A preliminary study on the climatic and environmental changes at the turn from pleistocene to holocene in East Asia

This paper examines the regional climatic and environmental changes from the late Pleistocene to middle Holocene in Central-East Asia. A review is made of the published literature that are specific to pelaeoclimate and physical environment in some geographical regions.It is shown that (1) during the late Pleistocene the annual mean temperature was 5°–6° C lower than present in Qinghai-Xizang (Tibet) plateau, 6° to 9° C lower than today in NE China, 6° C lower than today in E China, and 4° C lower than present in Taiwan island; (2) during the middle Holocene, the annual mean temperature was 4° C warmer than present in Qinghai-Xizang (Tibet) plateau, 3° to 4° C warmer than today in NE China, 2° to 3° C warmer than today in Shanghai area, and only 2° to 2.5° C warmer in Taiwan island.     

Petrology of metamorphic rocks of almandine-amphibolite facies in Saidapuram-Podalakuru area,Nellore district,Andhra Pradesh,India

Summary Precambrian amphibolites and quartz-mica schists in the Saidapuram-Podalakuru area fall within the almandine-amphibolite facies of regional metamorphism. The analysed rocks represent metamorphosed basic igneous rocks. It is suggested that the quartz-muscovite-staurolite schists underwent metamorphism between 550° and 700° C at an average pressure of 7.2 kb; the quartz-muscovite (±biotite), hornblende-biotite (±garnet), and hornblende-garnet schists between 600°–700° C/7.5 kb; and the quartz-biotitekyanite schists between 650°–700° C/8 kb.

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Petrologie der metamorphen Gesteine in Almandin-Amphibolit-Fazies im Gebiet von Saidapuram-Podalakuru, Distrikt Nellore, Andhra Pradesh, Indien

Zusammenfassung Präkambrische Amphibolite und Quarz-Glimmer-Schiefer im Gebiet von Saidapuram-Podalakuru gehören der Almandin-Amphibolit-Fazies an. Die analysierten Gesteine stellen metamorphe basische Erstarrungsgesteine dar. Die Quarz-Muskovit-Staurolith-Schiefer wurden bei 550°–700°C und einem durchschnittlichen Druck von 7,2 kb metamorph, die Quarz-Muskovit-(±Biotit-), die Hornblende-Biotit- (±Granat-) und die Hornblende-Granat-Schiefer bei 600°–700° C/7,5 kb, die Quarz-Cyanit-Schiefer bei 650°–700° C/8 kb.

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With 6 Figures     

Palaeomagnetic results on the Deccan trap lavas of the Aurangabad region and their tectonic significance

Detailed palaeomagnetic measurements have been carried out on a 600 m sequence of Deccan trap lava flows sampled in a 300 km long, NW-SE traverse through the trap country between Aurangabad (19°51′N 75°16′E) and Diglur town (19°48′N 77°36′E) which is located on the eastern margin of the traps. From 28 basalt flows between altitudes of 344 m to 927 m were collected 175 oriented block samples. Stable remanent magnetic directions obtained after alternating field demagnetisation tests indicate that all the lava flows are reversely magnetised. The mean value for the remanent directions was found to be: azimuth 150° and inclination 48° downwards; the palaeomagnetic pole position corresponding to this direction is 33°N 73°W.     

Evaluation of rock slope stability for Yujian River dam site by kinematic and block theory analyses

Lithological information, rock mass fracture data and discontinuity shear strength obtained through field investigations have been used to conduct kinematic and block theory analyses for the rock slopes that exist in the dam site to evaluate the stability of the slopes. The analyses were performed using mean discontinuity set orientations for each rock mass region under gravitational loading to calculate the maximum safe slope angles (MSSA) for different cut slope directions. Results show that final MSSAs obtained from kinematic analysis are less than or equal to that obtained from block theory analysis. The following conclusions have been made based on the block theory analysis results, which are closer to the reality: (1) The final MSSA range between 30° and 47°, 44° and 70°, 47° and 69° for cut slope dip directions of 20–30°, 105–210°, and 270–355°, respectively; (2) For cut slope dip directions of 20–30°, 200–210° and 275–315°, wide ranges of values have been obtained for the final MSSA reflecting the influence of variability of fracture orientations on MSSA; (3) Apart from the region R-d-1 for slope dip directions in the range 20–30°, rest of the regions at the dam site seem to be stable for slope angles less than 40°. Detailed comparisons are given between the kinematic and block theory analyses covering both the theoretical concepts and application results. Also a brief comparison is included between the laboratory and in situ discontinuity shear strength results.     

