Kumamotoa, an early Late Cretaceous non-marine bivalve, from Fujian, south China     

Chen Jin-Hua  Toshifumi Komatsu  Cao Mei-Zhen  Frank Stiller 《Journal of Asian Earth Sciences》2006,27(6):943-951

The non-marine bivalve species Trigonioides (Kumamotoa) quadratus Gu and Ma is described from the Fourth Member of the Hekou Formation in western Fujian, southeastern China. This species previously was regarded to belong to the subgenus Trigonioides (s.s.), which is restricted to the Early Cretaceous. Herein, it is included into the subgenus Kumamotoa. It is compared to Cenomanian (early Late Cretaceous) species from Japan and Korea such as Trigonioides (Kumamotoa) mifunensis Tamura, Trigonioides (Kumamotoa) matsumotoi Kobayashi and Suzuki and Trigonioides (Kumamotoa) paucisulcatus Suzuki. The age of the Fourth Member of the Hekou Formation is discussed.  相似文献   

Permo-Carboniferous Radiolarians from the Wupata＇erkan Group, Western South Tianshan, Xinjiang, China   总被引：1，自引：0，他引：1  

LIYuejun SUNLongde WUHaoruo ZHANGGuangya WANGGuolin HUANGZhibin 《《地质学报》英文版》2005,79(1):16-23

The Wupata‘erkan Group, also called Wupata‘erkan Formation, distributed in the South Tianshan, Xinjiang,China, mainly consists of gray and dark gray fine-grained clastic rocks, interlayered with volcanic rocks, carbonates and cherts. Some ultra-basic rocks (blocks) punctuate the formation. The formation was variously assigned to Silurian-Middle Devonian, Silurian-Lower Devonian, and pre-Devonian, mainly based on Atrypa bodini Mansuy, Hypothyridina parallelepipedia (Brour.) and Prismatophyllum hexagonum Yoh collected from the limestone interlayers, respectively.However, radiolarian fossils obtained from 24 chert specimens of the Wupata‘erkan Group, mainly include Albaillella sp.cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon, Albaillella sp. cf. A. indensis Won, Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto, Albaillella sp. and Latentifistulidae gen. et. sp.indet., are earliest Carboniferous and Late Permian. The earliest Carboniferous assemblage is characterized by Albaillella sp. cf. A. undulata Deflandre, Albaillella sp. cf. A. paradoxa Deflandre, Albaillella cf. A. deflandrei Gourmelon and Albaillella sp. cf. A. indensis Won, and the Late Permian assemblage by Albaillella sp. cf. A. excelsa Ishiga, Kito and Imoto. This new stratigraphic evidence indicates that the Wupata‘erkan Group is possibly composed of rocks with different ages from Silurian to Permian, and therefore, it is probably an ophiolite mrlange. The discovery of Late Permian Albaillella sp. cf. A. excelsa provides more reliable evidence supporting the existence of a Permian relic ancient oceanic basin in the western part of Xinjiang South Tianshan.  相似文献   

Vegetation,climate, and fire during the late-glacial–Holocene transition at Spruce Pond,Hudson Highlands,southeastern New York,USA     

TERRYANNE E. MAENZA-GMELCH 《第四纪科学杂志》1997,12(1):15-24

Pollen, plant macrofossil, and charcoal records from Spruce Pond (41°14′22″N, 74°12′15″W), southeastern New York, USA dated by AMS provide details about late-glacial–early Holocene vegetation development in the Hudson Highlands from >12410 to 9750 ¹⁴C yr BP. Prior to 12410 yr BP, vegetation was apparently open, dominated by herbs and shrubs (Cyperaceae, Gramineae, Tubuliflorae, Salix, Alnus, Betula), possibly with scattered trees (Picea and Pinus). However, Picea macrofossils are not found until 12410 yr BP. Development of a temperature deciduous–boreal-coniferous forest featuring Quercus, Fraxinus, Ostrya/Carpinus, Pinus, Picea, and Abies occurs between 12410 and 11140 yr BP. A return of predominantly boreal forest taxa between 11140 and 10230 yr BP is interpreted as an expression of the Younger Dryas cooling event. Holocene warming at 10230 yr BP is signalled by arrival of Pinus strobus, coincident with expansion of Quercus-dominated forest. Fire activity, as inferred from charcoal influx, appears to have increased as woodland developed after 12410 yr BP. Two charcoal influx peaks occur during Younger Dryas time. Early Holocene fire activity was relatively high but decreased for approximately 100 yr prior to the establishment of Tsuga canadensis in the forest at 9750 yr BP. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Palynodating of subsurface sediments,Raniganj Coalfield,Damodar Basin,West Bengal   总被引：1，自引：0，他引：1  

