Abstract Large amplitude aeromagnetic and gravity anomalies over a ∼16,000 km2 area of northeast Iowa and southeast Minnesota have been interpreted to reflect the northeast Iowa intrusive complex (NEIIC), a buried intrusive igneous complex composed of mafic/ultramafic rocks in the Yavapai Province (1.8-1.7 Ga). Hundreds of meters of Paleozoic sedimentary cover and a paucity of basement drilling have prevented detailed studies of the NEIIC. Long considered, but not proven, to be related to the ∼1.1 Ga Midcontinent Rift System (MRS), the NEIIC is comparable in areal extent to the richly mineralized Duluth Complex and is similarly located near the margin of the MRS. New geochronological and geophysical data together support an MRS affinity for the NEIIC. A dike swarm imaged in aeromagnetic data is cut by intrusions of the NEIIC, and a new apatite U-Pb date of ∼1170 Ma on one of the dikes thus represents a maximum age for the NEIIC. A minimum age constraint is suggested by (1) large-volume magmatism associated with the MRS that was the last such event to affect the region; and (2) the presence of reversely magnetized dikes, similar in character to MRS-related dikes elsewhere, that cut several intrusions of the NEIIC. The NEIIC is largely characterized by the presence of multiple zoned intrusions, many of which contain large volumes of mafic-ultramafic rocks and have strong geophysical similarities to alkaline intrusive complexes elsewhere, including the MRS-related Coldwell Complex of Ontario. The largest of the zoned intrusions are ∼40 km in diameter and are interpreted to have thicknesses of many kilometers. Suspected faults, alignments of intrusions, and intrusive margins tend to be aligned along northwest and northeast trends that match the trends of the Belle Plaine fault zone and Fayette structural zone, both previously interpreted as pre-MRS, possibly lithospheric-scale discontinuities that may have controlled NEIIC emplacement. These interpretations collectively imply notable potential for the NEIIC to host several different types of undiscovered base metal and critical mineral deposits.

中文翻译：

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隐藏的中大陆裂谷相关的爱荷华州东北部侵入复合体的证据

摘要 爱荷华州东北部和明尼苏达州东南部约 16,000 平方公里区域的大幅航磁和重力异常已被解释为反映了爱荷华州东北部侵入杂岩 (NEIIC)，这是一种由亚瓦派省 (1.8 -1.7 Ga）。数百米的古生代沉积覆盖层和缺乏基底钻探阻碍了对 NEIIC 的详细研究。长期以来，NEIIC 一直被认为与约 1.1 Ga 中大陆裂谷系统 (MRS) 相关，但并未得到证实，其面积与矿化丰富的德卢斯杂岩相当，并且同样位于 MRS 边缘附近。新的地质年代学和地球物理数据共同支持了 NEIIC 的 MRS 亲和力。在航磁数据中成像的堤防群被 NEIIC 的入侵切割，并且其中一个岩脉上的新磷灰石 U-Pb 日期约为 1170 Ma，因此代表了 NEIIC 的最大年龄。(1) 与 MRS 相关的大量岩浆活动是影响该地区的最后一次此类事件；(2) 反向磁化堤防的存在，其特征与其他地方与 MRS 相关的堤防相似，它切断了 NEIIC 的几次侵入。NEIIC 的主要特征是存在多个带​​状侵入体，其中许多含有大量的镁铁质-超镁铁质岩石，并且与其他地方的碱性侵入杂岩具有很强的地球物理相似性，包括与 MRS 相关的安大略科德威尔杂岩。最大的分区侵入体直径约 40 公里，据解释具有数公里的厚度。疑似故障，入侵对齐，和侵入边缘倾向于沿着与 Belle Plaine 断层带和 Fayette 构造带的趋势相匹配的西北和东北趋势对齐，这两个以前都被解释为 pre-MRS，可能控制了 NEIIC 侵位的岩石圈尺度不连续性。这些解释共同暗示了 NEIIC 拥有几种不同类型的未发现贱金属和关键矿床的显着潜力。