ABSTRACT

The Ottfjället Dyke Swarm (ODS) is a prominent component of the Ediacaran mafic magmatism associated with opening of the Iapetus ocean, and hosted in the Särv Nappe, Middle Allochthon of the Scandinavian Caledonides. A U-Pb baddeleyite age of 596.3 ± 1.5 Ma for a thick, well preserved, plagioclase-phyric dolerite dyke in Härjedalen, Sweden, dates emplacement of the swarm. The age represents a robust, inheritance-free reference age for variably deformed and metamorphosed tholeiitic dykes in sandstone-dominated sequences of the lower part of the Middle Allochthon, representing the proximal, rifted Baltoscandian margin preceding the opening of Iapetus. The new age is within the narrow time span between 610 and 595 Ma defined by the most reliable age estimates for mafic dykes in structurally higher nappes (upper part of Middle Allochthon), representing the distal margin during the opening of Iapetus. The Ottfjället Dyke Swarm cuts the Tossåsfjället Group succession, which includes sabkha-related carbonate platform and diamictite couples, one of several correlated Neoproterozoic glaciogenic successions in Scandinavia. The intrusion age of ca. 596 Ma therefore sets a minimum age for the glaciogenic successions. It implies that Neoproterozoic glaciations in Scandinavia predate the ca. 580 Ma Gaskiers glaciation event and are probably part of the ca. 635 Ma Marinoan “Snowball-Earth”-type glaciation.

摘要

Ottfjället堤防群（ODS）是与Iapetus海洋开放有关的Ediacaran镁铁质岩浆作用的重要组成部分，位于北欧斯堪的纳维亚喀里多尼德斯中陆变大陆SärvNappe。瑞典Härjedalen的厚厚，保存完好的斜长石-斑状白云母脉状岩的U-Pb八面体年龄为596.3±1.5 Ma，可追溯到该群成群。该年龄代表了中外陆生下部下部砂岩为主的层序中可变变形和变质的变质岩堤的稳健，无继承的参考年龄，代表了伊阿佩特斯开放前近端，裂谷的巴尔托斯卡纳边缘。新年龄是在610至595 Ma的狭窄时间范围内，该时间范围由结构上较高的尿布（中陆变质带的上部）中最基本的镁铁质岩脉年龄确定，代表Iapetus开放期间的远端边缘。OttfjälletDyke Swarm削减了TossåsfjälletGroup的继承权，其中包括sabkha相关的碳酸盐岩台地和铁矾土夫妇，这是斯堪的纳维亚半岛几个相关的新元古代冰川成因继承之一。入侵年龄约。因此，596 Ma为冰川期演替设定了最低年龄。这暗示着斯堪的纳维亚的新元古代冰川早于约公元前。580 Ma Gaskiers冰川事件，可能是ca的一部分。635马里诺（Mar Marinoan）“雪球地球”型冰川。入侵年龄约。因此，596 Ma为冰川期演替设定了最低年龄。这暗示着斯堪的纳维亚的新元古代冰川早于约公元前。580 Ma Gaskiers冰川事件，可能是ca的一部分。635马里诺（Mar Marinoan）“雪球地球”型冰川。入侵年龄约。因此，596 Ma为冰川期演替设定了最低年龄。这暗示着斯堪的纳维亚的新元古代冰川早于约公元前。580 Ma Gaskiers冰川事件，可能是ca的一部分。635马里诺（Mar Marinoan）“雪球地球”型冰川。