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•The Sidakan diabases are mostly low-K basalts with sabalkaline affinity.•The diabases are tholeiitic oceanic island arc basalts and N-MORB related.•The generation age of Sidakan ...diabases ranges between 34.6 ± 0.84 and 39.2 ± 1.81 Ma.•The Oceanic Island Arc (OIA) was formed during the initial stages of obduction.•The Iraqi Zagros Thrust Zone was formed subsequent to the formation of OIA.
This study presents petrography, geochemistry, mineral chemistry and geochronology of diabase dikes from Sidakan area, northeastern Iraq. The area consists of basalts and diabase dikes alternating with sedimentary rocks, hosted by Walash Metavolcanic Group (WMG) as part of the Zagros Fold-Thrust Zone (ZFTZ). These rocks are dark grey to pale brown in color, fine to medium in grain size, and have ophitic and porphyritic textures. They consist of plagioclase and clinopyroxene as essential minerals and minor olivine as well as their alteration and low-grade metamorphism products including amphibole, albite, epidote, chlorite, serpentine, calcite and sericite, with ilmenite as an accessory mineral. The diabase dikes consist (as average wt.%) of 51.41 SiO2, 15.82 Al2O3, 9.95 FeOt, 6.58 MgO, 9.63 CaO, 3.42 Na2O, 0.87 TiO2, 0.17 MnO, 0.35 K2O, 0.09 P2O5, and 1.92 LOI. The Harker diagrams indicate that the diabases were formed from fractional crystallization of tholeiitic parent magma. The classification diagram Nb/Y vs. Zr/TiO2 indicated that the studied diabases have affinities of subalkaline basalts, while the SiO2 vs. K2O diagram showed that they are divided between the low-K basalt and basaltic andesite. The tectonic discriminant diagrams show that the diabases are oceanic island-arc tholeiites with N-MORB geochemical affinities. The K − Ar age of the diabases is Late Eocene (Bartonian-Priabonian) ranging between 34.6 ± 0.84 to 39.2 ± 1.81 Ma representing their intrusion/crystallization age and possibly the age of the formation of Oceanic Island Arc and/or the initial collision stage between the Arabian-Iranian microplates.
The amphibolite and hornblendite dikes occur as part of the igneous complexes of Bulfat Ophiolite within the Zagros Suture Zone, NE Iraq. The igneous complex is part of the upper allochthonous ...ophiolite terrane within the second unit of the Penjween-Walash Subzone. This article discusses the petrogenetic characteristics and tectonic setting of the amphibolite rocks based on their petrography, mineral chemistry, and whole-rock geochemistry. Petrographically, both banded and massive amphibolites reveal that the main mineral constituents are amphibole and plagioclase with accessory clinopyroxene, opaques, sphene, apatite, rutile, zircon, sericite, epidote and chlorite; meanwhile the hornblendites consist of >90% amphibole with minor amounts of pyroxene, opaques, plagioclase, titanite, quartz, apatite, zircon, and chlorite. The amphibolites are divided into two types, banded (foliated) and massive, (non-foliated). The dominat textures of amphibolites are porphyroblastic, granoblastic, poikiloblastic, nematoblastic, and blasto-ophitic; meanwhile those of hornblendites are equigranular, poikilitic, cataclastic, and intergranular. The electron microprobe analysis (EPMA) showed that the amphiboles of the banded amphibolite range between tschermakite, magnesio-hornblende and pargasite; and those of the massive amphibolites range between magnesio-hornblende and actinolite; meanwhile those of hornblendites are dominantly tschermakite with minor magnesio-hornblende and pargasite. The plagioclase of the banded amphibolites is mainly oligoclase and andesine; and those of the massive amphibolites are mostly anorthite. Chemical classification diagrams indicated that the studied rocks are had low alkalies (Na2O+K2O), tholeiitic, ultrabasic to basic, alkaline to subalkaline and divided between foidite, picrobasalt and basalt. Various tectonic discriminating diagrams showed that most of studied rocks are mid-ocean ridge basalt (MORB). The studied amphibolites have been subjected to amphibolite facies metamorphism.
