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1.
Neoproterozoic igneous and metamorphic complexes occur as tectonic domes in the Longmen Mountains of the western margin of the Yangtze Block, and are important in reconstructing the Rodinian supercontinent and constraining the timing and mechanism of tectonic denudational processes. The Pengguan dome consists of granitic intrusions and metamorphic rocks of the Huangshuihe Group and is tectonically overlain by ductilly deformed Sinian to Paleozoic strata. The plutonic intrusions consist of granites with abundant amphibolite enclaves. New LA-ICP-MS zircon U-Pb dating yielded an emplacement age of 809±3 Ma and a protolith age of 844±6 Ma for the granite. The granitic rocks have geochemical signatures typical of A-type granites, indicating their formation under an extensional environment, by melting of newly formed tonalite-trondhjemite-granodiorite (TTG) rocks. A detachment fault, characterized by variable ductile shear deformation of S-C fabric and ESE-ward kinematics, separates the Pengguan dome from the Sinian-Paleozoic cover. 40Ar/39Ar dating of muscovite from the mylonite in the detachment fault of the dome demonstrates that ductile deformation occurred at ~160 Ma. This study indicates the existence of a Neoproterozoic magmatic arc-basin system, which was denudated by a Jurassic middle crustal ductile channel flow along the Longmenshan thrust belt.  相似文献   

2.
Field studies and seismic data show that semi-brittle flow of fault rocks probably is the dominant deformation mechanism at the base of the seismogenic zone at the so-called frictional-plastic transition. As the bottom of seismogenic fault, the dynamic characteristics of the frictional-plastic transition zone and plastic zone are very important for the seismogenic fault during seismic cycles. Granite is the major composition of the crust in the brittle-plastic transition zone. Compared to calcite, quartz, plagioclase, pyroxene and olivine, the rheologic data of K-feldspar is scarce. Previous deformation studies of granite performed on a quartz-plagioclase aggregate revealed that the deformation strength of granite was similar with quartz. In the brittle-plastic transition zone, the deformation characteristics of granite are very complex, temperature of brittle-plastic transition of quartz is much lower than that of feldspar under both natural deformation condition and lab deformation condition. In the mylonite deformed under the middle crust deformation condition, quartz grains are elongated or fine-grained via dislocation creep, dynamic recrystallization and superplastic flow, plagioclase grains are fine-grained by bugling recrystallization, K-feldspar are fine-grained by micro-fractures. Recently, both field and experimental studies presented that the strength of K-feldspar is much higher than that of quartz and plagioclase. The same deformation mechanism of K-feldspar and plagioclase occurred under different temperature and pressure conditions, these conditions of K-feldspar are higher than plagioclase. The strength of granite is similar to feldspar while it contains a high content of K-feldspar. High shear strain experiment studies reveal that granite is deformed by local ductile shear zones in the brittle-plastic transition zone. In the ductile shear zone, K-feldspar is brittle fractured, plagioclase are bugling and sub-grain rotation re-crystallized, and quartz grains are plastic elongated. These local shear zones are altered to local slip-zones with strain increasing. Abundances of K-feldspar, plagioclase and mica are higher in the slip-zones than that in other portions of the samples (K-feldspar is the highest), and abundance of quartz is decreased. Amorphous material is easily formed by shear strain acting on brittle fine-grained K-feldspar and re-crystallized mica and plagioclase. Ductile shear zone is the major deformation mechanism of fault zones in the brittle-plastic transition zone. There is a model of a fault failed by bearing constant shear strain in the transition zone:local shear zones are formed along the fractured K-feldspar grains; plagioclase and quartz are fine-grained by recrystallization, K-feldspar is crushed into fine grains, these small grains and mica grains partially change to amorphous material, local slip-zones are generated by these small grains and the amorphous materials; then, the fault should be failed via two ways, 1)the local slip-zones contact to a throughout slip-zone in the center of the fault zone, the fault is failed along this slip-zone, and 2)the local slip-zones lead to bigger mineral grains that are in contact with each other, stress is concentrated between these big grains, the fault is failed by these big grains that are fractured. Thus, the real deformation character of the granite can't be revealed by studies performing on a quartz-plagioclase aggregate. This paper reports the different deformation characters between K-feldspar, plagioclase and quartz under the same pressure and temperature condition based on previous studies. Then, we discuss a mode of instability of a fault zone in the brittle-plastic transition zone. It is still unclear that how many contents of weak mineral phase(or strong mineral phase)will control the strength of a three-mineral-phase granite. Rheological character of K-feldspar is very important for study of the deformation characteristic of the granitic rocks.  相似文献   

