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首页> 外文期刊>Contributions to Mineralogy and Petrology >Experimental effects of pressure and fluorine on apatite saturation in mafic magmas, with reference to layered intrusions and massif anorthosites
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Experimental effects of pressure and fluorine on apatite saturation in mafic magmas, with reference to layered intrusions and massif anorthosites

机译：压力和氟对镁铁质岩浆中磷灰石饱和度的实验影响，参考层状侵入体和块状钙长石

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Apatite is a cumulate phase in the upper parts of some mafic layered intrusions and anorthositic com-plexes. We investigated the effect of pressure and fluorine on apatite saturation in mafic magmas to better understand under which conditions this mineral crystallizes. Apatite saturation gives information about the formation of silicate rocks, and is of interest in explaining the formation of apatite-oxide-rich rocks (e.g. nelsonites comprising approximately, one-third apatite and two-third Fe-Ti oxide). Two models of formation are proposed for this rock type: crystal fractionation followed by accumulation of apatite and Fe-Ti oxides and liquid immiscibility. New experiments carried out with mafic compositions at 500 MPa confirm that the most important variables on phosphate saturation are SiO_2 and CaO. Fluorine addition leads to apatite saturation at lower SiO_2 and higher CaO concentrations. Comparison of our results with those of previous experimental studies on liquid-liquid immisci-bility at upper-to-mid-crustal conditions allows us to investigate the relative importance of apatite saturation versus liquid-liquid immiscibility in the petrogenesis of nelsonites and similar rocks. The liquid line of descent of three natural examples studied (the Sept-Iles intrusive suite, the anorthositic Complex of the Lac-St-Jean and the Skaergaard layered intrusion) do not cross the liquid-liquid immiscibility field before they reach apatite saturation. Thus, the apatite-oxide-rich rock associated with these three intrusive suites are best explained by crystal frac-tionation followed by accumulation of apatite and Fe-Ti oxides.
机译：磷灰石是一些镁铁质层状侵入体和无骨复合物上部的堆积相。我们研究了压力和氟对镁铁质岩浆中磷灰石饱和度的影响，以更好地了解这种矿物在何种条件下结晶。磷灰石饱和度可提供有关硅酸盐岩形成的信息，并且在解释富含磷灰石氧化物的岩石（例如，约有三分之一的磷灰石和三分之二的Fe-Ti氧化物的钠锌矿）的形成方面引起人们的兴趣。对于这种岩石类型，提出了两种形成模型：晶体分馏，其次是磷灰石和Fe-Ti氧化物的积累以及液体的不混溶性。用500 MPa的铁镁合金组成进行的新实验证实，磷酸盐饱和度最重要的变量是SiO_2和CaO。在较低的SiO_2和较高的CaO浓度下，添加氟会导致磷灰石饱和。将我们的结果与先前的实验结果进行了比较，研究了上中壳条件下的液-液不混溶性，这使我们能够研究磷灰石饱和度与液-液不混溶性在新钠铁矿和类似岩石成岩作用中的相对重要性。所研究的三个自然实例（Sept-Iles侵入套件，Lac-St-Jean的无畸形复合体和Skaergaard分层侵入体）的下降线在它们达到磷灰石饱和度之前没有越过液-液不混溶场。因此，与这三个侵入岩组相关的富含磷灰石氧化物的岩石最好通过晶体碎裂，随后堆积磷灰石和Fe-Ti氧化物来解释。

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