Discovery of granite and its tectonic significance in southwestern basin of the South China Sea
Discovery of granite and its tectonic significance in southwestern basin of the South China Sea
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发表时间：
2008
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通讯作者：
Peng Zhuo-lun
中科院分区：
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作者：
Peng Zhuo-lun
在南海西南海盆水深2800- 4000 m的三个地点，采集了花岗岩和变质沉积岩样品。根据重力和磁力资料计算，南海西南海盆的地壳厚度为8-10 km，一些构造地质学家将其视为洋壳。这些样品是由广州海洋地质调查局在进行1∶ 100万近海填图项目时拖采的。通过显微结构分析，三个样品的岩性分别为细花岗岩、石英变质沉积物和花岗闪长岩。用Ar-Ar法和K-Ar法测得细粒花岗岩的同位素年龄分别为109.7Ma和114.2Ma，离子探针测得锆石年龄为120 Ma。这些事实证实了该花岗岩形成于早白垩世晚期，可能属于华南中生代花岗岩带的一部分。这一发现有力地挑战了目前认为南海西南海盆地壳属于海底扩张形成的洋壳的观点。
The samples of granite and metamorphic-sediment rock have been obtained at three spots with the water depth of 2800- 4000m in southwestern sea basin of the South China Sea, where the crust thickness ranging 8-10 kilometres calculated by gravitational and magnetic data and taken for oceanic crust by some tectonic geologists. These samples were dragged by Guangzhou Marine Geo- logical Survey when they were doing the project of offshore mapping with 1∶1000000 scale. The lithology of three samples are respec- tively fine granitite, quartz metamorphic-sediment and granodioite by microstructure analysis. The isotopic age of the fine granitite is 109.7Ma and 114.2Ma measured by Ar-Ar and K-Ar methods and the zircon age is 120Ma, by ion microprobe. These realities have confirmed that the granites formed in the late of early Cretaceous, and therefore they belong to a part of Mesozoic granite zone in South China possibly. The discovery mentioned above strongly challenges the idea that the crust of southwestern sea basin in the South China Sea belongs to oceanic crust produced by seafloor spreading, which is considered, up to the present.