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The magmatic controls on the formation of porphyry Au-only deposits are still poorly understood. The Bilihe deposit (> 30 t at 2.7 g/t Au) located at the northern margin of the North China Craton is such an example, where apatite chemistry from a causative granodiorite intrusion constrains the physicochemical conditions and ore-forming potential of the porphyry-related magmas. Apatite can be subdivided by distinct CL intensities into early CL-bright and late CL-gray/dark sub-types both occurring in fresh (Ap-f), as well as in potassic (Ap-k) and phyllic (Ap-p) altered granodiorite. The mostly euhedral CL-bright apatite shows a homogeneous texture and is enriched in LREE and depleted in Fe, Mg, Mn, Y, and U compared to CL-gray/dark apatite, which develops patchy or oscillatory zoning. The CL-gray/dark apatite exhibits decreasing Fe and Mg contents, as well as δ18O values from Ap-f to Ap-k and Ap-p due to consecutive fluid alteration during porphyry evolution, which was generally not observed in CL-bright apatite. We thus conclude that all types of CL-bright apatite but only CL-gray/dark Ap-f inherit the original magma composition. Binary O–Nd isotope mixing simulations suggest that both magmatic CL-bright apatite and CL-gray/dark Ap-f were influenced by crustal sediment assimilation. Our results further indicate that the magma parental to the Bilihe porphyry Au-only deposit was H2O-poor (< 2 wt %), causing plagioclase fractionation in the absence of hornblende, as evidenced by relatively low Sr/Y (< 0.1) and significantly negative Eu anomalies in magmatic apatite. Pressure estimates by magmatic biotite that record the late crystallization stage yielded 48.9 ± 8.4 MPa, indicating a shallow final emplacement depth of 1.85 ± 0.32 km. The studied apatites formed under volatile-saturated conditions from S-deficient magmas at relatively reduced conditions (ΔFMQ +0.5) compared to porphyry Cu deposits. We thus conclude that these physicochemical parameters together with the low-pressure conditions result in a fertile magmatic-hydrothermal environment for the formation of Au-only porphyry deposits. [ABSTRACT FROM AUTHOR]

The intensive variables, geochemical, mineralogical, and petrogenetic constraints of the Iberian peraluminous rare metal granites (RMGs), many of them unknown, are presented. The mineral chemistry of ore and gangue minerals, whole rock analyses, geothermobarometry, melt water and phosphorus contents, mass balance, and Rayleigh modeling were performed to achieve these objectives. These procedures allow us to distinguish two main contrasting granitic types: Nb-Ta-rich and Nb-Ta-poor granites. The former have lower crystallization temperatures, higher water contents, and lower emplacement pressures than Nb-Ta-poor granites. Nb-Ta-rich granites also have higher fluoride contents, strong fractionation into geochemical twins, higher Na contents, and different evolutionary trends. At the deposit scale, the fractional crystallization of micas properly explains the variation in the Ta/Nb ratio in both Nb-Ta-poor and Nb-Ta-rich RMGs, although in higher-grade granites, the variation is not as clear due to the action of fluids. Fluid phase separation processes especially occurred in the Nb-Ta rich granites, thus transporting halogens and metals that increased the grades in the top and sometimes in the core of granites. Gas-driven filter pressing processes facilitated the migration of fluid and melt near solidus melt in Nb-Ta-rich granites. The geochemical signature of the Iberian rare metal granites mainly follows the trends of two-mica granites and P-rich cordierite granites, but also of granodiorites. [ABSTRACT FROM AUTHOR]

An east–west‐trending medium‐grained mafic sill containing co‐genetic Fe–Ti oxide ore lenses is found disposed within granite gneisses around Saltora‐Mejia area in the eastern part of the Chotanagpur Granite Gneissic Complex (CGGC) of eastern India. CGGC is considered as a Proterozoic mobile belt as it witnessed multiple phases of deformation and high‐ grade metamorphism during 1.8–0.8 Ga. Occurrence of such Fe–Ti oxide ore‐bearing mafic sill is unique in the entire CGGC which is a vast Proterozoic orogenic belt and has witnessed many phases of voluminous mafic and felsic magmatisms. The mafic rock is of gabbronorite composition which contains plagioclase, clinopyroxene, orthopyroxene as major constituent primary minerals and amphibole as late magmatic mineral. The rock shows sub‐ophitic, intergranular, mosaic and poikilitic texture (defined by larger pargasitic grain). The gabbronorite shows iron enriched tholeiitic character, low Mg#, low abundances of Ni and Cr, slight enrichment in LILE, LREE and slight depletion in HFSE like Nb and Ti. The computed melt in equilibrium with the studied gabbronorite shows transitional orogenic to anorogenic, within‐plate and E‐MORB‐like geochemical character. In this study, the U–Pb zircon crystallization age (~960 Ma) of the Saltora‐Mejia gabbronorite is reported for the first time which coincides with the late tectonic stage of the most pervasive orogenic activity in the CGGC around 1.2–0.9 Ga. Transitional orogenic to anorogenic geochemical character, late tectonic evolution and other field and laboratory evidences together suggest evolution of the Saltora‐Mejia gabbronorite sill in a late tectonic extensional environment which might have been facilitated by delamination of a subducted plate and upwelling of asthenospheric mantle during the waning stage of a major orogeny in the CGGC. [ABSTRACT FROM AUTHOR]

Clinopyroxene, one of the primary rock-forming minerals in mafic rocks, is the major host of lithophile elements in the mantle lithosphere and plays a crucial role in understanding mantle evolution and rock petrogenesis. Taking the Bingdaban ophiolite as an example, this study employed electron probe microanalysis and in situ trace element analysis to investigate the geochemistry of clinopyroxene in gabbros to determine the magma series and evolution, constrain the physicochemical conditions of the magmatic processes and explore the petrogenesis and tectonic setting. Representative gabbro samples were subjected to zircon U–Pb isotopic analysis, yielding an age of 424.3 ± 5.9 Ma. Geochemical investigations revealed that the Bingdaban gabbros exhibit tholeiitic composition, suggesting a genesis associated with enriched mid-ocean ridge basalt (E-MORB). Mineralogical analyses indicated that the clinopyroxene in the gabbros was Mg-rich, Fe-poor, and alkali-poor, representing a subalkaline series. The compositional end members of clinopyroxene were calculated as Wo38.9–48.0En30.9–48.1Fs10.4–24.4, indicating a predominance of diopside with a minor amount of augite. Temperature–pressure conditions imply that these rocks formed in a high-temperature, low-pressure, and shallow-source environment. Compositional estimates of the melt in equilibrium with clinopyroxene are consistent with the overall characteristics of the host rock, reflecting an E-MORB setting. The Bingdaban gabbro likely originated from an initially depleted mantle source that later received an input of enriched mantle material, indicating formation in either an initial oceanic or immature back-arc basin tectonic setting. [ABSTRACT FROM AUTHOR]

