Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Massonne, H.-J. Articles by Theye, T. Search for Related Content GeoRef GeoRef Citation

Dating of zircon and monazite from diamondiferous quartzofeldspathic rocks of the Saxonian Erzgebirge – hints at burial and exhumation velocities

¹ Institut für Mineralogie und Kristallchemie, Universität Stuttgart, Azenbergstr. 18, D-70174 Stuttgart, Germany
² Department of Applied Physics, Curtin University of Technology, Kent St. Bentley WA, 6102, Australia
³ Institut für Mineralogie und Kristallographie, Universität Wien, Althanstr. 14, A-1090 Vienna, Austria

^* E-mail: h-j.massonne{at}mineralogie.uni-stuttgart.de

In order to better understand the formation and evolution processes of ultrahigh pressure (UHP) felsic rocks, we determined the ages of various domains of zircon and monazite crystals from the diamondiferous quartzofeldspathic rocks of the Saxonian Erzgebirge. According to cathodoluminescence imagery and Th/U ratios, three zircon zones were distinguished. Each was dated using several spot analyses from a sensitive high-resolution ion microprobe analysing Pb, U and Th isotopes. The results were: (1) core zone – 21 analyses: Th/U 0.023 and 337.032.7 Ma (2, combined ²⁰⁶Pb/²³⁸U-²⁰⁷Pb/²³⁵U age); (2) diamond-bearing intermediate zone – 23 analyses: Th/U 0.037 and 336.832.8 Ma; and (3) rim zone – 12 analyses: Th/U = 0.015–0.038 (plus one analysis of 0.164) and 330.235.8 Ma. The U-Pb obtained ages are virtually concordant. Furthermore, two oscillatory zoned zircon cores (Th/U 0.8) yielded (concordant) ages of 400 Ma. Six SHRIMP analyses of monazites gave an age of 332.432.1 Ma. In addition, Pb, Th and U contents in monazite were analysed with an electron microprobe (EMP). A mean age of 324.738.0 (2) Ma was acquired from 113 analyses.

By combining the defined ages with previously published P-T conditions, minimum velocities for burial and exhumation were estimated. In addition, we present a likely geodynamic scenario involving age data from the literature as well as this study: beginning 340 million years ago, gneisses at the base of a thickened continental crust (1.8 GPa, 650°C) were transported to depths of at least 130 km, possibly as deep as 250 km. Here they were heated (>1050°C) and partially melted and as a result began to rise rapidly. The burial and subsequent ascent back to a depth of 50 km, where zircon rims and monazite formed, took only a few million years and perhaps significantly less.

KEYWORDS: zircon, monazite, geochronology, SHRIMP, EMP, Saxonian Erzgebirge, Variscan, ultrahigh pressure metamorphism, exhumation

This article has been cited by other articles:

				H. R. Marschall, A. V. Korsakov, G. L. Luvizotto, L. Nasdala, and T. Ludwig On the occurrence and boron isotopic composition of tourmaline in (ultra)high-pressure metamorphic rocks Journal of the Geological Society, July 1, 2009; 166(4): 811 - 823. [Abstract] [Full Text] [PDF]