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Ultrapotassic lamproitic rocks in the Western Alps, Tuscany-Corsica and SE Spain ( c. 30 to 1 Ma) show high MgO, Ni and Cr denoting a mantle origin, but also have incompatible element and radiogenic isotope abundances that resemble upper crustal rocks, such as local metapelites and global subducting sediments. The coexistence of mantle and crustal signatures in lamproites indicates a genesis in a lithospheric mantle, which had been contaminated by crustal rocks. The occurrence of lamproitic magmatism along the Alpine collision front suggests that mantle contamination occurred during east-verging Cretaceous-Oligocene subduction of the European plate beneath the African margin. We suggest that crustal material originated from the overriding continental margin, which was eroded by the low-angle subducting European slab. Mantle melting and generation of lamproites took place later, during diachronous opening of Western Mediterranean basins, contemporaneously with a new cycle of magmatism, which was genetically related to the west-north-dipping Apennine-Maghrebian subduction. [ABSTRACT FROM AUTHOR]

To evaluate the dissolution processes of diamond crystals in kimberlitic and lamproitic magmas, a series of diamond dissolution experiments were carried out in the graphite stability field at 1300-1420 °C and 1 GPa under the W1, MW, and HM buffers. Dissolution agents used include an aphanitic kimberlite from Wesselton Mine, South Africa, and a lamproite from Mount North, West Kimberley, Australia. With increasing run duration, diamond morphology changed from a sharp octahedron through combinations of octahedron and tetrahexahedroidal forms to spherical tetrahexahedroid having rounded faces. Negatively oriented trigons were formed on the octahedral {111} face. As the degree of diamond dissolution increased, the trigons changed from smaller shallow types to larger deep types. The dissolution rate in the kimberlitic solvent at 1300 °C was 0.12 mm/h under the HM buffer, 0.0034 mm/h under the MW buffer, and 0.0017 mm/h under the WI buffer, whereas that at 1420 °C was 0.014 mm/h under the WI buffer. In the lamproitic solvent, the dissolution rate was 0.0024 mm/h at 1420 °C under the WI buffer. The data indicate that diamond dissolves in silicate melts as carbonate ions through an oxidizing reaction. The degree of dissolution strongly depends on temperature, oxidation state, and the compositional dependence of CO2 solubility in the melts. [ABSTRACT FROM AUTHOR]

The Serbian province of Tertiary ultrapotassic volcanism is related to a post-collisional tectonic regime that followed the closure of the Tethyan Vardar Ocean by Late Cretaceous subduction beneath the southern European continental margin. Rocks of this province form two ultrapotassic groups; one with affinities to lamproites, which is concentrated mostly in the central parts of the Vardar ophiolitic suture zone, and the other with affinities to kamafugites, which crops out in volcanoes restricted to the western part of Serbia. The lamproitic group is characterized by a wide range of 87Sr/86Sri (0·70735–0·71299) and 143Nd/144Ndi (0·51251–0·51216), whereas the kamafugitic group is isotopically more homogeneous with a limited range of 87Sr/86Sri (0·70599–0·70674) and 143Nd/144Ndi (0·51263–0·51256). The Pb isotope compositions of both groups are very similar (206Pb/204Pb 18·58–18·83, 207Pb/204Pb 15·62–15·70 and 208Pb/204Pb 38·74–38·99), falling within the pelagic sediment field and resembling Mesozoic flysch sediments from the Vardar suture zone. The Sr and Nd isotopic signatures of the primitive lamproitic rocks correlate with rare earth element fractionation and enrichment of most high field strength elements (HFSE), and can be explained by melting of a heterogeneous mantle source consisting of metasomatic veins with phlogopite, clinopyroxene and F-apatite that are out of isotopic equilibrium with the peridotite wall-rock. Decompression melting, with varying contributions from depleted peridotite and ultramafic veins to the final melt, accounts for consistent HFSE enrichment and isotopic variations in the lamproitic group. Conversely, the most primitive kamafugitic rocks show relatively uniform Sr and Nd isotopic compositions and trace element patterns, and small but regular variations of HFSE, indicating variable degrees of partial melting of a relatively homogeneously metasomatized mantle source. Geochemical modelling supports a role for phlogopite, apatite and Ti-oxide in the source of the kamafugitic rocks. The presence of two contrasting ultrapotassic suites in a restricted geographical area is attributable to the complex geodynamic situation involving recent collision of a number of microcontinents with contrasting histories and metasomatic imprints in their mantle lithosphere. The geochemistry of the Serbian ultrapotassic rocks suggests that the enrichment events that modified the source of both lamproitic and kamafugitic groups were related to Mesozoic subduction events. The postcollisional environment of the northern Balkan region with many extensional episodes is consistent at regional and local levels with the occurrence of ultrapotassic rocks, providing a straightforward relationship between geodynamics and volcanism. [ABSTRACT FROM AUTHOR]