Xingdi mafic-ultramafic rock belt in the northern Tarim craton is composed of No.Ⅰ, No.Ⅱ, No.Ⅲ and No.Ⅳ intrusions. The lithology of Xingdi No.Ⅰ and No.Ⅳ intrusions is mainly gabbro facies, while Xingdi No.Ⅱ and No.Ⅲ intrusions have various rocks of olivine, pyroxenite and gabbro facies, and the lithofacies zonation is clear. The Cu-Ni sulfide ore bodies are mainly hosted in lherzolite and websterite of Xingdi No.Ⅱ and No.Ⅲ intrusions, and the Cu-Ni sulfide ores are stellate, speckled, sparse-disseminated and dense-disseminated in structure. Most of the sulfides occur as aggregate of pyrrhotite, pentlandite and chalcopyrite. The total contents of platinum group element(PGE)are(0.41-4.54)×10-9 of bulk rocks in Xingdi No.Ⅱ and No.Ⅲ intrusions, which are lower than that of primitive mantle and show positive correlations with MgO contents. The contents of IPGE(Os, Ir and Ru)are slightly higher than that of PPGE(Ru, Pt and Pd)with IPGE/PPGE ratios of 0.08-0.48, and primitive mantle-normalized PGE spider diagrams of rocks are left-declined pattern. Their Pd/Ir and Ni/Cu ratios range from 3.28 to 23.33 and from 3.67 to 10.00, respectively, indicating that parental magmas of Xingdi No.Ⅱ and No.Ⅲ intrusions are high-Mg basaltic. It is consistent with the result estimated from olivine-melt equilibrium. According to bulk rock Cu/Pd ratio((6.58-83.33)×104)and correlation between Cu/Zr and Ni, it is concluded that sulfide dissociation occurs in the source and during emplacement, resulting in a significant loss of PGE in remnant magma. It is comprehensively concluded that Xingdi No.Ⅱ and No.Ⅲ intrusions have good prospecting prospect. [ABSTRACT FROM AUTHOR]

Deep in the Western Desert of Egypt, in the southernmost part, between Qaret El-Maiyit and Bir Safsaf, swarms of dykes cut through the Neoproterozoic rocks. This area lies halfway between the juvenile crust of the Arabian-Nubian Shield (ANS) and the Gebel Kamil terrains, close to the border with Libya. Acidic dykes include rhyolites and trachy-dacites. Intermediate dykes include trachy-andesite, basalt-trachy-andesite, and basalt-andesite, while basic dykes consist of basalt. Felsic dykes are more numerous and younger compared to the mafic (intermediate and basic) dykes. Felsic dykes trend mostly run to the northeast and northwest, while mafic dykes mainly run to the northwest, less frequently to the eastwest. Acidic and intermediate dykes show elevated REE concentrations (up to 164 and 203 ppm, respectively) with highly fractionated patterns (av. (La/Lu) N = 20.56 and 18) and moderately fractionated HREEs (av. (Gd/Lu) N = 2.5 and 3.2) and LREEs (av. (La/Sm)N = 5.7 and 3.6 respectively). The basic dyke samples exhibit modest REE concentrations (up to 112 ppm), weakly fractionated patterns (av. (La/Lu) N = 8), and mildly to weakly fractionated HREE (av. (Gd/Lu) N = 2.3) and LREEs (av. (La/Sm) N = 2.5) patterns. There are no recognizable Eu anomalies in the dyke samples. The magma ascended in an extensional setting and the geochemical features indicate a subduction mode, possibly originating from the Atmur-Delgo suture zone in northern Sudan or by mantle delamination during the early Neoproterozoic. Both the felsic and mafic dykes are derived from a mafic calc-alkaline melt and show fractionation on a single downward line, indicating a genetic relationship. The mafic dykes were formed by partial melting of an enriched mantle source (about 10%) that started at 2.7–3.0 GPa and a solidus temperature of about 1420 °C. The enrichment of the mantle melt beneath the Saharan metacraton, which is the origin of the studied melts, could be related to mantle delamination. • Dyke swarms of Saharan metacraton consist of basic, intermediate, felsic suites. • Different dyke suites are formed from a single parental magma. • Mafic magma formed by batch melting of enriched lithospheric garnet-bearing mantle materials. • The mantle melt was altered by subduction processes linked to accretion and subduction events in northern Sudan. • The enrichment of mantle melt is linked to mantle delamination. [ABSTRACT FROM AUTHOR]

Ore-bearing mafic–ultramafic layered intrusions are widespread in the Emeishan large igneous province (ELIP). The ore genesis and sulfide evolution/saturation in these layered intrusions remain debated, due to the lack of constraints on their parental magma compositions. Although trace element partition coefficients may be able to provide a reasonable estimate for the parental magma compositions, finding suitable partition coefficient for the parental magma composition calculation can be a challenge. This is due to the variability of potential mineral constituents, magma compositions, and crystallization temperature and pressure. In this study, we use the phenocryst-groundmass method and LA-ICP-MS analysis to establish new trace element partition coefficients and mathematical expression for the clinopyroxene (Cpx) in the ELIP basalts. Similarity in the estimated magma compositions (with our partition coefficients) to those of the Emeishan high-Ti basalts and the microgabbro chilled margin indicates that this method can reliably yield parental magma compositions for mafic plutons in the ELIP. • Crystal compositions can control Cpx-basaltic melt trace element partitioning. • Parental composition of Panzhihua intrusion is likely microgabbro or high-Ti basalt. • D value from natural sample can be used to calculate parental magma composition. [ABSTRACT FROM AUTHOR]

