Structural evolution of the Warrawoona Greenstone Belt and adjoining granitoid complexes, Pilbara Craton, Australia: implications for Archaean tectonic processes
- 作者：Kloppenburg ; A. ; White ; S.H. ; Zegers ; T.E.
- 关键词：Archaean ; Pilbara Craton ; Structural analyses ; Compression ; Extension ; Strike&ndash ; slip ; Core complex ; Diapirism
- 刊名：Precambrian Research
- 出版年：2001
- 期刊代码：75_03019268
- 类别：ear
- 出版时间：November 15, 2001
- 卷：112
- 期：1-2
- 页码：107-147
- 文件大小：23 M
摘要
The Pilbara granite–greenstone terrain (3.6–2.8 Ga), Australia, is quoted as the key area formed by passive, gravity-driven solid-state diapirism. But, contrasting views have been reported recently, which led us to re-examine the key area: the Warrawoona Greenstone Belt and the adjoining Mt Edgar and Corunna Downs Granitoid Complexes. We found: (i) an asymmetric, non-synclinal distribution of metamorphic grade and deformation intensity across the Warrawoona Greenstone Belt; (ii) a major shear zone on the margin of the Mt Edgar granitoid complex with a unidirectional stretching lineation pattern; (iii) a NE-trending transcurrent shear zone within the central gneiss complex of the Mt Edgar Granitoid Complex; (iv) coeval magmatic activity and doming of the granitoid complexes; and (v) the loss of about 9 km of stratigraphic units in the Warrawoona Greenstone Belt. The area has had a prolonged history with at least four deformation phases between ca. 3.47 and 2.8 Ga. The main domal geometry of the Mt Edgar granitoid complex was obtained during active NE–SW extension at 3.31 Ga (Dx+2), which appears to been in response to E–W compression. Possibly, the E–W compression resulted in crustal thickening and partial melting, probably of a 3.46–3.43 Ga granitic basement, causing crustal weakening, collapse and extrusion of the 3.31 Ga granitoids. Extension at 3.31 Ga was accommodated by the Mt Edgar Shear Zone, a mid-crustal detachment, and by the associated Beaton Well Zone, which acted as a transfer zone within the gneissic basement. Doming of the Mt Edgar Granitoid Complex is interpreted to have occurred in an active, extensional core complex-type mode. An indication for deformation prior to 3.32 Ga comes from syntectonically intruded gabbro/diorite and dolerite sills within the Mt Edgar Shear Zone, which intruded possibly as early as 3.46–3.45 Ga (Dx+1). Ultramafic schistose xenoliths within the gabbro/diorite intrusions are the oldest observed deformed rocks, formed during Dx. Post-doming deformation involved NE–SW compression, Dx+3, followed by dextral transcurrent deformation, Dx+4, during NW–SE compression. The latter may be related to the regional phase of deformation at 2.93 Ga, during which the eastern and western Pilbara were amalgamated. Comparison of this deformation sequence to others within the Marble Bar Domain suggests a common tectonic history from 3.46 Ga onwards. Our structural and kinematic data, especially the 3.31 Ga unidirectional stretching lineation pattern, lead us to reject solid-state diapirism due to convectional overturn as the main cause for doming of the Mt Edgar Granitoid Complex. We suggest that the cause lies in a plate tectonic process.