塔里木克拉通Columbia聚合后大陆裂解的高热事件痕迹

The high-heat events in the Tarim craton after assembly of the Columbia supercontinent

对塔里木克拉通大红山花岗岩进行了LA-ICP-MS锆石U-Pb年代学以及主量、微量、稀土元素和氧同位素地球化学研究.LA-ICP-MS锆石U-Pb年代学分析获得的w(^(207)Pb)/w(^(206)Pb)加权平均年龄为1 732.3±7.4 Ma.大红山花岗岩的全岩δ^(18)O_(V-SMOW)=7.6‰~8.6‰,它们富硅、富碱,具有强烈的Eu负异常以及较高的w(Rb)、w(Th)、w(Y)、w(Ga)、w(Nb)和较低的w(Sr),w(Zr)+w(Nb)+w(Ce)+w(Y)和10~4×w(Ga)/w(Al)均较高,因此,它们具有A型花岗岩的地球化学特征.结合w(Sc)/w(Nb)-w(Y)/w(Nb)图解,大红山花岗岩为A,型花岗岩.通过计算18个花岗岩样品的锆石饱和温度T_(Zr)=732.45~1 128.33℃,属高温花岗岩.大红山花岗岩是由挤压体制向伸展转变过程的地质记录,可能受地幔底辟作用,软流圈地幔上涌带来的热导致下地壳在高温低压条件下发生部分熔融形成,记录了塔里木克拉通在Columbia超大陆聚合后的高热事件,是克拉通大规模裂解初期阶段的痕迹.

A combined study of the LA-ICP-MS zircon U-Pb chronology and the geochemistry of main elements, trace elements, rare earth elements and oxygen isotopes was carried out on the Dahongshan granites in the Tarim craton. The LA-ICP-MS zircon U-Pb dating yielded the weighted mean w（^207Pb）/w（^206 Pb） age of 1 732.3±7.4 Ma, which reveals that the Dahongshan granites fromed in the late Paleoproterozoic. The studied samples are rich in silicon, alkali and have negative anomaly of 6 Eu. They have high contents of w（Rb）, w（Th）, w（Y）, w（Ga） and w（Nb）, and high sum of w（Zr）＋w（Nb）＋w（Ce）＋w（Y） and rate of 10^4×w（Ga）/w（Al）, but low content of w（Sr） which indicate that Dahongshan granites have the geochemical characteristics of A-type granites. By the diagram of w（Sc）/w（Nb）-w（Y）/w（Nb）, the Dahong- shan granites belong to the type of A1-granites. The Dahongshan granites have high zircon saturation temperature （732.45-1 128.33℃） and belong to high temperature granites. Combined with the regional tectonic evolution, the Dahongshan granites are the A1-type granites derived from the partial melting of crust rocks during the tectonic system changing from the assembly to the lithosphere thinning and the curst extension, which may be induced by the upwelling of the asthenosphere mantle and the Dahongshan granites were the record of high heat event and have recorded the assembly and breakup of the Columbia supercontinent in the Tarim craton.