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1.
Magnetic anomaly data are presented from a new helicopter-borne high-resolution aeromagnetic survey in southern McMurdo Sound. Anomaly data have been acquired at a common 305 m elevation above the McMurdo and southern McMurdo ice shelves and draped over the volcanic islands that pin them. The resulting anomaly patterns provide a significant advance in the understanding of the rift related geology beneath the floating ice shelves. More extensive Erebus Volcanic Province (McMurdo Volcanic Group) rocks are indicated along with a significant blanket of glaci-volcaniclastic sediment on the seafloor between the volcanic islands in southern McMurdo Sound. These glaci-volcaniclastic sediments are inferred to originate from former grounding of the southern McMurdo Ice Shelf as a marine ice sheet. A strong N–S fabric is also observed in the anomaly data suggesting that the rift structure observed in the Victoria Land basin persists to the south beneath the McMurdo and southern McMurdo ice shelves. W–N–W transfer faults identified within the Transantarctic Mountain rift flank to the west are not obvious in the aeromagnetic data set, implying that the 'Discovery Accommodation Zone' may be restricted to the region between a southward extension of the range bounding fault that marks the limit of the Victoria Land Basin and the right lateral offset in the Transantarctic Mountain front in southern Victoria Land.  相似文献   

2.
基于非结构三角形网格的FVCOM(Finite-Volume Coastal Ocean Model)海洋数值模式,对白令海峡及其邻近海域的潮汐、潮能进行数值模拟研究。模拟结果同验潮站和实测海流资料符合良好,较好地反映了白令海峡及其邻近海域的潮汐、潮流分布特征和运动状况。根据计算结果绘制了主要分潮的同潮图和潮流椭圆图,对该海域潮汐潮流特征进行了系统分析。结果表明,白令海陆架区、白令海峡和楚科奇海主要以M2分潮为主,而在诺顿湾海域以K1分潮为主,M2分潮潮流在白令海陆架东南部及阿纳德尔湾较强,K1分潮潮流在诺顿湾潮流达到最大值。在此基础上,对其潮汐能的传播与耗散进行分析,结果发现研究海域潮能通量较小,主要分潮在研究海域潮能耗散总量约为751 MW,M2潮能耗散占该总量的52%,K1潮能耗散占38%,潮能进入白令海陆架后,M2分潮主要在圣劳伦斯岛以南陆架区耗散,K1分潮主要在诺顿湾海区耗散。  相似文献   

3.
Interpretation of seismic reflection data have led to a new model of the development of the Queen Charlotte Basin. New multi-channel data collected in 1988 and an extensive network of unpublished older single- and multi-channel profiles from industry image a complex network of sub-basins. Structural styles vary along the axis of the basin from broadly spaced mainly N-trending sub-basins in Queen Charlotte Sound, to closely spaced NW-trending sub-basins in Hecate Strait, to an E-W en echelon belt of sub-basins in Dixon Entrance. Transtensional tectonics dominated in the Miocene and transpression dominated in the Pliocene except in Queen Charlotte Sound. The data we present prove that the origin of the basin is extensional and its most recent deformation is compressive. Evidence for the strike-slip origin of tectonism includes along-axis variations in structures, simultaneous extension and compression in adjacent sub-basins, lack of correlations across faults, and mixed normal and reverse faults within structures. We infer that the Pacific-North America plate boundary has been west of the Queen Charlotte Islands since the Miocene when relative plate motions have been dominantly strike-slip. The formation and development of the Queen Charlotte Basin is the result of distributed shear; by which a small percentage of the plate motion has been taken up in a network of faults across the continental margin. As this region of crust deforms it interacts with neighbouring rigid crust resulting in extension dominating in the south of the basin and compression in the north. Continental crust adjacent to some transform plate boundaries can be sheared over a wide region; the network of basins in southwestern California is a good analogue for the Queen Charlotte Basin.  相似文献   

4.
Heat capacities of the rocks within a sedimentary basin can significantly influence geothermal gradients if sedimentation or erosion is rapid. This paper provides data on specific heat capacities of minerals and nonporous rocks at 20°C, derives equations for calculating specific heat capacities of minerals and nonporous rocks at temperatures between 0°C and 1200°C, and shows that pressure effects on heat capacities of solids can be neglected. It derives an equation for estimating specific heat capacity of any mineral or nonporous rock as a function of density. Finally, it shows how to calculate the specific heat capacity of any mixture of solid materials. A companion paper discusses specific heat capacities of the fluids in pore spaces of rocks and of fluid-filled porous rocks. The data for minerals and rocks provided herein can be incorporated directly into existing modeling software by users. However, the temperature-dependent equations would have to be incorporated by software developers.  相似文献   

