Serpentinites and their tectonic signature along the Northwest Zagros Thrust Zone, Kurdistan Region, Iraq

Abstract

Two types of serpentinized peridotites are distinguished within the Northwest Zagros Thrust Zone (NW-ZTZ) in Kurdistan region of Iraq. One is found as lower members of ophiolite sequences, such as the Mawat and Penjwin ophiolites of the upper Cretaceous age. The other is represented by intraformational isolated serpentinite bodies in Betwat, Qaladeza, and Qalander areas within the Walash-Naopurdan volcano-sedimentary unit of the Paleocene to Eocene paleo-arc tectonic setting. Serpentinites within the NW-ZTZ consist mainly of lizardite and chrysotile, with subordinate amounts of syn-serpentinization magnetite, carbonates, chromium chlorite, tremolite, and talc as secondary minerals, and olivine, clinopyroxene, and chromian spinel as primary minerals. Minor antigorite is also found in the sheared serpentinites often found in ophiolite sequences. Petrological and geochemical studies of serpentinites from the NW-ZTZ show that, of the original protoliths of serpentinites, those associated with ophiolites are residual depleted harzburgite and dunite. The Cr# ¼ Cr= ð Cr þ Al ð Þ atomicratio: Cr þ Al ð Þ atomicratioÞ of chromian spinel is more than 0.6, and the forsterite content of olivine is 91-92. On the other hand, the original protolith of isolated serpentinite bodies is less depleted harzburgite or depleted lherzolite, which has spinel with Cr# less than 0.6 and olivine with 90-91 forsterite contents. Whole rock chemistry of major, trace, and rare earth elements shows that the serpentinites of ophiolite sequences are depleted in CaO, Al 2 O 3 , and SiO 2 , Sr, and Zr, and are enriched in MgO, Ni, and Cr, in comparison with the isolated serpentinites. Cr# of the disseminated unaltered chromian spinels indicates that the serpentinites of both types had been originated from the supra-subduction zone tectonic setting; the serpentinites of ophiolite sequences obducted and thrusted over the continental margin during the obduction of the Tethyth oceanic crust onto the Arabian continental margin during the upper Cretaceous period. Isolated serpentinite bodies represent serpentinized forearc mantle wedge peridotites emplaced by diapiric upwelling into non-accretionary forearc tectonic settings during the Paleocene to Eocene age.

Geochemistry and geodynamics of the Mawat mafic complex in the Zagros Suture zone, northeast Iraq

“…The ultramafic rocks are classified into three groups: the first is dunite, which is composed mainly of fresh olivine, some of which show serpentine minerals around the rims and within fractures. Previous studies [32] have shown that the serpentine in these rocks is mostly chrysotile that formed at high temperature. Kink and deformation bands appear in dunite with disseminated chromite.…”

“…Mawat ultramafics show false bedding because of parallel fractures (Fig. 4 a and b), and are variably serpentinized [32] and rich in chromite pods 32, 33. The harzburgite and dunite are cut by some fresh clinopyroxene dykes (Fig.…”

Mineralogy and Origin of the Manganese Deposit in the Sulaimani Province, Kurdistan Region of Iraq: Insight to Serpentinization-Induced Manganese Production Scenario

“…Mineralogical and chemical data from meta harzburgite of the Penjween ophiolite indicate that the parent olivine and spinel contain up to 0.4 wt. % and 1.2 MnO respectively (Mohammad, 2011). Meanwhile up on hydrothermal alteration the products of these two minerals represented by chromium magnetite and serpentine show decreasing MnO to 0.1 and 0.25 wt.…”

“…1c). The Penjween ophiolite consists of about 300 m thick mantle sequences mostly serpentinized harzburgite with some restricted dunite, pyroxenite veins and chromite pods to the southwest, occupying the summit of Mlakawa mountain, to the west followed by about 2 Km crustal sequences represent by various types of gabbro's (Ali and Rostum, 2021), dykes of diorite and volcanic rocks at the Mlakawa mountain slope and base respectively (Mohammad, 2011;Mohammad et al, 2021). Within the volcanic units occasionally bolder of metalliferous recrystallized quartz dominated rock occurs north of the Kani Manga village.…”

“…Our proposal begins with the occurrence of protrusion of an ultramafic body of harzburgite composition through a ridge axis. We proposed that the upper mantle unit of the Penjween ophiolite have been subjected to a variable degree of the serpentinization process via infiltration deep seawater infiltrating through fractures in the oceanic crust to the reaction zone prior obduction (Mohammad, 2011;Mohammad, 2013;Mohammad and Mousa, 2009). In the reaction zone, syn serpentinization fluid rich in Fe and Mn, Ca, Mg is heated by hot mantle substrate and or exothermic serpentinization reaction where it becomes buoyant and quickly proceeds to the ocean floor to be discharged through a plumes and vent structure or infiltrating through more fractures, diluting with seawater and being discharged as diffuse hydrothermal fluid rich in Mn and Fe.…”