Análisis estadístico de poblaciones de circones detríticos en rocas metasedimentarias del basamento continental pre-jurásico del sur de la Patagonia

Abstract

The record of detrital zircons in pre-Jurassic metasedimentary complexes from southern Patagonia provided novel record to constrain the provenance sources of sediments and the maximum depositional ages of turbiditic successions that spread along the western margin of Gondwana (Hervé et al., 2003, 2010; Augustsson and Bahlburg 2003a. 2006, 2008; Castillo et al., 2015). The pre-Jurassic continental basement of southern Patagonian Andes (Fig.1A) is constituted by the Eastern Andean Metamorphic Complex (EAMC) and the Cordillera Darwin Metamorphic Complex (CDMC), which are located east and north, respectively, of the Patagonian batholiths. Those units located west of the batholiths are the Chonos Metamorphic Complex (CMC) and the Duque de York Complex (DYC). On the basis of detrital zircon analyses (Hervé et al., 2003; Augustsson et al., 2003a; Augustsson et al., 2008) the EAMC includes sedimentary components deposited between the late Devonian and early Carboniferous, as well as younger turbidites deposited during the Permian and Triassic. Older successions show Ordovician, Devonian and Early Carboniferous peaks of detrital zircons and the younger rocks show peaks of Permian zircons with variable proportions of Carboniferous, Devonian, Ordovician and Cambrian grains. The detrital zircon spectra the CDMC is characterized by Mississippian peaks (of ca. 330-340 Ma) with a variable proportion of Devonian, Ordovician, Cambrian, and Neo-to Meso-proterozoic components (Hervé et al., 2010). Detrital zircons ages in the CMC show characteristic peaks of Upper Triassic with variable proportions of Permian, Carboniferous, Devonian and Cambrian components (Hervé et al., 2003). Detrital zircon age data from rocks of the DYC shows a dominant peak of Permian zircons (ca. 270-290 Ma) (Hervé et al., 2003; Sepúlveda et al., 2010; Castillo et al., 2015). These rocks also comprise subordinate Carboniferous and Ordovician zircons populations, the latter becoming an important contribution in the southernmost outcrops of this unit. The statistical analysis of detrital zircon age distribution patterns is a useful tool to establish the tectonic setting of the basin in which the sediments were deposited (Cawood et al. 2012). This study performed a statistical analyzed of detrital zircons of the above mentioned tectono-metamorphic units. The Cumulative Distribution Function (CDF) and the relation between the crystallization vs. depositional ages of detrital zircons from Paleozoic metamorphic complexes are shown in Figure 1. Based on these results is possible to discriminate between different geological settings (cf. Cawood et al., 2012) and consider the crystallization age (CA) for a detrital zircon grain and the depositional age (DA), is important mentioned that the depositional age is different for each metasedimentary complex, the maximum depositional for EAMC is 364 Ma, and minimum depositional age is 250 Ma; CMC is 213 Ma; DYC to close 234 Ma (Thomson and Hervé; Hervé et al., 2008, 2010).