权益分类	功能权益	普通用户	{{item.name}}会员
{{category.name}}	{{benefitItem.name}}

Platinum enrichment processes in ultramafic massifs of the Uralian Platinum belt, Russia - evidence for mineralization at the magmatic to hydrothermal transition

俄罗斯乌拉尔铂矿带超镁铁质地块中的铂富集过程——岩浆到热液转变过程中矿化的证据

基本信息

批准号：
325281966
负责人：
Professor Dr. Christian Gerhard Ballhaus
金额：
--
依托单位：
Abteilung Geochemie/Petrologie
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2017
资助国家：
德国
起止时间：
2016-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/325281966?language=en
关键词：
Platinum enrichment processes ultramafic massifs

项目摘要

Chromite and native Pt are usually considered to be early high temperature phases of primitive basaltic melts. Consequently, when chromite and Pt-Fe alloy are found enriched within primitive magmatic cumulates, it is assumed that these phases were enriched at magmatic temperature.The chromite-Pt enclaves in the massifs of the Uralian Platinum belt show many features that argue against a purely magmatic origin. Compared with the respective liquidus phases in basaltic melts, chromite and Pt-Fe alloys in the Uralian massifs can be orders of magnitude more coarse-grained. Hydrous silicates are commonplace, and chromite carries many generations of late hydrous phases within euhedral cavities that follow the crystal symmetry of chromite. The question is whether the fluid phases were derived directly from the parental melts of the cumulates or whether they reflect a random overprint. Primitive island arc melts - the potential parents to the ultramafic Uralian massifs - contain ~ 4 wt.% H2O. That H2O concentration is sufficient to render derivative melts and their cumulates saturated with a hydrous fluid phase. The working hypothesis is whether and to what extent magmatic chromite and Pt-Fe microliths can be mobilized and concentrated by intercumulus melts and fluids segregating from the crystallizing plutonic roots of island arc ankaramites.An important aspect to understand the enrichment processes is to date the mineralization. All platiniferous ultramafic massifs of the Uralian Platinum Belt are aligned parallel to the old suture marking the former Silurian convergent plate margin in the Ural mountains. Hence, if they outline a fossil volcanic arc, they should all return similar emplacements ages. The dating method of choice is the 190Pt-186Os decay scheme, tested here on Pt-Fe alloys from the Kondyor massif. If all platiniferous intrusions of the UPB return Pt mineralization ages identical within error, a genetic link must have existed between emplacement and cooling histories of the Uralian massifs and their Pt mineralization.

铬铁矿和自然铂通常被认为是原始玄武岩熔体的早期高温相。因此，当在原始岩浆堆积体中发现富铬矿和铂铁合金时，可以推测这些相是在岩浆温度下富集的。乌拉连铂带地块中的铬铁矿-铂包体显示出许多与纯粹岩浆成因相反的特征。与玄武岩熔体中的相应液相线相相比，乌拉维亚地块中的铬铁矿和铂-铁合金可以粗化一个数量级。水合硅酸盐很常见，铬铁矿在遵循铬铁矿晶体对称性的自面体空腔中携带着许多世代的晚期水合相。问题是，流体相是直接来自堆积物的母体熔体，还是它们反映了随机叠加。原始岛弧熔体--超镁铁质乌里安地块的潜在母体--含有约4wt.%的H2O。这种H2O浓度足以使衍生熔体及其堆积物饱和含水的流体相。工作假说是岩浆铬铁矿和铂-铁微石是否以及在多大程度上可以被从岛弧蓝晶石结晶的深成根部分离出来的堆间熔体和流体所活化和浓缩。了解富集化过程的一个重要方面是确定成矿作用的时间。乌拉尔白金带所有含铂超镁铁质地块与旧缝合线平行排列，标志着乌拉尔山脉前志留纪会聚板块边缘。因此，如果它们勾勒出一个化石火山弧，它们都应该返回类似的侵位年龄。选择的测年方法是190Pt-186Os衰变方案，这里测试的是来自康迪尔地块的铂-铁合金。如果UPB的所有含铂侵入体在误差范围内返回相同的铂成矿年龄，那么乌拉维亚地块的侵位和冷却历史与它们的铂成矿作用之间肯定存在着成因联系。