Hydrothermal environments during the genesis of silver deposits in the Northwest Territories of Canada: Evidence from fluid inclusions

The Ag-Ni-Co-Bi-As-U veins in the Northwest Territories of Canada are hosted by volcano-sedimentary and intrusive rocks of the Great Bear Batholithic Complex. Fluid inclusion data from the gangue minerals of the veins suggest a wide range in salinity and temperature for the hydrothermal fluids. The salinities of the fluids range from about 15 to 35 wt.% NaCl equivalent. The homogenization temperatures range from 150° to 250°C for stage I fluids; 220° to 480°C for stage II fluids; 250° to 350°C for stage III fluids; 150° to 250°C for stage IV fluids and 90° to 250°C for stage V fluids. The coexistence of liquid-rich and vapour-rich inclusions in stages II and III minerals suggest that the hydrothermal fluids were boiling or effervescing. The coexistence of saturated and unsaturated inclusions in stages II and III minerals may be due to effervescence of a less saline fluid, whilst for stages IV and V it may be due to mixing of a highly saline fluid with a less saline fluid, or due to alternation of hydrostatic and lithostatic pressures at the time of trapping of the inclusions.     

Composition of arsenopyrite from topaz greisen veins in southeastern Missouri

Arsenopyrite occurs in greisen-sulfide veins hosted by unmetamorphosed Precambrian granite and rhyolite in the Silver Mine district of southeastern Missouri, Greisenization and sulfide mineralization appear to have been a continuous depositional sequence which recorded falling temperature in a near-surface vein environment. Textural criteria imply that equilibrium existed between arsenopyrite and pyrite and that this pair crystallized in an intermediate paragenetic position between the greisen and hydrothermal stages. Thirty-eight electron microprobe spot analyses of 15 arsenopyrite crystals from the Einstein and Gabriel veins failed to disclose chemical zoning of As/S. The compositional range of the analyzed arsenopyrites is 32. 9 to 31. 0 atomic % As. A range of arsenopyrite crystallization temperature from 485°C (±15°) to 455°C (±15°) is indicated for the Gabriel vein. In contrast, arsenopyrites from the Einstein vein record a lower and broader crystallization range of 440°C (±15°) to 368°C (±15°).     

Palaeomagnetism of three dyke swarms in Nansen Land,north Greenland (83° N)

Three basic dyke swarms of post-Ellesmerian (post-Early Carboniferous) age in Nansen Land (83° N, 43° W) are still not dated numerically, but cross-cutting relationships show Group 1 to be older than Group 2, while Group 3 is the freshest and likely the youngest. Group 1 (the most northerly swarm) strikes N-S; Group 2 NW-SE, and Group 3 (the most southerly swarm) E-W. From more than 200 dykes 234 specimens from 28 sites were investigated palaeomagnetically. Group 1 dykes show unexpected shallow inclinations with a cleaned mean direction of (Dm, Im) = (151°, –5.8°), N = 7, k = 18.5, ₉₅ = 13.9°. They show hydrothermal alterations, some remagnetization by lightning, and the low inclination indicates a low palaeo latitude. The palaeopole is (Plat, Plon) = (8.9° S, 14.0° W) with (dp, dm) = (7°, 14°), and is close to the North American Early Carboniferous mean pole, suggesting a syn- or early late-tectonic dyke injection. The polarity is reverse. Groups 2 and 3 of presumed Cretaceous or Tertiary age show dominantly normal and reverse polarities, respectively. Their mean directions per polarity are well grouped, with (Dm, Im) = (–30.6°, 76.7°), n = 13, k = 191.4, ₉₅ = 3.9°, and (Dm, Im) = (133.4°, –76.7°), n = 10, k = 87.5, ₉₅ = 5.9°, respectively. They are antipodal within 95% significance, and combining both swarms gives (Dm, Im) = (–37.5°, 76.8°), n = 23, k = 124.3, ₉₅ = 2.7°, corresponding to a mean pole of (Plat, Plon) = (70.0° N, 185.1° E) with (dp, dm) = (4.7°, 5.0°), for which the spline of Late Cretaceous-Tertiary poles for all Greenland indicates a palaeomagnetic age of 57 ± 10 Ma. This pole (in present-day coordinates) is very close to the Late Cretaceous North American pole, in accordance with the fact that Greenland belongs to the North American craton, and that the two younger swarms are essentially postdating the opening of Baffin Bay.     

