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1.
冈底斯中段早侏罗世辉长岩-花岗岩杂岩体成因及其对新特提斯构造演化的启示:以日喀则东嘎岩体为例 总被引：12，自引：8，他引：4
以冈底斯中段日喀则东嘎出露的早侏罗世辉长岩-花岗岩杂岩体为对象,进行了锆石U-Pb年龄和Hf同位素,以及全岩元素地球化学组成的系统测定,据此探讨了岩石的成因及其对新特提斯构造演化的启示。该杂岩体中辉长岩主要由角闪石和钙质斜长石组成,缺乏辉石;花岗岩主要为英云闪长岩、花岗闪长岩等构成的TTG岩石组合;花岗岩中普遍发育呈塑变形态的镁铁质包体。锆石LA-ICP-MS U-Pb定年结果显示,英云闪长岩和镁铁质包体的成岩年龄十分接近,且与辉长岩的年龄基本一致,均为177~180Ma。化学组成上,辉长岩低硅、富铝、贫碱,富轻稀土和大离子亲石元素,贫高场强元素,相似于高铝玄武岩。英云闪长岩贫碱、准铝、富钠,属钙碱性I型花岗岩。镁铁质包体具有与寄主岩相似的矿物组成和微量元素分布模式,二者均具有显著亏损的锆石Hf同位素组成,εHf(t)值分别为+11.4~+15.0和+14.4~+18.6。综合分析表明,早侏罗世冈底斯南缘应处于新特提斯洋板片俯冲的构造背景,其中辉长质侵入体为遭受俯冲板片析出流体交代作用的亏损地幔部分熔融的产物,花岗质岩石起源于初生地壳的部分熔融,镁铁质包体为辉长质岩浆与花岗质岩浆二者经混合作用的产物。结合对区内其它辉长质侵入体及相关镁铁质包体资料的全面分析,表明在新特提斯洋板片的整个俯冲过程中(205~40Ma),冈底斯南缘应存在多次的基性岩浆底侵及其诱发的壳幔岩浆混合作用。 相似文献
2.
小兴安岭东南晚奥陶世鹤林侵入杂岩体成因探讨 总被引：1，自引：0，他引：1
小兴安岭东南晚奥陶世鹤林侵入杂岩体岩性变化较大,由角闪辉长岩—(石英)闪长岩—英云闪长岩—二长花岗岩组成,不同岩石类型在野外宏观上呈相互侵入、包裹和渐变的接触关系;在(石英)闪长岩、英云闪长岩和二长花岗岩中均发育微细粒闪长质包体,包体多具明显塑性流变特点的浑圆外形和典型岩浆结构、针状磷灰石及捕获的寄主岩钾长石、石英斑晶,为MME型岩浆混合成因包体;杂岩体相对富集LILE(Ba、Sr、Rb)、HFS(U、Th、Zr、Ce)元素等,显示出壳源特点,而较高的εNd(t)值(-2.38~-3.77)显示以幔源为主的特点。研究表明杂岩体具明显的壳幔岩浆混合成因的岩相学、岩石化学和地球化学特征,形成于基性岩浆底侵作用下的陆缘弧型活动大陆边缘构造环境。 相似文献
3.
位于扬子克拉通西缘的新元古代宝兴杂岩主要由中低级变质的辉长质片麻岩、闪长质片麻岩、英云闪长质到花岗闪长质片麻岩和块状二长花岗岩组成。岩石地球化学和Sm-Nd同位素特征表明,辉长质片麻岩和闪长质片麻岩为同源岩浆演化序列,原始岩浆起源于亏损地幔尖晶石橄榄岩的部分熔融,在上升和侵位过程中受到了地壳岩石强烈混染。英云闪长质和花岗闪长质岩浆形成于下地壳玄武质岩石部分熔融,而二长花岗质岩浆形成于杂砂岩的部分熔融。综合分析宝兴杂岩的岩石组合、微量元素和同位素特征,该杂岩体最有可能形成于新元古代活动大陆边缘火山弧构造背景,并可能经历了碰撞过程。 相似文献
4.
