DOI: 10.1016/j.earscirev.2020.103108
论文题名: High-temperature overprint in (U)HPM rocks exhumed from subduction zones; A product of isothermal decompression or a consequence of slab break-off (slab rollback)?
作者: Faryad S.W. ; Cuthbert S.J.
刊名: Earth Science Reviews
ISSN: 00128252
出版年: 2020
卷: 202 语种: 英语
中文关键词: exhumation rate
; metamorphism
; subduction
; thermal overprint
英文关键词: exhumation
; geodynamics
; numerical model
; orogenic belt
; overprinting
; P-T-t path
; petrology
; slab
; subduction zone
; ultrahigh pressure metamorphism
; Bohemian Massif
英文摘要: This paper presents and discusses petrological observations from high- to ultrahigh-pressure (U)HP metamorphic terrains in relation to existing geophysical and numerical models for subduction and exhumation processes in orogenic belts. The interpretations are mostly based on observations from gneiss terrains bearing abundant bodies mafic (meta-)eclogite and ultramafic garnet peridotite and pyroxenite, exposed in collisional orogens. The inclusions and compositional zoning of minerals are considered to be first order information that is needed to constrain PT paths of HP-UHP rocks and reconstruct the related geodynamic models for subduction and exhumation of crustal and mantle rocks. The Bohemian Massif of the European Variscides is used as the basis for a model example to explain these processes, but (U)HP rocks from various other terrains are taken into consideration to discuss available PT paths in relation to proposed subduction and exhumation rates of (U)HP rocks based on geophysical and geochronological data. Primarily information used in this respect include textural relations and preserved prograde zoning in minerals from many (U)HP rocks, which reveal that a relatively cool geothermal gradient typical of subduction zones tended to prevail during the prograde and peak pressure segments of PT paths prior to initiation of exhumation and may have continued, even with cooling, if exhumation rates were rapid. The commonly applied interpretation of isothermal decompression during exhumation is critically appraised, considering whether a simple thermal relaxation (and radiogenic heating) during exhumation is responsible for formation of post-peak pressure, retrograde mineral assemblages and textures observed in (U)HP rocks. We go on to consider whether this can satisfactorily explain the often pervasive medium-pressure, high-temperature metamorphic re-equilibration of (U)HP rocks or whether an additional, external source of heat is a better explanation. We conclude that the commonly observed high-temperature metamorphic overprint exhibited by (U)HP rocks occurs mostly after rocks have been exhumed from the subduction channel and have reached normal crustal positions, when mantle upwelling resulting from slab breakoff (delamination) or slab rollback takes place at the onset of continent-continent collision. We also explore contrasting PT trajectories for mantle rocks that have been entrained into crustal material during their subduction or exhumation; PT paths of mantle and subducted crustal rocks tend to converge as mantle rocks impinge upon the cooler subduction zone and, once entrained, share a common evolution that depends on the exhumation mechanism and rate. Considering all of the data presented in this work we conclude that the diverse, polyphase metamorphic evolution exhibited by (U)HP terrains, embodied in the PT paths of HP and UHP rocks, has important consequences for reconstructing their changing thermal regimes and provides important constraints for geodynamic models involving subduction and the transition to collision. © 2020 Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/166072
Appears in Collections: 气候变化与战略
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作者单位: Institute of Petrology and Structural Geology, Charles University, Prague, 12843, Czech Republic; Faculty of Geology, Geophysics and Environmental Protection, AGH University of Science and Technology, al. Mickiewicza, 30-059 Krakow, Poland
Recommended Citation:
Faryad S.W.,Cuthbert S.J.. High-temperature overprint in (U)HPM rocks exhumed from subduction zones; A product of isothermal decompression or a consequence of slab break-off (slab rollback)?[J]. Earth Science Reviews,2020-01-01,202