The Altiplano of southern Peru displays a large spectrum of Cenozoic potassic (K) and ultrapotassic (UK) mafic rocks that delineate two deep lithospheric mantle blocks that have undergone different depletion and enrichment events. Phlogopite lamproites indicate that the eastern Altiplano block is underlain by a metasomatized harzburgitic mantle of Paleoproterozoic to Archean age (depleted mantle age, TDM = 1130-2485 Ma; ϵNd = -5.0 to -11.4; 87Sr/86Sri = 0.7100-0.7159). Beneath the western Altiplano block, the presence of a younger (TDM = 837-1259 Ma; ϵNd = +0.6 to -6.3; 87Sr/86Sri = 0.7048-0.7069) metasomatized lherzolitic mantle is deduced from multiple occurrences of diopside-rich K-UK lavas (leucitites, leucite-bearing tephrites, olivine, and diopside trachybasalts). A third suite of young (<2 Ma) K-UK rocks outlines the active Cusco Vilcanota fault system separating the western and eastern Altiplano blocks; this third suite, composed of diopside-phlogopite lamproites and augite kersantites, minettes, and trachybasalts, sampled a composite mantle source that probably included an asthenospheric component (TDM = 612-864 Ma; ϵNd = -1.1 to -3.5; 87Sr/86Sri = 0.7051-0.7062), in addition to lithospheric components inherited from the eastern and western Altiplano blocks. The spatial distribution of the south Peruvian K-UK magmatism suggests that K-UK melts reached the surface through reuse of older translithospheric weakness zones extending at least to the depth of magma generation. These latter were reactivated by a dextral tran- spressional regime imposed on the two rigid lithospheric blocks by the Andean orogen. [ABSTRACT FROM AUTHOR]

The distribution of kimberlite, lamproite and related alkaline volcanism in Australia can be broadly related to the structure of the Australian continent and lithosphere. Diamondiferous kimberlites and lamproites, with the apparent exception of the weakly diamondiferous Orrorro kimberlites in the Adelaide Fold Belt, lie within the large Precambrian shield where seismic tomographic models and heat flow data indicate the presence of relatively cold, high seismic wave speed lithosphere (tectosphere) typically some 200 km thick or more beneath the Archaean cratons and up to 300 km in parts of central Australia. Many of the diamondiferous intrusions appear to lie at the margins rather than in the centre of the lithosphere domains. The highest concentration of diamondiferous intrusions (kimberlites and lamproites) is on and around the Kimberley Craton where seismic data indicate crustal thicknesses of 35–40 km and a lithosphere up to 275 km thick that is distinct from Proterozoic northern Australia.Many, but clearly not all, of the intrusions show evidence of regional and local structural controls. Some are spatially associated with known crustal structures, especially regional faults. Others are aligned, either singly or in clusters, along or near discontinuities and/or gradients evident in regional scale potential field data, especially the total horizontal gradients of gravity data continued upward tens to hundreds of kilometres. Many of these features are not evident in the original datasets as their signatures are masked by shorter wavelength (near surface) anomalies. In some cases, the kimberlites and associated rocks lie within crustal blocks and domains defined by discontinuities in the potential field data rather than at domain boundaries.Our overview suggests that analysis of potential field data, especially horizontal gradients in upwardly continued potential field data, at all scales can assist definition of crustal and, potentially, lithospheric structures that may influence the distribution of diamond pipes. However, more definitive mapping of Australia''s diamond prospective regions requires the integration of data on crustal structures, especially trans-lithospheric faults, and geodynamic settings with high resolution tomographic models and other geophysical, petrologic, and isotopic information on the nature of the lithosphere beneath the Australian continent. [Copyright &y& Elsevier]

Diamond exploration in India over the past decade has led to the discovery of over 80 kimberlite-inferred and lamproite-related intrusions in three of the four major Archean cratons that dominate the subcontinent. These intrusions are Proterozoic (1.1 Ga), and are structurally controlled: locally (at the intersections of faults); regionally (in a 200 km wide, 1000 km long diamond corridor); and globally (in the reconstructed supercontinent of Rodinia). The geochemistry of 57 samples from 13 intrusions in the southern Dharwar Craton of Andhra Pradesh has been determined by XRF spectrometry. The bodies are iron-rich with mg#=50–70 and are neither archetypal kimberlites nor ideal lamproites; this may be the underlying reason that conventional exploration techniques have thus far failed to locate the primary sources of India''s historically famous diamonds. The two major fields of kimberlite-clan rocks (KCR) in the Dharwar Craton, Wajrakur and Narayanpet, are separated by a NW–SE trending, transcontinental (Mumbai-Chennai) gravity lineament. About 80% of intrusions in Wajrakur are diamondiferous, but diamonds have not yet been reported in Narayanpet. The gravity anomaly may mark the boundary of an architectural modification in the keel of the sub-continental lithosphere, a suggestion that is supported by differences in kimberlite mineralogy, chemistry, mantle xenoliths, structural setting and crustal host rocks. [Copyright &y& Elsevier]

Partition coefficients for compatible and incompatible trace elements for use in modelling the origin and evolution of lamproitic and other potassic rocks are reported. These are based on values obtained by in situ determination using laser ablation microprobe-inductively coupled plasma-mass spectrometry (LAM-ICP-MS) on mineral/glass pairs in examples of the Gaussberg olivine leucitite, a classic leucite lamproite. Leucite/melt partition coefficients for 32 elements show values above 1 only for Cs and Rb, whereas values for Ni, Ga and Co are 0.4–0.1. DLc/Lq for most other elements are in the range 0.07–0.0005, and delineate a gently sloping pattern to lower values for elements generally considered to be “incompatible”. Olivine/melt partition coefficients show higher values for the compatible elements Ni, Co, Mn and Cr than in all basaltic systems investigated experimentally to date. DOl/Lq for heavy rare earth elements (HREE) are slightly lower than in basalts, whereas most other elements give similar values. Clinopyroxene/melt partition coefficients appear to vary widely as a function of the Al2O3 content of the rock. Values obtained here for the Gaussberg rock consistently show appreciably higher DCpx/Lq than in basaltic systems for the incompatible elements Cs, Rb, Ba, Th, U, Nb, Ta, La and Ce, which is attributed to a larger M2 site. Early salitic cores have patterns with lower D-values for these elements and higher values for HREE, similar to those known from alumina-rich potassic rocks. Thus, the values obtained here should be applied only with caution to nonlamproitic rocks. Other notable characteristics are high DU/DTh and low DZr and DHf, the latter of which is attributed to structural characteristics of peralkaline melts. [Copyright &y& Elsevier]

