Contribución a la geoquímica del complejo plutónico Papudo-Quintero, Chile central: implicancias petrogenéticas

Abstract

ABSTRACT. Contribution to the geochemistry of the Papudo-Ouintero Plutonic Complex, Central Chile: petrogenetic implications. The Papudo-Ouintero Plutonic Complex (CPPO) corresponds to a Middle-Upper Jurassic intrusive event developed in the Coastal Range of central Chile. According to previous works, the CPPO includes four units, which covera wide compositional range from gabbro to leucogranite, however the intermediate granitoids prevail. This study is based on geochemical results from the two largest units: Limache and Cachagua units. The first one consists of hornblende and biotite tonalites and granodiorites which exhibit oriented mafic inclusions, and minor leucogranites, aplites and pegmatites. The Cachagua unit includes dioritic varieties, minor granodiorites and aplitic dikes. Mafic inclusions are almost absent in this unit. Trace element results obtained from the two units, led to the following conclusions: a. the mafic inclusions and its granitoid host of the Limache unit represent mingling and/or mixing of genetically related magmas through fractional crystallization; b. the two units underwent fractional crystallization processes, in which plagioclase was the main fractionating phase. Hornblende fractionation did not play an important role in the origin of the mafic and intermediate plutonites in spite of being an ubiquitous phase; c. the leucogranites and aplites of the two units differ from !he coastal Upper Triassic-Lower Jurassic leucogranites (located to the north of the area), which are assumed to be formed in the crust. On the contrary, they may represent residual liquid after hornblende fractionation from intermediate magmas; d. the mafic rocks of the two units have a common origin, probably from the evolution of a mantle-derived parental magma.