Trace element geochemistry of zircons from the Kahnouj ophiolite complex: implications for petrogenesis and geodynamic setting

The Coldbrook Group and related plutons in the Caledonian Highlands of southern New Brunswick contain voluminous late Ediacaran silicic rocks formed in a magmatic event not recognized in other parts of Avalonia in the northern Appalachian orogen. To better constrain the age and origin of these rocks, we used U-Pb zircon dating by laser ablation inductively coupled plasma (LA-ICP-MS) followed by chemical abrasion thermal ionization mass spectrometry (CA-TIMS). Four silicic samples were dated from the Coldbrook Group, one from the Bonnell Brook pluton, and, for comparison, a felsic lithic-crystal tuff sample from the older arc-related Broad River Group. Overlapping CA-TIMS dates of 551.57 ± 0.23, 551.38 ± 0.24 Ma, and 551.70 ± 0.20 Ma for samples from the lower, middle, and upper Coldbrook Group, respectively, and 551.71 ± 0.19 Ma for granite from the Bonnell Brook pluton show that these units crystallized in 760,000 years or less, consistent with a super-eruption event. Rhyolite from the uppermost unit of the Coldbrook Group yielded a younger date of 549.18 ± 0.09 Ma, but the large extent of that unit suggests the possibility of a second younger super-eruption. The Broad River Group sample yielded a date of 615.48 ± 0.16 Ma, consistent with previously published dates from that group and associated plutons. Differences in zircon chemistry between the Broad River Group sample and the late Ediacaran samples are consistent with the contrasting subduction-related vs within-plate extensional tectonic settings as suggested by previous studies of whole-rock petrological characteristics of the two age groups.

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The journey of the Band-e-Zeyarat ophiolite (Makran Accretionary Wedge, SE Iran) from the mid-ocean ridge to the accretionary complex: new insights from its sedimentary cover and associated basaltic dykes and sills

Barbero,

Pandolfi,

Delavari

et al. 2023

JGS

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The Band-e-Zeyarat ophiolite (BEZO) sedimentary cover in the Makran Accretionary Prism (SE Iran) records a complex tectono-sedimentary evolution, extending from its formation at a mid-ocean ridge setting to deformation in an accretionary prism. Stratigraphic and biostratigraphic data indicate the occurrence of a Valanginian transition zone sequence separating the volcanic sequence and pelagic sedimentary cover. The latter consists of lower Hauterivian cherty limestone passing upwards to upper Hauterivian – Barremian marl and limestone. The pelagic sedimentary cover continues with post-Barremian – Cenomanian (?) marls. Arenites are interlayered in the sedimentary cover; they are composed of rock fragments derived from volcanic arc and continental margin settings. The BEZO sedimentary cover is intruded by dykes and sills showing enriched mid-ocean ridge (MOR) basalt chemical affinity. Structural analysis indicates a polyphase deformation history that involved faulting and folding. Our multidisciplinary results indicate that the BEZO formed in a MOR setting and that it was subsequently overprinted by off-axis and within-plate magmatism as it spread away from this MOR. The Band-e-Zeyarat oceanic crust was incorporated into the Makran prism in the latest Late Cretaceous – Paleocene, and was further deformed via strike-slip faulting along the dextral Minab-Sabzevaran fault during the Miocene - Pliocene. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists Supplementary material: https://doi.org/10.6084/m9.figshare.c.6843835

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Trace element geochemistry of zircons from the Kahnouj ophiolite complex: implications for petrogenesis and geodynamic setting

Cited by 4 publications

References 71 publications

Origin of Fe Ti mineralization in the Late Jurassic to Early Cretaceous Kahnouj ophiolitic complex, Makran accretionary prism, SE Iran

Origin of Fe Ti mineralization in the Late Jurassic to Early Cretaceous Kahnouj ophiolitic complex, Makran accretionary prism, SE Iran

Precise U–Pb zircon dates from silicic super-eruptions during late Ediacaran extension in the Avalonian Caledonia terrane of southern New Brunswick, Canada

The journey of the Band-e-Zeyarat ophiolite (Makran Accretionary Wedge, SE Iran) from the mid-ocean ridge to the accretionary complex: new insights from its sedimentary cover and associated basaltic dykes and sills

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