Processes involving soil CO_(2)dynamic in a sector of Chaco-Pampean plain,Argentina:An isotope geochemical approach

The magnitude and spatial variability of CO_(2)surface emissions and processes involving CO_(2)released to the atmosphere from the soils are relevant issues in the context of climate change.This work evaluated CO_(2)fluxes and^(13)C/^(12)C ratio of vegetation,organic matter,and soil gases from no disturbed soils of Chaco Pampean Plain(Argentina)with different soil properties and environmental conditions(PL and PA units).Soil organic decomposition from individual layers was accompanied byδ^(13)C of total organic carbon(δ^(13)C-TOC)values more enriched to depth.δ^(13)C-TOC values in the upper soil profile~ca.0–15 cm were like the plant community of this area(~−33 to−29‰)whileδ^(13)CTOC varied stronger bellow horizon A,till~−24‰.Bothδ^(13)C-TOC and soilδ^(13)C-CO_(2)were similar(~−24 to 26‰)at deeper horizons(~50–60 cm).Toward the superficial layers,δ^(13)C-TOC andδ^(13)C-CO_(2)showed more differences(till~4‰),due influence of the diffusion process.Horizon A layer(~0–20 cm)from both PL and PA units contained the most enrichedδ^(13)C-CO_(2)values(~−15–17‰)because atmospheric CO_(2)permeated the soil air.A simple two-component mixing model between sources(atmosphericδ^(13)C-CO_(2)and soil CO_(2))confirmed that process.Isotopically,CO_(2)fluxes reflected the biodegradation of C3 plants(source),diffusive transport,and CO_(2)exchange(atmosphere/soil).Soil moisture content appeared as a determining factor in the diffusion process and the magnitude of CO_(2)surface emissions(12–60 g·m^(−2)·d^(−1)).That condition was confirmed by CO_(2)diffusion coefficients estimated by air-filled porosity parameters and soil radon gradient model.

Coupling between fluids and rock deformation in the continental crust:Preface

1.Introduction Fluids are essential and widespread components of the Earth crust.They regulate the main process of mass and energy transport,conditioning the geochemical and geophysical evolution of the crust(Bredehoeft and Norton.1990)and,consequently,its properties and mechanical behavior.The coupling between fluids,rock deformation,and heat are crucial engines for plate tectonics,playing a leading role in the rheology and evolution of the lithosphere(e.g.Jamtveit et al.,2000;Kennedy and van Soest,2007;Thompson,2010;Miller.2013;Yardley and Bodnar,2014:Hirauchi et al.,2016:Menzies et al.,2016;Plümper et al.,2017;Vizán et al.,2017).

New insights into petrogenesis of Miocene magmatism associated with porphyry copper deposits of the Andean Pampean flat slab,Argentina

The Paramillos de Uspallata mining district located in the backarc region of the Pampean flat-slab segment(28°-33°S) features porphyry-type deposits genetically associated with Middle Miocene volcanics. This mineralizing magmatism comprising hydrothermally altered(sodic-calcic, potassic and phyllic alteration) subvolcanic and pyroclastic rocks of andesite-basaltic andesite and dacite-rhyolite composition with a typical arc signature, represents the eastward broadening of the Farellones arc by ~17 Ma. Its geochemistry also reveals a residual mineralogy of amphibole ± garnet with limited plagioclase fractionation resulting in an adakitic signal; however, according to the isotopic data collected in our study, the contributions of MASH(melting-assimilation-storage-homogenization) processes in the acquisition of this signal cannot be disregarded.Both the broadening of the Farellones arc and its residual mineralogy e typical of relatively deep magmatic chambers e are consistent with a slab shallowing and outcoming crustal thickening setting.This tectonic scenario could be interpreted as a result of an early effect of the Juan Fernandez Ridge collision that was further to the north by ~17 Ma. Our findings suggest that magmas were fertile for porphyry type deposits during the early stages of the slab shallowing.