5.
A two-layer lithospheric stretching model that includes the effects of decompression melting was used to estimate the deformation and thermal evolution of the Queen Charlotte Basin, British Columbia. The basin contains up to 6 km of Tertiary fill and is postulated to have been formed during a transtensional stage of Cenozoic plate motion between the Pacific and North American plates. Several models of basin formation have been proposed to explain the sediment distribution, contemporaneous volcanism and high present-day heat flow. We used bathymetry, Tertiary sediment thickness and crustal thickness to calculate the amount of stretching in the crust and lower lithosphere, and the volume of melt generated during advection of mantle rocks. A second set of calculations traced the thermal evolution of the sediments and lithosphere, and we show maps of estimated present-day heat flow and sediment maturity. This study differs significantly from previous work in the use of gridded data that provide coverage over a large region and permit lateral variations in lithospheric deformation and thermal properties to be clearly defined, a difficult quest in studies based on single-point or profile data. In addition, the use of crustal thickness, derived from a regional interpretation of gravity data and constrained by seismic refraction results, as an input allows reliable estimates of extension to be made despite recent deformation of sedimentary strata in Hecate Strait. We present results for a model which used a prerift crustal thickness of ≈34 km and a short rifting period from 25 to 20 Ma. This model infers that significant thinning occurred beneath south-western Hecate Strait and southern Queen Charlotte Sound, and several kilometres of igneous crust were added at these sites, without requiring elevated asthenospheric temperatures prior to extension. Net lithospheric extension is surprisingly uniform within the basin and averages 76%, or ≈50 km, across the margin. This amount is consistent with other estimates of extension and may provide information useful in refining models of plate motion along this margin.  相似文献   

6.
Summary. Multichannel seismic reflection sections recorded across Vancouver Island have revealed two extensive zones of deep seismic reflections that dip gently to the northeast, and a number of moderate northeasterly dipping reflections that can be traced to the surface where major faults are exposed. Based on an integrated interpretation of these data with information from gravity, heat flow, seismicity, seismic refraction, magnetotelluric and geological studies it is concluded that the lower zone of gently dipping reflections is due to underplated oceanic sediments and igneous rocks associated with the current subduction of the Juan de Fuca plate, and that the upper zone represents a similar sequence of accreted rocks associated with an earlier episode of subduction. The high density/high velocity material between the two reflection zones is either an underplated slab of oceanic lithosphere or an imbricated package of mafic rocks. Reprocessing of data from two of the seismic lines has produced a remarkable image of the terrane bounding Leech River fault, with its dip undulating from >60° near the surface to 20° at 3 km depth and ∼38° at 6 km depth.  相似文献   

7.
The Racetrack Playa's unusual surface features known as sliding rocks have been the subject of an ongoing debate and several mapping projects for half a century, although the causative mechanism remains unresolved. Clasts ranging in volume from large pebbles to medium boulders have, unwitnessed, maneuvered around the nearly flat dry lake over considerable distances. The controversy has persisted partly because eyewitness accounts of the phenomenon continue to be lacking, and the earlier mapping missions were limited in method and geographic range. In July 1996, we generated the first complete map of all observed sliding rock trails by submeter differential Global Positioning System (DGPS) mapping technology. The resulting map shows 162 sliding rocks and associated trails to an accuracy of approximately 30 cm. Although anemometer data are not available in the Racetrack wilderness, wind is clearly a catalyst for sliding rock activity; an inferred wind rose was constructed from DGPS trail segment data. When the entire trail network is examined in plan, some patterns emerge, although other (perhaps expected relations) remain elusive: terrain analysis of the surrounding topography demonstrates that the length and morphology of trails are more closely related to where rocks rested at the onset of motion than to any physical attribute of the rocks themselves. Follow-up surveys in May 1998, May 1999, August 1999, and November 1999 revealed little modification of the July, 1996 sliding rock configuration. Only four rocks were repositioned during the El Niño winter of 1997–1998, suggesting that activity may not be restricted to winter storms.  相似文献   

