Two episodes of monazite crystallization during metamorphism and crustal melting in the Everest region of the Nepalese Himalaya (2000)

Research Article| May 01, 2000 Two episodes of monazite crystallization during metamorphism and crustal melting in the Everest region of the Nepalese Himalaya Robert L. Simpson; Robert L. Simpson 1Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, UK Search for other works by this author on: GSW Google Scholar Randall R. Parrish; Randall R. Parrish 2NERC Isotope Geosciences Laboratory, Keyworth, Nottingham NG12 5GG, UK, and Department of Geology, Leicester University, Leicester LE1 7RH, UK Search for other works by this author on: GSW Google Scholar Mike P. Searle; Mike P. Searle 1Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, UK Search for other works by this author on: GSW Google Scholar David J. Waters David J. Waters 1Department of Earth Sciences, Oxford University, Parks Road, Oxford OX1 3PR, UK Search for other works by this author on: GSW Google Scholar Geology (2000) 28 (5): 403–406. https://doi.org/10.1130/0091-7613(2000)28<403:TEOMCD>2.0.CO;2 Article history received: 11 Oct 1999 rev-recd: 02 Feb 2000 accepted: 16 Feb 2000 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Robert L. Simpson, Randall R. Parrish, Mike P. Searle, David J. Waters; Two episodes of monazite crystallization during metamorphism and crustal melting in the Everest region of the Nepalese Himalaya. Geology 2000;; 28 (5): 403–406. doi: https://doi.org/10.1130/0091-7613(2000)28<403:TEOMCD>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract New monazite U-Pb geochronological data from the Everest region suggest that ∼20–25 m.y. elapsed between the initial India-Asia collision and kyanite-sillimanite–grade metamorphism. Our results indicate a two-phase metamorphic history, with peak Barrovian metamorphism at 32.2 ± 0.4 Ma and a later high-temperature, low-pressure event (620 °C, 4 kbar) at 22.7 ± 0.2 Ma. Emplacement and crystallization of the Everest granite subsequently occurred at 20.5–21.3 Ma. The monazite crystallization ages that differ by 10 m.y. are recorded in two structurally adjacent rocks of different lithology, which have the same postcollisional pressure-temperature history. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armored within silicate minerals. During the low-pressure metamorphic event, the armoring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite-producing reactants, and spots within monazite that are rich in Ca, Fe, Al, and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.