[Display omitted] • Petrogenesis of the Daxigou anorthosite complex (DAC), NW China. • The diabase is the last episode of parental magma with U–Pb age of 1804 ± 7 Ma. • Zircon coronas were formed by exsolution and hydrothermal overprint at 1813 ± 9 Ma. • The DAC was formed under post-collisional slab break-off. Massif-type anorthosites, mainly Proterozoic in age, have long been recognized as a signature of crust-mantle interactions. The Daxigou Anorthosite Complex (DAC) is one such massif situated in the Kuluketage block, a tectonically important domain between the Tarim Craton and the Central Asian Orogenic Belt. In this contribution, a combination of geochronological and geochemical analyses of fine-grained DAC diabase are used to constrain the characteristics of the parental magma and the initiation time of DAC magmatism. We then pinpoint the DAC's closure time by in-situ petrographic thin section U–Pb dating of zircon coronas around Fe-Ti oxides identified in a gabbroic anorthosite. Within data uncertainty, we find that the closing age of 1813 ± 9 Ma, is indistinguishable from the 1804 ± 7 Ma crystallization age of its last episode of parental magma. MELTS simulations of the parental diabase magma suggest a pressure of 8 kbar at a fayalite-magnetite-quartz oxygen fugacity leads to broadly observed mineral compositions and mineral phases. The bulk rock major and trace elements, integrated with the whole-rock Sr–Nd and Hf isotopes in zircon, indicate that the DAC was formed by partially melting of a metasomatized sub-continental lithospheric mantle, which was likely induced by a post-collisional slab break-off with minor crustal assimilation. Finally, we propose that the DAC magmatism can be ascribed to a series of Paleoproterozoic tectono-thermal events along the northern and southern margins of the Tarim Craton, which could have provided important implications for the Tarim Craton and the North China Craton associated with the assembly of Columbia supercontinent. [ABSTRACT FROM AUTHOR]

Troctolite blocks with compositions akin to the Hidden Zone are exposed in a tholeiitic dyke cutting across the Skaergaard intrusion, East Greenland. Plagioclase in these blocks contains finely crystallised melt inclusions that we have homogenised to constrain the parental magma to 47.4–49.0 wt.% SiO2, 13.4–14.9 wt.% Al2O3 and 10.7–14.1 wt.% FeOT. These compositions are lower in FeOT and higher in SiO2 than previous estimates and have distinct La/SmN and Dy/YbN ratios that link them to the lowermost volcanic succession (Milne Land Formation) of the regional East Greenland flood basalt province. New major- and trace element compositions for the FG-1 dyke swarm, previously taken to represent Skaergaard magmas, overlap with the entire range of the regional flood basalt succession and do not form a coherent suite of Skaergaard like melts. These dykes are therefore re-interpreted as feeder dykes throughout the main phase of flood basalt volcanism.

About 20 mafic-ultramafic layered intrusions in the northern Fennoscandian shield were emplaced during a widespread magmatic event at 2.5–2.4 Ga. The intrusions host orthomagmatic Ni-Cu-PGE and Cr-V-Ti-Fe deposits. We update the magmatic stratigraphy of the 2.44-Ga Näränkävaara mafic-ultramafic body, northeastern Finland, on the basis of new drill core and outcrop observations. The Näränkävaara body consists of an extensive basal dunite (1700 m thick), and a layered series comprising a peridotitic–pyroxenitic ultramafic zone (600 m thick) and a gabbronoritic–dioritic mafic zone (700 m thick). Two reversals are found in the layered series. The composition of the layered series parental magma was approximated using a previously unidentified marginal series gabbronorite. The parental magma was siliceous high-Mg basalt with high MgO, Ni, and Cr, but also high SiO2 and Zr, which suggests primary magma contamination by felsic crust. Cu/Pd ratio below that of primitive mantle implies PGE-fertility. The structural position of the marginal series indicates that the thick basal dunite represents an older wallrock for the layered intrusion. A subeconomic reef-type PGE-enriched zone is found in the border zone between the ultramafic and mafic zones and has an average thickness of 25 m with 150–250 ppb of Pt + Pd + Au. Offset-type metal distribution and high sulfide tenor (50–300 ppm Pd) and R-factor (105) suggest reef formation by sulfide saturation induced by fractional crystallization. The reef-forming process was probably interrupted by influx of magma related to the first reversal. Metal ratios suggest that this replenishing magma was PGE-depleted before emplacement. [ABSTRACT FROM AUTHOR]

Jotunites (hypersthene monzodiorites/ferromonzodiorites) are rocks coeval with plutonic AMCG (anorthosite-mangerite-charnockite-rapakivi granite) suites, which are characteristic of the Proterozoic Eon. It has been experimentally shown that jotunite magma can be recognised as parental to anorthosites and related rocks: since then, research on these rocks has taken on a particular importance. Jotunites were recently described within the deeply buried c. 1.5 Ga Suwałki and Sejny anorthosite massifs in the crystalline basement of NE Poland. The major and trace element compositions of Polish jotunites show them to have a calc-alkalic to alkali-calcic and ferroan character, with a relatively wide range of SiO2 content (40.56 wt. % up to 47.46 wt. %) and high concentrations of Fe (up to 22.63 wt. % Fe2O3), Ti (up to 4.34 wt. % TiO2) and P (up to 1.46 wt. % P2O5). Slight differences in textural features, mineralogical compositions, and geochemistry of whole-rock jotunite samples from distinct massifs allow us to distinguish two kinds: a primitive one, present in the Sejny Intrusion, and a more evolved one, related to the Suwałki Massif. [ABSTRACT FROM AUTHOR]

