DOI: 10.1016/j.epsl.2020.116359
论文题名: Unraveling the exhumation history of high-pressure ophiolites using magnetite (U-Th-Sm)/He thermochronometry
作者: Schwartz S. ; Gautheron C. ; Ketcham R.A. ; Brunet F. ; Corre M. ; Agranier A. ; Pinna-Jamme R. ; Haurine F. ; Monvoin G. ; Riel N.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2020
卷: 543 语种: 英语
中文关键词: (U-Th-Sm)/He
; exhumation
; high-pressure ophiolites
; magnetite
; modeling
; thermochronometry
英文关键词: Erosion
; Fission reactions
; Magnesite
; Magnetite
; Phosphate minerals
; Rocks
; Samarium compounds
; Silicate minerals
; Temperature
; Zircon
; Apatite fission tracks
; Brittle to ductile transition
; Closure temperatures
; Geochemical characterization
; Grain morphologies
; Hydrothermal conditions
; Oscillatory zoning
; Subduction dynamics
; Thorium compounds
; exhumation
; high pressure
; magnetite
; ophiolite
; P-T-t path
; radiocarbon dating
; tectonic setting
; thermochronology
; Alps
; Western Alps
; Schistes
英文摘要: Magnetite is a ubiquitous oxide in ultramafic and mafic rocks, which is present in a large range of geological and tectonic settings. In the case of high-pressure ultramafic rocks, exhumation timing is commonly constrained by geochronometers in nearby lithologies. The development of the magnetite (U-Th-Sm)/He method (MgHe) has opened new perspectives to refine the exhumation history of such rocks. However no thermal history has been deduced using MgHe data so far. Here we applied MgHe dating to magnetite from an HP-LT alpine ophiolite body (Rocher Blanc) from the Schistes lustrés units (Western Alps, France) where part the P-T-t history is constrained to further refine the thermal history and demonstrate validity of the method. Textural and geochemical characterizations of the magnetite grains reveal two crystallization environments leading to distinct grain morphologies, euhedral and pseudo-euhedral, with different amounts of mineral inclusions (titanite, chlorite and augite-aegirine). Both magnetite types crystallized during the same retrograde path at T>250 °C, under hydrothermal conditions shown by Si and V oscillatory zoning and low Ti content. MgHe ages derived from euhedral magnetite crystals range from 14.8 ± 2.1 to 20.9 ± 3.0 Ma, between zircon and apatite fission track (ZFT) and (AFT) ages deduced from the literature. Pseudo-euhedral grains display older ages interpreted as resulting from the implantation of He from U-rich neighboring minerals such as titanite. For the first time, MgHe data are inverted along with AFT and ZFT data to refine the thermal history of an ophiolite related to their exhumation. The MgHe data suggest that the Rocher Blanc sample has undergone an exhumation in ductile conditions related to subduction dynamics and underplating processes, followed by an exhumation reflecting denudation by erosion under brittle conditions. This exhumation regime change is found to take place at ∼20 Ma, as opposed to a less constrained ∼26 Ma cooling as would be inferred from the ZFT and AFT ages alone. Considering published thermochronometric data along the Western Alps, we propose that the exhumation is controlled by the upward indentation of the Apulian mantle producing regional tilting and associated erosion. With the present Schistes lustrés ophiolite example, we demonstrate that the MgHe method can be used as a low-temperature thermochronometer (closure temperature in the 200-250 °C range) that aids in unraveling the cooling history associated with exhumation of high-pressure ultramafic and mafic rocks at the brittle to ductile transition. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165259
Appears in Collections: 气候变化与战略
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作者单位: ISTerre, Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, IRD, IFSTTAR, Grenoble, 38041, France; GEOPS, Univ. Paris-Sud, CNRS, Université Paris-Saclay, Orsay, 91405, France; Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, United States; Laboratoire Domaines Océaniques, CNRS, IUEM, Université de Bretagne Occidentale, Plouzané, 29280, France; Institute of Geosciences, Johannes Gutenberg University Mainz, Mainz, D-55128, Germany
Recommended Citation:
Schwartz S.,Gautheron C.,Ketcham R.A.,et al. Unraveling the exhumation history of high-pressure ophiolites using magnetite (U-Th-Sm)/He thermochronometry[J]. Earth and Planetary Science Letters,2020-01-01,543