bluuebunny/crossref_metadata_2025 huggingface dataset:
Psychoneurological symptoms during interferon therapy in patients with chronic hepatitis: prospective study on predictive use of Cornell Medical Index and electroencephalogram
Authors: Tanaka Yuji , Nagaki Masahito , Tomita Eiichi , Murase Masahiko , Enya Masamichi , Nishigaki Yohichi , Sugihara Jun'ichi , Moriwaki Hisataka
Published: October 2004

Abstract: Background/Aims: We assessed the usefulness of the Cornell Medical Index (CMI) and electroencephalogram (EEG) in the prediction and early detection of psychoneurological symptoms associated with interferon (IFN) therapy for chronic viral hepatitis.

Methods: Forty‐eight consecutive patients received IFN for chronic viral hepatitis for 8–24 weeks. CMI was measured before IFN therapy. Serial EEGs were recorded before IFN therapy, 2, 4 weeks, and thereafter every 4 weeks in the therapy.

Results: Psychoneurological symptoms including insomnia, depression, and restlessness were seen in 11 (23%) of 48 patients. Five (13%) of 40 patients with CMI I and II and six (75%) of eight with CMI III developed psychoneurological symptoms (P<0.001). Sensitivity, specificity, and predictive accuracy of CMI III were 55%, 95%, and 75%, respectively. Abnormal EEG such as slow basic rhythm, appeared in 13 patients (27%) during IFN therapy. Psychoneurological symptoms were seen in six (46%) of the 13 patients with abnormal EEG, and in five (14%) of 35 in whom EEG remained normal (P<0.05).

Conclusions: CMI is useful for the prediction of IFN‐induced psychoneurological symptoms in patients with chronic viral hepatitis. Serial EEGs contribute to the screening and auxiliarily assessing the adverse effects of IFN on the central nervous system.
Expression of matrix metalloproteinase‐2 and ‐14 persists during early resolution of experimental liver fibrosis and might contribute to fibrolysis
Authors: Zhou Xiaoying , Hovell Christopher J. , Pawley Susannah , Hutchings Matthew I. , Arthur Michael J. P. , Iredale John P. , Benyon R. Christopher
Published: October 2004

Abstract: Background/Aims: Resolution of liver fibrosis is possible but the identity of the matrix metalloproteinases (MMPs) which degrade the accumulated collagens is uncertain. We examined MMP‐2 and MMP‐14 expression in established and resolving fibrosis to assess their role in resolution of liver fibrosis.

Methods: MMP and tissue inhibitor of metalloproteinase (TIMP)‐2 expression in liver extracts was examined by ribonuclease protection assay, Western blotting and gelatin zymography. MMP activity was examined by 14C gelatin degradation.

Results: In human cirrhotic liver, MMP‐14 mRNA was increased to 230–330% of normal liver expression. Both 63 kDa proenzyme and 60 kDa activated form were present. Cirrhotic livers had 270–320% of normal liver expression of MMP‐2 protein with 20–25% being the 62 Da activated form. Protein and mRNA for MMP‐2 and MMP‐14 progressively increased during 8 weeks of CCl4 treatment in rats. Between 3 and 7 days of resolution from CCl4 liver fibrosis, MMP‐2 and MMP‐14 persisted at elevated levels. Gelatinolytic activity in liver homogenates peaked at 7 days of recovery, being 140% above that in livers at peak fibrosis.

Conclusions: Increased expression and activation of MMP‐2 and ‐14 occurs even under conditions of elevated TIMPs during liver fibrogenesis. During liver fibrosis resolution, as TIMP expression decays, the persistence of MMP‐2 and MMP‐14 may permit collagen degradation.
Gut and liver handling of asymmetric and symmetric dimethylarginine in the rat under basal conditions and during endotoxemia
Authors: Nijveldt Robert J. , Siroen Michiel P. C. , Teerlink Tom , Van Lambalgen Antonie A. , Rauwerda Jan A. , Van Leeuwen Paul A. M.
Published: October 2004

Abstract: Introduction/Aim: Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthase enzymes, whereas symmetric dimethylarginine (SDMA) competes with arginine transport. Although both dimethylarginines may be important regulators of the arginine‐NO pathway, their metabolism is largely unknown. In previous studies, evidence was found for the liver in the metabolism of dimethylarginines. We aimed to investigate dimethylarginine handling of the gut and the liver in detail under basal conditions and during endotoxemia.

Methods: Twenty‐one male Wistar rats were used for this study. Endotoxemia was induced by lipopolysaccharide (LPS) infusion (8 mg/kg). Blood flow was measured using radiolabeled microspheres according to the reference sample method. Concentration of dimethylarginines were measured by high‐performance liquid chromatography. The combination of arteriovenous concentration difference and organ blood flow allowed calculation of net organ fluxes and fractional extraction (FE) rates.

Results: Arterial plasma concentration of ADMA was lower in LPS rats, in contrast to a higher SDMA concentration. For the gut, net release of ADMA was found, which was higher in LPS rats. In contrast, for the gut, net uptake of SDMA was found, which was lower in LPS rats. For the liver, a high net uptake of ADMA was found in both groups, while FE was significantly increased in LPS rats. Hepatic handling of SDMA was negligible.

