Fluid flow and faulting history of the Iano tectonic window (Southern Tuscany, Italy) (original) (raw)
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International Journal of Earth Sciences, 2010
An integrated study based on fluid inclusion, d18O composition and structural analyses was carried out on a Pliocene fossil hydrothermal system, located to the South of the present active Larderello geothermal field, in the Boccheggiano-Montieri area. The study area is typified by mineralized cataclastic levels related to Late Oligo- cene–Early Miocene thrust surfaces, and to the following two generations of normal faults of Miocene and Pliocene ages, respectively. Within the damage zone of the Pliocene Boccheggiano fault, the mineralization is mainly made up of quartz and pyrite. Quartz ? Pb–Zn sulfides, or quartz ? Pb–Zn sulfides ? fluorite ? carbonates assem- blages occur instead in the older cataclastic levels. Two generations of liquid-rich fluid inclusions were recognized in quartz and fluorite: the first one, with homogenization emperatures ranging between 172 and 331°C and salinity between 0.0 and 8.8 wt.% NaClequiv., records the early stage of hydrothermal activity. The second generation of fluid inclusions documents a later stage, with homogeni- zation temperature from 124 to 288°C and salinity from 0.2 to 1.9 wt.% NaClequiv.. Fluid inclusions analyses also indicate that mixing of fluid with distinct salinities and/or temperatures was a widespread process during the early stage, and that fluid temperatures decreased moving from the Boccheggiano fault toward the more distal and older cataclastic levels. The d18O values of water in equilibrium with hydrothermal quartz, which range from -5.7 to -0.1%, are related to the circulation of meteoric water mixed with saline water that leached the evaporite level and enriched in d18O through water–rock interaction, and/ or with magmatically derived fluids. Results indicate that the damage zone of the Pliocene Boccheggiano fault rep- resented the main channel for the flow of meteoric water, which was heated at depth, then mixed with high salinity fluids, and finally ascend to infiltrate along the older cataclastic levels. Our results, based on fluid inclusions, oxygen isotopic compositions and structural analyses indicate that a single fluid flow path run through the damage zone of the Boccheggiano fault and the older cataclasites, which were thus hydraulically connected.
Mineralogy and Petrology, 2005
The low-pressure emplacement of a quartz diorite body in the metapelitic rocks of the Gennargentu Igneous Complex (Sardinia, Italy) produced a contact metamorphic aureole and resulted in migmatisation of part of the aureole through partial melting. The leucosome, formed by dehydration melting involving biotite, is characterised by granophyric intergrowth and abundant magnetite crystals. A large portion of the high temperature contact aureole shows petrographic features that are intermediate between quartz diorite and migmatite s.s. (i.e. hybrid rocks). A fluid inclusion study has been performed on quartz crystals from the quartz diorite and related contact aureole rocks, i.e. migmatite sensu stricto (s.s.) and hybrid rocks. Three types of fluid inclusions have been identified: I) monophase V inclusions, II) L + V, either L-rich or V-rich aqueous saline inclusions and III) multiphase V + L + S inclusions. Microthermometric data characterised the trapped fluid as a complex aqueous system varying from H2O–NaCl–CaCl2 in the quartz diorite to H2O–NaCl–CaCl2–FeCl2 in the migmatite and hybrid rocks. Fluid salinities range from high saline fluids (50 wt% NaCl eq.) to almost pure aqueous fluid. Liquid-vapour homogenisation temperatures range from 100 to over 400 °C with an average peak around 300 °C. Temperatures of melting of daughter minerals are between 300 and 500 °C. Highly saline liquid- and vapour-rich inclusions coexist with melt inclusions and have been interpreted as brine exsolved from the crystallising magma. Fluid inclusion data indicate the formation of fluid of high iron activity during the low-pressure partial melting and a fluid mixing process in the hybrid rocks.
2006
The present paper deals with an integrated geological, mineralogical and geochemical study on mineralized faults and fractures recognized in the Macigno Formation at Calafuria in the Livorno Mountains of northern Tuscany. In the field, two main different systems of faults were recognized: an earlier one related to a compressive phase with NE- SW, NW-SE and N-S trending faults, and a younger one related to a relaxation phase with reactivation of N-S and NW-SE trending faults. They distinguish for specifi c mineral assemblages, consisting mainly of quartz in the former, and barite-marcasite-pyrite in the latter. Minerals were analyzed for fl uid inclusions and isotopic composition. Data on fl uid inclusions indicate that three main mineralizing episodes affected the fault systems. In the fi rst episode, the fl uids deposited quartz in the fault systems related to the compressive phase. The second episode was the main one, and led to the deposition of euhedral quartz in the NE-SW fault...
Tectonophysics, Elsevier, 2019
Structural features such as faults and fractures play an important role in fluid circulation within the crust, and influence geothermal exchange potential. Based on this consideration, we examined the subsurface structural setting of the Marche Region (Central Italy) in terms of detailed data we obtained on the groundwater in wells; detailed analyses of its physical properties, particularly electrical conductivity, revealed some anomalies in several localities which appear to be related to the local tectonic structures. In addition, we interpreted data from seismic reflection profiles provided by ENI S.p.A, and kindly shared with us, for the SW-NE area crossing the Apennine chain and extending to the Adriatic Sea. Our interpretation indicates the presence of important subsurface and deep Plio-Quaternary structures linked to outcropping ones with possible hydrogeological implications. Our interpretation of these seismic profiles enabled us to identify some high angle structures affecting the whole sedimentary sequence and routed at depth (> 10 km), thus allowing us to gain an understanding of the recent structural evolution of the Apennine Marche sector. We interpreted these mainly NW-SE trending structures to be transpressive structures, related to lower depth SW and NE-dipping high-angle reverse faults (positive flower structures), probably involving the upper crust basement. We identified them along three main parallel alignments (transects) from SW to the coastline, crossing the Mio-Pliocene Apennine range and its external Plio-Quaternary sector. Our analyses of the groundwater in wells throughout the study area indicated possible relationship with deep geological structures. It seems that the high degree of fracturing that accompanies these complex and recent fault systems could facilitate the exchange between superficial and deeper fluids. This is supported by the observation that there is a direct relationship between the electrical conductivity of the water in wells located along the calcareous-marly Apennine Marche ridge, and the amount of rainfall.