San Quintín Volcanic Field

Today, the cones rest on over a kilometer of unconsolidated Plio-Quaternary sediment overlaid on the volcanic basement of the lower Cretaceous Alistos Formation.

[4] The ten volcanic complexes recognized in the San Quintín field include Media Luna and Woodford in a northern group; a southern group consisting of Basu, Riveroll, Kenton, Picacho Vizcaino, Sudoeste, and Ceniza; and the isolated complexes Monte Mazo and Isla San Martín.

[3] The Santillán and Barrera Line, an important tectonic boundary, is found about 16 km (9.9 mi) NE of the volcanic field.

On the other side lies the Stable Peninsula Province, an area mostly devoid of faulting (as opposed to the Gulf of California escarpment) and covered in pre-batholithic and batholithic crystalline rocks.

[6] The arrival of the Pacific-Farallon spreading center at the trench formed two triple junctions that migrated in opposite directions, northward and southward, along the coast.

[8] Over time, the direction of relative motion between these plates swung west, accommodated by extension in the protogulf of the Gulf of California.

[13] The ten volcanic complexes of San Quintín are all aligned N-S to NW-SE, parallel to an offshore fault, the Santillán and Barrera line, and the main escarpment of the Gulf of California.

[3] Following eruptions in the northern gulf area covered the San Quintin Volcanic Field in alkalic, diopside-rich basalts.

It has been proposed that the slab fully subducted in the relevant latitudes of the San Quintín field,[17][18] so that a "no-slab window" allowed the plate to directly access asthenospheric mantle.

Partial melting in the mantle, or the progressive exhaustion of incompatible elements in the source, led to a decrease in abundances of these volatiles as the field evolved.

[3] The primitive magmas differ from other reported intraplate-type mafic alkalic suites by having relatively high Al2O3 and Yb, as well as low ratios of La/Yb and CaO/Al2O3.

[21] Alternatively, more complicated models suggest that a shallow, active shear zone deformed the xenoliths and it was only later that the deeper, source magmas modified the chemical composition of the field.