Estimation of an ephemeral cooling for silicic magma reservoirs using thermal simulation

Abstract

• A thermal simulation is to constrain the cooling time of silicic magma reservoirs. • The cooling time is dominantly controlled by pluton’s shape and emplacement depth. • Shallow magma reservoirs require extra heat to maintain liquid for a longer time. • A cooling time of ∼20 kyr is proposed for the ca. 44 km 2 Jiuxiantang intrusion. Understanding the processes involved in magmatic evolution is one of the most fundamental aspects of geological research. The limitations of available chronological and geophysical methods hinder their precise depictions of the short residence time of small-volume magma reservoirs in the upper crust, while thermal simulation may provide an alternative solution for the key issue. In this contribution, a numerical simulation is built to constrain the processes of magma reservoirs in terms of heat conduct. The sensitivities of magma cooling time on relevant factors (including pluton shape, size, emplacement depth, heat dissipation efficiency, and thermal gradient) are explored. Our simulation suggests that the depth and shape (size and radius/thickness ratio) of magma reservoirs affect the cooling time significantly. An ephemeral cooling time of ∼20.4 kyr (thousand years) from liquidus (994 ℃) to solidus (664 ℃) for the homogeneous ca 820 Ma (million years ago) Jiuxiantang intrusion in South China is revealed. An overall ‘mush’ state of the magma reservoir is proposed for the most lifetime of the intrusion. This contribution provides a unique perspective to understanding the thermal budget of the magma system and the residence time of magma reservoirs in the upper crust.