Rutile to Titanite Transformation in Eclogites and its Geochemical Consequences:An Example from the Sumdo Eclogite,Tibet  

作　　者：ZHAO Linghao ZENG Lingsen GAO Li’e HU Mingyue SUN Dongyang ZHANG Lifei 

机构地区：[1]Key Laboratory of Deep-Earth Dynamics,Ministry of Natural Resources,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China [2]Key Laboratory of In-situ Elemental Microprobe and Speciation Analysis,Chinese Geological Survey,National Research Center for Geoanalysis,Beijing 100037,China [3]School of Earth and Space Sciences,Peking University,Beijing 100871,China

出　　处：《Acta Geologica Sinica(English Edition)》2023年第1期122-133,共12页地质学报（英文版）

基　　金：supported by the National Science Foundation of China(Grant Nos.92055202);the Second Tibetan Plateau Scientific Expedition and Research(Grant No.2019QZKK0702);the China Geological Survey(Grant Nos.DD20221817 and DD20221630)。

摘　　要：The formation of titanite coronae after rutile is common in retrograde high-to ultrahigh-pressure meta-mafic rocks,which provides a good opportunity to address the geochemical behavior of HFSE in crustal environments.In the Sumdo eclogite,titanite occurs either as a corona around rutile grains or as semi-continuous veins cross-cutting the major foliation,whereas rutile grains occur either as inclusions in garnet or omphacite or as a relict core surrounded by titanite.Textural relationships and trace elements characteristics of rutile and titanite with different occurrences indicate that both minerals preferentially incorporate Nb and Hf over Ta and Zr in aqueous fluid.Moreover,the breakdown of omphacite and epidote could release substantial amounts of aqueous fluids enriched in Ca,Si,Fe and REE,which would react with rutile to form titanite coronae and veins.During this process,water-insoluble elements,like HFSE and HREE,behave like mobile elements,but they do not migrate substantially out of the system,instead,tending to react in situ.This suggests that the aqueous fluids released during the retrograde metamorphic reactions in mafic rocks could not substantially transfer fluidimmobile elements into the overlying mantle wedge in subduction environments.

关 键 词：Sumdo eclogite RUTILE TITANITE trace element geochemistry Nb-Ta fractionation 

分 类 号：P612[天文地球—矿床学] P588.1[天文地球—地质学] P595