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Potassic Volcanic Rocks in NE China: Geochemical Constraints on Mantle Source and Magma Genesis |
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| Authors: | ZHANG MING; SUDDABY PAUL; THOMPSON ROBERT N; THIRLWALL MATTHEW F; MENZIES MARTIN A |
| Institution: | 1DEPARTMENT OF GEOLOGY, IMPERIAL COLLEGE, UNIVERSITY OF LONDON LONDON SW7 2BP, UK 2DEPARTMENT OF GEOLOGICAL SCIENCES, UNIVERSITY OF DURHAM SOUTH ROAD, DURHAM DH1 3LE, UK 3DEPARTMENT OF GEOLOGY, ROYAL HOLLOWAY UNIVERSITY OF LONDON EGHAM, SURREY TW20 0EX, UK |
| Abstract: | Potassic volcanic rocks from the Wudalianchi, Erkeshan and Keluo(WEK) fields in NE China are located between the Mesozoic SongliaoBasin and the Palaeozoic Xing'am Mountains fold belt. Theserocks erupted during three main eruptive episodes-Miocene (9•6–7•0Ma), Pleistocene (0•56–0•13 Ma) and Recent (AD1719–1721)-and are subdivided into three types-olivineleucitite, leucite basanite and trachybasalt—on the basisof modal composition. In comparison with Cenozoic alkaline basaltsfrom East China that are similar to oceanic island basalts (OIBs),WEK volcanic rocks are lower in Al2O3, CaO, Fe2O3 and Sc, buthigher in K2O (3•5–7•1 wt %), K2O/Na2O (>1)and incompatible elements. High 87Sr/86Sr (0•7050–0•7056),low 143Nd/144Nd (0•51238–0•51250) and 206Pb/204Pb(17•06–16•61) ratios also distinguish them fromoceanic and Chinese basalts. Trace element and isotope dataindicate that a post-Archaean subcontinental lithospheric mantlesource similar to the postulated EM1 component (enriched mantlewith low l43Nd/144Nd and moderate high 87Sr/86Sr) must haveplayed a significant role in magma generation. The source rockis considered to be refractory phlogopite-bearing garnet peridotiteheterogeneously enriched in both large ion lithophile elementsand light rare earth elements by ancient metasomatism duringProterozoic times. This source may have mixed recently withOIB-like melts, but has not been modified by subduction of theKula-Pacific plate. Primitive WEK potassic magma was generatedby a low degree of partial melting, initiated by an extensionalphase beginning in the late Tertiary, at pressures of 20–45kbar and in the presence of mixed volatile components of H2O,CO2 and halogens. KEY WORDS: potassic volcanic rocks; NE China; geochemistry; montle sourc *Corresponding author. Present address: Centre for Petrology and Lithoipheric Studies, School of Earth Sciences, Macquarie University, NSW 2109, Australia |
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