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Diapirs of crystal-rich slurry explain granite emplacement temperature and duration.

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Copley, Alex 
Weller, Owen 
Bain, Hero 


The mechanism, temperature, and timescale of granite intrusion remain controversial, with wide-ranging implications for understanding continental growth, differentiation, rheology, and deformation dynamics. In this paper we present a method for determining intrusion emplacement temperature and timescale using the characteristics of the surrounding metamorphic aureole, and apply it to the Skiddaw granite in northern England. The estimated emplacement timescale (0.1-2 Myr) implies magma transport velocities of 1-100 mm/year. At the absent or low melt fractions relevant to our estimated emplacement temperature (580-650 [Formula: see text]C), such velocities are incompatible with pluton formation by successive injections through dykes. Instead, our results indicate the intrusion of a diapir of crystal-rich slurry, solidifying before emplacement, with a rheology governed by the solid crystals. The emplacement depth is likely to be governed by the depth-dependent rheology of the surrounding rocks, occurring close to the brittle-ductile transition. The wider implications of our results relate to (1) the appreciation that much of the chemical and textural characteristics of plutons may relate to pre-emplacement crystallisation at depth, passively transported to higher crustal levels, and (2) an explanation of the difficulty of seismically imaging active plutonism.


Acknowledgements: This work was partly supported by by NERC grant NE/W00562X/1, and partly by COMET (the NERC Centre for Observation and Modelling of Earthquakes, Volcanoes, and Tectonics). The authors thank Poppy Williams for help during model code development, Iris Buisman for EMPA support, and Jeremie Asselin for Raman support. Andrew Smye and Roberto Weinberg provided helpful and insightful reviews, and we thank Xiaolei Wang for editorial handling.


37 Earth Sciences, 3703 Geochemistry, 3705 Geology, 3706 Geophysics

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Nature Portfolio
NERC (NE/W00562X/1)
NERC (via University of Leeds) (RG.EVEA.117755)