The dependence of K-Ar age on the mineralogy of various particle size ranges in a shale

Hower, John; Hurley, Patrick; Pinson, W. H.; Fairbairn, H. W.

doi:10.1016/0016-7037(63)90080-2

Cited by 76 publications

(36 citation statements)

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“…A2). It has previously been suggested that the percentage of the 2M 1 illite polytype in pelites is related to and perhaps equal to the amount of detrital illite (e.g., Hower et al 1963;Grathoff and Moore 1996;Grathoff et al 2001). However, our findings suggest that for correlative Middle Cambrian pelites in the western United States, in which the amount of detrital illite was probably relatively uniform, major variations in illite polytype composition are caused by differences in metamorphic grade and not differences in the proportion of detrital illite.…”

Section: Discussionmentioning

confidence: 99%

Variations in the Illite to Muscovite Transition Related to Metamorphic Conditions and Detrital Muscovite Content: Insight from the Paleozoic Passive Margin of the Southwestern United States

Verdel

Niemi

Pluijm

2011

The Journal of Geology

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press A B S T R A C TX-ray diffraction (XRD) analysis of the illite to muscovite transition in pelitic rocks has been widely used in regional studies of low-grade metamorphism. Variations in detrital muscovite content of sediments are also measurable with XRD and may, in fact, be difficult to distinguish from metamorphic gradients. We utilize field transects to isolate detrital muscovite versus metamorphic reaction components of illite-muscovite variations in Paleozoic rocks of the western United States. One transect focuses on a single stratigraphic interval (Middle Cambrian pelites) and extends from Death Valley in the west to the Grand Canyon in the east. Detrital muscovite content is roughly constant along this 500-km-long transect, so illite-muscovite variations are ascribed to differences in low-grade metamorphism. In terms of both illite crystallinity and polytype composition, there is an overall increase in metamorphic grade to the west along the transect, from the diagenetic metapelitic zone at the Grand Canyon to epizone-low anchizone conditions near Death Valley. Most of the regional variation in illite parameters occurs between Frenchman Mountain and the southern Nopah Range, corresponding to the transition from cratonic to miogeoclinal facies and also to the leading edge of the Sevier thrust belt. In contrast to this "horizontal" transect that highlights metamorphic reactions, a vertical transect through the Paleozoic stratigraphy of the Grand Canyon targets temporal variations in the flux of detrital muscovite. In the Grand Canyon, illite crystallinity reaches a maximum at the base of the Pennsylvanian Supai Group before decreasing upsection. Deposition of the Supai Group was coeval with formation of basementcored uplifts during the Ancestral Rocky Mountains orogeny, and we suggest that the upsection change in illite composition at the Grand Canyon reflects input of detrital muscovite eroded from these uplifts.Online enhancement: appendix. IntroductionThe transformation of illite to muscovite is the basis for defining low-grade metamorphism of pelites (e.g., Frey 1987;Merriman and Frey 1999) tal structure of illite occur during subgreenschist facies metamorphism and, given sufficient time and temperature, result in crystallites that are indistinguishable from muscovite. These crystallographic variations, which are observable with both x-ray diffraction (XRD) and transmission electron microscopy (TEM), track metamorphism from the diagenetic zone to the epizone, or from roughly 100Њ to 300ЊC (Merriman and Frey 1999).However, direct inference of metamorphic grade from illite-muscovite parameters is complicated by variations in detrital musc...

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Section: Discussionmentioning

confidence: 99%

Variations in the Illite to Muscovite Transition Related to Metamorphic Conditions and Detrital Muscovite Content: Insight from the Paleozoic Passive Margin of the Southwestern United States

Verdel

Niemi

Pluijm

2011

The Journal of Geology

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“…This is generally attributed to mixing of predeposition detrital illite or muscovite, which dominates the coarser fractions, with post-deposition diagenetic illite, predominant in the finer fractions (e.g., Bailey et al, 1962;Hower et al, 1963;Pevear, 1992;Grathoff et al, 1998Grathoff et al, , 2001. Faults commonly exhibit similar grain size-potential to survive low-temperature reactivations.…”

Section: Interpretation Of Inclined Age Spectramentioning

confidence: 99%

Post-Caledonian brittle deformation in the Bergen area, West Norway: results from K–Ar illite fault gouge dating

