skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Paleomagnetism and age of the Leucite Hills Volcanic complex, Wyoming: Implications for eruptive history, landscape evolution, and the geomagnetic instability timescale (GITS)
Title: Paleomagnetism and age of the Leucite Hills Volcanic complex, Wyoming: Implications for eruptive history, landscape evolution, and the geomagnetic instability timescale (GITS)
The Leucite Hills Volcanic Field, southwest Wyoming comprises two dozen volcanic features including necks, flows, dikes, and plugs. It has been the focus of many petrologic studies as its volcanic and shallow intrusive rocks are one of the only surficial manifestations of ultrapotassic lamproite. We build on paleomagnetic findings of Sheriff and Shive (1980) by providing further paleomagnetic data from the Boars Tusk dike and Black Rock flows. We also characterize the magnetic mineral assemblage of these lamproites. Principal component analysis of alternating field (AF) and thermal demagnetization data indicate that the dike and breccias of Boars Tusk record a reversed magnetic polarity and the Black Rock lava records a normal polarity, both consistent with previous findings. This recording is typically carried by minerals with coercivities >15 mT and susceptibility measurements indicate magnetite, maghemite, and titanomagnetite as likely magnetic carriers. AF and thermal demagnetization experiments evince secondary magnetizations held by lower coercivity grains, likely caused by lightning strikes. 40Ar/39Ar incremental heating experiments from Boars Tusk and Black Rock give plateau ages of ∼ 2500 ka and ∼ 900 ka, respectively. Recent advances in the chronology of geomagnetic field reversals and excursions during the Quaternary permit integration of the Boars Tusk dike into the lower Matuyama chron, whereas the Black Rock lavas most probably record the Kamikatsura excursion. Notably, Black Rock records high inclinations that suggest the short-lived excursion achieved a full geomagnetic reversal, something not observed at other localities recording the Kamikatsura excursion. The Leucite Hills offer further opportunities to refine the Quaternary geomagnetic instability time scale (GITS), and to improve understanding of the eruptive and geomorphic evolution of this unusual volcanism.  more » « less
Award ID(s):
1813278 1813508
PAR ID:
10543786
Author(s) / Creator(s):
; ; ; ; ; ;
Publisher / Repository:
Journal of Volcanology and Geothermal Research
Date Published:
Journal Name:
Journal of Volcanology and Geothermal Research
Edition / Version:
na
Volume:
444
Issue:
C
ISSN:
0377-0273
Page Range / eLocation ID:
107942
Format(s):
Medium: X Other: na
Sponsoring Org:
National Science Foundation
More Like this
  1. (, Frontiers in Earth Science)
    A combined magnetostratigraphy for the Rainstorm Member of the Ediacaran Johnnie Formation was constructed using the sediment accumulation rates determined by rock magnetic cyclostratigraphy for three localities of the Rainstorm Member to provide a high resolution, time-calibrated record of geomagnetic field reversal frequency at a critical time period in Earth history. Two previously reported magnetostratigraphy records from Death Valley, California, the Nopah Range and Winters Pass Hills ( Minguez et al., 2015 ), were combined with new paleomagnetic and cyclostratigraphic results from the Desert Range locality of the Rainstorm Member in south central Nevada, United States . The Johnnie oolite marker bed is at the base of each of the three sections and allows their regional correlation. The Nopah Range and Desert Range localities have similar sediment accumulation rates of ∼5 cm/ka, so their stratigraphic sections can be combined directly. The Winters Pass Hills locality has a higher sediment accumulation rate of 8.4 cm/ka, therefore its stratigraphic positions are multiplied by 0.6 to combine with the Desert Range and Nopah Range magnetostratigraphy. The thermal demagnetization results from the Desert Range locality isolates characteristic remanent magnetizations that indicate two nearly antipodal east-west and shallow directions and a mean paleopole (11.7˚N, 348.4˚E) that is consistent with “shallow” Ediacaran directions. The Desert Range also yields a magnetic susceptibility rock magnetic cyclostratigraphy that records short eccentricity, obliquity, and precession astronomically-forced climate cycles in the Ediacaran. The high-resolution combined magnetostratigraphy with nearly meter-scale stratigraphic spacing (nominally 23 ka, based on the Desert Range sediment accumulation rate), indicates 11 polarity intervals in a cyclostratigraphy-calibrated duration of 849 ka, indicating a reversal frequency of 13 R/Ma. The Rainstorm Member records the Shuram carbon isotope excursion, hence its age is ∼574 Ma. Given the recent cyclostratigraphy-calibrated reversal frequency of 20 R/Ma from the Zigan Formation ( Levashova et al., 2021 ) at 547 Ma, our results show that reversal frequency was high but fluctuated during the Ediacaran. 
    more » « less
  2. (, Proceedings of the International Ocean Discovery Program)
    null (Ed.)
