Azizi Panjeh Lithos 18.Pdf

Lithos 308–309 (2018) 364–380 Contents lists available at ScienceDirect Lithos journal homepage: www.elsevier.com/locate/lithos The Late Jurassic Panjeh submarine volcano in the northern Sanandaj-Sirjan Zone, northwest Iran: Mantle plume or active margin? Hossein Azizi a,⁎, Federico Lucci b,RobertJ.Sternc, Shima Hasannejad d, Yoshihiro Asahara e a Mining Department, Faculty of Engineering, University of Kurdistan, Sanandaj, Iran b Dipartimento di Scienze, Sez. Scienze Geologiche, Università Roma Tre, Largo S. L. Murialdo 1, 00146 Roma, Italy c Geosciences Department, University of Texas at Dallas, Richardson, TX 75083-0688, USA d Earth Sciences Department, Faculty of Basic Sciences, University of Kurdistan, Sanandaj, Iran e Department of Earth and Environmental Sciences, Graduate School of Environmental Studies, Nagoya University, Nagoya 464-8601, Japan article info abstract Article history: The tectonic setting in which Jurassic igneous rocks of the Sanandaj-Sirjan Zone (SaSZ) of Iran formed is contro- Received 3 January 2018 versial. SaSZ igneous rocks are mainly intrusive granodiorite to gabbroic bodies, which intrude Early to Middle Accepted 17 March 2018 Jurassic metamorphic basement; Jurassic volcanic rocks are rare. Here, we report the age and petrology of volca- Available online 28 March 2018 nic rocks from the Panjeh basaltic-andesitic rocks complex in the northern SaSZ, southwest of Ghorveh city. The Panjeh magmatic complex consists of pillowed and massive basalts, andesites and microdioritic dykes and is as- Keywords: sociated with intrusive gabbros; the overall sequence and relations with surrounding sediments indicate that this Intra-oceanic arc system Ocean island basalt is an unusually well preserved submarine volcanic complex. Igneous rocks belong to a metaluminous sub-alka- fi – Supra-subduction zone line, medium-K to high-K calc-alkaline ma c suite characterized by moderate Al2O3 (13.7 17.6 wt%) and variable Sanandaj Sirjan Zone Fe2O3 (6.0–12.6 wt%) and MgO (0.9–11.1 wt%) contents. Zircon U-Pb ages (145–149 Ma) define a Late Jurassic Neo-Tethys realm (Tithonian) age for magma crystallization and emplacement. Whole rock compositions are enriched in Th, U and light rare earth elements (LREEs) and are slightly depleted in Nb, Ta and Ti. The initial ratios of 87Sr/86Sr (0.7039–0.7076) and εNd(t) values (−1.8 to +4.3) lie along the mantle array in the field of ocean island basalts and subcontinental metasomatized mantle. Immobile trace element (Ti, V, Zr, Y, Nb, Yb, Th and Co) behavior sug- gests that the mantle source was enriched by fluids released from a subducting slab (i.e. deep-crustal recycling) with some contribution from continental crust for andesitic rocks. Based the chemical composition of Panjeh mafic and intermediate rocks in combination with data for other gabbroic to dioritic bodies in the Ghorveh area we offer two interpretations for these (and other Jurassic igneous rocks of the SaSZ) as reflecting melts from a) subduction-modified OIB-type source above a Neo-Tethys subduction zone or b) plume or rift tectonics involving upwelling metasomatized mantle (mostly reflecting the ~550 Ma Cadomian crust-forming event). © 2018 Elsevier B.V. All rights reserved. 1. Introduction time (e.g. Aliani et al., 2012; Berberian et al., 1982; Berberian and Berberian, 1981; Davoudian et al., 2008; Ghasemi and Talbot, 2006; Understanding the tectonic setting and timing of Jurassic igneous ac- Mahmoudi et al., 2011; Mohajjel et al., 2003; Mohajjel and Fergusson, tivity in the Sanandaj-Sirjan Zone (SaSZ) is key for reconstructing the 2014; Moinevaziri et al., 2015; Nadimi and Konon, 2012; Shahbazi et tectonomagmatic evolution of SW Eurasia. This occurred from 143 to al., 2010, 2014; Stöcklin and Nabavi, 1973). This study is focused on 187 Ma (Fig. 1) with a peak of igneous activity in Middle Jurassic time, the heretofore-unstudied Panjeh mafic complex in the northern SaSZ ~165 Ma (Bayati et al., 2017). Most SaSZ igneous rocks are gabbro to sy- (Fig. 2a, b). In this paper U-Pb zircon ages, whole-rock geochemistry enite intrusions emplaced between 160 and 180 Ma, but younger intru- and Sr-Nd isotopic ratios are used to constrain Panjeh complex sions (144–156 Ma) are found in the far NW SaSZ (e.g., Suffi Abad magma genesis and its possible geodynamic implications. Specifically, granite, Ghorveh plutonic complex, Almagholagh diorite, and granitoids we focus on the controversy about the tectonic setting in which these of the Alvand plutonic complex; Bayati et al., 2017). However, Jurassic magmas formed, volcanic arc environment or rift/mantle-plume tec- volcanic rocks in the SaSZ are rare and still poorly studied. Here we re- tonic setting. port results of a first study of Jurassic volcanic rocks and use these results to better understand the evolution of the SaSZ, considered to mark the start of a Neo-Tethys convergent margin in Middle Jurassic 2. Geological setting ⁎ Corresponding author. The SaSZ extends for 1500 km along the Zagros