Contact metamorphism and crystal size distribution studies in the Shivar aureole, NW Iran

Abstract

The Shivar pluton, a large granodiorite-monzonite intrusion in NW Iran, was intruded into Cretaceous sedimentary rocks during the Oligo-Miocene. Its thermal aureole contains a variety of pelitic, basic and calc-silicate hornfelses. Mineral parageneses in the pelitic and calc-silicate hornfelses are studied here and mineralogical zones are determined. The maximum pressure of contact metamorphism is estimated to have been about 2.2 kbar on the basis of mineral parageneses in the pelitic rocks, indicating that the intrusion was emplaced no deeper than 8 km in the crust. Crystal size distribution (CSD) studies in the calc-silicate hornfelses indicate that the degree of overstepping was high near the igneous contact. Secondary solid phases (SSP) inhibited growth of calcite grains in the calc-silicate rocks and impure marbles. Garnet had a greater inhibitory effect as a SSP than tremolite or clinopyroxene. The time required for coarsening of calcite is calculated for two samples collected at different distances from the igneous contact. The time required for calcite coarsening is about 33 000 years for the sample 800 m from the contact and about 226 000 years for the sample 120 m from the contact.

Origin of migmatites by deformation‐enhanced melt infiltration of orthogneiss: a new model based on quantitative microstructural analysis

“…The observed CSD trend may be explained by one of three different mechanisms: (1) solid‐state deformation under decreasing temperature and or increasing strain rate (Hickey & Bell, 1996; Azpiroz & Fernández, 2003; Lexa et al. , 2005); (2) a different degree of reaction overstepping (Waters & Lovegrove, 2002; Moazzen & Modjarrad, 2005); and (3) a different degree of undercooling (Marsh, 1988).…”

Porphyry copper assessment of the Tethys region of western and southern Asia: Chapter V in <i>Global mineral resource assessment</i>

“…With the exception of evolved garnet-biotite granites, which appear to have been derived from assimilation of subducted sediments, older and younger suites of the Shaivar Dagh Batholith exhibit radiogenic isotope signatures that are similar to those of the Khankandi Batholith. Barometric estimates indicate a large range of emplacement depths based on emplacement pressures between 0.4 and 2.0 kb (Moazzen and Modjarrad, 2005;Aghazadeh and others, 2011). These estimates suggest variable levels of exposure likely produced by normal faulting.…”

Garnetization as a ground preparation process for copper mineralization: evidence from the Mazraeh skarn deposit, Iran

“…A variety of pelitic, mafic and calc-silicate hornfelses have been developed in the thermal aureole of this pluton. Based on mineral parageneses in the pelitic rocks and using the petrogenetic grids of Spear and Cheney (1989), Moazzen and Modjarrad (2005) estimated the maximum pressure and depth of contact metamorphism and magma emplacement to be *2.2 kbar and 8 km, respectively.…”