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Geochemistry and petrology of garnet‐bearing S‐type Shir‐Kuh Granite, southwest Yazd, Central Iran
Author(s) -
Sheibi Mariyam,
Esmaeily Dariush,
Nédélec Ann,
Bouchez Jean Luc,
Kananian Ali
Publication year - 2010
Publication title -
island arc
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.554
H-Index - 58
eISSN - 1440-1738
pISSN - 1038-4871
DOI - 10.1111/j.1440-1738.2010.00707.x
Subject(s) - geology , geochemistry , batholith , felsic , monazite , plagioclase , mafic , zircon , biotite , rare earth element , petrology , mineralogy , quartz , rare earth , paleontology , tectonics
The Jurassic Shir‐Kuh granitoid batholith in Central Iran intrudes Lower Jurassic sandstones and shales. The batholith consists of three main facies: (i) a granodioritic facies to the north; (ii) a monzogranitic facies spread throughout the batholith; and (iii) a leucogranitic facies along the northwestern margin. The granodiorites are composed mainly of plagioclase, quartz, K‐feldspar, biotite, and some muscovite, garnet, cordierite, ilmenite, zircon, apatite, and monazite. This facies contains variable amounts of restite minerals which are mainly defined by calcic plagioclase cores and small aggregates of biotite. The monzogranites, with mineral assemblages similar to those in the granodiorites, range from relatively mafic (cordierite‐bearing) to felsic (muscovite‐rich) rocks. The leucogranites, exposed as small stock and dykes, consist mainly of quartz, K‐feldspar, and sodic plagioclase. The batholith is peraluminous, calc‐alkaline, and typical of S‐type, as indicated by Na 2 O content (2.74%), molecular Al 2 O 3 /(CaO + Na 2 O + K 2 O) (A/CNK) ratio (1.17), K 2 O/Na 2 O ratio (1.39), and isotopic data ([ 87 Sr/ 86 Sr] i = 0.715). The rocks are characterized by enrichment in large ion lithophile elements such as Rb, Th and K and depletion in high field strength elements such as Nb and Ti. Chondrite‐normalized rare earth element (REE) patterns are characterized by light rare earth element (LREE) enrichment, with values of (La/Yb) N between 4.5 and 19.53, unfractionated heavy rare earth element (HREE) with values of (Gd/Yb) N between 0.98 and 2.88, and a distinct negative Eu. The parental magma of the Shir‐Kuh Granite was derived from a plagioclase‐rich metasedimentary source (local anatexis of metagreywacke) in the crust, with heat input from mantle melt components. The separation of restite crystals from the primary melt followed by the fractional crystallization appears to have been an effective differentiation process in the batholith.