准噶尔盆地东部巴塔玛依内山组玻质碎屑岩的发现及地质意义

Discovery and geological significance of hyaloclastite of Batamayineishan Formation in Eastern Junggar Basin

玻质碎屑岩是岩浆水下喷发的直接证据,对火山岩喷发环境的确定至关重要。以准噶尔盆地东部白碱沟地区巴塔玛依内山组地层发育的玻质碎屑岩为研究对象,通过野外剖面实测、薄片鉴定、激光剥蚀电感耦合等离子体质谱仪LA-ICP-MS锆石U-Pb定年、烃源岩测试等手段对玻质碎屑岩的岩石学、年代学特征以及泥岩夹层的特征进行研究。结果表明:白碱沟地区的玻质碎屑岩可分为流纹质和玄武质2种,这为五彩湾和白碱沟地区火山岩水下喷发环境的确定提供了最直接的证据。玻质碎屑岩形成于333. 8±4. 6 Ma,属于早石炭世。结合前人研究成果,认为研究区巴塔玛依内山组火山岩在早石炭世和晚石炭世均有发育,水下喷发环境很可能从早石炭世晚期(333. 8±4. 6 Ma)开始一直延续至晚石炭世(300. 4±1. 3 Ma)。长时间的水下喷发一方面使烃源岩的有机质丰度提高;另一方面有机质热演化释放的有机酸使火山岩储层产生次生溶蚀孔,从而在巴塔玛依内山组内部与烃源岩接触的火山岩中形成有利的次生孔隙发育带。

Hyaloclastite is a type of volcanic rock that results from magma erupting under water or quenching abruptly with water contact.Hyaloclastite of Batamayineishan Formation that develops in Baijiangou is studied using field profile measurements,thin section authentication,LA-ICP-MS zircon U-Pb dating and source rock analysis.The results show that the hyaloclastite can be divided into two categories,including rhyolitic hyaloclastite and basaltic hyaloclastite.This provides a direct evidence for the subaquatic eruption environment of volcanic rocks in Wucaiwan and Baijiangou.The rhyolitic hyaloclastite formed at 333.8±4.6 Ma ago in the Early Carboniferous.Combining the results of previous studies,the volcanic rocks of Batamayineishan Formation were developed in both Early Carboniferous and Late Carboniferous.The under-water eruption probably began in the Early Carboniferous(333.8±4.6 Ma)and continued to the Late Carboniferous(300.4±1.3 Ma).Long duration of under water eruptions increased the organic abundance of source rock,and the organic acid which was released by thermal evolution of organic matter further resulted in secondary dissolution pores in the reservoir.