Rutile geochemistry and its potential use in quantitative provenance studies

Abstract

Rutile is among the most stable detrital minerals in sedimentary systems. Information contained in rutile is therefore of prime importance, especially in the study of mature sediments, where most diagnostic minerals are no longer stable. In contrast to zircon, rutile provides information about the last metamorphic cycle as rutile is not stable at greenschist facies conditions. Several known geochemical characteristics of rutile can be used to retrace provenance. The lithology of source rocks can be determined using Nb and Cr contents in rutile, because the most important source rocks for rutile, metapelites and metabasites, imprint a distinct Nb and Cr signature in rutiles. Since Zr in rutile, coexisting with zircon and quartz, is extremely temperature dependent, this relationship can be used as a geothermometer. Metapelites always contain zircon and quartz, thus the Nb and Cr signatures of metapelites indicate rutiles that can be used for thermometry. The result is effectively a single-mineral geothermometer, which is to our knowledge the first of its kind in provenance studies. Several other trace elements are variably enriched in rutile, but the processes creating these variations are so far not understood. In a case study, Al, Si, V, Cr, Fe, Zr, Nb and W contents in rutiles were obtained by electron microprobe from three sediment samples from Upstate New York. A Pleistocene glacial sand, whose source was granulite-facies rocks of the southern Adirondacks, has detrital rutile geochemical signatures which are consistent with the local Geology; a predominantly metapelitic source with a minor metabasitic contribution. Calculated temperatures for the metapelitic rutiles from the glacial sand are consistent with a predominantly granulite-facies source. The two other samples are from Paleozoic clastic wedges deposited in the foreland of the Taconian and Acadian orogenies. Here several geochemical patterns of detrital rutiles are comparable to rutiles derived from the Adirondacks, implying that rutiles eroded from the Taconian and Acadian orogens were originally derived from similar high grade gneiss terranes, like those found in the Adirondacks. The preferred tectonic scenario calls for an accretionary wedge where eroded Grenville province sediments accumulated, which were later recycled during the Taconian and Acadian orogenies. © 2004 Elsevier B.V. All rights reserved.