8.
Peter Copeland 《Basin Research》2020,32(6):1532-1546
Placing geologic events in a temporal framework is essential to telling the story of Earth history. However, clastic sedimentary rocks can be difficult to date in an absolute reference because they are made up of grains that are older than the rock in which they are now found, and some clastic rocks do not contain fossils that allow precise reference to the Geologic Timescale. For such rocks, the isotopic dating of detrital minerals can be used to estimate the time of deposition; the clastic rock must be younger than the youngest grain analysed. However, many researchers eschew this simple and straightforward approach in favour of schemes that estimate the maximum allowable depositional age as the weighted mean of the age of several grains, chosen by a variety of selection criteria. This is a mistake; in the absence of a geochemical resemblance apart from the similarity of their age, detrital grains should not be assumed to have originated in the same system and therefore any averaging or other manipulation of such data is statistically invalid and produces results without geologic significance. In the absence of interbedded volcanic rocks or index fossils, dating of detrital minerals can be an important aid in understanding the time of deposition of clastic rocks, but the best estimate will come from taking note of the youngest single grain and not by inappropriately averaging data.  相似文献   

9.
Ｎｅｗ￣（４０）Ａｒ／￣（３９）ＡｒａｇｅｅｖｉｄｅｎｃｅｆｏｒｔｈｅＣｅｔａｃｅｏｕｓｖｏｌｃａｎｉｃｒｏｃｋｓｏｆｔｈｅＭｏｕｎｔＢｏｗｌｅｓＦｏｒｍａｔｉｏｎｉｎＬｉｖｉｎｇｓｔTX＠郑祥身＠胡世玲＠刘嘉麒Ｎｅｗ４０Ａｒ／３９Ａｒａｇｅｅｖｉｄｅｎｃｅ...  相似文献   

10.
This paper evaluates recent changes in narwhal ( Monodon monoceros ) catches in Siorapaluk, the northernmost community in Greenland, in consideration of the effects of changing climate and uncertainty of stock delineation. The catch statistics show a significant increase in narwhal catches by hunters in Siorapaluk after 2002, which does not appear to be a result of increased effort. Hunters attribute the increase to changed sea-ice conditions providing access by boat to Smith Sound as early as June and July. This indicates that climate change is likely to have a considerable impact on narwhal hunting in northern Greenland. Traditional ecological knowledge and scientific surveys suggest that narwhal in Smith Sound constitute an independent stock. The absence of scientific recommendations for this stock has been seen as an opportunity to increase quotas in West Greenland. Scientific management recommendations are urgently needed to allow the authorities to assign sustainable quotas for this stock. The development of collaborative management agreements and locally based monitoring are recommended to ensure local acceptance of regulations, and to allow rapid responses to climate change.  相似文献   

11.
With the help of complexity indices, we quantitatively studied multifractals, frequency distributions, and linear and nonlinear characteristics of geochemical data for exploration of the Daijiazhuang Pb–Zn deposit. Furthermore, we derived productivity differentiation models of elements from thermodynamics and self-organized criticality of metallogenic systems. With respect to frequency distributions and multifractals, only Zn in rocks and most elements except Sb in secondary media, which had been derived mainly from weathering and alluviation, exhibit nonlinear distributions. The relations of productivity to concentrations of metallogenic elements and paragenic elements in rocks and those of elements strongly leached in secondary media can be seen as linear addition of exponential functions with a characteristic weak chaos. The relations of associated elements such as Mo, Sb, and Hg in rocks and other elements in secondary media can be expressed as an exponential function, and the relations of one-phase self-organized geological or metallogenic processes can be represented by a power function, each representing secondary chaos or strong chaos. For secondary media, exploration data of most elements should be processed using nonlinear mathematical methods or should be transformed to linear distributions before processing using linear mathematical methods.  相似文献   