新疆东天山黄山东岩体岩石地球化学特征与岩石成因 总被引：12，自引：7，他引：5
黄山东岩体位于东天山北部的土墩-黄山-图拉尔根镁铁-超镁铁质岩带中段,受康古尔塔格-黄山深大断裂控制,是由辉长闪长岩、角闪辉长岩、橄榄辉长岩、辉长苏长岩及二辉橄榄岩组成的复式岩体。主量元素化学组成部分属拉斑玄武岩系列,也有部分属钙碱性系列。大部分岩石相对富集LREE、适度亏损高场强元素(Nb、Ta、Ti)。元素地球化学和Nd、Sr、Pb同位素体系证明,岩浆遭受了5%～8%的中-上地壳物质的同化混染作用。岩浆源区由被消减板片交代的地幔楔物质和软流圈地幔物质组成。岩石圈根部拆沉和软流圈地幔上涌过程中生成了黄山东岩体。富铁硅酸盐的分离结晶作用对硫化物富集并分凝起到了关键性作用,成矿过程应该是岩浆自身演化过程的有机组成部分。 相似文献
5.
华北克拉通东部中生代期间受到古太平洋板块俯冲并引发一系列的构造-岩浆-成矿作用,但古太平洋俯冲作用开始的具体时限仍未有定论。本文对辽西兴城地区中生代药王庙-磨盘山岩体进行了系统的岩相学研究、锆石U-Pb同位素定年、全岩地球化学和锆石原位Hf同位素测试分析,结果显示,花岗质岩石中岩浆成因锆石加权平均年龄为193～186 Ma,岩体侵位于早侏罗世;岩石组合为石英二长岩-花岗闪长岩-二长花岗岩-正长花岗岩;岩石全碱含量较高,属准铝-弱过铝质、高钾钙碱性系列,具有与Ⅰ型花岗岩类似的岩石地球化学特征;岩石相对富集轻稀土元素和大离子亲石元素K、Pb等,而相对亏损高场强元素Nb、Ta、Ti等及P元素;岩浆成因锆石εHf(t)值为-12.94～-7.39,Hf同位素二阶段模式年龄为2.05～1.69 Ga,其初始岩浆可能来源于古老地壳的部分熔融并可能有幔源物质的参与。辽西兴城地区早侏罗世花岗岩岩石组合、岩石地球化学特征和与俯冲作用有关的活动陆缘花岗岩特征类似,岩石形成于古太平洋俯冲作用导致的活动陆缘构造背景下,结合区域研究资料,认为古太平洋对华北克拉通东部的俯冲作用开始于晚三叠世—早侏罗世,而早侏罗世花岗质岩浆活动是古太平洋板块对华北克拉通俯冲作用的响应。 相似文献
6.
藏南冈底斯带中段始新世岩浆作用的厘定及其大地构造意义 总被引：7，自引：0，他引：7
本文对藏南冈底斯带中段的花岗岩类和角闪辉长岩进行了锆石U-Pb年代学和全岩地球化学分析,据此阐明了岩体的形成机制与演化过程,并探讨了成岩时的大地构造背景。分析结果显示,研究区内花岗岩类和角闪辉长岩体的LA-ICPMS锆石U-Pb定年结果为41~55Ma,为始新世早-中期岩浆活动的产物,代表了区内岩体的成岩年龄。在地球化学组成上,花岗岩类属于钙碱性到高钾钙碱性系列,均富集轻稀土(LREE)和大离子亲石元素(LILE)(Rb、Ba和K),强烈亏损Nb、Ta、P等高场强元素(HFSE),具有弧型岩浆岩的地球化学组成。此外,花岗岩类的铝饱和指数(A/CNK)小于1.1,属于准铝质到弱过铝质的I型花岗岩。角闪辉长岩为石榴橄榄岩部分熔融的产物,并在后期侵位的过程中遭受到了壳源物质的混染。综合分析表明,研究区内的岩体形成于初始碰撞向主碰撞的转化阶段。始新世早期(～50Ma)新特提斯洋板片的断离引起软流圈物质上涌,导致岩石圈地幔发生部分熔融形成基性岩浆,随后基性岩浆底侵至下地壳并诱发下地壳发生部分熔融形成花岗岩质岩浆,最后经过岩浆混合作用形成始新世早-中期冈底斯地区的花岗岩类。 相似文献
7.
