Mantle Source Of Magmas Research Articles

The oxygen fugacity of intermediate shergottite NWA 11043: implications for Martian mantle evolution

Shergottite meteorites, classified as depleted, intermediate, or enriched based on incompatible trace elements and specific radiogenic isotope compositions (Sr, Nd, and Hf isotope ratios), point to multiple Martian mantle source regions. The oxygen fugacity (fO2) of these mantle regions, determined from early crystallizing minerals using the olivine-pyroxene-spinel oxybarometer, appears to correlate with incompatible trace element enrichment and isotope compositions. However, values derived from the vanadium-in-olivine oxybarometer challenge this correlation, hinting at potential biases in oxybarometry or complexities in the redox conditions of the Martian mantle. By analyzing the intermediate shergottite Northwest Africa (NWA) 11043 with various oxybarometers, this study deduced its origin from a reduced mantle source, with an average fO2 value of −0.77 ± 0.35 relative to the iron-wüstite (IW) buffer. Notably, these values coincide with those of depleted shergottites, which represent the depleted Martian mantle region. This redox similarity between intermediate and depleted shergottites contrasts with earlier notions that postulated intermediate shergottites as a mix of depleted and enriched mantle derivatives. Moreover, intermediate shergottites such as NWA 11043, Elephant Moraine (EETA) 79001A, and Allan Hills (ALH) 77005 display 176Hf/177Hf values akin to those of depleted shergottites, suggesting that intermediate mantle components can be separated from the depleted mantle source at approximately 2.2 Ga based on model age calculations. Therefore, there presents a consistent redox state between mantle magma sources of both intermediate and depleted shergottites since the Hesperian period, while enriched shergottites lean toward more oxidized conditions past source formation.This study prompts a reassessment of conventional theories, emphasizing the nuanced redox evolution of the Martian mantle across distinct mantle source regions and underscoring the complexity of the redox evolution of the Martian mantle. The emergence of chemically diverse mantle reservoirs might predominantly arise from early magma ocean differentiation processes, albeit with inherent oxidation nuances. The differences in fO2 observed between intermediate and depleted shergottites underscore the need for more in-depth studies to decipher Martian mantle differentiation and evolution.

The crust-mantle velocity structure beneath the Wudalianchi-Erkeshan-Keluo volcanic belt by joint inversion of receiver functions and ambient noise

The Wudalianchi-Erkeshan-Keluo (WEK) volcanic belt is a significant component of intraplate volcanism in Northeast China and is composed of the Wudalianchi, Erkeshan, and Keluo volcanic clusters. Using joint inversion of receiver functions and ambient noise, we construct a high-resolution 3-D S-wave velocity model of the WEK volcanic belt and its adjacent region, taking advantage of a deployed dense seismic array around this volcanic belt. There is a prominent low-velocity anomaly at 8–15 km depth beneath the Wudalianchi volcanic cluster, suggesting the presence of a crustal magma chamber. Low-velocity anomalies are also observed at 30–35 km depth beneath the Erkeshan volcanic cluster and 30–40 km depth beneath the Keluo volcanic cluster, resulting in discontinuous velocity structures at the Moho discontinuity. We further find a distinct low-velocity anomaly in the uppermost mantle beneath the WEK volcanic belt. Combined with previous geophysical and geochemistry studies, we propose a magma system scenario for the WEK volcanic belt. The upwelling molten material from the asthenosphere accumulated in the uppermost mantle and the magma chamber was formed, which provided the same uppermost mantle magma sources for the WEK volcanic belt.

Three-Dimensional Lithospheric Electrical Structure beneath the Handan-Xingtai District, North China: Implications for Tectonic Control of Skarn-Iron Mineralization

In this study, we determined the lithospheric electrical structure beneath the Handan-Xingtai district and its adjacent regions using magnetotelluric sounding data. To the west of the Handan-Xingtai district, the crust and upper mantle beneath the Taihang Mountains are mainly characterized by high resistivity (>1000 Ωm, which we interpreted to be the relic cratonic lithosphere. In contrast, the lithosphere beneath the North China Plain to the east shows high-conductivity features (<100 Ωm) overall, which may indicate that it has suffered significant modifications. Additionally, other geological and geophysical studies suggested that this district was located in a significant boundary zone where the lithospheric thickness, temperature and geochemistry properties sharply changed. Combined with our resistivity model, we attributed this to the different degrees of lithospheric modification. Specifically, since the late Mesozoic, the subduction, roll-back and dehydration of the Pacific slab caused an unsteady asthenospheric flow and upwelling; therefore, the deep-derived melts and fluids concentrated within the uppermost mantle had even underplated or intruded into the crust, while this process had a negligible effect on the Taihang Mountains. Small-scale mantle convection and upwelling are likely to occur in this kind of transfer zone of lithospherice properties, leading to mantle-derived melts and fluids transporting upwardly near the surface, which was confirmed by the significantly enhanced conductivity beneath the ore district in our resistivity model. During this process, Fe derived from mantle-source magma or relic Precambrian metamorphic basement beneath the Taihang Mountains was extracted and emplaced along with the Yanshanian magmatism.