    The paleomagnetic shipboard data of International Ocean Discovery Program Site U1475, with a record reaching back to approximately 7 Ma, allowed for the identification of major magnetic polarity chrons and subchrons back to ~3.5 Ma. However, the natural remanent magnetization (NRM) was very weak, and transitional intervals with unclear polarity were as thick as several meters. The midpoints of these transitional intervals were reported in the shipboard results without decimal places because of the poor data quality. To evaluate and possibly refine the shipboard magnetostratigraphy, subsampling was performed across the polarity transitions. Detailed alternating field (AF) demagnetization experiments were conducted on these discrete samples and were complemented by anhysteretic remanent magnetization acquisition measurements and subsequent demagnetization. AF demagnetization data of NRM were analyzed using anchored principal component analysis (PCA) to obtain the characteristic remanent magnetization. These PCA results generally confirm the smoothed signal across polarity transitions at Site U1475. However, the midpoint depths of the top of the Keana Subchron, the Gauss-Matuyama and Matuyama-Brunhes boundaries, and the base of the Olduvai Subchron were adjusted. 
    more » « less
  3. ; ; (, Geochemistry, Geophysics, Geosystems)
    Abstract Continuous sedimentary records of paleomagnetic directional variability and relative paleointensity (RPI) provide valuable information on the evolution of the geodynamo while also facilitating stratigraphic correlation and age control. While the Quaternary RPI record has received much attention, Pliocene records are relatively rare. Here, a u‐channel paleomagnetic study from Integrated Ocean Drilling Program (IODP) Site U1396 in the Caribbean Sea refines the shipboard‐derived polarity stratigraphy and generates an RPI and directional record extending back 4.5 Ma. Rock magnetic data reveal changes in magnetic coercivity around 2.1 Ma that influences the quality of the paleomagnetic record; while the older record is well‐resolved and passes RPI quality criteria, much of the younger section does not. To facilitate the development of the RPI record, spike noise associated with discrete intervals of volcanogenic sediments are filtered from the data set. The resulting record passes RPI reliability criteria between 0–0.6 Ma and 2.1–4.5 Ma and represents the highest resolution RPI record extending into the early Pliocene. We use this record to refine the existing benthic δ18O chronology and open the door to high‐resolution RPI chronostratigraphies during the Pliocene. Although we find no evidence for a previously observed increase in magnetic field intensity after ∼4 million years ago, we do observe an asymmetrical form to RPI in the normal polarity intervals of the Gauss chron. We also find a polarity bias in inclination that cannot be simply explained by a drill string overprint, suggesting polarity‐driven field asymmetries that are particularly pronounced during the Pliocene. 
    more » « less
  4. ; ; ; ; ; (, Journal of Geophysical Research: Solid Earth)
    Abstract The late Ediacaran to early Cambrian witnessed significant Earth system changes, including animal life diversification and an enigmatic paleomagnetic record. This study focuses on the Nama Group, a key geological unit for understanding the Ediacaran‐Cambrian transition. Previous paleomagnetic studies in the Nama Group identified complex remagnetization patterns but lacked a detailed examination of remanence carriers. To address this, we conducted a series of rock magnetic experiments on unweathered borehole core samples to better constrain the remagnetization mechanisms. Thermal demagnetization identified two magnetic components.C1, a recent viscous remanent magnetization, used for borehole core orientation, andC2, a stable remagnetization component carried by single‐domain (SD) pyrrhotite and magnetite. Magnetic mineralogy and paleomagnetic data suggest that the remanence acquisition mechanism ofC2is best explained by thermoviscous remanent magnetization (TVRM) and thermal remanent magnetization (TRM), rather than chemical remanent magnetization (CRM). The presence of low unblocking temperatures, coupled with thermochronological evidence of prolonged heating during tectonic collisions and subsequent cooling, supports this interpretation. The remagnetization event is linked to the final consolidation of West Gondwanaland during the late stages of megacontinent assembly (∼490–480 Ma), coinciding with regional uplift and a stable geomagnetic field during the Moyero reverse superchron. These findings challenge the CRM hypothesis, as the quasi‐synchronous remagnetization across cratonic blocks and the predominance of single reverse polarity are better explained by thermal processes. This study highlights the critical role of thermoviscous relaxation in large‐scale remagnetization and provides new insights into the tectonic evolution of West Gondwanaland. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Geochemistry, Geophysics, Geosystems)
    Abstract By studying deep‐sea drilled records from the North Atlantic Ocean, several magnetic instabilities of short duration, such as the Iceland Basin (188 ka), the Björn (1,255 ka) and the Gardar (1,460 ka) excursions, were discovered. These records have contributed to our understanding of Earth's magnetic field and are the foundation of the Geomagnetic Instability Time Scale (GITS) in the Quaternary. Here, we present the magnetostratigraphy from Sites U1555 (0 to ∼2.7 Ma) and U1563 (0 to ∼5.2 Ma) drilled during the International Ocean Discovery Program Expedition 395C on the eastern side of the modern Mid‐Atlantic Ridge (∼60°N, 20–30°W). Shipboard paleomagnetic and microfossil data provided a preliminary age model, extending the regional record to 3.4 Ma. The Virtual Geomagnetic Pole latitudes from archive halves, corroborated with data from discrete samples, were used to build a high‐resolution magnetostratigraphy, which contained the expected Brunhes and Matuyama Chrons and their respective Subchrons. We also identified most of the magnetic events reported in the GITS, including the less well‐documented ones, such as Osaka, Kamitzukara, Huckleberry Ridge, Reunion, Gardar, Halawa and L4 events. The high‐resolution magnetostratigraphy from Sites U1555 and U1563 is compared with two previous legacy sites and contributes toward an increasingly robust GITS, expanding its use as a correlation and dating tool. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email