• Stability of steady frictional sliding, inertia and the quasi-static limit • work on ps 4; see course web site

The Mechanics Of Earthquakes And Faulting

Smectite illitization is a common mineralogical reaction occurring during the burial diagenesis of clay-rich sediments and shales, and has thus attracted sustained interest over the last fifty years. Prior studies have concluded that smectite illitization proceeds through a steady set of homogeneous reactions involving intermediate mixed layers of varying compositions. In these intermediate structures, illite and smectite, or, more generally, expandable layers (I and Exp layers, respectively) coexist among the same crystallites giving rise to non-periodic structures (I-Exp) characterized by specific diffraction effects. Consistent with this model, reaction progress was characterized by the simultaneous increase in the illite content in I-Exp and in their stacking order leading to the following mineralogical sequence: smectite → randomly interstratified I-Exp with high smectite contents (> 50% Exp layers) → ordered I-Exp with high illite contents (> 50% I layers) → illite. Although reaction mechanisms have been extensively debated, this structural characterization has not been challenged, possibly due to a methodological bias. In the present study, X-ray diffraction patterns typical of the diagenetic illitization of smectite are interpreted using modern approaches involving profile fitting (multi-specimen method). Novel insights into the structure of intermediate reaction products are thus obtained. In particular, original clay parageneses are described including the systematic presence of illite, kaolinite, chlorite and a mixed layer containing kaolinite and expandable layers (K-Exp). In contrast to previous descriptions, the early stages of smectite illitization are characterized by the coexistence of discrete smectite and of a randomly interstratified I-Exp with a high content of illite layers (>50% I layers). Both the smectite and the I-Exp are authigenic and form under shallow burial, that is at low temperature conditions. With increasing burial depth, the relative proportion of I-Exp increases, essentially at the expense of discrete smectite, and the composition of I-Exp becomes slightly more illitic. In the second stage of smectite illitization, two illite-containing mixed layers are observed. They result from two parallel reaction mechanisms affecting the randomly interstratified I-Exp present in the shallow section of the series. The first reaction implies the dissolution of this randomly interstratified I-Exp and leads to the crystallization of an ordered I-Exp without significant illitization, possibly because of the low K-availability. The second reaction affecting the randomly interstratified I-Exp implies the growth of trioctahedral (Mg, Al) hydroxide sheets in Exp interlayers, thus developing di-trioctahedral chlorite layers (Ch layers) in the initial I-Exp to form an I-Exp-Ch. A layer-by-layer mechanism is hypothesized for this reaction. In this scheme, Mg cations released by the dissolution-recrystallization reaction of I-Exp likely represent the source of Mg for the formation of brucite-like sheets in expandable interlayers, and thus of the I-Exp-Ch. The reported structural characterization of smectite illitization intermediate products contradicts the conventional wisdom of a homogeneous reaction through a series of pure mixed layers of variable composition. In contrast, the coexistence of different phases implies a heterogeneous reaction via a sequence of intermediate phases and requires reassessing the reaction mechanisms proposed in the literature. The compositional range (relative proportion of the different layer types) of these phases is limited and smectite illitization proceeds essentially as relative proportions of the different phases vary. In addition, reaction kinetics and stability of the different intermediate products also need to be reconsidered.

/pdf/diagenetic-smectite-to-illite-transition-in-clay-rich-2gva27wm8i.pdf

Diagenetic smectite-to-illite transition in clay-rich sediments: A reappraisal of X-ray diffraction results using the multi-specimen method

Effect of mineralogy and pedoclimatic variations on Ni and Cr distribution in serpentine soils under temperate climate

http://diposit.ub.edu/dspace/bitstream/2445/160419/1/628945.pdf

Garnierites and garnierites: Textures, mineralogy and geochemistry of garnierites in the Falcondo Ni-laterite deposit, Dominican Republic

