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The Mad Gap Yards ultramafic lamprophyre (UML) dykes in the East Kimberley region of northern Western Australia form part of a widespread Neoproterozoic (~ 842-800 Ma) alkaline mafic-ultramafic magmatic province in the north, east and central regions of the Kimberley Craton of Western Australia. The NE-trending Mad Gap Yards dykes lie at the southeastern margin of the Kimberley Basin adjacent to the Greenvale Fault and intrude the Paleoproterozoic Elgee Siltstone. The dykes are classified as alnöite, and contain abundant macrocrystic olivine in a groundmass of phlogopite, perovskite, spinels, diopside, apatite, andradite-hydroandradite, serpentine, calcite, pseudomorphs after melilite and rare gittinsite. Mantle-derived olivine macrocrysts have compositions in the range Mg#.sub.91-92, similar to moderately refractory peridotite from other parts of the Kimberley Craton, whereas magmatic olivine phenocrysts have Mg#.sub.88-90. Olivine and chromian spinel were the earliest phenocrysts; they record equilibration temperatures of ~ 1030-920â under moderately reducing conditions with fO.sub.2 values below the fayalite-magnetite-quartz (FMQ) oxygen buffer ([DELTA] FMQ = mostly - 0.8 to - 1.7 log units). Magnetite rims and groundmass grains crystallised at ~ 850-740â under more oxidising conditions with [DELTA] FMQ ~ + 0.6 to - 0.75 log units. Perovskite is well preserved in parts of the dykes and indicates crystallisation inside this fO.sub.2 range. The perovskite yielded a SHRIMP .sup.206Pb/.sup.238U age of 842 ± 8 Ma. The Mad Gap Yards dykes carry rare partially altered spinel-peridotite xenoliths containing olivine (Mg#.sub.86.3-90), Cr-diopside, enstatite and Al-Cr spinel, and well as mantle xenocrysts of Cr-Al spinel and Cr-diopside. Bulk rock trace-element geochemistry, Cr-diopside thermobarometry and Sr-Nd-isotopic compositions of perovskite suggest that the UML magma was derived from partial melting of a garnet-bearing asthenospheric mantle source at ~ 200 km depth. Nd depleted-mantle model ages (T.sub.DM) for perovskite range from 1106-865 Ma and broadly correlate with regional mantle metasomatism during the Yampi Orogeny (~ 1000-800 Ma). Rare evidence of mantle metasomatism by LILE and HFSE-enriched melts has been found in the form of priderite and loveringite replacing Mg-rich ilmenite in an olivine macrocryst. The timing of emplacement of the Mad Gap Yards UML dykes at ~ 842 Ma correlates with the early stages of the breakup of Rodinia., Author(s): Peter J. Downes [sup.1], A. Lynton Jaques [sup.2], Cristina Talavera [sup.3] [sup.4], William L. Griffin [sup.5], Sarah E. M. Gain [sup.5], Noreen J. Evans [sup.3], Wayne R. Taylor [sup.6], [...]

A suite of mantle-derived xenoliths and xenocrysts in Cretaceous volcanic rocks from Mount Carmel, North Israel has been investigated to establish the regional paleo-geotherm and constrain the evolution of the lower crust and lithospheric mantle. Garnet pyroxenite xenoliths can be subdivided into low-MgO (MgO 15%) types. The low-MgO garnet websterites, with high equilibration pressures and temperatures (P = 20-23 kb, T = 1143-1192 â) and convex-upward REE patterns, are inferred to be cumulates from partial melts derived from a sub-lithospheric, fossilized plume head that impinged on the pre-existing lithospheric base during the early Mesozoic. In contrast, high-MgO pyroxenites, with lower T estimates, P defined by extrapolation to the inferred geotherm (1012-1046 â and ~ 14-15 kb) and mantle-like geochemical compositions, are deduced to represent cumulates from mafic magmas extracted from asthenospheric peridotitic mantle during late Proterozoic continental crustal growth in the region. Granulite xenoliths are mainly plagioclase-rich and equilibrated at depths of ~ 18-34 km. They have lower MgO contents but trace-element patterns similar to those of the low-MgO garnet pyroxenites, and probably originated as cogenetic crystallized melts and cumulates intruded around the Moho. U-Pb dating of apatite indicates ages around ~ 250 Ma, consistent with major magmatism dated by zircon xenocrysts. The lithospheric mantle has a two-layered structure, comprising a shallow (and relatively ancient) layer dominated by spinel peridotite and high-MgO garnet pyroxenites, and a deeper layer with fertile garnet-bearing peridotites intercalated with the low-MgO garnet pyroxenites., Author(s): Jiang-Gu Lu [sup.1] [sup.2], William L. Griffin [sup.2], Jin-Xiang Huang [sup.2], Hong-Kun Dai [sup.2] [sup.3], Montgarri Castillo-Oliver [sup.2], Suzanne Y. O'Reilly [sup.2] Author Affiliations: (1) grid.473484.8, 0000 0004 1760 [...]