Conclusion: The liver plays an important role in eliminating ADMA from the circulation and endotoxemia stimulates this capacity. In contrast to the liver, the gut releases ADMA. Endotoxemia results in a reduced systemic ADMA concentration.
Implication of inflammation‐related cytokines in the natural history of liver cirrhosis
Authors: Girón‐González José A. , Martínez‐Sierra Carmen , Rodriguez‐Ramos Claudio , Macías Manuel A. , Rendón Paloma , Díaz Fernando , Fernández‐Gutiérrez Clotilde , Martín‐Herrera Leopoldo
Published: October 2004

Abstract: Background/Aims: Increased serum concentrations of pro‐inflammatory cytokines have been detected in patients with liver cirrhosis. However, their role in the natural history of cirrhosis and portal hypertension, in the absence of infection, and the prognostic significance of inflammation‐related cytokines have not been reported. Our objective was the analysis of the prognostic value of inflammation‐related cytokines in cirrhotic patients.

Patients and methods: Serum concentrations of tumor necrosis factor (TNF‐α) and its soluble receptors I and II and interleukin 6 (IL‐6), as well as mean blood pressure, plasma renin activity, aldosterone, vasopressin and norepinephrine concentrations were determined in 72 cirrhotic patients (Child–Pugh score: A 50%, B 33.3%, C 16.7%), without any evidence of infection, and in 25 healthy controls. Patients were followed up for a median of 35.9 (range 6–60) months.

Results: Increased concentrations of soluble TNF receptors were detected in cirrhotic patients when compared with healthy controls. TNF receptors and IL‐6 concentrations were both significantly more elevated in advanced phases of cirrhosis (Child–Pugh score C vs B and vs A). Sixteen patients died as a related consequence of liver cirrhosis. Multivariant analysis demonstrated that Child–Pugh score, mean blood pressure and serum levels of TNF receptor I were associated with mortality.

Conclusions: In addition to the classic factors implicated in mortality (Child–Pugh score and hemodynamic parameters), alterations in inflammation‐related components are of prognostic significance in cirrhotic patients.
The role of midkine and pleiotrophin in liver regeneration
Authors: Ochiai Keiko , Muramatsu Hisako , Yamamoto Satoshi , Ando Hisami , Muramatsu Takashi
Published: October 2004

Abstract: Background/Purpose: We studied roles of two closely related heparin‐binding growth factors, midkine (MK) and plieotrophin (PTN) in the processes of liver regeneration after partial hepatectomy.

Methods: Liver regeneration was comparatively analyzed using mice deficient in the MK gene (Mdk), mice deficient in the pleiotrophin gene (Ptn) and wild‐type mice.

Results: Migration of neutrophils and macrophages to the liver 1–5 days after partial hepatectomy was suppressed in Mdk (−/−) mice. Liver damage as assessed by serum aspartate aminotransferase was also less severe in the deficient mice. On the other hand, cell growth in the liver was generally suppressed in the deficient mice 3–14 days after partial hepatectomy. The weight of the liver 7 and 14 days after partial hepatectomy was significantly less in Mdk (−/−) mice than wild‐type mice. Very similar results were obtained using Ptn (−/−) mice except that a significant difference in the repaired liver weight was not observed between Ptn (−/−) mice and wild‐type mice.

Conclusions: MK and PTN are involved both in the inflammatory and reparative processes after partial hepatectomy, and as a whole are beneficial for liver regeneration.
Kinetic analysis of daily hemofiltration
Authors: Yamashita Akihiro C , Kawanishi Hideki
Published: October 2004

Background:  Daily hemofiltration (D‐HF) is a new treatment modality that shows unique solute removal characteristics and possibly provides a high quality of life for patients with end‐stage renal disease. We evaluated solute removal characteristics of D‐HF for five patients by kinetic modeling analysis.

Methods:  Five patients treated with normal 3 × 4 hr/week hemodialysis (HD) were switched to D‐HF (6 × 2 hr/week). Ultrafiltration rates (QF) or small‐solute clearances ranged from 63 to 106 mL/min. All the necessary kinetic parameters were determined from patients' physical data and HD portion of the clinical measurements. The two‐compartment kinetic model predicted the concentration changes after switching from normal HD to D‐HF.

Results:  Concentrations of small solutes such as urea nitrogen (UN) increased, whereas that of β2‐microglobulin (β2‐MG) decreased after switching from normal HD to D‐HF in all five patients. Predicted solute concentrations and clinical measurements for UN and β2‐MG were in good agreement with mean error less than 10%. The model predicted that QF = 155 mL/min may be necessary for time‐averaged concentration (TAC) of UN to be unchanged. The model also predicted that the 7 times/week D‐HF should not increase the pretreatment concentration of UN, expecting even much lower β2‐MG concentration after switching from normal HD to D‐HF.

Conclusion:  D‐HF is superior to normal HD for removing larger solutes but may increase the TAC of small solutes. Seven‐day (7 times/week) D‐HF may improve the solute removal capacity of small solutes.
Associations with home hemodialysis modality failure and mortality
Authors: Young Bessie A , Hynes Janey , McComb Timothy , Blagg Christopher R
Published: October 2004

Background: Limited data exist on risk factors for home hemodialysis (HH) failure and mortality. We sought to determine whether age, helper status, or ethnicity was associated with home dialysis failure or mortality.

Methods: We conducted a retrospective cohort study of all prevalent and incident patients from a regional dialysis unit who initiated HH training from December 2000 to September 2002. Baseline demographics, program entry and exit dates, and mortality were ascertained. Characteristics of those more likely to remain in the program were assessed using logistic regression; survival was determined using Cox proportional hazards models.

