Sample records for adamellite

  1. Pegmatoid schlieren with tourmaline in granitoids of eastern russia as an attribute of intrusive series completed by ore-bearing Li-F granites

    NASA Astrophysics Data System (ADS)

    Alekseev, V. I.; Marin, Yu. B.


    Tourmaline schlieren in pegmatoids and host granites are widespread in Cretaceous granitoid plutons occurring in tin districts of eastern Russia. These schlieren were formed under the action of fluoricboron fluids, which are considered to be forerunners of rare-metal granite magmatism. The tourmaline schlieren in adamellites, biotite, and two-mica granites are reliable attributes of intrusive series completed by emplacement of ore-bearing Li-F granites.

  2. Lead isotope systematics of some igneous rocks from the Egyptian Shield

    NASA Technical Reports Server (NTRS)

    Gillespie, J. G.; Dixon, T. H.


    Lead isotope data on whole-rock samples and two feldspar separates for a variety of Pan-African (late Precambrian) igneous rocks for the Egyptian Shield are presented. It is pointed out that the eastern desert of Egypt is a Late Precambrian shield characterized by the widespread occurrence of granitic plutons. The lead isotope ratios may be used to delineate boundaries between Late Precambrian oceanic and continental environments in northeastern Africa. The samples belong to three groups. These groups are related to a younger plutonic sequence of granites and adamellites, a plutonic group consisting of older tonalites to granodiorites, and the Dokhan volcanic suite.

  3. Structural characteristics and LA-ICP-MS U-Pb zircon geochronology of the deformed granitic rocks from the Mesozoic Xingcheng-Taili ductile shear zone in the North China Craton

    NASA Astrophysics Data System (ADS)

    Liang, Chenyue; Liu, Yongjiang; Neubauer, Franz; Jin, Wei; Zeng, Zuoxun; Genser, Johann; Li, Weimin; Li, Wei; Han, Guoqing; Wen, Quanbo; Zhao, Yingli; Cai, Libin


    We describe the recently detected ENE-trending Xingcheng-Taili ductile strike-slip shear zone, which is an important Mesozoic low- to middle-grade tectonic element formed during the reactivation of the North China Craton (NCC) at the eastern termination of the Yanshanian orogenic belt. Within the Xingcheng-Taili ductile shear zone, the degree of deformation weakens gradually from NW to SE. Three main types of banded granitic gneisses represent low- to middle-grade metamorphic tectonites. New U-Pb zircon dating gives a wide range of protolith ages. Neoarchean granitic rocks with an emplacement age of 2498.4 ± 6.3 Ma have obvious E-W trending banded structures. Upper Triassic granitic rocks with U-Pb zircon ages of 219.7 ± 1.1 Ma, 218.74 ± 0.61 Ma, 212.1 ± 1.6 Ma and 212.3 ± 1.9 Ma are considered to relate to the collision of the NCC and Yangtze craton in early Mesozoic times. The emplacement of biotite adamellite bodies with ages of 159.0 ± 0.8 Ma and 152.4 ± 1.9 Ma is related to the thinning of the NCC's continental crust. An ENE-trending sinistral ductile shear zone developed within these granites. The strongly deformed biotite adamellite bodies bear a gneissosity with S-C fabrics, ENE-trending sinistral shear zones and show the deformation characteristics of a shallow crustal level, reflecting decratonization of the NCC. Crystal lattice preferred orientations (LPO) of quartz, determined by electron back-scatter diffraction, suggest sinistral strike-slip shear and a deformation temperature at about 400 to 500 °C. Quartz mainly shows low-temperature fabrics with a dominant {0001}-slip system similar to the temperature estimated by the micro-structural characteristics of quartz and feldspar. This deformation event might have occurred in Early Cretaceous times and is related to the lithospheric thinning and extension of the North China Craton triggered by an ongoing roll-back of the Pacific Plate beneath the eastern North China Craton.

  4. Rare earth elements content in geological samples from eastern desert, Egypt, determined by instrumental neutron activation analysis.