Ksienzyk¹,

Wemmer²,

Jacobs³

et al. 2016

NJG

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Post-Caledonian extension during orogenic collapse and Mesozoic rifting in the West Norway-northern North Sea region was accommodated by the formation and repeated reactivation of ductile shear zones and brittle faults. Offshore, the Late Palaeozoic-Mesozoic rift history is relatively well known; extension occurred mainly during two rift phases in the Permo-Triassic (Phase 1) and Mid-Late Jurassic (Phase 2). Normal faults in the northern North Sea, e.g., on the Horda Platform, in the East Shetland Basin and in the Viking Graben, were initiated or reactivated during both rift phases. Onshore, on the other hand, information on periods of tectonic activity is sparse as faults in crystalline basement rocks are difficult to date. KAr dating of illite that grows synkinematically in fine-grained fault rocks (gouge) can greatly help to determine the time of fault activity, and we apply the method to nine faults from the Bergen area. The K-Ar ages are complemented with X-ray diffraction analyses to determine the mineralogy, illite crystallinity and polytype composition of the samples. Based on these new data, four periods of onshore fault activity could be defined: (1) the earliest growth of fault-related illite in the Late Devonian-Early Carboniferous (>340 Ma) marks the waning stages of orogenic collapse; (2) widespread latest Carboniferous-Mid Permian (305-270 Ma) fault activity is interpreted as the onset of Phase 1 rifting, contemporaneous with rift-related volcanism in the central North Sea and Oslo Rift; (3) a Late Triassic-Early Jurassic (215-180 Ma) period of onshore fault activity postdates Phase 1 rifting and predates Phase 2 rifting and is currently poorly documented in offshore areas; and (4) Early Cretaceous (120-110 Ma) fault reactivation can be linked either to late Phase 2 North Sea rifting or to North Atlantic rifting.

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“…Complete isolation of the diagenetic and detrital components in shale clay separates is much more difficult than in sandstones, where diagenetic components are typically much finer-grained than the detrital clasts. Because of size similarities between detrital and diagenetic illitic clays in shales, sample contamination is an ever-present problem, and measured K-Ar ages generally have questionable geologic significance (Hower et al, 1963), unless the K-Ar contribution of the contaminating material is quantified. Detrital illite.…”

Section: K-ar Age Of Illitic Clays In Mesozoic Shalesmentioning

confidence: 99%

Shale Diagenesis in the Bergen High Area, North Sea

Glasmann¹

1989

Clays and clay miner.

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Abstract--Illite diagenesis in Tertiary and Mesozoic shales in the Bergen High area, northern North Sea, was studied using mineralogic, isotopic, and computerized thermal modeling techniques. The Tertiary shales are dominated by smectite, with lesser amounts ofillite, kaolinite, and chlorite. At present burial temperatures of > 70~ smectite is absent, and the shales contain abundant lath-shaped illite which yields a mixed-layer illite/smectite (I/S) X-ray powder diffraction (XRD) pattern. Transmission electron microscopy (TEM) indicates that the illite laths increase in abundance and thickness with increasing depth; XRD patterns indicate a progressive increase in the illite component of the I/S. The deepest samples were found to contain long-range ordered (R=3) I/S, which showed platy particle morphology with the TEM. K-Ar ages of most of the < 0.1-#m-size illite separates imply that illitization was a relatively brief event affecting a thick sequence of sediments during late Cretaceous to early Paleocene time (65-87 Ma); however, measured ages were affected by trace levels of detrital Ar contamination and do not represent the true age of diagenesis.Several methods of quantifying Ar contamination were used to correct measured ages to obtain a reasonable estimate of the true age of diagenesis. The corrected ages are imprecise due to uncertainties in quantifying the levels of sample contamination, but generally suggest a Paleogene (38-66 Ma) period of illitization. In contrast, simple kinetic models of smectite-illitization suggest much younger ages of diagenesis (0-40 Ma at the Veslefrikk field; 0-60 Ma at the Huldra field). The timing of the diagenesis and the morphologic aspects of the authigenic illite suggest that illite precipitated before late Tertiary compaction and resulted in a decrease in fluid permeability. Low trapping efficiency of early Tertiary sediments, vertical escape of warm fluid from the Brent sandstone, and high heat flow may have promoted illite diagenesis in the shales prior to deep late-Tertiary burial.

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The dependence of K-Ar age on the mineralogy of various particle size ranges in a shale

Cited by 76 publications

References 3 publications

Variations in the Illite to Muscovite Transition Related to Metamorphic Conditions and Detrital Muscovite Content: Insight from the Paleozoic Passive Margin of the Southwestern United States

Variations in the Illite to Muscovite Transition Related to Metamorphic Conditions and Detrital Muscovite Content: Insight from the Paleozoic Passive Margin of the Southwestern United States

Post-Caledonian brittle deformation in the Bergen area, West Norway: results from K–Ar illite fault gouge dating

Shale Diagenesis in the Bergen High Area, North Sea

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