DOI: 10.1016/j.epsl.2020.116589
论文题名: Exploring laser ablation U–Pb dating of regional metamorphic garnet – The Straits Schist, Connecticut, USA
作者: Millonig L.J. ; Albert R. ; Gerdes A. ; Avigad D. ; Dietsch C.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 552 语种: 英语
中文关键词: Acadian orogeny
; garnet
; LA-ICP-MS
; regional metamorphism
; U–Pb dating
英文关键词: Ablation
; Laser ablation
; Metamorphic rocks
; Monazite
; Phosphate minerals
; Silicate minerals
; Zircon
; Data evaluation
; Detrital zircon
; Grain size analysis
; Inclusion sizes
; Metamorphic conditions
; Metamorphic process
; Regression lines
; Temperature evolution
; Garnets
; Acadian orogeny
; garnet
; inductively coupled plasma method
; laser method
; mass spectrometry
; metamorphism
; schist
; uranium-lead dating
; Connecticut
; United States
英文摘要: Garnet is a prominent recorder of metamorphic processes and plays a pivotal role in deciphering the pressure-temperature evolution of metamorphic rocks. However, the potential of regional metamorphic garnet for laser ablation U–Pb dating remains unexplored, as variable and low U (<0.1 μg/g) coupled with elevated initial Pb contents make analyses challenging, and the presence of U-rich inclusions can affect results. We applied LA-ICP-MS U–Pb dating to garnet and zircon, monazite, and xenotime from The Straits Schist, western Connecticut, USA, to constrain the timing of garnet growth within the overall Acadian-age metamorphic history recorded by this unit. We assessed the effects of U-rich inclusions on garnet U–Pb data using high-resolution microbeam sampling, grain size analysis, and calculations assessing how inclusion size and abundance affect U concentrations measured in garnet. When analysing garnet, our results demonstrate that by scrutinizing the time-resolved U-signal, U-rich inclusions can be identified and effectively removed during data evaluation. If U-rich inclusions are unaccounted for, ‘garnet’ analyses have elevated U contents compared to pure garnet and in a Tera-Wasserburg diagram, data points are shifted to the left, right, or along the garnet regression line, for inclusions older, younger or of the same age as the garnet, respectively. Garnet from two metapelitic samples yielded lower intercept ages of 409 ± 10 Ma and 406 ± 15 Ma, and a combined U–Pb age of 406.1 ± 8.3 Ma. Metamorphic zircon yielded age clusters at 446.2 ± 4.2 Ma, 413.3 ± 3.0 Ma, and 382.9 ± 2.8 Ma, monazite ages range between 390 and 355 Ma, and xenotime yielded 370.1 ± 5.6 Ma. The ∼446 Ma age peak is attributed to detrital zircon formed during the waning stages of the Taconian orogeny. Early Acadian metamorphism is recorded by garnet and ∼413 Ma zircon, whereas monazite and zircon ages of 390 to 383 Ma, coincide with peak metamorphic conditions. Early Carboniferous monazite and xenotime ages could reflect the incursion of fluids into The Straits Schist during Neo-Acadian metamorphism, coeval plutonism in New England, or breakdown of garnet during regional exhumation. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165167
Appears in Collections: 气候变化与战略
There are no files associated with this item.
作者单位: Department of Geosciences, Goethe-University Frankfurt, Altenhöferallee 1, Frankfurt am Main, 60438, Germany; Frankfurt Isotope and Element Research Center (FIERCE), Goethe-University Frankfurt, Frankfurt am Main, Germany; Institute of Earth Sciences, Hebrew University of Jerusalem, Givat Ram, 9190401, Israel; Department of Geology, University of Cincinnati, P.O. Box 0013, Cincinnati, OH 45221-0013, United States
Recommended Citation:
Millonig L.J.,Albert R.,Gerdes A.,et al. Exploring laser ablation U–Pb dating of regional metamorphic garnet – The Straits Schist, Connecticut, USA[J]. Earth and Planetary Science Letters,2020-01-01,552