Mineralogical and geochemical study of a newly discovered mafic granulite, northwest China: Implications for tectonic evolution of the Altay Orogenic Belt   总被引：5，自引：0，他引：5  

Han-Lin  Chen  Zi-Long  Li  Shu-Feng  Yang  Chuan-Wan  Dong  Wen-Jiao  Xiao  Yoshiaki  Tainosho 《Island Arc》2006,15(1):210-222

Abstract A mafic granulite body was newly discovered in the Altay Orogenic Belt, northwest China. The rocks comprise a suite of coarse‐grained and fine‐grained granulites. Orthopyroxenes (hypersthenes) in the rocks have high X_Mg and low Al₂O₃ contents, whereas clinopyroxenes have low TiO₂ and Al₂O₃ contents. Amphiboles and biotites have a high Mg/(Mg + Fe²⁺) ratio and low contents of F and Cl. The peak metamorphic pressure–temperature (P–T) conditions are estimated as 750–780°C and 6–7 kbar, and retrograde P–T conditions are in the range of 590–620°C and 2.3–3.7 kbar, indicating significant decompression. Metamorphic reactions and P–T estimates define a clockwise P–T path. Geochemically, the rocks are high in Mg/(Mg + Fe) and Al₂O₃, depleted in U, Th, K and Rb, and characterized by light rare earth element enrichment and a weak positive Eu anomaly. The Altay mafic granulite shows depleted Nb, P and Ti contents in the mid‐oceanic ridge basalt normalized spider diagram. The geochemical characteristics suggest that the protolith of the Altay mafic granulite was calc‐alkaline basalt and andesite with an island‐arc affinity. The rock has a high ¹⁴³Nd/¹⁴⁴Nd ratio with ?Nd(0) > 0, indicating derivation from a mantle‐depleted source. In the present study, a two‐stage model for the evolution of the Altay mafic granulite is proposed: an early stage in which calc‐alkaline basalt and andesite with island‐arc affinity were subducted into a deeper level of the crust and subjected to granulite‐facies metamorphism generating the mafic granulite, followed by the later stage exhumation of the system into the upper crust by the late Paleozoic thrusting.  相似文献   

Tectonothermal history of the basement rocks in the western zone of the North China Craton and its tectonic implications   总被引：47，自引：0，他引：47  

Guochun Zhao  Simon A. Wilde  Peter A. Cawood  Liangzhao Lu 《Tectonophysics》1999,310(1-4):37-53

The basement of the North China Craton can be divided into the eastern, central and western zones, based on lithological, structural, metamorphic and geochronological data. The western zone comprises two different petrotectonic units: Archaean tonalitic–trondhjemitic–granodioritic (TTG) grey gneisses and metamorphic mafic rocks, and Palaeoproterozoic khondalite series. The former is characterized by isobaric cooling (IBC)-type anticlockwise P–T paths in the north-northwestern part of the zone and near-isothermal decompression (ITD)-type clockwise P–T paths in the eastern part, adjacent to the central zone. On the other hand, the tectonothermal evolution of Palaeoproterozoic khondalite series rocks is characterized exclusively by nearly isothermal decompression following the peak of metamorphism and then cooling, defining clockwise P–T paths. The Archaean TTG gneisses and associated mafic rocks with anticlockwise metamorphic P–T paths reflects an origin related to underplating and intrusion of mantle-derived magmas which may be derived from mantle plumes. They represent a late Archaean continental block in the western part of the North China Craton. The Palaeoproterozoic khondalite series rocks represent passive continental margin deposits. They were metamorphosed and deformed in the late Palaeoproterozoic during the amalgamation of the western continental block with another continental block in the east part of the North China Craton. The ITD-type clockwise P–T–t paths of the Palaeoproterozoic khondalite series rocks record the tectonothermal histories of the collision of the western and eastern continental blocks which resulted in the final assembly of the North China Craton at c. 1800 Ma.  相似文献   

大别山北部蛇绿岩的地球化学制约   总被引：8，自引：1，他引：7  

刘贻灿  徐树桐 《矿物岩石》1999,19(1):68-73

常量元素,微量元素,稀土元素,Ｎｄ同位素及氧同位素地球化学特征表明,太别山北部变质镁铁－超镁铁质岩带中存在变质的蛇绿岩,它主要由变质橄榄岩,辉长岩（－辉绿岩？）和基性熔岩三部分组成,其中,变质的基性熔岩的亏损地幔模式年龄ｔＤＭ／Ｍａ＝１０３６．８～１２９３．８,εＮｄ（ｔ）＝７．２～７．７,表明它可能代表１０００Ｍａ左右形成于中等扩张速率（２ｃｍ／ａｄ左右）洋盆条件下的洋壳残片。  相似文献   

Volcanism in the Vitim Volcanic Field, Siberia: Geochemical Evidence for a Mantle Plume Beneath the Baikal Rift Zone   总被引：6，自引：1，他引：5  

JOHNSON  J. S.; GIBSON  S. A.; THOMPSON  R. N.; NOWELL  G. M. 《Journal of Petrology》2005,46(7):1309-1344

