The adakitic rock was recently found in Permian ophiolite complex of the Hongji Mountain within central and western Qiangtang Block. It intruded into the Permian ophiolite in the form of veinlets. The authors studied petrology, zircon LA-ICP-MS U-Pb age and whole-rock geochemistry of the adakitic rock, with the emphasis placed on its petrogenesis and geological implications. The adakitic rock is muscovite granite. Its high Th/U (0.22~0.63) and clear zoned zircons indicate magamatic origin. Zircon LA-ICP-MS age of muscovite granite is 271.7Ma ± 2.3Ma, indicating that the crystallization of adakitic rock took place in Early Permian. The adakitic rock is characterized by high SiO2 and Al2O3 and low K2O/Na2O, thus belonging to aluminous-peraluminous granite. The REE model is characterized by enrichment of light REE, moderate fractionations in HREE and small Eu anomalies. The values of Y, Yb are low and the content of Sr is moderate. The primitive mantle normalized trace element spider patterns show that they are enriched in Rb, U, K and have negative anomalies of Nb, Ta, Ti. Geochemical characteristics are similar to features of the adakite formed by partial melting of the subducted oceanic crust. The Hongji Mountain adakitic rock was most probably generated by partial melting of the subducted Paleo-Tethys oceanic crust under the amphibolite-eclogite facies condition, whereas the residual facies were hornblende and garnet. The earlier adakitic melt sufficiently replaced the mantle peridotite, whereas the later melt weakly replaced mantle peridotite. The plagioclase experienced fractional crystallization during the upward migration of the melt. The discovery of Hongji Mountain adakitic rock indicates that the Paleo-Tethys oceanic crust subducted in Early Permian and entered into the regression stage.%近期在羌塘中西部红脊山地区一套二叠纪蛇绿岩中首次发现了埃达克质岩石,呈脉状侵入到蛇绿岩中。对该套岩石进行了详细的岩石学、锆石U-Pb年龄和地球化学研究,重点讨论岩石成因及地质意义。埃达克质岩石岩性为白云母花岗岩,岩石中锆石晶形较完整,具典型的岩浆生长环带,结合Th/U值(0.22~0.63),表明其为典型的岩浆锆石。锆石LA-ICP-MS定年结果为271.7Ma±2.3Ma,表明其形成时代为早二叠世。岩石具有较高的SiO2、Al2O3含量和较低的K2O/Na2O值,为弱过铝质岩石。稀土元素配分模式呈右倾的曲线,重稀土元素分馏中等,Eu异常变化较小;微量元素Y、Yb含量较低,Sr含量中等,在微量元素蛛网图上表现出Rb、U、K正异常和Nb、Ta、P、Ti负异常。这与俯冲洋壳熔融形成的埃达克质岩石特征相似。红脊山埃达克质岩石是俯冲的古特提斯洋在角闪岩相-榴辉岩相条件下部分熔融形成的,残留相主要为石榴子石+角闪石。较早产生的熔体与地幔橄榄岩充分发生交代作用,后产生的熔体与地幔橄榄岩交代作用较弱,向上运移过程中斜长石发生分离结晶。红脊山埃达克质岩石的发现,表明古特提斯洋在早二叠世开始俯冲消减,大洋进入消退阶段。
展开▼
机译:北美北美前寒武纪丛林结构的摘要,皮埃蒙特高原结构,如马里兰州所示。 Edward B.纽约曼哈顿岛的锥形分层和蛇纹石的Mathewsgenesis。 A. A.北卡罗来纳州朱安格林。 T. L. Watson新英格兰西南部地质结构。威廉H.大西洋边境地区的兴趣爱好者。关于变质形态的论述。查尔斯R. Van Hisethe Menominee密歇根州的铁轴承区。 W. S. Bayley HeNominee特殊作品作案。 Charles R. Van Hise,W.S. Bayley The威斯康星州巴拉布煤炭区。莫塞河流域的Weidman经济资源。詹姆斯·贝尔·阿伯比比地区。乔治F.凯河畔嘉师的分类。 A. Archean和第Archean的P. Colemanthe联系了大湖区。 A. B.威廉特北部镍系列。 A. P. ColemanReport关于哈德森湾东海岸的探索。 A. P. Lowthe新发现的Sioux Falls,南达科他州的岩石。 J. E.密苏里州的待办生表产业。 E. R. Buckley,H.A.Buehler经济资源的北黑山。 J. D.印度领土和俄克拉荷马州阿尔库鲁特和威奇托山脉地质的欧文普通报告。 Joseph A. Taffan Temonte of Greenstone Schists在圣胡安山脉,科罗拉多。 Ernest Howethe营地区的铜矿床,怀俄明州。亚瑟C.蒙大拿和爱达荷州的Bitterroot Range和Clearwater Mountains的Spencera地质侦察。 Waldemar Lindgrenthe地质和矿石沉积物的Bisbee四边形。 F. L. Graneegegorge的地球铜区,亚利桑那州。地球Quadrangle的评论。Bisbee Quadrangle的评论。在蒙大拿州和爱达荷州的Bitterroot系列和清水山上的地质侦察。 Waldemar Lindgren.