The Early Palaeozoic high-grade metamorphism at the active continental margin of West Gondwana in the Andes (NW Argentina/N Chile)

Abstract

The evolution of the Early Palaeozoic orogen of West Gondwana in the Cambrian to Ordovician basement of the Andes between *18°and 32°S is investigated for pressure and temperature conditions and age of metamorphism. It is characterized by mid-crust temperatures commonly above the wet granite solidus (*650°C). Widespread felsic migmatite and rare granulite formed at pressures of ca 0.5-0.7 GPa, locally 1.0 GPa. These rocks represent the deepest exhumed sections of the Early Palaeozoic crust. High pressure-low temperature rocks are absent. The crystallization ages, compiled from the literature in combination with new data, for near peak metamorphic conditions of these high-grade metamorphic rocks in NW Argentina and N Chile are *530-500 Ma and *470-420 Ma. Both age groups are spatially overlapping. Radiogenic isotope signatures (Sr, Nd, Pb) are used to characterize the Early Palaeozoic basement. The Pb and Sr isotope compositions of the Early Palaeozoic basement indicate mixing arrays between pre-Palaeozoic unradiogenic and radiogenic crust. Crustal residence ages (Sm-Nd T DM ) indicate a prominent event of crust formation around *2 Ga, which is known continent-wide. This material was recycled during Midproterozoic and Early Palaeozoic orogenies without prominent additions of new crust present in the isotope record, i.e. accretion of compositional exotic material is absent.

0.3 byr of drainage stability along the Palaeozoic palaeo-Pacific Gondwana margin; a detrital zircon study

“…The age peaks correlate with the timing for Famatinian activity (Table 3), because both peak magmatic activity and medium-to high-grade metamorphism were reached at 490-460 Ma in the Puna region of northwesternmost Argentina (Lucassen et al 2011;Hongn et al 2014), in the Sierras Pampeanas further south ( Fig. 1; e.g.…”

“…Niemeyer 1989). Metamorphism took place c. 470-420 Ma (Middle to Late Ordovician time) in northern Chile and northwestern Argentina (Lucassen et al 2011). In this study, deposits of the foreland basin are represented by the Middle Ordovician Lower Turbidite System of the Puna Turbidite System in northwestern Argentina (Bahlburg 1990;Bahlburg et al 1990), which is mainly composed of marine, turbiditic sandstone and pelite (Bahlburg 1990).…”

Low‐P melting of metapelitic rocks and the role of H2O: Insights from phase equilibria modelling

“…Therefore, the western margin of Gondwana could have been affected by successive events of medium to high-grade metamorphism during the Early Palaeozoic (Lucassen & Becchio, 2003). However, Pampean and Famatinian metamorphic and magma crystallization ages seem to be continuous and occur in the same areas, especially in the northwestern Argentina and north of Chile (Lucassen & Becchio, 2003;Lucassen, Becchio, & Franz, 2011;Lucassen et al, 2000;Pankhurst, Rapela, & Fanning, 2000).…”

Cenozoic foreland basin system in the central Andes of northwestern Argentina: Implications for Andean geodynamics and modes of deformation

“…First‐cycle sources of detrital zircons with early Paleozoic ages are abundant in felsic rocks of the Famatina magmatic belt (sample CPLoire, Figure 12) and the Santa Rosa de Tastil granite [ Pankhurst et al , 1998; Kirschbaum et al , 2006; Hongn and Riller , 2007; Ramos , 2009; Hongn et al , 2010; Lucassen et al , 2011] of the Cordillera Oriental. Detrital zircons with ages in all three of the major populations recovered from the Cenozoic samples (∼500 Ma, 555–994 Ma, ∼1050 Ma) are present in Cambrian, Ordovician, and Cretaceous samples from the eastern Puna and Cordillera Oriental (Figure 12).…”