Detrital zircon U-Pb ages and trace element compositions from Cambrian rocks of western North America
Date
2019-02-08
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Abstract
The evolution of the western margin of Laurentia (present coordinates), associated with the disassembly of supercontinent Rodinia, comprises a greater than 200 Myr rift history. Neoproterozoic and Cambrian zircons found in Cambrian units across western North America are used to supplement the igneous record of rift-related magmatic activity along the margin and provide timing constraints for continental rifting. Zircons were measured by LA-ICP-MS through three rounds of ablation: (1) screening round to identify Neoproterozoic and Cambrian grains; (2) trace element round; (3) higher-precision age round. U-Pb ages and trace element compositions detrital zircons are used to define two episodes of rift-related magmatism and are used to test and revise models of Rodinia’s disassembly. The first episode includes late Tonian 780-720 Ma mafic magmatism related to the initial crustal thinning followed by mafic and intermediate magmatism within Cryogenian (720-635 Ma) rift basins. Apparent magmatic quiescence from 630 to 580 Ma coincides with margin-wide subsidence. The second episode of magmatism (580 to 520 Ma) is related to resumed rift tectonism and is followed by the establishment of the lower Paleozoic passive margin of western Laurentia (Sauk transgressive sequence). Cambrian zircon populations (near-depositional age zircons) provide important radiometric constraints on the timing of the Sauk transgression that marks the final breakup of Rodinia.
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Keywords
Rodinia, Laurentia, Sauk sequence, detrital zircon, U-Pb geochronology, zircon trace element content, continental rifting, tectonics
Citation
Madronich, L. I. (2019). Detrital zircon U-Pb ages and trace element compositions from Cambrian rocks of western North America (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.