Lead Isotope and Trace Element Variation in Tenerife Pumices: Evidence for Recycling within an Ocean Island Volcano

J. A. Wolff and Z. A. Palacz
Department of Geology, University of Texas at Arlington, Box 19049, Arlington, Texas 76019, USA
VG Isotopes Ltd., Ion Path Road Three, Winsford, Cheshire CW7 3BX, UK

Abstract: Three voluminous Quaternary phonolitic pumice fall deposits erupted from the compositionally-zoned Tenerife magma chamber exhibit variability in Sr and Pb isotope ratios. It has been previously argued that the Sr isotope variations are due to syn-eruptive interaction between magma and hydrothermal fluids (Palacz and Wolff, 1989). Pb compositions are not correlated with Sr, and are believed to reflect magmatic values. Pb isotope ratios exhibit regular variation with degree of fractionation, and one zoned deposit is heterogeneous in Pb. The highest values seem to characterize the most fractionated upper parts of the zoned system. This is unlikely to be a consequence of magmatic recharge. Isotopic and trace element behaviour is instead consistent with combined assimilation and fractional crystalliza- tion, involving the recycling of material containing relatively radiogenic Pb, from within the volcanic edifice. Assimilation of sediment intercalated within the submarine portion of the pile is ruled out by the isotopic data. The most probable contaminant is a felsic igneous rock. Early trachytes reported by Sun (1980) have the required Pb isotope compositions and may approximately represent the assimilant.

Keywords: lead isotopes • trace elements • pumice • Tenerife • Canary Islands • recycling

Mineralogical Magazine; December 1989 v. 53; no. 373; p. 519-525; DOI: 10.1180/minmag.1989.053.373.01
© 1989, The Mineralogical Society
Mineralogical Society (www.minersoc.org)