The Songshugou peridotite massif is located in the north of Shangdan suture zone, North Qinling orogenic belt of Central China. The massif is mainly composed of fine-grained mylonitic dunites, coarse-grained dunites, fine- and coarse-grained harzburgites, and minor clinopyroxenites. The coarsegrained dunites as well as parts of the harzburgites host small-scale chromitites. Chromite grains from various textural types of chromitites and dunites pervasively contain primary and secondary silicate inclusions. Primary inclusions are dominated by monophase olivine, with minor clinopyroxene and a few multiphase mineral assemblages consisting of olivine and clinopyroxene. Secondary inclusions, mainly Cr-chlorite and tremolite, show irregular crystal shapes. Besides, Cr2O3 contents (0.08 wt.%–0.71 wt.%) of primary olivine inclusions are remarkably higher than those of interstitial olivine (<0.1 wt.%). Chromites in the Songshugou peridotite massif are high-Cr type, with Cr# and Mg# values ranging of 67.5–87.6, and 23.4–41.2, respectively. The Cr-chlorite, formed by reactions between olivine and chromite in the presence of fluid under middle temperature, indicates the Songshugou peridotite massif has undergone alteration/metamorphism process during emplacement. Chromite grains are modified by these processes, resulting in the various degrees of enrichment of Fe2O3, Cr2O3, Zn, Co and Mn, depletion of MgO, Al2O3, Ga, Ti and Ni. Due to low silicate/chromite ratios in the massive ores, chromites from them are slightly influenced by alteration/metamorphism and thus preserve the pristine magmatic compositions. The parental magma calculated based on them has 11.17 wt.%–13.57 wt.% A12O3 and 0.15 wt.%–0.27 wt.% TiO2, which is similar to the parental melts of high-Cr chromitites from elsewhere and comparable with those of boninites. Combined with informations from previous studies, major and trace elements geochemistry of chromite, as well as the nature of the parental magma, it can be revealed that the Songshugou chromitities formed in a supra-subduction zone environment. [ABSTRACT FROM AUTHOR]

This paper reports the results of a study of naturally and experimentally quenched melt inclusions in magnesian olivine (Fo77–89) from a basalt sample from the Karymsky volcanic center, which is located in the middle segment of the Eastern Volcanic Front of Kamchatka. The conditions of parental magma formation were estimated using modern methods of trace-element thermometry. Based on direct H2O measurements in inclusions and thermometry of coexisting olivine and spinel, it was shown that the parent melts contained at least 4.5 wt % H2O and crystallized at a temperature of 1114 ± 27°C and an oxygen fugacity of ΔQFM = 1.5 ± 0.4. The obtained estimates of H2O content and crystallization temperature are among the first and currently most reliable data for the Eastern Volcanic Front of Kamchatka. The primary melt of the Karymsky volcanic center was derived from peridotitic material and could be produced by ~12–17% melting of an enriched MORB source (E-DMM) at ~1230–1250°C and ~1.5 GPa. Our estimates of mantle melting temperature beneath Kamchatka are slightly lower than values reported previously and up to 50°C lower than the dry peridotite solidus, which indicates the influence of a slab-derived hydrous melt. The combined approach to the estimation of the initial H2O content of melt employed in this study can provide a more reliable data in future investigations, and its application will probably decrease the existing temperature estimates for the mantle wedge above subduction zones. [ABSTRACT FROM AUTHOR]

In situ trace element analysis of cumulus minerals may provide a clue to the parental magma from which the minerals crystallized. However, this is hampered by effects of the trapped liquid shift (TLS). In the Main Zone (MZ) of the Bushveld Complex, the Ti content in plagioclase grains shows a clear increase from core to rim, whereas most other elements [e.g. rare earth elements (REE), Zr, Hf, Pb] do not. This is different from the prominent intra-grain variation of all trace elements in silicate minerals in mafic dikes, which have a faster cooling rate. We suggest that crystal fractionation of trapped liquid occurred in the MZ of Bushveld and the TLS may have modified the original composition of the cumulus minerals for most trace elements except Ti during slow cooling. Quantitative model calculations suggest that the influence of the TLS depends on the bulk partition coefficient of the element. The effect on highly incompatible elements is clearly more prominent than that on moderately incompatible and compatible elements because of different concentration gradients between cores and rims of cumulate minerals. This is supported by the following observations in the MZ of Bushveld: (1) positive correlation between Cr, Ni and Mg# of clinopyroxene and orthopyroxene; (2) negative correlation between moderately incompatible elements (e.g. Mn and Sc in clinopyroxene and orthopyroxene; Sr, Ba and Eu in plagioclase); but (3) poor correlation between highly incompatible elements and Mg# of clinopyroxene and orthopyroxene or An# of plagioclase. Modeling suggests that the extent of the TLS for a trace element is also dependent on the initial fraction of the primary trapped liquid, with strong TLS occurring if the primary trapped liquid fraction is high. This is supported by the positive correlation between highly incompatible trace element abundances in cumulus minerals and whole-rock Zr contents. We have calculated the composition of the parental magma of the MZ of the Bushveld Complex. The compatible and moderately incompatible element contents of the calculated parental liquid are generally similar to those of the B3 marginal rocks, but different from those of the B1 and B2 marginal rocks. For the highly incompatible elements, we suggest that the use of the sample with the lowest whole-rock Zr content and the least degree of TLS is the best approach to obtain the parental magma composition. The heavy REE contents of the magma calculated from orthopyroxene are similar to those of B3 rocks and lower than those of B2 rocks. The calculated REE contents from clinopyroxene are generally significantly higher than for B2 or B3 rocks, and those from plagioclase are in the lower level of B2, but slightly higher than for B3. However, the calculated REE patterns for both clinopyroxene and plagioclase show strong negative Eu anomalies, which are at the lower level of the B2 field and within the B3 field, respectively. We suggest that Eu may be less affected by TLS than other REE owing to its higher bulk compatibility. Based on this and the fact that the calculated REE contents of the parental magma should be higher than the real magma composition owing to some degree of crystal fractionation and TLS, even for the sample with the lowest amount of trapped liquid, we propose that a B3 type liquid is the most likely parental magma to the MZ of the Bushveld Complex. In the lowermost part of the MZ, there is involvement of the Upper Critical Zone (UCZ) magma. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Combined study of major and trace elements of chromite and Li isotopes of silicate minerals. • Transitional parental magma of the Kızıldağ chromitites between MORB and boninitic melts. • Link between intermediate chromitite formation and subduction initiation. Abstract Chromitites in the Kızıldağ ophiolite mostly occur in the mantle harzburgites and some of them in crustal cumulate dunites. Olivine in both the dunites and chromitites is highly magnesian (Fo = 90.5–92.8 and 90.2–96.1, respectively), while the coexisting chromite varies widely in composition (Cr# = 52.9–68.6 and 57.1–76.2, respectively), placing it between high-Al and high-Cr varieties. Concentrations of Ni, V and Ga in the chromite (Ni: 741–1310 ppm; V: 521–1227 ppm; Ga: 20–51 ppm) are also highly variable, straddling the range of high-Al and high-Cr chromite. Olivine in the dunites and chromitites has a large range of Li concentrations (0.27–2.47 ppm) and δ7Li values (−7.20–29.90‰). Based on the calculated Al 2 O 3 (12.1–17.2 wt.%) contents, FeO/MgO values (0.92–1.57) and trace element concentrations of the parental magmas of the dunites and chromitites, it is suggested that they are transitional between MORB and boninitic melts, and should have been derived by mixing of geochemically and spatially distinct magmas generated by partial melting of different sources. The Li isotopic compositions of olivine from the dunites and chromitites (except KZ14-38 and KZ15-38) are neither controlled by diffusion nor fractional crystallization, and thus may be intrinsic features of their parental melts. The range of δ7Li values of olivine in the dunites and chromitites is analogous to that of arc lavas and marine sediments, indicating that the chromitites record various degrees of melt penetration. The wide range of Li isotopic variations in olivine and chemistry in chromite from the Kızıldağ chromitites suggest that the parental melts were originated in a proto-forearc mantle during subduction initiation. [ABSTRACT FROM AUTHOR]