12.
利文斯顿岛火山岩是南极南设得兰岩浆弧的一部分。对岩石的Ｓｒ、Ｎｄ、Ｐｂ同位素组成以及８７Ｓｒ／８６Ｓｒ与１／Ｓｒ、Ｒｂ、Ｋ和ＳｉＯ２关系的研究表明,利文斯顿岛火山岩具有不同的源区特征。百耳斯半岛和史莱夫角的火山岩、西多斯角的粗玄岩和第三纪的英云闪长岩显示出同成因的特点,和依诺特角第四纪橄榄玄武岩一样,它们均具有原生地幔的同位素组分,源区岩浆可能直接来自上地幔。汉那角和中利文斯顿岛火山岩岩浆则受到地壳成分的混染。不相容元素对Ｌａ／Ｓｍ－Ｌａ和Ｃｅ／Ｙｂ－Ｃｅ的研究进一步显示出,上述不同产地的岩石分别为不同源岩浆不同程度部分熔融的产物。结合岩相学和岩石化学特征的研究,提出百耳斯半岛和史莱夫角的火山岩以及西多斯角的粗玄岩是上地幔发生部分熔融所生成的玄武岩岩浆从深部岩浆囊沿构造薄弱带直接喷出形成的。古生代基底岩系的存在对中利文斯顿岛和汉那角火山岩的成因过程有重要的影响,即来自深部岩浆囊的原始岩浆在上地壳中的浅部岩浆囊受到了壳源物质混染。更新世－现代火山岩的源区岩浆直接自上地幔部分熔融生成,火山作用与晚新生代时该区的拉张构造有关。  相似文献   

13.
summary . The electrical conductivity of cylindrical cores of Westerly granite, Indiana limestone and Nugget, St Peter and Kayenta sandstones was measured at about 25°C in vacuo , in air, and after saturation in distilled water, tap water, and 0.1 MNaCl solution. The three-electrode technique with a guard ring and the twoelectrode technique without a guard ring were used. Core aspect ratio over the range of 2.00 to 0.25, as well as frequency over the range of 50 Hz to 10 kHz, influences the conductivity of all rocks, especially those measured in vacuo . Measurements from water-saturated samples using a guard ring are not appreciably different from those obtained without a guard ring. The conductivity of rocks saturated in 0.1 MNaCl solution changes least with a change in aspect ratio; for these rocks a linear relationship, known as Archie's Law, exists between log porosity and log conductivity. No simple correlation was found between those factors in rocks saturated with tap or distilled water. Thus, it appears Archie's Law is of questionable value for correlating laboratory data from rocks saturated with low-conductivity fluids.  相似文献   

14.
In the frequency range from millihertz to hundreds of megahertz, many different physical and physico-chemical processes contribute to the electrical polarization of porous water-bearing rocks. This makes the interpretation of their electrical spectra a complicated problem and requires both elaborate theories and model experiments. At high frequencies, the Maxwell–Wagner–Bruggeman–Hanai (MWBH) theory of effective media, which takes into account only bulk properties, shape and partial volume of components, is very appropriate. At low frequencies, surface films, polarization of the electrical double layer (EDL) and clustering of conductive components can produce very strong polarization; corresponding theoretical models are considered in a companion paper ( Chelidze & Gueguen 1999 , hereafter referred to as Paper I). This paper is devoted to the review of experimental data and their comparison with theoretical models.
  Experiments on saturated mineral powders and rocks with various surface areas and surface chemistries confirm the existence of significant surface contributions to the electrical spectra of conductivity and polarization of water-bearing rocks and the dominance of this contribution over MWBH values at low frequencies. The effective dielectric constant of porous saturated rocks increases with the surface-to-volume ratio of the system and strongly depends on the surface charge ( ζ potential). At ζ potential, equal to zero, the low-frequency dielectric permittivity (DP) is minimal. The experimental data on relaxation times and the magnitude of the surface polarization of water-bearing porous systems can be satisfactorily explained by theories of film polarization, diffusional polarization generated by deformation of an 'open' electrical double layer (EDL) and percolation.  相似文献   

15.
Summary. Velocities of compressional waves are determined for central California rocks at pressures up to 0.7 GPa (7 kb) and temperatures up to 450°C. These data are used to interpret the seismic velocity structure of the crust in the California Coast Ranges. The seismic data on both sides of the San Andreas fault are consistent with the following model; besides some patches of surface sediments the upper 10—15 km of the crust on the northeast side consists predominantly of sedimentary and metasedimentary rocks of the Franciscan assemblage; the lower crust, of a thickness of 15—20 km, may be composed of gabbroic or other mafic rocks. Across the fault on the south-west side, the entire crustal section is probably a granitic complex similar to that exposed on the surface. The proposed model is shown to be consistent with the observed gravity anomaly.  相似文献   

