UNSTABLE FLOW, MAGMA MIXING AND MAGMA-ROCK DEFORMATION IN A DEEP-SEATED CONDUIT - THE GIL-MARQUEZ COMPLEX, SOUTH-WEST SPAIN

The Gil-Marquez Complex is an exceptional outcrop of plutonic rocks ra nging in composition from diorites to granites emplaced into Devonian terrigenous metasediments of the southernmost part of the Hercynian ba sement of Iberia. A combined study of this complex, including field ge ology, petrology, structural geology and geochemistry, reveals that it represents an ancient conduit of magma transport through the continen tal crust. This conduit allowed the intrusion of magmas of contrasted compositions. Two end-members and several hybrids are identified. The first end-member is a biotite granite and the second is a basaltic mag ma generated by partial melting of a depleted-mantle source. Both magm as rose through a common channel in which favorable conditions for uns table flow and magma mixing occurred. The observed relations in the Gi l-Marquez Complex show that mixing in conduits may be an important mec hanism for producing homogeneous hybrid magmas.