牛鼻子梁岩体位于柴达木地块的北缘,出露面积约8 km2,平面形态呈长条状,主要由斜长二辉橄榄岩、斜长单辉橄榄岩、角闪二辉橄榄岩、角闪橄榄岩、角闪橄榄二辉岩、黑云母化二辉岩、角闪辉石岩、橄榄辉石角闪石岩、角闪橄榄辉长岩、细粒辉长岩、似斑状辉长岩、暗色辉长岩、辉长岩、淡色辉长岩、石英闪长岩和英云闪长岩组成。文章通过岩石学、矿物学、地球化学研究,得到锆石U-Pb年龄为(361.5±1.2)Ma,Sm-Nd等时线年龄为(347±26)Ma。研究认为,牛鼻子梁基性-超基性岩体含矿岩石产于大陆边缘环境。岩体形成于泥盆纪晚期。岩浆分异充分,岩石类型丰富,岩浆演化过程中主要发生了橄榄石和斜长石的分离结晶/堆晶作用。岩体的母岩浆应属于拉斑玄武岩质岩浆。从目前发现的矿化情况来看,牛鼻子梁基性-超基性杂岩体为含矿岩体,有很好的找矿前景。 相似文献
8.
牛鼻子梁镁铁质-超镁铁质杂岩体岩石特征 总被引：1，自引：1，他引：0
牛鼻子梁岩体位于柴达木地块的北缘,出露面积约8 km2,平面形态呈长条状,主要由斜长二辉橄榄岩、斜长单辉橄榄岩、角闪二辉橄榄岩、角闪橄榄岩、角闪橄榄二辉岩、黑云母化二辉岩、角闪辉石岩、橄榄辉石角闪石岩、角闪橄榄辉长岩、细粒辉长岩、似斑状辉长岩、暗色辉长岩、辉长岩、淡色辉长岩、石英闪长岩和英云闪长岩组成。文章通过岩石学、矿物学、地球化学研究,得到锆石U-Pb年龄为（361.5±1.2） Ma,Sm-Nd等时线年龄为（347±26） Ma。研究认为,牛鼻子梁基性-超基性岩体含矿岩石产于大陆边缘环境。岩体形成于泥盆纪晚期。岩浆分异充分,岩石类型丰富,岩浆演化过程中主要发生了橄榄石和斜长石的分离结晶/堆晶作用。岩体的母岩浆应属于拉斑玄武岩质岩浆。从目前发现的矿化情况来看,牛鼻子梁基性-超基性杂岩体为含矿岩体,有很好的找矿前景。 相似文献
9.
本文对湘赣交界地区发育的万洋山岩体进行锆石SHRIMP U-Pb定年和岩石学、地球化学分析。该岩体由英云闪长岩、花岗闪长岩和二长花岗岩组成,本次主要讨论英云闪长岩及其中发育的石英闪长岩包体,并获得英云闪长岩的锆石U-Pb年龄为438.0±3.0 Ma,石英闪长岩包体的锆石U-Pb年龄为425.6±3.1 Ma,为晚志留世。英云闪长岩矿物组合为斜长石、钾长石、黑云母、石英以及少量的角闪石、磁铁矿和榍石;地球化学特征显示为低硅、准铝质及钙碱性的花岗岩,在岩石类型判别图解中为I型花岗岩。石英闪长岩包体为细粒结构,矿物组合为角闪石、斜长石、黑云母、石英及少量辉石,表明岩石包体是岩浆成因的;包体中存在异常共生矿物斜长石斑晶、针状磷灰石,CIPW标准矿物计算中未出现刚玉分子,地球化学组成显示其具有低硅、低碱、准铝质的钙碱性岩类特征;包体还表现为富Mg、Fe以及高Mg#值(45~50),显示出包体高镁、偏基性的特征;包体与寄主岩稀土元素配分模式图和微量元素蛛网图分布特征基本一致,表明二者在成因上相关联。石英闪长岩包体分异指数DI=45~48与辉长岩接近,SiO_2含量略高于辉长岩,表明石英闪长岩包体源于上地幔基性辉长质岩浆、经岩浆混合演化形成。英云闪长岩显示为岛弧岩浆岩、具有活动大陆边缘岩浆岩特征,结合英云闪长岩的岩石类型、岩石包体成因认为:万洋山岩体可能是扬子板块与华夏板块在俯冲消减的地球动力学背景下,软流圈地幔上涌,诱发岩石圈地幔和上覆的古老地壳物质重熔,形成以壳源为主、壳幔混合成因的花岗岩。 相似文献
10.
