Interpreting data dispersion and “inverted” dates in apatite (U–Th)/He and fission-track datasets: An example from the US midcontinent

Flowers, Rebecca M.; Kelley, Shari A.

doi:10.1016/j.gca.2011.06.016

Cited by 156 publications

(144 citation statements)

References 46 publications

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“…One reason for this disparity may lie in regional Early Jurassic reheating (Veselovskiy et al, 2013). Similar mismatches between geological and geomorphological indicators of denudation depths and AFT results have, however, been reported from other shield and platform areas (Gunnell, 2000;Hall & Bishop, 2002;Gunnell et al, 2003;Peulvast et al, 2008;Flowers & Kelley, 2011). Specifically, identification of reheating in AFT studies has led to appeals for burial by thick sedimentary covers of which few, if any traces remain (Gunnell, 2000).…”

Section: Synthesissupporting

confidence: 52%

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

Hall¹

2015

NJG

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Contrasting views exist on the stability of the Earth's shield regions over the last 1 Ga that have major implications for reconstructing erosion patterns on shields and the supply of sediment to intra-cratonic and marginal basins. This paper explores Phanerozoic denudation rates and patterns on the northern part of the Fennoscandian Shield in the Kola Peninsula, Northwest Russia. This shield region was intruded by magmatic rocks of the Kola Alkaline Province (KAP) in the Devonian and Early Carboniferous. The KAP comprises a varied suite of alkali-ultramafic plutonic and hypabyssal intrusions, diatremes and dykes that was emplaced at various depths in the crust and allows assessment of depths and rates of erosion during and since the KAP magmatic episode. Further evidence of long-term denudation is provided by Mesoproterozoic and Neoproterozoic cover rocks found around the margins of the Kola Peninsula and in the White Sea. The burial and exhumation history is compared to available Apatite Fission Track (AFT) data for the Kola Peninsula and adjacent areas. Post-Devonian denudation rates on the shield rocks of the Kola Peninsula have varied in space and time. Around the periphery of the Kola Peninsula, low long-term denudation of shield rocks is indicated by the survival of Riphean cover rocks and Late Devonian lavas, kimberlite crater facies and near-surface emplacement of dykes. In contrast, in the main belts of KAP intrusions, 4-6 km of rock was removed in response to doming between 460 and 360 Ma. Deep denudation is indicated by the emplacement depths of alkaline intrusions and Phoscorite-Carbonatite pipes (PCPs). Erosion on the Kola Peninsula since 360 Ma has been far more limited. Extensive, shallow, late-stage magmatism associated with PCPs, dykes and the large alkaline intrusions in the KAP indicates that erosion depths nowhere exceeded 2 km. PostDevonian denudation has removed <1 km of rock from the margins of the Kola Peninsula and from the backslope of the Saariselkä-Karelia scarp in northern Finland. AFT data point to an important phase of erosion in the early Mesozoic but depths of unroofing of 3-5 km based on AFT cooling ages for this later phase are in conflict with the evidence of lesser erosion provided by the late-stage KAP intrusions and also require unrealistic depths of former Devonian to Triassic cover rocks. Mean denudation rates were greatest (up to 40 m/Myr) during the KAP magmatic phase. Post-Devonian rates across the Kola Peninsula and adjacent shield areas were much lower (<3-6 m/Myr) and are compatible with low long-term denudation rates for other cratons. Further resolution of long-term denudation patterns and rates on the Kola Peninsula requires the application of low-temperature thermochronometry, detailed examination of the regional geomorphology and firmer dating of ancient weathering episodes.

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Section: Synthesissupporting

confidence: 52%

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

Hall¹

2015

NJG

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“…11C and 12B) suggests that, in some cases, anomalously large sample dispersion may indicate a problem with apatite eU zonation. A recent study showed that substantial AHe data dispersion for a cratonic basement sample without date-eU and date-grain size correlations could be reasonably explained using a viable range of eU zonation (Flowers and Kelley, 2011). Thus, simply not interpreting data from irreproducible AHe datasets that lack date-eU and date-grain size patterns is a straightforward approach to avoiding misinterpretation of such samples (Flowers and Kelley, 2011).…”