A specific methodology was developed to refine the complex clay mineralogy commonly encountered in soil environments. The soil examined was a Cambisol developed into a ferralitic paleosol. The sample was split into four sub-fractions of different particle sizes (<0.05, 0.05-0.1, 0.1-0.2, and 0.2-2 mu m), and their respective mass contributions to the overall <2 mu m clay fraction were determined. For each sub-fraction, X-ray diffraction (XRD) patterns were modeled using a trial-and-error approach based on the direct comparison of experimental and calculated profiles. Quantitative information derived from the fitting procedure for the different sub-fractions allowed for the determination of the complex mineralogy of the <2 mu m clay fraction through the identification and quantification of eight clay phases. The results show that the finest and most reactive clay fraction (<0.05 pm) was totally hidden in the XRD pattern of the <2 mu m fraction, the fraction commonly considered in soil mineralogical analyses. Similarly, this procedure revealed the presence of illite-smectite-chlorite and kaolinite-illite mixed-layer minerals seldom described in soil literature using classical methods. The use of this methodology improved our understanding of the pedogenesis of this soil through the identification and quantification of clay phases structural properties. The analysis of the evolution of structural parameters with particle size allowed for the detection of local modifications in the interlayer composition of expandable and hydroxy-interlayered vermiculite layers. Following this approach, key information can be derived to determine subtle changes in clay mineralogical composition that are related to microorganism and/or plant activity

Unraveling complex <2 μm clay mineralogy from soils using X-ray diffraction profile modeling on particle-size sub-fractions: Implications for soil pedogenesis and reactivity

Ahstract-Interstratified serpentine-smectite was found in the fine-grained fraction of altered metasomatic contact biotite-schists developed between serpentinite and granite-type rocks (Lower Silesia ophiolite sequence, Poland). Ni-rich serpentine-smectite is R0-interstratified lizardite (0.80)-stevensite (0.15)-vermiculite-like (0.05), with a coherent scattering domain (csd) of 5 layers (mean value). The Mg-rich variety of serpentine-smectite is R1 lizardite (0.80)-stevensite (0.20) with a csd size of 7 layers (mean value). A transmission electron microscope study revealed complex layer relationships, with zones composed of various serpentine-smectite packets having lizardite/smectite ratios of 3:1, 2:1, 1:1, 4:1 and scarce serpentine segregations. In both cases, the serpentine-smectites appear to be late products of alteration of the parent biotite-schist. Experimental and calculated positions and intensities of reflections of the ethylene glycol-saturated, heated (250°C, thermal stage), and air-dried samples are in good agreement. Calculated X-ray diffraction patterns for interstratified glycolated and anhydrous serpentine-smectite are included in the Appendix.

Serpentine-smectite interstratified minerals from lower silesia (sw poland)

The weathering crust at Szklary is known as a classical location of a nickeliferous laterite deposit derived from the chemical weathering of ultrabasic rocks. The layer silicates from the Szklary massif have been studied since the eighteenth century; moreover, this locality is considered to be an exceptional location of different minerals including nickel containing corrensite, interstratified kerolite-stevensite, interstratified serpentine-smectite, kerolite-pimelite, and clintonite. Ni-corrensite and irregularly mixed-layer serpentine-smectites with a variable layer ratio were found in Szklary for the first time. The origin of the layer silicates from Szklary is complex: (1) serpentine, chlorite, and clintonite are products of hydrothermal metamorphism related to the serpentinization of ultramafic rocks and posterior metamorphism and (2) the mixed-layer minerals, sepiolite, and kerolite-pimelite formed due to the hydrothermal and supergeneous alteration of ultrabasic rocks and various metamorphic schists.

https://geojournals.pgi.gov.pl/gs/article/download/13797/12239

Layer silicates from Szklary (Lower Silesia): from ocean floor metamorhism to continental chemical weathering

Coarse-grained vermiculite from a serpentinite-pegmatite thermal zone displays a rational series of narrow 14.4 A basal reflections and an unusual broad 28 A peak. X-ray diffraction simulations and fitting techniques show that the 28 A peak is related to 28 A domains consisting of elongated 2:1 layers of different lengths. The domains are located at the crystal edges of the vermiculite.

Unusual X-Ray Characteristics of Vermiculite from Wiry, Lower Silesia, Poland

PUMPEILYITE IN ALTERED VOLCANIC BASIC ROCKS FROM THE REGION OF GORZOW WIELKOPOLSKI (NORTH-WEST PART OF FORE SUDETIC MONOCLINE): EVIDENCES OF VERY LOW GRADE METAMORPHISM (VLGM)

