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Recent volcanic history of Irazu volcano, Costa Rica: alternation and mixing of two magma batches, and pervasive mixing

Special Paper of the Geological Society of America

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DOI: 10.1130/2006.2412(14)

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Abstract

40Ar/39Ar dates, field observations, and geochemical data are reported for Irazú volcano, Costa Rica. Volcanism dates back to at least 854 ka, but has been episodic with lava shield construction peaks at ca. 570 ka and 136–0 ka. The recent volcanic record on Irazú volcano comprises lava flows and a variety of Strombolian and phreatomagmatic deposits, with a long-term trend toward more hydrovolcanic deposits. Banded scorias and hybridized rocks reflect ubiquitous magma mixing and commingling. Two distinct magma batches have been identified. One magma type or batch, Haya, includes basalt with higher high field strength (HFS) and rare-earth element contents, suggesting a lower degree melt of a subduction modified mantle source. The second batch, Sapper, has greater enrichment of large ion lithophile elements (LILE) relative to HFS elements and rare-earth elements, suggesting a higher subduction signature. The recent volcanic history at Irazú records two and one half sequences of the following pattern: eruptions of the Haya batch; eruptions of the Sapper batch; and finally, an unusually clear unconformity, indicating a pause in eruptions. In the last two sequences, strongly hybridized magma erupted after the eruption of the Haya batch. The continuing presence of two distinct magma batches requires two active magma chambers. The common occurrence of hybrids is evidence for a small, nearer to the surface chamber for mixing the two batches. Estimated pre-eruptive temperatures based on two-pyroxene geothermometry range from ∼1000–1176 °C in basalts to 922 °C in hornblende andesites. Crystallization occurred mainly between 4.6 and 3 kb as measured by different geobarometers. Hybridized rocks show intermediate pressures and temperatures. High silica magma occurs in very small volumes as banded scorias but not as lava flows. Although eruptions at Irazú are not often very explosive, the pervasiveness of magma mixing presents the danger of larger, more explosive hybrid eruptions.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Recent volcanic history of Irazu volcano, Costa Rica: alternation and mixing of two magma batches, and pervasive mixing
Series title:
Special Paper of the Geological Society of America
DOI:
10.1130/2006.2412(14)
Issue:
412
Year Published:
2006
Language:
English
Publisher:
Geological Society of America
Description:
18 p.
First page:
259
Last page:
276
Country:
Costa Rica
Other Geospatial:
Irazu volcano
Online Only (Y/N):
N
Additional Online Files(Y/N):
N