Composite dykes consisting of leucominette and dacite as well as discrete dykes and flows of minette and lamproite composition, occur in the Veliki Majdan area, western Serbia. This area is part of the Serbian Tertiary magmatic province, which consists of numerous small occurrences of ultrapotassic igneous rocks. The composite dykes have leucominette margins (up to 150 cm thick) enclosing a central part of dacite up to 100 m in width. Between these two lithologies, a decimetre-sized transition zone may occur. Petrography, mineral chemistry and bulk-rock geochemistry, including Sr, Nd and Pb isotopes, provide evidence that the minettes and leucominettes formed by hybridization between a felsic magma similar in composition to dacite and a mantle-derived lamproitic magma. The leucominettes and minettes contain all phenocryst types (biotite, plagioclase, quartz) present in the dacites, but in partly resorbed and reacted form. The mica displays a great diversity of resorption textures as a result of partial dissolution, incipient melting and phlogopitization, suggesting superheating of the felsic melt during hybridization; the mineral modes and mineral compositions of the leucominettes and minettes resemble those in the lamproites. A model for the modification of lamproite melt towards minette is presented in which minette is formed by mixing of lamproite and <30% felsic magma. The lack of any significant correlation between Pb isotopic ratios and some of the ‘mixing-indices’ (SiO2, Zr, Zr/Nb, 143Nd/144Ndi) recognized in the hybridization model for the Veliki Majdan dykes may be a result of similarity of the Pb-isotopic signature in the two end-members. Highly phlogopitized biotite xenocrysts in the minettes are ascribed to the retention of volatile components after magma mixing and crystallization of a new generation of phlogopite from the hybridized magma. The magma-mixing model explains the reverse zoning and resorption features of phlogopite macrocrysts commonly recognized in calcalkaline lamprophyres elsewhere. Therefore, this mixing mechanism may be globally applicable for the origin of minettes associated with calcalkaline granitic plutonism in post-orogenic settings. [ABSTRACT FROM AUTHOR]

In the East European Alpine belt, leucite-sanidine-phlogopite-olivine-bearing volcanic rocks of Late Cenozoic age occur at eight localities within the Vardar suture zone and at one locality in the Southern Carpathian fold-and-thrust belt. Most of these volcanics are characterized by high Mg# (66.6–78.6), high abundances of Ni (117–373 ppm) and Cr (144–445 ppm) as well as high primary K2O contents (5.63–7.01 %) and K2O/Na2O values (1.93–4.91). Rocks with more differentiated compositions are rare. A lamproite affinity of these rocks is apparent from their relatively low contents of Al2O3 (9.9–14.3 wt%) and CaO (6.2–8.3 wt%) in combination with high abundances of Rb (85–967 ppm), Ba (1,027–4,189 ppm), Th (18.9–76.5 ppm), Pb (19–54 ppm), Sr (774–1,712 ppm) and F (0.16–0.52 wt%), and the general lack of plagioclase. Although eruption of the magmas took place in post-collisional extensional settings, significant depletions of Nb and Ta relative to Th and La, low TiO2 contents (0.92–2.17 %), low ratios of Rb/Cs, K/Rb and Ce/Pb as well as high ratios of Ba/La and Ba/Th suggest close genetic relationships to subduction zone processes. Whereas Sr and Nd isotope ratios show relatively large variations (87Sr/86Sr = 0.7078–0.7105, 143Nd/144Nd = 0.51242–0.51215), Pb isotope ratios display a very restricted range with 206Pb/204Pb = 18.68–18.88 and variable but generally high Δ7/4 (11–18) and Δ8/4 (65–95) values. The observed petrographic, geochemical and isotopic characteristics are best explained by a genetic model involving preferential melting of phlogopite-rich veins in an originally depleted lithospheric mantle source, whereby the metasomatic enrichment of the mantle source is tentatively related to the addition of components from subducted sediments during consumption of Tethyan oceanic lithosphere. [ABSTRACT FROM AUTHOR]

The Se´gue´la area in Ivory Coast is known for its diamond-bearing field related to dykes of kimberlite and lamproite. These dykes, devoid of any deformation and metamorphism, crosscut the Birimian formations. Their N 170° orientation is controlled by the tectonized contact between the Archean and the Paleoproterozoic shields of the West-African craton. Discovery of a diatreme, with its pipe breccias and well-preserved maar sediments, below the present-day colluvia, attests for the probable recent geological age (Cretaceous?) of the kimberlitic activity. To cite this article: A. Pouclet et al., C. R. Geoscience 336 (2004). [Copyright &y& Elsevier]

