34-10 High-resolution geologic mapping and structural analysis of the southern sector of the Mencenares Volcanic Complex, Loreto Basin, Baja California Sur, Mexico

Session: Recent Advances in the Gulf of California Oblique Rift: Offshore and Onshore Studies // Avances Recientes en el Rift Oblicuo del Golfo de California: Estudios Marinos y Terrestres (Posters)

Poster Booth No.: 10

Presenting Author:

Orestes de la Rosa Mora

Authors:

de la Rosa Mora, Orestes Antonio¹, Boijseauneau López, Mario Emmanuel², Tapia Flores, Daniel³, Camacho Ascanio, Miguel⁴, del Ángel Hernández, Víctor Manuel⁵

(1) UNAM, Instituto de Geología, CD. MX., Mexico, (2) UNAM, Escuela Nacional de Estudios Superiores Morelia, Morelia, Michoacán, Mexico, (3) UNAM, Instituto de Geofísica, CDMX, Mexico, (4) UNAM, Instituto de Geofísica, CDMX, Mexico, (5) UNAM, Instituto de Geofísica, CDMX, Mexico,

Abstract:

The northern margin of San Juan Creek, south of the Mencenares Volcanic Complex (Cerro Mencenares), preserves an exceptional record of volcanic and volcaniclastic rocks interbedded with Loreto Basin infill. This study presents an integrated analysis combining high-resolution geologic mapping and field-based structural data with satellite gravimetry (Bouguer anomaly). The Bouguer anomaly patterns reveal contrasting density domains across the plain, allowing for the differentiation of structural provinces, analysis of fault continuity, and verification of large-scale fault cross-cutting relationships.

Our mapping refines the lithological contacts and structural framework of key Plio–Pleistocene volcanic units, as well as Pleistocene coastal deposits and terraces. Stratigraphic contacts in the region are complex, characterized by both erosional unconformities and subsequent faulting. Notably, floodplain deposits contain shell-rich fossiliferous carbonate beds interbedded with volcanic material along the San Juan Creek bed. This succession highlights the close coupling between coastal sedimentary environments and coeval volcanism. Furthermore, the current elevation of these shallow-to-transitional deposits indicates significant post-depositional uplift.

Structurally, the volcanic field is controlled by N–S-trending extensional faults subparallel to the Sierra de la Giganta escarpment, which later reactivated as lateral faults (both sinistral and dextral). In the southern sector of the complex, an E–W-trending extensional fault system truncates the earlier N–S structures. We attribute this later system to the development of a Pleistocene graben south of the Mencenares Volcanic Complex, signaling a transition to post-volcanic, N–S-directed extension.

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

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