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Koh-i-Noor and other world-famous diamonds such as Hope, Orloff, Great Mogul, Nizam, and Pitt, well-known in the industry as 'Golkonda Diamonds' are very well recognised for their rare colours, large carat sizes, and because of the paucity of nitrogen atoms majority of them have been classified as Type IIa diamonds. These renowned Golkonda diamonds were recovered from placers mined on the banks of the Krishna River in southern India; however, their primary source rocks (either kimberlites or lamproites) remain questioned and untraced. Precise identification of the primary sources of such large-sized, dominantly Type IIa diamonds (i.e., CLIPPIRS) is crucial for understanding their deep mantle origin, nature and timing of magmatism carrying them and essential from economic and geological perspectives. We employed a multidisciplinary approach incorporating xenocrystic mineral composition and bulk-rock geochemistry, field geological and remote sensing (GIS) studies to locate the probable primary sources of these renowned diamonds, know the origin of Type IIa Golkonda diamonds in southern India, and to understand the mechanism and timing of diamond transport and dispersal as placers in the Krishna River basin. Our study rules out the possibility of various lamproite occurrences of the Eastern Dharwar Craton and Banganapalle conglomerates as being sources of Koh-i-Noor and other Golkonda diamonds. The absence of Type IIa diamonds in the highly diamondiferous Late Cretaceous kimberlites of Wajrakarur likewise excludes them as source of Golkonda diamonds. Among southern India's two significant kimberlite fields, i.e., Wajrakarur and Narayanpet, compositions of indicator minerals from the Wajrakarur Kimberlite Field (WKF) reveal their ultimate diamond preservation potential, presence of strong diamondiferous mantle roots and deeper source regions, hence recognising them to be the potential sources of Golkonda diamonds. GIS and remote sensing tools were used to calculate moisture content, vegetation indices, and to locate paleo-channel of the Penner River, which was primarily responsible for the transportation of diamonds from their Mesoproterozoic (ca. 1.1 Ga) source rocks at Wajrakarur to their final sites of recovery, i.e., Kolluru and other mines situated on the banks of the Krishna River. The occurrence of alluvial placer deposits in Krishna River drainage system is analogous to the Orange River drainage system in South Africa. Both areas have diamonds sourced from primary kimberlite pipes, transported by rivers, and deposited in specific areas. Similarities in the origin, mechanism of diamond transport, dispersal and deposition have played a crucial role in significant diamond production from alluvial deposits in Krishna and Orange Rivers. [ABSTRACT FROM AUTHOR]

The 17.44 Ma Walgidee Hills lamproite in the West Kimberley province of Western Australia is the type locality for several K-, Ba- and Ti-rich minerals characteristic of lamproites and, at 490 ha, the largest known lamproite. The Walgidee Hills pipe comprises a thin sequence of tuffs and breccia formed by explosive eruptions that excavated a large shallow crater that was infilled by lamproite magma which cooled and crystallised in situ. The lamproite is zoned in grain size, mineralogy, and mineral and rock composition from porphyritic olivine lamproite at the margin through medium-grained lamproite comprised of olivine (altered), titanian phlogopite, diopside, leucite (altered) and titanian potassic richterite to coarse gained lamproite rich in potassic richterite, priderite, jeppeite, perovskite, apatite, wadeite and noonkanbahite at the centre of the body. Compositional zoning is evident across the lamproite in phlogopite (to lower Mg and Al, higher Fe), potassic richterite (to higher Fe and Na, lower Ti), priderite (to lower Cr) and perovskite (to lower Cr and Fe, higher Na, Sr, Y, Nb, U, REE). The Walgidee Hills lamproite is ultrapotassic and ranges from olivine lamproite (up to ~21 wt % MgO, ~800 μg/g Ni, ~4 wt % K2O) to sanidine/leucite-rich lamproite (~7 wt % MgO, ≤100 μg/g Ni, ~8 wt % K2O) at the centre of the pipe. The lamproite has low Al2O3, total Fe, Na2O and CaO (except for intensely carbonate-veined rocks at the centre) and is highly enriched in TiO2 (3–6.5 wt %), Ba, Rb, Sr, Zr and LREE (LaN = 150–520 x primitive mantle). A transect and geochemical contours show MgO, Ni and Cr contents decrease and P, K, Ti, Fe, Rb, Sr, Y, Zr, Nb, REE, Hf, Pb, Th and U abundances increase inwards to the most evolved rocks at the centre of the pipe, consistent with fractionation by inwards in situ crystallisation. The parent magma is estimated from the composition of the porphyritic olivine lamproite at the margins of the pipe to have ~16 ± 1 wt % MgO, ~600 μg/g Ni, ~6 wt % K2O with La/Yb ~ 150. Modelling suggests that the most MgO-rich lamproites result from entrainment of ~15–20 wt % mantle olivine in the parent magma. Cooling of the magma resulted in fractional crystallisation of olivine and in situ crystallisation with the evolved coarse-grained lamproites at the centre of the pipe crystallised from residual magma enriched in the more incompatible elements. Mantle xenocrysts include abundant Cr–Al spinel, chrome diopside, chrome pyrope, and rare diamond. Thermobarometry on the Cr diopside xenocrysts defines a cold paleogeotherm of ~38 mW/m2 and a thick lithosphere (~235 km) extending from the Kimberley craton. Many of the Cr diopsides from the deeper lithospheric mantle are enriched in K, Ba and LREE and these, and the Ti-rich spinel xenocrysts, are inferred to be derived from metasomatised mantle peridotite. The enriched trace element and Sr–Nd–Pb isotopic signatures of the Walgidee Hills lamproite suggest derivation from or extensive incorporation of ancient formerly depleted lithospheric mantle that has undergone metasomatism and long term (≥2 Ga) geochemical enrichment including by melts from Paleoproterozoic subducted crust. [ABSTRACT FROM AUTHOR]

The continental lithospheric mantle (CLM) beneath the southern margin of the Congo craton has remained elusive, mainly because of the thick Phanerozoic sedimentary cover concealing possible kimberlite and lamproite diatremes. In this study, we explore this lithospheric mantle section using major and trace element compositions of mantle-derived clinopyroxene and garnet xenocrysts from kimberlites of the ca. 84 Ma Nxau Nxau cluster in northwest (NW) Botswana, which is part of the poorly known Xaudum kimberlite province extending into northern Namibia. We utilize these data to better understand the thermal and compositional evolution of the lithospheric mantle at the southern margin of the Congo craton. The clinopyroxene population (83 individual grains) comprises Cr-rich and Cr-poor diopsides with variable major (Al2O3, Na2O, Mg#) and incompatible trace element (U, Th, Zr, Hf, Nb, Ta, REEs) compositions. The large garnet population studied (496 individual grains) is dominated by lherzolitic G9 (38%) and 'megacrystic' G1 (41%) compositions, with minor contributions from Ti-metasomatized G11 (7%) and eclogitic G3 (6%) cratonic mantle sources. Harzburgitic G10 garnet is very rare (two grains only), consistent with a lherzolite-dominated CLM section in a craton margin position. The eclogitic garnet population has compositions similar to garnet from high-Mg cratonic mantle eclogite xenoliths, and such compositions have recently been interpreted as metasomatic in origin within the mantle xenoliths literature. Pressure–temperature calculations using the single-grain clinopyroxene technique reveal a relatively cold cratonic geotherm of 37–38 mW/m2 for the study region during the Late Mesozoic. For peridotitic garnets, projections of calculated Ni-in-garnet temperatures onto the independently constrained regional conductive geotherm suggest that lherzolite dominates at <145 km depth, whereas high-Ti lherzolitic G11 garnets and 'megacrystic' G1 garnets originate mostly from greater depths, reaching down to the lithosphere base at 150 to 210 km depth. The apparent confinement of 'megacrystic' G1 garnet to the bottom of the lithosphere suggests formation from infiltrating asthenosphere-derived proto-kimberlite liquids during melt–rock interactions. In general, the data suggest that the CLM beneath NW Botswana is depleted to about 145 km depth, and between 145 and 210 km depth, a thick metasomatized layer is identified, representing the transition into the underlying asthenosphere. A relatively thin lithosphere beneath NW Botswana is consistent with the proposed craton margin setting, especially when compared with the thicker cratonic roots beneath the central regions of the Congo and Kalahari cratons in Angola and South Africa, respectively, reaching down to 250 km depth and possibly even deeper. The compositional dissimilarity between the deepest-derived garnets from kimberlites in NW Botswana (i.e. from the diamond stability field) and garnets that occur as inclusions in diamond from cratons worldwide suggests extensive overprinting of the lowermost cratonic lithosphere by oxidative melt-related metasomatism. This finding, together with the very low diamond grades of the Xaudum kimberlites, points to a diminished diamond potential of the large and mostly unexposed 'cratonic' region (e.g. covered by thick desert sand) located between the major diamond mining districts of the Congo craton to the north (e.g. Catoca) and the Kalahari craton to the south (e.g. Orapa and Jwaneng). [ABSTRACT FROM AUTHOR]

Detailed textural and compositional study of calc-alkaline lamprophyres and minettes from Zeneta, SE Spain Neogene Volcanic Province (NVP) are used to unravel the magma sources and differentiation processes involved in their formation. The presence of xenocrysts of various origins indicates a hybrid nature involving mantle-derived alkaline lamproitic and continental crust-derived granitic parental magmas. A new U-Th-Pb zircon age of Zeneta minettes allows contextualizing their generation in time and space during regional lamproite magma intrusion and crustal anatexis in the NVP. Interaction and mixing of these compositionally contrasted magmas resulted in the formation of hybrid calc-alkaline lamprophyre minette. This process is reflected by the phases that crystallized from the hybrid magma, particularly phlogopite, and by the whole-rock composition of the less fractionated rocks. The calculated contribution of lamproitic and crustal-derived magma end-members in minette formation are 30–40% and 60–70%, respectively. Mixing of end-member magmas of contrasting rheological properties was possible only in a calculated thermal-window of 1025–1125°C, after cooling of intruding lamproitic magma and heating of host granitic anatectic region. The calculated thermal window fits with the estimated rheological properties of Zeneta minettes and the crystallization temperature of early minette-derived phlogopite. Furthermore, fractional crystallization was identified for the first time in the Zeneta minettes, based on the observed whole-rock line of descent from the less evolved mixed magmas through intermediate to felsic minettes and associated textural and compositional features of late crystallized phases. Polytope Vector Analysis allowed an integrated quantitative characterization of magma differentiation, including magma mixing and subsequent fractional crystallization. The identification of mixing and fractionation processes in calc-alkaline minettes genesis, which otherwise does not show spatial and temporal association in the field with granitic bodies, opens a new scenario to be considered in understanding the petrogenesis of these rocks. [ABSTRACT FROM AUTHOR]

