冀中坳陷北部地区古近纪岩浆活动特征及控制因素

冀中坳陷位于渤海湾盆地西北部，广泛发育古近纪同裂陷阶段的岩浆活动。本文利用钻井和三维地震数据，通过剖面解释以及平面均方根振幅属性提取等手段对冀中坳陷北部的廊固凹陷和文安斜坡地区进行岩浆活动研究。结果显示，廊固凹陷主要发育沙河街四段火成岩，岩石类型为玄武岩、辉绿岩和凝灰岩，地层内发育较多的岩墙及岩脉等构造，岩浆一般通过小型岩浆通道运移至地表，并呈团块状分布，具有中心式喷发的特征；文安斜坡主要发育沙河街三段火成岩，主要岩石类型为玄武岩和凝灰岩，以及少量的辉绿岩，地层内基本不发育岩墙及岩脉等构造，岩浆通过一些大型的断层运移到地表，在地表呈平行于断裂的线状分布，具有裂隙式喷发的特征。本文认为断裂发育特征的差异是控制岩浆活动差异的重要因素。廊固凹陷缺少贯通浅层和深层的大型高角度断层，因此岩浆只能分散式的通过众多岩墙及岩脉进行向上运移。文安斜坡发育了贯通深层和浅层的高角度正断层，因此岩浆可以集中地通过这些断层进行向上运移。因此是否存在贯通深层、浅层的大型断层是控制岩浆活动不同产出方式的重要因素。

Characteristics and controlling factors of the Paleogene magmatic activities in the northern Jizhong Depression

• The Jizhong Depression is located in the northwest of Bohai Bay Basin, with the Paleogene syn-rifting magmatic and volcanic activities widely developed. With drilling and three-dimensional seismic data, we investigate the magmatic activities in the Langgu Sag and the Wen´an Slope in the north of Jizhong Depression by means of profile interpretation and RMS Amplitude attribute extraction. The results show that igneous rocks of Es⁴ are mainly developed in the Langgu Sag, with basalt, diabase and tuff found by drilling, as well as large number of dykes recognized on profile. The Wenan slope yields igneous rocks of mainly Es³, with basalt and tuff, as well as a small amount of diabase revealed by drilling, but barely any dykes recognized on profile. We conclude that the fault geometry in rift basin is an important factor controlling the type of magmatic and volcanic activities. In the Langgu Sag, there are no high?angle large?scale faults developed that penetrates strata layers vertically to become magma channels. As a result, magma was migrated upward dispersedly through a large number of dykes to the surface and accumulated in circular shapes, resembling to the features of central eruption. High-angle normal faults penetrating strata layers are developed in the Wen´an Slope, therefore, through these faults the vast majority of magma is migrated upward to the surface along major faults and accumulated linearly, resembling to the features of fracture eruption. Our analysis suggests the existence of high?angle faults that cut through strata layers is an important factor controlling the occurrence of different types of magmatic activities in rift basins.