3.
The spatial distribution map of 65 mid-large gold-deposits hosted in the granite-greenstone terrains of the North China Craton is first drawn. These gold deposits mainly concentrate in the Mesozoic remobilized Yinshan-Yan-shan-Liaoning-Jilin intracontinental collisional orogenic belt, the northern Qinling and the Jiaodong Mesozoic collisional orogenic belts, and the Mesozoic intracontinental fault-magmatic belts developed along the Taihangshan and the Tan-Lu faults; their mineralizing time is predominantly Jurassic-Cretaceous, i. e. the Yanshanian. The metallogenic geodynamic background is exactly the compression-to-extension transition regime during continental collision. The results are partly from the project entitled “The main types of gold mineralizations in China and their metallogenic model” (89-El) supported by the Ministry of Metallurgical Industry of China, and projects “Geology and metallogenesis of the main type gold deposits in East Chinan” (Grant No. 9488010) and “Study on ore-forming fluids of the Wangfeng gold deposit, Xinjiang” supported by the National Natural Science Foundation of China (Grant No. 49672119).  相似文献   

4.
Laboratory and field data indicate that rocks subjected to sufficiently high loads clearly deviate from linear behavior. Non-linear stress–strain relations can be approximated by including third and higher-order terms of the strain tensor in the elastic energy expression (e.g., the Murnaghan model). Such classical non-linear models are successful for calculating deformation of soft materials, for example graphite, but cannot explain with the same elastic moduli small and large non-linear deformation of stiff rocks, such as granite. The values of the third (higher-order) Murnaghan moduli estimated from acoustic experiments are one to two orders of magnitude above the values estimated from stress–strain relations in quasi-static rock-mechanics experiments. The Murnaghan model also fails to reproduce an abrupt change in the elastic moduli upon stress reversal from compression to tension, observed in laboratory experiments with rocks, concrete, and composite brittle material samples, and it predicts macroscopic failure at stress levels lower than observations associated with granite. An alternative energy function based on second-order dependency on the strain tensor, as in the Hookean framework, but with an additional non-analytical term, can account for the abrupt change in the effective elastic moduli upon stress reversal, and extended pre-yielding deformation regime with one set of elastic moduli. We show that the non-analytical second-order model is a generalization of other non-classical non-linear models, for example “bi-linear”, “clapping non-linearity”, and “unilateral damage” models. These models were designed to explain the abrupt changes of elastic moduli and non-linearity of stiff rocks under small strains. The present model produces dilation under shear loading and other non-linear deformation features of the stiff rocks mentioned above, and extends the results to account for gradual closure of an arbitrary distribution of initial cracks. The results provide a quantitative framework that can be used to model simultaneously, with a small number of coefficients, multiple observed aspects of non-linear deformation of stiff rocks. These include, in addition to the features mentioned above, stress-induced anisotropy and non-linear effects in resonance experiments with damaged materials.  相似文献   

