U-Pb isotope systematics of micro-zircon inclusions: Implications for the age and origin of eclogite xenolith from the Colorado Plateau

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Abstract

We improved the U-Pb zircon dating method employing HR-SIMS by applying i) preparation of precise and homogeneous zircon standards by ID-TIMS, ii) simultaneous analysis of Pb isotopes by multi-collection system, and iii) use of a highly focused primary ion beam as small as 5 μm in diameter. Using the improved HR-SIMS technique, U-Pb ages of zircons in an eclogite xenolith from the Colorado Plateau were determined. Zircon occurs as small inclusions (<20 μm) in most constituent minerals. Ten zircons were measured, and the concordant analyses of these zircon data yielded a weighted mean value of 65.2 ± 0.7 Ma for the age of crystallization. Petrographic and geochemical observations suggest that this zircon age represents the age of initial subduction of basaltic oceanic crust. We conclude that the eclogite xenolith was a fragment of basaltic oceanic crust subducted to > 90 km depth along a cold geotherm with a subduction rate of > 2 cm/y in Tertiary.

Original languageEnglish
Pages (from-to)51-56
Number of pages6
JournalProceedings of the Japan Academy Series B: Physical and Biological Sciences
Volume78
Issue number3
DOIs
Publication statusPublished - Mar 2002

Fingerprint

Colorado Plateau (US)
eclogite
Isotopes
secondary ion mass spectrometry
isotopes
Preparation
plateaus
Inclusion
inclusions
dating
ion beams
preparation
Ions
ions
zircon
Standards
methodology

Keywords

  • Colorado Plateau
  • Eclogite xenolith
  • HR-SIMS
  • ID-TIMS
  • U-Pb age
  • Zircon

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • General
  • Mathematics(all)

Cite this

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title = "U-Pb isotope systematics of micro-zircon inclusions: Implications for the age and origin of eclogite xenolith from the Colorado Plateau",
abstract = "We improved the U-Pb zircon dating method employing HR-SIMS by applying i) preparation of precise and homogeneous zircon standards by ID-TIMS, ii) simultaneous analysis of Pb isotopes by multi-collection system, and iii) use of a highly focused primary ion beam as small as 5 μm in diameter. Using the improved HR-SIMS technique, U-Pb ages of zircons in an eclogite xenolith from the Colorado Plateau were determined. Zircon occurs as small inclusions (<20 μm) in most constituent minerals. Ten zircons were measured, and the concordant analyses of these zircon data yielded a weighted mean value of 65.2 ± 0.7 Ma for the age of crystallization. Petrographic and geochemical observations suggest that this zircon age represents the age of initial subduction of basaltic oceanic crust. We conclude that the eclogite xenolith was a fragment of basaltic oceanic crust subducted to > 90 km depth along a cold geotherm with a subduction rate of > 2 cm/y in Tertiary.",
keywords = "Colorado Plateau, Eclogite xenolith, HR-SIMS, ID-TIMS, U-Pb age, Zircon",
author = "Tomohiro Usui and Katsura Kobayashi and Eizou Nakamura",
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T1 - U-Pb isotope systematics of micro-zircon inclusions

T2 - Implications for the age and origin of eclogite xenolith from the Colorado Plateau

AU - Usui, Tomohiro

AU - Kobayashi, Katsura

AU - Nakamura, Eizou

PY - 2002/3

Y1 - 2002/3

N2 - We improved the U-Pb zircon dating method employing HR-SIMS by applying i) preparation of precise and homogeneous zircon standards by ID-TIMS, ii) simultaneous analysis of Pb isotopes by multi-collection system, and iii) use of a highly focused primary ion beam as small as 5 μm in diameter. Using the improved HR-SIMS technique, U-Pb ages of zircons in an eclogite xenolith from the Colorado Plateau were determined. Zircon occurs as small inclusions (<20 μm) in most constituent minerals. Ten zircons were measured, and the concordant analyses of these zircon data yielded a weighted mean value of 65.2 ± 0.7 Ma for the age of crystallization. Petrographic and geochemical observations suggest that this zircon age represents the age of initial subduction of basaltic oceanic crust. We conclude that the eclogite xenolith was a fragment of basaltic oceanic crust subducted to > 90 km depth along a cold geotherm with a subduction rate of > 2 cm/y in Tertiary.

AB - We improved the U-Pb zircon dating method employing HR-SIMS by applying i) preparation of precise and homogeneous zircon standards by ID-TIMS, ii) simultaneous analysis of Pb isotopes by multi-collection system, and iii) use of a highly focused primary ion beam as small as 5 μm in diameter. Using the improved HR-SIMS technique, U-Pb ages of zircons in an eclogite xenolith from the Colorado Plateau were determined. Zircon occurs as small inclusions (<20 μm) in most constituent minerals. Ten zircons were measured, and the concordant analyses of these zircon data yielded a weighted mean value of 65.2 ± 0.7 Ma for the age of crystallization. Petrographic and geochemical observations suggest that this zircon age represents the age of initial subduction of basaltic oceanic crust. We conclude that the eclogite xenolith was a fragment of basaltic oceanic crust subducted to > 90 km depth along a cold geotherm with a subduction rate of > 2 cm/y in Tertiary.

KW - Colorado Plateau

KW - Eclogite xenolith

KW - HR-SIMS

KW - ID-TIMS

KW - U-Pb age

KW - Zircon

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