“松科二井”邻域岩石圈精细结构特征及动力学环境——深地震反射剖面的揭示

Fine structure of the lithosphere beneath the Well SK-2 and its adjacent:Revealed by deep seismic reflection profile

为揭示"松科二井"邻域岩石圈精细结构特征,布设了一条过井近南北向的深地震反射剖面,采用多尺度药量结合的激发技术,长排列、重点段加密接收高次覆盖的采集方式,通过高保真、高保幅的处理流程获得高分辨率、高信噪比的叠前时间偏移剖面.结果显示:T4反射轴之下沉积岩层状反射与火成岩杂乱反射相间,有两处疑似上古生界地层,分别位于松科二井下方(双程走时,Two way travel time,TWT,3.5～4s)和任民—永安断隆下方(CDP,3500～4500,TWT,3～4s);中下地壳可观察到近平行的北倾反射,中和断陷下方存在上下关联的透镜状强反射,整体轮廓呈蘑菇云状,解释其为岩石圈伸展构造中发育的深部热流底辟体;北部莫霍面呈近水平连续强反射,南部徐家围子断陷区域莫霍面反射较弱,同时剖面上存在3种明显的岩石圈上地幔反射,包括倾斜地幔反射、近水平地幔反射和超深地幔反射,推断其分别为早期俯冲遗迹、早期增厚地壳底界面以及现今岩石圈底界面.本文利用过松科二井地震剖面的最新成果,揭示出古亚洲洋、蒙古—鄂霍茨克洋和古太平洋三大构造域先后作用下,保留在松嫩地块岩石圈内的结构特征,为探讨松辽盆地形成原因、构造背景及动力学因素提供新视野.

In order to reveal the fine structure of the lithosphere adjacent to Well SK-2,a deep seismic reflection profile crossing Well SK-2 was laid out in the Songliao Basin(SB),with the trend north to south.Data acquisition was featured in the shooting technique of multi-scale explosive source and data reception by large offset with smaller trace distance in key area.Besides,processing flow of high fidelity and amplitude-preservation was undertaken to get the pre-stack migrated seismic reflection profile with high resolution and high signal-to-noise ratio.As the result,the profile shows strong reflections from settled layers alternate with and weak reflections of igneous rock beneath T4 reflector,and two residuals of upper Paleozoic stratums are distinguished out,one is beneath Well SK-2(TWT,3.5~4 s),the other is beneath the Renmin-Yong′an Terrace(CDP,3500~4500,TWT,3.5~4 s).Some paralleled seismic patterns dipping north can be observed in the middle and lower crust,as well as some strong but short lenticular reflectors are observed beneath Zhonghe Fault Depression,and the overall contour of these lenticular reflectors is like a mushroom cloud,we interpret this phenomenon as the hot material from downward in the lithosphere extension environment.The Moho in the north part shows strong near-horizontal continuous reflection,while the Moho in the Xujiaweizi Fault Depression in the south shows weak reflection.Three types of upper mantle reflections are distinguished on the deep seismic profile,including inclined mantle reflections,near-horizontal mantle reflections and super-deep reflections in the mantle.It is inferred that they are the early subduction relics,bottom of early thickened crust and the present lithosphere-asthenosphere boundary(LAB).Based on the latest results of deep seismic profile detecting crossing Well SK-2,this paper study structure features preserved in the lithosphere of Songnen Massif with tectonic superposition of Palo-Asia Ocean regime,Mongol-Okhotsk regime and Palo-Pacific regime,thus providing a new perspective for the discussion of the formation cause,tectonic background and dynamic factors of Songliao Basin.