本文關(guān)鍵詞：南海西南次海盆擴張期后巖漿活動及其殘留擴張中心的縱橫波速度結(jié)構(gòu)　出處：《浙江大學(xué)》2016年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 海底地震儀 速度結(jié)構(gòu) 擴張期后巖漿活動 殘留擴張中心 西南次海盆 南海

【摘要】：西南次海盆是漸進式擴張的海盆,在其擴張停止后仍然存在著強烈的巖漿活動,使得西南次海盆包含了邊緣海構(gòu)造演化的各個階段,成為了邊緣海演化研究的熱點區(qū)域。目前擴張期后的巖漿活動是大家關(guān)注的熱點問題,但其內(nèi)部結(jié)構(gòu)尚未揭示,極大的影響了我們對擴張期后巖漿活動的深入研究。而西南次海盆海底擴張最后階段研究較少的現(xiàn)狀,使海底擴張到擴張停止之間缺少銜接的依據(jù)。因此本文從速度結(jié)構(gòu)的角度出發(fā),以西南次海盆軸部海山和殘留擴張中心的結(jié)構(gòu)為切入點,探討海盆擴張期后巖漿活動和海底擴張最后階段的巖漿和構(gòu)造活動。本文基于2010年南海西南次海盆所采集的OBS數(shù)據(jù),首先利用射線追蹤正演方法得到西南次海盆東北段殘留擴張中心和軸部海山的縱橫波速度結(jié)構(gòu)。為了能夠更好的控制模型結(jié)果,我們同時利用地震層析成像的反演方法開展了殘留擴張中心縱波速度結(jié)構(gòu)的研究,獲得了以下成果：(1)基于速度等值線形態(tài)與巖漿加載機制的關(guān)系,提出了軸部海山是巖漿噴發(fā)占主導(dǎo)的新認(rèn)識。利用海山速度、結(jié)構(gòu)和多波束地形地貌計算擴張停止后龍南海山巖漿的加載量獲得了巖漿噴發(fā)/侵入比1.92。(2)基于洋殼厚度與巖漿供應(yīng)的關(guān)系,通過分析西南次海盆洋殼厚度變化,揭示了西南次海盆巖漿供應(yīng)量時空變化的特點。在磁異常條帶C6n和C5En期間整個西南次海盆內(nèi)部的供給量相似,都表現(xiàn)出較多的巖漿活動。從磁異常條帶C5En到C5Cr期間,海盆局部區(qū)域內(nèi)的巖漿供給量減少,表現(xiàn)為局部區(qū)域洋殼厚度的減薄。擴張中心處的洋殼要比兩側(cè)的薄,表明海底擴張最后階段的巖漿供量相對較少。擴張停止后西南次海盆東北部的巖漿活動明顯強于西南部,表明了巖漿供給量的強烈不均一。(3)通過地震學(xué)特征對比和構(gòu)造環(huán)境分析,在西南次海盆殘留擴張中心的NW側(cè)發(fā)現(xiàn)拆離斷層的存在,這條拆離斷層的存在對海盆擴張最后階段的演化具有重要的意義。西南次海盆殘留擴張中心兩側(cè)具有不對稱的縱波速度結(jié)構(gòu),局部伴隨著莫霍面的強烈抬升和洋殼的減薄。而且西南次海盆是一個慢速擴張的海盆,其軸部洋脊段的半擴張速率小于40 mm/yr,此處構(gòu)造環(huán)境適合斷層發(fā)育且地震學(xué)特征也與斷層一致。(4)依據(jù)擴張期和擴張期后巖漿活動情況,將殘留擴張中心重新劃分為三類：(1)擴張最后階段及擴張停止后巖漿量相對增加,致使軸部洋殼厚于離軸洋殼；(2)擴張最后階段巖漿量相對減少,而擴張停止后巖漿量相對增加,致使軸部洋殼厚度先小于離軸洋殼,增生后又厚于離軸洋殼；(3)擴張最后階段及擴張停止后巖漿少,致使軸部洋殼厚度始終薄于離軸洋殼。
[Abstract]:The southwest subbasin is a gradual spreading basin, and there are still strong magmatic activities after its expansion stops, which makes the southwest subbasin include each stage of the tectonic evolution of the marginal sea. It has become a hot spot in the study of marginal sea evolution. At present, magmatic activity after expansion period is a hot issue of concern, but its internal structure has not been revealed. This has greatly affected our in-depth study of post-expansionist magmatic activity. However, there is little research on the last stage of seafloor expansion in the southwest subbasin. There is no basis for the connection between the expansion of the sea floor and the stop of the expansion. Therefore, from the point of view of the velocity structure, the paper takes the structure of the seamounts in the axis of the southwest subbasin and the residual spreading center as the starting point. In this paper, the magmatic and tectonic activities in the late stage of sea basin expansion are discussed. This paper is based on the OBS data collected from the southwest subbasin of the South China Sea in 2010. First, the longitudinal and shear wave velocity structures of the residual spreading center and axial seamounts in the northeast part of the southwest subbasin are obtained by using the ray tracing forward method in order to better control the model results. At the same time, we use the inversion method of seismic tomography to study the longitudinal wave velocity structure of residual spreading center. The following results are obtained: 1) based on the relationship between velocity isoline shape and magmatic loading mechanism. It is proposed that the axial seamounts are dominated by magmatic eruptions. Structure and multi-beam topographic geomorphology calculation of magma loading in Longnan seamounts after the stop of expansion the magmatic eruption / intrusion ratio of 1.92. 2) based on the relationship between the thickness of oceanic crust and magmatic supply. By analyzing the thickness variation of the oceanic crust in the southwest subbasin, the characteristics of the temporal and spatial variation of magma supply in the southwest subbasin are revealed. The supply quantity in the whole southwest subbasin is similar during the period of the magnetic anomaly strip C6n and C5En. During the period from C _ 5E _ n to C _ 5Cr, the magma supply in the local area of the basin decreased. The oceanic crust at the center of expansion is thinner than that on both sides. The magmatic activity in the northeast of the southwest subbasin is obviously stronger than that in the southwest after the end of the expansion. It shows that the strong heterogeneity of magma supply. 3) through the comparison of seismological characteristics and tectonic environment analysis, the detachment fault is found in the NW side of the residual extension center of the southwest subbasin. The existence of this detachment fault is of great significance to the evolution of the basin in the last stage of its expansion. There is an asymmetric longitudinal wave velocity structure on both sides of the residual spreading center of the southwest subbasin. The strong uplift of the Moho surface and the thinning of the oceanic crust are accompanied locally. The southwest subbasin is a slow-spreading basin with a semi-spreading rate of less than 40 mm/yr at the axis of the ridge. The tectonic environment here is suitable for fault development and the seismological characteristics are consistent with the fault. 4) according to the magmatic activity during and after the spreading period. The residual spreading center is divided into three classes: 1) the magma volume increases relatively at the last stage of the expansion and after the expansion stops, resulting in the thickness of the axial oceanic crust than that of the off-axis oceanic crust; (2) the magmatic volume decreases relatively in the last stage of the expansion, but the magma volume increases relatively after the expansion stops, which results in the thickness of the axial oceanic crust being smaller than that of the off-axis oceanic crust, and then thicker than the off-axis oceanic crust after the expansion; 3) the thickness of the axial oceanic crust is always thinner than that of the off-axis oceanic crust.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：P736.1

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