Crystallization conditions and petrogenesis of the lava dome from the ∼900 years BP eruption of Cerro Machín Volcano, Colombia

Laeger, Kathrin, Halama, Ralf, Hansteen, Thor H., Savov, Ivan P., Murcia, Hugo F., Cortés, Gloria P. and Garbe-Schönberg, Dieter (2013) Crystallization conditions and petrogenesis of the lava dome from the ∼900 years BP eruption of Cerro Machín Volcano, Colombia Journal of South American Earth Sciences, 48 . pp. 193-208. DOI 10.1016/j.jsames.2013.09.009.

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Supplementary data:


• Whole-rock, mineral and isotope chemical data of Cerro Machín Volcano.
• Mixing of distinct mafic and silic melts produced hybrid magma.
• Amphibole thermobarometry indicates resident magma reservoir at 13 ± 2 km depth.
• Dacites have adakitic geochemical signature.

The last known eruption at Cerro Machín Volcano (CMV) in the Central Cordillera of Colombia occurred ∼900 years BP and ended with the formation of a dacitic lava dome. The dome rocks contain both normally and reversely zoned plagioclase (An24–54), unzoned and reversely zoned amphiboles of dominantly tschermakite and pargasite/magnesio-hastingsite composition and olivine xenocrysts (Fo = 85–88) with amphibole/clinopyroxene overgrowth, all suggesting interaction with mafic magma at depth. Plagioclase additionally exhibits complex oscillatory zoning patterns reflecting repeated replenishment, fractionation and changes in intrinsic conditions in the magma reservoir. Unzoned amphiboles and cores of the reversely zoned amphiboles give identical crystallization conditions of 910 ± 30 °C and 360 ± 70 MPa, corresponding to a depth of about 13 ± 2 km, at moderately oxidized conditions (fO2 = +0.5 ± 0.2 ΔNNO). The water content in the melt, calculated based on amphibole chemistry, is 7.1 ± 0.4 wt.%. Rims of the reversely zoned amphiboles are relatively enriched in MgO and yield higher crystallization temperatures (T = 970 ± 25 °C), slightly lower melt H2O contents (6.1 ± 0.7 wt.%) and overlapping pressures (410 ± 100 MPa). We suggest that these rims crystallized following an influx of mafic melt into a resident magma reservoir at mid-crustal depths, further supported by the occurrence of xenocrystic olivine. Crystallization of biotite, albite-rich plagioclase and quartz occurred at comparatively low temperatures (probably <800 °C) during early stages of ascent or storage at shallower levels. Based on amphibole mineral chemistry, the felsic resident melt had a rhyolitic composition (71 ± 2 wt.% SiO2), whereas the hybrid magma, from which the amphibole rims crystallized, was dacitic (64 ± 3 wt.% SiO2). The bulk rock chemistry of the CMV lava dome dacites is homogenous. They have elevated (La/Nb)N ratios of 3.8–4.5, typical for convergent margin magmas, and display several geochemical characteristics of adakites. Both Sr and Nd isotope compositions (87Sr/86Sr ∼0.70497, 143Nd/144Nd ∼0.51267) are among the most radiogenic observed for the Northern Volcanic Zone of the Andes. They are distinct from oceanic crust that has been subducted in the region, pointing to a continental crustal control on the isotope composition and hence the adakitic signature, possibly in a crustal “hot zone”

Document Type: Article
Additional Information: WOS:000328096400014
Keywords: Colombian Andes; Cerro Machín Volcano; Magma mixing; Amphibole geothermobarometry; Trace element geochemistry
Research affiliation: Kiel University
OceanRep > SFB 574
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Refereed: Yes
DOI etc.: 10.1016/j.jsames.2013.09.009
ISSN: 0895-9811
Projects: SFB574
Contribution Number:
SFB 574260
Date Deposited: 14 Oct 2013 12:53
Last Modified: 05 Oct 2017 12:15

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