Subduction Erosion Revealed by Late Mesozoic Magmatism in the Gangdese Arc, South Tibet

AbstractSubduction of oceanic lithosphere can cause crustal growth and destruction, but whether this balancing act is common in a single fossil convergent system has been unclear. Here we report geochronologic‐geochemical‐isotopic data on Mesozoic igneous rocks in the central‐eastern Gangdese arc. Our results reveal: (a) A coupling of magmatic arc migration toward the continent interior with a marked incompatible enrichment of sub‐arc mantle magma sources; (b) numerous Late Cretaceous adakites were generated via combined partial melting of both eroded forearc crust debris and subducted oceanic crust; (c) the truncation of forearc crust and extremely short arc‐suture distance. Our work demonstrates that although there was significant vertical growth of juvenile crust throughout the Gangdese arc during the Late Mesozoic, a large amount of continental crust was returned back into the mantle through lateral subduction erosion at the same time. This study provides important insights into long‐term material recycling on Earth.

Construction and Destruction of Bontău Composite Volcano in the Extensional Setting of Zărand Basin during Miocene (Apuseni Mts., Romania)

The Eastern part of the Miocene Zărand extensional basin witnessed the generation and evolution of the largest composite volcano in Apuseni Mts., named recently Bontău. The volcano is filling the basin at the junction between the South and North Apuseni Mountains. The Bontău Volcano is known to be active roughly between ~14–10. In spite of heavily forested and poorly exposed volcanic deposits, it was possible to identify its complex evolution. The volcano suggests an original oval-shaped edifice base currently showing a north-oriented horseshoe-shaped debris avalanche eroded crater. The early effusive volcanic activity was contemporaneous with the emplacement of individual and/or clustered volcanic lava Domes. Late-stage summit dome generation was followed by several volcanic collapses all around the volcanic edifice producing large volcanic debris avalanche deposits (DADs), accompanied by numerous debris flows all around the volcano periphery. Thick pumice pyroclastic flow deposits found below DADs at the periphery may suggest that the slope failures were proceeded by a Plinian eruption. The debris avalanche crater is the last event in the volcano evolution exposing several intrusive andesitic-dioritic bodies and associated hydrothermal and mineralization processes, most probably including the former central vent area of the volcano. The volcano proximal effusive and explosive deposits display a change in the composition of the erupting magma (increased SiO2 from 53.4% to 60.6%) that resulted in an increase of viscosity and the construction of the summit lava domes. Such domes are however only found as various size blocks in DADs. The volcanism connects with the two steps of geotectonic evolution of the Zărand Basin: The initial construction period during regional extension started ~16 Ma up to 12.3–12.1 when the Bontău volcano and surrounding domes were generated. The second period, younger than 12 Ma, corresponds to NW-SE compressional tectonics developed only in the Bontău volcano with summit dome generation and, finally, assists volcano destruction and DADs generation. Newly performed geochemical and Sr and Nd isotopic data studies attest to a calc-alkaline character and suggest an evolution via assimilation-fractional crystallization processes of a dominant MORB-like mantle source magma. Also, they confirm the amphibole (±pyroxene) andesites to be the most evolved lithology. The stepwise changes in fracture propagation in the Zărand extensional setting along with a change to more hydrated and fractionated magma favored in ~4 Myrs of the evolution of the Bontău volcano lead to multiple pulses of the longest-lived magma chamber in the whole Miocene volcanism of the Apuseni Mts.

40Ar/39Ar Ages and Geochemistry of Seamount Basalts from the Western Pacific Province

Seamounts are features generated by hot spots and associated intraplate volcanic activity. The geochemical characteristics of igneous rocks constituting seamounts provide evidence of important details of dynamic processes in the Earth, such as mantle magma source areas, and are key to understanding how mantle plume processes control the formation and evolution of seamounts and their resulting geochemical characteristics. The Pacific Ocean contains a large number of hitherto unstudied seamounts, whose ages and geochemical characteristics remain poorly known. This study presents the geochemical characteristics of six basalt samples from five seamounts in the Western Pacific and the 40Ar/9Ar ages of three samples are determined. The new analysis yielded 40Ar/39Ar ages for seamounts samples MP3D21, MP5D11, and MP5D15A of 95.43 ± 0.33, 62.4 ± 0.26, and 99.03 ± 0.4 Ma, respectively. The geochemical profiles of seamounts samples MP3D04, MP3D21, MP5D11, MP5D15A, MPID201, and MPID202 are consistent with alkaline basalts, as evidence by alkali-rich, silicon-poor compositions along with high titanium concentrations. The primitive mantle normalized rare-earth elements and trace elements spider pattern are similar to those of ocean island basalts. The Ta/Hf and Nb/Zr ratios and La/Zr-Nb/Zr discriminant diagrams indicate that the six seamounts formed from magma that originated in the deep mantle.

