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1.
Malcolm J Drury 《Tectonophysics》1985,115(1-2)
Six new heat flow determinations are presented for Proterozoic mobile belts of the Churchill Province of the Canadian Shield, an area that was affected by several stages of the Hudsonian orogenic sequence (1.9-1.6 Ga ago). With other, previously published, values the mean of eight determinations considered reliable and representative and corrected for the effects of Pleistocene glaciation is 44 ± 7 mW m−2. Heat generation measurements have also been made; values range from 0.1–1.04 μW m−3.A linear relation between heat flow and heat production is apparent. The heat flow axis intercept is 37 mW m−2, and the scale depth is 11 km, compared with 28 mW m−2 and 13.6 km for the Archaean Superior Province. Approximately 20% of the Churchill heat flow appears to be derived from radioactive decay in the upper crust, compared with 30% for the Superior Province and shields as a whole. The observations imply that the heat flow-heat production relation for the Churchill Province should be written as Q = Qc + Qe + A0b where Qc is equivalent to the reduced heat flow for the Archaean terrain, b is similar for the two, and Qe is an additional component of heat flow in the Proterozoic mobile belts of the Churchill Province.A speculative tectonic model is presented. It is suggested that rifting along two axes of an original craton, which had lateral variations in near surface radiogenic element concentration, followed by erosion of the radiogenic layer and subsequent reconvergence of the cratonic segments, led to widespread redistribution of radioactive elements into the reactivated inter-rift crustal block. One result would be that crustal temperatures are higher in that part of the Churchill Province than in the Superior. 相似文献
2.
On the formation of granulites 总被引：23，自引：0，他引：23
S. R. BOHLEN 《Journal of Metamorphic Geology》1991,9(3):223-229
The tectonic settings for the formation and evolution of regional granulite terranes and the lowermost continental crust can be deduced from pressure–temperature–time (P–T–time) paths and constrained by petrological and geophysical considerations. P–T conditions deduced for regional granulites require transient, average geothermal gradients of greater than 35°C km?1, implying minimum heat flow in excess of 100 mWm?2. Such high heat flow is probably caused by magmatic heating. Tectonic settings wherein such conditions are found include convergent plate margins, continental rifts, hot spots and at the margins of large, deep-seated batholiths. However, particular P–T–time paths do not allow specific tectonic settings to be distinguished at this time. Under different conditions, both clockwise, CW (Pmax attained before Tmax), and anticlockwise, ACW (Pmax attained slightly after Tmax), paths are possible in the same tectonic setting. Both CW and ACW end-member paths can yield nearly isobaric cooling, IBC, paths. Such cooling paths are clearly not an artefact of thermobarometry, but can be constrained by solid–solid and devolatilization equilibria and geophysical modelling. In terms of understanding the evolution of the deep crust, a potentially significant group of regional granulite terranes are those that show evidence for ACW-IBC paths. Such paths are the likely result of: (i) episodic igneous activity resulting in intrusions within all levels of the crust, (ii) thickening of the crust by magmatic underplating, (iii) slow uplift as a result of the formation of a deep, garnet-rich crustal root and (iv) excavation resulting from a later tectonic event unrelated to that resulting in the formation of the granulites. The later event might be triggered by the delamination of the garnet-rich, lowermost crust. 相似文献
3.
Chandler A. Swanberg M.D. Chessman Gene Simmons S.B. Smithson G. Grnlie K.S. Heier 《Tectonophysics》1974,23(1-2)
Fifteen heat-flow determinations based on data from 34 drill holes throughout central and southern Norway are presented. Five combined heat-flow — heat-generation measurements from homogeneous Precambrian and Permian crystalline rocks from southern Norway confirm a linear relation between heat flow and heat generation of the form Q = Q0 + bA, where Q is surface heat flow (1hfu = 10−6 cal cm−2 sec−1), A is surface heat generation (1hgu = 10−13 cal cm−3 sec−1), and b and Q0 are constants. The slope of the line (b = 8.4 km) is in good agreement with results obtained from other stable continental areas, but the intercept (Q0 = 0.48 hfu) is considerably lower, suggesting the presence of a zone of low heat flow in southern Norway.Nine heat-flow determinations are from the Paleozoic, Caledonian orogenic belt. These values range from 1.09 to 1.29 hfu with an average value of 1.18, are consistent with model data from other Paleozoic orogenic areas including the Appalachian system of North America, and do not appear to reflect the low heat flow observed in southern Norway. 相似文献
4.