    El-Taher, A


    Twenty representative geological samples (tonalite, granodiorite, adamellite, syenogranite, rapakivi syenogranite, alkali feldspar granite and monzogranite) were collected from G. Kattar area in Eastern Desert, Egypt, for analysis by instrumental neutron activation as a sensitive nondestructive analytical tool for the determination of 14 rare earth elements (REEs) and to find out the following: (1) what information could be obtained about the REEs and distribution patterns of REEs in geological samples under investigation, (2) to estimate the accuracy, reproducibility and detection limit of the INAA method in case of the given samples. The samples were properly prepared together with standard reference material and simultaneously irradiated in a neutron flux of 7x10(11)n/cm(2)s in the TRIGA Mainz research reactor facilities. The gamma spectra were collected by an HPGe detector and the analysis was done by means of a computerized multichannel analyzer. The choice of the nuclear reaction, irradiation and decay times, and of the proper gamma radiation in counting are presented and discussed. The results are found to be in good agreement with certified values. PMID:20236830

  5. Magma mixing in the Kalaqin core complex, northern North China Craton: Linking deep lithospheric destruction and shallow extension

    NASA Astrophysics Data System (ADS)

    Fu, Lebing; Wei, Junhao; Tan, Jun; Santosh, M.; Zhang, Daohan; Chen, Jiajie; Li, Yanjun; Zhao, Shaoqing; Peng, Lina


    The widespread Mesozoic magmatism in the North China Craton (NCC) has received considerable attention as a trigger for large scale lithospheric destruction. Here we investigate the Early Cretaceous Jiguanzi adamellite from the northern part of the NCC which is contemporaneous with shallow extensional deformation and deep lithospheric destruction. This intrusion emplaced at ca. 133 Ma is located in the foot wall of the Kalaqin metamorphic core complex (MCC), and occurs as a synextensional ring complex with numerous magmatic equigranular (Group 1) and porphyritic (Group 2) enclaves. Hornblende and plagioclase from the host adamellite and xenocrysts of Group 2 enclaves show distinct inverse zoning with Mg- and Ca-rich mantle. The Group 2 enclaves are characterized by plagioclase xenocrysts hosting hornblende, biotite and apatite inclusions, quartz ocelli with fine-grained rim enriched in biotite and hornblende, and poikilitic biotite surrounded by hornblende. Geochemically, the host intrusion is calc-alkaline to alkaline and metaluminous with variable contents of SiO2 (60.70-72.20 wt.%), Al2O3 (14.19-17.22 wt.%), Na2O + K2O (6.16-9.42 wt.%), and Mg# values (28.0-47.7), whereas the Group 2 enclaves exhibit low SiO2 (54.05-55.55 wt.%), high Fe2O3 (8.18-8.64 wt.%) and TiO2 (2.08-2.28 wt.%), and moderate Mg# (44.0-44.1). Both the host intrusion and Group 2 enclaves are enriched in large-ion lithophile and light rare earth elements, and depleted in high field strength elements and heavy rare earth elements except that the latter has lower Ba and high Nb, Ta and Ti contents. The major and trace element contents of the Group 1 enclaves are broadly similar to those of the host intrusion. Analyses of Sr-Nd-Hf isotopes in the host intrusion, and in Group 1 and Group 2 enclaves show (87Sr/86Sr)ihost = 0.70600-0.70618, εNd(t)host = - 8.2 to - 9.6, T2DM(Nd)host = 1592-1706 Ma, εHf(t)host = - 9.2 to - 12.0, (87Sr/86Sr)iGroup 1 = 0.70590-0.70635, εNd(t)Group 1 = - 9.6 to - 10

  6. Radioelement distributions in the Proterozoic granites and associated pegmatites of Gabal El Fereyid area, Southeastern Desert, Egypt.


    Abd El-Naby, H H; Saleh, G M


    Lithologically, the rock types in the Gabal El Fereyid area are dominantly granites with minor amounts of pegmatites. The granites range in composition from tonalite to granite-adamallite with minor acidic dikes, quartz and pegmatite veins. The granite-adamallite is peraluminous and formed as a result of partial melting of amphibole-bearing rocks at depths of approximately 24-30 km and at temperatures of 800-950 degrees C. Among the different rock types, the muscovite-rich pegmatites had the highest U and Th contents (66 and 38 ppm on average, respectively). The high level of radioactivity in pegmatites is attributed to the presence of the radioactive minerals thorianite, uranophane and allanite as confirmed by XRD analysis. Binary relations of Zr/U, Zr/Th, Ce/U and Ce/Th against either U or Th in the granite-adamellite exhibit significant negative correlations indicating that both elements are not preferentially hosted in the accessory minerals phases such as zircon and monazite, but could be associated with major forming minerals such as biotite, muscovite, plagioclase and quartz, or U is situated within labile sites within granite. The uranium and thorium enrichment in the pegmatites is a two-stage process. The primary stage is magmatic whereas the secondary enrichment is from hydrothermal concentration. The magmatic U and Th are indicated by the presence of thorianite and allanite, whereas evidence of hydrothermal mineralization is the alteration of rock-forming minerals such as feldspar and the formation of secondary minerals such as uranophane and pyrite. PMID:14522238