orogen from south- E-mail address: [email protected] (H. Azizi). east to northwest Iran (Fig. 1). The term was first introduced by Stöcklin https://doi.org/10.1016/j.lithos.2018.03.019 0024-4937/© 2018 Elsevier B.V. All rights reserved. H. Azizi et al. / Lithos 308–309 (2018) 364–380 365 Fig. 1. Simplified geology map of the Sanandaj-Sirjan zone (SaSZ), which shows the intrusive bodies that are extend parallel to the Zagros thrust fault in western Iran (modified from Bayati et al., 2017). Inset map is a simplified geological structural map of Iran (Stöcklin and Nabavi, 1973). in 1968 and it is to be considered as the southwestern part of the Iranian Volcanic rocks provide especially important insights because these micro-continent (Azizi et al., 2016; Hassanzadeh et al., 2008; Hosseini et better approximate magma compositions than do plutonic rocks, al., 2015). The SaSZ is 50–100 km wide and is delimited by the Zagros which are more affected by crystal accumulation and because struc- suture zone in the west and the Urumieh-Dokhtar magmatic arc tures such as pillows and interbedded marine sediments reveal de- (UDMA) in the east (Falcon, 1974; Stöcklin, 1968; Stöcklin and position in a marine environment. The Panjeh magmatic complex, Nabavi, 1973). It also separates Late Cretaceous ophiolites into Inner the object of this study, provides especially useful insights into this and Outer Belts (Moghadam and Stern, 2015). The SaSZ has been Jurassic SaSZ igneous activity because it is a well-preserved volcanic subdivided into northern and southern sectors (Eftekharnejad, 1981). complex. The southern part is dominated by Middle to Late Triassic metamorphic The Panjeh study area is located near the village of Kangareh in the rocks with minor Jurassic igneous rocks but Jurassic igneous rocks are northern SaSZ of northwestern Iran (Fig. 2a, b). The local basement con- more common in the northern SaSZ (Fig. 1). Jurassic igneous rocks of sists of the Songhor-Ghorveh metamorphic complex composed of mar- the SaSZ are generally interpreted as having formed at an active margin ble, greenschist and amphibolite (Azizi et al., 2015a). Fossils in the (e.g. Agard et al., 2005; Azizi et al., 2011, 2013; Azizi and Asahara, 2013; Songhor-Ghorveh metasedimentary rocks define a depositional age Berberian et al., 1982; Berberian and Berberian, 1981; Davoudian et al., from Late Triassic to Middle Jurassic (Hosseiny, 1999) in a marine 2008; Ghasemi and Talbot, 2006; Mahmoudi et al., 2011; Mohajjel et al., basin environment. Metamorphic basement in the study area is covered 2003; Mohajjel and Fergusson, 2014; Moinevaziri et al., 2015; Nadimi by unmetamorphosed Cretaceous sedimentary rocks (Hosseiny, 1999) and Konon, 2012; Shahbazi et al., 2010, 2014; Stöcklin and Nabavi, indicating metamorphism in Middle to Late Jurassic time (Azizi et al., 1973). However, this paradigm has been challenged by Hunziker et al. 2015a; Hosseiny, 1999). Considering the absence of Precambrian base- (2015) who infer formation in a Jurassic rift of some sort. One of the ob- ment, Azizi et al. (2015a) interpreted the Songhor-Ghorveh complex jectives of the present study is to shed light on this controversy. as an oceanic island arc remnant, metamorphosed during the Late Cim- An interesting feature of SaSZ Jurassic igneous rocks is that there is a merian orogeny. In Middle to Late Jurassic times (180–140 Ma), the progression of ages, from ~175 Ma in the SE to ~145 Ma in the NW Songhor-Ghorveh basement was intruded by magmatic complexes (Bayati et al., 2017). This progression is difficult to reconcile with forma- such as the 143.5 ± 1.3 to 147.5 ± 1.3 Ma Suffi Abad granite (Azizi et tion at a convergent plate margin, where igneous activity would be ex- al., 2011), as well as the Mobarak-Abad (Azizi and Asahara, 2013), pected to occur all along the margin at the same time, and to continue Ghalaylan (Azizi et al., 2015b) and Kangareh-Taghiabad gabbroic bodies for several millions or tens of millions of years. Such a protracted mag- (Azizi et al., 2015a). Many of these magmatic complexes are also cov- matic history along a well-defined magmatic front like those of modern ered by unmetamorphosed Cretaceous sedimentary rocks (see Azizi et magmatic arcs is not seen in the distribution of SaSZ igneous rocks. al., 2015a; Hosseiny, 1999). 366 H. Azizi et al. / Lithos 308–309 (2018) 364–380 Fig. 2. (a) Distribution of intrusive bodies in southwest of Ghorveh, which cut the metamorphic basement (after Hosseiny, 1999). (b) Simplified geological map of the Panjeh area (after Hosseiny, 1999; Azizi and Asahara, 2013; Azizi et al., 2015a) showing the distribution of Late Jurassic igneous rocks relative to Songhor-Ghorveh basement and the Kangareh-Taghiabad gabbroic complex. The Panjeh volcanic complex is composed of basalts and andesites possible shear zone is beyond the scope of this paper and will be pre- and, together with the nearby 158 ± 10 Ma Taghiabad maficbody(to sented elsewhere.

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