A Field Study of the Liquid Line of Descent of Hydrous Alkaline-rich Magmas at Elevated Pressures (0.5-1.0 GPa): The Dariv Alkaline Intrusive Complex

高压（0.5-1.0 GPa）含水碱性岩浆下降液线的现场研究：达里夫碱性侵入杂岩

• 批准号: 1322032
• 负责人: Oliver Jagoutz
• 金额: $ 30万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1322032&HistoricalAwards=false
• 关键词: Field; Study; Liquid; Line; Descent

Understanding the origin of the highly diverse nature of felsic magmas, erupted as rhyolite or emplaced as large upper-crustal batholiths, is crucial to the investigation of the mechanisms that generate the silica-enriched continental crust. General consensus exists that strongly so-called peraluminous granites are derived, at least to some significant extent, from muscovite- and biotite-dehydration melting of metasedimentary protholiths. The origin of so-called meta-aluminous granites, however, is less certain. This project aims to investigate the hydrous liquid line of descent (LLD) of an alkaline magma and the relative roles of hydrous fractional crystallization versus partial melting in the formation of meta-aluminous alkaline granites through a field-based study. While alkaline granites are volumetrically less significant than calk-alkaline granites, their petrogenesis is of particular importance as they are often associated with economically significant mineralization. We will study a newly discovered exposures in the Dariv arc complex (Altai region of western Mongolia). The project will investigate a layered sequence ranging from phologopite-dominated ultramafic/mafic to intermediate (quartz-) monzonite and (quartz-) syenites rocks is spatially associated with large alkali-feldspar granite bodies. A similarly complete alkaline plutonic sequence has, to our knowledge, never been described in the geological literature before. In particular, the ultramafic rock assemblages exposed in Mongolia are currently only described as xenoliths from alkaline basaltic magmas. The complete exposures from ultramafic to felsic rocks provide an unrivaled opportunity to investigate crystal fractionation as a possible mechanism of alkali-feldspar granite formation.

了解长英质岩浆（以流纹岩形式喷发或以大型地壳上岩基形式侵位）高度多样化性质的起源，对于研究富硅大陆地壳的形成机制至关重要。人们普遍认为，所谓的过铝花岗岩至少在一定程度上是由变质沉积原岩的白云母和黑云母脱水熔融形成的。然而，所谓的变质铝质花岗岩的起源却不太确定。本项目旨在通过野外研究，探讨碱性岩浆的含水液体下降线（LLD），以及含水分晶与部分熔融在偏铝碱性花岗岩形成中的相对作用。虽然碱性花岗岩在体积上不如钙碱性花岗岩重要，但它们的岩石成因却特别重要，因为它们通常与经济上重要的矿化有关。我们将研究在达里夫弧杂岩（蒙古西部阿尔泰地区）新发现的暴露。该项目将研究一个层状序列，从以磷长岩为主的超镁铁质/基性到中间（石英-）二长岩和（石英-）正长岩，在空间上与大型碱长石花岗岩体相关。据我们所知，以前的地质文献中从未描述过类似的完整碱性深成层序。特别是蒙古的超基性岩石组合，目前只被描述为碱性玄武岩岩浆的捕虏体。从超镁铁质到长英质岩石的完全暴露为研究晶体分馏作为碱长石花岗岩形成的可能机制提供了无与伦比的机会。