  7. Pan-African alkali granites and syenites of Kerala as imprints of taphrogenic magmatism in the South Indian shield

    NASA Technical Reports Server (NTRS)

    Santosh, M.; Drury, S. A.; Iyer, S. S.


    Granite and syenite plutons with alkaline affinities ranging in age from 550 to 750 Ma sporadically puncture the Precambrian granulites of the Kerala region. All the bodies are small (20 to 60 sq km), E-W to NW-SE elongated elliptical intrusives with sharp contacts and lie on or close to major late Proterozoic lineaments. Geochemical plots of A-F-M and An-Ab-Or relations show an apparent alkali enrichment trend on the former, but the plutons define relatively distinct fields on the latter. Most of the plutons are adamellitic to granitic by chemistry. The variations of SiO2 with log sub 10 K2O/MgO (1) brings out the distinct alkaline nature of the plutons. Some of the granites are extremely potassic, like the Peralimala pluton, which shows up to 11.8 percent K2O. On a SiO2-Al2O3-Na2O+K2O (mol percent) plot, the plutons vary from peraluminous to peralkaline, but none are nepheline normative. Low MgO, low to moderate CaO and high Fe2O3/FeO values are other common characteristics. Among trace elements, depletion of Ba, Sr and Rb with high K/Ba and K/Rb values are typical. Overall, the plutons show a trend of decreasing K/Rb ratio with increasing K content. Individual plutons show more clearly defined trends similar to those from granitic masses characterized by plagioclase fractionation.

  8. Evolution and Metallogenesis of the Great Serpentinite Belt in the New England Orogen, N.S.W. Australia

    NASA Astrophysics Data System (ADS)

    Manton, R. J.; Buckman, S.; Nutman, A.


    Current tectonic interpretations of disrupted ophiolitic complexes and scattered HP/LT eclogite-blueschist blocks within the New England Orogen are still problematic due to limited or unreliable geochronological data. Ophiolitic, island-arc and accretionary complex terranes are contained or spatially associated within the 'alpine-type' Great Serpentinite Belt, which is controlled by the ~350km long, NNW-SSE orientated, Peel-Manning Fault System. The Cambro-Ordovician blocks within the mélange contrast with the Permian emplacement age for the serpentinite. Early Cambrian (530 Ma) ages of the igneous zircons extracted from plagiogranites and tonalities record the formation of the ophiolitic protolith making them the oldest rocks in eastern Australia (Aitchison et al., 1992 Geology v. 20). The timing of serpentinite emplacement is problematic. The minimum age is constrained by the stitching pluton of the Late Permian Moonbi Adamellite (256 × 4 Ma) and the presence of serpentinite clasts within adjacent Early? Permian Manning Group rocks. However, the maximum emplacement age is less well constrained and limited to the absence of serpentinite clasts in older adjacent Carboniferous sedimentary rocks, thereby suggesting the serpentinite belt was not exposed until the Early Permian. In this study we present zircon U-Pb dates and REE chemistry of an eclogite block in the serpentinite belt at Attunga. REE chemistry of the zircons shows an age of 492 × 13 Ma for high pressure metamorphism. Igneous inheritance in metamorphic zircon has an age of ~530 Ma. Titanium in zircon thermometry (zircon + rutile + quartz) indicate high pressure zircon growth at 650 - 700°C. This is higher than the previously calculated 290 - 600°C, which was based on the distribution of Fe and Mg between co-existing garnet and pyroxene (Shaw and Flood 1974, AJES v. 21). We interpret this block as being a portion of the metamorphic sole of the original ophiolite. Ongoing studies will further

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

    NASA Astrophysics Data System (ADS)

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


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