东印度洋东经90°海岭的地球物理特征和成因探讨

Geophysical Characteristics and Genesis of the Ninetyeast Ridge in the Eastern Indian Ocean

东经90°海岭发育于东印度洋,自孟加拉沉积扇向南穿越赤道直至印度洋南部布罗肯脊,是世界上最长的线性构造。海岭的形成机制与东印度洋晚白垩世至新生代的多阶段演化有关,由于其跨越赤道、长度大于5 000 km,南北不同区域的构造背景较为复杂,因此,其不同分段的地球物理特征也各具特色。通过分析海岭不同分段的形貌、浅层结构、重磁、地壳厚度及洋底年龄等地质地球物理数据,结合东印度洋海底扩张演化史,探讨了海岭的不同分段的成因机制。结果表明,90°E海岭的形成与板内热点活动、地幔柱-洋中脊相互作用、板块扩张与扩张中心跃迁,以及转换断层等诸多因素有关,是多种地质作用和地质过程综合作用的结果。2°N以北的海岭可能形成于远离扩张中心的印度板块内部,与板内火山作用有关联;18°S以南的部分形成于印度板块与南极洲板块边界转换断层附近;而2°N~18°S之间的中部区域则最为复杂,推测中段的形成受到了凯尔盖朗热点与沃顿扩张脊的相互作用,以及海岭下方的多次洋脊跳跃等因素的影响。分析认为,海岭中段是深入认识海岭成因机制、解决海岭构造演化和动力学机制以及脊-柱相互作用等重大科学问题的关键区域。未来在海岭中段开展地球物理测量及钻探工作,丰富海岭中段的地球物理综合数据,揭示中段不同位置岩石的物质组成与形成年代,是解决上述重大科学问题的必由之路。

The Ninetyeast Ridge(NER)developing in the Eastern Indian Ocean,extending from the Bengal sedimentary fan to the Brocken Ridge,is the longest Lineament in the world.The formation mechanism of the Ridge is related to the multi-stage evolution of the East Indian Ocean during Late Cretaceous to Cenozoic era.The length of the Ridge is more than 5000 kilometers,and the tectonic settings in the northern and southern regions are very complex,showing obivous different geophysical characteristics in different segments.This study analyzed geological and geophysical data including the morphology,shallow structure,gravity and magnetism,crustal thickness,and ocean floor age of different sections of the ridg.The data,combining with the evolution history of seafloor expansion in the Eastern Indian Ocean,are uesd to explore the genetic mechanisms of different segments of the Ridge.The results show that the formation of the NER is related to many factors,such as intraplate hot spot activity,the interaction of mantle plume and mid-oceanic ridge,plate expansion and the transition of the expansion center,as well as transform faults,and is the result of the combination of multiple geological processes.The ridge to the north of 2°N may be formed in the interior of Indian Plate far away from the spreading center,which is related to intraplate volcanism.The part to the south of 18°S was formed near the transform fault between Indian Plate and Antarctica Plate.The central region between 2°N and 18°S is the most complex,and it is speculated that the formation of the region is influenced by some factors such as the interaction between the Kerguelen hotspot and the Wharton spreading ridge,and multiple mid-oceanic ridge jumps below the Ridge.We suggests that the central region of the Ridge is a key area for understanding the genetic mechanism of the Ridge,solving major scientific problems such as structural evolution and dynamic mechanisms of the Ridge,and interactions between mic-oceanic ridge and mantle plume.Finally,we proposed that the only way to solve some major scientific problems mentioned above in the near future is to carry out geophysical survey and drilling work in the central region of the Ridge,and to reveal the material composition and formation age of basement rocks at different locations in the central region of the ridge.