Cordierite breakdown under high-pressure hydrous conditions

Green and Vernon (1974) have experimentally determined a divariant field of cordierite-orthoamphibole-kyanite-quartz with a slope of 12±4 bars per °C occurring between 8.0 and 10.4 kbar at 750° C and between 9.5 and 11.3 kbar at 850° C. However, the writers' thermodynamic calculation of the divariant band indicates a more limited range of 0.65 and 0.7 kbar at 750° C and 850° C respectively, with an estimated error of ±0.2 kbar.     

Exsolution in the mss-pentlandite system: Textural and genetic implications for Ni-sulfide ores

Experimentation in synthetic systems is essential for a correct interpretation of ore-mineral textures such as the pyrrhotite-pentlandite (po-pn) intergrowths of Ni-sulfide deposits. Within the Fe-Ni-S system, isothermal and cooling exsolution experiments were performed on monosulfide solid solution (mss) of various compositions using sealed, evacuated silica-glass tubes. The charges were annealed between 400° and 200°C for periods ranging from 20 minutes to 5 weeks; also, charges were cooled from 500° to 100°C at 1°C/h. Early-formed isothermal textures form by nucleation and growth, and depend on the initial degree of supersaturation and metal diffusivities; the final textures result from further growth and coarsening of the early forms and are particularly sensitive to the diffusivities, which are a function of temperature. The cooling-rate experiments indicate that massive pn develops by exsolution between 610° and about 250°C during slow cooling from temperatures above the mss-pn solvus; coarsened pn forms along basal planes in the mss matrix between about 250° and 150°C; pn "Flames" result at 150°C or slightly below. Crossing pn lamellae, obtained isothermally at high degrees of supersaturation and virtually unknown in ores, cannot form during slow cooling.     

A differential thermal analysis study of the high-temperature polymorphism of calcite at high pressure

A DTA-investigation has been conducted in the stable field of calcite between 8 to 45 kb and 400 to 1300 ° C. Two high temperature transitions of calcite with moderate pressure dependency were encountered in the temperature range of 700 to 800 ° C and around 1,000 ° C. In addition the calcite-aragonite transition was reexamined between 10 to 45 kb and two triple points were located at 720±20 ° C/18±1 kb and at 1,030±20 ° C/31 ± 1kb.     

Palaeomagnetism of late Cretaceous sediments from southern Tibet: Evidence for the consistent palaeolatitudes of the southern margin of Eurasia prior to the collision with India

Twenty sites were drilled in the late Cretaceous Shexing Formation for palaeomagnetic studies in the Lhasa terrane near the locality of Maxiang (29.9°N/90.7°E). The stepwise thermal demagnetizations successfully isolated high unblocking temperature characteristic directions. The tilt-corrected mean direction is D/I = 350.8°/32.1° with α₉₅ = 8.1° and N = 20 sites, corresponding to a paleopole at 75.0°N, 306.7°E with A₉₅ = 6.8°. Positive fold tests indicate a primary origin for the characteristic remanence. Based on previous Cretaceous data mainly from the Takena Formation and Paleocene data from the Linzizong volcanic rocks near the city of Lhasa, the latitude of the southern margin of Asia is located at about 15°N, and yields a stable position of the Lhasa terrane during Cretaceous and Paleocene. Compared with expected paleomagnetic directions from the stable India and Eurasia blocks, the collision palaeolatitude further implies the total latitudinal convergence was accommodated by 1700 ± 800 km (16.2 ± 7.6°) between southern Tibet and stable Eurasia and 1500 ± 830 km (14.4 ± 7.9°) between southern Tibet and stable India since the collision of India and Eurasia. A collision age between c. 54 and 47 Ma was determined using the results for the southern margin of Eurasia according to our new data and the extent of ‘Greater India’.     

