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 $\text{λ}{}^{87}\text{Rb}\text{= 1.42 · 10}{}^{\mathrm{?11}}\text{a}{}^{\mathrm{?1}}$, 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	$\text{> 2718 ± 50}$	$\text{0.7007 ± 0.0004}$
(2) Voluminous tonalite, the Lawlers Tonalite	$\text{2652 ± 20}$	$\text{0.70152 ± 0.00012}$
	$\text{2576 ± 14}$	$\text{0.70218 ± 0.00021}$
(3) A less voluminous leucogranite, and a large complex pegmatite cutting the Perseverance nickel orebody	$\text{2588 ± 18}$	$\text{0.7624 ± 0.0068}$
(4) Aplitic leucotonalite (very minor volumes but widespread)	$\text{2474 ± 14}$	$\text{0.70193 ± 0.00012}$
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