Investigating low dispersion isotope dissolution Lu-Hf garnet dates via in situ Lu-Hf geochronology, Kanchenjunga Himal

Abstract

Re-examination of three specimens from the Kanchenjunga Himal of Nepal via in situ Lu-Hf garnet geochronology yields evidence of multiple garnet growth events. Spot analyses from grain cores in two specimens define Paleozoic regressions whereas analyses from grain rims in the same specimens define low-precision regressions consistent with the timing of Himalayan orogenesis. These dates contrast with previously published low dispersion, ca. 290 Ma isotope dissolution (ID) Lu-Hf garnet dates for the same rocks. Modelling of Lu and spot age distribution in representative grains from the specimens examined yields calculated dates that approximate the Permian-age regressions through the original ID data. These findings demonstrate that it is possible to generate low dispersion ID Lu-Hf data from multi-generational garnet with significantly different-age growth events when approximately equal proportions of the different age reservoirs are included in multi-component aliquots.