南海盆海山火山碎屑岩的发现及其地质意义

Characteristics of volcaniclastic rocks from seamounts in the South China Sea and its geological implications.

海山火山碎屑岩是水下爆发性火山作用的产物。南海盆两座海山上发现火山碎屑岩表明海山顶部曾经一度高于PCL(压力补偿深度)。岩相学特征显示这些火山碎屑岩的胶结物主要为一混合相,包括粘土矿物和黑色铁质矿物等,这从一个侧面反映海山的正地形限制了粗粒外生碎屑到达海山顶部。岩石的单矿物组分、主量元素化学特征与同海山玄武质熔岩具有可比性,属碱性岩浆系列。计算获得海山平均最小下沉速率为0.06mm/年,最大可能达0.30mm/年。海山岩石的机械风化产物对周围海盆的沉积作用作出重要贡献。

Volcaniclastic rock on seatnount is the product of subaqueous explosive volcanism. The finding of volcaniclastic rocks from two seamounts in the South China Sea suggests that the top of seamounts once exceeded the pressure compensation level ( PCL). Petrographic characteristics display that the cementing material mainly is a mixed phase including clay minerals and Fe-oxides, which, to one's extent, reflects that it is difficult for coarse-size epiclastic debris to reach the top of seatnount due to the obstruction of positive relief of seamount. The characteristics of mineral compositions and major element of volcaniclastic rocks are comparable to those of alkali basaltic rocks from the same seamount, and these volcaniclastic rocks also belongs to alkali magma series based on mineralogy and major element data. The calculated minimal and maximal subsidence rates for seamounts in the South China Sea are 0. 06mm/year and 0. 30mm/year, respectively. Physical weathering products of rocks from seamounts have a significant contributor to the adjacent basin.