PETROLOGY AND GEOCHEMISTRY OF MONTANA GUAZA; ASSIMILATION AND FRACTIONAL CRYSTALLIZATION OF THE MAGMA CHAMBER, TENERIFE (CANARY ISLANDS)

The Canary Islands are an east-west trending archipelago situated off the western coast of Africa between Morocco and Western Sahara. Tenerife, located in the middle of this island trend, is the largest island in the chain (2,053 km2) and is home to Pico Teide (3,718m), the highest peak in the chain. Much research has been done in the Canary Islands concerning the primitive magma evolution, however little research has been done on the evolution of the island's smaller volcanoes. Montana Guaza, located in southwestern Tenerife, is home to a small, 0.67 Ma quaternary trachyte-phonolite volcano. Santin and Lopez (1978) have suggested this volcano has evolved from an endogenous dome to an exogenous dome and finally to a true volcano during the time of its emplacement.

XRF and petrographic analyses were carried out on nine stratographically different samples from Mt. Guaza. Field evidence shows as Mt. Guaza evolved, clear stratographic layering resulted from the progressive extrusions. Major, minor, and trace element analysis trends show an evolved magma. XRF evidence suggests the volcano deposited layers of enriched lava followed by progressively more basic lava compositions, issuing support for a zoned magma chamber. In addition, XRF data show evidence of assimilation of the thick overlying lithosphere contaminating the magma chamber in addition to fractional crystallization. Trace element data plotted against volcano height show similar evidence. XRF data analyzed during this fieldwork on Mt. Guaza further support results of Santin and Lopez (1978).