UHP metamorphism recorded by phengite eclogite from the Caledonides of northern Sweden: P–T path and tectonic implications
UHP metamorphism recorded by phengite eclogite from the Caledonides of northern Sweden: P–T path and tectonic implications
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瑞典北部喀里多尼德斯多硅白云母榴辉岩记录的超高压变质作用：P-T路径和构造意义
DOI：
10.1111/jmg.12306
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发表时间：
2018
影响因子：
3.4
通讯作者：
J. Luptáková
中科院分区：
文献类型：
--
作者：
M. Bukała;I. Klonowska;C. Barnes;J. Majka;Karolina Kośmińska;M. Janák;K. Fassmer;C. Broman;J. Luptáková
斯堪的纳维亚加里多尼德山脉的SeveNappe杂岩(SNC)记录了高压和超高压变质作用的历史。SNC榴辉岩产于瑞典的两个地区，即Jämtland和Norrbotten。Jämtland榴辉岩及其伴生岩石得到了较好的研究，为晚奥陶世超高压变质作用提供了证据，而形成于晚寒武世/早奥陶世的Norrbotten榴辉岩还没有得到如此详细的研究，特别是在其形成的P-T条件方面。在所研究的榴辉岩中，单斜辉石含有一个高钠核和两个边缘：内、中钠和外、低钠。石榴石由高钙真面体核心、低钙内缘和中钙外缘组成。在多硅白云母中也出现了类似的模式，其中高硅核心被中硅和低硅边缘所包裹。矿核、内缘和外缘的成分反映了榴辉岩变质演化的三个阶段。应用石英-石榴石地质压力测量和锆石-金红石地质测温，表明石榴石成核(E0阶段)发生在1.5-1.6 Gpa和620-660℃。榴辉岩峰值压力组合在E1阶段发育，由石榴石+绿辉石+多硅白云母+金红石+柯石英？在NCKFMMnASHT体系中，得到了由常规地温压计和热力学模型所约束的2.8-3.1 Gpa和660-780℃的P-T条件。随后，低压阶段E2和E3分别记录了2.2-2.8 Gpa，680-780℃和2.1 Gpa，735℃的条件。榴辉岩的进退变质演化来自石榴石中绿帘石、角闪石和单斜辉石的包裹体。角闪石-石英-斜长石共晶、次生绿帘石/橄榄石和钛铁矿取代金红石的存在记录了在<；1.5 Gpa(称为E4阶段)发生的较晚的逆行变化。所获得的P-T条件表明，Norrbotten榴辉岩经历了一个以顺时针P-T路径为特征的变质演化过程，在相对较低的俯冲体制下(7.8℃/km)，峰值变质作用达到柯石英稳定场。这些结果首次证明了北极圈以上SNC的超高压变质作用，证明了加里东造山早期深俯冲巴尔的冈边缘的冷俯冲体制和多阶段折返作用。
The Seve Nappe Complex (SNC) of the Scandinavian Caledonides records a well‐documented history of high pressure (HP) and ultra‐high pressure (UHP) metamorphism. Eclogites of the SNC occur in two areas in Sweden, namely Jämtland and Norrbotten. The Jämtland eclogites and associated rocks are well‐studied and provide evidence for late Ordovician UHP metamorphism, whereas the Norrbotten eclogites, formed during the late Cambrian (Furongian)/Early Ordovician, have not been studied in such detail, especially in terms of the P–T conditions of their formation. Within the studied eclogite, clinopyroxene contains a high‐Na core and two rims: inner, medium‐Na and outer, low‐Na. Garnet consists of a high‐Ca euhedral core, low‐Ca inner rim and medium‐Ca outer rim. A similar pattern occurs within phengite, where high‐Si cores are enveloped by medium and low‐Si rims. The compositions of the mineral cores, inner rims and outer rims reflect three stages in the metamorphic evolution of the eclogite. Applied Quartz‐in‐Garnet geobarometry, coupled with Zr‐in‐rutile geothermometry reveal that garnet nucleation (E0 stage) took place at 1.5–1.6 GPa and 620–660°C. The eclogite peak‐pressure assemblage developed during the E1 stage, it consists of garnet+omphacite+phengite+rutile+coesite? and yields P–T conditions of 2.8–3.1 GPa and 660–780°C as constrained by conventional geothermobarometry and thermodynamic modelling in the NCKFMMnASHT system. Later, lower‐pressure stages E2 and E3 record conditions of 2.2–2.8 GPa, 680–780°C and 2.1 GPa, 735°C, respectively. The prograde metamorphic evolution of the eclogite is inferred from inclusions of epidote, amphibole and clinopyroxene within garnet. The presence of amphibole–quartz–plagioclase symplectites, secondary epidote/zoisite and titanite replacing rutile record the later retrograde changes taking place at <1.5 GPa (referred as E4 stage). The obtained P–T conditions indicate that the Norrbotten eclogites underwent a metamorphic evolution characterized by a clockwise P–T path with peak metamorphism reaching up to coesite stability field within a relatively cold subduction regime (7.8°C/km). The obtained results provide the first evidence for UHP metamorphism in the SNC above the Arctic Circle and document cold subduction regime and multistage exhumation of the deeply subducted Baltican margin at early stage of the Caledonian Orogeny.
超越石榴石等梯度：QuiG 气压测量法和热力学模型的比较
影响因子：
3.5
作者：
Spear, Frank S.;Thomas, Jay B.;Hallett, Benjamin W.
通讯作者：
Hallett, Benjamin W.
斯堪的纳维亚喀里多尼德山脉中奥陶世大陆地壳俯冲：瑞典塞韦纳佩杂岩 Tjeliken 的一个例子
影响因子：
3.5
作者：
Fassmer;Klonowska;Walczak;Andersson;Froitzheim;Fonseca;Münker;Janák;Whitehouse
通讯作者：
Whitehouse