7 nm and 269 m{sup 2}/g for 15 nm gold nanoparticles was observed. UV–vis studies assert the excitations over the visible region due to transverse and longitudinal surface plasmon modes. The gold nanoparticles exhibit excellent size dependant antifungal activity and greater biocidal action against Candida isolates for 7 nm sized gold nanoparticles restricting the transmembrane H{sup +} efflux of the Candida species than 15 nm sized gold nanoparticles.« less

Foreland-forearc collisional granitoid and mafic magmatism caused by lower-plate lithospheric slab breakoff: The Acadian of Maine, and other orogens

USGS Publications Warehouse

Schoonmaker, A.; Kidd, W.S.F.; Bradley, D.C.

2005-01-01

During collisional convergence, failure in extension of the lithosphere of the lower plate due to slab pull will reduce the thickness or completely remove lower-plate lithosphere and cause decompression melting of the asthenospheric mantle; magmas from this source may subsequently provide enough heat for substantial partial melting of crustal rocks under or beyond the toe of the collisional accretionary system. In central Maine, United States, this type of magmatism is first apparent in the Early Devonian West Branch Volcanics and equivalent mafic volcanics, in the slightly younger voluminous mafic/silicic magmatic event of the Moxie Gabbro-Katahdin batholith and related ignimbrite volcanism, and in other Early Devonian granitic plutons. Similar lower-plate collisional sequences with mafic and related silicic magmatism probably caused by slab breakoff are seen in the Miocene-Holocene Papuan orogen, and the Hercynian-Alleghenian belt. Magmatism of this type is significant because it gives evidence in those examples of whole-lithosphere extension. We infer that normal fault systems in outer trench slopes of collisional orogens in general, and possibly those of oceanic subduction zones, may not be primarily due to flexural bending, but are also driven by whole-lithosphere extension due to slab pull. The Maine Acadian example suggests that slab failure and this type of magmatism may be promoted by pre-existing large margin-parallel faults in the lower plate. ?? 2005 Geological Society of America.

Seismic anisotropy beneath the southern Ordos block and the Qinling-Dabie orogen, China: Eastward Tibetan asthenospheric flow around the southern Ordos

NASA Astrophysics Data System (ADS)

Yu, Yong; Chen, Yongshun John

2016-12-01

SKS wave splitting analysis is performed to estimate the seismic anisotropy in the upper mantle using teleseismic data recorded by a temporary seismic array of 180 stations called SOSArray deployed in the southern Ordos block and the Qinling-Dabie orogen. The most important finding is that large delay times with NW-SE fast polarization directions in the northeastern Tibet are continuous across the boundary into the southwestern part of the Ordos block, where the SKS wave splitting results are significantly different from those in the rest of the Ordos block. Based on our SKS wave splitting results in addition to the results from previous studies, we propose an asthenospheric flow model for the eastward extrusion of the Tibetan upper mantle. The model consists of two corner flows around the southwestern corner and the southeastern corner of the Ordos block and the eastward flow along the Weihe graben and the Qinling-Dabie orogen for the escaping Tibetan upper mantle. Finally, the clockwise turning flow of the asthenosphere around the southwestern corner of Ordos block has currently extended laterally into the interior of the Ordos block, suggesting that the thick cold lithospheric root of the southwestern Ordos block there is currently being replaced with hot Tibetan asthenosphere at depths, that is, we observed an on-going process of thermal erosion of a cratonic lithosphere by lateral hot asthenospheric flow.

Reconnaissance guidelines for gold exploration in Central Alaska

USGS Publications Warehouse

Light, T.D.; Moll, S.H.; Bie, S.W.; Lee, G.K.

1993-01-01

Distribution of more than 300 gold-bearing samples from the Livengood (Tolovana) and parts of the Fairbanks and Rampart mining districts in central Alaska, USA, indicate that the concentration of gold in placers is spatially related both to structural features and to Late Cretaceous and (or) Tertiary felsic plutons. The regional consistency of these spatial relationships is demonstrated by proximity analysis using a Geographic Information System (GIS), and suggests a genetic association between faults, felsic plutons, and gold occurrences. The local presence of gold within several of the plutons indicates that these are the source of some of the gold. In addition, some gold occurs proximal to faults where plutons are not present, suggesting that some of the gold was also derived from the country rock. We envision a model whereby weakly mineralized solutions, thermally driven by latent plutonic heat, were enriched by circulation through clastic units that may have had a naturally elevated gold background. The resultant enriched solutions were channeled and reconcentrated along or adjacent to large-scale fault systems. Future exploration to define individual target areas should be directed toward areas where Late Cretaceous and (or) Tertiary felsic plutons occur near major faults. ?? 1993.