We present a new dataset on the composition of high-density fluids (HDFs) in cloudy (n = 25), coated (n = 10) and cuboid (n = 10) diamonds from the Nyurbinskaya kimberlite pipe. These diamonds represent different populations each showing distinct growth histories. The cores of coated diamonds display multiple growth stages and contrasting sources of carbon. Fibrous coats and cuboid diamonds have similar carbon isotopes and nitrogen systematics, suggesting their formation in the last metasomatic events related to kimberlite magmatism, as is common for most such diamonds worldwide. The HDFs in most of these diamonds span a wide range from low-Mg carbonatitic to hydrous silicic compositions. The major- and trace-element variations suggest that the sources for such HDFs range in composition between the depleted mantle and more fertile mantle reservoirs. Hydrous-silicic HDFs could originate from a .sup.13C-enriched source, which originates through subduction of crustal metasedimentary material. Percolation of such HDFs through carbonated eclogites and peridotites facilitates the formation of cuboid diamonds and fibrous coats in the mantle section beneath the corresponding area of the Siberian craton. Cloudy diamonds represent an apparently older population, reflecting continuous diamond formation predominantly from high-Mg carbonatitic HDFs that caused discrete episodes of diamond precipitation. Their high Mg# and enrichment in incompatible elements support a metasomatized peridotitic source for these HDFs., Author(s): Dmitry A. Zedgenizov [sup.1] [sup.2], Sergei Yu. Skuzovatov [sup.2] [sup.3], William L. Griffin [sup.4], Bogdan S. Pomazansky [sup.5], Alexey L. Ragozin [sup.1] [sup.2], Viktoria V. Kalinina [sup.1] [sup.2] Author [...]

Primary carbonates in kimberlites are the main CO.sub.2 carriers in kimberlites and thus can be used to constrain the original carbon and oxygen-isotope composition of kimberlite melts and their deep mantle sources. However, the contribution of syn- and post-emplacement processes to the modification of the C-O-isotope composition of kimberlites is yet to be fully constrained. This study aims to shed new light on this topic through a detailed textural, compositional (major and trace elements), and in situ C-O-Sr isotopic characterisation of carbonates in the Benfontein kimberlite sills (Kimberley, South Africa). Our multi-technique approach not only reveals the petrographic and geochemical complexity of carbonates in kimberlites in unprecedented detail, but also allows identification of the processes that led to their formation, including: (1) magmatic crystallisation of Sr-rich calcite laths and groundmass; (2) crystallisation of late groundmass calcite from hydrothermal fluids; and (3) variable degrees of crustal contamination in carbonate-rich diapirs and secondary veins. These diapirs most likely resulted from a residual C-O-H fluid or carbonate melt with contributions from methane-rich fluids from the Dwyka shale wall rock, leading to higher .sup.87Sr/.sup.86Sr and [delta].sup.18O, but lower [delta].sup.13C values than in pristine magmatic calcite. Before coalescing into the diapiric segregations, these fluids/melts also variably entrained early formed calcite laths and groundmass phases. Comparison between in situ and bulk-carbonate analyses confirms that O isotopic analyses of bulk carbonates from kimberlite rocks are not representative of the original isotopic signature of the kimberlite magma, whereas bulk C-isotope compositions are similar to those of the pristine magmatic carbonates. Calcite laths and most groundmass grains at Benfontein preserve isotopic values ([delta].sup.18O = 6-8â° and [delta].sup.13C = - 4 to - 6â°), similar to those of unaltered carbonatites worldwide, which, therefore, probably correspond to those of their parental melts. This narrow range suggests kimberlite derivation from a mantle source with little contribution from recycled crustal material unless the recycled material had isotopic composition indistinguishable from typical mantle values., Author(s): Montgarri Castillo-Oliver [sup.1] [sup.4], Andrea Giuliani [sup.1] [sup.2] [sup.3], William L. Griffin [sup.1], Suzanne Y. O'Reilly [sup.1], Russell N. Drysdale [sup.4] [sup.5], Adam Abersteiner [sup.6] [sup.7], Emilie Thomassot [sup.3] [...]

The Loma Baya complex in south-western Mexico is a volume of chromitite-bearing oceanic mantle that records a complex metamorphic history, defined by a first stage of hydrous metamorphism overprinted by a short-lived thermal event associated with an Eocene granite intrusion. During the hydrous metamorphism, the primary magmatic chromite-olivine assemblage was replaced by a secondary, porous intergrowth of Fe.sup.2+-rich chromite and chlorite. The heat supplied by an Eocene-age granite intrusion reversed the hydration reaction, producing chromite rims with perfectly developed crystal faces. This third-generation chromite is in equilibrium with highly magnesian (neoformed) olivine and defines a chemical trend analogous to the original magmatic one. The preservation of both reactions in the Loma Baya chromitite provides compelling evidence that the hydration of chromite can be reversed by either prograde metamorphism or any heating event, confirming previous thermodynamic predictions. Understanding these complex features is of particular interest due to the fact that changes in temperature and variable degrees of fluid/rock interaction during metamorphism and intrusion have also significantly affected the chromite-hosted IPGE carrier phases. Here, we propose that the metamorphic fluids involved in the hydrous metamorphism have caused the desulphurization of laurite RuS.sub.2, releasing minute particles of Ru-Os-Ir alloys Electronic supplementary material The online version of this article (doi:10.1007/s00410-015-1169-9) contains supplementary material, which is available to authorized users., Author(s): Jose M. Gonzalez-Jimenez[sup.1] [sup.2 ] , Martin Reich[sup.1] , Antoni Camprubi[sup.3] , Fernando Gervilla[sup.4] , William L. Griffin[sup.2] , Vanessa Colas[sup.5] , Suzanne Y. O'Reilly[sup.2] , Joaquin A. Proenza[sup.6] [...]

