Abstract
Abstract We produced a crustal magnetization model for the Maud Rise in the southwest Indian Ocean off the coast of East Antarctica using magnetic observations from the Ørsted satellite and near-surface surveys complied by the Antarctic Digital Magnetic Anomaly Project (ADMAP). Joint inversion of the two anomaly fields suggests that the magnetic effects due to crustal thickness variations and remanence involving the normal polarity Cretaceous Quiet Zone (KQZ) dominate at satellite altitude (~700 km). The crustal thickness effects were modeled in the Ørsted data using crustal thickness variations derived from satellite altitude gravity data. Modeling of the residual Ørsted and near-surface magnetic anomalies supports extending the KQZ eastwards to the Astrid Ridge. The remaining near-surface anomalies involve crustal features with relatively high frequency effects that are strongly attenuated at satellite altitudes. The crustal modeling can be extended by the satellite magnetic anomalies across the Indian Ocean Ridge for insight on the crustal properties of the conjugate Agulhas Plateau. The modeling supports the Jurassic reconstruction of Gondwana when the African Limpopo-Zambezi and East Antarctic Princess Astrid coasts were connected as part of a relatively demagnetized crustal block.
Highlights
Continents are composed of crustal blocks with different ages, compositions, tectonic histories, and contrasting magnetic properties dominated mostly by induction (Hinze and Zietz, 1985) with effects that can be detected at satellite altitude (e.g., von Frese et al, 1986; Taylor and Frawley, 1987; Ravat et al, 1992)
We adopted an average susceptibility of 0.03 SI (e.g., Thomas, 1987) that reflects the induced magnetic characteristics of oceanic layer 2 (e.g., Roeser et al, 1996). This value compares well with the 0.033–0.038 SI range of susceptibilities inferred by Fullerton et al (1994) for the induced and viscous crustal remanent magnetizations of Maud Rise based on geochemical data from alkali basalt at Site 690 (65.1◦S, 1.1◦E) of the Ocean Drilling Program (Schandl et al, 1990)
To test our Ørsted anomalies of the Maud Rise, we upward continued to 700 km the 1◦ crustal anomaly estimates for the region of the Agulhas Plateau that were obtained at 400 km from a combined data set of POGO and Magsat magnetic observations (Arkani-Hamed et al, 1994)
Summary
Continents are composed of crustal blocks with different ages, compositions, tectonic histories, and contrasting magnetic properties dominated mostly by induction (Hinze and Zietz, 1985) with effects that can be detected at satellite altitude (e.g., von Frese et al, 1986; Taylor and Frawley, 1987; Ravat et al, 1992). This value compares well with the 0.033–0.038 SI range of susceptibilities inferred by Fullerton et al (1994) for the induced and viscous crustal remanent magnetizations of Maud Rise based on geochemical data from alkali basalt at Site 690 (65.1◦S, 1.1◦E) of the Ocean Drilling Program (Schandl et al, 1990) Combining this simple model of crustal susceptibilities with the Ørsted core field (Olsen et al, 2000) updated to 1999.0 and the crustal thickness variations (Fig. 2(B)) yields the magnetic anomaly estimates in Fig. 3(A) at 700 km altitude. The comprehensive crustal magnetization model for the Maud Rise in Fig. 5(A) obtained by this optimal EV predicts magnetic effects that correlate at 0.94 and 0.95 with the residual Ørsted and low-pass filtered near-surface ADMAP anomalies, respectively
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