Kyanite-andalusite equilibrium

The solubilities of macrocrystalline andalusite and kyanite have been measured in water between 400 and 550 °C and at pressures of 1–3 kilobars. Resulting data indicate that the phases are in equilibrium at 398 °C (1 kb,), 472 °C (2 kb) and 534 °C (3 kb). Due to the inherent difficulty of measuring small solubility differences errors in these temperatures could be as much as ±40 °C although experimental reproducibility suggests greater precision.     

Experimental studies on the phase systems Fe-Ni-Pd-S and Fe-Pt-Pd-As-S applied to PGE deposits

Summary In the present paper current results of experimental investigation of the phase system Pd-Fe-Ni-S at 900°C, 725°C, 550°C and 400°C as well as of the phase system Pt-Fe-As-S at 850°C and 470°C are summarized. A preliminary note on the system Pt-Pd-As-S is added. Individual phase assemblages are presented, data on solubility of PGE in base metal sulphides/arsenides or alloys are given and solid solution ranges of important minerals are described as a function of temperature and phase assemblage. The extent and role of sulphide/arsenide melts in these systems are presented together with hints for, and examples of the application of the current experimental results for the explanation of ore-geological processes.

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Bisherige Ergebnisse experimenteller Untersuchungen in den Systemen Fe-Ni-Pd-S und Fe-Pt-Pd-As-S und ihre Bedeutung für Lagerstätten der Platin-Gruppen-Elemente

Zusammenfassung In der vorliegenden Arbeit werden bisherige Ergebnisse experimenteller Untersuchungen in den Phasensystemen Pd-Fe-Ni-S bei 900°C, 725°C, 550°C sowie 400°C, bzw. Pt-Fe-As-S bei 850°C und 470°C zusammengefasst. Vorläufige Anmerkungen zum System Pt-Pd-As-S werden gegeben. Die Phasenbeziehungen und die Löslichkeitsdaten von PGE's in Buntmetall-Sulfiden/Arseniden sowie deren Verbindungen werden präsentiert. Die Mischungsbereiche der wichtigsten Minerale werden als Funktion von Temperatur und Phasenvergesellschaftung diskutiert. Die Rolle von Sulfid/Arsenid Schmelzen in diesen Systemen und Beispiele für die Anwendung dieser experimentellen Ergebnisse zur Erklärung lagerstättenkundlicher Prozesse werden beschrieben.

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With 6 Figures     

Fluid inclusion study of Xihuashan tungsten deposit in the southern Jiangxi province,China

The Xihuashan tungsten deposit is closely related to a small highly evolved granitic intrusion. The fluid phases associated with the wolframite-bearing quartz veins have been investigated using microthermometry and the Raman microprobe; they are highly variable in density and composition. The earlier fluids are low-density and low-salinity CO₂-bearing aqueous solutions circulating at temperatures up to 420 °C, and low-salinity (2–3 equiv. wt% NaCl) aqueous solutions without traces of CO₂ circulating at high temperatures 280°–400 °C) involved in a specific hydrothermal fracturing event; limited unmixing occurs at 380 °C and 200–100 bar in response to a sudden pressure drop. The second types of fluids related to deposition of idiomorphic drusy quartz are typical CO₂-bearing aqueous solutions with low salinity (2.5 equiv. wt% NaCl) homogenizing at low to moderate temperatures (180°–340 °C). The late fluids characterize the sulfide deposition stage; they are aqueous fluids with variable salinities homogenizing in the liquid phase between 100° and 275 °C. The Xihuashan hydrothermal evolution resulted from a discontinuous sequence of specific events occurring between 420° and 150 °C and during a continuous hydrothermal evolution of the system during cooling. The role played by the CO₂-rich fluids in the transport and deposition of tungsten in the hydrothermal environment is discussed.     

