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

ABSTRACT

Here we define the Comallo volcanic sedimentary complex of the western North Patagonian Massif. It is composed by two members that include 9 lithofacies and 7 facies associations. The lower member is represented by massive and stratified lapilli tuffs, lithic and tuffaceous breccias, coherent andesite-dacite lava-flows, andesitic breccias, and massive crystalline limestones. The upper member consists of red conglomerates, parallel and cross-stratification sandstones, and mudstones. The lower member is interpreted as having been deposited by dilute and dense pyroclastic currents, block and ash deposits and lava-flow, and hypersaline lacustrine environments. The upper member is considered to have been deposited in fluviatile environments. A new U-Pb age of 192.0 ± 3.0 Ma (Sinemurian) was obtained for this complex. It is coeval with several volcanic sedimentary units that crop out along the western North Patagonian Massif, the Neuquén basin and the Extraandean Chubut in pull-apart or rift depocentres. The movements of the NW-SE strike-slip faults that border the northern and southern limits of the Comallo depocentre made possible the development of a pull-apart basin as well as the volcanism and the fluvial system. This and other coeval units were deposited in similar environmental conditions along the North Patagonian Massif, the Neuquén basin and the extraandean Chubut, indicating a similar tectonomagmatic setting, in a tensional rear-arc during Lower Jurassic times.

Graphic Abstract

KEYWORDS:

• Comallo
• Jurassic volcanism
• North Patagonian Massif
• Argentina

Highlights

The Comallo volcanic sedimentary complex is formed by volcanic and sedimentary members.

Includes pyroclastic flows, effusive lavas, limestones, conglomerated and sandstones.

The age is 192.0 ± 3.0 Ma, and is coeval with other units of Patagonia.

Acknowledgments

This study is part of the research projects “Prospección geofísica de la Provincia de Rio Negro” (grant 24/H061), “Ciclos tectomagmáticos de la República Argentina” (grant 24/H060), and Gondwánico y Patagonídico del Macizo Nordpatagónico occidental (grant 24/H121 and 24H140), granted by the Universidad Nacional del Sur.

The Agencia Nacional de Promoción Científica y Tecnológica-UNS gave a grant to the project “Análisis de la configuración y evolución geológico–geofísica del sector oriental de la Comarca Nordpatagónica” (grant 546). Finally, Significado y evolución de los eventos tectonomagmáticos Gondwánicos y Patagonídicos del norte de Patagonia (grant 11220150100184) was financed by CONICET.

Many thanks to the Torrontegui, Ramírez, and Martínez families and the owner of Estancia La Porfía for allowing access to their lands. Special thanks to people of the Comallo locality, its Major Mr Raúl Hermosilla, and his family for help during the field trips. The English usage of an early version of this manuscript was corrected by David Gorman.

We are also deeply grateful for the comments and suggestions made by Editor-in-Chief Dr. Robert Stern, Dra. Claudia Zaffarana and by an anonymous reviewer who provided a detailed critique of the manuscript which considerably improved its quality.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the Consejo Nacional de Investigaciones Científicas y Técnicas [11220150100184];Agencia Nacional de Promoción Científica y Tecnológica-UNS [546];Secretaría General de Ciencia y Tecnología, Universidad Nacional del Sur [24/H060,24/H061,24/H121,24H140].