Summary
Rotliegend metavolcanic rocks in the Gorzow Wielkopolski region (NW part of the Fore Sudetic Monocline) overlie the Paleozoic basement and are covered by the Zechstein evaporitic sequence as well as the Mesozoic sequence. The metavolcanic series provides the first documentation that very low grade metamorphism (VLGM) affected Rotliegend volcanic rocks from the Fore Sudetic Monocline. Up to the present assemblages including chlorite, celadonite, carbonates, quartz, albite, adularia, anhydrite, zeolites, barite, etc. were tentatively interpreted as products of a post-volcanic hydrothermal activity. The altered volcanic rocks typically contain no relict mineraIs; scarce relict clinopyroxene, ilmenite and Cr-spinel were identified only in vesiclepoor varieties. The very low grade metamorphic (<200°C and about 2 kbar) assemblage includes abundant pumpellyite, laumontite, quartz and chalcedony, corrensite-type mineral, albite, smectite, calcite, minor anhydrite, potassium feldspar, titanite, hematite, pyrite, and accessory prehnite and chalcopyrite. This assemblage occurs in amygdales, veinlets, and in a bulk rock. The phenocrysts of mafic mineraIs, both olivine and orthopyroxene (?) did not survive alteration and were completely obliterated by clay mineraIs and pumpellyite. Primary Ca-rich primary plagioclase is totally albitized and overprinted by Al-pumpellyite and K-feldspar. The groundmass contains irregularly distributed clay mineraIs, laumontite, pumpellyite, chalcedony, quartz, calcite, hematite, and titanite. Hydraulic fracturing commonly dismembered metavolcanic rocks into fragments of highly altered volcanic fragments successively cemented by younger anhydrite, chalcedony, quartz, and calcite, producing breccia-type species. The fan-shaped pumpellyite in amygdales is commonly zoned with the Fe-rich bas e and Al-rich apex; moreover, Fe-rich pumpellyite fragments are frequently trapped in amygdale filling and veiny quartz. The amygdales and veinlets can contain abundant albertite-type bitumens concomitant with Al-rich pumpellyite. Detailed petrographic study combined with extensive XRD and microprobe analysis reveal the folIowing mineral sequence: anhydrite+Fe-pumpellyite+laumontite+albite (older) Al-pumpellyite + layer silicates (younger). There were several episodes of Si02 group mineraIs and calcite formation. The VLG metamorphism of Rotliegend volcanic rocks can be tentatively attributed to the penetration of sea water through an evaporite sequence; however, albertite seems to be a product of upwelling fluids released during burial metamorphism of sedimentary rock series underlying extrusive Permian unit.

https://geojournals.pgi.gov.pl/pg/article/download/16100/13438

Pumpellyit w zmienionych zasadowych skałach wulkanicznych z okolic Gorzowa Wielkopolskiego (północno-zachodnia część monokliny przedsudeckiej): przejawy metamorfizmu bardzo niskiego stopnia (VLGM)

The structural pattern developed within metre to microscopic scale thrust and strike-slip fault zones exposed in the Palaeogene flysch rocks of the Fore-Dukla Thrust Sheet in the south-eastern part of the Silesian Nappe, Outer Carpathians, Poland, reveals evidence for upper crustal deformation and fluid flow. Syntectonic dawsonite [NaAlCO3(OH)2] indicates the following series of deformational events within the fault zones: i) detachment and buckle folding resulting from movement along thrust faults; ii) faulting as a compensation of the shortening, resulting in the fault propagation folding, breakthrough thrust faulting and imbrications; and iii) strike-slip faulting. The microstructural pattern coupled with the growth of a related sequence of carbonate minerals within the fault zones, followed by present-day dawsonite precipitation and tufa formation, indicate a continuing influence of fluids within the Silesian Nappe up to and including modern time. Structural observations at metre to microscopic scales coupled with EDS mapping of rocks indicate that dawsonite is a unique tool for the reconstruction of subsequent deformation in the Fore-Dukla Thrust Sheet.

https://geojournals.pgi.gov.pl/agp/article/download/27937/pdf

Dawsonite as an indicator of multistage deformation and fluid pathways within fault zones: Insights from the Fore-Dukla Thrust Sheet, Outer Carpathians, Poland

Grzegorz Kaproń

Papers

Serpentine-smectite interstratified minerals from lower silesia (sw poland)

Layer silicates from Szklary (Lower Silesia): from ocean floor metamorhism to continental chemical weathering

Unusual X-Ray Characteristics of Vermiculite from Wiry, Lower Silesia, Poland

Pumpellyit w zmienionych zasadowych skałach wulkanicznych z okolic Gorzowa Wielkopolskiego (północno-zachodnia część monokliny przedsudeckiej): przejawy metamorfizmu bardzo niskiego stopnia (VLGM)

Dawsonite as an indicator of multistage deformation and fluid pathways within fault zones: Insights from the Fore-Dukla Thrust Sheet, Outer Carpathians, Poland