Zircon U–Pb and Hf isotopic study of gneissic rocks from the Chinese Altai: Progressive accretionary history in the early to middle Palaeozoic     

Min Sun  Chao Yuan  Wenjiao Xiao  Xiaoping Long  Xiaoping Xia  Guochun Zhao  Shoufa Lin  Fuyuan Wu  A. Kröner 《Chemical Geology》2008,247(3-4):352-383

Gneissic rocks in the Chinese Altai Mountains have been interpreted as either Paleozoic metasedimentary rocks or Precambrian basement. This study reports geochemical and geochronological data for banded paragneisses and associated gneissic granitoids collected along a NE–SW traverse in the northwestern Chinese Altai. Petrological and geochemical data suggest that the protoliths of the banded gneisses were possibly immature sediments with significant volcanic input and that the gneissic granitoids were derived from I-type granites formed in a subduction environment. Three types of morphological features can be recognized in zircons from the banded gneisses and are interpreted to correlate with different sources. Zircons from five samples of banded paragneiss cluster predominantly between 466 and 528 Ma, some give Neoproterozoic ages, and a few yield discordant Paleoproterozoic to Archean ages. Zircon Hf isotopic compositions indicate that both juvenile/mantle and crust materials were involved in the generation of the source rocks from which these zircons were derived. In contrast, zircons occur ubiquitously as elongated euhedral prismatic crystals in the four samples of the gneissic granitoids, and define single populations for each sample with mean ages between 380 and 453 Ma. The general absence of Precambrian inheritance and positive zircon ?Hf values for these granitoids suggest insignificant crustal contribution to the generation of the precursor magmas. Our data can be interpreted in terms of a progressive accretionary history in early to middle Palaeozoic times, and the Chinese Altai may possibly represent a magmatic arc built on a continental margin dominated by Neoproterozoic rocks.  相似文献   

The Temaguessine Fe-cordierite orbicular granite (Central Hoggar,Algeria): U–Pb SHRIMP age,petrology, origin and geodynamical consequences for the late Pan-African magmatism of the Tuareg shield     

《Journal of African Earth Sciences》2008,50(4-5):153-178

The Temaguessine high-level subcircular pluton is intrusive into the LATEA metacraton (Central Hoggar) Eburnian (2 Ga) basement and in the Pan-African (615 Ma) granitic batholiths along a major NW–SE oriented major shear zone. It is dated here (SHRIMP U–Pb on zircon) at 582 ± 5 Ma. Composed of amphibole–biotite granite and biotite syenogranite, it comprises abundant enclaves: mafic magmatic enclaves, country-rock xenoliths and remarkable Fe-cordierite (#Fe = 0.87) orbicules. The orbicules have a core rich in cordierite (40%) and a leucocratic quartz–feldspar rim. They are interpreted as resulting from the incongruent melting of the meta-wacke xenoliths collapsed into the magma: the breakdown of the biotite + quartz assemblage produced the cordierite and a quartz–feldspar minimum melt that is expelled, forming the leucocratic rim. The orbicule generation occurred at T < 850° and P < 0.3 GPa. The Fe-rich character of the cordierite resulted from the Fe-rich protolith (wacke with 4% Fe₂O₃ for 72% SiO₂). Strongly negative ε_Nd (−9.6 to −11.2), Nd T_DM model ages between 1.64 and 1.92 Ga, inherited zircons between 1.76 and 2.04 Ga and low to moderately high I_Sr (0.704–0.710) indicate a Rb-depleted lower continental crust source for the Temaguessine pluton; regional considerations impose however also the participation of asthenospheric material. The Temaguessine pluton, together with other high-level subcircular pluton, is considered as marking the end of the Pan-African magma generation in the LATEA metacraton, resulting from the linear delamination along mega-shear zones, allowing asthenospheric uprise and melting of the lower continental crust. This implies that the younger Taourirt granitic province (535–520 Ma) should be considered as a Cambrian intraplate anorogenic event and not as a very late Pan-African event.  相似文献   

