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Published January 2017 | public
Journal Article

Constraining the time scales of magmatic differentiation with U-Pb zircon geochronology


Quantifying the time scales of magmatic differentiation is critical for understanding the rate at which silicic plutonic and volcanic rocks form. Directly dating this process is difficult because locations with both clear evidence for fractional crystallization and the accessory phases necessary for radiometric dating are rare. Early zircon saturation, however, appears to be characteristic of many high-K, arc-related melts due to their generally elevated initial Zr concentrations. Thus, high-K plutonic series are ideal candidates to study the time scales of magmatic differentiation using zircon U-Pb geochronology. This study focuses on the Dariv Igneous Complex in western Mongolia where early saturation of zircon in a suite of cogenetic, upper crustal (<0.5 GPa) igneous rocks ranging from ultramafic cumulates to evolved granitoids allows us to date magmatic differentiation. Crystallization ages from six samples across the sequence indicate that magmatic fractionation from a basalt to high-silica (>65 wt% SiO_2) melt occurred in ≤590 ± 350 k.y. This estimate is greater than modeled time scales of conductive cooling of a single intrusion and physical segregation of minerals from a melt, suggesting that continued influx of heat through magmatic activity in the complex may have prolonged cooling and thus time scales associated with the production of silica-enriched melts.

Additional Information

© 2016 Geological Society of America. Manuscript received 22 August 2016; Revised manuscript received 5 October 2016; Manuscript accepted 5 October 2016; First Published on November 03, 2016. Support at the Massachusetts Institute of Technology comes from the National Science Foundation grant EAR-1322032 and the EARTHTIME initiative. We thank N. Chatterjee for assistance with CL imaging, and J. Pu and E. Barry for help with sample preparation. Comments by Bruce Watson, Haibo Zou, Kyle Samperton, and one anonymous reviewer improved a previous version of this manuscript.

Additional details

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