Petrologic studies of the Robles Formation, south central Puerto Rico

<p>The Robles Formation of south central Puerto Rico is composed primarily of andesitic lavas and pyroclastic rocks. Two important andesitic lava members are present within the formation. One, the Lapa Lava Member, is enriched in potassium. Another, the Las Tetas Lava Member, is poor in potassium. Mineralogy of the flows was strongly governed by crystal settling both in the magma chamber before eruption and within individual flows at the time of eruption. All of the igneous rocks associated with the Robles Formation belong to the calc-alkaline series.</p> <p>Plagioclase and olivine phenocrysts contain a series of metamorphic alteration phases as follows: (1) analcime, celadonite, chlorite, sericite; (2) laumontite and albite; (3) prehnite; (4) pumpellyite; (5) epidote; (6) actinolite. Assemblages containing analcime, celadonite, and laumontite belong to the zeolite facies of metamorphism. Remaining assemblages belong to the prehnite-pumpellyite facies. Secondary mineralogy of the rocks is consistent with residual chemistry after removal of relic plagioclase and metastable clinopyroxene fractions. The degree of alteration seems related to permeability: phases appear in greater quantities in porous pyroclastics.</p> <p>Absolute quantities of potassium. rubidium. and copper in the Lapa Lava Member are independent of phenocryst or mafic content. and decrease toward the south. This may represent original inhomogeneity of the magmas, or it may be the result of metasomatism through either hydrothermal activity or metamorphism.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Geological Sciences

Year

1970

Author dc:creator

• Jolly, Wayne Travis

Contributors dc:contributor

• Thomas W. Donnelly
• Don L. Kissling
• William D. MacDonald

• Petrology
• Puerto Rico
• Robles Formation

Repository record dc:identifier

https://orb.binghamton.edu/dissertation_and_theses/157

OAI identifier oai:identifier

oai:orb.binghamton.edu:dissertation_and_theses-1163