Zeolite facies mineralization in the Hvalfjordur area, Iceland

NHM researcher: Rune S. Selbekk
Associated researcher: Tobias Weisenberger

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Spatial and temporal development of pore-filling mineral assemblages in the Hvalfjördur area. The vertical axis depicts depth below land surface at the time of each event depicted in the figure. Time elapsed after eruption increases to the right.

The Hvalfjördur area, 30 km north of Iceland's capital Reykjavik, belongs to the sequence of Late Tertiary to early Quaternary flood basalts with minor intercalations of hyaloclastites and rhyolites. The basalts are affected by progressive low-temperature metamorphism, caused by the burial of the lava succession and higher heat flow from nearby central volcanoes. Low-grade zeolite facies metamorphism of basaltic lavas in the Hvalfjördur area results in two distinct mineral parageneses that can be correlated to events in the burial and hydrothermal history of the lava pile. Stage Ia represents syn-eruptive near-surface alteration in which celadonite and silica were precipitated along primary pores. During regional burial metamorphism (stage Ib), hydrolysis of olivine and glass led to the formation of mixed-layer chlorite/smectite clays. The chlorite content of stage Ib phyllosilicate vesicle rims increases with increasing burial depth and temperature.

Stellerite crystals from the Hvalfjördur area, Iceland.

Stage II occurred after the burial and is marked by zeolite mineralization caused by higher heat flow from the Laxarvogur and Hvalfjördur central volcanoes. Altogether 11 different zeolites were found in the Hvalfjördur area: analcime, chabazite, epistilbite, heulandite, laumontite, levyne, mesolite, stilbite, stellerite, thomsonite and yugawaralite. In total, three separate depth and temperature-controlled ''zeolite zones'' occur in the Hvalfjördur area.

References

Selbekk, R.S. & Weisenberger, T. 2005. Stellerite from the Hvalfjordur area, Iceland. Jökull, 55, 49-52.
Weisenberger, T. & Selbekk, R.S. 2009. Multi stage zeolite facies mineralization in the Hvalfjordur area, Iceland. International Journal of Earth Sciences in press, DOI 10.1007/s00531-007-0296-6, 15 p.

Published Apr. 20, 2010 2:00 PM - Last modified Mar. 1, 2012 11:35 AM