ABSTRACT The Herräng mafic dykes form an E-W-trending dyke swarm within the Bergslagen lithotectonic unit of the Svecofennian orogen in east-central Sweden. They intrude the Svecofennian supracrustal rocks and early-orogenic granitoids, but are themselves cut by late Svecofennian pegmatites, and have undergone Svecofennian amphibolite-facies metamorphism, leading to their classification as “intraorogenic” Svecofennian dykes. They can be assigned an age between 1870 and 1850 Ma, with metamorphism of the dykes dated at 1848 ± 13 Ma by U-Pb in titanite. Their current mineralogy is dominated by metamorphic plagioclase and amphibole, with variable amounts of quartz and biotite, and minor to accessory titanite, apatite, epidote, pyrite, magnetite, ilmenite and zircon. Textures range from massive to strongly foliated. Twenty samples of dyke rocks from three subareas in the Roslagen region, including the Herräng type area, range in composition from basaltic to andesitic with 47 to 60 wt% SiO2, broadly similar to the Dannemora dykes and the Avesta-Östhammar gabbros and diorites. Initial 87Sr/86Sr ratios (at 1870 Ma) varies between 0.7026 and 0.7038, corresponding to initial εSr between +5 and +21, and initial εNd between −0.4 and +1.3, suggesting a slightly enriched to mildly depleted mantle source, similar to other Svecofennian mafic rocks. The dykes dominantly show a calc-alkaline volcanic arc signature related to subduction. They formed during an extensional episode, possibly related to incipient back-arc spreading or subduction roll-back following the main early-orogenic subduction-related Svecofennian magmatism, but penecontemporaneous with amphibolite-facies metamorphism in the area.

中文翻译：

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瑞典中东部的“造山带内”Svecofennian Herräng 基性岩脉群：年龄、地球化学和构造意义

摘要 Herräng 基性岩脉在瑞典中东部 Svecofennian 造山带的 Bergslagen 岩石构造单元内形成了一个 EW 趋势的岩脉群。它们侵入了 Svecofennian 上壳岩和早造山花岗岩，但本身被 Svecofennian 伟晶岩切割，并经历了 Svecofennian 角闪岩相变质作用，导致它们被归类为“内造山” Svecofennian 岩墙。它们的年龄可以确定为 1870 至 1850 Ma，岩脉的变质作用可以追溯到 1848 ± 13 Ma，由钛铁矿中的 U-Pb 确定。它们目前的矿物学以变质斜长石和角闪石为主，含有数量不等的石英和黑云母，次要为副钛矿、磷灰石、绿帘石、黄铁矿、磁铁矿、钛铁矿和锆石。纹理范围从大量到强烈的叶状。来自 Roslagen 地区三个分区（包括 Herräng 类型区域）的 20 个岩脉样品的成分范围从玄武岩到安山岩，SiO2 含量为 47 至 60%（重量），与 Dannemora 岩脉和 Avesta-Östhammar 辉长岩和闪长岩大致相似。初始 87Sr/86Sr 比率（在 1870 Ma）在 0.7026 和 0.7038 之间变化，对应于 +5 和 +21 之间的初始 εSr，以及 -0.4 和 +1.3 之间的初始 εNd，表明地幔源略微富集到轻度耗尽，类似于其他Svecofennian 镁铁质岩石。岩脉主要显示出与俯冲有关的钙碱性火山弧特征。它们形成于伸展事件期间，可能与早期造山带俯冲相关的斯韦科芬期岩浆作用之后的弧后扩张或俯冲回滚有关，