Srikanta Murthy  B. Chakraborti  M. D. Roy 《Journal of Earth System Science》2010,119(5):701-710

The Gondwana sediments comprising fine-grained shales, carbonaceous shales, sandstones and the coal horizon in borecore RT-4 (approximately 547.00m thick) from Tamra block, Raniganj Coalfield, Damodar Basin, are analyzed palynologically. Based on the distribution pattern of marker palynotaxa, two assemblage zones are identified. In the Barren Measures Formation, dominance of enveloping monosaccate (Densipollenites) along with striate bisaccate (Striatopodocarpites, Faunipollenites) pollen taxa, and the FAD’s of Kamthisaccites and Arcuatipollenites observed at 30.75, have equated this strata (30.75–227.80 m thick) with the Raniganj Formation of Late Permian in age. Downwards in the Barakar Formation, between 423.80–577.70 m depths, an abundance of non-striate (Scheuringipollenites) and striate (Faunipollenites and Striatopodocarpites) bisaccate pollen taxa is observed, that dates late Early Permian in age.  相似文献   

Succession,palaeoecology, evolution,and speciation of Pennsylvanian non‐marine bivalves,Northern Appalachian Basin,USA     

R. M. C. Eagar  E. S. Belt 《Geological Journal》2003,38(2):109-143

Seventeen horizons of non‐marine bivalves are described within the Appalachian succession from the base of the Pottsville Group of Westphalian A‐B age to the Uniontown coal of Stephanian C age at the top of the Carboniferous System. A new highly variable fauna of Anthraconaia from the roof shales of the Upper Freeport coal near Kempton, west Maryland, dates from late Westphalian D or very early Cantabrian time, on the evidence of non‐marine shells and megafloras. Below this horizon, the Appalachian sequence reveals zones of Anthraconauta phillipsii and Anthraconauta tenuis in the same order as in Britain, whereas faunas of Anthraconaia of these zones are less common and differ from those of Britain. In all horizons above the Upper Freeport coal all non‐marine bivalve faunas consist of stages in the sequences of two natural species, the groups of Anthraconaia prolifera and Anthraconaia puella‐saravana. The first shows evidence of having lived in well‐oxygenated, probably shallow, fresh water conditions of relatively wide extent. The second group lived preferentially in a plant‐rich environment of relatively stagnant fresh water. Both groups are found in horizons associated with coal seams and may be seen together in the same habitats, but diagrams of variation (pictographs) suggest that there was no interbreeding between the two groups in either the Northern Appalachians or in southern Germany where the species split was first recognized. In the northern Spanish coalfields of Guardo‐Valderrueda and Central Asturia, facies evidence suggests how an initial split may have taken place in the same morphological directions and into the same palaeoenvironments as the later split into two species. Appalachian deposition was generally slow and intermittent with frequent palaeosols. There is also evidence of erosion and of small palaeontological breaks in the sequence, especially near the eastern edge of the Northern Appalachian Basin in western Maryland. The amount of accumulated sediment was less than one‐tenth of that of western Europe when basin centre deposition is compared. We found no evidence of a major palaeontological break representing Westphalian D strata overlain by Stephanian C strata. We figure non‐marine bivalve faunas of Stephanian B age in association with the Pittsburgh and the Little Pittsburgh coals. Two new species of non‐marine bivalves are described: Anthraconaia anthraconautiformis sp. nov. and Anthraconaia extrema sp. nov. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Phase relations, singularities and thermobarometry of metamorphic assemblages containing phengite, chlorite, biotite, K-feldspar, quartz and H2O     