The 3.1 Ga Nuggihalli greenstone belt in the Western Dharwar craton is comprised of chromitite-bearing sill-like ultramafic-mafic rocks that are surrounded by metavolcanic schists (compositionally komatiitic to komatiitic basalts) and a suite of tonalite-trondhjemite-granodiorite gneissic rocks. The sill-like plutonic unit consists of a succession of serpentinite (after dunite)-peridotite-pyroxenite and gabbro with bands of titaniferous magnetite ore. The chromitite ore-bodies (length [almost equal to]30-500 m; width [almost equal to]2-15 m) are hosted by the serpentinite-peridotite unit. Unaltered chromites from massive chromitites (>80 % modal chromite) of the Byrapur and Bhaktarhalli chromite mines in the greenstone belt are characterized by high Cr# (100Cr/(Cr + Al)) of 78-86 and moderate Mg# (100 Mg/(Mg + Fe.sup.2+)) of 45-55. In situ trace-element analysis (LA-ICPMS) of unaltered chromites indicates that the parental magma of the chromitite ore-bodies was a komatiite lacking nickel-sulfide mineralization. In the Ga/Fe.sup.3+# versus Ti/Fe.sup.3+# diagram, the Byrapur chromites plot in the field of suprasubduction zone (SSZ) chromites while those from Bhaktarhalli lie in the MOR field. The above results corroborate our previous results based on major-element characteristics of the chromites, where the calculated parental melt of the Byrapur chromites was komatiitic to komatiitic basalt, and the Bhaktarhalli chromite was derived from Archean high-Mg basalt. The major-element chromite data hinted at the possibility of a SSZ environment existing in the Archean. Altered and compositionally zoned chromite grains in our study show a decrease in Ga, V, Co, Zn, Mn and enrichments of Ni and Ti in the ferritchromit rims. Trace-element heterogeneity in the altered chromites is attributed to serpentinization. The trace-element patterns of magnetite from the massive magnetite bands in the greenstone belt are similar to those from magmatic Fe-Ti-V-rich magnetite bands in layered intrusions, and magnetites from andesitic melts, suggesting that magnetite crystallized from an evolved gabbroic melt. Enrichments of Ni, Co, Te, As and Bi in disseminated millerite and niccolite occurring within chromitites, and in disseminated bravoite within magnetites, reflect element mobility during serpentinization. Monosulfide solid solution inclusions within pyroxenes (altered to actinolite) in pyroxenite, and interstitial pyrites and chalcopyrites in magnetite, retain primary characteristics except for Fe-enrichment in chalcopyrite, probably due to sub-solidus re-equilibration with magnetite. Disseminated sulfides are depleted in platinum-group elements (PGE) due to late sulfide saturation and the PGE-depleted nature of the mantle source of the sill-like ultramafic-mafic plutonic rocks in the Nuggihalli greenstone belt. Electronic supplementary material The online version of this article (doi:10.1007/s00410-015-1148-1) contains supplementary material, which is available to authorized users., Author(s): Ria Mukherjee[sup.1] [sup.2] , Sisir K. Mondal[sup.1] [sup.4] , Jose M. Gonzalez-Jimenez[sup.3] [sup.5] , William L. Griffin[sup.3] , Norman J. Pearson[sup.3] , Suzanne Y. O'Reilly[sup.3] Author Affiliations: (1) PGE [...]

Episodic refertilization and metasomatism of depleted subcontinental lithospheric mantle (SCLM) is rarely revealed within a single orogenic peridotite. We have investigated the Shenglikou peridotite massif in the North Qaidam Orogen (NE Tibet, China) to understand its origin and secular re-enrichment history and possible links with global tectonism, using multiple chemical and isotopic techniques. The massif contains two main groups of rocks, one rich in olivine (Ol) and the other rich in pyroxene (Pyro). In situ Re-Os isotope analyses on sulfides and previous reported whole-rock Os data show the Shenglikou peridotite massif has an Archean origin. The Ol-rich group has Mg# up to 0.923, Al.sub.2O.sub.3 contents down to 0.55 wt%, low FeO contents, whole-rock HREE ~0.01-0.1 times chondritic values and high spinel Cr# (up to 0.71). Modeling suggests that the Ol-rich peridotites are residues after ~30-40 % melt extraction at ~1600-1500 °C and [less than or equal to]5 GPa. Mineral compositions, oxygen-isotope compositions ([delta].sup.18O.sub.V-SMOW = 5.7 ± 0.1 â°) and attainment of Hf-isotope internal equilibration at ~1.5-1.4 Ga with initial ratios similar to that of depleted convective mantle indicate that the Ol-rich group was refertilized by silicate melts derived from the depleted asthenosphere at ~1.5-1.4 Ga, corresponding to one phase in the breakup of the Columbia supercontinent. On the other hand, chemical compositions and Hf-O isotopic signatures of the pyroxene-rich rocks suggest a second refertilization superimposed on the Archean lithospheric mantle at ~700 Ma, coeval with the global extension that affected Rodinia. Both groups show metasomatism by fluids, sourced from subducting slabs during the early Paleozoic convergence between the Qaidam and Qilian blocks. This study shows that the episodic refertilization and metasomatism of depleted Archean SCLM, temporally linked to supercontinental cycles, can be revealed in a single orogenic peridotite, and suggests that continental extension and convergence play an important role in the destruction of cratonic keels. Electronic supplementary material The online version of this article (doi:10.1007/s00410-015-1126-7) contains supplementary material, which is available to authorized users., Author(s): Qing Xiong[sup.1] [sup.2] , William L. Griffin[sup.2] , Jian-Ping Zheng[sup.1] , Suzanne Y. O'Reilly[sup.2] , Norman J. Pearson[sup.2] Author Affiliations: (1) State Key Laboratory of Geological Processes and Mineral [...]

