168-6 Peripatetic Laurentian Terranes: Relations of Cuyania and the Ellsworth-Whitmore Mountains Block to the Laurentian 'Mainland'

Session: Laurentia Without Borders: Pre-Pangea Intercontinental Connections

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Integral to evolution of south-central Laurentia are the Ellsworth-Whitmore Mountains (EWM), now in Antarctica, and the Cuyania terrane, now in Argentina. Cuyania originated in the western Ouachita embayment. The port of debarkation for the Ellsworth block, however, warrants further definition. Elements common to those terranes, and to southern Laurentia, range from Mesoproterozoic foundations through Cambrian supercontinent fragmentation.

PRE-RODINIA.  Laurentian Mesoproterozoic detritus is common in Ellsworth and Cuyania siliciclastics. In the Lower Heritage Group (lower to mid-Cambrian) of the Ellsworths, 1400-Ma zircons indicate a Granite-Rhyolite Province (G-RP) source. In Cuyania, detrital zircon U/Pb ages from the lower Cambrian Caucete Group in Sa. Pie de Palo constitute an almost unimodal G-RP population -- dominantly 1360 Ma.

RODINIA ASSEMBLY. Amalgamation of Rodinia is manifested in Grenvillian intraplate and collisional tectonomagmatism in Llano Uplift, Devils River Uplift, and western Texas. EWM and Coats Land were sutured to the Kalahari craton along the Grenville-Maud belt at ~1 Ga. In the Haag Nunataks, Grenvillian intraplate felsic rocks are coeval (~1260 to 1100 Ma) with those in the Franklin Mts. Dates for ultramafic complexes in the W. Sierras Pampeanas of Cuyania (1100 - 1070 Ma) align with those of the Pecos Mafic Intrusive Complex, but equivalents are not yet reported from EWM.

RIFTING.  Ellsworth-Laurentia correlatives. Cryogenian rift magmatism includes Ellsworth microdiorite (682 Ma), mafic volcanic boulders within Marathon basin sediments (706 Ma), and detrital zircons in Cambrian siliciclastics (780-700 Ma) in Devils River Uplift. Cambrian activity produced basaltic andesite in the Ellsworths (516 Ma); microgranite in the Haag Nunataks (517 Ma); a felsic tuff boulder (520 Ma) and bentonite (580-520 Ma) in Marathon Fm., Marathon Basin; and detrital zircons (580-530 Ma) in Cambrian siliciclastics, Devils River Uplift.

Cuyania-Laurentia correlatives. Cuyania occurrences include A-type granites (776 Ma) of Laurentian character and carbonatite (570 Ma) in Sa. de Maz; metasediments in Sa. Pie de Palo (697-532 Ma); Laguna Amarga metamafics in Catamarca (569-562 Ma); and Puncoviscana tuff in the Puna (537 Ma).

DRIFTING. As EWM and Cuyania departed, drift-phase regimes differed. The Heritage Group comprises unmetamorphosed siliciclastics hosting an exceptionally preserved molluscan fauna, also found in Laurentia. Throughout southern Laurentia and Cuyania a carbonate platform developed, with exclusively Laurentian faunas. Culmination of the shared history is marked by the break-up unconformity at ~490 Ma.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11348

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