Apatite (U-Th-Sm)/He thermochronology of rapidly cooled samples; the effect of He implantation

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doi: 10.1016/j.epsl.2009.05.045
Author(s): Spiegel, Cornelia; Kohn, Barry P.; Belton, David; Berner, Zsolt; Gleadow, Andrew J. W.
Author Affiliation(s): Primary:
Universität Bremen, Geowissenschaften, Bremen, Federal Republic of Germany
University of Melbourne, Australia
Universität Karlsruhe, Federal Republic of Germany
Volume Title: Earth and Planetary Science Letters
Source: Earth and Planetary Science Letters, 285(1-2), p.105-114. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X CODEN: EPSLA2
Note: In English. Supplemental information/data is available in the online version of this article. 43 refs.; illus., incl. 2 tables, sketch map
Summary: Apatite (U-Th-Sm)/He (AHe) thermochronology is increasingly used for reconstructing geodynamic processes of the upper crust and the surface. Results of AHe thermochronology, however, are often in conflict with apatite fission track (AFT) thermochronology, yielding an inverted age-relationship with AHe dates older than AFT dates of the same samples. This effect is mainly explained by radiation damage of apatite, either impeding He diffusion or causing non-thermal annealing of fission tracks. So far, systematic age inversions have only been described for old and slowly cooled terranes, whereas for young and rapidly cooled samples 'too old' AHe dates are usually explained by the presence of undetected U and/or Th-rich micro-inclusions. We report apatite (U-Th-Sm)/He results for rapidly cooled volcanogenic samples deposited in a deep ocean environment with a relatively simple post-depositional thermal history. Robust age constraints are provided independently through sample biostratigraphy. All studied apatites have low U contents (<5 ppm on average). While AFT dates are largely in agreement with deposition ages, most AHe dates are too old. For leg 43, where deposition age of sampled sediment is 26.5-29.5 Ma, alpha-corrected average AHe dates are up to 45 Ma, indicating overestimations of AHe dates up to 50%. This is explained by He implantation from surrounding host U-Th rich sedimentary components and it is shown that AHe dates can be "corrected" by mechanically abrading the outer part of grains. We recommend that particularly for low U-Th-apatites the possibility of He implantation should be carefully checked before considering the degree to which the alpha-ejection correction should be applied. Abstract Copyright (2009) Elsevier, B.V.
Year of Publication: 2009
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: (U-Th)/He; 03 Geochronology; Absolute age; Actinides; Age; Annealing; Apatite; Atlantic Ocean; Atlantic Ocean Islands; Bermuda Rise; Broken Ridge; Canary Islands; Cenozoic; Cooling; Cretaceous; Dates; Deep Sea Drilling Project; Diffusion; Fission-track dating; Geochronology; Helium; IPOD; Leg 121; Leg 129; Leg 43; Leg 47; Mesozoic; Metals; Miocene; Neogene; Noble gases; North Atlantic; North Pacific; Northwest Pacific; Ocean Drilling Program; Pacific Ocean; Paleogene; Phosphates; Pigafetta Basin; Tertiary; Thermal history; Thermochronology; Uranium; West Pacific
Coordinates: N310000 N410000 W0510000 W0680000
N260000 N410000 W0100000 W0160000
S310148 N052304 E0933525 E0873548
N120546 N215523 E1562136 E1521919
Record ID: 2009094518
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands