The Fosdick migmatite–granite complex in West Antarctica records evidence for two high-temperature metamorphic events, the first during the Devonian–Carboniferous and the second during the Cretaceous. The conditions of each high-temperature metamorphic event, both of which involved melting and multi...
| Main Authors: | , , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.431.9568 http://www.geol.umd.edu/facilities/LCP/KorhonenFJBrownMGroveMSiddowayCSBaxterEFandInglisJD2012.pdf |
| Summary: | The Fosdick migmatite–granite complex in West Antarctica records evidence for two high-temperature metamorphic events, the first during the Devonian–Carboniferous and the second during the Cretaceous. The conditions of each high-temperature metamorphic event, both of which involved melting and multiple melt-loss events, are investigated using phase equilibria modelling during successive melt-loss events, microstructural observations and mineral chemistry. In situ SHRIMP monazite and TIMS Sm–Nd garnet ages are integrated with these results to constrain the timing of the two events. In areas that preferentially preserve the Devonian–Carboniferous (M1) event, monazite grains in leucosomes and core domains of monazite inclusions in Cretaceous cordierite yield an age of c. 346 Ma, which is interpreted to record the timing of monazite growth during peak M1 metamorphism ( 820–870 °C, 7.5–11.5 kbar) and the formation of garnet–sillimanite–biotite–melt-bearing assemblages. Slightly younger monazite spot ages between c. 331 and 314 Ma are identified from grains located in fractured garnet porphyroblasts, and from inclusions in plagioclase that surround relict garnet and in matrix biotite. These ages record the growth of monazite during garnet breakdown associated with cooling from peak M1 conditions. The Cretaceous (M2) overprint is recorded in compositionally |
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