Pietranik, A., Hawkesworth, C.J., Storey, C.D., Kemp, T.I.S., Sircombe, K.N., Whitehouse, M.J., and Bleeker, W. (2008) Episodic, mafic crust formation in the Slave craton, Canada. In: Geochimica et Cosmochimica Acta (72) A748-A748. From: 18th Annual Goldschmidt Conference, July 2008, Vancouver, Canada.

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Abstract

Hf model ages of zircons provide information on the timing of new crust extraction from mantle. However, many model ages are hybrid due to mixing in the sedimentary environment. Zircons with mantle δ18O values (5.0-5.6‰) [1] are more likely to preserve Hf model ages that reflect actual crust forming events.

Hf and O isotopes have been analysed in 3.9-2.8 Ga detrital zircons from the ~2.8 Ga Mesoarchean cover succesion in the Slave craton, Canada [2]. The zircons with mantle-like δO18 form two linear arrays in zircon crystallization age versus initial εHf plots consistent with two episodes of crust formation at ~3.45 Ga and ~3.75 Ga. Slopes of the linear arrays correspond to ¹⁷⁶Lu/¹⁷⁷Hf ratios of ~0.022 suggesting that the sources of the magmas from which zircons crystallized was mafic in composition. The zircons with the lowest initial εHf through time all have elevated δ18O values, but they also scatter around a linear array with the slope corresponding to ¹⁷⁶Lu/¹⁷⁷Hf ratio of ~0.022 consistent with mafic crust deriavtion from the mantle at ~4.4-4.5 Ga. Zircons that crystallized during crust formation and crustal recycling events both show a range of initial εHf and often elevated δ18O consistent with derivation of magmas from heterogenous crust composed of both unaltered, igneous and weathered, probably sedimentary rocks. Mafic crust generated in three episodes in the Slave Province was the source of magmas throughout the Archean, and zircons from Gondwana indicate that similar unaltered mafic crust could have had even longer residence times of over 1.5 Ga [3].

Item ID:	27993
Item Type:	Conference Item (Abstract / Summary)
ISSN:	0016-7037
Date Deposited:	09 Jul 2013 02:51
FoR Codes:	04 EARTH SCIENCES > 0402 Geochemistry > 040299 Geochemistry not elsewhere classified @ 100%
SEO Codes:	97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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