Detailed studies of terrestrial heat flow in southern and central Alberta estimated on the basis of an order of magnitude larger data base than ever used before (33653 bottom-hole temperature data from 18711 wells) and thermal conductivity values based on detailed rock studies and measured rock conductivities show significant regional and local variations and variations with depth. Heat flow values were estimated for each 3 × 3 township/range area (28.8 × 28.8 km). A difference in heat flow exists between Paleozoic and Mesozoic strata. Generally lower heat flow values are observed in the strata above the Paleozoic erosional surface (20–75 mW m−2). Much higher values are estimated for the Younger Paleozoic formations, with large local and regional variations between 40 and 100 mW m−2.Average heat flow values based on heat flow determinations below and above the Paleozoic surface that agree within 20% show an increase from values less than 40 mW m−2 in southern and southwestern Alberta to values as high as 70 mW m−2 in central Alberta. The predominance of regional downward groundwater flows in Mesozoic strata seem to be responsible for the generally observed heat flow increase with depth.The results show that the basin heat flow pattern is influenced by water movement and even careful detailed heat flow measurements will not give correct values of background steady-state heat flow within the sedimentary strata. 相似文献
5.
We present original heat flow determinations carried out during the Flumed surveys by the CEPM along three transects of the Provençal Basin (Gulf of Lions-West Sardinia; Toulon-Ajaccio; Nice-Calvi). A total of 121 thermal gradients and 37 conductivities are examined together with previous heat flow determinations along depth sections based on previous geophysical investigations. The mean observed heat flows are clearly shown to increase from NW to SE along the profiles (expect for the Toulon-Calvi transect, where results are ambiguous). The observed heat flow increases from 55–65 mW m−2 (Gulf of Lions) to 85 ± 14 mW m−2 (West Sardinia) and from 55–65 mW m−2 (Var Basin) to 103–108 mW m−2 (lower Corsican margin), suggesting an asymmetrical distribution of the observed heat flow. We examine whether this asymmetry could be caused by thermal refraction above salt structures or by any other superficial cause (sedimentation, topography, etc.) and conclude that an asymmetrical distribution of the subcrustal heat flow is probably the cause of this thermal regime. The elevated heat flows observed to the east in the abyssal plain, corrected for sedimentation, cannot be accounted for by the standard age/heat flow relations established for oceanic or attenuated continental lithosphere. The geodynamic significance of this speculative subcrustal origin remains poorly constrained, but could be related to post-rifting magmatic activity. Further investigations are necessary to elucidate the apparent high local variability of the heat flow on the upper margin of the Gulf of Lions and on the Provençal margin of the Ligurian Sea. 相似文献
6.
7.
