Formation of corrensite, chlorite and chlorite-mica stacks by replacement of detrital biotite in low-grade pelitic rocks

Transmission and scanning electron microscopy were utilized to investigate the nature and mechanisms of alteration of abundant detrital biotite of volcanic origin and progressive modification of phyllosilicate aggregates in a prograde sequence of pelitic rocks (illite crystallinity index = 0.19–0.58dΛ2θ) from the GaspÉ Peninsula in Quebec. Detrital biotite has been diagenetically altered to form corrensite and chlorite through two mechanisms; (1) layer-by-layer replacement gave rise to interstratification of packets of layers and complex mixed layering via several kinds of layer transitions between biotite and chlorite, corrensite or smectite; (2) dissolution-transport-precipitation resulted in the formation of relatively coarse-grained aggregates of randomly orientated, corrensite-rich flakes and fine-grained corrensite intergrown with chlorite and illite in the matrix. The data show that stacks consisting of alternating packets of trioctahedral and dioctahedral phyllosilicates originated during early diagenesis when lenticular fissures in strained altering biotite were filled by dioctahedral clays. Subsequent prograde evolution of dioctahedral clays occurred through deformation, dissolution and crystallization, and overgrowth. Illite evolved to muscovite, with K in part provided through biotite alteration, and corrensite/chlorite to homogeneous chlorite. The alteration of detrital biotite is closely related to the formation of titanite and magnetite in diagenetic rocks, and pyrite, calcite and anatase or rutile in the higher grade rocks. The observations demonstrate that detrital biotite of volcanic origin may be the principal precursor of chlorite in chlorite-rich metapelites originating in marginal basins. The mineral parageneses suggest that the transitions from corrensite to chlorite and illite to muscovite may be a function of local chemistry and time.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75643/1/j.1525-1314.1994.tb00065.x.pd

The structures and crystal chemistry of bustamite and rhodonite

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Geology, 1962.Vita.Includes bibliographical references.by Donald Ralph Peacor.Ph.D

SEM/STEM observations of magnetite in carbonates of eastern North America: Evidence for chemical remagnettzation during the Alleghenian Orogeny

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95085/1/grl5458.pd

Behavior of illite and chlorite during pressure solution of shaly limestone of the Kalkberg Formation, Catskill, New York

Textural and chemical changes occurring in illite and chlorite concomitant with pressure solution of limestone were studied in samples from the Kalkberg Formation of Catskill, New York, using XRD and TEM/AEM. Samples on one limb of an anticline are massive shaly limestones, but those on the other have undergone extensive pressure solution and well-developed cleavage is present. Illite and chlorite from the uncleaved shaly limestone are found in small individual packets (100-800 A thick) dispersed throughout the carbonate matrix with crystal morphologies characteristic of burial diagenesis. Phyllosilicates from the limb more affected by pressure solution occur in larger units (>1 [mu]m thick) as stacks of subparallel packets (150-500 A thick). Such stacks are inferred to represent coalescence of smaller packets. These data imply that the phyllosilicates are largely passive during pressure solution of limestone; however, localized solution-recrystallization is required by the coherent to semi-coherent packet boundaries and the crystal morphologies present in the pressure solution sample. The largely passive role is in contrast with the more active role of phyllosilicates in many shales and slates.XRD data for illite show an increase in crystallinity in the pressure solution sample under isothermal conditions. Differences in illite crystallinity are adequately explained in large part by differences in crystal size with some contribution due to strain. The data demonstrate that illite crystallinity cannot be unambiguously used in determining absolute or even relative temperatures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27590/1/0000634.pd

Pyrometamorphism and partial melting of shales during combustion metamorphism: mineralogical, textural, and chemical effects

Eocene shales metamorphosed by a naturally ignited coal seam in the Powder River Basin, Wyoming record a continuum of mineralogic and textural changes from relatively unaltered shale to melt developed during pyrometamorphism. Samples collected along a section 2 m in length, corresponding to a temperature range of approximately 1300°C, were examined optically and by XRD, SEM, and STEM. The low temperature samples are comprised primarily of silt-sized quartz, K-feldspar, and minor amounts of other detrital minerals in a continuous matrix of illite/smectite (I/S). Delamination of phyllosilicates due to dehydroxylation occurs early in the sequence with curling of individual layers from rim to core. Within one-half meter of melted areas, phyllosilicates have undergone an essentially isochemical reconstitution with nucleation and growth of mullite crystals with maximum diameters of 50 nm, randomly distributed within a non-crystalline phase that replaces I/S. Large detrital grains remain for the most part unaffected except for the inversion of quartz to tridymite/cristobalite. Within 1 mm of the solid/melt interface, the mullitebearing clay mineral matrix is essentially homogeneous in composition with obscure grain boundaries, caused by apparent homogenization of poorly crystalline material. This material is similar in composition to parent clays and acts as a matrix to angular, remnant tridymite/cristobalite grains. Rounded, smaller silica grains have reaction rims with the non-crystalline matrix; K-feldspar is no longer present (apparently reacted with the matrix) and the matrix contains abundant pore space due to shrinkage upon dehydroxylation. As isolated pods of paralava (glass) or fractures are approached, Fe−Ti−Al oxides become abundant. Vesicular glass is separated from clinker by a well-defined interface and contains numerous phenocrysts. XRF analyses and reduced area rastering using EDS imply enrichment of the melt phase in Fe, Ca, Mg and Mn, apparently due to vapor transport from other layers lower in the sedimentary sequence.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47303/1/410_2004_Article_BF00310784.pd

