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Medium-high grade igneous-metamorphic basement unit in Central Patagonia, Argentina at its relation with the Terra Australis Orogen
Encuentro; Metamorphic Studies Group?s 40th anniversary conference; 2021
During the Late Neoproterozoic to middle Paleozoic time span, the southwestern margin of Gondwana has been exposed to protracted subduction [1,2,3,4], which has been considered as part of the widespread Gondwanan Terra Australis Orogen (TAO) [2]. In southwestern Gondwana, the TAO comprises a series of accretionary systems which are associated with crustal extension and back-arc basin development [2]. This tectonic setting alternates with sporadic contractional episodes related with increased plate coupling, accretion of oceanic material, or collision ofallochthonous/para-autochthonous crustal blocks [1,2,3,4].In this context, the Patagonian continental block has been considered as a peri-Gondwanan block, accreted either in Early or Late Paleozoic times [5,6,7]. In recent years, compelling evidence points out to an Early Paleozoic accretion of the northern part of Patagonia [7,8], within the tectonic framework of TAO. However, the Middle to Late Paleozoic tectonic history of central and southern Patagonia, the tectonic setting of Gondwanide orogeny, and therefore the proper assessment of the culmination of TAO in this area are yet a matter of debate [9,10].In the past decades, a Middle-Late Paleozoic igneous-metamorphic belt was described in Central Patagonia[5,6], a key area for integrating central and southern Patagonia, and its precise location, crossing this area with a ~NNW-SSE structural trend, was defined by geophysical means [9]. This belt comprises a series of fault-controlled basement blocks, formed by medium-high grade metamorphic complexes and coeval magmatism [5,10,11]. Recently, the Lagunita Salada Igneous-Metamorphic Complex was defined in this area. The regional metamorphism of this complex attained upper amphibolite-lower granulite facies, constrained by Th-U-Pb EPMA monazite ages between ca- 379-320 My [12]. Based on dated syn- and post-tectonic granitoid intrusions in the area an isotopic system re-opening could not be discarded for the ~320 Ma isochron monazite model age. Moreover, a magmatic lull of ~20 My coeval or slightly posterior to the medium-high grade metamorphism [12], could present important implications for the tectonic regime for the the TAO in this area, previous to the syn- to postectonic Upper Carboniferous ? Early Permian magmatism andthe initiation of Gondwanide orogeny in southwestern Gondwana.