A comagmatic suite of lamproites, ultramafic lamprophyres, and minettes was intruded at ∼100 Ma into thick siliciclastic sequences deposited in five intracratonic basins which developed during Gondwana rifting in eastern India. Lamproites are dominated by microphenocrysts of Ti-rich phlogopite, and olivine pseudomorphed by serpentine and talc, with variable modal abundances of aegirine, amphibole, apatite, carbonates, Cr-spinel, fluorite, perovskite, priderite, and titanomagnetite. Compositionally, lamproites are characterized by extremely high contents of TiO2 (4.2–10 wt%), K2O, and P2O5, over a range of Mg# from 80 to 75, in keeping with lamproites worldwide. They have high abundances of Ba, Th, U, and REE (1019–5400 ppm), with pronounced fractionation of REE, where La/Smcn=3.5–5.6, and Gd/Ybcn=7.3–18, consistent with residual garnet in the mantle source. Nitrogen isotope compositions range from +1.6 to +8.7‰ with an average of 3.8‰, and N contents average 107 ppm. Mantle δ15N averages −5‰, with a N content of 2 ppm, whereas continental crust varies from 2 to 6‰ with 30–90 ppm N. Atmospheric N2 is sequestered by N-fixing microorganisms, and stored as kerogen with an average δ15N of +3‰ in sedimentary rocks. Some of the organic N is converted to NH4+ which substitutes for K in crustal K-silicates. The 15N-enriched lamproites are interpreted to have formed from partial melting of enriched harzburgitic mantle lithosphere by decompressional melting accompanying extension. Enrichment resulted from subduction–erosion of continental crust, or subduction of sediments, low-degree partial melting, hybridization of the melts with mantle lithosphere and incubation, prior to decompressional melting. Consequently, some crustal N is recycled to the mantle. [Copyright &y& Elsevier]

Phlogopite lamproites occur in the Inner Arc Tectono-Magmatic Domain of the Eastern Altiplano (southern Peru, Andean Cordillera), a geotectonic setting characterizing lamproites at destructive plate margins. One sample free from contamination by crustal felsic melts displays many diagnostic features of «Mediterranean» lamproites as regards mineral assemblages and the bulk-rock composition [56.6 wt.% SiO2, 12.9 wt.% Al2O3, K2O/Al2O3<0.8, MgO<8 wt.%, CaO<3.5 wt.%, very strong LILE enrichment (La/YbN=27) and Sr, Nb, Ta and Ti negative anomalies (Sr/NdN=0.49, La/NbN=0.38)]. In thin sections, the rock shows a volumetrically dominant fluidal groundmass (82 vol.%) enclosing 1–3 mm olivine-rich polycrystalline aggregates [Mg–Ni-rich olivine, (88

The Prairie Creek lamproite is the largest of seven ultramafic vents that make up the Prairie Creek lamproite province. Diamonds were first discovered in 1906, and commercial mining continued intermittently until about 1931. The evaluation program undertaken by the Arkansas State Parks Commission in the 1990s resulted in the mapping and evaluation of four major vent facies rock types: olivine lamproite, epiclastic sediments, phlogopite-rich tuff and olivine-rich tuff. Significant diamond contents were found only within the phlogopite-rich tuff (∼0.11 carat/100 tonnes) and olivine-rich tuff (∼1.1 carats/100 tonnes).Stratigraphic relationships indicate that the diamondiferous tuffs have undergone <50 m of erosion. Extrapolation of the surface rock units and their diamond contents to the pre-erosion surface suggests that ∼93,000 carats of diamonds were liberated and then concentrated as a natural surface enrichment. Early commercial production focused on the natural surface concentrations, an assumption supported by historic mining records. Historical grades suggest that ∼58,000 carats were contained in these surface deposits, about half of those diamonds being recovered during commercial operation. These relationships suggest that ∼35,000 carats remain as eluvial and alluvial deposits adjacent to the existing tourist area. This erosion model minimizes the prospects for either primary or alluvial commercial mining; however, it does validate early historic mining records and suggests areas for further tourist development within existing park boundaries. [Copyright &y& Elsevier]

Provides information on a study that investigated the implications of Kjakebeinet lamproite dykes dated at 159 Ma in Dronning Maud Land, Antarcitca for Gondwana breakup processes. Samples and methods used; Results and discussion; Conclusions.

Kokchetav ‘lamproite’ occurs in the east end of Kokchetav massif and consists of phenocryst (mainly clinopyroxene) and matrix (mainly feldspar). The compositions of clinopyroxene, magnetite and biotite phenocryst were determined using wavelength dispersive spectrometry on a JEOL Super-probe 8900 electron microprobe for the purpose of revealing the process of magma evolution. Analyses revealed a core–rim variation, which is consistent with three stages of magmatic evolution: Mg-rich clinopyroxene cores (diopside) and biotite cores (phlogopite) crystallized in a deep magma chamber (stage I); Fe-rich clinopyroxene rim (salite) and biotite rim crystallized at low pressure in a shallow magma chamber (stage II); Magnetite phenocryst core also crystallized in a shallow magma chamber, and co-exists with Fe-rich clinopyroxene rim and biotite rim. The magnetite rims probably formed during magma eruption at the same time when groundmass crystallized (stage III). The calculated temperatures for ilmenite–magnetite pair range from 679 to 887°C, log fO2 values range from −11.1 to −14.9 log units. These values represent the latest conditions of magma as ilmenite exsolution in magnetite probably occurred during magma eruption from the shallow chamber to surface. [Copyright &y& Elsevier]