G. D. H. Simpson  A. B. Thompson  J. A. D. Connolly 《Contributions to Mineralogy and Petrology》2000,139(5):555-569

The phase relations of divariant and trivariant assemblages involving combinations of phengite, chlorite, biotite, K-feldspar, quartz and H₂O in the KFASH, KMASH and KFMASH systems were calculated using a single thermodynamic data set (Holland and Powell 1998). The stability fields of the various equilibria are represented in P-T projections by contouring sets of compositional isopleths for the Tschermak (Al₂(Fe,Mg)₋₁Si₋₁) and FeMg₋₁ exchanges controlled by the coexisting phases. Five multivariant continuous equilibria, which occur in different regions of P-T-X space, are calibrated as thermobarometers in metamorphic rocks of pelitic to quartzofeldspathic composition. More subtle P-T information, relating to the trajectories (dT/dz) along which reacting rocks have been buried or exhumed, can be extracted from the continuous reactions by investigating the recorded compositional trends in the Al₂(Fe,Mg)₋₁Si₋₁ and FeMg₋₁ solutions. Singularities in P-T space are associated with some of these reactions and may result in unusual mineral textures and compositional trends. A fluid-absent singularity has particular petrological significance because it marks the transition between hydration and dehydration along a single reaction with increasing pressure and temperature. This behaviour causes the sequence of reactions among these minerals observed during metamorphism to be critically dependent on the P-T trajectory. Thermobarometric calculations show good agreement with respect to experimental and field-based data for phengite compositions less than about 50 mol% celadonite (<∼3.5 Si p.f.u. phengite). Received: 15 November 1999 / Accepted: 3 April 2000  相似文献   

Titanium,Ti, A New Mineral Species from Luobusha,Tibet, China     

FANG Qingsong  BAI Wenji  YANG Jingsu  RONG He  SHI Nicheng  LI Guowu  XIONG Ming  MA Zhesheng 《《地质学报》英文版》2013,87(5):1275-1280

We describe the new mineral species titanium,ideally Ti,found in the podiform chromitites of the Luobusha ophiolite in Tibet,People’s Republic of China.The irregular crystals range from 0.1 to 0.6 mm in diameter and form an intergrowth with coesite and kyanite.Titanium is silver grey in colour,the luster is metallic,it is opaque,the streak is grayish black,and it is non-fluorescent.The mineral is malleable,has a rough to hackly fracture and has no apparent cleavage.The estimated Mohs hardness is 4,and the calculated density is 4.503 g/cm3.The composition is Ti 99.23-100.00 wt%.The mineral is hexagonal,space group P63 /mmc.Unit-cell parameters are a 2.950(2),c 4.686(1),V 35.32(5) 3,Z = 2.The five strongest powder diffraction lines [d in(hkl)(I/I0)] are: 2.569(010)(32),2.254(011)(100),1.730(012)(16),1.478(110)(21),and 0.9464(121)(8).The species and name were approved by the CNMNC(IMA 2010–044).  相似文献   

Suspended Matter,Chl-a,CDOM, Grain Sizes,and Optical Properties in the Arctic Fjord-Type Estuary,Kangerlussuaq, West Greenland During Summer     

Lars Chresten Lund-Hansen  Thorbjørn Joest Andersen  Morten Holtegaard Nielsen  Morten Pejrup 《Estuaries and Coasts》2010,33(6):1442-1451

Optical constituents as suspended particulate matter (SPM), chlorophyll (Chl-a), colored dissolved organic matter (CDOM), and grain sizes were obtained on a transect in the arctic fjord-type estuary Kangerlussuaq (66°) in August 2007 along with optical properties. These comprised diffuse attenuation coefficient of downwelling PAR (K _d(PAR)), upwelling PAR (K _u(PAR)), particle beam attenuation coefficient (c _p), and irradiance reflectance R(−0, PAR). PAR is white light between 400 and 700 nm. The estuary receives melt water from the Greenland Inland Ice and stations covered a transect from the very high turbid melt water outlet to clear marine waters. Results showed a strong spatial variation with high values as for suspended matter concentrations, CDOM, diffuse attenuation coefficient K _d(PAR), particle beam attenuation coefficients (c _p), and reflectance R(−0, PAR) at the melt water outlet. Values of optical constituents and properties decreased with distance from the melt water outlet to a more or less constant level in central and outer part of the estuary. There was a strong correlation between inorganic suspended matter (SPMI) and diffuse attenuation coefficient K _d(PAR) (r ² = 0.92) and also for particle beam attenuation coefficient (c _p; r ² = 0.93). The obtained SPMI specific attenuation—K _d^*(PAR) = 0.13 m² g⁻¹ SPMI—and the SPMI specific particle beam attenuation—c _p^* = 0.72 m² g⁻¹—coefficients were about two times higher than average literature values. Irradiance reflectance R(−0, PAR) was comparatively high (0.09−0.20) and showed a high (r ² = 0.80) correlation with K _u(PAR). Scattering dominated relative to absorption—b(PAR)/a(PAR) = 12.3. Results strongly indicated that the high values in the optical properties were related to the very fine particle sizes (mean = 2–6 μm) of the suspended sediment. Data and results are discussed and compared to similar studies from both temperate and tropical estuaries.  相似文献   

