Timing of magmatism and metamorphism in the Gruinard Bay area of the Lewisian Gneiss Complex: comparison with the Assynt Terrane and implications for terrane accretion—reply
Timing of magmatism and metamorphism in the Gruinard Bay area of the Lewisian Gneiss Complex: comparison with the Assynt Terrane and implications for terrane accretion—reply
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刘易斯片麻岩杂岩格鲁纳德湾地区岩浆作用和变质作用的时间：与Assynt地体的比较及其对地体增生的影响——回复
DOI：
10.1007/s00410-006-0156-6
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发表时间：
2004
影响因子：
3.5
通讯作者：
G. J. Love
中科院分区：
文献类型：
--
作者：
C. Friend;P. Kinny;G. J. Love
从选定的片麻岩样品的U-Pb锆石数据提供估计的时间的火成岩原岩侵位和麻粒岩相变质作用在格鲁纳德湾，巴德尔湾和洛钦韦尔地区的大陆刘易斯片麻岩复杂的苏格兰西北部。锆石从片麻岩包含复杂的分带模式，使他们服从SHRIMP离子探针分析，继承锆石区分岩浆生长和变质重结晶。格吕纳德湾的英云闪长质麻粒岩产生了2，825 ±8 Ma的变质带锆石核的原岩年龄，再结晶的低铀边缘保留了2，733 ±12 Ma的年龄。在一个奥长片麻岩样品中识别出一个继承的2，905 ±15 Ma的年龄分量，估计其原岩侵位时间为2，858 ±11 Ma。还存在低铀边缘，其年龄为2，729 ±20 Ma，与麻粒岩的边缘年龄一起被认为是格吕纳德地区麻粒岩相变质作用的年代。为了与Gruinard湾片麻岩进行比较，对Assynt省Baddall湾麻粒岩相岩石中的奥长花岗岩部分熔融物和奥长花岗岩片进行了分析。年龄数据没有显示明确的关系，在锆石的分区模式，并显示一个蔓延沿着协和典型的以前的离子探针年龄数据从斯库里片麻岩。然而，这两个样品都显示出在2,480 Ma时的显著同位素扰动，这是对巴德卡尔变质作用的最新估计。原岩年龄的组件Assynt的范围之间的CA。2，900和3，030 Ma，似乎比来自Gruinard Bay地区的2，860 - 2，825 Ma片麻岩原岩更古老。麻粒岩相变质作用的时间也似乎是不同的两个地区之间，这表明大陆的两个麻粒岩地区可能并不像以前认为的那样相关。相反，他们被解释为一个的ESTLE增生模型，即这两个地区的发展作为单独的块之前，他们在古元古代并置。由于观测到的北侧2，480 Ma和南侧2，730 Ma的年龄特征，两个火山口之间的边界被认为位于洛钦韦尔以南，与斯特拉森线相对应。通过定义一个新的大陆板块，格吕纳德地体，大陆板块的数量，其中包括Assynt（中央），Rhiconich（北方）和南部的板块，已经扩大。
U-Pb zircon data from selected gneiss samples provide estimates of the timing of igneous protolith emplacement and granulite facies metamorphism in the Gruinard Bay, Badcall Bay and Lochinver areas of the mainland Lewisian Gneiss Complex of north-west Scotland. Zircons from the gneisses contain complex zoning patterns making them amenable to SHRIMP ion microprobe analysis, with inherited zircon distinguishable from magmatic growth and metamorphic recrystallisation. From Gruinard Bay, a tonalitic granulite yielded a protolith age of 2,825±8 Ma for oscillatory-zoned zircon cores, with recrystallised low-U rims preserving an age of 2,733±12 Ma. An inherited 2,905±15 Ma age component was recognised in a sample of trondhjemitic gneiss, the protolith of which is estimated to have been emplaced at 2,858±11 Ma. Low-U rims yielding an age of 2,729±20 Ma are also present, which together with the rim age from the granulite are considered to date granulite facies metamorphism in the Gruinard region. For comparison with the Gruinard Bay gneisses, a trondhjemitic partial melt and trondhjemite sheet were analysed from the granulite facies rocks at Badcall Bay in the Assynt terrane. Age data do not show definitive relationships with zoning patterns in the zircons, and show a spread along concordia typical of previous ion microprobe age data from the Scourie gneisses. Both samples do, however, show a significant isotopic disturbance at 2,480 Ma, the most recent estimate for the Badcallian metamorphism. Protolith ages for components of the Assynt terrane range between ca. 2,900 and 3,030 Ma, and appear to be older than the 2,860–2,825 Ma gneiss protoliths from the Gruinard Bay area. The timing of granulite facies metamorphism also appears to be different between the two areas, suggesting that the two granulite regions of the mainland may not be related as previously thought. Instead, they are interpreted in terms of a terrane accretion model whereby the two areas evolved as separate blocks prior to their juxtaposition during the Palaeoproterozoic. The boundary between the two terranes is thought to lie to the south of Lochinver, corresponding with the Strathan Line, because of the observed 2,480 Ma age signature to the north and 2,730 Ma signature to the south. By defining a new mainland terrane, the Gruinard Terrane, the number of mainland blocks, which includes the Assynt (central), Rhiconich (northern) and Southern terranes, has been expanded.