Results: Of the 1117 patients enrolled for dialysis, 116 patients were trained in the HH program (6.8%). Of those, 45.7% remained in the program, 10.3% received a transplant, 10.3% returned to in‐center dialysis, 1.7% were lost to follow‐up, and 31.7% expired. Compared to patients who returned to center or received a transplant, patients who remained on HH were more likely to be older, to have been on dialysis longer, and to have diabetes as their primary renal disease. Ethnicity, sex, or type of helper did not affect home program status. Among those who remained in the HH program, those with hypertension or other renal diseases had better survival than those with diabetes, as did those who had related helpers compared to those with unrelated helpers.

Conclusions: Older and younger ages, but not ethnicity, helper status, or sex, were associated with home dialysis failure. Diabetes remained an independent risk factor for increased mortality. HH remains a viable option for many patients.
Six years of experience with nightly home hemodialysis access
Authors: Pipkin Mary , Craft Viola , Spencer Maureen , Lockridge Robert S
Published: October 2004

Background:  Lynchburg Nephrology Dialysis Incorporated started its nightly home hemodialysis (NHHD) program in September 1997.

Purpose:  The purpose of this study was to evaluate episodes of exit‐site infections, catheter sepsis, and safety and longevity of accesses for patients doing NHHD.

Method:  If internal jugular (IJ) catheter was chosen, the patient was started on 2 mg coumadin per day when catheter was placed. If catheter malfunctioned, it was blocked with a thrombolytic agent and coumadin was adjusted to meet a goal international normalized ratio (INR) of 1.5 to 2.25. If the problem persisted, the catheter was exchanged. For catheters, a threaded lock cannula (BD InterLink device, BD) was used to prevent air emboli and infections and a locking device was used to prevent disconnects. If arteriovenous (AV) fistula was used, four buttonholes were established using 16‐gauge needles. If AV graft was used, patients were taught the rope ladder cannulation technique using 16‐gauge needles.

Results:  As of September 1, 2003, 45 patients have completed training and have performed 27,063 treatments at home. Total catheter time at home was 930 months. Total AV fistula and AV graft times at home were 190 and 20 months, respectively. Upon completion of training, 34 patients were using tunneled IJ catheters, 10 were using AV fistulas, and 1 was using an AV graft. The IJ catheter exit‐site and sepsis infection rates were 0.35 and 0.52 episodes per 1000 patient‐days, respectively. Mean catheter life was 8.5 months with the longest being 66.7 months and the shortest being 0.2 months. The AV fistula and graft exit‐site and sepsis infection rates were 0.16 and 0 episodes per 1000 patient‐days, respectively. Catheter complications included one episode of disconnect due to patient's failure to use the locking device, one episode of central stenosis, and one episode of intracranial hemorrhage, due to prolonged INR, with resolution of symptoms.

Conclusion:  Data support the fact that tunneled IJ catheters, AV fistulas, and AV grafts are effective and safe permanent accesses for patients on NHHD.
The International Quotidian Hemodialysis Registry: Rationale and methods
Authors: Nesrallah Gihad E , Suri Rita S , Garg Amit X , Moist Louise M , Awaraji Christian , Lindsay Robert M ,   the Frequent Dialysis Regimens Workgroup
Published: October 2004

The HEMO study has provided evidence that a higher dialysis dose per session does not improve survival in conventional three times a week hemodialysis (HD). Attention has therefore shifted to HD schedules that vary in frequency and/or duration of dialysis. Although observational data favoring the use of frequent dialysis are steadily accumulating, compelling evidence supporting its superiority is still lacking. Several advances have recently been made with a view to put this form of therapy on much more solid footing. Upcoming research initiatives including clinical trials of frequent HD and the quotidian HD registry will provide a wealth of analytic and descriptive data that will help define the role for frequent HD regimens as a therapy for end‐stage renal disease.
Peptide‐coated vascular grafts: An in vivo study in sheep
Authors: Li Cheng , Hill Arthur , Imran Mir , Tio Fermin
Published: October 2004

The data on function and patency of prosthetic vascular grafts in various clinical settings are limited. The purpose of this in vivo study was to compare the function and patency of P15‐coated expanded polytetrafluoroethylene (ePTFE) vascular grafts to uncoated ePTFE grafts in sheep. The P15 cell‐binding peptide was covalently immobilized onto the surface of ePTFE grafts by a novel atmospheric plasma coating method. We evaluated the amount of neointimal tissue ingrowth present at the arterial and venous sides of the anastomoses and the degree of endothelial cell resurfacing of the luminal surface of the graft. Four P15‐coated grafts and two control grafts were implanted as arteriovenous grafts between the femoral artery and vein and the carotid artery and jugular vein in two sheep (n = 6). One animal was euthanized after 14 days and the other after 28 days. The study showed the intimal ingrowth was significantly less. The average intimal thickness of P15‐coated grafts (658 µm) was approximately two and a half times less than that of uncoated samples (1657 µm). The newly formed endothelial cell lining was thicker and its coverage was more uniform for P15‐coated grafts compared to the uncoated controls.
Blood compatibility and filtration characteristics of a newly developed polyester polymer alloy membrane
Authors: Yamashita Akihiro C , Tomisawa Narumi , Takezawa Azusa , Sakurai Kenji , Sakai Tadasu
Published: October 2004

Background:  Many synthetic polymeric membranes have been widely used for blood purification therapies for removing larger solutes and for better blood compatibility.

