Mesoproterozoic subduction under the eastern edge of the Kalahari-Grunehogna Craton preceding Rodinia assembly : the Ritscherflya detrital zircon record, Ahlmannryggen (Dronning Maud Land, Antarctica)

Abstract

The reconstruction of the palaeogeography and supercontinent amalgamation processes in the Precambrian is generally guided by the age of magmatic and metamorphic rocks in orogenic belts, which formed along the sutures of colliding continents or smaller terranes (e.g., Wareham et al., 1998; Dalziel et al., 2000). Yet, the investigation and interpretation of these belts becomes increasingly difficult with increasing age of the orogenic cycles, due to metamorphic overprint, fragmentation by subsequent rifting processes, erosive loss, and covering by younger deposits or by ice. An alternative and important recorder of geodynamic processes are clastic sediments that are fed from the eroding orogenic belts and are deposited on stable cratonic platforms, where they may escape erosion and high-grade metamorphism for billions of years. These clastic sediment deposits generally contain abundant detrital zircon, which provides an age record of the eroded orogenic belts, reflecting a large number of rock types. The age spectra of detrital zircon recovered from sedimentary basins can be used to distinguish between different tectonic settings in which the sediments were deposited, such as convergent margins, collisional orogens or extensional settings (von Eynatten & Dunkl, 2012; Cawood et al., 2012). The supercontinent Rodinia formed by convergence and collision of all the major landmasses between 1200 and 950Ma, i.e. in the late Mesoproterozoic (Hoffman, 1991; Li et al., 2008). Key evidence for the collisions is found in the late Mesoproterozoic orogenic belts, which span thousands of kilometres through North and South America, southern Africa, Australia, Asia and East Antarctica. Yet, the paleogeographic reconstruction of Rodinia is still uncertain, and at least three different configurations have been discussed (Li et al., 2008). Issues arise in part from the uncertainties in terrane boundaries within East Antarctica and possible connections to the African Kalahari Craton. At least one major late Mesoproterozoic (Stenian) suture must be located in Dronning Maud Land (DML; East Antarctica), but its location and the extent of possible crustal blocks are still enigmatic (Jacobs et al., 2008a).