四川汶川地震断裂带科学钻探2号孔(WFSD-2)岩性特征和断裂带的结构
摘要
以WFSD-2钻孔岩心为研究对象,通过详细的岩心编录和岩石学、构造地质学等研究,识别出该钻孔岩心具有6段岩性,从上向下依次为彭灌杂岩(0~599.31m)、三叠系须家河组二段(599.31~1211.49m)、彭灌杂岩(1211.49~1679.51m)、三叠系须家河组三段(1679.51~1715.48m)、彭灌杂岩(1715.48~2081.47m)、三叠系须家河组四段(2081.47~2283.56m)。彭灌杂岩主要以花岗岩和火山岩为主,三叠系须家河组沉积岩以砂岩、粉砂岩、泥岩、页岩、煤层(线)和砾岩为主。3套彭灌杂岩与三叠系须家河组沉积岩重复出现,时代较老的岩性段逆冲覆盖在新的地层之上,表明龙门山构造带由一系列逆冲岩片叠置而成。岩心中断裂岩较为发育,主要为断层角砾岩、碎裂岩和断层泥,反映出脆性变形作用的特点。通过对断裂岩的统计分析,厘定了20余条产状不同、规模不等的次级断裂带,断裂带宽度和断裂密度峰值显示FZ600、FZ720、FZ782、FZ817、FZ922、FZ951、FZ1449、FZ1681、FZ2082为主要断裂带,其中FZ1681系规模最大的一条断裂。依据断裂岩的组合特征可以将岩心中断裂带的结构以断层泥为核部划分为两大类:对称型断裂带和不对称型断裂带。根据地表破裂带、WFSD-1钻孔岩心中主滑移带位置的几何关系、岩性分层等因素,可推断汶川地震主滑移带应位于FZ1134、FZ1449或FZ1681之中,同时也暗示该地区经常发生类似汶川地震的大地震活动。研究表明,龙门山地区经历了强烈的构造缩短和快速隆升作用,暗示龙门山地区构造活动非常强烈。
With the WFSD-2 drill hole as the object,the authors studied core logging,petrology and structural geology.The results show that the cores can be divided into six segments,which are in downward succession the Pengguan complex(0~599.31m),the second Member of the Xujiahe Formation(599.31~1211.49m),the Pengguan complex(1211.49~1679.51m),the third Member of the Xujiahe Formation(1679.51~1715.48m),the Pengguan complex(1715.48~2081.47m) and the fourth Member of the Xujiahe Formation(2081.47~2283.56m).The Pengguan complex mainly consists of granite and volcanic rocks,and the Xujiahe Formation comprises Triassic sedimentary rocks of sandstone,slitstone,mudstone,shale,coal beds(streaks) and conglomerate.Three sections of the Pengguan complex and three sections of the Xujiahe Formation occur in alternate repetition in the WFSD-2,indicating that the Longmenshan tectonic belt is composed of a series of thrust lithologic sheets.There are a lot of fault-related rocks in the WFSD-2 cores,such as fault breccia,cataclasites and fault gouge,reflecting the brittle deformation.Based on a statistical analysis of the fault-related rocks,the authors detected twenty fault zones in the WFSD-2,indicating that many earthquakes like 2008 Wenchuan Earthquake occurred in Longmenshan area.Of the nine primary fault zones of FZ600,FZ720,FZ782,FZ817,FZ922,FZ951,FZ1449,FZ1681,FZ2082 and FZ1681,the FZ1681 is the biggest primary fault zone in the whole WFSD-2.According to the association characteristics of fault-related rocks,the fault zones can be divided into symmetric and asymmetric fault zones,with fault gouge as the center.According to the dip angles of the trench and WSFD-1 primary slip zone(PSZ),the PSZ in the WFSD-2 should occur within one of the primary fault zones of FZ1134,FZ1681 and FZ1681,which all have fault gouge and reasonable geometrical interpretation among rupture zones in WFSD-1 and WFSD-2.An integrated analysis of four thrust rock segments,twenty fault zones and high breakage density shows that the Longmenshan area must have experienced powerful tectonic activities.
With the WFSD-2 drill hole as the object,the authors studied core logging,petrology and structural geology.The results show that the cores can be divided into six segments,which are in downward succession the Pengguan complex(0~599.31m),the second Member of the Xujiahe Formation(599.31~1211.49m),the Pengguan complex(1211.49~1679.51m),the third Member of the Xujiahe Formation(1679.51~1715.48m),the Pengguan complex(1715.48~2081.47m) and the fourth Member of the Xujiahe Formation(2081.47~2283.56m).The Pengguan complex mainly consists of granite and volcanic rocks,and the Xujiahe Formation comprises Triassic sedimentary rocks of sandstone,slitstone,mudstone,shale,coal beds(streaks) and conglomerate.Three sections of the Pengguan complex and three sections of the Xujiahe Formation occur in alternate repetition in the WFSD-2,indicating that the Longmenshan tectonic belt is composed of a series of thrust lithologic sheets.There are a lot of fault-related rocks in the WFSD-2 cores,such as fault breccia,cataclasites and fault gouge,reflecting the brittle deformation.Based on a statistical analysis of the fault-related rocks,the authors detected twenty fault zones in the WFSD-2,indicating that many earthquakes like 2008 Wenchuan Earthquake occurred in Longmenshan area.Of the nine primary fault zones of FZ600,FZ720,FZ782,FZ817,FZ922,FZ951,FZ1449,FZ1681,FZ2082 and FZ1681,the FZ1681 is the biggest primary fault zone in the whole WFSD-2.According to the association characteristics of fault-related rocks,the fault zones can be divided into symmetric and asymmetric fault zones,with fault gouge as the center.According to the dip angles of the trench and WSFD-1 primary slip zone(PSZ),the PSZ in the WFSD-2 should occur within one of the primary fault zones of FZ1134,FZ1681 and FZ1681,which all have fault gouge and reasonable geometrical interpretation among rupture zones in WFSD-1 and WFSD-2.An integrated analysis of four thrust rock segments,twenty fault zones and high breakage density shows that the Longmenshan area must have experienced powerful tectonic activities.
引文
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[30]刘静,张智慧,文力,等.汶川8级大地震同震破裂的特殊性及构造意义[J].地质学报,2008,82(12):1707-1722.
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