Thiosulfate leaching of gold from waste mobile phones.

PubMed

Ha, Vinh Hung; Lee, Jae-chun; Jeong, Jinki; Hai, Huynh Trung; Jha, Manis K

2010-06-15

The present communication deals with the leaching of gold from the printed circuit boards (PCBs) of waste mobile phones using an effective and less hazardous system, i.e., a copper-ammonia-thiosulfate solution, as an alternative to the conventional and toxic cyanide leaching of gold. The influence of thiosulfate, ammonia and copper sulfate concentrations on the leaching of gold from PCBs of waste mobile phones was investigated. Gold extraction was found to be enhanced with solutions containing 15-20 mM cupric, 0.1-0.14 M thiosulfate, and 0.2-0.3 M ammonia. Similar trends were obtained for the leaching of gold from two different types of scraps and PCBs of waste mobile phones. From the scrap samples, 98% of the gold was leached out using a solution containing 20 mM copper, 0.12 M thiosulfate and 0.2 M ammonia. Similarly, the leaching of gold from the PCBs samples was also found to be good, but it was lower than that of scrap samples in similar experimental conditions. In this case, only 90% of the gold was leached, even with a contact time of 10h. The obtained data will be useful for the development of processes for the recycling of gold from waste mobile phones. Copyright 2010 Elsevier B.V. All rights reserved.

Gold absorbing film for a composite bolometer

NASA Technical Reports Server (NTRS)

Dragovan, M.; Moseley, S. H.

1984-01-01

The principles governing the design of metal films are reviewed, with attention also given to the choice of metals. A description is then given of the characteristics of a bolometer with a gold absorbing film. It is demonstrated that gold is effective as an absorbing film for a millimeter bolometer operated at 1.5 K. At 1.5 K, gold is significantly better than bismuth since gold has a lower heat capacity for the absorbing film. At 0.3 K, gold and bismuth are both suitable. It is pointed out that at temperatures below 0.3 K, a superconducting absorbing film can have a heat capacity low enough not to dominate the heat capacity of the detector; for this reason, it may give better performance than a nonsuperconducting absorbing film.

A Placer-Gold Evaluation Exercise.

ERIC Educational Resources Information Center

Tunley, A. Tom

1984-01-01

A laboratory exercise allowing students to use drillhole data to simulate the process of locating a placer gold paystreak is presented. As part of the activity students arithmetically compute the value of their gold, mining costs, and personal profits or losses, and decide on development plans for the claim. (BC)

Bottom-up formation of robust gold carbide

PubMed Central

Westenfelder, Benedikt; Biskupek, Johannes; Meyer, Jannik C.; Kurasch, Simon; Lin, Xiaohang; Scholz, Ferdinand; Gross, Axel; Kaiser, Ute

2015-01-01

A new phenomenon of structural reorganization is discovered and characterized for a gold-carbon system by in-situ atomic-resolution imaging at temperatures up to 1300 K. Here, a graphene sheet serves in three ways, as a quasi transparent substrate for aberration-corrected high-resolution transmission electron microscopy, as an in-situ heater, and as carbon supplier. The sheet has been decorated with gold nanoislands beforehand. During electron irradiation at 80 kV and at elevated temperatures, the accumulation of gold atoms has been observed on defective graphene sites or edges as well as at the facets of gold nanocrystals. Both resulted in clustering, forming unusual crystalline structures. Their lattice parameters and surface termination differ significantly from standard gold nanocrystals. The experimental data, supported by electron energy loss spectroscopy and density-functional theory calculations, suggests that isolated gold and carbon atoms form – under conditions of heat and electron irradiation – a novel type of compound crystal, Au-C in zincblende structure. The novel material is metastable, but surprisingly robust, even under annealing condition. PMID:25772348

