Evolution of the Jurassic Comallo volcanic sedimentary complex in the western north Patagonian Massif, Río Negro province, Argentina

MERCEDES BARROS; DANIEL A. GREGORI; BENEDINI, LEONARDO; MARCOS, PAULO; LEONARDO STRAZZERE; CECILIA PAVON PIBETTA; GERALDES, MAURO

INTERNATIONAL GEOLOGY REVIEW

TAYLOR & FRANCIS INC

Lugar: Londres; Año: 2020 vol. XX

0020-6814

Here we define the Comallo volcanic sedimentary complex of the western NorthPatagonian Massif. It is composed by two members that include 9 lithofacies and 7facies associations. The lower member is represented by massive and stratifiedlapilli tuffs, lithic and tuffaceous breccias, coherent andesite-dacite lava-flows,andesitic breccias, and massive crystalline limestones. The upper memberconsists of red conglomerates, parallel and cross-stratification sandstones, andmudstones.The lower member is interpreted as having been deposited by dilute and densepyroclastic currents, block and ash deposits and lava-flow, and hypersalinelacustrine environments.The upper member is considered to have been deposited in fluviatileenvironments.A new U-Pb age of 192.0 ± 3.0 Ma (Sinemurian) was obtained for this complex. Itis coeval with several volcanic sedimentary units that crop out along the westernNorth Patagonian Massif, the Neuquén basin and the Extraandean Chubut in pullapartor rift depocenters. The movements of the NW-SE strike-slip faults thatborder the northern and southern limits of the Comallo depocenter made possiblethe development of a pull-apart basin as well as the volcanism and the fluvialsystem.This and other coeval units were deposited in similar environmental conditionsalong the North Patagonian Massif, the Neuquén basin and the extraandeanChubut, indicating a similar tectonomagmatic setting, in a tensional rear-arc duringLower Jurassic times.