Numerical modeling of thermal structure, circulation of H2O, and magmatism–metamorphism in subduction zones: Implications for evolution of arcs 总被引：2，自引：2，他引：0
Numerical models on thermal structure, convective flow of solid, generation and transportation of H2O-rich fluid in subduction zones are consolidated to have a comprehensive view of the subduction zone processes: heat balance, circulation of H2O magmatism–metamorphism, growth of arcs and continental margins. A large scale convection model with steady subduction of a cold old slab (130 Myr old) predicts rapid ( 100 Myr) cooling of subduction zones, resulting in cessation of magmatism. The model also predicts that the mantle temperature beneath arcs and continental margins is greatly affected by the effective temperature of the subducting slab, i.e., the age of the subducting slab. If subduction of a young hot slab, including ridge subduction, occurs every 60 to 120 Myr as is suggested for eastern Asia, the average temperature beneath arcs is increased by about 300 °C, which may explain the long-lasting magmatism in eastern Asia. Associated with subduction of young slabs and ridges, thermal structure and circulation of H2O are greatly modified to cause a transition from (1) normal arc magmatism, (2) forearc mantle melting, to (3) slab melting to produce a significant amount (100 km3) of granitic melts, associated with both high-P/T and low-P/T type metamorphism. The last stage of (3) can result in formation of a granitic batholith belt and a paired metamorphic belts. Synthesis of the numerical models and observations suggest that episodic subduction of young slabs and ridges can explain heat source for generating a large amount of granitic magmas of batholiths, synchronous formation of batholith and regional metamorphic belts, and P–T conditions of the paired metamorphism. Even the high-P/T metamorphism requires an elevated geothermal structure in the forearc region, associated with ridge subduction. Although the emplacement of the batholiths and the regional metamorphic belts, and the mass balance in subduction zones are not well constrained at present, the episodic event associated with ridge subduction is thought to be essential for net growth of arcs and continental margins, as well as for the long-term heat balance in subduction zones. 相似文献
8.
Nine new heat flow determinations and several measurements of radioactive heat generation are presented for the Superior Province. The average value of twenty-one heat flows now published for the Superior, corrected for Pleistocene glaciation, is 40 ± 8 mW/m2. Heat generation values are low generally less than 3 μWW/m3. Although individual values of the ratio of thorium to uranium vary considerably, the geometrical average of four is lower than results from other Archean rocks.A linear relation between the heat flow and radioactive heat generation may exist. The reduced heat flow, 21 mW/m2, and the characteristic depth, 14 km, from this relation are quite different from other heat flow provinces. Since large thicknesses of the crust have been eroded away and since the original heat generation was much larger than the values measured now, a linear relation equivalent to those found in younger heat flow provinces is not expected.To account for the large differences in heat flow and heat generation observed in different Archean shields an Archean crustal model is proposed which includes thin (2–4 km) radioactive surface veneers over some areas.The thermal parameters of a young crust may well determine whether or not it will survive. Since Archean times the heat flow of each newly stabilized region has been a constant, and since the time of formation or last orogeny the heat flow in each province has steadily decreased. The geothermal gradients in Archean crust have decreased the most, causing significant underplating, and increasing the strength of the crust. 相似文献
9.
Heat flow increases northward along Intermontane Belt in the western Canadian Cordillera, as shown by geothermal differences
between Bowser and Nechako sedimentary basins, where geothermal gradients and heat flows are ∼30 mK/m and ∼90 mW/m2 compared to ∼32 mK/m and 70 –80 mW/m2, respectively. Sparse temperature profile data from these two sedimenatary basins are consistent with an isostatic model
of elevation and crustal parameters, which indicate that Bowser basin heat flow should be ∼20 mW/m2 greater than Nechako basin heat flow. Paleothermometric indicators record a significant northward increasing Eocene or older
erosional denudation, up to ∼7 km. None of the heat generation, tectonic reorganization at the plate margin, or erosional
denudation produce thermal effects of the type or magnitude that explain the north–south heat flow differences between Nechako
and Bowser basins. The more southerly Nechako basin, where heat flow is lower, has lower mean elevation, is less deeply eroded,
and lies opposite the active plate margin. In contrast, Bowser basin, where heat flow is higher, has higher mean elevation,
is more deeply eroded, and sits opposite a transform margin that succeeded the active margin ∼40 Ma. Differences between Bowser
and Nechako basins contrast with the tectonic history and erosion impacts on thermal state. Tectonic history and eroded sedimentary
thickness suggest that Bowser basin lithosphere is cooling and contracting relative to Nechako basin lithosphere. This effect
has reduced Bowser basin heat flow by ∼10–20 mW/m2 since ∼40 Ma. Neither can heat generation differences explain the northerly increasing Intermontane Belt heat flow. A lack
of extensional structures in the Bowser basin precludes basin and range-like extension. Therefore, another, yet an unspecified
mechanism perhaps associated with the Northern Cordilleran Volcanic Province, contributes additional heat. Bowser basin’s
paleogeothermal gradients were higher, ∼36 mK/m, before the Eocene and this might affect petroleum and metallogenic systems. 相似文献
10.
