Evolucion del basamento paleozoico en el area de Punta Claditas, Region de Coquimbo, Chile (31-32°S)

Abstract

RESUMEN. Las unidades paleozoicas que afloran en la costa de Chile central son: el Complejo Metamorfico del Choapa (CMC) y las formaciores Puerto Manso y Huentelauquen. El CMC, cuyo protolito consistio en grauwacas, arcosas y basaltos oceanicos, esta constituido por cinco unidades de litologia e historia deformacional diversa, que afloran generalmente separadas por zonas de falla. Todas estas unidades exhiben una intensa deformacion polifasica. En algunos casos, se pueden correlacionar estructuras generadas en un determinado evento de deformacion de una unidad a otra. Asi, por ejemplo, el cuarto evento de deformacion de los Esquistos Grises de Punta Claditas se correlaciona con el evento que genero la foliacion S2 de los esquistos anfibolicos, datada en 359±36 Ma (Devonico Medio). El CMC sufrio sucesivos episodios de metamorfismo regional con gradientes P/T bajos a medios. La Formacion Puerto Manso, devonica a carbonifera irferior, es turbiditica, con dos deformaciones. La Formacion Huentelauquen, carbonifera superior a permica, es pelitica, con marcado clivaje de pizarra. Las unidades estudiadas se originaron en un complejo de subduccion desarrollado entre antes del Devonico Medio y el Permico, en el margen de Gondwana. Con el desarrollo del prisma y la deformacion de los depositos se habrian generado una dorsal de arco externo y una cuenca de antearco, que recibio a los sedimentos provenientes del continente y de la dorsal. Las Metaturbiditas de Agua Dulce y la Formacion Puerto Manso corresponderian a niveles menos profundos de la dorsal o de la cuenca, sucesivamente mas jovenes y menos deformados y metamorfizados. La Formacion Huentelauquen representa los depositos con que se cierra la evolucion del prisma. ABSTRACT. Evolution of the Paleozoic basement at Punta Claditas, Coquimbo Region, Chile (31-32°S). The studied units are the remnants of a Paleozoic accretionary prism exposed along the central Chilean coast. The Choapa Metamorphic Complex (CMC) and the Puerto Manso and Huentelauquen formations have been recognized. The CMC consists of intensely deformed quartz-mica schists and phyllites, amphibole schists and epimetamorphic rocks, generally bounded by fault zones. AII these units have a poliphase deformation, and in some cases a correlation can be established from one unit to another. For example, the fourth deformation event recognized in the Punta Claditas Gray Schists is correlated to the event that generated the S2 foliation of the amphibole schists, which was dated at 359+/-36 Ma (Middle Devonian). These rocks underwent several episodes of regional metamorphism, with low to middle P/T gradients. The protolith of the quartz-mica units are graywackes and arkoses, deposited in a submarine fan, while the protolith of the amphibole schists are oceanic basalts. The Puerto Manso Formation is a turbiditic series (Devonian to Lower Carboniferous), showing two deformations. The Huentelauquen Formation is a pelitic unit (Upper Carboniferous to Permian), with slaty cleavage. AII these units were originated in a subduction complex developed since before the Middle Devonian to the Permian, along the margin of Gondwana. With the development of the accretionary prism and the deformation of these deposits, an outer arc ridge and a forearc basin to the East of it might have formed. This basin received the sediments originated on the continent and the emerged ridge. The Agua Dulce Metaturbidites and the Puerto Manso Formation could represent increasingly shallower, younger and less deformed and metamorphosed levels of the ridge or the basin. The Huentelauquen Formation represents the end stadium of the evolution of the prism.