Cap rock efficiency of geothermal systems in fold-and-thrust belts:evidence from paleo-thermal and structural analyses in Rosario de La Frontera geothermal area (NW Argentina)

Cap rock characterization of geothermal systems is often neglected despite fracturing may reduce its efficiency and favours fluid migration. We investigated the siliciclastic cap rock of Rosario de La Frontera geothermal system (NW Argentina) in order to assess its quality as a function of fracture patterns and related thermal alteration. Paleothermal investigations (XRD on fine-grained fraction of sediments, organic matter optical analysis and fluid inclusions on veins) and 1D thermal modelling allowed us to distinguish the thermal fingerprint associated to sedimentary burial from that related to fluid migration. The geothermal system is hosted in a Neogene N-S anticline dissected by high angle NNW- and ENE-striking faults. Its cap rock can be grouped into two quality categories: ● rocks acting as good insulators deformed by NNW–SSE and E–W shear fractures, NNE-SSW gypsum- and N-S striking calcite-filled veins formed during the initial stage of anticline growth. Maximum paleo-temperatures (<60°C) were experienced during deposition to folding phases. ● rocks acting as bad insulators deformed by NNW-SSE fault planes and NNW- and WNW-striking sets of fractures associated to late transpressive kinematics. Maximum paleo-temperatures higher than about 115°C are linked to fluid migration from the reservoir to surface (with a reservoir top at maximum depths of 2.5 km) along fault damage zones. This multi-method approach turn out to be particularly useful to trace the main pathways of hot fluids and can be applied in blind geothermal systems where either subsurface data are scarce or surface thermal anomalies are lacking

Structural characterization and K–Ar illite dating of reactivated, complex and heterogeneous fault zones: lessons from the Zuccale Fault, Northern Apennines

We studied the Zuccale Fault (ZF) on Elba, part of the Northern Apennines, to unravel the complex deformation history that is responsible for the remarkable architectural complexity of the fault. The ZF is characterized by a patchwork of at least six distinct, now tightly juxtaposed brittle structural facies (BSF), i.e. volumes of deformed rock characterized by a given fault rock type, texture, colour, composition, and age of formation. ZF fault rocks vary from massive cataclasite to foliated ultracataclasite, from clay-rich gouge to highly sheared talc phyllonite. Understanding the current spatial juxtaposition of these BSFs requires tight constraints on their age of formation during the ZF lifespan to integrate current fault geometries and characteristics over the time dimension of faulting. We present new K–Ar gouge dates obtained from three samples from two different BSFs. Two top-to-the-east foliated gouge and talc phyllonite samples document faulting in the Aquitanian (ca. 22 Ma), constraining east-vergent shearing along the ZF already in the earliest Miocene. A third sample constrains later faulting along the exclusively brittle, flat-lying principal slip surface t

Early stages of metal corrosion in coastal archaeological sites. Effects of chemical composition in silver and copper alloys

In this study, metal disks with different chemical composition (two Ag-based alloys and three Cu-based alloys) were buried in the soil of coastal archaeological sites for a period of 15 years. The aim was to naturally induce the growth of corrosion patinas to obtain a deeper insight into the role of alloying elements in the formation of the patinas and into the degradation mechanisms occurring in the very early stages of burial. To reach the aim, the morphological, compositional and structural features of the patinas grown over 15 years were extensively characterized by optical microscopy, field emission scanning electron microscopy coupled with energy dispersive spectrometry, X-ray diffraction and micro-Raman spectroscopy. Results showed that the Cu amount in Ag-based alloys strongly affected the final appearance, as well as the composition and structure of the patinas. Corrosion mechanisms typical of archaeological finds, such as the selective dissolution of Cu, Pb and Zn and internal oxidation of Sn, occurred in the Cu-based alloys, even if areas enriched in Zn and Pb compounds were also detected and attributed to an early stage of degradation. In addition, some unusual and rare compounds were detected in the patinas developed on the Cu-based disks

A strength inversion origin for non-volcanic tremor

Non-volcanic tremor is a particularly enigmatic form of seismic activity. In its most studied subduction zone setting, tremor typically occurs within the plate interface at or near the shallow and deep edges of the interseismically locked zone. Detailed seismic observations have shown that tremor is composed of repeating small low-frequency earthquakes, often accompanied by very-low-frequency earthquakes, all involving shear failure and slip. However, low-frequency earthquakes and very-low-frequency earthquakes within each cluster show nearly constant source durations for all observed magnitudes, which implies characteristic tremor sub-event sources of near-constant size. Here we integrate geological observations and geomechanical lab measurements on heterogeneous rock assemblages representative of the shallow tremor region offshore the Middle America Trench with numerical simulations to demonstrate that these tremor events are consistent with the seismic failure of relatively weaker blocks within a stronger matrix. In these subducting rocks, hydrothermalism has led to a strength-inversion from a weak matrix with relatively stronger blocks to a stronger matrix with embedded relatively weaker blocks. Tremor naturally occurs as the now-weaker blocks fail seismically while their surrounding matrix has not yet reached a state of general seismic failure

