Revealing the Mineralogical and Petrographic Signs of Fluid-Related Processes in the Kelebia Basement Area (Szeged Basin, S Hungary): A Case Study of Alpine Prograde Metamorphism in a Permo-Triassic Succession

Figure 7

Thin-section photomicrographs of the Permian ignimbrites: crystal and juvenile components ((a, c–f) well Kel–7 core #8; (b) well Kel–11 core #5). (a, b) Crystal fragments in the fine-grained matrix showing a weakly developed foliation (yellow line in a). Note: the strongly altered (flattened and sericitized) pumice shards are oriented, and the feldspar also reflects sericitic alterations. (c) Altered juvenile components (sericitized pumice and pumice shards). In the relict pumice clast, the original internal vesicular microstructure has been destroyed. (d) Fractured quartz, altered broken K-feldspar, and apatite+opaque mineral pseudomorphs after biotite in the strongly recrystallized groundmass. Quartz crystals and fragments generally exhibit a reverse zoning pattern with low-intensity blue CL cores overgrown by a relatively high-intensity red CL rim. Small apatite grains show uniform bright yellow luminescence. (e, f) A resorbed and deformed crystal of volcanic quartz displaying variable blue to red (rim and embayments) CL colors. Abbreviations: PPL: plane-polarized light; XPL: cross-polarized light; CL: cathodoluminescence; Ap: apatite; Bt: biotite; Kfs: K-feldspar; Pl: plagioclase; Qz: quartz.

(a)

(b)

(c)

(d)

(e)

(f)