Mineralogy and petrology of Grenada, Lesser Antilles island arc

TLDR: The mineralogy and petrology of volcanic and plutonic rocks from the island of Grenada are described in this paper, where the conditions of equilibration of basanitoids with potential upper mantle materials using the results of high pressure experiments are compared with estimates from thermodynamic data.

Abstract: The mineralogy and petrology of volcanic and plutonic rocks from the island of Grenada are described The volcanic rocks include basanitoids, alkalic and subalkalic basalts, andesites and dacites Phenocryst phases in the basanitoids and basalts are olivine (Fo90−71), zoned calcic augite, spinel ranging from ferrian pleonaste through chromite to titaniferous magnetite, and plagioclase Some of the basalts contain pargasitic amphibole Andesites and dacites generally contain hypersthene and augite, and one pigeonite-hypersthene-augite-bearing andesite was found Apatite commonly occurs as a phenocryst in the andesites and dacites and quartz is present in some dacites as well as being a possible xenocryst in both alkalic and subalkalic basalts Plutonic cumulates found as ejected fragments in tuffs and ashes are composed of variable proportions of olivine, magnetite, calcic augite, amphibole and plagioclase One peridotitic (ol-cpx-opx) fragment was found but spinel or garnet peridotitis are absent Despite the alkalic nature of the association, calcalkalic characteristics such as calcic plagioclase, restricted Feenrichment in coexisting pyroxenes and generally low TiO2 content relative to oceanic suites are present in Grenada Estimates of conditions of equilibration of the basanitoids with potential upper mantle materials using the results of high-pressure experiments are compared with estimates from thermodynamic data Equating $$a_{{\text{SiO}}_{\text{2}} } $$ and $$a_{{\text{Al}}_{\text{2}} {\text{O}}_{\text{3}} } $$ basanitoid with hypothetical garnet peridotite assemblages gives a pressure and temperature of equilibration in the region of 35–38 kbar and 1550–1625 ° K Experimental results are not supportive of these estimates