Late Tertiary/Quaternary volcanics of southern Costa Rica and northern Panama
The recent tectonic evolution of the Isthmus of Panama is marked by a complexity imparted by a subduction zone - magmatic arc, a transform plate boundary, and the attempted subduction of an aseismic ridge. In northern Panama andesites form the morphologically young Chiriqui stratovolcano, while in southern Costa Rica they are found interbedded with thick lahars. Two groups of andesites occur in the region. One is low in Si and K (Group I); the other high in Si and K (Group II). The Panamanian andesites belong to both the groups, while Costa Rican andesites are restricted to Group II. Group I andesites are glassy, plagioclase-phyric (An45 rims), and contain abundant augite (Wo46En46Fs8) and magnetite. Rare, resorbed olivine (Fo82) and amphibole are occasionally observed. The Group II andesites have similar mineralogy but also contain abundant pargasitic hornblende and minor orthopyroxene or pigeonite. Xenoliths are common in the Group II andesites of Chiriqui Volcano. Two types of xenoliths are recognized. Cumulate-textured, hornblende gabbro xenoliths vary from nearly pure plagioclase to nearly pure amphibole. These gabbroic xenoliths contain plagioclase (An90 cores to An53 rims), augite, and pargasitic hornblende often displaying the same reaction products as found in the andesites. These xenoliths are interpreted as cognate. These andesites are all characterized by high alkalis and alkali earths; Group II have over 1500 ppm Ba and 1000 ppm Sr. They are apparently produced by partial melting of a highly metasomatised mantle followed by high-pressure fractionation dominated by hornblende.
- Research Organization:
- Louisiana State Univ., Baton Rouge (USA)
- OSTI ID:
- 6460630
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ANDESITES
MINERALOGY
PETROLOGY
COSTA RICA
PANAMA
FELDSPARS
GEOLOGIC HISTORY
HORNBLENDE
OLIVINE
QUATERNARY PERIOD
SUBDUCTION ZONES
TERTIARY PERIOD
VOLCANISM
ALKALINE EARTH METAL COMPOUNDS
AMPHIBOLE
CENOZOIC ERA
CENTRAL AMERICA
DEVELOPING COUNTRIES
GEOLOGIC AGES
GEOLOGY
IGNEOUS ROCKS
IRON COMPOUNDS
IRON SILICATES
LATIN AMERICA
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MINERALS
OXYGEN COMPOUNDS
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VOLCANIC ROCKS
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)