中国大陆科学钻探孔区三维地震资料的初步解释
Interpretation of 3D seismic renection data in the Chinese Continental Scientific Drilling site
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摘要: 利用中国大陆科学钻探岩心、测井与VSP资料来标定地震反射体，大大提高了大陆科学钻探孔区地质构造解释的可信度。超高压变质带地壳波速特征主要表现在上地壳顶部的高速层，其厚度一般小于10km；其下方正常的中下地壳波速结构反映了中新生代地壳的拉张与伸展。孔区三维地震拱形反射由榴辉岩及切穿它们的晚期破碎带共同形成的。在CCSD主孔东南方深部重力高部位有多个这样的拱形反射，预示在地表陡倾榴辉岩的延伸方向还有多个一定规模的隐伏榴辉岩体。孔区广泛发育韧性剪切带，韧性剪切带产生强反射的主要机制是韧性剪切复合岩套，由糜棱岩和经剪切错动产生的表壳岩片互层组成。三维地震调查提供了三维的反射地震波场，使揭示孔区三维的地质构造成为可能。450ms以上的时间切片与地袁地质构造和地磁异常相关，而1000～1200ms的时间切片与深部重力异常相关，主要反映由隐伏榴辉岩体产生的反射波场．根据上述研究结果，编制了沿三维地震主剖面的推断地质构造图。Abstract: Seismic reflection investigations have been carried out for the Chinese Continental Scientific Drilling Project (CCSDP) , showing that many reflectors occurred in the upper crust of the drilling area. Calibration of the reflectors by using cores, well-logging and VSP data can significantly enhance reliability of their interpretation. In the CCSD site, thickness of the ultrahigh-pressure (UHP) rock-slice is usually less than 10 km, beneath the UHP slice velocities of the middle and lower crust are normal among usual extensional areas. Ached the seismic reflectors in the 3D seismic main line are caused by the high-velocity eclogite bodies plus low-velocity fractures; strong dipping reflectors are caused the ductile shear rock-suites that consist of . mylonite and interbed of thin eclogites and gneiss. The 3D survey provides 3D reflection wave-field that can be shown by time-slice sets. . Time slices above 450ms are intensively correlated with surface geology and magnetic anomalies, whilst slices of 1000 - 1200ms correlate with the gravity anomalies, indicating buried eclogite bodies. Based on the interpretation a structural section across the CCSD main hole is presented.
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