Argon Geochronology Active
This project supports the USGS argon geochronology laboratory in Denver. The USGS 40Ar/39Ar geochronology laboratory is a state-of-the-art research facility for determining absolute ages of minerals and rocks. The 40Ar/39Ar laboratory contributes critical geochronology to individual USGS research projects and to partners in academia and other Federal agencies. This laboratory develops methodology for small and difficult sample analysis often at the limits of existing mass spectrometer technology.
Science Issue and Relevance
The 40Ar/39Ar Method: 40Ar/39Ar geochronology is an experimentally robust and versatile method for constraining the age and thermal history of rocks. Such information is extremely valuable for understanding a variety of geological processes including the formation of ore deposits, mountain building and history of volcanic events, paleo-seismic events, and paleo-climate. The 40Ar/39Ar isotopic dating method has evolved into the most commonly applied geochronological method, and can be applied to many geological problems that require precise and accurate time and temperature control.
Methodology to Address Issue
This project provides partial support for the USGS argon geochronology laboratory in Denver. The USGS 40Ar/39Ar geochronology laboratory is a state-of-the-art research facility for determining absolute ages of minerals and rocks. The 40Ar/39Ar laboratory contributes critical geochronology to individual USGS research projects and to partners in academia and other Federal agencies. This facility houses necessary equipment for sample preparation and analysis, including high-sensitivity noble gas mass spectrometers and ultraviolet (UV) and infrared (IR) lasers. The versatility of the 40Ar/39Ar method permits determining the timing of processes and events such as igneous intrusions and extrusions, ore mineralization and hydrothermal fluid circulation, metamorphic cooling and exhumation, mineral formation and recrystallization, and shallow crustal faulting. Scientists are dependent on the geochronologist for data and interpretations to determine these parameters. This laboratory develops methodology for small and difficult sample analysis often at the limits of existing mass spectrometer technology.
Below are other science projects associated with this project.
Below are data releases associated with this project. Visit USGS Geochron - a database of geochronologic and thermochronologic dates and data.
Below are publications associated with this project.
High-precision 41K/39K measurements by MC-ICP-MS indicate terrestrial variability of δ41K
Characteristics and 40Ar/39Ar geochronology of the Erdenet Cu-Mo deposit, Mongolia
Sediment unmixing using detrital geochronology
Emergence and evolution of Santa Maria Island (Azores)—The conundrum of uplifted islands revisited
Instrumentation development for In Situ 40Ar/39Ar planetary geochronology
Episodic formation of the world-class Waihi epithermal Au-Ag vein system, Hauraki Goldfield, New Zealand
Preservation of ancient impact ages on the R chondrite parent body: 40Ar/39Ar age of hornblende-bearing R chondrite LAP 04840
Tracking the timing of subduction and exhumation using 40Ar/39Ar phengite ages in blueschist- and eclogite-facies rocks (Sivrihisar, Turkey)
U-Pb, Re-Os, and Ar/Ar geochronology of rare earth element (REE)-rich breccia pipes and associated host rocks from the Mesoproterozoic Pea Ridge Fe-REE-Au deposit, St. Francois Mountains, Missouri
Mid-Cretaceous oblique rifting of West Antarctica: Emplacement and rapid cooling of the Fosdick Mountains migmatite-cored gneiss dome
Himalayan gneiss dome formation in the middle crust and exhumation by normal faulting: New geochronology of Gianbul dome, northwestern India
The emergence of volcanic oceanic islands on a slow-moving plate: The example of Madeira Island, NE Atlantic
In addition to the USGS National Cooperative Geologic Mapping Program and the Geosciences and Environmental Change Science Center, below are partners associated with this project.
- Overview
This project supports the USGS argon geochronology laboratory in Denver. The USGS 40Ar/39Ar geochronology laboratory is a state-of-the-art research facility for determining absolute ages of minerals and rocks. The 40Ar/39Ar laboratory contributes critical geochronology to individual USGS research projects and to partners in academia and other Federal agencies. This laboratory develops methodology for small and difficult sample analysis often at the limits of existing mass spectrometer technology.
Science Issue and Relevance
The 40Ar/39Ar Method: 40Ar/39Ar geochronology is an experimentally robust and versatile method for constraining the age and thermal history of rocks. Such information is extremely valuable for understanding a variety of geological processes including the formation of ore deposits, mountain building and history of volcanic events, paleo-seismic events, and paleo-climate. The 40Ar/39Ar isotopic dating method has evolved into the most commonly applied geochronological method, and can be applied to many geological problems that require precise and accurate time and temperature control.
