排序方式: 共有77条查询结果,搜索用时 46 毫秒
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桐柏山高压变质带及其区域构造型式 总被引:23,自引:4,他引:23
桐柏山是秦岭-大别山造山带的重要组成部分。新近的构造学和岩石学详细研究表明,该区广泛分布有大量的、大小不一的榴辉岩及退变质榴辉岩块体,构成一个延展长约200km和宽约40km的高压变质带。由榴辉岩或退变质榴辉岩、遭受过高压变质作用的沉积和火山岩、由榴辉岩退变质而成的片麻岩和片岩,以及面理化的含榴或不含榴的花岗岩组成的高压变质单位(HP),在组成及变质演化特征方面,均与大别-苏鲁地区的高压单位类似。构造上,显示一典型的西北美型变质核杂岩。分隔开由桐柏杂岩组成的核部杂岩单位(CC)及上覆的高压单位的km尺度的伸展拆离带,具有下和中伸展拆离带的复合性质,是在高压变质作用期后伸展体制下形成的。桐柏山高压变质带是与大别山地区的高压变质带相联接的,据其岩石学、构造学及相关的主要构造边界展布特征,推测该高压变质带穿过南襄盆地有继续向东秦岭延伸的趋势。桐柏山高压变质带是东秦岭造山带与大别-苏鲁超高压和高压变质带间的构造纽带。 相似文献
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Extensional Tectonic Framework of Post High and Ultrahigh Pressure Metamorphism in Dabieshan, China 总被引:3,自引:0,他引:3
INTRODUCTIONThestudyofhigh-pressure(HP)andultrahigh-pressure(UHP)metamorphicrocksisoneofthemajorhottopicsinthesolidearthscien... 相似文献
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超高压——高压剪切带 总被引:4,自引:2,他引:4
超高压-高压剪切带是大陆碰撞造山过程中变质-变形分解作用形成的一类特殊的剪切带。剪切带内的构造以含柯石英、金刚石等超高压-高压矿物的榴辉岩、面理化超基性-基性岩、片麻岩、大理岩为特征,具有复杂的变形组构和变形历史。最终形成布丁-基质或残斑-基质结构。深入研究超高压-高压剪切带的几何学、运动学和流变学特征,对分析超高压-高压变质岩石的形成-折返过程及碰撞造山动力学,具有重要的实际和理论意义。 相似文献
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小灶火软玉矿床位于东昆仑造山带西段,同新疆和田玉处于昆仑山脉同一条成矿带上。该矿床软玉种类主要为青玉,其中透闪石含量达99%以上,为特殊的镁矽卡岩矿床。对该矿区青玉及其相关的黑云二长花岗岩进行了系统的LA-MC-ICP-MS锆石微量元素、U-Pb及Lu-Hf同位素研究。结果显示,黑云二长花岗岩中均为具典型韵律振荡环带的岩浆成因锆石,锆石U-Pb定年得到其成岩年龄为415.8±1.7 Ma;锆石ε_(Hf)(t)值为1.5~6.6,亏损地幔Hf模式年龄(tDM)为779~965 Ma,指示黑云二长花岗岩为东昆仑原特提斯造山带后碰撞阶段新生的新元古代地壳物质熔融的产物。青玉中的锆石可分为两类,其中主要锆石群——I类锆石呈补丁状环带、面状环带或无环带,且具有与黑云二长花岗岩中的岩浆锆石明显不同的稀土元素及Hf同位素特征,显示典型的热液锆石特点,其U-Pb年龄416.4±1.5 Ma代表了青玉的形成时间;II类锆石(416 Ma、471 Ma、818 Ma)呈韵律振荡环带,为热液流体从围岩中捕获的继承锆石。小灶火地区成岩-成矿作用的同时性(~416 Ma)表明岩浆岩侵入是软玉矿床形成的岩浆岩条件,软玉成矿作用方式为热液交代和充填作用。值得注意的是,用热液锆石的Hf同位素来示踪软玉成矿流体性质时应十分谨慎,因为成矿热液中的Hf元素在同时结晶的两种不同矿物(热液锆石和透闪石)间发生了重新分配。 相似文献
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Rui Liu Hanwen Zhou Li Zhang Zengqiu Zhong Wen Zeng Hua Xiang Song Jin Xinqian Lu Chunzhong Li 《Lithos》2010,119(3-4):163-180
U–Pb ages, trace elements, and Hf isotope compositions of zircons from the Mayuan migmatite complex in NW Fujian province have been determined to provide constraints on the source and genesis of anatexis and tectonothermal evolution related to the Caledonian orogeny in South China. The migmatites investigated consist of various amounts of mesosome, leucosome, and melansome. Zircons extracted from mesosome, leucosome, and granite samples are characterized by oscillatory overgrowths enclosing inherited cores or occur as newly grown grains. The ages of the inherited zircons from the leucosome and granite samples are consistent with those of adjacent basement paragneiss in the study area, suggesting that both leucosome and granite were generated by partial melting of the latter. A comparison of Hf isotopes between the newly-formed zircons and inherited cores indicates that the former resulted from the breakdown of preexisting inherited zircons and/or less Hf-rich minerals other than zircons at the source. One mesosome sample contains typical metamorphic zircons that yielded a weighted mean 206Pb/238U age of 453 ± 3 Ma. They show enrichments in heavy REEs (LuN/LaN up to 22,709), indicating their growth prior to garnet crystallization. The other mesosome sample, in contrast, contains both newly-formed metamorphic rims and grains that gave a weighted mean 206Pb/238U age of 442 ± 8 Ma. They are characterized by relatively low Th/U ratios, depletions in heavy REEs (LuN/LaN = 117–396), and low 176Lu/177Hf ratios, suggesting their growth synchronous with garnet crystallization. The U–Pb ages of the mesosome samples are interpreted as recording the time of early (ca. 453 Ma) to peak (442 Ma) stages of a regional metamorphic event. Two leucosome and two granite samples yield consistent U–Pb ages of 438 ± 5 Ma to 442 ± 4 Ma, which provide constraints on the timing of subsequent anatexis and magmatism. The geochronological data reported here reveal a consecutive sequence of regional metamorphism, anatexis, and magmatism in NW Fujian province, lasting for at least 15 Myr, which was driven by the Caledonian orogeny that have affected a major part of the SCB. 相似文献
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秦岭大别碰撞造山带中隆升最高的结晶基底便是大别杂岩,在超高压变质岩和某些高级变质岩中均发现典型的近等温减压(ITD)型的退变质结构,多呈后成合晶或冠状体的形式取代或包绕原生矿物晶粒(主晶),显示退变质不平衡反应的过程.然而超高压变质岩与大别杂岩中的高级变质岩,变质地温梯度截然不同,暗示它们形成的构造条件极不相同,超高压变质岩早期由岩石圈深处(120km±)折返到下地壳与那里的高级变质岩构造混合,平行并置,而后才一起隆升.退变质不平衡结构与寄主岩的面理无关,说明这种近等温的减压退变质作用发生于后造山时期近绝热条件下的隆升体制,近绝热隆升的热源可能是中生代以来大别山地区岩石圈减薄所引起 相似文献
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