Geology, geochemistry, and petrogenesis of Jebal Ruro A-type granite, Blue Nile State, Sudan: implications for origin of HFSE mineralization

The Jebal Ruro granites occur west of the late Proterozoic Ingessana-Kurmuk suture of the Arabian-Nubian Shield located in the southeastern region of the Blue Nile State of the Sudan. A-type post-collisional granitoids from Jebal Ruro region were here studied through new field, petrographical and whole-rock data. These granitic intrusions comprise alkali granites consisting of aegirine granite, aegirine-arfvedsonite granite, and arfvedsonite granite. Geochemically, they are characterized by high Na2O, K2O, Fe/Mg, Ga/Al, Zr, Y, Nb, and REE (except Eu), and low abundances of CaO, MgO, TiO2, P2O5, and molar (Na2O+ K2O)/Al2O3 ratio ≥ 1 represent their peralkaline affinity. The Jebal Ruro granites show enrichment in Zr, Hf, Y, Nb, Ta, U, Th, Zn, and REE particularly in the aegirine granite and aegirine-arfvedsonite granite. Ruro granites show relatively high ratios of Nb/Ta and Zr/Hf close to that estimated for mantle magma source as well as Th/Ta, Th/U, Zr/Nb, La/Nb, and Rb/Nb. Furthermore, Ta+Yb vs. Gd/Yb, Sm/Yb, La/Yb, and Ta/Yb plots show that Ruro granites have distinguishable characteristics among arc and slab wedge-derived A-type magmas. In this study, we concluded that Jebal Ruro granites are A-type peralkaline to transitional metaluminous granites generated mainly by fractional crystallization from a mantle-derived OIB-like parent magma, emplaced in within-plate post-collisional tectonic environment.

Mush, Melts and Metasediments: a History of Rhyolites from the Okataina Volcanic Centre, New Zealand, as Captured in Plagioclase

Abstract The Okataina Volcanic Centre (OVC), located in the Taupo Volcanic Zone, New Zealand, is a dominantly rhyolitic magmatic system in an arc setting, where eruptions are thought to be driven by mafic recharge. Here, Sr–Pb isotopes, and compositional and textural variations in plagioclase phenocrysts from 10 rhyolitic deposits (two caldera, one immediately post-caldera, four intra-caldera, and three extra-caldera) are used to investigate the OVC magmatic system and identify the sources and assimilants within this diverse mush zone. Plagioclase interiors exhibit normal and reverse zoning, and are commonly in disequilibrium with their accompanying glass, melt inclusions, and whole-rock compositions. This indicates that the crystals nucleated in melts that differed from their carrier magma. In contrast, the outermost rims of crystals exhibit normal zoning that is compositionally consistent with growth in cooling and fractionating melts just prior to eruption. At the intra-crystal scale, the total suite of 87Sr/86Sr ratios are highly variable (0·7042–0·7065 ± 0·0004 average 2SE); however, the majority (95 %) of the crystals are internally homogeneous within error. At whole-crystal scale (where better precision is obtained), 87Sr/86Sr ratios are much more homogeneous (0·70512–0·70543 ± 0·00001 average 2SE) and overlap with their host whole-rock Sr isotopic ratios. Whole-crystal Pb isotopic ratios also largely overlap with whole-rock Pb ratios. The plagioclase and whole-rock isotopic compositions indicate significant crustal assimilation (≥20 %) of Torlesse-like metasediments (local basement rock) by a depleted mid-ocean ridge mantle magma source, and Pb isotopes require variable fluid-dominant subduction flux. The new data support previous petrogenetic models for OVC magmas that require crystal growth in compositionally and thermally distinct magmas within a complex of disconnected melt-and-mush reservoirs. These reservoirs were rejuvenated by underplating basaltic magmas that serve as an eruption trigger. However, the outermost rims of the plagioclase imply that interaction between silicic melts and eruption-triggering mafic influx is largely limited to heat and volatile transfer, and results in rapid mobilization and syn-eruption mixing of rhyolitic melts. Finally, relatively uniform isotopic compositions of plagioclase indicate balanced contributions from the crust and mantle over the lifespan of the OVC magmatic system.

An Awakening Magmatic System beneath the Udina Volcanic Complex (Kamchatka): Evidence from Seismic Unrest of 2017–2019

Abstract —The Udina volcanic complex located in the southeastern part of the Klyuchevskoy group of volcanoes in Kamchatka remained dormant for several thousand years, but the magmatic system beneath the area may be awakening judging by seismic unrest. Seismicity in the area is characterized by data from permanent regional seismic stations and campaign local stations, as well as by data of the Kamchatka earthquake catalog. Seismic activity having nucleated at shallow depths in the vicinities of the Udina volcanoes since October 2017 may reflect a beginning cycle of volcanism. The earthquakes are mainly long-period (LP) 0.5–5 Hz events, which are commonly attributed to the movement of viscous magma and resonance phenomena in magma conduits. Such earthquakes may be a response to inputs of new magma batches to the plumbing system that feeds the volcanoes and thus may be precursors of volcanic unrest. Seismic campaigns of May–July 2018 near the Udina complex provided more rigorous constraints on earthquake coordinates and origin depths and showed that most of the earthquakes originated within 5 km beneath the Bolshaya Udina Volcano. Seismic tomographic inversion using the LOTOS code revealed a zone of high P-wave velocities, low S-wave velocities, and a high vP/vS ratio directly beneath the volcano. Such a combination of parameters typically occurs in active volcanic areas and marks intrusion of partially molten magma and/or liquid fluids. The velocity anomaly detected in 2018 is shallower than that recovered in 2014–2015. The seismic evidence, along with the available geological and geophysical data, record the movement of viscous magma related to the Udina feeding system in the middle crust, which is implicit proof for connection between the intermediate crustal and deep mantle magma sources renewed after a long lull.

