Ophiolite Complex Research Articles

On the Origin of New and Rare Minerals Discovered in the Othrys and Vermion Ophiolites, Greece: An Overview

In this contribution we review the mineralogical characteristics of five new and rare minerals discovered in the Othrys and Vermion ophiolites located in Greece, with the aim to better understand their origin. Three new minerals, namely tsikourasite Mo3Ni2P(1+x) (x < 0.25), grammatikopoulosite NiVP and eliopoulosite V7S8, were found in the chromitite from the Agios Stefanos deposit, whereas arsenotučekite Ni18Sb3AsS16 was discovered in the Eretria (Tsangli) chromium mine, located in the Othrys ophiolite complex. The formation of the new phosphides tsikourasite and grammatikopoulosite and the sulfide eliopoulosite from Agios Stefanos took place after the precipitation of the host chromitite. Very likely, they formed at lower pressure in an extremely low fO2 and reducing environment during the serpentinization that affected the host ophiolite. The origin of arsenotučekite in chromitites coexisting with Fe–Ni–Cu-sulfide mineralization and magnetite at the Eretria (Tsangli) mine, is believed to be related to a circulating hydrothermal system. The most salient feature of theophrastite Ni(OH)2 and associated unnamed (Ni,Co,Mn)(OH)2 with a varying compositional range and a concentrating development, as successive thin layers, composed by fine fibrous crystals. The extremely tiny crystals of these hydroxides and the spatial association of mixed layers of Ni-silicides with theophrastite may reflect the significant role of the interaction process between adjacent layers on the observed structural features. The scarcity in nature of the new minerals reviewed in this paper is probably due to the required extreme physical-chemical conditions, which are rarely precipitated.

A record of metasomatism and crustal contamination of the Mediterranean lithosphere in chromitites of the Orhaneli Ophiolite Complex (NW Türkiye)

• Orhaneli chromitites include Middle Devonian to Mesoproterozoic zircon and rutile . • Chromite trace elements points a metasomatic signature in relics within chromitites. • More data should be sought for ultrahigh-pressure history of Orhaneli chromitites. This study provides the first-ever report of U-Pb isotopic ages of zircon and rutile from high-Cr chromitites of the Orhaneli Ophiolite Complex (OOC). The chromites within the OOC chromitites yield Cr-numbers between 0.77 and 0.86, Mg-numbers between 0.46 and 0.71 and TiO 2 < 0.26 wt%. They exhibit V, Ga and Ni depletion and Sc, Ti, Zn, Co and Mn enrichment relative to MORB spinels, with significant Sc and Ti positive anomalies. This, and the Al 2 O 3 and TiO 2 compositions of the parental melts, suggest that the studied chromitites formed from island arc melts of boninitic affinity, in a supra-subduction environment. In addition to zircons, chromites host other solid mineral inclusions, including Os- and Ir-dominant platinum-group minerals (PGM), base-metal sulfides (BMS), alloys, ubiquitous silicate (some as micron-sized oriented lamellae), and two poorly defined Fe-Cr-O and Ti-Si-C grains. The zircons show Th/U ratios typical for magmatic zircons from felsic melts, and present Middle Devonian to Mesoproterozoic U-Pb isotopic ages. Although the reworked/resorbed forms of the zircons suggest a xenocrystic origin, coupling of U-Pb data from some zircons and rutile with the Ti positive anomaly in the chromites raises the possibility for an earlier Neoproterozoic metasomatic event affecting the relics now included within the chromitite bands. The current state of knowledge about the silicate micro-lamellae within the chromites has prompted reassessment of their early interpretation as direct evidence of deep mantle recycling. We currently suggest a more cautious approach on this issue by seeking additional evidences for an ultrahigh-pressure (UHP) history.

Depositional Facies Model and Reservoir Quality of Paleogene Limestone in Labengki Island, Southeast Sulawesi