16.
The structure and tectonic evolution of an evaporite basin are investigated in this case study, which combines the interpretation of magnetic data with the more commonly applied seismic reflection and gravity methods. The Maritimes Basin contains up to 18 km of Upper Palaeozoic sedimentary rocks resting on the basement of the Acadian orogeny. Carboniferous rocks are intensely deformed to the southeast of the Magdalen Islands as a result of deformation of evaporites of the Viséan Windsor Group. Short‐wavelength (<5 km) magnetic lineations define NNE‐ and ENE‐trending linear belts, coincident with the mapped pattern of salt structures. Magnetic models show that these lineations can be explained by the infill of subsidence troughs by high‐susceptibility sediment and/or the presence of basaltic rocks, similar to those uplifted and exposed on the Magdalen Islands. Additional shallow, magnetic sources are interpreted to result from alteration mineralization in salt‐impregnated, iron‐rich sedimentary rocks, brecciated during salt mobilization. Magnetic susceptibility measurements of samples from the Pugwash mine confirm the presence of higher susceptibility carnallite‐rich veins within salt units. Salt tectonism and basin development were influenced by the structure of the base group, the deepest regionally continuous seismic reflections (ca. 5–11 km), associated with an unconformity at the base of the Windsor Group, sampled at the Cap Rouge well. Salt structural evolution, formation of the magnetic lineations and geometry of the base group are associated with regional dextral transpression during basin development (late Carboniferous) and/or Alleghanian Orogeny (late Carboniferous to Permian). In this and similar studies, the effective use of magnetics is dependent upon the presence of rocks of high magnetic susceptibility in contrast to the low‐susceptibility salt bodies. In the absence of high‐susceptibility rocks, magnetic lows over the salt structures may be modelled, similar to commonly applied gravity techniques, to derive the internal structure and geometry.  相似文献   

17.
The onset of continent-wide glaciation in Antarctica is still poorly understood, despite being one of the most important palaeoclimatic events in the Cenozoic. The Eocene/Oligocene boundary interval has recently been recognized as a critical time for Antarctic climatic evolution, and it may mark the preglacial–glacial transition. Magnetic susceptibility, intensity of natural and artificial remanences, hysteresis parameters and magnetic anisotropy of the lower half (late Eocene/early Oligocene) of the CIROS-1 core (from McMurdo Sound, Antarctica) reveal alternating intervals of high and low magnetic mineral concentrations that do not correspond to lithostratigraphic units in the core. Pseudo-single-domain magnetite is the main magnetic mineral throughout the sequence, and sharp changes in magnetite concentration match changes in clay mineralogy beneath and at the Eocene/Oligocene boundary. The detrital magnetite originated from weathering of the Ferrar Group (which comprises basic extrusive and intrusive igneous rocks). Weathering processes and input of magnetite to the Victoria Land Basin were intense during periods when the Antarctic climate was warmer than today, but during intervals when the climate was relatively cool, chemical weathering of the Ferrar Group was suppressed and input of detrital magnetite to the Victoria Land Basin decreased. Our results also indicate that a cold and dry climate was not established in Antarctica until the Eocene/Oligocene boundary, with major ice sheet growth occurring at the early/late Oligocene boundary. Some earlier cold intervals are identified, which indicate that climate had begun to deteriorate by the middle/late Eocene boundary.  相似文献   

18.
Rocks used as construction aggregate in temperate climates deteriorate to differing degrees because of repeated freezing and thawing. The magnitude of the deterioration depends on the rock's properties. Aggregate, including crushed carbonate rock, is required to have minimum geotechnical qualities before it can be used in asphalt and concrete. In order to reduce chances of premature and expensive repairs, extensive freeze-thaw tests are conducted on potential construction rocks. These tests typically involve 300 freeze-thaw cycles and can take four to five months to complete. Less time consuming tests that (1) predict durability as well as the extended freeze-thaw test or that (2) reduce the number of rocks subject to the extended test, could save considerable amounts of money. Here we use a probabilistic neural network to try and predict durability as determined by the freeze-thaw test using four rock properties measured on 843 limestone samples from the Kansas Department of Transportation. Modified freeze-thaw tests and less time consuming specific gravity (dry), specific gravity (saturated), and modified absorption tests were conducted on each sample. Durability factors of 95 or more as determined from the extensive freeze-thaw tests are viewed as acceptable—rocks with values below 95 are rejected. If only the modified freeze-thaw test is used to predict which rocks are acceptable, about 45% are misclassified. When 421 randomly selected samples and all four standardized and scaled variables were used to train aprobabilistic neural network, the rate of misclassification of 422 independent validation samples dropped to 28%. The network was trained so that each class (group) and each variable had its own coefficient (sigma). In an attempt to reduce errors further, an additional class was added to the training data to predict durability values greater than 84 and less than 98, resulting in only 11% of the samples misclassified. About 43% of the test data was classed by the neural net into the middle group—these rocks should be subject to full freeze-thaw tests. Thus, use of the probabilistic neural network would meanthat the extended test would only need be applied to 43% of the samples, and 11% of the rocks classed as acceptable would fail early.  相似文献   

