松辽盆地北部徐家围子断陷下白垩统营城组火山机构类型与喷发模式研究

Volcanic edifice types and eruption model of Yingcheng Formation, Lower Cretaceous,in Xujiaweizi fault depression, northern Songliao Basin.

火山岩油气藏已成为我国东部中、新生代陆内裂谷盆地内一种重要的油气藏类型。松辽盆地北部徐家围子断陷营城组火山岩中形成大规模气藏,不同火山岩相对油气的储集性差异很大,因此探究断陷内火山机构类型和喷发模式成为天然气勘探开发的基础。徐家围子断陷发育中酸性火山岩,识别出层状火山、熔岩穹隆、破火山口等3种主要火山机构赋存类型。受区域垂向和斜向两期拉张作用控制,在断裂上盘、下盘和断裂带,火山机构分别以不同形式展布:断裂下盘的掀斜肩部火山机构发育、断裂带火山机构串珠状叠置、断裂上盘火山爆发强烈并形成大型徐东破火山口。徐东破火山口的形成说明岩浆侵位于地壳底部,形成扁平状的岩浆房。岩浆垂直上升喷发或沿断裂喷发,形成徐家围子断陷中心式-裂隙式火山喷发模式。

Volcanic hydrocarbon reservoir has already been one of the most important reservoir types in Mesozoic-Neozoic rift basin in eastern China. Volcanic rocks, mainly dacitic to rhyolitic rocks, of Yingcheng Formation in Xujiaweizi fault depression, which contain natural gas, have been the key for exploration and production, hence we must make sure volcanic edifice types and eruption model first. According to investigation, there are three types of volcanic edifices, including stratovolcano, lava done, and caldera, in Xujiaweizi fault. depression. Controlled by two phases of orthogonal and oblique extension in Xujiaweizi fault depression, there are three types of spatial patterns of volcanic edifices around the regional fault. In the footwall of fault, volcanic edifices develop; in the fault belt, there is the pattern of volcanic edifices overlapping one by one; in the hanging wall of fault, it is occupied by remarkable amount of volcanic rocks and Xudong caldera. The formation of Xudong caldera indicates that the magma chamber with low aspect ratio intruded to the bottom of crust, and then magma erupted out of the ground to form volcanic edifices. It is a center-fissure eruption model controlled by both the magma chamber and regional fault in Xujiaweizi fault depression.