Famennian microbial reef facies, Napier and Oscar Ranges, Canning Basin, western Australia   总被引：5，自引：0，他引：5  

Nat P. Stephens  Dawn Y. Sumner 《Sedimentology》2003,50(6):1283-1302

Following the Frasnian–Famennian mass extinction, which eliminated most skeletal reef-building fauna, the early Famennian reefs of the Canning Basin were constructed primarily by reef-framework microbial communities. In the Napier and Oscar Ranges, the Famennian reef complexes had high-energy, reef-flat depositional environments on a reef-rimmed platform that transitioned into low-energy, deep-water reefs growing in excess of 50 m below sea level. High-energy, reef-flat depositional environments contain doming fenestral stromatolites that grade into porous thrombolites and are associated with coarse-grained sandstones and grainstones. The reef-margin subfacies contains mounds of microdigitate thrombolites, which are more delicate than the reef-flat thrombolites and locally contain abundant red algae, Girvanella, renalcids and sediment-filled tubes. Within the thrombolites, the red algae are in upright growth positions, suggesting that the thrombolites are largely composed of carbonate that precipitated in situ. Reefal-slope environments are dominated by Wetheredella and Rothpletzella with locally abundant Girvanella, renalcids and Uralinella. In reefal-slope strata, delicate fans and microdigitate stromatolites of Wetheredella and Rothpletzella are often oriented horizontal or diagonal to bedding and are interpreted as syndepositionally toppled over. Most mesoscale microbial community structures contain several species of microbial fossils, and no single microbial species appears to have controlled the morphology of the community structure. Therefore, the depositional environment must have determined the distribution and morphology of the stromatolites, thrombolites and other microbial community structures. The adaptability of microbial communities to various reef environments allowed them to fill ecological niches opportunistically after the Frasnian–Famennian mass extinction.  相似文献   

The influence of salinity on seagrass growth,survivorship, and distribution within Biscayne Bay,Florida: Field,experimental, and modeling studies   总被引：1，自引：0，他引：1  

Diego?LirmanEmail author  Wendell?P.?Cropper 《Estuaries and Coasts》2003,26(1):131-141

We evaluate if the distribution and abundance ofThalassia testudinum, Syringodium filiforme, andHalodule wrightii within Biscayne Bay, Florida, are influenced by salinity regimes using, a combination of field surveys, salinity exposure experiments, and a seagrass simulation model. Surveys conducted in June 2001 revealed that whileT. testudinum is found throughout Biscayne Bay (84% of sites surveyed),S. filiforme andH wrightii have distributions limited mainly to the Key Biscayne area.H. wrightii can also be found in areas influenced by canal discharge. The exposure of seagrasses to short-term salinity pulses (14 d, 5–45‰) within microcosms showed species-specific susceptibility to the salinity treatments. Maximum growth rates forT testudinum were observed near oceanic salinity values (30–40‰) and lowest growth rates at extreme values (5‰ and 45‰).S. filiforme was the most susceptible seagrass species; maximum growth rates for this species were observed at 25‰ and dropped dramatically at higher and lower salinity.H. wrightii was the most tolerant, growing well at all salinity levels. Establishing the relationship between seagrass abundance and distribution and salinity is especially relevant in South Florida where freshwater deliveries into coastal bays are influenced by water management practices. The seagrass model developed by Fong and Harwell (1994) and modified here to include a shortterm salinity response function suggests that freshwater inputs and associated decreases in salinity in nearshore areas influence the distribution and growth of single species as well as modify competitive interactions so that species replacements may occur. Our simulations indicate that although growth rates ofT. testudinum decrease when salinity is lowered, this species can still be a dominant component of nearshore communities as confirmed by our surveys. Only when mean salinity values are drastically lowered in a hypothetical restoration scenario isH. wrightii able to outcompeteT. testudinum.  相似文献   