Byline: Kreshimir Nenadovitch Malitch (1), Elena A. Belousova (2), William L. Griffin (2), Inna Yu Badanina (1), Norman J. Pearson (2), Sergey L. Presnyakov (1), Evgeniya V. Tuganova (1) Keywords: Zircon; U--Pb age; Trace-elements; Hf-isotopes; Mafic and ultramafic rocks; Nd-isotopes; Magmatic evolution; Kharaelakh intrusion; Siberian Craton Abstract: The ultramafic--mafic Kharaelakh intrusion in the northwestern part of the Siberian Craton (Russia) hosts major economic platinum-group-element (PGE)--Cu--Ni sulphide deposits. In situ U--Pb, REE and Hf-isotope analyses of zircon from these rocks, combined with detailed study of crystal morphology and internal structure, identify four zircon populations. U--Pb ages of these populations cover a significant time span (from 347 +- 16 to 235.7 +- 6.1 Ma) suggesting multiple magmatic events that cluster around 350 and 250 Ma, being consistent with two recognised stages of active tectonism in the development of the Siberian Craton. The oldest zircon population, however, represents previously unknown stage of magmatic activity in the Noril'sk area. Epsilon-Hf values of +2.3 to +16.3 in the analysed zircons reflect a dominant role of mantle-derived magmas and suggest that juvenile mantle material was the main source for the ultramafic--mafic Kharaelakh intrusion. A significant range in initial 176.sup.Hf/ [.sup.177]Hf values, found in zircons that cluster around 250 Ma, indicate mixing between mantle and crustal magma sources. Our findings imply that economic intrusions hosting PGE--Cu--Ni deposits of the Noril'sk area have a far more complex geological history than is commonly assumed. Author Affiliation: (1) A.P. Karpinsky Russian Geological Research Institute, Sredny pr. 74, 199106, St. Petersburg, Russia (2) Department of Earth and Planetary Sciences, GEMOC ARC National Key Centre, Macquarie University, Sydney, NSW, 2109, Australia Article History: Registration Date: 05/10/2009 Received Date: 25/12/2008 Accepted Date: 05/10/2009 Online Date: 24/10/2009 Article note: Communicated by C. Ballhaus. Electronic supplementary material The online version of this article (doi: 10.1007/s00410-009-0452-z) contains supplementary material, which is available to authorized users.

Byline: Claudio Marchesi (1,2), William L. Griffin (2), Carlos J. Garrido (3), Jean-Louis Bodinier (1), Suzanne Y. O'Reilly (2), Norman J. Pearson (2) Keywords: Subcontinental lithospheric mantle; Partial melting; Proterozoic; Re--Os isotopes; Sulfide; Ronda massif Abstract: The western part of the Ronda peridotite massif (Southern Spain) consists mainly of highly foliated spinel-peridotite tectonites and undeformed granular peridotites that are separated by a recrystallization front. The spinel tectonites are interpreted as volumes of ancient subcontinental lithospheric mantle and the granular peridotites as a portion of subcontinental lithospheric mantle that underwent partial melting and pervasive percolation of basaltic melts induced by Cenozoic asthenospheric upwelling. The Re--Os isotopic signature of sulfides from the granular domain and the recrystallization front mostly coincides with that of grains in the spinel tectonites. This indicates that the Re--Os radiometric system in sulfides was highly resistant to partial melting and percolation of melts induced by Cenozoic lithospheric thermal erosion. The Re--Os isotopic systematics of sulfides in the Ronda peridotites thus mostly conserve the geochemical memory of ancient magmatic events in the subcontinental lithospheric mantle. Os model ages record two Proterozoic melting episodes at ~1.6 to 1.8 and 1.2--1.4 Ga, respectively. The emplacement of the massif into the subcontinental lithospheric mantle probably coincided with one of these depletion events. A later metasomatic episode caused the precipitation of a new generation of sulfides at ~0.7 to 0.9 Ga. These Proterozoic Os model ages are consistent with results obtained for several mantle suites in Central/Western Europe and Northern Africa as well as with the Nd model ages of the continental crust of these regions. This suggests that the events recorded in mantle sulfides of the Ronda peridotites reflect different stages of generation of the continental crust in the ancient Gondwana supercontinent. Author Affiliation: (1) Geosciences Montpellier, UMR 5243, CC 60, CNRS-Universite Montpellier II, Place E. Bataillon, 34095, Montpellier, France (2) GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia (3) Instituto Andaluz de Ciencias de la Tierra (IACT), CSIC-Universidad de Granada, Avenida Fuentenueva s/n, 18002, Granada, Spain Article History: Registration Date: 13/07/2009 Received Date: 02/02/2009 Accepted Date: 13/07/2009 Online Date: 14/08/2009 Article note: Communicated by J. Hoefs.