Eastern Indonesia has become an attractive venture for hydrocarbon exploration since 10 years ago. The discovery of hydrocarbon from Miocene carbonate of Tondo Formation has opened a new opportunity and hopes in the Southeast Sulawesi region. Can we find other potential reservoirs in Southeast Sulawesi? In this study, we assess and reconstruct the depositional model and the reservoir quality of the Paleogene Tampakura Formation in Labengki Island, Southeast Sulawesi. This field observation and petrographical study revealed that: (1) Tampakura Formation comprises mainly of grainstone, boundstone and floatstone with minor packstone and dolomitic wackestone/mudstone, (2) Tampakura Formation was deposited mainly in wide carbonate sand shoals and reef margin belt of rimmed carbonate shelf, (3) Boundstone and floatstone facies could be the best reservoir candidate in the region since they show extensive porosities development of cavernous and fracture porosity, (4) Dolomite cementation has deteriorated the reservoir quality of packstone which was deposited in platform interior-restricted marine, (5) Extensive calcite cementation in grainstone facies has reduced the reservoir quality of Tampakura Formation. However, locally, solution enlarged fracture porosity may have enhanced it. We suggest that post collision event of Late Oligocene - Early Miocene between Australian-originated microcontinent and ophiolite complex was highly responsible to create cavernous porosity. The collision resulted in the folding and uplifting of Tampakura Formation to the subaerial exposure. The carbonate strata were exposed to the surface developing a cavernous porosity and potentially becoming the best reservoir candidate for the next exploration target.Keywords: Carbonate facies, Kendari Basin, reservoir quality, Tampakura Formation.

Mineralogical-Petrographical Record of Melt-Rock Interaction and P–T Estimates from the Ozren Massif Ophiolites (Bosnia and Herzegovina)

The Dinaride Ophiolite Belt formed from the Jurassic part of the Neotethys. The investigated Ozren ophiolite complex in Bosnia and Herzegovina consists of peridotites, plagioclase peridotites, plagiogranites, troctolites and other gabbroic rocks, and fewer basalts. Lherzolites and harzburgites contain corroded ortho- and clinopyroxene1 porphyroclasts enclosed in the olivine matrix. The boundaries between olivine aggregates and pyroxene1 and spinel1 are infilled by medium-grained undeformed aggregates of clinopyroxene2, less orthopyroxene2, spinel2, and often clinopyroxene3-spinel3 symplectites. These textures indicate the final crystallization of peridotite in subsolidus conditions. Partial dissolution of deformed pyroxene1 porphyroclasts and coarse-grained spinel1 most likely occurred due to their reaction with the rest melt present in the grain boundaries. The Al decrease from pyroxene1 to pyroxene2 and 3, or the Cr decrease and Al increase from spinel1 to spinel2 and 3 is characteristic. Peridotites are associated with inferred remnants of a gabbro-dolerite layer, whereas basalts and radiolarites occur as rare dm-size fragments in an ophiolitic breccia. Troctolites display interstitial crystallization of plagioclase, clinopyroxene, less Na-Ti-rich amphiboles, and phlogopite in the olivine-spinel matrix, indicating the replacive character of impregnating melt within the dunite layers. Clinopyroxene-plagioclase-ilmenite-±amphibole gabbroic and fewer basaltic dykes in peridotites formed due to subridge extension, mantle thinning, and the deeper mantle melting. Iron-enriched olivines occur in the peridotite-dyke interfaces and troctolites. Hydrated ultramafics and mafics contain amphiboles, biotite, phlogopite, clinozoisite, epidote, and chlorite aggregates. Estimated magmatic to subsolidus T from peridotite two-pyroxene thermometry are 1000–850 °C, for the spinel facies. Ca-in-orthopyroxene1 thermometry provided T of 1028–1068 °C, and Ca-in-orthopyroxene2 thermometry gave 909–961 °C at estimated P of 1.1–0.9 GPa. However, the gabbroic dyke magmatic crystallization T was constrained to 1200–1100 °C at P of 0.45–0.15 GPa by single clinopyroxene thermobarometry. The obtained P–T conditions constrained the deeper mantle environment for the formation of peridotites than troctolites and crosscutting dykes. The ophiolitic thrust-sheet hanging wall conditions in an obduction-related accretionary wedge were estimated from amphibolites at 620 °C and 0.85 GPa by Ti-in-amphibole thermometry and amphibole-plagioclase thermobarometry. 300 °C and 0.5 GPa were determined from an exhumation shear zone using a combination of chlorite thermometry and Si-in-phengite barometry.

