György BUDA¹ & Elemér PÁL-MOLNÁR^2
1Department of Mineralogy, Eötvös Loránd University, H-1117 Budapest, Pázmány P. str. 1/C, Hungary
²Department of Mineralogy, Geochemistry and Petrology, University of Szeged, H-6701 Szeged, P.O. Box 651, Hungary (palm@geo.u-szeged.hu)

APATITE AS A PETROGENETIC INDICATOR OF VARISCAN GRANITOIDS IN TISZA MEGA-UNIT (SOUTH HUNGARY)

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Apatite is an excellent indicator of the origin of granitoid rocks. Two types of granitoids occur in Tisza Mega-Unit, south Hungary: one is in Kunságia (Mórágy Subunit); the other is in Békésia Unit (Battonya Subunit). Both granitoids contain apatite as accessory mineral. Apatite in metaluminous granitoids of Mórágy Subunit is characterized by REE- (Ce enriched) and chlorine-bearing fluorapatite, depleted in Mn, and is zoned, acicular, or prismatic with rather small grain sizes that are almost inclusion-free. In Battonya Subunit apatite is found in basic quartz monzodiorite and it is acicular and Mn-free; in the peraluminous granitoids it is Mn-rich, low REE-bearing, chlorine-poor, and unzoned, containing monazite and zircon inclusions, with stubby habit and large grain sizes. The two contrasting chemistries, textures, and crystal habits of apatite are due to the different origins of the granitoid melts. In Mórágy Subunit the I-type granitoids crystallized at higher temperature and therefore the oxidized Mn³⁺ could not enter in the apatite structure, and due to the low Al-content of the melt, REEs entered the allanite and apatite, whereas in the majority of Battonya Subunit the S-type granitoid melt had a lower temperature and consequently Mn²⁺ entered the apatite structure, substituting for Ca²⁺, and at first monazite crystallized from the peraluminous melt, consuming REEs from the melt, causing depletion in the REEs of apatite, and the sedimentary origin probably caused chlorine depletion.