Cenomanian radiolitid bivalves from Malchina, Karst of Trieste, Italy     

Jose Maria Pons  Enric Vicens  Alceo Tarlao 《Cretaceous Research》2011,32(6):647-658

A radiolitid fauna, rudist bivalves, composed of Durania acuticostata Caffau and Pleni?ar, Eoradiolites fleuriausus (d’Orbigny), Eoradiolites liratus (Conrad), Paronaites zuffardii (Parona), and Sauvagesia sharpei (Bayle) is described from the upper Cenomanian Monrupino Formation in the Malchina area, Karst of Trieste. The taxonomic part includes [1] the proposal of the new genus Paronaites and [2] neotypes for E. liratus, [3] the identification of several junior synonyms (Eoradiolites zucchii Caffau and Pleni?ar and Praeradiolites acutilamellosus Caffau and Pleni?ar for E. fleuriausus; Eoradiolites zizensis Astre and Eoradiolites adriaticus Caffau and Pleni?ar for E. liratus; and Eoradiolites carsicus Caffau and Pleni?ar for P. zuffardii), [4] the discrimination between E. liratus and Eoradiolites schweinfurthi Zittel, and [5] the identification in Europe of species so far only reported in North Africa, besides [6] illustrating the diagnostic characters and morphologic variability of the treated species. All this facilitates their proper identification and certainly helps the stratigraphic correlation of the Cenomanian shallow water carbonates deposited on the margins of the Tethys.  相似文献   

Conductively driven,high‐thermal gradient metamorphism in the Anmatjira Range,Arunta region,central Australia     

J. R. Anderson  D. E. Kelsey  M. Hand  W. J. Collins 《Journal of Metamorphic Geology》2013,31(9):1003-1026

LA–ICP–MS in situ U–Pb monazite geochronology and P–T pseudosections are combined to evaluate the timing and physical conditions of metamorphism in the SE Anmatjira Range in the Aileron Province, central Australia. All samples show age peaks at c. 1580–1555 Ma, with three of five samples showing additional discrete age peaks between c. 1700 and 1630 Ma. P–T phase diagrams calculated for garnet–sillimanite–cordierite–K‐feldspar–ilmenite–melt bearing metapelitic rocks have overlapping peak mineral assemblage stability fields at ~870–920 °C and ~6.5–7.2 kbar. P–T modelling of a fine‐grained spinel–cordierite–garnet–biotite reaction microstructure suggests retrograde P–T conditions evolved down pressure and temperature to ~3–5.5 kbar and ~610–850 °C. The combined geochronological and P–T results indicate the SE Anmatjira Range underwent high‐temperature, low‐pressure metamorphism at c. 1580–1555 Ma, and followed an apparently clockwise retrograde path. The high apparent thermal gradient necessary to produce the estimated P–T conditions does not appear to reflect decompression of high‐P assemblages, nor is there syn‐metamorphic magmatism or structural evidence for extension. Similar to previous workers, we suggest the high‐thermal gradient P–T conditions could have been achieved by heating, largely driven by high heat production from older granites in the region.  相似文献   

Late Cretaceous Aquatic Angiosperms from Jiayin,Heilongjiang, Northeast China     

QUAN Cheng  SUN Ge 《《地质学报》英文版》2008,82(6):1133-1140

Three taxa of Late Cretaceous aquatic angiosperms, Queruexia angulata （Lesq.） Krysht., Cobbania corrugata （Lesq.） Stockey et al. and Nelumbites cf. extenuinervis Upchurch et al. from Jiayin of Heilongjiang, NE China, are described in detail. Among them, Cobbania and Nelumbites from the Upper Cretaceous in China are reported for the first time. The aquatic angiosperm assemblage of Queruexia-Cobbania-Nelumbites appears to imply a seasonal, warm and moist environment in the Jiayin area during the Santonian-Campanian time.  相似文献   