Origin and Heavy Metals of Plagio-Granites in Egyptian Shield Oceanic Complexes: A Case Study of Abu Dabbab Area, Central Eastern Desert, Egypt

Several outcrops of felsic melt, commonly known as oceanic plagio-granites, appear as melt pockets, irregular bosses, and dikes. Three main rock successions were exposed in the Abu Dabbab area: ophiolitic sequence, island arc assemblage, and rare metal-bearing albite granites. Plagio-granite is composed mainly of plagioclase and quartz, and chemically contains high SiO2, Al2O3, and Na2O values. The petrogenetic and geochemical studies concluded that the magmas of plagio-granites and associated felsic rocks were derived from partial melting of highly depleted mantle harzburgite and/or pre-existing oceanic crustal rocks (basalts and/or gabbros). The geochemical characteristics reveal that Abu Dabbab plagio-granites are identical to the typically low-K series of ophiolitic complexes and resemble the ocean ridge granites. Elements such as Co, Nb, Pb, and Nd in Abu Dabbab plagio-granites have high Clarke concentrations (more than 1.88). This indicates Abu Dabbab plagio-granite derived from partial melting of pre-existing oceanic crustal rocks. The average concentration values of 238 U and 232 Th are lower than those of the world’s average and the average activities in granitic rocks. The scope of estimated exercises generally contrasted as their quality in rock tests relies upon their physical, synthetic, and geo-concoction properties and the appropriate condition.

Sulfide mineralization in Sikhuran ophiolite complex, Esfandagheh, Iran: Implications from trace element composition of silicate and sulfides

The Sikhuran ophiolite complex in Esfandagheh, Kerman province, is considered one of the important chromite mining areas in southern Iran. The complex is comprised of mainly tectonized harzburgite of residual upper mantle, depleted harzburgite, chromitite, dunite, and orthopyroxenite of the transition zone, as well as upper cumulates of ultramafic-mafic rocks. Sulfide disseminations, i.e., pentlandite, chalcopyrite, chalcocite, millerite, and heazlewoodite are hosted by dunite and chromitite in the upper part of the transition zone. The abundance of Base Metal Sulfides (BMS) as interstitials of olivine shows early stage sulfur saturation in Mg-rich magmas. Low Ni contents of ubiquitous olivine indicate that Ni in the primary silicate melt is preferentially concentrated in the sulfide liquid. The high activity of Ni in the melt is evidenced by the dominance of Ni-rich pentlandite and other Ni-bearing minerals from the Sikhuran ophiolite complex. Major and trace element compositions indicate that pentlandite is the main PGE-carrier with ƩPGE up to 44 ppm. Palladium, the most abundant PGE, is partitioned into pentlandite by diffusion of Monosulfide Solid Solution (MSS). The factors affecting this mechanism include the initial concentration of Pd, low compatibility of Pd compared to IPGEs, and decreasing solubility of Pd in MSS with decreasing temperature. Generally, although no detailed studies have been conducted on the occurrence of sulfide minerals in Iran; sulfide mineralization with coarse sulfide minerals in the Sikhuran can be a new perspective for mining companies and economic geologists.

ALMUS (TOKAT) YÖRESİNDEKİ AKİKLERİN JEOKİMYASAL ÖZELLİKLERİNİN DEĞERLENDİRİLMESİ

The Upper Cretaceous Artova ophiolite complex, represented by metabasic and ultrabasic rocks, overlies the Paleozoic aged Tokat metamorphites, which form the basis of the study area, by the tectonic boundary. Haydaroğlu formation, which includes Middle Eocene aged volcanogenic units, cuts and covers the older units. Agates (agates) in the Almus region are found in the form of nodules in the volcanogenic sandstones of the Haydaroğlu formation along an approximately E-W trending fault. The Lower Miocene aged Almus formation, which consists of sedimentary rocks such as sandstone, conglomerate and marine limestone, also unconformably overlies all units.&#x0D; Almus region agates contain on average 93.4% SiO2, 3.59% Fe2O3, 0.03% MgO, 0.72% CaO, 793 ppm Cr2O3, 12 ppm Ni, 13.4 ppm Cu, 4.7 ppm Pb, 35.4 ppm Zn. The high Cr and Ni in agates are associated with the Artova ophiolite complex in the region. Cu, Pb and Zn are associated with the early stages of volcanism. The high Fe2O3 content in agates is associated with hematite and goethite, and they were transported into agates before SiO2 emplacement. The CaO in the agate is the product of the last phase of the solution forming the agate, and MgO is associated with the presence of dolomite. &#x0D; Evaluation of the results of geochemical analysis shows that SiO2, which is the main component due to the hydrothermal activities that occurred after the rock formation of the Haydaroğlu formation, unlike the volcanic bedrocks of the agates according to the main oxides, trace and rare earth elements, was emplaced epigenetically as a result of the circulations in the volcanogenic sandstones.

