东南大陆岩石圈板块地体构造

LITHOSPHERE PLATE-TERRANE TECTONICS OF THE SOUTHEAST CHINA CONTINENT

东南大陆的地质构造模型,具有欧亚大陆边缘向洋增生的独特形式。除外来地体之外,或以扩张、地幔上涌,洋壳向大陆地壳转化,并不断向洋增生;或是大陆分裂,地幔柱——热点物质不断注入变薄和破裂了的地壳,形成区域性新的生长构造层,构造岩浆地质体表现为有独特属性的“A型”花岗岩和流纹岩链。这些高DI值的富硅富碱富钠质岩石,出现在欧亚大陆边缘的重力梯度带上。裂解带的地壳结构模式是上地壳存在着重力不稳定的硅铝低速带;中地壳有洋——陆过渡型地壳的“类裂谷型”结构,P波速度为6.3～6.4km/s的中间壳层;在下地壳下部有速度为7.0～7.4km/s的壳——幔混合型高速层;随着“异常”的上地幔的形成,有大范围的热活动和壳——幔边界穹窿,穹窿的地盖比正常区为为薄。由于化学库和化学边界层的横向不连续,可划分出古老基底和后期地质发展史完全迥异的两个亚板块;和以壳层(或幔层)断裂为边界特点的八个地体;一个以分裂为主,并具热点径迹的最新生长构造层的扩张——裂解构造岩浆地体。

The results from synthetic study on geology, geochemistry, geophysics in southeast China indicate that the geotectonic pattern of southeast China continent is charaterized by offshore accretion of Eurasia continental margin. Besides exotic terrane, the more distinctive pattern in the area is growth terrane and breakuptectonic magmatic terrane. The for- mer, which was caused by crustal spreading and mantle upwarping, developed in form of transformation of oceanic crust to continental crust and offshore accretion, while the latter was caused by unstability of crust leading to continental breakup, intrusion of mantle prism-hotspot materials into thinned-disrupted crust and formation of new regional growth structure layer. The breakup-tectonic magmatic terrane consists of such distinctive magmatic complex as A-type granite, rhyolitic chain etc. These silica-, alkali-, and sodium-rich rocks with high DI value occurred in the gravity gradient belt of Eurasia continental margin. The crustal structure models of breakup belts are as follows: the upper crust contains a silica-alumina low velocity zone of unstable gravity; the intermediate crust consists of oceanic-continental transitional crust with 'similar rift type' crustal structure, and P-wave velocity of 6.3-6.4 km / s; the bottom of lawer crust contains a zone of crust-mantle mixture type with high velocity of 7.0-7.4 km / s. Along with the forming of 'anomalously' upper mantle, thermal activity and crust-mantle border upwarp took place on a large scale. The upwarp is charaterized by thinner crust than that of normalously region. Because of the difference of crustal structures in southeast China, chemical reservoir and chemical boundary layer aren't continuous in transverse, the geologic history displays intensive uncoordinated in different terranes. Consulting compilatory principles of Tectonostratigraphic Terrane Map of Circum-Pacific Region(compiled by D · G · Howell et.al., 1983), we have compiled Lithosphere Plate-Terrane 'iectonic Map of the Southeast China Continent at a scale of 1:1 million. Which stresses on space accretion model, onshore accretion of oceanic crust and breakup-tectonic magmatic terrane. Therefore, we have divided southeast China continent into two sub-plates with different paleobasement and late period geologic history, eight terranes being of geologic entities bounded by crust (or mantle) fault and charaterized by a geologic history distinct from that of neighboring terranes and one spread-breakup tectonic magmatic terrane of recently growth structure layer mainly caused by breakup and composed of hotspot tracks, which is rather importent in Eurasia continental margin.