Byline: Giovanna T. Sapienza (1), William L. Griffin (2), Suzanne Y. O'Reilly (2), Lauro Morten (1) Keywords: Gabbro xenoliths; In situ Sr isotopes; Sr--Nd--Hf isotope data; MARID; Hyblean Plateau Abstract: In situ trace-element and isotopic [(.sup.87]Sr/ [.sup.86]Sr) data and whole-rock Sr--Nd--Hf data on 12 gabbro xenoliths from the Hyblean Plateau (south-eastern Sicily) illustrate the complex petrogenetic evolution of this lithospheric segment. The gabbros formed by precipitation of plagioclase + clinopyroxene from a HIMU-type alkaline melt, then were cryptically metasomatized by a low-Rb, high- 87.sup.Sr/ [.sup.86]Sr fluid, and finally infiltrated by an exotic, late Fe--Ti-rich melt with 87.sup.Sr/ [.sup.86]Sr ~ 0.7055, carrying high concentrations of Sr, Rb and HFSE. The geochemical and isotopic features of both the metasomatizing fluid and the Fe--Ti-rich melt are compatible with their common derivation by the progressive melting of an amphibole--phlogopite--ilmenite metasomatic domain (MARID-type?) that probably resided within the subcontinental lithospheric mantle. Therefore, both the astenosphere and the lithosphere underneath the Hyblean Plateau contributed to the petrogenesis of the gabbros. Sm--Nd dating yields an age of 253 +- 60 Ma for the cumulitic pile, roughly coinciding with a hydrothermal event recorded by crustal zircons in the area. We suggest that the Hyblean Plateau suffered a thermal event--probably related to lithospheric thinning and upwelling and melting of the asthenosphere--in Permo-Triassic time (the opening of the Ionian Basin?). The induced perturbation in the lithosphere caused consequent melting of some previously metasomatised portions. Author Affiliation: (1) Dipartimento di Scienze della Terra e Geologico-Ambientali, Universita di Bologna, Piazza Porta San Donato 1, 40126, Bologna, Italy (2) ARC National Key Centre for Geochemical Evolution and Metallogeny of Continents, Department of Earth and Planetary Sciences, Macquarie University, Macquarie, NSW, 2109, Australia Article History: Registration Date: 28/05/2008 Received Date: 20/02/2008 Accepted Date: 28/05/2008 Online Date: 17/06/2008 Article note: Lauro Morten deceased, November 18, 2006. Communicated by J. Hoefs.

Group II (143-117 Ma) and Group I kimberlites (108-74 Ma) intrude across the southwest boundary of the Kaapvaal craton, sampling the same volume of the subcontinental lithospheric mantle (SCLM) in two time slices. Major and trace element analyses of 3699 peridotitic garnet xenocrysts were used to construct paleogeotherms for 17 kimberlite localities, and to place each garnet at its depth of origin. The Ti contents of each garnet and the calculated [X.sub.Mg] of its coexisting olivine were projected onto a southwest-northeast section across the craton boundary, and splines were used to interpolate between the virtual boreholes in each age group. The sections show that the cratonic SCLM extends at least 75 km southwest of the mapped craton boundary, suggesting a dipping contact. Marked differences between the time-slice sections show that between 117 and 108 Ma the SCLM on both sides of the craton boundary was heated and chemically refertilized by infiltrating asthenosphere-derived melts, thinning the depleted layer by ~40 km. The thermal and geochemical changes record a significant tectonothermal event that may be related to changes in the stress field associated with opening of the South Atlantic, or with mantle upwelling. Keywords: South Africa, lithosphere evolution, lithosphere structure, mantle xenocrysts, mantle garnets.

Cratons are old, stable parts of the continental crust that have survived at least since Proterozoic rime and have not undergone strong magmatism or tectonism since their stabilization. Traditionally, the growth of continental crust in the North China craton is considered to have been complete by Paleoproterozoic time, Phanerozoic events being largely restricted to surrounding orogenic belts. However, the eastern part of the North China craton contains large volumes of Mesozoic igneous rocks, with widespread metamorphic core complexes and pull-apart basins. Hf isotope compositions of magmatic zircon grains from igneous rocks in the Liaodong Peninsula indicate that widespread late Mesozoic granitoids formed by partial melting of ancient crust, but with significant input of a mantle component via magma mixing and crustal assimilation. This magmatism has resulted from removal and modification of lithospheric mantle, accompanied by asthenospheric upwelling. The Hf isotopic signatures thus record the addition of juvenile crust beneath the eastern part of the North China craton, which appears related to major extension and possibly slab rollback of the Pacific plate. Whatever the mechanism, it is apparent that since ca. 200 Ma, ancient lithosphere beneath the eastern North China craton has been progressively reactivated and replaced, resulting in 'decratonization.' Tertiary to Holocene volcanism in the area and major subsidence around the Gulf of Bohai suggest that the effects of the process are continuing. Similar processes probably operated in the geological past, leading to significant modification of continental crust and requiring reconsideration of mechanisms for continental breakup and dispersal and of continental growth rates. Keywords: decratonization, Phanerozoic crustal growth, North China craton, zircon, Hf isotope, magmatism.

