TY - JOUR

T1 - Fractionation vs. magma mixing in the Wangrah Suite A-type granites, Lachlan Fold Belt, Australia

T2 - Experimental constraints

AU - Klimm, Kevin

AU - Holtz, Francois

AU - King, Penelope L.

N1 - Funding Information: We thank B.W. Chappell for providing the natural samples from the Wangrah Suite and W. Johannes for the initiation of the project. The technical assistance of O. Dietrich and J. Koepke is gratefully appreciated. Helpful and constructive comments were provided by A.E. Patiño Douce and B. Landenberger on an earlier version of the manuscript. The reviews of B. Scaillet and O. Eklund are gratefully acknowledged. This study was supported by the German Science Foundation (DFG, project no.: Jo64/34). Copyright: Copyright 2011 Elsevier B.V., All rights reserved.

PY - 2008/5

Y1 - 2008/5

N2 - The Wangrah Suite granites (Lachlan Fold Belt, Australia) reflect different stages of differentiation in the magmatic history of an A-type plutonic suite. In this study we use experimentally determined phase equilibria of four natural A-type granitic compositions of the Wangrah Suite to constrain phases and phase compositions involved in fractionation processes. Each composition represents a distinct granite intrusion in the Wangrah Suite. The intrusions are the Danswell Creek (DCG), Wangrah (WG), Eastwood (EG) and Dunskeig Granite (DG), ordered from "most mafic" to "most felsic" by increasing SiO2 and decreasing FeOtotal. Experimental investigation show that the initial water content in melts from DCG is between 2-3 wt. % H2O. If the DCG is viewed as the parental magma for the Wangrah Suite, then (1) fractionation of magnetite, orthopyroxene and plagioclase (∼ 20 wt. %) of the DCG composition, leads to compositions similar to that of the EG; (2) further fractionation of plagioclase, quartz, K-feldspar and biotite (∼ 40 wt. %) from the EG composition, leads to the DG composition. These fractionation steps can occur nearly isobarically and are confirmed by bulk rock Ba, Sr, Rb and Zr concentrations. In contrast, the generation of the most abundant WG composition cannot be explained by fractional crystallisation from the DCG at isobaric conditions because of the high K2O content of this granite. Magma Mixing could be the process to explain the chemical distinctiveness of the Wangrah Granite from all the other granites of the Wangrah Suite.

AB - The Wangrah Suite granites (Lachlan Fold Belt, Australia) reflect different stages of differentiation in the magmatic history of an A-type plutonic suite. In this study we use experimentally determined phase equilibria of four natural A-type granitic compositions of the Wangrah Suite to constrain phases and phase compositions involved in fractionation processes. Each composition represents a distinct granite intrusion in the Wangrah Suite. The intrusions are the Danswell Creek (DCG), Wangrah (WG), Eastwood (EG) and Dunskeig Granite (DG), ordered from "most mafic" to "most felsic" by increasing SiO2 and decreasing FeOtotal. Experimental investigation show that the initial water content in melts from DCG is between 2-3 wt. % H2O. If the DCG is viewed as the parental magma for the Wangrah Suite, then (1) fractionation of magnetite, orthopyroxene and plagioclase (∼ 20 wt. %) of the DCG composition, leads to compositions similar to that of the EG; (2) further fractionation of plagioclase, quartz, K-feldspar and biotite (∼ 40 wt. %) from the EG composition, leads to the DG composition. These fractionation steps can occur nearly isobarically and are confirmed by bulk rock Ba, Sr, Rb and Zr concentrations. In contrast, the generation of the most abundant WG composition cannot be explained by fractional crystallisation from the DCG at isobaric conditions because of the high K2O content of this granite. Magma Mixing could be the process to explain the chemical distinctiveness of the Wangrah Granite from all the other granites of the Wangrah Suite.

KW - A-type granite

KW - Australia

KW - Crystallisation

KW - Experiments

KW - Fractional crystallisation

KW - Magma-mixing

UR - http://www.scopus.com/inward/record.url?scp=42949170053&partnerID=8YFLogxK

U2 - 10.1016/j.lithos.2007.07.018

DO - 10.1016/j.lithos.2007.07.018

M3 - Article

AN - SCOPUS:42949170053

VL - 102

SP - 415

EP - 434

JO - Lithos

JF - Lithos

SN - 0024-4937

IS - 3-4

ER -