🌋علوم الأرض و الكون

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    Contribution à l’étude pétrographique et minéralogique de
    (University center Ali Kafi of Tindouf, 2024-06-10) BOULANOUAR Anfal; Auteur
    Abstract The Hoggar massif has experienced several magmatic episodes, with mafic episodes being only a minority. This master's thesis contributes to the study of the East Laouni mafic intrusion (ELMI), which presents a well-preserved concentric magmatic structure and was emplaced in syn-kinematic Pan-African granites and older metamorphic rocks. In this study, two cumulative facies were studied: the first is an olivine gabbro and the other is a gabbronorite. The plagioclases of the olivine gabbro are moderately more calcic (An59-64) and are divided into two populations distinct in their sizes and shapes, suggesting the presence of mixing phenomena between two magmas. This mixing (between the injected magma and the residual magma) is also evidenced by a plagioclase grain showing reverse zoning (core An59 and rim An64). The plagioclases of the gabbronorite are moderately less calcic (An56-61) and show more signs of deformation, indicating that this cumulate has undergone much more stress. Olivine is observed only in the olivine gabbro, its absence in the gabbronorite signaling a higher SiO2 content in its parent magma. The clinopyroxenes of the olivine gabbro are more xenomorphic than those of the gabbronorite, with many apophyses. The clinopyroxenes are augites and diopsides with a fairly high XMg number ranging between 74 and 77. Their chemical characteristics prove that they fractionated from a tholeiitic magma. Orthopyroxene, in an intercumulus status in the olivine gabbro, becomes more abundant and in a cumulus status in the gabbronorite, which is an indication of differentiation in the ELMI chambe