5.
Ｓｔｕｄｙｏｎｔｈｅｐａｔｔｅｒｎａｎｄｍｏｄｅｏｆｖｅｒｔｉｃａｌｃｒｕｓｔａｌｄｅｆｏｒｍａｔｉｏｎｄｕｒｉｎｇｔｈｅｓｅｉｓｍｏｇｅｎｉｃｐｒｏｃｅｓｓｏｆｉｎｔｒａｐｌａｔｅｓｔｒｏｎｇｅａｒｔｈｑｕａｋｅｓ杨国华，桂昆长，巩曰沐，杨春花，韩...  相似文献   

6.
A suite of alkali-rich porphyry with 26. 5–37. 6Ma occur along the Jinsha River suture zone in west Yunnan. They are characterized by LREE-rich distribution patterns and no Eu anomaly. These porphyries have formed in post-collisional environment; (87Sr/8bSr) of porphyries, amphibolite xenolithes and associated basalts are 0.707 3, 0.706 5-0.707 l and0.705 8-0.706 5, ENd(T) are -3.4-6.3, -2.1-7.4 and -3.3 respectively. Pb isotope compositions of these rocks also show a little difference. The evidence shows that the porphyry could be derived from partial melting of the “crust-mantle mixed layer”. The relation between Cenozoic magmatism and intraplate deformation since Paleogene has been discussed. Project supported by the Nat~onal Natural Science Foundation of China (Grant Nos. 49472102 and 49232030).  相似文献   

7.
Olivine flow mechanisms at 8 GPa   总被引：1，自引：0，他引：1  
The mechanisms responsible for high-temperature olivine deformation are investigated at a pressure of 8 GPa and temperatures up to 1780 K. San Carlos olivine specimens of different average grain sizes (0.5 and 5 μm) were deformed simultaneously between hard-alumina pistons during relaxation experiments. These experiments are carried out in a multi-anvil high-pressure apparatus coupled with synchrotron X-ray radiation. The different grain-size specimens experienced identical P-T-stress condition at any given time. A new method for measuring strains and strain rates (≥10−6 s−1) of specimens at high pressure is documented. This method uses time-resolved in situ X-ray imaging and an image-analysis computation. The microstructures of run products, recovered after being quenched at different temperatures were characterized by transmission electron microscopy (TEM). We find that high-temperature olivine flow is grain-size insensitive at 8 GPa, which suggests that dislocation creep dominates olivine deformation at high pressure. This result is confirmed by the TEM investigation of our deformed specimens in which we find evidences of the activation of olivine dislocation slip systems. Specimen microstructures are consistent with dynamic recrystallization as an assisting process in olivine deformation during the high-pressure experiments. Extrapolation of our results to the low stress level and large grain size expected in the mantle suggests that dislocation creep assisted by dynamic recrystallization may also dominate natural olivine deformation in the upper mantle.  相似文献   

8.
Analysis of cut-and-cover tunnels against large tectonic deformation   总被引：2，自引：0，他引：2  
Tunnels are believed to be rather “insensitive” to earthquakes. Although a number of case histories seem to favor such an argument, failures and collapses of underground structures in the earthquakes of Kobe (1995), Düzce–Bolu (1999), and Taiwan (1999) have shown that there are exceptions to this “rule”. Among them: the case of tunnels crossed by fault rupture. This paper presents the analysis and design of two highway cut-and-cover tunnels in Greece against large tectonic dislocation from a normal fault. The analysis, conducted with finite elements, places particular emphasis on realistically modeling the tunnel-soil interface. Soil behavior is modeled thorough an elastoplastic constitutive model with isotropic strain softening, which has been extensively validated through successful predictions of centrifuge model tests. A primary conclusion emerging from the paper is that the design of cut-and-cover structures against large tectonic deformation is quite feasible. It is shown that the rupture path is strongly affected by the presence of the tunnel, leading to development of beneficial stress-relieving phenomena such as diversion, bifurcation, and diffusion. The tunnel may be subjected either to hogging deformation when the rupture emerges close to its hanging-wall edge, or to sagging deformation when the rupture is near its footwall edge. Paradoxically, the maximum stressing is not always attained with the maximum imposed dislocation. Therefore, the design should be performed on the basis of design envelopes of the internal forces, with respect to the location of the fault rupture and the magnitude of dislocation. Although this study was prompted by the needs of a specific project, the method of analysis, the design concepts, and many of the conclusions are sufficiently general to merit wider application.  相似文献   