The Alfeu-I lamproite is one of the few alkaline rock occurrences in the South of Brazil that represents the alkaline event related to the South Atlantic opening and the enormous magmatic activity that formed the Paraná basalts. Alfeu-I lamproite is a diatreme facies and exhibits an inequigranular texture with macrocrysts of mica, spinel, garnet, and ilmenite and microcrysts of mica, pyroxene, and rare olivine, all immersed in a groundmass of pyroxene, spinel, perovskite, rutile, ilmenite, and, more rarely, olivine. Major element compositions of Alfeu-I pyroxene, garnet, ilmenite, mica, and olivine were determined by electron microprobe analyses, and trace element concentrations of clinopyroxene, garnet, ilmenite, and mica were measured using laser-ablation inductively coupled plasma mass spectrometry techniques. Temperature, pressure, and oxygen fugacity (fO2) conditions during the crystallization of Alfeu-I lamproite were calculated with the geothermobarometers and olivine, spinel, garnet, and orthopyroxene. The resulting mean equilibrium temperature ranges from 1375°C at 4 GPa to 1395°C at 5 GPa, whereas the fO2 points to ΔFMQ = +2.4 (at 4 GPa) and ΔFMQ = +2.2 (at 5 GPa). Rb-Sr and Sm-Nd isotopic data together with the trace element concentrations of minerals suggest that melting of a mantle source enriched in incompatible elements and volatiles due to previous subduction events occurred during the Gondwana breakup around 125 Ma ago. Fluids that may have originated from subducting slabs in the old subduction zone are probably the cause of the high fO2 conditions in Alfeu-I lamproite. [ABSTRACT FROM AUTHOR]

'Transitional kimberlite' is a collective term previously used to classify rocks occurring in southern Africa that show bulk rock geochemical and Sr–Nd isotope features intermediate between (cratonic) lamproites and kimberlites. However, it is now well established that detailed petrographic and mineral chemical criteria represent a more robust approach towards the classification of kimberlites, lamproites and related rocks. Here, we re-assess the classification of southern African 'transitional kimberlites' by combining new petrographic observations and mineral compositional results for samples from six localities (Leicester, Frank Smith, Wimbledon, Melton Wold, Droogfontein, and Silvery Home) straddling the southwestern margin of the Kaapvaal Craton. These new data indicate that Leicester and Frank Smith are archetypal kimberlites, whereas Wimbledon, Melton Wold, Droogfontein, and Silvery Home represent bona fide olivine lamproites. We combine the mineral chemical results with new (Wimbledon) and existing bulk rock trace element and Nd–Hf isotope compositions, and emplacement ages, to assess whether the previously documented trends in Nd–Hf isotope vs time for these 'transitional kimberlites' constrain their petrological evolution. Modal groundmass mineralogy, bulk rock K/La and chromite compositions, the latter being a proxy for primitive melt composition, are linearly correlated with emplacement age and initial Nd–Hf isotope compositions. These observations suggest derivation of both older lamproites (181–115 Ma) and younger kimberlites (114–93 Ma), from a common evolving source. The temporal evolution of Nd–Hf isotope compositions in these rocks converge to values typical of archetypal Cretaceous kimberlites elsewhere in the Kaapvaal Craton, but are clearly different from the isotopic compositions of on-craton Kaapvaal lamproites (previously known as orangeites). This observation distinguishes the petrogenesis of the Wimbledon, Melton Wold, Droogfontein, and Silvery Home lamproites from those of 'typical' Kaapvaal lamproites. We hypothesize that progressive consumption of enriched and hence fertile K-bearing components in a common sub-lithospheric (i.e. convective mantle) source beneath the southwestern margin of the Kaapvaal Craton might represent a plausible scenario to explain the temporal evolution of petrographic and geochemical traits of the examined lamproites and kimberlites. A source in the lithospheric mantle is considered at odds with the contrasting location of the current localities as they occur both off- and on-craton. Migration of the African plate between 180 and 90 Ma over a relatively stationary convective mantle (plume?) source is not compatible with the spatial–temporal distribution of 'transitional kimberlites'. Instead, we invoke viscous coupling between an upper asthenospheric source and the lithosphere to reconcile a single evolving source with the geographic and age distribution of these rocks. This work supports the hypothesis that olivine lamproites occurring in intra-continental settings share similar genetic features with kimberlites. [ABSTRACT FROM AUTHOR]

We identified a ca. 180 Ma diamondiferous lamproite event in Zambia, establishing a link between ultrapotassic volcanism and the early Jurassic Karoo flood basalt province of sub-Saharan Africa. The cratonic lamproites erupted through the Permo–Triassic Luangwa Rift structure, but MgO-rich ultrapotassic magma formation was unrelated to rifting and triggered by plume–lithosphere interactions during the Karoo LIP event. Elevated Li–Zn–Ti concentrations in magmatic olivine (up to 18.5 ppm Li at 86–90 mol.% forsterite) and strong Sr–Nd–Hf–Pb isotopic enrichment of the host lamproites (87Sr/86Sr = 0.70701–0.70855, εNd = −10.8 to −10, εHf = −20.3 to −19.1, 206Pb/204Pb = 16.8–17.5) suggest partial melting of phlogopite-metasomatized lithospheric mantle domains, at approximately 180–200 km depth. The mantle-like δ7Li values (+2.8 to +5.7‰) of the most pristine lamproite samples are compatible with source enrichment by asthenosphere-derived melts, without significant involvement of recycled sedimentary components. This geochemical fingerprint stands in sharp contrast to the negative δ7Li compositions of primitive K-rich volcanic rocks from collision zone settings, where the shallow mantle sources contain recycled sediment. Isotope modelling demonstrates that the sub-Saharan lamproites originate from a MARID-style metasomatized peridotitic mantle source that underwent incompatible element enrichment at ca. 1 Ga, during tectonic activity associated with Rodinia supercontinent formation. Plume-sourced basaltic and picritic magmas of the 180 Ma Karoo LIP interacted with such K-rich hydrous lithospheric mantle domains, thereby attaining enriched incompatible element and radiogenic isotope compositions. Nd–Hf isotope mass balance suggests that up to 25% of MARID-sourced lamproite melt component contributed to some of the high-Ti flood volcanic units. Although large quantities of volatiles can be transferred from Earth's mantle to the atmosphere via plume–lithosphere interactions, it is unlikely that outgassing of mantle-sourced sulphur can exceed the climatic impact caused by the release of much more abundant carbon from thick continental roots. Thus, the excess SO 2 required to account for transient atmospheric cooling during the early Jurassic, coincident with the Karoo LIP event, must have had a thermogenic origin near the surface of Earth. [ABSTRACT FROM AUTHOR]

The accurate and precise determination of the compositions of silicate glasses formed from melts containing volatile components H2O and CO2 recovered from high-pressure, high-temperature experiments is essential to our understanding of geodynamic processes taking place within the planet. Silicate melts are often difficult to analyze chemically because the formation of quench crystals and overgrowths on silicate phases is rapid and widespread upon quenching of experiments, preventing the formation of glasses in low-SiO2 and volatile-rich compositions. Here, we present experiments conducted in a novel rapid quench piston cylinder apparatus on a series of partially molten low-silica alkaline rock compositions (lamproite, basanite, and calk-alkaline basalt) with a range of water contents between 3.5 and 10 wt %. Quench modification of the volatile-bearing silicate glasses is significantly reduced compared to those produced in older piston cylinder apparatuses. The recovered glasses are almost completely free of quench modification and facilitate the determination of precise chemical compositions. We illustrate significantly improved quench textures and provide an analytical protocol that recovers accurate chemical compositions from both poorly quenched and well-quenched silicate glasses. [ABSTRACT FROM AUTHOR]

Transitional boundaries of the craton and mobile belt mark diverse and long‐term tectono‐thermal events like hot and cold lithospheric contact, back‐arc‐type subduction, and also constitute a favourable locale for metallogeny. The exact nature and origin of such metallogenic enrichment in the lithospheric mantle source beneath contact zones are still uncertain. The contact of Bastar Craton and the Eastern Ghat Mobile Belt (EGMB), India, provides an ideal geological setup to study the metallogenic enrichment processes. In this study, we present a detailed petrographic and mineralogical investigation of various iron oxide phases and titanites in spatially and temporally distinct lamprophyre and mafic dykes from the diamondiferous Nuapada Lamproite Field (NLF) at the contact between Bastar Craton and EGMB. Diverse textural assemblages of oxides, namely, trellis, sandwich‐type exsolutions and reaction–replacement, are widespread. Ilmenites, magnetites and titanites from the mafic dykes as well as lamprophyre exhibit an anomalous enrichment of vanadium (V2O3 up to 3.7 wt%), whereas ilmenites are also characterized by their elevated manganese content (MnO up to 3.8 wt%). Mineral chemistry‐based plots and thermo‐oximetric studies suggest the magmatic origin of iron oxides belonging to the Fe–Ti–V‐type ore in which partitioning and sequestration of the elements were controlled by differential crystallization, exsolution and fractionation rather than any imprints of contamination. Multiphase sequestration of vanadium as well as manganese in lamprophyre and mafic dykes, separated in space as well in relative depths of origin, signifies the presence of a fertile mantle. The role of subduction‐derived metasomatized fluids as a causative factor of vanadium metallogeny in this domain is evaluated. Low‐Mg and high‐Mn ilmenites of this study are consistent with the reported occurrences of diamonds from the NLF and adjoining areas of the Bastar Craton. [ABSTRACT FROM AUTHOR]

Abstract—The paper demonstrates the possibility of application of the 143Nd/144Nd–Sm/Nd and Nb/Y–Zr/Y diagrams to systematics of basic–ultrabasic complexes of different age: Paleozoic Kalinovsky, Cambrian Sergeevsky and Vladimiro-Aleksandrovsky, and Jurassic and Paleocene ones. The position of data points of the Kalinovsky, Sergeevsky, and Vladimiro-Aleksandrovsky complexes in the diagrams indicates their derivation from a primitive mantle-type (BSE) source, the derivatives of which are frequently associated with Cu, Ni, Co, and PGE mineralization. The position of data points of metabasic rocks of the Avdokimovsky complex and peridotite rocks of the Dalny Kut massif in these diagrams suggests that they have originated from depleted mantle and are promising for the discovery of PGE-bearing chromite mineralization. Data points of Paleocene explosive structures of Sikhote-Alin in the Nb/Y–Zr/Y diagram fall on the trend of recycled crust as a source. This explains the alkaline (to subalkaline) type of magmatism and the high gas saturation of magmas. The explosive structures resemble lamproite pipes, while their rocks are geochemically and mineralogically close both to lamproites and kimberlites. [ABSTRACT FROM AUTHOR]