An Ordovician ophiolitic complex in West Junggar, NW China: Implications for subduction initiation and oceanic arc evolution of the Paleo-Asian Ocean

As a key step of the Wilson cycle, subduction initiation is regarded as a start hallmark of the ocean-continent transformation. However, the crust-mantle interaction and crustal growth processes related to subduction initiation remain enigmatic. Here we report a newly recognized complete magmatic sequence containing three rock assemblages in the Hongguleleng ophiolitic complex (HOC) in West Junggar, NW China. Group I contains typical Mid-Oceanic Ridge (MOR)-derived rocks including abyssal peridotite, gabbro, plagiogranite, and basalt. Group II consists of forearc basalt (FAB) and boninitic gabbro and has a high continentality index (CI > 130), similar to the rock assemblages in the Mariana proto-arc. Group III composed of calc-alkaline andesite and arc tholeiite basaltic andesite exhibits middle CI values (50 < CI < 100), suggesting that they form in a transitional oceanic arc. Zircon U-Pb ages show that the N-MORB gabbro and plagiogranite samples are emplaced at 483–481 Ma, and the boninitic rocks, calc-alkaline andesites, and arc tholeiite basaltic andesites have the crystalline ages of 472–467 Ma, 456 Ma, and 452 Ma, respectively. An increasing trend of Ba/Th and V/Ti ratios from Group I to Group II suggests the addition of aqueous fluid and elevated oxidation in the mantle source during subduction initiation. However, it exhibits an uptrend in Th/Nb and (La/Sm)cn ratios but a downtrend in Ba/Th ratios from Group II to Group III, indicating a significant contribution of slab-derived sediments to the mantle during oceanic arc evolution. Combined with regional data, we consider that there developed an E-W–trending sub-ocean basin of the Paleo-Asian Ocean spanning northern West Junggar and East Kazakhstan during the Middle Cambrian–Ordovician. The MOR-type and forearc ophiolites in northern West Junggar as well as our results suggest that the ocean happened mid-ocean ridge spreading at ca. 512–478 Ma and subduction initiation at ca. 476–467 Ma, and developed a transitional oceanic arc at ca. 456–452 Ma.

Tectonic evolution of the Beishan orogen in central Asia: Subduction, accretion, and continent-continent collision during the closure of the Paleo-Asian Ocean

AbstractThe Beishan orogen is part of the Neo-proterozoic to early Mesozoic Central Asian Orogenic System in central Asia that exposes ophiolitic complexes, passive-margin strata, arc assemblages, and Precambrian basement rocks. To better constrain the tectonic evolution of the Beishan orogen, we conducted field mapping, U-Pb zircon dating, whole-rock geochemical analysis, and Sr-Nd isotopic analysis. The new results, when interpreted in the context of the known geological setting, show that the Beishan region had experienced five phases of arc magmatism at ca. 1450–1395 Ma, ca. 1071–867 Ma, ca. 542–395 Ma, ca. 468–212 Ma, and ca. 307–212 Ma. In order to explain the geological, geochemical, and geochronological data from the Beishan region, we present a tectonic model that involves the following five phases of deformation: (1) Proterozoic rifting that separated the North Beishan block from the Greater North China craton that led to the opening of the Beishan Ocean, (2) early Paleozoic north-dipping subduction (ca. 530–430 Ma) of the Beishan oceanic plate associated with back-arc extension followed by collision between the North and South Beishan microcontinental blocks, (3) northward slab rollback of the south-dipping subducting Paleo-Asian oceanic plate at ca. 450–440 Ma along the northern margin of the North Beishan block that led to the formation of a northward-younging extensional continental arc (ca. 470–280 Ma) associated with bimodal igneous activity, which indicates that the westward extension of the Solonker suture is located north of the Hongshishan-Pengboshan tectonic zone, (4) Late Carboniferous opening and Permian north-dipping subduction of the Liuyuan Ocean in the southern Beishan orogen, and (5) Mesozoic-Cenozoic intracontinental deformation induced by the final closure of the Paleo-Asian Ocean system in the north and the Tethyan Ocean system in the south.

