New high precision U-Pb ages and Hf isotope data from the Karoo large igneous province; implications for pulsed magmatism and early Toarcian environmental perturbations

Greber, Nicolas D.; Davies, Joshua; Gaynor, Sean P.; Jourdan, Fred; Bertrand, Hervé; Schaltegger, Urs

doi:10.1016/j.ringeo.2020.100005

Cited by 34 publications

(15 citation statements)

References 68 publications

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“…The province also contains basalt flows which erupted into rift basins in Morocco, Algeria, Portugal, Brazil, Bolivia, and NE North America and two large layered mafic intrusions in Guinea and Sierra Leone. In terms of timing, the province was emplaced in ~ 1 Ma (Marzoli et al 1999;Blackburn et al 2013;Davies et al 2017;Heimdal et al 2018) which is similar to other well-known Phanerozoic LIPs (Siberian Traps, Karoo-Farrar, Deccan, Columbia river flood basalts Svensen et al 2012;Greber et al 2020;Kasbohm and Schoene 2018;Schoene et al 2019). The CAMP is, however, distinct from these other LIPs, since it has very few preserved flood basalt lava flows and contains gabbroic intrusions that cover an extremely large area over ~ 8000 km from northern France to southern Bolivia (Jourdan et al 2003;Bertrand et al 2014) with a volume of at least 3 million km 3 .…”

Section: Camp Magmatic Province Overviewsupporting

confidence: 58%

“…Zircon and other Zr-bearing phases (e.g., baddeleyite and zirconolite) may be found in rocks from mafic large igneous provinces (LIPs) and are frequently used to provide highprecision age control of these events (Svensen et al 2009;Schoene et al 2010a;Svensen et al 2012;Blackburn et al 2013;Davies et al 2017;Greber et al 2020). Precise U-Pb geochronology from mafic LIPs in the Phanerozoic has led to new insights into how these eruptions influence the Earth's atmosphere, hydrosphere, and biosphere.…”

Section: Introductionmentioning

confidence: 99%

“…Currently, zircon Hf isotope measurements are not commonly used in studying LIPs especially from mafic rocks (baddeleyite Hf isotopes have been used in a few studies). These data are available for the Emeishan LIP, although mostly from the felsic portion of the province (see review by Shellnutt 2014), Central Atlantic magmatic province (CAMP Davies et al 2017;Callegaro et al 2017), the Tarim LIP (Zhang et al 2016), the Paranà-Etendeka (Hartmann et al 2019;Rocha et al 2020), Karoo LIP (Greber et al 2020), and also some mafic dyke swarms, which may have been associated with flood basalt eruptions; e.g., the dykes in the Qiangtang terrane (Zhai et al 2013). Other LIP zircon geochemical information, e.g., trace elements, have been measured from some CAMP basalts (Schoene et al 2010b;Davies et al 2017), and oxygen isotopes have been investigated from mafic zircon in the Tarim LIP (Zhang et al 2016) and the Scourie dyke swarm (Davies et al 2015).…”

Section: Introductionmentioning

confidence: 99%

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Zircon petrochronology in large igneous provinces reveals upper crustal contamination processes: new U–Pb ages, Hf and O isotopes, and trace elements from the Central Atlantic magmatic province (CAMP)

Davies

Marzoli

Bertrand

et al. 2021

Contrib Mineral Petrol

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Zircon occasionally crystallizes in evolved melt pockets in mafic large igneous province (LIP) magmas, and in these cases, it is used to provide high-precision age constraints on LIP events. The precision and accuracy of high-precision ages from LIPs are crucially important, because they may be implicated in mass extinctions. However, why zircon crystallizes in these magmas is not clearly understood, since their mafic compositions should limit zircon saturation. Here, we investigate the occurrence of zircon (and baddeleyite) in intrusive and extrusive mafic rocks from Central Atlantic Magmatic Province (CAMP) using petrography, trace-element analysis, Ti temperatures, Hf and oxygen isotopes, and high-precision U–Pb geochronology, along with petrological and thermal modeling. We provide new ages for CAMP sills that intruded into Paleozoic sediments in Brazil, indicating that the high and low Ti magmatism in this area occurred synchronously over 264 ± 57 ka. We show that upper crustal assimilation, especially of shales, during the emplacement of the CAMP likely led to zircon saturation. Assimilation of upper crustal sediments is also supported by high δ18O values and some rare negative εHf values in the zircon crystals. The only extrusive sample analyzed was the North Mountain basalt in Nova Scotia, Canada. This sample contains a large age variation in its zircon crystals (up to 4 Ma), and the older crystals have slightly more negative εHf values suggesting the presence of small (micron scale) xenocrystic cores associated with very late-stage sediment assimilation. However, the CAMP dataset as a whole suggests that the presence of xenocrystic cores is rare. Assuming no xenocrystic cores, and considering the zircon undersaturated nature of LIP mafic melts, the oldest zircon age clusters in a population should record the magma emplacement (or time when assimilation occurred), and the younger ages in a population are more likely to reflect Pb loss, especially given the high U concentrations of LIP zircon. Our identification of heterogeneous isotopic and elemental compositions in LIP zircon indicates that zircon in these magmas saturate in isolated minute melt pockets just before the system cools below its solidus.

