The crustal nature of the northern Mozambique Ridge, Southwest Indian Ocean

摘要

The Mozambique Ridge(MOZR)is one of the basement high structures located in the Southwest Indian Ocean,parallel to the Southeast African continental margin.It was formed as a result of the tectono-magmatic evolution of the Gondwana breakup.The origin of the MOZR has been highly debated,with models suggesting either continental or oceanic origin.With new free-air gravity anomaly and multichannel seismic(MCS)reflection data,we present results of 2D density modeling along two seismic profiles acquired by R/V Xiangyanghong 10 at the northern Mozambique Ridge(N-MOZR)between 26°S and 28°S.We observed high free-air gravity anomaly and strong positive magnetic anomaly related to the emplaced seaward dipping reflectors(SDR)and high density lower crustal body(HDLCB),and high Bouguer gravity anomaly associated with the thinning of the continental crust underneath the N-MOZR over a distance of~82 km.This suggests a thinned and intruded continental crust bound by the Mozambique Fracture Zone(MFZ)that is characterized by gravity low and negative magnetic anomaly.This fracture zone marks the continent-ocean boundary(COB)while the N-MOZR is the transform margin high,i.e.,marks the continent-ocean transition(COT)of the Southern Mozambique margin,following the definition of transform margins.We suggest that the N-MOZR was formed by continental extension and subsequent breakup of the MFZ,accompanied by massive volcanism during the southward movement of the Antarctica block.The presence of SDR,HDLCB,and relatively thick oceanic crust indicates the volcanic nature of this transform margin.