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Full-Text Articles in Geophysics and Seismology
The Temporal Evolution Of Subduction Initiation In The Samail Ophiolite: High-Precision U–Pb Zircon Petrochronology Of The Metamorphic Sole, Matthew Rioux, Joshua M. Garber, Michael Searle, James L. Crowley, Sally Stevens, Mark Schmitz, Andrew Kylander-Clark, Kayla Leal, Tyler Ambrose, Andrew J. Smye
The Temporal Evolution Of Subduction Initiation In The Samail Ophiolite: High-Precision U–Pb Zircon Petrochronology Of The Metamorphic Sole, Matthew Rioux, Joshua M. Garber, Michael Searle, James L. Crowley, Sally Stevens, Mark Schmitz, Andrew Kylander-Clark, Kayla Leal, Tyler Ambrose, Andrew J. Smye
Geosciences Faculty Publications and Presentations
High-precision dating of the metamorphic sole of ophiolites can provide insight into the tectonic evolution of ophiolites and subduction zone processes. To understand subduction initiation beneath a young, well-preserved and well-characterized ophiolite, we performed coupled zircon laser-ablation inductively coupled mass spectrometry trace element analyses and high-precision isotope dilution-thermal ionization mass spectrometry U–Pb dating on 25 samples from the metamorphic sole of the Samail ophiolite (Oman-United Arab Emirates). Zircon grains from amphibolite- to granulite-facies (0.8–1.3 GPa, ~700–900°C), garnet- and clinopyroxene-bearing amphibolite samples (n = 18) show systematic trends of decreasing heavy rare earth element slope (HREE; Yb/Dy) with decreasing Yb …
Synchronous Emplacement Of The Anorthosite Xenolith-Bearing Beaver River Diabase And One Of The Largest Lava Flows On Earth, Yiming Zhang, Nicholas L. Swanson-Hysell, Mark D. Schmitz, James D. Miller, Margaret S. Avery
Synchronous Emplacement Of The Anorthosite Xenolith-Bearing Beaver River Diabase And One Of The Largest Lava Flows On Earth, Yiming Zhang, Nicholas L. Swanson-Hysell, Mark D. Schmitz, James D. Miller, Margaret S. Avery
Geosciences Faculty Publications and Presentations
New geochronologic and paleomagnetic data from the North American Midcontinent Rift (MCR) reveal the synchronous emplacement of the Beaver River diabase, the anorthosite xenoliths within it, and the Greenstone Flow—one of the largest lava flows on Earth. A U-Pb zircon date of 1091.83 ± 0.21 Ma (2σ) from one of the anorthosite xenoliths is consistent with the anorthosite cumulate forming as part of the MCR and provides a maximum age constraint for the Beaver River diabase. Paired with the minimum age constraint of a cross-cutting Silver Bay intrusion (1091.61 ± 0.14 Ma; 2σ), these data tightly …
A Mélange Of Subduction Ages: Constraints On The Timescale Of Shear Zone Development And Underplating At The Subduction Interface, Catalina Schist (Ca, Usa), K. M. Harvey, S. Walker, P. G. Starr, S. C. Penniston-Dorland, M. J. Kohn, E. F. Baxter
A Mélange Of Subduction Ages: Constraints On The Timescale Of Shear Zone Development And Underplating At The Subduction Interface, Catalina Schist (Ca, Usa), K. M. Harvey, S. Walker, P. G. Starr, S. C. Penniston-Dorland, M. J. Kohn, E. F. Baxter
Geosciences Faculty Publications and Presentations
The presence of mélange at the subduction interface influences numerous geochemical and geophysical processes. However, the relationship between the timescales of mélange development, deformation, and resultant mass transport is poorly understood. Here, we use Sm-Nd garnet geochronology to elucidate the timing of peak metamorphism for five garnet amphibolite tectonic blocks from the amphibolite-facies mélange zone of the Catalina Schist (Santa Catalina Island, CA). Ages range from 108 to 116 Ma and do not appear to correlate with the peak metamorphic temperature recorded by each block (between 640 and 740°C). The lack of correlation between age and peak temperature favors the …
Petrology And Geochronology Of Metamorphic Zircon, Matthew J. Kohn, Nigel M. Kelly
Petrology And Geochronology Of Metamorphic Zircon, Matthew J. Kohn, Nigel M. Kelly
Geosciences Faculty Publications and Presentations