Petrography and tectonic provenance of the Permian Tunas Formation:Implications on the paleotectonic setting during the ClaromecóForeland Basin evolution,southwestern Gondwana margin,Argentina

The Claromec o Basin is located at the south-western sector of the Buenos Aires province,Argentina.This basin is considered a foreland basin closely related to the evolution of the southwestern Gondwana margin.This contribution focuses on the provenance analysis of the Tunas Formation(Permian,Pillahuinc o Group),which represents the last filling stage for the Claromec o Foreland Basin.Petrographic and tectonic provenance analyses were performed in sandstones recovered from subsurface(PANG 0001 and PANG0003 exploration wells)and outcrops located close to the basin center(Gonzales Chaves locality).In the subsurface,the analyzed succession is composed of medium-to fine-grained sandstones interbedded with tuffs,mudrocks,carbonaceous mudrocks and coal beds.In outcrops,the succession is dominated by mediumto fine-grained sandstones interbedded with siltstones.Modal composition patterns are distributed into the recycled orogen and transitionally recycled to mixed fields.Petrographic analyses,in addition to provenance and sedimentological studies,confirm that sedimentary material was derived from a mixed source,which largely comes from the Sierras Australes fold and thrust belt,located towards the W-SW,where the sedimentary succession is interbedded with volcanic material.The Tunas Formation shows clear differences in its modal composition,paleocurrent direction and paleoenvironmental conditions with respect to the underlying units of the Pillahuinc o Group(Sauce Grande,Piedra Azul and Bonete formations).Source areas changed from cratonic to mixed fold belt/arc-derived material,suggesting variations in the Claromec o Basin configuration during the Late Paleozoic.Changes in the paleotectonic scenario during the deposition of the Tunas Formation have been interpreted as a consequence of a compressive post-collisional deformation event,the product of adjustment,accommodation and translation of terrains towards the equator during the Permian-Triassic to form Pangea.

The transition from backarc extension to Andean growth:Insights from geochronologic,sedimentologic,and structural studies of Mesozoic and Cenozoic sedimentary and volcanic rocks in south-central Chile(36°S)

Many studies propose a significant shift in the tectonic and paleogeographic evolution of the Andes in south-central Chile and Argentina during the Late Cretaceous.It has been proposed that the preceding Jurassic-Early Cretaceous extensional regime that resulted in a low-relief volcanic arc and the backarc Neuquén basin came to an end,giving way to shortening and Andean growth from the Late Cretaceous onward.Nevertheless,there are disagreements regarding the timing and nature of this transition to Andean orogenesis.To address these issues,we conducted geochronologic(U-Pb and^(40)Ar/&(39)Ar),sedimentologic,and structural studies on Mesozoic-Cenozoic sedimentary and volcanic rocks in the Río Maule area(Principal Cordillera,Chile,36°S).From our findings and prior analyses,we propose the following tectono-stratigraphic evolution of the region.(1)Marine deposition of the Tithonian-Hauterivian Baños del Flaco Formation took place in an extensional backarc basin.(2)After a~40 Myr hiatus,fluvial deposits of the Colimapu Formation and volcanic rocks of the Plan de los Yeuques Formation accumulated during the Cenomanian-Danian.Whereas the Colimapu Formation displays evidence of syndepositional shortening,the Plan de los Yeuques Formation exhibits synextensional growth strata.Contrary to other studies,our results suggest that the Chilean part of the Principal Cordillera was largely a zone of active deposition rather than an elevated fold-thrust belt during the Late Cretaceous.We propose that sedimentation occurred within a series of relatively stable intermontane subbasins generated by shortening,followed by extension.(3)After a~20 Myr hiatus,middle Eocene to early Miocene(Lutetian-Aquitanian)accumulation of a thick succession of andesitic lavas and minor clastic sediments of the Abanico Formation occurred in an intraarc extensional basin.(4)Finally,major shortening and uplift of previously deposited Mesozoic-Cenozoic rocks took place throughout the Neogene.This phase constituted the primary contractional deformation in the Andes of south-central Chile and Argentina.In terms of the transition to early Andean deformation,we propose that structural deformation did not generate a major,regional-scale fold-thrust belt during the late Albian-Santonian.Modest extension,tectonic quiescence,or low-magnitude shortening seem to have dominated during the early to middle Cenozoic.