Controls on the PGE distribution of Permian Emeishan alkaline and peralkaline volcanic rocks in Longzhoushan, Sichuan Province, SW China

Abstract The ~ 260-Ma Emeishan large igneous province in SW China and northern Vietnam contains low-Ti tholeiitic basalts, high-Ti alkaline basalts and minor peralkaline volcanic rocks. The flood basalts in Longzhoushan, Sichuan Province, SW China, comprise four units, each of which has volcanic breccia at the base. From the base upward, rocks of Units 1 and 2 are high-Ti basalts with relatively high MgO (7.6–11.0 wt.%), TiO 2 (1.7–4.5 wt.%) and Ti/Y ratios (420–790). Unit 3 is composed of tephrites with lower MgO (0.87–6.2 wt.%), TiO 2 (0.96–2.14 wt.%) and Ti/Y ratios (190–530), whereas Unit 4 consists of basaltic andesites with moderate MgO (3.5–4.8 wt.%), TiO 2 (2.2–3.1 wt.%) and Ti/Y ratios (383–606). The high-Ti basalts may have been derived from an OIB-like mantle source and the basaltic andesites were probably generated by crustal contamination and fractionation of high-Ti basaltic magmas. The tephrites show high Nb/Y (1.2 to 2.7) and Th/Y (0.31 to 0.55) ratios, variable Zr/Hf ratios (40 to 49) and relatively low e Nd( t ) (− 0.7 to + 0.28) values, suggesting an asthenospheric mantle contribution modified by carbonate-rich fluids. The high-Ti basalts contain relatively high and variable PGE and their Cu/Pd ratios are relatively constant (compared to the tephrites) and vary from 8,500 to 86,000. We attribute such relative constancy of the Cu/Pd ratios to the presence of residual sulphide in the source of the high-Ti rocks and subsequent crystallization from S-undersaturated melts. The basaltic andesites have relatively high and constant Cu/Pd ratios (130,000–370,492) and the lowest PGE contents (average 0.12 ppb for Pd, 0.20 ppb for Pt), suggesting an earlier removal of sulfide due to crustal contamination before emplacement. The tephrites have PGE abundances (0.057 to 1.89 ppb for Pt and 0.11 to 2.10 ppb for Pd) higher than those for basaltic andesites, however, the Cu/Pd ratios (33,300 to 429,000) of the rocks are more variable than those for the basaltic andesites, suggesting that the tephrites may have undergone both S-saturated fractionation during emplacement of the magmas and weak removal of sulfides from the source magmas. Early fractionation of chromite together with removal of laurite and/or Os–Ir–Ru alloys from the parental magmas may be responsible for the negative Ru anomalies of the tephrites, high-Ti basalts and basaltic andesites.

[1]  V. Batanova,et al.  Formation of podiform chromitite deposits : implications from PGE abundances and Os isotopic compositions of chromites from the Troodos complex, Cyprus , 2004 .

[2]  C. Dupuy,et al.  Zr/hf fractionation in intraplate basaltic rocks: Carbonate metasomatism in the mantle source , 1992 .

[3]  T. Green.  Significance of Nb/Ta as an indicator of geochemical processes in the crust-mantle system , 1995 .

[4]  S. Hiemstra.  The role of collectors in the formation of the platinum deposits in the Bushveld Complex , 1979 .

[5]  Sun‐Lin Chung,et al.  Plume-lithosphere interaction in generation of the Emeishan flood basalts at the Permian-Triassic boundary , 1995 .

[6]  G. A. Macdonald,et al.  Chemical Composition of Hawaiian Lavas1 , 1964 .

[7]  R. Keays,et al.  Two melting regimes during Paleogene flood basalt generation in East Greenland: combined REE and PGE modelling , 2006 .

[8]  S. Beresford,et al.  Platinum-group element alloy inclusions in chromites from Archaean mafic-ultramafic units: evidence from the Abitibi and the Agnew-Wiluna Greenstone Belts , 2004 .

[9]  K. Govindaraju,et al.  1994 REPORT ON ZINNWALDITE ZW‐C ANALYSED BY NINETY‐TWO GIT‐IWG MEMBER‐LABORATORIES , 1994 .

[10]  Mei-Fu Zhou,et al.  Geochemistry of the Emeishan flood basalts at Yangliuping, Sichuan, SW China: implications for sulfide segregation , 2006 .

[11]  C. Wang,et al.  Evaluation of a technique for determining Re and PGEs in geological samples by ICP-MS coupled with a modified Carius tube digestion , 2007 .

[12]  J. Malpas,et al.  Origin and tectonic significance of a Mesozoic multi-layer over-thrust system within the Yangtze Block (South China) , 2003 .

[13]  C. Wang,et al.  Permian flood basalts and mafic intrusions in the Jinping (SW China)–Song Da (northern Vietnam) district: Mantle sources, crustal contamination and sulfide segregation , 2007 .

