西秦岭北缘关子镇蛇绿岩的形成时代：来自辉长岩中LA-ICP-MS锆石U-Pb年龄的证据   总被引：8，自引：0，他引：8       下载免费PDF全文

裴先治丁仨平  李佐臣刘战庆李高阳  李瑞保王飞 李夫杰 《地质学报》2007,81(11):1550-1561

西秦岭北缘天水地区关子镇蛇绿岩由变质基性火山岩(斜长角闪片岩)和蛇纹岩、变辉石岩、变辉长岩等构造岩块组成.其中的变质基性火山岩具有N-MORB的地球化学特征,显示关子镇蛇绿岩是洋脊型蛇绿岩残片.对蛇绿岩中的辉长岩进行了LA-ICP-MS锆石U-Pb定年,得到206Pb/238U加权平均年龄为(499.7±1.8)Ma(MSWD=2.2),代表了辉长岩的结晶年龄,表明关子镇蛇绿岩是晚寒武世在西秦岭北缘李子园-关子镇-武山洋盆扩张过程中岩浆活动的产物,代表了东秦岭早古生代商丹古洋盆在西秦岭造山带北缘向西延伸的组成部分.  相似文献   

北天山巴音沟蛇绿岩形成于早石炭世:来自辉长岩LA-ICPMS锆石U-Pb年龄的证据   总被引：25，自引：2，他引：25  

徐学义  李向民  马中平  夏林圻  夏祖春  彭素霞 《地质学报》2006,80(8):1168-1176

北天山巴音沟蛇绿岩中堆晶辉长岩的LA-ICPMS锆石U-Pb测年结果确定:巴音沟蛇绿岩中辉长岩形成的同位素地质年代为344.0±3.4Ma。表明巴音沟蛇绿岩所代表的洋盆形成于早石炭世。综合前人天山石炭纪蛇绿岩及构造演化的研究成果,笔者认为巴音沟蛇绿岩是大陆板内强烈拉张的产物。  相似文献   

Variations in Melt Productivity and Melting Conditions along SWIR (70{degrees}E-49{degrees}E): Evidence from Olivine-hosted and Plagioclase-hosted Melt Inclusions   总被引：1，自引：0，他引：1  

Font  L.; Murton  B. J.; Roberts  S.; Tindle  A. G. 《Journal of Petrology》2007,48(8):1471-1494

Melt inclusion and host glass compositions from the easternend of the Southwest Indian Ridge show a progressive depletionin light rare earth elements (LREE), Na₈ and (La/Sm)_n, but anincrease in Fe₈, from the NE (64°E) towards the SW (49°E).These changes indicate an increase in the degree of mantle meltingtowards the SW and correlate with a shallowing of the ridgeaxial depth and increase in crustal thickness. In addition,LREE enrichment in both melt inclusions and host glasses fromthe NE end of the ridge are compatible with re-fertilizationof a depleted mantle source. The large compositional variations(e.g. P₂O₅ and K₂O) of the melt inclusions from the NE end ofthe ridge (64°E), coupled with low Fe₈ values, suggest thatmelts from the NE correspond to a variety of different batchesof melts generated at shallow levels in the mantle melting column.In contrast, the progressively more depleted compositions andhigher Fe₈ values of the olivine- and plagioclase-hosted meltinclusions at the SW end of the studied region (49°E), suggestthat these melt inclusions represent batches of melt generatedby higher degrees of melting at greater mean depths in the mantlemelting column. Systematic differences in Fe₈ values betweenthe plagioclase- and the olivine-hosted melt inclusions in theSW end (49°E) of the studied ridge area, suggest that theplagioclase-hosted melt inclusions represent final batches ofmelt generated at the top of the mantle melting column, whereasthe olivine-hosted melt inclusions correspond to melts generatedfrom less depleted, more fertile mantle at greater depths. KEY WORDS: basalt; melt inclusions; olivine; plagioclase; Southwest Indian Ridge  相似文献   

