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首页> 外文期刊>Contributions to Mineralogy and Petrology >Braided peridotite sills and metasomatism in the Rum Layered Suite, Scotland
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Braided peridotite sills and metasomatism in the Rum Layered Suite, Scotland

机译：苏格兰兰姆分层套件的编织橄榄石谱系和偏定术

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The Rum Eastern Layered Intrusion (ELI; Scotland) is an open-system layered intrusion constructed of 16 macro-rhythmic units. Each of the macro-rhythmic units consists of a peridotite base and a troctolite (+/- gabbro) top, previously attributed to the fractional crystallisation of a single magma batch. This classic paradigm has been challenged, however, with evidence presented for the emplacement of peridotite sills in Units 9, 10, and 14, such as cross-cutting relationships, upward-oriented apophyses, and lateral discontinuities. To test whether the other major peridotites within the ELI represent sills, we have carried out new field, petrographic, and mineral chemical analyses of the peridotites in Units 7, 8 and 9. The peridotites display large- and small-scale cross-cutting relationships with the overlying troctolite, indicative of an intrusive relationship. The peridotites also show large-scale coalescence and lateral spatial discontinuities such that the ELI unit divisions become arbitrary. Harrisite layers and Cr-spinel seams found throughout Units 7, 8, and 9 suggest the peridotites were constructed incrementally via repeated injections of picritic magma. Our observations allow for distinct subtypes of peridotite to be defined, separated by intrusive contacts, allowing for their relative chronology to be determined. Older, poikilitic peridotite, rich in clinopyroxene, is truncated by younger, well-layered peridotite, containing abundant harrisite layers. In addition to the new peridotite subtypes defined in this study, we find strong evidence for laterally oriented metasomatism within clinopyroxene-rich wehrlites at the top of the Unit 8 peridotite. The wehrlites and surrounding peridotites record a complex series of metasomatic reactions that transformed thin picrite sills into clinopyroxene-rich wehrlites without any evidence for the sort of vertical melt movement typically posited in layered intrusions. The observations presented in this study from the ELI cannot be reconciled with the classic magma chamber paradigm and are better explained by the emplacement of composite sills into pre-existing feldspathic cumulate (gabbro or troctolite). The evidence for sill emplacement presented here suggests that the layered complex was constructed by a combination of sill emplacement and metasomatism, forming many of the unusual (often clinopyroxene-rich) lithologies that surround the sills. The broad-scale formation of the layered peridotites via incremental sill emplacement, suggested by the occurrence of upward-oriented apophyses, coalescence, and lateral discontinuity, could be applied to much larger ultramafic intrusions, which might have formed by similar mechanisms.
机译：朗姆酒东部分层入侵（Eli;苏格兰）是一种由16个宏观节奏单元构成的开放式分层侵入。每个宏观节奏单元由恒星碱和脱岩（+/- Gabbro）顶部组成，以前归因于单一岩浆批次的分数结晶。然而，这种经典范式受到挑战，有证据表明在9,10和14个单元中的恒星岩石座，例如横切关系，向上取向的Apophyses和横向不连续性。为了测试ELI内的其他主要云板代表窗台，我们在单位7,8和9中开展了恒星的新领域，岩画和矿物学分析。橄榄石显示出大型和小规模的横切关系随着覆盖的速块，表示具有侵入性的关系。恒星还显示大规模的聚结和横向空间不连续性，使得ELI单位部门成为任意。在整个单元7,8和9中发现的哈里塔貂层和Cr-尖晶石接缝表明恒星通过重复注射皮肤岩浆逐渐构建。我们的观察结果允许定义恒星的不同亚型，通过侵入式接触分离，允许确定其相对年表。富含Clinoceoxene的较旧的，富含肺结石的Poikilitic恒星，被较年轻，层状的橄榄石截断，含有丰富的卤石层。除了在本研究中定义的新的橄榄石亚型外，我们还发现了强有力的证据，在第8单元顶部的Closopoyroxene的Wehrlites内横向导向的偏定术。 Wehrlites及周围的恒星记录了一种复杂的一系列态化反应，即将薄的菠菜谱系转变为富含贫肾上腺素的Wehrlites，而没有任何证据于通常在层状入侵中定位的垂直熔体运动的任何证据。从ELI中提出的本研究中呈现的观察不能与经典的岩浆室范例协调，并且最好通过复合网尔进入预先存在的长期性累积（Gabbro或Trocolite）来说。这里提出的窗台施加的证据表明，层状复合物由迹线施加和偏索术的组合构成，形成围绕门槛的许多异常（通常是贫富的）岩性。通过增量尺寸施加的层状不连续的层状恒星的大规模形成可以应用于向上取向的apophyses，聚结和横向不连续性，可以应用于更大的超近外侵入性，这可能通过类似机制形成。

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