Continental flood basalts, derived from mantle plumes that rise from the convecting mantle and possibly as deep as the core mantle boundary, are major hosts for world-class Ni-Cu-PGE ore deposits. Each plume may have a complex history and heterogeneous composition. Therefore, some plumes may be predisposed to be favourable for large-scale Ni-PGE mineralisation ('fertile'). Geochemical data from 10 large igneous provinces (LIPs) have been collected from the literature to search for chemical signatures favourable for Ni-PGE mineralisation. The provinces include Deccan, Kerguelen, Ontong Java, Paranfi, Ferrar, Karoo, Emeishan, Siberia, Midcontinent and Bushveld. Among these LIPs, Bushveld, Siberia, Midcontinent, Emei Mt and Karoo are 'fertile', hosting magmatic ore deposits or mineralisation of various type, size and grade. They most commonly intruded through, or on the edges of, Archaean-Paleoproterozoic cratonic blocks. In contrast, the 'barren' LIPs have erupted through both continental and oceanic crustal terranes of various ages. Radiogenic isotopic signatures indicate that almost all parental LIP magmas are generated from deep-seated mantle plumes, and not from the more widespread depleted asthenospheric mantle source: this confirms generally accepted plume models. However, several important geochemical signatures of LIPs have been identified in this study that can discriminate between those that are 'fertile' or 'barren' in terms of their Ni PGE potential. The fertile LIPs generally contain a relatively high proportion of primitive melts that are high in MgO and Ni, low in [Al.sub.2][O.sub.3] and [Na.sub.2]O, and are highly enriched in most of the strongly incompatible elements such as K, P, Ba, Sr, Pb, Th, Nb, and LREE. They have relatively high Os contents ([greater than or equal to] 0.03 to 10 ppb) and low Re/Os ( Barren LIPs contain fewer high-MgO lavas. The barren LIP lavas in general have low Os contents (mostly [less than or equal to] 0.02 ppb) with high Re/Os (10-[greater than or equal to] 200). They show isotopic variations between plume and EM2 geochemical signatures and have high Rb/Ba ratios. These signatures may indicate involvement of deep recycled material in the mantle sources or crustal contamination for barren LIPs, but low degrees of interaction with old lithospheric-type roots. Keywords: continental flood basalts; nickel and PGE mineralisation; mantle plumes; lithospheric mantle; cratonic lithosphere; lithospheric sulfides

Byline: Sonja Aulbach (1,2), William L. Griffin (1,3), Norman J. Pearson (1), Suzanne Y. O'Reilly (1), Buddy J. Doyle (4) Keywords: Mantle peridotite origins; Mantle melting; Plume mantle; Subcontinental lithosphere formation; Lac de Gras lithospheric mantle Abstract: Major-element compositions of minerals in peridotite xenoliths from the Lac de Gras kimberlites provide constraints on the mode of lithosphere formation beneath the central Slave Craton, Canada. Magnesia contents of reconstructed whole rocks correlate positively with NiO and negatively with CaO contents, consistent with variable partial melt extraction. Alumina and [Cr.sub.2]O.sub.3 contents are broadly positively correlated, suggestive of melt depletion in the absence of a Cr--Al phase. Garnet modes are high at a given [Al.sub.2]O.sub.3 content (a proxy for melt depletion), falling about a 7 GPa melt depletion model. These observations, combined with high olivine Mg and major-element relationships of FeO-poor peridotites (3 GPa (residual FeO content being a sensitive indicator of melt extraction pressure), and similar high pressures of last equilibration ([proportional to]4.2 to 5.8 GPa), provide multiple lines of evidence that the mantle beneath the central Slave Craton has originated as a residue from high-pressure melting, possibly during plume subcretion. Apparent low melt depletion pressures for high-FeO peridotites (>7.5 wt%) could suggest formation in an oceanic setting, followed by subduction to their depth of entrainment. However, these rocks, which are characterised by low SiO.sub.2 contents ( Author Affiliation: (1) GEMOC ARC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW, 2109, North Ryde, Australia (2) Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada, T6G 2E3 (3) CSIRO Exploration and Mining, N. Ryde, NSW, 2113, Australia (4) Lithosphere Services, 4009 Edinburgh Street, Burnaby, BC, Canada, V5C 1R4 Article History: Registration Date: 03/04/2007 Received Date: 27/09/2006 Accepted Date: 02/04/2007 Online Date: 08/05/2007 Article note: Communicated by T.L. Grove.

Author(s): Olivier Alard (corresponding author) [1, 2, 3]; Ambre Luguet [4, 5]; Norman J. Pearson [1]; William L. Griffin [1]; Jean-Pierre Lorand [4]; Abdelmouhcine Gannoun [2]; Kevin W. Burton [2]; [...]

The Yangkou garnet-peridotite complex in the Sulu UHP terrane, eastern China, consists of several blocks, tens of meters across, enclosed within gneiss. The blocks consist mainly of garnet lherzolite and garnet clinopyroxenite with small amounts of eclogite. The complex displays a finely layered stRucture from outcrop to thin-section scales. Lherzolitic garnet is generally homogenous in composition ([Prp.sub.64-67][Alm.sub.23-24][Grs.sub.10-12][Sps.sub.1]). Garnet (PrpsI-63) from clinopyroxenite contains more pyrope component than eclogitic garnets ([Prp.sub.29-35]). Porphyroblastic garnet from clinopyroxenite and eclogite contains abundant exsolved rods of futile and apatite ([+ or -]Cpx). Lherzolitic garnet exhibits an unusual sinusoidal REE pattern characterized by a decrease in abundance from La to Pr and an increase from Nd to the HREE, and shows Ba and Pb enrichment and negative Nb and Ni anomalies in primitive mantle-normalized trace-element plots. In contrast, diopside shows a normal REE pattern with decreasing abundances from La to Lu, a peak at Ba and Pb, and depletion in Co and Ni. Garnet from eclogite has a REE pattern with increasing abundances from La to Lu, or a maximum at Eu. Eclogitic clinopyroxene shows humped REE patterns with a peak at Nd. Except for slightly lower [[delta].sup.18][O.sub.VSMOW] of +4.40% for olivine, O-isotopic compositions (+5.03 to +5.53%) of analyzed garnets and clinopyroxenes from all three rock types lie in the range of mantle [[delta].sup.18]O values of +5.1 to +6.6%0. Small O-isotope fractionations ([DELTA]Grt-Cpx: -0.16 to -0.35) in eclogite suggest isotopic equilibrium. On the basis of petrochemical and isotopic data, this garnet-peridotite complex was initially a mantle peridotite cut by mafic veins. These rocks experienced metasomatism and subduction-zone UHP metamorphism at 750 [+ or -] 50 [degrees]C and 40 to 45 kbar with a low thermal gradient. The fine-scale layering probably formed as a result of strong shear deformation during exhumation.

