冀东马兰峪背斜南翼与西部倾伏端盖层变形特征及其构造意义

Tectonic deformations of the cover in the southern limb and western plunging zone of the Malanyu anticlinorium, eastern Hebei, China, and its tectonic implications

燕山中部冀东遵化、迁西、青龙一带以太古宇深变质结晶岩系为核部的东西向构造形迹长期以来被认为是一个复式背斜构造,近年来又有学者提出它是一个中生代变质核杂岩。这2种不同认识涉及到华北克拉通北部中生代区域大地构造演化和稳定克拉通内部大型基底结晶岩系的剥露机制问题。对马兰峪背斜南翼和西部倾伏端盖层岩系开展的详细构造研究表明,变形总体表现为连续的褶皱变形及伴生的逆冲构造;构造样式表现为基底卷入式的厚皮构造与盖层内部软弱岩系控制的薄皮构造共存的特征;变形机制表现为顺层挤压导致的纵弯弯曲和相关的断裂构造;近南北向的缩短率介于16%～27%之间。盖层岩系中未发现变质核杂岩构造模型所预期的系列高角度正断层。基底与盖层不整合面接触带尽管在后期构造变形过程中曾经发生过局部的差异性滑动,但并不是造成大规模构造剥蚀和地壳柱切失的剥离断层。因此,冀东马兰峪背斜不是中生代的变质核杂岩,而是水平挤压背景下基底结晶岩系与盖层共同卷入纵弯褶皱变形的厚皮式褶皱构造。

The large-scale E-W-trending tectonic deformation terrane cored by the Archean high-grade metamorphic crystalline basement rocks in Zunhua, Qianxi and Qinglong county, eastern Hebei Province, central part of the intraplate Yanshan orogenic belt has long been regarded as an anticlinorium. In recent years, however, some researchers have suggested that it is a late Mesozoic metamorphic core complex. The two different views concern the Mesozoic tectonic evolution in the northern North China craton and the mechanism for the exhumation of the basement crystalline rocks in the interior of the stable craton. Detailed mapping was conducted in the southern limb and the western plunging zone of the Malanyu anticlinorium. It is revealed that： deformation is generally manirested by continuous folding and associated thrust; structural style is characterized by coexistence of basement-involved thick-skinned deformation structures and thin-skinned controlled by weak members within covers; the deformation mechanism by buckling and faulting resulted from bedding-parallel compression; nearly N-S shortening is estimated to be ranging from 16% to 27%. No highangle or listric normal faults as expected by the metamorphic core complex model have been identified so far in the covers. Although the unconfomtity between the cover and basement underwent local differential slide during late-stage stmctural deformation, it is not a detachment fault causing large-scale tectonic erosion and crustal column excisement. Therefore the Malnayu anticlinorium in eastern Hebei is not a late Mesozoic metamorphic core complex but a basement-involved thick-skinned fold romped under lateral compression.