蛇绿岩及蛇绿岩中浅色岩的SHRIMP U-Pb测年   总被引：101，自引：2，他引：101  

简平  刘敦一  张旗  张福勤  石玉若  施光海  张履桥  陶华 《地学前缘》2003,10(4):439-456

文中简要评述了蛇绿岩的层状辉长岩,斜长岩和斜长花岗岩,以橄榄岩为主岩的花岗岩和蛇绿岩中的埃达克岩的锆石SHRIMP U-Pb年龄的地质意义。层状辉长岩(或堆晶层状辉长岩)通常起源于洋脊下的岩浆房,因而它的形成年龄代表洋壳形成的时代。斜长岩与层状辉长岩的时代相近或略晚。斜长花岗岩年龄的解释极其依赖锆石组成和地球化学证据。橄榄岩为主岩的花岗岩,可能记录蛇绿岩的侵位时代。蛇绿岩中的埃达克岩是消减洋壳在深部的部分熔融的产物。文中发表了新疆扎河坝蛇绿岩SHRIMP定年的中间成果,并简略地介绍了滇川西部金沙江和内蒙古图林凯等地的研究实例。根据层状辉长岩的测定结果,扎河坝蛇绿岩形成于(489±4)Ma,金沙江蛇绿岩形成于(328±8)Ma。内蒙古图林凯蛇绿岩中埃达克岩形成于(467±13)Ma～(429±7)Ma。块状辉长岩、斜长花岗岩和橄榄岩为主岩的花岗质岩石记录了蛇绿岩的复杂演化。新疆扎河坝蛇绿岩中的块状辉长岩中存在多组锆石年龄值。较老的一组为468～511 Ma,与层状辉长岩和斜长岩相似,记录了蛇绿岩或洋壳的形成时代,但是,岩石中的大部分锆石年龄为396～419 Ma,加权平均年龄为(406±4)Ma,可能反映了一次部分熔融事件。滇川西部金沙江蛇绿岩中的斜长花岗岩的形成年龄为约300～285Ma,晚于层状辉长岩和?  相似文献   

小松山超基性杂岩体橄榄石的岩组分析     

赵东宏 《陕西地质》2003,21(2):45-48

沿贺兰山台褶带北部西缘深大断裂带分布的小松山超基性杂岩体属岩浆结晶分异形成的似层状含铬岩体，岩组分析表明岩体中橄榄石具有高度的定向性。笔者通过研究认为，这种定向性系岩浆上侵过程中的流动分异作用影响造成，反映了小松山岩体系构造动荡环境下的产物。  相似文献   

南极三块（L3）陨石球粒结构类型及其矿物学物征     

陶克捷琚宜太  刘小汉李金雁 《岩石学报》2005,21(3):1015-1028

我国第16次南极考察队回收到6块稀少种类陨石-L3型,GRV99001,GRV99019,GRV99020,GRV99021, GRV99022,GRV99026。本文对其中3块陨石进行研究,研究它们的球粒结构和矿物化学成分．它们虽然都属于非平衡普通球粒陨石(L3),但它们的亚类不同,GRV 99001为L3．4,GRV99026为L3．5,GRV99019为L3．6．它们的球粒结构和球粒内的矿物晶体完整性和矿物组合变化比较大,橄榄石和辉石以高镁为特征．这三块陨石的球粒结构种类比较多,有班状的、炉条状的、扇形的和隐晶质的等．在GRV99001陨石中班状结构的球粒内能见到一个或两个以上完整的单晶橄榄石构成的球粒,也能见到多个细小的或是破碎橄榄石,被包裹在辉石晶体内．而在GRV99019和GRV99026陨石中只能见到多个细小单晶体或是破碎的橄榄石晶体．GRV99001陨石的炉条状结构,好象是由一条带状长石矿物,穿插在单个橄榄石晶体中构成．扇形和伞形结构的球粒,以一个点为中心,向外放射呈扇形．如GRV99019陨石中扇形结构球粒,它们是以辉石为主,陨硫铁充填在低钙辉石缝隙中,形成扇形．另一种是以多个点为中心,如GRV99001陨石,它们是由橄榄石、低钙辉石和长石质的玻璃,构成多个小伞形,形状类似三维立体的球,裂缝中也充填有金属矿物．隐晶质的球粒在GRV99026陨石中有两种,一种是在一厘米等于 100un时呈现隐晶质矿物,而放大到一厘米等于5un时,就可以清楚看到两种低钙辉石矿物,在低钙辉石中还有金属矿物．另一种隐晶质结构球粒由极细小破碎的橄榄石和辉石矿物构成．这三块陨石中的橄榄石和辉石都以高镁为特征．班状结构球粒,在GRV99001陨石中橄榄石的MgO-33．37-51．21,辉石为35．9-36．61;GRV99019陨石中橄榄石23．33-56．58,辉石 21．38-33．07;GRV99026陨石中橄榄石45．91-52．63,辉石34．48-37．35．扇形结构球粒,在GRV99001陨石中橄榄石29．94 -46．22,辉石28．17-30．36;GRV99019陨石中橄榄石29．17-34．38,辉石23．11-27．79．炉条状结构的球粒,在GRV99001 陨石中橄榄石51．84-56．03．隐晶质结构球粒,在GRV99026陨石中辉石20．17-21．54,橄榄石30．84-32．66．由此看出矿物晶体完整性越好镁的含量越高．  相似文献   

Modeling of in-situ crystallization processes in the Permian mafic layered intrusion of Mont Collon (Dent Blanche nappe, western Alps)     

Philippe Monjoie  Fran  ois Bussy  Henriette Lapierre  Hans-Rudolf Pfeifer 《Lithos》2005,83(3-4):317-346