Chromian Spinels from Kazanian-Stage Placers in the Southern Pre-Urals, Bashkiria, Russia: Morphological and Chemical Features and Evidence for Provenance

Six minor alluvial chromite placers (Kolkhoznyi Prud, Verkhne-Yaushevo, Sukhoy Izyak, Bazilevo, Novomikhaylovka, Kiryushkino) and one major littoral placer (Sabantuy) were found in sandy sediments of the Kazanian stage of the Permian System (Late Roadian and Wordian Stages) in the Southern Pre-Urals. It is shown that the morphological features of chromian spinels are diverse, which is not evidence of the heterogeneity of the source. The bulk chemical composition of chromian spinels from all placers is similar and generally correlates with compositions of chromian spinels from the Kraka ophiolitic complex in the Southern Urals. The morphological diversity of grains, varied chemical composition and presence of melt inclusions in Ti-high octahedral grains of chromian spinels comply with the ophiolitic nature of the source. Thus, there is no need to refer to other sources for chromite ores but ophiolitic. The new placers expand the dissemination area of chromite-bearing deposits on the east edge of the East-European Platform and offer a prospect to discover new placers.

Microtextural evolution of chrome spinels in dunites from Mayodia ophiolite complex, Arunachal Pradesh, India: Implications for a missing link in the “two-stage” alteration mechanism

Although occurring as an accessory phase in mafic-ultramafic rocks, the universal presence of chrome spinel in ophiolitic settings bears importance in deciphering the tectonic setting of the ophiolite. Compositional and textural modification of chrome spinel via post-magmatic processes (metamorphism and fluid-induced alteration) is widely reported from host chromitites and peridotites, however, well-documented studies from dunite in ophiolitic settings are sparse. Here we present a detailed petrographic and geochemical account of accessory chrome spinels from previously unreported massive dunite bodies of Mayodia ophiolitic complex, Arunachal Pradesh, India, that portrays a microtextural evolution during alteration/metamorphism. Although having massive appearance, the bodies are crudely foliated and deformed. Severe alteration obliterated primary spinel chemistry as well as pre-alteration mineralogical assemblages. From textural and chemical point of view, the disseminated accessory chrome spinel grains are classified into four broad groups: (1) less chloritized spinel, (2) heavily chloritized spinel, (3) patchy-zoned spinel, and (4) homogeneous spinel. The chloritized spinels are relatively coarse grained, compositionally enriched in Cr and Fe2+ (ferrous chromite). They contain Cr-rich chlorite inclusions and are surrounded by a mixed matrix of Cr-rich chlorite and Cr-rich serpentine. Unzoned, homogeneous spinels appear as aggregates and are devoid of chlorite inclusions. They are compositionally different from the chloritized spinels, being enriched in Fe3+ and depleted in Cr (ferrian chromite). The patchy-zoned spinels have a non-uniform zoning with patches of ferrous chromite floating within ferrian chromite, separated from each other by micro fracture networks. Adapting a novel technique, we reconstruct bulk rock composition based on global data compilation, which has been applied to thermodynamic modelling. Comparing our integrated results with global examples we infer that fluid-induced alteration (chloritization) caused the formation of chloritized spinels from their primary counterpart. Later oxidizing fluid interacted with the chloritized spinels and converted them to homogeneous spinel; supporting the two-stage alteration model. We interpret the patchy zoning as an arrested intermediate stage between chloritized spinel and homogeneous spinel, preserving the characters of both stages. From a regional perspective, we postulate that the chrome spinel microtextures evolved between ~780 °C and ~ 550 °C during amphibolite facies retrogression of the dunite bodies, possibly related to exhumation of Mayodia ophiolitic complex.

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

The Manganese deposits in Sulaimani metallogenic province mainly occur within the top Qulqula Radiolarite chert unit of the Penjween ophiolite complex as strata bound type deposits near Kani Saif village, 15 km south of the Penjween district within the Imbricated zone, Kurdistan Region of Iraq. A restricted occurrence of massive manganese boulders was identified, 1 km north to the Mawat District, associated with the Oligocene Merga Red beds Group. The Qulqula Radiolarite represents the Middle Jurassic-Early Cretaceous sedimentary cover of Neo-Tethys oceanic crust deposits throughout the early to mature stages of the Neo-Tethys ocean opening along the northern and eastern margins of the Afro-Arabian plate. The field and petrographical data indicated that the nature of manganese mineralization in the area is of various forms including veins, brecciated, micronodules, banded and massive types. Reflected light microscopy, high resolution scanning electron microscope and X-ray diffraction reveal that the mineral assemblages are dominated by barunite, rhodinite, hematite, quartz and carbonate for the massive metamorphosed type deposit in the Mawat area. Meanwhile, the mineralogy of the vein, micronodule and banded types are simple and dominated by pyrolusite, hollandite minerals close to Kain Saif village. Combinations of the modal manganese minerals, filed and textural observations, a paragenetic-time model suggests that the manganese deposit in the area formed via a sequence of multiple processes (1) serpentinization of the upper mantle at mid oceanic ridge during the Cretaceous period, (2) deposition from diluted hydrothermal fluids in the Neo-Tethys mature oceanic basin, (3) the diagenetic modification of the manganese bearing sediment and (4) metamorphism of sediment a combing Zagros orogeny in Paleogene. Overall data suggest that the manganese deposits in the Kurdistan region of Iraq are cogenetic and spatially related to those which occur along the entire margin of the Arabian plates from Oman to Turkey associated with the radiolarite facies.

