Petrogenesis of metabasalt rocks in the Bulfat complex, Kurdistan region, Iraqi Zagros Suture Zone

Metabasaltes are exposed in the Bulfat complex north of Qaladeza that is a part of the Northwestern Zagros Suture Zone (NZSZ).Petrographic and geochemical study of metabasaltes have been conducted in order to provide insights into the origin and evolution of magmatism found at Neotethyian subducted plate margins and to determine their protolith nature and geodynamic setting. The whole rock chemistry indicates basalt to andesite composition for the metabasaltes. The geochemical investigation strongly suggests that the metabasaltes are derived from calic alkaline basalt and were emplaced in arc tectonic setting.

Minor body of ultrabasic rocks and very limited occurrence of acid differentiates are also present. Xenoliths of the country rocks and very high grade thermal metamorphism up to the pyroxene hornfels facies is characteristic for the Bulfat complex [3]. In this paper, the petrogenesis of Qaladeza metabasaltes has been demonstrated. This was achieved via integrated whole-rock petrography and geochemistry.

2.GEOLOGICAL BACKGROUND
The study area lie between longitude 45 o 14 / 39.54 // E and latitudes 36 o 11 / 55.3 // N, and it is situated along the Iraq-Iran-border,30 km east Qala Deza City, Kurdistan region, NE Iraq. The study area contains unexploded landmines, limiting sampling to the boundary of main roads. The study area forms part of the Western Zagros Fold-Thrust Belt, which developed as a response to collision of the Arabian and Iranian plates [1] Figures (1 and 2), and it is an integral part of the Zagros suture zone [4]. The complex comprises allochthonous detachment of the Albian-Cenomanian Gemo-Qandil Sequence (Upper Allochthon) and the Paleocene-Eocene Walash Volcano-sedimentary Sequence (Lower Allochthon; [5&6]). On the basis of recent studies [4, 5&6], these two allochthonous sheets were juxtaposed and amalgamated into a single nappe (Walash-Penjween Subzone) following the closure of the Neo-Tethys. Coeval volcanic activity of Walash-Naopurdan 'Lower Allochthon' with the multiphase intrusion of the Bulfat Complex is common along the entire length of the Iraqi Zagros Suture Zone and the volcanic activity represents widespread arc-back arc volcanism during the Paleogene. With the exception of the Bulfat Complex, the remainder of the Lower Allochthon does not show any similar intrusive features [7]. Field evidence shows that the nappe which incorporates the two amalgamated sheets rests on top of various units: Tertiary Mollasses (Tertiary Red Beds), Neoautochthonous flysch (Maastrichtian) and parautochthonous radiolarite (Albian-Cenomanian; [8]). Exhumation of the Bulfat Complex occurred through the formation of nappes in a continental collision [7] that terminated during the Middle Miocene [8].

4.PETROGRAPHY AND MINERAL CHEMISTRY
The metabasalt rocks have mostly grey to brownish grey weathering. Study of 10 thin-sections shows that these rocks display decussate, porphyritic, and intergranular textures Figures (3A, 3B &3C).Phenocrysts include altered plagioclase, Amphibole, Biotite, clinopyroxene, and iron oxide. Secondary minerals such as chlorite, serpentine, sericite and epidote are present in most samples.

Plagioclase
Microprobe analyses of plagioclase in the most metabasalt rocks samples are provided in There are noticeable differences between the compositions of plagioclase crystals in the various rock groups ranging from Anorthite to Albite Table (

Amphibole
Primary amphibole is the most abundant mafic mineral in the studied rocks. It is essentially homogeneous in composition, and corresponds mostly to calcic amphibole (e.g. Magnesiohornblende) Table (

Pyroxene
Only one clinopyroxene grain was observed in the QH9 sample with diopside composition

Iron oxides
Iron oxides are found as fine crystals randomly scattered in the groundmass. Three spots in three samples (QL3, QH8 &QH4) were analyzed and the formulae were calculated on the basis of 6 oxygen Table (

Biotite
Textural and petrological studies indicate that the biotite in QL3. The composition of the biotite is Fe-and Ti-rich and Al-poor, taken in conjunction with (Fe exclusively present as Fe 2+ ).
Accordingly, the biotite is classified as Fe-biotite on the Foster classification diagram [11], Table   (

Major Elements
The bulk chemistry of Qaladeza metabasalts is deduced from the 10 analyses Table (

Trace Elements
The ranges for Cr, Ni, and Co in the Qaladeza metabasalt samples are 140-2478, 44.8-2041, and 5.3-115.4 ppm, respectively Table (2). Cr is highly compatible and is concentrated in clinopyroxene, and spinel [14], and hence it shows a significant positive correlation with MgO

Rare earth elements and spider diagrams
The

6.DISCUSSION AND CONCLUSIONS
The petrographic study shows that these rocks were affected by metamorphic alteration under greenschist facies conditions and that is clear in most samples, particularly, in QH1 which it has high loss-on-ignition value due to high content of serpentine minerals (e.g. lizardite ). Despite