Thin section scans of gabbro nodules, scoria, plagioclase-phyric basalt, hyaloclastite from Gígöldur, central Iceland
Plane-polarised light (PPL), partial cross-polarised light (PXPL), and cross-polarised light (XPL) thin section scans were obtained for gabbroic nodules, scoria, plagioclase-phyric basalt, and hyaloclastite from Gígöldur, central Iceland. The PXPL scans are captured with a polariser-analyser angle of 45° to avoid the complete extinction of the silicate phases. The scale bars represent 5mm.
Gígöldur is a broad NNE–SSW-trending ridge composed of interlayered hyaloclastites and postglacial craters, located in the highlands north of Vatnajökull glacier. Samples were collected from three locations along the ridge: Gígöldur North (GO23-04), Gígöldur Central (GO19-01 & GO23-01), and Gígöldur South (GO19-02, GO23-02 & GO23-03).
The nodules, 5-10 cm in size, are rounded to sub-angular and consist primarily of plagioclase aggregates encased in glass. They contain small but variable amounts of interstitial olivine and, occasionally, dark green clinopyroxene. The nodules exhibit high vesicularity and significant textural and compositional variability.
The scoria clasts, 2-5 cm in size, are highly vesicular, with predominantly circular, uncoalesced vesicles. Some regions contain large, irregularly shaped coalesced vesicles, while others feature dense, glass-rich domains. The phenocryst load is substantial, primarily composed of plagioclase aggregates, along with individual plagioclase and olivine grains.
The hyaloclastite samples consist of angular glass shards, plagioclase and olivine crystals, and fine-grained volcanic debris, typically forming poorly consolidated, friable layers. The matrix is composed of volcanic glass with variable porosity. The glass shards often contain small, circular vesicles.
The plagioclase-phyric basalt consists of plagioclase and mafic phenocrysts set in a variably porous glassy matrix. The vesicularity is generally low, with small, circular vesicles dispersed throughout the groundmass.
