A model of the tectonic development of Irtysh shear zone in terms of present day radioisotope data

Purpose. To present the model of tectonic development of the Irtysh shear zone, based on recent uranium-lead dating for zircon. Methodology. The authors analyzed the results of studies of foreign and domestic scientists, conducted field research, sample preparation, carried out iso-tope studies using SHRIMP-2 and LA-ICP-MS technology; determined small elements by the fusion method using ICP. Findings. Based on more than ten uranium-lead dating for zircon using the local method and the given geological and structural data, model of the Irtysh shear zone tectonic development has been proposed Originality. A tectonic model has been developed and the age and structural relationships of the Irtysh shear zone with the Kalba-Narym zone based on uranium-lead zircon dating have been established. Practical value. The article considers the structural and age relationships of the Irtysh crush zone which prove its formation along the deep Irtysh fault in the course of a long multi-stage tectogenesis.

When Dinosaurs Walked Through Diamonds: Constraining the Age of Early Cretaceous Footprints in Volcanic Crater Sediments

The volcanic rocks of the Catoca Diamond Mine, northeastern Angola, were formed in an eruption ~118 million years ago. Above these rocks, researchers discovered Early Cretaceous mammalian, crocodilian, and sauropod dinosaur footprints in crater lake sediments. These footprints are among the relatively few vertebrate fossils from the Cretaceous Period (145-66 million years ago) found in Sub-Saharan Africa. The ~118 million-year-old age, which is the maximum age of the footprints, is provided by the uranium and lead isotope ratios in the zircon crystals from these volcanic rocks. The presence of dinosaur footprints limits the minimum age to 66 million years ago. Detrital zircons from the sediments were collected for uranium-lead dating because these lake sediments may contain not only the ~118 million-year-old zircons but also zircons from younger eruptions, which could more precisely constrain the maximum age of these sediments. Forty zircons have been analyzed from this sediment sample, yielding an age range of 2.9 billion years ago to 150 million years ago. None of these zircons was ~118 million years old. Work is currently underway to find more zircons and to determine why no ~118 million-year-old zircons have been found in the lake bed sample.

Age control of the first appearance datum for Javanese Homo erectus in the Sangiran area

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.

U-Pb geochronology by zircon of fine-grained granite of the Osnitsky complex. (Volinsky megablok US)

The article presents the results of uranium-lead dating of zircon from fine-grained granite of the Osnytsia block of the Volyn megablock of the Ukrainian Shield. The variety of granites of the Osnitsky complex is manifested starting from their appearance. They are dominated by massive medium-grained rocks, limitedly developed fine-grained, even less common coarse-grained varieties. The age of typical Osnitsky granites, determined by the uranium-lead method according to zircon, is 1980-1950 million years. Granitoids after gabbroids were formed, and their rooting took place in two stages. At the first stage, depending on the physicochemical and tectonic conditions, a whole range of acid rocks was formed – from leptitelike (fine-grained) to large-medium-grained granites. In the second stage, coarse-grained, typical Osnitsky granites took root. One of the most characteristic macroscopic features of Osnitsky granites is that quartz is almost always represented by lilac-gray rounded grains. According to the results of uranium-lead isotope dating, the age of zircon from fine-grained granite is 1973.6 ± 8.4 million years, and 14 ± 24 million years, according to the lower. The weighted average value of the isotopic age in the isotope ratio 207Pb/206Pb is 1969.3 ± 6 million years. The obtained age for zircon from fine-grained granite of the Osnitsky complex corresponds to the time of formation of granites of the Osnitsky block.

Reinterpreting the Age and Origins of Taiwan’s Yuli Belt Terrane

Uranium-lead dating of zircons from Taiwan’s east central metamorphic belt offers robust evidence that this uplifted terrane is some 90 million years younger than previously thought.