Field-Petrochemical Investigation of Ultrahigh-Pressure Garnet Periodotites from the Sulu Terrane, Eastern China

9814468 Liou以前的研究允许在苏鲁-大别超高压（UHP）岩石中识别两种不同类型的石榴橄榄岩。A型橄榄岩代表中朝板块地幔楔的碎片，B型橄榄岩是扬子板块俯冲前侵位于陆壳的壳源镁铁质-超镁铁质杂岩。这些橄榄岩中的橄榄石、石榴石和辉石含有微小的矿物包裹体，这些矿物包裹体可能是非常高磷的相或致密的含水镁硅酸盐。 此外，有史以来最负的三角洲18-氧值记录的石榴石，绿辉石和多硅白云母表明非常有限的流体/岩石的相互作用，在超高压变质作用和随后的折返，因此，主要地幔功能，预计将得到很好的保存。本研究填补了地幔岩石学和矿物物理学之间的差距，并将解决以下问题：（1）超高压石榴石橄榄岩是否能提供上地幔岩石构造过程的新约束？(2)矿物的地球化学显微分析对了解地幔-板片和岩石/流体相互作用过程有什么贡献？(3)超高压矿物中出溶层的意义是什么？(4)还有什么矿物学证据记录了石榴橄榄岩的超高压变质作用？苏禄海岩芯和地表样品的主要逆冲断层包括：（1）石榴橄榄岩的岩石学特征和变质演化;（2）其源区和初始构造环境的地球化学制约;（3）评价壳幔和岩石/流体相互作用的放射性和稳定同位素组成;（4）各种方法的年龄测定，包括锆石SHRIMP定年。这种综合的岩石化学和年代学约束是评价与大陆碰撞和俯冲有关的上地幔性质的先决条件。

9814468LiouPrevious studies allowed identification of two distinct types of garnet peridotites in the Sulu-Dabie ultra-high pressure (UHP) terrane. Type A peridotites represent fragments of the mantle wedge of the Sino-Korean plate and Type B peridotites are crustal-derived mafic-ultramafic complexes of the Yangtze plate emplaced into continental crust prior to subduction. Olivine, garnet, and pyroxene of these peridotites contain minute mineral inclusions that may be very high-P phases or dense hydrous magnesian silicates. Furthermore, the most negative delta 18-oxygen values ever recorded for garnet, omphacite and phengite suggests extremely limited fluid/rock interactions during UHP metamorphism and subsequent exhumation; thus primary mantle features are expected to be well preserved. This research bridges the gap between mantle petrology and mineral physics and will address the following questions: (1) Can UHP garnet peridotites provide new constraints on petrotectonic processes of the upper mantle? (2) What can geochemical microanalyses of minerals contribute to understanding the processes of mantle-slab and rock/fluid interactions? (3) What is the significance of exsolution lamellae in UHP minerals? (4) What other mineralogical evidence records the UHP metamorphism of garnet peridotites? Major thrusts on both core and surface samples from the Sulu terrane include: (1) petrological characteristics and metamorphic evolution of garnet peridotites; (2) geochemical constraints for their source and initial tectonic setting; (3) both radioactive and stable isotopic compositions to evaluate interactions of crust/mantle and rock/fluid; and (4) age determinations by various methods including SHRIMP dating of zircons. Such comprehensive petrochemical and geochronological constraints are prerequisites to evaluate the nature of the upper mantle associated with continental collision and subduction.