19.

Oil from the Oligocene oil sands of the Lower Ganchaigou Formation in the Northern Qaidam Basin and the related asphaltenes was analyzed using bulk and organic geochemical methods to assess the organic matter source input, thermal maturity, paleo-environmental conditions, kerogen type, hydrocarbon quality, and the correlation between this oil and its potential source rock in the basin. The extracted oil samples are characterized by very high contents of saturated hydrocarbons (average 62.76%), low contents of aromatic hydrocarbons (average 16.11%), and moderate amounts of nitrogen–sulfur–oxygen or resin compounds (average 21.57%), suggesting that the fluid petroleum extracted from the Oligocene oil sands is of high quality. However, a variety of biomarker parameters obtained from the hydrocarbon fractions (saturated and aromatic) indicate that the extracted oil was generated from source rocks with a wide range of thermal maturity conditions, ranging from the early to peak oil window stages, which are generally consistent with the biomarker maturity parameters, vitrinite reflectance (approximately 0.6%), and Tmax values of the Middle Jurassic carbonaceous mudstones and organic-rich mudstone source rocks of the Dameigou Formation, as reported in the literature. These findings suggest that the studied oil is derived from Dameigou Formation source rocks. Furthermore, the source- and environment-related biomarker parameters of the studied oil are characterized by relatively high pristane/phytane ratios, the presence of tricyclic terpanes, low abundances of C27 regular steranes, low C27/C29 regular sterane ratios, and very low sterane/hopane ratios. These data suggest that the oil was generated from source rocks containing plankton/land plant matter that was mainly deposited in a lacustrine environment and preserved under sub-oxic to oxic conditions, and the data also indicate a potential relationship between the studied oil and the associated potential source rocks. The distribution of pristane, phytane, tricyclic terpanes, regular steranes and hopane shows an affinity with the studied Oligocene Lower Ganchaigou Formation oil to previously published Dameigou Formation source rocks. In support of this finding, the pyrolysis–gas chromatography results of the analyzed oil asphaltene indicate that the oil was primarily derived from type II organic matter, which is also consistent with the organic matter of the Middle Jurassic source rocks. Thus, the Middle Jurassic carbonaceous mudstones and organic rock mudstones of the Dameigou Formation could be significantly contributing source rocks to the Oligocene Lower Ganchaigou Formation oil sand and other oil reservoirs in the Northern Qaidam Basin.

  相似文献   

20.
The metamorphism of upper greenschist facies metasediments exposed in the extreme southwestern portion of St. Jonsjorden, Svalbard, is described. The rocks form part of the Mullerneset Formation of the late Precambrian age Kongsvegen Group and constitute a portion of the central-western Spitsbergen Cale-donides. Four deformations (D, -D4) and two metamorphic episodes (Mi and M2) have affected the rocks of the Mullerneset area. Mi was a prograde event which was initiated prior to the onset of the Di and continued through this deformation. Pre-Dt metamorphism reached biotite grade whereas garnet grade was attained syn-Di. M2 was a lower-middle greenschist facies metamorphism associated with D2. The results of quantitative geothermometry in the pelitic rocks show that peak Mi metamorphic temperatures decrease southwards across the field area from about 540°C to 510°C. Geobarometry and estimates of depth of burial indicate that Mi pressures were in the range of 5–7 kb. The data are consistent with geothermal gradients in the range of 21 ± 4°C/km to 24 ± 5°C/km. M2 metamorphic conditions are not precisely determinable but temperatures and pressures were probably less than those attained during Mi. It is suggested that the rocks of central-western Spitsbergen were originally deposited in an aulacogen before the initiation of Caledonian diastrophism.  相似文献   

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