Granites and Earth Evolution.
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PETROLOGY, MINERALOGY AND GEOCHEMISTRY OF VOLCANIC ROCKS FROM

SAHAND VOLCANO (NW IRAN)


Pirmohammadi F.*, Amery A.**, Gahangiry A.**, Modjtahedy M.**

*Geology Department, Faculty of science, Islamic Azad University/Shabestar Branch, Iran

petrofarhad@yahoo.com

**Geology Department, Faculty of science, Tabriz University, Iran


Abstract

Volcanic rocks of Sahand occur 40 km south of Tabriz. The volcanic rocks comprise principally lava flow, domes and volcanic debris flow. These rocks are basaltic andesite, andesite, dacite and rhyodacite. Disequilibrium texture, for example, dusty plagioclase, reaction rims, resorbed mineral shapes are observed in some of these rocks. Textural and geochemical characteristics of plagioclase phenocrysts from these rocks record intrusion of basalt magma into dacitic host magma chamber. Plagioclase phenocrysts in dacitic rocks are identified by oscillatory zoning and low An content (An35-An50). These plagioclase phenocrysts are engulfed, and resorption and dusty zone develops during intrusion of basalt magma. Content increases toward rim of these minerals. Chemical and textural zoning patterns that are preserved in plagioclase phenocrysts provide useful information on magma evolutions.

Key word: Tabriz, Sahand, plagioclase, basaltic andesite, dacite, rhyodacite, magma.


References

Allen S.R., Cas R.A.F. (1998). Rhyolitic fallout and pyroclastic density current deposits from aphreatoplinaian eruption in the eastern Aegean, Greece. Bull. Volcanol. 86, P.219 – 251.

Branney M.J. and Kokelaar P. (1992). A reappraisal of ignimbrite emplacement: progressive aggradation and changes from particulate to non-particulate flow during emplacement of high-grade ignimbrite. Bull. Volcanol. 54, P.504–520.

Hiscott R.N. (1994). Traction-carpet stratification in turbidites – fact or fiction? J. Sediment. Res. A 64, P.204–208.

Huppert H.E., Sparks R.S.J. (1985). The cooling and contamination of mafic and ultramafic magma during ascent through the continental crust. Earth Planet. Sci. Lett. 74, P.371-386.

Martin H. (1999). The adakitic magmas: modern analogues of Archaean granitoids. Lithos 46 (3), P.411– 429.

Moayyed M., Moazzen M. Calagari A.A. Jahangiri A. and Modjarrad M. (2006). Geochemistry and petrogenesis of lamprophyric dykes and associated rocks from Eslamy peninsula, NW Iran: Implications for deep-mantle metasomatism. Chemie der Erde - Geochemistry, In Press, Corrected Proof.

Neri A. and Dobran F. (1994). Influence of eruption parameters on the thermofluid dynamics of collapsing volcanic columns. J. Geophys. Res. 99, P.11833–11857.

Pearce J.A. (2004). The application of ICP – MS methods to tephrochronological problems. Applied Geochemistry, 19, P.289-322.

Rudnick R.L., Gao S. (2003). Composition of the continental crust, pp 1-64. In: The Crust (ed. R.L. Rudnick) Volume 3 Treatise on Geochemistry (eds. H.D. Holland and K.K. Turekian), Elsevier-Pergamon, Oxford.

Rune S. Selbekk and Reidar G. Trønnes (2007). The 1362 AD Öræfajökull eruption, Iceland: Petrology and geochemistry of large-volume homogeneous rhyolite.  Journal of Volcanology and Geothermal Research, Volume 160, Issues 1-2, Pages 42-58. Smith, R.T. and Houghton, B.F., (1995). Vent migration and changing eruptive style during the 1800a Taupo eruption: new evidence from the Hatepe and Rotongaio phreatoplinian ashes. Bull. Volcanol. 57, P.432–439.

Sparks R.S. J., Huppert H. E. (1984). Densiy changes during fractinal crystallization of basaltic magmas: fluid dynamic implications. Contrib. Mineral. Petrol. 85, P.300-309.

Stadlbauer E. (1988). Vulkanologisch-geochemische Analyse eines jungen Ignimbrites: Der Kos-Plateau-Tuff (Südost-Ägäis). PhD thesis, Freiburg.

Walker G.P.L. (1983). Ignimbrite types and ignimbrite problems. J. Volcanol. Geotherm. Res. 17, P.65–88.