Zircon Hf Isotopic Evidence for Mixing of Crustal and Silicic Mantle-derived Magmas in a Zoned Granite Pluton, Eastern Australia
Zircon Hf Isotopic Evidence for Mixing of Crustal and Silicic Mantle-derived Magmas in a Zoned Granite Pluton, Eastern Australia
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DOI：
10.1093/petrology/egn078
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发表时间：
2009
影响因子：
3.9
通讯作者：
S. Shaw;R. Flood
中科院分区：
文献类型：
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作者：
S. Shaw;R. Flood
锆石Hf同位素数据从分区岩体的Moonbi超套房，新英格兰岩基，澳大利亚东部，是一致的岩浆混合之间的两个熔融，每个来自同位素不同的来源。虽然Walcha Road岩体内三个带的锆石给出的U^Pb结晶年龄为249 - 3 Ma，但每个带的锆石群都有一个“Hf”范围。来自镁铁质角闪石、黑云母二长花岗岩岩体边缘和中间带的锆石eHf为5 ~ 11，而来自岩体较长英质中心的锆石eHf为7 ~ 16，代表11个eHf单位的总变化。亏损Lu^Hf的地幔模式年龄范围为-650 ~250 Ma，较年轻的锆石只出现在长英质岩体中心，eHf的变化表明至少有两个来源的地幔熔体参与，一个是新元古代模式年龄的地壳组分，另一个是与岩体U^Pb结晶年龄相似的原始幔源组分。锆石反映了熔体产生和最终深圳湾构造之间地壳来源的硅质熔体相对于地幔来源的硅质熔体的不同比例的同位素组成。Walcha Road岩体被认为是由混合、补充和晶体与熔体分离产生的越来越多的长英质熔体批次的增量组装形成的，最终的岩体构造涉及作为晶体糊状物区域的机械浓缩。分区的岩体，更广泛地说，Moonbi超套提供了岩浆混合的例子，其中更多的岩石单元有更多的年轻的同位素组成的结果，从玄武岩分馏残余熔体的比例增加，相对于地壳部分熔融。
Zircon Hf isotopic data from a zoned pluton of the Moonbi supersuite, New England batholith, eastern Australia, are consistent with magma mixing between two silicic melts, each derived from isotopically distinct sources. Although zircons from three zones within the Walcha Road pluton give a U^Pb crystallization age of 249 � 3 Ma, zircon populations from each zone have a range in "Hf. Zircons from the mafic hornblende^biotite monzogranite pluton margin and intermediate zones have eHf �þ 5t oþ11, whereas those from the more felsic centre of the pluton have eHf �þ 7t o þ16, representing a total variation of 11 eHf units. The Lu^Hf depleted mantle model ages range from � 650 to 250 Ma, with the younger zircons present only in the felsic pluton centre.The variation in eHf indicates the involvement of silicic melts from at least two sources, one a crustal component with a Neoproterozoic model age and the other a primitive mantle-derived component with model ages similar to the U^Pb crystallization age of the pluton. The zircons reflect the isotopic compositions of the different proportions of crustal-derived silicic melt, relative to mantle-derived silicic melt, between melt generation and final pluton construction. The Walcha Road pluton is considered to have formed by incremental assembly of progressively more felsic melt batches resulting from mixing, replenishment and crystal^melt separation, with final pluton construction involving mechanical concentration as zones of crystal mush. The zoned pluton and, more broadly, the Moonbi supersuite provide examples of magma mixing by which the more silicic units have more juvenile isotopic compositions as a result of increasing proportions of residual melt from basalt fractionation, relative to crustal partial melt.