H.C. Hardee 《Tectonophysics》1982,84(2-4)
Thermal convection above large shallow magma bodies in the crust is treated as a one-dimensional bottom-heated convection process in permeable media. Solutions for single-phase convection are briefly reviewed and a solution is developed for two-phase permeable convection in bottom-heated media. Heat flow measurement techniques are discussed for permeable geologic zones above magma bodies and these techniques give consistent results for solidifying lava lakes in Hawaii (Kilauea Iki, q=257 W/m2) and Iceland (Heimaey, q = 465 W/m2).The heat loss from a magma body is a strong function of the permeability when a two-phase convection zone occurs above the magma body, and the heat loss is independent of the thickness of the two-phase convection zone. In steady-state two-phase convection zones, where permeability does not vary appreciably with depth, convective heat flow restrictions tend to limit the maximum saturation temperatures at depth to around 250°C—an effect observed in many geothermal steam fields. A conduction-dominated transition zone tends to occur between the two-phase zone and the magma body and the thickness of this transition zone may easily range from a few meters to several kilometers, depending on the permeability. 相似文献
11.
Debris flow occurs frequently in mountainous regions in China. Because of the difficulties involved in predicting and catching
live debris flows, an assessment of the potential for debris flow is crucial in hazard mitigation. Magnitude–frequency (MF)
relations are of special significance in such assessments. In previous studies, MF relations have been inferred by analyzing
environmental factors and historical records and using empirical relations. This paper is concerned with the derivation of
MF relations at regional and valley scales, using a large database of statistics. At the regional scale, it is represented
by the distribution of the valley area, because the area is often taken to indicate the potential magnitude of debris flow.
Statistics from over 5,000 debris flow valleys in various provinces in China show that a power law holds for the distribution,
i.e., p(A) ∼ A
−n
, where p(A) is the percentage of valleys with area A and n varies with region and thus describes regional differences. At the valley scale, a case study focusing on Jiangjia Gully
(JJG) was conducted, and the MF relations derived from it were expressed by the distributions of discharge and runoff (i.e.,
the total volume) of living debris flows observed over the last 40 years. The distributions can be expressed as exponential
functions where the exponents vary with the events. These MF relations provide not only a potential quantitative reference
for practical purposes but also hint at the intrinsic properties of the debris flow. 相似文献
12.
辽河盆地东部凹陷热历史及构造—热演化特征 总被引：9，自引：5，他引：9
根据辽河盆地东部凹陷大地热流测量和镜质体反射率数据,恢复了该区的热历史,结果表明:东部凹陷热流呈现古热流高现今热流低的变化特征,沙河街组三段沉积期到东营组沉积期(距今43～25Ma)盆地热流为66～82mWm2,现今热流值为47～70mWm2。构造沉降史分析显示,盆地经历了早期的裂谷阶段(距今43～25Ma)和后期的热沉降阶段,裂谷阶段包含了两个裂谷亚旋回。盆地现今较低的大地热流和较高的古热流及典型的裂谷型构造沉降样式为东部凹陷的构造—热演化提供了重要认识。 相似文献
13.
