南海西沙海槽岩石圈的密度结构与热-流变结构  

DENSITY, THEMAL AND RHEOLOGICAL STRUCTURESOF XISHA TROUGH, SOUTH CHINA SEA

作　　者：施小斌[1] 周蒂[1] 张毅祥[1] 丘学林[1] 

机构地区：[1]中国科学院南海海洋研究所,广东广州510301

出　　处：《热带海洋学报》2002年第2期23-31,共9页Journal of Tropical Oceanography

基　　金：中国科学院知识创新工程项目(KZCX2-209-04;KZCXZ-SW-117);重大项目(KZ952-BI-406);国家重点基础研究发展规划项目(G2000046701);国家自然科学基金资助项目(49804005);中科院南海海洋研究所所长基金资助项目(SJ000401)

摘　　要：在中德合作获得的速度－深度模型基础上，通过重力异常拟合以及地温场和流变性质的估算，获得了西沙海槽的密度结构、热结构和流变结构。计算表明，海槽中部上地壳的密度比两侧低；“热”岩石圈底界在海槽中部埋深为54 km，向南北两侧逐渐加深，在神弧隆起区为76km，在西沙－中沙地块达到 70km；地壳热流贡献量比地幔热流小，海底热流主要来自深部；在海槽中部地幔热流最高，并且具有较高的流变强度；研究区的流变学结构具有纵向分层性及横向变化的特点，向两侧韧性层变厚，脆性层逐渐减薄。地幔顶部的脆性层底界埋深大约为26km左右，相当于 650℃等温线。分析表明，海槽中部强度增加主要归因于后期的热松弛，而块体空间移动困难以及西南次海盆的扩张可能是西沙海槽没有进一步破裂的重要原因。Based on the ve1ocity--depth model along profile OBH--4 across the XishaTrough, density, thermal and rheological structures of the profile are estimated. Theresults show that the density of the center of the upper crust is a little lower than twoflanks. The lower boundary of the 'thermal' lithosphere is buried at about 54km in thecenter, and deepens toward two sides, and about 76km at the Shenhu Uplift and about70km at the Xisha--Zhongsha Massif. Crustal heat contribution is smaller than Mohoheat flow, and the latter contributes to most of the surface heat flow. In the center ofthe trough, Moho heat f1ow is larger than in the two sides, and its strength is the lar-gest; while towards two sides, ductile layers become thicker and brittle layers becomethinner. The lower boundary of the brittle layer in the uppermost mantle is buried at a-bout 26km, equal to isotherm 650 ℃. The results show that the strengthening of the cen-ter is mainly due to the cooling since 30Ma, and special moving of blocks and the sea-floor spreading of the Southwest Subbasin may be responsible for that the breakup didnot turn up finally along the Xisha Trough.

关 键 词：南海 西沙海槽 热结构 流变结构 古裂谷 岩石圈 密度结构 

分 类 号：P736.1[天文地球—海洋地质]