Ages and origin of felsic rocks from the Eastern Erenhot ophiolitic complex, southeastern Central Asian Orogenic Belt, Inner Mongolia China

NASA Astrophysics Data System (ADS)

Yang, Jinfu; Zhang, Zhicheng; Chen, Yan; Yu, Haifei; Qian, Xiaoyan

2017-08-01

The Central Asian Orogenic Belt (CAOB) is known for its massive Phanerozoic generation of juvenile crust. The tectonic evolution of the CAOB during the late Paleozoic era is still debated. The Eastern Erenhot ophiolite complex (EOC) has been recognized as one of the numerous late Paleozoic ophiolitic blocks in the southeastern part of the CAOB. Zircon U-Pb dating on rhyolite and plagiogranite from the EOC yielded a tight range of ages from 360 to 348 Ma, indicating that the complex formed in the early Carboniferous. The primitive mantle-normalized spider diagram of rhyolites (εNd(t) values of +6.8 and +7) and basalts almost overlaps. Such rhyolites may have been derived from partial melting of juvenile basaltic rocks during the initial opening of the Erenhot-Hegenshan oceanic basin. All of the plagiogranites exhibit similar trace element behaviours of High Field-Strength Elements, such as U, Zr and Hf, and Large Ion Lithophile Elements, such as Ba and Rb, to these of gabbros. These plagiogranites were considered products of episodes of partial melting of hydrous gabbros during ocean floor spreading. We conclude that the northern subduction of the Paleo-Asian Ocean stopped before 360 Ma and the southeastern CAOB experienced extension during the late Paleozoic era. The Erenhot-Hegenshan Ocean, which is comparable to the present Red Sea, originated from syn-collisional crustal thickening, subsequent lithosphere extension, and upwelling of the asthenosphere during orogenic quiescence with an age of 20 Ma.

Formation of neutral and charged gold carbonyls on highly facetted gold nanostructures

NASA Astrophysics Data System (ADS)

Chau, Thoi-Dai; Visart de Bocarmé, Thierry; Kruse, Norbert; Wang, Richard L. C.; Kreuzer, Hans Jürgen

2003-12-01

We show that gold mono- and di-carbonyls are formed on gold field emitter tips during interaction with carbon monoxide gas at room temperature and in the presence of high electrostatic fields. The experiments are done in a time-of-flight atom probe to obtain mass spectra. The yield of monocarbonyl cations is about twice that of di-carbonyl ions. Density functional theory calculations are reported that explain the field stabilization of adsorbed carbonyls and the desorption yield of their cations.

Flexural bending-induced plumelets and their seamounts in accretionary (Japanese-style) and collisional (Tethyan-style) orogenic belts

NASA Astrophysics Data System (ADS)

Hirano, N.; Dilek, Y.

2015-12-01

Seamounts and seamount chains are common in both the upper and lower plates of active subduction zones. Their OIB-type volcanic products are distinctly different from suprasubduction zone (arc, forearc and backarc) generated volcanic rocks in terms of their compositions and mantle sources. Tectonic accretion of such seamounts into the Japanese archipelago in the NW Pacific and into subduction-accretion complexes and active margins of continents/microcontinents within the Tethyan realm during the Cretaceous played a significant role in continental growth. Seamount assemblages comprise alkaline volcanic rocks intercalated with radiolarian and hemipelagic chert, and limestone, and may also include hypabyssal dolerite and gabbro intrusions. In the Tethyan orogenic belts these seamount rocks commonly occur as km-scale blocks in mélange units beneath the late Jurassic - Cretaceous ophiolites nappes, whereas on the Japanese islands they form discrete, narrow tectonic belts within the late Jurassic - Cretaceous accretionary prism complexes. We interpret some of these OIB occurrences in the Japanese and Tethyan mountain belts as asperities in downgoing oceanic plates that formed in <10 million years before their accretion. Their magmas were generated by decompressional melting of upwelling asthenosphere, without any significant mantle plume component, and were brought to the seafloor along deep-seated brittle fractures that developed in the flexed, downgoing lithosphere as it started bending near a trench. The modern occurrences of these "petit-spot volcanoes" are well established in the northwestern Pacific plate, off the coast of Japan. The proposed mechanism of the formation of these small seamounts better explains the lack of hotspot trails associated with their occurrence in the geological record. Magmatic outputs of such flexural bending-induced plumelets should be ubiquitious in the accretionary (Japanese-style) and collisional (Tethyan-style) orogenic belts.

