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首页> 外文期刊>Lithos: An International Journal of Mineralogy, Petrology, and Geochemistry >The Friningen Garnet Peridotite (central Swedish Caledonides). A good example of the characteristic PTt path of a cold mantle wedge garnet peridotite
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The Friningen Garnet Peridotite (central Swedish Caledonides). A good example of the characteristic PTt path of a cold mantle wedge garnet peridotite

机译：弗里宁根石榴石橄榄石（瑞典中部喀里多尼德群岛）。冷地幔楔形石榴石橄榄岩的特征PTt路径的一个很好的例子

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摘要

We present pseudosections of Cr-bearing garnet peridotite that together with new mineral-chemical data allow quantification of the early PT conditions of the original lithospheric mantle assemblage (M1) of the Friningen Garnet Peridotite (FGP) located in the central/middle belt of the Seve Nappe Complex in central Sweden. Results indicate that the early, coarse grained, olivine + orthopyroxene + clinopyroxene + "high Cr" garnet assemblage (M1a) was formed at 1100 +/- 100 degrees C and 5.0 +/- 0.5 GPa. These metamorphic conditions were followed by an inferred late Proterozoic exhumation event down to 850-900 degrees C and 1.5 GPa (M1b). The latter PT estimate is based on the breakdown of high-Cr M1a garnet (Cr# = 0.065) + olivine into an orthopyroxene + clinopyroxene + spinet (Cr# = 0.15-0.25) +/- pargasite kelyphite (M1b) and the exsolution of garnet from Al-rich orthopyroxene and dinopyroxene. The M1b kelyphite is overprinted by an early-Caledonian UHPM mineral assemblage (M2; T = 800 degrees C and P = 3.0 GPa), equivalent to the earlier discovered UHP assemblage within an eclogitic dyke that cross-cuts FGP. In the garnet peridotite M2 is displayed by low-Cr garnet (Cr# = 0.030) growing together with spinet (Cr# = 0.35-0.45), both these minerals form part of the olivine + orthopyroxene + clinopyroxene + garnet + spinet + pargasite M2 assemblage. The formation of plagioclase + diopside symplectites after omphacite and breakdown of kyanite to sapphirine + albite in internal eclogite and the breakdown of M2 olivine + garnet to amphibole + orthopyroxene + spinet assemblages (M3) in garnet peridotite indicate post-UHP isothermal decompression down to 750-800 degrees C and 0.8-1.0 GPa (= M3). Multiphase solid-and fluid inclusion assemblages composed of Sr-bearing magnesite, dolomite or carbon decorate linear defect structures within M1a-b minerals and/or form subordinate local assemblages together with M2 minerals. The latter are interpreted as evidence for infiltration of early-Caledonian COH-bearing subduction zone fluids. The well-defined PTt-deformation path of the FGP resembles that of a mantle wedge garnet peridotite. The M1 assemblage originates from the base of a cold, old and thick subcontinental lithospheric mantle that is inferred to extend asymmetrically leading to extreme exhumation of FGP down to lithospheric conditions around 1.5 GPa and 850-900 degrees C. After that the FGP became incorporated into the subducting continental crust of the SNC during "early-Caledonian" subduction (M2) down to UHPM conditions (800 degrees C/3.0 GPa), subsequently followed by eduction back to sub-crustal levels. As such, FGP is the first locality in the Swedish Caledonides from which two UHP metamorphic events are described, the first event can be related to the formation of an ancient (>1.0 Ga) lithosphere underneath a craton (Rodinia) and the second is of early-Caledonian age. (C) 2015 Elsevier B.V. All rights reserved.
机译：我们介绍了含铬石榴石橄榄岩的假剖面，再加上新的矿物化学数据，可以对位于中部和中部弗里宁根石榴石橄榄岩（FGP）的原始岩石圈地幔组合（M1）的早期PT条件进行量化。瑞典中部的Seve Nappe建筑群。结果表明，在1100 +/- 100摄氏度和5.0 +/- 0.5 GPa的温度下，形成了早期的粗粒橄榄石+邻苯二茂基+斜茂铁基+“高Cr”石榴石组合（M1a）。在这些变质条件之后，推断出了一个低至850-900摄氏度和1.5 GPa（M1b）的晚元古代晚期发掘活动。后者的PT估算是基于高铬M1a石榴石（Cr＃= 0.065）+橄榄石分解为邻苯二茂铁+ Clinopyroxene +尖晶石（Cr＃= 0.15-0.25）+/-合成辉石（M1b）和富含铝的邻苯二甲酚和二苯并rox的石榴石。 M1b陨石覆盖着早期的Caledonian UHPM矿物组合（M2; T = 800摄氏度，P = 3.0 GPa），相当于较早发现的横穿FGP的弧状堤内的UHP组合。在石榴石橄榄岩M2中，低Cr石榴石（Cr＃= 0.030）与尖晶石（Cr＃= 0.35-0.45）一起生长，这两种矿物均构成橄榄石+邻苯二茂铁+斜ino石+石榴石+尖晶石+石棉M2装配。辉绿岩中辉长岩后斜长石+透辉石共生体的形成以及内部榴辉岩中蓝晶石分解为蓝宝石+钠长石以及石榴石橄榄石中M2橄榄石+石榴石分解为闪石+邻苯二酚+棘突组合（M3）表明UHP等温降压至750 -800摄氏度和0.8-1.0 GPa（= M3）。由含锶的菱镁矿，白云石或碳组成的多相固相和流体包裹体组合物装饰了M1a-b矿物中的线性缺陷结构，并且/或者与M2矿物一起形成了下级局部组合物。后者被解释为早期带有Caledonian COH的俯冲带流体渗透的证据。 FGP明确定义的PTt形变路径类似于地幔楔形石榴石橄榄岩。 M1组合起源于一个寒冷，古老而厚实的亚大陆岩石圈地幔的底部，据推测该地幔不对称地延伸，导致FGP极度发掘到1.5 GPa和850-900摄氏度左右的岩石圈条件。此后，FGP被并入在“早期-Caledonian”俯冲（M2）期间，SNC的俯冲大陆壳下降到UHPM条件（800摄氏度/3.0 GPa），随后又回到俯冲壳之下。因此，FGP是瑞典喀里多尼斯的第一个地点，描述了两个UHP变质事件，第一个事件与克拉通（Rodinia）下方古代（> 1.0 Ga）岩石圈的形成有关，第二个是早期的卡莱多尼亚时代。 （C）2015 Elsevier B.V.保留所有权利。

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