The origin of Cuyania revealed by Hf isotopes of zircon
Abstract
The proto-Andean margin of South America is scattered with suspect terranes. The origin of one such terrane, Cuyania in western Argentina, is the cause of considerable debate. There are two prevailing models for the origin of Cuyania: the Laurentian microcontinent model, in which Cuyania rifted from the Ouachita Embayment in the Cambrian and collided with Gondwana in the mid-Ordovician; and, the parautochthonous Gondwanan model, where Cuyania rifted from southwest Gondwana in the early-mid Ordovician, and was transported laterally before re-accreting to the Gondwanan margin in the Silurian-Devonian. We present new zircon U-Pb-Hf data from Paleozoic Cuyanian strata and Mesoproterozoic basement inliers of central Argentina, and compare these with published data from the Grenville margin of Laurentia and the Namaqua-Natal belt of Kalahari (southwest Gondwana). Mesoproterozoic zircons from the Grenville margin of Laurentia have characteristically depleted ɛHf, and so are easily distinguishable from Namaqua-Natal belt zircons, which record crustal reworking of the Kalahari craton with Mesoproterozoic zircons yielding enriched ɛHf values.
Detrital zircon results from Cuyania (Fig. 1) show a variation in provenance up-sequence. Cambrian strata yield Mesoproterozoic zircons with depleted ɛHf correlating with Grenville samples, as well as a Cambrian zircon population that correlates directly with rift related rocks from the Ouachita Embayment. In contrast to the lower sequences, zircon deposited in mid-upper Ordovician strata record a larger range of Mesoproterozoic ɛHf values, correlated with zircons from inboard proto-Andean Mesoproterozoic inliers, and reflecting provenance from the Gondwana margin. Zircons from the Namaqua-Natal belt do not correlate with Cuyanian strata, suggesting that the Kalahari craton was not the source of these sediments. Variation in provenance between Cambrian and Ordovician strata reflects the tectonic evolution of Cuyania proposed by the Laurentian microcontinent model: Cambrian rift-drift sediments were sourced from the margin of Laurentia and Ordovician syn-orogenic sediments were sourced from the Gondwanan margin. These data not only obviate the parautochthonous Gondwana model, but verify the Laurentian microcontinent model for the origin of Cuyania.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T52A..02M
- Keywords:
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- 1165 Sedimentary geochronology;
- GEOCHRONOLOGYDE: 8108 Continental tectonics: compressional;
- TECTONOPHYSICSDE: 8169 Sedimentary basin processes;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS