河北滦平周台子条带状铁矿地质特征、围岩时代及其地质意义   总被引：5，自引：4，他引：1  

相鹏  崔敏利  吴华英  张晓静  张连昌 《岩石学报》2012,28(11):3655-3669

河北滦平县周台子铁矿位于华北克拉通北缘,是产于前寒武纪单塔子群变质岩系中的鞍山式铁矿,具有条带状铁建造(BIF)特征。矿石主要呈条带状构造,有的呈条纹和致密块状构造。矿石类型主要以石英磁铁矿型为主,含铁介于30%~35%。前寒武纪变质岩是矿床的主要围岩,出露有黑云母(角闪)斜长片麻岩和斜长角闪岩,局部见花岗片麻岩。原岩恢复表明,黑云母(角闪)斜长片麻岩的原岩为英安岩-流纹岩,斜长角闪岩原岩为玄武岩。花岗片麻岩的SiO₂含量大于56%,MgO含量小于3%,Al₂O₃含量大于15%,Sr含量大于500×10^-6,Yb含量均小于1.9×10^-6,轻重稀土元素分异明显,重稀土元素强烈亏损,并且Eu负异常不明显,表明该片麻岩具埃达克质岩石的地球化学特征。锆石U-Pb定年结果显示出几组年龄,分别是2512±21Ma, 2452±9.6Ma,2394±55Ma。大体看,2512Ma代表了火山喷发和周台子铁矿BIF沉淀年龄,2452Ma左右的锆石年龄代表了TTG质花岗片麻岩的侵位结晶年龄,2394Ma锆石年龄代表了周台子铁矿经历了一次变质作用,并对原有的岩石和矿石进行了改造。锆石Hf同位素特征显示斜长角闪岩和TTG质片麻岩的岩浆源区受到过古老地壳物质的混染。周台子铁矿构造环境可能是与裂谷有关的张性环境。  相似文献   

Geochemistry of granitoids of Bilgi area,northern part of eastern Dharwar craton,southern India — Example of transitional TTGs derived from depleted source   总被引：1，自引：0，他引：1  

Sukanta Dey  A. K. Rai  Anjan Chaki 《Journal of the Geological Society of India》2009,73(6):854-870

Mildly deformed granitoids exposed around Bilgi in the northernmost part of the eastern Dharwar craton are divided into two groups viz. granodiorites and monzogranites. The granodiorites contain microgranular enclaves and amphibolite xenoliths, and show low-Al TTG affinity with high SiO₂ (71–74 %), Na₂O, Y and Sr/Y, moderate to moderately high Mg#, Cr and Ni, low to moderate LILE, and low Nb and Ta. However, compared to similar TTGs from different cratons the Bilgi granodiorites have distinctly higher K₂O, K₂O/Na₂O, Rb and lower REE and Th. The amphibolite xenoliths are characterized by variable enrichment of K₂O, Rb, Ba and Th and depletion of Ti, Zr and P compared to MORB. The microgranular enclaves are quartz diorite to granodiorite in composition with high Mg, Ni and Cr, and compared to MORB, are enriched in LILE and depleted in Ti and Y. The monzogranites, compared to the granodiorites, display higher SiO₂, K₂O and Rb with lower Mg#, although still maintaining the high Na₂O, Ni and Cr and low REE character. The Bilgi granodiorites are explained as transitional TTGs late synkinematic with respect to regional deformation. Geochemical signatures and regional geological set up suggest that they are probably derived from partial melting of a highly depleted slab material (metabasalt) followed by variable contamination or assimilation of intermediate crustal rocks in a subduction zone set up. Late stage fluid activity on the granodioritic magma is probably responsible for the generation of monzogranites. The amphibolite xenoliths predate the granodiorites and possibly represent fragments of a schist belt carried away by the granitic magma. They are probably island arc basalt derived from mantle source that has been metasomatized by slab-derived fluids. The microgranular enclaves are coeval with the Bilgi granodiorites and also likely to be island arc magmas derived from mantle variably enriched in slab-derived and within-plate components.  相似文献   

REE-HFSE distribution/partitioning between garnetiferous restites and TTG from Nademavinapura area,Western Dharwar craton     

S. N. Charan  E. V. S. S. K. Babu  S. M. Naqvi  J. G. Rana Prathap  M. Ram Mohan  D. Srinivasa Sarma 《Journal of the Geological Society of India》2009,73(3):371-378