A temporal investigation of grazer dynamics, nutrients, seagrass leaf productivity, and epiphyte standing stock     

T. A. Frankovich  J. C. Zieman 《Estuaries and Coasts》2005,28(1):41-52

An investigation of seagrass-epiphyte controlling factors was conducted within aThalassia testudinum meadow in Florida Bay from March 2000 to April 2001. Univariate and multivariate analyses were performed using water column nutrient concentrations, temperature, salinity, and turbidity, and gastropod grazer abundances, seagrass leaf area index, and leaf turnover rate data to explain the variation in total epiphyte standing stock, epiphyte chlorophylla, and epiphyte autotrophic index. Turbidity was positively correlated with total epiphyte standing stock and accounted for the most variation. Observations of adhered sediment onT. testudinum leaves and the combination, of increased total epiphyte standing stocks and low autotrophic indices observed in February and April 2001 suggest that the settling of resuspended sediments following turbidity events is one of the temporal mechanisms for increased epiphyte accumulation. Total epiphyte standing stock was also negatively correlated with the abundance of a robust gastropod grazer community dominated byTurbo castanea, Tegula fasciata, andModulus modulus. Distinct temporal size cohorts ofT. castanea andT. fasciata throughout the study period suggest recruitment in spring and an annual lifespan. Nutrient concentrations can also account for some of the temporal variation in total epiphyte standing stock, epiphyte chlorophylla, and autotrophic index. The low variation ofT. testudinum leaf turnover rates was unable to account for any of the variation in the epiphyte parameters.  相似文献   

Discrete proterozoic structural terranes associated with low-P, high-T metamorphism, Anmatjira Range, Arunta Inlier, central Australia: tectonic implications     

W.J. Collins  R.H. Vernon  G.L. Clarke 《Journal of Structural Geology》1991,13(10)

Structural overprinting relationships indicate that two discrete terranes, Mt. Stafford and Weldon, occur in the Anmatjira Range, northern Arunta Inlier, central Australia. In the Mt. Stafford terrane, early recumbent structures associated with D_1a,_1b deformation are restricted to areas of granulite facies metamorphism and are overprinted by upright, km-scale folds F_1c), which extend into areas of lower metamorphic grade. Structural relationships are simple in the low—grade rocks, but complex and variable in higher grade equivalents. The three deformation events in the Mt. Stafford terrane constitute the first tectonic cycle (D₁-D₂) deformation in the Weldon terrane comprises the second tectonic cycle. The earliest foliation (S_2a) was largely obliterated by the dominant reclined to recumbent mylonitic foliation (S_2b), produced during progressive non-coaxial deformation, with local sheath folds and W- to SW-directed thrusts. Locally, (D_2d) tectonites have been rotated by N—S-trending, upright (F_2c) folds, but the regional upright fold event (F_2d), also evident in the adjacent Reynolds Range, rotated earlier surfaces into shallow-plunging, NW—SE-trending folds that dominate the regional outcrop pattern.The terranes can be separated on structural, metamorphic and isotopic criteria. A high-strain D₂ mylonite zone, produced during W- to SW-directed thrusting, separates the Weldon and Mt. Stafford terranes. 1820 Ma megacrystic granites in the Mt. Stafford terrane intruded high-grade metamorphic rocks that had undergone D_1a and D_1b deformation, but in turn were deformed by S_1c, which provides a minimum age limit for the first structural—metamorphic event. 1760 Ma charnockites in the Weldon terrane were emplaced post-D_2a, and metamorphosed under granulite facies conditions during D_2b, constraining the second tectonic cycle to this period.Each terrane is associated with low-P, high-T metamorphism, characterized by anticlockwise P—T—t paths, with the thermal peaks occurring before or very early in the tectonic cycle. These relations are not compatible with continental-style collision, nor with extensional tectonics as the deformation was compressional. The preferred model involves thickening of previously thinned lithosphere, at a stage significantly after (>50 Ma) the early extensional event. Compression was driven by external forces such as plate convergence, but deformation was largely confined to and around composite granitoid sheets in the mid-crust. The sheets comprise up to 80% of the terranes and induced low-P, high-T metamorphism, including migmatization, thereby markedly reducing the yield strength and accelerating deformation of the country rocks. Mid-crustal ductile shearing and reclined to recumbent folding resulted, followed by upright folding that extended beyond the thermal anomaly. Thus, thermal softening induced by heat-focusing is capable of generating discrete structural terranes characterized by subhorizontal ductile shear in the mid-crust, localized around large granitoid intrusions.  相似文献   

