Samuel A. Bowring's research while affiliated with Massachusetts Institute of Technology and other places

Publications (430)

Article
Uranium‑lead perovskite in situ geochronology has become a cornerstone technique for determining the emplacement timing of alkaline, ultrapotassic, and silica-undersaturated igneous rocks, kimberlites, and carbonatites. Accurate in situ dates are dependent on the availability of matrix matched mineral reference materials which themselves are chemic...
Article
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We report extensive major and trace element data for the Permian-Triassic boundary (PTB) at Meishan, China. Analyses of 64 samples from a 2.5 m section span the last 75 kyr of the Permian and the first 335 kyr of the Triassic, from beds 24 to 34. We also report data for 20 acetic acid extracts that characterize the carbonate fraction. Whole rock ma...
Article
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Understanding the tectonic setting in which ophiolites form is necessary to determine how they can be used to study ocean spreading and subduction zone processes. Here we present high‐precision U‐Pb zircon dates and Sm‐Nd isotopic data from two late magmatic series in the Samail ophiolite (Oman‐United Arab Emirates), which constrain its tectonic de...
Article
Perturbations to the global carbon cycle as recorded in the isotopic compositions of marine deposits have been commonly associated with major shifts in the climate and/or biologic activity, including mass extinctions. The Late Ordovician Guttenberg isotopic carbon excursion (GICE) is a large, globally correlative positive shift (∼3‰) in the carbon...
Article
New U–Pb radioisotopic ages on early Cambrian volcanic zircons condition a high-resolution Bayesian age model that constrains the first occurrences and zonations of West Gondwanan archaeocyaths and trilobites in southern Morocco. The oldest archaeocyaths in the Tiout Member of the Igoudine Formation (519.71 + 0.26/− 0.35 Ma) are c. 6 Ma younger tha...
Article
We report high-resolution, high-precision δ44/40Ca, δ88/86Sr, and ⁸⁷Sr/⁸⁶Sr records spanning the Permian-Triassic boundary (PTB) from the Meishan and Dajiang carbonate successions in south China. The goal of the study was to understand the behavior of Ca and Sr isotopes during a time period in Earth history characterized by severe biological and en...
Article
Proxy estimates of atmospheric CO2 are necessary to reconstruct Earth's climate history. Confidence in paleo-CO2 estimates can be increased by comparing results from multiple proxies at a single site, but so far this strategy has been implemented only for marine-based techniques. Here we present CO2 estimates for the well-studied early Paleocene Ca...
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Previous studies of the end-Permian mass extinction have established that it was geologically rapid, but condensed sections have made it difficult to establish the exact timing of the extinction relative to fluctuations in the ocean carbon cycle, oxygen levels, and temperature. Integrated high-precision U-Pb geochronology, biostratigraphy, and chem...
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Mass extinction events are short-lived and characterized by catastrophic biosphere collapse and subsequent reorganization. Their abrupt nature necessitates a similarly short-lived trigger, and large igneous province magmatism is often implicated. However, large igneous provinces are long-lived compared to mass extinctions. Therefore, if large igneo...
Article
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In this study we investigate the origin and alteration history of serpentinites in two dredge hauls from the North Wall of the Puerto Rico Trench, where the North American plate subducts beneath the Greater Antilles island arc. Faulting of the North American plate at the North Wall of the Puerto Rico Trench exposes oceanic basement in a nearly spre...
Preprint
We have determined 238U/235U ratios for a suite of commonly used natural (CRM 112a, SRM 950a, and HU-1) and synthetic (IRMM 184 and CRM U500) uranium reference materials by thermal ionisation mass-spectrometry (TIMS) using the IRMM 3636 233U–236U double spike to accurately correct for mass fractionation. Total uncertainty on the 238U/235U determina...
Preprint
Full-text available
A statistical approach to evaluating uncertainties in the calibration of multi-element isotopic tracers has been developed and applied to determining the isotopic composition of mixed U-Pb (202Pb-205Pb-233U-235U) tracers used for accurate isotope dilution U-Pb geochronology. Our experiment, part of the EARTHTIME initiative, directly links the trace...
