HR: 10:40h
AN: SF32A-02 INVITED     [Abstracts]
TI: Global Oceanic Basalt Geochemistry From EarthChem Databases
AU: * Hofmann, A W
EM: hofmann@mpch-mainz.mpg.de
AF: Max-Planck-Inst. Chemie, Postfach 3060, Mainz, 55020 Germany
AU: Sarbas, B
EM: sarbas@mpch-mainz.mpg.de
AF: Max-Planck-Inst. Chemie, Postfach 3060, Mainz, 55020 Germany
AU: Jochum, K P
EM: jochum@mpch-mainz.mpg.de
AF: Max-Planck-Inst. Chemie, Postfach 3060, Mainz, 55020 Germany
AU: Stracke, A
EM: stracke@mpch-mainz.mpg.de
AF: Max-Planck-Inst. Chemie, Postfach 3060, Mainz, 55020 Germany
AB: For the past 21 years, global trace element systematics in oceanic basalts have been systematically developed, using mass spectrometry, by the MPI geochemistry department in Mainz, starting with Ba-Rb-Cs, and continuing with K-U-Th, Nb-U-Th, Pb-Ce, Pr-Mo, Nb-Ta, Sn-REE, Sb-REE, and Y-Ho relations. These were complemented by other groups, contributing e.g. Sr-REE relationships and more refined Nb-Ta systematics. Goal of these investigations was to establish relative trace element compatibilities during mantle melting, the corresponding enrichment and depletion patterns in MORB, OIB, subduction-related volcanics and the continental crust, and the relationships to Bulk Silicate Earth abundances through comparisons with element abundances in meteorites and in the continental crust (see e.g. [1]). Most of these studies were initially based on extremely limited data sets, often fewer than 100 analyses, because routine analytical techniques such as XRF and INAA were inadequate, either in sensitivity or accuracy or both, for many of the elements of interest. The advent of ICPMS technology has increased the volume of available, useable data enormously. The most recent development of laser source ICPMS is accelerating the acquisition of comprehensive trace element data even more dramatically. Although the general quality of recent trace element analyses has improved significantly, there remain large differences in reliability between published data because of varying analytical uncertainties and sample alteration. Thus, quality assurance remains an enormous task. In any case, now and in the foreseeable future, it will be impossible to assess global geochemical data without the use of comprehensive databases. Such databases are now available under http://www.earthchem.org/, comprising http://beta.petdb.ciesin.columbia.edu/; http://georoc.mpch-mainz.gwdg.de/, and http://navdat.geo.ku.edu/ . Unfortunately, the use of such databases is not without pitfalls. Often, appropriate metadata are inadequate or absent, and a significant fraction of the primary data and metadata contain errors, either in the original publication or in the transfer to the database. Therefore, analysis of these databases must be performed by experienced geochemists, who are best qualified to recognize erroneous or low-quality data. Even so, elimination of such erroneous or poor data frequently requires subjective judgment. Such evaluations should then produce "expert data sets", which can subsequently be used by non-experts, including non-specialist geochemists, geophysicists, and geologists. A partial expert evaluation of global MORB geochemistry has been prepared by Su [2], who gives segment-by-segment MORB averages. We are preparing an expert data set for global trace element and isotope geochemistry of ocean island basalts. On the basis of these data, we reevaluate global compatibility relationships. At this stage, these relationships are remarkably similar to those summarized by Hofmann [3], and by Sun and McDonough [4], using extremely limited data. This validates the original methodology used by these authors. At the same time, basalt suites containing geochemical anomalies can now be more clearly delineated. Thus, EarthChem databases allow us to develop a comprehensive view of global chemical differentiation of the Earth. [1] Hofmann, A.W. (2003) in Treatise on Geochemistry, ed. R.W. Carlson, Vol.2, 61-101. [2] Su,, Y.J. (2002) PhD Thesis, Columbia University, 472p. [3] Hofmann, A.W. (1988) Earth Planet. Sci. Lett. 90, 297-314. [4] Sun, S.-S. & McDonough, W.F. (1989) Geol. Soc. Spec. Publ. 42 (eds. A.D. Saunders & M.J. Norry), 313-345.
DE: 1040 Isotopic composition/chemistry
DE: 1045 Low-temperature geochemistry
DE: 1050 Marine geochemistry (4835, 4850)
DE: 1065 Trace elements (3670)
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Special Focus: Advances in Data Acquisition, Management, Analysis and Display [SF]
MN: 2004 AGU Fall Meeting