The Puesto Piris Formation: Evidence of basin-development in the North Patagonian Massif during crustal extension associated with Gondwana breakup

The Marifil Volcanic Complex, exposed in the eastern North Patagonian Massif, Argentina, includes up to 550 m of red conglomerates, sandstones, black siltstones, limestones, and reworked tuff of the Puesto Piris Formation. The basal part of this unit, which was deposited in high-gradient topographic relief, is composed of conglomerates and sandstones with thin layers of reworked tuffs. The lithofacies associations of the basal part indicate that the depositional mechanisms were mantled and gravitational flows.The middle part of the unit consists of fine sandstones, limestones, and black siltstones that were deposited in low-energy fluvial and lacustrine environments. The outcrops are located along the NEe SW direction and the major thickest units represented by limestones and siltstones, occur near the southeastern border of this NEeS W depocenter. Since the rhyolitic and trachytic lava flows and tuffs of the Marifil Volcanic Complex are interbedded with the sedimentary sequences of the Puesto Piris Formation,both units are coeval. Zircon Ue Pb age was obtained for a trachytic lava flow(193.4 ±3.1 Ma) suggesting that sedimentation and volcanism are Sinemurian. This extensional episode was recorded in the eastern,western, and southwestern sectors of the North Patagonian Massif, and is possibly associated with the Gondwana supercontinent breakup.

Pennsylvanian glacimarine sedimentation in the Cushamen Formation,western North Patagonian Massif

The metasedimentary sequence of the Cushamen Formation in the western North Patagonian Massif is540 m thick and comprises six sedimentary lithofacies associations related to a glacimarine environment.Four of these lithofacies represent distal glacimarine environments, whereas another one was deposited in proximal glacimarine environments, and the last includes subglacial environments. The organization and configuration of these lithofacies associations represent the advance and retreat of the glacier masses. The maximum glacial advance is correlatable with the G2 glacial interval of the Pennsylvanian Pampa de Tepuel, Las Salinas and Valley Chico, formations of the Extraandean Chubut, and the southern part of Neuquen Cordillera. Contemporaneously, in southern Chile there are marine and glacimarine sediments. The chronostratigraphic relationships between the Silurian to Permian units allow five paleogeographic stages to be distinguished. The middle Silurian-late Devonian igneous rocks represent the first magmatic stage. The second stage, which is transitional to the first, is represented by a marine basin that includes the late Devonian-early Carboniferous Esquel and Rio Pescado formations and the Llanquihue Complex. The third stage(early-late Carboniferous) includes granitoids of the second magmatic event that partially overlapped the first magmatic igneous belt. The fourth stage belongs to the late Carboniferous sedimentation of the Cushamen and equivalent formations. The extended early Permian magmatism was the last Paleozoic event in the studied area.

Characterization of Arroyo Verde Epithermal Deposit:Paragenesis,Mineral Geochemistry,Geochronology and Fluid Inclusions in Lower Chon Aike Volcanism,Argentina

Arroyo Verde epithermal deposit,in the North Patagonia region of Argentina,is located within the Lower Chon Aike volcanism and is developed between 192.6±2.5 Ma(mineralization host rock)and 189.5±2.6 Ma(overlying lava).Marifil volcanic complex is the host rock for these veins,veinlets and breccias.This particular small deposit has developed low to intermediate sulphidation characteristics,with gangue mineral textures associated with several ore minerals.Electron probe microanalysis determines electrum,silver minerals such as acanthite,and tetrahedrite,related Ag-Cu minerals like jalpaite,mckinstryite,stromeyerite,and base metals like chalcopyrite,sphalerite,galena and pyrite.Fluid inclusions in quartz of two out of five events indicate that these Low Jurassic veins were formed due to subtle boiling and dilution mechanisms and by low-salinity(3.4 wt.%to 6.7 wt.%NaCl Eq)magmatic-hydrothermal fluid at 225 to 310℃.The fluid inclusion measurements that indicate boiling(Event 3)were plotted,and based on this data,we interpret that the Arroyo Verde deposit has been eroded between 550 and 700 m.This particular character has not been previously recorded for other sectors of the eastern north Patagonian region.