中国大陆科学钻探主孔1200米构造柱及变形构造初步解析

在利用成象测井资料准确地恢复岩心空间位置的基础上，建立了位于江苏省东海县毛北村的中国大陆科学钻探主孔岩心1200m精细构造柱。划分了由榴辉岩与超镁铁质岩组成的第一岩性-构造单元及由副片麻岩夹榴辉岩与超镁铁质岩透镜体组成的第二岩性-构造单元，自上而下岩石的面理产状由向东陡倾变为向南东缓倾。第一岩性-构造单元的榴辉岩与超镁铁质岩是毛北榴辉岩杂岩体的组成部分，在榴辉岩中发现以南北向拉伸线理及由北往南的剪切指向为特征的超高压变质岩早期变形举止。位于第二岩性一构造单元下部(770-1130m深度)300多米厚的韧性剪切带是地表出露的毛北韧性剪切带在孔下的延伸，剪切应变及石英组构分析表明，在伴随的退变质角闪岩相一绿帘角闪岩相一绿片岩相的转换过程中，剪切应变由自SE往NW的“逆冲”转为NW向SE的正向滑移。结合钻孔围区地质，重塑了上部由毛北榴辉岩杂岩体与副片麻岩围岩组成的轴面向SE倾斜的同斜倒转褶皱系，以及下部为韧性剪切带的构造模型。钻孔验证了VSP地震反射剖面中850-1200m深度的强反射层与韧性剪切带相吻合。结合苏鲁超高压变质地体的折返构造的研究，提出该构造模型的成因与折返阶段超高压变质地体的斜向上的挤出及后折返阶段的穹隆形成有关。

The structure profile of 0 - 1200m in the main borehole, Chinese Continental Scientific Drilling and its preliminary deformation analysis

Based on the reconstruction of the spatial location of the drilling cores by using logging image data, we established a fine structural profile of the main hole (0 - 1200 m) of the Chinese Continental Scientific Drilling Project. Two lithological-tectonic units were recognized, the first one is composed of eclogite and ultramafic rocks, and the second one consists of paragneiss intercalated with eclogitic and ultramafic lenses. The foliations of the rocks from top to bottom change from steeply eastward dipping to gently southeastward dipping. Eclogite and ultramafic rocks in the first unit belong to the component of the Maobei eclogite complex. SN trending stretching lineations and shear fabric indicative of shearing deformation from north to south found in the eclogites represent the early stage deformation of the ultrahigh-pressure ( UHP) metamorphic rocks. A 300 m thick ductile shear zone, possibly a downward extension of the Maobei ductile shear zone in the drilling hole, is found in the lower part of the profile between 738 and 1130 m within the second unit. Accompanying with from amphibolite to greenschist facies retrograde metamorphism, the shear deformation changed from early thrusting from SE to NW to later normal motion from NW to SE, as suggested by the shear strain and preferential orientation of quartz. In the context of regional geology around the borehole, we propose a new tectonic model in which (1) the upper part is inverted syncline fold systems composed of the Maobei eclogite complex and paragneiss country rocks with SE plunge axial planes, and ( 2 ) the lower part is a ductile shear zone. The elasticity wave and thermal conductivity profiles of the core provide important petrophysical constraints to the interpretation of the seismic reflection and geothermal data. The VSP seismic profile reveals the deeply structure of the tectonic slices. The main hole verified that the strong reflective layer between 850 to 1130 m deep is equivalent to the ductile shear zone. Combined with results from field investigation of the exhumed Sulu UHP metamorphic terrain, these new data suggest an oblique extrusion of the UHP metamorphic terrain occurred concurrently with, but the dome formation postdated the exhumation.