Petrogenetic models for the origin of lamproites are evaluated using new major element, trace element, and Sr, Nd, and Pb isotope data for Holocene lamproites from the Gaussberg volcano in the East Antarctic Shield. Gaussberg lamproites exhibit very unusual Pb isotope compositions (206Pb/204Pb = 17·44–17·55 and 207Pb/204Pb = 15·56–15·63), which in common Pb isotope space plot above mantle evolution lines and to the left of the meteorite isochron. Combined with very unradiogenic Nd, such compositions are shown to be inconsistent with an origin by melting of sub-continental lithospheric mantle. Instead, a model is proposed in which late Archaean continent-derived sediment is subducted as K-hollandite and other ultra-high-pressure phases and sequestered in the Transition Zone (or lower mantle) where it is effectively isolated for 2–3 Gyr. The high 207Pb/204Pb ratio is thus inherited from ancient continent-derived sediment, and the relatively low 206Pb/204Pb ratio is the result of a single stage of U/Pb fractionation by subduction-related U loss during slab dehydration. Sr and Nd isotope ratios, and trace element characteristics (e.g. Nb/Ta ratios) are consistent with sediment subduction and dehydration-related fractionation. Similar models that use variable time of isolation of subducted sediment can be derived for all lamproites. Our interpretation of lamproite sources has important implications for ocean island basalt petrogenesis as well as the preservation of geochemically anomalous reservoirs in the mantle. [ABSTRACT FROM PUBLISHER]

Focuses on the emplacement ages of lamproites in the Guinzhou Province in China. Influence of the whole-rock Sm-Nd and Rb-Sr isochron methods in constraining the lamproites; Occurrence of intrusive activities of lamproites in the region; Emplacement of the upwelling of hot materials derived from the deep mantle from the Late Cambrian to the Early Ordovician.

Presents a study on mineral haggertyite, which belongs to the magnetoplumbite family and occurs in the Prairie Creek, Arkansas. Description of the lamproite and its xenoliths; Compositions of minerals in the Prairie Creek lamproite; Petrogenesis of haggertyite; Origin of the xenoliths.

Dynamic metasomatism experiments were performed by reacting a lamproite melt with garnet peridotite by drawing melt through the peridotite into a vitreous carbon melt trap, ensuring the flow of melt through the peridotite and facilitating analysis of the melt. Pressure (2–3 GPa) and temperature (1050–1125 °C) conditions were chosen where the lamproite was molten but the peridotite was not. Phlogopite was formed and garnet and orthopyroxene reacted out, resulting in phlogopite wehrlite (2 GPa) and phlogopite harzburgite (3 GPa). Phlogopites in the peridotite have higher Mg/(Mg + Fe) and Cr2O3 and lower TiO2 than in the lamproite due to buffering by peridotite minerals, with Cr2O3 from the elimination of garnet. Compositional trends in phlogopites in the peridotite are similar to those in natural garnet peridotite xenoliths in kimberlites. Changes in melt composition resulting from the reaction show decreased TiO2 and increased Cr2O3 and Mg/(Mg + Fe). The loss of phlogopite components during migration through the peridotite results in low K2O/Na2O and K/Al in melts, indicating that chemical characteristics of lamproites are lost through reaction with peridotite so that emerging melts would be less extreme in composition. This indicates that lamproites are unlikely to be derived from a source rich in peridotite, and more likely originate in a source dominated by phlogopite-rich hydrous pyroxenites. Phlogopites from an experiment in which lamproite and peridotite were intimately mixed before the experiment did not produce the same phlogopite compositions, showing that care must be taken in the design of reaction experiments. [ABSTRACT FROM AUTHOR]

Chrome-pyrope garnet is a minor but widespread phase in ultramafic rocks of the continental lithosphere; its complex chemistry preserves a record of events related to fluid movements in the mantle, including melt extraction and metasomatism. We have examined the major-element and trace-element composition of >12 600 Cr-pyrope (Cr2O3 > 1 wt %) xenocrysts in volcanic rocks to evaluate their compositional ranges and interelement relationships. Samples have been divided into three major groups (Archon, >= 2·5 Ga; Proton, 2·5-1 Ga; Tecton, <1 Ga) depending on the age of the last major tectonothermal event in the crust penetrated by the host volcanic rock. Relative depths of garnets within each sample have been determined by measurement of Nickel Temperature (TNi). Mn, Ni and Zn contents of Cr-pyrope garnets are controlled by T-dependent partitioning between garnet and mantle olivine. The expected correlation of mg-number with T is largely masked by effects of bulk composition and crystal chemistry. The Cr content of garnet is a primary indicator of the degree of depletion of the host rock; Fe, Y, Ti and Ga show negative correlations with Cr, suggesting that all have been removed as part of the primary depletion process. In garnets with TNi < 1200°C, the average degree of depletion as measured by these elements decreases from Archon to Proton to Tecton. High-temperature metasomatism, reflecting the introduction of asthenospheric melts, produces strong positive correlations between Fe, Zr, Ti, Y and Ga, and leads to `refertilization' of previously depleted rocks. The prominent Ca-Cr correlation (`lherzolite trend') seen in garnets from clinopyroxene-bearing rocks is controlled primarily by the Cr/Al of the host rock, and Ca shows a strong negative association with Mg. The position and slope of the lherzolite trend vary with temperature and tectonic setting, suggesting that the P/T ratio exerts a control on Ca/Cr in lherzolite garnets. Garnets with less Ca than the lherzolite trend (`subcalcic garnets') are largely confined to Archon suites, where they typically are concentrated in the 130-180 km depth range. The few subcalcic garnets from Proton suites typically are lower in Cr and occur at shallower depths (100-120 km). Subcalcic garnets are absent in Tecton suites analysed in this work. The complexity of the geochemical relationships illustrated here, and their variation with temperature and tectonic setting, suggests that it is possible to define meaningful compositional populations of garnets, which can be used to map the stratigraphy and structure of the lithospheric mantle. [ABSTRACT FROM PUBLISHER]