新疆哈密卡拉塔格铜(锌)矿红石幅1∶50 000矿产地质图数据库     

王丰丰  邓小华  李德东  卫晓锋  吕晓强  王燕超  李永胜 《中国地质》2020,47(S2):185-195

新疆哈密卡拉塔格铜(锌)矿红石幅(K46E009008)1∶50 000矿产地质图数据库是根据《固体矿产地质调查技术要求(1∶50 000)》(DD2019-02)和行业其他标准及要求，在充分利用1∶200 000、1∶50 000等区域地质调查工作成果资料的基础上，采用数字填图系统进行野外地质专项填图，并应用室内与室外填编图相结合的方法完成。本数据库将中-上奥陶统荒草坡群大柳沟组、下志留统红柳峡组和卡拉塔格组的建造类型进行了重新划分，把图幅内侵入岩时代划分为志留纪、泥盆纪、二叠纪等3期，建立了岩浆岩演化序列。图幅区内有大中小型矿床和矿点共8个，成矿时代集中分布在志留纪、石炭纪，赋矿围岩为火山碎屑岩和次火山岩，该区优势矿产以铜锌金为主，矿床类型以VMS型和次火山热液脉型矿床为主，分布在图幅东南一带。除金属矿产外，尚有膨润土矿床产出，具有较好的找矿潜力。本数据库包含5个地层单位和3期岩浆岩资料，数据量约为 15.1 MB。这些数据充分反映了该图幅 1∶50 000 矿产地质调查示范性成果，对该区矿产资源研究和勘查等具有参考意义。  相似文献   

Highly fractionated Late Triassic I-type granites and related molybdenum mineralization in the Qinling orogenic belt: Geochemical and U–Pb–Hf and Re–Os isotope constraints     

《Ore Geology Reviews》2014

We present new data on the highly fractionated Late Triassic I-type Liyuantang granite, which is located in the middle segment of the South Qinling Subzone of central China and is associated with molybdenum mineralization. Zircon U–Pb dating indicates that the granite was emplaced at 210.1 ± 1.9 Ma, with a single zircon containing an inherited core that yielded an age of 449.8 ± 7.1 Ma. Magmatic zircons from the granite have ε_Hf(t) values of − 4.0 to + 1.5, whereas the inherited zircon core has a ε_Hf(t) value of − 5.3. Calculated Hf model ages of crust formation are indicative of substantial contributions from melting of Proterozoic crust that ranges in age from 1501 to 1155 Ma. The granite contains high concentrations of Si, Al, Na, and K, is enriched in Rb, Th, and U, has elevated Rb/Sr and Ga/Al ratios, and is depleted in Ti, Fe, Mn, Mg, Ca, and P, with significantly negative Eu anomalies (δEu = 0.33–0.50), similar to other highly fractionated I-type granites. These data indicate that the magmas that formed the Liyuantang pluton were produced during partial melting of Proterozoic garnet-absent quartz amphibolites. The magmas then fractionated apatite, feldspar, Ti-bearing phases, biotite, and hornblende prior to emplacement.Re–Os isotope analysis of molybdenite from the study area yields a mineralization age of 200.9 ± 6.2 Ma, suggesting that the Liyuantang molybdenum deposit formed during a previously unrecognized mineralization event. The present results, together with previous data, demonstrate that highly fractionated I-type granites associated with the second pulse of magmatism in the South Qinling subzone should be considered highly prospective for mineral exploration, focusing on Triassic–Early Jurassic granitoids.  相似文献   

Tectonic evolution of the Qinling orogen and adjacent orogenic belts     

《Gondwana Research》2016

  相似文献   

Generation of peraluminous granitic magma in a post-collisional setting: A case study from the eastern Qilian orogen,NE Tibetan Plateau     