The Baikal Rift is a zone of active lithospheric extension adjacentto the Siberian Craton. The 6–16 Myr old Vitim VolcanicField (VVF) lies approximately 200 km east of the rift axisand consists of 5000 km³ of melanephelinites, basanites, alkaliand tholeiitic basalts, and minor nephelinites. In the volcanicpile, 142 drill core samples were used to study temporal andspatial variations. Variations in major element abundances (e.g.MgO = 3·3–14·6 wt %) reflect polybaric fractionalcrystallization of olivine, clinopyroxene and plagioclase. ⁸⁷Sr/⁸⁶Sr_i(0·7039–0·7049), ¹⁴³Nd/¹⁴⁴Nd_i (0·5127–0·5129)and ¹⁷⁶Hf/¹⁷⁷Hf_i (0·2829–0·2830) ratiosare similar to those for ocean island basalts and suggest thatthe magmas have not assimilated significant amounts of continentalcrust. Variable degrees of partial melting appear to be responsiblefor differences in Na₂O, P₂O₅, K₂O and incompatible trace elementabundances in the most primitive (high-MgO) magmas. Fractionatedheavy rare earth element (HREE) ratios (e.g. [Gd/Lu]_n > 2·5)indicate that the parental magmas of the Vitim lavas were predominantlygenerated within the garnet stability field. Forward major elementand REE inversion models suggest that the tholeiitic and alkalibasalts were generated by decompression melting of a fertileperidotite source within the convecting mantle beneath Vitim.Ba/Sr ratios and negative K anomalies in normalized multi-elementplots suggest that phlogopite was a residual mantle phase duringthe genesis of the nephelinites and basanites. Relatively highlight REE (LREE) abundances in the silica-undersaturated meltsrequire a metasomatically enriched lithospheric mantle source.Results of forward major element modelling suggest that meltingof phlogopite-bearing pyroxenite veins could explain the majorelement composition of these melts. In support of this, pyroxenitexenoliths have been found in the VVF. High Cenozoic mantle potentialtemperatures (1450°C) predicted from geochemical modellingsuggest the presence of a mantle plume beneath the Baikal RiftZone. KEY WORDS: Baikal Rift; mafic magmatism; mantle plume; metasomatism; partial melting  相似文献   

Late-Stage Mafic Injection and Thermal Rejuvenation of the Vinalhaven Granite, Coastal Maine   总被引：11，自引：0，他引：11  

WIEBE  R. A.; MANON  M. R.; HAWKINS  D. P.; McDONOUGH  W. F. 《Journal of Petrology》2004,45(11):2133-2153

The Vinalhaven intrusive complex consists mainly of coarse-grainedgranite, inward-dipping gabbro–diorite sheets, and a fine-grainedgranite core. Small bodies of porphyry occur throughout thecoarse-grained granite. The largest porphyry body (roughly 0·5km by 2·5 km) occurs with coeval gabbro, hybrid rocks,and minor fine-grained granite in the Vinal Cove complex, whichformed during the waning stages of solidification of the coarse-grainedVinalhaven granite. Porphyry contacts with surrounding coarse-grainedgranite are irregular and gradational. Compositions of wholerocks and minerals in the porphyry and the coarse-grained graniteare nearly identical. Neighboring phenocrysts in the porphyryvary greatly in degree of corrosion and reaction, indicatingthat the porphyry was well stirred. Thermal rejuvenation ofa silicic crystal mush by a basaltic influx can explain thecomposition and texture of the porphyry. Comparable rejuvenationevents have been recognized in recent studies of erupted rocks.Weakly corroded biotite phenocrysts in the porphyry requirethat hydrous interstitial melt existed in the granite duringremelting. Field relations, along with thermal calculations,suggest that cooling and crystallization of coeval mafic magmacould have generated the porphyry by thermal rejuvenation ofgranite crystal-mush containing about 20% melt. Field relationsalso suggest that some of the porphyry matrix may representnew felsic magma that was emplaced during remelting. KEY WORDS: granite; magma chamber; mafic replenishment; rejuvenation  相似文献   

扬子地台西南缘传统型铂族矿产地质特征          下载免费PDF全文

丁俊  杨家瑞 《沉积与特提斯地质》2004,24(3):1-14

传统型铂族矿产，系指与镁铁质岩浆成矿作用有关的铂族矿产资源。华力西运动时期，扬子地台西南缘沿超壳深断裂带发生的大陆裂谷作用，为来自上地幔的镁铁质(拉斑玄武岩质)岩浆的上涌和侵位提供了极为有利的前提条件。含铂基性超基性岩的时空分布，受到大陆裂谷作用的主要发生发展时期和裂谷活动带的控制。通过对典型矿床特征及其成矿作用的探讨，论述了扬子地台西南缘主要的铂族矿床类型；并从四维成矿的角度，阐述了对区域成矿规律的一些基本认识。  相似文献   

