Geology topics

Kelly D. Thomson

Publications and source records attributed to Kelly D. Thomson.

5 recordsLinked to original sources

USGS2026

USGS Geochron—A database of geochronological and thermochronological dates and data—Technical documentation

Geochronological and thermochronological data are essential for constraining the timing and rates of geological processes, supporting geologic mapping, natural hazard assessment, and resource exploration. The U.S. Geological Survey (USGS) Geochron Database is a centralized, relational database that integrates USGS and State geological survey data in accordance with the National Geologic Mapping Act of 1992 and its reauthorizations. This report documents the structure and development of the database, including its standardized schema, controlled vocabularies, and protocols for compiling legacy and newly published data. The database is designed to adhere to FAIR (Findable, Accessible, Interoperable, and Reusable) data principles and currently (2026) includes data from a wide range of geochronological and thermochronological methods. Public access is provided through the USGS Geochron Database Explorer, a browser-based geographic information system (GIS) interface, and through versioned data releases available on ScienceBase, which provide sample-level summary data and detailed analytical information. The USGS Geochron Database is structured to be extensible, supporting the inclusion of additional methods and data types as they are compiled. This format ensures long-term utility and aligns with the Mapping Act’s directive to create a national archive of geochronological information that adds interpretive value to geologic map data. Its design reflects a commitment to data transparency, scientific reproducibility, and national geoscience priorities.

Data Report↗

USGS2026

USGS Geochron Database

Introduction Geochronology helps us understand Earth’s history by determining when important events, like volcanic eruptions, the rise of mountains, the formation of mineral resources, and changes in the landscape, happened. Geochronological data directly support geologic mapping and can inform decisions about geologic hazard mitigation, natural resource management, and infrastructure resilience. The U.S. Geological Survey (USGS) Geochron database provides access to more than 300,000 published, publicly available age measurements from more than 40,000 geological samples. This database is the result of a collaborative effort with State geological surveys and geoscientists from across the globe. The USGS Geochron database is the most comprehensive collection of geochronological data available for the United States. Users can view data through an interactive map explorer, download datasets, and integrate data into geospatial software or other analysis tools.

Fact Sheet↗

USGS2026

Reconstructing ancient sedimentary source-to-sink systems – Examples from southern Laurentia’s Proterozoic accretionary orogens

Provenance analysis is a powerful tool for investigating sediment delivery networks, constraining magmatic histories, and reconstructing the tectonic evolution of orogenic belts and basins. Basin analysis studies increasingly use detrital zircon (DZ) U-Pb forward mixture modeling to enhance provenance interpretations by quantifying the relative contributions of different sources. Forward mixture modeling requires significant a priori knowledge that limits deep-time applications. This challenge is overcome with an inverse mixture modeling approach non-negative matrix factorization to reconstruct the number and age distributions of paleo-source regions of Proterozoic metasedimentary rocks in the southwestern United States. This analysis indicates eight reconstructed end-member distributions representing unique sediment sources: two multi-modal end members characterized by ages older than ca. 1.8 Ga from cratonic Laurentia, five unimodal age distributions between ca. 1.80 Ga and 1.65 Ga consistent with Paleoproterozoic arc magmatic sources, and a ca. 1.6−1.5 Ga end member likely derived from exotic cratons in supercontinent Nuna (Columbia). Sediments deposited between ca. 1.80 Ga and 1.73 Ga yield heterogeneous age distributions suggesting multiple arc-backarc systems and several phases of slab roll back, contraction, and accretionary orogenesis, including input from pre−1.8 Ga Laurentian cratons. Homogenization of DZ signatures during the Yavapai orogeny (ca. 1.72−1.68 Ga) reflect crustal assembly as well as the uplift of Paleoproterozoic arcs in the orogenic hinterland. Detrital zircon age distributions from strata deposited during the Mazatzal orogeny (ca. 1.65−1.60 Ga) suggest the Mazatzal Province is a continental arc constructed on older crust. Mesoproterozoic samples are consistent with multiple basins derived from local recycling and long-distance sediment transport. Collectively, these data record the tectonic transition from the episodic accretion of disparate crustal domains to an increasingly integrated continental margin. These results provide new insights into the Proterozoic tectonic and paleogeographic evolution of the southwestern United States at basin to orogen scales and highlight the power of inverse DZ modeling to extract geologically meaningful quantitative mixture models from sedimentary records alone, offering a powerful tool for deep-time tectonic and basin analysis.

Arizona, California, Colorado, New Mexico, Nevada,↗

USGS2025

Enhancing mineral systems exploration through geochronology, thermochronology, and isotope analysis: USGS Geochron and USGS Isotope databases

A mineral systems approach to mineral exploration provides a comprehensive framework for understanding ore deposit formation by examining the geodynamic, magmatic, hydrothermal, and sedimentary processes responsible for mineralization, alteration, and remobilization of economic mineral deposits. Temporal and thermal constraints on ore genesis are crucial for refining mineral system models and guiding predictive exploration strategies. Geochronology and thermochronology offer invaluable insights into the timing and thermal evolution of ore-forming processes, whereas isotopic analyses provide critical information on the source and geochemical history of ore-forming fluids. Combining these methodologies have proven highly effective for mineral exploration in regions like Australia, however, their combined application has been limited in the United States. To apply these tools to mineral systems-based exploration, the U.S. Geological Survey (USGS) has developed two products: (1) The USGS Geochron Database, and (2) the USGS Isotope Database. These databases provide centralized repositories of geo/thermochronological dates and data (Geochron Database) and both radiogenic and stable isotope data (Isotope Database) generated by the USGS and partners over the past decades. Integrating these datasets together and with traditional exploration approaches provides the mineral exploration community with powerful tools for determining the temporal and thermal histories of ore systems and identifying metallogenic source provinces.

Continental United States↗

USGS2024

Tracking cycles of Phanerozoic opening and closing of ocean basins using detrital rutile and zircon geochronology and geochemistry

Sedimentary basins provide a deep time archive of tectonic and Earth-surface processes that can be leveraged by detrital mineral U-Pb dating and geochemistry to track paleogeography, magmatism, and crustal evolution. Zircon preserves the long-term (billions of years) record of supercontinent cycles; however, it is biased toward preserving felsic crustal records. Detrital rutile complements the detrital zircon record by providing constraints on the time and temperature of rifting and mafic magmatism, metamorphism, exhumation of the middle and lower crust, subduction, and amagmatic orogenesis. We use detrital zircon U-Pb and detrital rutile U-Pb geochronology and trace element analysis of Permian to Eocene siliciclastic rocks in the southern Pyrenees to capture supercontinent cycles of ocean basins opening and closing. Detrital rutile age spectra show peaks at ca. 100 Ma associated with rifting and hyperextension in the Pyrenean realm, 200 Ma associated with the Central Atlantic Magmatic Province, and 330 Ma, 375 Ma, and 400 Ma associated with subduction and Rheic Ocean crust formation. Zr-in-rutile thermometry and rutile Cr-Nb systematics provide further insight into metamorphic facies (peak metamorphic temperatures) and source rock lithology (mafic versus felsic affinity). Detrital zircon age spectra have peaks at ca. 300 Ma, 450 Ma, and 600 Ma associated with major orogenic events and felsic magmatism, and Th/U ratios provide information on relative zircon formation temperatures. Comparison of these independent records shows that detrital rutile reflects rifting, magma-poor orogenesis, and oceanic lithospheric processes, while detrital zircon detects continental lithospheric processes. Integrated detrital zircon and rutile data sets archive past geological events across multiple Wilson cycles.

Geology↗