Age and temperature-time evolution of retrogressed eclogite-facies rocks in the Paleoproterozoic Nagssugtoqidian Orogen, South-East Greenland: Constrained from U-Pb dating of zircon, monazite, titanite and rutile
Age and temperature-time evolution of retrogressed eclogite-facies rocks in the Paleoproterozoic Nagssugtoqidian Orogen, South-East Greenland: Constrained from U-Pb dating of zircon, monazite, titanite and rutile
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DOI：
10.1016/j.precamres.2018.07.002
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发表时间：
2018-09
影响因子：
3.8
通讯作者：
Sascha Müller;A. Dziggel;S. Sindern;T. Kokfelt;A. Gerdes;J. Kolb
中科院分区：
文献类型：
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作者：
Sascha Müller;A. Dziggel;S. Sindern;T. Kokfelt;A. Gerdes;J. Kolb
利用锆石、独居石、钛铁矿和金红石的LA-ICP-MS U-Pb定年方法，研究了格陵兰东南部古元古代纳格苏格托其甸造山带库穆特地体榴辉岩相岩石的温度-时间演化。地体以太古代TTG片麻岩和多种表壳岩为主，古元古代变形期间基性脉侵入片麻岩。石榴石-蓝晶石片岩中的碎屑锆石给出了太古代至古元古代的年龄，并将变质沉积物前体的最大沉积限制在2107 ± 21 Ma。变质基性岩墙的侵入时间分别为2146 ± 63和2092 ± 22 Ma，与碎屑锆石年龄误差不大，可能是近同期岩墙侵位和沉积的结果。大约2亿年。在岩脉就位后，Kuummiut地体经历了顺时针PT演化，包括榴辉岩相变质作用和随后的折返进入中地壳。绝大多数锆石、独居石和钛铁矿的变质年龄在1891 ± 10 ~ 1882 ± 3 Ma之间。虽然变质锆石的稀土元素模式反映了榴辉岩相条件下的生长，锆石与退变质矿物组合和它们的日期是无法区分的角闪岩相的钛铁矿。这可能被解释为表明榴辉岩相和高压角闪岩相变质作用的时间在误差范围内重叠，与快速和构造控制的折返一致。然而，以往的研究表明，在退变质过程中，锆石中的REE和U-Pb系统可能是不耦合的，因此，年龄范围最能反映高压角闪岩相退变质过程中矿物的生长和重结晶。独居石和钛铁矿年龄在1872 ± 70和1821 ± 31 Ma之间，反映了区域中压角闪岩相变质作用，标志着Kuummiut地体挤压变形的最后阶段。随后的热演化与钛铁矿的生长有关，直到1738 ± 61 Ma，此时大多数金红石冷却到其闭合温度以下。最年轻的金红石年龄为1645 ± 63和1617 ± 91 Ma，与构造后侵入杂岩的侵位有关。总的来说，这些数据表明，经过最初的构造控制的折返，Kuummiut地体经历了相对缓慢的，侵蚀控制的冷却，只有轻微的热扰动在变质和岩浆活动的衰退阶段。
LA-ICP-MS U-Pb dating of zircon, monazite, titanite and rutile was carried out to investigate the temperature-time evolution of eclogite-facies rocks in the Kuummiut Terrane of the Paleoproterozoic Nagssugtoqidian Orogen in South-East Greenland. The terrane is dominated by Archean TTG gneiss and a variety of supracrustal rocks; basic dykes intruded the gneiss during Paleoproterozoic deformation. Detrital zircon in garnet-kyanite schist gives Archean to Paleoproterozoic dates and confines the maximum deposition of the metasediment precursor to 2107 ± 21 Ma. Intrusion of the metabasic dykes occurred at 2146 ± 63 and 2092 ± 22 Ma, within error of the detrital zircon date, possibly indicating near-contemporaneous dyke emplacement and sedimentation. About 200 m.y. after dyke emplacement, the Kuummiut Terrane underwent a clockwise PT-evolution, involving eclogite-facies metamorphism and subsequent exhumation into the mid crust. The majority of zircon, monazite and titanite give metamorphic dates between 1891 ± 10 and 1882 ± 3 Ma. Although the REE patterns in metamorphic zircon reflect growth at eclogite-facies conditions, the zircons are associated with retrograde mineral assemblages and their dates are indistinguishable from amphibolite-facies titanite. This may be interpreted to indicate that the timing of eclogite- and high-pressure amphibolite-facies metamorphism overlap within error, consistent with rapid and tectonically-controlled exhumation. However, previous studies have shown that the REE and U-Pb systematics in zircon may be decoupled during retrograde metamorphism, and the range in dates is thus best interpreted to reflect mineral growth and recrystallization during high-pressure amphibolite-facies retrogression. Monazite and titanite dates between 1872 ± 70 and 1821 ± 31 Ma reflect regional medium-pressure amphibolite-facies metamorphism and mark the final stages of compressional deformation in the Kuummiut Terrane. The subsequent thermal evolution was associated with titanite growth until 1738 ± 61 Ma, a time where the majority of rutile cooled below its closure temperature. The youngest rutile dates at 1645 ± 63 and 1617 ± 91 Ma correlate with the emplacement of post-tectonic intrusive complexes. Collectively, the data show that after an initial tectonically-controlled exhumation, the Kuummiut Terrane experienced relatively slow, erosion-controlled cooling with only minor thermal perturbations during the waning stages of metamorphic and magmatic activity.