Early Permian to Late Triassic tectonics of the southern Central Asian Orogenic Belt: geochronological and geochemical constraints from gabbros and granites in the northern Alxa area, NW China

AbstractSituated between the North China Craton to the east and the Tarim Craton to the west, the northern Alxa area in westernmost Inner Mongolia in China occupies a key location for interpreting the late-stage tectonic evolution of the southern Central Asian Orogenic Belt. New LA-ICP-MS zircon U–Pb dating results reveal 282.2 ± 3.9 Ma gabbros and 216.3 ± 3.2 Ma granites from the Yagan metamorphic core complex in northern Alxa, NW China. The gabbros are characterized by low contents of Si, Na, K, Ti and P and high contents of Mg, Ca, Al and Fe. These gabbros have arc geochemical signatures with relative enrichments in large ion lithophile elements and depletions in high field strength elements, as well as negative εNd(t) (−0.91 to −0.54) and positive εHf(t) (2.59 to 6.37) values. These features indicate that a depleted mantle magma source metasomatized by subduction fluids/melts and contaminated by crustal materials was involved in the processes of magma migration and emplacement. The granites show high-K calc-alkaline and metaluminous to weakly peraluminous affinities, similar to A-type granites. They have positive εNd(t) (1.55 to 1.99) and εHf(t) (5.03 to 7.64) values. These features suggest that the granites were derived from the mixing of mantle and crustal sources and formed in a postcollisional tectonic setting. Considering previous studies, we infer that the final closure of the Palaeo-Asian Ocean in the central part of the southern Central Asian Orogenic Belt occurred in late Permian to Early–Middle Triassic times.

Origin of the Triassic Lincang granites in the southeastern Tibetan Plateau: Crystallization from crystal mush

The crustal generation of the Paleo-Tethys orogenic belt in the southeastern Tibetan Plateau is a major unresolved geological problem. The Changning-Menglian suture in the southeastern Tibetan Plateau represents a remnant of the Paleo-Tethys Ocean. The Lincang batholith and associated volcanic rocks (the Manghuai rhyolites and Xiaodingxi basalts) are located to the east of the Changning-Menglian suture, and represent important constraints for the abovementioned geological problem. New zircon UPb ages, together with previously published results, indicate that the Manghuai rhyolites were emplaced at 229–239 Ma and the Lincang batholith yielded longer age span (211–239 Ma). Broad age span of zircons (to 28 million years) from these rocks record a long-lived crustal magmatic system in the Changning-Menglian Paleo-Tethys orogenic belt. These intrusive and associated volcanic rocks have significant differences between them in terms of geochemistry. In this study, these rocks are geochemically classified into three groups: (1) Group 1 comprises biotite granite and granodiorite rocks; (2) Group 2 includes alkali feldspar granite, two-mica granite, and rhyolite, which are high-silica (generally >70 wt%) rocks that have low TiO2, Al2O3, FeOtot, MgO, CaO, P2O5, Eu, and Sr contents, compared to those of Group 1. Based on their geochemical relationships and mineral textures, Groups 1 and 2 include cumulative- and fractionated-type granitoids, respectively; (3) while Group 3 is comprised of dioritic enclaves and the Xiaodingxi basalts. Based on more robust evidence, dioritic enclaves are derived from a mantle source magma. The Lincang granites have high and variable initial 87Sr/86Sr ratios (0.703122–0.728476), significantly negative εNd (t = 220 Ma) values (−13.4 to −7.5), negative εHf (t) values (−17.7 to −6.8), and old TDM2 ages. The Manghuai rhyolites and Xiaodingxi basalts have lower initial 87Sr/86Sr ratios (0.695970–0.709398), and higher εNd (t) values (−3.4 to −0.6) and εHf (t) values (−1.2 to +3.7) than those of the Lincang granites. Geochemical data suggest that the Manghuai rhyolites could be seen as fractionated and erupted melts from crystal mush reservoirs, which later crystallized to form the Lincang granites. The Manghuai rhyolites provide an instantaneous snapshot of the state of the crystal mush at the time of eruption. The Lincang granites are interpreted to record prolonged histories of open-system magmatic evolution, involving magma mixing, wall-rock assimilation, and multiple cycles of crystallization from the crystal mush reservoirs. Magmatic evolution was likely related to mantle upwelling in a post-collisional setting, forming large-volume granites and volcanics in the Changning-Menglian Paleo-Tethys orogenic belt. Thus, this crystal mush model provides an integrated picture of the Triassic silicic magmatism, linking the evolution of the Lincang batholith and Manghuai rhyolites before storage in the Changning-Menglian Paleo-Tethys orogenic belt.