Geochemical and Nd-Sr-Pb isotope characteristics of synorogenic lower crust-derived granodiorites (Central Damara orogen, Namibia)

NASA Astrophysics Data System (ADS)

Simon, I.; Jung, S.; Romer, R. L.; Garbe-Schönberg, D.; Berndt, J.

2017-03-01

The 547 ± 7 Ma old Achas intrusion (Damara orogen, Namibia) includes magnesian, metaluminous to slightly peraluminous, calcic to calc-alkalic granodiorites and ferroan, metaluminous to slightly peraluminous, calc-alkalic to alkali-calcic leucogranites. For the granodiorites, major and trace element variations show weak if any evidence for fractional crystallization whereas some leucogranites are highly fractionated. Both, granodiorites and leucogranites are isotopically evolved (granodiorites: εNdinit: - 12.4 to - 20.5; TDM: 2.4-1.9; leucogranites: εNdinit: - 12.1 to - 20.6, TDM: 2.5-2.0), show similar Pb isotopic compositions, and may be derived from late Archean to Paleoproterozoic crustal source rocks. Comparison with melting experiments and simple partial melting modeling indicate that the granodiorites may be derived by extensive melting (> 40%) at 900-950 °C under water-undersaturated conditions (< 5 wt.% H2O) of felsic gneisses. Al-Ti and zircon saturation thermometry of the most primitive granodiorite sample yielded temperatures of ca. 930 °C and ca. 800 °C. In contrast to other lower crust-derived granodiorites and granites of the Central Damara orogen, the composition of the magma source is considered the first-order cause of the compositional diversity of the Achas granite. Second-order processes such as fractional crystallization at least for the granodiorites were minor and evidence for coupled assimilation-fractional crystallization processes is lacking. The most likely petrogenetic model involves high temperature partial melting of a Paleoproterozoic felsic source in the lower crust ca. 10-20 Ma before the first peak of regional high-temperature metamorphism. Underplating of the lower crust by magmas derived from the lithospheric mantle may have provided the heat for melting of the basement to produce anhydrous granodioritic melts.

Highly active thermally stable nanoporous gold catalyst

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

Biener, Juergen; Wittstock, Arne; Biener, Monika M.

In one embodiment, a system includes a nanoporous gold structure and a plurality of oxide particles deposited on the nanoporous gold structure; the oxide particles are characterized by a crystalline phase. In another embodiment, a method includes depositing oxide nanoparticles on a nanoporous gold support to form an active structure and functionalizing the deposited oxide nanoparticles.

Local density variation of gold nanoparticles in aquatic environments

NASA Astrophysics Data System (ADS)

Hosseinzadeh, F.; Shirazian, F.; Shahsavari, R.; Khoei, A. R.

2016-10-01

Gold (Au) nanoparticles are widely used in diagnosing cancer, imaging, and identification of therapeutic methods due to their particular quantum characteristics. This research presents different types of aqueous models and potentials used in TIP3P, to study the effect of the particle size and density of Au clusters in aquatic environments; so it can be useful to facilitate future investigation of the interaction of proteins with Au nanoparticles. The EAM potential is used to model the structure of gold clusters. It is observed that in the systems with identical gold/water density and different cluster radii, gold particles are distributed in aqueous environment almost identically. Thus, Au particles have identical local densities, and the root mean square displacement (RMSD) increases with a constant slope. However in systems with constant cluster radii and different gold/water densities, Au particle dispersion increases with density; as a result, the local density decreases and the RMSD increases with a larger slope. In such systems, the larger densities result in more blunted second peaks in gold-gold radial distribution functions, owing to more intermixing of the clusters and less FCC crystalline features at longer range, a mechanism that is mediated by the competing effects of gold-water and gold-gold interactions.

