New insights into the genesis of Neoproterozoic low-δO granitoids in the Seychelles:crustal cannibalization within an intra-plate extensional setting  

塞舌尔新元古代花岗质岩石“O同位素亏损机制”的新认识

作　　者：Jiu-Long Zhou Xian-Hua Li Robert D.Tucker 周久龙;李献华;Robert D.Tuckere(State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China;College of Earth Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Innovation Academy for Earth Science,Chinese Academy of Sciences,Beijing 100029,China;Bureau des Recherches Géologiques et Minières,Orléans 45060,France)

机构地区：[1]State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China [2]State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing 210023,China [3]College of Earth Sciences,University of Chinese Academy of Sciences,Beijing 100049,China [4]Innovation Academy for Earth Science,Chinese Academy of Sciences,Beijing 100029,China [5]Bureau des Recherches Géologiques et Minières,Orléans 45060,France

出　　处：《Science Bulletin》2020年第22期1880-1883,M0003,共5页科学通报（英文版）

基　　金：supported by the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(XDB18030300);the National Natural Science Foundation of China(41703040);the State Key Laboratory of Lithospheric Evolution(K201709);the Fundamental Research Funds for the Central Universities(0206-14912220)。

摘　　要：Linking global rock records geologically and paleomagnetically in deep time has revealed that plate motion of Earth's lithosphere is characterized by periodic supercontinent cycles.Two mutually competing geodynamic models have been proposed to explain the break-up of the Neoproterozoic supercontinent Rodinia,which invoke either underlying mantle plumes(i.e.,a superplume)[1]or surrounding accretionary orogenic systems[2].A precise under-standing of the tectonic setting of Neoproterozoic magmatism around the periphery of Rodinia is crucial for distinguishing between these two contrasting hypotheses.塞舌尔曾经位于Rodinia超大陆西缘,是检验"Rodinia西缘发育安第斯型陆弧"假说的一个切入点.本文对塞舌尔新元古代花岗质岩石开展了SIMS锆石U–Pb定年和O同位素微区原位分析,结果显示:(1)这些岩石侵位于约810和750 Ma两期次;(2)810 Ma没有出现O同位素亏损,而750 Ma普遍出现亏损,其中起源于新生地壳的岩石比起源于古老基底的岩石呈现出更强烈的亏损;(3)部分锆石颗粒记录了δ18O从核至边降低的趋势.前人认为塞舌尔花岗质岩石的O同位素亏损是继承自古老基底源区,但这一机制难以解释上述观察.更可能是在大陆裂谷(热点)环境下,由于足够高的地热梯度和区域尺度的地壳伸展破碎,岩浆系统通过"地壳自噬作用"(crustal cannibalization)与地表水实现了高效的O同位素交换,从而获得低δ18O特征.我们认为Rodinia西缘的800–750 Ma洋壳俯冲可能并不存在(至少需要寻找新的岩石记录),Rodinia超大陆的最终裂解更可能是下覆的地幔柱活动所触发,而不是外围的环形俯冲.

关 键 词：RODINIA超大陆 O同位素 微区原位分析 新元古代 大陆裂谷 地壳伸展 洋壳俯冲 地热梯度 

分 类 号：P534.3[天文地球—古生物学与地层学] P588.121[天文地球—地质学] P597