Kerguelen Plateau crustal structure and basin formation from seismic and gravity data (original) (raw)

2001, Journal of Geophysical Research: Solid Earth

We use multichannel seismic data, gravity, and subsidence modeling, in conjunction with plate reconstructions, to evaluate the crustal origin and composition of the Kerguelen Plateau. Predominantly oceanic crust of the southern and parts of the central Kerguelen Plateau appears to include continental fragments related to the breakup of India and Antarctica; these fragments may have been metamorphosed during emplacement of the main plateau. The upper crust is basaltic, the middle crust is intrusive mafic rock and intruded continental crust, and the lower crust is a plagioclase-rich metamorphic rock. The Labuan Basin crust is predominantly oceanic with stranded Kerguelen Plateau fault blocks. High-density lower crust in the Labuan Basin is probably composed of serpentinized peridotites formed during slow rifting and spreading. Plate reconstruction models indicate opening between eastern Broken Ridge and southern Kerguelen Plateau at ~90 Ma, heralding the formation of the Labuan Basin and Diamantina Zone; crustal attenuation and slow accretion of oceanic crust continued until the Australian and Antarctic plates separated at C 18 time (-40 Ma). Plate reconstructions of the free-air gravity field indicate that the Naturaliste Plateau fits against Antarctica and that Elan Bank and India were juxtaposed until ~110 Ma. Both Naturaliste Plateau and Elan Bank are probable microcontinents. A ~1 km positive residual depth anomaly in the oceanic basins adjacent to the plateau, along with the positive geoid anomaly centered beneath the northern Kerguelen Plateau, imply that the lithosphere is partially dynamically supported by an upwelling hot asthenosphere of the Kerguelen hot spot. 1. Introduction The Kerguelen Plateau in the southern Indian Ocean (Figure 1) is one of the world's two most voluminous large igneous provinces (LIPs) [Coffin and Eldholm, 1994]. Oceanic plateaus form by massive, transient magmatic activity, commonly attributed to mantle plumes, which is typically followed by continuous, but less voluminous magmatism [Coffin and Eldholm, 1994]. LIPs associated with the Kerguelen Plateau and the conjugate Broken Ridge include the Bunbury Basalts in SW Australia (130/123 Ma) [Frey et al., 1996], the Rajmahal Traps (116 Ma) [Kent et al., 1997], the Naturaliste Plateau (-100 Ma), and Ninetyeast Ridge (82-38 Ma) (Figure 1); all are possibly related to the breakup of the Indian, Australian and the Antarctic plates [Mahoney et al., 1983; Frey et al., 2000]. The' Kerguelen Plateau, in contrast to many smaller, subaerially-emplaced oceanic LIPs (e.g., Iceland, Hawaiian Ridge), is characterized by well-developed sedimentary basins that contain detailed records of its early erosional and subsidence history. The most prominent among these basins are the Raggatt Basin and the Banzare Bank on the southern plateau, the Labuan Basin