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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]

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]

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]

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: Several sulfide ore-bearing mafic–ultramafic intrusions occur along the southern margin of the Late Paleozoic Central Asian Orogenic Belt (CAOB) in north Xinjiang, NW China. Their origin, magma evolution and relationship with the Permian basalts in the region remain equivocal. In this study, we investigate the Xiangshanzhong mafic–ultramafic intrusion in eastern Tianshan, dominantly composed of diorite, hornblende gabbro, gabbro, hornblende pyroxenite, olivine websterite and lherzolite. We report the occurrence of olivine clinopyroxenite in the intrusive complex with visible pyroxene cumulate structure, high Mg, low Cr, Na, and Ti contents, and characterized by distinctively low trace element contents. Our data suggest that the clinopyroxene in the olivine clinopyroxenite probably crystallized from an earlier batch of magma. The rare earth element (REE) patterns and εNd values of the Xiangshanzhong mafic–ultramafic units suggest that these rocks represent cumulates of basaltic composition that were likely co-genetic and derived from the same magmatic source. The presence of phlogopite and amphibole, occurrence of Zr, Hf, Nb, and Ta negative anomalies, the trace element abundances of the parental magma, and the Nd isotopes (+5.9–+8.3) of whole-rocks suggest that the source of the Xiangshanzhong complexes may be a depleted mantle metasomatized by subducted slab-derived fluid or melt. Furthermore, the (87Sr/86Sr)i ratios, εNd(t) values and trace element geochemistry of whole-rock and clinopyroxene grains are consistent with those of the Permian Tuha basin basalts. The Xiangshanzhong intrusion has characteristics of both plume and subduction-related origin and we therefore speculate that the partial melting of subduction-related depleted mantle triggered by Permian plume activity during the post-collision extension regime generated the parental magmas of the Xiangshanzhong intrusion. [Copyright &y& Elsevier]

Abstract: Major and trace element concentrations in whole-rock and cumulus and intercumulus minerals were determined in cumulate rocks from the Lower and the Lower Critical Zones of the Bushveld Complex, South-Africa. These new geochemical data are combined with microtextural observations to provide insights on the formation of the cumulates. The results are used to evaluate methods of calculation of parental liquid composition from which the cumulate rocks crystallized. Cumulus (orthopyroxene and olivine) and intercumulus (clinopyroxene and plagioclase) minerals have a relatively constant composition in terms of major and trace element throughout the Lower and the Lower Critical Zones suggesting that the minerals formed from a magma with a relatively constant composition and followed a similar crystallization history. The minerals are in most cases unzoned in terms of major and trace elements. However, Ti zonations are observed in pyroxene and are consistent with the steady increase in Ti concentrations in interstitial plagioclase with decreasing An. These features are interpreted to be the result of the crystallization of the trapped melt during closed system fractional crystallization without significant intercumulus melt migration as suggested by the absence of dihedral angle modification. Our calculations indicate that the rocks from the Lower and the Lower Critical Zones crystallized from a magma similar in composition to B1-type magma as suggested by previous authors. Our study illustrates that the combined analysis of whole-rock chemistry and cumulus and intercumulus minerals give useful results which allow the estimation of parental liquid composition from cumulate rocks for a wide range of elements. Moreover, our results indicate that the simple assumption of equilibrium between a melt and a mineral to calculate a parental magma can only be applied to pure adcumulate rocks. The methods of calculation presented in this study may be used to infer parental magma composition associated with Ni-Cu-PGE sulfide deposits and can potentially be used as an additional tool for mineral exploration to fingerprint prospective magma suites. [Copyright &y& Elsevier]

