Abstract
Large magnesian ilmenite “nodules” occur in a quaternary basanitic volcano near Silet in the Tahalra volcanic area (Central Ahaggar, Southern Algeria). Their texture, from foliated to polygonal, is ascribed to solid state flow and dynamic recrystallization in upper mantle conditions.
Their composition is similar to that of kimberlitic Mg-ilmenite nodules, as regards Mg, Fe, Al and Cr contents; the geikielite content ranges from 25 to 37 mol %. No outwards Mg enrichment of the nodules has been observed. Peripheral secundary products (pseudobrookite, magnetite and hematite) result from reaction with the host magma.
From textural relationships and microprobe analyses, the Mg-ilmenite nodules from Tahalra are thought to be early cumulates from a mafic melt fractionnated in the upper-mantle; later, after solid-state deformation, these ilmenitite rocks were sampled and carried up to the surface by a fast-rising basanitic liquid.
Rocks almost exclusively made of ilmenite do therefore presently exist within the upper-mantle and form a new type of petrological heterogeneity.
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References
Allègre CJ, Dupré B, Lambert B, Richard P (1981) The subcontinental versus suboceanic debate. I. Lead-Neodymium-strontium isotopes in primary alkali-basalts from a shield area: the Ahaggar volcanic suite. Earth Planet Sci Lett 52:85–92
Arène J, Byramjee R, Thebault JY (1959) Le volcanisme basique de la Tahalra. Bull Sci Econ BRMA, Alger 6:25–51
Basu AR, McGregor ID (1975) Chromite spinels from ultramafic xenoliths. Geochim Cosmochim Acta 39:937–945
Binns RA (1969) High-pressure megacrysts in basanitic lavas near Armidale, New South Wales. Am J Sci 267A:33–49
Boctor NZ, Boyd FR (1980) Oxide minerals in the Liqhobong kimberlite, Lesotho. Am Mineral 65:631–638
Boyd FR, Nixon PH (1975) Origins of the ultramafic nodules from some kimberlites of northern Lesotho and the Monastery Mine, South Africa. Phys Chem Earth 9:431–454
Boyd FR, Nixon PH (1978) Ultramafic nodules from the Kimberley pipes, South Africa. Geochim Cosmochim Acta 42:1367–1382
Chevremont P, Johan Z (1980) Complexe intrusif stratifié de Wadi Kamal — Wadi Murattigah (Arabie Saoudite), son évolution magmatique et métallogénique. Bull Bur Rech Geol Mineral, Orléans, Sect II (1–2):21–40
Conquéré F, Girod M (1968) Contribution à l'étude des paragenèses précoces des basaltes alcalins: les spinelles du volcan de l'Oued Temorte (Massif de l'Atakor, Sahara algérien). Contrib Mineral Petrol 20:1–29
Duchesne JC (1972) Iron-titanium oxide minerals in the Bjerkrem-Sogndal massif, south-western Norway. J Petrol GB 13:57–81
Eggler DH, McCallum ME, Smith CB (1979) Megacryst assemblages in kimberlite from northern Colorado and southern Wyoming: petrology, geothermometry-barometry and areal distribution. In: The mantle sample: inclusions in kimberlites and other volcanics, pp 213–226, AGU, Washington
Frey A, Greer DH, Roy SA (1978) Integrated models of basalt petrogenesis: a study of quartz tholeiites to olivine melilitites from south eastern Australia utilizing geochemical and experimental petrological data. J Petrol 19:463–513
Girod M (1967) Données pétrographiques sur des pyroxénolites à grenat en enclaves dans des basaltes du Hoggar (Sahara central). Bull Mineral 90:202
Girod M, Dautria JM, De Giovanni R (1981) A first insight into the constitution of the upper mantle under the Hoggar area (southern Algeria): the lherzolite xenoliths in the Alkali basalts. Contrib Mineral Petrol 77:66–73
Green DH, Edgar AD, Beasley P, Kiss E, Ware NG (1974) An upper mantle source for some hawaïtes, mugearites and bemmoreites. Contrib Mineral Petrol 48:33–43
Green DH, Sobolev NV (1975) Coexisting garnets and ilmenites synthesized at high pressures from pyrolite and olivine basanite and their significance for kimberlitic assemblages. Contrib Mineral Petrol 50:217–229
Haggerty SE (1975) The chemistry and genesis of opaque minerals in kimberlites. Phys Chem Earth 9:295–503
Haggerty SE, Hardie III RB, McMahon BM (1979) The mineral chemistry of ilmenite nodule associations from the Monastery diatreme. In: Boyd FR, Meyer HOA (eds) The mantle sample Proc 2nd Int Kimberlite Conf, Vol 2, pp 249–256, Am Geophys Union, Washington DC
Mercier JC (1972) Structure des péridotites en enclaves dans quelques basaltes d'Europe et d'Hawaï. Regards sur la constitution du manteau supérieur. Thèse Doct 3e cycle, Univ Sci Nantes, 229 p
Mercier JC, Nicolas A (1975) Textures and fabrics of upper mantle peridotites as illustrated by xenoliths from basalts. J Petrol 16:454–487
Mitchell RH (1973) Magnesian ilmenite and its role in kimberlite petrogenesis. J Geol 81:301–311
Mitchell RH (1978) Manganoan magnesian ilmenite and titanian clinohumite from the Jacupiranga carbonatite, Sao Paulo, Brazil. Am Mineral 63:544–547
Molyneux TG (1970) The geology of the area in the vicinity of magnet heights, eastern Transvaal, with special reference to the magnetic iron ore. Geol Soc South Africa, Spec Publ 1:228–241
Nicolas A, Bouchez JL, Boudier F, Mercier JC (1971) Textures, structures and fabrics due to solid state flow in some European lherzolites. Tectonophysics 12:55–85
Nicolas A, Poirier JP (1976) Crystalline plasticity and solid state flow in metamorphic rocks. Wiley and Sons (ed), 444 pp
Pasteris JD (1980) The significance of groundmass ilmenite and megacryst ilmenite in kimberlites. Contrib Mineral Petrol 75:315–325
Wass SY (1979) Fractional crystallisation in the mantle of late stage kimberlitic liquids — Evidence in xenoliths from the Kiama area, NSW, Australia. In: The mantle sample: inclusions in kimberlites and other volcanics, pp 266–373, AGU, Washington
Webster AH, Wright NF (1961) The system iron-titanium-oxygen at 1,200° C and oxygen partial pressure between 1 atm and 2×10−14 atm. J Am Ceram Soc 44:110–116
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Leblanc, M., Dautria, J.M. & Girod, M. Magnesian ilmenitite xenoliths in a basanite from Tahalra, Ahaggar (Southern Algeria). Contr. Mineral. and Petrol. 79, 347–354 (1982). https://doi.org/10.1007/BF01132063
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DOI: https://doi.org/10.1007/BF01132063