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This paper investigates hydrothermal fluid circulation in pre-and syn-tectonic sediments associated with detachments faults. The study area, located in the Err Nappe (SE-Switzerland), preserves a portion of the Adriatic distal margin. Two sites were studied in combining fieldwork, petrography, geochemistry and fluid inclusion analysis: the Piz Val Lunga and Fuorcla Cotschna areas. Both preserve relationships between a spectacularly exposed rift-related extensional detachment fault and its footwall and hangingwall that consist of extensional allochthons and syn-to posttectonic sediments. These areas register a complex fluid flow history characterized by dolomitization, de-dolomitization, calcite cementation, dolomite and quartz veining and diffuse silicification. Meso-and micro-scale observations allow defining two steps in fluid evolution, which are related to Jurassic rift activity. A first carbonate-rich event occurred before the exhumation of the granitic basement, and this was followed by a second event marked by a change in the fluid towards a silica-dominated chemistry. Homogenization temperatures of fluid inclusions (average T h = 120-130°C), negative d 18 O values and a radiogenic 87 Sr/ 86 Sr signatures of carbonate minerals support the hypothesis that both the pre-tectonic rocks constituting the allochthons and the syn-tectonic sediments overlying the detachment fault were crossed by a flux of over-pressured hydrothermal fluids originating from seawater that penetrated into the basement through fault and fracture systems. Field relationships show that this fluid circulation started latest in middle Early Jurassic time, when fault activity migrated from the proximal to the future distal margin. We propose that it evolved chemically as a result of the involvement of the granitic basement forming the footwall of the extensional detachment system. Hydrothermal activity continued until the Middle/Late Jurassic, when tectonic activity shifted outwards leading to the exhumation of mantle rocks. This paper provides an original contribution to better understand the complex evolution of hyperextended continental rift domains and to constrain their thermal regimes.
This paper investigates hydrothermal fluid circulation in pre-and syn-tectonic sediments associated with detachments faults. The study area, located in the Err Nappe (SE-Switzerland), preserves a portion of the Adriatic distal margin. Two sites were studied in combining fieldwork, petrography, geochemistry and fluid inclusion analysis: the Piz Val Lunga and Fuorcla Cotschna areas. Both preserve relationships between a spectacularly exposed rift-related extensional detachment fault and its footwall and hangingwall that consist of extensional allochthons and syn-to posttectonic sediments. These areas register a complex fluid flow history characterized by dolomitization, de-dolomitization, calcite cementation, dolomite and quartz veining and diffuse silicification. Meso-and micro-scale observations allow defining two steps in fluid evolution, which are related to Jurassic rift activity. A first carbonate-rich event occurred before the exhumation of the granitic basement, and this was followed by a second event marked by a change in the fluid towards a silica-dominated chemistry. Homogenization temperatures of fluid inclusions (average T h = 120-130°C), negative d 18 O values and a radiogenic 87 Sr/ 86 Sr signatures of carbonate minerals support the hypothesis that both the pre-tectonic rocks constituting the allochthons and the syn-tectonic sediments overlying the detachment fault were crossed by a flux of over-pressured hydrothermal fluids originating from seawater that penetrated into the basement through fault and fracture systems. Field relationships show that this fluid circulation started latest in middle Early Jurassic time, when fault activity migrated from the proximal to the future distal margin. We propose that it evolved chemically as a result of the involvement of the granitic basement forming the footwall of the extensional detachment system. Hydrothermal activity continued until the Middle/Late Jurassic, when tectonic activity shifted outwards leading to the exhumation of mantle rocks. This paper provides an original contribution to better understand the complex evolution of hyperextended continental rift domains and to constrain their thermal regimes.
Al though no un doubted oce anic crustal rock com plexes of Penninic af fin ity par tic i pate in the pres ent sur face struc ture of the West ern Carpathians, in di rect lines of ev i dence sug gest pro lon ga tion of the South Penninic-Vahic oce anic tract into the an cient Carpathians. The sed i men tary re cord of both the syn-rift and syn-orogenic clastic de pos its re veal their or i gin be tween the outer Tatric (Austroalpine) and the in ner Oravic (Mid dle Penninic) mar gins. The rift ing re gime is ex em pli fied by the nor mal fault-re lated scarp brec cias of the Ju ras sic Borinka Unit in the Malé Karpaty Mts., which are char ac ter ized by lo cal, grad u ally de nuded source ar eas. Two other re gions pro vide exam ples of a contractional re gime, both re lated to short en ing and clo sure of the Vahic oce anic do main. The Belice Unit in the Považský Inovec Mts. in cludes Up per Ju ras sic-Lower Cre ta ceous eupelagic, mostly si li ceous de pos its and a thick en ing-up wards Senonian sequence of turbiditic sand stones, con glom er ates and cha otic brec cias. It is in ferred that this suc ces sion rep re sents the sed i men tary cover of oce anic crust ap proach ing a trench, its in cor po ra tion in the accretionary com plex and fi nally underthrusting be low the outer Tatric mar gin. In the Oravic units of the Pieniny Klippen Belt, deep-ma rine con glom er ate/brec cia bod ies with olistoliths in di cate col li sion-related thrust stack ing that started from the Maastrichtian (Gregorianka Brec cia of the Sub-Pieniny Unit) and ter mi nated with the Lower Eocene Milpoš Brec cia in the Šariš Unit. In ad di tion, a ten ta tive re cy cling scheme of "ex otic" clastic ma te rial from mid-Cre ta ceous conglom er ates of the Klape Unit to var i ous Klippen Belt units is out lined. This ma te rial is con sid ered to be un re lated to the Vahic oce anic realm and its clo sure, and likely rep re sents ero sional prod ucts of more dis tant orogenic zones. Dušan Plašienka, De part ment of Ge ol ogy and Palae on tol ogy, Fac ulty of Nat u ral Sci ences, Comenius Uni ver sity,
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