Olivine phenocryst origins and mantle magma sources for monogenetic basalt volcanoes in northern New Zealand from textural, geochemical and δ18O isotope data

Olivine phenocrysts in basalts erupted in the Kaikohe-Bay of Islands volcanic field (KBIVF), a cluster of Quaternary monogenetic edifices in northern New Zealand, provide an opportunity to investigate magma source and assembly. The phenocryst population has both cognate and non-cognate origins with respect to the carrier magma. Common large subhedral-euhedral phenocrysts with compositions of Fo80–86 are autocrysts, having nucleated in a melt equivalent of the host whole-rock (~Mg#56–63). A subordinate population of large subhedral-euhedral phenocrysts that are Mg-rich (>Fo86) nucleated in a melt more mafic (>Mg#65). These are antecrystic and are likely to have a deep cumulate origin, perhaps the product of fractionation of a primitive parental magma. Smaller anhedral phenocrysts have compositions (~Fo70–75) that would have crystallised in a more evolved melt (~Mg#42–48). These are xenocrysts from stalled and fractionated crystal mush zones or intrusions in the mid and upper crust. Other small phenocrysts (Fo66–79) are euhedral and reversely zoned with mafic mantle zones (Fo80–85). They also nucleated in a more evolved crustal magma, but subsequently experienced magma-mixing with a more mafic magma. The olivine assemblage requires a vertically extensive magma system through the crust and upper mantle involving deep cognate crystallisation, and recycling of non-cognate crystals from deep and shallow intrusive bodies. This in accord with varied origins for the accompanying plagioclase and clinopyroxene populations in the rocks demonstrated in previous studies. This study presents the first δ18O analyses of olivines from monogenetic volcanoes in New Zealand. SIMS analysis of cognate and cumulate olivine phenocrysts in KBIVF basalts, and those from other volcanoes in northern New Zealand basaltic fields, show that they are non-zoned (δ18O ± 0.4‰). The inter-crystal range at most volcanoes is narrow (0.5‰), although the olivine population at a few volcanoes are more varied (range up to 1.25‰), requiring more than one source. The isotopic data for the more northern fields KBIVF (δ18O mean = 5.60‰; range = 5.12–6.20‰) and Whangarei volcanic field (δ18O mean = 5.50‰; range = 4.98–6.12‰) include values higher than that of olivine from MORB-HIMU sources, and overlap those associated with EMI/EMII sources or subduction zone magmas. Whole-rock trace element and Pb-isotope data from these fields have been interpreted as the result of subduction-induced contamination of the mantle wedge, a relic signal from now extinct Miocene-Pliocene arc volcanism. The magma compositions are also consistent with source depths above the garnet facies zone. This could explain the higher olivine δ18O values. In contrast, olivines from more southern fields do not display this O-isotope signature, consistent with postulated greater source depths.

Sediment contribution in post-collisional high Ba-Sr magmatism: Evidence from the Xijing pluton in the Alxa block, NW China

High Ba-Sr granitoids occur in a number of tectonic settings, and variable petrogenetic models have been proposed. Those from post-collisional settings are rarely studied and are the focus of this study. Zircon U-Pb geochronology and whole-rock elemental and Sr-Nd-Hf isotopic data are presented for a suite of high Ba-Sr granitoids from the southern margin of the Alxa block, NW China. U-Pb zircon dating shows that the Xijing high Ba-Sr granitoids were emplaced in two periods at ~440 Ma and ~410 Ma, and they are characterized by elevated Ba and Sr contents. The older ~440 Ma high Ba-Sr granitoids range from monzodiorite to quartz monzonite, and the younger ~410 Ma high Ba-Sr granites tend to be more evolved. Both suites have similar enriched Sr-Nd-Hf isotopic ratios, low Ba/Th and Sr/Th ratios, and high Th contents and Th/Ce ratios indicative of a sediment contribution. This is potentially linked to previous subduction of the North Qilian ocean slab. Major and trace element calculations suggest that the older ~440 Ma granitoids experienced up to ~60% fractionation at 4–6 kbar with a crystallizing assemblage dominated by amphibole and plagioclase. The younger ~410 Ma granites could in turn have been formed by a further 80% fractional crystallization at lower pressures (1–2 kbar). Trace element and Sr-Nd isotopic modeling suggest incorporation of ~5% slab-derived sediment into mantle magma source of these high Ba-Sr granitoids. We note that post-collisional granitoids with high Ba and Sr characteristics may also reflect a sediment contribution in their source region, and this may be a key aspect of why such granites plot in the field of post-collisional granites in the Rb vs Y + Nb diagram. Some sanukitoids with high Ba and Sr contents in the late Archean also appear to reflect sediment subduction and they hence may represent early stages of crustal recycling.