Liquidus to near-solidus phase relations between 0.8 ad 12.0 GPa and 900 and 1200°C were determined for an SiO2-rich lamproite from Smoky Butte, Montana. At 7–10 GPa, assemblages between liquidus and solidus are clinopyroxene+garnet, garnet+clinopyroxene+coesite, garnet+clinopyroxene+coesite+rutile+K–Ti silicate, and garnet+clinopyroxene+K–Ti silicate+phlogopite+coesite+rutile. At 12 GPa, comparable assemblages are garnet, garnet+clinopyroxene+coesite, and garnet+clinopyroxene+K silicate+coesite+rutile. At 6–12 GPa, K–Ti silicates and K–Ba phosphate compounds occur between 1200 and 1400°C. At 12 GPa, K silicate replaces the K–Ti silicate compound present at lower pressures. At >6 GPa, clinopyroxene and garnet incorporate K in their structures, particularly at lower temperatures. Near-liquidus phase relations of the Smoky Butte lamproite are compared with those of previously investigated lamproite of a similar composition. It is considered unlikely that near-liquidus garnetite mineral assemblages at 7–12 GPa could reflect the source of these magmas. A more likely source for these SiO2-rich lamproitic magmas is an assemblage comparable with the near-solidus assemblage of garnet+clinopyroxene+phlogopite and minor K-, Ti-, Ba-enriched compounds. On partial melting such an assemblage would yield a composition comparable with that of the SiO2-rich magma from Smoky Butte. SiO2-rich lamproite magmas may be primary melts from an enriched source from deep in the lithospheric mantle. [ABSTRACT FROM AUTHOR]

Provides information on a study which uncovered a new titanate mineral, haggertyite, from the Prairie Creek lamproite in Arkansas. Description of the mineral; Overview of the geologic setting; Physical and optical properties of haggertyite.

Studies the formation of sanidine crystals from lamproitic magmas of the Leucite Hills in Wyoming. Experimental procedure; Geologic setting background; Paragenesis; Electron diffraction patterns; Crystallization trends; Origin of Fe-rich sanidine.

It is known that the lamproites occur in the southeastern Guizhou Province and in the Dahong Mountains area, Hubei Province; and many para-lamproite occurrences spread in the west half part of the South China landmass. The para-larnproite diatremes in Ningxiang County, Hunan Province, contain a few of fine grains of diamond. Parts of the kimberlite pipes and dykes in Mengyin County, Shandong Province, consist locally of basic kimberlite; and the kimberlite dykes in the Maping kimberlite area, Zhenyuan County, Guizhou Province, consist of basic kimberlite principally. Although the diamondiferous kimberlites and lamproites occur always in the cratons within continental plate, both the potassium-rich ultramafic rocks display the geochemical features of the magmatism of post-collision in orogenic belt. Both the kimberlite and lamproite magmas may originate from the local parts of the mantle transition zone, where the mantle contains the matter of ancestor slab of ancient subduction zone. And, both the K-rich ultramafic magmas generated in an active mantle plume, which came from the boundary between the core and the lower mantle. The basic kimberlite magma may be more capable of preserving the crystals of the diamond type 11. [ABSTRACT FROM AUTHOR]

Variscan orogenic lamproites in the Bohemian Massif predominantly occur as 1 to 2 m wide and petrographically uniform dykes along the eastern borders of the Moldanubian and Saxo-Thuringian zones. Variscan orogenic lamproites were derived by preferential melting of subduction-related olivine-free metasomatic vein assemblages stabilised in the lithospheric mantle. These lamproitic melts may subsequently undergo extensive differentiation. In this study, we present the first combined petrographic and Sr–Nd–Pb–Li isotope characteristics of a complex lamproite exposed at ca 100 m long profile near Horní Rokytnice (Czech Republic) in the Saxo-Thuringian Zone. This lamproite is characterised by the primary mineral assemblage of K-amphibole + K-feldspar ± aegirine and quartz that petrographically varies from relatively primitive (fine-grained, mafic) to more differentiated (medium- to coarse-grained, felsic) pegmatitic lamproite domains. These domains may represent the product of crystallisation of immiscible liquids that had separated from the mafic melt. The primitive lamproite zone is characterised by the typomorphic minerals – baotite, benitoite, and henrymeyerite. The more differentiated pegmatitic domains are free of aegirine and show replacement of primary red-luminescent (Fe3+-rich) K-feldspar by blue-luminescent (Fe-poor) K-feldspar. Residual fluids rich in Ca, Ti, and HFSE in combination with the decreasing peralkalinity of the lamproite system resulted in the local formation of secondary zircon, titanite and quartz at the expense of the primary Ti–Ba–Zr–K lamproitic mineral assemblages. Lamproites from the Moldanubian and Saxo-Thuringian zones fall on separate mixing trends in the 87Sr/86Sr (t) - εNd (t) diagram, which indicates that the mantle beneath these two zones had been metasomatised by different crustal material. The scatter in the peralkalinity index vs. δ7Li diagram indicates that the Li isotope composition is not controlled by mixing of two end members metasome and ambient depleted mantle alone, but may also be affected by late-stage magmatic and hydrothermal processes. The compositionally zoned Horní Rokytnice dyke is special as the petrographically different types show a variation of about 4 δ-units in δ7Li due to dyke-internal processes, such as fractionation, which increases δ7Li in late-stage lamproitic melts, and post-emplacement interaction with fluids that reduced δ7Li in samples that have lost Li. Post-emplacement alteration also led to the disturbance in the Pb isotope systematics of the differentiated orogenic lamproite as indicated by variable over-correction of in situ radiogenic Pb ingrowth. Unlabelled Image • Recently recognised Variscan lamproite in the Saxo-Thuringian Zone • Primary mineral assemblage of K-amphibole + K-feldspar ± aegirine and quartz • Dyke-internal processes increases δ7Li in late-stage lamproitic melts • Post-emplacement interaction with fluids reduces δ7Li in samples that have lost Li [ABSTRACT FROM AUTHOR]