Metallic-Mineral Prospecting Using Integrated Geophysical and Geochemical Techniques: A Case Study from the Bela Ophiolitic Complex, Baluchistan, Pakistan

An integrated geophysical and geochemical investigation was conducted to investigate the metallic minerals hosted in the mafic and ultramafic rocks in the Bela Ophiolitic Complex. Two thousand magnetic observations were made along with six vertical electrical soundings, with Induced Polarization (IP) targeting the anomalous magnetic zones. The magnetic raw field data were interpreted qualitatively and quantitatively, and two anomalous zones (A1 and A2) were identified on the magnetic maps. The residual magnetic values in the high-magnetic-anomalous zone (A2) ranged from 310 nT to 550 nT, while the magnetic signatures in the low-magnetic zone (A1) ranged from –190 nT to 50 nT. The high-anomalous zone (A2) was distinguished by a high IP value ranging from 3.5 mV/V to 15.1 mV/V and a low apparent and true resistivity signature of 50 ohm·m. Whereas, the low-anomalous zone (A1) was distinguished by very low IP values ranging from 0.78 mV/V to 4.1 mV/V and a very high apparent and true resistivity of 100 ohm·m. The Euler deconvolution was used to determine the depth of the promising zone, which for A1 and A2 was in the 100 m range. The statistical analysis was carried out using hierarchical classification to distinguish between background and anomalous data. The high-magnetic anomalous signature of probable mineralization was in the range of 46,181 nT–46,628 nT, with a total intensity range of 783 nT–1166 nT. The major and trace-element analysis of the 22 rock and stream sediments collected from the high-magnetic-anomalous zone confirmed the mineralization type. The geomagnetic and geophysical cross sections revealed that anomalous mineralization was concentrated with the anticlinal Bela Ophiolitic Complex. The generated results also aided in the identification of rock boundaries, depth, and hidden faults in the area. The findings revealed that the study area has excellent mineralization associated with the ultramafic-rock sequence.

Tectonic setting and mineralisation potential of the Cowley Ophiolite Complex, north Queensland

Northeast Queensland contains multiple slices of mafic–ultramafic units, strung out along regional faults that mark major tectonic boundaries. One such complex is the Cowley Ophiolite Complex, which is situated along the Russell-Mulgrave Fault. The Cowley Ophiolite Complex is a differentiated mafic–ultramafic complex composed of gabbro, chlorite schist, anthophyllite schist and serpentinite. We interpret that the alteration assemblages observed throughout the Cowley Ophiolite Complex reflect an amphibolite facies metasomatic overprint within a supra-subduction zone setting. This interpretation is consistent with geochemical discrimination of the gabbro, and chromite grains from the anthophyllite schist. The Cowley Ophiolite Complex records a higher metamorphic grade than the surrounding Hodgkinson Formation, and we interpret this to reflect the allochthonous structural setting of the complex, positioned along an ancient subduction margin. This subduction margin is represented today by the Russell-Mulgrave Fault. Metasomatism and emplacement of the complex probably pre-dated deposition of the Mossman Orogen’s active margin successions. Our interpretation of an active subduction complex, which pre-dated the formation of the Mossman Orogen, suggests that the Russell-Mulgrave Fault is a Paleozoic, continental suture zone. The Cowley Ophiolite Complex presents little indication of economic mineralisation; however, much of the complex remains unexplored. KEY POINTS The Cowley Ophiolite Complex is a differentiated, mafic–ultramafic complex formed within a supra-subduction zone setting. Emplacement of the Cowley Ophiolite Complex, along the Russell-Mulgrave Fault, pre-dated the formation of the Hodgkinson Province. The Russell-Mulgrave Fault represents an ancient subduction margin, and is interpreted as a Paleozoic, continental suture zone.