Reconnaissance paleomagnetism of Late Triassic blocks, Kuyul region, Northern Kamchatka Peninsula, Russia     

William Harbert  Sergei Sokolov  Maxim Alexutin  Kirill Krylov  Vladimir Grigoriev  Alexander Heiphetz   《Tectonophysics》2003,361(3-4):215-227

The northernmost Kamchatka Peninsula is located along the northwestern margin of the Bering Sea and consists of complexly deformed accreted terranes. Progressing inland from the northwestern Bering Sea, the Olyutorskiy, Ukelayat and Koryak superterranes (OLY, UKL and KOR) are crossed. These terranes were accreted to the backstop Okhotsk-Chukotsk volcanic-plutonic belt (OChVB) in northernmost Kamchatka. A sedimentary sequence of Albian to Maastrichtian age overlaps the terranes and units of the Koryak superterrane, and constrains their accretion time. A paleomagnetic study of blocks within the Kuyul (KUY) terrane of the Koryak superterrane was completed at two localities (Camp 2: λ=61.83°N, φ=165.83°E and Camp 3: λ=61.67°N, φ=164.75°E). At both localities, paleomagnetic samples were collected from Late Triassic (225–208 Ma) limestone blocks (2–10 m in outcrop height) within a melange zone. Although weak in remanent magnetization, two components of remanent magnetization were observed during stepwise thermal demagnetization at 32 sites. The A component of magnetization was observed between room temperature and approximately 250 °C. This magnetic component is always of downward directed inclination and shows the best grouping at relatively low degrees of unfolding. Using McFadden–Reid inclination-only statistics and averaging all site means, the resulting A component mean is I_opt=60.3°, I₉₅=5.0° and n=36 (sites). The B magnetic component is observed up to 565 °C, at which temperature, most samples have no measurable remanent magnetization, or growth of magnetic minerals has disrupted the thermal demagnetization process. Combining sites with Fisher estimates of kappa (k-value)≥13 and n (sites)≥3, where bedding orientation differs within a block, most of these sites show the best grouping of B component directions at 100% unfolding, and two of the blocks display remanent magnetizations of both upward and downward directed magnetic inclination. Combining sites with Fisher estimates of kappa (k-value)≥13 and n (sites)≥3, the resulting overall B component paleolatitude and associated uncertainty are λ_obs=30.4°N or S, λ₉₅=8.9° and n=19 (sites). When compared with the expected North America paleolatitude of λ_{APWP expected}=57.9°N, our data support a model in which blocks within the Koryak superterrane are allochthonous and far travelled.  相似文献   

Planar, non-planar and refolded sheath folds in the Phulad Shear Zone, Rajasthan, India     

S. K. Ghosh  S. Hazra  S. Sengupta 《Journal of Structural Geology》1999,21(12):171

Progressive ductile shearing in the Phulad Shear Zone of Rajasthan, India has produced a complex history of folding, with development of planar, non-planar and refolded sheath folds. There are three generations of reclined folds, F₁, F₂ and F₃, with a striping lineation (L₁) parallel to the hinge lines of F₁. The planar sheath folds of F₁ have long subparallel hinge lines at the flanks joining up in hairpin curves at relatively small apices. L₁ swerves harmoniously with the curving of F₁ hinge line. There is a strong down-dip mineral lineation parallel to the striping lineation in most places, but intersecting it at apices of first generation sheath folds. Both the striping and the mineral lineation are deformed in U-patterns over the hinges of reclined F₂ and F₃. Folding of axial surfaces and hinge lines of earlier reclined folds by later folds was accompanied by very large stretching and led to the development of non-planar sheaths. The reclined folds of all the three generations were deformed by a group of subhorizontal folds. Each generation of fold initially grew with the hinge line at a very low angle with the Y-axis of bulk non-coaxial strain and was subsequently rotated towards the down-dip direction of maximum stretching. The patterns of deformed lineations indicate that the stretching along the X-direction was extremely large, much in excess of 6000 percent.  相似文献   