The Hf isotope composition of rutile in mica-amphibole-rutile-ilmenite-diopside (MARID) xenoliths from the Kimberley area of South Africa has been analyzed in situ by laser ablation microprobe--multicollector--inductively coupled plasma mass spectrometry to investigate metasomatic processes in the lithospheric mantle. The [sup.176]Hf/[sup.177]Hf ratio shows a wide range, from 0.2811 to 0.2858 ([[epsilon].sub.Hf] = -55 to +110); much of this range is found within single samples and even within single grains. We suggest that the MARID rutiles initially resulted from the interaction of an asthenospheric melt with ancient depleted harzburgitic mantle with low [sup.176]Hf/[sup.177]Hf ratios ( Keywords: MARID xenoliths, mantle rutile, hafnium isotopes, mantle xenoliths, kimberlitic metasomatism, South Africa lithosphere.

Small volumes of garnet peridotite occur within large dunite bodies in the Western Gneiss Region of the Norwegian Caledonides. Previous Sm-Nd analyses of garnet peridotite yield Proterozoic ages close to the crystallization ages of the host gneisses. In situ (laser-ablation multicollector--inductively coupled plasma--mass spectrometry) Re-Os analysis of sulfides in the garnet peridotites gives a range of Proterozoic and Archean model ages. An Archean (2.7-3.1 Ga) protolith age is supported by whole-rock Re-Os data for sulfide-free dunites from several bodies. The Archean ages imply a melt-extraction event in the lithospheric mantle that predates the growth of the known Proterozoic upper crust in the region. Keywords: Norwegian Caledonides, mantle peridotites, sulfide ages, Re-Os ages, Archean lithospheric mantle.

The Os isotope compositions of sulfides in mantle xenoliths from the Penghu Islands, Taiwan Strait, reveal the presence of Proterozoic subcontinental lithospheric mantle beneath the highly extended southeast margin of the South China block. Both [T.sub.RD] (Re depleted) model ages for individual sulfides and model ages estimated from the initial [sup.187]Os/[sup.188]Os ratios of Re-Os mixing lines require that some volumes of the subcontinental lithospheric mantle formed prior to 2.3-1.9 Ga. Later events in the subcontinental lithospheric mantle may be recorded by [T.sub.RD] model ages of 1.5-1.2 Ga and ca. 0.9 Ga. The events recognized in the subcontinental lithospheric mantle are consistent with those known in the crust of the mainland South China block. The sulfide Os isotope data show that Proterozoic lithosphere beneath the South China block has survived the extensive Mesozoic Yanshanian magmatism on the continental margin and has not been delaminated even during the severe lithospheric extension that led to the subsidence of the Taiwan Strait. Keywords: lithospheric mantle, Re-Os, sulfides, Taiwan Strait, Proterozoic, South China block.

Quenched carbonate-silicate inclusions in lherzolitic clinopyroxene macrocrysts, derived from 200 km beneath the Slave craton in northern Canada, are interpreted as natural samples of mantle carbonatites. Oxygen, carbon, and strontium isotope data provide evidence for the involvement of subducted crustal material in the origin of these carbonatites, supporting suggestions that carbon recycling by subduction is an important prerequisite for carbonatite magmatism. The compositional range of the inclusions suggests that the parent melt was decreasing in silica content as it was trapped in the host crystal, a trend that is predicted experimentally. Isotopic disequilibrium between the carbonatitic inclusions and the host clinopyroxene indicates that they were trapped shortly before kimberlite eruption, suggesting a temporal link between the entrapment of the carbonatite in the host and the Paleocene eruption of the kimberlite. Keywords: carbonatites, isotopes, subduction, Slave province, mantle melts, xenoliths.

