Petrogenetic processes in granitic magmas and their igneous microgranular enclaves from Central Victoria, Australia: match or mismatch?

Abstract

Using chemical evidence, particularly the variations between titanium and iron + magnesium, we demonstrate that the petrogenetic processes that operated within Central Victorian granitic host magmas and their igneous microgranular enclave suites are dissimilar. Chemical variations within the granitic series result from a variety of what might be called ‘orderly’ processes, resulting in linear or curvilinear trends in chemical variation diagrams. Those that affected the enclave suites commonly resulted in scattered, chaotic variations. Even in cases where an enclave suite displays a more orderly chemical variation, it is demonstrable that the hypothesis of simple mixing between an enclave magma and a host granitic magma, to bring about the overall chemical variations, cannot be supported. The enclave magmas had vastly smaller volumes compared with their host granitic magmas. Thus, they have commonly undergone hybridisation through mixing with deep crustal melts and both chemical and mechanical interactions with wall rocks and their enclosing granitic magmas. As a result of this complex and chaotic set of processes, it remains extremely difficult to unravel the precise mechanisms that produced a given suite of enclave magmas. Due to the similarities between the studied granites and their enclaves with occurrences worldwide, we suggest that our findings are likely to have general applicability.

Keywords:

• granitic magmas
• igneous microgranular enclaves
• magma mixing
• crystal fractionation
• peritectic assemblage entrainment

ORCiD

J.D. Clemens http://orcid.org/0000-0002-8748-1569

Additional information

Funding

JDC and MAE acknowledge support from the South African NRF, in the form of Incentive Funds for Rated Researchers. GS acknowledges financial support through the NRF SARChI initiative.