Lisiguangite,CuPtBiS3, a New Platinum‐Group Mineral from the Yanshan Mountains,Hebei, China     

YU Zuxiang  CHENG Fanyun  MA Hongwei 《《地质学报》英文版》2009,83(2):238-244

Lisiguangite, CuPtBiS3, is a new mineral species discovered in a PEG-bearing, Co-Cu sulfide vein in garnet pyroxenite of the Yanshan Mountains, Chengde Prefecture, Hebei Province, China. It is associated with chalcopyrite and bornite, galena, minor pyrite, carrolite, molybdenite and the platinum-group minerals daomanite (CuPtAsS2), Co-bearing malanite (Cu(Pt, Co)2S4) sperrylite, moncheite, cooperite and malyshevite (CuPdBiS3), rare damiaoite (Pt2In3) and yixunite (Pt3In). Lisiguangite occurs as idiomorphic crystals, tabular or lamellae (010) and elongated [100] or as aggregates, up to 2 mm long and 0.5 mm wide. The mineral is opaque, has lead-gray color, black streak and metallic luster. The mineral is non-fluorescent. The observed morphology displays the following forms: pinacoids {100}, {010}, {001}, and prism {110}. No twining is observed. The a:b:c ratio, calculated from unit-cell parameters, is 0.6010:1:0.3836. Cleavage: {010} perfect, {001} distinct, {100} may be visible. H Mohs: 21/2; VHN25=46.7-49.8 (mean 48.3) kg/mm2. Tenacity: brittle. Lisiguangite is bright white with a yellowish tint. In reflected light it shows neither internal reflections nor bireflectance or pleochroism. It has weak to moderate anisotropy (blue-greenish to brownish) and parallel-axial extinction. The reflectance values in air (and in oil) for R3, R4 and (imR3, imR4), at the standard Commission on Ore Mineralogy wavelengths are: 37.5, 35.7 (23.4, 22.3) at 470 nm; 38.6, 36.5 (23.6, 22.6) at 546 nm; 39.4, 37.5 (23.6, 22.7) at 589 nm and 40.3, 38.2 (23.7, 22.9) at 650 nm. The average of eight electron-microprobe analyses: Cu 12.98, Pt 30.04, Pd 2.69, Bi 37.65 and S 17.55, totaling 100.91%, corresponding to Cu1.10(Pt 0.83, Pd0.14)Σ0.97Bi0.97S2.96 based on six atoms apfu. The ideal formula is CuPtBiS3. The mineral is orthorhombic. Space group: P212121, a=7.7152(15)?,b=12.838(3)?, c=4.9248(10)?, V=487.80(17)?3, Z=4. The six strongest lines in the X-ray powder-diffraction pattern [d in ? (I) (h k l) are 6.40(30)(020), 3.24(80)(031), 3.03(100)(201), 2.27(40)(051), 2.14(50)(250), 1.865(60)(232).  相似文献   

Transformations of the stuffed cristobalites, K2MSiO4, M=Mg, Zn, Co, Cd, with temperature and composition     

W. A. Dollase 《Physics and Chemistry of Minerals》1998,25(5):389-392

The effects of composition and of temperature on the orthorhombic, Pca2 ₁ to cubic, F4ˉ3m transition of the stuffed cristobalite structure are reported. A distorton index which measures the departure of the orthorhombic unit cell from a metrically cubic cell shows that at room temperature, distortion increases in the progression K₂CdSiO₄ <K₂MgSiO₄ <K₂ZnSiO₄≈K₂CoSiO₄. High temperature X-ray powder measurements document an apparently discontinuous transition to a structure of F4ˉ3m symmetry. Differential scanning calorimetry shows a sharp, reversible, first order transition to the high temperature phase at about 500–600 °C for these compounds. Measured transformation enthalpies in the range of 7 to 16 J/g correlate roughly with the distortion index. The transformation involves tetrahedral rotation to an orientationally disordered cubic structure which retains an ordered M²⁺/Si distribution. Received: 8 November 1996 / Revised, accepted: 14 October 1997  相似文献