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Re-evaluating monazite as a record of metamorphic reactions

Geoscience Frontiers 2022年第2期13卷 237-254页

作者： Kyle P.Larson Sudip Shrestha John M.Cottle Carl Guilmette T.Alex Johnson H.Daniel Gibson Félix Gervais Department of Earth Environmental and Geographic SciencesUniversity of British Columbia Okanagan3247 University WayKelownaBC V1V 1V7Canada Fipke Laboratory for Trace Element Research University of British Columbia Okanagan3247 University WayKelownaBC V1V 1V7Canada Department of Earth Science University of CaliforniaSanta BarbaraSanta BarbaraCA 93106-9630USA Géologie et Génie Géologique UniversitéLavalQuébec CityQuebecCanada Department of Earth Sciences Simon Fraser University8888 University DriveBurnabyBC V5A 1S6Canada Départment des Génies Civil Géologique et des MinesPolytechnique MontréalMontréalQC H3T 1J4Canada

This study presents a re-examination of historical specimens(DG136 and DG167)from the Monashee complex in the southeastern Canadian Cordillera that are critical to the current understanding of rare earth element(REE)distribution between garnet and monazite(and other accessory minerals)during ***-hundred and fifty-one new monazite petrochronology spot analyses on 29 different grains across two specimens outline detailed(re)crystallization *** element data collected from the same ablated volume,interpreted in the context of new phase equilibria modelling that includes monazite,xenotime and apatite,link ages to specific portions of the pressure-temperature(P-T)paths followed by the *** linkages are further informed by garnet Lu-Hf geochronology and xenotime *** clockwise P-T paths indicate prograde metamorphism was ongoing by ca.80 Ma in both *** structurally deeper specimen,DG136,records peak P-T conditions of~755-770℃and 8.8-10.4 kbar,interpreted to coincide with(re-)crystallization of low Y monazite at~75-70 ***-rim garnet isopleths from DG167 cross in the observed peak assemblage field at~680℃ and 9.3 *** conditions are interpreted to correspond with low Y monazite(re-)crystallisation at~65 *** specimens record decompression along their retrograde path coincident with high Y 70-55 Ma and 65-55 Ma monazite populations in DG136 and DG167,*** findings broadly agree with those initially reported~20 years ago and confirm early interpretations using trace elements in monazite as generally reliable markers of metamorphic *** phase equilibria modelling and in situ petrochronological analysis,however,provide additional insight into monazite behaviour during anatexis and the effects of potential trace element buffering by REE-bearing phases such as apatite.

关键词： monazite petrochronology Phase equilibria modelling Geochronology P-T-t paths

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Tectono-metamorphic discontinuities in the Greater Himalayan Crystalline,central Himalaya

Tectono-metamorphic discontinuities in the Greater Himalayan...

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2018年中国地球科学联合学术年会

作者： Gautam Khanal Jia-Min Wang Fu-Yuan Wu Jiang-Gang Wang Yang Lei 中国科学院地质与地球物理研究所岩石圈演化国家重点实验室

The Himalayan Metamorphic Core in the central Nepal Himalaya can be separated into the Lesser Himalayan Sequence(LHS),the Lower Greater Himalayan Crystalline(GHC) and the Upper GHC by tectono-metamorphic *** nature and evolution of these discontinuities are vital to understand the Himalayan convergence accommodation *** petrochronology combined with geothermobarometry have revealed existence of two tectono-metamorphic discontinuities within the Himalayan Metamorphic core in Rasuwa-Gadhi section,central *** pressures and temperatures were determined by conventional thermobarometry and Zr-in-Rutile *** LHS in the study area has P–T conditions of 30℃/km in the upper GHC).The lower discontinuity(rise in P-T) and the upper discontinuity(jump in T/depth) can be correlated with the Main Central Thrust and the Langtang Thrust,*** Th – Pb ages in metapelite range from 36 to 13 Ma and are linked to metamorphic conditions on the basis of trace elements,mineral inclusions and mineral *** prograde monazite growth in the upper GHC rocks continued at least until 27 Ma,whereas retrograde cooling occurred during 20–15 Ma,which is supported by REE patterns showing feldspar growth and garnet breakdown after 22 *** the lower GHC,the prograde monazite growth lasted until around 15 *** combining prograde and retrograde monazite ages in the immediate hanging wall and footwall,initial active timing of the Langtang Thrust and Main Central Thrust in the Rasuwa Gadhi section is constrained to be ～22 Ma and ～15 Ma,*** data support the tectonic model that in-sequence thrusting is responsible for the diachronous burial and exhumation of the high-grade Himalayan Metamorphic Core.

关键词： Himalayan Metamorphic Core Tectono-metamorphic discontinuities Main Central Thrust geothermobarometry monazite petrochronology

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