Methodology to Address Issue
This project provides partial support for the USGS argon geochronology laboratory in Denver. The USGS 40Ar/39Ar geochronology laboratory is a state-of-the-art research facility for determining absolute ages of minerals and rocks. The 40Ar/39Ar laboratory contributes critical geochronology to individual USGS research projects and to partners in academia and other Federal agencies. This facility houses necessary equipment for sample preparation and analysis, including high-sensitivity noble gas mass spectrometers and ultraviolet (UV) and infrared (IR) lasers. The versatility of the 40Ar/39Ar method permits determining the timing of processes and events such as igneous intrusions and extrusions, ore mineralization and hydrothermal fluid circulation, metamorphic cooling and exhumation, mineral formation and recrystallization, and shallow crustal faulting. Scientists are dependent on the geochronologist for data and interpretations to determine these parameters. This laboratory develops methodology for small and difficult sample analysis often at the limits of existing mass spectrometer technology.
- Science
Below are other science projects associated with this project.
- Data
Below are data releases associated with this project. Visit USGS Geochron - a database of geochronologic and thermochronologic dates and data.
Filter Total Items: 19No Result Found - Publications
Below are publications associated with this project.
Filter Total Items: 66High-precision 41K/39K measurements by MC-ICP-MS indicate terrestrial variability of δ41K
Potassium is a major component in continental crust, the fourth-most abundant cation in seawater, and a key element in biological processes. Until recently, difficulties with existing analytical techniques hindered our ability to identify natural isotopic variability of potassium isotopes in terrestrial materials. However, measurement precision has greatly improved and a range of K isotopic composAuthorsLeah E. Morgan, Danielle P. Santiago Ramos, Brett Davidheiser-Kroll, John Faithfull, Nicholas S. Lloyd, Rob M. Ellam, John A. HigginsCharacteristics and 40Ar/39Ar geochronology of the Erdenet Cu-Mo deposit, Mongolia
The Early to Middle Triassic Erdenet porphyry Cu-Mo deposit, in northern Mongolia, developed in a continent-continent arc collision zone, within the Central Asian orogenic belt. The porphyry system is related to multiple intrusions of crystal-crowded biotite granodiorite porphyry, which formed a composite stock about 900 m in diameter, with multiple porphyritic microgranodiorite dikes. Wall rocksAuthorsImants Kavalieris, Bat-Erdene Khashgerel, Leah E. Morgan, Alexander Undrakhtamir, Adiya BorohulSediment unmixing using detrital geochronology
Sediment mixing within sediment routing systems can exert a strong influence on the preservation of provenance signals that yield insight into the influence of environmental forcings (e.g., tectonism, climate) on the earth’s surface. Here we discuss two approaches to unmixing detrital geochronologic data in an effort to characterize complex changes in the sedimentary record. First we summarize ‘toAuthorsGlenn R. Sharman, Samuel JohnstoneEmergence and evolution of Santa Maria Island (Azores)—The conundrum of uplifted islands revisited
The growth and decay of ocean-island volcanoes are intrinsically linked to vertical movements. While the causes for subsidence are better understood, uplift mechanisms remain enigmatic. Santa Maria Island in the Azores Archipelago is an ocean-island volcano resting on top of young lithosphere, barely 480 km away from the Mid-Atlantic Ridge. Like most other Azorean islands, Santa Maria should be exAuthorsRicardo Ramalho, George Helffrich, Jose Madeira, Michael A. Cosca, Christine Thomas, Rui Quartau, Ana Hipolito, Alessio Rovere, Paul Hearty, Sergio AvilaInstrumentation development for In Situ 40Ar/39Ar planetary geochronology
The chronology of the Solar System, particularly the timing of formation of extra-terrestrial bodies and their features, is an outstanding problem in planetary science. Although various chronological methods for in situ geochronology have been proposed (e.g., Rb-Sr, K-Ar), and even applied (K-Ar), the reliability, accuracy, and applicability of the 40Ar/39Ar method makes it by far the most desirabAuthorsLeah E. Morgan, Madicken Munk, Brett Davidheiser-Kroll, Nicholas H. Warner, Sanjeev Gupta, Rachel Slaybaugh, Patrick Harkness, Darren MarkEpisodic formation of the world-class Waihi epithermal Au-Ag vein system, Hauraki Goldfield, New Zealand