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Section: Camp Magmatic Province Overviewsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Zircon petrochronology in large igneous provinces reveals upper crustal contamination processes: new U–Pb ages, Hf and O isotopes, and trace elements from the Central Atlantic magmatic province (CAMP)

Davies

Marzoli

Bertrand

et al. 2021

Contrib Mineral Petrol

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“…Zircon (ZrSiO 4 ) is a particularly useful accessory mineral phase for this purpose, as it incorporates abundant U up to 1000's of ppm, with negligible initial Pb (e.g., (1)). As a result, it is commonly used to reconstruct the precise durations and rates of geological processes, including the duration and tempo of magmatism (e.g., (2), ( 3), ( 4), ( 5), ( 6), ( 7), ( 8)), timescales of tectonic activity (e.g., ( 9), ( 10)), the formation of ore deposits (e.g., (11), (12), ( 13), ( 14)), dynamics of sedimentary systems (e.g., (15)), timescales of global climate and biotic change (e.g., (16), (17), (18)), and potential causal relationships between volcanic activity in large igneous provinces and global biotic and environmental deterioration (e.g., (19), (20), (21), (22), ( 23), (24), (25)). Precise U-Pb dates are crucial tools in the reconstruction of geological processes, therefore it is of paramount importance to know their accuracy, and to intercalibrate different mass spectrometry equipment and analytical protocols that are employed in different laboratories.…”

Section: Introductionmentioning

confidence: 99%

Long-term repeatability and interlaboratory reproducibility of high-precision ID-TIMS U–Pb geochronology

Schaltegger

Ovtcharova

Gaynor

et al. 2021

J. Anal. At. Spectrom.

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“…As put forward by Burgess and Bowring (2015), the beginning of intrusive activity throughout the STLIP is unconstrained, and future U-Pb geochronology endeavors should focus on the sills buried beneath the surface in the Tunguska Basin, despite their mafic composition. High-precision U-Pb data were successfully obtained on mafic sills in sedimentary basins from other LIPs (Greber et al 2020;Davies et al 2021), where zircon and baddeleyite crystallized in evolved interstitial pockets similar to those observed for the TB dolerites.…”

Section: Relative Chronology and Potential Implicationsmentioning

confidence: 73%

Geochemistry of deep Tunguska Basin sills, Siberian Traps: correlations and potential implications for the end-Permian environmental crisis

Callegaro

Svensen

Neumann

et al. 2021

Contrib Mineral Petrol

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A vast portion of the plumbing system of the Siberian Traps Large Igneous Province (STLIP) is emplaced in the Tunguska Basin, where borehole data reveal ubiquitous and abundant sills with great lateral extension. These intrusions intersect Cambrian–Ordovician evaporite, carbonate and siliciclastic series, and locally coal-bearing Permian host rocks, with a high potential for thermogenic gas generation. Here we present new geochemical data from 71 magmatic and 4 sedimentary rock samples from the Tunguska Basin center and periphery, recovered from 15 deep sills intercepted by boreholes. The studied samples are all low-Ti basalt and basaltic andesites, confirming absence of high-Ti and alkaline STLIP magmatism in the Tunguska Basin. The sills derive from picritic parental melts produced by extensive melting of a mantle source with recycled crustal components below a thinned lithosphere (50–60 km), within the spinel stability field. The mantle source was dominantly peridotitic, with enriched pyroxenitic domains formed by recycled lower crust, in agreement with previous models for the main tholeiitic STLIP phase. Limited amounts (up to 5%) of highly radiogenic granitoids or moderately radiogenic metapelites were assimilated in upper crustal magma reservoirs. After emplacement, sills intruded in Cambrian evaporites assimilated marlstones and interacted with the evaporitic host rocks, probably via fluids and brines. This is the first time that such process is described in subvolcanic rocks from all across the volcanic basin. The sills are correlated geochemically with the established chemostratigraphy for the on-craton STLIP lava piles and intrusions (Norilsk region). Sills correlated with the Morongovsky–Mokulaevsky Fm. and the Norilsk-type intrusions are the most voluminous, present all across the central Tunguska Basin, and bear the strongest evidence of interaction with evaporites. Massive discharge of thermogenic volatiles is suggested by explosive pipes and hydrothermal vent structures throughout the Tunguska Basin. We propose that this voluminous pulse of magmatism is a good candidate for the hitherto unidentified early intrusive phase of the STLIP, and may link the deep Tunguska basin sills to the end-Permian environmental crisis.

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New high precision U-Pb ages and Hf isotope data from the Karoo large igneous province; implications for pulsed magmatism and early Toarcian environmental perturbations

Cited by 34 publications

References 68 publications

Zircon petrochronology in large igneous provinces reveals upper crustal contamination processes: new U–Pb ages, Hf and O isotopes, and trace elements from the Central Atlantic magmatic province (CAMP)

Zircon petrochronology in large igneous provinces reveals upper crustal contamination processes: new U–Pb ages, Hf and O isotopes, and trace elements from the Central Atlantic magmatic province (CAMP)

Long-term repeatability and interlaboratory reproducibility of high-precision ID-TIMS U–Pb geochronology

Geochemistry of deep Tunguska Basin sills, Siberian Traps: correlations and potential implications for the end-Permian environmental crisis

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