Mafic rocks spatially associated with Devonian felsic intrusions of the southern Lachlan Fold Belt: A possible mantle contribution to crustal evolution processes |
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| Authors: | A Soesoo I Nicholls |
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| Institution: | Department of Earth Sciences , Monash University , Clayton, Vic., 3168, Australia |
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| Abstract: | Devonian basaltic to andesitic dykes and compositionally similar plutons of the southern Lachlan Fold Belt are often temporally and spatially closely associated with large granitic complexes. Mafic intrusions play a major role in the transfer of heat into the continental crust, providing a thermal ‘engine’ which leads to crustal melting, and geochemical/isotopic evidence indicates that they contribute chemical constituents to the products of this melting. Studied mafic‐intermediate dykes in the southern Lachlan Fold Belt have tholeiitic to alkaline affinities and include groups with both high and low Ti and K. Several dyke generations may be associated with a single felsic complex. Primitive mantle‐normalised trace‐element abundance patterns with negative Nb and Ti anomalies for basaltic/andesitic and gabbroic/dioritic rocks as young as Early Devonian most resemble those of modern island arcs and suggest an influence of subduction on mantle magma sources. However, some Middle and Late Devonian mafic rocks are enriched in light rare‐earth elements and other incompatible elements, lack significant Nb anomalies, and confirm the change to continental‐rift extensional settings clearly indicated by Lachlan Fold Belt geology. |
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| Keywords: | granitic rocks Lachlan Fold Belt mafic rocks mantle magmas |
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