The world-class Waihi vein system in New Zealand has produced more than 248,400 kg Au and 1.43 million kg Ag. New high-precision 40Ar/39Ar dates of adularia from different veins show that some veins formed at different times (6.15 Ma Martha vs. 5.83 and 5.85 Ma Empire and Welcome, respectively), even though they have similar mineralogy. The Martha vein formed over a period of approximately 150,000AuthorsErin Gasston, Jeffrey L. Mauk, Michael A. Cosca, Leah E. Morgan, Chris M. HallPreservation of ancient impact ages on the R chondrite parent body: 40Ar/39Ar age of hornblende-bearing R chondrite LAP 04840
The hornblende- and biotite-bearing R chondrite LAP 04840 is a rare kind of meteorite possibly containing outer solar system water stored during metamorphism or postshock annealing deep within an asteroid. Because little is known regarding its age and origin, we determined 40Ar/39Ar ages on hornblende-rich separates of the meteorite, and obtained plateau ages of 4340(±40) to 4380(±30) Ma. These weAuthorsKevin Righter, Michael A. Cosca, Leah E. MorganTracking the timing of subduction and exhumation using 40Ar/39Ar phengite ages in blueschist- and eclogite-facies rocks (Sivrihisar, Turkey)
Geochronologic studies of high-pressure/low-temperature rocks can be used to determine the timing and rates of burial and exhumation in subduction zones by dating different stages of the pressure–temperature history. In this study, we present new in situ UV laser ablation 40Ar/39Ar phengite ages from a suite of lawsonite blueschist- and eclogite-facies rocks representing different protoliths (metaAuthorsKatherine F. Fornash, Michael A. Cosca, Donna L. WhitneyU-Pb, Re-Os, and Ar/Ar geochronology of rare earth element (REE)-rich breccia pipes and associated host rocks from the Mesoproterozoic Pea Ridge Fe-REE-Au deposit, St. Francois Mountains, Missouri
Rare earth element (REE)-rich breccia pipes (600,000 t @ 12% rare earth oxides) are preserved along the margins of the 136-million metric ton (Mt) Pea Ridge magnetite-apatite deposit, within Mesoproterozoic (~1.47 Ga) volcanic-plutonic rocks of the St. Francois Mountains terrane in southeastern Missouri, United States. The breccia pipes cut the rhyolite-hosted magnetite deposit and contain clastsAuthorsJohn N. Aleinikoff, David Selby, John F. Slack, Warren C. Day, Renee M. Pillers, Michael A. Cosca, Cheryl Seeger, C. Mark Fanning, Iain SamsonMid-Cretaceous oblique rifting of West Antarctica: Emplacement and rapid cooling of the Fosdick Mountains migmatite-cored gneiss dome
In Marie Byrd Land, West Antarctica, the Fosdick Mountains migmatite-cored gneiss dome was exhumed from mid- to lower middle crustal depths during the incipient stage of the West Antarctic Rift system in the mid-Cretaceous. Prior to and during exhumation, major crustal melting and deformation included transfer and emplacement of voluminous granitic material and numerous intrusions of mantle-deriveAuthorsRory McFadden, Christian Teyssier, Christine Siddoway, Michael A. Cosca, C. Mark FanningHimalayan gneiss dome formation in the middle crust and exhumation by normal faulting: New geochronology of Gianbul dome, northwestern India
A general lack of consensus about the origin of Himalayan gneiss domes hinders accurate thermomechanical modeling of the orogen. To test whether doming resulted from tectonic contraction (e.g., thrust duplex formation, antiformal bending above a thrust ramp, etc.), channel flow, or via the buoyant rise of anatectic melts, this study investigates the depth and timing of doming processes for GianbulAuthorsForrest Horton, Jeffrey Lee, Bradley Hacker, Meilani Bowman-Kamaha'o, Michael A. CoscaThe emergence of volcanic oceanic islands on a slow-moving plate: The example of Madeira Island, NE Atlantic
The transition from seamount to oceanic island typically involves surtseyan volcanism. However, the geological record at many islands in the NE Atlantic—all located within the slow-moving Nubian plate—does not exhibit evidence for an emergent surtseyan phase but rather an erosive unconformity between the submarine basement and the overlying subaerial shield sequences. This suggests that the transiAuthorsRicardo Ramalho, António Brum da Silveira, Paulo Fonseca, Jose Madeira, Michael A. Cosca, Mário Cachão, Maria M. Fonseca, Susana Prada - Web Tools
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- Partners
In addition to the USGS National Cooperative Geologic Mapping Program and the Geosciences and Environmental Change Science Center, below are partners associated with this project.