Phase relations and mineral assemblages in the Ag-Bi-Pb-S system

Phase relations within the Ag-Bi-S, Bi-Pb-S, and Ag-Pb-S systems have been determined in evacuated silica tube experiments. Integration of experimental data from these systems has permitted examination and extrapolation of phase relations within the Ag-Bi-Pb-S quaternary system. — In the Ag-Bi-S system liquid immiscibility fields exist in the metal-rich portion above 597±3°C and in the sulfur-rich portion above 563±3°C. Ternary phases present correspond to matildite (AgBiS₂) and pavonite (AgBi₃S₅). Throughout the temperature range 802±2°C to 343±2°C the assemblage argentite (Ag₂S) + bismuth-rich liquid is stable; below 343°C this assemblage is replaced by the assemblage silver + matildite. — Five ternary phases are stable on the PbS-Bi₂S₃ join above 400°C — phase II (18 mol-% Bi₂S₃), phase III (27 mol-% Bi₂S₃), cosalite (33.3 mol-% Bi₂S₃), phase IV (51 mol-% Bi₂S₃), and phase V (65 mol-% Bi₂S₃). Phase IV corresponds to the mineral galenobismutite and is stable below 750±3°C. Phases II, III, and V do not occur as minerals, but typical lamellar and myrmekitic textures commonly observed among the Pb-Bi sulfosalts and galena evidence their previous existence in ores. Phase II and III are stable from 829±6°C and 816±6°C, respectively, to below 200°C; Phase V, stable only between 730±5°C and 680±5°C in the pure Bi-Pb-S system is stabilized to 625±5°C by the presence of 2% Ag₂S. Experiments conducted with natural cosalites suggest that this phase is stable only below 425±25°C in the presence of vapor. — In the Ag-Pb-S system the silver-galena assemblage is stable below 784±2°C, whereas the argentite + galena mineral pair is stable below 605±5°C. — Solid solution between matildite and galena is complete above 215±15°C; below this temperature characteristic Widmanstätten structure-like textures are formed through exsolution. Schematic phase relations within the quaternary system are presented at 1050°C, at 400°C, and at low temperature.

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Zusammenfassung Die Phasenbeziehungen in den Systemen Ag-Bi-S, Bi-Pb-S und Ag-Pb-S wurden durch Versuche in evakuierten Quarzglasröhrchen bestimmt. Die Auswertung aller experimentellen Daten gestattete eine Extrapolation der Phasenbeziehungen im quaternären System Ag-Bi-Pb-S. — Im System Ag-Bi-S besteht ein Zwei-Schemlzenfeld im metallreichen Teil über 597±3°C und im schwefelreichen Teil über 563±3°C. Die ternären Phasen entsprechen den Mineralien Schapbachit (AgBiS₂) und Pavonit (AgBi₃S₅). Zwischen 802±2°C und 343±2°C ist die Paragenese Silberglanz (Ag₂S) + Bi-reiche Schmelze stabil; unterhalb 343°C wird sie jedoch ersetzt durch die Paragenese Silber + Schapbachit. — Fünf ternäre Phasen sind stabil im Schnitt PbS-Bi₂S₃ oberhalb von 400°C: Phase II (18 Mol-% Bi₂S₃), Phase III (27 Mol-% Bi₂S₃), Cosalite (33.3 Mol-% Bi₂S₃), Phase IV (51 Mol-% Bi₂S₃) und Phase V (65 Mol-% Bi₂S₃). Phase IV entspricht dem Mineral Galenobismutit und ist stabil unterhalb 750±3°C. Die Phasen II, III und V kommen zwar nicht in der Natur vor, jedoch weisen typische myrmekitische und lamellare Gefüge, die man häufig in Pb-Bi-Sulfosalzen und deren Verwachsungen mit Bleiglanz beobachtet, auf die ehemalige Existenz solcher Phasen in diesen Erzen hin. Die Phasen II und III sind stabil von 829±6°C bzw. 816±6°C bis unter 200°C. Die Phase V, die im reinen System Bi-Pb-S zwischen 730±5°C und 680±5°C auftritt, wird in Gegenwart von 2% Ag₂S stabilisiert bis herab zu 625±5°C. Versuche mit natürlichen Cosaliten lassen darauf schließen, daß diese Phase nur unterhalb 425±25°C in Gegenwart einer Gasphase stabil ist. — Im System Ag-Pb-S ist die Paragenese Silber-Bleiglanz unterhalb von 784±2°C stabil, die Paragenese Silberglanz-Bleiglanz dagegen unterhalb 605±5°C. — Die Mischkristallreihe von Schapbachit und Bleiglanz ist vollständig oberhalb 215±15°C; unterhalb dieser Temperatur entstehen charakteristische Entmischungsgefüge ähnlich den Widmannstättenschen Figuren. Für das quaternäre System werden schematische Phasenbeziehungen für 1050°C, 400°C und eine noch tiefere Temperatur gegeben.