The Kighal Porphyry Cu–Mo Deposit, NW Iran: Insights into Origin and Evolution of the Mineralizing Fluids

Abstract —The Kighal porphyry Cu–Mo deposit, located at 46°42′36″ N and 38°37′06″ E, occurs 120 km north of Tabriz and 12 km north of Varzeghan in the Arasbaran magmatic belt, NW Iran. The geologic units in the Kighal area are Eocene and Oligocene volcanic rocks associated with Miocene intrusive and subvolcanic rocks. Quartz-monzonite porphyry in the Kighal area hosts porphyry style Cu–Mo mineralization consisting of four alteration zones (potassic, phyllic, argillic, and propylitic) and abundant quartz veinlets. Based on mineralogy and geochemistry data, the intrusive and subvolcanic rocks belong to quartz-diorite, diorite, and granite units with high-K calc-alkaline to calc-alkaline affinities. All samples are enriched in LILE and depleted in HFSE, pointing to a mantle magma source contamination with subducted oceanic-crust material. Three types of fluid inclusions are identified in quartz from different quartz-sulfide veinlets, including multiphase (LVS) and liquid-rich (LV) inclusions in the potassic zone, liquid-rich (LV) and vapor-rich (VL) inclusions in the phyllic zone, and liquid-rich (LV) inclusions in the silicic zone. Microthermometry studies showed that Th in multiphase fluid inclusions in the potassic zone varied from 265 to 450 °C and salinity, from 38 to 59 wt.% NaCl-equiv. These values are higher than those of two-phase fluid inclusions in the phyllic zone (Th of 163 to 466 °C and salinity of 0.3 to 11 wt.% NaCl-equiv.). The calculated δ18OH2O and δDH2O values in biotite, sericite, and quartz from potassic, phyllic, and silicic zones showed that it is predominantly magmatic water with a lesser amount of meteoric water that is responsible for mineralization in the potassic zone. Light δDH2O values of biotite in the potassic zone suggest a magma degassing process and/or a change in the fluid composition with magmatic water influx to a hydrothermal system.

Petro-Geochemistry, Genesis and Economic Aspect of Syenitic and Mafic Rocks in Mindif Complex, Far North Cameroon, Central Africa

Syenitic and mafic rocks in Mindif Complex (Far North of Cameroon) were surveyed and characterized to classify them, understand their formation history, and assess their economic interest. Syenitic bodies (hololeucocratic microsyenites; mesocratic aplitic quartz-syenite; leucocratic porphyritic quartz-biotite syenite, and leucocratic porphyritic biotite-syenite) are silica-oversaturated to silica-saturated, alkaline, and metaluminous. Hololeucocratic microsyenites are structural oriented rocks, cooled in shallow depth from low trace and REE dry residual alkaline melts. Mesocratic aplitic quartz-syenite also crystallized in shallow depth from a much Ba-rich less dry residual melt. Leucocratic porphyritic quartz-biotite and biotite syenitic stocks represent two different rock types cooled from hydrous-rich melts in deep seated environments. The Mindif syenites probably crystallized in crustal source magmas (with important alkali feldspar accumulation) from partial melting of pre-existing igneous protoliths. Medium to coarse-grained-peraluminous granite found at the edge of pink microsyenitic dykes (in contact with granite host), is probably a crystallized product from magmatic mixture between the intrusive syenitic melt and a melt from partial fusion of the granite host rock. Mafic igneous rocks in Mindif are peridotgabbro and gabbro with different characteristics. Peridotgabbro, alkaline, holomelanocratic, medium-grained and ultrabasic, is an REE and incompatible elements depleted rock crystallized in shallow depth from a more evolved mantle source magma with plagioclase accumulation. Tholeiitic gabbro, melanocratic, and also medium-grained, was cooled in shallow depth, from a low-K and slightly LILE-enrichment magma probably originated from partial melting ultradepleted mantle source in sub-duction environment. Syenites and peridotgabbro with their high aluminum content (up to 18.5 wt%) greater than that of many parent rocks of lateritic bauxite in Cameroon, can be good parent rocks for bauxite-rich soils if found in a plateau topography and hot-humid tropical climate. The geochemical features of Mindif syenites are close to that of some syenites mined and used as raw materials in ceramic and glass industries. This similarity shows that these syenites are good for glass and ceramic manufacture.