[14]  R. Keays,et al.  Re-Os isotope geochemistry of Tertiary picritic and basaltic magmatism of East Greenland: constraints on plume-lithosphere interactions and the genesis of the Platinova reef, Skaergaard intrusion , 1999 .

[15]  He Duancheng.  Late Permian Basalt-Phonolite Suite from Longzhoushan in the Panxi Rift Zone , 2003 .

[16]  R. Keays,et al.  Siderophile and Chalcophile Metal Variations in Flood Basalts from the Siberian Trap, Noril’sk Region: Implications for the Origin of the Ni-Cu-PGE Sulfide Ores , 2005 .

[17]  J. S. Kane,et al.  International Association of Geoanalysts Certificate of Analysis: Certified Reference Material OU‐6 (Penrhyn Slate) , 2005 .

[18]  G. Delpech,et al.  Platinum-group elements and the multistage metasomatic history of Kerguelen lithospheric mantle (South Indian Ocean) , 2004 .

[19]  J. Brenan,et al.  HIGH-TEMPERATURE STABILITY OF LAURITE AND Ru–Os–Ir ALLOY AND THEIR ROLE IN PGE FRACTIONATION IN MAFIC MAGMAS , 2001 .

[20]  W. McDonough,et al.  Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes , 1989, Geological Society, London, Special Publications.

[21]  M. Andreoli,et al.  Platinum-group elements in the Morokweng impact structure, South Africa: Evidence for the impact of a large ordinary chondrite projectile at the Jurassic-Cretaceous boundary , 2001 .

[22]  C. Wang,et al.  Determination of low concentrations of platinum group elements in geological samples by ID-ICP-MS , 2004 .

[23]  B. Fryer,et al.  Evidence for mantle heterogeneity from platinum-group-element abundances in Indian Ocean basalts , 1992 .

[24]  J. Crocket,et al.  Platinum-group elements in igneous rocks of the Kutch rift basin, NW India: Implications for relationships with the Deccan volcanic province , 2008 .

[25]  Sun-Lin Chung,et al.  Petrologic and geochemical constraints on the petrogenesis of Permian Triassic Emeishan flood basalts in southwestern China , 2001 .

[26]  Qiu-li Li,et al.  Zircon age and Nd–Hf isotopic composition of the Yunnan Tethyan belt, southwestern China , 2007 .

[27]  H. Puchelt,et al.  Platinum-Group Elements (PGE) in Basalts of the Seaward-Dipping Reflector Sequence, SE Greenland Coast , 2001 .

[28]  Conny Bockrath,et al.  Stabilities of laurite RuS2 and monosulfide liquid solution at magmatic temperature , 2004 .

[29]  R. Merkle.  Platinum-group minerals in the middle group of chromitite layers at Marikana, western Bushveld Complex: indications for collection mechanisms and postmagmatic modification , 1992 .

[30]  Mei-Fu Zhou,et al.  Zircon U-Pb geochronology and elemental and Sr–Nd isotope geochemistry of Permian mafic rocks in the Funing area, SW China , 2006 .

[31]  K. Rosman,et al.  Isotopic compositions of the elements 1989 , 1991 .

[32]  Yigang Xu,et al.  Chemostratigraphic Correlation of Upper Permian Lavas from Yunnan Province, China: Extent of the Emeishan Large Igneous Province , 2003 .

[33]  R. Keays,et al.  The behaviour of platinum-group elements in basalts from the East Greenland rifted margin , 2002 .

[34]  J. Crocket.  PGE in fresh basalt, hydrothermal alteration products, and volcanic incrustations of Kilauea volcano, Hawaii , 2000 .

[35]  Mei-Fu Zhou,et al.  Geochemical significance of a garnet lherzolite from the Dahongshan kimberlite, Yangtze Craton, southern China , 2001 .

[36]  R. Keays.  The role of komatiitic and picritic magmatism and S-saturation in the formation of ore deposits , 1995 .

[37]  M. Humayun,et al.  Platinum group elements in Kostomuksha komatiites and basalts: Implications for oceanic crust recycling and core-mantle interaction , 2000 .

[38]  J. Crocket,et al.  Platinum-group elements in Deccan mafic rocks: a comparison of suites differentiated by Ir content , 2004 .

[39]  R. Keays,et al.  THE PETROGENESIS AND PLATINUM-GROUP ELEMENT GEOCHEMISTRY OF THE NEWER VOLCANIC PROVINCE, VICTORIA, AUSTRALIA , 1997 .

[40]  S. Barnes,et al.  The behaviour of platinum-group elements during partial melting, crystal fractionation, and sulphide segregation: An example from the Cape Smith Fold Belt, northern Quebec , 1993 .

[41]  C. Neal,et al.  Platinum-group element constraints on source composition and magma evolution of the Kerguelen Plateau using basalts from ODP Leg 183 , 2005 .

