ELSEVIER Earth and Planetary Science Letters 157 ( 1998) 4 l-56 EPSL Mingling in mafic magma chambers replenished by light felsic inputs: fluid dynamical experiments Roberto F. Weinberg ‘, Alison M. Leitch * Research School of Earth Sciences, Australian National UniversiQ, Cunherra, ACT 0200, Australiu Received 7 April 1997; revised version received 12 January 1998: accepted 30 January 1998 Abstract We investigate, by means of laboratory analogues, the fluid dynamics of magma hybridisation caused by the intrusion of felsic magma into a mafic magma chamber. The ‘input’ felsic magma is modelled by a cold, low density fluid and the ‘resident’ mafic magma by a layer of fluid wax close to its solidification point. The cold, rising input drives convection and solidification in the resident fluid, and the solidification causes significant perturbations to an otherwise simple input flow, greatly enhancing mixing and mingling between the two model magmas. The dimensionless parameters controlling the evolution of the system are determined and different morphologies of the solid mass fit into clearly defined fields in the parameter space. The most important implication of the experiments is that the freezing of mafic chambers due to felsic intrusion may give rise to intense hybridization of large volumes of magma. This potentially important mechanism for hybridization has, to date, received little attention in the literature. 0 1998 Elsevier Science B.V. All rights reserved. Keywords: felsic composition; mafic magmas; fluid dynamics; models 1. Introduction Hybridisation of magmas through mixing and mingling has now become established as a major petrogenetic process [l]. The mixing of magmas re- sults in a homogenous rock of intermediate compo- sition, whereas in a mingled rock, the end-members are dispersed or intertwined in each other, typically on a centimetre to decimetre scale, but retain their compositional identities. Using fluid dynamical ex- periments, we investigate hybridisation caused by the intrusion from below of low density, cold felsic magma into a mafic magma chamber. Most past work on magma hybridisation has con- sidered the replenishment of a felsic magma chamber by intruding mafic magmas; however, the intrusion of felsic magmas into mafic chambers may be more common than so far realised [2]. It is well known that the order of emplacement of magmas in many large batholiths is from more primitive magmas to more felsic magmas [2-4], providing the appropriate conditions for felsic intrusions into mafic chambers, and a few examples of granite intrusion into dioritic magma chambers have been described [2,5,6]. Iden- tifying the intrusion of felsic magmas into mafic chambers in the field is difficult because: (a) the dispersion of mafic enclaves in the felsic intruder *Corresponding author. Tel.:+61 (6) 249-3242; Fax: +61 (6) 249-0738; E-mail: alison.leitch@anu.edu.au ’ Present address: Department of Earth Sciences, Oxford Univer- sity, Parks Road, Oxford OXI 3PR, UK. 0012-821X/98/$19.00 0 1998 Elsevier Science B.V. All rights reserved PII SOO12-821X(98)00025-9