Geological map of the Tocomar Basin (Puna Plateau, NW Argentina): Implication for the geothermal system investigation

This paper presents a detailed geological map at the 1:20,000 scale of the Tocomar basin in the Central Puna (north-western Argentina), which extends over an area of about 80 km2 and displays the spatial distribution of the Quaternary deposits and the structures that cover the Ordovician basement and the Tertiary sedimentary and volcanic units. The new dataset includes litho-facies descriptions, stratigraphic and structural data and new 234U/230Th ages for travertine rocks. The new reconstructed stratigraphic framework, along with the structural analysis, has revealed the complex evolution of a small extensional basin including a period of prolonged volcanic activity with different eruptive centres and styles. The geological map improves the knowledge of the geology of the Tocomar basin and the local interplay between orogen-parallel thrusts and orogen-oblique fault systems. This contribution represents a fundamental support for in depth research and also for encouraging geothermal exploration and exploitation in the Puna Plateau regionFil: Filipovich, Ruben Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Baez, Walter Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Groppelli, Gianluca. CNR Istituto di Geologia Ambientale e Geoingegneria; ItaliaFil: Ahumada, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Aldega, Luca. Università degli Studi di Roma "La Sapienza"; ItaliaFil: Becchio, Raul Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Berardi, Gabriele. Università Roma Tre III; ItaliaFil: Bigi, Sabina. Università degli Studi di Roma "La Sapienza"; ItaliaFil: Caricchi. Chiara. Istituto Nazionale di Geofisica e Vulcanologia; ItaliaFil: Chiodi, Agostina Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Corrado, Sveva. Università Roma Tre III; ItaliaFil: De Astis, Gianfilippo. Istituto Nazionale di Geofisica e Vulcanologia; ItaliaFil: De Benedetti, Arnaldo Angelo. Università Roma Tre III; ItaliaFil: Invernizzi, Chiara. Universita Degli Di Camerino; ItaliaFil: Norini, Gianluca. CNR Istituto di Geologia Ambientale e Geoingegneria; ItaliaFil: Soligo, Michele. Università Roma Tre III; ItaliaFil: Taviani, Sara. University of Milano-Bicocca; ItaliaFil: Viramonte, Jose German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Giordano, Guido. CNR Istituto di Geologia Ambientale e Geoingegneria; Italia. Università Roma Tre III; Itali

Late orogenic deformation of the shallowest portion of an orogenic wedge: Coeval activity of extensional and compressional tectonics in the western Northern Apennines (Italy)

[No abstract available

Relationships between tectonic/sedimentary burial and exhumation in the evolution of the Apennines by means of clay mineralogy.

In the last thirty years the reconstruction of thermal and burial history of sedimentary successions in the disciplines concerning basin analysis has represented one of the major goals in the research applied to oil exploration over the world. This type of research includes the integration of stratigraphic, structural, petrographic and petrophysic data with thermal evolution parameters obtained from techniques both of the inorganic and organic fraction of the sediment. These researches have led to one-dimensional models and, later on, to more refined two dimensional models that allow us to define the entity of the tectonic and sedimentary load and to determine the exhumation history in chain areas. These methods represent a powerful tool to understand the geological structures and to reconstruct the volumes of rocks that are presently missing in the chain and their removal due to erosion and/or tectonic events. The determination of tectonic and/or sedimentary loads in the Apennines fold-and-thrust-belt by means of clay mineralogy represents a still uncompleted datum. The acquisition of this datum will contribute greatly to the reconstruction of geometries and kinematics of the deformation, to the implications for palaeogeographic reconstructions and, therefore, to the geodynamic models already existing. The aim of this work is to show the potential of clay mineralogy analysis as a tool for understanding the structural framework and the Neogene-Quaternary evolution of the Apennines fold-and-thrust belt and reconstructing the volume of rocks that nowadays are partially or totally eroded. To define the thermal evolution of some sedimentary successions involved in the orogenic wedge, three different areas were chosen as case studies: the Modena-Bologna area the inner zone of the Northern Apennines fold-and-thrust belt; the Lucania area in the axial zone of the Southern Apennines fold-and-thrust belt; the Nebrodi Mts.-Iblei Mts. section in the Eastern Sicily fold-and-thrust belt