The Mont Collon mafic complex is one of the best preserved examples of the Early Permian magmatism in the Central Alps, related to the intra-continental collapse of the Variscan belt. It mostly consists (> 95 vol.%) of ol + hy-normative plagioclase-wehrlites, olivine- and cpx-gabbros with cumulitic structures, crosscut by acid dikes. Pegmatitic gabbros, troctolites and anorthosites outcrop locally. A well-preserved cumulative sequence is exposed in the Dents de Bertol area (center of intrusion). P–T calculations indicate that this layered magma chamber emplaced at mid-crustal levels at about 0.5 GPa and 1100 °C. The Mont Collon cumulitic rocks record little magmatic differentiation, as illustrated by the restricted range of clinopyroxene mg-number (Mg#_cpx = 83–89). Whole-rock incompatible trace-element contents (e.g. Nb, Zr, Ba) vary largely and without correlation with major-element composition. These features are characteristic of an in-situ crystallization process with variable amounts of interstitial liquid L trapped between the cumulus mineral phases. LA-ICPMS measurements show that trace-element distribution in the latter is homogeneous, pointing to subsolidus re-equilibration between crystals and interstitial melts. A quantitative modeling based on Langmuir's in-situ crystallization equation successfully duplicated the REE concentrations in cumulitic minerals of all rock facies of the intrusion. The calculated amounts of interstitial liquid L vary between 0 and 35% for degrees of differentiation F of 0 to 20%, relative to the least evolved facies of the intrusion. L values are well correlated with the modal proportions of interstitial amphibole and whole-rock incompatible trace-element concentrations (e.g. Zr, Nb) of the tested samples. However, the in-situ crystallization model reaches its limitations with rock containing high modal content of REE-bearing minerals (i.e. zircon), such as pegmatitic gabbros. Dikes of anorthositic composition, locally crosscutting the layered lithologies, evidence that the Mont Collon rocks evolved in open system with mixing of intercumulus liquids of different origins and possibly contrasting compositions. The proposed model is not able to resolve these complex open systems, but migrating liquids could be partly responsible for the observed dispersion of points in some correlation diagrams. Absence of significant differentiation with recurrent lithologies in the cumulitic pile of Dents de Bertol points to an efficiently convective magma chamber, with possible periodic replenishment.  相似文献   

Geochronologic Constraints on the Magmatic Underplating of the Gangdisê Belt in the India-Eurasia Collision: Evidence of SHRIMP II Zircon U-Pb Dating     

DONG Guochen  MO Xuanxue  ZHAO Zhidan  GUO Tieying  WANG Liangliang  CHEN Tao 《《地质学报》英文版》2005,(6)

  相似文献   

Geochemistry and petrogenesis of anorogenic basic volcanic-plutonic rocks of the Kundal area,Malani Igneous Suite,western Rajasthan,India     

A. Krishnakanta Singh  G. Vallinayagam 《Journal of Earth System Science》2004,113(4):667-681

The Kundal area of Malani Igneous Suite consists of volcano-plutonic rocks. Basalt flows and gabbro intrusives are associated with rhyolite. Both the basic rocks consist of similar mineralogy of plagioclase, clinopyroxene as essential and Fe-Ti oxides as accessories. Basalt displays sub-ophitic and glomeroporphyritic textures whereas gabbro exhibits sub-ophitic, porphyritic and intergrannular textures. They show comparable chemistry and are enriched in Fe, Ti and incompatible elements as compared to MORB/CFB. Samples are enriched in LREE and slightly depleted HREE patterns with least significant positive Eu anomalies. Petrographical study and petrogenetic modeling of [Mg]-[Fe], trace and REE suggest cogenetic origin of these basic rocks and they probably derived from Fe-enriched source with higher Fe/Mg ratio than primitive mantle source. Thus, it is concluded that the basic volcano-plutonic rocks of Kundal area are the result of a low to moderate degree (< 30%) partial melting of source similar to picrite/komatiitic composition. Within plate, anorogenic setting for the basic rocks of Kundal area is suggested, which is in conformity with the similar setting for Malani Igneous Suite.  相似文献   

Origin of layering in cumulate gabbros in the Oman ophiolite: Insights from magnetic susceptibility measurements in the Wadi Sadm area     

Kiichiro  Kawamura  Takahiro  Hosono  Huda Mohamed  Allawati  Yujiro  Ogawa  Hidetsugu  Taniguchi 《Island Arc》2005,14(4):564-570

Abstract   Magnetic susceptibility and the anisotropy of magnetic susceptibility were measured on an 800-cm-thick succession of cumulate gabbro in the Sadm area of the Oman ophiolite. The section contained three distinct cumulate units. The susceptibility tends to decrease upward in each from a melanocratic layer (several tens of centimeters thick) to a leucocratic layer (a few meters thick). The susceptibility decreases in accordance with the decreasing number of magnetite grains, which are the alteration product mainly of olivine minerals. This suggests the cyclic downward accumulation of olivine in the cumulate gabbro. The apparent strain deduced from the patterns of magnetic and grain fabrics was the result mostly of simple shear, so that the layering of gabbro is understood to be formed primarily by a crystal cumulus process followed by simple shear deformation.  相似文献