Final inversion of the Midcontinent Rift during the Rigolet Phase of the Grenvillian Orogeny
Final inversion of the Midcontinent Rift during the Rigolet Phase of the Grenvillian Orogeny
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DOI：
10.1130/g49439.1
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发表时间：
2022-02-11
期刊：
影响因子：
5.8
通讯作者：
Stolper, Daniel A.
中科院分区：
文献类型：
--
作者：
Hodgin, Eben B.;Swanson-Hysell, Nicholas L.;Stolper, Daniel A.
晚中元古代北美中大陆裂谷虽然是一个突出的大陆尺度特征，但并没有导致Laurentia的断裂，而是发生了构造反转。反演的时机对于限制造山作用的远场效应和与裂谷破裂有关的过程至关重要。美国密歇根州北部的Keweenaw断裂是一条与裂谷反转有关的逆冲构造；它将约1093 Ma裂谷火山岩置于裂谷后雅各布维尔组之上，雅各布维尔组在下盘褶皱。先前通过激光烧蚀-电感耦合等离子体质谱（LA-ICP-MS）进行的碎屑锆石（DZ） U-Pb地质年代学将雅各布维尔组的最大年龄定为约950 Ma，并使研究人员将其沉积和变形解释为约1090-980 Ma的格伦维里安造山运动。在这项研究中，我们使用LA-ICP-MS再现了相似的DZ日期，然后使用高精度化学磨损-同位素稀释-热电离质谱（CA-ID-TIMS）测定了19个最年轻的DZ颗粒。CA-ID-TIMS测定的最年轻DZ为992.51 +/- 0.64 Ma(20)，重新确定了Jacobsville组的最大沉积年龄，并与角化Keweenaw断裂带内晚运动方解石脉的U-Pb LA-ICP-MS测定的985.5 +/- 35.8 Ma（20）相重叠。总的来说，这些数据被解释为雅各布维尔组的沉积和最终的裂谷反转发生在1010-980年格伦维利安造山运动的Ma Rigolet阶段，之后是渥太华反转的早期阶段。在格伦维利亚造山运动的渥太华和里戈莱特阶段，远场变形向大陆内部传播了约500公里。
Despite being a prominent continental-scale feature, the late Mesoproterozoic North American Midcontinent Rift did not result in the break-up of Laurentia, and subsequently underwent structural inversion. The timing of inversion is critical for constraining far-field effects of orogenesis and processes associated with the rift's failure. The Keweenaw fault in northern Michigan (USA) is a major thrust structure associated with rift inversion; it places ca. 1093 Ma rift volcanic rocks atop the post-rift Jacobsville Formation, which is folded in its footwall. Previous detrital zircon (DZ) U-Pb geochronology conducted by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) assigned a ca. 950 Ma maximum age to the Jacobsville Formation and led researchers to interpret its deposition and deformation as postdating the ca. 1090-980 Ma Grenvillian Orogeny. In this study, we reproduced similar DZ dates using LA-ICP-MS and then dated 19 of the youngest DZ grains using high-precision chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS). The youngest DZ dated by CA-ID-TIMS at 992.51 +/- 0.64 Ma (20) redefines the maximum depositional age of the Jacobsville Formation and overlaps with a U-Pb LA-ICP-MS date of 985.5 +/- 35.8 Ma (20) for late-kinematic calcite veins within the brecciated Keweenaw fault zone. Collectively, these data are interpreted to constrain deposition of the Jacobsville Formation and final rift inversion to have occurred during the 1010-980 Ma Rigolet Phase of the Grenvillian Orogeny, following an earlier phase of Ottawan inversion. Far-field deformation propagated >500 km into the continental interior during the Ottawan and Rigolet phases of the Grenvillian Orogeny.