Mineralogy, geochemistry and geodynamic setting of the granitoids from NW Iran

Abstract

The Mahneshan granitoids intruded the Neoproterozoic-Lower Cambrian regional metamorphic rocks in northwestern Iran. These granitoids consisting mainly of K-feldspar, plagioclase, quartz, muscovite, garnet and biotite display a number of subtypes in terms of structure, texture and mineralogy. Geochemically, they are peraluminous and (or) slightly peraluminous with variable normative corundum contents (0.28-4.50%), and medium to high potassic with calc-alkaline affinity. Chondrite-normalized REE patterns indicate that these granitoids can be divided into three distinct groups, supported by petrographic data. The REE patterns of the first group are shallow-sloping in LREE relative to HREE ([La/Yb]n ¼ 1.37-2.48), exhibiting pronounced negative Eu (Eu/Eu à ¼ 0.23-0.35). The second group granitoids are characterized by strong LREE-enrichment relative to HREE ([La/Yb]n ¼ 3-6.20), with positive Eu anomalies (Eu/Eu à ¼ 1.15-1.47). The third group of granitoids is depleted in the middle REE relative to other LREE and HREE. These REE patterns suggest the role of plagioclase and hornblende in their source of granitoids for group 1 and groups 2 and 3, respectively. The trends of Eu/Eu à ratio versus silica contents suggest mixing of mafic material with components formed by crustal melting with a plagioclase-rich residue. Furthermore, thermobarometric estimations indicate that these rocks may have been formed at depths of 15-18 km at relatively low temperatures. The Mahneshan granitoids are S-type and may have been emplaced in a syn-to post-collisional tectonic setting, consistent with an origin of water-saturated magmas with heterogeneous composition derived from different crustal rocks.

Geochemical and petrological characteristics of xenoliths in Mansehra Granite, NW Himalaya, Pakistan: implications for petrogenesis and tectonic settings

“…Based on petrographic studies, the host rock of the restites (Mansehra Granite) represents abundance of Al-rich minerals specifically muscovite ( Fig. 5j) and absence of allanite and titanite suggesting anatectic and S-type character of this pluton which is consistent with the interpretations of Villaseca et al (2007) and Saki (2010). Apart from this, the geochemical plotting constructed for the Mansehra Granite (MG) placed this pluton in strongly peraluminous and calc-alkaline domain ( Fig.…”

“…In the meantime, tourmaline and hematite are identified sporadically. Petrographic studies reveal that the granite is augmented in Al-rich minerals, especially muscovite and indicates absence of allanite and titanite, which is suggestive of S-type character of this pluton (Saki, 2010). Modal mineralogical composition of the granite is displayed in Table 1. .…”

Mineral chemistry and thermobarometry of the staurolite-chloritoid schists from Poshtuk, NW Iran

“…The strips of ultramafic rocks in the Takab Complex can be interpreted as lithospheric remnants of the Proto-Tethyan, which closed during the Pan-African Orogeny (Hajialioghli et al . 2007; Saki, 2011). Therefore, it is included in the Central Iran Zone.…”

“…The metamorphic rocks in the Poshtuk area include garnet-staurolite micaschists, chloritoid-staurolite micaschists, meta-limestone, augen-gneisses and amphibolites. The igneous rocks of the area are composed of two types (Saki, 2011): (1) S-type granitoids (anatectic alkali granite) and (2) white to light grey I-type igneous rocks. Samples for this study were collected from the mountains northwest of Poshtuk village.…”

Rapid exhumation of young granites in an extensional domain: the example of the Giglio Island pluton (Tuscany)

“…These microstructures have been found in wall rocks close to the contact with the magma (e.g. Johnson et al 2004;Droop & Moazzen, 2007;Saki, 2010). Hence, the andalusite-bearing xenoliths and xenocrysts of the Giglio granite, after disaggregation from wall and roof rocks, underwent partial melting upon incorporation into the magma (Barrese et al 1987).…”