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The Bijiashan intrusion belt, one of the basic–ultrabasic intrusion belts in the Beishan Terrane, northeastern Tarim Craton, is composed of the Hongshishan, Hongshishanxi, Xuanwoling, Bijiashandong, and Bijiashan intrusions. These intrusions are mainly composed of dunite, troctolite, olivine gabbro, and gabbro. Magma evolution of the intrusions was strongly controlled by fractional crystallization, and the crystallization sequence was mainly olivine → plagioclase → pyroxene. This is evidenced by whole‐rock MgO contents that are positively correlated with TFe2O3 and negatively correlated with Al2O3, CaO, and Na2O and an increase in total rare‐earth element and trace elements contents from ultrabasic to basic rocks. Most of the basic–ultrabasic rocks are enriched in large ion lithophile elements (Cs, Rb, Sr, and U) and depleted of high field strength elements (Zr, Hf, Nb, Ta, and Ti). The variable and relatively low Ce/Pb (0.17–7.3) and Nb/U (0.13–10.1) ratios, variable Th/Yb (0.02–4.1) ratio, initial 87Sr/86Sr ratios (0.7033 to 0.7094) and εNd (t) (7.54 to −4.25), suggest less than 6% crustal contamination. Based on the maximum Fo value of olivine (Fo90), whole‐rock average composition and olivine–liquid compositional relationships, the parental magma is of high‐Mg basaltic magma containing 13.4 wt.% MgO. According to rare‐earth element contents and Sr–Nd isotopic compositions, the parental magma was originated from partial melting of depleted sub‐continental lithospheric mantle. [ABSTRACT FROM AUTHOR]

Magmatic sulfide deposits in subduction-collision settings are genetically related to oxidized and hydrous magmas, where the degree of partial melting, fractional crystallization, and sulfide saturation are all expected to differ significantly from those in dry and reduced magmas associated with most giant magmatic sulfide deposits in intracratonic settings. This study provides petrological and geochemical data as well as multiple modeling approaches for the post-collisional Xiarihamu magmatic sulfide deposit of the eastern Kunlun Orogen to investigate melting mechanism and magmatic differentiation in an oxidized and hydrous magmatic system. Petrographical observations and whole-rock geochemistry suggest that the olivine orthopyroxenite, orthopyroxenite, websterite and gabbronorite in the Xiarihamu complex were cumulates. Pressures estimated from clinopyroxene and hornblende compositions and oxygen fugacities from hornblende and biotite compositions further suggest that these cumulates crystallized under moderate- to high-pressure, oxidized conditions. The Xiarihamu parental magma was high-MgO basalt as evidenced by multiple modeling methods. This parental magma was generated from a metasomatized mantle peridotite source in the spinel stability field with moderate melting degrees and then experienced a fractional crystallization process with a first iron-enriched and then silica-enriched trend under moderate-high pressures to form the observed crystallization sequence and mineral compositions. Minor amounts of wall rock assimilation during magmatic evolution were supported by Sr-Nd isotopic modeling. Sulfide saturation previously proposed by crustal sulfur addition at Xiarihamu was not straightforward but was likely caused by an oxygen fugacity decrease triggered by magmatic differentiation. [ABSTRACT FROM AUTHOR]

We have first generalized geochemical and mineralogical data indicating the important role of crystallization of Os-Ir-Ru phases and fractionation of refractory iridium subgroup of PGE (IPGE) at the early stages of the evolution of parental magmas and primitive cumulates from the Yoko-Dovyren layered massif (northern Baikal area, Russia). The object of study was two types of plagioclase peridotites from the lower part of the intrusion, differing in the porosity of primary olivine cumulates: less melanocratic (but more primitive) type I and more melanocratic type II. Inclusions of refractory IPGE (Os, Ir, and Ru) discovered during LA-ICP-MS studies of aluminochromite from type I rocks are the first evidence for the presence of Os-Ir-Ru phases. Subsequent electron microscopy examinations revealed more than 25 grains of laurite and Ir-containing osmium in aluminochromite from plagioperidotites of both types. Attention is focused on the importance of the Ru/Cr 2 O 3 and Ir/Cr 2 O 3 ratios in rocks for the separation of IPGE at early and late fractionation stages. The conclusion is drawn that the higher Ru/Cr 2 O3 and Ir/Cr 2 O3 ratios in type I plagioperidotites indicate higher enrichment of aluminochromite in inclusions of refractory IPGE minerals. This is consistent with the fact that these rocks are assigned to the most primitive high-temperature ultramafites genetically related to the parental magma, which was in equilibrium with olivine Fo88 at ~ 1290 °C. We have established that the parental Dovyren magma was already depleted in IPGE and rhodium before its entrance into a chamber. No signs of early sulfide-silicate immiscibility have been detected. © 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. [ABSTRACT FROM AUTHOR]

