Welcome to Geological Journal of China Universities ! Today is
Share:

J4

• Article • Previous Articles     Next Articles

STUDY ON TRACE ELEMENT AND Nd-Sr ISOTOPIC GEOCHEMISTRY OF MESOZOIC POTASH-RICH VOLCANIC ROCKS AND LAMPROPHURES IN WESTERN SHANDONG PROVINCE

Qiu jian-sheng1;2, Wang De-zi1, Zeng Jia-hu1, Brent I. A. McInnes2   

  1. 1. Department of Earth Sciences, Nanjing University, Nanjing, 210093, P. R. China; 2. CSIRO Division of Exploration and Mining, PO Box 136, North Ryde, NSW 2113, Australia
  • Received:1997-12-20 Revised:1997-12-20 Online:1997-12-20 Published:1997-12-20

Abstract: The Mesozoic potash-rich volcanic rocks in western Shangdong occurred mainly in terriestrial depression volcanic basins. Their distribution were controlled obviously by deep faults, and the typical localities of them are Zouping volcanic basin, Linqu volcanic basins, and mainly distributed in two areas, one is in the vicinity of Zaozhuang, such as Xuecheng, Shagou, Tengxian etc., the other is in Xinzhuang. Both potash-rich volcanic rocks and lamprophyres were formed in early Cretaceous (Rb-Sr isochron age of potash-rich volcanic rocks in Mengyin is 119.6±3.7 Ma and K-Ar ages of lamprophyres in Zaozhuang and Xinzhuang are 125~126Ma and 113Ma respectively ). According to their mineral constitutions and chemical compositions, the lithological association of potash-rich volcanic rocks in western Shangdong belongs to a set of trachybasalt-basaltic trachyandesite-reachyandesite-latite-trachyte, of which the latite is the predominant rock type. Lamprophyres in Zaozhuang are of alkaline-rich ultramafic categories, such as cascadite, olivine and pyroxene-bearing kersantite etc., and those in xinzhuang belong to a set of alkaling-rich intermediate to basic types, such as leucite-bearing lamprophyres, kersantite and spessartite etc. Geochemical investigation shows that both potash-rich volcanic rocks and lamprophyres have similar characteristics on major elements, trace elements and Nd-Sr isotopic compositions, i.e., they are all rich in alkali, potassium, LREE and LILE, but poor in HFSE and siderophile elements, and have quit low εNd values and obviously higher Isr rations. The 87Sr/88Sr rations andεNd values of potash-rich volcanic rocks and lamprophyres are 0.71103~0.71322, -11.02~-17.54 and 0.70953~0.71109, -11.57~19.54 respectively, similar to the carbonatite in this district. Based on detailed geochemical investigations and comprehensive studies of their tectonic setting, it is concluded that both potash-rich volcanic rocks and lamprophyre in western Shangdong were originated mainly from the partial melting of enriched mantle.