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The Early Cretaceous Ramona plutonic complex is an elliptical-in-plan structure that intruded the mid- to upper crust of the western zone of the Peninsular Ranges batholith. The complex is composed of a dozen concentrically arranged silicic to intermediate plutons with minor gabbro. Lithologically, these plutons represent six regional plutonic suites, each of which consists of multiple plutons in this part of the batholith. Seven new U-Pb zircon ages indicate that plutons are younger toward the center of the complex, from an age possibly as old as ca. 115 Ma to ca. 101 Ma. The composition of the Ramona plutonic complex and a magmatic history conceivably as long as ~14 m.y. indicate that it was constructed as a series of intrusive pulses.

Inward from the margin of the Ramona plutonic complex, plutons vary from leucogranodiorite and leucomonzogranite to tonalite–quartz gabbro. Amphibolite-facies country rocks and Middle Jurassic metagranite comprise screens within the complex. External contacts with surrounding country rocks, internal plutonic contacts, and magmatic and metamorphic foliations dip steeply (~60°–90°) both inward and outward. Emplacement mechanisms included forceful intrusion, magmatic wedging or diking, stoping, magma mingling, and downward ductile flow of country rocks. Although emplacement of the major part of the Ramona plutonic complex appears to have postdated western zone volcanic activity (ca. 138–119 Ma), the occurrence within the complex of a metavolcanic inclusion with a zircon U-Pb age of 119 Ma suggests that early intrusions in the area may have fed a preexisting shallow subsidence system.

The Ramona plutonic complex intruded and deformed a suture zone that extends for ~800 km along the axis of the batholith. Suturing occurred during a period of contraction along the continental margin between ca. 129 and 101 Ma that was accompanied by (1) accretion of a Late Jurassic fringing volcanic arc and the inception of the overlying Early Cretaceous Santiago Peak volcanic arc and (2) closure of a Middle Jurassic–Early Cretaceous backarc basin. Although plutons of the Ramona plutonic complex show only minor evidence of ductile deformation, pluton ages and concordance of structures of the complex with those in surrounding amphibolite-facies country rocks indicate that the intrusive sequence was emplaced during regional metamorphism.

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