辽南地壳的收缩作用及伸展作用

CRUSTAL CONTRACTION AND EXTENSION IN SOUTHERN LIAONING

辽南盖层中强烈的变形构造为稳定地台中少见。变形构造动力学的研究表明,具典型薄壳结构的辽南地壳曾经历了中生代的收缩作用及伸展作用。最早期的较强大的收缩应变,表现为太古宙变质基底与晚元古代至古生代地台盖层之间发生的自东往西的深层滑脱作用、大范围剪切流变及形成的逆冲体系;后期的伸展应变则表现为垂直主压应力作用下大量韧-脆性低角度正断层体系的发育。收缩作用至伸展作用转化的因素,可能与剪切局部熔融及等温线上升所引起基底上隆与地壳伸展、减薄有关。

The crust in southern Liaoning has a typical thin-skinned structure. Between the Archean and Lower Proterozoic metamorphic basement and the Upper Proterozoic to Paleozoic platformal covers there exists a detachment surface characterized by an amphibolitic mylonite zone and middle-pressure metamorphic zone.Imbricate thrusts, klippen, listric structures and progressive deformation and metamorphism from above downward in the cover sheet of southern Liaoning were formed by large-scale westward gliding since the Indosinian. After the detachment-thrust event, the crust underwent superposcd contraction due to nearly E-W and N-S compression. Shear heat caused by the deep-level detachment led to partial melting, increase of ductility in rocks, acceleration of deformation and thickening of the detachment zone as well as uplift of basement and extentional mechanism (vertical σ_1), thus forming a series of ductile and brittle normal faults (lag faults). The tectonic and uplift histories since the Mesozoic are histories of contraction and extention of the crust in southern Liaoning. The former made the crust imbricated and thickened, while the latter caused crustal extension and thinning.