柴达木地块北缘牛鼻子梁镁铁质-超镁铁质岩体岩石成因与成矿条件 总被引：4，自引：3，他引：1
牛鼻子梁岩体位于柴达木地块西北缘。岩体出露面积约8km2,平面形态呈长条状,长轴方向近东西向。锆石LA-ICP-MS U-Pb年龄为367.0±2.0Ma。岩体中堆晶结构、堆晶韵律和旋回发育,属典型的层状岩体。岩浆分异充分,岩石类型丰富。主要岩石类型有斜长二辉橄榄岩、斜长单辉橄榄岩、角闪二辉橄榄岩、角闪橄榄岩、角闪橄榄二辉岩、角闪二辉岩、橄榄二辉角闪石岩、角闪橄榄辉长岩、细粒辉长岩、似斑状辉长岩、暗色辉长岩、辉长岩、淡色辉长岩、石英闪长岩、英云闪长岩。岩浆源区为高镁拉斑玄武质岩浆（MgO=10.8%）,主体岩浆结晶温度为1100~1178℃。岩浆演化过程中主要发生了橄榄石的分离结晶作用,此外还有少量斜长石的分离结晶/堆晶作用。野外地质观察、岩石薄片观察及岩石地球化学特征表明岩体与围岩之间发生了较强的同化混染作用,并且同化混染强度伴随着岩浆演化过程而逐渐增大。大量的同化混染导致岩石化学系列从拉斑玄武质系列转化为钙碱性系列。岩浆源区属亏损型地幔源区。岩体形成的构造环境为大陆边缘裂解环境。从构造环境、原生岩浆、岩体类型、岩浆分异程度、岩浆含水量、同化混染和橄榄石镍含量七个方面来看牛鼻子梁岩体形成镍铜硫化物矿床的潜力很大。 相似文献
11.
佳木斯地块东北缘早二叠世六连岩体的岩浆混合成因：岩相学、年代学和地球化学证据 总被引：9，自引：6，他引：3
本文报道了佳木斯地块东北缘六连岩体中主岩花岗闪长岩和暗色微粒包体的岩相学、锆石U-Pb年代学、全岩地球化学以及锆石Hf同位素资料,以确定该岩体的形成时代、岩石成因及其构造属性。主岩花岗闪长岩和暗色微粒包体中角闪辉长岩分别获得了284Ma 和278Ma 的成岩年龄,表明六连岩体形成于早二叠世而非前人认为的晚印支期。包体具有岩浆结构,部分包体存在塑性流变特征,包体中可见淬冷边、反向脉和针状磷灰石,包体和主岩中均发育矿物异常共生或不平衡结构,结合主岩和包体的年代学和地球化学特征可以判定六连岩体为早二叠世岩浆混合作用的产物。全岩地球化学和锆石Hf同位素特征揭示出,六连岩体中主岩和包体的原始岩浆分别起源于新元古代增生的深部陆壳基性火成岩和受俯冲流体交代的亏损地幔楔的部分熔融。结合同时代火成岩组合的空间变异特征以及区域构造演化历史,认为佳木斯地块东北缘早二叠世六连岩体形成于活动大陆边缘环境,其地球动力学机制与佳木斯地块东侧古洋板块的西向俯冲作用有关。 相似文献
12.
拉萨地体南部早侏罗世岩浆岩的成因和构造意义 总被引：9，自引：7，他引：2
本文从拉萨地体南部原来被认为是前寒武纪变质基底的冈底斯岩群中厘定出了一套早侏罗世的岩浆岩.锆石U-Pb年代学研究表明,这些岩浆岩侵位于202～ 180Ma.岩石类型包括辉长闪长岩、二长岩和花岗闪长岩,是一套中酸性、偏铝质钙碱性、Ⅰ型花岗岩类.微量元素表现出消减带富集大离子亲石元素、亏损高场强元素的特征,并具有岛弧花岗岩的亲缘性.锆石Hf同位素研究表明,加查地区中酸性岩石来自新生地壳物质的熔融,偏基性岩石来自于亏损地幔.而桑日地区的酸性岩石来自于古老地壳物质的重熔.本文认为包括研究区在内的南拉萨地体中的晚三叠世-早侏罗世岩浆岩为俯冲到南拉萨地体之下的松多洋壳断离或回卷,软流圈地幔上涌,地幔楔熔融并加热上覆地壳的产物. 相似文献
13.
