Applications of biotite inclusion composition to zircon provenance determination
Applications of biotite inclusion composition to zircon provenance determination
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DOI：
10.1016/j.epsl.2017.06.012
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发表时间：
2017-09
影响因子：
5.3
通讯作者：
E. Bell;P. Boehnke;T. M. Harrison
中科院分区：
文献类型：
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作者：
E. Bell;P. Boehnke;T. M. Harrison
碎屑锆石是唯一被证实的>4.03 Ga地壳的残存物，而较年轻的碎屑锆石则提供了与结晶岩中保存的地壳演化相平行的更近地壳演化记录。锆石经常保存包裹体，这些包裹体可能为沉积记录中背景外颗粒的起源提供线索。以前的研究已经确定，岩浆锆石中的黑云母包裹体的成分匹配良好的源岩基质中的黑云母，虽然没有直接应用到古代碎屑锆石。大量研究表明，不同源岩和构造背景的岩浆黑云母中Fe、Mg和Al含量存在差异，表明黑云母包裹体确实可以作为碎屑锆石的物源指示。与以往的研究结果一致，我们发现大陆弧、碰撞和板内环境中岩浆黑云母的FeO_（20）/MgO比值随相对氧化态和全岩FeO_（20）/MgO而变化，而其Al_2O_3/（FeO_（20）+ MgO）随全岩A/CNK（摩尔Al/（2 <$Ca + Na + K））而变化。氧化变质花岗岩和还原S型花岗岩中的黑云母可以很容易地用FeO_2 O_3/MgO和Al_2 O_3/（FeO_2 O_3 + MgO）来区分，而还原I型花岗岩和氧化过铝花岗岩中的黑云母在某些情况下可能更模糊。过碱性和还原型A型花岗岩中的黑云母也分别以Al_2O_3/（FeO_xO + MgO）和FeO_xO/MgO与其他类型的黑云母区分开来。来自西澳大利亚杰克山的冥古宙锆石中的黑云母包裹体表明混合了变铝质和还原S型寄主岩石，而来自Nuvvuagittuq表壳带的3.6-3.8 Ga碎屑锆石中的包裹体表明更多的氧化过铝质岩浆。这些结果突出了地球早期长英质物质的多样性，并表明黑云母包裹体适用于整个沉积记录的锆石来源。
Detrital zircons are the only confirmed surviving remnants of >4.03 Ga crust while younger detrital zircons provide a parallel record of more recent crustal evolution to that preserved in crystalline rocks. Zircons often preserve inclusions that may provide clues as to the origins of out-of-context grains in the sedimentary record. Previous studies have established that inclusions of biotite in magmatic zircon are compositionally well-matched to biotite in the source rock matrix, although a direct application to ancient detrital zircons has not been made. A number of studies have documented variations in the Fe, Mg, and Al contents of magmatic biotite from different source rocks and tectonic settings, suggesting that biotite inclusions may indeed serve as provenance indicators for detrital zircons. Consistent with earlier studies, we find that the FeO⁎/MgO ratio of magmatic biotite from continental arcs, collisional, and within-plate settings varies with relative oxidation state as well as whole-rock FeO⁎/MgO, while its Al2O3/(FeO⁎+ MgO) varies with whole-rock A/CNK (molar Al/(2 ⋅ Ca + Na + K)). Biotite from oxidized metaluminous and reduced S-type granitoids can be readily distinguished from each other using FeO⁎/MgO and Al2O3/(FeO⁎+ MgO), while biotite from reduced I-type and oxidized peraluminous granites may in some cases be more ambiguous. Biotite from peralkaline and reduced A-type granites are also distinguishable from all other categories by Al2O3/(FeO⁎+ MgO) and FeO⁎/MgO, respectively. Biotite inclusions in Hadean zircons from Jack Hills, Western Australia indicate a mixture of metaluminous and reduced S-type host rocks, while inclusions in 3.6–3.8 Ga detrital zircons from the Nuvvuagittuq Supracrustal Belt indicate more oxidized peraluminous magmas. These results highlight the diversity of felsic materials on the early Earth and suggest that biotite inclusions are applicable to zircon provenance throughout the sedimentary record.