Laser-ICP-MS U–Pb zircon ages and geochemical and Sr–Nd–Pb isotopic compositions of the Niyasar plutonic complex, Iran: constraints on petrogenesis and tectonic evolution

Abstract

We conducted geochemical and isotopic studies on the Oligocene-Miocene Niyasar plutonic suite in the central Urumieh-Dokhtar magmatic belt, in order better to understand the magma sources and tectonic implications. The Niyasar plutonic suite comprises early Eocene microdiorite, early Oligocene dioritic sills, and middle Miocene tonalite + quartzdiorite and minor diorite assemblages. All samples show a medium-K calc-alkaline, metaluminous affinity and have similar geochemical features, including strong enrichment of large-ion lithophile elements (LILEs, e.g. Rb, Ba, Sr), enrichment of light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs, e.g. Nb, Ta, Ti, P). The chondrite-normalized rare earth element (REE) patterns of microdiorite and dioritic sills are slightly fractionated [(La/Yb) n = 1.1-4] and display weak Eu anomalies (Eu/Eu * = 0.72-1.1). Isotopic data for these mafic mantle-derived rocks display I Sr = 0.70604-0.70813, ε Nd (microdiorite: 50 Ma and dioritic sills: 35 Ma, respectively) = +1.6 and −0.4, TDM = 1.3 Ga, and lead isotopic ratios are ( 206 Pb/ 204 Pb) = 18.62-18.57, ( 207 Pb/ 204 Pb) = 15.61-15.66, and ( 208 Pb/ 204 Pb) = 38.65-38.69. The middle Miocene granitoids (18 Ma) are also characterized by relatively high REE and minor Eu anomalies (Eu/Eu * = 0.77-0.98) and have uniform initial 87 Sr/ 86 Sr (0.7065-0.7082), a range of initial Nd isotopic ratios [εNd(T)] varying from −2.3 to −3.7, and Pb isotopic composition ( 206 Pb/ 204 Pb) = 18.67-18.94, ( 207 Pb/ 204 Pb) = 15. and ( 208 Pb/ 204 Pb) = 38.73-39.01. Geochemical and isotopic evidence for these Eocene-Ologocene mafic rocks suggests that the magmas originated from lithospheric mantle with a large involvement of EMII component during subduction of the Neotethyan ocean slab beneath the Central Iranian plate, and were significantly affected by crustal contamination. Geochemical and isotopic data of the middle Miocene granitoids rule out a purely crustal-derived magma genesis, and suggest a mixed mantle-crustal [MASH (melting, assimilation, storage, and homogenization)] origin in a post-collision extensional setting. Sr-Nd isotope modelling shows that the generation of these magmas involved ∼60% to 70% of a lower crustal-derived melt and ∼30% to 40% of subcontinental lithospheric mantle. All Niyasar plutons exhibit transitional geochemical features, indicating that involvement of an EMII component in the subcontinental mantle and also continental crust beneath the Urumieh-Dokhtar magmatic belt increased from early Eocene to middle Miocene time.

Long-lived, stationary magmatism and pulsed porphyry systems during Tethyan subduction to post-collision evolution in the southernmost Lesser Caucasus, Armenia and Nakhitchevan

“…This study have allowed us to clarify the magmatic, geodynamic and metallogenic evolution , 2011Asiabanha and Foden, 2012;Castro et al, 2013), IV -Eocene rocks from central Alborz (Verdel et al, 2011), V -Eocene to Mio-Pliocene rocks from the northern UrumiehDokhtar belt (Omrani et al, 2008;Rezaei-Kahkhaei et al, 2011;Sarjoughian et al, 2012;Yeganehfar et al, 2013;Honarmand et al, 2014). The Zangezur and Nakhitchevan blocks belong to the South Armenian block of Gondwanian origin.…”

“…GPa from Rapp (1995), Rapp and Watson (1995) and Sen and Dunn (1994), and experimental hybrid melts from Rapp et al (1999). (2013) and Honarmand et al (2014); Mio-Pliocene from Omrani et al (2008). See Figure 1 for location of data from Alborz and northern Urumieh-Dokhtar.…”

“…from Yeganehfar et al (2013) and Honarmand et al (2014). Upper crust and orogene lead isotopic evolution curves generated by the plumbotectonics model of Zartman and Doe (1981).…”

Zircon U–Pb ages, geochemical and Sr–Nd–Pb–Hf isotopic constraints on petrogenesis of the Tarom-Olya pluton, Alborz magmatic belt, NW Iran

“…The SSZ is considered as the main magmatic arc resulting from Neo-Tethyan subduction during the Mesozoic (Azizi et al, 2011;Berberian and King, 1981), whereas the UDMA and AMB are interpreted to be associated with early to late Cenozoic subduction-related magmatism on the Zagros hinterland (Berberian and King, 1981;Berberian et al, 1982;Stöcklin, 1971), slab break-off (Agard et al, 2011;Ghasemi and Talbot, 2006;Haschke et al, 2010), slab roll-back (Jahangiri, 2007;Verdel et al, 2011) and post-collisional relaxation (Castro et al, 2013;Nabatian et al, 2014). Several petrogenetic models have been proposed for some of the magmatic segments in the UDMA and AMB including continental arc magmatism Hassanzadeh, 1993) to continental rifting (Amidi et al, 1984) and post-collisional tectonic setting (Aghazadeh et al, Ahmadian et al, 2009;Berberian and King, 1981;Castro et al, 2013;Honarmand et al, 2013;Nabatian et al, 2014).…”

“…6) with overall higher average K 2 O contents than those of UDMA (e.g. Honarmand et al, 2013;Omrani et al, 2008;Rezaei-Kahkhaei et al, 2011) and Andean arcs (e.g., Haschke et al, 2002) plutonic rocks. The Tarom-Olya samples display a general descending trend for most compatible elements and ascending trend for large ion lithophile elements (LILEs) against SiO 2 contents (Fig.…”