气候变化领域集成服务门户(CCPortal): Petrochronological close-up on the thermal structure of a paleo-subduction zone (W. Alps)

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DOI	10.1016/j.epsl.2020.116446
	Petrochronological close-up on the thermal structure of a paleo-subduction zone (W. Alps)
	Dragovic B.; Angiboust S.; Tappa M.J.
发表日期	2020
ISSN	0012821X
卷号	547
英文摘要	We present the results from a study combining zoned geochronology, mineral trace element geochemistry and phase equilibria modeling of a mafic lithology from the Zermatt Saas Ophiolite in order to elucidate the tectonic rates and thermal structure of the Western Alps paleo-subduction interface. The Zermatt-Saas Ophiolite represents dismembered slices derived from an eclogitized, 60-km wide coherent fragment of Tethyan oceanic lithosphere. Two cm-sized garnet crystals from a pyrite-rich chlorite-talcschist (representative of sub-seafloor hydrothermally-altered basalts) from the Servette mine locality (St. Marcel Valley, Italy) were microdrilled to separate core and rim growth generations and dated using Sm-Nd geochronology to determine the overall duration of garnet growth. Garnet cores were dated to 46.9±1.6Ma, signifying the timing of the initiation of garnet growth. Garnet rims were dated to 43.5±1.3Ma, signifying the timing of burial to peak depths (constrained to ∼75 km). Major and trace element zoning in garnet suggest two distinct generations of garnet growth. Garnet crystal cores display evidence for rapid nucleation and growth, while garnet crystal rims suggest growth at relatively slow (tectonic) rates. The duration of garnet growth (3.4±2.1Ma), when coupled to constraints from phase equilibria modeling and Zr-in-rutile thermometry, provides estimates on the burial and heating rate of 4.7 (+7.9−2.1) km/Myr and 13.2 (+17.8−6.1) °C/Myr, respectively. Using the depth and temperature conditions recorded by laterally equivalent meta-ophiolites from across the Western Alps, a ‘snapshot’ of the geothermal gradient at the Alpine subduction interface is presented. This reveals a pressure-temperature trajectory highlighted by a significant decrease of the thermal gradient from ∼10 °C/km down to ∼3 °C/km at ∼45 Ma. We further present geometric calculations to identify the tectonic parameters that best fit this dual-segmented thermal gradient. Using convergence rates from paleogeographic reconstructions during Eocene times (on the order of 1.5-2 cm/yr), our calculations require a paleo-slab angle of 15-20°, in line with dip estimates from most modern subduction zones. This study highlights how a detailed petrochronology-based approach enables assessing the thermal structure and geometry of a paleo-subduction zone, with implications on seismicity, stress distribution, and devolatilization potential of deeper portions of the subduction interface. © 2020 Elsevier B.V.
关键词	garnet petrochronology Sm-Nd subduction Western Alps
英文关键词	Binary alloys; Crystals; Geochronology; Lithology; Neodymium alloys; Oxide minerals; Phase equilibria; Pyrites; Samarium alloys; Structural geology; Tectonics; Thermal gradients; Titanium dioxide; Trace elements; Geometric calculations; Geothermal gradients; Major and trace elements; Paleogeographic reconstruction; Subduction interface; Temperature conditions; Temperature trajectory; Trace element geochemistry; Garnets; chemical composition; chlorite; convergence; Eocene; petrochemistry; petrogenesis; petrology; subduction zone; trace element
语种	英语
来源期刊	Earth and Planetary Science Letters
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/202569
作者单位	School of the Earth, Ocean and Environment, University of South Carolina, Columbia, SC, United States; Department of Geoscience, Boise State University, Boise, ID, United States; Université de Paris, Institut de Physique du Globe de Paris, CNRS, Paris, F-75005, France; Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, MA, United States
推荐引用方式 GB/T 7714	Dragovic B.,Angiboust S.,Tappa M.J.. Petrochronological close-up on the thermal structure of a paleo-subduction zone (W. Alps)[J],2020,547.
APA	Dragovic B.,Angiboust S.,&Tappa M.J..(2020).Petrochronological close-up on the thermal structure of a paleo-subduction zone (W. Alps).Earth and Planetary Science Letters,547.
MLA	Dragovic B.,et al."Petrochronological close-up on the thermal structure of a paleo-subduction zone (W. Alps)".Earth and Planetary Science Letters 547(2020).