Synchronous very low-grade metamorphism, contraction and inversion in the central part of the Welsh Lower Palaeozoic Basin

Робертс, Б.; Merriman, R. J.; Hirons, Steven; Fletcher, C. J. N.; Wilson, David Gordon

doi:10.1144/gsjgs.153.2.0277

Cited by 26 publications

(14 citation statements)

References 16 publications

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“…The dominant factor controlling the increase in IC index value is temperature although many other factors have been cited including fluid pressure, stress, lithology, crystal chemistry, mineralogy and time (Frey 1987). Deformation associated strain energy can also be important in aggradation of IC index values (Roberts and Merriman 1985;Merriman et al 1990;Roberts et al 1990Roberts et al , 1996. The temperature range from diagenetic to beginning of epizone is 100-300 • C Merriman and Peacor 1999).…”

Section: Variation Of Ic Index and Its Controlling Factors Along And mentioning

confidence: 99%

“…Abundance of illite in most mudrocks in sedimentary basins makes it possible to measure the thermal maturity in a basin-wide scale and to detect the potential heat sources. IC is especially useful in reconstructing the structural and metamorphic history in very low-to low-grade metamorphic rocks (e.g., Frey et al 1980;Roberts and Merriman 1985;Frey 1988;Gutierrez-Alonso and Nieto 1996;Roberts et al 1996;Warr et al 1996;Lee and Ko 1997;Mukherjee 2003;Ruiz et al 2008;Hara and Kurihara 2010;Verdel et al 2011;Fitz-Díaz et al 2014;Fukuchi et al 2014). In addition, the spatial variation in sediment thickness (e.g., Awan and Woodcock 1991) and the existence of concealed plutons (e.g., Roberts et al 1990; Lee and Lee 2001) can be examined on the basis of IC variation.…”

Section: Introductionmentioning

confidence: 99%

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Illite crystallinity index from the Mesoproterozoic sedimentary cover of the Kaladgi basin, southwestern India: Implications on crustal depths of subsidence and deformation

2019

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The grade of metamorphism and thermal maturity of the Mesoproterozoic Bagalkot Group in the Kaladgi basin of southwestern India has been determined using the illite crystallinity (IC) index. IC index was determined from the argillite samples of four stratigraphic levels viz., Ramdurg Formation (basal unit), Yargatti Formation (intermediate lower unit), Yadahalli Formation (intermediate upper unit) and Hoskatti formation (upper unit). IC index (Kubler equivalent) values range between 0.54 • Δ2θ and 0.24 • Δ2θ (in a set of 37 samples) and indicate a deep diagenetic to high anchizone metamorphic grade within a temperature range of ∼180 to 300 • C. The Mesoproterozoic sedimentary cover of the Kaladgi basin is deformed due to southerly directed gravity gliding of the cover over the basement. The general variation of the IC index along and across the basin as indicated by the distribution of IC index values and isocryst contour patterns is due to the combined effect of deformation and variable subsidence of the Mesoproterozoic cover of the basin. Considering an average Mesoproterozoic geothermal gradient of 35 • C/km, the crustal depth of deformation and/or subsidence of the Mesoproterozoic cover up to the sample point is estimated to vary between 5.14 and 8.57 km.

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Section: Variation Of Ic Index and Its Controlling Factors Along And mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Illite crystallinity index from the Mesoproterozoic sedimentary cover of the Kaladgi basin, southwestern India: Implications on crustal depths of subsidence and deformation

2019

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“…Strain energy can also be important in the aggradation of illite crystallites (Roberts and Merriman, 1985;Roberts et al, 1990Roberts et al, , 1996Merriman et al, 1990). In the Gyeongsang Basin, however, no prominent fold or thrust is found within the basin.…”

Section: Controlling Factors Of Kimentioning

confidence: 99%

“…KI is especially useful in reconstructing structural and metamorphic history in very low-to low-grade pelitic rocks (e.g., Frey et al, 1980;Roberts and Merriman, 1985;Frey, 1988;Roberts et al, 1996;Warr et al, 1996;Lee and Ko, 1997). Also, the spatial variation in sediment thickness (e.g., Awan and Woodcock, 1991) and the existence of concealed plutons (e.g., Roberts et al, 1990) can be examined on the basis of KI variation.…”

Section: Introductionmentioning

confidence: 99%

Kübler Illite “Crystallinity” Index of the Cretaceous Gyeongsang Basin, Korea: Implications for Basin Evolution

Lee

2001

Clays and clay miner.