Central Pamir crustal thickening to thinning switch: timing of an orogen wide event?

NASA Astrophysics Data System (ADS)

Rutte, D.; Fox, M.; Stuebner, K.; Ratschbacher, L.

2017-12-01

Asian deep crust exposed in gneiss domes of the Pamir permits the investigation of shortening and extension over 30-50 km of Asian crustal section during the India-Asia collision. In the Central Pamir a stack of fold nappes and thrust sheets records >100 km of N-S shortening at >35-22 Ma. N-S extensional structures crosscut this stack and exhumed the Central Pamir domes at 22-15 Ma. In the South Pamir a similar switch to N-S extension is observed, likely with a coeval onset compared to the Central Pamir, but most extension occurred later at 16-2 Ma. N-S extension in the Karakorum and south Tibet may have onset roughly coeval at 25-20 Ma, too. What forced this switch to N-S extension? While the Central Pamir domes extend >400 km along strike of the orogen, little variation in the amount and timing of the exhumation during N-S extension is observed. In contrast, extension in the South Pamir varies along strike. We scrutinize the exhumation history of the Central Pamir domes. We explore the vast P-T-t-d dataset established in recent publications using one-dimensional thermal models that account for the advection of heat driven by exhumation and thus enable interpretation in an internally consistent framework. Rock trajectories are tracked through the evolving thermal field; T-t paths are used to predict thermochronometric data. Comparison of our predictions with the P-T-t-d data provides best fit exhumation rate histories. Our models suggest that the exhumation rate was initially very high, exceeding 6 km/Myr at 22 Ma, and then exponentially decreased to 0.5 km/Myr by 15 Ma. This requires decreasing extension rates from 22­-15 Ma in the Central Pamir. In contrast, extension rates from age-distance relations in the South Pamir Shakdara dome appear constant during extension from 16-2 Ma. Based on comparisons of the geometry, timing and rates of gneiss dome exhumation in the Central and South Pamir we explore how respective boundary conditions shaped the different dome

Deformation of the Songshugou ophiolite in the Qinling orogen

NASA Astrophysics Data System (ADS)

Sun, Shengsi; Dong, Yunpeng

2017-04-01

The Qinling orogen, middle part of the China Central Orogenic Belt, is well documented that was constructed by multiple convergences and subsequent collisions between the North China and South China Blocks mainly based on geochemistry and geochronology of ophiolites, magmatic rocks as well as sedimentary reconstruction. However, this model is lack of constraints from deformation of subduction/collision. The Songshugou ophiolite outcropped to the north of the Shangdan suture zone represents fragments of oceanic crust and upper mantle. Previous works have revealed that the ophiolite was formed at an ocean ridge and then emplaced in the northern Qinling belt. Hence, deformation of the ophiolite would provide constraints for the rifting and subduction processes. The ophiolite consists chiefly of metamorphosed mafic and ultramafic rocks. The ultramafic rocks contain coarse dunite, dunitic mylonite and harzburgite, with minor diopsidite veins. The mafic rocks are mainly amphibolite, garnet amphibolite and amphibole schist, which are considered to be eclogite facies and retrograde metamorphosed oceanic crust. Amphibole grains in the mafic rocks exhibit a strong shape-preferred orientation parallel to the foliation, which is also parallel to the lithologic contacts between mafic and ultramafic rocks. Electron backscattered diffraction (EBSD) analyses show strong olivine crystallographic preferred orientations (CPO) in dunite including A-, B-, and C-types formed by (010)[100], (010)[001] and (100)[001] dislocation slip systems, respectively. A-type CPO suggests high temperature plastic deformation in the upper mantle. In comparison, B-type may be restricted to regions with significantly high water content and high differential stress, and C-type may also be formed in wet condition with lower differential stress. Additionally, the dunite evolved into amphibolite facies metamorphism with mineral assemblages of olivine + talc + anthophyllite. Assuming a pressure of 1.5 GPa

Analogue modeling of rotational orogenic wedges: implications for the Neogene structural evolution of the Southern Central Andes (33°-35°S)

NASA Astrophysics Data System (ADS)

Herrera, S. S.; Farías, M.; Pinto, L.; Yagupsky, D. L.; Guzman, C.; Charrier, R.

