Authors: R. Gordon Gastil, Richard P. Phelps, and Edwin C. Allison
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The prebatholithic terrane of Baja California is represented by a western belt of rocks like those of the Franciscan assemblage, a belt of Mesozoic volcanic-volcaniclastic rocks, a belt of Mesozoic(?) slate and metasandstone, and, along the Gulf of California, Paleozoic rocks of various types. The volcanic-volcaniclastic rocks are, in part, contemporaneous with batholithic emplacement. The Mesozoic thermal event that produced regional metamorphism and the emplacement of batholithic rocks can be described in terms of four metamorphic zones: (1) essentially unmetamorphosed rocks, (2) slate to phyllitic rocks, (3) schist and amphibolite, and (4) rocks in which the premetamorphic fabric has been entirely destroyed. Most of the discrete plutons are found in zone 3; zone 4 includes generalized metamorphic-plutonic rocks that have been deep in the crust for a prolonged time. The granitic exposures are made up of tonalite (73 percent), granodiorite (23 percent), and gabbro (2 percent). The plutons of largest diameters are formed of tonalite; plutons of smallest diameters, of gabbro and granite. Gabbro is common in the western half of the batholithic belt and rare in the eastern half. No systematic increase in ( K2O + Na2 0 ) / SiO2 is recognized across the peninsula…
Published: 2/01/1975
ISBN Number: 0-8137-1140-1
Pages: 170
Product Category: Memoirs