Th/U Relations as an Indicator of the Genesis of Metamorphic Zircons (On the Example of the North of the Urals)

Pystina, Yu. I.; Pystin, A. M.

doi:10.1007/978-3-030-22974-0_30

Cited by 3 publications

(2 citation statements)

References 6 publications

(4 reference statements)

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“…These results are consistent with previous zircon U‐Pb geochronology results from the Beartooth Mountains (Mueller et al., 2008; Wooden et al., 1988). Analyses with ages ≥2,791.4 Ma, comprising 10/11 concordant analyses, had Th/U values > 0.2 (see Figure S1d in Supporting Information S1), suggesting these ages record magmatic growth of zircon (e.g., Pystina & Pystin, 2019). A lower Th/U value of 0.04 was obtained for a single analysis with an age of 2,688.97 ± 12.90 Ma, consistent with minor Neoarchean metamorphic growth of zircon.…”

Section: Analytical Resultsmentioning

confidence: 99%

Orogens of Big Sky Country: Reconstructing the Deep‐Time Tectonothermal History of the Beartooth Mountains, Montana and Wyoming, USA

et al. 2023

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Thank you, Miranda Grover, for being the most supportive person in the world. I would have certainly lost weight and likely sanity without your nurturing love, understanding, and latenight leftover deliveries. I am grateful to my friend Caden Howlett-every discussion with you leaves me with a renewed enthusiasm for the mysteries of the natural world. Thank you to Stuart Parker, Mariah Romero, Sophie Black, and other student researchers for serving as sources of geologic inspiration. I am indebted to my undergraduate and graduate professors for sharing their knowledge and excitement with me. I am grateful to Dr. Colleen Elliot, Katie McDonald, and others at the MBMG for sharing their knowledge of Montana geology. I am also thankful to Chris Kussmaul, Dom D'Amato, Chris Baird, and others who assisted me with field work. I express immense love and appreciation for my mother and father-Amby and Kyle Ronemus-to whom I owe the entirety of my curiosity. Thank you for your support, encouragement, and understanding unceasing since the day I was born. Finally, this project would not have been possible without financial support from Montana State University, the MSU Department of Earth Sciences and the Tobacco Root Geological Society.

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Section: Analytical Resultsmentioning

confidence: 99%

Orogens of Big Sky Country: Reconstructing the Deep‐Time Tectonothermal History of the Beartooth Mountains, Montana and Wyoming, USA

et al. 2023

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“…U/Th ratios and U concentrations were obtained during U-Th-Pb analysis on the Element2 LA-ICP-MS. U/Th ratios are often used for first order petrogenetic characterization of zircons, though caveats exist and the ratio should not be used in isolation (e.g., Kirkland et al, 2015;Pystina & Pystin, 2019;Rubatto, 2002).…”

Section: U/th Ratios and U Concentrationmentioning

confidence: 99%

Triassic–Jurassic Accretionary History and Tectonic Origin of Stikinia From U‐Pb Geochronology and Lu‐Hf Isotope Analysis, British Columbia

et al. 2021

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The timing of assembly and tectonic origins of terranes in the northern Cordillera of Alaska, British Columbia, and the Pacific Northwest are debated. Stikinia, a long-lived arc terrane, has an enigmatic regional Mesozoic accretionary history and its tectonic origins remain unconstrained. Zircon U-Pb geochronology and Lu-Hf isotopic data on Triassic-Jurassic sedimentary and igneous rocks from central Stikinia shed light on the terrane-scale effects of a latest Triassic-Early Jurassic collision between Stikinia and pericratonic Yukon-Tanana terrane. Main age peaks from central Stikinia are 250-160 Ma, reflecting ongoing Mesozoic arc-related igneous activity within Stikinia. Comparison of isotopic evolution and unconformity development between central Stikinia and northern Stikinia (Whitehorse trough) provide new constraints on regional latest Triassic-earliest Jurassic deformation. We attribute the shortening-related deformation to variable along-strike interactions during end-on collision with the Yukon-Tanana terrane, with significant crustal thickening at the northern apex of Stikinia that did not persist farther south. A small pre-Devonian zircon population is significant, as the oldest exposed rocks in Stikinia are Early Devonian. Pre-Devonian age peaks differ from those of the northern Yukon-Tanana terrane, but resemble zircons from southern Wrangellia. These zircons are likely multi-cyclic, derived from crust that originated in the Arctic region near the northern end of the Caledonide orogeny. We suggest that Stikinia was an independent crustal block prior to latest Triassic onset of collision with Yukon-Tanana terrane. The ongoing, end-on collision in turn promoted oroclinal assembly of the peri-Laurentian terranes. GEORGE ET AL.

