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Title: Jorullo Volcano, Michoacan, Mexico: the earliest stages of fractionation in calc-alkaline magmas

Abstract

Between 1759 and 1774, Jorullo Volcano and four associated cinder cones erupted approximately 2 km/sup 3/ of magma which evolved progressively with time from early ol-hy-normative primitive basalts (Mgnumber=73, 516 ppm Cr, 260 ppm Ni) to late-stage qtz-hy-normative basaltic andesites. All lavas contain <6 vol% phenocrysts of magnesian olivine (fO/sub 90-70/) with Cr-Al-Mg spinel inclusions, and microphenocrysts of plagioclase and augite. Smooth whole-rock major and trace element compositional trends through the suite can be largely modeled by simple crystal fractionation of olivine, augite, plagioclase, and minor spinel. In order for augite and plagioclase to have been near-liquidus phases, the modeled crystal fractionation event must have occurred at lower-crustal to upper-mantle pressures (8-15 Kb). The crystals actually present in the Jorullo lavas, however, formed at low pressures. Compared to modeled abundances, La, Ce, Rb, Sr, Ba, Hf, Th, and Ta are anomalously enriched in the late-stage basaltic andesites and Dy, Yb, and Lu are anomalously depleted. These discrepancies apparently indicate the importance of other magma-chamber processes. Most high-alumina basalts reported in the literature have 18 to 21 wt% Al/sub 2/O/sub 3/, but are too depleted in MgO, Cr, and Ni to be direct mantle products. These high-alumina basalts have probably undergonemore » significant fractionation of olivine, augite, plagioclase, and spinel from primitive parental basalt similar to the early Jorullo magmas. For hydraulic reasons, such primitive basalts are rarely erupted in mature arcs, and may be completely absent from mature stratovolcanoes.« less

Authors:
;
Publication Date:
Research Org.:
Franklin and Marshall College, Lancaster, PA (USA)
OSTI Identifier:
6453125
Alternate Identifier(s):
OSTI ID: 6453125
Report Number(s):
CONF-8510489-
Journal ID: CODEN: GAAPB
Resource Type:
Conference
Journal Name:
Geol. Soc. Am., Abstr. Programs; (United States)
Additional Journal Information:
Journal Volume: 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; ANDESITES; CHEMICAL COMPOSITION; MINERALOGY; PETROGENESIS; BASALT; MEXICO; ERUPTION; FELDSPARS; FRACTIONATION; INCLUSIONS; LAVA; MAGMATISM; OLIVINE; PETROCHEMISTRY; SPINELS; VOLCANISM; VOLCANOES; ALKALINE EARTH METAL COMPOUNDS; ALUMINIUM COMPOUNDS; ALUMINIUM OXIDES; CHALCOGENIDES; DEVELOPING COUNTRIES; IGNEOUS ROCKS; IRON COMPOUNDS; IRON SILICATES; LATIN AMERICA; MAGNESIUM COMPOUNDS; MAGNESIUM OXIDES; MAGNESIUM SILICATES; MINERALS; NORTH AMERICA; OXIDE MINERALS; OXIDES; OXYGEN COMPOUNDS; ROCKS; SEPARATION PROCESSES; SILICATE MINERALS; SILICATES; SILICON COMPOUNDS; TRANSITION ELEMENT COMPOUNDS; VOLCANIC ROCKS 580400* -- Geochemistry-- (-1989); 580300 -- Mineralogy, Petrology, & Rock Mechanics-- (-1989)

Citation Formats

Luhr, J., and Carmichael, I.S.E. Jorullo Volcano, Michoacan, Mexico: the earliest stages of fractionation in calc-alkaline magmas. United States: N. p., 1985. Web.
Luhr, J., & Carmichael, I.S.E. Jorullo Volcano, Michoacan, Mexico: the earliest stages of fractionation in calc-alkaline magmas. United States.
Luhr, J., and Carmichael, I.S.E. Tue . "Jorullo Volcano, Michoacan, Mexico: the earliest stages of fractionation in calc-alkaline magmas". United States.
@article{osti_6453125,
title = {Jorullo Volcano, Michoacan, Mexico: the earliest stages of fractionation in calc-alkaline magmas},
author = {Luhr, J. and Carmichael, I.S.E.},
abstractNote = {Between 1759 and 1774, Jorullo Volcano and four associated cinder cones erupted approximately 2 km/sup 3/ of magma which evolved progressively with time from early ol-hy-normative primitive basalts (Mgnumber=73, 516 ppm Cr, 260 ppm Ni) to late-stage qtz-hy-normative basaltic andesites. All lavas contain <6 vol% phenocrysts of magnesian olivine (fO/sub 90-70/) with Cr-Al-Mg spinel inclusions, and microphenocrysts of plagioclase and augite. Smooth whole-rock major and trace element compositional trends through the suite can be largely modeled by simple crystal fractionation of olivine, augite, plagioclase, and minor spinel. In order for augite and plagioclase to have been near-liquidus phases, the modeled crystal fractionation event must have occurred at lower-crustal to upper-mantle pressures (8-15 Kb). The crystals actually present in the Jorullo lavas, however, formed at low pressures. Compared to modeled abundances, La, Ce, Rb, Sr, Ba, Hf, Th, and Ta are anomalously enriched in the late-stage basaltic andesites and Dy, Yb, and Lu are anomalously depleted. These discrepancies apparently indicate the importance of other magma-chamber processes. Most high-alumina basalts reported in the literature have 18 to 21 wt% Al/sub 2/O/sub 3/, but are too depleted in MgO, Cr, and Ni to be direct mantle products. These high-alumina basalts have probably undergone significant fractionation of olivine, augite, plagioclase, and spinel from primitive parental basalt similar to the early Jorullo magmas. For hydraulic reasons, such primitive basalts are rarely erupted in mature arcs, and may be completely absent from mature stratovolcanoes.},
doi = {},
journal = {Geol. Soc. Am., Abstr. Programs; (United States)},
number = ,
volume = 17,
place = {United States},
year = {1985},
month = {1}
}

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