Geochronological Methods Applied to the Exploration of Tectonic and Geological Processes

Dear Colleagues,

In 1905, Ernest Rutherford demonstrated that radioactivity follows an exponential decay and promptly recognized its potential as a natural clock for determining the age of uranium-containing rocks. A few decades later, A. Holmes of Imperial College (as well as geochemist E.K. Gerling of the Russian Academy of Sciences working independently) separated minerals, particularly zircon, known to contain uranium and provided preliminary estimates of the Earth's age. Their estimates were somewhat above 3 billion years, about 1.5 billion years short of the more accurate modern estimate of 4.54 billion years. A. Nier, G. Patterson, W. Libby, B. Boltwood, and others advanced the pioneering work of their predecessors, extending beyond the U-Pb decay series and establishing the science of determining the age of geological materials as a distinct discipline within geology: geochronology. With the increased distribution of mass spectrometers in academia during the late 1950s and 1960s, geochronology emerged as a fully developed field, complete with dedicated faculty positions and specialized graduate programs. The previously "uncharted oceans" of Deep Time, which had been arduously but speculatively explored by stratigraphers, paleontologists, tectonicians, geochemists, and other earth scientists, suddenly acquired precise temporal coordinates, leading to one of the greatest intellectual achievements: the geologic time scale.

Geochronology, particularly radioisotopic techniques, revolutionized our understanding of Earth's history and processes. Alongside geochronology, thermochronology—initially seen as a limitation due to the diffusive loss of daughter isotopes—has also become a crucial tool in geology. It provides valuable insights into geological processes by studying temperature-related changes in rocks over time. Several radioisotopic dating systems have been developed for geochronology and thermochronology. Some of them include U–Th–Pb (from, e.g., zircons), K–Ar (from alkali-feldspars, micas, amphiboles, and plagioclase), and ⁴⁰Ar/³⁹A (from, e.g., micas and feldspars); Re–Os (from organic-rich sediments, iron meteorites, molybdenite, and other sulfides) and Pt–Os; Rb–Sr (from, e.g., plagioclase), Sm–Nd, and Lu–Hf (from, e.g., garnet); uranium-series geochronology (from, e.g., marine carbonates and volcanic crystals); meteoric or in situ cosmogenic nuclides such as ¹⁰Be, ²⁷Al, ³⁶Cl and others (from, e.g., quartz or calcite). Additionally, (U–Th)/He (from zircon or apatite) dating is also used.

Beyond radioactive decay, other nuclear processes like radiation damage in minerals, manifested as fission tracks (FT) in zircon or apatite, thermoluminescence (TL), and optically stimulated luminescence (OSL) from quartz and feldspar, as well as electron spin resonance (ESR), also exhibit chronometric properties and are widely used in geochronology and thermochronology. Paleomagnetism, on the other hand, involves determining the age of rocks and sediments by analyzing the changes in Earth's magnetic field recorded within them. ¹⁴C dating measures the age of organic materials by the decay of carbon-14, while dendrochronology determines the age of wooden remains through the analysis of tree-ring growth patterns. Therefore, the modern arsenal of geochronology includes a variety of (thermo-) chronometers that span timescales from billions of years to mere decades covering, thus, a wide range of temporal resolutions. The timing and rates of tectonic processes and events, often called chronotectonics, necessitate combining geochronological and thermochronological information with tectonic analysis to sequence the temporal evolution of tectonic structures and their activity history. This field encompasses tectonic processes at all scales, from plate tectonics and major tectonic events such as mountain building (including rift initiation, sedimentation, basin inversion, thrust stacking, folding, metamorphosis, and exhumation) to active-fault dating within the context of paleoseismology and seismotectonics.

Geochronology's transformative power has made it a cornerstone of modern geoscience. Apart from tectonics, it addresses research questions ranging from melt extraction events from the mantle and ore geology to the study of lunar samples and metamorphic rocks. Geochronology also tackles diverse problems such as magma generation, transport, and storage, reconstruction of paleo sea-levels and paleoclimates, paleoanthropology, paleoseismology, groundwater dating, paleoceanography, and dating of cave deposits (speleothems). Additionally, it is essential for understanding pedogenesis, landforms, ground deformation (e.g., landslides), active faulting, erosion rates, sedimentation rates, ice cores, plate tectonics, archaeological sites, and more. Living in the Anthropocene era, geochronology can also significantly contribute to energy and environmental sustainability by examining the replenishment cycles of natural resources (e.g., the geological time required for geothermal reservoirs to mature), as well as infrastructure resilience to temporal patterns of natural disasters while also disentangling the temporal cycles of natural climate change from human-induced global warming. By understanding the present dynamics within a broader geological timeframe, geochronology enables forward-looking projections, supporting the development of sustainable practices and resilience strategies. This Special Issue invites original research and review articles on the aforementioned topics. A Special Issue is a rare occasion to encompass advances in geochronology, both in classical and applied geology. We anticipate that this Special Issue will receive the recognition it deserves.

Dr. Constantin Athanassas
Guest Editor

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• radiometric dating
• structural geology
• geoscience
• radiation damage dating
• applications
• environmental change