Whole rock major and trace element and Sr-, Nd- and Hf-isotope data, together with zircon U-Pb, Hf- and O-isotope data, are reported for the Nb-Ta ore bearing granites from the Lingshan pluton in the Southeastern China, in order to trace their petrogenesis and related Nb-Ta mineralization. The Lingshan pluton contains hornblende-bearing biotite granite in the core and biotite granite, albite granite and pegmatite at the rim. In addition, numerous mafic microgranular enclaves occur in the Lingshan granites. Zircon SIMS U-Pb dating gives consistent crystallization ages of ca. 132 Ma for the Lingshan granitoids and enclaves, consistent with the Nb-Ta mineralization age of ∼132 Ma, indicating that mafic and felsic magmatism and Nb-Ta mineralization are coeval. The biotite granites contain hornblende, and are metaluminous to weakly peraluminous, with high initial 87Sr/86Sr ratios of 0.7071–0.7219, negative εNd(t) value of −5.9 to −0.3, εHf(t) values of −3.63 to −0.32 for whole rocks, high δ18O values and negative εHf(t) values for zircons, and ancient Hf and Nd model ages of 1.41–0.95 Ga and 1.23–1.04 Ga, indicating that they are I-type granites and were derived from partial melting of ancient lower crustal materials. They have variable mineral components and geochemical features, corresponding extensive fractionation of hornblende, biotite and feldspar, with minor fractionation of apatite. Existence of mafic microgranular enclaves in the biotite granites suggests a magma mixing/mingling process for the origin of the Lingshan granitoids, and mantle-derived mafic magmas provided the heat for felsic magma generation. In contrast, the Nb-Ta mineralized albite granites and pegmatites have distinct mineral components and geochemical features, which show that they are highly-fractionated granites with extensive melt and F-rich fluid interaction in the generation of these rocks. The fluoride-rich fluids induce the enrichment in Nb and Ta in the highly evolved melts. Therefore, we conclude that the Nb-Ta mineralization is the result of hydrothermal process rather than crystal fractionation in the Lingshan pluton, which provides a case to identify magmatic and hydrothermal processes and evaluate their relative importance as ore-forming processes. 相似文献
14.
《Chemie der Erde / Geochemistry》2017,77(2):281-302
Kolah-Ghazi granitoid (KGG), situated in the southern part of the Sanandaj–Sirjan Zone (SNSZ), Iran, is a peraluminous, high K calc-alkaline, cordierite-bearing S-type body that is mainly composed of monzogranite, granodorite and syenogranite. Zircon U–Pb ages indicate that the crystallization of the main body occurred from 175 Ma to 167 Ma. Two kinds of xenoliths are found in KKG rocks: (i) xenoliths of partially melted pelites including cordierite xenocrysts and aluminoslicates, and (ii) mafic microgranular enclaves that reflect the input of mantle-derived mafic magmas. Field observations and geochemical data of KGG rocks are consistent with their derivation from a multiple sources including melts of metasediments and mantle-derived melts. We infer that these magmas originated by the anatexis of a metasedimentary source (mixture of metapelite and metagreywacke) in the mid- to lower-crust under low water-vapor pressures (0.5-1 Kbar) and temperature of ∼800 °C. KGG is the product of biotite incongruent melting of this metasedimentary source. S-type granites are commonly thought to be produced in continent-continent collision tectonic environment. However, trace element discrimination diagrams show that S-type KGG rocks formed in an arc-related environment. The roll-back of Neo- Tethyan subducting slab accompanying oblique subduction in Late Triassic to Early Jurassic time induced trench rollback, back arc basin opening and filling with turbidite flysch and molasse- type siliciclastic sediments of the Shemshak Group on the overriding plate. Further changes in the subducting slab to flat subduction in Middle Jurassic time, the time of peak magmatism in the SNSZ, led to thickening and high temperature-low pressure metamorphism of the backarc turbidite deposits and consequent anatexis of the metasedimentary source to produce the KGG S- type rocks along with several other I-type granitoids in the SNSZ. 相似文献
15.
