Mafic Archean continental crust prohibited exhumation of orogenic UHP eclogite

作     者：Richard M.Palin James D.P.Moore Zeming Zhang Guangyu Huang Jon Wade Brendan Dyck Richard M.Palin;James D.P.Moore;Zeming Zhang;Guangyu Huang;Jon Wade;Brendan Dyck

作者机构：Department of Earth SciencesUniversity of OxfordOxford OX13ANUnited Kingdom Earth Observatory of SingaporeNanyang Technological UniversitySingapore Institute of GeophysicsSGEESVictoria University of WellingtonWellingtonNew Zealand Institute of GeologyChinese Academy of Geological SciencesBeijing 100037China State Key Laboratory of Lithospheric EvolutionInstitute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China Department of EarthEnvironmental and Geographical SciencesUniversity of British ColumbiaKelowna V1V 1V7Canada 

出 版 物：《Geoscience Frontiers》 (地学前缘（英文版）)

年 卷 期：2021年第12卷第5期

页      面：411-420页

核心收录：

学科分类：0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学] 

基　　金：Royal Society Te Apārangi 

主　　题：Archean Eclogite Exhumation Secular change Geodynamics Density 

摘      要：The absence of ultrahigh pressure(UHP)orogenic eclogite in the geological record older than c.0.6 Ga is problematic for evidence of subduction having begun on Earth during the Archean(4.0-2.5 Ga).Many eclogites in Phanerozoic and Proterozoic terranes occur as mafic boudins encased within low-density felsic crust,which provides positive buoyancy during subduction;however,recent geochemical proxy analysis shows that Archean continental crust was more mafic than previously thought,having greater proportions of basalt and komatiite than modern-day ***,we show via petrological modelling that secular change in the petrology and bulk composition of upper continental crust would make Archean continental terranes negatively buoyant in the mantle before reaching UHP *** or delaminated Archean continental crust passes a point of no return during metamorphism in the mantle prior to the stabilization of coesite,while Proterozoic and Phanerozoic terranes remain positively buoyant at these *** orogenic eclogite may thus readily have formed on the Archean Earth,but could not have been exhumed,weakening arguments for a Neoproterozoic onset of subduction and plate ***,isostatic balance calculations for more mafic Archean continents indicate that the early Earth was covered by a global ocean over 1 km deep,corroborating independent isotopic evidence for large-scale emergence of the continents no earlier than c.3 *** findings thus weaken arguments that early life on Earth likely emerged in shallow subaerial ponds,and instead support hypotheses involving development at hydrothermal vents in the deep ocean.