We report the first occurrence of magmatic haggertyite (BaFe6Ti5MgO19) from the Miocene lamproites of the West Kimberley region of Western Australia. This contrasts with the metasomatic formation reported in an olivine lamproite host at the type locality, Prairie Creek, Arkansas. Haggertyite occurs in the groundmass of a diamondiferous olivine lamproite pipe in the Ellendale field, and within the large zoned Walgidee Hills lamproite where it forms part of an extensive suite of Ba- and K-bearing titanate and Ti-rich silicate minerals. The haggertyite co-exists with chromian spinel, perovskite, and ilmenite in the Ellendale lamproite, and with priderite and perovskite and, in one locality, with priderite, jeppeite, ilmenite, and perovskite, in the Walgidee Hills lamproite. Unlike priderite and perovskite, which are common groundmass phases in the Ellendale olivine lamproites and present throughout the Walgidee Hills lamproite, haggertyite appears restricted in its occurrence and crystallization interval, with sparse ilmenite apparently mostly crystallizing as an alternative phase. In the Walgidee Hills lamproite the haggertyite-bearing assemblage is succeeded by the Ba-titanate assemblage priderite plus jeppeite in the evolved central part of the body. The haggertyite in the main zone of the Walgidee Hills lamproite has an average composition of (Ba0.7K0.3)1.0(Ti5.0Fe3+2.1Cr0.1Fe2+ 3.8Mn0.2Mg0.6Na0.1)12O19 and is thus very similar to the original haggertyite described from xenoliths in the Prairie Creek lamproite apart from being poorer in Cr and Ni. Haggertyite in the groundmass of the Ellendale olivine lamproite and the central zone of the Walgidee Hills lamproite, in addition to variations in Mg and Cr, show significant variation in Ti and Fe contents and in calculated Fe3+ and Fe2+. A linear inverse relationship between Ti and Fe, and Ti and Fe3+, indicates that Fe3+ is accommodated by the coupled substitution Ti4+ + Fe2+ D 2 Fe3+. A marked trend to higher Fe3+ in the haggertyite in Ellendale 9 olivine lamproite is ascribed to increasing oxidation during crystallization, with fO2 estimated from the olivine-spinel thermometer and oxygen barometer at Dlog FMQ = -1 to +3 at temperatures of 790-660 °C. The haggertyite in the central zone of the Walgidee Hills lamproite, in contrast, shows a marked trend to Fe2+ enrichment, which is associated with decreasing Fe in perovskite. This is inferred to indicate formation under more reducing conditions, but sufficiently oxidized to permit Fe3+ in co-existing priderite and jeppeite. Trace-element analysis by LA-ICP-MS shows the Walgidee Hills haggertyite contains minor amounts of Na, Si, Ca, V, Co, Zn, Sr, Zr, Nb, and Pb, and only traces of Al, P, Sc, Rb, REE, Hf, and Ta. Moreover, the haggertyite is preferentially enriched in certain lithophile (Ba, Sr), siderophile (Mn, Fe, Co, Ni), and chalcophile (Zn, Pb) elements relative to co-existing priderite. Haggertyite crystallization appears to be a consequence not only of the very high Ba, Ti, and K contents of the lamproite, but of relatively high-Fe concentrations and low temperatures in evolved olivine lamproite magma with the Fe3+/Fe2+ ratio determined by the prevailing fO2. The new data suggest that haggertyite might also be present but previously unrecognized in the evolved groundmass of other olivine lamproites. Haggertyite is one of an increasing number of new minerals in upper mantle rocks and volcanics derived from the upper mantle hosting large-ion-lithophile and high field strength cations. [ABSTRACT FROM AUTHOR]

A suite of potassium‐bearing minerals from the Walgidee Hills lamproite intrusion in the Kimberley region of Western Australia was selected for 39Ar/40Ar dating. These included wadeite, jeppeite, priderite, potassium richterite, and phlogopite. All recorded excellent plateau ages, with the mean age of the combined data set being 17.3±0.3 Ma. Phlogopite recorded the largest uncertainty, whereas, of the other minerals, wadeite gave the best precision. Although rare to absent in common magmatic rocks, these minerals are widely distributed in alkaline complexes and in lamproite, kimberlite and orangeite intrusions. The results indicate this suite of minerals is excellent for 39Ar/40Ar dating and that they can be used singly or in combination to obtain the precise magmatic crystallization ages of ultra‐alkaline rocks. Because of the stability of potassium richterite at mantle depths, 39Ar/40Ar dating of MARID (mica‐amphibole‐rutile‐ilmenite‐diopside) xenoliths should be a more widely‐applied technique to investigating mantle geodynamics. [ABSTRACT FROM AUTHOR]

