U-Pb zircon age constraints on two episodes of Paleoproterozoic magmatism and development of the Grizzly Creek shear zone, White River Uplift, western Colorado, U.S.A.

Q3 Earth and Planetary Sciences Rocky Mountain Geology Pub Date : 2013-03-01 DOI:10.2113/GSROCKY.48.1.15
James V. Jones, C. Shaw, Joseph L. Allen, T. Housh
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引用次数: 3

Abstract

New U-Pb zircon ages from Precambrian exposures in the White River Uplift of western Colorado reveal at least two episodes of Proterozoic granitic magmatism and help to constrain the age of the 1-km-thick Grizzly Creek shear zone. Gneissic granite exposed along Mitchell Canyon northwest of Glenwood Springs, crystallized at 1765±9 Ma and is the oldest igneous unit recognized in the area. The gneissic foliation is defined by alternating layers of biotite and elongated pink K-feldspar up to 5 cm in size, and the fabric strikes west-northwest and dips moderately to steeply north. Cross-cutting relationships with gneissic country rocks and other igneous units exposed in adjacent drainages were not observed. However, deformation and metamorphism are inferred to be between the age of intrusion (ca. 1765 Ma) and the age of younger, unfoliated, coarse-grained to K-feldspar megacrystic granite exposed near the mouth of No Name Canyon, which crystallized at 1743±8 Ma. This younger granite is cut by the Grizzly Creek shear zone to the north and only contains a locally developed magmatic foliation south of the shear zone. Foliated to mylonitic, fine-grained biotite granite exposed in the hanging wall of the shear zone along No Name Canyon crystallized at 1745±10 Ma, suggesting that it might be related to coarse-grained granite exposed in the shear zone footwall. These new ages define two granitic magmatic events in this area at ca. 1765 and 1745 Ma and provide a maximum age of deformation in the Grizzly Creek shear zone of 1743 Ma. Similarities in the orientation, structural style, and kinematics between the Grizzly Creek shear zone and other well-documented structures in the region raise the possibility that the shear zone records multiple episodes of both Paleoproterozoic and Mesoproterozoic (ca. 1.4 Ga) deformation, in which case the younger events would have occurred in the absence of local magmatism. Thus, the Grizzly Creek shear zone might represent a kinematic link between major crustal shear zones to the north and south throughout crustal assembly and stabilization in southern Laurentia, but details of the timing and kinematic relationships between these structures remain uncertain.
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美国科罗拉多州西部白河隆起两期古元古代岩浆活动与Grizzly Creek剪切带发育的锆石年龄约束
来自美国科罗拉多州西部白河隆起前寒武纪暴露物的新的U-Pb锆石年龄揭示了至少两期元古代花岗质岩浆活动,并有助于限制1公里厚的灰熊溪剪切带的年龄。片麻岩花岗岩暴露在格伦伍德泉西北的米切尔峡谷,结晶于1765±9 Ma,是该地区已知的最古老的火成岩单元。片麻岩片理由黑云母和细长的粉红色k长石层交替形成,大小可达5厘米,织物走向西北偏西,向北倾斜中至陡峭。未观察到与邻近排水中暴露的麻质乡村岩石和其他火成岩单元的横切关系。然而,变形和变质作用被推断为介于侵入时代(约1765 Ma)和暴露在无名峡谷口附近的较年轻的、无片理的、粗粒的k -长石微晶花岗岩之间,这些花岗岩在1743±8 Ma结晶。这片较年轻的花岗岩在北部被Grizzly Creek剪切带切割,仅包含剪切带南部局部发育的岩浆片理。无名峡谷剪切带上盘的细粒黑云母花岗岩在1745±10 Ma时呈片理-糜棱质结晶,可能与剪切带下盘的粗粒花岗岩有关。这些新年龄确定了该区约1765和1745 Ma的两次花岗质岩浆事件,并提供了1743 Ma的Grizzly Creek剪切带的最大变形年龄。Grizzly Creek剪切带与该地区其他有充分记录的构造在方向、构造样式和运动学上的相似性,提高了剪切带记录古元古代和中元古代(约1.4 Ga)多期变形的可能性,在这种情况下,较年轻的事件可能发生在没有局部岩浆作用的情况下。因此,Grizzly Creek剪切带可能代表了Laurentia南部地壳组装和稳定过程中南北主要地壳剪切带之间的运动学联系,但这些结构之间的时间和运动学关系的细节仍不确定。
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Rocky Mountain Geology
Rocky Mountain Geology Earth and Planetary Sciences-Geology
CiteScore
1.10
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0.00%
发文量
4
期刊介绍: Rocky Mountain Geology (formerly Contributions to Geology) is published twice yearly by the Department of Geology and Geophysics at the University of Wyoming. The focus of the journal is regional geology and paleontology of the Rocky Mountains and adjacent areas of western North America. This high-impact, scholarly journal, is an important resource for professional earth scientists. The high-quality, refereed articles report original research by top specialists in all aspects of geology and paleontology in the greater Rocky Mountain region.
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