DISTINCTIVE CHARACTER AND KEY ATTRIBUTES OF THE PENINSULAR RANGES BATHOLITH

The Peninsular Ranges batholith (PRB) of southern and Baja California is a unique geologic province with distinctive lithologic, geochemical, and provenance characteristics. The clastic Paleozoic to earliest Cretaceous framework rocks of the PRB exhibit three distinct Proterozoic-Early Paleozoic provenance signatures: SW Laurentian, NW Laurentian, and Gondwanan. The PRB features a belt of middle Jurassic granitoids with mostly S-type affinities that were intruded into the continental slope deposits floored by Triassic-Jurassic arc-ophiolitic basement. The Jurassic plutons extend the legnth of the batholith and occur well outboard of the better known Jurassic arc that was established at the same time throughout SE California, Azizona, and Mainland Mexico. The western PRB is defined by compositionally diverse and isotopically primitive plutons and volcanic rocks emplaced mainly between 130-100 Ma. However, the most distinctive character of the PRB is imparted by the eastern zone La Posta tonalite-trondhjemite-granodiorite (TTG) plutonic suite. Emplacement of the La Posta TTG represented a major eastern relocation of the batholith and coincided with major underplating in the offshore accretionary complex. The La Posta TTG account for >50% of the intrusive volume of the >1100 km PRB and represent a flux of 100-200 km3/km strike legnth/m.y. between 98-92 Ma. Denudation of the PRB occured in two primary intervals (Cenomanian-Turunian and Late Campanian-early Paleocene). The second stage was triggered 10-15 m.y after emplacement of the La Posta TTG by initiation of Late Cretaceous flat-slab subduction. In the northern PRB, erosion depths between 12-20 km were attained synchronously with west-directed emplacement of thrust sheets along the eastern margin. Cenomanian-Paleocene forearc strata are wholly PRB in affinity. By the Eocene however, a regional, topographically subdued erosion surface had developed throughout the PRB and was traversed by extraregional river systems that extended as far east as the Mogollon Highlands and western Mainland Mexico. Final definition of the PRB provenance occured during Late Miocene-Pliocene transtension and dextral shearing that ultimately produced the Baja California microplate and nascent oceanic crust within the Gulf of California.