9.
ＣｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｆａｕｌｔｒｏｃｋｓａｎｄｐａｌｅｏｅａｒｔｈｑｕａｋｅｓｏｕｒｃｅａｌｏｎｇｔｈｅＫｏｋｔｏｋａｙＥｒｔａｉｆａｕｌｔｚｏｎｅ，Ｘｉｎｊｉａｎｇ，ＣｈｉｎａＬＡＮＢＩＮＳＨＩ１）（史兰斌）ＣＨＵＡＮＹＯＮ...  相似文献   

10.
Attempts to build a “constant-stress-drop” scaling of an earthquake-source spectrum have invariably met with difficulties. Physically, such a scaling would mean that the low-frequency content of the spectrum would control the high-frequency one, reducing the number of the parameters governing the time history of a shear dislocation to one. This is technically achieved through relationships of the corner frequency of the spectrum to the fault size, inevitably introduced in an arbitrary manner using a constant termed “stress drop”. Throughout decades of observations, this quantity has never proved to be constant. This fact has fundamental physical reasons. The dislocation motion is controlled by two independent parameters: the final static offset and the speed at which it is reached. The former controls the low-frequency asymptote of the spectrum while the latter its high-frequency content. There is no physical reason to believe that the static displacement should predetermine the slip rate, which would be implied if the “stress drop” were constant. Reducing the two parameters to just one (the seismic moment or magnitude) in a “scaling law” has no strict justification; this would necessarily involve arbitrary assumptions about the relationship of one parameter to the other. This explains why the “constant-stress-drop” scaling in seismology has been believed in but never reconciled with the data.  相似文献   

11.
Gabbroic rocks and amphibolites were collected from the KR03‐01‐D10 dredge site located on the West Arm Rise of the Godzilla Megamullion, close to the Parece Vela Rift which appears to correspond to the termination area of a detachment fault, the Philippine Sea. The gabbroic rocks and amphibolites reveal the occurrence of a high hydrothermal activity in the lower crust close to a paleo‐ridge. In the gabbroic rocks, plagioclase compositions of both porphyroclasts and matrix were transformed into sodium‐rich compositions close to albite. Amphiboles are of secondary rather than igneous origin based on their microstructural occurrences. In the amphibolites, anorthite contents of porphyroclasts and matrix plagioclase are relatively lower than those of the gabbroic rocks, whereas the chemical compositions of amphibole within the amphibolites are similar to those of amphibole within the gabbroic rocks. Amphibolites represent the product of retrograde metamorphism associated with hydrothermal alteration of the gabbroic body by the reaction: clinopyroxene + calcic plagioclase + fluid → amphibole + sodic plagioclase. The estimated temperatures of the amphibolites derived from the amphibole thermobarometer and the gabbroic rocks derived from the hornblende–plagioclase geothermometer show ～700–950°C and 650–840°C, respectively. The hydrothermal alteration recorded in the gabbroic rocks possibly occurred under high‐T conditions; the rocks were then metamorphosed to the amphibolites during a retrogressive stage. Our study indicates that amphibolitization took place with various degrees of deformation. It may imply that the hydrothermal activity increased as the Godzilla Megamullion developed as an oceanic core complex in the paleo‐ridge.  相似文献   