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First report of an Ediacarian basement in the Western Alps: the Serre Chevalier crystalline unit (Briançonnais domain, France)

Thiéblemont,

Jacob,

Lach

et al. 2023

BSGF - Earth Sci. Bull.

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We report new LA-ICP-MS U-Pb zircon ages of varied crystalline rocks occurring in an allochtonous unit of basement terrain located at the top of the Briançonnais nappes stack ~5 km west of Briançon city. Mapped as an undifferentiated metasedimentary basement on the geological map at 1/50,000 scale, this unit actually displays varied lithologies including alternating micaschist, paragneiss, quartzite, coarse-grained conglomerate and felsic (leptynite) to mafic (amphibolite) gneiss of magmatic origin. All rocks were metamorphosed in response to a dominant pre-Alpine event under garnet-amphibolite facies conditions. Retrogression under amphibolite to greenschits facies was associated with alpine events. Zircon ages were obtained on four types of rocks: (i) a micaceous quartzite from the core of the metasedimentary unit displays a dominant age population around 610 Ma and subordinated age populations at c. 940 Ma, 1825 Ma and 2100-2560 Ma ; (ii) a granite boulder from a coarse-grained conglomerate yields a dominant magmatic age of 582 ± 5 Ma and subordinated inherited ages between 1800 and 2200 Ma. Zircon metamorphic rims provide a concordant age of 492 ± 4 Ma ; (iii) a gneissic band in the vicinity of the conglomerate is dated at 597 ± 4 Ma ; (iv) a coarse-grained garnet amphibolite yields an age of 517 ± 3 Ma interpreted as the emplacement age of the protolith. The mainly Ediacarian record in the metasediments (quartzite and granite boulder in conglomerate) with no evidence of younger zircons indicates that this material resulted from the erosion of a nearby Ediacarian (Cadomian ?) basement. The age of 517 Ma obtained on the amphibolite provide a minimum age for the sedimentary succession which deposition is therefore bracketed between 582 Ma and 517 Ma. This interval is comparable to that of the metasedimentary units of the Brioverian group of the Armorican Massif. Based on their low Th/U ratio, the 492 Ma-old zircon rims in the granite boulder are attributed to an Upper Cambrian metamorphic event, but it is not yet clear whether this event corresponds to the garnet - amphibolite facies metamorphism recorded in the Serre Chevalier crystalline terrain.

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Th/U Relations as an Indicator of the Genesis of Metamorphic Zircons (On the Example of the North of the Urals)

Cited by 3 publications

References 6 publications

Orogens of Big Sky Country: Reconstructing the Deep‐Time Tectonothermal History of the Beartooth Mountains, Montana and Wyoming, USA

Orogens of Big Sky Country: Reconstructing the Deep‐Time Tectonothermal History of the Beartooth Mountains, Montana and Wyoming, USA

Triassic–Jurassic Accretionary History and Tectonic Origin of Stikinia From U‐Pb Geochronology and Lu‐Hf Isotope Analysis, British Columbia

First report of an Ediacarian basement in the Western Alps: the Serre Chevalier crystalline unit (Briançonnais domain, France)

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