The attention of the present authors is drawn to what looks like odd or even erroneous evidence p... more The attention of the present authors is drawn to what looks like odd or even erroneous evidence presented by a paper recently published by Karim and Al-Bidry (2020), focusing on the Zagros Metamorphic Core Complex and providing an example from Bulfat Mountain, Qala Diza area, Kurdistan Region, northeast Iraq. For instance, the ophiolite at Mawat is of the Cretaceous age (105 ±5 Ma; Mohammad and Qaradaghi (2016), the plagiogranites are also of the Cretaceous age, but are slightly younger (92.6 ±1.2 Ma - Mohammad and Qaradaghi (2016), 96.0 ±2.0 Ma - Ismael et al. (2017) and the Hasanbag ophiolite is 106-92 Ma (Ali et al., 2012). On the other hand, 40Ar- Ar dates on the magmatic feldspar separates from the Walash and Naopurdan volcanic rocks indicate an Eocene-Oligocene age (43.01 ± 0.15 to 24.31 ± 0.60 Ma; Ali, 2012; Ali et al., 2013). Many studies of the Zagros region have been undertaken on structure, origin of the ophiolites and the related igneous rocks, as well as on the geodynam...
Events in the tectono-magmatic framework of the Eocene Bulfat Igneous Complex in the Kurdistan re... more Events in the tectono-magmatic framework of the Eocene Bulfat Igneous Complex in the Kurdistan region of northeastern Iraq are revealed through the integrated field, petrographic, geochemical and zircon petrography and U–Pb geochronology of the Qaladeza trondhjemite sheets that cut gabbros of the complex. The trondhjemite sheets are variably deformed, with the cataclasis of large plagioclase feldspars. The trondhjemites are albitic, and geochemical features such as strong enrichment of the light REE relative to the heavy REE and low Ti and REE content show that they did not form as late differentiates of a MORB-like source, but instead by hydrous partial melting of mafic rocks, possibly also involving some more evolved crustal source as well. Qaladeza trondhjemite oscillatory-zoned magmatic zircon has an age of 48.0 ± 0.6 Ma (95% confidence). These domains have been etched to form voids in the zircons, the walls of which have thin coatings of Th- and Ca-bearing species. Subsequent p...
Events in the tectono-magmatic framework of the Eocene Bulfat Igneous Complex in the Kurdistan re... more Events in the tectono-magmatic framework of the Eocene Bulfat Igneous Complex in the Kurdistan region of northeastern Iraq are revealed through the integrated field, petrographic, geochemical and zircon petrography and U-Pb geochronology of the Qaladeza trondhjemite sheets that cut gabbros of the complex. The trondhjemite sheets are variably deformed, with the cataclasis of large plagioclase feldspars. The trondhjemites are albitic, and geochemical features such as strong enrichment of the light REE relative to the heavy REE and low Ti and REE content show that they did not form as late differentiates of a MORB-like source, but instead by hydrous partial melting of mafic rocks, possibly also involving some more evolved crustal source as well. Qaladeza trondhjemite oscillatory-zoned magmatic zircon has an age of 48.0 ± 0.6 Ma (95% confidence). These domains have been etched to form voids in the zircons, the walls of which have thin coatings of Th-and Ca-bearing species. Subsequent partial recrystallization of the zircons obliterated the voids and increased the Th/U of the recrystallized zircon, which mostly formed at 38.74 ± 0.74 Ma. The 48 Ma domains relate to recycling of mafic crust in a proto-arc tectonic setting and are congruent with Eocene proto-arc magmatic activity within the Neotethyan oceanic basin. The 39 Ma domains relate to later tectonic-induced recrystallisation events coeval with the closure of Neotethys resulting from the late Eocene collision between the Arabian plate and Eurasia in Kurdistan.
