Gibson, G.M., Rubenach, M.J., Neumann, N.L., Southgate, P.N, and Hutton, L.J. (2008) Syn- and post-extensional tectonic activity in the Palaeoproterozoic sequences of Broken Hill and Mount Isa and its bearing on reconstructions of Rodinia. Precambrian Research, 166 (1-4). pp. 350-369.

PDF (Published Version) Restricted to Repository staff only

 

64

3

Abstract

Palaeoproterozoic sequences deformed during the 1600 Ma Olary and Isa orogenies in the Broken Hill and Mount Isa terranes preserve an earlier record of syn-extensional magmatism, deformation and low-pressure/high-temperature metamorphism linked to basin formation and normal faulting at upper crustal levels. Crustal extension occurred nearly continuously from 1800 to 1640 Ma and produced several stacked sedimentary basins, the content of which was mainly controlled by growth faulting along the margins of NNW- and NW-trending half-graben. Mid-crustal magmatic rocks intruded and unroofed during the course of extension are commonly mylonitised and were carried to higher structural levels on extensional shear zones active at the time of sedimentation. Metamorphic monazite ages from deformed host rocks of the syn-extensional Sybella Granite at Mount Isa support this interpretation and include a 1675 Ma population that is much too old to be related to either later crustal shortening or the Isan orogeny. This record of near continuous extension at upper and mid-crustal levels is difficult to reconcile with existing reconstructions of Rodinia in which the Broken Hill and Mount Isa terranes are juxtaposed against rocks of similar age in southwest Laurentia that preserve a history of contractional deformation related to terrane accretion, amalgamation and collision. Equally difficult to reconcile are palaeogeographical reconstructions of Australia which place the Broken Hill and Mount Isa terranes adjacent to each other in a back-arc position while maintaining an along-strike continuity with the rocks of southwest Laurentia. In such a configuration, the Mojave, Yavapai, and Mazatzal provinces lie south of the proposed common Palaeoproterozoic suture (Cheyenne Belt) whereas their inferred age equivalents in the Broken Hill and Mount Isa terranes lie north of this former convergent plate margin. An alternative reconstruction of Proterozoic eastern Australia is proposed in which back-arc extension in the Broken Hill and Mount Isa terranes was linked to retreat of a west-dipping (present-day coordinates) subduction zone and associated magmatic arc that now resides partially or wholly within North America. Eastern Australia and Laurentia ceased to be part of a single continental landmass soon after 1800 Ma and thereafter followed increasingly divergent tectonic paths until re-amalgamated during collision at ca. 1600 Ma. Extension in the Broken Hill and Mount Isa terranes produced a North American Basin-and-Range-style crustal architecture that has no obvious counterpart in southwest Laurentia.

Actions (Repository Staff Only)

Item Control Page