《Gondwana Research》2016

Early Paleozoic peraluminous granites are abundant in the eastern part of the Qilian orogen, northeastern margin of the Tibetan Plateau. A combined study involving geochronology, whole-rock geochemical and Sr–Nd–Hf isotopic compositions for three Early Paleozoic peraluminous granitic plutons (Jishishan, Ledu and Shichuan plutons) from the eastern Qilian orogen was carried out to evaluate the causes of chemical variations and generation mechanisms of peraluminous granitic magmas. These granitic plutons have magma crystallization ages of 455–427 Ma and are moderately to strongly peraluminous (A/CNK = 1.03–1.18). Geochemical and Sr–Nd–Hf isotopic data indicate that they consist substantially of crust-derived melts. The Jishishan and Ledu peraluminous granites were dominantly produced by partial melting of Precambrian orthogneisses. The Shichuan monzogranites, with low HREE contents (e.g., Yb = 0.80–1.83 ppm) and slightly negative ε_Nd(t) (− 5.3 to − 2.3) and positive ε_Hf(t) (+ 1.6 to + 3.4), could be derived from immature crustal materials. Relatively high average zircon saturation temperatures (> 750 °C for each pluton), obvious negative Eu anomalies (Eu/Eu* = 0.28–0.80) and low Pb/Ba ratios (0.03–0.16) for the Jishishan, Ledu and Shichuan granites are consistent with crustal melting involving biotite breakdown under fluid-absent conditions. Our results suggest that compositional variations of moderately to strongly peraluminous granitic magmas are mainly controlled by source compositions and melting conditions, while the processes such as mixing with mantle-derived magma, fractional crystallization, restite unmixing and peritectic assemblage entrainment were insignificant (or only play secondary roles) in their genesis. Late Ordovician to Middle Silurian crustal anatexis in the eastern Central Qilian was probably linked with slab break-off which may be an important mechanism in addition to lithospheric delamination for the generation of moderately to strongly peraluminous granites in a post-collisional setting.  相似文献   

Geochemistry and petrogenesis of Early Carboniferous volcanic rocks in East Junggar,North Xinjiang: Implications for post-collisional magmatism and geodynamic process     

《Gondwana Research》2016,29(4):1466-1481

Early Carboniferous volcanic rocks in the Batamayineishan Formation overlie unconformably the molasse deposits and the ophiolitic mélanges and are restricted in narrow zones along both sides of the Kalamaili orogenic belt in North Xinjiang, southern Central Asian Orogenic Belt. These rocks demonstrate the post-collisional setting in East Junggar commenced in Tournaisian and also mark an important transitional period from the final amalgamation to late Paleozoic voluminous juvenile granitoids in East Junggar. The volcanic rocks are composed of basalt, basaltic andesite, andesite, trachyte and rhyolite. Both mafic and felsic rocks are characterized by enrichments in large ion lithophile elements, light rare earth elements and depletion in Nb and Ta, low initial ⁸⁷Sr/⁸⁶Sr and high, positive ɛ_Nd(t). Three groups of mafic rocks have been identified: Shoshonitic group 1 has the highest MgO, CaO, Ni and Cr and the lowest Na₂O, Al₂O₃, La, Ba, La/Yb and Ba/Th with primary magma features; group 2 calc-alkaline and high-K calc-alkaline mafic rocks have the lowest K₂O, P₂O₅, Th and Th/Nb, and the highest TiO₂; and group 3 (shoshonitic to potassic alkaline) has the highest K₂O, P₂O₅, La, Ba, La/Yb and Th/Nb, and the lowest TiO₂. The A-type-like felsic rocks were derived from the differentiation of the mafic magma. Geological and geochemical evidences indicate that the Batamayineishan Formation was generated from the process of slab breakoff (detachment). Group 1 samples are produced by decompressional melting of the upwelling asthenosphere mainly composed of spinel and garnet (50:50) lherzolite which has been enriched by overlying metasomatized lithosphere during ascent. Group 2 is derived from 5–10% partial melting of shallower spinel-bearing lithospheric mantle induced by the hot rising asthenosphere, where the contribution of slab-derived fluid is predominant. Low partial melting (3–5%) of the mantle wedge and/or thickened lithospheric mantle enriched by slab-derived components generates group 3. Slab breakoff as an important geodynamic process accounts for the post-collisional magmatism between 343.5 Ma–330 Ma, providing a model for post-collisional crust–mantle interaction in the CAOB.  相似文献   