Methods:  Five different filters with polyester polymer alloy (PEPA) membrane (Nikkiso) that included polyvinylpyrrolidone (PVP), that is, standard‐pore‐size FLX (PEPA with PVP(–)), standard‐pore‐size FDX (PEPA with PVP(+)), new FDX (PEPA with PVP(++)), larger‐pore‐size FDY (PEPA with PVP(+)), and new FDY (PEPA with PVP(++)), were evaluated in terms of in vivo blood compatibility and aqueous in vitro sieving coefficient (s.c.) for albumin.

Results:  FDY showed excellent small changes in C3a concentration during the treatment right after switching from polysulfone membrane, leaving no significant changes in other blood‐compatible indices. New FDY, in contrast, showed less biocompatible characteristics in terms of C3a, which may be caused by increased use of PVP. FLX (no PVP) showed the highest s.c. for albumin. With a hydrophilic agent (PVP), the s.c. was greatly reduced in FDX. By enlarging the pore diameter in FDY, the s.c. increased in accordance with the enlargement. Generally speaking, polysulfone filters with PVP(+++) reach the peak s.c. value approximately 10 min after starting the experiment. The s.c. of the PEPA membrane with no or small amount of PVP, which showed excellent blood compatibility, never showed peaks, whereas the peak s.c. values were found in new PEPA with increased amount of PVP that showed higher C3a changes.

Conclusions:  The separation characteristics of aqueous albumin may be related to its blood compatibility.
Cuffed‐catheter‐related Lemierre syndrome
Authors: Hennigan Allison , Collinge Neil , Halker Raj , Agraharkar Mahendra
Published: October 2004

Sepsis is a common problem in patients who have cuffed catheters for hemodialysis. Line sepsis, however, has not often been associated with septic thrombophlebitis as seen in Lemierre syndrome. Thrombophlebitis of a central vein associated with catheter placement is extremely rare and when encountered is known to affect the femoral or the subclavian vein. Thrombophlebitis of the internal jugular vein after hemodialysis catheter placement has not been reported. We present the case of a woman with line sepsis who developed Lemierre syndrome, a serious complication of which the medical community should be aware. Lemierre syndrome requires a high index of suspicion for diagnosis and can have a fatal outcome if not treated with appropriate antibiotics.
A report on four new cases of nephrogenic fibrosing dermopathy in chronic hemodialysis patients
Authors: Sreenarasimhaiah Vijay P , Brown Wendy W , Cortese Cherize , Sirintrapun Joe , Janney Christine , Philipneri Marie , Gellens Mary , Flynn Lauren , Joseph Amy , Bastani Bahar
Published: October 2004

Nephrogenic fibrosing dermopathy (NFD) is a rare clinical entity affecting patients with renal failure, often on chronic dialysis or after transplantation. The patient profile at risk for this debilitating condition is undefined. Lack of awareness of the condition has hampered epidemiologic work in identifying the etiology. We present four chronic hemodialysis (HD) patients who developed this disease. The patients' ages ranged from 26 to 75 years, and they had received HD from between 20 months and 10 years before the diagnosis of NFD. Two patients had a history of renal transplantation. All patients had progressive thickening and woody induration of the skin associated with contractures, leading to difficult ambulation, and permanent disability within weeks of the diagnosis. In one case, the diaphragm, psoas muscle, and pericardium were involved. The latter is likely the first report of pericardial involvement of NFD. In all four patients, the skin findings were restricted to the extremities, sparing the trunk and face. Skin biopsy findings included thickened dermis with particularly thickened collagen bundles, fibroblast proliferation, minimal mucin deposition, and nearly absent inflammation. The pathologic findings were distinct from scleromyxedema and scleroderma. We found no laboratory evidence of autoimmune disease or thyroid dysfunction to account for alternate etiologies. CD34‐positive cells were documented in the skin biopsies as well as in the diaphragm, psoas muscle, and pericardial tissue of the concerned case. NFD is a novel fibrosing disorder of progressively debilitating nature which needs further clinical characterization and recognition to guide investigation of its pathogenesis.
Fluid flow paths and mechanisms of fluid infiltration in carbonates during contact metamorphism: the Beinn an Dubhaich aureole, Skye
Authors: HOLNESS M. B.
Published: October 2004

A textural study of marbles from the Beinn an Dubhaich granite contact aureole, Skye, has shown that mass transport by diffusion was probably negligible during the metamorphic event, and that the bulk of the carbonates reacted as a consequence of silica metasomatism, permitting the use of calcsilicates as a tracer for fluid infiltration pathways. Fracture‐controlled infiltration was predominant in undeformed marbles, whereas pervasive infiltration occurred during synmetamorphic ductile deformation. Some calcite marbles contain disseminated unoriented calcsilicate minerals that are associated with neither fractures nor a ductile deformation fabric, consistent with an origin via infiltration of fluid along an interconnected grain‐edge porosity. The inference of limited pervasive infiltration of undeformed carbonates is consistent with predictions based on experimentally determined fluid–solid dihedral angles.
Three‐dimensional quantitative textural analysis of metamorphic rocks using high‐resolution computed X‐ray tomography: Part I. Methods and techniques
Authors: DENISON* C. , CARLSON† W. D. , KETCHAM R. A.
Published: October 2004

