Computer Science
Scientific paper
Jul 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000e%26psl.179..453b&link_type=abstract
Earth and Planetary Science Letters, Volume 179, Issue 3-4, p. 453-467.
Computer Science
3
Scientific paper
Rhenium-Osmium (Re-Os) isotope and elemental data are presented for mafic-ultramafic rocks from the central region of the Lewisian Archean terrain in northwest Scotland. These results give a best estimate for the time of emplacement of the mafic-ultramafic bodies of 2686.7+/-14.7 Myr (2σ). The initial 187Os/188Os isotope ratio of 0.10940+/-0.00076 indicates that such material possessed a chondritic Os isotope composition, which suggests that these rocks were formed by direct melting of mantle material, consistent with major and trace element constraints on their formation. Nevertheless, the Re-Os systematics of some of the mafic-ultramafic rocks in the Lewisian have been significantly disturbed, such that the original age information has been lost. These rocks lie on a regression line that defines an age of ~3260 Myr, and a negative initial Os isotope composition, suggesting perturbation of the Re-Os system, either through assimilation or post-emplacement elemental exchange. Such a process also appears to have affected the Sm-Nd systematics in the same samples. Crustal assimilation can account for the observed Os and Nd isotope variations but only if the assimilated material possessed 187Os/188Os values of ca. 25 at ~2687 Myr. In contrast, the surrounding gneisses and metasediments preserve present-day measured 187Os/188Os values of between 3 and 16. Rather, the spatial variation of initial Os and Nd isotope compositions suggests that isotope perturbation was caused by local sub-solidus element exchange between different lithologies, consistent with major element data and petrographic observations. Taken together, these results highlight the utility of the Re-Os isotope system for obtaining precise ages for Archean mafic-ultramafic rocks, and as a sensitive petrogenetic tracer capable of discriminating between assimilation or elemental exchange.
Allègre Claude J.
Birck Jean-Louis
Burton Kevin W.
Capmas Françoise
Cohen Seth A.
No associations
LandOfFree
Resolving crystallisation ages of Archean mafic-ultramafic rocks using the Re-Os isotope system does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Resolving crystallisation ages of Archean mafic-ultramafic rocks using the Re-Os isotope system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Resolving crystallisation ages of Archean mafic-ultramafic rocks using the Re-Os isotope system will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1718532