The suprasubduction Bulfat Igneous Complex in NE Iraq is one of the discontinuous Neotethys ocean... more The suprasubduction Bulfat Igneous Complex in NE Iraq is one of the discontinuous Neotethys oceanic lithosphere fragments preserved in the Zagros region. Reported here are new geochronological, petrological and geochemical data from this assemblage. At the study locality, Eocene arc-related magmatic rocks are intruded by extensive dykes of Shaki-Rash gabbro. The key reason to focus on these rocks is the remarkable lack of hydrothermal alteration, including preservation of very fresh olivine. Besides olivine the gabbros contain plagioclase and clinopyroxene, with lesser orthopyroxene, biotite, brown hornblende and alkali feldspar. From mineral chemistry, the crystallization conditions of the olivine gabbros are ~ 950-1050°C and ~ 5-3 Kbar. Shaki-Rash gabbro shows alkaline affinity. SHRIMP U-Pb dating of magmatic zircon from the gabbro yielded a mean 206Pb/238U age of 39.0±0.5 Ma (Eocene). Most of the Shaki-Rash gabbro samples have Ti/V of 100 to 50 and fall in the back-arc basin (BAB...
Abstract Closure of Neo-Tethys between the Late Cretaceous and Miocene caused obduction of intra-... more Abstract Closure of Neo-Tethys between the Late Cretaceous and Miocene caused obduction of intra-Neo-Tethys volcanic arc allochthons onto the northern margin of the Arabian-Nubian Shield. This loading led to downwarping of the shield forming a flexural basin in which the Tanjero Formation and later Red Beds accumulated. Analysis of the detrital zircon populations in these sedimentary units provides additional evidence supporting the petrographic data for the presence and unroofing of the allochthons. Both the Tanjero Formation and Red Beds show evidence of initial derivation of detritus from the Nubian-Arabian Shield together with minor Paleozoic detritus from Egypt, Turkey and/or Iran. The youngest detrital zircon grains in the Tanjero Formation are of Paleocene age and probably represent northern derivation from the Sanandaj-Sirjan Zone. In contrast, the upper Miocene Red Beds contain detrital zircon of Eocene age that confirms the petrographic evidence for derivation from, and hence emplacement of, the lower allochthon of intra-Neo-Tethys Walash-Naopurdan rocks.
Abstract In far North Greenland at the head of Victoria Fjord (∼81°30′N), a ∼1000 km2 exposure of... more Abstract In far North Greenland at the head of Victoria Fjord (∼81°30′N), a ∼1000 km2 exposure of Precambrian crystalline basement rocks is a window through the region's extensive latest Neoproterozoic and Paleozoic Arctic Platform sedimentary cover sequence. These basement rocks, named here the Victoria Fjord terrane, are dominated by weakly-foliated granodioritic orthogneisses, with lesser amounts of migmatite. These are intercalated with strips of supracrustal rocks dominated by paragneisses. This poorly-exposed Archean terrane at Greenland's northern tip is succeeded to the south by the extensive east-west trending Paleoproterozoic Inglefield Mobile Belt of juvenile arc rocks. The Victoria Fjord terrane granodiorites have zircon U-Pb ages from 3292 ± 14 Ma to ∼3260 Ma. Reconnaissance U-Pb dating on schlieric migmatite zircons yielded ages of ∼3280, 3400 and 3500 Ma. Paragneiss detrital zircons have ages of mostly ∼2710 Ma, with a minority of 3000–2900 Ma grains. This demonstrates that these sedimentary rocks were not derived from the local basement. Post- Archean magmatic or metamorphic zircon was not detected in any of the samples. Initial eHf of 3290–3260 Ma granodiorite and granite zircons ranges from −4 to +2, and the magmatic protoliths are interpreted as sourced from the melting of somewhat older (3500–3400 Ma) Paleoarchean crust, represented by paleosome in the migmatites. The paragneiss 3000–2900 Ma detrital zircons were derived from juvenile felsic crust of that age. The ∼2710 Ma group show negative correlation of Th/U and initial eHf, such that those with high Th/U up to >2.0 have eHf values of −6 to −10. The ∼2710 zircons were sourced from mafic rocks formed by melting of much older (Paleoarchean?) enriched mantle which was variably contaminated by 3000–2900 Ma crust during its ascent. The Victoria terrane is unique amongst the Archean basement terranes in Greenland because it is dominated by 3500–3260 Ma crust. However, the Arctic basin contains detrital zircons of that age, and rocks of that age also occur in eastern Siberia and northwestern Canada. Implications for high Arctic early Precambrian geodynamics are discussed.
