Magmatism and tectonics in continental Chiloé, Chile (42°–42°30′S)

Pankhurst, R.J.; Hervé, F.; Rojas, L.; Cembrano, J.. 1992 Magmatism and tectonics in continental Chiloé, Chile (42°–42°30′S). Tectonophysics, 205 (1-3). 283-294. 10.1016/0040-1951(92)90431-5

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Official URL: http://dx.doi.org/10.1016/0040-1951(92)90431-5

Abstract/Summary

The Chiloé-Chonos region seems to preserve the oldest depositional events in the fore-arc accretionary complex of the Southeast Pacific margin. There are isolated occurrences of low-grade metamorphic rocks, including slates with a Devonian trilobite fauna and schists that give Rb-Sr evidence of a ca. 290 Ma metamorphism. Pillow basalts and ultramafic rocks may represent parts of the Pan-Thalassic ocean floor on which the Palaeozoic sediments were laid down. Emergence of a magmatic arc is indicated by Jurassic to Early Cretaceous volcanogenic and marine deposits. During the mid-Cretaceous climax of plutonic activity, these were intruded by monzogranites, which here constitute the eastern portion of the North Patagonian batholith. They give Rb-Sr isochron ages of 120-100 Ma (Barremian-Albian). Initial 87Sr/86Sr ratios of 0.7040–0.7045, and ϵNdt values of +0.5 to +1.5, indicate a simple petrogenesis with a mantle source. The western part of the batholith is petrologically more primitive, being composed predominantly of tonalite, diorite and gabbro, and initial 87Sr/86Sr ratios are more variable. Late Cenozoic movement of the Liquiñe-Ofqui fault zone (LOFZ) generated deep pull-apart basins to the west of the uplifted batholith/basement complex. These were filled by thick marine sequences of volcanogenic debris, indicating the wide extent of a mainly rhyolitic volcanic field during Miocene times. Pliocene tonalite and granodiorite plutons (dated by a Rb-Sr whole-rock isochron at 4.7 ± 0.5 Ma) and Holocene andesite-basalt stratovolcanoes are located along the LOFZ. The latter feature has thus been a major influence on the tectonic evolution of the area. There is no evidence for major post-Palaeozoic compression or crustal shortening.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	10.1016/0040-1951(92)90431-5
ISSN:	00401951
NORA Subject Terms:	Earth Sciences
Date made live:	02 Jan 2018 14:31 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/518837

Item Type:

Publication - Article

Digital Object Identifier (DOI):

10.1016/0040-1951(92)90431-5

ISSN:

00401951

NORA Subject Terms:

Earth Sciences

Date made live:

02 Jan 2018 14:31 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/518837