The Palaeozoic history of an unusual intracratonic thrust belt in central Australia based on ⁴⁰ Ar- ³⁹ Ar, K-Ar and fission track dating

Abstract

Intraplate thrusting, involving reactivation of a mid-Proterozoic province boundary within the basement metamorphic rocks of the Arunta block, occurs at the northern margin of the late Proterozoic to mid-Palaeozoic Amadeus Basin in central Australia. Earlier geological and geophysical studies show that the thrust system, referred to as the Alice Springs orogen, is 'thick-skinned' in the central part of the thrust belt and was dominated by the crust-cutting Redbank thrust zone. Several episodes of thrusting, defined stratigraphically, began about 400 Ma ago. Analysis and modelling of 40 Ar- 39 Ar age spectra on K-feldspar from the basement rocks, combined with regional geological constraints, point to cooling rates of 3–10 °C/Ma and moderate overall exhumation rates of 100–400 m/Ma during the Alice Springs orogeny, without appreciably increased heat flow. However, final uplift along the thrust front at 300–320 Ma was rapid, as the time of final closure of small domains in K-feldspar approximates apatite fission track ages. By using 40 Ar- 39 Ar age data as a constraint, together with available geological and geophysical data, crustal shortening across the thrust belt is thought to be approximately 20 to 30%. Overall convergence rates of 0.6–3 km/Ma are slow compared with rates of ≥ 5 km/Ma for continent-continent collision zones.

Kwangsian and Indosinian reworking of the eastern South China Block: Constraints on zircon U–Pb geochronology and metamorphism of amphibolites and granulites

“…Wang et al, , 2007bWang et al, 2010Wang et al, , 2011, it can be inferred that there was most likely a Paleozoic ocean beyond the southern/southeastern margins of the current SCB. The Kwangsian and Indosinian intracontinental events of the eastern SCB could be attributed to the tectonic response of the region to the far-field stress field related to subduction/collision systems beyond the southern margin of the eastern SCB (e.g., Hendrix et al, 1992;Shaw et al, 1992). Li (1998) and Wang et al (2010) proposed that the Kwangsian orogenesis of the SCB might be the result of the interactions of the eastern SCB, even the Indochina Block, with the Australian-Indian plate during the course of rapid northward movement of east Gondwana (also see Li, 1998;Li and Powell, 2001;Stampfli and Borel, 2002;Yu et al, 2007) although the exact plate boundary conditions are unclear.…”

Low-temperature (<110°C) thermal history of the Mt Isa and Murphy Inliers, northeast Australia: evidence from apatite fission track thermochronology *

“…However, radiogenic ages ranging between ca 400 and 270 Ma (Rb -Sr, 40 Ar/ 39 Ar, K/Ar, fission track) are commonly obtained from the Arunta Inlier, and are attributed to shearing, uplift and cooling of basement rocks during the intraplate, Carboniferous Alice Springs Orogeny (Cooper et al 1988;Tingate 1990;Shaw & Black 1991;Shaw et al 1992;Dunlap & Teyssier 1995;Dunlap 1996). The large range in ages has been interpreted to be the result of either cooling following a thermal pulse (*3008C over a period of *10 6 y) in the Late Palaeozoic (Shaw et al 1984) or very slow cooling (0.18C/million years) followed by rapid cooling during crustal uplift and erosion of *7 -12 km at a rate of approximately 108C/million years (Shaw et al 1992, assuming a geothermal gradient of 258C/km). Approximately 65 -85 km of Late Palaeozoic north over south crustal shortening occurred in the southeastern Arunta Block (Teyssier 1985;Dunlap 1996).…”

“…Approximately 65 -85 km of Late Palaeozoic north over south crustal shortening occurred in the southeastern Arunta Block (Teyssier 1985;Dunlap 1996). This was probably accommodated by progressive exhumation of an upthrust wedge, which cooled at rates of *108C/million years (corresponding to an exhumation rate of *0.4 km/million years assuming a geothermal gradient of 258C/km: Shaw et al 1992). This rate is low for an evolving thrust belt compared with plate-margin orogens such as the Alps and the Himalayas ( The driving force for the Alice Springs Orogeny was probably an unusually high compressive-stress field (Shaw et al 1992), and several intraplate stress mechanisms have been proposed (Shaw & Black 1991;Hand et al 1997).…”

“…This was probably accommodated by progressive exhumation of an upthrust wedge, which cooled at rates of *108C/million years (corresponding to an exhumation rate of *0.4 km/million years assuming a geothermal gradient of 258C/km: Shaw et al 1992). This rate is low for an evolving thrust belt compared with plate-margin orogens such as the Alps and the Himalayas ( The driving force for the Alice Springs Orogeny was probably an unusually high compressive-stress field (Shaw et al 1992), and several intraplate stress mechanisms have been proposed (Shaw & Black 1991;Hand et al 1997). Stress in the continental elastic lithosphere may be related to collisional orogenic activity at the plate margins of Gondwana throughout the latest Devonian and Carboniferous (Teyssier 1985).…”

Caractérisation et transfert des magmas felsiques dans la croûte moyenne à profonde :

“…Le cycle tectonique se termine par l'orogenèse intracratonique d'Alice Springs, considérée par Shaw et al, (1992a) comme une orogenèse intracontinentale pendant l'événement thermal de l'ouest de l'Arunta. L'événement est limité et met en évidence le champ de contrainte compressif au niveau des intraplaques continentales, et par conséquent ramène la croûte profonde à la surface par un chevauchement intracratonique Collins et Teyssier 1989;Goleby étal.…”