青藏高原南羌塘基性岩墙群U-Pb和Sm-Nd同位素定年及构造意义   总被引：17，自引：0，他引：17  

李　才和钟铧  李惠民 《中国地质》2004,31(4):384-389

羌塘地区是青藏高原古特提斯研究的关键地区,羌塘南部地区基性岩墙群的侵位时代与构造背景对确定古特提斯阶段联合古陆解体的具体时间和青藏高原构造演化有重要意义。选择单颗粒锆石U-Pb法和全岩Sm-Nd等时线法对基性岩墙进行定年研究,获得了(312±4)Ma单颗锆石U—Pb谐合线年龄和(299±13)Ma和(314±5)Ma两个Sm-Nd全岩等时年龄。结合区域地质资料研究认为,基性岩墙群为羌塘地块裂离作用的产物,所获得的同位素年龄代表了基性岩墙群的侵位时间,为羌塘地块裂解提供了构造事件年龄,为重塑龙木错—双湖古特提斯洋盆的形成演化过程提供了重要信息。  相似文献   

冀西北石榴基性麻粒岩中辉石的演化及其地质意义   总被引：2，自引：0，他引：2  

耿元生  沈其韩 《岩石学报》2000,16(1):29-38

冀西北石榴基性麻粒岩中的辉石可分为三个世代。第一世代的单斜和斜方辉石包裹于石榴石变斑晶中, 它们形成的温压条件为 T=750～830℃, P=1.0～1.26GPa。第二世代的单斜和斜方辉石分布于基质中, 它们和斜长石常构成120°交角的稳定共生结构, 形成条件 T=780～860℃, P=0.83～0.92GPa。第三世代的辉石产于石榴石的冠状反应边内, 形成条件 T=720～750℃, P=0.554～0.679GPa。从第一世代单斜辉石到第三世代单斜辉石, 它们的Al  相似文献   

东天山哈密地区早二叠世花岗岩体及镁铁质包体的年代学, 岩石地球化学特征及其构造意义   总被引：2，自引：0，他引：2  

陈希节  张奎华  周健 《地质学报》2016,90(9):2334-2354

花岗岩中包体是区域构造与深部过程研究结合的良好窗口,对研究花岗岩的成因和壳-幔相互作用有非常重要的意义。东天山南山口黑云母二长花岗岩中广泛发育镁铁质包体。主量元素组成上,寄主花岗岩岩具有中酸性、准铝质、富碱、富钾等特征;镁铁质包体则偏基性、贫钾。微量和稀土元素组成上,富集Rb、K、Th、U,贫Sr、P、Nb、Ta、Ti,且Zr、Hf含量相对较高,具中-强的铕负异常(0.46~0.57)。镁铁质包体与寄主岩具有相似的微量元素特征,但相对富集Sr、P,贫Zr、Hf,铕负异常中等或不明显(0.80~0.93)。闪长质包体属于同源包体,为寄主花岗岩同源母岩浆经结晶分异形成的早期产物。运用LA-ICP-MS锆石U-Pb定年技术,该南山口岩体暗色镁铁质微粒包体与寄主黑云母二长花岗岩的锆石U-Pb年龄分别为298.2±2.0Ma和294.0±2.7Ma,包体与寄主岩样品具有相似的Hf同位素组成,暗示其母岩浆来自新元古代晚期和早古生代亏损地幔中分离的新生地壳。该高钾钙碱性的花岗岩及其包体可能形成于东天山后碰撞背景下的板片断离后引起软流圈上涌,底侵体带来的热能使得新元古代晚期和早古生代的新生地壳发生部分熔融。  相似文献   

华北克拉通东部鲁西早白垩纪基性岩墙成因:来自锆石年龄、地球化学和Sr-Nd-Hf同位素的证据   总被引：2，自引：2，他引：0  

刘燊  冯彩霞  翟明国  胡瑞忠  赖绍聪  陈俊瑾  颜军 《岩石学报》2016,32(3):629-645

中生代基性辉绿岩墙广泛分布于华北克拉通东部山东地区。本研究给出代表性岩墙的U-Pb锆石年龄、地球化学和Sr-Nd-Hf同位素证据,4个代表性锆石的LA-ICP-MS年龄范围处于121.9±0.6Ma和124.3±0.5Ma之间(早白垩纪)。岩石的主量元素组成变化较小,岩石富集轻稀土元素和大离子亲石元素(如,Rb、Ba、U、K和Pb),以及亏损高场强元素(如,Nb、Ta和Ti)。另外,基性岩墙具有相对一致的(⁸⁷Sr/⁸⁶Sr)_i比值(~0.7098),负的ε_Nd(t)值(-14.7~-14.5)、ε_Hf(t)值(-31.4~-26.7)和高的Hf模式年龄(t_DM1=1817~2024Ma)。研究显示基性岩墙来自富集岩石圈地幔的部分熔融作用,并在上升侵位过程中经历了一定程度的地壳混染作用影响。总体研究表明,基性岩墙的成因机制与扬子克拉通与华北克拉通的碰撞有关,岩浆源区为晚中生代前受俯冲扬子地壳沉积物交代后的富集岩石圈地幔。  相似文献