Stop 18: Copacoya Dome
Traveling south from Chillahuita, near the Tatio geothermal fields, we come across Copacoya, yet another large silicic dome of the APVC. Like its brethren, it takes on the typical “torta” shape with steep sides and a flat top.
Petrographic and mineralogic details
Also like its brethren, Copacoya is dacitic in composition and crystal rich (40%+). Mineralogically it contains phenocrysts of plagioclase, quartz, hornblende and some devitrified glass in a glassy matrix. The matrix is much denser than seen at previous domes, due to the lack of microvesiculation within the lava. Mafic enclaves are also seen frequently – more andesitic, finer grained.
There are lines of evidence pointing to this dome being around the same age and close to the source of the Sifon Ignimbrite as the Sifon is greater than 300m think in this area.
- Geology of the Altiplano
- Field Guide Stops 1-10
- Field Guide Stops 11-20
- Field Guide Stops 21-30
- Field Guide Stops 31-35
- Altiplano 09 Acknowledgements
- Altiplano Gallery 09
- Samples Gallery 09