Preprint
Geochronology is essential for understanding Neoproterozoic Earth history. Here we review the types of rocks and minerals that are used to date geologic events and the analytical protocols for the different radio-isotopic decay systems employed. We discuss the limitations and potential of these methodologies for dating Neoproterozoic stratigraphy,...
Article
Radioisotopic age determinations targeted at key stratigraphic successions worldwide continue to refine the geological timescale with increasing precision and accuracy and to unravel the tempo of global geological, palaeoclimatic and palaeobiotic processes that have shaped our planet. The last decade has witnessed significant progress in the calibr...
Preprint
Full-text available
Mixed 235U–233U–205Pb(–202Pb) tracers for U–Pb isotope-dilution isotope ratio mass spectrometry have been prepared under the auspices of the EARTHTIME Initiative. The methods and results for the preparation and calibration of the U/Pb ratio and isotopic abundances are given, and the various sources of uncertainty are discussed and quantified. The a...
Article
Subduction of continental lithosphere to mantle depths results in the recrystallization of crustal material during ultrahigh-pressure (UHP) metamorphism. Knowledge of the duration and pressure and temperature (P-T) conditions at which UHP rocks equilibrate is fundamental for assessing the rates and mechanisms involved in the transfer of crustal mat...
Article
Sheeted intrusive complexes represent unequivocal examples of incremental intrusive activity in plutonic systems and thus provide an opportunity to constrain processes associated with incremental magma emplacement. We present field observations, U-Pb zircon data, and whole-rock and mineral chemistry from the sheeted intrusive complex of the ca. 92...
Article
Hornblende from the Lone Grove Pluton, Llano Uplift, Texas, has served as an irradiation reference material in 40Ar/39Ar studies for decades. In order to evaluate the apparent age bias that currently exists between the U-Pb and 40Ar/39Ar systems, zircon and titanite were dated by isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) from...
Article
Full-text available
Based on analyses of 565 conodonts from Meishan, Liangfengya, and Daijiagou (South China), and Abadeh (central Iran), we propose a revision of the seawater ⁸⁷Sr/⁸⁶Sr curve for the time period spanning 200kyr prior to the Permian-Triassic boundary (PTB) to 330kyr after the PTB. With carefully designed sample cleaning, conodonts faithfully record sea...
Article
Paleomagnetism of the North American Midcontinent Rift provides a robust paleogeographic record of Laurentia (cratonic North America) from ca. 1110 to 1070 Ma, revealing rapid equatorward motion of the continent throughout rift magmatism. Existing age and paleomagnetic constraints on the youngest rift volcanic and sedimentary rocks have been interp...
Article
The Acasta Gneiss Complex of the Northwest Territories, Canada, contains some of the earliest terrestrial continental crust and thus provides a critical sample set for characterization of crust-forming processes on the early Earth. Here we report the results of a combined Lu–Hf and U–Pb isotopic study of zircons from predominantly felsic orthogneis...
Article
Quantifying the time scales of magmatic differentiation is critical for understanding the rate at which silicic plutonic and volcanic rocks form. Directly dating this process is difficult because locations with both clear evidence for fractional crystallization and the accessory phases necessary for radiometric dating are rare. Early zircon saturat...
Article
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The snowball Earth hypothesis predicts that low-latitude glacia-tion lasted millions of years while CO 2 built up to critical levels to culminate in catastrophic deglaciation in a supergreenhouse climate. The Gaskiers Formation of eastern Newfoundland (Canada) has been attributed to a snowball glaciation event, but the lack of robust paleo-magnetic...
Article
The Yanliao Biota of northeastern China comprises the oldest feathered dinosaurs, transitional pterosaurs, as well as the earliest eutherian mammals, multituberculate mammals, and new euharamiyidan species that are key elements of the Mesozoic biotic record. Recent discovery of the Yanliao Biota in the Daxishan section near the town of Linglongta,...
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Studies of plutons indicate that they are the result of a complex interplay of magmatic processes occurring during magma generation, ascent, and emplacement. A critical tool for deciphering these processes is high-precision geochronology, which can help determine the timing and rates of magmatism in the crust. We conducted a field and U-Pb geochron...