     

Geology and geothermometry of vein-type W-Sn deposits at Pennaichaung and Yetkanzintaung Prospects,Tavoy Township,Tennasserim Division,southern Burma

The Pennaichaung and Yetkanzintaung W-Sn Prospects are located in Tavoy Township, Tennasserim Division, southern Burma. The W-Sn mineralization at the Pennaichaung is closely related with a small, satellitic granitoid pluton of presumably Late Mesozoic age, which intruded the metaclastic rocks of Mergui Group (mostly Carboniferous). The mineralized quartz veins at the Pennaichaung penetrated the granitoid-metasedimentary rocks contact. In contrary to the Pennaichaung deposit, the W-Sn veins at the Yetkanzintaung are exclusively in the metasedimentary rocks of slates and quartzites of Margui Group. Mineralized quartz veins in the Pennaichaung area trend NNE-SSW, NW-SE and NE-SW with a maximum thickness of 30 cm, but only quartz veins trending NNE-SSW are found to be productive and contained economically workable wolframite and cassiterite. Majority of the mineralized quartz veins in the Yetkanzintaung area trend approximately N-S with easterly dip of 50°–70°. The thickness of the ore veins in the Yetkanzintaung area are thinner than those of the Pennaichaung and range from 1 cm to 20 cm with an average width of 5 cm. Fluid inclusion studies of the quartz from the ore veins cutting the granitoid in the Pennaichaung area have yielded a filling temperature range of 170°–270°C with a maximum mode of 220°C, while quartz crystals from the ore veins in the nearby metasedimentary rocks gave a filling temperature range of 140°–220°C with a maximum mode of 160°C. Hence, the Pennaichaung deposit was thought to have emplaced under a filling temperature range of 140°–270°C. A similar low filling temperature range was recorded for the Yetkanzintaung deposit. Quartz from the Yetkanzintaung ore veins have yielded filling temperatures of 200°–240°C, whereas the fluorites associated with the mineralized quartz veins gave a temperature range of 140°–160°C. Limited freezing runs indicate a salinity of less than 5 NaCl equivalent weight percent for inclusions in quartz from both orebodies. No fluid inclusion evidence of boiling of ore fluids nor presence of liquid CO₂ was observed in this study. Thus, the ore fluids responsible for the W-Sn mineralization at the Pennaichaung and Yetkanzintaung areas were of low temperature, diluted, CO₂-deficient, NaCl brines.     

Stability of pyrope-quartz in the system MgO-Al2O3-SiO2

Pyrope and quartz are stable with respect to aluminous enstatite and sillimanite at 1400 °C, 20 kb and at 1100 °C, 16 kb. The phase boundary limiting the coexistence of pyrope and quartz towards lower pressures is probably slightly curved. A slope of 15 bars/°C at 1400° and of 10 bars/°C at 1000 °C has been estimated from the experimental data. Between 1050 and 1100 °C the curve is intersected by the kyanite-sillimanite phase boundary. The calculated slope of the reaction aluminous enstatite + kyanite pyrope + quartz is negative (ca. 18–25 bars/°C). The existence of a negative slope has been demonstrated experimentally. Experimental evidence indicates that the assemblage aluminous enstatite and sillimanite is metastable with respect to sapphirine + quartz at high temperature. The invariant point involving the phases pyrope-sapphirine-aluminous enstatite-sillimanite-quartz is estimated to occur at 1125°±25 °C and 16±1 kb. A model phase diagram for the silicasaturated part of the system MgO-Al₂O₃-SiO₂ has been constructed. The position of three invariant points in this system has been estimated on the basis of presently available data.     

