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首页> 外文期刊>Contributions to Mineralogy and Petrology >Petrogenesis of Fe–Ti oxides in amphibole-rich veins from the Lherz orogenic peridotite (Northeastern Pyrénées, France)
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Petrogenesis of Fe–Ti oxides in amphibole-rich veins from the Lherz orogenic peridotite (Northeastern Pyrénées, France)

机译：Lherz造山橄榄岩富含闪石的静脉中Fe-Ti氧化物的成岩作用（法国东北比利牛斯）

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摘要

Accessory, homogeneous ilmenite and rutile are important oxide phases in amphibole-rich high-pressure cumulate veins which crosscut the Lherz orogenic lherzolite massif. Those veins crystallized from alkaline melts at P = 1.2–1.5 GPa within the uppermost lithospheric mantle. Transitional basalts contaminated by peridotitic wall-rocks and then uncontaminated alkali basalts (basanites) reused the same vein conduits. Petrographic observations give evidence that Fe–Ti oxide saturation depends on the silica contents of each parental melt. The water-poor silica-rich transitional melts that generated websterites and plagioclase-rich clinopyroxenites reached early Ti-oxide saturation (1,200°C; 1.5 GPa). Rutile is as abundant as ilmenite. It is enriched with Nb–Zr–Hf by a factor of 10–100 relative to either amphibole or ilmenite. The amphibole pyroxenites and hornblendites crystallized from basanites reached late Fe–Ti oxide saturation after precipitation of amphibole, with ilmenite crystallizing along with phlogopite in the latter. The Lherz ilmenites are devoid of exsolution and contain very little trivalent iron. This compositional feature indicates more reducing crystallization conditions than usually inferred for alkali lavas and their megacrysts (FMQ ± 1). The veins incompletely equilibrated for redox conditions with their wall-rock peridotites which record more oxidizing conditions (FMQ ± 1). The veins also exchanged magnesium and chromium, as suggested by Cr-bearing, Mg-rich ilmenite (up to 44 mol% MgTiO3) in veins less than 3–4 cm thick. Mg-rich ilmenite megacrysts occurring in alkali basalts could be actually xenocrysts from veins similar in thickness to those occurring at the Lherz massif, although crystallized from more oxidized magmas.
机译：附件，均一的钛铁矿和金红石是富含闪石的高压累积矿脉中重要的氧化物相，这些脉横切了Lherz造山型锂铁矿地块。这些岩石从最上层岩石圈地幔中的P = 1.2–1.5 GPa的碱性熔体中结晶出来。被橄榄石化的围岩污染的过渡玄武岩，然后被未污染的碱性玄武岩（玄武岩）再利用了相同的脉管。岩相学观察表明，Fe-Ti氧化物的饱和度取决于每个母体熔体的二氧化硅含量。贫水的富含二氧化硅的过渡熔体产生了维氏石和斜长石的斜辉石岩达到了早期的Ti氧化物饱和（1200°C； 1.5 GPa）。金红石和钛铁矿一样丰富。相对于角闪石或钛铁矿，它富含Nb-Zr-Hf的10-100倍。从闪锌矿中结晶出的闪石辉石岩和角闪石在闪石沉淀后达到Fe-Ti氧化物后期饱和，钛铁矿和金云母在其中结晶。 Lherz钛铁矿没有脱溶现象，并且几乎不含三价铁。这种组成特征表明，与通常认为是碱熔岩及其超晶质（FMQ±1）相比，降低的结晶条件更多。静脉在氧化还原条件下无法完全平衡，其壁岩橄榄岩记录了更多的氧化条件（FMQ±1）。如含铬，富含Mg的钛铁矿（最高达44 mol％MgTiO 3）所示，静脉还交换了镁和铬。碱玄武岩中富含镁的钛铁矿超晶实际上可能是来自脉的异种晶，其厚度与发生在莱尔兹地块的相近，尽管它们是从更多的氧化岩浆中结晶出来的。

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