Rodingitization,commonly coupled with serpentinization of ultramafic rocks,bears significant information for fluid-rock interactions and element transfer from sea-floor to subduction zone environments.Numerous outcrops of rodingites are exposed along the Yarlung Zangbo suture zone(YZSZ)of southern Tibet,providing us an excellent opportunity to probe the petrogenetic processes,and unravel their implications for regional tectonic evolution.Several studies have been performed on rodingites from the eastern to central portions of the YZSZ,whereas limited work has ever been conducted on rodingitized rocks from the western segment of the YZSZ,precluding a comprehensive understanding of this lithological type.In this paper,we present detailed studies of petrology,mineral,whole-rock geochemistry and phase equilibrium modeling on a suite of newly recognized rodingites within the Purang ophiolite massif in the southwestern part of the YZSZ.The rodingites have a major metasomatic mineral association of chlorite,clinozoisite,amphibole and minor amounts of plagioclase,representing products of an early-stage rodingitization.They generally present compositions of low SiO2(48.89 wt.%–53.57 wt.%),Fe2O3^T(3.77 wt.%–5.56 wt.%),Na2O(1.31 wt.%–1.93 wt.%),Al2O3(4.78 wt.%–8.84 wt.%),moderate CaO(9.69 wt.%–11.23 wt.%),and high MgO(24.11 wt.%–26.08 wt.%)concentrations with extremely high Mg^# values[Mg^#=100×Mg/(Mg+Fe^2+)molar]of 89–92.Bulk-rock recalculation reveals that the rodingites have a protolith of mantle-derived olivine gabbro or gabbronorite.They have low rare earth element compositions(∑REE=2.4 ppm–6.5 ppm)and are characterized by flat LREE and slightly enriched HREE patterns with positive Eu anomalies;they also exhibit positive anomalies in Sr,U and Pb and negative anomalies in high-field strength elements,including Nb,P and Ti,suggesting for a subduction-zone imprinting.Phase equilibrium modeling shows that the rodingitization did take place at P<2 kbar and T=~350–400℃,consistent with low greenschist f
Songjie WangXu-Ping LiWenyong DuanFanmei KongZeli Wang
南海是西太平洋地区最大的边缘海之一。自古生代以来，南海及邻近区域经历了复杂的构造演化历史。作为东南亚地区重要的组成部分，南海地区已经成为本区域许多古生代-中生代古地理重建的焦点地区（如，Karig，1971；Hamilton，1979；Taylorand Hayes，1983；Tapponnier,1986；Metcalfe，1996；鄢全树和石学法，2007；Zhou et al．，2008；Morley，2012；Yan et al.，2014）。
在发育有全球最大、最复杂的弧—沟—盆体系的西太平洋地区,集中了全球75%左右的边缘海盆(弧后盆地)。根据磁异常条带年龄,这些边缘海盆可粗略分为3个扩张幕。主要根据DS-DP,ODP和IODP计划实施以来所获得的成果,结合其他海洋调查航次研究成果,系统阐述了分属3个扩张幕的西菲律宾海盆(第一扩张幕)、南海—四国海盆(第二扩张幕)和冲绳海槽(第三扩张幕)—马里亚纳海槽内的岩浆活动特点。西菲律宾海盆(扩张时代为65～35 Ma BP)从原先的赤道位置迁移至现今的位置,其内存在如似正常洋中脊玄武岩(NMORB)、洋岛玄武岩(OIB)及弧火山岩等多种岩石类型,其地球动力学背景分别与弧后扩张、地幔柱及火山弧等背景有关,其复杂的构造演化样式需要进一步研究;四国海盆(扩张时代为27～15 Ma BP)是由古伊豆—小笠原—马里亚纳弧(IBM)裂解形成的,其内除发育正常(N)—富集(E)的洋中脊玄武岩(NMORB-EMORB)外,还在扩张停止的同时出现了板内火山作用,形成了中K-超K碱性玄武岩。四国海盆的扩张模式并没有从岩石学和地质年代学角度进行明确制约,板内火山作用的地球动力学背景也不甚清楚。南海(扩张时代为32～15.5 Ma BP)是由来自华南地块的一些微陆块向东南裂离后的海底扩张所形成,并在海底扩张后2～8 Ma出现板内火山作用,截止目前,并没有获取到洋壳基底样品,主要获取到了南海海山似OIB的玄武岩,未来需要从岩石学和地质年代学角度对南海海底扩张动力学和时代以及扩张期后的板内火山作用动力学背景进行进一步制约。马里亚纳海槽(扩张时代为5 Ma BP至今)为一年青的洋内弧后盆地,其北段处于裂解增进阶段,其内出露有似MORB(中南段)及介于似MORB与似岛弧岩石之间过渡类型的玄武岩(增进端);虽然在扩张时代上与马里亚纳海槽相当,但冲绳海槽(扩张时代为4 Ma BP至今)�
