Accessory mineral chemistry of high Ba-Sr granites from northern Scotland: constraints on petrogenesis and records of whole-rock signature
Accessory mineral chemistry of high Ba-Sr granites from northern Scotland: constraints on petrogenesis and records of whole-rock signature
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DOI：
10.1093/petrology/egu037
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发表时间：
2014-08
影响因子：
3.9
通讯作者：
E. Bruand;C. Storey;M. Fowler
中科院分区：
文献类型：
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作者：
E. Bruand;C. Storey;M. Fowler
苏格兰北方高地的Rogart和Strontian高Ba-Sr岩体包括从长英质到超镁铁质岩石的一系列岩性。后者是幔源的，其分化产生的岩体的长英质成分是分离结晶和周围的莫因变质沉积物的变量同化的结果。这里提出的新结果表明，辅助矿物化学可以提供进一步深入了解其岩石成因，并突出磷灰石和钛铁矿的岩石学潜力。高Ba-Sr岩体的主要副矿物为钛铁矿、磷灰石和锆石，它们含有大部分的稀土元素。磷灰石和钛铁矿的结果表明，仔细的成像和原位微量元素分析提供了对寄主岩石的成岩历史的制约。在这两个岩体中，磷灰石和钛铁矿记录原位结晶和分馏。在Strontian，花岗岩类中的磷灰石和钛铁矿都记录了与镁铁质岩浆在其边缘成分的混合事件。磷灰石和钛铁矿的化学成分对其母岩（长英质岩与超镁铁质岩）的性质很敏感，某些元素（如Sr、V）密切反映了全岩化学成分和分馏程度。在某些情况下，全岩微量元素浓度可以根据辅助矿物化学计算。因此，副矿物中微量元素的研究可以直接反映深圳湾深成岩石的性质和结晶历史。这种岩石学工具可能有助于使用辅助矿物进行物源研究，并且由于最近已将高Ba-Sr岩体等同于西印度群岛sanukitoids，因此这在约束这种重要岩浆类型的时间分布方面也可能很重要。
The Rogart and Strontian high Ba–Sr plutons (Northern Highlands, Scotland) comprise a range of lithologies from felsic to ultramafic rocks. The latter are mantle-derived and their differentiation to produce the felsic components of the plutons is the result of fractional crystallization and variable assimilation of the surrounding Moine metasediments. New results presented here demonstrate that accessory mineral chemistry can provide further insight into their petrogenesis and highlight the petrological potential of apatite and titanite. The main accessory minerals titanite, apatite and zircon contain most of the rare earth elements (REE) in the high Ba–Sr plutons. Results for apatite and titanite show that careful imaging and in situ trace element analysis provide constraints on the petrogenetic history of the host-rock. In both plutons, apatite and titanite record in situ crystallization and fractionation. In Strontian, both apatite and titanite from the granitoids record a mixing event with mafic magma in their rim compositions. Apatite and titanite chemistries are sensitive to the nature of their host-rocks (felsic versus ultramafic) and some elements (e.g. Sr, V) closely reflect whole-rock chemistry and the degree of fractionation. In some cases, whole-rock trace element concentrations can be calculated based on accessory mineral chemistry. Thus, trace elements in accessory minerals can give direct access to the nature and crystallization history of plutonic rocks. This petrological tool may be helpful in provenance studies using accessory minerals, and because high Ba–Sr plutons have recently been equated with Archaean sanukitoids, this might also be important in constraining the temporal distribution of this important magma type.