In order to decipher the origin and tectonothermal history of the Kuncha nappe, we undertook a geological investigation in the Taplejung window in eastern Nepal, and carried out multichronological analyses of zircon, apatite, and mica of the Kuncha Formation and Taplejung granites. Three granite bodies that intrude into the Kuncha Formation show fission-track (FT) ages of 6.2 to 4.8 Ma for zircon and 2.9 to 2.

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Zircon OD-3 from the Paleogene Kawamoto Granodiorite (Mihara body) in Japan has been identified as a potential multi-grain secondary standard for U-Pb dating. We have carried out an inter-laboratory evaluation in order to evaluate possible heterogeneity amongst the OD-3 zircon grains. U-Pb ages were obtained using two analytical techniques (a sensitive high-resolution ion microprobe and a laser ablation-inductively coupled plasma-mass spectrometry) in eight laboratories. All the 238 U-206 Pb ages show good agreement, with an overall weighted average 238 U-206 Pb age of 33.0 Ϯ 0.1 Ma (2s). The U-Pb age results revealed no significant variation or heterogeneity in the U-Pb ages of the OD-3 grains. Twelve fission-track (FT) ages from three laboratories are also reported, and have a weighted average of 32.6 Ϯ 0.6 Ma (2s). Despite the different closure and annealing temperatures of the U-Pb and FT chronometers, respectively, the FT age is in good agreement with the U-Pb age. This suggests that the OD-3 zircon had a relatively fast cooling history and has not experienced later thermal annealing. The chronological dataset reported here clearly demonstrates that the OD-3 zircon could be a useful and reliable secondary standard for use during U-Pb dating studies of Cenozoic zircons.

The chronology of the World Heritage Site of Sangiran in Indonesia is crucial for the understanding of human dispersals and settlement in Asia in the Early Pleistocene (before 780,000 years ago). It has been controversial, however, especially regarding the timing of the earliest hominin migration into the Sangiran region. We use a method of combining fission-track and uranium-lead dating and present key ages to calibrate the lower (older) Sangiran hominin-bearing horizons. We conclude that the first appearance datum for the Sangiran hominins is most likely ~1.3 million years ago and less than 1.5 million years ago, which is markedly later than the dates that have been widely accepted for the past two decades.

Newly discovered peloidal limestone from the summit of Mount Qomolangma (Mount Everest) contains skeletal fragments of trilobites, ostracods and crinoids. They are small pebble-sized debris interbedded in micritic bedded limestone of the Qomolangma Formation, and are interpreted to have been derived from a bank margin and redeposited in peri-platform environments. An exposure of the Qomolangma detachment at the base of the first step (8520 m), on the northern slope of Mount Qomolangma was also found. Non-metamorphosed, strongly fractured Ordovician limestone is separated from underlying metamorphosed Yellow Band by a sharp fault with a breccia zone. The 40 Ar-39 Ar ages of muscovite from the Yellow Band show two-phase metamorphic events of approximately 33.3 and 24.5 Ma. The older age represents the peak of a Barrovian-type Eo-Himalayan metamorphic event and the younger age records a decompressional high-temperature Neo-Himalayan metamorphic event. A muscovite whole-rock 87 Rb-86 Sr isochron of the Yellow Band yielded 40.06 ± 0.81 Ma, which suggests a Pre-Himalayan metamorphism, probably caused by tectonic stacking of the Tibetan Tethys sediments in the leading margin of the Indian subcontinent. Zircon and apatite grains, separated from the Yellow Band, gave pooled fission-track ages of 14.4 ± 0.9 and 14.4 ± 1.4 Ma, respectively. These new chronologic data indicate rapid cooling of the hanging wall of the Qomolangma detachment from approximately 350°C to 130°C during a short period .

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A multichronological study of the weakly metamorphosed Early Miocene fluvial Dumri Formation and the overlying Kuncha and Lesser Himalayan Crystalline nappes has helped to clarify the timing and heat source of the metamorphism, as well as the history of emplacement and cooling of the nappes. U–Pb ages of detrital zircons from the Dumri Formation show peaks at ca 1 Ga and 500–600 Ma, and fission‐track dating indicates a thermal imprint on the formation at 11–10 Ma. In the Naudanda Quartzite, overlying the Kuncha Formation, reset fission‐track detrital zircon ages are 9.5 Ma, but the U–Pb ages are older than 1.7 Ga. The differences in the U–Pb ages for detrital zircons from the Dumri and Kuncha Formations indicate that the Kuncha nappe was never exposed at the surface during the Early Miocene when the Dumri Formation was deposited. Two‐mica garnet schists of the Main Central Thrust (MCT) zone have fission‐track detrital zircon ages of 7.8 Ma and 40Ar–39Ar muscovite ages of 19 Ma, though the zircons have U–Pb ages older than 600 Ma. Our interpretation is that the heat for the Dumri Formation metamorphism came from the overlying nappes. The timing of the thermal imprint on the Dumri Formation indicates that the metamorphic nappe reached its present position before ca 10 Ma. The Parajul Khola granite in the frontal zone of the Kuncha nappe yields U–Pb zircon ages of 1.89 Ga, and it underwent an Early Miocene thermal event, cooling below 240°C at 14.7 Ma and below 100°C at 10.3 Ma. These thermochronological data suggest that the frontal part of the Kuncha nappe was exposed at the surface around 15–14 Ma and cooled immediately, but inner parts of the nappe were still hot during its emplacement.

The main tectono‐stratigraphic unit (Shirataki unit) of the Sanbagawa metamorphic complex in central Shikoku is characterized by abundant mafic schist layers that show the mid‐ocean ridge basalt (MORB) affinity. These MORB‐derived schist layers are absent in a southern (structurally lower) domain within the unit. Instead, sporadic occurrences of small metabasite lenses that contain relict igneous minerals (Ti‐rich augite and kaersutite) indicative of alkali basalt magmatism are newly recognized in the southern domain. Compositions of relict clinopyroxene in metabasalt are useful to identify the tectonic setting and origin of the protolith basalt, and those in each unit of the Sanbagawa metamorphic complex are presented. The metamorphic grade of the Shirataki unit generally increases structurally upwards in the southern side of the highest‐grade zone, and metamorphic zonation is subparallel to lithostratigraphic succession. The protolith assemblage of the Shirataki unit shows a distinct change from the southern low‐grade domain (lower Shirataki subunit) composed of terrigenous sedimentary rocks (mudstone and sandstone) with minor alkali basalt to the northern higher‐grade domain (upper Shirataki subunit) consisting of terrigenous and pelagic sedimentary rocks with abundant MORB. The youngest detrital zircon U–Pb ages (ca 95–90 Ma) suggest that both domains have Late Cretaceous depositional ages at the trench. Progressive peeling of oceanic plate stratigraphy during subduction can account for the observed change of lithological association in the Shirataki unit.