The Huaqiao clinopyroxenite and Maodu gabbro are Neoproterozoic mafic-ultramafic rocks located in the western Jiangnan Orogen. Both rocks contain fresh clinopyroxenes. The in situ analysis of fresh clinopyroxenes from these rocks provides essential information about their parental magmas and mantle sources. Here, we present in situ major and trace element compositions of clinopyroxenes from these rocks to determine their petrogenesis and tectonic setting. Clinopyroxene grains from the Huaqiao clinopyroxenite exhibit relatively high values of Mg# (80.6–84.1), Cr 2 O 3 (0.38–1.00 wt%), TiO 2 (0.44–1.84 wt%), Ni (324–460 ppm), V (314–611 ppm), and Co (37–46 ppm); the calculated Mg# values of the parental liquid(s) are 52–58 (average 55). Clinopyroxene grains from the Maodu gabbro display lower Mg# (71.5–79.1), Cr 2 O 3 (0–0.88 wt%), Al 2 O 3 (1.72–4.75 wt%), and Na 2 O (0.24–0.88 wt%) contents but higher TiO 2 (0.88–1.89 wt%) contents than those from the Huaqiao clinopyroxenite; they show relatively high Cr (15–4145 ppm, with an average of 1774 ppm), V (34–663 ppm, with an average of 535 ppm), and Co (32–60 ppm) contents; the Mg# values of the parental liquid(s) are estimated to be 39–49 (average 45). Therefore, we infer that clinopyroxene grains from the Huaqiao clinopyroxenite and Maodu gabbro crystallized from evolved basaltic melts. Mineral-melt partition coefficients reveal that the estimated parental magma composition in equilibrium with clinopyroxene for the Huaqiao clinopyroxenite exhibits slight enrichments in light rare earth elements (LREEs, La N /Yb N = 1.12–2.71; subscript N: chondrite normalized) with flat heavy REEs (HREEs, Gd N /Yb N = 1.15–1.85). It displays negative high field strength element (HFSE, such as Nb, Zr, and Hf) anomalies, resembling those of typical arc basalt. The calculated parental melt for the Maodu gabbro is characterized by pronounced enrichments in LREEs with La N /Yb N ratios of 11.36–19.02, and in large ion lithophile elements (LILEs) relative to HFSEs and lacks significant Nb, Zr, and Hf troughs, comparable to those of ocean island basalts (OIBs). Hence, we infer that the magma source of the Huaqiao clinopyroxenite was an arc mantle metasomatized by subduction melts and/or fluids from the subducted slab formed in a subduction setting; the nature of the source for the Maodu gabbro was the asthenospheric mantle that experienced upwelling and partial melting in an extensional setting. • We determined the in situ elemental compositions of clinopyroxene. • The parental magma was estimated using the mineral-melt partition coefficients. • The sources were the arc mantle and the asthenospheric mantle, respectively. • The Nanhua rift opened as a back-arc basin at ca. 770 Ma in response to Rodinia breakup. [ABSTRACT FROM AUTHOR]

Our experimental thermobarogeochemical study of the primary melt inclusions in olivine (Fo91) from poikilitic harzburgite to dunite of the Uitkomst Complex in the Bushveld Igneous Province revealed a series of melt compositions that are the result of combined fractional crystallization and assimilation. The primary melt inclusions up to 50 μm in size are fully crystallized and composed of predominantly olivine and orthopyroxene with highly subordinate chromite, sulfide, amphibole and plagioclase accompanied by a fluid phase in shrinkage voids. The most primitive melt within the series has a re-homogenization temperature of >1450 °C and contains 22.47 wt% MgO, 12.57 wt% FeO, 51.90 wt% SiO 2 , 2.50 wt% CaO, 8.27 wt% Al 2 O 3 and 1.69 wt% Na 2 O recalculated to equilibrium with the host olivine. This is the first direct measurement of the komatiitic parental magma of the Bushveld magmas, inferred in previous studies. The estimated maximum PT parameters of the melt corresponds to 2.5 GPa and 1590 °C implying that the primitive melt inclusions in the olivine were trapped while still in the upper mantle and before further crustal assimilation. This primitive melt shows the steepest slope (La/Yb) PM , the highest Ni and is depleted in volatile components (168 ppm H 2 O, 264 ppm Cl, 258 ppm F and 114 ppm S according to secondary ion mass spectrometry measurements) compared to more evolved compositions, which were progressively enriched in volatiles up to 7665 ppm Н 2 О, 1728 ppm Cl, 2288 ppm S, and 549 ppm F as the rehomogenization temperature fell to 1335 °C. The progressive assimilation of crustal material responsible for magma modification is also manifested by the occurrence of Ca Na volatile-rich minerals (such as amphibole, phlogopite, albite, sodalite, natrolite, pectolite, Cl-apatite and carbonate) in the interstitial assemblage and in "exotic" polyphase inclusions in cumulus olivine. The concentrations and ratios of the incompatible elements in the melt inclusions in Uitkomst olivine are similar to those in the model compositions of the ultramafic Bushveld parental magma and support a common source of ultramafic melts in the Bushveld Province. The main components of the melts, however, are not in accord with either boninitic or komatiitic lineages indicating a unique nature for the Bushveld magmas. • Primary melt inclusions in olivine contain up to 22.47 wt% MgO and 168 ppm H 2 O. • Primitive melt inclusions were trapped at 2.5 GPa and 1590 °C in the upper mantle. • Primary melts evolved via fractional crystallization and crustal assimilation. • Primary melts were derived from metasomatically-enriched mantle harzburgites. [ABSTRACT FROM AUTHOR]