Macroscopic textures resulting from different atomic‐scale mechanisms for metamorphic crystallization display different degrees of order, clustering, intergrowth and relative isolation of porphyroblasts. Data on the sizes and locations of thousands of crystals in a three‐dimensional volume are required to identify reliably the mechanisms governing nucleation and growth of porphyroblasts from these textural features. These data can now be acquired by means of high‐resolution computed X‐ray tomography. Numerical models that simulate porphyroblast formation governed by either interface‐controlled or diffusion‐controlled reaction mechanisms indicate that quantitative textural analysis can discriminate between these possibilities. These numerical models also allow a comparison between textures predicted for different crystallization mechanisms and textures measured in natural samples, from which inferences can be drawn concerning the relative importance of these mechanisms in nature. An independent test of the validity of such inferences is possible for porphyroblasts such as garnet that may preserve prograde growth zoning and allow the examination of normalized radius–rate relations.
Interpretation of discordant U‐Pb zircon ages: An evaluation
Authors: MEZGER K. , KROGSTAD E. J.
Published: October 2004

The most widely used technique for the determination of high precision mineral growth ages in igneous and metamorphic rocks is dating of zircons with the U‐Pb method. The interpretation of these ages, particularly in metamorphic settings, is hampered by an incomplete understanding of the common phenomenon of partial Pb‐loss in zircon. In principle, this Pb‐loss may occur in four very different ways: diffusion in metamict zircon, diffusion in pristine zircon, leaching from metamict zircon and recrystallization of metamict zircon. Here it is argued that, under conditions common in the continental crust, Pb‐loss is only possible in partially to strongly metamict zircons. Pb‐diffusion in the pristine zircon lattice is insignificant up to temperatures of at least 1000 °C. Pb‐loss is only possible if the zircons experienced a time interval below their annealing temperature of about 600–650 °C, because only below this temperature can the lattice damage through α‐decay and spontaneous fission accumulate. Zircons that remain above this temperature do not lose Pb by diffusion and will stay closed systems. Complete resetting of the U‐Pb system in zircon under crustal conditions is only possible through dissolution and reprecipitation of zircon. Partial resetting results from recrystallization, leaching or diffusion in metamict zircon. As a consequence, special care has to be taken to interpret lower intercepts on concordia diagrams defined by discordant U‐Pb data. Lower intercept ages may be significant only if they are defined by zircons with low U‐content (<100 p.p.m.) or if confirmed by other geochronological methods. In addition, the accuracy of the lower intercept should be confirmed by abrading the zircon fractions that define the discordia.
Metamorphic convergence of the upper and lower plates of the Vincent thrust, San Gabriel Mountains, southern California, USA
Authors: JACOBSON C. E.
Published: October 2004

The Vincent thrust of the San Gabriel Mountains, southern California, separates eugeoclinal Pelona Schist from overlying Precambrian to Mesozoic igneous and metamorphic rocks of North American continental affinity. The thrust is generally considered to be synmetamorphic because of similarity in structural orientations and mineral assemblages between the Pelona Schist and mylonites at the base of the upper plate. In this study, compositions of calcic amphibole and plagioclase in the upper plate and structurally high Pelona Schist were compared to further test this interpretation. Amphibole in the schist is mostly actinolite to actinolitic hornblende with high Na/Al ratio, indicating relatively high‐P/low‐T  metamorphism. Individual grains are zoned, with concentrations of both Na and Al decreasing from cores to rims. Premylonitic amphibole in the upper plate is hornblende, tschermakite and pargasite with compositions indicative of low‐ or medium‐P metamorphism. During mylonitization, this amphibole was replaced by actinolite to actinolitic hornblende with a similar range of Na and Al as amphibole rims in the Pelona Schist, but with slightly lower Na/Al ratio. This is consistent with the decrease of Na/Al up‐section previously noted within the Pelona Schist of this area, and is considered to be the result of an inverted thermal gradient during thrusting. Convergence of composition between schist and upper plate also occurs for K and Ti contents of amphibole and An content of plagioclase. These features provide strong evidence that mylonitization of the upper plate is closely related in space and time to metamorphism of the Pelona Schist and therefore that the Vincent thrust is a remnant of the primary fault along which the Pelona Schist and correlative units were subducted beneath North America. Nonetheless, very fine‐scale differences in amphibole composition between the schist and upper plate may indicate that metamorphic re‐equilibration could not quite keep pace with movement on the fault.
Melting, carbonic fluids and water recycling in the deep crust: an example from the Limpopo Belt, South Africa
Authors: STEVENS G.
Published: October 2004

The proposed retrograde orthoamphibole isograd in the Southern Marginal Zone of the Limpopo Belt separates hydrated, amphibolite grade metapelites from their granulite grade precursors and provides an intriguing geological dilemma. Widespread rehydration of metapelitic granulites under conditions of 660–600 °C and ≥0.6 GPa, and CO2‐dominated fluid‐inclusion populations appear to suggest thorough flushing of the high‐grade crust with an externally derived carbonic fluid. However, past studies of the carbon and oxygen isotope geochemistry of the hydrated rocks have not demonstrated the involvement of any voluminous out of equilibrium’ fluid in the evolution of the rocks. This contribution proposes a model wherein the hydrating fluids are derived from crystallizing anatectic leucosomes, generated by in situ fluid‐absent biotite melting along the prograde path. Model equilibrium fluid compositions suggest that reaction between this melt‐derived H2O and biogenic graphite produced CO2‐rich fluid compositions and potentially high fluid:rock ratios at the wet granite solidus. Declining temperature resulted in fluid compositions shifting to higher XH2O, with the precipitation of graphite essentially at the sites of initial fluid generation, thereby preserving original (pre‐metamorphic) isotopic heterogeneities. The hydration pattern of the Southern Marginal Zone appears to be a function of melt migration. In the hydrated zone, leucosomes generally approximate minimum melt compositions and in this zone H2O was effectively recycled between the prograde and retrograde assemblages. In contrast, leucosomes in the granulite grade portion of the terrane have lost a K2O‐ and H2O‐rich melt fraction, and although some hydration has occurred in this zone, orthopyroxene is generally preserved in metapelites. In a general context, in situ crystallization of graphitic partially melted source rocks has the potential to produce high fluid‐rock ratios at temperatures close to the wet granite solidus. This single process holds the potential for widespread retrogression of formerly high‐grade assemblages, at a variety of aH2O values, without external fluid input.
The effect of Mn on mineral stability in metapelites
Authors: MAHAR E. M. , BAKER J. M. , POWELL R. , HOLLAND T. J. B. , HOWELL N.
Published: October 2004