The Dovyren Intrusive Complex (DIC, Northern Baikal region, 728 Ma) includes the layered dunite-troctolite-gabbronorite Yoko-Dovyren massif (YDM), associated mafic-ultramafic sills, and dykes of olivine-rich to olivine-free gabbronorite. Major rock types of the DIC are presented, including a diversity of olivine orthocumulates to olivine-plagioclase and gabbroic adcumulates, carbonate-contaminated ultramafics and Cu-Ni-PGE mineralisation. Detailed comparisons of complete cross-sections of the YDM in its centre and at the NE and SW margins demonstrate differences in the cumulate succession, mineral chemistry, and geochemical structure that likely reflect variations in parental magma compositions. Combining petrochemical reconstructions for most primitive rocks and calculations using the COMAGMAT-5 model, it is shown that the central and peripheral parts of the intrusion formed by olivine-laden parental magmas ranged in their temperatures by 100 °C, approximately from 1290 °C (~11 wt% MgO, olivine Fo88) to 1190 °C (~8 wt% MgO, olivine Fo86). Thermodynamic modelling suggests that the most primitive high-Mg magma was S-undersaturated, whereas its derivatives became S-saturated at T < 1240–1200 °C. These estimates are consistent with geological observations that mostly sulphide-poor mineralisation occurs in the centre of the intrusion, whereas Cu-Ni sulphide ores (locally net-textured) occur in its NE and SW parts, as well as in the underlying peridotite sills. The primitive S-undersaturated olivine cumulates became sulphide-saturated at a post-cumulus stage. As a result, Ni-rich immiscible sulphides formed within and migrated through the early olivine-rich cumulate piles to generate poorly-mineralised plagiodunite. In the troctolite and gabbroic parts of the Dovyren chamber, sulphide immiscibility likely occurred at lower temperatures, producing Cu-rich sulphide precursors, which gave rise to the ‘platinum group mineral’ (PGM-containing) troctolite and low-mineralised PGE-rich anorthosite in the Main Reef. The geochemical structure of the YDM demonstrates C-shaped distributions of TiO 2 , K 2 O, P 2 O 5 , and incompatible trace elements, which are 3–5 fold depleted in the cumulate rocks from the inner horizons of the intrusion with respect to the relatively thin lower and upper contact zones. In addition, a marked misbalance between estimates of the average composition of the YDM and that of the proposed olivine-laden parental magmas is established. This misbalance reflects a significant deficit of the YDM in incompatible elements, which argues that 60–70% of basaltic melts had to have been expelled from the Dovyren magma chamber during its consolidation. A possible scenario of the evolution of the open magma chamber is proposed. [ABSTRACT FROM AUTHOR]

The Hongshishan mafic-ultramafic complex is located in the western Beishan Terrane, NW China, and hosts an economic Ni-Cu deposit. Chromite as accessory mineral from the complex is divided into three types based on its occurrence and morphology. Quantitative electron probe microanalysis (EPMA) have been conducted on the different types of chromites. Type 1 chromite occurs as inclusions within silicate minerals and has relatively homogeneous composition. Type 2 chromite occurs among serpentine, as interstitial phase. Type 3 chromite is zoned and exhibits a sudden change in compositions from core to rim. Type 1 chromite occurs in olivine gabbro and troctolite showing homogeneous composition. This chromite is more likely primary. Interstitial type 2 and zoned type 3 chromite has compositional variation from core to rim and is more likely modified. Abundant inclusions of orthopyroxene, phlogopite and hornblende occur within type 2 and type 3 chromites. The parental melt of type 1 chromite has an estimated composition of 14.5 wt% MgO, 12.3 wt% AlO and 1.9 wt% TiO and is characterized by high temperature, picritic affinity, hydrous nature and high Mg and Ti contents. Compositions of chromite and clinopyroxene are distinct from those of Alaskan-type complexes and imply that the subduction-related environment is not reasonable. Post orogenic extension and the early Permian mantle plume are responsible for the emplacement of mafic-ultramafic complexes in the Beishan Terrane. The cores of zoned chromites are classified as ferrous chromite and the rims as ferrian chromite. The formation of ferrian rim involves reaction of ferrous chromite, forsterite and magnetite to produce ferrian chromite and chlorite, or alternaively, the rim can be simply envisioned as the result of external addition of magnetite in solution to the already formed ferrous chromite. [ABSTRACT FROM AUTHOR]

The Jacupiranga Complex is one of several Meso-Cenozoic alkaline intrusive complexes along the margins of the intracratonic Paraná Basin in southern Brazil. The complex encompasses a wide range of rock-types, including dunites, wehrlites, clinopyroxenites, melteigites-ijolites, feldspar-bearing rocks (diorites, syenites, and monzonites), lamprophyres and apatite-rich carbonatites. While carbonatites have been extensively investigated over the last decades, little attention has been paid to the silicate rocks. This study presents new geochonological and geochemical data on the Jacupiranga Complex, with particular emphasis on the silicate lithotypes. 40 Ar/ 39 Ar ages for different lithotypes range from 133.7 ± 0.5 Ma to 131.4 ± 0.5 Ma, while monzonite zircon analyzed by SHRIMP yields a U-Pb concordia age of 134.9 ± 1.3 Ma. These ages indicate a narrow time frame for the Jacupiranga Complex emplacement, contemporaneous with the Paraná Magmatic Province. Most of the Jacupiranga rocks are SiO 2 -undersaturated, except for a quartz-normative monzonite. Based on geochemical compositions, the Jacupiranga silicate lithotypes may be separated into two magma-evolution trends: (1) a strongly silica-undersaturated series, comprising part of the clinopyroxenites and the ijolitic rocks, probably related to nephelinite melts and (2) a mildly silica-undersaturated series, related to basanite parental magmas and comprising the feldspar-bearing rocks, phonolites, lamprophyres, and part of the clinopyroxenites. Dunites and wehrlites are characterized by olivine compositionally restricted to the Fo 83-84 interval and concentrations of CaO (0.13–0.54 wt%) and NiO (0.19–0.33 wt%) consistent with derivation by fractional crystallization, although it is not clear whether these rocks belong to the nephelinite or basanite series. Lamprophyre dikes within the complex are considered as good representatives of the basanite parental magma. Compositions of calculated melts in equilibrium with diopside cores from clinopyroxenites are quite similar to those of the lamprophyres, suggesting that at least a part of the clinopyroxenites is related to the basanite series. Some feldspar-bearing rocks (i.e. meladiorite and monzonite) show petrographic features and geochemical and isotope compositions indicative of crustal assimilation, although this may be relegated to a local process. Relatively high CaO/Al 2 O 3 and La/Zr and low Ti/Eu ratios from the lamprophyres and calculated melts in equilibrium with cumulus clinopyroxene point to a lithospheric mantle metasomatized by CO 2 -rich fluids, suggesting vein-plus-wall-rock melting mechanisms. The chemical differences among those liquids are thought to reflect both variable contributions of melting resulting from veins and variable clinopyroxene/garnet proportions of the source. [ABSTRACT FROM AUTHOR]

