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Fluid geochemistry versus tectonic setting: the case study of Morocco

By
F. Tassi
F. Tassi
1
Department of Earth Sciences, University of Florence, Via G. La Pira, 4,50121 Florence, Italy
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O. Vaselli
O. Vaselli
1
Department of Earth Sciences, University of Florence, Via G. La Pira, 4,50121 Florence, Italy
2
CNR-Institute of Geosciences and Earth Resources, Via G. La Pira, 4, 50121 Florence, Italy (e-mail: gmoratti@geo.unifi.it>
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G. Moratti
G. Moratti
2
CNR-Institute of Geosciences and Earth Resources, Via G. La Pira, 4, 50121 Florence, Italy (e-mail: gmoratti@geo.unifi.it>
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L. Piccardi
L. Piccardi
2
CNR-Institute of Geosciences and Earth Resources, Via G. La Pira, 4, 50121 Florence, Italy (e-mail: gmoratti@geo.unifi.it>
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A. Minissale
A. Minissale
2
CNR-Institute of Geosciences and Earth Resources, Via G. La Pira, 4, 50121 Florence, Italy (e-mail: gmoratti@geo.unifi.it>
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A. Poreda
A. Poreda
3
Department of Earth and Environmental Sciences, University of Rochester,227 Hutchinson Hall, Rochester, NY 14627, USA
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A. Delgado Huertas
A. Delgado Huertas
4
stacion Experimental de Zaidin (CSIC), Prof. Albareda 1, 18008 Granada, Spain
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A. Bendkik
A. Bendkik
5
Ministère de l’Energie et des Mines, Direction du Devéloppement Minier, BP 6208,Rabat-Institut, Morocco
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M. Chenakeb
M. Chenakeb
5
Ministère de l’Energie et des Mines, Direction du Devéloppement Minier, BP 6208,Rabat-Institut, Morocco
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D. Tedesco
D. Tedesco
6
Department of Environmental Sciences, 2nd University of Napoli, Via Vivaldi 43,81100 Caserta, Italy
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Published:
January 01, 2006

Abstract

This paper presents the results of an extensive chemical and isotopic investigation on natural thermal and cold fluids (spring waters and associated gases) discharging throughout the main geological domains of Morocco. The chemical features of the thermal springs are mainly dependent on rock dissolution involving Triassic evaporite formations, producing either Na–Cl or Ca–S04composition, although mixing with shallower connate high-saline waters in Neogene post-orogenic sedimentary layers cannot be ruled out. Only in the Moroccan Meseta and Anti-Atlas domains have spring discharges probably undergone equilibration as a result of water-rock interaction in granites. Of the chemical and isotopic features of the gas seeps,3He/4He ratios and δ13C–C02values indicate the occurrence of a significant contribution of mantle-derived gas, especially at Oulmès (Moroccan Meseta) and Tinejdad-Erfoud (Anti -Atlas), where associated waters are found to equilibrate at relatively high temperatures (c. 130 °C). These areas are also characterized by the presence of Pliocene to Quaternary basaltic volcanic rocks. Thermal discharges located along the Rif front and related to the NE–SW-oriented main strike-slip faults are associated with a CH4- and/or N2-rich gas phase, derived respectively from a crustal or an atmospheric source. Some of them have significant contents of 3He that could indicate the rising of mantle fluids. Such a striking isotopic signature, which is not related to any recent volcanism visible at surface, is likely to be associated with cooling magma at depth related to transpressive fault systems. Similarly, in the northeastern area, the small, although significant, enrichment of 3He in the gas discharges seeping out along the Nekor seismic active fault and related to Pliocene-Quaternary basalts also suggests a deep-seated (magmatic) contribution. The distribution of thermal discharges is strongly related to the main active tectonic structures of Morocco. Moreover, this study indicates the presence of deep active tectonic structures in areas until now considered as stable. In particular, the NE–SW-trending Nekor fault may be part of a major system that extends to the Moroccan Meseta and into the Smaala–Oulmés fault system, thus emerging as a deep structure with crustal significance.

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Contents

Geological Society, London, Special Publications

Tectonics of the Western Mediterranean and North Africa

G. Moratti
G. Moratti
CNR-Institute of Geosciences and Earth Resources, Italy
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A. Chalouan
A. Chalouan
University of Mohammed V Agdal, Rabat, Morocco
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Geological Society of London
Volume
262
ISBN electronic:
9781862395107
Publication date:
January 01, 2006

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