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Hydrothermal fluids influence on the thermal evolution of the Stephanian sequence, the Sabero Coalfield (NW Spain)

Botor D.

Geology, Geophysics and Environment

2012

Vol. 38, no. 4

369--393

In the present study, the thermal history of the Late Carboniferous (Stephanian) coal-bearing sediments of the Sabero Coalfield has been reconstructed in order to elucidate coal rank. The Sabero Coalfield is located in a small intramontane coal-bearing basin along the Sabero-Gordón fault zone, one of the major E-W trending strike-slip fault systems of the southern part of the Cantabrian Zone (NW Spain). The total thickness of the Stephanian succession is in excess of 2,000 m, and is composed of siliclastic rocks and intercalated coal seams with tonsteins. Mean vitrinite reflectance values in the Stephanian rocks in the Sabero Coalfield are in the range from 0.61 to 3.14% Rr, but most values are in the range from 0.8 to 1.5% Rr (based on 84 samples). Average vitrinite reflectance gradient is high (0.73% Rr/km), which suggests high value of average paleogeothermal gradient (52°C/km). The maximum paleotemperatures calculated from vitrinite reflectance values for the Stephanian rocks range between 89°C (top of the Stephanian) and 195°C (bottom of the Stephanian). Coalification of the organic matter in the Stephanian rocks was achieved in the Early Permian, and was most likely related to several almost simultaneous related to magmatic and hydrothermal activity during high subsidence period in the pull-apart basin. The primary, burial-related maturity pattern, was probably slightly overprinted by fluid migration event, which is supposed to have occurred in Early Permian time.

Geochemia górnokarbońskich tonsteinow z zagłębia węglowego Sabero (NW Hiszpania)

Botor D.

Zeszyty Naukowe. Górnictwo / Politechnika Śląska

2005

z. 268

19-30

Geochemia górnokarbońskich tonsteinow z zagłębia węglowego Sabero (NW Hiszpania) Przeprowadzono wstępną charakterystykę geochemiczną tonsteinów w basenie węglonośnym Sabero (NW Hiszpania). Tonsteiny charakteryzują się średnią do wysokiej zawartością pierwiastków ziem rzadkich, Zn, Li, Y, Sr, Zr, Th i U oraz niską zawartością Sc, V, Cr, Co, Hf, P, Ta Ni, Nb, Ti. Stosunek Th/U jest względnie wysoki. Tonsteiny te cechuje znacząca anomalia negatywna Eu oraz wzbogacenie w LREE względem HREE. Powyższa charakterystyka sugeruje, ze źródłem tych tonsteinow była raczej magma o składzie odpowiadającym ryodacytom do ryolitow.

Preliminary geochemical characterization tonsteins has been performed in the Sabero coalfield. Tonsteins in the study area are medium to high concentration in REE, Zn, Li, Y, Sr, Zr, Th and U; whereas, low in concentration Sc, V, Cr, Co, Hf, P,Ta Ni, Nb, Ti and relatively high Th/U ratio as well distinctive Eu anomaly. All this is consistent generally with a silicic magmatic source. Particularly, enrichment of LREE and low content of Hf, Ta, and Ti depletion of indicates rather highly evolved magmas which have incorporated either subcrustal material from the continental plate or subducted sediments high in volatiles. Based on the mentioned data it can be concluded that the Sabero tonsteins were likely derived from a calc-alkaline rhyodacitic to rhyolitic eruptive source.