What triggers fertile porphyritic Mo magmas in subduction setting: A case study from the giant Daheishan Mo deposit, NE China

The Daheishan porphyry Mo deposit in Jilin Province, NE China, is classified as a giant porphyry deposit with a total reserve of 1.87 Mt. @0.07% Mo. It is located within the Lesser Xing'an-Zhangguangcai Ranges at the eastern part of Central Asian Orogenic Belt, which was tectonically shaped by both the Paleo-Asian Ocean and the Paleo-Pacific Ocean regimes. The Mo mineralization (167 Ma) is related to the Daheishan intrusive complex which comprises of the barren Changgangling biotite granodiorite (177.9 Ma), the fertile Qiancuoluo biotite granodiorite (169.9 Ma) and the Qiancuoluo granodioritic porphyry (166.6 Ma). The Daheishan intrusive complex is high-silica, alkali-rich, metaluminous to slightly peraluminous in composition, belonging to high-K calc-alkaline series. In addition, they are characterized by enrichment in large ion lithophile elements (LILEs, e.g. K, Rb, Ba, Sr, U and Th) and light rare earth elements (LREEs), and relative depletion in high-field strength elements (HFSEs, e.g. Nb, Ta, P and Ti), suggesting the formation in oceanic arcs above subduction zones and an involvement of the oceanic component. The Sr-Nd-Pb isotopic compositions (87Sr/86Sr = 0.705413–0.707889, εNd(t) = −1.28 to +0.92, and 206Pb/204Pb = 18.44–18.73) of the Daheishan intrusive complex are consistently comparable to values of the regional mantle derived rocks, suggesting a source of depleted mantle wedge for the magmas. The trace element signatures, i.e. Th/Ce, Th/Sm, Th/Yb and Ba/La ratios, identify a minor (~4%) contribution of slab melts that metasomatized the mantle magma source. Geochemical particularity, i.e. high water content and oxygen fugacity, has been recorded at both bulk rock and mineral scales to account for the fertility of magmas of the Qiancuoluo granodioritic porphyry and Qiancuoluo biotite granodiorite relative to the barren Changgangling biotite granodiorite. The mineralization of the Daheishan supergiant porphyry Mo deposit, in association with the intrusion of contemporaneous granitoids in the region, was formed in an active continental margin environment due to the subduction of Mudanjiang Ocean between the Jiamusi and Songliao blocks in the early Jurassic, which, in a larger framework, was driven by the westward subduction of the Palaeo-Pacific Ocean. Under the subduction environment, an input of slab melts, which secured abundant molybdenum from the shales overlying the oceanic plate, is proven to have improved the fertility of primary magmas by comparing the geochemical compositions of the fertile and barren granitoids (porphyry Mo mineralization related-) in the Lesser Xing'an-Zhangguangcai Ranges. To conclude, factors such as contribution of slab melts, high water content and high oxygen fugacity, are regarded to be crucial for generating fertile magmas for porphyry Mo mineralization in the Lesser Xing'an-Zhangguangcai Ranges.

Geochronological Constraints on the Haftcheshmeh Porphyry Cu‐Mo‐Au Ore Deposit, Central Qaradagh Batholith, Arasbaran Metallogenic Belt, Northwest Iran

AbstractThe Haftcheshmeh porphyry Cu‐Mo‐Au deposit in the Arasbaran metallogenic belt (AMB) of NW Iran contains more than 185 Mt of ore, with a grade ranging from 0.3% to 0.4%. It is hosted within a porphyritic diorite to granodiorite intruded into an older gabbro ‐ diorite intrusion. 40Ar/39Ar analyses of primary magmatic hornblende from the granodiorite porphyry and gabbro ‐ diorite show plateau ages of 26.41 ± 0.59 Ma, with an inverse isochron age of 25.9 ± 1.0 Ma and a plateau age of 27.47 ± 0.17 Ma, with an inverse isochron age of 27.48 ± 0.35 Ma for these two rock types, respectively. Comparing these new age data with those from the nearby Sungun (20.69 ± 0.35 Ma) and Kighal porphyry deposits defines a northwest‐southeast Cu‐Mo‐Au mineralization zone extending for 20 km over the time span of ∼27 to 20 Ma. Geochemically, Haftcheshmeh rocks are calc‐alkaline with high potassium affinities with tectonic setting in relation to volcanic arc setting. Large ion lithophile elements (LILE) such as Th, U and K show enrichment on a primitive mantle normalized diagram (specially Pb), and are depleted in high field strength elements (HFSE) such as Ti and Nb, pointing to a mantle magma source contamination with crustal materials by subducted oceanic crust.

Olivine-hosted melt inclusions as an archive of redox heterogeneity in magmatic systems

