摘要
南海西南海盆的西北边缘和东南边缘在地形地貌上不对称，在地质构造特征上东南边缘为上板块边缘，西北边缘为下板块边缘，它们为一对共轭边缘。新生代张性构造运动和海底扩张活动中，上地壳呈脆性，发生过脆性变形，产生了一系列倾斜正断裂及一系列断块，断块沿断层面转动，在地表出现一系列半地堑，在拉张应力的进一步作用下，上地壳沿断层面被拉开；下地壳呈塑性，发生塑性变形，最后以瓶颈方式被拉断。由此可见，在张性应力场作用下，岩石圈的变形方式是分层而异的：上地壳以简单剪切方式变形，下地壳以纯剪切方式变形。因此。
Here we discussed the geotectonic characters of the northwest
and southeast margins of Southwest Subbasin of the South China Sea.It’s found that
the conjugated margins are topographically and geomorphically asymmetric.The
southeastern margin is the lower plate,the upper crustal slab there has suffered
differential isostatic subsidence and formed a semilunar swale on the basement surface.
Under the basement and the upper crust there are chaotic reflections and weak
reflections.On the sole of the upper crust there is a continuous reflection,which
expresses that it is a smooth and strong wave impedance surface.There appears some
non continuous and sub horizontal reflections in lower crust,indicating some non
continuous interfaces.The Moho reflection is a low frequency reflection.The northwestern
margin of Southwest Subbasin is a upper plate margin.There are not continuous
reflections in the upper crust,but appears a continuous and strong reflection in the
subsurface of the upper crust,indicating a smooth surface.In the lower crust there are
chaotic reflections,showing that it has not been deformed.We believe that it was formed
by the magma from the partial melting upper mantle in Cenozoic.From above discusses
we can see that under the extensional stress the upper crust has brittle nature and
experienced brittle deformation,a series of faults were formed,and the faulted blocks
rotated along the faulting surfaces.Following this the half grabens formed in the surface.
Therefore,we believe that the upper crust was deformed by simple shear model.The
lower crust in ductile character has ductile deformation under the extensional stress.So
it was deformed by pure shear model.For above reason,we believe that the layered
shear model is correct for the lithospheric deformation under the extensional stress.
出处
《海洋地质与第四纪地质》
CAS
CSCD
北大核心
1999年第2期37-48,共12页
Marine Geology & Quaternary Geology
关键词
脆性变形
南海
岩石圈
张裂模式
海盆
南海
upper crust lower crust brittle deformation ductile deformation the South
China Sea