Article
Ocean Drilling Program Hole 735B at Atlantis Bank on the Southwest Indian Ridge sampled 1508 m of plutonic oceanic crust, hosted in the footwall of an oceanic detachment fault. We present new high-precision isotope dilution-thermal ionization mass spectrometry (ID-TIMS) U–Pb zircon dates from samples spanning the length of Hole 735B, and from the s...
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Full-text available
The North Cascades orogen (northwestern USA) provides an exceptional natural laboratory with which to evaluate potential temporal and kinematic links between processes operating at a wide range of crustal levels during collapse of a continental arc, and particularly the compatibility of strain between the upper and lower crust. This magmatic arc re...
Article
The rates at which large volumes of eruptible, silicic (> 65 wt% SiO2) magma (magma chambers) are assembled, as well as their longevity in the upper crust, remain controversial. This controversy is due, in part, to a missing record of granitoid plutonic complexes that represent large fossil upper crustal magma chambers. We present new geologic mapp...
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We present Pb and Sr isotopic compositions and elemental concentrations for dentin and enamel from 28 human teeth from 10 locations in the southwestern United States. These teeth represent Native American communities that were functioning between 300 BCE - 1200 CE. We wished to assess whether Pb isotopic data can extend the interpretations made fro...
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The Organ Mountains caldera and batholith expose the volcanic and epizonal plutonic record of an Eocene caldera complex. The caldera and batholith are well exposed, and extensive previous mapping and geochemical analyses have suggested a clear link between the volcanic and plutonic sections, making this an ideal location to study magmatic processes...
Conference Paper
The oldest Mesozoic deposits on the Colorado Plateau are the disconformity-bounded Moenkopi Formation (Fm.), a Middle Triassic (Anisian) unit containing a temnospondyl-dominated fauna with no ornithodirans. The earliest fossil record of dinosauromrphs in North America is preserved in the fluvial rocks of ca. 229 to <208 Ma Chinle Fm. that overlie t...
Conference Paper
Full-text available
The Neoproterozoic stratigraphy of the Avalon terrane in Newfoundland includes glacigenic diamictites of the Gaskiers Formation, which are thought to capture a possible Snowball glaciation event. The Snowball Earth hypothesis requires a several million year duration for glaciation in order for atmospheric CO 2 from volcanic outgassing to reach high...
Data
A limiting factor in the accuracy and precision of U/Pb zircon dates is accurate correction for initial disequilibrium in the 238U and 235U decay chains. The longest-lived-and therefore most abundant-intermediate daughter product in the 235U isotopic decay chain is 231Pa (T1/2 = 32.71 ka), and the partitioning behavior of Pa in zircon is not well c...
Conference Paper
Vertebrate fauna belonging to the Yanliao Biota have been recovered and extensively studied from the Jurassic Lanqi Formation in Jianchang, western Lioaning Province of China. Earlier geochronological investigations by the U-Pb SIMS and LA-ICPMS methods on the volcanic and pyroclastic rocks associated with the Lanqi and correlative formations in no...
Conference Paper
The early dinosaur evolutionary history is obscured due to a fragmentary fossil record, taxonomic uncertainties and speculative correlations among widely dispersed fossil-bearing successions. The Triassic early dinosaurs and their dinosauromorph precursors were comparatively low in abundance (and diversity) and were only minor components of tetrapo...
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The Neoproterozoic Tsagaan-Olom Group is exposed in the Zavkhan Terrane of southwestern Mongolia and hosts unique geochemical, paleoclimate, and paleontological records that have become central to our understanding of this pivotal interval of Earth history. New sedimentological, stratigraphic, geochronological, and geochemical data provide context...
Article
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Oceanic detachment faults are increasingly recognized as playing an integral role in the seafloor spreading process at slow and ultraslow spreading mid-ocean ridges, with significant consequences for the architecture of the oceanic lithosphere. Although melt supply is considered to play a critical control on the formation and evolution of oceanic d...
Conference Paper
Full-text available
Mollusk-­rich assemblages with Watsonella crosbyi with or without Aldanella spp. represent a temporally problematical, earliest Cambrian interval. Although frequently regarded as Tommotian-­equivalents (upper Terreneuvian), new biotic and carbon isotope data demonstrate a pre­-Tommotian (middle Terreneuvian) age for early W. crosby-i­A. spp. assemb...
