2-4 Early Rifting in the Southern Gulf of California from Integration of Marine Geology, Seismic Profiles, and Geochronology: Implication for the Tectonic Setting of the Comondú group

Session: Tectonic setting of Comondú group: a discussion on alternative interpretations

Presenting Author:

Luca Ferrari

Authors:

Ferrari, Luca¹, Gonzalez, Mario², Orozco-Esquivel, Teresa³, Lopez Martinez, Margarita⁴, Gallegos, Cristian⁵, Arregui, Sergio⁶, Mastache, Agustin⁷

(1) UNAM - Campus Juriquilla, Instituto de Geociencias, Juriquilla, QRO, Mexico, (2) CICESE, Ensenada, Baja California, Mexico, (3) UNAM Campus Juriquilla, Instituto de Geociencias, Queretaro, QRO, , (4) CICESE, Ensenada, BC, , (5) CICESE, Ensenada, BC, Mexico, (6) CICESE, Ensenada, BC, Mexico, (7) CICESE, Ensenada, BC, Mexico,

Abstract:

The initial rift stage of the Gulf of California is partially preserved in the onshore and offshore regions between Loreto and La Paz. Here, we integrate marine geological data, Ar-Ar and U-Pb ages, and multichannel seismic profiles to illustrate its structure and age. In the offshore region, a ~330 km long structural high—termed here the Concepción-Cerralvo basement high (CCBH)—extends from the Concepción Peninsula to Cerralvo Island. It is composed of Late Cretaceous (101-85 Ma) granitic to granodioritic rocks, correlative with the Los Cabos, Jalisco, and Sinaloa batholiths, and is subaerially exposed on the islands of Santa Catalina, Santa Cruz, San José, and Espíritu Santo. Submarine samples and seismic profiles confirm the CCBH's continuity, although probably segmented by left-lateral accommodation zones south of Loreto and San José Island.

The CCBH is covered only by thin ignimbrites (~22-19 Ma), synchronous with the last silicic ignimbrites of the Sierra Madre Occidental, whose distal parts are interbedded in the lower member of the Comondú Group. Intermediate-composition lavas (~18.6-14 Ma) and shallow intrusions, correlative with the middle member of the Comondú Group, occur in extensional basins on both sides of the CCBH. Their absence atop the CCBH, combined with the ubiquitous occurrence of Late Cretaceous detrital zircons in the lower and middle Comondú strata, suggests the CCBH was a horst separating two main extensional basins: a western one (now exhumed at Sierra La Giganta) and an eastern, submerged basin between the Foca and Cerralvo banks. The eastern basin contains a lower sequence with synsedimentary normal faulting affecting ~19-14 Ma rocks, predating transtensional deformation. The eastern counterparts of these basins are the offshore San Blas (Mazatlán) basin, with initial deposition at ~19 Ma, and the onshore Conitaca basin in Sinaloa, which contains ~18-15 Ma silicic to intermediate domes and lava flows feeding sedimentary breccias, resembling the middle member of the Comondú Group. Our data confirm that rifting in the future Gulf of California initiated at ~19-18 Ma, concurrent with the focused eruption of predominantly intermediate-composition volcanism now exposed on both margins.

Geological Society of America Abstracts with Programs. Vol. 58, No. 3, 2026

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