Comparison of diagenetic and low-grade metamorphic evolution of chlorite in associated metapelites and metabasites: an integrated TEM and XRD study

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73635/1/j.1525-1314.2000.00272.x.pd

Modified lattice parameter/Curie temperature diagrams for Titanomagnetite/titanomaghemite within the quadrilateral Fe 3 O 4 ‐ Fe 2 TiO 4 ‐Fe 2 O 3 ‐Fe 2 TiO 5

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94971/1/grl9245.pd

Sr and Nd isotopic evidence for punctuated clay diagenesis, Texas Gulf Coast

We report Rb---Sr, Sm---Nd and mineralogical data for leached whole rock, 87Sr/86Sr from 0.708 to 0.711 in exchangeable sites. Leached authigenic illite from the 1200 m, independent of the duration of burial. The exchangeable Sr in the clay has remained an open system and has undergone isotopic exchange since that time. Minimum fluid/rock ratios of 0.2 to 2 are modeled from Sr isotopic data, consistent with rock-dominated, open system diagenesis. Leachates and residues of the 147Sm/144Nd ( 147Sm/144Nd as high as 0.188. This Sm/Nd fractionation, in conjunction with the preserved isotopic equilibrium may be useful for dating diagenesis and associated fluid-rock interaction in older rocks.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29242/1/0000298.pd

Mobility and fractionation of rare earth elements in argillaceous sediments: Implications for dating diagenesis and low-grade metamorphism

We report Sm-Nd and Rb-Sr data for the fine fractions of Lower Paleozoic argillaceous rocks from Wales, UK and New York, USA, spanning the range of low-grade metamorphic conditions from the diagenetic zone (zeolite facies) to the epizone (greenschist facies). In all cases, leaching of the fine fractions results in a high 147Sm/144Nd (0.09-0.29) acid-soluble component and a complementary low 147Sm/144Nd (0.05-0.14) residual component. The observed fractionation is an ancient feature related to diagenesis, burial and metamorphism. The magnitude of Sm-Nd fractionation between leachates and residues, as well as the resulting Sm-Nd ages, vary as a function of grain size and metamorphic grade. Uncleaved Welsh mudrocks of the diagenetic zone yield Sm-Nd leachate-residue ages of 453-484 Ma, in agreement with their Llanviian to Caradocian biostratigraphic ages, whereas higher grade rocks of the anchizone and epizone yield Sm-Nd ages as young as 413 Ma. These ages are transitional between the time of deposition and the time of regional deformation related to the Acadian Orogeny at 390 Ma. Distinct convex-upward rare earth element (REE) patterns of the leachates suggest that the precipitation of early diagenetic apatite controls the trace element budget of the rock, forcing a depletion of middle REEs on the subsequently formed diagenetic phyllosilicates. The amount of organic matter present and the extent of later prograde reactions are probable modifiers of this fractionation process. Ordovician and Devonian clastic rocks associated with the Trenton and Onondaga limestones of New York yield single-sample and multi-sample Sm-Nd isochron ages that agree well with their biostratigraphic ages of 454 Ma and 390 Ma, respectively. The REE fractionation observed in shale leachates of the Ordovician Utica Formation is related to Ca/Mg of the bulk rock and hence to the composition of the diagenetic carbonate cement. In all cases the Sm-Nd system remained closed subsequent to the peak of diagenesis or metamorphism, including the North American rocks that show no evidence of being isotopically reset during widespread remagnetization of the subjacent limestone units in the late Paleozoic.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31915/1/0000868.pd

SEM/STEM observation of magnetic minerals in presumably unremagnetized Paleozoic carbonates from Indiana and Alabama

The Silurian Wabash Formation in Indiana and the Mississippian Pride Mountain Formation in Alabama appear not to have been affected by a late Paleozoic remagnetization event. In an attempt to characterize the magnetic mineralogy in these (presumably) unremagnetized carbonates and in order to compare their magnetic mineralogy to that of remagnetized carbonates, scanning and scanning transmission microscope (SEM/STEM) observations and rock magnetic investigations were carried out.It is possible to recognize differences in magnetic mineralogy in the unremagnetized carbonate from that in remagnetized carbonates: 1. (1) iron oxides associated with iron sulfides are hematite (in this study) as a result of replacement of pyrite (instead of magnetite as was found elsewhere);2. (2) occurrences of large euhedral pure-iron oxides of secondary origin are common in the unremagnetized carbonates3. (3) a rare occurrence of fine-grained single-crystal magnetite capable of carrying a remanence in the unremagnetized carbonates is noticeable as compared to the abundance of such grains in the remagnetized carbonates. Although the abundance of the fine-grained magnetite grains in remagnetized carbonates is inferred to be a diagnostic factor to distinguish the remagnetized from the unremagnetized carbonates, this clarifies only the carriers in the remagnetized rocks and leaves the question of the carriers in unremagnetized limestones unresolved to a large extent.The lack of remagnetization is commonly attributed to a restricted amount of fluid influx into the rocks. For the Wabash and the Pride Mountain Formations this may also be true; early cementation has significantly reduced the porosity and permeability in the Wabash Formation in Indiana, whereas the presence of the impermeable Chattanooga Shale may have `protected' the Mississippian Pride Mountain Formation in Alabama.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29677/1/0000004.pd