Calculations based on a KMnFMASH petrogenetic grid derived using an internally consistent thermodynamic dataset indicate that the principal effect of the presence of Mn in average subaluminous pelite compositions is to stabilize garnet to higher and lower pressures and temperatures over a wide range of bulk compositions. Garnet‐bearing fields expand to lower temperatures and pressures with the addition of Mn, and garnet appears as an extra phase at low pressures. The addition of Mn also increases the number and extent of four AMnFM phase assemblages and stabilizes five AMnFM phases along univariant reactions. The KMnFMASH system predictions for typical subaluminous pelite bulk compositions match the sequence of isograds and assemblages observed in the Barrovian zones. The sequence of assemblages observed in the Stonehaven section can also be predicted if there is variation in bulk composition within the stratigraphic section. Mn appears to be less important in producing the sequence of isograds and garnet‐absent assemblages in the low‐pressure Buchan zones. The addition of Mn to the calculations does not change the sequence of isograds that are predicted to be stable in a regional metamorphic terrane, but the P–T position of these isograds does change. In particular, the predicted temperature of the garnet‐in isograd is lowered by as much as 100 °C by the addition of Mn to KFMASH. Mn also increases the range of metapelite bulk compositions that develop the assemblages traditionally identified as metapelite isograds.
Partial transformation of gabbro to coesite‐bearing eclogite from Yangkou, the Sulu terrane, eastern China
Authors: ZHANG R. Y. , LIOU J. G.
Published: October 2004

An ultra‐high‐pressure (UHP) metamorphic slab at Yangkou Beach near Qingdao in the Sulu region of China consists of blocks of eclogite facies metagabbro, metagranitoid, ultramafic rock and mylonitic orthogneisses enclosed in granitic gneiss. A gradational sequence from incipiently metamorphosed gabbro to completely recrystallized coesite eclogite formed at ultra‐high‐pressures was identified in a single 30 m block; metagabbro is preserved in the core whereas coesite eclogite occurs along the block margins. The metagabbro contains an igneous assemblage of Pl+Aug+Opx+Qtz+Bt+Ilm/Ti‐Mag; it shows relict magmatic textures and reaction coronas. Fine‐grained garnet developed along boundaries between plagioclase and other phases; primary plagioclase broke down to Ab+Ky+Ms+Zo±Grt±Amp. Augite is rimmed by sodic augite or omphacite, whereas orthopyroxene is rimmed by a corona of Cum±Act and Omp+Qtz layers or only Omp+Qtz. In transitional rocks, augite and orthopyroxene are totally replaced by omphacite, and the lower‐pressure assemblage Ab+Ky+Phn+Zo+Grt coexists with domains of Omp (Jd70–73)+Ky±Phn in pseudomorphs after plagioclase. Both massive and weakly deformed coesite‐bearing eclogites contain Omp+Ky+Grt+Phn+Coe/Qtz+Rt, and preserve a faint gabbroic texture. Coesite inclusions in garnet and omphacite exhibit limited conversion to palisade quartz; some intergranular coesite and quartz pseudomorphs after coesite also occur. Assemblages of the coronal stage, transitional and UHP peak occurred at about 540±50 °C at c. 13 kbar, 600–800 °C at ≥15–25 kbar and 800–850 °C at >30 kbar, respectively.

Garnet from the coronal‐ through the transitional‐ to the eclogite‐stage rocks show a decrease in almandine and an increase in grossular±pyrope components; garnet in low‐grade rocks contains higher MnO and lower pyrope components. The growth textures of garnet within pseudomorphs after plagioclase or along grain boundaries between plagioclase and other phases are complex; the application of garnet zoning to estimate P–T  should be carried out with caution. Some garnet enclosing quartz aggregates as inclusions shows radial growth boundaries; these quartz aggregates, as well as other primary and low‐P phases, persisted metastably at UHP conditions due to sluggish reactions resulting from the lack of fluid during prograde and retrograde P–T  evolution.
Thermobarometry of phengite‐bearing eclogites in the Dabie Mountains of central China
Authors: CARSWELL D. A. , O'BRIEN P. J. , WILSON R. N. , ZHAI M.
Published: October 2004

Pressure–temperature conditions for formation of the peak metamorphic mineral assemblages in phengite‐bearing eclogites from Dabieshan have been assessed through a consideration of Fe2+–Mg2+ partitioning between garnet–omphacite and garnet–phengite pairs and of the reaction equilibrium celadonite+pyrope+grossular=muscovite+diopside, which incorporates an evaluation of the extent of the strongly pressure‐dependent inverse Tschermak's molecule substitution in the phengites. For the latter equilibrium, the calibration and recommended activity–composition models indicated by Waters & Martin (1993) have been employed and importantly yield results consistent with petrographic evidence for the stability at peak conditions of coesite in certain samples and quartz in others.

