西南印度洋U1473A钻孔大洋斜长花岗岩的成因：副矿物Sr-Nd-Hf-O同位素制约

Oceanic plagiogranites are referred to the evolved felsic rocks, including diorites, quartz diorites, tonalites and trondhjemites, which are ubiquitous in gabbros of the lower crust and ophiolites. Currently, it is still highly debated over the formation mechanism of the oceanic plagiogranites. Different models have been proposed, including extreme differentiation of basaltic melts, liquid immiscibility and hydrous remelting of the gabbroic rocks. Hole U1473A was drilled 789.7 m beneath seafloor in the center of the Atlantis Bank wave-cut platform during the IODP Expedition 360. Oceanic plagiogranites are widely but randomly distributed throughout the section, representing ~ 1.5% of the core. This project will conduct detailed petrological and geochemical studies on the oceanic plagiogranites from Hole U1473A, in particular, the Sr-Nd-Hf-O isotopes of accessory minerals in these plagiogranites, including zircon, apatite and titanite. These isotopic data will provide constraints on whether seawater was involved in the genesis of the oceanic plagiogranites or not, and thus help us effectively discriminate the petrogenesis of oceanic plagiogranites.

大洋斜长花岗岩是包括闪长岩、石英闪长岩、英云闪长岩和奥长花岗岩在内的一系列长英质岩石的统称，它广泛出露在下部洋壳的辉长岩以及蛇绿岩剖面中。大洋斜长花岗岩的成因存在较大争议，提出的模式包括玄武质岩浆高程度结晶分异、液相不混溶以及辉长质岩石的含水熔融等。国际大洋发现计划 (IODP)第360航次在西南印度洋亚特兰蒂斯浅滩地区布置了U1473A钻孔，总共钻进深度为789.7米，获得了约468.5米长的辉长岩岩芯。大洋斜长花岗岩在整个U1473A岩芯不同深度都有出露，其体积大约占整个岩芯的1.5%。本项目拟对U1473A大洋斜长花岗岩开展详细的岩石地球化学研究，尤其是针对锆石、磷灰石和榍石等副矿物进行微区Sr-Nd-Hf-O同位素研究。在此基础上，以限定大洋斜长花岗岩的形成过程是否有海水的参与，从而帮助我们有效地鉴别其成因机制。

大洋斜长花岗岩是包括闪长岩、石英闪长岩、英云闪长岩和奥长花岗岩在内的一系列长英质岩石的统称，它广泛出露在下部洋壳的辉长岩以及蛇绿岩剖面中。大洋斜长花岗岩的成因存在较大争议，提出的模式包括玄武质岩浆高程度结晶分异、液相不混溶以及辉长质岩石的含水熔融等。在西南印度洋Atlantis Bank大洋核杂岩上实施的U1473A钻孔，总共获得了约468.5米长的辉长岩岩芯，其中大洋斜长花岗岩在整个岩芯的不同深度都有出露。已经完成对锆石的离子探针U-Pb年龄与Hf-O同位素分析，获得U1473A钻孔斜长花岗岩的形成时代为11.29-12.57 Ma，ℇHf(t)范围为+12.7~+15.3，δ18O范围为+4.81~+5.50‰。利用激光剥蚀获得了磷灰石和榍石的143Nd/144Nd分别为0.51309-0.51313和0.51310-0.51316。基于这些数据，提出U1473A钻孔的斜长花岗岩是玄武岩高程度结晶分异的产物，形成过程中并没有海水的大规模参与。在本项目的资助下，已经在Geology、Journal of Petrology、Contributions to Mineralogy and Petrology和Lithos等国际学术刊物上发表SCI论文11篇。