Petrology and U-Pb Geochronology of Footwall Porphyritic Rhyolites from the Wolverine Volcanogenic Massive Sulfide Deposit, Yukon, Canada: Implications for the Genesis of Massive Sulfide Deposits in Continental Margin Environments *
Petrology and U-Pb Geochronology of Footwall Porphyritic Rhyolites from the Wolverine Volcanogenic Massive Sulfide Deposit, Yukon, Canada: Implications for the Genesis of Massive Sulfide Deposits in Continental Margin Environments *
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DOI：
10.2113/gsecongeo.103.1.5
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发表时间：
2008
期刊：
影响因子：
5.8
通讯作者：
S. Piercey;J. Peter;J. Mortensen;S. Paradis;D. Murphy;T. L. Tucker
中科院分区：
文献类型：
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作者：
S. Piercey;J. Peter;J. Mortensen;S. Paradis;D. Murphy;T. L. Tucker
斑状流纹岩岩床是加拿大育空地区金刚狼火山成因块状硫化物（VMS）存款下盘的重要组成部分，并出现在紧邻存款区（金刚狼/Lynx区）矿化附近，且沿走向（Fisher、Puck和Sable区）沿着处于相似的地层水平。斑状流纹岩有两种类型：较古老的石英-长石斑状（QFP）流纹岩套;和较年轻的长石斑状（FP）流纹岩套。QFP和FP两套侵入体均为不整合的，显示出类似于岩坎的形态，并被细脉矿化蚀变和横切，表明它们是前-同矿化。QFP系列侵入体的边缘含有周围页岩的少量捕虏体和不发达的冷却边缘，表明侵位到部分固结的沉积岩中，而FP系列侵入体显示发育良好的冷却边缘，表明侵位到完全固化的沉积岩中。这些特征表明，QFP套件的侵入体代表一个较老的阶段流纹质岩浆活动，而FP套件代表一个年轻的事件。FP岩系的锆石U-Pb年龄为352.4 ± 1.5Ma，FP岩系的锆石U-Pb年龄为347.8 ± 1.3Ma和346.0 ± 2.2Ma。两套斑岩均继承了元古宙锆石，并具有La/SmUCN ~1和Nb/ThUCN ~1比值（UCN-上陆壳标准化），表明其来源于古老的上陆壳物质或与之发生了广泛的相互作用。然而，FP套件具有升高的高场强元素（HFSE）和稀土元素（REE）含量，高锆石饱和温度，以及比QFP套件更高的Nb/Ta比和更低的Ti/Sc比。这些特征被解释为反映了FP系列岩浆的温度更高（>900°C），在其成因中具有更大的地幔成分。然而，这两个套房，被解释为已形成由于玄武岩上涌，地壳熔融，并在硅铝石弧后盆地活动的壳幔混合。金刚狼盆地内地幔热的存在时间为~352 ~~347 ~ 346 Ma，最少为5百万年，表明持续的地幔热流对金刚狼斑岩的成因至关重要。这也表明，这种持续的地幔热是金刚狼热液系统的原因，上涌地幔可能是必要的，即使在大陆边缘型VMS环境中（例如，巴瑟斯特，伊比利亚黄铁矿带）。金刚狼斑岩是全球与VMS矿化有关的最富HFSE和REE的长英质岩石之一。这些岩石中的高HFSE和REE浓度被解释为由于
Porphyritic rhyolite sills form an important component of the footwall of the Wolverine volcanogenic massive sulfide (VMS) deposit, Yukon, Canada, and occur proximal to mineralization in the immediate deposit area (Wolverine/Lynx zone) and at similar stratigraphic levels along strike (Fisher, Puck, and Sable zones). Porphyritic rhyolites are of two types: an older quartz-feldspar porphyritic (QFP) rhyolite suite; and a younger feldspar porphyritic (FP) suite. Both the QFP and FP suites of intrusions are semiconcordant, suggesting a silllike morphology, and are altered and crosscut by veinlet mineralization, suggesting that they are pre- to synmineralization. The margins of QFP suite of intrusions contain minor xenoliths of surrounding shales and poorly developed chilled margins suggesting emplacement into partially consolidated sedimentary rocks, whereas the FP suite of intrusions shows well-developed chilled margins indicative of emplacement into fully solidified sedimentary rock. These features suggest that the QFP suite of intrusions represents an older phase of rhyolitic magmatism, whereas the FP suite represents a younger event. This is supported by U-Pb zircon ages, which indicate a 352.4 ± 1.5 Ma emplacement age for the FP suite and a ~347 to 346 Ma emplacement for the FP suite (two ages at 347.8 ± 1.3 and 346.0 ± 2.2 Ma). Both suites of porphyries have inherited Proterozoic zircon and have ratios of La/SmUCN ~1 and Nb/ThUCN ~1 (UCN ‐ upper continental crust normalized), indicating derivation from and/or extensive interaction with ancient upper continental crustal materials. The FP suite, however, has elevated high field strength element (HFSE) and rare earth element (REE) contents, high zircon saturation temperatures, and higher Nb/Ta ratios and lower Ti/Sc ratios than the QFP suite. These features are interpreted to reflect that the FP suite of magmas was hotter (>900°C) melts with a greater mantle component in their genesis. Both suites, however, are interpreted to have formed due to basaltic upwelling, crustal melting, and crust-mantle mixing during ensialic back-arc basin activity. The presence of mantle heat within the Wolverine basin from ~352 to ~347 to 346 Ma, a minimum of 5 m.y., suggests that sustained mantle heat flow was critical to the genesis of the Wolverine porphyries. It is also suggested that this sustained mantle heat was responsible for the Wolverine hydrothermal system and that upwelling mantle may be essential in providing the heat to drive hydrothermal systems even in continental margin-type VMS environments (e.g., Bathurst, Iberian pyrite belt). The Wolverine porphyries are among the most HFSE- and REE-enriched felsic rocks associated with VMS mineralization globally. The high HFSE and REE concentrations in these rocks are interpreted to be due to