Mineral chemistry of Plio-Quaternary subvolcanic rocks, southwest Yazd Province, Iran


Sherafat S., YAVUZ F. , NOORBEHESHT I., Yildirim D.

INTERNATIONAL GEOLOGY REVIEW, vol.54, no.13, pp.1497-1531, 2012 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 54 Issue: 13
  • Publication Date: 2012
  • Doi Number: 10.1080/00206814.2011.644748
  • Title of Journal : INTERNATIONAL GEOLOGY REVIEW
  • Page Numbers: pp.1497-1531

Abstract

The NW-SE-trendingLate Cretaceous-Cenozoic Urumieh-Dokhtar Magmatic Arc (UDMA) in southwest Iran hosts numerous Plio-Quaternary subvolcanic porphyritic andesitic to rhyodacitic domes intruded into a variety of rock sequences. Bulk-rock geochemical data show that the calc-alkaline dacitic to rhyodacitic subvolcanic rocks share compositional affinities with high-silica adakites, including high ratios of Na2O/K2O > 1, Sr/Y (most > 70), and La/Yb (> 35), high Al2O3 (> 15 wt.%), low Yb (< 1.8 ppm) and Y (< 18 ppm) contents, no significant Eu anomalies, and flat to gently upward-sloping chondrite-normalized heavy rare-earth element (HREE) patterns. All analysed rocks are characterized by enrichment in large-ion lithophile elements (LILEs) and depletion in high field strength elements (HFSEs). They also display typical features of subduction-related calc-alkaline magmas. In chondrite-normalized rare-earth element patterns, the light rare-earth elements (LREEs) are enriched ((La/Sm)(N) = 3.49-7.89) in comparison to those of the HREE ((Gd/Yb)(N) = 1.52-2.38). Except for the G-Aliabad Dome, plagioclase crystals in the Shamsabad, Ostaj, Abdollah, and Bouragh Domes are mostly oligoclase to andesine (An(19-49)). Amphibole and biotite are abundant ferromagnesian minerals in the subvolcanic rocks. Calcic amphiboles are dominantly magnesiohornblende, magnesiohastingsite, and tschermakite with Mg/(Mg + Fe-tot) ratios ranging from 0.58 to 0.78. In all the studied domes, amphiboles are typically ferric iron-rich, but that those the Shamsabad Dome have the highest Fe3+/(Fe3+ + Fe2+) ratios, between 0.69 and 0.98. Amphiboles from the Ostaj and Shamsabad Domes are relatively rich in F (0.39-1.01 wt.%) in comparison to the other studied domes. This phase commonly shows pargasitic and hastingsitic substitutions with a combination of tschermakitic and edenitic types.