Geologic framework of Cretaceous plutons along a west-to-east transect in the southern Peninsular Ranges batholith, Baja California, Mexico: Insights from geochemical, isotopic, and geochronologic data

Cretaceous plutons of the Peninsular Ranges batholith (PRB) intruded two different host rock sequences in the central part of the Baja California peninsula, Mexico. The western sequence is the volcanic-volcaniclastic Alisitos oceanic arc, and the eastern lithologies are mainly metasedimentary pre-Mesozoic units. We analyze the ~116 Ma San Jerónimo (SJe) pluton in the PRB western zone and the Compostela (COM) and San Pedro (SP) plutons (~97 Ma and ~104 Ma, respectively) in the PRB eastern zone. The SJe pluton varies from pyroxene-hornblende gabbro to hornblende-biotite tonalite. Their rocks are subalkaline, calcic/calc-alkaline, and metaluminous, which are akin to island arc granite settings; and yield εNd_t values of +5.6 and +6.8, indicating a depleted mantle source without discernible crustal assimilation. The SJe pluton shows subparallel REE patterns (La_N/Yb_N = 0.5–4.4), with progressive enrichments in REE abundances in the tonalites, suggesting differentiation by fractional crystallization of a single magmatic system. Also, show low Sr/Y values (<20) and La/Yb (<10), suggesting a thin (~20 km) crust beneath the western zone of this Alisitos arc segment. The COM pluton varies from biotite tonalite and biotite-hornblende granodiorite. The SP pluton consists of biotite-muscovite granodiorite and biotite-muscovite granite. These rocks from COM and SP are subalkaline, magnesium, calcic/calc-alkaline, and mainly peraluminous. The eastern zone plutons yield εNd_t values from +4.2 to −2.3, indicating mantle-derived melts with the contribution of assimilated crustal material. Their strongly fractionated REE patterns (La_N/Yb_N = 8–38.3) are characteristic of evolved melts or magmas differentiated within the crust. The high Sr/Y (~90) and La/Yb (~21) further suggest thicker crustal zones (>45 km). Permeation features and parallelism between the metamorphic foliations of the prebatholithic rocks and the magmatic foliation of the plutons indicate a post-deformational emplacement of the mid-Late Cretaceous plutons of the southern PRB. Our data restricts the deformation event before ca. 100–105 Ma.