Abstract

The paper reports major relations and trends determined in the distributions of trace elements and the Sr and Nd isotope composition of leucogranites of the Turga massif in Eastern Transbaikalia. Three varieties of the leucogranites are distinguished: porphyritic biotite granites, equigranular granites with Li-siderophyllite, and amazonite granites that make up small stocks and dikes. All of the rocks define a single Rb–Sr isochron that corresponds to an age of 134 ± 1 Ma at IR_(Sr) = 0.71768 ± 22 and MSWD = 1.2, i.e., all of these rocks crystallized within a narrow age span. The porphyritic biotite granites, which are thought to be parental for the leucogranites, crystallized at lower temperatures (710–740°C) than the younger granites with Li-siderophyllite (810–850°C). Moreover, the granites with Li-siderophyllite have elevated Fe concentrations, which is reflected in that their micas are Fe-rich. The leucogranites are enriched in HFSE (270 ± 59 ppm Zr, 337 ± 93 ppm REE, 72 ± 31 ppm Th, and 16 ± 6 ppm U), which is atypical of amazonite granites in the study area. Considered together with very low Sr and low Ti and P concentrations, these compositional features are distinguishing features of A-type granites. The rare-metal granites of the Turga massif are unique in composition: being similar to amazonite granites in mineralized massifs, these rocks carry accessory minerals typical of peralkaline rocks. They contain LREE fluorides and fluorcarbonates (fluocerite, bastnaesite, and parisite), minerals of the pyrochlore and samarskite groups, and minerals of the isostructural group of REE–Y–Zr–Th–U silicate-phosphates. Our data provide grounds for classifying the rare-metal granites of the Turga massif with an unusual transitional geochemical subtype: peraluminous columbite-bearing amazonite granites of elevated alkalinity with peralkaline REE–Nb–Zr–Th–U mineralization.

中文翻译：

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具有REE-Nb-Zr-Th-U专业化的亚马逊岩Li-F花岗岩：东贝巴卡利亚东部图尔加地块的地球化学，矿物学和同位素年代学

摘要

该论文报道了在东贝贝卡利亚东部的图尔加地块的白云石中微量元素的分布以及Sr和Nd同位素组成所确定的主要关系和趋势。区分了白垩纪花岗岩的三种变体：斑状黑云母花岗岩，具有锂铁叶绿石的等粒花岗岩和构成小种群和堤防的亚马逊石花岗岩。所有的岩石都定义了一个单一的Rb–Sr等时线，对应于IR _（Sr）时的年龄为134±1 Ma= 0.71768±22，MSWD = 1.2，即所有这些岩石均在狭窄的年龄段内结晶。斑状黑云母花岗岩被认为是白云母的母体，在较低的温度（710–740°C）下结晶，而年轻的含锂铁橄榄石的花岗岩（810–850°C）则结晶。而且，具有锂铁叶绿石的花岗岩具有较高的铁浓度，这反映在它们的云母富含铁。无色花岗岩富含HFSE（270±59 ppm Zr，337±93 ppm REE，72±31 ppm Th和16±6 ppm U），这在研究区域内是非典型的玛瑙花岗岩。与非常低的Sr和低的Ti和P浓度一起考虑时，这些组成特征是A型花岗岩的显着特征。Turga地块的稀有金属花岗岩具有独特的成分：这些岩石与矿化断层中的亚玛瑙花岗岩相似，这些岩石中携带着典型的高碱性岩石辅助矿物。它们包含LREE氟化物和碳酸盐（氟陨石，玄武岩和方铁矿），烧绿石和sa马铁矿族的矿物，以及REE–Y–Zr–Th–U硅酸盐-磷酸盐的等结构组的矿物。我们的数据为对具有异常过渡地球化学亚型的图尔加断层的稀有金属花岗岩进行分类提供了基础：碱度高的高钙铝矾土含钙霞石花岗岩与高碱性REE–Nb–Zr–Th–U矿化。稀土-Y-Zr-Th-U硅酸盐-磷酸盐同构群的矿物和矿物。我们的数据为对具有异常过渡地球化学亚型的图尔加断层的稀有金属花岗岩进行分类提供了基础：碱度高的高钙铝矾土含钙霞石花岗岩与高碱性REE–Nb–Zr–Th–U矿化。稀土-Y-Zr-Th-U硅酸盐-磷酸盐同构群的矿物和矿物。我们的数据为对具有异常过渡地球化学亚型的图尔加断层的稀有金属花岗岩进行分类提供了基础：碱度高的高钙铝矾土含钙霞石花岗岩与高碱性REE–Nb–Zr–Th–U矿化。