作为全球三大成矿域之一,特提斯成矿域发育众多的世界级成矿带(矿床),例如,旁地德斯、萨汉德-巴兹曼、贾盖、玉龙、冈底斯成矿带等。为了进一步了解特提斯成矿域中新世斑岩铜矿的成因及成矿作用,本文对萨汉德-巴兹曼、贾盖和冈底斯铜矿带典型矿床的地质、地球化学、Sr-Nd-Pb数据进行对比分析,探讨含矿斑岩岩石成因、源区特征和构造环境,归纳其构造演化与其成矿作用过程。地球化学数据显示,这三个铜矿带中新世斑岩体总体显示钙碱性I型花岗岩的特征,具有埃达克岩亲和性。与冈底斯铜矿带相比较,萨汉德-巴兹曼铜矿带和贾盖铜矿带斑岩体显示出弧岩浆岩与埃达克岩过渡的地球化学特征,暗示其岩浆源区MORB质角闪榴辉岩或榴辉岩可能发生的较大程度的部分熔融。Sr-Nd-Pb同位素数据显示,这些含矿斑岩主要来源于受岩浆作用控制的壳幔混合物质,显示DUPAL异常。综合研究分析,认为这些含矿斑岩可能形成于岛弧造山带演化过程中,是洋壳俯冲消减和大陆碰撞过程中增厚下地壳部分熔融的结果。 相似文献
16.
17.
为确定延边地区明月沟组火山岩的形成时代、成因及构造背景,对明月沟组中的安山岩开展了岩石学、SIMS锆石U-Pb年代学、岩石地球化学及锆石Hf同位素特征研究。结果表明:明月沟组安山岩中的锆石为岩浆成因锆石。代表安山岩形成时代的两件样品中锆石的~(206)Pb/~(238)U加权平均年龄分别为(111±4)Ma(n=6,MSWD=3.2)和(113±3)Ma(n=6,MSWD=1.4),属早白垩世晚期。岩石地球化学特征上,明月沟组安山岩相对富钠,属高钾钙碱性系列,具有明显富集大离子亲石元素(K、Ba)和轻稀土元素,亏损重稀土元素和Ta、Nb等高场强元素的特征,结合其Hf同位素组成特征,暗示明月沟组安山岩的源岩应为受俯冲板片流体成份参与的亏损地幔。结合区域构造演化背景,明月沟组安山岩的形成应与早白垩世古太平洋板块向欧亚大陆板块的斜向俯冲作用相关。 相似文献
18.
A mafic–ultramafic intrusive belt comprising Silurian arc gabbroic rocks and Early Permian mafic–ultramafic intrusions was recently identified in the western part of the East Tianshan, NW China. This paper discusses the petrogenesis of the mafic–ultramafic rocks in this belt and intends to understand Phanerozoic crust growth through basaltic magmatism occurring in an island arc and intraplate extensional tectonic setting in the Chinese Tianshan Orogenic Belt (CTOB). The Silurian gabbroic rocks comprise troctolite, olivine gabbro, and leucogabbro enclosed by Early Permian diorites. SHRIMP II U-Pb zircon dating yields a 427 ± 7.3 Ma age for the Silurian gabbroic rocks and a 280.9 ± 3.1 Ma age for the surrounding diorite. These gabbroic rocks are direct products of mantle basaltic magmas generated by flux melting of the hydrous mantle wedge over subduction zone during Silurian subduction in the CTOB. The arc signature of the basaltic magmas receives support from incompatible trace elements in olivine gabbro and leucogabbro, which display enrichment in large ion lithophile elements and prominent depletion in Nb and Ta with higher U/Th and lower Ce/Pb and Nb/Ta ratios than MORBs and OIBs. The hydrous nature of the arc magmas are corroborated by the Silurian gabbroic rocks with a cumulate texture comprising hornblende cumulates and extremely calcic plagioclase (An up to 99 mol%). Troctolite is a hybrid rock, and its formation is related to the reaction of the hydrous basaltic magmas with a former arc olivine-diallage matrix which suggests multiple arc basaltic magmatism in the Early Paleozoic. The Early Permian mafic–ultramafic intrusions in this belt comprise ultramafic rocks and evolved hornblende gabbro resulting from differentiation of a basaltic magma underplated in an intraplate extensional tectonic setting, and this model would apply to coeval mafic–ultramafic intrusions in the CTOB. Presence of Silurian gabbroic rocks as well as pervasively distributed arc felsic plutons in the CTOB suggest active crust-mantle magmatism in the Silurian, which has contributed to crustal growth by (1) serving as heat sources that remelted former arc crust to generate arc plutons, (2) addition of a mantle component to the arc plutons by magma mixing, and (3) transport of mantle materials to form new lower or middle crust. Mafic–ultramafic intrusions and their spatiotemporal A-type granites during Early Permian to Triassic intraplate extension are intrusive counterparts of the contemporaneous bimodal volcanic rocks in the CTOB. Basaltic underplating in this temporal interval contributed to crustal growth in a vertical form, including adding mantle materials to lower or middle crust by intracrustal differentiation and remelting Early-Paleozoic formed arc crust in the CTOB. 相似文献
19.
