Structurally controlled hydrothermal dolomites in Albian carbonates of the Asón valley,Basque Cantabrian Basin,Northern Spain |
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| Authors: | MA López-Horgue E Iriarte S Schröder PA Fernández-Mendiola B Caline H Corneyllie J Frémont M Sudrie S Zerti |
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| Institution: | 1. Estratigrafia eta Paleontologia Saila, Zientzia eta Teknologia Fakultatea, Euskal Herriko Unibertsitatea, Sarriena z/g, E-48940 Leioa, Basque Country, Spain;2. Departamento Ciencia e Ingeniería del Terreno y los Materiales, Geología Aplicada, E.T.S. Ingenieros de Caminos, Canales y Puertos, Universidad de Cantabria, Avda. de Los Castros s/n, E-39005 Santander, Spain;3. TOTAL E & P Recherche Developpement, Carbonate Sedimentology Group, Avenue Larribau s/n, 64018 Pau Cedex, France |
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| Abstract: | Shallow marine carbonate sedimentation dominated during the Albian in the western part of the Basque Cantabrian Basin in Northern Spain, forming the large Ramales Platform. This platform originated on a less subsiding tectonic block facing deeper and more subsiding areas to the south and east, which were created by tectonic activity in the Basin. Fracture-related hydrothermal dolomites hosted in these Albian carbonates are well exposed in the Asón valley area. Mapping in the studied area revealed several dolomite bodies related to main faults that cut the stratification almost at right angles. The bodies show a vertical development along fault-strike up to 900 m thick from which kilometre-scale branches expand following the stratification. Dolomitization is pervasive and independent of the limestone facies. Main dolomite facies are fine replacive, sucrosic and saddle. Petrography, C, O and Sr isotopes and fluid-inclusion analysis support a polyphase hydrothermal dolomitization at fluid temperatures between 75 °C and 240 °C and highly variable salinity of up to 22 wt.% NaCl. Fine dolomite replaced limestone first and then, sucrosic and saddle dolomites replaced part of the first dolomite and cemented newly created fracture porosity together with different calcite cements. Zebra dolomites and hydroclastic breccias are products of this later stage. Burial analysis of the host rock supports maximum burial temperatures of 80 °C and intense tectonic activity from the Albian to Turonian with a latest Albian peak subsidence. Albian stretching of the crust and subsequent ascent of the isotherms in the area is suggested to have produced sufficient heat to the dolomitizing fluids. The structural analysis indicates a strong transtensional tectonic activity in the studied area during Albian to Turonian time with the creation of an overstep between W–E trending and N–S trending faults. Fluids moved from subsiding areas to fractured uplifted parts of the Ramales Platform, enhanced by diapiric activity. |
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| Keywords: | Dolomites Hydrothermal fluid Fracture-related Rifting Transtension Subsidence Albian&ndash Turonian Northern Spain |
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