The widespread mid-Cretaceous igneous rocks in the northern margin of the Lhasa Block play an important role in understanding deep geologic processes, matter exchange at depth, and tectonic evolution of the Tibetan Plateau. In this paper, we report new zircon U-Pb ages, whole-rock major and trace element data, and Sr-Nd-Pb-Hf isotope data from the Talabuco andesites and basalts, which were dated at ~111 Ma. These rocks belong to the high-K calc-alkaline and shoshonite series, and show enrichment in terms of large-ion-lithophile elements (LILEs, e.g. Rb, U, and Th) and light rare earth elements (LREEs), but depletion of high-field-strength elements (HFSEs, e.g. Nb and Ti). The (87Sr/86Sr)iratios of the Talabuco andesites range from 0.7043 to 0.7048, and theεNd(t) contents range from 0.68 to 4.33. The ratios of206Pb/204Pb,207Pb/204Pb, and208Pb/204Pb are 18.6064–18.8993, 15.6233–15.6707, and 38.8634–39.1720, respectively. The176Lu/177Hf and176Hf/177Hf ratios of one sample range from 0.00081 to 0.00206 and 0.28280 to 0.28296, respectively. TheεHf(t) values for this sample range from 3.4 to 9.1, and the two-stage model Hf age (TDM2) is 0.59–0.95 Ga. Combined with previous studies, the geochemical and isotopic data reveal that the parental magma of the Talabuco andesites was probably derived by partial melting of EM II-type sub-continental lithospheric mantle (SCLM). The Talabuco andesites are most likely generated by fractionation of mafic magma contaminated by subducted oceanic sediment and represent product of arc magmatism due to northward subduction of the Yarlung Zangbo Neo-Tethyan slab or southward subduction of the Bangong Meso-Tethyan slab. [ABSTRACT FROM AUTHOR]

Olivine-hosted melt inclusions provide an archive of the parental magma and early magma history that is unavailable from bulk-rock analyses of cumulates. For those olivine-bearing mafic-ultramafic intrusions, a combined in situ analysis of major elements and Pb isotopic compositions for the melt inclusions and host olivine crystals may provide an effective way to understand the nature of the parental magma of the intrusions. In this study, we take the Nantianwan intrusion in the Emeishan large igneous province (SW China) as an example to analyze the melt inclusions and the host olivine. The Nantianwan intrusion is mainly composed of gabbronorite, with minor olivine gabbro. The olivine crystals in the olivine gabbro have Fo contents varying from 81.1 to 89.2 and Ni from 0.05 to 0.30 wt.%. The melt inclusion hosted in the most Mg-rich olivine has 50.9 wt.% SiO 2 , 1.0 wt.% TiO 2 , 15.1 wt.% MgO and 2.9 wt.% Na 2 O + K 2 O, indicating that the parental magma of the intrusion was of high-Mg basaltic composition. The melt inclusions overall have 208 Pb/ 206 Pb ratios of 2.0567–2.1032 and 207 Pb/ 206 Pb of 0.8287–0.8481, similar to the Pb isotopic compositions of the Emeishan flood basalts and consistent with insignificant crustal contamination. Given that the Nantianwan intrusion contains the most Mg-rich olivine among the Ni-Cu-(PGE) sulfide-bearing mafic-ultramafic intrusions in the Emeishan LIP, we infer that the composition of the melt inclusion in the most Mg-rich olivine from the Nantianwan intrusion may represent the least evolved parental magma of the Ni-Cu-(PGE) sulfide-bearing mafic-ultramafic intrusions in the Emeishan LIP. This can be further used to constrain the magma process related to Ni-Cu-(PGE) sulfide mineralization. [ABSTRACT FROM AUTHOR]

Products of alkaline basaltic volcanism extend from the Lučenec Basin and Cerová Highland to the northern Hungary. Volcanic activity in this area has created a large number of volcanic forms. This paper describes apatite from heavy mineral assemblages recovered from volcanoclastic fillings of maars and diatremes. Euhedral to subhedral crystal fragments of apatite with variable colour represented approximately 2% of heavy mineral assemblages. A total of 27 apatite samples from Hodejov, Fiľakovo - Castle Hill and Jelšovec maars, the Hajnáčka diatreme and from recently discovered maar structure near Gemerské Dechtáre village have been analysed using electron microprobe and Raman spectroscopy. Amount of substitution in diagrams Ca/100-Mn-Fe, S/100-P-Si and Fe-Ce-Mn sites correspond to the apatite from mafic magmatic rocks. A middle range of the Tetrahedral Substitution Index (TSI) between 0.63 and 7.56 is consistent with the apatites from alkaline magmatic rocks. These findings corroborate magmatic origin of apatite and its crystallization from alkaline basaltic parental magma. [ABSTRACT FROM AUTHOR]