Magma mixing is a widespread magmagenic process. However, its significance in the formation of ultrapotassic magmas has been largely overlooked so far as they are commonly thought to originate directly from the mantle and ascend rapidly through the crust. The Hezhong ultrapotassic lavas in Western Yunnan (SW China) are (basaltic) trachy-andesitic in composition. These rocks display porphyritic textures with olivine, clinopyroxene (Cpx), spinel, and phlogopite occurring as both phenocryst and glomerocryst. Disequilibrium textures and complex zonation of crystals are commonly observed. Specifically, based on the textural and compositional characteristics, olivines can be classified into three different populations: two populations are characterized by highly to moderately magnesian olivines with normal chemical core-rim zonation (Fo~94–86 to Fo~89–79 and Fo~91–89 to Fo~86–84, respectively). The third population lacks obvious crystal zonation, but individual crystals exhibit some compositional variety at lower Fo contents (Fo83–76). Similarly, four populations of Cpx and two populations of spinel phenocrysts are recognized in terms of texture and composition. Notably, Cpx with reverse zoning contains a 'green-core' surrounded by a colourless mantle and rim. Hence, based on the variations of mineral assemblage, types of inclusions, and chemical compositions, all phenocryst/glomerocryst minerals can be divided into three groups. Mineral Group I (MG I) consists of high Fo cores of olivine, cores of the zoned spinel, and phlogopite. MG II only includes the green cores of reversed zoned Cpx (green-core Cpx), and MG III is composed of micro phenocrysts without obvious zoning and rims of large phenocrysts. Comparing these mineral groups with relevant minerals occurring in typical temporally and spatially associated igneous rocks, we suggest that the MG I and II could have been derived from magmas with compositions resembling an olivine lamproite and a trachyte, respectively. The overall bulk-rock geochemical and isotopic features of Hezhong lavas also agree with a mixing process between these two endmembers. Hence, we infer that mixing between these two magmas played a key role in the petrogenesis of the ultrapotassic Hezhong lavas and that the MG III crystallized from the mixed magmas. Our study highlights the complex formation of ultrapotassic magmas inferring that caution must be taken when using bulk chemical magma compositions are to deduce source signatures. [ABSTRACT FROM AUTHOR]

Cratonic lamproites are diamondiferous ultrapotassic rocks that are emplaced through thick continental lithosphere and thought to derive from melting of metasomatized (i.e., geochemically enriched) regions of the subcontinental lithospheric mantle (SCLM). We explored the alternative hypothesis that melts sourced from sublithospheric (i.e., convective mantle) sources dominate the genesis of cratonic lamproites. Supporting evidence includes a robust linear correlation between the Mg/Fe ratios of xenocrystic and magmatic olivine in lamproites worldwide, overlapping the trend observed for kimberlite olivine. This indicates that, similar to kimberlites, primary lamproite melts originate from broadly similar sublithospheric mantle sources before assimilating SCLM material of variable composition. The lamproites are also characterized by a direct correlation between olivine Mg/Fe ratio and bulk-lamproite K2O/Al2O3, an index of potassium enrichment in the melt that is independent of mantle-xenocryst entrainment and magmatic differentiation. Quantitative modeling indicates that this correlation results from the interaction between carbonate-bearing sublithospheric melt and phlogopite-rich wall rocks in the SCLM. Our data show that cratonic lamproites and kimberlites have similar mantle sources in the convective mantle, with lamproites acquiring their peculiar enrichment in K by interaction with metasomatized SCLM en route to the surface. Modification of sublithospheric melts during transit through the continental lithosphere might represent a common process for the genesis of alkaline mafic/ultramafic magmas. [ABSTRACT FROM AUTHOR]

The dynamic properties and melting behavior of the Earth's mantle are strongly influenced by the presence of volatile species, including water, carbon dioxide, and halogens. The role that halogens play in the mantle has not yet been fully quantified: their presence in only small quantities has dramatic effects on the stability of mantle minerals, melting temperatures, and in generating halogen-rich melts such as lamproites. Lamproites are volumetrically small volcanic deposits but are found on every continent on the planet: they are thought to be melts generated from volatile-rich mantle sources rich in fluorine and water. To clarify the mantle sources of lamproites, we present experimentally determined mineral/melt partition coefficients for fluorine and barium between phlogopite and lamproite melts. Both fluorine and barium are compatible in phlogopite [ D F (Phl/Melt) 0.96 ± 0.02 − 3.44 ± 0.33 , D Ba (phl/Melt) 0.52 ± 0.05 − 3.68 ± 0.43 ] at a range of pressures (5–30 kbar), temperatures (1000–1200 °C), and fluid compositions (C-O-H mixtures). Using our partition coefficients, we model the melt compositions produced by potential lamproite sources, including phlogopite garnet lherzolite, phlogopite harzburgite, and hydrous pyroxenite. The results demonstrate that hydrous pyroxenites and phlogopite garnet lherzolite can produce melts with F and Ba contents similar to lamproites, but only hydrous pyroxenites fully reproduce other geochemical characteristics of lamproites including high K2O, low CaO contents, and high F/H2O ratios. [ABSTRACT FROM AUTHOR]

The Marepalli dyke of the Vattikod cluster of the Ramadugu Lamproite Field, Nalgonda district, Telangana, India consists of pseudomorphed leucite, phlogopite (Al-poor, Ti-rich zoned phlogopite micas), pseudomorphed olivine, fluorapatite and Al-poor diopside embedded in groundmass consisting mainly of poikilitic Fe-rich titanian phlogopite and potassic amphibole. Other groundmass minerals are Al-Na-poor diopside, Al-poor spinels (titanian magnesian chromites to titanian chromites), Sr-rich fluorapatite and late-stage interstitial anhedral crystals of titanite and K-feldspar. The late-stage deuteric minerals present are REE-rich allanite, pyrite, magnetite, chalcopyrite, galena, hydro-zircon, carbonates (calcite, witherite and strontianite), baryte and cryptocrystalline SiO2. Apatite is an early crystallising phase and is present as inclusions in phlogopite and pyroxene. Phlogopite and amphibole occur as inclusions in titanite and K-feldspar. The compositional trends of phlogopite are of almost constant Al2O3 content with FeOT and TiO2 enrichment, and are typical of lamproitic micas. The FeOT enrichment is accompanied additionally by MgO depletion (reflecting VIFe2+ enrichment) from core to rim together with a slight increase in the tetraferric iron component. Diopside is characterised by <0.4 wt.% alumina and <0.6 wt.% sodium contents and exhibits typical lamproitic affinity. The spinels are alumina-poor with un-evolved titanian magnesian chromite to titanian chromite compositions. The presence of K-richterite, as an abundant amphibole, indicates a lamproite affinity, and on the basis of the typomorphic mineralogy, this rock is classified as a 'pseudoleucite-amphibole-phlogopite lamproite'. The Marepalli lamproite shows significant difference in compositional ranges of phlogopite, amphibole, pyroxene and spinel in comparison to those reported from the Vattikod, Gundrapalli, Ramadugu, Somavarigudem and Yacharam lamproites of Ramadugu Lamproite Field. These lamproites are considered to form from a common parent magma under reducing conditions as evidenced from: (1) low tetraferric iron content in phlogopite; (2) low Fe3+# and Ti# in spinels; and (3) high F content in phlogopite and apatite. [ABSTRACT FROM AUTHOR]

The mineral chemistry of diamond indicator minerals is used to trace mineralizations in primary rocks such as lamproites/kimberlites and in secondary deposits. Subcalcic garnets and magnesian ilmenites are both minerals associated with the diamond potential described in many deposits in the Alto Paranaíba Igneous Province where several kimberlitic pipes and alluvial deposits occur. Our study was conducted on the Romaria diamond deposit of (Brazil), where garnet, ilmenite and tourmaline grains were recovered from a diamon-bearing breccia were analyzed under electron microprobe. The garnet composition is compatible with G10, G9 and G5 types. Ilmenite grains are Mg- to Mn-rich. Nearly 80% of the tourmaline grains are dravite-type. This association of dravite tourmaline with diamond in rocks of lamproitic affinity may be common, as evidenced in the Argyle, Ellendale, Prairie Creek, Sask, Presidente Olegário and Ymi-1 pipes. We therefore suggest a possible lamproite origin for the studied diamond deposit. [ABSTRACT FROM AUTHOR]

The paper presents detailed petrographic research using optical microscopy on lamproite rocks around the village of Mrzen, North Macedonia. Detailed microscopic examinations of 5 specimens show that the rocks have typical porphyritic structures and in some places they also show sub-rounded textures with cavities filled with secondary calcite. Phenocrystals that have idiomorphic forms are represented by olivine, clinopyroxene, orthopyroxene, plagioclase, and magnetite. In some places there are changes - alterations in phenocrystals that are represented by iddingsite, smectite-chlorite-goethite), clay and/or zeolites, and calcite. Microscopic examination shows that they are lamproites. [ABSTRACT FROM AUTHOR]

Origin of abundant alkaline and related lamproite massifs and dykes in Aldan shield have no explanation and the geochemistry of rocks and their xenocrysts is used for the explanation. Bulk-rock geochemistry, mineral chemistry data of the Kayla lamproites of Russia and mineral chemical data (trace and rare elements) of the mantle xenocrysts found in these lamproites was studied using ICP MS and electron microprobe analyses (EPMA). The trace element spectrum of Kayla tuffs and breccias show the similarity with the olivine lamproites and belong to the orogenic type according to Th–U–Nb systematics. Primitive mantle normalized trace element (TRE) spider diagrams show right-leaning patterns with the peaks in large ion lithophile elements Sr, Pb, U, and troughs in Ta, Nb suggesting melting of original peridotites mixed with the ancient EMI (according to Nd, Sr isotopes) source probably belonging to eclogites or lower crust. The age of the emplacement is 132–134 Ma, similar to the Chompolo lamprophyres and many other alkaline Aldan complexes. Thermo-barometric estimation from Cr-diopsides and chromites xenocrysts suggest the origin from the spinel-garnet transition in the lithospheric mantle region. The P–T estimates derived from low-Cr-clinopyroxene xenocrysts, and related to lamproites show a high heat flow of 90 mW/m2 due to interaction with the plume-related magma. The Cr-diopsides and chromites give 45 mW/m2 geotherm similar to regional heat flow. The chondrite normalized rare earth element (REE) pattern for chrome-diopsides is steeper, compared to the low-chrome varieties. Primitive mantle normalized spidergram of Cr-diopsides displays peaks for Sr, U, and Th, and deep troughs of Nd, Nb, Ta. REE. The trace element spider diagrams of both types of xenocrysts show that they were equilibrated with the lamproitic melts and reconstructed parental melts of low-Cr-clinopyroxene coincides with the lamproite spectrums. [ABSTRACT FROM AUTHOR]

The present study attempts a conjugate analysis of satellite-based remote sensing, gravity, and magnetic data for evaluation of structures and tectonic for new insights on Kimberlite emplacement around the Bundelkhand Craton. Initially, Landsat Operational Land Imager (OLI) data has been enhanced using high-pass filtering for the delineation of lineaments. A combined lineament density map has been prepared from the processed Landsat image, Bouguer gravity, and RTP (Reduction to pole) magnetic data, which are further correlated with the reported Kimberlite/Lamproite pipes. The depth to the lithospheric Mantle of the study area has been estimated from EIGEN6C4 Bouguer gravity data using the Parker-Oldenburg algorithm. The association of the reported Kimberlite/Lamproite pipes in the study area have been analyzed with the i) composite lineament density map, ii) different mantle blocks of high and low Moho depths, iii) lithospheric mantle density, and iv) tectonic setting. Some new potential zones for Kimberlite/Lamproites emplacement have been identified based on the integrated analysis of the above mentioned parameters. [ABSTRACT FROM AUTHOR]

