Mapping & Petrography Appendices · appendix-11
Petrography — Sheet 11
The BV micrograph shows a holocrystalline, porphyritic intermediate volcanic clast with plagioclase, hornblende, quartz, opaque minerals and a fine groundmass, plus weak sericitic alteration.
SOURCE-LED TECHNICAL READING
Geological interpretation and evidential boundary
The BV micrograph shows a holocrystalline, porphyritic intermediate volcanic clast with plagioclase, hornblende, quartz, opaque minerals and a fine groundmass, plus weak sericitic alteration. A QAP-normalised composition near Q20-P75.5-A4.4 supports andesite under the cited Streckeisen framework, provided groundmass treatment and point-count method are documented. Zoning and intergranular relationships may constrain crystallisation history, but one clast cannot define the full volcaniclastic unit. Alteration can shift apparent feldspar proportions, and quartz identification should be verified. The appropriate inference is clast-scale andesitic provenance; formation-wide source composition requires replicate petrography across clast types, matrix and localities.
- Source
- Private geological appendix archive · controlled source record
- Location in source
- Source-linked record
- Image quality
- HD
- Record ID
- appendix-11
