TECTONO-STRATIGRAPHY OF LATE ARCHEAN GREENSTONE TERRANES IN THE SOUTHERN EASTERN GOLDFIELDS, WESTERN-AUSTRALIA

Late Archaean greenstone terranes in the southern part of the Eastern Goldfields are regionally extensive, fault-bounded entities defined on the basis of small but distinct differences in stratigraphy and struc ture. The greenstones comprise volcano-sedimentary successions that we re all deposited at the same time (c. 2720-2675 Ma) on sialic crust. H ence, the terranes are interpreted to represent contemporaneous, proba bly adjacent, basins. These basins were affected by the same history o f granite plutonism and regional deformation (c. 2675-2620 Ma). Early subhorizontal deformation is poorly understood, but includes at least locally significant thrust stacking (D1) with a south to north movemen t direction. This was followed by regional east-west extension affecti ng all supracrustal successions above a province-wide detachment, now lying at depths between 4 and 7 km. This detachment may have evolved f rom the greenstone-basement contact, but only after extensive reworkin g. Clastic basins developed along or above major extensional faults bu t no volcanism is associated with this extension. Subsequent east-west (D2) shortening resulted in regional scale thrusting, folding and ass ociated late-stage transcurrent fault movements. The D2 event is conte mporaneous with a major thermal event represented by voluminous granit e emplacement (c. 2660 Ma) and associated peak regional metamorphism i n the greenstone succession. Predominantly monzo granite, derived from older sialic crust, was emplaced throughout the period of basin forma tion and deformation: early synvolcanic granite (c. 2719-2710 Ma) is a minor component, late synvolcanic granite (c. 2685-2675 Ma) is widesp read, and syn-D2 granite (c. 2660 Ma) is abundant. There are a few sma ll late tectonic intrusions (c. 2640 Ma to?2600 Ma). The lateral litho stratigraphic persistence of the contemporaneous basins, the syn-D2 lo w pressure regional metamorphism, and the province-wide monzo granite magmatism suggest that the greenstone basins possibly developed in a t ectonic setting similar to that of failed rifts above aborted spreadin g centres. The basins closed in response to far-held compressional str esses. (C) 1997 Elsevier Science B.V.