2017-12-01

Structural evolution of the southernmost Central Andes is a major subject of debate. Overall vergence within the range and how intra-continental subduction prompts Andean orogeny are controversial topics. Between 33°-35° S, strike of the western slope main structures shifts southwards, from N-S to NNE-SSW, defining the Maipo Orocline. Likely, width of the Principal Cordillera increases southwards. Despite, a progressive southward decrease in orogenic volume has been determined for the segment. To understand such latitudinal variations, and to provide explanations for overall vergence, we carry out analogue models of contractional wedges to explore upper-crustal thrust system development with a progressive variation of the convergence vector. The model setup consisted of a fixed plate on which a mobile plate generated a velocity discontinuity. The upper-crust was simulated using low-cohesive quartz sand. The mobile plate was fixed at its northern end to a pivot, thus progressively incrementing shortening and the obliquity of convergence southwards. PIV photogrammetry recorded wedge evolution. A classical doubly-vergent wedge was formed, consisting of a steep 35° dipping, static thrust on the retro-side, an uplifted core, and an incipient forward-breaking, 25° critically tapered imbricated thrust fan on the pro-side, wider (in plan-view) where the imposed shortening reached the maximum. The resulting wedge is reminiscent of: the steep western Andean slope, in which the bordering thrust has maintained its present position during the Neogene; and the east-vergent fold-and-thrust belt of the eastern slope. The asymmetrical doubly vergence of the model suggests west-directed subduction of the South American continent beneath the orogen. The southward width increase is geometrically comparable to the natural analogue, yet we observe a flat contrast with orogenic shortening and volume estimates for the region. This can be attributed to the fact that uplift and erosion

Extensional unroofing of the metamorphic core of the southern Appalachian orogen prior to the breakup of Pangea: Insights from 40Ar/39Ar thermochronology

NASA Astrophysics Data System (ADS)

Ma, C.; Foster, D. A.; Hames, W. E.; Mueller, P. A.

2017-12-01

Orogenic collapse commonly occurs following the collisional phase of an orogeny and often leads to exhumation of deep crustal metamorphic rocks. The Alleghanian orogeny in the southern Appalachian orogen (SAO) occurred during final assembly of Pangea. 40Ar/39Ar data of hornblende, muscovite, and biotite from Alleghanian granitic plutons in Georgia, Alabama, and Florida of the SAO give cooling ages that progressively young toward the south-southeast prior to ca. 280 Ma and young locally toward the north-northwest after ca. 280 Ma. These cooling-age gradients, along with geometry of the Suwannee suture zone and timing/structures of the South Georgia basin, suggest that metamorphic rocks north of the Suwannee suture in the study area formed the lower plate of a metamorphic core complex. The faults of the Suwannee suture zone were reactivated to form a master extensional detachment fault with the Suwannee terrane comprising the upper plate. Thermochronologic data show that rapid extension of the metamorphic core complex footwall started at ca. 300-295 Ma and the extension continued to at least ca. 240 Ma. The maximum average extension rate is estimated to be 10.3 km/m.y. during ca. 300-280 Ma along the master detachment fault and 2.4 km/m.y. during ca. 280-240 Ma along a secondary detachment fault, reflecting differential extension over time. Main cooling rates of 10‒85˚C/m.y. and exhumation rates of 0.3‒2.8 km/m.y. are calculated for the Alleghanian granitic plutons studied. This work shows that, in the southernmost Appalachians, orogenic collapse resulted in metamorphic core complex-style extension between about 300 and 240 Ma. The horst-and-graben systems of the South Georgia basin formed within the upper plate in this tectonic setting. Metamorphic core complex-style extension, therefore, played a critical role in initial rifting that led to the eventual breakup of Pangea and formation of the Atlantic Ocean and the Gulf of Mexico.

Effects of dissolucytotic gold ions on recovering brain lesions.

PubMed

Danscher, Gorm; Larsen, Agnete

2010-04-01

Recent experimental research has shown that metallic gold releases charged gold atoms when placed intracerebrally and that the liberated gold ions affect inflammation in the brain. The observations suggest that metallic gold can be used as a safe suppressor of inflammation in the central nervous system.