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 Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Mulcahy, S. R. Articles by Vervoort, J. D. GeoRef GeoRef Citation

Lawsonite Lu-Hf geochronology: A new geochronometer for subduction zone processes

¹ Department of Geoscience, University of Nevada–Las Vegas, Las Vegas, Nevada 89154-4010, USA
² School of Earth & Environmental Sciences, Washington State University, Pullman, Washington 99164, USA

Correspondence: *E-mail: sean.mulcahy{at}unlv.edu.

We present a new method for Lu-Hf geochronology using lawsonite, an index mineral of high-pressure, low-temperature metamorphism. The method uses common cation exchange chromatography to purify Lu and Hf from the sample and analysis by multicollector inductively coupled plasma–mass spectrometry. Lawsonite ¹⁷⁶Lu/¹⁷⁷Hf ratios are elevated and are similar to other minerals commonly used in Lu-Hf geochronology such as garnet or apatite. We obtain an age of 145.5 ± 2.4 Ma for lawsonite-blueschist facies metamorphism at Ring Mountain within the Franciscan Complex, California, the lawsonite type locality. The age agrees well with published geochronology and thermochronology for the Franciscan Complex. The new method provides a powerful tool to investigate processes and time scales of blueschist to eclogite facies metamorphism, crust-mantle recycling via subduction, and the geodynamics of convergent margins.