本文關鍵詞： 遠震 各向異性 P波 長江中下游成礦帶 流動方向 板塊俯沖　出處：《中國地質(zhì)大學(北京)》2017年碩士論文　論文類型：學位論文

【摘要】：長江中下游地區(qū)分布著我國重要的多金屬成礦帶。190～230 Ma年前,長江中下游成礦帶巖漿-礦化作用強烈,形成了重要的內(nèi)生金屬礦藏。研究區(qū)范圍為東經(jīng)115°～122°,北緯28°～36°,主要涵蓋安徽、江蘇、江西和浙江等四省,處于中下?lián)P子地塊,而且西側的深大斷裂帶—郯廬斷裂帶被認為是巖漿上涌的通道。已有的研究結果表明長江中下游成礦帶下方上地幔內(nèi)存在明顯的低速異常體,這似乎與中生代巖石圈拆沉相關。為了深入討論該地區(qū)的深部動力學過程,本文采用遠震P波各向異性層析成像方法,通過挑選從中國地震臺網(wǎng)獲取的103個固定臺站及野外布設的72個流動臺站中所記錄的300個震級大于5.5的遠震事件數(shù)據(jù),利用我們改進的多道互相關技術(MMCC),從遠震波形資料計算得到22800個P波相對走時殘差數(shù)據(jù)。通過以上數(shù)據(jù)反演了研究區(qū)域上地幔三維速度結構和各向異性分布情況,嘗試給出地幔深部上涌的軟流圈流體流動方向的直接證據(jù),嘗試解釋不同深度各向異性產(chǎn)生的原因。研究上地幔各向異性對于地震預測、軟流圈對流動力學過程、巖石圈拆沉理論的完善有著重要意義。在網(wǎng)格剖分時,在水平方向上,由于分辨率原因,在300km以上深度采用1°×1°水平網(wǎng)格,在400 km以下深度采用2°×2°;在垂直方向上,分辨率為50～100 km不等。各向同性速度研究結果表明,研究區(qū)內(nèi)上地幔頂部100km以上深度,西側顯示為低的速度異常,東側顯示為高的速度異常。而深度范圍為200～400 km深度范圍中,西側出現(xiàn)高速異常。這一變化被認為是由于巖石圈部分拆沉所引起。各向異性反演結果顯示出,在100km以上深度內(nèi)地震波速度快軸方向與地表的構造背景一致,為NE、NNE、NNW方向;從100 km往下,隨著深度加深,最快速度方向逐漸轉變?yōu)榻较?并且當?shù)卣鸩ㄓ龅轿鱾雀咚佼惓ｓw時,各向異性方位有拐彎的跡象,這可能指示地幔深部流體在上涌過程中的具體的流動方向。本文認為在地質(zhì)解釋和構建深部動力學模型時,在300 km以上深度,地震波快軸方向主要受控于低速異常體的蠕動或上涌狀態(tài),即地幔熱物質(zhì)的運移方向是南北向的;而在400km以下深度,太平洋板塊的俯沖作用則發(fā)揮一定影響。
[Abstract]:An important polymetallic metallogenic belt distributed in the middle and lower reaches of the Yangtze River. 230 Ma ago, magma mineralization was strong in the metallogenic belt of the middle and lower reaches of the Yangtze River, forming an important endogenic metal deposit. The study area was 115 擄/ 122 擄E and 28 擄N / 36 擄N, mainly covering Anhui Province. Jiangsu, Jiangxi and Zhejiang provinces are in the middle and lower Yangtze block. Moreover, the deep fault zone in the west is considered to be a channel of magmatic upwelling. The results show that there are obvious low velocity anomalies in the upper mantle beneath the middle and lower reaches of the Yangtze River metallogenic belt. This seems to be related to the Mesozoic lithospheric desubsidence. In order to discuss the deep dynamic process in this area, a method of P-wave anisotropic tomography is used in this paper. By selecting 300 teleseismic events with magnitude greater than 5.5 recorded from 103 fixed stations and 72 mobile stations deployed in the field from the China Seismic Network, By using our improved multichannel cross-correlation technique, MMCC, 22800 P-wave relative travel time residuals are obtained from the remote seismic waveform data. The 3-D velocity structure and anisotropic distribution of the upper mantle in the studied area are inversed from the above data. This paper attempts to give direct evidence of the direction of flow of asthenosphere fluid in deep mantle upwelling, and try to explain the causes of anisotropy at different depths. It is of great significance to perfect the theory of lithospheric desubsidence. In the horizontal direction, for the reason of resolution, 1 擄脳 1 擄horizontal grid is used in the depth above 300 km, 2 擄脳 2 擄in the depth below 400 km, and in the vertical direction, when the meshes are divided into meshes, the depth is 1 擄脳 1 擄and the depth below 400 km is 2 擄脳 2 擄. The resolution varies from 50 to 100 km. The results of isotropic velocities show that the depth of the upper mantle is more than 100 km in the study area, the velocity anomaly in the west is low and the velocity anomaly in the east is high, while the depth range is 200 ~ 400 km. A high speed anomaly appears on the west side. This change is believed to be caused by the partial desubsidence of the lithosphere. The anisotropic inversion results show that the fast axis direction of seismic wave velocity is consistent with the tectonic background of the surface in the depth of more than 100 km, which is the NNE NW direction. From 100 km down, along with the depth deepening, the fastest velocity direction gradually changes to the near horizontal direction, and when the seismic wave meets the high-speed anomaly body on the west side, the anisotropic azimuth shows the sign of turning. This may indicate the specific flow direction of deep mantle fluids during upwelling. The fast axis direction of the seismic wave is mainly controlled by the creep or upwelling state of the low-velocity anomaly, that is, the direction of the mantle thermal material migration is north-south, but the subduction of the Pacific plate plays a certain role in the depth below 400km.
【學位授予單位】：中國地質(zhì)大學(北京)
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：P631.4

【參考文獻】

相關期刊論文 前10條

1 常利軍;丁志峰;王椿鏞;;南北構造帶北段上地幔各向異性特征[J];地球物理學報;2016年11期

2 呂子強;雷建設;周智剛;張剛;張書建;于澄;顏啟;;環(huán)渤海地區(qū)Pn波速度結構與各向異性[J];地球物理學報;2016年06期

3 張明輝;徐濤;呂慶田;白志明;武澄瀧;武振波;滕吉文;;長江中下游成礦帶及鄰區(qū)三維Moho面結構:來自人工源寬角地震資料的約束[J];地球物理學報;2015年12期

4 江國明;張貴賓;呂慶田;史大年;徐\，

本文編號：1521681