Chlorite Polytype Geothermometry

Walker, J.R.

doi:10.1346/ccmn.1993.0410212

Cited by 58 publications

(29 citation statements)

References 17 publications

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“…-~ Ib (~ = 90 ~ --~ lib (13 = 97 ~ occurs in chlorites in sedimentary rocks with increasing temperature, and that the final transformation from type-I to type-II chlorite requires a temperature of about 150-200~ However, as recently reviewed by Walker (1993), other factors including grain size of the host rock, may be at least as important as temperature in controlling the stability of type-I chlorite polytypes. In addition, systematic studies suggest that type-II chlorite is stable at temperatures well below 200~ and that it can form as the initial chlorite phase without passing through any intermediate polytypic stages (Walker 1993).…”

Section: Illite Average Column Length (Urn)mentioning

confidence: 99%

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Diagenesis and Metamorphism of Clay Minerals in the Helvetic Alps of Eastern Switzerland

Wang

Frey

Stern

1996

Clays and clay miner.

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Abstract--Helvetic sediments from the northern margin of the Alps in eastern Switzerland were studied by clay mineralogical methods. Based on illite "crystallinity" (Ktibler index), the study area is divided into diagenetic zone, anchizone and epizone. Data on the regional distribution of the following index minerals are presented: smectite, kaolinite/smectite mixed-layer phase, kaolinite, pyrophyllite, paragonite, chloritoid, glauconite and stilpnomelane. Isograds for kaolinite/pyrophyllite and glauconite/stilpnomelane are consistent with illite "crystallinity" zones. Using the ordering of mixed-layer illite/smectite, the diagenetic zone is subdivided into three zones. The illite domain size distribution was analyzed using the Warren-Averbach technique. The average illite domain size does not change much within the diagenetic zone, but shows a large increase within the anchizone and epizone. The average illite bo value indicates conditions of an intermediate-pressure facies series.The Helvetic nappes show a general increase in diagenetic/metamorphic grade from north to south, and within the Helvetic nappe pile, grade increases from tectonically higher to lower units. However, a discontinuous inverse diagenetic/metamorphic zonation was observed along the Glarus thrust, indicating 5-10 km of offset after metamorphism. In the study area, incipient metamorphism was a late syn-to post-nappe-forming event.

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Section: Illite Average Column Length (Urn)mentioning

confidence: 99%

“…In addition, systematic studies suggest that type-II chlorite is stable at temperatures well below 200~ and that it can form as the initial chlorite phase without passing through any intermediate polytypic stages (Walker 1993).…”

Section: Illite Average Column Length (Urn)mentioning

confidence: 99%

Diagenesis and Metamorphism of Clay Minerals in the Helvetic Alps of Eastern Switzerland

Wang

Frey

Stern

1996

Clays and clay miner.

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“…2M1 250-350°C Srondón and Eberl, 1984;Walker, 1993;Yates and Rosenberg, 1996;Rosenberg, 2002 3T 1M XRD Grathoff andMoore, 1996 Grathoff andMoore, 1996;Pevear, 1999;van der Pluijm et al, 2001;Zwingmmann et al, 2010;Yamasaki et al, 2013 K-Ar…”

Section: °mentioning

confidence: 99%

Meso-scale brittle deformation structures in and around the Ikoma fault zone

Mitamura

Okudaira

Mitamura

2016

Jour. Geol. Soc. Japan

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We report the results of field observations and microstructural analyses of meso-scale faults that cut Cretaceous granitoids along and near lineaments of the Ikoma active fault zone. Based on measurements of the slip direction on fault planes, a paleostress of N-S extension is determined using the multiple inverse method. This stress field differs from the present-day regional stress field of predominant E-W compression, inferred from the seismic data inversion and the multiple inverse method applied to the active faults. Illite crystals of various sizes collected from a fault gouge, give K-Ar ages of .. Ma for the . -. µm fraction and .. Ma for the . -. µm fraction. High-and low-temperature components of illite are quantified by decomposing X-ray diffraction patterns to extrapolate the authigenic and detrital end-members. The ratios of low-temperature illite ( M d ) to high-temperature illite ( M and M) from a fault gouge are indistinguishable from one another. Based on the relative K-Ar ages of illite composites and of biotites from the host granitoid, the upper age limit of fault gouge formation is ca. Ma. These results suggest that formation of the fault gouge occurred between ~ and Ma, indicating that the meso-scale faults in basement rocks formed by N-S extension during the late Eocene to early Oligocene, rather than active tectonics under E-W compression.

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“…It has been established that the transformation from Ib → IIb type chlorites occurs at temperatures <200 °C [10]; the chlorites investigated here are IIb and those for Turhal Metamorphites within the UKC units are of 2M1 polytype [20], both of which indicate a similar degree of metamorphism.…”

Section: Geochemistrymentioning

confidence: 99%

“…Moreover, it represents degradation (negative transformation) in igneous rocks from trioctahedral mica and ferromagnesian minerals, and residual and authigenic minerals in sedimentary rocks [1]. The most significant mineralogical and chemical changes/transformations in chlorite occur during burial diagenesis/metamorphism (e.g., [2][3][4][5][6][7][8][9][10][11][12][13]). The fact that the half-height width of the 7-Å chlorite peak [14] decreases with the increasing diagenetic/metamorphic grade has been used as a mineralogical parameter for the determination of the diagenetic/metamorphic grade; in particular for metabasic (metavolcanic) rocks, despite these not being as widespread as illites (e.g., [15][16][17][18]).…”

Section: Introductionmentioning

confidence: 99%

Approaches to the Low Grade Metamorphic History of the Karakaya Complex by Chlorite Mineralogy and Geochemistry

2015

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Abstract:In this study, chlorite is used to investigate the diagenetic-metamorphic evolution and accurate geological history of the different units belonging to the Karakaya complex, Turkey. Primary and secondary chlorite minerals in the very low-grade metamorphic rocks display interference colors of blue and brown and an appearance of optical isotropy. Chlorites are present in the matrix, pores, and/or rocks units as platy/flaky and partly radial forms. X-ray diffraction (XRD) data indicate that Mg-Fe chlorites with entirely IIb polytype (trioctahedral) exhibit a variety of compositions, such as brunsvigite-diabantite-chamosite. The major element contents and structural formulas of chlorite also suggest these were derived from both felsic and metabasic source rocks. Trace and rare earth element (REE) concentrations of chlorites increase with increasing grade of metamorphism, and these geochemical changes can be related to the tectonic structures, formational mechanics, and environments present during their generation.

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Chlorite Polytype Geothermometry

Cited by 58 publications

References 17 publications

Diagenesis and Metamorphism of Clay Minerals in the Helvetic Alps of Eastern Switzerland

Diagenesis and Metamorphism of Clay Minerals in the Helvetic Alps of Eastern Switzerland

Meso-scale brittle deformation structures in and around the Ikoma fault zone

Approaches to the Low Grade Metamorphic History of the Karakaya Complex by Chlorite Mineralogy and Geochemistry

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