The calcite-aragonite transition,reinvestigated

The calcite-aragonite equilibrium has been investigated between 200 and 600° C both in a carefully calibrated hydrothermal apparatus and in a piston-cylinder device of high precision. The equilibrium pressure is 5 kb at 180° C, 7 kb at 300° C, 9 kb at 400° C, and 11 kb at 480° C.The calcite-aragonite transition boundary which has been bracketed is continuously curved between 300 and 500° C and is more or less straight above and below this temperature range. It is shown that the calcite I-calcite II reaction is probably a second (and not a first) order transition.The experimental result shows that aragonite may already be formed out of calcite at a depth of 15 km if the temperature is not much higher than 100° C. The calcitearagonite and the albite-jadeite-quartz curves intersect at about 750° C and 20 kb. There is a P-T-field (up to 3.5 kb broad) where aragonite and albite coexist.     

The Cu-Se system

Phase-relations in the Cu-Se system were determined by evacuated silica-tube experiments. The phase diagram up to 1100° C was obtained from the results of differential thermal analyses of pure compounds and of their mixtures. The phases in the system are: Cu₂Se — undergoes a polymorphic transformation at 150° C. The symmetry of the low temperature form is not yet known. The high form is cubic with a fluorite-type structure. Cu_2–xSe — cubic, with x variable in a very narrow range, at room temperature. Cu₃Se₂ — tetragonal, breaks down to Cu_2–xSe and CuSe at 150° C. CuSe — hexagonal below 60° C and, presumably, orthorhombic at higher temperature, melts incongruently at 387° C to Cu_2–xSe and a Se-rich liquid. CuSe₂ — orthorhombic, melts incongruently at 347° C to CuSe and a Se-rich liquid. The presence of an eutectic at 523° C was inferred from differential thermal heating and cooling curves.

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Zusammenfassung Die Phasenbeziehungen im Cu-Se System wurden durch Versuche mit Hilfe evakuierter Quarzampullen bestimmt. Bis zu 1100° C wurden die Ergebnisse der Differential-Thermoanalyse verwendet. Die Phasen im System sind: Cu₂Se: wandelt sich bei 150° C polymorph um. Die Symmetrie der Tieftemperaturform ist noch nicht bekannt, während die Hochtemperaturform kubisch ist (Flusspatstruktur). Cu_2–xSe (kubisch) hat bei Raumtemperatur einen sehr kleinen x-Wert. Cu₃Se₂ (tetragonal) spaltet sich bei 150° C zu Cu_2–xSe und CuSe. CuSe (hexagonal) ist unterhalb 60° C vermutlich rhombisch und bei höherer Temperatur (387° C) zersetzt es sich inkongruent zu Cu_2–xSe und einer Se-reichen Schmelze. CuSe₂ (rhombisch) zersetzt sich bei 347° C inkongruent zu CuSe und einer Se-reichen Schmelze. Die Anwesenheit eines Eutektikum bei 523° C wird aufgrund von DTA-Analysen angenommen.

     

上海黏土强度特性真三轴试验研究

利用自主改造的、大主应力与小主应力方向由刚性加压板加载、中主应力方向由围压室液压加载的自动控制刚柔复合真三轴仪,对上海原状软土进行同一π面上不同洛德角真三轴固结排水剪切试验。原状土样通过分块抽样法获取,共进行了5组不同洛德角（0°、15°、30°、45°和60°）排水剪切试验。试验结果显示,上海原状软土抗剪强度、屈服和破坏点位置随洛德角的增大而减小,体积变化量先增大后减小。三向应力状态下上海软土的破坏强度接近空间滑移面（SMP）破坏准则。