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Crustal development in the Agnew region, Western Australia, as shown by Rb/Sr isotopic and geochemical studies

Crustal development in the Agnew region, Western Australia, as shown by Rb/Sr isotopic and geochemical studies
Crustal development in the Agnew region, Western Australia, as shown by Rb/Sr isotopic and geochemical studies
Rb/Sr geochronology on a folded greenstone-granitoid complex in the Agnew area, Western Australia, yields four distinct ages of igneous activity that conform with stratigraphic and intrusive relationships. They are (using View the MathML source, NBS 70A = 522 ppm Rb and 65.3 ppm Sr):

Ma 87Sr/86Sr initial (IR)
(1) Differentiated gabbro-granophyre from a stratigraphically old (Kathleen Valley) greenstone sequence > 2718 ± 50 0.7007 ± 0.0004
(2) Voluminous tonalite, the Lawlers Tonalite 2652 ± 20 0.70152 ± 0.00012
2576 ± 14 0.70218 ± 0.00021
(3) A less voluminous leucogranite, and a large complex pegmatite cutting the Perseverance nickel orebody 2588 ± 18 0.7624 ± 0.0068
(4) Aplitic leucotonalite (very minor volumes but widespread) 2474 ± 14 0.70193 ± 0.00012
Table options

Earlier measurements by Roddick et al. (1976), 70 km to the north, of the Mount Keith Granodiorite (2632 ± 17 Ma, IR = 0.70149 ± 0.00015) and Jones Creek Pegmatites (2481 ± 18 Ma, IR = 0.7253 ± 0.0002) appear to fit groups (2) and (4), respectively. The two principal deformational events in the area are bracketed by groups (2) and (3), and by groups (3) and (4), respectively. Strontium IRs and major and trace-element chemistry suggest that the tonalite-granodiorite and the later leucotonalite were obtained by partial melting of tholeiitic material with garnet as a controlling mineral phase. The leucogranite more likely resulted from remelting of tonalite-granodiorite under similar conditions with garnet again a controlling mineral phase. These four magmatic events constitute a massive addition to the crust from the mantle lasting about 250 Ma. About 90% of the silicic material was emplaced 80 Ma after activity began (tonalite-granodiorite stage) and at least 99% had been emplaced after 140 Ma (leucogranite stage).
0301-9268
31-59
Cooper, J.A.
0aa1c44c-3784-4a17-a0d6-3dc7fa75ae55
Nesbitt, R.W.
6a124ad1-4e6d-4407-b92f-592f7fd682e4
Platt, J.P.
ad287bef-8559-4b24-b295-fb4383549ac7
Mortimer, G.E.
b26cbb15-465c-4ca8-ae7a-ba5d40da3f2f
Cooper, J.A.
0aa1c44c-3784-4a17-a0d6-3dc7fa75ae55
Nesbitt, R.W.
6a124ad1-4e6d-4407-b92f-592f7fd682e4
Platt, J.P.
ad287bef-8559-4b24-b295-fb4383549ac7
Mortimer, G.E.
b26cbb15-465c-4ca8-ae7a-ba5d40da3f2f

Cooper, J.A., Nesbitt, R.W., Platt, J.P. and Mortimer, G.E. (1978) Crustal development in the Agnew region, Western Australia, as shown by Rb/Sr isotopic and geochemical studies. Precambrian Research, 7 (1), 31-59. (doi:10.1016/0301-9268(78)90004-9).

Record type: Article

Abstract

Rb/Sr geochronology on a folded greenstone-granitoid complex in the Agnew area, Western Australia, yields four distinct ages of igneous activity that conform with stratigraphic and intrusive relationships. They are (using View the MathML source, NBS 70A = 522 ppm Rb and 65.3 ppm Sr):

Ma 87Sr/86Sr initial (IR)
(1) Differentiated gabbro-granophyre from a stratigraphically old (Kathleen Valley) greenstone sequence > 2718 ± 50 0.7007 ± 0.0004
(2) Voluminous tonalite, the Lawlers Tonalite 2652 ± 20 0.70152 ± 0.00012
2576 ± 14 0.70218 ± 0.00021
(3) A less voluminous leucogranite, and a large complex pegmatite cutting the Perseverance nickel orebody 2588 ± 18 0.7624 ± 0.0068
(4) Aplitic leucotonalite (very minor volumes but widespread) 2474 ± 14 0.70193 ± 0.00012
Table options

Earlier measurements by Roddick et al. (1976), 70 km to the north, of the Mount Keith Granodiorite (2632 ± 17 Ma, IR = 0.70149 ± 0.00015) and Jones Creek Pegmatites (2481 ± 18 Ma, IR = 0.7253 ± 0.0002) appear to fit groups (2) and (4), respectively. The two principal deformational events in the area are bracketed by groups (2) and (3), and by groups (3) and (4), respectively. Strontium IRs and major and trace-element chemistry suggest that the tonalite-granodiorite and the later leucotonalite were obtained by partial melting of tholeiitic material with garnet as a controlling mineral phase. The leucogranite more likely resulted from remelting of tonalite-granodiorite under similar conditions with garnet again a controlling mineral phase. These four magmatic events constitute a massive addition to the crust from the mantle lasting about 250 Ma. About 90% of the silicic material was emplaced 80 Ma after activity began (tonalite-granodiorite stage) and at least 99% had been emplaced after 140 Ma (leucogranite stage).

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Published date: 1978
Organisations: Geochemistry

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Local EPrints ID: 361802
URI: https://eprints.soton.ac.uk/id/eprint/361802
ISSN: 0301-9268
PURE UUID: e6ee71e1-f012-4b92-b722-079c24cb4dca

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Date deposited: 03 Feb 2014 13:55
Last modified: 18 Jul 2017 02:58

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