The redox state of volcanic products determines their leverage on the oxidation of Earth's oceans and atmosphere, providing a long-term feedback on oxygen accumulation at the planet's surface. An archive of redox conditions in volcanic plumbing systems from a magma's mantle source, through crustal storage, to eruption, is carried in pockets of melt trapped within crystals. While melt inclusions have long been exploited for their capacity to retain information on a magma's history, their permeability to fast-diffusing elements such as hydrogen is now well documented and their retention of initial oxygen fugacities (fO2) could be similarly diffusion-limited. To test this, we have measured Fe3+/ΣFe by micro-XANES spectroscopy in a suite of 65 olivine-hosted melt inclusions and 9 matrix glasses from the AD 1783 Laki eruption, Iceland. This eruption experienced pre-eruptive mixing of chemically diverse magmas, syn-eruptive degassing at the vent, and post-eruptive degassing during lava flow up to 60 km over land, providing an ideal test of whether changes in the fO2 of a magma may be communicated through to its cargo of crystal-hosted melt inclusions.Melt inclusions from rapidly quenched tephra samples have Fe3+/ΣFe of 0.206±0.008 (ΔQFM of +0.7±0.1), with no correlation between their fO2 and degree of trace element enrichment or differentiation. These inclusions preserve the redox conditions of the mixed pre-eruptive Laki magma. When corrected for fractional crystallisation to 10 wt.% MgO, these inclusions record a parental magma [Fe3+/ΣFe](10) of 0.18 (ΔQFM of +0.4), significantly more oxidised than the Fe3+/ΣFe of 0.10 that is often assumed for Icelandic basalt magmas. Melt inclusions from quenched lava selvages are more reduced than those from the tephra, having Fe3+/ΣFe between 0.133 and 0.177 (ΔQFM from −0.4 to +0.4). These inclusions have approached equilibrium with their carrier lava, which has been reduced by sulfur degassing. The progressive re-equilibration of fO2 between inclusions and carrier melts occurs on timescales of hours to days, causing a drop in the sulfur content at sulfide saturation (SCSS) and driving the exsolution of immiscible sulfide globules in the inclusions.Our data demonstrate the roles of magma mixing, progressive re-equilibration, and degassing in redox evolution within magmatic systems, and the open-system nature of melt inclusions to fO2 during these processes. Redox heterogeneity present at the time of inclusion trapping may be overprinted by rapid re-equilibration of melt inclusion fO2 with the external environment, both in the magma chamber and during slow cooling in lava at the surface. This can decouple the melt inclusion archives of fO2, major and trace element chemistry, and mask associations between fO2, magmatic differentiation and mantle source heterogeneity unless the assembly of diverse magmas is rapidly followed by eruption. Our tools for understanding the redox conditions of magmas are thus limited; however, careful reconstruction of pre- and post-eruptive magmatic history has enabled us to confirm the relatively oxidised nature of ocean island-type mantle compared to that of mid-ocean ridge mantle.

Petro-geochemistry, Genesis and Economic Aspects of Mafic Volcanic Rocks in the West and Southern Part of The Mamfe Basin (SW Cameroon, Central Africa)

Geologic prospecting, petrographic and geochemical analyses of mafic volcanic exposures in the west and southern part of the Mamfe Basin (SW Cameroon) distinguishes: basanites, picro-basalts, alkali basalts and tholeiitic basalts. They are relatively LREE-enriched, undersaturated, saturated or oversaturated due to presence or absence of normative nepheline, hypersthene or quartz. Basanites mainly form pillow-like lavas, and are aphyric or porphyritic. They have significant concentration of Ni (up to 387 ppm) and Ba (up to 436 ppm). These alkaline rocks cooled from less evolved mantle source magma. Picro-basaltic fragments exclusively found in the western part of the basin are Ni (up to 259 ppm) Ba (up to 2090 ppm) -enriched porphyritic, alkaline or subalkaline rocks. They also cooled from less evolved mantle source magma. Basalts form volcanoclasts, flow and dykes. They are aphyric or porphyritic, alkaline, transitional or subalkaline. Some of these rocks are Al-enriched. They crystallized from variably evolved mantle source magma within the Oceanic Island Basalt and Continental Rift Basalt tectonic settings.

Zircon U–Pb ages and geochemistry of Devonian A-type granites in the Iraqi Zagros Suture Zone (Damamna area): New evidence for magmatic activity related to the Hercynian orogeny

The Damamna granite (DG) is located in the Shalair Valley area in northeast Iraq within the Sanandaj Sirjan Zone (SSZ). The zircon U–Pb ages for the DG rocks are 364–372Ma, indicating crystallization of the granitic body. The DG rocks are A-type granites, hypersolvus and peraluminous. They are enriched in SiO2, alkalis, Ga/Al, Ga, Zr and Rb/Sr and depleted in CaO, MgO, Sr, P, and Ti. These rocks show steep REE patterns, with LREE enrichment relative to HREE ((La/Yb)N=5.7–42.5) and pronounced negative Eu anomalies reflecting feldspar fractionation. The geochemical characteristics and relationships suggest that the DG rocks are anorogenic and were emplaced in an extensional tectonic regime having an OIB-like magma affinity. The DG rocks are characterized by low Y/Nb ratios (0.2–1.5) and positive εNd (371Ma) values (+1.6 to +4.2), which indicate a mantle origin. In the Y/Nb–Yb/Ta diagram, the DG rocks plot in the A1-type granite field, with slightly higher Y/Nb values and a tendency of transitioning from A1 to the nearby A2 field, which possibly indicates a slight crustal contamination effect. The isotopic and geochemical data suggest that a combination of enriched mantle source magma with crustal contamination and fractional crystallization contributed to the generation of the magma for the DG. The geochemical and geochronological results for the DG rocks in the SSZ suggest an extensional zone that probably represents an early stage of Neo-Tethys opening during the Late Devonian or earlier, and this was associated with the Hercynian orogeny and tectono-magmatic activity in northern Arabia and northwestern Iran.