The study of the geodynamic evolution of the Baltic Shield showed that the melts of diamondiferous kimberlites and related rocks were formed due to the pulling of "heavy" ferruginous sediments of the Early Proterozoic into subduction zones beneath the Archean cratons. Later, during the Neoproterozoic and Paleozoic stages of rifting, melts conserved in the lower crust and subcrustal lithosphere were able to penetrate into the near-surface zones of the crust and form magmatic complexes of alkaline–ultramafic and kimberlite magmatism. The authors showed that diamondiferous kimberlite and lamproite explosion pipes, as well as related carbonatite and alkaline–ultramafic intrusions, are mainly located above the subduction zones of the Svecofennian (Karelian) plates, which functioned about 2.0–1.8 Ga ago. At the same time, alkaline ultramafic intrusions and (sodium) carbonatites are located closest to the front of the subduction zone of Proterozoic plates (from 100 to 200–300 km). Then (at a distance of 200 to 400 km), there is a zone of location of calcite carbonatites and melilitites, and sometimes nondiamondiferous kimberlites. Diamondiferous kimberlite and lamproite diatremes are located farther than other similar formations approximately 300 to 600–650 km from its front. Such a regular spatial arrangement of magmatic complexes of a single series unambiguously indicates a change in depth of their origin. The farther from the surface boundary of the paleosubduction zone the magmatic bodies are located, the deeper the facies representing them. [ABSTRACT FROM AUTHOR]

A study of specific aggregates of corundum from kimberlite and lamproite of the Ukrainian Shield has been carried out. The presence of unusual segregations of oxides, silicates, and highly reduced phases is a characteristic feature of these aggregates. Oxide and silicate phases fill the interstitials between corundum grains and include oxide microcrystals (rutile, carmeltazite, hibonite, baddeleyite, and zirconolite) and a glass-like substance of feldspar composition. A rare variety of Al–Ti–diopside, namely grossmanite, was first discovered in terrestrial formations in these segregations. Oxygen-free phases are represented by osbornite TiN, khamrabaevite TiC, native iron, and the Si–Ti–Fe intermetallic alloy. The microstructural patterns of the corundum aggregate and the finding of corundum spherules indicate that its formation occurred through rapid cooling of the melt with an Al2O3 content of >95 wt %. The melt temperature was above the melting point of corundum and exceeded 2050°С. The presence of titanium nitrides and carbides, as well as other oxygen-free phases, indicates that the melt was formed under extreme reducing conditions. [ABSTRACT FROM AUTHOR]

Although irrefutable evidence for the presence of signs of diamondiferous kimberlite on the Taimyr Peninsula were obtained in the 1930s, it was only in 2020 that a macrodiamond (>1 mm) was first discovered in Eastern Taimyr. This was a colorless laminar crystal of a transitional shape from an octahedron to a rhombododecahedron. According to the set of features, the crystal is rare and atypical of the known primary and alluvial deposits of the Siberian Diamond Province. The find of this diamond indicates the presence of primary sources and the need for medium-scale geological survey and exploration over a large area from Anabar Bay (Pronchishchev Ridge) to the west to the Kiryaka–Tas and Tulai–Kiryaka highlands and to the northeast to Tsvetkov Cape. [ABSTRACT FROM AUTHOR]

Kareevlei is the first diamond mine to be hosted in a K-richterite- and leucite-bearing Kaapvaal lamproite (formerly termed Group II kimberlite). To constrain the petrogenesis and lithospheric setting of the Kareevlei Kaapvaal lamproites, we present petrography, groundmass mineral compositions, bulk-rock major and trace element concentrations and Sr Nd isotopes for 13 coherent-textured samples, along with garnet indicator mineral compositions and Ni-in-garnet thermobarometry. Two distinct mineralogical varieties of Kaapvaal lamproites are identified: (1) phlogopite-diopside olivine lamproites and (2) leucite-richterite olivine lamproites. Phlogopite macrocryst and microcryst laths have two distinct core populations, interpreted as xenocrysts from phlogopite peridotites and MARIDs, whereas rims represent crystallisation from the magma. The leucite-richterite lamproites are characterised by higher bulk-rock SiO 2 , Al 2 O 3, and Na 2 O, and lower MgO contents compared to the phlogopite-diopside lamproites. The two mineralogical varieties have distinct incompatible trace element concentrations, with the leucite-richterite samples having lower concentrations of light REEs (LREE: La = 656–828; Ce = 518–597; Nd = 234–261 times chondrite) compared to the phlogopite-diopside samples (La = 1125–1391; Ce = 817–1029; Nd = 333–415 times chondrite). Additionally, these two groups exhibit clear separation in trace element ratios, with higher La/Sm and Gd/Yb in the phlogopite-diopside lamproites, which is interpreted to represent formation by lower degrees of partial melting relative to the leucite-richterite lamproites. However, both lamproite varieties have similar 87Sr/86Sr i and 143Nd/144Nd i ratios, suggesting derivation from an isotopically homogeneous source in the SCLM. The indicator mineral suite at Kareevlei comprises, in decreasing abundances, oxides (predominantly ilmenite and chromite), garnet, corundum, and rare clinopyroxene. Garnets are largely eclogitic (59%) with only smaller proportions of peridotitic G9 (19%) and G10 (8%) garnets observed. Peridotitic garnet thermobarometry indicates a paleogeotherm with an estimated surface heat flux of ∼44.3–44.9 mW/m−2 and an estimated lithospheric thickness of ∼187–195 km, which is within error of the nearby highly diamondiferous Finsch Kaapvaal lamproite (cf. 192 ± 6 km). Single mineral garnet thermobarometry suggests that most peridotitic garnets at Kareevlei were sampled by the lamproite at relatively shallow depths above the diamond stability field. The dominance of eclogitic garnet and the absence of peridotitic garnet that equilibrated within diamond stability suggests that the high-value diamonds extracted from Kareevlei are predominantly eclogitic in origin. • Petrology of richterite- and leucite-bearing Kareevlei diamondiferous lamproites • Mineralogical / bulk-rock geochemistry related to variable degrees of partial melting • Indicator minerals suggest LAB at ±188 km • High-value diamonds likely eclogitic in origin [ABSTRACT FROM AUTHOR]

In-situ Rb-Sr dating of mica by laser ablation ICP-MS/MS has recently emerged as a new tool to date a range of geological processes including magmatic, metamorphic and hydrothermal events. The majority of age results presented to date are based on Rb/Sr calibration using the MicaMG pressed nano-powder pellet. However, some studies have reported low accuracy associated with mica Rb-Sr ages using this method, which are attributed to the different ablation properties of MicaMG and natural mica. In this work, we document the results of a systematic comparison between isotope-dilution and laser-ablation Rb/Sr ages of micas in Cretaceous diamondiferous kimberlites from Bultfontein (South Africa), Koidu and Tonguma (Sierra Leone), with additional in-situ data for the Mt. Dromedary mica (Australia). We adopt two different analytical strategies. While NIST610 SRM is employed to calibrate 87Sr/86Sr in both cases, the first approach follows the convention to utilise MicaMG as calibration material for Rb/Sr. In the second approach, Rb/Sr quantification is initially undertaken with NIST610, with a subsequent correction for Rb/Sr offset based on the age of isochronous micas (WBLK) from the Cretaceous Wimbledon lamproite (South Africa). We show that, using our instrumental set-up, employment of MicaMG as Rb/Sr calibration material commonly provides inaccurate results (generally 5–10% older than the solution-based ages). Conversely, our new approach returns accurate ages (within 3%) and represents a promising avenue to improve the accuracy of mica Rb-Sr age by laser ablation ICP-MS/MS especially once isochronous mica reference materials will be developed. Application of this methodology to multiple samples from Koidu and Tonguma shows that, contrarily to previous inferences based on age-dating of fewer samples, magmatism occurred at both localities in the 145–151 Ma interval. After a temporal hiatus, magmatism restarted exclusively in the Tonguma cluster between 135 and 139 Ma. The relative volumetric importance of these two magmatic stages in the Tonguma diamond mine awaits further evaluation. [ABSTRACT FROM AUTHOR]

The crystal structure of a potentially new mineral, the Fe2+-dominant analogue of armalcolite with the idealized formula Fe2+Ti2O5 has been solved. The sample studied originates from a pneumatolytic association related to the lamproite complex of SE Spain. The mineral is orthorhombic, space group Cmcm, the unit-cell parameters are a = 3.7325(1) Å, b = 9.7649(4) Å, c = 9.9902(3) Å, V = 364.12(2) Å3. The crystal-chemical formula (Z = 4) is in good agreement with the chemical composition of the mineral. [ABSTRACT FROM AUTHOR]

The Kolhan Group in the Singhbhum Craton of eastern India is a passive margin siliciclastic shelf to deep‐water carbonate ramp platform succession. It occupies a unique position in respect of the Central Indian Tectonic Zone (CITZ), widely considered as the suture joining the northern and southern Indian cratonic blocks at the time of amalgamation of the Mesoproterozoic supercontinent Columbia. The Kolhan succession is closely comparable to other Late Proterozoic 'Purana' successions of India including the siliciclastic‐carbonate Suasar Group from the central part of the CITZ. We report here the first U–Pb detrital zircon ages from the Kolhan Group. The youngest age population obtained from basal siliciclastics suggests it is not older than ca. 1,158 Ma. The absence of any concordant detrital zircon <1,000 Ma which is well represented in the adjoining Singhbhum Shear Zone and CITZ extensions, suggests that the sedimentation took place prior to ca. 1,000 Ma. The Kolhan Group, therefore, records an extensional event between two major episodes of supercontinent assembly (i.e., Columbia and Rodinia). A similar motif of extension and passive margin sedimentation across Mesoproterozoic Peninsular India together with the widespread Mesoproterozoic lamproite and kimberlite emplacement event suggests an episode of extension and major basin development across the Indian Shield in between the two supercontinent amalgamation cycles of Columbia and Rodinia. [ABSTRACT FROM AUTHOR]

Mesoproterozoic lamproite dykes occurring in the Banganapalle Lamproite Field of southern India show extensive hydrothermal alteration, but preserve fresh spinel, apatite and rutile in the groundmass. Spinels belong to three genetic populations. Spinels of the first population, which form crystal cores with overgrowth rims of later spinels, are Al-rich chromites derived from disaggregated mantle peridotite. Spinels of the second population include spongy-textured grains and alteration rims of titanian magnesian aluminous chromites that formed by metasomatic interactions between mantle wall-rocks and precursor lamproite melts before their entrainment into the erupting lamproite magma. Spinels that crystallised directly from the lamproite magma constitute the third population and show five distinct compositional subtypes (spinel-IIIa to IIIe), which represent discrete stages of crystal growth. First stage magmatic spinel (spinel-IIIa) includes continuously zoned macrocrysts of magnesian aluminous chromite, which formed together with Al–Cr-rich phlogopite macrocrysts from an earlier pulse of lamproite magma at mantle depth. Crystallisation of spinel during the other four identified stages occurred during magma emplacement at crustal levels. Titanian magnesian chromites (spinel-IIIb) form either discrete crystals or overgrowth rims on spinel-IIIa cores. Further generations of overgrowth rims comprise titanian magnesian aluminous chromite (spinel-IIIc), magnetite with ulvöspinel component (spinel-IIId) and lastly pure magnetite (spinel-IIIe). Abrupt changes of the compositions between successive zones of magmatic spinel indicate either a hiatus in the crystallisation history or co-crystallisation of other groundmass phases, or possibly magma mixing. This study highlights how different textural and compositional populations of spinel provide important insights into the complex evolution of lamproite magmas including clues to elusive precursor metasomatic events that affect cratonic mantle lithosphere. [ABSTRACT FROM AUTHOR]

