Multiphase cooling and exhumation of the southern Adelaide Fold Belt: constraints from apatite fission track data

Abstract

Data from apatite fission track analysis are presented for 20 outcrop samples collected in the southern Adelaide Fold Belt, South Australia. Interpretation of these data, with the aid of numerical models which allow inference of multiphase cooling histories, indicate three discrete cooling events that are likely to correlate with sedimentation events in surrounding depositional settings. An event beginning some time after 85 Ma (Late Cretaceous) was characterized by cooling throughout the study area from temperatures of roughly 50 to 70 °C. An event beginning at 300–270 Ma (Late Palaeozoic) was characterized by cooling from temperatures >120 °C in all areas except for the Mount Lofty Ranges and Murray Bridge region, where peak temperatures were only 95–115 °C prior to Palaeozoic cooling. Some samples from these subregions of relatively cool Late Palaeozoic temperatures also retain evidence for even earlier cooling from temperatures >120 °C, beginning prior to 350 Ma. We interpret the post 85‐Ma event as the consequence of regional exhumation from a depth of 1.0–1.6 km. The Late Palaeozoic event (300–270 Ma) is interpreted as cooling associated with the termination of the Alice Springs Orogeny, while cooling prior to 350 Ma probably represents the final stages of Early Middle Palaeozoic unroofing of the southern Adelaide Fold Belt. The results highlight the importance of regional, episodic postorogenic exhumation of Palaeozoic fold belts, where – in some cases – conventional methods have erroneously suggested relatively long‐term stability.

Shaping the Australian crust over the last 300 million years: Insights from fission track thermotectonic imaging and denudation studies of key terranes

“…1998; Kohn et al . 1999; Gibson & Stüwe 2000), a time that correlates well with a prominent peak in the denudation chronology history (Figure 6). Denudation may be difficult to explain at this time as cross‐cutting relationships that may independently shed some light on the cause of this event simply do not exist throughout southeastern Australia.…”

Bedrock erosion and relief production in the northern Flinders Ranges, Australia

“…However, it is unclear whether this sample cooled in response to exhumation or decreases in the local geothermal gradient (Mitchell et al, 2002). Alternatively, Gibson and Stüwe (2000) noted that the post ~85 Ma cooling recorded by apatite fission track data occurred throughout the broader region, and was not limited to the present-day ranges. These workers inferred that range uplift occurred after apatite fission track cooling below temperatures of ~50-70 °C.…”

Modes of active intraplate deformation, Flinders Ranges, Australia

“…[17] Following the Delamerian Orogeny a period of tectonic quiescence ensued with mild thermal perturbations attributed to the late Paleozoic Alice Springs Orogeny [Gibson and Stuwe, 2000;McLaren et al, 2002]. During the Mesozoic the region was reduced to a peneplain, after which episodes of fluvial to lacustrine deposition occurred in the Cretaceous, Eocene and Miocene.…”

“…This sedimentary package and its underlying crystalline basement were deformed in an orogenic setting in the Late Cambrian -Early Ordovician ($500 -490 Ma) Delamerian Orogeny, to form a distinctive oroclinal system now expressed in the strike ridge dominated topography of the Flinders Ranges. Subsequent reactivation during the Devonian and Carboniferous ''Alice Springs'' events is indicated by a number of low-temperature thermochronometric studies [Gibson and Stuwe, 2000;McLaren et al, 2002].…”