Two garnet growth events in polymetamorphic rocks in southwest Spitsbergen, Norway: insight in the history of Neoproterozoic and early Paleozoic metamorphism in the High Arctic
Two garnet growth events in polymetamorphic rocks in southwest Spitsbergen, Norway: insight in the history of Neoproterozoic and early Paleozoic metamorphism in the High Arctic
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挪威斯匹次卑尔根岛西南部多变质岩中的两次石榴石生长事件：洞察高北极新元古代和早古生代变质作用的历史
DOI：
10.1139/cjes-2015-0142
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发表时间：
2015
影响因子：
1.4
通讯作者：
M. Manecki
中科院分区：
文献类型：
--
作者：
J. Majka;Karolina Kośmińska;S. Mazur;J. Czerny;K. Piepjohn;M. Dwornik;M. Manecki
在挪威斯瓦尔巴群岛西南部的Wedel Jarlsberg Land北部进行的年代学研究表明，在Torellian （c. 640 Ma）和早期Caledonian （470-460 Ma）事件期间，Tonian （c. 950 Ma）火成岩经历了变质作用。该区主要发育产于托尼期原岩的长丝片麻岩，片岩由两种不同的变质矿物组合组成。M1 （Torellian）组合由石榴石- 1 +石英+斜长石- 1 +黑云母- 1 +白云母- 1组成，形成于角闪岩相条件下，温度为550 ~ 600℃，温度为5 ~ 8 kbar （1 kbar = 100 MPa）。M2（加里东期）组合由石榴石- ii +石英+斜长石- ii +黑云母- ii +白云母- ii +黝帘石+绿泥石组成，结晶温度为500-550℃，9-12 kbar，对应于绿帘石-角闪石相条件。M2矿物组合构成了普遍存在的加里东构造的片岩，随后在左侧走滑剪切机制中被重新激活。古近纪尤里坎造山运动期间的大规模被动旋转导致原构造顺时针旋转70°至现在的位置。新的压力-温度估算表明，研究区变质基底在托雷连统中级活动期间被固结，然后被加里东期中-高压俯冲相关变质作用叠加。随后的左旋剪切带组装了现在的基底单元结构。我们的研究结果提出了一个问题，即在高北极地区加里东基底的托雷利亚前体的可能范围及其随后参与加里东早期俯冲的规模。结合之前的研究，结果表明斯匹次卑尔根岛西南部和埃尔斯米尔岛的皮尔亚地层之间可能存在关联。
Geochronological studies in northern Wedel Jarlsberg Land, southwestern Svalbard (Norway), showed that the Tonian (c. 950 Ma) igneous rocks were subjected to metamorphism during the Torellian (c. 640 Ma) and early Caledonian (470–460 Ma) events. Predominant augen gneisses, derived from a Tonian protolith, are intercalated in that area, with schists comprising two distinct metamorphic mineral assemblages. The M1 (Torellian) assemblage containing garnet-I + quartz + plagioclase-I + biotite-I + muscovite-I was formed under amphibolite-facies conditions at c. 550–600 °C and 5–8 kbar (1 kbar = 100 MPa). The M2 (Caledonian) assemblage comprising garnet-II + quartz + plagioclase-II + biotite-II + muscovite-II + zoisite + chlorite crystallized at c. 500–550 °C and 9–12 kbar, corresponding to epidote–amphibolite facies conditions. The M2 mineral assemblage constitutes the pervasive Caledonian fabric of the schists that was subsequently reactivated in a left-lateral strike-slip shear regime. The subsequent c. 70° clockwise rotation of the original structure to its present position was caused by a large-scale passive rotation during the Paleogene Eurekan orogeny. The new pressure–temperature estimates suggest that metamorphic basement in the study area was consolidated during the Torellian middle-grade event and then overprinted by Caledonian moderate- to high-pressure subduction-related metamorphism. A following sinistral shear zone assembled the present structure of basement units. Our results pose a question about the possible extent of Torellian precursor to the Caledonian basement across the High Arctic and the scale of its subsequent involvement in early Caledonian subduction. In conjunction with previous studies, the results suggest a possible correlation between southwestern Spitsbergen and the Pearya Terrane in Ellesmere Island.