Primary Studies of Taessa-Torak Granitic Massif: Petrography and Mineralogy (Central Hoggar, Algeria)

Abstract

The Taessa massif, located in the Laouni Terrane (LATEA, Hoggar), belongs to the Tamanrasset Taourirt group. The region was the seat of an important post-orogenic magmatic activity during which large volumes of granite were set up. The petrographic and mineralogical study implemented on the Torak unit granitoids revealed the persistence of three types of granites: two-mica granite, biotite granite and alaskite, characterized with the following mineralogical features: Essential minerals, namely: quartz, plagioclage (albite-oligoclase), alkaline feldspar (orthose and microcline), micas (protolithionite to Sidérophyllite group, phengite to Li-phengite group). The accessory minerals, specifically: zircon, monazite, allanite and opaque oxides (magnetite and rutile). Secondary minerals, mainly: chlorite (brunsvigites, dia-banites), fluorite and secondary muscovite. The trioctahedral micas (biotites), as perceived in the samples, appear to have been crystallized in three different stages: 521 °C < T < 657 °C for primary micas, 426 °C < T < 372 °C for rebalanced micas, and T < 372 °C for the neoformed ones. These micas belong to the range of hyperaluminous granitoids, which display close similarities to the protolithionites of the albite-topaz granite pertaining or belonging to the Tamanrasset region. In this massif, they initiate the alumino-potassic line represented by the lithic micas, noticeably persisten in the highly evolved facies of the “Taourirts” complexes.