Sarmad A Ali

Tectono-stratigraphy and structure of the northwestern Zagros collision zone across the Iraq-Iran border

Tectono-stratigraphic units within the Zagros Oroge n in northeast Iraq (foreland) and northwest Iran ( hinterland) are correlated to provide an integrated map along t he collision zone. Access to this part of Iraq duri ng the past four decades has been limited due to geopolitical s ituation. Structural cross-sections across the Zagr os Suture Zone in this area reveal the relationships between the tectonic terranes of various ages and different origins. Terranes of oceanic affinity have accreted onto the Arabian plate during collision-accretion events th at started in the Late Cretaceous. The collision resulted in clos ure of the Neotethys Ocean and the construction of a structurally complex suture zone. Jurassic-Cretaceo us deep ocean radiolarites of the Qulqula-Kermansha h terrane and ophiolitic melange serpentinites were s tructurally accreted against the Arabian passive ma rgin during an ophiolite arc-continent collision event in the L ate Cretaceous. The overthrust radiolarites and oph iolitic melange terranes initiated the development of the f oreland basin overlapping flysch (turbidites) and m olasse assemblages on the now active Arabian margin. Eocene-Oligocene volcano-sedimentary rocks of the WalashNaopurdan-Kamyaran terrane developed as an intra-oceanic island-arc within the intervening Neotethys O cean. They now structurally overlie the older ophiolite m elange and radiolarite terranes as a result of cont inued convergence onto the margin of the Arabian Plate. T hese younger thrust sheets and nappes have been tra nsported over the Miocene molasse unit of the Tertiary Red B eds in the flexural foreland basin and covered the Late Cretaceous accretionary complex terranes and forela nd basin assemblages. The Qulqula-Kermanshah terrane is exposed in a tectonic window in the northeastern pa rt of the mapped area indicating that the Late Cret aceous accreted terranes occur below the Walash-Naopurdan-Kamyaran thrust sheet. A Late Cretaceous ophiolitebearing terrane named the “Upper Allochthon” (i.e. Gemo-Qandil nappe, 97-118 Ma) was emplaced by younger thrust sheets over the Eocene-Oligocene Walash-Naopurdan-Kamyaran terrane by out-of-sequence thrusting. Mesozoic metamorphic rocks from the hinterland, including volcanic and intrusive rocks of the active I ranian continental margin (Sanandaj-Sirjan zone), were emplaced during continent-continent collision and occu r in the youngest nappes and klippes along the Zagros Suture Zone.

Petrography, geochemistry, and provenance of the Chalki rocks in Kurdistan region, North Iraq

Outcrops of the Paleozoic Chalki volcanic rocks are restricted to part of the northern Thrust Zone of Iraq close to Iraqi-Turkish border. Petrographically, the volcanic rocks from the Chalki area are mainly layered, appearing fresh in the field and exhibiting some basaltic lava flows. Porphyritic, amygdaloidal, and microlite-porphyric are the main observed textures. Phenocrysts of primary phases (i.e., olivine, iron oxides) are in a groundmass of feldspars and clinopyroxene. Chalki Formation is intercalated with Pirispiki Formation which consists of thin to medium bedded, greenish gray marl, red mudstone, and veins of calcite. The Chalki rocks are mafic of theolitic basalt type. Geochemically, they have high chromium and nickel concentrations in most samples. Rare earth element (REE) patterns illustrate parallel to sub-parallel, moderately fractionated REE patterns. The low heavy REE (HREE) contents in the studied samples appear to be due to partial melting of metamorphosed oceanic crust leaving HREE-rich accessory minerals (i.e., garnet) as a residual phase in the source. No Eu anomalies were observed in the Chalki samples which may indicate a back-arc basin pattern. The non-subduction signature of the Chalki rocks is confirmed by the Nb/Yb versus Th/Yb diagram, which shows that most of the studied rocks fall in the compositional field of non-arc-related rocks—well within the field of the mid-ocean ridge basalt (MORB)-ocean island basalt (OIB) mantle array.