Abstract In NE Iraq, the eastern edge of the Arabian plate is overlain by arc rock allochthons wh... more Abstract In NE Iraq, the eastern edge of the Arabian plate is overlain by arc rock allochthons whose genesis and tectonic emplacement were related to the consumption and closure of the Neotethys Ocean. This paper demonstrates the occurrence of unrelated Paleogene arc rocks in two adjacent allochthons. The Bulfat Igneous Complex at Wadi Rashid (NE Iraq) is an intrusion within the Upper Allochthon Albian–Cenomanian Gimo–Qandil sequence suprasubduction zone assemblage. A thrust separates this allochthon from the underlying Lower Allochthon of the Eocene-Oligocene Walash–Naopurdan volcanic-sedimentary arc rocks. The Bulfat Igneous Complex at Wadi Rashid consists of gabbro and granitic composite intrusions in which components mingle down to a small scale. Textural relationships in the Bulfat Igneous Complex rocks indicate emplacement at high crustal levels with rapid cooling, which is consistent with amphibole geobarometry indicating crystallisation pressures between ~ 250 and 300 Mpa. Ti-rich igneous pargasite and Ti-rich igneous Fe-biotite from gabbroic and granitic components yielded 40Ar/39Ar ages of 39.23 ± 0.21 and 38.87 ± 0.24 Ma respectively. These ages agree within analytical error and suggest coeval emplacement and rapid cooling of mafic and felsic magmas in the Eocene, in an event that was distinct and much younger than the host Albian–Cenomanian rocks. This igneous event was unrelated to formation of Cenozoic rocks in the underlying, tectonically separate, lower allochthon. The trace element signatures of the Wadi Rashi volcanic rocks show volcanic-arc characteristics for the granites and the gabbroic rocks resemble E type MORB. The presence of Eocene arc-related rocks in two allochthons suggests complexity in Paleogene subduction systems, with possibly two subduction zones operating at that time.
The Hasanbag igneous complex is situated near Sidekan, 100 km northeast of Erbil city, Kurdistan ... more The Hasanbag igneous complex is situated near Sidekan, 100 km northeast of Erbil city, Kurdistan Region, within the Iraqi Zagros suture zone. It forms part of an ophiolite-bearing terrane referred to as the “Upper Allochthon” or Gemo-Qandil Group. The Hasanbag igneous complex consists predominantly of calc-alkaline basaltic andesites to andesites cut by microgabbro and diorite dikes, which previously were interpreted as a part of the Eocene Walash volcanic group.
The world's largest ongoing collisional orogeny is the Europe Alps-Himalayan-SE Asian bel... more The world's largest ongoing collisional orogeny is the Europe Alps-Himalayan-SE Asian belt and is a natural laboratory to understand many processes that have shaped the continents. Due to political instability and conflict throughout this millennium, the Iraq (Kurdish) sector of the Zagros mountain chain is the least studied part of this orogenic system. In Iraq, the Zagros contains the suture between the Arabian subcontinent to the south and west and the Iranian edge of the Eurasian continent to the north and east. The suture zone is marked by several allochthons of Neotethyan ophiolitic and volcanic arc assemblages that were obducted onto the Arabian margin. New geochronological data, including SHRIMP U-Pb zircon, integrated with whole rock geochemistry, indicates that both Cretaceous (˜96 Ma) and Cenozoic (˜40 Ma) assemblages are present. The relationships between these units are complicated, thus some Cretaceous arc rocks were intruded by Cenozoic arc rocks, and out-of-sequence thrusting has interleaved and juxtaposed assemblages of different ages. Ongoing wrench faulting since continental collision at˜14 Ma has further complicated the pattern of lithotectonic units, particularly those that were obducted out of the Neotethyan realm. The new data indicate that the Iraqi sector of Neotethys was not 'quiet' in the Cretaceous, but contains fragments of arcs of that age, contiguous with those along strike in Turkey, Iran and the Himalayas.
