Joint inversion of gravity and seismic along the CMD01 profile on the southwestern margin of Madagascar and analysis of crustal structure

doi:10.3969/j.issn.1001-909X.2024.04.008

Abstract

Abstract:

This study was based on the actual gravity, magnetic and multichannel seismic data obtained during the international cooperative survey in 2021. Through joint inversion of gravity and seismic along the CMD01 profile traversing the southwestern margin of Madagascar, combined with interpretation and analysis of seismic profiles, the crustal structure, tectonic units, and evolution of the southwestern margin of Madagascar were studied. A crustal density model of the southwestern margin of Madagascar was established, revealing thinned continental crust and the presence of magmatic underplating in certain segments. Structural units such as thinned continental crust, continental-ocean transition zone and oceanic crust domain can be delineated from land to sea, among which, due to the influence of Davie Fracture Zone strike-slip tectonics on the margin, the continental-ocean transition zone exhibited typical characteristics of a transform margin. By combining plate reconstruction and crustal density model, the developmental evolution of the southwestern margin of Madagascar was reconstructed. The research results have important theoretical significance and practical application value for deepening the understanding of the breakup and separation of the Gondwana, the developmental evolution of the East African passive margin, and maritime delineation.

Key words: The continental edge of East Africa, Davie Fracture Zone, continental-ocean transition zone, transform margin, joint inversion of gravity and seismic, deep crustal structure, crustal density model, lower crustal high-density body

CLC Number:

P736.1

ZHANG Yongqi, TANG Yong, DONG Chongzhi, WU Zhaocai, LI He, GUO Chufeng, REN Jianye, CHAO Peng, YANG Tianyi. Joint inversion of gravity and seismic along the CMD01 profile on the southwestern margin of Madagascar and analysis of crustal structure[J]. Journal of Marine Sciences, 2024, 42(4): 83-99.

Figures/Tables 13

Fig.1 The tectonic map of the region around the southwestern margin of Madagascar Island

Tab.1 Seismic reflection characteristics of sequence in the southwestern margin of Madagascar Island

层序	内部反射特征	频率	振幅	连续性
U₅(T₀~T₁)	平行-亚平行	高频,变化较小	低-中振幅,局部空白	好-中等
U₄(T₁~T_b)	亚平行,局部嘈杂状	中频	低-中振幅,局部空白	中等-差
U₃(T₁~T₂)	平行-亚平行,局部波状	高-中频,局部有变化	中振幅,局部空白	好-中等
U₂(T₂~T₃)	亚平行,局部嘈杂状	中频	中振幅	好
U₁(T₃~T₄)	亚平行,局部嘈杂状	变化较大	高-中振幅	好-中等

Fig.2 Stratigraphic framework of the southwestern margin of Madagascar Island (T4 was formed at the beginning of the Late Carboniferous intracontinental rift period and is not noted in the figure. Figure is modified from reference [16].)

Fig.3 CMD01 2D seismic profile (U represents stratum, U1 is the stratum between T3 and T4, U2 is the stratum between T2 and T3, U3 is the stratum between T1 and T2, U4 is the stratum between T1 and Tb, U5 is the stratum between T0 and T1.)

Tab.2 Crustal density model and velocity model of the southwestern margin of Madagascar Island[7,28-29]

地层	密度/(g·cm^-3)	层速度/(m·s^-1)
海水	1.03	1 500
沉积层1	2.20	2 000
沉积层2	2.30~2.45	3 300
沉积层3	2.52~2.56	3 500
沉积层4	2.57~2.64	4 000
洋壳	2.93	6 500
上地壳	2.67~2.74	5 700~6 300
下地壳	2.90~2.94	6 400~7 000
下地壳高密度体	3.10~3.16	7 000~7 500
地幔	3.30	8 000~8 100

Fig.4 The free-space gravity anomaly (a) and topographic map (b) of the southwestern margin of Madagascar Island

Fig.5 CMD01 2D seismic profile (a), magnetic anomaly curve (b) and gravity anomaly curve (c)

Fig.6 Continental-ocean boundary in CMD01 seismic profile

Fig.7 Rift area and magmatic intrusions within the basin in CMD01 seismic profile

Fig.8 Uplift stratigraphic in CMD01 seismic profile

Fig.9 Graben structure in CMD01 seismic profile

Fig.10 The inversion results of the crustal density model interface for CMD01 (D represents density.)

Fig.11 Evolution map of the southwestern margin of Madagascar Island (Figure is modified from references [19] and [53].)

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