岩浆与构造作用对洋壳厚度的影响——以西北印度洋为例

洋中脊及邻区洋盆的洋壳厚度能很好地反映区域岩浆补给特征,对于研究洋中脊内部及周缘岩浆活动和构造演化过程具有很好的指示意义.西北印度洋中脊作为典型的慢速扩张洋中脊,其扩张过程与周缘构造活动具有很强的时空关系.本文利用剩余地幔布格重力异常反演了西北印度洋洋壳厚度,由此分析区域内洋壳厚度分布和岩浆补给特征.研究发现,西北印度洋洋壳平均厚度为7.8 km,受区域构造背景影响厚度变化较大.根据洋壳厚度的统计学分布特征,将区域内洋壳分为三种类型:薄洋壳(小于4.5 km)、正常洋壳(4.5~6.5 km)和厚洋壳(大于6.5 km),根据西北印度洋中脊周缘(~40 Ma内)洋壳厚度变化特征可将洋中脊划分为5段,发现洋中脊洋壳厚度受区域构造活动和地幔温度所控制,其中薄洋壳主要受转换断层影响造成区域洋壳厚度减薄,而厚洋壳主要受地幔温度和地幔柱作用影响,并在S4洋中脊段显示出较强的热点与洋中脊相互作用,同时微陆块的裂解和漂移也可能是导致洋壳厚度差异的原因之一.

Influence of magmatic and tectonic processes on the oceanic crustal thickness in the Northwest Indian Ocean

The oceanic crustal thickness of mid-ocean ridges and adjacent ocean basins can well reflect the characteristics of melt accretion of the mid-ocean ridges,which is of great significance for the study of magmatic activities and tectonic evolution along the mid-ocean ridges and their surroundings.As a typical slow-spreading mid-ocean ridge,the spreading patterns of the Northwest Indian Ocean Ridge(NWIR)has a strong spatio-temporal relationship with tectonic patterns.In this paper,oceanic crustal thickness model derived from gravity shows the distribution of oceanic crustal thickness and melt accretion characteristics of NWIR.It is found that the average thickness of the oceanic crust within Northwest Indian Ocean is 7.8 km,and the thickness distribution of oceanic crust is different.According to the statistical distribution characteristics of oceanic crustal thickness,the crust is divided into three types:thin oceanic crust(<4.5 km),normal oceanic crust(4.5~6.5 km)and thick oceanic crust(>6.5 km).The NWIR is divided into five segments within 40 Ma,in that case,oceanic crustal thickness around ridge segment is controlled by regional tectonic processes and mantle temperature.The thin oceanic crust is mainly influenced by transform faults which make regional oceanic crust thickness thinning,while thick oceanic crust is affected by the mantle temperature and hot spot.S4 ridge segment shows a strong interaction between hot spot and mid-ocean ridge.Besides,cracking and drift of micro-continents may also be one of the causes of oceanic crust thickness variation.