The attention of the present authors is drawn to what looks like odd or even erroneous evidence p... more The attention of the present authors is drawn to what looks like odd or even erroneous evidence presented by a paper recently published by Karim and Al-Bidry (2020), focusing on the Zagros Metamorphic Core Complex and providing an example from Bulfat Mountain, Qala Diza area, Kurdistan Region, northeast Iraq. For instance, the ophiolite at Mawat is of the Cretaceous age (105 ±5 Ma; Mohammad and Qaradaghi (2016), the plagiogranites are also of the Cretaceous age, but are slightly younger (92.6 ±1.2 Ma - Mohammad and Qaradaghi (2016), 96.0 ±2.0 Ma - Ismael et al. (2017) and the Hasanbag ophiolite is 106-92 Ma (Ali et al., 2012). On the other hand, 40Ar- Ar dates on the magmatic feldspar separates from the Walash and Naopurdan volcanic rocks indicate an Eocene-Oligocene age (43.01 ± 0.15 to 24.31 ± 0.60 Ma; Ali, 2012; Ali et al., 2013). Many studies of the Zagros region have been undertaken on structure, origin of the ophiolites and the related igneous rocks, as well as on the geodynam...
Events in the tectono-magmatic framework of the Eocene Bulfat Igneous Complex in the Kurdistan re... more Events in the tectono-magmatic framework of the Eocene Bulfat Igneous Complex in the Kurdistan region of northeastern Iraq are revealed through the integrated field, petrographic, geochemical and zircon petrography and U–Pb geochronology of the Qaladeza trondhjemite sheets that cut gabbros of the complex. The trondhjemite sheets are variably deformed, with the cataclasis of large plagioclase feldspars. The trondhjemites are albitic, and geochemical features such as strong enrichment of the light REE relative to the heavy REE and low Ti and REE content show that they did not form as late differentiates of a MORB-like source, but instead by hydrous partial melting of mafic rocks, possibly also involving some more evolved crustal source as well. Qaladeza trondhjemite oscillatory-zoned magmatic zircon has an age of 48.0 ± 0.6 Ma (95% confidence). These domains have been etched to form voids in the zircons, the walls of which have thin coatings of Th- and Ca-bearing species. Subsequent p...
Events in the tectono-magmatic framework of the Eocene Bulfat Igneous Complex in the Kurdistan re... more Events in the tectono-magmatic framework of the Eocene Bulfat Igneous Complex in the Kurdistan region of northeastern Iraq are revealed through the integrated field, petrographic, geochemical and zircon petrography and U-Pb geochronology of the Qaladeza trondhjemite sheets that cut gabbros of the complex. The trondhjemite sheets are variably deformed, with the cataclasis of large plagioclase feldspars. The trondhjemites are albitic, and geochemical features such as strong enrichment of the light REE relative to the heavy REE and low Ti and REE content show that they did not form as late differentiates of a MORB-like source, but instead by hydrous partial melting of mafic rocks, possibly also involving some more evolved crustal source as well. Qaladeza trondhjemite oscillatory-zoned magmatic zircon has an age of 48.0 ± 0.6 Ma (95% confidence). These domains have been etched to form voids in the zircons, the walls of which have thin coatings of Th-and Ca-bearing species. Subsequent partial recrystallization of the zircons obliterated the voids and increased the Th/U of the recrystallized zircon, which mostly formed at 38.74 ± 0.74 Ma. The 48 Ma domains relate to recycling of mafic crust in a proto-arc tectonic setting and are congruent with Eocene proto-arc magmatic activity within the Neotethyan oceanic basin. The 39 Ma domains relate to later tectonic-induced recrystallisation events coeval with the closure of Neotethys resulting from the late Eocene collision between the Arabian plate and Eurasia in Kurdistan.
