Monazite begets monazite: evidence for dissolution of detrital monazite and reprecipitation of syntectonic monazite during low-grade regional metamorphism |
| |
| Authors: | Birger Rasmussen Janet R Muhling |
| |
| Institution: | (1) School of Earth and Geographical Sciences M006, The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia;(2) Centre for Microscopy, Characterisation and Analysis M010, The University of Western Australia, 35 Stirling Highway, Crawley, WA, 6009, Australia |
| |
| Abstract: | Back-scattered electron (BSE) imaging and X-ray element mapping of monazite in low-grade metasedimentary rocks from the Paleoproterozoic
Stirling Range Formation, southwestern Australia, reveal the presence of distinct, high-Th cores surrounded by low-Th, inclusion-rich
rims. Previous geochronology has shown that the monazite cores are older than 1.9 Ga and overlap with the ages of detrital
zircon grains (∼3.5–2.0 Ga), consistent with a detrital origin. Many cores have scalloped and embayed surfaces indicating
partial dissolution of former detrital grains. Textural evidence links the growth of the monazite rims (∼1.2 Ga) to deformation
and regional metamorphism during the Mesoproterozoic Albany-Fraser orogeny. These results indicate that high-Th detrital monazite
is unstable under low-grade metamorphic conditions (<400°C) and was partially or completely dissolved. Dissolution was followed
by near-instantaneous reprecipitation and the formation of low-Th monazite and ThSiO4. This reaction is likely to operate in other low-grade metasedimentary rocks, resulting in the progressive replacement of
detrital monazite by metamorphic monazite during regional prograde metamorphism. |
| |
| Keywords: | Monazite Accessory minerals Low-grade metamorphism Geochronology Rare earth elements Metamorphic reactions |
| 本文献已被 SpringerLink 等数据库收录！ |
|
