Mesoproterozoic plume-modified orogenesis in eastern Precambrian Australia

摘要

Tectonic models for the latest Paleoproterozoic to earliest Mesoproterozoic evolution of eastern Australia (circa 1620-1500 Ma) are diverse and either emphasize plume or plate margin activity, neither of which satisfactorily explains all geological observations. The dichotomy is largely attributed to geochemical, spatial and temporal data that suggest voluminous A-type felsic magmas are plume related, whereas distribution of arc-related magmas and intense orogenic overprint suggest plate margin activity. The salient geological events include arc-related magmatism at circa 1620-1610 Ma followed by a magmatic hiatus coincident with north-south crustal shortening (1610-1590 Ma) and a magmatic flare-up of A-type felsic magmas throughout the Gawler Craton (circa 1595-1575 Ma). These magmas form the oldest component of a northward younging hot spot track that extends to the Mount Isa Inlier. At circa 1590-1550 Ma, arc magmatism resumed along the northern margin of the Gawler Craton and the rest of eastern Australia records a 90° shift in the regional shortening direction related to activity along the eastern margin of the Australian continent. A plume-modified orogenic setting satisfies all of the spatial and temporal relationships between magma generation and orogenic activity. In this model, the Gawler Craton and the adjacent subduction zone migrated over a mantle plume (circa 1620-1610 Ma). Resultant flat subduction caused transient orogenesis (1610-1595 Ma) in the overriding plate. Slab delamination and thermal assimilation of the plume and the subducting slab caused a switch to crustal extension in the overriding plate, resulting in extensive mantle-derived and crustal melting in the Gawler Craton (1595-1575 Ma).