本文選題：南沙海槽 + 陸殼結(jié)構(gòu)��； 參考：《地學(xué)前緣》2017年03期

【摘要】：南沙海槽前陸盆地是我國(guó)南海南緣陸架區(qū)重要的含油氣盆地,海槽之下陸殼減薄的原因、前陸區(qū)逆沖推覆構(gòu)造的變形機(jī)制是南海地球動(dòng)力學(xué)研究的重要科學(xué)問(wèn)題。利用地震、重磁、地?zé)嵊^測(cè)資料,依據(jù)地震沉積地層分析、重磁反演分析、地幔流應(yīng)力場(chǎng)分析、熱-流變學(xué)分析方法,文中計(jì)算了南沙海區(qū)地殼結(jié)構(gòu)特征、南沙海槽逆沖推覆熱-流變學(xué)結(jié)構(gòu)。結(jié)果表明:南沙海區(qū)Moho面深度在18~26km,其中海槽區(qū)Moho面最淺,由海槽中心向東南至陸坡,Moho面由20km快速下降到26km深度,說(shuō)明南沙海區(qū)陸殼結(jié)構(gòu)曾發(fā)生過(guò)強(qiáng)烈的構(gòu)造變動(dòng)。南沙海區(qū)地殼累積流變強(qiáng)度FC與巖石圈累積流變強(qiáng)度FL之比小于80%,顯示為一個(gè)整體陸殼地塊,島礁區(qū)大部分地段地殼熱流QC與海底熱流Q0之比大于60%,為"熱殼冷幔"型熱結(jié)構(gòu),而海槽區(qū)情況正相反,QC/Q0小于40%,為"冷殼熱幔"型熱結(jié)構(gòu)。南沙海槽Moho面溫度在300~700℃,地殼整體溫度較低,地溫梯度在垂向上高、低相間成層分布,地殼淺層地溫梯度在15~30℃/km,深層地溫梯度大于45℃/km。南沙海槽南北兩側(cè)應(yīng)力分布特征不同,北側(cè)擠壓,南側(cè)伸展。北側(cè)擠壓區(qū),地層擠壓收縮量由深向淺減小,南側(cè)伸展區(qū),地層伸展量由深向淺增大,類似手風(fēng)琴風(fēng)箱結(jié)構(gòu)。北側(cè)黏滯系數(shù)高、流變強(qiáng)度大,南側(cè)黏滯系數(shù)低、流變強(qiáng)度小。南側(cè)的黏滯系數(shù)、流變強(qiáng)度大約比北側(cè)低2~3個(gè)數(shù)量級(jí),因此南沙海槽南側(cè)比北側(cè)更容易發(fā)生構(gòu)造變形。由計(jì)算結(jié)果推測(cè),南沙Moho面起伏或陸殼減薄與"地殼重力均衡作用"和"地幔熱隆升作用"有關(guān),海槽東南緣逆沖推覆體構(gòu)造變形機(jī)制主要是"地殼縮短"作用,其次是"重力滑脫"作用。文中沒(méi)有涉及南沙陸塊不同地質(zhì)時(shí)期Moho面、"地殼均衡"、"地幔熱隆升"之間的演化關(guān)系,也沒(méi)有涉及南沙海槽基底變形中"彈性撓曲"和"逆沖推覆"之間的關(guān)系。
[Abstract]:Nansha trough Foreland basin is an important oil and gas bearing basin in the continental shelf area of the South China Sea. The reason of continental crust thinning under the trough and the deformation mechanism of the thrust nappe structure in the Foreland region are important scientific problems in the study of the South China Sea geodynamics. Based on seismic, gravity, magnetic and geothermal observation data, according to seismic sedimentary stratigraphic analysis, gravity and magnetic inversion analysis, mantle flow stress field analysis, thermo rheological analysis method, the crustal structure characteristics in Nansha sea area are calculated in this paper. Thermal rheological structure of thrust nappe in Nansha trough. The results show that the depth of Moho surface in Nansha sea area is at 18 ~ 26km, among which the Moho surface is the shallowest in the trough area, from the center of trough to southeast to the continental slope Moho surface decreases rapidly from 20km to 26km depth, indicating that the continental crust structure in Nansha sea area has experienced strong tectonic changes. The ratio of crustal cumulative rheological strength FC to lithospheric accumulative rheological strength FL is less than 80, which shows that it is a whole continental crust block, and the ratio of crustal heat flow QC to submarine heat flow Q _ 0 is greater than 60 in most parts of island and reef area, which is a "hot crust cold mantle" type thermal structure. On the contrary, QC / Q _ 0 is less than 40, which is a "cold crust and hot mantle" type heat structure. The temperature of Moho surface in Nansha trough is 300 ~ 700 鈩，

本文編號(hào)：2071708