Confirmation that in some phengite‐eclogite samples peak silicate mineral assemblages have equilibrated at confining pressures sufficient for the stability of coesite (and in some cases even diamond) rather negates previous suggestions that coesite may have been stabilized in only very localized, possibly just intracrystalline, domains. Inherent difficulties in the evaluation of peak metamorphic temperatures from Fe2+–Mg2+ partitioning between mineral phases, due to uncertainties over Fe3+/Fe2+ ratios in the minerals (especially omphacites), and to re‐equilibration during extensive retrograde overprinting in some samples, are also assessed and discussed.

Our results indicate the existence in south‐central Dabieshan of phengite eclogites with markedly different equilibration conditions within two structurally distinct tectonometamorphic terranes. Thus our data do not support earlier contentions that south‐central Dabieshan comprises a structurally coherent continental‐crust terrane with a regional P–T  gradient signalling previous deepest‐level subduction in the north. Instead, we recognize the Central Dabie ultra‐high‐pressure (coesite eclogite‐bearing) terrane to be structurally overlain by a Southern Dabie high‐pressure (quartz eclogite‐bearing) terrane at a major southerly dipping shear zone along which late orogenic extensional collapse appears to have eliminated at least 20 km of crustal section.
Evolution of 2:1 layered silicates in low‐grade metamorphosed Liassic shales of Central Switzerland
Authors: LIVI K. J. T. , VEBLEN D. R. , FERRY J. M. , FREY M.
Published: October 2004

White mica from the Liassic black shales and slates in Central Switzerland was analysed by transmission electron microscopy (TEM) and electron microprobe to determine its textural and compositional evolution during very low‐grade prograde metamorphism. Samples were studied from the diagenetic zone, anchizone and epizone (T ≈100°–450 °C). Phyllosilicate minerals analysed include illite/smectite (I/S), phengite, muscovite, brammallite, paragonite, margarite and glauconite. Textural evolution primarily is towards larger, more defect‐free grains with compositions that approach those of their respective end‐members. The smectite‐to‐illite transformation reduced the amounts of the exchange components SiK−1Al−1, MgSiAl−2, and Fe3+Al−1. These trends continue to a lesser degree in the anchizone and epizone. Correlations between the proportion of smectite in I/S and the composition of I/S indicate that smectite layers may contain a high layer charge. Illite in I/S bears a compositional resemblance to macrocrystalline phengite in some samples, but is different in others. Paragonite first appears in the upper diagenetic zone or lower anchizone as an interlayer‐deficient brammallite, and it may be mixed with muscovite on the nanometre scale. Owing to the small calculated structure factor for paragonite‐muscovite superstructures, conventional X‐ray powder diffraction cannot distinguish between mixed‐layer structures and a homogeneous compositionally intermediate solid solutions. However, indirect TEM evidence shows that irregularly shaped domains of Na‐ and K‐rich mica exist below 10 nm. Subsequent coarsening of domains at higher grades produced discrete paragonite grains at the margins of muscovite crystals or in laths parallel to the basal plane of the host muscovite. Margarite appears in the epizone and follows a textural evolution similar to paragonite in that mixtures of margarite, paragonite, and muscovite may initially occur on the nanometre scale. However, no evidence of interlayer‐poor margarite has been found.
Sm–Nd garnet dating of polyphase metamorphism: northern Coast Mountains, south‐eastern Alaska, USA
Authors: STOWELL H. H. , GOLDBERG S. A.
Published: October 2004

Sm–Nd ages of garnet from the northern Coast Mountains of south‐eastern Alaska, USA, constrain the timing of thermal events in polyphase metamorphic rocks of the western metamorphic belt and provide new data on the spatial extent of Cretaceous regional metamorphism. Bulk garnet–whole‐rock Sm–Nd ages for a sillimanite‐zone amphibolite (Taku Inlet) and a biotite‐zone metapelite (Tracy Arm) are 77±17 Ma and 59±12 Ma, respectively. Garnet core–whole‐rock (80±9 Ma), core–matrix (84±9 Ma), rim–whole‐rock (59±4 Ma) and rim–matrix (62±4 Ma) ages were obtained from a sample collected 200 m west of a Palaeocene Coast plutonic–metamorphic complex sill‐like pluton that separates medium‐grade metamorphic rocks from high‐grade metamorphic rocks and voluminous Tertiary plutons in the core of the orogen. The garnet core ages of c. 80 Ma indicate that the regional metamorphic grade reached garnet zone prior to the intrusion of the plutons and high‐grade metamorphism of rocks to the east. Similar ages for the younger plutons, the youngest garnets and the rim of a multistage garnet (c. 59 Ma) indicate a later episode of contact metamorphic garnet growth. Documentation of pre‐71 Ma garnet‐zone metamorphism along the western edge of the Coast plutonic–metamorphic complex confirms that Albian to Late Cretaceous metamorphism associated with crustal thickening affected this part of the orogen. The similarity of garnet Sm–Nd ages to independent age estimates for metamorphic events confirms that this technique provides useful estimates for the timing of Late Cretaceous to Tertiary thermal events. The c. 20 Myr difference between garnet core and rim ages suggests that the Sm–Nd isotope systematics of a single garnet grain can be used for distinguishing between multiple metamorphic events.
Disequilibrium for Ca during growth of pelitic garnet
Authors: CHERNOFF C. B. , CARLSON W. D.
Published: October 2004

Compositional zoning in hundreds of almandine‐rich garnets in amphibolite by facies micaceous quartzites from the Picuris Range, north‐central New Mexico USA, indicates that although Mn, Mg and Fe achieve chemical equilibrium at hand‐sample scale during garnet growth, Ca does not. Instead, Ca concentrations at the surface of growing garnets appear to depend strongly on kinetic factors that govern the local chemical environment, yielding disequilibrium for Ca at scales larger than the region immediately surrounding an individual porphyroblast.