The Leucite Hills Volcanic Field, southwest Wyoming comprises two dozen volcanic features including necks, flows, dikes, and plugs. It has been the focus of many petrologic studies as its volcanic and shallow intrusive rocks are one of the only surficial manifestations of ultrapotassic lamproite. We build on paleomagnetic findings of Sheriff and Shive (1980) by providing further paleomagnetic data from the Boars Tusk dike and Black Rock flows. We also characterize the magnetic mineral assemblage of these lamproites. Principal component analysis of alternating field (AF) and thermal demagnetization data indicate that the dike and breccias of Boars Tusk record a reversed magnetic polarity and the Black Rock lava records a normal polarity, both consistent with previous findings. This recording is typically carried by minerals with coercivities > 15 mT and susceptibility measurements indicate magnetite, maghemite, and titanomagnetite as likely magnetic carriers. AF and thermal demagnetization experiments evince secondary magnetizations held by lower coercivity grains, likely caused by lightning strikes. 40Ar/39Ar incremental heating experiments from Boars Tusk and Black Rock give plateau ages of ∼ 2500 ka and ∼ 900 ka, respectively. Recent advances in the chronology of geomagnetic field reversals and excursions during the Quaternary permit integration of the Boars Tusk dike into the lower Matuyama chron, whereas the Black Rock lavas most probably record the Kamikatsura excursion. Notably, Black Rock records high inclinations that suggest the short-lived excursion achieved a full geomagnetic reversal, something not observed at other localities recording the Kamikatsura excursion. The Leucite Hills offer further opportunities to refine the Quaternary geomagnetic instability time scale (GITS), and to improve understanding of the eruptive and geomorphic evolution of this unusual volcanism. • New 40Ar/39Ar data constrains eruptive history of Leucite Hills volcanic complex. • New paleomagnetic and electron microprobe data reported for Leucite Hills. • First paleomagnetic record of Kamikatsura geomagnetic excursion in North America. [ABSTRACT FROM AUTHOR]

• We simulate mantle metasomatism by reacting sediment or basanite with dunite. • Sediment/dunite reaction is a precursor for K-rich magmatism with orogenic signature. • The reaction of melt with refractory mantle dynamically increases K/Na ratio. • K-enrichment of melts is independent from the experiments' starting composition. Potassium-rich lavas with K/Na of >2 are common in orogenic and anorogenic intraplate magmatic provinces. However, in the primitive mantle, the concentration of Na exceeds that of K by 10 times. The source of K-rich lavas thus needs to be either K-enriched or Na-depleted to account for high K/Na ratios. The geochemical and isotopic compositions of high 87Sr/86Sr post-collisional lavas show that their mantle source contains a recycled crustal component. These highly K-enriched lavas with crustal like trace element patterns are termed "orogenic lamproites" and are compositionally distinct from K-rich "anorogenic lamproites" that show lower 87Sr/86Sr and a trace element pattern that resembles that of primary mantle melts. For both groups the processes of K-enrichment within their source are uncertain and are thought to be linked to melts of sedimentary rocks for "orogenic lamproites" and low-degree melts of ultramafic mantle rocks for "anorogenic lamproites". In both cases, metasomatism of the mantle lithosphere is the precursor to K-rich magmatism. In this study we experimentally determine the effects of mantle metasomatism by sediment- and hydrous mantle melts. The experiments simulate the interaction of refractory lithospheric mantle and metasomatizing melt in a 2-layer reaction experiment. The sediment/dunite reaction experiments lead to formation of a strongly K-enriched phlogopite-pyroxenite layer sandwiched between the two starting materials. The low temperature of the sediment/dunite reaction runs at <1000 °C simulates a fore-arc subduction environment, in which the melts of sediment are consumed during interaction with dunite as the temperature is below the solidus of the produced phlogopite-pyroxenites. The hydrous mantle melt/dunite reaction run is simulated by reacting a hydrated basanite with dunite. Since the temperature of the reaction is higher than the solidus of the resulting phlogopite-pyroxenites (1200 °C), the hydrous melt is not consumed but flows further, increasing in K 2 O and K/Na as it reacts with the refractory peridotite. In both cases, melts are enriched in K and K/Na increases by crystallizing a low K and low K/Na eclogitic residue. Compositions of glass and phlogopite from both types of reactions are comparable to glasses and phlogopites found within post-collisional lavas. Since the enrichment of K within the reaction zone is strongly controlled by the formation of low K/Na and low-K residues, metasomatic enrichment of the mantle lithosphere in K does not need a highly K-enriched metasomatic agent. [ABSTRACT FROM AUTHOR]

We describe the mineralogy of a lamproite dyke from Gundrapalli village (Nalgonda district), Telangana, India. The dyke consists of a mineral assemblage characteristic of lamproites in terms of the presence of amphiboles (mainly potassic-richterite together with potassic-arfvedsonite, magnesio-riebeckite, Ti-rich potassic-magnesio-arfvedsonite, potassic-magnesio-arfvedsonite, katophorite and potassic-ferri-katophorite), Al-poor pyroxene, phlogopite (Ti-rich, Al-poor), pseudomorphed leucite, spinel (chromite-magnesiochromite), fluorapatite, baryte, titanite, rutile, barytocalcite, calcite, ilmenite, hydro-zircon, baotite, strontianite, allanite, quartz and pyrite. The absence of wadeite and priderite have been compensated for by the presence of baotite, rutile, titanite, baryte and hydro-zircons. The presence of the secondary phases: allanite, hydro-zircon, chlorite, quartz and cryptocrystalline silica, implies that the dyke has undergone deuteric alteration. On the basis of its typomorphic mineralogy the Gundrapalli dyke has been classified as a pseudoleucite-phlogopite-amphibole-lamproite. We report the presence of the rare mineral baotite from this lamproite, the first recognition of baotite from a lamproite in India. The mineralogy of the baotite-bearing Gundrapalli lamproite is analogous to the baotite-bearing Kvaløya lamproite from Troms, Norway. [ABSTRACT FROM AUTHOR]

Abstract The ~1100 Ma CC2 and P13 lamproite dykes in the Wajrakarur Kimberlite Field (WKF), Eastern Dharwar Craton, and ~65 Ma Kodomali and Behradih lamproite diatremes in the Mainpur Kimberlite Field (MKF), Bastar Craton share a similar mineralogy, although the proportions of individual mineral phases vary significantly. The lamproites contain phenocrysts, macrocrysts and microcrysts of olivine set in a groundmass dominated by diopside and phlogopite with a subordinate amount of spinel, perovskite, apatite and serpentine along with rare barite. K-richterite occurs as inclusion in olivine phenocrysts in Kodomali, while it is a late groundmass phase in Behradih and CC2. Mineralogically, the studied intrusions are classified as olivine lamproites. Based on microtextures and compositions, three distinct populations of olivine are recognised. The first population comprises Mg-rich olivine macrocrysts (Fo89–93), which are interpreted to be xenocrysts derived from disaggregated mantle peridotites. The second population includes Fe-rich olivine macrocrysts (Fo82–89), which are suggested to be the product of metasomatism of mantle wall-rock by precursor lamproite melts. The third population comprises phenocrysts and overgrowth rims (Fo83–92), which are clearly of magmatic origin. The Mn and Al systematics of Mg-rich olivine xenocrysts indicate an origin from diverse mantle lithologies including garnet peridotite, garnet–spinel peridotite and spinel peridotite beneath the WKF, and mostly from garnet peridotite beneath the MKF. Modelling of temperatures calculated using the Al-in-olivine thermometer for olivine xenocrysts indicates a hotter palaeogeotherm of the SCLM beneath the WKF (between 41 and 43 mW/m2) at ~1100 Ma than beneath the MKF (between 38 and 41 mW/m2) at ~65 Ma. Further, a higher degree of metasomatism of the SCLM by precursor lamproite melts has occurred beneath the WKF compared to the MKF based on the extent of Ca Ti enrichment in Fe-rich olivine macrocrysts. For different lamproite intrusions within a given volcanic field, lower Fo olivine overgrowth rims are correlated with higher phlogopite plus oxide mineral abundances. A comparison of olivine overgrowth rims from the two fields shows that WKF olivines with lower Fo content than MKF olivines are associated with increased X Mg in spinel and phlogopite and vice versa. Melt modelling indicates relatively Fe-rich parental melt for WKF intrusions compared to MKF intrusions. The Ni/Mg and Mn/Fe systematics of magmatic olivines indicate derivation of the lamproite melts from mantle source rocks with a higher proportion of phlogopite and/or lower proportion of orthopyroxene for the WKF on the Eastern Dharwar Craton compared to those for the MKF on the Bastar Craton. This study highlights how olivine cores provide important insights into the composition and thermal state of cratonic mantle lithosphere as sampled by lamproites, including clues to elusive precursor metasomatic events. Variable compositions of olivine rims testify to the complex interplay of parental magma composition and localised crystallisation conditions including oxygen fugacity variations, co-crystallisation of groundmass minerals, and assimilation of entrained material. Highlights • Olivines in the studied lamproites exhibit three distinct populations: xenocrystic, metasomatic, and magmatic. • Xenocrystic olivines indicate a hotter palaeogeotherm of the SCLM beneath the Dharwar Craton than beneath the Bastar Craton. • Metasomatic olivines resulted from interaction of precursor lamproite melts with the mantle wall rock. • Magmatic olivines indicate relatively Fe-rich parental melt for Dharwar lamproites compared to Bastar lamproites. [ABSTRACT FROM AUTHOR]

Underground mining and deep drilling of the richly diamondiferous ~1.2 Ga Argyle lamproite in Western Australia has prompted a re-evaluation of the geology of the pipe. Argyle is considered to be a composite pipe that formed by the coalescence of several diatremes and has been offset and elongated by post-emplacement faulting. Recent geological studies have recognised at least five distinct volcaniclastic lamproite lithofacies with differing diamond grades. The new data suggest that the centre of the southern (main) diatreme is occupied by well-bedded, olivine lamproite lapilli tuff with very high diamond grades (>10 ct/t). Characteristic features include a clast-supported fabric and high modal abundance of densely packed lamproite lapilli and coarse-grained, likely mantle-derived olivine now replaced by serpentine and/or talc. The persistence of small-scale graded and cross-bedding in this lithofacies to depths of ~1.5 km below the original surface prior to erosion suggests phreatomagmatic volcanism forming the diatreme was syn-eruptively accompanied by subsidence of the tephra, maintaining a steep-walled diatreme in the water-saturated country rock sediments. [ABSTRACT FROM AUTHOR]

