Lithologic and geochemical composition of samples from the Circum Superior Belt, North America

The ca. 1880 Ma Circum-Superior Large Igneous Province (LIP) consists of a number of discontinuous segments known to cover a significant portion of the margin of the Superior Province craton in North America. New geochemical and isotopic data from western segments of this LIP support a common origin for the these segments and suggest that magmatism in the Lake Superior region may have been fed through the ~ 600 km long Pickle Crow dyke from a source north of the Fox River Belt in northeastern Manitoba. The Fox River Belt, Pickle Crow dyke and sections of the Hemlock Formation in the Lake Superior region possess trace element signatures which are similar to those of more recent oceanic plateaux. The Hemlock Formation displays a heterogeneous geochemical signature. This chemical heterogeneity can in part be explained by lithospheric contamination and possibly by source heterogeneity. The tectonomagmatic setting in which these igneous rocks were formed could have involved a mantle plume. Evidence supporting a plume origin includes high MgO volcanic rocks, high calculated degrees of partial melting and geochemical signatures similar to those of oceanic plateaux.

约18.8亿年（ca. 1880 Ma）前的环苏必利尔大型火成岩省（Large Igneous Province，LIP）由一系列不连续岩段组成，已知其覆盖了北美苏必利尔克拉通（Superior Province craton）边缘的广阔区域。针对该LIP西部岩段新获取的地球化学与同位素数据，证实了这些岩段具有共同成因，并表明苏必利尔湖地区的岩浆作用，可能通过长约600千米的Pickle Crow岩墙（Pickle Crow dyke），从马尼托巴省东北部福克斯河带（Fox River Belt）北侧的源区获得岩浆补给。苏必利尔湖地区的福克斯河带、Pickle Crow岩墙以及Hemlock组（Hemlock Formation）的部分地层，其微量元素特征与更年轻的大洋高原（oceanic plateaux）相似。Hemlock组表现出不均一的地球化学特征，该化学不均一性可部分由岩石圈混染（lithospheric contamination）解释，也可能与源区不均一性有关。这些火成岩形成的构造岩浆环境，可能涉及地幔柱（mantle plume）活动；支持地幔柱成因的证据包括高MgO火山岩、较高的估算部分熔融程度，以及与大洋高原相似的地球化学特征。