西南印度洋中脊49°E—52°E区域洋壳增生的构造与岩浆特征  

Magmatic and tectonic crustal accretion at the Southwest Indian Ridge between 49°E and 52°E

作　　者：冯博 李江海[1,2] 陶春辉 刘持恒 FENG Bo;LI JiangHai;TAO ChunHui;LIU ChiHeng(The Key Laboratory of Orogenic Belts and Crustal Evolution,Ministry of Education,School of Earth and Space Sciences,Peking University,Beijing 100871,China;Institute of Oil and Gas,School of Earth and Space Sciences,Peking University,Beijing 100871,China;Key Laboratory of Submarine Geosciences,Second Institute of Oceanography,Ministry of Natural Resources,Hangzhou 310012,China;Division of Geology and Mineral Resources,Beijing Research Institute of Uranium Geology,Beijing 100029,China)

机构地区：[1]造山带与地壳演化教育部重点实验室,北京大学地球与空间科学学院,北京100871 [2]北京大学石油与天然气研究中心,北京大学地球与空间科学学院,北京100871 [3]自然资源部海底科学重点实验室,自然资源部第二海洋研究所,杭州310012 [4]地质矿产资源部北京铀地质研究所,北京100029

出　　处：《地球物理学报》2024年第12期4733-4747,共15页Chinese Journal of Geophysics

基　　金：中国大洋“十三五”课题(DY135-S2-1-01,DY135-S1-1-03)资助.

摘　　要：慢速-超慢速扩张洋中脊的洋壳增生方式在沿轴和穿轴方向有着较大的差异.在岩浆供给贫乏地区或贫瘠时期,洋中脊扩张过程在很大程度上是通过构造作用进行的.目前,我们对这种构造扩张程度较高的洋中脊洋壳增生的构造与岩浆特征及其形成机制的研究还不够深入.本文利用高精度船载多波束水深及重力数据研究了西南印度洋中脊(SWIR)49°E—52°E区域洋壳增生的构造与岩浆特征,结果表明研究区洋壳增生的构造过程和岩浆活动随时空强烈变化.依据研究区地形坡度、曲率、粗糙度特征识别出了火山地貌、断层地貌、沉积地貌3种主要地貌样式,C型断层、E型断层、拆离断层3种断层样式.然后在垂直于洋脊的剖面上计算出构造伸展作用在整个扩张过程中所占的比例,即构造应变比率T值,从而间接得到岩浆增生比率M=(1−T)的值.不对称洋壳增生区域在两翼水深、T值以及地貌特征等方面均有显著差异.此外,研究区T值、地貌特征尤其是断层样式在沿轴方向的变化规律与剩余地幔布格重力异常(RMBA)反映的岩浆供给变化具有非常好的相关性.在岩浆供给贫瘠的区域,通常产生较薄的洋壳,T值较大,多发育水平断距较大的拆离断层和E型断层;在岩浆供给充足的区域,通常产生较厚的洋壳,T值较小,断层水平断距较小,多发育水平断距较小的C型断层.At slow-ultraslow spreading mid-ocean ridges,crustal accretion style can vary significantly along and across ridge segments.In magma-poor regions or periods,seafloor spreading can be accommodated largely by tectonic processes.However,the tectonic and magmatic characteristics and formation mechanism of such highly tectonized crust are not fully understood.In this study,we utilized the high-resolution shipboard multibeam bathymetry and gravity data to investigate the tectonic and magmatic crustal accretion of the Southwest Indian Ridge(SWIR)between 49°E and 52°E.The results show that the processes of crustal accretion and magma activity in the study area have undergone significant spatial and temporal changes.Based on the terrain slope,curvature,and roughness characteristics of the study area,three main geomorphic patterns were identified:volcanic,fault,and sedimentary geomorphology,along with three fault types:C-type,E-type,and detachment faults.The proportion of tectonic extension in the entire spreading process,referred to as the strain ratio(T-value),was calculated along the profile perpendicular to the ridge axis,which indirectly provided the value of magma accretion rate(M-value)as(1−T).Asymmetric crustal accretion regions exhibit significant differences in terms of water depth,T-value,and geomorphic features on both sides.Furthermore,there is a good correlation between T-value,geomorphic features,and particularly fault types,and the variations in magma supply reflected by the residual mantle Bouguer gravity anomaly(RMBA)in the along-axis direction.In regions with insufficient magma supply,thinner oceanic crust is typically produced,with a larger T-value and detachment faults and E-type faults with large horizontal fault heaves are mostly developed;In regions with sufficient magma supply,thicker oceanic crust is usually produced,with a small T-value and C-type faults with small horizontal fault offsets are mostly developed.

关 键 词：西南印度洋中脊 多波束地形 构造作用 岩浆活动 

分 类 号：P736[天文地球—海洋地质]