Interpretation of the Magma Chamber Processes with the help of Textural Stratigraphy of the Plagioclases (Konya-Central Anatolia)

Abstract

The variations in the chemical composition and micro-texture of a mineral from the core to the rim allow the sequencing of the formation of the magma chamber processes and the interpretation of which texture might have been formed by which process. In this contribution, the textural and chemical zoning of the plagioclases, which are a significant recorder of magma chamber processes, from some enclavecontaining andesites (calc-alkaline) and basalts (calc-alkaline) from the Karapınar-Karacadağ Volcanic Units, were examined and their textural mineral stratigraphies were investigated to enlight the magma chamber processes. Plagioclases from the andesitic host-rock and their enclaves generally exhibit different composition from core to rim. The composition in the enclave ranges from oligoclase to labradorite (core:An25-72), however, in the host rock it ranges from andesine to labradorite (core:An46-64). It is noteworthy that the plagioclases in the host-rock are mostly rounded, and reverse and oscillatory zoned with Anorthite, Fe, Mg, Sr, and Ba. However in the enclaves they display generally fine sieve and dusty sieve textures. The cores of the plagioclase micro-phenocrysts in calc-alkaline basalts are andesine-labrador (An32-66) in composition. Remarkably, plagioclases in basalts show reverse and oscillatory zoning with An, Fe, Mg, Sr, and Ba, and as well as exhibit coarse-grained sieve texture with glass and microlitic inclusions, and spongy cellular textures. Combined with their An, Fe, Mg contents it is suggested that some of the plagioclases from the basalts may be xenocrysts rather than phenocrysts. Considering the textural and chemical properties of the plagioclases, in the formation of reverse and oscillatory zoning in the basaltic rocks, the decompression processes in addition to the magma mixing processes (magma mixing/self-mixing) also have an impact on the genesis of the basalts. However, in the formation of andesitic rocks, the magma replenishment processes have a key role rather than decompression or temperature-pressure change.

Distribution and Mineralogical Characteristic of Raya Volcanics, West Kalimantan

“…Its fluctuating chemical zoning from core to rim indicated the raising of temperature during the crystallization process followed by slow cooling at the end of crystallization [15]. It may relate to some Ca-rich magma injection in a deep magma chamber [16], [17]. Unlike plagioclase and hornblende (Figure 7D), zoning identified in pyroxene under micro XRF scanline common shows as normal zoning.…”