We studied the petrography, mineralogy, thermobarometry and whole-rock chemistry of 120 peridotite and pyroxenite xenoliths collected from the 156–138 Ma Chidliak kimberlite province (Southern Baffin Island). Xenoliths from pipes CH-1, -6, -7 and -44 are divided into two garnet-bearing series, dunites–harzburgites–lherzolites and wehrlites–olivine pyroxenites. Both series show widely varying textures, from coarse to sheared, and textures of late formation of garnet and clinopyroxene. Some samples from the lherzolite series may contain spinel, whereas wehrlites may contain ilmenite. In CH-6, rare coarse samples of the lherzolite and wehrlite series were derived from P = 2·8 to 5·6 GPa, whereas predominant sheared and coarse samples of the lherzolite series coexist at P = 5·6–7·5 GPa. Kimberlites CH-1, -7, -44 sample mainly the deeper mantle, at P = 5·0–7·5 GPa, represented by coarse and sheared lherzolite and wehrlite series. The bulk of the pressure–temperature arrays defines a thermal state compatible with 35–39 mW m^–2 surface heat flow, but a significant thermal disequilibrium was evident in the large isobaric thermal scatter, especially at depth, and in the low thermal gradients uncharacteristic of conduction. The whole-rock Si and Mg contents of the Chidliak xenoliths and their mineral chemistry reflect initial high levels of melt depletion typical of cratonic mantle and subsequent refertilization in Ca and Al. Unlike the more orthopyroxene-rich mantle of many other cratons, the Chidliak mantle is rich (∼83 vol%) in forsteritic olivine. We assign this to silicate–carbonate metasomatism, which triggered wehrlitization of the mantle. The Chidliak mantle resembles the Greenlandic part of the North Atlantic Craton, suggesting the former contiguous nature of their lithosphere before subsequent rifting into separate continental fragments. Another, more recent type of mantle metasomatism, which affected the Chidliak mantle, is characterized by elevated Ti in pyroxenes and garnet typical of all rock types from CH-1, -7 and -44. These metasomatic samples are largely absent from the CH-6 xenolith suite. The Ti imprint is most intense in xenoliths derived from depths equivalent to 5·5–6·5 GPa where it is associated with higher strain, the presence of sheared samples of the lherzolite series and higher temperatures varying isobarically by up to 200 °C. The horizontal scale of the thermal-metasomatic imprint is more ambiguous and could be as regional as tens of kilometers or as local as <1 km. The time-scale of this metasomatism relates to a conductive length-scale and could be as short as <1 Myr, shortly predating kimberlite formation. A complex protracted metasomatic history of the North Atlantic Craton reconstructed from Chidliak xenoliths matches emplacement patterns of deep CO₂-rich and Ti-rich magmatism around the Labrador Sea prior to the craton rifting. The metasomatism may have played a pivotal role in thinning the North Atlantic Craton lithosphere adjacent to the Labrador Sea from ∼240 km in the Jurassic to ∼65 km in the Paleogene.

中文翻译：

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北大西洋克拉通下方的交化地幔：奇德里亚克·金伯利特省（加拿大东北）的橄榄岩透钙磷石的见解

我们研究了从156-138 Ma Chidliak金伯利岩省（南巴芬岛）收集的120个橄榄岩和辉绿岩异岩的岩石学，矿物学，热压法和全岩石化学。CH-1，-6，-7和-44管道中的异种石被分为两个石榴石系列，即榴辉岩–哈茨堡铁矿–锂铁矿和辉绿岩–橄榄石辉石岩。这两个系列均显示出从粗到剪的广泛变化的质地，以及石榴石和斜柏基石后期形成的质地。锂铁矿系列的某些样品可能含有尖晶石，而辉绿岩可能含有钛铁矿。在CH-6中，从P  = 2·8至5·6 GPa衍生出稀有的锂铁矿和辉绿岩系列粗样品，而主要的剪切和粗糙的锂铁矿系列样品共存于P = 5·6–7·5 GPa。金伯利岩CH-1，-7，-44样品主要位于P  = 5·0–7·5 GPa的较深地幔，由粗切变的锂铁矿和辉绿岩系列表示。大部分压力-温度阵列定义的热状态与35–39 mW m ^–2兼容表面热流，但是在较大的等压热散射中，特别是在深度，以及低的热梯度中，明显的热不平衡现象是不明显的。Chidliak异岩的整个岩石中的Si和Mg含量及其矿物化学反应，反映出克拉通地幔典型的初始高熔体耗竭水平以及随后在Ca和Al中的精化作用。与许多其他克拉通中富含邻苯二酚的地幔不同，Chidliak地幔富含镁橄榄石（约占体积的83％）。我们将其归因于硅酸盐-碳酸盐交代作用，这引发了地幔的渗水作用。Chidliak地幔类似于北大西洋克拉通的格陵兰部分，表明其岩石圈以前是连续的，随后又裂成独立的大陆碎片。另一个，影响Chidliak地幔的新近地幔交代作用的特征是辉石和榴石中的Ti升高，这是CH-1，-7和-44的所有岩石类型中的典型特征。CH-6异种岩套件中基本上没有这些交代样品。Ti痕迹在相当于5·5-6·5 GPa深度的异岩中最强烈，这与较高的应变，锂铁矿系列剪切样品的存在和较高的温度等压变化高达200°C有关。热介子烙印的水平尺度比较模糊，可能在几十公里以内是局部的，而在<1 km内则是局部的。这种交代作用的时间尺度与传导长度尺度有关，并且可能短于<1 Myr，很快就形成了金伯利岩。在克拉通裂谷之前，在拉布拉多海周围有富含₂和富含Ti的岩浆作用。变质作用可能在拉布拉多海附近的北大西洋克拉通岩石圈变薄方面发挥了关键作用，从侏罗纪的约240 km到古近纪的约65 km。