Granites of the East-Central Minnesota Batholith
Granites of the East-Central Minnesota Batholith
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明尼苏达州中东部岩基花岗岩
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
W. R. Schmus
中科院分区：
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作者：
T. J. Boerboom;D. Holm;W. R. Schmus
北美中部大陆的1，870至1，830 Ma佩诺克造山岩是古元古代晚期在劳伦蒂亚-波罗的海大陆南缘增生的巨大幼年地壳带的一部分。随后，Penokean造山带两次形成了一代地壳熔融岩基的源区：第一次是在明尼苏达州中东部的1，790 - 1，770 Ma（霍尔姆等人，2005年），第二次是在威斯康星州中部的1，470 Ma（货车Schmus等人，1975年; DeWane和货车Schmus，2003年）。古前寒武纪岩浆成因的驱动力很难评估。例如，主要长英质的后Penokean geon 17岩浆作用的产生在历史上被归因于过厚地壳的热弱化（Windley，1993;霍尔姆and Lux，1996）、地幔柱（霍夫曼，1989）和地幔岩石圈突然拆沉（霍尔姆，1999; Boerboom and霍尔姆，2000）。最近，详细的U-Pb锆石年龄数据使我们认为，苏必利尔湖南部上级地区的第17号江岩浆活动是由新增生的Penokean岩下的西北方向俯冲作用驱动的（霍尔姆等人，2005年）。在这次实地考察中，我们研究了构成圣克劳德区明尼苏达州中东部岩基的主要花岗岩类岩石。虽然体积小，镁铁质岩浆也明显产生，并与更丰富的长英质岩浆混合在整个约（约）。两千万年前岩基生成间隔期。它们的存在证明了地幔在岩浆成因过程中的重要贡献。岩浆活动的时间跨度和它的位置在大陆边缘的活动板块边缘建议的岩基代表一个古老的折返大陆岩浆弧类似于许多中生代环太平洋大陆弧。这次实地考察突出了作者为期五年的合作研究的结果，以更好地了解后Penokean岩浆活动在克拉通这一部分的增长和稳定中的重要作用。除了地质上的重要性，圣克劳德地区的花岗岩类岩石也是建筑材料的重要来源。该地区有着悠久的采石历史，在1930年至1940年期间达到顶峰，当时有18家不同的采石公司在运营（Thiel和达顿，1935年）。目前，明尼苏达州中东部岩基的岩石拥有五个活跃的尺寸石采石场和几个碎石骨料采石场，这些采石场是双子城交通和建筑基础设施的重要组成部分。
The 1,870 to 1,830 Ma Penokean orogenic rocks of the North American midcontinent are part of a vast belt of juvenile crust accreted onto the southern margin of Laurentia-Baltic continent during late Paleoproterozoic time. Subsequently, the Penokean orogenic belt twice formed the source region for a generation of crustal-melt batholiths: first at 1,790 to 1,770 Ma in east-central Minnesota (Holm and others, 2005), and then again at 1,470 Ma in central Wisconsin (Van Schmus and others, 1975; DeWane and Van Schmus, 2003). The driving forces for magma genesis in ancient Precambrian terranes are difficult to assess. For instance, the generation of dominantly felsic post-Penokean geon 17 magmatism has historically been attributed to thermal weakening of overthickened crust (Windley, 1993; Holm and Lux, 1996), to plumes (Hoffman, 1989), and to abrupt mantle lithospheric delamination (Holm, 1999; Boerboom and Holm, 2000). Most recently, detailed U-Pb zircon age data have led us to suggest that geon 17 magmatism in the southern Lake Superior region was driven by northwest directed subduction beneath the newly accreted Penokean terrane (Holm and others, 2005). On this field trip, we examine the dominantly granitoid rocks that make up the eastcentral Minnesota batholith in the St. Cloud District. Although volumetrically small, mafic magmas were also apparently generated and commingled with the more abundant felsic magmas during the entire circa (ca.) 20 m.y. interval of batholith generation. Their existence attests to an important mantle contribution in the process of magma genesis. The time span of magmatism and its location on the continental edge of an active plate margin suggest the batholith represents an ancient exhumed continental magmatic arc analogous to many Mesozoic Pacific-rim continental arcs. This field trip highlights the results of a fiveyear collaborative study by the authors to better understand the important role of post-Penokean magmatism in the growth and stabilization of this part of the craton. In addition to their geologic importance, the granitoid rocks of the St. Cloud district have been an important source of building materials. The area has a long quarrying history that peaked between 1930 and 1940 when 18 different quarry companies were operating (Thiel and Dutton, 1935). Currently, rocks of the east-central Minnesota batholith host five active dimension-stone quarries and several crushed-rock aggregate quarries that are essential building blocks to the Twin Cities transportation and building infrastructure.