The Geochemistry of Biotite from TTG Batholiths and A-type Complexes (Silet Region, Hoggar, Algeria): A Marker of Geodynamic Evolution

International audienceThis work aims to compare the chemical composition of electron microprobe analysed biotite (n = 245) from four Trondhjemite-tonalite-granodiorite (TTG) batholiths and four A-type complexes. All of them are exposed in the central part of the Silet terrane (western Hoggar, Algeria) and crosscut Pharusian volcano-sedimentary series. According to Nd isotope values, the rocks are geographically arranged in two narrow N-S oriented bands separated by the Tin-Dahar fault. Negative isotopic values characterize all rocks of the narrow eastern band (ENB) (−2.91 < εNd < −8.10), and biotite is the only mafic mineral. On the other hand, in the western band, rocks display positive (WPB) isotopic values (+0.52 < εNd <  + 4.57) and amphibole in addition to biotite. WPB biotites are magnesian (0.50 < Mg < 3.31) and calc-alkaline, while ENB biotites are ferroan (0.31 < Mg < 2.55) and alkali-calcic to alkaline. ENB biotites are relatively poor in Altotot (2.58 < Altotot < 2.89) compared with WPB biotites (2.72 < Altotot < 3.10). On the other hand, a-type biotites have high Al tot values in the WPB rocks (2.67 < Altot < 4.18) compared to ENB (2 < Altot < 3.18). The distinctive features of the studied biotites evidence the Tin-Dahar fault as a major regional feature