ABSTRACT Active and remnant back-arc regions do not follow a typical conductive lithosphere cooling model, but instead have an apparent two-stage cooling, defined by a high heat flow back-arc region during subduction and a second post-subduction heating event that extends elevated heat flow for several 10s million years. Numerical one-stage cooling models have not reproduced observed heat flow anomalies in active subduction zones using physically realistic parameters and require a secondary post-subduction heating mechanism. Here, an extension driven-volcanism model is developed to examine extension driven heating and volcanism as a mechanism to produce a prolonged thermal anomaly within back-arc lithosphere. This model is tested using the recorded thermal evolution of the Northern Cordillera Volcanic Province (NCVP), a Neogene-Quaternary alkaline volcanic province located in the remnant back-arc region of the Pacific-North American subduction zone in British Columbia, Canada. A single steady-state lithosphere geotherm does not intersect all previously published temperature estimates, suggesting previous data record the thermal evolution of the NCVP. Calculated geotherms at equilibrium with the minimum and maximum MELTS temperatures predict an increase in reduced mantle heat flow (Qm ) from 43 to 72 mW/m2 and lithosphere thinning from a depth of 87 to 48 km. The newly developed extension-volcanism model reproduced the calculated pre- and post-volcanism thermal regimes for the NCVP and supports that extension within the remnant back-arc could produce the present heat flow anomaly and volcanism. The model most readily produces volcanism when Qm is ~45–65 mW/m2, a typical range for back-arcs. Back-arc regions are prime locations for limited volcanism because their warmer thermal regime minimizes tectonic stress requirements to produce volcanism. Additionally, two-stage cooling of back-arcs can be explained with a time-dependent extension-volcanism thermal feedback mechanism that is possible because of the subduction driven pre-heating of back-arc regions. 相似文献
14.
A major late Paleozoic depocentre, the Sverdrup Basin, Canadian High Arctic, has been largely left out of the latest Permian extinction debate, as early workers presumed Middle to Late Permian strata were absent. Basin-scale sequence-stratigraphic and chemostratigraphic correlations indicate Late Permian strata are only missing on the basin margins, where they were removed by sub-Triassic erosion, whereas continuous deposition is recorded in the basin centre. The varying degree of sub-Triassic erosion has significant impact on the carbon-isotope record across the Latest Permian Extinction event, where both the apparent rate and magnitude of carbon-isotope shift vary as a function of basin position. The intrabasin variability in apparent δ13Corg shift across the event is equivalent to that observed globally. In contrast to the abrupt isotope shifts recorded on the basin margin, similar to many records reported globally, the basin centre section shows a systematic shift associated with the Latest Permian Extinction. The Earth likely underwent a prolonged period of increasing environmental stress leading up to the event. 相似文献
15.
Quantitative Expression of Heat Flow versus Tectonic Deformation in the China Continent： The Effects of Plastic-Flow Network and Stable Block 总被引：1，自引：0，他引：1
WANG Sheng-zu Institute of Geology State Key Laboratory of Earthquake Dynamics China Earthquake Administration Beijing 《《地质学报》英文版》2006,80(1):97-109
1 Introduction It has been understood in the study of terrestrial heat flow that the distribution of heat flow in the interior of continent is influenced by a large number of factors, involving heat sources (e.g. mantle heat flow, heat production of radioactive elements in the crust, magmatic activity, and heat production of tectonic deformation), heat transfercondition (e.g. thermal conductivity and thickness of media), groundwater circulation, etc. On the background of these factors it is pa… 相似文献
16.
Successive temperature logs have been obtained over a period of two years in three closely-spaced boreholes in the Lac du Bonnet batholith of the Superior Province of the Canadian Shield. Two of the boreholes, of depth 450 m and 830 m, intersect a dipping fracture zone at 435–450 m. In both holes water is flowing from near the surface to the fracture zone at approximately 1.5–1.9·10−5 m3 s−1, the flow being inferred from analysis of the temperature logs. Below 25 m, temperatures in these two holes are 0.22–0.28 K lower than those in the third, 145 m, hole.The temperature data have been combined with over 200 thermal conductivity measurements on core samples to produce heat flow values. In the deepest hole heat flow above the fracture zone is 16% higher than that below the zone. This indicates that water is flowing up the fracture zone. The flow rate is approximately 0.3 g s−1 m−1, and the flow has existed for thousands of years.Observation of thermal effects of water flow in massive, relatively unfractured plutons in a region having little topographic relief causes one to be concerned about the reliability of heat flow values measured in similar environments.The regional heat flow is taken to be 50 mW m−2 after correction for glaciation effects. The average value of 24 determinations of radioactive heat generation in granitic core samples is 5.23 ± 1.11 μW m−3, which is more than three times higher than expected for such a heat flow in the Superior Province. This implies that the layer of high radioactive heat generation is thin, being not more than 4 km and probably about 1.3 km thick. 相似文献
17.
