刘持恒^1,2,,
李江海^1,2,,,
张华添¹,
刘仲兰^1,3,
范庆凯^1,2
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. Lamont Doherty Earth Observatory, Columbia University, Palisades 10964, NY, USA

基金项目: 多金属硫化物合同区资源勘探与评价（DY135-S1-1-03），国家重点研发计划课题（2016YFC0503301），大型油气田及煤层气开发国家科技重大专项（2016ZX05033002-007）资助


详细信息

作者简介: 刘持恒, 男, 1989年生, 博士研究生, 主要从事构造地质学和海洋地质研究.E-mail:liuchiheng@yeah.net

通讯作者: 李江海, 男, 1965年生, 教授, 博士, 主要从事全球构造研究.E-mail:jhli@pku.edu.cn

中图分类号: P738

收稿日期:2017-08-14
修回日期:2017-09-14
上线日期:2018-07-05

Magma supply of the southwest Indian Ocean: evidence from crustal thickness anomalies

LIU ChiHeng^1,2,,
LI JiangHai^1,2,,,
ZHANG HuaTian¹,
LIU ZhongLan^1,3,
FAN QingKai^1,2
1. Key Laboratory of Orogenic Belts and Crustal Evolution, Ministry of Education, School of Earth and Space Sciences, Peking University, Beijing 100871, China
2. Institute of Oil and Gas, School of Earth and Space Sciences, Peking University, Beijing 100871, China
3. Lamont Doherty Earth Observatory, Columbia University, Palisades 10964, NY, USA


More Information

Corresponding author: LI JiangHai,E-mail:jhli@pku.edu.cn

MSC: P738

--> Received Date: 14 August 2017
Revised Date: 14 September 2017
Available Online: 05 July 2018


摘要
摘要:西南印度洋中脊为典型的超慢速扩张洋中脊，其岩浆补给具有不均匀分布的特征.洋壳厚度是洋中脊和热点岩浆补给的综合反映，因此反演洋壳厚度是研究大尺度洋中脊和洋盆岩浆补给过程的一种有效方法.本文通过对全球公开的自由空气重力异常、水深、沉积物厚度和洋壳年龄数据处理得到剩余地幔布格重力异常，并反演西南印度洋地区洋壳厚度，定量地分析了西南印度洋的洋壳厚度分布及其岩浆补给特征.研究发现，西南印度洋洋壳平均厚度7.5 km，但变化较大，标准差可达3.5 km，洋壳厚度的频率分布具有双峰式的混合偏态分布特征.通过分离双峰统计的结果，将西南印度洋洋壳厚度分为0~4.8 km的薄洋壳、4.8~9.8 km的正常洋壳和9.8~24 km的厚洋壳三种类型，洋中脊地区按洋壳厚度变化特征可划分为7个洋脊段.西南印度洋地区薄洋壳受转换断层控制明显，转换断层位移量越大，引起的洋壳减薄厚度越大，减薄范围与转换断层位移量不存在明显相关性.厚洋壳主要受控于该区众多的热点活动，其中布维热点、马里昂热点和克洛泽热点的影响范围分别约340 km，550 km和900 km.Andrew Bain转换断层北部外角形成厚的洋壳，具有与快速扩张洋中脊相似的转换断层厚洋壳特征.
关键词: 西南印度洋中脊/
剩余地幔布格重力异常/
地壳厚度/
热点/
洋底高原

Abstract:The Southwest Indian Ridge (SWIR) is a typical ultraslow spreading ridge (< 20 mm·a^-1), symbolized by non-uniform magma supply and crustal accretion. Oceanic crustal thickness is a critical parameter to understand the magmatic process at mid-ocean ridges and near hotspots. Here, we present residual mantle oceanic crustal thickness distribution of the Southwest Indian Ocean (2°W-72°E, 20°S-60°S). The gravity-derived crustal thickness model reveals a huge range of crustal thickness in the Southwest Indian Ocean and the frequency of crustal thicknesses shows a bimodal mixed skewed distribution. The average of oceanic crustal thickness in the Southwest Indian Ocean is 7.5 km with a standard deviation 3.5 km. Three types of ocean crust are distinguished in this area by this thickness model. Overall 20.31% of the study area has the thickness of oceanic crust less than 4.8 km, designated as the thin crust type. The thickness of oceanic crust in majority of the region (60.99%) is between 4.8 km and 9.8 km, defined as the normal crust type. The remaining area (18.70%) where crustal thickness is greater than 9.8 km is known as the thick crust type. The southwest mid-ocean ridge is classified into seven segments by crustal thickness anomalies. Transform faults are the key factor in decreasing crustal thickness. The more reduction crustal thickness is produced by larger offsets of transform faults, while there is no obvious correlation between the reduction range and fault displacement. Meanwhile underlying cold and depleted mantle can also reduce oceanic crust. The active hotspots can provide abundant heat beneath mid-ocean ridges or ocean basins and thicken the oceanic crust. The influence ranges of Bouvet, Marion and Crozet hotspots are 340 km, 550 km and 900 km respectively. Notably, the excess crustal thickness towards the north end of the Andrew Bain transform fault shows the characteristic is similar to fast spreading ridges.
Key words:Southwest Indian Ridge/
Residual mantle Bouguer anomaly/
Crustal thickness/
Hotspot/
Oceanic plateau



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