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1880百万年（Ma）的环苏必利尔大型火成岩省（Large Igneous Province，LIP）由若干不连续岩段构成，已知其覆盖了北美苏必利尔克拉通（Superior Province craton）边缘的大片区域。本研究针对该LIP西部岩段获取的全新地球化学与同位素数据，证实了各岩段具备共同成因，并提出苏必利尔湖区域的岩浆作用或通过长约600千米的皮卡洛鸦岩墙（Pickle Crow dyke），由马尼托巴省东北部福克斯河带（Fox River Belt）以北的岩浆源区补给。福克斯河带、皮卡洛鸦岩墙以及苏必利尔湖地区的铁杉组（Hemlock Formation）的微量元素特征，与近代大洋高原的特征高度相似。铁杉组展现出不均一的地球化学信号，该化学不均一性可部分归因于岩石圈混染作用，也可能与源区本身的不均一性相关。这些火成岩形成的构造-岩浆环境可能涉及地幔柱。支持地幔柱成因的证据包括高MgO含量火山岩、较高的估算部分熔融程度，以及与大洋高原一致的地球化学特征。