AbstractsEarth & Environmental Science

The basement rocks in central Queensland are largely obscured by the Phanerozoic sedimentary succession and the basement geology is known from limited drill holes. Constrained regional potential field analysis is applied to unveil the crustal architecture of the Proterozoic southern Mount Isa terrane and the Phanerozoic Thomson Orogen in Queensland. The Mount Isa terrane forms part of the Palaeoproterozoic North Australian Craton. The exposed Mount Isa Inlier preserves geological record that spans more than 350 million years between ca. 1870 and 1500 Ma. An early cycle of a ca. 1870 Ma orogenesis and ca. 1870 Ma - 1850 Ma extensive batholith emplacement was succeeded by ca. 1800 - 1600 Ma superimposed rifting and subsidence. This was followed by major period of Mesoproterozoic orogeny. Constrained aeromagnetic and gravity data indicate that the depositional sequences and the regional architecture of the Mount Isa terrane extend for ~250 km south of the exposed Inlier, beneath Palaeozoic cover. In the southern parts of the Mount Isa terrane, Palaeoproterozoic sedimentation and volcanism were controlled by NNW-trending structures in half graben setting, resulting in complex superimposed and stacked basins prior to intense basin inversion associated with the Isan Orogeny. Petrophysically constrained geophysical interpretation indicates that prominent regional magnetic and gravity anomalies of the region reflect shallowing of the Pre-1800 Ma crystalline basement and the distribution of meta-sedimentary and meta-volcanic rocks deposited during the development of the ca. 1790 Ma to 1730 Ma Leichhardt Superbasin. Regional low magnetic and low gravity responses coincide with sedimentary successions deposited during the development of the Calvert and Isa superbasins. The ca. 1600 - 1500 Ma Isan Orogeny reactivated the existing extensional fault network and determined the current regional architecture. Extensive low density batholith emplacement occurred at that time. The Thomson Orogen forms the northen extent of the eastern Australian Tasmanides. The region records a protracted tectonic evolution that spans the Neoproterozoic to Triassic and is coincident with one of the largest period of continental growth of the Australian continent. Combined potential field and seismic interpretation indicates that NE- and NW-trending high angle reverse thrusts represent the main crust-scale structural elements in the mid- to lower crust. Gravity data indicate that the eastern and western portions of the Thomson Orogen have a different crustal architecture. The eastern Thomson Orogen is characterized by a regional NE trend and a network of orthogonal faults resulting in a series of troughs and highs. The negative gravity anomalies reflect mostly the distribution of the basinal sequences inferred from drill holes and deep seismic surveys. The western part appears as a series of NW-trending structures interpreted to reflect reverse thrust faults. The smooth magnetic signature of the Thomson Orogen is interpreted to represent source bodies…