The major part of the Peninsular Gneiss in Dharwar craton is made up of Trondjhemite-Tonalite-Granodiorite (TTG) emplaced at different periods ranging from 3.60 to 2.50 Ga. The sodic-silicic magma precursors of these rocks have geochemical features characteristic of partial melting of hydrated basalt. In these TTGs, enclaves of amphibolites (± garnet) are abundant. These restites are considered to be the residue of a basaltic crust after its partial melting. A detailed study of these (residue) enclaves reveals textures formed due to the process of partial melting. Major, trace and REE analysis of these residue enclaves and the melt TTGs and microprobe analysis of the coexisting minerals show partitioning of REE and HFSE between the precursor melt of TTGs and the upper amphibolite facies residues. Formation of garnetiferous amphibolites with biotite, Cpx and plagioclase consequent to melting, has squeezed the original MORB type of basaltic crust and given rise to the TTGs, depleted in Y, Yb, K₂O, MgO, FeO, TiO₂ and enriched in La, Th, U, Zr and Hf. Coevally during the process of melting, the hydrated basalt was depleted in Na₂O, Al₂O₃, LREE, Th, U and enriched in K₂O, MgO, Nb, Ti, Yb, Y, Sc, Ni, Cr and Co. Mineral chemistry of co-existing garnet-biotite and amphibole-plagioclase in these amphibolitic (restite) enclaves indicates an average temperature of 700 ± 50° C and pressure of 5 ± 1 Kbar. These data are inferred to indicate that during the garnet stability field metamorphism, effective fractionation of HREE and HFSE has taken place between the restites having Fe-Mg silicates, ilmenites and the extracted melt generated from the MORB type of hydrated basalt. These results are strongly substantiated by the reported melting experiments on hydrated basalts.  相似文献   

变质玄武岩体系相平衡及矿物 熔体微量元素分配：限定TTG/埃达克岩形成条件和大陆壳生长模型   总被引：3，自引：1，他引：2  

熊小林  韩江伟  吴金花 《地学前缘》2007,14(2):149-158

埃达克质岩石是高Na、Al和Sr、低Y和HREE以及Nb、Ta亏损的钠质花岗质岩石,奥长花岗岩-英云闪长岩-花岗闪长岩(TTG)是早期(太古宙)大陆壳主要组分,成分与埃达克质岩石相似,这些成分独特的岩石总体上认为是俯冲洋壳、下地壳和拆沉的下地壳中变质玄武岩部分熔融的产物。文中综述我们近年来在变质玄武岩体系相平衡和矿物-熔体微量元素分配实验研究成果:相平衡实验和熔体微量元素特征研究表明,变质玄武岩部分熔融过程中金红石是导致TTG/埃达克岩浆Nb、Ta亏损的必要残留矿物,从而否定了前人“TTG由无金红石的角闪岩熔融产生”的观点;证实金红石仅仅在压力1.5GPa以上才能稳定存在,从而限定TTG/埃达克岩熔体必定产生在大约50km以上,表明TTG/埃达克岩是在相对较深的含金红石榴辉岩相条件下熔融产生的。矿物(石榴子石、角闪石,单斜辉石和金红石)-熔体微量元素分配系数测定和部分熔融模拟结果进一步限定俯冲洋壳和下地壳起源的TTG/埃达克岩浆由含金红石角闪榴辉岩熔融产生,而拆沉下地壳起源的埃达克岩浆的产生要求软流圈地幔高温,由无水或含有少量含水矿物的榴辉岩熔融产生。  相似文献   

河北平山英云闪长质片麻岩锆石SHRIMP年代学   总被引：14，自引：0，他引：14  

杨崇辉  杜利林  万渝生  刘增校 《高校地质学报》2004,10(4):514-522

平山板桥沟地区的英云闪长质片麻岩常量元素具有高硅、高铝、高钠和低钾的特点,稀土元素显示强烈分异,具有较高的(La／Yb)。值(34),同时具有明显的Nb,Ta,Ti和P负异常,与太古宙TTG的特征完全一致。阴极发光和背散射研究表明,英云闪长质片麻岩中锆石具有密集震荡环带和较高的Th／U值,表现典型岩浆锆石的特点,但其外侧都有一高亮度(CL)的狭窄变质增生边。SHRIMP测试结果表明TTG的形成年龄为2536．5±9．8Ma,变质年龄为1802±43Ma。推测2500Ga西部块体向东部陆块俯冲形成了TTG,并导致五台陆块与太行山陆块拼合,使华北克拉通化,1．8Ga则为陆内的另一次构造事件。  相似文献   

胶北地块前寒武纪基底研究新进展   总被引：3，自引：1，他引：2  

徐扬  冯岩  李日辉 《现代地质》2011,25(5):965-974

胶北地块位于鲁东的沂沭断裂和五莲—烟台断裂之间,以出露不同变质程度的太古宙—古元古代的结晶基底为特征,其岩石组合为TTG质(英云闪长岩-奥长花岗岩-花岗闪长岩)片麻岩和少量变质表壳岩(变质火山岩-变质沉积岩),它们构成了胶北的花岗-绿岩体。对变质(超)基性岩、TTG岩系的岩石组合、地球化学特征和同位素年代学的研究表明,胶北地块造壳的主要时期为新太古代的2.8～2.7 Ga;在经历了2.5 Ga左右构造事件后,胶北地块进入稳定陆壳沉积阶段,并接受了古元古代的孔兹岩系沉积;最后于1.8 Ga左右发生变质。与苏鲁造山带不同,胶北地块前寒武纪基底具有许多亲华北板块的特征,二者的界线可能是五莲—烟台断裂。  相似文献   