The Miocene lamproites of the West Kimberley region, Western Australia include olivine-leucite lamproites (≤10 wt% MgO) containing olivine and leucite microphenocrysts, and diamondiferous olivine lamproites (20-30 wt% MgO) containing olivine phenocrysts and larger (1-10 mm) olivine as mantle xenocrysts and dunite micro-xenoliths. Olivine phenocrysts and thin (<100 μm) magmatic rims define trends of decreasing Cr and Ni, and increasing Ca and Mn, with decreasing olivine Mg#, consistent with fractional crystallisation of olivine (and minor chromite). Many phenocrysts are zoned, and those with cores of similar Mg# and trace element abundances to the mantle xenocrysts may be xenocrysts overgrown by later olivine crystallised from the lamproite magma. Magmatic olivines Mg#91-92 are estimated to have been in equilibrium with olivine lamproite magma(s) containing ~22-24 wt% MgO. The xenocrystic mantle olivines Mg90-92.5 in the olivine lamproites are inferred from trace element abundances to be mostly derived from garnet peridotite with equilibration temperatures estimated from the Al-in-olivine thermometer (Bussweiler et al. 2017) to be ~1000-1270 °C at depths of 115-190 km. Olivines from the deeper lithosphere are less depleted (lower Mg#, higher Na, Al, P, Ti, Zr etc) than those at shallower depths, a feature suggested to reflect the combined effects of metasomatic re-enrichment of the craton roots (Ti, Fe, Zr etc) and increasing temperature with depth of origin (Na, Al, Ca). The West Kimberley lamproite olivines are not enriched in Li, as might be expected if their source regions contained continental sedimentary material as has been previously inferred from lamproite large-ion-lithophile trace elements, and Sr and Pb isotopes. [ABSTRACT FROM AUTHOR]

Pre-1.6 Ga rocks comprise around 45% of the onshore area of Western Australia (WA), constituting the West Australian Craton (WAC) (including the Archean Yilgarn and Pilbara Cratons) and the western part of the North Australian Craton (NAC). These areas provide the conditions suitable for diamond formation at depth, and numerous diamondiferous lamproite and kimberlite fields are known. As emplacement ages span close to 2500 Ma, there are significant opportunities for diamond-affinity rocks being present near-surface in much of the State, including amongst Phanerozoic rocks. WA's size, terrain, infrastructure and climate, mean that many areas remain underexplored. However, continuous diamond exploration since the 1970s has resulted in abundant data. In order to advance future exploration, a comprehensive database of results of diamond exploration sampling (Geological Survey of Western Australia 2018) has been assessed. The Yilgarn and Pilbara Cratons have spinel indicators almost exclusively dominated by chromite (>90% of grains), whereas (Mg,Fe,Ti)-bearing Al-chromites account for more of the indicator spinels in the NAC, up to 50% of grains at the Northern Territory (NT) border. Increasing dominance of Al in chromites is interpreted as a sign of weathering or a shallower source than Al-depleted Mg-chromites. Garnet compositions across the State also correlate with geological subdivisions, with lherzolitic garnets showing more prospective compositions (Ca-depleted) in WAC samples compared to the NAC. WAC samples also show a much broader scatter into strongly diamond-prospective G10 and G10D compositions. Ilmenites from the NAC show Mg-enriched compositions (consistent with kimberlites), over and above those present in NT data. However, ilmenites from the WAC again show the most diamond-prospective trends. Numerous indicator mineral concentrations throughout the State have unknown sources. Due in part to the presence of diamondiferous lamproites, it is cautioned that some accepted indicator mineral criteria do not apply in parts of WA. For example Ca-depleted garnets, Mg-depleted ilmenites and Cr-depleted and Al-absent clinopyroxenes are all sometimes associated with strongly diamondiferous localities. Quantitative prospectivity analysis has also been carried out based on the extent and results of sampling, age of surface rocks relative to ages of diamond-prospective rocks, and the underlying mantle structure. Results show that locations within the NAC and with proximity to WA's diamond mines score well. However, results point to parts of the WAC being more prospective, consistent with mineral chemical data. Most notable are the Hamersley Basin, Eastern Goldfields Superterrane and the Goodin Inlier of the Yilgarn Craton. Despite prolific diamond exploration, WA is considerably underexplored and the ageing Argyle mine and recent closure of operations at Ellendale warrant a re-evaluation of diamond potential. Results of mineral chemistry and prospectivity analysis make a compelling case for renewed exploration. [ABSTRACT FROM AUTHOR]

Distinctly different groundmass mineralogy characterise the hypabyssal facies, Mesoproterozoic diamondiferous P3 and P4 intrusions from the Wajrakarur Kimberlite Field, southern India. P3 is an archetypal kimberlite with macrocrysts of olivine and phlogopite set in a groundmass dominated by phlogopite and monticellite with subordinate amounts of serpentine, spinel, perovskite, apatite, calcite and rare baddeleyite. P4 contains mega- and macrocrysts of olivine set in a groundmass dominated by clinopyroxene and phlogopite with subordinate amounts of serpentine, spinel, perovskite, apatite, and occasional gittinsite, and is mineralogically interpreted as an olivine lamproite. Three distinct populations of olivine, phlogopite and clinopyroxene are recognized based on their microtextural and compositional characteristics. The first population includes glimmerite and phlogopite-clinopyroxene nodules, and Mg-rich olivine macrocrysts (Fo 90-93) which are interpreted to be derived from disaggregated mantle xenoliths. The second population comprises macrocrysts of phlogopite and Fe-rich olivine (Fo 81-89) from P3, megacrysts and macrocrysts of Fe-rich olivine (Fo 85-87) from P4 and a rare olivine-clinopyroxene nodule from P4 which are suggested to have a genetic link with the precursor melt of the respective intrusions. The third population represents clearly magmatic minerals such as euhedral phenocrysts of Fe-rich olivine (Fo 85-90) crystallised at mantle depths, and olivine overgrowth rims formed contemporaneously with groundmass minerals at crustal levels. Close spatial association and contemporaneous emplacement of P3 kimberlite and P4 lamproite is explained by a unifying petrogenetic model which involves the interaction of a silica-poor carbonatite melt with differently metasomatised wall rocks in the lithospheric mantle. It is proposed that the metasomatised wall rock for lamproite contained abundant MARID-type and phlogopite-rich metasomatic veins, while that for kimberlite was relatively refractory in nature. [ABSTRACT FROM AUTHOR]

Southwestern Turkey is a tectonically active region where extensional, strike-slip, and compressional tectonics cooccur. The Burdur-Fethiye Shear Zone is located in the middle of this complex area. Understanding the tectonic evolution of this region is crucial, but the controversial Neogene chronostratigraphy does not allow robust synthesis because of poor age control. The middle section of the Burdur-Fethiye Shear Zone includes three basins: the Acıpayam, Çameli, and Gölhisar basins. All these basins represent restricted portions of ancient larger carbonate lakes. The lacustrine sediments are locally covered or cut by lamproites with sparse intercalations of tuff levels. New 40Ar-39Ar biotite and U-Pb zircon radiometric ages from volcanics and a tuff layer in this study demonstrate that the previously suggested Pliocene ages for these sediments are incorrect and that these Neogene sediments are middle Miocene in age. [ABSTRACT FROM AUTHOR]

In this study, we show how veined lithospheric mantle is involved in the genesis of ultrapotassic magmatism in cratonic settings. We conducted high pressure experiments to simulate vein + wall rock melting within the Earth's lithospheric mantle by reacting assemblages of harzburgite and phlogopite-rich hydrous mantle xenoliths. These comprised a mica-, amphibole-, rutile-, ilmenite-, diopside (MARID) assemblage at 3–5 GPa and 1325–1450 °C. Melting of the MARID assemblages results in infiltration of melt through the harzburgite, leading to its chemical alteration. At 3 and 4 GPa, melts are high in K 2 O (> 9 wt%) with K 2 O/Na 2 O > > 2 comparable to anorogenic lamproites. Higher pressures and temperatures (5 GPa/1450 °C) lead to increasing MgO contents of the melt and to some extent lower K 2 O contents (5–7 wt%) at equally high K 2 O/Na 2 O ratios. Our experiments provide insights into the role of alkalis in nickel-partitioning (D Ni ) between olivine and ultrapotassic melt. We observe that the high contents of Na, K, and Al are indicative of high D Ni values, implying that the melt polymerization is the dominant factor influencing the olivine/melt nickel partitioning. The change of D Ni as a function of melt composition results in a pressure independent, empirical geothermometer: T ° C = − 88.14 · ln liq ( Na 2 O + K 2 O · liq 1 + SiO 2 TiO 2 · liq Al 2 O 3 liq MgO + FeO · D Ni + 1906.2 Element oxides represent the composition of the glass (in wt%), and D Ni is the liquid/olivine Ni-partitioning coefficient. We propose that this geothermometer is applicable to all natural silicate melts that crystallized olivine in a temperature interval between 1000 and 1600 °C. Application to glass-olivine pairs from calc-alkaline settings (Mexico), MORB (East Pacific Rise), and OIB (Hawaii) yielded reasonable values of 996–1199 °C, 1265 °C, and 1330 °C, respectively. [ABSTRACT FROM AUTHOR]

The Seiland Igneous Province (SIP), Northern Norway, contains > 5000 km 2 of mafic and ultramafic intrusions with minor alkaline, carbonatite and felsic rocks that were intruded into the lower continental crust at a depth of 25 to as much as 35 km. The SIP can be geochemically and temporally correlated to numerous dyke swarms throughout Scandinavia at 560–610 Ma, and is linked to magmatic provinces in W-Greenland and NE-America that are collectively known as the Central Iapetus Magmatic Province (CIMP). Revised mapping show that the SIP exposes 85–90% layered tholeiitic- alkaline- and syeno-gabbros, 8–10% peridotitic complexes, 2-5% carbonatite, syenite and diorite that formed within a narrow (< 10 Ma) time frame in the Ediacaran (560–570 Ma). Large peridotite complexes were emplaced into the still hot and unconsolidated gabbro (no dating available) and are regarded as the main-conduit systems. Gravimetric data implies an average thickness of igneous rocks of 4–5 km and also features six deep lithospheric roots of ultramafic rocks extending min 9 km into the crust. Together, the root structures represent the main volcanic conduits conveying thousands of km 3 of mafic-ultramafic melts from the asthenosphere to the lithosphere. The ultramafic complexes were predominantly emplaced into the layered gabbros at four major igneous centres, respectively, Nordre Brumandsfjord, Melkvann, Kvalfjord and Reinfjord. All complexes are situated in a right-way-up position and are steep sided forming large plugs. A marginal hybrid zone forms at the contact with country-rock and transitions gradually from olivine-mela-gabbro over pyroxenites that grades in to an olivine-clinopyroxenite zone, which is followed by a wehrlite zone and, finally, the centre of the complexes comprises pure dunite. From pyroxenite to dunite, olivine changes from Fo 72 to Fo 85 and clinopyroxene from Di 80 to Di 92 i.e. the complexes observe a reverse fractional crystallisation sequence with time. Parental melt compositions modelled from early dykes indicate komatiitic to picritic melts with 16–22 wt% MgO, Cr of 1594 ppm and Ni of 611 ppm, which were emplaced at 1450–1500 °C. Melt compositions calculated from clinopyroxene compositions from Reinfjord are OIB-like with LREE enriched over HREE. The high abundance of carbonatites and lamproites demonstrates the volatile-rich nature of the mantle source region and is further corroborated by the unusually high abundance of magmatic sulphides (0.5–1%) and carbonated and hydrous assemblages (c. 1%) throughout the region. In Reinfjord, they are also closely associated with PGE-Cu-Ni reef deposits. Essentially, the ultramafic complexes in the SIP comprises deep-seated transient magma chambers that facilitated mixing and homogenisation of a rich diversity of fertile asthenospheric melts en route to the upper parts of the continental crust. [ABSTRACT FROM AUTHOR]

