Geochemistry and geochronology of the shallow-level La Esperanza magmatic system (Permian-Triassic), Northern Patagonia

Abstract

The La Esperanza plutonic-volcanic complex is the largest Late Paleozoic-Early Triassic composite magmatic system of northern Patagonia. This paper reports new SHRIMP U-Pb zircon ages and K-Ar muscovite dating as well as whole-rock geochemical data for selected units. In addition, we present some new and reprocessed whole-rock Sr isotopic compositions. On the basis of the new and published data, three compositionally and isotopically distinct high-K magnesian calc-alkaline series were distinguished. Two of these are characterized by high Ba-Sr: (i) biotite and muscovite bearing rhyolites and granites (265 ± 2 Ma; 260 ± 2 Ma) and (ii) metaluminous amphibole-biotite bearing granodiorites (273 ± 2 Ma), monzogranites (255 ± 2 Ma), dacites (253 ± 2 Ma), and slightly peraluminous granites (dated herein as 251 ± 2 Ma). There is also a low Ba-Sr series of high-silica metaluminous rocks (granites and acid dike swarms; 250 ± 2 Ma and ≈244 ± 2 Ma). Geochemistry coupled with geochronology revealed a pulsatory multi-sourced open magmatic system with mafic magma replenishment and reactivation of crystal mushes that occurred before upward migration to upper crustal levels. Mafic magmas alternated with crust-derived magmas incrementally assembled in subvolcanic levels over 30 Ma. Zircon crystallization and mica cooling ages in the granite units allowed detection of two magmatic lulls, between 270 and 265 Ma and between 260 and 255 Ma. Both episodes coincide with a period of exhumation in upper crustal levels. The new temporal and geochemical constraints allow correlation of the La Esperanza plutonic-volcanic complex with the Los Menucos Group (258-248 Ma), encompassing a volume of magmatism comparable to a moderately sized large igneous silicic province. These mid-to-late Permian to Middle Triassic rocks record the transition between subduction-related magmatism (> 273 Ma) and post-orogenic extensional magmatism (< 250 Ma) in the Gondwana margin. Even though this magmatism would be coeval with the proposed collision of the Patagonia terrane, no expected syn-collisional magmatism or associated deformation were found in upper crustal levels. However, the different nature and melting conditions of the inferred sources of the magmas that crystallized before 270 Ma, between 265 and 260 Ma, and from 255 to 245 Ma, suggest that the La Esperanza plutonic-volcanic complex was assembled during a 30 Ma period of major plate reorganization.

Catastrophic slab loss in southwestern Pangea preserved in the mantle and igneous record

“…S5 and S 6 ). In general, these findings are not compatible with a subduction-related setting for the totality or part of the Choiyoi Magmatic Province 3 – 5 , 8 , 20 – 26 , 29 – 31 . The recognition of a Permian-Triassic slab beneath southern South America and the Antarctic Peninsula 39 , 43 reinforces a subduction-related origin as suggested for the Permian magmatism in that area 18 , 37 (Fig.…”

“…Underplating of these melts would have also prompted melting of a hydrous mafic lower crust inherited from previous subduction stages 3 , 22 , 75 and magma hybridization 5 , 20 , 29 , 34 , 35 . Incorporation of older continental crust and arc basement is evident by the presence of inherited zircons (e.g., Andean region 420–1440 Ma 35 ; North Patagonian massif region 320–1000 Ma 16 ).…”

“…These works have also attributed variable roles to the gravitational collapse of the Early Permian fold and thrust belts along the southwestern Pangea margin 1 , 2 , 6 , 8 , 13 – 15 , 30 , and the concomitant NE–SW tensional stresses linked to the prelude of the Pangea breakup 6 , 13 , 14 , 22 . Most recent studies have favored a subduction-related setting for part or the totality of the Choiyoi Magmatic Province based on the documentation of a geochemical magmatic arc signature that is locally diluted at the top of this SLIP showing characteristics of a within-plate or post-orogenic environment (e.g., 3 – 5 , 8 , 20 , 21 , 23 , 25 , 26 , 29 , 31 , 32 ). In the intracratonic magmatic belt of this igneous province, this geochemical change is not documented, and a clear within-plate affinity is dominant 33 , 34 (Fig.…”

Geochemistry of the (meta-)mafic rocks from the Gonzalito mining district, northern Patagonia

“…1), or a continuation of the Ross-Delamerian Orogen of Antarctica (González et al 2018). The NB manifests a protracted orogenic evolution from subduction related-arc-marginal basin and magmatism through crustal extension and metamorphism (540-470 Ma) (González et al 2018;Pankhurst et al 2014Pankhurst et al , 2006Rapalini et al 2013Rapalini et al , 2010 coeval with bimodal intrusive magmatism (490-450 Ma) (Gozálvez, 2009;López de Luchi et al 2014;Martínez Dopico et al 2017a), followed by uplift and development of foreland basins (450-360 Ma) (Rustán et al 2013;Uriz et al 2011) and widespread intracontinental magmatism in the context of a Permo-Triassic Large Igneous Province (280-240 Ma) (Luppo et al 2018;Martínez Dopico et al 2019;Rapela and Caminos 1987) (Fig. 1).…”