The Northern Zagros Suture Zone (NZSZ), formed as a result of the collision between Arabian and Sanandaj-Sirjan microplate, is considered as part of the Zagros orogenic belt. NZSZ is marked by two ...allochthonous thrust sheets in upward stacking order: lower and upper allochthon. The Bulfat complex is a part of the upper allochthon or “Ophiolite-bearing terrane” of Albian-Cenomenion age (97–105 Ma). Voluminous highly sheared serpentinites associated with ophiolites occur within this upper allochthon. In addition, the Gemo-Qandil Group is characterized by gabbroic to dioritic Bulfat intrusion with a crystallization age spanning from ~45 to ~ 40 Ma, as well as extensive metapelites with contact to the Walash-Naupurdam metavolcanic rocks. Due to the deformation in the Sanandaj-Sirjan Zone along the eastern side of the Iraqi segment of NZSZ, the Gemo-Qandil Group was regionally metamorphosed during late Cretaceous (~ 80 Ma). This tectono-compressional dynamics ultimately caused an oscillatory deformation against Arabian continental margin deposits as well. During these events, gabbro-diorite intrusion with high-grade contact metamorphic aureoles occurred near Bulfat. Thus, there is an overlap between regional and contact metamorphic conditions in the area. The earlier metamorphic characteristic can be seen only in places where the latter contact influence was insignificant. Generally, this can only observed at a distance of more than 2.5 km from the contact. According to petrographic details and field observations, the thermally metamorphosed metapelitic units of the metasediment have been completely assimilated, with only some streaks of biotite and relicts of initial foliation. They strongly resemble amphibolite-grade slices from the regional metamorphic rocks in the region. Metapelitic samples far from the intrusion give similar biotite cooling ages as the intrusive rocks. Thus, they may be affected by the same thermal event.
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Ar dating of biotite in metapelite rocks of Bulfat by step-wise heating with laser gave average weighted isotopic ages of 34.78 ± 0.06 Ma. This is interpreted as crystallization/recrystallization age of biotite possibly representing the time of cooling and uplift history of the Bulfat intrusion. Cooling and exhumation rates for the Bulfat gabbro-diorite rocks were estimated as ~ 400 °C/Ma and ~ 3.3 mm/year respectively. According to petrographic details, field observations and Ar/Ar dating concerning the contact metamorphism near Bulfat due to the gabbro-diorite intrusion, no significant deformation is visible during exhumation processes after the Paleogene tectono-thermal event, indicating that isotopic ages of 34.78 ± 0.06 Ma could mark the timing of termination of the island arc activity in the Ophiolite-bearing terrane (upper allochthon).
Penjween ophiolite is one of the ophiolitic complexes of northeastern Iraq. The serpentinites within the Penjween Ophiolite hosts many pods of hornblendite and amphibolite, and dikes of diorite among ...many other igneous bodies. These pods have very sharp contacts with the surrounding mantle serpentinized harzburgites. The hornblendites and amphibolites are usually intimately intergrown together as extremely hard, dark green to black colored, fine-to medium-grained pods with ∼2 x ∼2 x ∼(0.5–1) m dimensions. This study presents petrography, mineral chemistry, whole-rock major and trace element geochemistry, and electron probe microanalyses (EPMA) for the major minerals in the studied rocks. The hornblendite is composed entirely of amphiboles (>99% vol.), meanwhile the amphibolite consists of comparable amounts of amphibole and plagioclase which occasionally occurs as layered rocks with banded texture. The diorite dikes are white in color and consist dominantly of coarse-grained plagioclase and less amphiboles. The amphiboles of these rocks belong to pargasite (Mg# 0.69–0.77) ─ edenite (Mg# 0.74–0.79) endmembers where pargasite is by far the predominant mineral; meanwhile the plagioclase is albite (Ab93.4An6.4Or0.2). The amphiboles are replacement products of pyroxenes indicated from the relict pyroxene within their crystals. The amphiboles are abnormally rich in various dust-like inclusions of transparent minerals like REE-rich epidote, rutile, zircon, apatite, titanite, and ore minerals like ilmenite, and pyrrhotite, oriented along the crystallographic axes and form distinct zones in the core of amphibole crystals. The geochemical characteristics of the studied hornblendite (MgO = 13.07%, Ni = 260 ppm, Mg# = 66.57) as well as the high Sc (33 ppm) and V (254 ppm) concentrations are collectively consistent with a mantle-derived, igneous origin. The primitive-mantle normalized trace elements spidergram showed enrichment (hump) in Ba, Th, U, La, Ce, Pb, and Sr, and depletion (trough) in Nb, Ta, K, and Ti. The chondrite-normalized REE diagram showed enrichment of LREE relative to HREE, indicated from the smooth and steady decrease in the negative slope from LREE towards HREE with a negligible Eu-anomaly. Various tectonic discriminating diagrams showed that the studied hornblendite, amphibolite pods and diorite dikes are of igneous fore-arc origin, formed from calc-alkaline and/or tholeiitic magma within an active continental margin setting. The 40Ar/39Ar laser age of hornblendite is late Paleocene (Thanetian) (57.8 ± 5.1 Ma) which might represent an event during the obduction between the oceanic fore-arc Island and the Arabian Plate during the Late Cretaceous/Paleocene period.
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•The studied rocks are hornblendite, amphibolite and diorite rocks.•The hornblendite is monomineralic and consists of amphiboles.•The amphibolite and diorite consist of comparable amounts of amphibole and plagioclase.•These rocks are calc-alkaline island arc basalts,•The 40Ar/39Ar laser age of the hornblendite is late Paleocene (Thanetian) (57.8 ± 5.1 Ma).
