Mineral assemblages dating techniques smithsonian

On a bulk chemical basis, the Seneca sandstone is relatively poor in Mn, containing ~500 ppmw.In contrast, the rock varnish is greatly enriched in Mn relative to the stone and to a lesser degree in Pb, Ca, Zn, Cu and Ni.

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Portable x-ray fluorescence (XRF) spectrometry links the discoloration with elevated Mn concentrations.The discolored patches resemble rock varnish, a Mn-rich coating observed on rock surfaces formed in a variety of environments.Bulk rock and varnish chemistry, in addition to microscopy and microanalysis of the varnish, are presented here.Both plutons were likely generated in a volcanic arc and have been affected by compressional and extensional deformation.The granitic rocks of which this pluton consists show microcracks and other microtectonic features.

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