Two typical lamproitic dykes were found in Noril'sk region of the north-western Siberian Craton, which according to mineralogical, geochemical and isotopic criteria belong to anorogenic, non-diamondiferous type of lamproites. According to the geologic relationships, they cut through the Noril'sk-1 intrusion of the Siberian flood basalt province and thus are younger than ~ 251 Ma. 40 Ar/ 39 Ar dating of the two dykes yielded ages of 235.24 ± 0.19 Ma and 233.96 ± 0.19 Ma, showing that they were emplaced in Carnian of the Late Triassic, about 16 Ma after the flood basalt event. There are some indications that there were multiple lamproitic dyke emplacements, including probably emplacement of diamondiferous lamproites, which produced Carnian-age diamond-rich placer deposits in other parts of the Siberian Craton and in adjacent regions. Lead isotope modelling shows that the source of the studied lamproites was formed with participation of recycled crust, which underwent modification of its U/Pb ratio as early as 2.5 Ga. However, the exact mechanism of the recycling cannot be deciphered now. It could be either through delamination of the cratonic crust or subduction of a mix of ancient terrigenous sediments into the mantle transition zone. [ABSTRACT FROM AUTHOR]

The Man Craton in West Africa hosts two clusters of highly micaceous kimberlites at Koidu and Tonguma with mineralogical and geochemical features transitional towards those of cratonic lamproites. To develop a better understanding of the genesis of these peculiar rocks, which have also been documented elsewhere (e.g., South Africa, China, Russia, India), we have undertaken a geochemical and isotopic study of representative fresh samples from Koidu and Tonguma. New mica Rb Sr dating by isotope dilution confirms the Jurassic age of Koidu (∼145 Ma) and establishes that the Tonguma dykes are marginally younger (∼138 Ma). Bulk-rock analyses of samples from both localities show strong enrichment in K 2 O (up to 4.4 wt%), but also CaO and CO 2 (up to 24 wt% and 18 wt%, respectively), which is entirely consistent with the micaceous nature of these rocks and their variable abundance of calcite. Despite their highly potassic compositions, the incompatible trace element systematics (e.g., Ba/Nb) of these rocks are typical of archetypal kimberlites and unlike those of cratonic lamproites. The Sr-Nd-Hf isotopic composition of the bulk samples range between moderately depleted values (age-corrected 87Sr/86Sr ∼ 0.7032; εNd = +3.8; εHf = +3.9) resembling the common depleted (Prevalent Mantle or PREMA-like) kimberlite component and more geochemically enriched compositions (87Sr/86Sr ∼ 0.7058; εNd = −0.4; εHf = +0.3). The direct relationship between bulk-rock Nd isotopes and average Mg# of magmatic olivine, combined with the previously reported correlation between average Mg# of magmatic and xenocrystic olivine of lithospheric mantle derivation in these kimberlites, suggests that the observed spread in radiogenic isotope compositions stems from the following petrogenetic scenario. Primary kimberlite melts of similar asthenospheric origin with unradiogenic Sr and moderately radiogenic Nd and Hf isotopes interacted with variably metasomatised (i.e., containing phlogopite) and hence geochemically enriched lithospheric mantle wall rocks. Mass balance calculations suggest that the transfer of incompatible elements to the asthenospheric melts was mediated by incongruent melting of metasomatic components in the lithospheric mantle rather than their bulk addition. This study reinforces previous suggestions that interaction between carbonate-rich asthenospheric melts and the sub-continental lithospheric mantle can generate the range of potassic magmas observed within cratons. • Highly micaceous kimberlites with petrological features transitional to lamproites at Koidu and Tonguma. • New geochemical and radiogenic isotope data confirm an affinity to kimberlites. • Sr-Nd-Hf isotope variations from PREMA-like to more geochemically enriched compositions. • Enrichment in mica and isotopic variability due to interaction of asthenospheric melts with metasomatised lithosphere. • Incongruent melting of lithospheric mantle components favoured over their bulk assimilation. [ABSTRACT FROM AUTHOR]

The paper presents new palaeomagnetic results and reassesses complete set of published palaeomagnetic results on the lamproite intrusions in the Gondwana formations of the Eastern India. Altogether eleven sites register reliable characteristic magnetisations corresponding to the c. 110 Ma emplacement age of the lamproites. A mean ChRM is estimated with D = 331.3°; I = −62.4° (α 95 = 6.2°, k = 55; N = 11). The palaeomagnetic pole of λ = 14.9°: Φ = 287.6° (A 95 = 8.4°) is established for the lamproites and it averaged the secular variation and confirms to the Geocentric Axial Dipole (GAD). The pole compares remarkably well with the grand mean pole reported for the Rajmahal traps that are attributed to represent location of the Kerguelen mantle plume head. The palaeolatitudes transferred to Rajmahal coordinates (25.05°: 87.84°) are situated ∼6° north of the present location of the Kerguelen hotspot location. The interpretations are consistent with earlier suggestions of southward migration of the plume based on palaeomagnetic results of Site 1138 of the ODP Leg 183 and with the predictions of numerical models of global mantle circulation. [ABSTRACT FROM AUTHOR]

Petrological-geochemical study showed that the alkaline-ultramafics of the Jetty Oasis (rift zone of the Lambert glacier, East Antarctica) are similar in the age (117-110 Ma) and geochemistry to the ultrapotassic alkali basalts of eastern India (Jharia and Raniganj intrusions). Alkaline magmatism in India and Antarctica is related to the activity of the Kerguelen plume, which significantly affected the evolution of the entire eastern Indian Ocean, in particular, determined geodynamic peculiarities of the ocean opening (existence of non-spreading blocks, fragments of the Gondwana lithosphere in oceanic areas) and geochemical characteristics of erupted tholeiitic magmas. Enriched magma sources related to the Kerguelen plume were formed by melting of ancient Gondwana-derived continental fragments, which experienced multiple transformations during its evolution up to the formation of metasomatized mantle under the impact of the Kerguelen plume on the Antarctic and India margins. [ABSTRACT FROM AUTHOR]

Micas from mafic ultrapotassic rocks with lamproitic affinity from several localities of the Central Mediterranean region were studied through single-crystal X-ray diffraction (SC-XRD), electron microprobe analysis (EMPA) and Secondary Ion Mass Spectrometry (SIMS); Mössbauer Spectroscopy (MöS), when feasible, was also applied to minimise the number of unknown variables and uncertainties. Analysed lamproitic samples cover the most important Central Mediterranean type localities, from Plan d'Albard (Western Alps) to Sisco (Corsica), Montecatini Val di Cecina and Orciatico (Tuscany, Italy) and Torre Alfina (Northern Latium, Italy). The studied crystals show distinctive chemical and structural features; all of them belong to the phlogopite-annite join and crystallise in the 1 M polytype, except for micas from Torre Alfina, where both 1 M and 2 M 1 polytypes were found. Studied micas have variable but generally high F and Ti contents, with Mg/(Mg + Fe) ranging from ~ 0.5 to ~ 0.9; 2 M 1 crystals from Torre Alfina radically differ in chemical composition, showing high contents of Ti and Fe as well as of Al in both tetrahedra and octahedra, leading to distinctive structural distortions, especially in tetrahedral sites. SIMS data indicate that studied micas are generally dehydrogenated with OH contents ranging from ~ 0.2 apfu (atoms per formula unit) for Orciatico and Torre Alfina to ~ 1.4 for Plan d'Albard crystals; this feature is also testified by the length of the c parameter, which decreases with the loss of hydrogen and/or the increase of the F → OH substitution. Chemical and structural data suggest that the entry of high charge octahedral cations is mainly balanced by an oxy mechanism and, to a lesser extent, by a M 3 +,4 + -Tschermak substitution. Our data confirm that Ti preferentially partitions into the M2 site and that different Ti and F contents, as well as different K/Al values, are both dependant upon f H2O and the composition of magma rather than controlled by P and T crystallisation conditions. The obtained data help to discriminate among lamproite-like rocks formed within a complex geodynamic framework but still related to a destructive tectonic margin and evidence different trends for micas from the youngest Torre Alfina (Northern Latium) lamproites, referred to the Apennine orogeny and those of the older lamproites from Orciatico, Montecatini Val di Cecina (Tuscany), Western Alps, and Corsica, the latter referred to the Alpine orogeny. Phlogopite crystals from the older lamproites fall within the compositional and structural field of worldwide phlogopites from both within-plate and subduction-related settings. Phlogopite from the Plio-Pleistocene lamproite-like occurrence in Tuscany and Northern Latium, despite crystals with low Mg# of the Torre Alfina rock plot well within the general field of the other crystals in less evolved samples, follows a different evolution trend similar to that of shoshonites from Tuscany and Northern Latium. On this basis, we argue that the observed differences are inherited by slight differences in the magma compositions that are related to different genetic and evolution pathways. [ABSTRACT FROM AUTHOR]

A mineralogical study of the hypabyssal facies, late Cretaceous macrocrystic pulse of TK1 intrusion and the Mesoproterozoic aphanitic pulse of TK4 intrusion in the Wajrakarur Kimberlite Field of southern India shows that the rocks contain macrocrysts of forsteritic olivine, phenocrysts and microphenocrysts of Al–Na-poor diopside and phlogopite set in a groundmass mainly of Al–Na-poor diopside and phlogopite. Other groundmass minerals are spinel, perovskite and fluorapatite in TK1, and spinel, titanite, chlorite, calcite and gittinsite in TK4. K-richterite and perovskite occur only as inclusions in phlogopite and titanite, respectively in TK4. Late-stage deuteric phases include pyrite and barite in TK1, and strontianite, chalcopyrite, galena and pentlandite in TK4. Diopside microphenocrysts in TK4 exhibit oscillatory zoning with characteristics of diffusion controlled magmatic growth. TK1 spinels show magmatic trend 2 that evolves from magnesiochromite and culminates in titaniferous magnetite, whereas TK4 spinels are less evolved with magnesiochromite composition only. TK1 phlogopites show a simple compositional trend that is typical of lamproite micas, while four distinct growth zones are observed in TK4 phlogopites with the following compositional characteristics: zone I: high Cr 2 O 3 and TiO 2 and low BaO; zone II: low Cr 2 O 3 ; zone III: low TiO 2 and high BaO; zone IV: low BaO. Forsterite contents and trace element concentrations reveal two xenocrystic core populations and one magmatic rim population for TK1 olivines. Mineralogically, both TK1 and TK4 are classified as diopside–phlogopite lamproites rather than archetypal kimberlites. The two lamproites are considered to have formed from the same parent magma but crystallised under distinct oxygen fugacity conditions. With elevated content of Fe 3 + in phlogopite, spinel and perovskite, TK1 appears to have crystallised in a relatively high oxygen fugacity environment. Multiple growth generations of phlogopite, spinel and fluorapatite in TK4 indicate a complex evolutionary history of the magma. Close spatial and temporal associations of Mesoproterozoic kimberlites and lamproites in southern India can possibly be explained by a unifying model which accounts for the generation of diverse magmas from a range of geochemical resevoirs in a continental rift setting. [ABSTRACT FROM AUTHOR]