M. Wilding Sharon Webb D. Dingwell Giray Ablay Joan Marti 《Contributions to Mineralogy and Petrology》1996,125(2-3):151-160
Silicate melts form glasses in a variety of geological environments. The relaxation (equilibration) of the frozen glass structure
provides a means of investigating the quench rates of natural glasses, and this cooling history provides an important constraint
for models of melt dynamics. Phonolite glasses from the central volcanic edifice of Tenerife, Canary Islands indicate a range
of five orders of magnitude cooling rate, determined by modeling the relaxation of the structure-dependent property, enthalpy
(H) across the glass transition. The relaxation of enthalpy is determined by heat capacity (c
p
= ΔH/ΔT) measurement of natural glass samples by differential scanning calorimetry (DSC). Upon heating, the heat capacity curve in
the vicinity of the glass transition has a geometry characteristic of the previous cooling rate. A series of thermal treatments
applied to each individual sample results in a set of sample-specific parameters which are used to model the heat capacity
curve of the naturally cooled glass. The cooling rate is then derived. The equivalence of shear and enthalpic relaxation enables
the relaxation of enthalpy for these volcanic samples to be described by a general term for the evolution of fictive temperature.
Quench rates for thirty-one glasses are calculated to be within the range 10°C s–1 to 7°C per day. The cooling rates quoted are linear approximations across the glass transition. Within different volcanic
facies cooling rates depend on several factors. The most rapidly cooled glasses occur where samples lose heat by radiation
from the surface. Our analyses indicate that in certain environments, a natural annealing process results in slow quench rates.
This is interpreted as either a slow initial cooling process or the reheating of a glass to an annealing temperature within
the glass transition interval. The latter results in relaxation to a lower temperature structure. Controls on these processes
include the initial temperature and dissipation of thermal energy from the volcanic body. Our results are consistent with
an influence of volatiles on quench rates in volcanic bombs where glass adjacent to vesicular layers is relatively rapidly
quenched. We interpret this as a rapid quench rate frozen into the glass resulting from a change in viscosity due to volatile
degassing. In lava flows, the conduction of heat from the hot flow interior controls the cooling process and diminishes the
effect of volatile exsolution. Relaxation geospeedometry can be applied to glass samples from a variety of geological environments
where cooling rates cannot be measured directly. Such measurements provide a means of determining cooling rates for a variety
of volcanic processes, an independent calibration for existing temperature and time data and a means for testing cooling-rate-dependent
models.
Received: 9 January 1996 / Accepted: 13 May 1996 相似文献
18.
《Applied Geochemistry》1993,8(6):643-647
Mazor (1992) has reinterpreted several previous 36Cl studies. The studies he revised used extensive physical hydrogeological data to aid in interpretation of the 36Cl measurements. Major ion chemistry and other isotope tracers were considered in order to evaluate the groundwater geochemistry. The studies then used simple geochemical models to account for Cl behavior in the subsurface. The result of these 36Cl dating studies was in reasonable agreement with both numerical models of the aquifer systems and with independent geochemical studies.Mazor (1992) has reinterpreted these studies based on the assumption that spatial variation in chemical and isotope data should be attributed to unspecified “discontinuities” in the flow regime. The conceptual models of aquifer hydrodynamics resulting from this approach differ radically not only from the previous 36Cl interpretations, but also from the findings of virtually all previous hydrogeological and geochemical investigations. Although Mazor's “reinterpretations” are provocative, he does not show how they explain the data of the numerous previous studies better than the conceptual models presented by the authors of those studies, nor has he demonstrated that his new models are consistent with the fundamental physical laws governing groundwater flow. Until this is satisfactorily accomplished I will continue to prefer the original 36Cl interpretations. 相似文献
19.
