苏州地区I-A型花岗岩特征与成因的对比研究   总被引：5，自引：0，他引：5       下载免费PDF全文

周若  杨静  任进 《地球科学》1997,6(3)

应用岩石学、矿物学、地球化学及岩浆物理学等的理论和方法，对苏州地区Ｉ型和Ａ型花岗岩的特征及成因进行了对比研究，得出以下主要结论：Ｉ型花岗岩为晚侏罗世火山弧压性环境产物，侵位较深；而Ａ型者为Ａ２型花岗岩，为早白垩世造山后张性环境产物，侵位较浅，具晶洞构造．Ａ型比Ｉ型花岗岩以酸度、碱度、Ａｌ，Ｆ含量高而Ｈ２Ｏ＋含量低，以ＲＥＥ及不相容元素丰度高，负Ｅｕ异常强，而ｗ（ＬＲＥＥ）／ｗ（ＨＲＥＥ）低为特色．Ａ型者矿物结晶顺序先浅色后暗色，暗色矿物以富铁贫镁、ＲＥＥ分配系数高及负Ｅｕ异常明显及长石富碱贫钙，而与Ｉ型花岗岩不同．Ａ型者副矿物４０余种，属锆石－褐帘石－萤石型，锆石结晶温度高，（１１０），（１１１）晶面发育；而Ｉ型者仅１０余种，属榍石－锆石－磷灰石型，锆石结晶温度低，（１００），（３１１）晶面发育．Ｉ型花岗岩为幔源岩浆与下地壳部分熔融岩浆混合及ＡＦＣ作用产物，而Ａ型花岗岩为残余下地壳（麻粒岩相）熔融后分离结晶产物，二者并非同源岩浆演化关系．Ａ型比Ｉ型岩浆来源浅，酸度大，含水少；故岩浆密度小，粘度大，上升慢，冷凝长．受密度筛影响，Ａ型花岗岩岩浆房及侵位深度小于Ｉ型  相似文献   

内蒙古西部甜水井地区中二叠世A型花岗岩   总被引：8，自引：0，他引：8  

贺锋  许立权  苏宏伟  李新仁 《西北地质》2004,37(3):7-14

内蒙古北山甜水井地区龙脊山—神蛇岭岩体，总体呈北西向长椭圆状，面积大于100km^2。按岩石谱系单位划分为一单元含斑细粒黑云母二长花岗岩、二单元含斑中细粒黑云母二长花岗岩和三单元中细粒花岗岩,归并为一龙脊山序列。岩石富硅碱，ALK在7．23％～8．37％．AKI小于1,A／CNK=1．01～1．07；OX较高．在0．47～0．83。相对富集大离子亲石元素、轻稀土元素，亏损Ba、Nb、Sr、Zr、Ti。稀土配分曲线呈现显著的“V”字型。副矿物组合为Mt-Ap-Zi型。由早单元到晚单元。向酸碱性增强方向演化，显示深源浅成铝质A型(A2型)花岗岩特征。各类构造环境判别图解投点．具造山后或后造山特征。同位素测年(锆石U-Pb法)为267．1Ma。反映本区中二叠世碰撞造山作用的存在。中二叠晚期已转入稳定的陆内发展环境。  相似文献   

粤北笋洞花岗岩的形成时代、地球化学特征与成因   总被引：25，自引：10，他引：25  

凌洪飞沈渭洲  邓平蒋少涌  高剑峰叶海敏濮巍  谭正中 《岩石学报》2004,20(3):413-424

笋洞花岗岩体是粤北贵东复式花岗岩体的一个重要组成部分。锆石U-Pb年龄为189.1±0.7Ma,是燕山早期岩浆活动产物。该岩体的主要元素显示富硅、富碱、强过铝质和低 CaO/Na_2O比值等特征;微量元素方面,富集Rb,Th,U,Ce,Sm,Y,亏损 Ba,Sr,P,Ti;LREE轻微富集(LREE/HREE=6.6～8.8,(La/Yb)_N=6.44～10.74),Eu亏损明显(δEu=0.14～0.31);它具有低的ε_(Nd)(t)(-11.4～-9.3),高的δ~(18)O(10.2～12.7‰)、(~(87)Sr/~(86)Sr);(0.72949～0.74923)、~(206)Pb/~(204)Pb(18.180～18.488)、~(207)Pb/~(204)Pb(15.655～15.661)和古老的Nd模式年龄(1762～1933Ma)。上述这些特征表明,笋洞岩体属于典型的壳源型花岗岩,是在地壳伸展-减薄的构造背景下,通过以泥质成分为主的古-中元古代变质沉积岩部分熔融的方式形成。  相似文献   

Magmatic evolution of Li–F, rare-metal granites: a case study of melt inclusions in the Khangilay complex, Eastern Transbaikalia (Russia)     