While recycling of subducted oceanic crust is widely proposed to be associated with oceanic island, island arc, and subduction-related adakite magmatism, it is less clear whether recycling of subducted continental crust takes place in continental collision belts. A combined study of zircon U–Pb dating, major and minor element geochemistry, and O isotopes in Early Cretaceous post-collisional granitoids from the Dabie orogen in China demonstrates that they may have been generated by partial melting of subducted continental crust. The post-collisional granitoids from the Dabie orogen comprise hornblende-bearing intermediate rocks and hornblende-free granitic rocks. These granitoids are characterized by fractionated REE patterns with low HREE contents and negative HFSE anomalies (Nb, Ta and Ti). Although zircon U–Pb dating gives consistent ages of 120 to 130 Ma for magma crystallization, occurrence of inherited cores is identified by CL imaging and SHRIMP U–Pb dating; some zircon grains yield ages of 739 to 749 Ma and 214 to 249 Ma, in agreement with Neoproterozoic protolith ages of UHP metaigneous rocks and a Triassic tectono-metamorphic event in the Dabie–Sulu orogenic belt, respectively. The granitoids have relatively homogeneous zircon δ18O values from 4.14‰ to 6.11‰ with an average of 5.10‰ ± 0.42‰ (n = 28) similar to normal mantle zircon. Systematically low zircon δ18O values for most of the coeval mafic–ultramafic rocks and intruded country rocks preclude an AFC process of mafic magma or mixing between mafic and felsic magma as potential mechanisms for the petrogenesis of the granitoids. Along with zircon U–Pb ages and element results, it is inferred that the granitic rocks were probably derived from partial melting of intermediate lower crust and the intermediate rocks were generated by amphibole-dehydration melting of mafic rocks in the thickened lower crust, coupled with fractional crystallization during magma emplacement. The post-collisional granitoids in the Dabie orogen are interpreted to originate from recycling of the subducted Yangtze continental crust that was thickened by the Triassic continent–continent collision. Partial melting of orogenic lithospheric keel is suggested to have generated the bimodal igneous rocks with the similar crustal heritage. Crustal thinning by post-collisional detachment postdated the onset of bimodal magmatism that was initiated by a thermal pulse related to mantle superwelling in Early Cretaceous. 相似文献
20.
The Zhongchuan district is an important component of the metallogenic belt in the Western Qinling. The Zhongchuan granite pluton occurring in the centre of the Zhongchuan metallogenic area has been poorly constrained, though the Triassic granite in Western Qinling has been well documented. In‐situ zircon U–Pb ages, Hf isotopic compositions and whole‐rock geochemical data are presented for host granite and mafic microgranular enclaves (MMES) from the Zhongchuan pluton, in order to constrain its sources, petrogenesis and tectonic setting of the pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMES and the host granitic rocks mainly due to interactions between coeval felsic host magma and mafic magma. The zircon U–Pb age of host granite (231.6 ± 1.5 to 235.8 ± 2.3 Ma) has overlapping uncertainty with that of the MMES (236.6 ± 1.3 Ma), establishing that the mafic and felsic magmas were coeval. The Hf isotopic composition of the MMES (εHf(t) = −13.4 to 4.0) is distinct from the host granite (εHf(t) = −15.7 to 0.0), indicating that both enriched subcontinental lithosphere mantle (SCLM) and crustal sources contributed to their origin. The zircons have two‐stage Hf model ages of 1064 to 1798 Ma for the host granite and 858 to 1747 Ma for the MMES. This suggests that the granitic pluton was likely derived from partial melting of a Late Mesoproterozoic crust, with subsequent interaction with the SCLM‐derived mafic magmas in tectonic affinity to the South China Block. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献