The correlation between reduction in fission-track diameter and areal track density in volcanic glass shards and its application in dating tephra beds

Sandhu, A.S.; Westgate, John A.

doi:10.1016/0012-821x(95)00022-5

Cited by 53 publications

(48 citation statements)

References 25 publications

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“…Obtaining an accurate age also depends on whether the tracks are etched sufficiently so that their mean diameter is in the range 6-8 mm (Westgate 1989). Sandhu and Westgate (1995) suggest that an optimum etch size for glasses is ca. 7 mm.…”

Section: Geochronologymentioning

confidence: 99%

“…Samples are heated at 150 7C for 30 days. a Etched in 26% HF b Ratio of mean spontaneous track diameter (Ds) to mean induced track diameter c Number of tracks counted d Weighted by inverse of the variance e Unheated age determined f Unheated age corrected by multiplying the spontaneous density by Di/Ds(Shane et al 1994;Sandhu and Westgate 1995). Ages calculated from the equation ofPrice and Walker (1963) using the following parameters: lDp1.55!10 P10 year P1 ; lFp7.03!10 P17 year P1 ; sFp580!10 P24 cm 2 ; Ip7.252B10 P3 .…”

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confidence: 99%

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Chronological and palaeomagnetic constraints on widespread welded ignimbrites of the Taupo volcanic zone, New Zealand

et al. 1996

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Large volume (100-1000 km 3 ), widespread rhyolitic ignimbrites are the main products of the Taupo volcanic zone (TVZ) of New Zealand, one of the most active silicic volcanic regions on Earth. Several factors have made correlation and the eruptive history of the ignimbrites difficult to resolve, including limited exposure and chronological data, broadly similar lithologies and the lack of stratigraphic successions visible in the field. We have used the isothermal plateau fission track (ITPFT) method on glass shards from the nonwelded basal zones to obtain new eruption ages for the widespread units: Ongatiti (1.25B0.12 Ma), Whakamaru group (0.34B0.03 Ma), Matahina (0.34B0.02 Ma), Chimp (0.33B0.02 Ma), Kaingaroa (0.31B0.01 Ma) and Mamaku (0.23B0.01 Ma) ignimbrites. These glasses show little evidence of geochemical alteration and allow the units to be fingerprinted for correlation.The glass ages we have obtained for the late Quaternary units provide an independent check on chronological data obtained from phenocryst phases. The ITPFT method is a useful dating approach for sanidine-poor eruptives which limit the application of 40 Ar/ 39 Ar. Errors as limited as 10-30 ka can be obtained from the weighted mean of several age determinations. The thermoremanent magnetic (TRM) direction recorded in the units provides a means of correlation over a wide area of the TVZ, because each ignimbrite can be distinguished by its unique record of palaeosecular variation. These data indicate that the four separately mapped members of the Whakamaru group represent the same phase of activity, occurring within a period of 100 years. The TRM data indicate that the widespread Ahuroa ignimbrite erupted during an excursion in Earth's magnetic field, perhaps associated with the Cobb Mountain subchron (ca. 1.2 Ma). The youngest widespread welded unit, Mamaku ignimbrite (ca. 0.23 Ma), also erupted during an excursion and may represent a southern hemisphere record of the Pringle Falls geomagnetic episode found in the western United States. The palaeomagnetic and ITPFT data for the widespread late Quaternary ignimbrites suggest a major period of caldera formation at 0.34-0.30 Ma. This interval represents the eruption of multiple units from the Whakamaru caldera, followed by the formation of the Okataina and Reporoa calderas in rapid succession.

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Section: Geochronologymentioning

confidence: 99%

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confidence: 99%

Chronological and palaeomagnetic constraints on widespread welded ignimbrites of the Taupo volcanic zone, New Zealand

et al. 1996

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“…Number of tracks counted is given in brackets. Glass-fission-track age of UT-1366 is uncorrected for partial track fading; UT-1366* dated by the diameter-correction fission-track method (Sandhu & Westgate 1995). Accuracy of the glass-ITPFT method has been monitored on other occasions by use of reference glasses: JAS-G1 (UT-1141) with an 40 Ar/ 39 Ar age of 0.947 + 0.005 Ma (Kitada & Wadatsumi 1995;Balestrieri et al 1998) to the analytical error, and is common amongst MioceneRecent tephras in New Zealand (Shane 2000).…”

Section: Glass Shard Chemistrymentioning

confidence: 99%

Deep‐ocean record of major late Cenozoic rhyolitic eruptions from New Zealand

Carter

Alloway

Shane

et al. 2004

New Zealand Journal of Geology and Geophysics

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A 12 m.y. record of large rhyolitic eruptions from the Coromandel (CVZ) and Taupo (TVZ) Volcanic Zones of New Zealand is contained in cores retrieved by Leg 181 of the Ocean Drilling Program. Site 1124, located 670 km from the TVZ, has a maximum of 134 macroscopic tephra layers with a total thickness of 13.18 m. These units, along with between 7 and 63 tephras from 3 other sites, were dated by a combination of magnetostratigraphy, biostratigraphy, isothermal plateau fission track determinations, and geochemical correlation with onshore tephra deposits. Additional time control for the last 3 m.y. came from an orbitally tuned, benthic, oxygen isotope profile for Site 1123.Results extend the incomplete terrestrial record of volcanism by placing the first major rhyolitic eruption in the CVZ at c. 12 Ma, c. 1.6-1 m.y. earlier than previously known. Tephras became thicker and more frequent from the late Miocene into the Quaternary-a trend that probably reflected (1) more frequent and intense volcanism and (2) reduced distances between sources and depositional sites on the evolving Australian/Pacific plate system. The passage from CVZ to Quaternary TVZ occurred without a major hiatus in activity, suggesting the transition was gradational. The ensuing TVZ volcanism was more continuous than known previously from the onshore geology. Ash dispersal was primarily eastward, highlighting the dominance of westerly winds since the middle Miocene. Nevertheless, variations in dispersal patterns suggest periodic changes in wind direction/speed and/or ejection of ash beyond the Roaring Forties.

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“…Two are mentioned here. Experimental studies by Sandhu and Westgate (1995) The isothermal plateau FT (ITPFT) method uses a single heat treatment of 150 C for 30 days to correct fully for PTF (Westgate 1989). The FT age of a sample is proportional to r s /r i , and the point at which this ratio does not change with increasing time at a specified temperature -the plateau condition -signals a full correction for PTF and is confirmed by D s ¼ D i .…”

Section: Correction Methods For Ptf In Glassesmentioning

confidence: 99%