Interpretation of reconnaissance gravity and aeromagnetic surveys of the Antarctic Peninsula

Abstract

Two‐dimensional models are presented for the crustal structure of the Antarctic Peninsula, a Mesozoic‐Cenozoic magmatic arc on the southeast Pacific margin. The models are constrained by measured rock properties. The West Coast Magnetic Anomaly (WCMA) is caused by a zone of mafic plutons which is 70–150 km wide and over 1500 km long. In modelling of Bouguer anomalies, isostatic compensation is maintained by crustal thickness variations. The model Moho is deepest (35 km) beneath the mid‐Cretaceous axis of the arc and shallowest (<20 km) beneath a Late Cenozoic marginal basin. Positive isostatic residual gravity anomalies are associated with the WCMA and a mafic terrane in the Mesozoic accretionary complex. Three broad areas of consistent crustal structure are identified. The junctions of these areas are sinistral fault zones which displace the curvilinear magnetic, physiographic, and gravity patterns by several tens of kilometers.

Autochthonous v. accreted terrane development of continental margins: a revised in situ tectonic history of the Antarctic Peninsula

“…During the recommencement of active subduction, extensional passive margin tectonics resulted in sedimentation on Alexander Island and Adelaide Island (Western Domain) and OIBand MORB-like intrusive and volcanic magmatism on Alexander Island as fertile non-metasomatized mantle upwelled. A high isostatic residual gravity anomaly over Alexander Island reveals these mafic intrusions to be extensive at depth, forming up to 7.5 km of the vertical crustal stratigraphy (Garrett 1990;Ferraccioli et al 2006). These events argue against formation of the Western Domain as an accretionary wedge to a distal oceanic arc (see above) and mark the resumption of subduction (see above) and subsequent increase in magmatic activity during the Cretaceous.…”

“…This thinned the crust on the eastern side of the Antarctic Peninsula, as revealed by a decrease in the Bouguer gravity anomaly relative to the Peninsula's spine (Garrett 1990;Ferraccioli et al 2006). The intraplate rifting resulted in the onset of Latady Group and Mount Hill Formation deposition (Eastern Domain) in back-arc basin settings at 188 Ma (Fanning & Laudon 1999;Willan 2003).…”

Opening history of Powell Basin, Antarctic Peninsula

“…A major continental magnetic anomaly, the Paci¢c Margin Anomaly (PMA), about 100 km wide with peak-to-peak amplitudes typically exceeding 1000 nT, is thought to represent the Mesozoic arc-batholith in the region, having highs coincident with ma¢c outcrops on the Antarctic Peninsula (Garrett et al, 1986;Garrett, 1990;Maslanyj et al, 1991). Plutonism within the arc occurred from V240 Ma until 10 Ma, peaking in the early Cretaceous (142^97 Ma; Leat et al, 1995).…”

Interpretation of new aeromagnetic anomaly data from the central Antarctic Peninsula

“…Although no constraints from complementary geophysical data have been used directly in the models presented here, the models are based on previous modeling of detailed [Johnson, 1997] and reconnaissance data [Garrett, 1990] which used some of the sparse gravity data as constraints. The models provide an indication of the differences in depth to the upper surfaces of the magnetic sources.…”

“…The tectonic segmentation of the Antarctic Peninsula crust has been discussed by a number of authors using combinations of physiographic evidence [Hawkes, 1981;Garrett and Storey, 1987], marine magnetic anomaly data [Barker 1982], and reconnaissance magnetic anomaly data [Garrett and Storey, 1987;Garrett, 1990;Maslanyj et al, 1991]. These authors divided the Antarctic Peninsula into three or four segments and related the segment boundaries to the extrapolation of offshore fracture zones.…”