New U-Pb zircon ages of plagiogranites from the Coastal Complex ophiolite and Twillingate batholith, Newfoundland: Evidence for the oldest and overlapping silicic magmatism in the nascent Cambrian peri-Laurentia forearc and arc terranes

The Coastal Complex (CC) and Bay of Islands Complex (BOIC) represent two supra-subduction zone (SSZ) forearc ophiolitic assemblages of different ages within the Taconic Humber Arm Allochthon of the Western Newfoundland Appalachians. To further constrain age relationships between the CC and BOIC and earliest initiation of Iapetus subduction, we acquired LA-ICP-MS U-Pb zircon ages for eleven plagiogranites sampled along strike of the CC belt. These ages combined with three prior legacy ages establish an age range of 514.3–502.7 Ma for the six CC plagiogranite plutons. The oldest precise ca. 514.3 Ma CC pluton age represents the oldest Taconic arc-related plutonic activity yet documented in Western Newfoundland and provides a minimum age for the intruded CC ophiolite basement and initiation of westerly vergent subduction within the peri-Laurentian Iapetus Ocean. This confirms the Early Cambrian CC mafic–ultramafic basement is significantly older than the juxtaposed SSZ BOIC, which formed by later rifting of the CC forearc along younger forearc spreading center in the Late Cambrian by ca. 488.3 Ma. After subduction initiation a prolonged early period CC forearc silicic magmatism lasted at least ∼ 11.6 Ma until ca. 502.7 Ma, a range consistent with age spans of magmatism in modern juvenile forearcs. We also reinvestigated the Central Newfoundland Twillingate Granite batholith thought to be one of the earliest major felsic batholiths formed within the adjacent juvenile arc massif of the Notre Dame Subzone, part of the same peri-Laurentian arc. We determined a precise 3-sample composite age of 504.3 ± 1.8 Ma that signals the formation of earliest Notre Dame arc edifice developed by Middle Cambrian. It overlaps the end-stage CC forearc plagiogranite magmatism and places a minimum mid-Cambrian age constraint on intruded ophiolitic arc tholeiitic and boninitic pillow lavas of the Sleepy Cove and correlated Lushs Bight volcanics, suggesting basement continuity with the CC.

Metamorphic Evolution of the Bulfat Belt (NE-Iraq): Evidence from 40Ar/39Ar Age Spectrum Measurements

The Bulfat Ophiolite Complex (upper allochthonous thrust sheet) which represents a part of the Iraqi Zagros Suture Zone is situated at the boundary between the Arabian Plate and the Iranian Microplate. We have examined the metamorphic and cooling history of metapelitic rocks of Bulfat Complex using the whole-rocks 40Ar/39Ar age determination. The results of four samples match to the definition of the plateau and revealed to 40Ar/ 39Ar age of 42.4 ±0.5 Ma (sample 1), 32.9 ±0.8 Ma (sample 2), 44.3 ±0.8 Ma (sample 3), and 43 .6 ±1.5 Ma (sample 5). However, samples 4 and 6 yielded an age range between 35- 40 Ma and 40- 50 Ma respectively. Generally, plateau ages (32.9-50 Ma) are identical and considered reliable, but the presence of excess argon (40Ar) remains possible in samples (e.g., sample 6) having initial40 Ar/36Ar ratios higher than the present atmospheric 40 Ar/36Ar = 295.5. The excess argon is derived from the mantle by plumes of mafic magmas into the earth crust and/ or released from minerals and rocks during metamorphic processes. Bulfat Complex is subjected to two metamorphic events: the earlier regional occurred during the period Albian-Cenomanian (97-105 Ma) and associated with the intraoceanic infant supra-subduction zone. The later thermal metamorphism overprinted the previous one, and took place due to the intrusion of igneous body pre – 50 Ma age. This igneous activity is considered one of the multi-event magmatism that happened along the Zagros Fold-Thrust Belt during the period from Upper Cretaceous and Mid – Late Miocene. It seems evident that the thermal metamorphic slice of Bulfat Complex (Gemo-Qandil Sequence) represents a part of the oceanic slab that has been subducted beneath the Iranian microplate. This event probably forming the last evolved episode of island arc system ended with the final closure of Neo-Tethys and the collision between the Arabian Plate and Iranian Microplate occurred at Mid-late Miocene.

Mineralogy, geochemistry, and 40Ar/39Ar dating of hornblendite/amphibolite pods in Penjween Ophiolite of northeastern Iraq: Implications for petrogenesis and tectonics

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.