新疆富蕴县北部金格岩体斜长花岗岩LA-ICP-MS锆石U-Pb年龄及其地质意义     

蔺新望  王星  赵江林  赵端昌  周少伟  袁璋 《地质通报》2019,38(11):1813-1824

对新疆富蕴县北部金格岩体斜长花岗岩进行LA-ICP-MS锆石U-Pb年龄测定,获得了402.7±2.9Ma(MSWD=0.17)的岩浆结晶年龄,表明岩体形成时代为早泥盆世。金格岩体岩性组合为英云闪长岩-奥长花岗岩-花岗闪长岩,具有TTG组合特征,暗示与洋俯冲作用有关。岩石地球化学具有高硅(SiO_2=72.55%～77.41%),富钠(Na_2O=4.94%～6.63%),贫钾(K_2O=0.24%～0.95%)的特征,Al_2O_3含量为12.11%～15.30%,铝饱和指数在0.94～1.04之间,呈低钾拉斑玄武岩系列、准铝质-弱过铝质、I型花岗岩的特征。稀土元素显示轻稀土元素富集、重稀土元素相对亏损,中等-弱负Eu异常的右倾型,微量元素Rb、Th、U等大离子亲石元素富集,呈明显的"峰",Nb、Ta、Ti等高场强元素强烈亏损,呈明显"TNT"负异常,显示了与俯冲作用有关的岩浆岩特征。结合区域地质资料,金格岩体形成于与洋俯冲作用有关的活动大陆边缘的陆弧环境,金格—正格河地区在早泥盆世处于局部拉张环境。  相似文献   

华北地台北缘鞍山白家坟奥长花岗岩地球化学特征、锆石U-Pb年龄及意义     

温德娟 《地质通报》2019,38(10):1711-1717

太古宙TTG岩石的成因及年代学研究是理解前板块构造和板块构造开始及其演化过程的关键,是陆壳增生的重要标志,为太古宙地质体研究的热点和难点之一。对鞍山地区的白家坟岩体进行了地球化学研究和锆石U-Pb测年。数据结果显示,该岩体具有正片麻岩特征,Si、Na含量高,TFeO、MgO、CaO含量低,轻、重稀土元素分异程度低,且具有一定变化。稀土元素总量偏低(12.6×10~(-6)～119.34×10~(-6)),LREE/HREE值为8.98～13.11。微量元素富集K、Rb、Ba,亏损Nb、Ce、Zr、Sm、Ti、Y、Yb;K/Rb平均值为229.37,Rb/Sr平均值为0.58,Ba/Sr平均值为3.28,Y/Nb平均值为3.36。表明该岩体为岩浆作用的产物,也有部分为壳内再循环的产物或受到陆壳物质影响。测得~(207)Pb/~(206)Pb年龄加权平均值为3816±14Ma,锆石具有清晰的振荡环带结构,所有核部锆石分析点的Th/U值在0.05～0.54之间,具有岩浆锆石的特点,代表了白家坟奥长花岗质岩石的结晶时代。3613～3651Ma和3331Ma两组年龄数据代表早太古代的一次岩浆事件及重要的陆壳增生时期的热事件。  相似文献   

新疆北阿尔泰造山带早古生代花岗岩类侵入序列及其构造意义   总被引：7，自引：4，他引：3  

董连慧  屈迅  赵同阳  徐仕琪  周汝洪  王克卓  朱志新 《岩石学报》2012,28(8):2307-2316

新疆阿尔泰早古生代造山带侵入岩占构造带面积50％以上,近年大量高精度SHRIMP和LA-ICP-MS锆石U-Pb年代学资料反映其构造属性为奥陶纪碰撞前序列和中志留-早泥盆世后碰撞序列.碰撞前序列岩石组合为(石英)闪长岩-英云闪长岩/奥长花岗岩/花岗闪长岩-二长花岗岩序列,类似TTG组合,锆石U-Pb同位素年龄峰值为450～ 465Ma.后碰撞由二长花岗岩-正长花岗岩及少量碱长花岗岩组成,属于广义的GG组合,同位素年龄峰值390～ 415Ma.前者主要分布在中南部,后者主要分布中北部,分布的极性显示俯冲带在南侧.而区域南侧的阿尔曼太蛇绿岩带同位素年龄与北阿尔泰奥陶纪碰撞前序列时代相同,本文推测该蛇绿岩带与北阿尔泰岩浆链带构成洋脊俯冲带模式;其间的南阿尔泰晚古生代增生带、额尔齐斯强变形带、北准噶尔晚古生代洋内弧带都是后来的上叠产物.  相似文献   

河南鲁山地区中-新太古代灰色片麻岩   总被引：6，自引：0，他引：6  

杨长秀  王世炎  刘振宏  雷正化  杨长青 《地质论评》2008,54(3)

河南鲁山地区原划归太古宇太华群中解体出中—新太古代变形侵入体,由魏庄片麻岩和榆树庄片麻岩组成,变质程度达角闪岩相,局部为麻粒岩相。地球化学特征显示高铝质片麻岩特征,原岩为奥长花岗岩—英云闪长岩—花岗闪长岩(TTG岩系),从而为该地区发育中—新太古代花岗岩—绿岩带提供了证据。  相似文献