Interpretation of the Magma Chamber Processes of the Andesites from Karacadag Volcanites (Central Anatolıa) with the Help of Amphibole Trace Element Data

Abstract

Amphibole major and trace element compositions from 2 different types of andesites from the Karacadağ Volcanites, southwestern part of Capadoccia Volcanic Province, in Konya (Turkey) have been analyzed by electron microprobe and laser ablation inductively coupled plasma mass spectrometry. From the core to the rim, especially the changes in the contents of REE, Li V, Zr, Cr, Ti, Sc, Nb in the amphiboles give considerably significant information about the replenishment processes of the magma, the formation sequence of the minerals and can be a signature to estimate how many different types of amphibole minerals can be found in the rocks. MORB and Chondrite normalized diagrams of the amphibole cores suggest that there are 3 types of amphiboles in the andesites from the Karacadağ Volcanites (in andesite-1 and andesite-2). Type-1 amphibole (GK-80C3), from core to rim, contains Li = 55-67-86-98-52-58 ppm, V = 596-563-506-533-588-626 ppm, Cr = 70-93-30-12-129-47 ppm, Ba = 97-92-99-130-101-105 ppm, Gd = 5.30-4.1-8-5.5-5.5-4.25 ppm. Type-2 amphibole (GK 35C6), from core to rim, has Li = 53-112-97 ppm, V = 496-520-351 ppm, Cr = 10-69-11 ppm, Ba = 166-144-88 ppm, Gd = 14.30-8.40-35.7 ppm. However Type-3 amphibole (GK-6C5) includes Li = 17- 35-50 ppm, V = 475-532-615 ppm, Cr = 137-16-10 ppm, Ba = 131-124-181 ppm, Gd = 5.40-4.74-7.10 ppm. Geothermobarometer calculations of Type-1 amphibole have yielded temperature and pressure estimates 946°C-3.38 kbar, respectively. However for Type-2 and Type-3 amphiboles temperature estimates are 915-1023°C and pressure estimates are 2.17-6.78 kbar, respectively. According to MORB and Chondrite-normalized diagrams, along with the geothermobarometer calculations, the most primitive amphibole is Type-3 amphibole and the last evolved amphibole is Type-2 amphibole. Oscillatory and inverse zonnig of the amphiboles in terms of Li, V, Cr, Ba, Gd, etc. indicate (repeated or not) magma recharging processes. From core to rim, increasing in the Li content of the minerals is the most important evidence for the crustal contamination effect on their formation. Amphibole trace element chemistry data and geothermobarometer calculations indicate that there are 3 different types of amphiboles in the Karacadağ andesites, which crystallized at various depths of the crust from 25 km to 5 km depth, and the rocks were clearly exposed to magma replenishment and crustal contamination processes.