Metamorphic history of glaucophane‐paragonite‐zoisite eclogites from the Shanderman area, northern Iran

Abstract

The Shanderman eclogites and related metamorphosed oceanic rocks mark the site of closure of the Palaeotethys ocean in northern Iran. The protolith of the eclogites was an oceanic tholeiitic basalt with MORB composition. Eclogite occurs within a serpentinite matrix, accompanied by mafic rocks resembling a dismembered ophiolite. The eclogitic mafic rocks record different stages of metamorphism during subduction and exhumation. Minerals formed during the prograde stages are preserved as inclusions in peak metamorphic garnet and omphacite. The rocks experienced blueschist facies metamorphism on their prograde path and were metamorphosed in eclogite facies at the peak of metamorphism. The peak metamorphic mineral paragenesis of the rocks is omphacite, garnet (pyrope-rich), glaucophane, paragonite, zoisite and rutile. Based on textural relations, post-peak stages can be divided into amphibolite and greenschist facies. Pressure and temperature estimates for eclogite facies minerals (peak of metamorphism) indicate 15-20 kbar at~600°C. The pre-peak blueschist facies assemblage yields <11 kbar and 400-460°C. The average pressure and temperature of the post-peak amphibolite stage was 5-6 kbar,~470°C. The Shanderman eclogites were formed by subduction of Palaeotethys oceanic crust to a depth of no more than 75 km. Subduction was followed by collision between the Central Iran and Turan blocks, and then exhumation of the high pressure rocks in northern Iran.University of Tabriz. We thank U. Altenberger, P. O'Brien and M. Konrad-Schmolke for their helpful discussions. Invaluable scientific comments by G. Droop are highly appreciated. We are grateful to C. Gunter and A. Musiol for their help with analysis and J. Sabouri (Geological Survey of Iran) for sharing some information on the geology of the Shanderman area. C. Fischer is acknowledged for preparing excellent thin sections. Thoughtful reviews by Y. Rolland and J. Gilotti improved the manuscript, for which we are grateful. Dr. Rolland provided us with some of his publications and unpublished data on geology of Armenia and the adjacent areas. We are grateful to D. Whitney and D. Robinson for generous help and editorial handling of the manucript.

Whole Rock Geochemistry and Tectonic Setting of Jurassic Aged Lisar Granite, Talesh Mountains, North Iran

“…This opinion is debated and other researchers consider the continuation of Palaeotethys to the north and outside of the Iranian crust (Zanchetta et al, 2009). Study of Palaeotethys ophiolites and high pressure rocks (eclogites and blueschists) helps to work out the location of this suture in northern Iran (Zanchetta et al, 2009;Omrani et al, 2013;Shafaii Moghadam et al, 2015). Granitoids play an important role in this regard and study of granitoid plutons at different tectonic settings can help to reconstruct the geodynamic evolution of the Palaeotethys Ocean (Majidi, 1975;Debon et al, 1987;Erkül et al, 2008;Hennig et al, 2009).…”

“…Most researchers believe that the continuation of the Palaeotethys suture from China into west Turkey can be traced in North Iran along the Alborz Mountains (Alavi, 1991;Omrani et al, 2013, Shafaii Moghadam et al, 2015. This opinion is debated and other researchers consider the continuation of Palaeotethys to the north and outside of the Iranian crust (Zanchetta et al, 2009).…”

“…The evolution of the Alborz belt mainly occurred in the Cenozoic (Rezaeian et al, 2012). Opening and subsequent closure of the Neotethys along the Zagros Mountains and opening of the Red Sea had important effects on the structural evolution of the Alborz belt (Axen et al, 2001;Guest et al, 2006;Omrani et al, 2013). Collision of the Gondwana-derived blocks with Eurasia occurred in the Late Triassic, resulting in the Eo-Cimmerian deformation in North Iran, followed by a strong but poorly known Neo-Cimmerian compression event in Middle-Late Jurassic times that mainly affected Central Iran ).…”

“…The Talesh Mountain range is a continuation of the Alborz range towards the west. Rock units considered by different researchers to mark the Palaeotethys suture in North Iran are accretionary units of the Mashhad area (Alavi, 1991;Majidi, 1991;Mirnejad et al, 2013;Shafaii Moghdam et al, 2015), Gorgan schists (Ghavidel et al, 2007;Delaloy et al, 1981), metamorphic rocks of the Gasht and Masuleh area (Clark et al, 1975) and Shanderman eclogites (Zanchetta et al, 2009;Omrani et al, 2013). The Palaeotethys suture can be traced to the east to Afghanistan and China and towards the west into Turkey .…”

Iranshahr blueschist: subduction of the inner Makran oceanic crust

“…1). Northern Iran ophiolites and high-pressure and low-temperature (HP-LT) metamorphic rocks (along Alborz Mountain ranges; Omrani et al, 2013a) are considered as Palaeotethys and the other ophiolites [along Zagros, Eastern Iran Zone and around Central Iranian Micro-continental blocks (CIM)] are considered as Neotethys suture zones respectively (e.g. Shafaii Moghadam & Stern, 2011;Omrani et al, 2013b).…”