Comparison of Some of the Geochemical Features and Tectonic Particular Reference to Australia Setting of Archaean and Proterozoic Granulites, with Particular Reference to Australia

Wilson A.F. and Anantha T.R. (1978) Comparison of Some of the Geochemical Features and Tectonic Particular Reference to Australia Setting of Archaean and Proterozoic Granulites, with Particular Reference to Australia. Developments in Precambrian Geology, 1 C: 241-267. doi:10.1016/S0166-2635(08)70101-4


Author Wilson A.F.
Anantha T.R.
Title Comparison of Some of the Geochemical Features and Tectonic Particular Reference to Australia Setting of Archaean and Proterozoic Granulites, with Particular Reference to Australia
Journal name Developments in Precambrian Geology
ISSN 0166-2635
Publication date 1978-01-01
Sub-type Article (original research)
DOI 10.1016/S0166-2635(08)70101-4
Volume 1
Issue C
Start page 241
End page 267
Total pages 27
Subject 1907 Geology
Abstract Irregular patches of Archaean hypersthene-bearing granulites, widely ranging in size, are common throughout the Wheat Belt of southwestern Australia (60000 km 2) which is now composed dominantly of biotite or hornblende gneisses intruded by large coarse 2600 MA grey granitic domes. Some of the granulites were Archaean sediments, volcanic rocks (both mafic and silicic) and highly magnesian ultramafic rocks, whereas some large areas appear to be older Archaean basement now converted to dark greasy rocks like the silicic charnockites of India. Although some mafic granulites are strongly lineated and some silicic granulites show well-developed platy quartz grains, most granulites exhibit ill-defined linear elements, and present the appearance of having suffered thermal metamorphism rather than strong deformation. Cordierite, sillimanite, spinel and olivine are common in rocks of appropriate composition, but kyanite and high pressure clinopyroxene-garnet assemblages are unknown. Linear belts of granulites, which yield Proterozoic ages by Rb-Sr methods, engirdle on three sides the Archaean block of the Wheat Belt and adjoining greenstones to the east. The Fraser Block (8000 km 2), separated from the Archaean by an extensive mylonite zone and intense Bouguer gravity anomaly, is dominated by anhydrous mafic granulites of higher pressure than the Archaean granulites of the Wheat Belt, The mafic granulites were basic lavas and small intrusives of continental tholeiite type set within an intracratonic linear zone, and metamorphosed at 1338 MA (Rb-Sr). In the Musgrave Ranges silicic and mafic granulites were formed at about 1380 MA, and are of both anhydrous and hydrous types, and range from low to intermediate granulites. These granulites are intruded by large bodies of "magmatic" charnockitic adamellite at about 1130 MA. Older silicic and mafic granulites (1860 MA) appear in the Strangways Range within the Arunta Block, and in places have recorded a second granulite event at c. 1470 MA. Archaean basement has not yet been recognised within the Arunta Block, and the granulites form imbricate thrust slices of deep-seated igneous and sedimentary rocks. Major and trace element and REE studies reveal a close correspondence of the mafic granulites of the Fraser Range to continental tholeiites, whereas those of both the Musgrave and Strangways Ranges mostly show island arc or oceanic tholeiitic characters. Element mobility during granulite facies metamorphism was Strongly controlled by thermal and fluid gradients. Large increase in total pressure but at approximately constant temperature produced no significant element mobility in dry mafic granulites along 100 km traverse in the Fraser Range, and U and Th values are not correlated with metamorphic grade. In the Musgrave Ranges, where granulite hornblende and biotite are common, Th, U, Rb, Ni and Co were depleted with increase of both total pressure and temperature, whereas Ba, Sr, REE, Na, Ca and P were enriched. Elements showing less than 20% change are Si, Al, Mn, Ca, K, Zn, Cr, Y, Nb, Fe 3, Fe 2, Mg, Ti, Zr, V and Pb. In the aureole of a large charnockitic intrusive pluton where F was active there is a marked increase in U, Th and Rb, but a depletion of Zr and Ti, two elements normally considered immobile elements. Silicic granulites in all three terrains show depletion, with increase of grade, of U, Th and Rb and increase with K/Rb, as noted in several Archaean shields. In view of the varying influence of partial pressures of the fluids, and temperature, complications of polymetamorphism, and differing tectonic setting of many terrains, significant chemical differences cannot yet be recognised between Archaean and Proterozoic granulites.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
Collection: Scopus Import - Archived
 
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Created: Tue, 28 Jun 2016, 18:26:01 EST by System User