A suite of metasomatised xenoliths from the Letlhakane kimberlite (Botswana) forms a metasomatic sequence from garnet peridotite to garnet phlogopite peridotite to phlogopite peridotite. Before the modal metasomatism, most of the Letlhakane xenoliths were depleted harzburgites that had been subjected to an earlier cryptic metasomatic event. Modal phlogopite and clinopyroxene [+ or -] Cr-spinel increase at the expense of garnet and orthopyroxene with increasing degrees of metasomatism. The most metasomatised xenolith is a wehrlite. With progressive modal metasomatism, the clinopyroxene becomes enriched in Sr, Sc and the LREE, orthopyroxene becomes depleted in Ca and Ni, but enriched in Al and Mn, and olivine becomes depleted in Al and V. Garnet chemical composition largely remains unchanged. The garnet replacement reaction seen in most xenoliths allows the measurement of the flux of trace elements through detailed modal analysis of the pseudomorphs. Mass balance calculations show that the modally metasomatised rocks became enriched in incompatible elements such as Sr, Na, K, the LREE and the HFSE (Ti, Zr and Nb). Major elements (Al, Cr and Fe) and garnet-compatible trace elements (V, Y, Sc, and the HREE) were removed during this metasomatic process. The modal metasomatism caused a strong depletion in Al, and the results challenge previous suggestions that this metasomatic process merely occurred within an Al-poor environment. The data suggest that the xenoliths represent the mantle wallrock adjacent to a major conduit for an alkaline basic silicate melt (with high contents of volatile and incompatible elements). The volatile and incompatible element-enriched component of this melt percolated into the wallrock along a strong temperature gradient and caused the observed range of metasomatism.

Author(s): Olivier Alard (corresponding author) [1]; William L. Griffin [1, 2]; Jean Pierre Lorand [3]; Simon E. Jackson [1]; Suzanne Y. O'Reilly [1] The abundances of highly siderophile (iron-loving) elements [...]

Mineral inclusions in the corundum grains show a different range of mineral phases, such as Nb-Ta oxides, Ca feldspars, zircons, Fe,Cu-sulphide and Ca,Th-phosphates, crystallized with corundum megacrysts. The unique chemical features of mineral inclusions indicate that granite/syenite pegmatite and bonatite components are involved in the formation of corundum megacrysts. This inclusion model give a new 'hybrid rock hypothesis' for corundum megacrysts.

A suite of eclogites from the Roberts Victor kimberlite has been extensively characterized in terms of petrology and geochemical compositions (Greau et al. in Geochim Cosmochim Acta 75(22):6927-6954, 2011; Huang et al. in Lithos 142-143:161-181, 2012a). In the present study, the water contents of eclogitic garnet and omphacite were analyzed by Fourier transform infrared spectrometry. Garnet does not contain measureable OH in any sample. The water content of omphacite in the studied eclogites ranges from 211 to 1,496 ppm. Mantle metasomatism has modified the water content of some of the eclogites, while others retain water contents characteristic of their original environment. The OH contents of the metasomatized eclogites may be mainly controlled by the [H.sub.2]O fugacity and mineral compositions. The OH contents of the non-metasomatized samples are interpreted to be more sensitive to their mantle equilibration temperature, pressure, and the local fugacities of [H.sub.2]O and [O.sub.2]. The calculated water content of the metasomatic medium is similar to that of carbonatitic-kimberlitic melts/fluids. Eclogites contain more water than peridotites recorded in the literature (341 ± 161 vs 122 ± 54 ppm) and represent an important water reservoir in the lithospheric mantle wherever they occur. This is an important parameter to be considered in the interpretation of mantle processes and geophysical data such as seismic wave speeds and electrical conductivity, and in geodynamic modeling. Keywords Eclogites * Xenoliths * Water content * Mantle metasomatism * Kaapvaal craton, Introduction Hydrogen (H), as one of the main volatile elements, plays an important role in Earth's evolution and dynamics (Dasgupta and Dixon 2009; and references therein). It is incorporated into [...]

Spinel lherzolite and wehrlite xenoliths from the Cenozoic Calatrava volcanic field carry the geochemical imprint of metasomatic agents that have affected the subcontinental lithospheric mantle beneath Central Iberia. Some xenoliths (mainly wehrlites) were enriched in REE, Sr, P, and C[O.sub.2] by silicic-carbonate-rich metasomatic melts/ fluids, while others record the effects of subduction-related hydrous silicate fluids that have precipitated amphibole and induced high Ti/Eu in primary clinopyroxene. The petrographic observations and geochemical data suggest that interstitial glass in the xenoliths represent the quenched products of Si-rich melts that infiltrated the mantle peridotite shortly before the entrainment of the xenoliths in the host magmas that erupted ca 2 million years ago. During their infiltration, the metasomatic melts reacted with peridotite, resulting in silica enrichment, while remobilizing grains of iron-rich monosulfide solid solution (Fe-rich Mss) initially enclosed in, or intergranular to, primary olivine and pyroxenes. In situ laser ablation inductively coupled plasma-mass spectrometry analysis of single sulfide grains reveals that the Fe-rich Mss in glass shows platinum-group element (PGE) patterns and [sup.187]Os/[sup.188]Os compositions identical to the Fe-rich Mss occurring as inclusions in, or at grain boundaries of primary silicates. Moreover, independent of its microstructural position, Fe-rich Mss exhibits PGE and [sup.187]Os/[sup.188]Os signatures typical of Mss either residual after partial melting or crystallized directly from sulfide melts. Our findings reveal that young metasomatic melt(s)/fluid(s) may carry remobilized sulfides with PGE and Os-isotopic signatures identical to those of texturally older sulfides in the peridotite xenolith. These sulfides thus still provide useful information about the timing and nature of older magmatic events in the subcontinental mantle. Keywords Mantle sulfides * Mantle xenoliths * Mantle metasomatism * Mantle melts * PGE and Re-Os signatures * Lithospheric mantle * Spain lithosphere, Introduction The in situ analysis of PGE and Re-Os isotopic compositions by laser sampling of individual sulfide grains in mantle xenoliths provides critical information on episodes of partial melting or [...]