Origin of the Río Verde Batholith, Southern Mexico, as Inferred from its Geochemical Characteristics

Abstract

The Rio Verde batholith, in southern Mexico, represents a pulse of voluminous magmatism occurring over a relatively short time span, followed by uplift and erosion. The batholith consists predominantly of calc-alkaline rocks ranging from tonalites to granites with biotite and hornblende as the main mafic minerals. Intrusion ages for the three recognized plutons range from 29.9 ± 1.1 to 23.5 ± 0.6 Ma, with a younging trend toward the east. Isotopically, these granitoids are characterized by eNd values between −3.0 and +0.9 and 87Sr/86Sr initial ratios ranging from 0.70419 to 0.70532. The small differences between hornblende and biotite ages suggest rapid cooling rates. Geobarometric determinations performed on hornblendes yield a pressure of 5.3 ± 0.6 kbar, which corresponds to a depth of emplacement of 19.7 ± 2.2 km. Using trace-element abundances as well as the Sr- and Nd-isotopic data, we modeled possible magmatic processes of partial fusion, fractional crystallization, and assimilation assuming differe...