Detailed zoning profiles were obtained for 371 garnet crystals in a small volume of a single sample of garnetiferous quartzite, and core analyses were made of 97 additional crystals. Each analysis was made on a section that passed precisely through the morphological centre of the crystal, located by means of 3‐D imagery from computed X‐ray tomography. The data reveal strong correlations between crystal size and concentrations of Mn, Mg and Fe (but not Ca) in garnet cores; a relationship between crystal size and isolation; rigorous cross‐correlations among concentrations of Mn, Mg and Fe (but not Ca); and systematic variations in Ca concentrations as a function of crystal size and core composition that are anomalous in comparison to the behaviour of the other divalent cations.

We interpret these observations as the result of thermally accelerated diffusion‐controlled garnet growth, in circumstances that promoted rapid intergranular diffusion and thus rock‐wide equilibration of Mn, Mg and Fe, but that prevented equilibration at similar scale for Ca because of its more sluggish intergranular diffusion. The anomalous behaviour of Ca is made evident in these garnets by the presence of sharp spikes in Ca concentration, which are demonstrably not a consequence of any simultaneous rock‐wide event, such as a change in pressure, temperature, or some other intensive parameter. Instead, Ca concentrations probably reflect the local extent of reaction in the immediate vicinity of each porphyroblast. To the degree that such kinetic factors introduce departures from chemical equilibrium for Ca, thermobarometric estimates that involve grossular contents of pelitic garnet will be in error.
Constraints on element mobility associated with the conversion of granulite to eclogite along fractures in an anorthositic complex on Holsnøy, Norway
Authors: ROCKOW K. M. , HASKIN L. A. , JOLLIFF * B. L. , FOUNTAIN D. M.
Published: October 2004

On Holsnøy, an island off the coast of Western Norway, an anorthositic complex metamorphosed to granulite facies was partially overprinted by a later eclogite facies metamorphism. Eclogite facies rocks (containing omphacite, garnet, kyanite and hydrous phases such as mica and zoisite) occur in shear zones of various scales and adjacent to veins. Previous studies of shear zones on Holsnøy reported evidence for substantial element mobility (Jamtveit et al., 1990; Mattey et al., 1994). In this work, we compare chemical compositions of granulite and its undeformed eclogitized equivalent adjacent to veins in locations where a single band of granulite can be traced and sampled as it approaches the vein. This tracing is crucial because the pre‐granulite rocks cover a substantial compositional range, indicative of a petrologically variable protolith consisting of anorthosite, gabbro and jotunite. We analysed multiple core samples collected across nine separate granulite‐eclogite transition zones located at veins in anorthositic, jotunitic and gabbroic protoliths for major and trace elements. For each transition, no compositional difference between the average granulite and average eclogite composition was found at the 90% confidence level except for LOI (loss on ignition), which was consistently significantly higher in the eclogite samples. Although not significant at the 90% confidence level for any single traverse, the average eclogite concentrations of SiO2 , Na2O, Cs, As and Br exceed the average granulite concentrations for eight or all nine of the traverses. For most traverses, statistical analysis of the data limits any gain of SiO2 in the eclogites to no more than a few relative per cent. Other than the introduction of volatile substances, presumably an H2O‐rich fluid, eclogitization associated with vein formation was essentially isochemical.
Mechanical controls on fluid flow during regional metamorphism: some numerical models
Authors: ORD A. , OLIVER N. H. S.
Published: October 2004

The control of fluid flow by plastic deformation during metamorphism is critical to our understanding of metamorphic processes. Various geological observations and field studies demonstrate the consequences of fluid flow control by deformation, so that the concept appears to be accepted, at least for small‐scale PUBLIC (for example faults and vein PUBLIC). However, the concept appears to be less well recognized at regional scales. Considered here are examples of simple, conceptual models based on fully coupled mechanical–fluid flow concepts; they include deformation of a section of fluid‐saturated crust containing a block or a layer of material of different properties from its surrounds. In particular, rheological and permeability contrasts between rock types during deformation associated with regional metamorphism are sufficient to control the form of fluid flow over the range of a few kilometres. Low contrasts and small strains allow pervasive fluid flow, whereas greater contrasts and increasing strains cause focusing of the flow. Such focusing is generally associated with localization of the deformation, especially for a strongly dilatant elastic–plastic material. However, a rate of fluid flow much greater than the rate of deformation may result in pervasive flow, although for most models pervasive flow is difficult to attain over regional distances. Furthermore, lateral and downward fluid flow may occur, demonstrated here by simple models for folding and for deformation of regions containing plutons. Therefore, such modelling may be used as a means of testing the various hypotheses concerning the volumes of fluid predicted to have passed through some rock volumes. Numerical models of the future will become increasingly complex and powerful, allowing greater coupling of thermal, mechanical, chemical and fluid flow effects, and based more on the physical processes involved. Combined field and laboratory studies will provide correspondingly greater understanding and will permit the determination of the timing of fluid flow and structural controls on fluid flow patterns.