[Display omitted] • Emplacement ages of the diamondiferous rocks in South China have been constrained. • They were formed intermittently and eccentrically between 492 and 441 Ma. • They may be induced by the contribution of the upwelling of the lowest mantle. • The mantle evolution and the diamond potential have been reviewed. Mantle-derived magmas provide windows to the deep earth, and precise dating of the deep magmatic rocks such as kimberlite and related lithologies is crucial to attaining a better understanding of the mantle evolution and mantle-crust interaction in conjunction with global geodynamic cycle. Here we report a geochronology investigation of the diamondiferous kimberlite and related rocks from the southeastern side of the Yangtze Craton in China with the aim to constrain the deep mantle magma emplacement patterns and mantle evolution through time. Ultrabasic magmatic events occurred intermittently between 492 and 441 Ma, as inferred from apatite U-Pb dating and phlogopite 40Ar-39Ar dating. Combined with the previous data, two pulses of diamondiferous magmatism (ca. 488 Ma and ca. 450 Ma) are identified. The emplacement ages and patterns of these deep-seated diamondiferous magmas are unrelated to the reported Pan-African tectonothermal event (peak at ca. 522 Ma), Kwangsian Orogeny (peak at ca. 435 Ma), and Emeishan plume event (peak at ca. 260 Ma) in the South China Continent. Instead, we infer that the kimberlite and associated rocks in the South China Continent may be related to the upwellings from the edges of the Large Low Shear Velocity Province located at the core-mantle boundary at that time. The lack of magmatic event during 760 to 460 Ma and the existence of the thick lithosphere (>175 km) beneath the South China Continent are suitable for lithospheric diamond formation during the Early Paleozoic. These data suggest that future diamond exploration should be focused on the kimberlites emplaced during the Cambrian–Ordovician transition on the southeastern side of the former Yangzte Craton. [ABSTRACT FROM AUTHOR]

Detailed textural and mineral chemistry characterisation of lamproites from the Socovos fault zone, SE Spain Neogene Volcanic Province (NVP) combining X-ray element maps and LA-ICP-MS spot analyses has provided valuable information about mantle depth ultrapotassic magma mixing processes. Despite having similar whole-rock compositions, rocks emplaced in the Socovos fault are mineralogically varied: including type-A olivine-phlogopite lamproites; and type-B clinopyroxene-phlogopite lamproites. The Ol-lacking type-B predates Ol-bearing type-A by c . 2 million years. We propose that the mineralogical variations, which are representative of lamproites in the NVP as a whole, indicate mantle source heterogeneities. Major and trace element compositions of mineral phases suggest both metasomatised harzburgite and veined pyroxenite sources that were most likely closely spatially related. Thin section scale textural and compositional variations in mineral phases reveal heterogeneous mantle- and primitive magma-derived crystals. The variety of crystals points to interaction and mingling-mixing of ultrapotassic magma batches at mantle depths prior crustal emplacement. The mixing apparently occurred in a mantle melting zone with a channelised flow regime and localised magma chambers-reservoirs. Magma interaction was interrupted when the Socovos and other lithosphere-scale faults tore down to the mantle source region, triggering rapid ascent of the heterogeneous lamproite magma. [ABSTRACT FROM AUTHOR]

Following the commencement of assembly of Columbia at ca. 2.0 to 1.8 Ga with its normal convergent margin metallogeny rich in orogenic gold and VMS Cu-Zn-Pb systems, the Earth entered the Boring Billion phase from 1800 to 800 Ma from Late Paleoproterozoic to the dawn of the Neoproterozoic, a transitional period prior to the assembly and breakup of Rodinia. The Boring Billion is considered as a static period in terms of the evolution of global tectonics, the atmosphere, oceans, and life itself. Unlike the history of previous supercontinents, there is limited evidence of extensive breakup and continental drift during the transition from breakup of Columbia to the assembly of Rodinia. The low strain accordion-style tectonic regime appears to have been typified by intermittent periods of variable degrees of extension, rifting, and asthenosphere upwelling followed by compression and closure of extensional basins. The anomalous accordion-type tectonics resulted in the formation and preservation of an equally anomalous but richly endowed metallogeny. Varying degrees of rifting, asthenospheric upwelling, intermittent magmatism derived both from mantle melting, and induced hydrothermal circulation resulted in a variety of giant mineral deposits that were preserved on the margins of buoyant lithosphere during mild compression. In accordance with their inferred relationship to accordion tectonics, the metallogeny was episodic with peaks at ca. 1.7–1.6, 1.4, and 1,1 Ga. The world's largest IOCG, carbonatite REE, lamproite diamond, unconformity U, SEDEX, and BHT deposits represent a metallogenetic bonanza during this period. The more intensively metal endowed blocks within Columbia were smaller blocks with largely Paleoproterozoic lithosphere, particularly Central Australia, and the North American Craton with its myriad of internal blocks. These appear to have been most susceptible to rifting under relatively low strain accordion-style tectonism due to their high density of lithosphere margins relative to their surface area. Overall, it appears that it was the relative lack of tectonic activity and continental drift in the Boring Billion that was responsible for the not-so-boring but, rather spectacular and unique, metallogeny of that period of Earth's history. [Display omitted] • The Boring Billion from 1800 to 800 Ma marks the transition from Columbia to Rodinia. • Accordion-type tectonics led to formation and preservation of anomalous but richly endowed metallogeny. • A variety of giant mineral systems preserved on the margins of buoyant lithosphere during mild compression. [ABSTRACT FROM AUTHOR]

Two early Cretaceous potassic sill intrusions from Ramnagore and Rajpura in the Raniganj Gondwana Sedimentary Basin of eastern India consist of macrocrysts and microcrysts of olivine, together with phenocrysts and microphenocrysts of mica, apatite and diopside set in a groundmass of mica, diopside, K-feldspar, apatite and rutile. Titanian magnesian aluminous chromite occurs as a groundmass phase in the Ramnagore rocks. The compositional characteristics of olivine are similar to those of peridotite-derived mantle xenocrysts in terms of their high forsterite and Ni contents coupled with low Mn, Ca, Al and Ti. Mineralogically, the sill intrusions are classified as phlogopite–diopside–K-feldspar–apatite olivine lamproites. Mica and apatite crystals commonly show core–overgrowth rim textures with up to three distinct compositional zones. The mica zones are M-I core: high Ti, low-to-high Cr and moderate Ba; M-II inner rim: moderate Ti, low Cr and high Ba; and M-III outer rim: low Ti, Cr and Ba. Rajpura mica show a fourth zone (M-IV), which occurs as patches at the crystal margins, characterized by higher Fe T and lower K compared to the other three zones. M-I phlogopite is interpreted to be "antecrystic", whereas M-II and M-III mica represent magmatic growth zones. M-IV mica has probably developed during hydrothermal alteration. Both the Rajpura and Ramnagore mica exhibit a trend of decreasing Al 2 O 3 with increasing FeO T , which is typical for bona fide lamproites. Rajpura apatite crystals show three distinct compositional zones, viz. Ap-I core: high-Sr–low-LREE; Ap-II inner rim: high-Sr–high-LREE; and Ap-III microporous outer rim: moderate-Sr–low-LREE and considerable quantities of Ba and Na. The Ap-I and Ap-II generations represent two distinct magmatic growth zones, whereas Ap-III developed during hydrothermal alteration. Ramnagore apatite exhibit oscillatory zoning with fluctuations in Sr and LREE contents. Diopside has Al–Na-poor compositions, typical of lamproitic clinopyroxene. The study demonstrates how the mineralogy of lamproites records crystallization from multiple pulses of mantle-derived K-rich magmas, with protracted magmatic differentiation and late-stage hydrothermal evolution. • Two phlogopite–diopside–K-feldspar–apatite olivine lamproites from eastern India. • High-Fo olivine grains are peridotite mantle-derived xenocrysts. • High Cr Ti phlogopite record earlier failed lamproite activity at mantle depths. • Magmatic mica and apatite zones reflect different stages of magma differentiation. • Metasomatic mica and apatite record late-stage hydrothermal alteration. [ABSTRACT FROM AUTHOR]

Rotations of large-scale crustal blocks deduced from paleomagnetism are usually invoked to support evolutionary tectonic models in orogens. However, the regional representativeness of local paleomagnetic rotations strongly depends on the structural context and can lead to conflicting results. This work analyzes an unusual cluster of almost coeval lamproite dikes (9.3–7.1 Ma) intruded along a 25 km-long segment of the Socovos transpressive fault zone in the Eastern Betics, with a view to determine rotations at the metre-scale. This fault zone has contrasting deformation styles, depending on the rheology of the rocks, which vary from ductile evaporites (gypsum) to brittle carbonates. The volcanic and subvolcanic rocks present a primary acquisition of high quality natural remanent magnetization, which defines a single directional component with very narrow α95. Matching the outcrop scale structures with the apparently dispersed paleomagnetic directions in the fault zone allows us to differentiate four deformational domains with distinctive characteristics: (1) a brittle zone with deformation concentrated in planes that bound blocks with no rotation or rotations below the expected secular variation (± 16° in inclination and ± 21° declination); (2) transpressive decametre-scale duplexes or single horses, also limited by brittle faults, where inclined axis rotations below 60° occur as rigid blocks; (3) buckling folds in ductile units associated with local reverse faulting; and (4), a triclinic transpressive ductile shear zone affecting a gypsum layer, where volcanic boudins have a rotation that is the sum of folding parallel to the shear zone walls plus an angular shear of 36°. These paleomagnetic results indicate that fault displacement continues after 7 Ma with the same kinematics as previously. Besides regional findings, this study illustrates the potential usefulness of small-scale paleomagnetic analysis for determining strain partitioning and deformation mode along large and complex transpressive fault zones, as well as the necessity to know the local structure to attribute regional meaning to the paleomagnetic rotation data. • Metric-scale block rotations are analyzed using paleomagnetism on a transpressive fault. • 9.3–7.1 Ma lamproite volcanic dikes present high quality remanent magnetization. • Brittle and ductile structures coexist in the transpressive fault zone after intrusion. • Structure and paleomagnetic rotations allow defining four deformational domains. • A combination of rotations is recognized in a triclinic transpressive ductile shear zone. [ABSTRACT FROM AUTHOR]