Multi-proxy evidence for subduction of the Neoproterozoic Adamastor Ocean and Wilson cycle tectonics in the South Atlantic Brasiliano Orogenic System of Western Gondwana

Field, petrographic, geophysical, geochronological, elemental and isotopic data support the identification of distinct components of a Wilson cycle (rift-drift-subduction-collision-collapse) in the South Atlantic Brasiliano Orogenic System (Mantiqueira Province). The main lines of evidence are: 1) Tonian-Cryogenian ophiolite complexes; 2) Hundreds of Hf-Nd-Sr isotope determinations indicating a temporal trend of juvenile to mixed Tonian-Cryogenian-Ediacaran igneous rocks comprising expanded calc-alkaline, magnesian, metaluminous gabbro-tonalite-granodiorite-granite/basalt-dacite-andesite-rhyolite series, developed in island arcs and in continental-margin (Andean-type) arcs; 3) Cratonic-sourced conglomerate-diamictite-sandstone-pelite-carbonate successions deposited in Tonian-Cryogenian rift-passive margins fringing the paleocontinental borders, covered by orogenic basins with contrasting provenance from the arc systems; 4) Paired negative-positive Bouguer anomalies typical of suture zones with ophiolite-bearing accretionary prisms in the lower plate and arc systems in the upper plate; 5) Paired HP/HTmetamorphic belts associated with Ediacaran suture zones and retro-eclogites associated with Tonian subduction. Proposed intracontinental models for this region, both original and revisited, are based on the visual interpretation of restricted space for an oceanic realm and rely on calculations using presumed spreading and subduction rates. However, those do not account for a number of pre-, syn- and post-collisional modifications of the original paleogeography and for plate configurations over a curved planetary surface, with asynchroneity of extensional, accretionary and collisional events over thousands-of-km long orogenic fronts. Scissor-shaped oceanic basins are the rule rather than the exception, with connection of (i) an aulacogen to (ii) a partially enclosed gulf that is, in turn, connected to (iii) an open ocean with complex subduction systems. This configuration leads, after closure of the oceanic realm, to the gradation found in the South Atlantic Brasiliano Orogenic System, with (i) an inverted rift (Paramirim) connected to (ii) a confined orogen with a pre-collisional continental-margin Andean-type arc (Araçuaí), connected, in turn, to (iii) complex accretionary-collisional orogens (Ribeira and Dom Feliciano) with accreted juvenile pre-collisional island arc terranes. This arrangement characterizes, thus, a prime example of a typical subduction-collision orogenic system. The various lines of evidence from distinct fields coherently indicate a full Wilson Cycle with generation and consumption of the Adamastor oceanic lithosphere, followed by continental collisions, ultimately giving birth to the Gondwana paleocontinent.

Influence of Petrogenesis on the Engineering Properties of Ultramafic Aggregates and on Their Suitability in Concrete

This study focuses on the use of petrology as a useful tool in construction applications (i.e., concrete). More specifically, this study investigates how the petrogenetic characteristics of ultramafic rocks derived from ophiolite complexes (Veria–Naousa, Gerania) can act as a key tool for the prediction of the final behaviour of ultramafic aggregates as concrete aggregates. For this reason, their petrographic, chemical and mineralogical characteristics were examined and correlated with their engineering properties for evaluating their suitability as concrete aggregates. This study had come up, for the first time, that the genesis environment of the ultramafic rocks is the determinant factor for their physico-mechanical characteristics. Their suitability is relevant to the impact of their mineralogical and structural characteristics both from the two different ophiolite complexes (Veria–Naousa and Gerania). Except serpentinization, the basic alteration process-index of ultramafic rocks, there are also other chemical indices which can be used for ultramafic rocks that may determine their properties. In this context the term ‘fertility rate’ (FR) was introduced which may characterize ultramafic rocks as fertile or not. Furthermore, the Ultramafic Rock Health Index (U.R.H.I.) as well as the Normalized U.R.H.I. (U.R.H.I.N) was also introduced and correlated with the engineering properties of the investigated aggregate rocks. The last index aims to assess and quantify the overall health conditions, encompassing the two major modifying factors that include removal of primary mineral phases, as well as the extent of serpentinization. The main conclusion of this paper is that the genesis environment of the ultramafic rocks is the critical factor that determines their mineralogical, petrographic and chemical characteristics which consequently determines the basic engineering properties of rocks that determine their suitability or not as concrete aggregates.

Age and Paleogeodynamic Nature of the Kalinovka Ophiolite Complex, Sikhote-Alin Orogenic Belt

Age and Paleogeodynamic Nature of the Kalinovka Ophiolite Complex, Sikhote-Alin Orogenic Belt