This study presents detailed petrographical and geochemical investigations on remarkably fresh olivines in kimberlites from the EKATI Diamond Mine™ located in the Tertiary/Cretaceous Lac de Gras kimberlite field within the Slave craton of Canada. Olivine, constituting about 42 vol.% of the analyzed samples, can be divided into two textural groups: (i) macrocrystic olivines , > 100 μm sub-rounded crystals and (ii) groundmass olivines , < 100 μm subhedral crystals. Olivines from both populations define two distinct chemical trends; a “mantle trend” with angular cores, showing low Ca (< 0.1 wt.% CaO) and high Ni (0.3–0.4 wt.% NiO) at varying Mg# (0.86–0.93), contrasts with a “melt trend” typified by thin (< 100 μm) rims with increasing Ca (up to 1.0 wt.% CaO) and decreasing Ni (down to 0.1 wt.% NiO) contents at constant Mg# (~ 0.915). These findings are in agreement with recent studies suggesting that virtually all olivine is composed of xenocrystic (i.e. mantle-related) cores with phenocrystic (i.e. melt-related) overgrowths, thereby challenging the traditional view that the origin of kimberlitic olivine can be distinguished based on size and morphology. The two main trends can be further resolved into sub-groups refining the crystallization history of olivine; the mantle trend indicates a multi-source origin that samples the layered lithosphere below the Slave craton, whereas the melt trend represents multi-stage crystallization comprising a differentiation trend starting at mantle conditions and a second trend controlled by the crystallization of additional phases (e.g. chromite) and changing magma conditions (e.g. oxidation). These trends are also seen in the concentrations of trace elements not routinely measured in olivine (e.g. Na, P, Ti, Co, Sc, Zr). Trace element mapping with LA-ICP-MS reveals the distribution of these elements within olivine grains. The trace element distribution between the two trends appears to be consistent with phenocrystic olivine overgrowths mainly originating from dissolved orthopyroxene, showing enrichment in Zr, Ga, Nb, Sc, V, P, Al, Ti, Cr, Ca and Mn in the melt trend. In a sample of magmatic kimberlite from the Leslie pipe, the amount of xenocrystic and phenocrystic olivine is estimated to be around 23 vol.% and 19 vol.%, respectively. Subtraction of this xenocrystic olivine from the Leslie bulk composition, aimed at estimating the parental kimberlite melt, results in a minor decrease of Mg# (by about 0.01) and SiO 2 content (by about 3 wt.%), whereas CaO increases (by about 3 wt.%). [ABSTRACT FROM AUTHOR]

Beishan Terrane, located in the northeast of the Tarim Block, in northwest China, has developed a 500-km long and 100-km wide belt of Permian mafic-ultramafic intrusions. One of these mafic-ultramafic intrusions, the Xuanwoling Intrusion, is composed of dunite, troctolite, olivine gabbros, and gabbros, with cumulate texture and rhythmic layering. The crystallization sequence is olivine + spinel → plagioclase → pyroxene, indicating that the crystallization pressure is lower than 0.5-0.8 GPa and that the intrusion has undergone variable degrees of crustal contamination, increasing from dunite to gabbros. The olivines found in the Xuanwoling Intrusion have high Fo values (up to 90), suggesting a primary magma with a high composition of mg. It is likely that this high-mg magma was produced at extremely high temperatures (1,330-1,350 °C), and as a result, Nd-Sr isotopic compositions similar to oceanic island basalts are found in the Xuanwoling Intrusion, which we propose arose from the mantle plume. [ABSTRACT FROM AUTHOR]

Samples of an early olivine gabbro in the lower plutonic sequence of the Troodos ophiolite were studied to constrain their thermal history and the compositions of their parental magma. These rocks exhibit typical orthocumulate textures and petrographic evidence of reaction between a migrating interstitial magma and a crystal mush, including embayed margins of olivine crystals and irregular ragged grain boundaries of clinopyroxenes, indicating dissolution of olivine and crystallization of clinopyroxene, followed by crystallization of plagioclase within the framework of olivine and clinopyroxene. All the minerals exhibit relatively homogeneous compositions, without any clear zoning in either their major or trace elements, indicating that the minerals and migrating magma reached equilibrium. The rare earth element (REE) distribution between clinopyroxene and plagioclase records an equilibrium temperature of about 1300 °C, but the Mg-exchange geothermometer yielded a lower temperature of about 1000 °C. These different closure temperatures indicate a rapid cooling history with a cooling rate of −2 °C/year log units. The low TiO 2 contents and additional trace element compositions of clinopyroxene show that the parental magma of the gabbro was related to boninitic magmas of the ophiolite. Consequently, we show that some boninitic lavas in the upper oceanic crust have been affected by melt-rock reaction process during their ascent through the lower crust, and therefore their composition cannot be directly used to constrain the composition of the primary boninites. • Gabbros of the Troodos ophiolite display petrographic evidence of reaction between a migrating magma and a crystal mush. • Trace elements of clinopyroxene indicate that the migrating magma is related to boninites in the UPL. • Some boninitic lavas affected by melt-rock reaction process cannot represent composition of the primary boninite. [ABSTRACT FROM AUTHOR]

Abstract: The Hongge layered intrusion hosts the largest Fe–Ti–V oxide ore deposit in the central part of the Emeishan Large Igneous Province, SW China. It is divided into Lower Zone (LZ), Middle Zone (MZ) and Upper Zone (UZ) from the bottom to the top. For the LZ, relatively higher Cr (250–3000ppm) and Ni (50–200ppm) contents of clinopyroxene, lower εNd259Ma and higher (87Sr/86Sr)259Ma values (−2.82 to −0.07 and 0.7057–0.7076, respectively) and plenty of hornblende demonstrate a more primitive parental hydrous magma. In contrast, relatively low Cr (<150ppm) and Ni (<100ppm) of the clinopyroxene, high εNd259Ma and low (87Sr/86Sr)259Ma values (−0.32 to 0.49 and 0.7058 to 0.7063, respectively) suggest that the MZ rocks were formed from more evolved, Fe–Ti enriched, and weakly contaminated magmas. MELTS calculation indicates that H2O played a key role in the early crystallization of magnetite and occurrence of abundance of hornblende in the LZ. Whereas, the critical factor for the formation of the massive Fe–Ti oxide layers at the bases of the cyclic units in the MZ is coupling of early crystallization of Fe–Ti oxides from the Fe–Ti highly enriched magma and gravitational resorting and settling of the Fe–Ti oxides. Such magmas were produced by fractional crystallization of olivine and pyroxene in deep-seated magma chamber, and compositional reversals of the cyclic units show repeatedly replenishment of such magmas from deep level. Extensively fractionation during the formation of the LZ and MZ resulted in phosphorus saturation and the formation of the apatite magnetite gabbros in the UZ. [Copyright &y& Elsevier]