基于多源数据约束的成矿动力学模拟——以宁芜盆地钟姑矿田典型矿床为例   总被引：1，自引：0，他引：1       下载免费PDF全文

贾 蔡 袁 峰李晓晖  胡训宇廖宝胜孙维安  张明明沈 乐 《地质科学》2018,(4):1327-1346

数据驱动是大数据分析的特点之一。成矿过程的数值模拟即采用数据驱动方式,在基本的物理化学方程及地质模型基础上,通过定量的手段,模拟不同阶段、不同条件下成矿系统的演化过程,从而能够更深入、直观的讨论各种地质要素对成矿系统的影响,验证已有的成矿理论,获得新的认识。姑山铁矿床和杨庄铁矿床是宁芜火山岩盆地钟姑矿田内的典型矿床。前人研究显示,杨庄铁矿床为典型的充填-接触交代型热液矿床,而姑山铁矿床目前在成因上仍存在争议,存在岩浆成因和热液成因等多种观点。为了更好的对比和了解姑山铁矿床和杨庄铁矿床的成因及成矿过程,本文基于多源数据的综合解译剖面,采用力-热耦合数值模拟方法对与热液矿床密切相关的扩容空间的形成机制和特点开展研究。模拟结果显示,姑山铁矿床和杨庄铁矿床可能分属不同的成因类型;随着岩体的逐渐冷却,杨庄铁矿床内岩体和地层接触带会出现明显的扩容空间,可为成矿流体的汇聚及矿质的沉淀提供良好的条件,有利于热液矿床的形成;而姑山铁矿床内岩体和地层接触带只有局部区域出现扩容空间,同时体应变数值较小且形态变化大,并不利于大规模的流体汇聚及矿质的沉淀,姑山铁矿床可能主要为岩浆成因,并受少量热液的叠加改造。  相似文献   

Discovery of the fossiliferous Cu Brei Formation (Lower Devonian) in the Kon Tum Block (South Viet Nam)     

《Journal of Asian Earth Sciences》2007,29(1):127-135

Lower Devonian corals and stromatoporoids have recently been discovered in limestones among low grade metamorphic rocks on the western margin of the Kon Tum Block (South Viet Nam). This unit has been identified as the Cu Brei Formation. Coral and stromatoporoid species have been described including Squameofavosites aff. spongiosus, Parallelostroma cf. multicolumnum, Amphipora cf. rasilis, A. cf. raritalis, Simplexodictyon cf. artyschtense, Stromatopora cf. boriarchinovi and Stromatopora sp. indet. The Cu Brei Formation is exposed in a small area 6 km in length and 3 km wide at the foot of Cu Brei Mountain (Sa Thay District, Kon Tum Province). As this formation is in marine shelf facies it is probable that further exposures of Lower Devonian sediments may be discovered in the Kon Tum Block. This discovery raises the question of the tectonic history of the metamorphic Kon Tum Block. It is possible that the block was not an area of positive uplift from the beginning of Paleozoic as has been supposed, but was submerged in a marine environment, at least on its outer margins, in the Devonian, and possibly even earlier, in Early Paleozoic.  相似文献   

Structure,age, and tectonic development of the Huoshishan–Niujuanzi ophiolitic mélange,Beishan, southernmost Altaids     

《Gondwana Research》2014,25(2):820-841

The Huoshishan–Niujuanzi ophiolitic mélange (HNO) is located near the central part of the Beishan Orogenic Belt in the southernmost Altaids. The HNO consists of ultramafic rocks, cumulate gabbros, gabbros, plagiogranites, diorites, diabases, basalts, andesites, rhyolitic volcaniclastic rocks and siliceous sedimentary rocks, many of which are in a schist matrix (Gongpoquan Group). Geochemical data of the mafic rocks indicate a calc-alkaline or a mixture of calc-alkaline and tholeiitic rocks with negative Nb, Ta and positive Pb, Ba and La anomalies, suggesting formation in an island arc or supra-subduction zone setting. A gabbro from a block in the mélange in the Niujuanzi area has a zircon age of 435.0 ± 1.9 Ma and a plagiogranite with an age of 444.3 ± 1.9 Ma, and another gabbro from the Huoshishan area has an age of 410.5 ± 3.7 Ma. The schist matrix has a zircon age of 512 ± 5.3 Ma and contains Silurian, Devonian and Carboniferous fossils, thus the mélange formed in the late Carboniferous or later. Our structural analysis of fault planes in the HNO, the crenulation cleavages (S₂) of the schist, and fold axial planes of early Permian sandy limestone/quartz veins and late Permian sandstones indicates that the mélange underwent a north-to-south compression, and the orientation of stretching lineations, slickensides and fold hinge lines implies that the HNO experienced top-to-the north (or -northwest) movement. The entire planar and linear structural data set suggests that the subduction polarity was probably to the south in the late Paleozoic. The emplacement age of the HNO was probably near the end-Permian based on the age of the youngest rocks in the ophiolitic mélange, and by the presence of a late Permian unconformity. From our work, integrated with published regional data, we outline a comprehensive geodynamic model for the central BOC.  相似文献