Terrane amalgamation in the Eastern Goldfields Superterrane, Yilgarn Craton: Evidence from tectonostratigraphic studies of the Laverton Greenstone Belt

Abstract

Tectonostratigraphic evolution of the Laverton Greenstone Belt involves amalgamation of structural relics of sedimentary basins and continental fragments in the Burtville Terrane to the east prior to their accretion to the Kurnalpi Terrane to the west. The Burtville Terrane records sedimentation and volcanism in a continental setting between ∼2758 Ma and ∼2715 Ma. The Kurnalpi Terrane is dominated by 2715–2700 Ma andesitic volcaniclastic rocks with erosional remnants of <2675 Ma siliciclastic sequences. Neither volcaniclastic nor siliciclastic sequences preserve evidence for sediment derivation from the Burtville Terrane, implying that accretion occurred after 2665 Ma. Nevertheless, there is evidence for early deformation episodes in the Kurnalpi Terrane because both the Wallaby and Mt Lucky sequences were deposited unconformably on folded strata. Uplift of the Margaret Dome, a granite–gneiss cored batholith north of the Laverton Domain, is interpreted to have been the main driving force for rapid deposition and burial of conglomeratic and turbiditic siliciclastic sequences in the Lake Carey basin. A switch from submarine canyon deposits to deep-water turbiditic rocks with time suggests extension and basin formation was initially driven by the uplift of the dome, however basin development switched to a flexural phase with increasing sediment load and ongoing uplift to the north. The ∼2663 Ma maximum depositional age for the Granny Smith Sequence indicates that active sedimentation may have been occurring contemporaneous with collisional orogeny. The collisional orogeny comprises four main episodes of compressive deformation starting after either ∼2675 Ma or 2665 Ma, and ending at ∼2650 Ma. D 1 involved development of N–S upright to inclined km-scale folds and axial planar foliation, and inversion of pre-collision extensional faults as reverse faults during east–west-directed compression. D 2 involved reactivation of D 1 reverse faults as transcurrent faults and development of NW–SE-directed dm-scale folds with associated axial planar foliation that overprints the early N–S foliation. D 2 occurred under a NE–SW-directed compressive stress field. To the west, the Celia Fault records D 2 as its first deformation, suggesting a westward migrating deformation front. The Celia Fault Zone records its second deformation episode (D 3) as sinistral reactivation of the fault zone and locally influenced lode-gold development. D 3 occurred during WNW–ESE-directed maximum compression. The final compressive deformation event (D 4) involved overprinting of the D 3 shear fabric by conjugate arrays of kink bands in the Celia Fault Zone during a clockwise rotation of the compressive stress field into a NNW–SSE orientation. The tectonic process responsible for such a rapid uplift and deposition of thick synorogenic sediments lateral to the deformation front and penecontemporaneous with collisional orogeny, invites comparisons with modern arc-related settings. The present suture zone between the Indo-Australian Plate and the Pacific Plate in New Guinea records active deposition of fluvial sediments laterally along the accretion zone and in thick deep-water fans onto the Bismarck Sea floor.