歧中北—沙西火成岩形成机制及油气地质意义

Formation mechanism of igneous rock and its geological significance in Qizhongbei-Shaxi Area

受渤海西部区域性构造活动的影响,歧口凹陷歧中北—沙西地区火成岩大面积分布,其分布主要受控于NNE和NW向一组共轭走滑断层。平面上火成岩整体呈环形分布,火山口—近火山口地区呈条带状分布,表明火山喷发呈现整体中心式喷发和火山口附近裂隙式喷发的特征。通过研究火成岩的厚度、平面分布及发育期次,结合区域构造特征分析认为,歧中北—沙西地区火成岩的发育特征与太平洋板块对中国大陆东部俯冲挤压作用相关,在挤压作用影响下,上地幔局部熔融产生玄武质岩浆沿深大断裂侵入地壳,喷溢出地表,形成受走滑断裂带控制的火山喷发;同时,受板块俯冲速度变化的影响,形成了该区2次火山喷发活动。由于火成岩不同岩相带物性变化较大,其中以火山口—近火山口区域物性较好,因此在火山口—近火山口区域易于形成火成岩油气藏;而火成岩远源区由于物性较差,限制了油气向上运移,则形成良好的盖层。

Igneous rocks show a large-scale distribution in Qizhungbei-Shaxi Area of Qikou Sag, affected by regional tectonic activity in the western area of Bohai Sea. Their distribution was controlled by a set of conjugate strike-slip fauhs included NNE and NW trends. The distribution of igneons rocks has the characteristics of the ring plane, while the crater-near crater areas are banded structure, which show that the voleanic eruption has the characteristics of overall eentral eruption and fissure eruption near the crater. We can conclude that the upgrowth characteristics of igneous rneks in Qizhongbei-Shaxi Area are related with the underthrusting and compactiou of Pacific plate on eastern Chinese mainland. Under the influence of compaction, partial melting of the upper mantle results in basahia magma to intrude the crust and to spray to the surface ahmg the deep faults, which form the volcanic eruption along strike-slip Fault zone. At the same time, twice volcanic eruptions formed in the area by the speed of changes of plate subduction. The igneous rocks of different faeies have different properties, in which the crater-near the crater area has better properties, so igneous reservoirs are formed easily in the crater-near the crater area. While the upward migration of hydrocarbon is controlled because igneous rock of far source area has poor properties, which forms a good cap rock.