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Abstract--Thermal maturity of the Lower Cretaceous Sindong and Hayang groups in the Gyeongsang Basin, Korea, was investigated using the Kfibler illite "crystallinity" index (KI) which is based on the numerical expression of the 10-A peak width after calibration to the Crystallinity Index Standard scale. The metamorphic grade of the Sindong and Hayang groups ranges from late diagenetic zone to high anchizone. Depth of burial was not a major factor controlling KI variation in the basin because Hayang mudrocks have higher thermal maturity than the underlying Sindong mudrocks. Short-lived heating by the emplacement of the Upper Cretaceous plutonic rocks is responsible for the higher thermal maturity in the Hayang mudrocks. A linear NNE-SSW trending belt is drawn by connecting the lowest KI values, and it seems to reflect a hidden fault trace beneath the Hayang Group, Emplacement of Upper Cretaceous plutonic rocks and introduction of hydrothermal fluids along the inferred fault may have been the main cause of the lowering of KI values along this belt. This inferred fault is interpreted to represent the buried eastern boundary of the Nagdong Trough, which was the main depositional site for the Sindong Group in the western part of the Gyeongsang Basin. Deposition of the Hayang Group occurred in the enlarged basin when the basin extended eastward. This study provides an example that KI values can be used in the reconstruction of an early history of basin evolution.

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“…Metamorphic maps of Wales, based on Ca-Al silicate assemblages in metabasites and on the distribution of illite crystallinity in shales, indicate a regional record of diagenetic to greenschist facies conditions in the lower Paleozoic rocks of the Welsh Basin (Kubler Index Range of 0.23 to 0.46 Њ2; Roberts et al 1996;Bevins and Robinson 1988;Fettes et al 1985;Robinson and Bevins 1986;Bevins and Robinson 1988). The clays in the Llanvirn-Llandeilo-Caradoc shales consist of well-ordered illite (R3) and have a Kubler Index Range of 0.20 to 0.46 Њ2, which is in general agreement with the proposed late diagenetic to epizone temperatures (200-300ЊC) recorded by clay mineralogy elsewhere in the Welsh Basin (Lev 1994).…”

Section: Caradoc Shales Southwest Wales Ukmentioning

confidence: 99%

Mineralogic controls on REE mobility during black-shale diagenesis

Lev¹,

McLennan²,

Hanson³

1999

Journal of Sedimentary Research

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The Llandeilo-Caradoc black shales of southwest Wales, U.K. record a paragenetic sequence that requires redistribution of rare earth elements (REE) on a mineralogic scale during diagenesis. The main evidence for this redistribution is formation and replacement of REE-rich apatite and monazite and variations in whole-rock REE patterns. The processes that produce these mineralogic changes create a diagenetic overprint on the Llandeilo-Caradoc black shales that obscures geochemical information related to both provenance and paleoenvironmental conditions of deposition. Periods of open-system conditions existed during the diagenetic alteration of the Llandeilo-Caradoc black shales, which allow an evaluation of the extent and timing of the REE redistribution inferred from petrography. The observed variations in La/Sm ratios in the whole-rock REE patterns are strong evidence that REE were redistributed on a scale greater than an individual hand sample. This change in the whole-rock REE pattern altered the Cerium anomaly by as much as 20% and produced a range in the Sm/Nd ratio from 0.14 to 0.20. This change in the whole-rock Sm/Nd ratio indicates a disturbance in the Sm-Nd isotopic system at about 460 Ma that can be directly linked to the formation and dissolution of diagenetic apatite and monazite during diagenesis. One effect of this disturbance is to alter the range in Nd model age for the Llandeilo-Caradoc black shales from 1.6 to 1.8 Ga to about 1.4 to 2.25 Ga, thus complicating any interpretation of provenance. The ability to link petrographic observations from a black shale to measurable wholerock geochemical changes provides us with one tool to evaluate the presence of a diagenetic overprint on trace elements commonly used in paleoenvironmental reconstruction.

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Synchronous very low-grade metamorphism, contraction and inversion in the central part of the Welsh Lower Palaeozoic Basin

Cited by 26 publications

References 16 publications

Illite crystallinity index from the Mesoproterozoic sedimentary cover of the Kaladgi basin, southwestern India: Implications on crustal depths of subsidence and deformation

Illite crystallinity index from the Mesoproterozoic sedimentary cover of the Kaladgi basin, southwestern India: Implications on crustal depths of subsidence and deformation

Kübler Illite “Crystallinity” Index of the Cretaceous Gyeongsang Basin, Korea: Implications for Basin Evolution

Mineralogic controls on REE mobility during black-shale diagenesis

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