The suprasubduction Bulfat Igneous Complex in NE Iraq is one of the discontinuous Neotethys ocean... more The suprasubduction Bulfat Igneous Complex in NE Iraq is one of the discontinuous Neotethys oceanic lithosphere fragments preserved in the Zagros region. Reported here are new geochronological, petrological and geochemical data from this assemblage. At the study locality, Eocene arc-related magmatic rocks are intruded by extensive dykes of Shaki-Rash gabbro. The key reason to focus on these rocks is the remarkable lack of hydrothermal alteration, including preservation of very fresh olivine. Besides olivine the gabbros contain plagioclase and clinopyroxene, with lesser orthopyroxene, biotite, brown hornblende and alkali feldspar. From mineral chemistry, the crystallization conditions of the olivine gabbros are ~ 950-1050°C and ~ 5-3 Kbar. Shaki-Rash gabbro shows alkaline affinity. SHRIMP U-Pb dating of magmatic zircon from the gabbro yielded a mean 206Pb/238U age of 39.0±0.5 Ma (Eocene). Most of the Shaki-Rash gabbro samples have Ti/V of 100 to 50 and fall in the back-arc basin (BAB...
Abstract Closure of Neo-Tethys between the Late Cretaceous and Miocene caused obduction of intra-... more Abstract Closure of Neo-Tethys between the Late Cretaceous and Miocene caused obduction of intra-Neo-Tethys volcanic arc allochthons onto the northern margin of the Arabian-Nubian Shield. This loading led to downwarping of the shield forming a flexural basin in which the Tanjero Formation and later Red Beds accumulated. Analysis of the detrital zircon populations in these sedimentary units provides additional evidence supporting the petrographic data for the presence and unroofing of the allochthons. Both the Tanjero Formation and Red Beds show evidence of initial derivation of detritus from the Nubian-Arabian Shield together with minor Paleozoic detritus from Egypt, Turkey and/or Iran. The youngest detrital zircon grains in the Tanjero Formation are of Paleocene age and probably represent northern derivation from the Sanandaj-Sirjan Zone. In contrast, the upper Miocene Red Beds contain detrital zircon of Eocene age that confirms the petrographic evidence for derivation from, and hence emplacement of, the lower allochthon of intra-Neo-Tethys Walash-Naopurdan rocks.
Abstract In far North Greenland at the head of Victoria Fjord (∼81°30′N), a ∼1000 km2 exposure of... more Abstract In far North Greenland at the head of Victoria Fjord (∼81°30′N), a ∼1000 km2 exposure of Precambrian crystalline basement rocks is a window through the region's extensive latest Neoproterozoic and Paleozoic Arctic Platform sedimentary cover sequence. These basement rocks, named here the Victoria Fjord terrane, are dominated by weakly-foliated granodioritic orthogneisses, with lesser amounts of migmatite. These are intercalated with strips of supracrustal rocks dominated by paragneisses. This poorly-exposed Archean terrane at Greenland's northern tip is succeeded to the south by the extensive east-west trending Paleoproterozoic Inglefield Mobile Belt of juvenile arc rocks. The Victoria Fjord terrane granodiorites have zircon U-Pb ages from 3292 ± 14 Ma to ∼3260 Ma. Reconnaissance U-Pb dating on schlieric migmatite zircons yielded ages of ∼3280, 3400 and 3500 Ma. Paragneiss detrital zircons have ages of mostly ∼2710 Ma, with a minority of 3000–2900 Ma grains. This demonstrates that these sedimentary rocks were not derived from the local basement. Post- Archean magmatic or metamorphic zircon was not detected in any of the samples. Initial eHf of 3290–3260 Ma granodiorite and granite zircons ranges from −4 to +2, and the magmatic protoliths are interpreted as sourced from the melting of somewhat older (3500–3400 Ma) Paleoarchean crust, represented by paleosome in the migmatites. The paragneiss 3000–2900 Ma detrital zircons were derived from juvenile felsic crust of that age. The ∼2710 Ma group show negative correlation of Th/U and initial eHf, such that those with high Th/U up to >2.0 have eHf values of −6 to −10. The ∼2710 zircons were sourced from mafic rocks formed by melting of much older (Paleoarchean?) enriched mantle which was variably contaminated by 3000–2900 Ma crust during its ascent. The Victoria terrane is unique amongst the Archean basement terranes in Greenland because it is dominated by 3500–3260 Ma crust. However, the Arctic basin contains detrital zircons of that age, and rocks of that age also occur in eastern Siberia and northwestern Canada. Implications for high Arctic early Precambrian geodynamics are discussed.