E. V. Badanina  I. V. Veksler  R. Thomas  L. F. Syritso  R. B. Trumbull 《Chemical Geology》2004,210(1-4):113-133

We report compositions of homogenized quartz-hosted melt inclusions from a layered sequence of Li-, F-rich granites in the Khangilay complex that document the range of melt evolution from barren biotite granites to Ta-rich, lepidolite–amazonite–albite granites. The melt inclusions are crystalline at room temperature and were homogenized in a rapid-quench hydrothermal apparatus at 200 MPa before analysis. Homogenization runs determined solidus temperatures near 550 °C and full homogenization between 650 and 750 °C. The compositions of inclusions, determined by electron microprobe and Raman spectroscopy (for H₂O), show regular overall trends of increasing differentiation from the least-evolved Khangilay units to apical units in the Orlovka intrusion. Total volatile contents in the most-evolved melts reach over 11 wt.% (H₂O: 8.6 wt.%, F: 1.6 wt.%, B₂O₃: 1.5 wt.%). Concentrations of Rb range from about 1000 to 3600 ppm but other trace elements could not be measured reliably by electron microprobe. The resulting trends of melt evolution are similar to those described by the whole-rock samples, despite petrographic evidence for albite- and mica-rich segregations previously taken as evidence for post-magmatic metasomatism.

Melt variation trends in most samples are consistent with fractional crystallization as the main process of magma evolution and residual melt compositions plot at the granite minimum in the normative Qz–Ab–Or system. However, melts trapped in the highly evolved pegmatitic samples from Orlovka deviate from the minimum melt composition and show compositional variations in Al, Na and K that requires a different explanation. We suggest that unmixing of the late-stage residual melt into an aluminosilicate melt and a salt-rich dense aqueous fluid (hydrosaline melt) occurred. Experimental data show the effectiveness of this process to separate K (aluminosilicate melt) from Na (hydrosaline melt) and high mobility of the latter due to its low viscosity and relatively low density may explain local zones of albitization in the upper parts of the granite.  相似文献   

Timing of Magma Mixing in the Gangdisě Magmatic Belt during the India-Asia Collision： Zircon SHRIMP U-Pb Dating     

MO Xuanxue  DONG Guochen  ZHAO Zhidan  GUO Tieying  WANG Liangliang  CHEN Tao 《《地质学报》英文版》2005,79(1):66-76

Abstract  Abundant mafic microgranular enclaves (MMEs) extensively distribute in granitoids in the Gangdisê giant magmatic belt, within which the Qüxü batholith is the most typical MME‐bearing pluton. Systematic sampling for granodioritic host rock, mafic microgranular enclaves and gabbro nearby at two locations in the Qüxü batholith, and subsequent zircon SHRIMP II U‐Pb dating have been conducted. Two sets of isotopic ages for granodioritic host rock, mafic microgranular enclaves and gabbro are 50.4±1.3 Ma, 51.2±1.1 Ma, 47.0±1 Ma and 49.3±1.7 Ma, 48.9±1.1 Ma, 49.9±1.7 Ma, respectively. It thus rules out the possibilities of mafic microgranular enclaves being refractory residues after partial melting of magma source region, or being xenoliths of country rocks or later intrusions. Therefore, it is believed that the three types of rocks mentioned above likely formed in the same magmatic event, i.e., they formed by magma mixing in the Eocene (c. 50 Ma). Compositionally, granitoid host rocks incline towards acidic end member involved in magma mixing, gabbros are akin to basic end member and mafic microgranular enclaves are the incompletely mixed basic magma clots trapped in acidic magma. The isotopic dating also suggested that huge‐scale magma mixing in the Gangdisê belt took place 15–20 million years after the initiation of the India‐Asia continental collision, genetically related to the underplating of subduction‐collision‐induced basic magma at the base of the continental crust. Underplating and magma mixing were likely the main process of mass‐energy exchange between the mantle and the crust during the continental collision, and greatly contributed to the accretion of the continental crust, the evolution of the lithosphere and related mineralization beneath the portion of the Tibetan Plateau to the north of the collision zone.  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   

Possible spatial variability in the Selwyn Block of Central Victoria: evidence from Late Devonian felsic igneous rocks   总被引：2，自引：0，他引：2  

J. D. Clemens  M. A. Elburg 《Australian Journal of Earth Sciences》2016,63(2):187-192

The Neoproterozoic to Cambrian Selwyn Block in Central Victoria forms the mainly unexposed basement to the Paleozoic metasediments, granitic rocks and felsic volcanic complexes of the Melbourne Zone of the Lachlan Orogen. The Late Devonian felsic rocks are largely products of partial melting of the Selwyn Block, and their chemistry implies that their sources were most probably arc-related andesite, dacite, volcaniclastic greywackes and some pelites. When plotted against the median longitudes of the plutons and volcanic complexes, the average values for ⁸⁷Sr/⁸⁶Sr_t and ?Nd_t (at 370 Ma) reveal broad trends interpreted to reflect possible compositional and/or age structure in the Selwyn Block. Assuming that the trends are real, from W to E, I-type sources are progressively less crustally evolved, probably younging eastward. The S-type sources show no trend in ?Nd_t, suggesting that there was efficient sediment mixing. The ⁸⁷Sr/⁸⁶Sr_t values, however, become more evolved eastward (opposite in sense to the apparent variation in the I-type sources). This is interpreted as the original Selwyn Block sediments having been more pelitic eastward, perhaps suggesting a deepening of the basin in this direction, as well as structurally upward in the succession. The opposite senses of variation highlights the spatial separation of the S- and I-type sources and suggest that the granitic magmas here are unlikely to represent any sort of mixing continuum.  相似文献   

