Arid
DOI10.1130/GES01238.1
Sources of volcanic detritus in the basal Chinle Formation, southwestern Laurentia, and implications for the Early Mesozoic magmatic arc
Riggs, N. R.1; Oberling, Z. A.1; Howell, E. R.1; Parker, W. G.2; Barth, A. P.3; Cecil, M. R.4; Martz, J. W.5
通讯作者Riggs, N. R.
来源期刊GEOSPHERE
ISSN1553-040X
出版年2016
卷号12期号:2页码:439-463
英文摘要

The Upper Triassic Chinle Formation in southwestern Laurentia is the oldest distinctive record of Early Mesozoic Cordilleran arc magmatism, in the form of detrital zircons and volcanic clasts. Initial deposition of the basal Shinarump and Mesa Redondo members, herein collectively called the Shinarump conglomerate, began in Late Triassic time, yet the earliest known arc magmatism is older by as much as 40 m.y.


Analysis of detrital zircons from eight sites in southeastern Nevada, southern Utah, and northeastern Arizona and volcanic-clast zircons from four of these sites provides a basis for understanding the evolution of the Early Meso-zoic arc. Most Permian and Triassic detrital zircons from the Shinarump conglomerate have ages from ca. 260 to 220 Ma with rare grains as old as 280 Ma. These ages are compatible with derivation from sources in the magmatic arc to the west and southwest, including plutons of corresponding age in the Mojave Desert. Volcanic clasts are uniformly in the range 232-224 Ma; their age and zircon geochemistry argue against a source in currently exposed Mojave Desert Triassic plutons.


As a further test, we compared Th/U ratios of clast and detrital zircons with those of possible sources to the west. Th/U values of many detrital grains support their derivation from Triassic Mojave Desert plutons. Some detrital grains and those from the clasts, however, have Th/U values that are uniformly higher than those in Permo-Triassic Mojave Desert plutons and therefore argue for a different, unexposed source.


We propose that the early arc lay offshore of western Laurentia. Over time, plutons were emplaced across a range of continental crustal thicknesses that likely increased toward the east. At approximately 235-230 Ma, a land connection between the arc and retro-arc areas was established and fluvial sedimentation began. The observation that the youngest grain ages in our detrital samples are variable suggests that this land connection was tenuous for perhaps 10 m.y. until well into Chinle Formation sedimentation.


类型Article
语种英语
国家USA
收录类别SCI-E
WOS记录号WOS:000373226700006
WOS关键词NATIONAL-PARK ARIZONA ; SUBDUCTION INITIATION ; CONTINENTAL-MARGIN ; SIERRA-NEVADA ; MOJAVE DESERT ; ZIRCON GEOCHRONOLOGY ; COLORADO PLATEAU ; CORDILLERAN ARC ; TRACE-ELEMENT ; PB
WOS类目Geosciences, Multidisciplinary
WOS研究方向Geology
资源类型期刊论文
条目标识符http://119.78.100.177/qdio/handle/2XILL650/193291
作者单位1.No Arizona Univ, Sch Earth Sci & Environm Sustainabil, Flagstaff, AZ 86011 USA;
2.Petrified Forest Natl Pk, Div Resource Management, Petrified Forest, AZ 86028 USA;
3.Indiana Univ Purdue Univ, Dept Earth Sci, Indianapolis, IN 46202 USA;
4.Calif State Univ Northridge, Dept Geol Sci, Northridge, CA 91330 USA;
5.Univ Houston Downtown, Dept Nat Sci, 1 Main St, Houston, TX 77002 USA
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Riggs, N. R.,Oberling, Z. A.,Howell, E. R.,et al. Sources of volcanic detritus in the basal Chinle Formation, southwestern Laurentia, and implications for the Early Mesozoic magmatic arc[J],2016,12(2):439-463.
APA Riggs, N. R..,Oberling, Z. A..,Howell, E. R..,Parker, W. G..,Barth, A. P..,...&Martz, J. W..(2016).Sources of volcanic detritus in the basal Chinle Formation, southwestern Laurentia, and implications for the Early Mesozoic magmatic arc.GEOSPHERE,12(2),439-463.
MLA Riggs, N. R.,et al."Sources of volcanic detritus in the basal Chinle Formation, southwestern Laurentia, and implications for the Early Mesozoic magmatic arc".GEOSPHERE 12.2(2016):439-463.
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