Article
It currently is unknown when Earth's dynamo magnetic field originated. Paleomagnetic studies indicate that a field with an intensity similar to that of the present day existed 3.5 billion years ago (Ga). Detrital zircon crystals found in the Jack Hills of Western Australia are some of the very few samples known to substantially predate this time. W...
Article
Full-text available
The utility of ICS International Chronostratigraphic Charts (ICS Charts) relies on the accuracy and precision of reported geochronologic dates and their relationship to the bases of global chronostratigraphic units. However, an examination of some early Paleozoic dates (i.e., Cambrian–Ordovician boundary and lowest Ordovician) on the ICS Charts sho...
Article
The presence of early Eocene neartrench magmatism in western Washington and southern British Columbia has led to speculation that this area experienced ridge-trench interaction during that time. However, the effects of this process as they are preserved in other parts of the geologic record are poorly known. We present highprecision U-Pb zircon geo...
Article
Combining high-spatial resolution and high-precision geochronology and geochemistry of zircon provides constraints on the timing and duration of ultrahigh-pressure (UHP) metamorphism resulting from the collision of Baltica-Avalonia and Laurentia during the Scandian orogeny in the Western Gneiss Region of Norway. Zircons were extracted from a layere...
Article
Full-text available
The end-Permian mass extinction was the most severe in the Phanerozoic, extinguishing more than 90% of marine and 75% of terrestrial species in a maximum of 61 ± 48 ky. Because of broad temporal coincidence between the biotic crisis and one of the most voluminous continental volcanic eruptions since the origin of animals, the Siberian Traps large i...
Article
Full-text available
A mid-Permian (Guadalupian epoch) extinction event at approximately 260 Ma has been mooted for two decades. This is based primarily on invertebrate biostratigraphy of Guadalupian-Lopingian marine carbonate platforms in southern China, which are temporally constrained by correlation to the associated Emeishan Large Igneous Province (LIP). Despite at...
Article
Full-text available
Mixed 235U-233U-205Pb(-202Pb) tracers for U-Pb isotope-dilution isotope ratio mass spectrometry have been prepared under the auspices of the EARTHTIME Initiative. The methods and results for the preparation and calibration of the U/Pb ratio and isotopic abundances are given, and the various sources of uncertainty are discussed and quantified. The a...
Article
A limiting factor in the accuracy and precision of U/Pb zircon dates is accurate correction for initial disequilibrium in the 238U and 235U decay chains. The longest-lived—and therefore most abundant—intermediate daughter product in the 235U isotopic decay chain is 231Pa (T1/2 = 32.71 ka), and the partitioning behavior of Pa in zircon is not well c...
Article
A statistical approach to evaluating uncertainties in the calibration of multi-element isotopic tracers has been developed and applied to determining the isotopic composition of mixed U-Pb ( Pb- Pb- U- U) tracers used for accurate isotope dilution U-Pb geochronology. Our experiment, part of the EARTHTIME initiative, directly links the tracer calibr...
Article
Full-text available
Astronomical calibration of the geological timescale has been limited until recently by the precision and accuracy of radioisotopic dates, especially for pre-Neogene records. Uncertainties for radioisotopic dates of older strata were typically much larger than a single precessional cycle, and dates were often sparse, leading to the practice of orbi...
Article
Full-text available
New U/Pb analyses of zircon and xenotime constrain the timing of magmatism, magmatic assimilation and hydrothermal metamorphism during formation of the lower crust at the Mid-Atlantic Ridge (MAR). The studied sample is an altered gabbro from the Vema lithospheric section (11ºN). Primary gabbroic minerals have been almost completely replaced by mult...
Article
Full-text available
The Never Summer Mountains in north-central Colorado, USA, are cored by two Oligocene, epizonal granitic plutons originally emplaced in the shallow levels of a short-lived (similar to 1 m.y.), small-volume continental magmatic system. The younger Mt. Cumulus stock (28.015 +/- 0.012 Ma) is a syenogranite equivalent compositionally to topaz rhyolites...
Chapter
Covering a key connection between geological processes and life on Earth, this multidisciplinary volume describes the effects of volcanism on the environment by combining present-day observations of volcanism and environmental changes with information from past eruptions preserved in the geologic record. The book discusses the origins, features and...