Abstract In NE Iraq, the eastern edge of the Arabian plate is overlain by arc rock allochthons wh... more Abstract In NE Iraq, the eastern edge of the Arabian plate is overlain by arc rock allochthons whose genesis and tectonic emplacement were related to the consumption and closure of the Neotethys Ocean. This paper demonstrates the occurrence of unrelated Paleogene arc rocks in two adjacent allochthons. The Bulfat Igneous Complex at Wadi Rashid (NE Iraq) is an intrusion within the Upper Allochthon Albian–Cenomanian Gimo–Qandil sequence suprasubduction zone assemblage. A thrust separates this allochthon from the underlying Lower Allochthon of the Eocene-Oligocene Walash–Naopurdan volcanic-sedimentary arc rocks. The Bulfat Igneous Complex at Wadi Rashid consists of gabbro and granitic composite intrusions in which components mingle down to a small scale. Textural relationships in the Bulfat Igneous Complex rocks indicate emplacement at high crustal levels with rapid cooling, which is consistent with amphibole geobarometry indicating crystallisation pressures between ~ 250 and 300 Mpa. Ti-rich igneous pargasite and Ti-rich igneous Fe-biotite from gabbroic and granitic components yielded 40Ar/39Ar ages of 39.23 ± 0.21 and 38.87 ± 0.24 Ma respectively. These ages agree within analytical error and suggest coeval emplacement and rapid cooling of mafic and felsic magmas in the Eocene, in an event that was distinct and much younger than the host Albian–Cenomanian rocks. This igneous event was unrelated to formation of Cenozoic rocks in the underlying, tectonically separate, lower allochthon. The trace element signatures of the Wadi Rashi volcanic rocks show volcanic-arc characteristics for the granites and the gabbroic rocks resemble E type MORB. The presence of Eocene arc-related rocks in two allochthons suggests complexity in Paleogene subduction systems, with possibly two subduction zones operating at that time.
The Hasanbag igneous complex is situated near Sidekan, 100 km northeast of Erbil city, Kurdistan ... more The Hasanbag igneous complex is situated near Sidekan, 100 km northeast of Erbil city, Kurdistan Region, within the Iraqi Zagros suture zone. It forms part of an ophiolite-bearing terrane referred to as the “Upper Allochthon” or Gemo-Qandil Group. The Hasanbag igneous complex consists predominantly of calc-alkaline basaltic andesites to andesites cut by microgabbro and diorite dikes, which previously were interpreted as a part of the Eocene Walash volcanic group.
The world's largest ongoing collisional orogeny is the Europe Alps-Himalayan-SE Asian bel... more The world's largest ongoing collisional orogeny is the Europe Alps-Himalayan-SE Asian belt and is a natural laboratory to understand many processes that have shaped the continents. Due to political instability and conflict throughout this millennium, the Iraq (Kurdish) sector of the Zagros mountain chain is the least studied part of this orogenic system. In Iraq, the Zagros contains the suture between the Arabian subcontinent to the south and west and the Iranian edge of the Eurasian continent to the north and east. The suture zone is marked by several allochthons of Neotethyan ophiolitic and volcanic arc assemblages that were obducted onto the Arabian margin. New geochronological data, including SHRIMP U-Pb zircon, integrated with whole rock geochemistry, indicates that both Cretaceous (˜96 Ma) and Cenozoic (˜40 Ma) assemblages are present. The relationships between these units are complicated, thus some Cretaceous arc rocks were intruded by Cenozoic arc rocks, and out-of-sequence thrusting has interleaved and juxtaposed assemblages of different ages. Ongoing wrench faulting since continental collision at˜14 Ma has further complicated the pattern of lithotectonic units, particularly those that were obducted out of the Neotethyan realm. The new data indicate that the Iraqi sector of Neotethys was not 'quiet' in the Cretaceous, but contains fragments of arcs of that age, contiguous with those along strike in Turkey, Iran and the Himalayas.
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Papers by Sarmad Ali