Section: Summary Of Eu Zonation Effects On Sample Ahe Datesmentioning

confidence: 99%

“…A recent study showed that substantial AHe data dispersion for a cratonic basement sample without date-eU and date-grain size correlations could be reasonably explained using a viable range of eU zonation (Flowers and Kelley, 2011). Thus, simply not interpreting data from irreproducible AHe datasets that lack date-eU and date-grain size patterns is a straightforward approach to avoiding misinterpretation of such samples (Flowers and Kelley, 2011). Alternatively, one could acquire additional information regarding eU zonation or evaluate other potential causes of dispersion such as He implantation from neighboring grains (e.g., Spiegel et al, 2009) or U-Th rich micro-inclusions (e.g., Vermeesh et al, 2007) to help decipher the significance of the dataset.…”

Section: Summary Of Eu Zonation Effects On Sample Ahe Datesmentioning

confidence: 99%

Is apatite U–Th zonation information necessary for accurate interpretation of apatite (U–Th)/He thermochronometry data?

Ault

Flowers

2012

Geochimica et Cosmochimica Acta

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“…Intrasample scatter of (U-Th)/ He apparent ages, some of which are older than coexisting AFT apparent ages (i.e., the inverted AHe-AFT age relationship) is not uncommon in AHe thermochronology and has been attributed to several different processes, including (1) differential He diffusion properties mainly controlled by radiation damage in individual apatite crystals (Green et al 2006;Shuster et al 2006;Flowers et al 2009;Flowers and Kelley 2012); (2) uneven distribution of U-Th within single-apatite grains, leading to incorrect alpha-recoil corrections and resulting in complex 4 He profiles and radiation damage distributions (Hourigan et al 2005;Farley et al 2011;Ault and Flowers 2012); (3) fragmentation of originally larger grains, resulting in AHe age that represents only a portion of He distribution in the original grain (Beucher et al 2012;Brown et al 2013); (4) injection of alpha particles from U-Th-rich inclusions such as zircon, monazite, or allanite (House et al 1997;Ehlers and Farley 2003;Vermeesch et al 2007); and (5) implantation of 4 He from adjacent U-Th-rich phases (Farley 2003;Spiegel et al 2009;Murray et al 2011).…”

Section: Discussionmentioning

confidence: 99%

“…Differential He diffusion parameters among different grains in the same sample may be amplified when apatite grains have a relatively large intergrain variation of eU (p [U] ϩ 0.235 [Th]) and have experienced prolonged residence at the shallow crustal level (Flowers and Kelley 2012). However, the ZFT ages from the Kythera and Peloponnese samples are in the range of 9.1-21.3 Ma, suggesting that the rocks experienced a subduction-related metamorphic reheating event at conditions above ∼240Њ ‫ע‬ 50ЊC (ZFT closure temperature; Brandon et al 1998).…”

Section: Discussionmentioning

confidence: 99%

Rapid Exhumation of High-Pressure Metamorphic Rocks in Kythera-Peloponnese (Greece) Revealed by Apatite (U-Th)/He Thermochronology

Marsellos

Min

Foster

2014

The Journal of Geology

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A B S T R A C TApatite (U-Th)/He and apatite fission-track cooling ages from high-pressure (HP) metamorphic rocks in the South Aegean forearc along the Kythera Strait (Kythera and southeastern Peloponnese) suggest rapid exhumation during Middle to Late Miocene times. HP rocks from the Kythera Strait exhibit two perpendicular extensional structures. Samples with arc-normal or arc-parallel extensional fabrics yielded apatite (U-Th)/He cooling ages of ∼8-10 Ma. The more precise (U-Th)/He ages are consistent with previously reported apatite and zircon fission-track ages obtained from the same rock units. The less precise, but still accurate, fission-track data provided a reference for (U-Th)/He dating on relatively young uranium-poor apatites. The combined data, therefore, precisely and accurately constrain the exhumation history of HP rocks and indicate that localized arc-parallel extension in the Kythera Strait was active for an ∼5 m.yr. interval during the regional arc expansion.

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Interpreting data dispersion and “inverted” dates in apatite (U–Th)/He and fission-track datasets: An example from the US midcontinent

Cited by 156 publications

References 46 publications

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

Phanerozoic denudation across the Kola Peninsula, Northwest Russia: implications for long-term stability of Precambrian shield margins

Is apatite U–Th zonation information necessary for accurate interpretation of apatite (U–Th)/He thermochronometry data?

Rapid Exhumation of High-Pressure Metamorphic Rocks in Kythera-Peloponnese (Greece) Revealed by Apatite (U-Th)/He Thermochronology

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