Diamondiferous rock types worldwide are broadly divided into kimberlite and lamproite, the latter of which have unique characteristics in different regions and include carbonate-rich varieties (formerly orangeites/Group II kimberlites). Diamondiferous rocks in West Africa are typically micaceous and share petrographic, mineralogical, and geochemical characteristics with both kimberlites and lamproites. To further constrain the classification and petrogenesis of diamondiferous rocks worldwide and their variability between different cratonic regions, in this study we combine detailed petrographic observations with olivine, phlogopite, and spinel chemistry for hypabyssal samples from the Jurassic Tongo dike (Sierra Leone) and the Neoproterozoic Weasua cluster (Liberia). The Tongo dike contains macrocrysts of olivine and phlogopite in a groundmass of olivine, abundant phlogopite, spinel, perovskite, and apatite with a base of calcite, dolomite, and lesser serpentine. The phlogopite is characterised by concurrent FeO and Al 2 O 3 enrichment, which is typical of kimberlites and unlike lamproites. These features and the kimberlite-like spinel compositions allow us to classify the Tongo samples as micaceous kimberlites. The Weasua rocks comprise macrocrysts of olivine in a groundmass of olivine, phlogopite, diopside (zoned towards aegirine-rich rims), spinel, perovskite, and apatite with a base of serpentine and less common calcite. The composition of Weasua phlogopite trends to significant FeO enrichment and Al 2 O 3 depletion, i.e. towards tetraferriphlogopite. The enrichment in mica, phlogopite chemistry and presence of magmatic diopside indicates that these rocks are olivine lamproites. The populations of olivine macrocrysts and microcrysts at Tongo and Weasua are similar and characterised by distinct core and rim zones. Two distinct olivine core populations are observed. 1) forsterite-rich (Fo > 90) olivine interpreted to reflect xenocrysts from typical mantle peridotites. Al-in-olivine thermometry suggests that these cores have P-T equilibration within diamond stability at Weasua and Tongo. 2) Al-, Ca- and Na- rich cores with P-T formation conditions extending beyond the mantle adiabat. These cores are interpreted to reflect metasomatic and thermal perturbation linked with the infiltration of kimberlite/lamproite melts in the deep lithosphere shortly before entrainment in the ascending magma. The olivine rims at Tongo and Weasua show limited variations in Fo contents at similar values of 88.9 ± 0.8 for Tongo and 89.6 ± 1.2 for Weasua, as well as similar minor and trace element concentrations. Thus, whereas the Tongo and Weasua rock types are classified as kimberlite and olivine lamproite, respectively, the olivine chemistry suggests a similar petrogenetic evolution. • Here we classify unusual transitional kimberlite-lamproites from West Africa. • Tongo rocks are micaceous transitional kimberlites. • Weasua rocks are diopside-bearing olivine lamproites. • West African diamondiferous rocks defy clear classification. • Olivine chemistry indicates similar petrogenesis both localities. [ABSTRACT FROM AUTHOR]

Mesozoic (125–135 Ma) cratonic low-Ti lamproites from the northern part of the Aldan Shield do not conform to typical classification schemes of ultrapotassic anorogenic rocks. Here we investigate their origins by analyzing olivine and olivine-hosted inclusions from the Ryabinoviy pipe, a well preserved lamproite intrusion within the Aldan Shield. Four types of olivine are identified: (1) zoned phenocrysts, (2) high-Mg, high-Ni homogeneous macrocrysts, (3) high-Ca and low-Ni olivine and (4) mantle xenocrysts. Olivine compositions are comparable to those from the Mediterranean Belt lamproites (Olivine-1 and -2), kamafugites (Olivine-3) and leucitites. Homogenized melt inclusions (MIs) within olivine-1 phenocrysts have lamproitic compositions and are similar to the host rocks, whereas kamafugite-like compositions are obtained for melt inclusions within olivine-3. Estimates of redox conditions indicate that "lamproitic" olivine crystallized from anomalously oxidized magma (∆NNO +3 to +4 log units.). Crystallization of "kamafugitic" olivine occurred under even more oxidized conditions, supported by low V/Sc ratios. We consider high-Ca olivine (3) to be a fingerprint of kamafugite-like magmatism, which also occurred during the Mesozoic and slightly preceded lamproitic magmatism. Our preliminary genetic model suggests that low-temperature, extension-triggered melting of mica- and carbonate-rich veined subcontitental lithospheric mantle (SCLM) generated the kamafugite-like melts. This process exhausted carbonate and affected the silicate assemblage of the veins. Subsequent and more extensive melting of the modified SCLM produced volumetrically larger lamproitic magmas. This newly recognized kamafugitic "fingerprint" further highlights similarities between the Aldan Shield potassic province and the Mediterranean Belt, and provides evidence of an overlap between "orogenic" and "anorogenic" varieties of low-Ti potassic magmatism. Moreover, our study also demonstrates that recycled subduction components are not an essential factor in the petrogenesis of low-Ti lamproites, kamafugites and leucitites. [ABSTRACT FROM AUTHOR]

The article discusses uranium-thorium-lead dating of accessary minerals for Kimberlite and Lamproite. It mentions that Kimberlite and lamproite are potassic ultramafic rocks originating from the deep lithospheric mantle. It mentions that the rocks are necessary for finding the composition and structure of the lithosphere.

The article focuses on a study for understanding of the evolution of southern Laurentia, the relationship between the Prairie Creek granite xenoliths and the deep structure of the Ouachita orogen. It mentions that ages for zircons in granite xenoliths that were extracted from the Prairie Creek lamproite, a volcanic pipe in southwestern Arkansas.