Zircon is unusually well suited for investigating metamorphic processes because it is readily analyzed for U‐Pb ages, it harbors diverse mineral inclusions, and its chemistry can be linked to metamorphic parageneses and P‐T paths. Metamorphic zircon chemistry and ages are relevant only at the sub‐grain micron scale, and consequently many analytical methods, such as depth profiling, have been developed to exploit such spatially resolute information. Here we review how metamorphic zircon grows, and how its chemistry and inclusion assemblages may be used to link the age of a zircon domain to its metamorphic P‐T condition. Domain‐specific ages and inclusion assemblages …
Bridging The Gap Between The Foreland And Hinterland Ii: Geochronology And Tectonic Setting Of Ordovician Magmatism And Basin Formation On The Laurentian Margin Of New England And Newfoundland, Francis A. Macdonald, Paul M. Karabinos, James L. Crowley, Eben B. Hodgin, Peter W. Crockford, John W. Delano
Bridging The Gap Between The Foreland And Hinterland Ii: Geochronology And Tectonic Setting Of Ordovician Magmatism And Basin Formation On The Laurentian Margin Of New England And Newfoundland, Francis A. Macdonald, Paul M. Karabinos, James L. Crowley, Eben B. Hodgin, Peter W. Crockford, John W. Delano
Geosciences Faculty Publications and Presentations
Ordovician strata of the Mohawk Valley and Taconic allochthon of New York and the Humber margin of Newfoundland record multiple magmatic and basin-forming episodes associated with the Taconic orogeny. Here we present new U-Pb zircon geochronology and whole rock geochemistry and neodymium isotopes from Early Paleozoic volcanic ashes and siliciclastic units on the northern Appalachian margin of Laurentia. Volcanic ashes in the Table Point Formation of Newfoundland and the Indian River Formation of the Taconic allochthon in New York yield dates between 466.16 ± 0.12 and 464.20 ± 0.13 Ma. Red, bioturbated slate of the Indian River Formation record a …
Tectono-Metamorphic History Of The Eastern Taureau Shear Zone, Mauricie Area, Québec: Implications For The Exhumation Of The Mid-Crust In The Grenville Province, Renaud Soucy La Roche, Félix Gervais, Alain Tremblay, James L. Crowley, Gilles Ruffet
Tectono-Metamorphic History Of The Eastern Taureau Shear Zone, Mauricie Area, Québec: Implications For The Exhumation Of The Mid-Crust In The Grenville Province, Renaud Soucy La Roche, Félix Gervais, Alain Tremblay, James L. Crowley, Gilles Ruffet
Geosciences Faculty Publications and Presentations
This study investigates the tectono-metamorphic history and exhumation mechanisms of the mid-crustal Mékinac-Taureau domain of the Mauricie area, central Grenville Province. Macro- and micro-structural analyses reveal the top-down-to-the-ESE sense of shear on the eastern Taureau shear zone, a major extensional structure that exhumed the mid-crustal Mékinac-Taureau domain and juxtaposed it against the lower grade rocks of the Shawinigan domain. Peak metamorphism in the Mékinac-Taureau domain, inferred to be the result of northwestward thrusting and regional crustal thickening, took place under P–T conditions of 1000–1100 MPa and 820–880 °C prior to 1082 ± 20 Ma. Retrograde conditions varying from …
Improved Confidence In (U-Th)/He Thermochronology Using The Laser Microprobe: An Example From A Pleistocene Leucogranite, Nanga Parbat, Pakistan, J. W. Boyce, K. V. Hodges, D. King, James L. Crowley, M. Jercinovic, N. Chatterjee, S. A. Bowring, M. Searle
Improved Confidence In (U-Th)/He Thermochronology Using The Laser Microprobe: An Example From A Pleistocene Leucogranite, Nanga Parbat, Pakistan, J. W. Boyce, K. V. Hodges, D. King, James L. Crowley, M. Jercinovic, N. Chatterjee, S. A. Bowring, M. Searle
Geosciences Faculty Publications and Presentations
The newly developed laser microprobe (U-Th)/He thermochronometer permits, for the first time, the ability to generate precise (U-Th)/He cooling ages for even very young (Ma) samples with a spatial resolution on the order of tens of micrometers. This makes it possible to test the reproducibility of independent (U-Th)/He age determinations within individual crystals, further increasing the reliability of the method. As an example, we apply it here to a Pleistocene granite from Nanga Parbat, Pakistan, where previous constraints on the thermal history are consistent with rapid exhumation and cooling. Twenty-one (U-Th)/He dates determined on two monazite crystals from a single …