Interaction of metamorphism, deformation and exhumation in large convergent orogens 总被引：11，自引：0，他引：11
Coupled thermal‐mechanical models are used to investigate interactions between metamorphism, deformation and exhumation in large convergent orogens, and the implications of coupling and feedback between these processes for observed structural and metamorphic styles. The models involve subduction of suborogenic mantle lithosphere, large amounts of convergence (≥ 450 km) at 1 cm yr?1, and a slope‐dependent erosion rate. The model crust is layered with respect to thermal and rheological properties — the upper crust (0–20 km) follows a wet quartzite flow law, with heat production of 2.0 μW m?3, and the lower crust (20–35 km) follows a modified dry diabase flow law, with heat production of 0.75 μW m?3. After 45 Myr, the model orogens develop crustal thicknesses of the order of 60 km, with lower crustal temperatures in excess of 700 °C. In some models, an additional increment of weakening is introduced so that the effective viscosity decreases to 1019 Pa.s at 700 °C in the upper crust and 900 °C in the lower crust. In these models, a narrow zone of outward channel flow develops at the base of the weak upper crustal layer where T≥600 °C. The channel flow zone is characterised by a reversal in velocity direction on the pro‐side of the system, and is driven by a depth‐dependent pressure gradient that is facilitated by the development of a temperature‐dependent low viscosity horizon in the mid‐crust. Different exhumation styles produce contrasting effects on models with channel flow zones. Post‐convergent crustal extension leads to thinning in the orogenic core and a corresponding zone of shortening and thrust‐related exhumation on the flanks. Velocities in the pro‐side channel flow zone are enhanced but the channel itself is not exhumed. In contrast, exhumation resulting from erosion that is focused on the pro‐side flank of the plateau leads to ‘ductile extrusion’ of the channel flow zone. The exhumed channel displays apparent normal‐sense offset at its upper boundary, reverse‐sense offset at its lower boundary, and an ‘inverted’ metamorphic sequence across the zone. The different styles of exhumation produce contrasting peak grade profiles across the model surfaces. However, P–T–t paths in both cases are loops where Pmax precedes Tmax, typical of regional metamorphism; individual paths are not diagnostic of either the thickening or the exhumation mechanism. Possible natural examples of the channel flow zones produced in these models include the Main Central Thrust zone of the Himalayas and the Muskoka domain of the western Grenville orogen. 相似文献
20.
Eleven new estimates of heat flow (q) from the southern Altai-Sayan Folded Area (ASFA) have provided update to the heat flow map of Gorny Altai. Measured heat flow in the area varies from 33 to 90 mW/m2, with abnormal values of >70 mW/mq at four sites. The anomalies may have a deep source only at the Aryskan site in the East Sayan (q = 77 mW/m2) while high heat flows of 75–90 mW/m2 obtained for the Mesozoic Belokurikha and Kalguty plutons appear rather to result from high radiogenic heat production in granite, which adds a 25–30 W/m2 radiogenic component to a deep component of 50–60 mW/m2. The latter value is consistent with heat flow estimates derived from helium isotope ratios (54 mW/m2 in both plutons). Heat flow variations at other sites are in the range from 33 to 60 mW/m2. The new data support the earlier inferences of a generally low heat flow over most of ASFA (average of 45–50 mW/m2) and of a “cold” Cenozoic orogeny in the area (except for southeastern ASFA), possibly driven by shear stresses associated with India indentation into Eurasia. 相似文献