江南造山带新元古代中期(830～750Ma)岩浆活动及对构造演化的制约     

邓奇  王剑  汪正江  崔晓庄  施美凤  杜秋定  马龙  廖世勇  任光明 《大地构造与成矿学》2016,(4):768-786

连接扬子地块和华夏地块的江南造山带是华南前寒武纪最重要的构造单元,其形成和演化长期以来备受关注。在江南造山带的范围内广泛发育了新元古代岩浆岩,它们是探讨江南造山带构造演化的重要对象,但其成因和形成的构造背景却备受争论。本文系统收集和分析了江南造山带830~820 Ma花岗岩、800~780 Ma酸性岩和800~750 Ma基性岩的地球化学数据。研究表明,不同时间段的岩石成因类型存在系统差异,830~820 Ma的花岗岩主要为S型花岗岩,800~780 Ma的酸性岩主要为A型酸性岩,而800~750 Ma的基性岩以拉斑系列和碱性系列为主,并在构造判别图中显示了板内玄武岩(WPB)和洋中脊玄武岩(MORB)的特征。综合同位素年代学、岩石地球化学和沉积学等学科领域的研究成果我们认为:扬子北缘和西缘应先于东南缘在1000~900 Ma期间发生碰撞,而此时的东南缘仍为活动大陆边缘;直到~830 Ma,扬子地块与华夏地块沿江南造山带发生拼贴,但只是陆-弧-(微)陆之间的"软碰撞",而无山脉隆升和高级变质作用,各个块体之间处于"联而不合"的状态,大洋岩石圈拆沉之后的软流圈上涌和由拆沉所引起的拉张作用导致了上覆岩石圈和陆壳发生部分熔融,产生了江南造山带830~820 Ma的S型花岗岩;随着全球Rodinia超大陆的裂解,~820 Ma,华南裂谷盆地开启,并在随后的裂解过程中发育了大量与伸展有关的800~780 Ma A型酸性岩和基性岩脉/墙,而其明显高于同时代MORB源区的地幔潜能温度显示,导致Rodina超大陆裂解的地幔柱可能对该时期岩浆岩的地幔源区有一定影响;随着拉张作用的不断加强,出现了760~750 Ma碱性系列和具MORB特征的基性岩,此时的软流圈地幔既提供热量又有物质供应。  相似文献   

黑河新生地区中侏罗世花岗质岩石锆石U-Pb年龄、地球化学特征及岩石成因     

李森林  陈跃军  李云峰  王雄  李勇  吴国学 《世界地质》2016,35(2):297-308

黑河新生地区西古兰河以北二长花岗岩的LA-ICP-MS锆石U-Pb同位素测试结果表明,其形成时代为中侏罗世((163.8±1)Ma)。这些中侏罗世二长花岗岩属于弱过铝质高钾钙碱性系列的Ⅰ型花岗岩,明显富集大离子亲石元素(Rb、Ba、Th)和亏损高场强元素(Zr、Hf、Nb、Ta),元素Sr具有明显的负异常,表明其原始岩浆起源于地壳火成岩的部分熔融。结合区域资料同时代火成岩的组合特征和古太平洋板块的构造演化,认为该二长花岗岩形成于活动大陆边缘,而其形成的地球动力学背景可能为古太平洋板块向欧亚板块俯冲造山后的伸展环境。  相似文献   

朝鲜半岛平南盆地中元古代岩浆事件   总被引：4，自引：2，他引：2  

朴贤旭  翟明国  杨正赫  金正男  郑哲珠  吴福元  金胜贤  韩龙渊  朴雄  金明哲  侯泉林 《岩石学报》2016,32(10):3033-3044

朝鲜平南盆地翁津地区发育中元古代黄海群和同时期(称之为瓮津期)花岗岩,花岗岩体侵入于黄海群。本文采用锆石原位微区U-Pb定年技术,对黄海群中的酸性火山岩及花岗岩进行了年龄测试。获得的数据表明,黄海群中下部层位及上部层位的酸性火山岩分别在1235±5Ma和1203±7Ma喷发,由此说明黄海群的沉积时代应为中元古代,而不是传统上认为的古元古代;两个翁津期花岗岩体(翁津和黄衣山岩体)的侵位年龄分别为1251±22Ma和1248±13Ma,为中元古代花岗质岩浆活动的产物。上述1251~1203Ma年龄的获得,表明朝鲜半岛发育中元古代岩浆作用,从而明确朝鲜黄海裂谷与华北东缘裂谷在时间上具有同期性,同时也表明中国华北与朝鲜在中元古代具有类似的发展历史。  相似文献