A tectonic model for the location of Palaeozoic ring complexes in Aïr (Niger, West Africa)
The Air region in Niger is one of the largest peralkaline granite provinces in the world. In addition to the granites, some plutons are characterized by an abundance of plagioclase-rich cumulates (gabbros, troctolites and anorthosites), with subordinate metaluminous granites and quartz syenites. The...
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Published in | Tectonophysics Vol. 234; no. 1; pp. 129 - 146 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
London
Elsevier B.V
15.06.1994
Amsterdam Elsevier Science New York, NY |
Subjects | |
Online Access | Get full text |
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Summary: | The Air region in Niger is one of the largest peralkaline granite provinces in the world. In addition to the granites, some plutons are characterized by an abundance of plagioclase-rich cumulates (gabbros, troctolites and anorthosites), with subordinate metaluminous granites and quartz syenites. These anorogenic ring complexes were intruded along a 400 km zone near the 9°E meridian. The province formed during a major magmatic event, newly dated at around 407 ± 8Ma, and comprises 28 plutons, which range from 0.8 to 65 km in diameter and show no correlation between distribution and age. Remote sensing over the whole Aïr massif demonstrates the existence of two main trends of faults or lineaments: N50°E–N90°E and N120°E–N150°E. Autocorrelation analysis of the ring complexes reveals three large, parallel, high-density strips orientated N20°E. Based on the structural and geological setting, coupled with map analysis, a new tectonic model for the location of the complexes is presented. We propose a dextral N5°E shear zone model, where the emplacement of the ring structures is controlled by N20°E dextral Riedel shear (
R) with a secondary N50°E tensional gash (
T). This tectonic model implies a control by lithospheric structures for the emplacement of the ring complexes, as well as a relationship between a transtensional tectonic regime and intra-plate alkaline magmatism. The new geochronological data on the Aïr massif allow us to derive a Silurian-Devonian palaeomagnetic pole (representative for Gondwana) which fits data for the other continents better than previous estimates. |
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ISSN: | 0040-1951 1879-3266 |
DOI: | 10.1016/0040-1951(94)90208-9 |