Timescales and significance of high-pressure, high-temperature metamorphism and mafic dike anatexis, Snowbird tectonic zone, Canada
Timescales and significance of high-pressure, high-temperature metamorphism and mafic dike anatexis, Snowbird tectonic zone, Canada
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加拿大雪鸟构造带高压高温变质作用和镁铁质脉深熔的时间尺度和意义
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发表时间：
2006
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通讯作者：
Michael L. Williams
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作者：
R. Flowers;S. Bowring;Michael L. Williams
新的地质年代学，同位素和地球化学数据的一个壮观的群深地壳混合岩基性岩脉提供了重要的洞察过程中运作的1.9 Ga高压，高温变质沿着雪鸟构造带在萨斯喀彻温省北方。高精度锆石U-Pb定年揭示了奇普曼基性岩脉在1896.2 ± 0.3 Ma时在1.0-1.2 GPa，>750°C条件下发生了同构造和同变质侵入作用。横切伟晶岩的U-Pb锆石年龄为1，894 - 1，891 Ma，这是当前暴露地壳水平上主要变质和变形的下限。高温持续约1400万年。年轻的U-Pb钛铁矿年龄和Sm-Nd全岩同位素数据表明伟晶岩是由镁铁质源熔融形成的，暗示了以下峰值条件。有限的熔融主机长英质片麻岩在1.9 Ga，尽管高温是一致的证据，他们以前的脱水麻粒岩相变质作用在太古代。基性岩墙和英云闪长质片麻岩深熔模式的空间不均匀性可归因于侧向峰值温度和成分的变化。我们相关的1,896马奇普曼基性岩脉侵位和变质作用与大量的1.9 Ga基性岩岩浆活动的最小沿走向范围的1,200公里的雪鸟构造带。这表明，一个重要的，整个大陆的软流圈上涌，导致大陆裂谷的初期。延伸随后终止与跨哈德逊增生和造山作用的腹地收缩。下地壳活动不大。6.5亿年元古宙变质作用和镁铁质岩浆作用之前，意味着一个延长的时间段的稳定性，被中断在1.9 Ga。这一不稳定事件与大多数保存完好的岩石圈长期稳定的记录形成对比，对于理解控制大陆毁灭或生存的岩石圈特征和构造环境非常重要。
New geochronological, isotopic and geochemical data for a spectacular swarm of deep crustal migmatitic mafic dikes offer important insight into processes operative during 1.9 Ga high pressure, high temperature metamorphism along the Snowbird tectonic zone in northern Saskatchewan. High-precision U–Pb zircon dates reveal anatexis of Chipman mafic dikes at 1,896.2 ± 0.3 Ma during syntectonic and synmetamorphic intrusion at conditions of 1.0–1.2 GPa, >750°C. U–Pb zircon dates of 1,894–1,891 Ma for cross-cutting pegmatites place a lower bound on major metamorphism and deformation at the currently exposed crustal levels. The persistence of elevated temperatures for ~14 m.y. following peak conditions is implied by younger U–Pb titanite dates, and by Sm–Nd whole rock isotopic data that suggest the derivation of the pegmatites by melting of a mafic source. Limited melting of the host felsic gneiss at 1.9 Ga despite high temperature is consistent with evidence for their previous dehydration by granulite facies metamorphism in the Archean. Spatial heterogeneity in patterns of mafic dike and tonalitic gneiss anatexis can be attributed to lateral peak temperature and compositional variability. We correlate 1,896 Ma Chipman mafic dike emplacement and metamorphism with substantial 1.9 Ga mafic magmatism over a minimum along-strike extent of 1,200 km of the Snowbird tectonic zone. This suggests a significant, continent-wide period of asthenospheric upwelling that induced incipient continental rifting. Extension was subsequently terminated by hinterland contraction associated with Trans-Hudson accretion and orogenesis. Little activity in the lower crust for ca. 650 m.y. prior to Proterozoic metamorphism and mafic magmatism implies an extended interval of cratonic stability that was disrupted at 1.9 Ga. This episode of destabilization contrasts with the record of long-term stability in most preserved cratons, and is important for understanding the lithospheric characteristics and tectonic circumstances that control the destruction or survival of continents.