[42]  M. Rehkämper,et al.  Determination of ultra-low Nb, Ta, Zr and Hf concentrations and the chondritic Zr/Hf and Nb/Ta ratios by isotope dilution analyses with multiple collector ICP-MS , 2002 .

[43]  P. Robinson,et al.  Late Permian rifting of the South China Craton caused by the Emeishan mantle plume? , 2004, Journal of the Geological Society.

[44]  F. Dudás,et al.  Precise calibration of Nd tracer isotopic compositions for Sm/1bNd studies☆ , 1992 .

[45]  P. Potts,et al.  GeoPT1. INTERNATIONAL PROFICIENCY TEST FOR ANALYTICAL GEOCHEMISTRY LABORATORIES — REPORT ON ROUND 1 (JULY 1996) , 1996 .

[46]  R. Keays,et al.  Experimentally determined sulfide melt-silicate melt partition coefficients for iridium and palladium , 1994 .

[47]  M. Fleet,et al.  Laboratory partitioning of platinum-group elements (PGE) and gold with application to magmatic sulfide–PGE deposits , 1999 .

[48]  W. McDonough,et al.  Carbonatite metasomatism in the northern Tanzanian mantle: petrographic and geochemical characteristics , 1993 .

[49]  M. Fleet,et al.  Partitioning of platinum group elements in the Fe‐O‐S System to 11 GPa and their fractionation in the mantle and meteorites , 1991 .

[50]  M. Norman,et al.  Rhenium and platinum group element abundances correlated with mantle source components in Hawaiian picrites: sulphides in the plume , 2000 .

[51]  Julian A. Pearce,et al.  Characteristics and tectonic significance of supra-subduction zone ophiolites , 1984, Geological Society, London, Special Publications.

[52]  W. Griffin,et al.  Mantle formation and evolution, Slave Craton: constraints from HSE abundances and Re–Os isotope systematics of sulfide inclusions in mantle xenocrysts , 2004 .

[53]  P. Robinson,et al.  Melting of the subcontinental lithospheric mantle by the Emeishan mantle plume; evidence from the basal alkaline basalts in Dongchuan, Yunnan, Southwestern China , 2008 .

[54]  M. Menzies,et al.  Geologic, geochemical, and geophysical consequences of plume involvement in the Emeishan flood-basalt province , 2004 .

[55]  T. Meisel,et al.  Reference materials for geochemical PGE analysis : new analytical data for Ru, Rh, Pd, Os, Ir, Pt and Re by isotope dilution ICP-MS in 11 geological reference materials , 2004 .

[56]  Yigang Xu,et al.  Distinct mantle sources of low-Ti and high-Ti basalts from the western Emeishan large igneous province, SW China: implications for plume–lithosphere interaction , 2004 .

[57]  W. Siebel,et al.  Geochronology of the Karadere basement (NW Turkey) and implications for the geological evolution of the Istanbul zone , 2002 .

[58]  S. Barnes,et al.  The concentrations of the noble metals in Southern African flood-type basalts and MORB: implications for petrogenesis and magmatic sulphide exploration , 2003 .

[59]  J. Malpas,et al.  A temporal link between the Emeishan large Igneous Province (SW China) and the end-Guadalupian mass extinction , 2002 .

[60]  M. Humayun,et al.  Platinum group element fractionation in a komatiitic basalt lava lake , 2001 .

[61]  Mei-Fu Zhou,et al.  Geochemical Constraints on the Mantle Source of the Upper Permian Emeishan Continental Flood Basalts, Southwestern China , 2001 .

[62]  D. Grégoire,et al.  Determination of trace elements in granites by inductively coupled plasma mass spectrometry. , 2000, Talanta.

[63]  S. Barnes,et al.  Platinum-Group Elements in Silicate Rocks of the Lower, Critical and Main Zones at Union Section, Western Bushveld Complex , 1999 .

[64]  K. Righter,et al.  Partitioning of Ru, Rh, Pd, Re, Ir, and Au between Cr-bearing spinel, olivine, pyroxene and silicate melts 1 1 Associate editor: C. R. Neal , 2004 .

[65]  S. Barnes,et al.  The fractionation of Ni, Cu and the noble metals in silicate and sulphide liquids , 1999 .

[66]  K. Jochum,et al.  The solar-system abundances of Nb, Ta, and Y, and the relative abundances of refractory lithophile elements in differentiated planetary bodies , 1986 .

[67]  Mei-Fu Zhou,et al.  Controls on platinum-group elemental distributions of podiform chromitites : A case study of high-Cr and high-Al chromitites from Chinese orogenic belts , 1998 .

[68]  J. Crocket.  Platinum-group elements in basalts from Maui, Hawai'i: Low abundances in Alkali Basalts , 2002 .

[69]  H. Rollinson.  Using Geochemical Data: Evaluation, Presentation, Interpretation , 1993 .