12.
Ar-Ar dating results of late Mesozoic-Cenozoic volcanic rocks from the Yanji area, NE China provide a new volcano-sedimentary stratigraphic framework. The previously defined “Triassic-Jurassic” volcanic rocks (including those from Sanxianling, Tuntianying, Tianqiaoling and Jingouling Fms.) were erupted during 118―106 Ma, corresponding to Early Cretaceous. The new eruption age span is slightly younger than the main stage (130―120 Ma) of the extensive magmatism in the eastern Central Asian Orogenic Belt and its adjacent regions. Subduction-related adakites occurring in the previously defined Quanshuicun Fm. were extruded at ca. 55 Ma. Based on these new Ar-Ar ages, the late Mesozoic to Palaeocene volcano-sedimentary sequences is rebuilt as: Tuopangou Fm., Sanxianling/Tuntianying Fm. (118―115 Ma), Malugou/Tianqiaoling Fm. (K1), Huoshanyan/Jingouling Fm. (108―106 Ma), Changcai Fm. (K2), Quanshuicun Fm. (~55 Ma) and Dalazi Fm. Our results suggest that subduction of the Pa- laeo-Pacific Ocean beneath the East Asian continental margin occurred during 106 to 55 Ma, consistent with the paleomagnetic observations and magmatic records which indicated that the Izanagi-Farallon ridge subduction beneath the southwestern Japan took place during 95―65 Ma.  相似文献   

13.
Based on study of Nd isotopic composition for 101 rocks of various types from Tianshan Orogen, the age and character of basement and continental crustal evolution of the Tianshan Orogen were proposed. It is deduced that the continental crustal basement of the Tianshan Orogen was formed 1. 8 Ga ago. The protolith of its metamorphic rocks was derived from long-term depleted mantle source in the ancient are tectonic setting probably. The Tianshan Orogen is obviously different from the North Tarim Block in age of basement and post-evolution history. It was also shown that Paleozoic continental crustal growth happened extensively in the Tianshan Orogen, which is distinguished from Yangtse Block and Cathaysia Block in eastern China. Project supported by the National Natural Science Foundation of China (Grant No. 49633250). It belongs to the National “305” Project in Xinjiang, which is one of the National Key Projects in the Ninth Five-Year Plan (96-915-07-05A).  相似文献   

14.
ＴｈｅｐａｔｔｅｒｎｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｔｈｅｔｅｎｄｅｎｃｙｖａｒｉａｔｉｏｎｓｏｆｅａｒｔｈｒｅｓｉｓｔｉｖｉｔｙａｎｄｉｔｓｒｅｌａｔｉｏｎｔｏｅａｒｔｈｑｕａｋｅｓＨｅ－ＹｕｎＺＨＡＯ（赵和云）（ＥａｒｔｈｑｕａｋｅＲｅｓｅａｒ...  相似文献   

15.
基于速率与状态依赖性摩擦本构关系理论框架,在热水条件下研究了角闪石断层泥的摩擦滑动性质并与闪长岩的另一种主要矿物斜长石的摩擦滑动性质进行了对比.摩擦实验是在三轴实验系统上完成,有效正应力200 MPa,孔隙压力30 MPa,并将加载速率在1.22 μm/s和 0.122 μm/s之间实施了切换.结果表明角闪石的摩擦系数均值为0.70±0.01,随着温度增加没有系统性的变化,整体低于斜长石的摩擦系数(0.75±0.01);计算与实验表明,角闪石和斜长石的摩擦系数的体积分数加权平均值与闪长岩的摩擦系数基本一致;角闪石在实验温度范围内(100～614 ℃)显示速率强化(a-b>0),与斜长石在整个温度范围内的速率弱化(a-b<0)正好相反;角闪石的速率依赖性在整个实验温度范围内无系统性的变化.  相似文献   

16.
The formation and development environment of the “old red sands” on South China coasts is discussed according to the investigation in the field and laboratory works. The authors believed that the “old red sands” are the aeolian sediments deposits in the last glacial period of late Pleistocene when the sea level was lower than the present, and the laterization took place under the hot and wet climate during the later interglacial and postglacial periods when the sea level was relatively high. Project supported by the National Natural Science Foundation of China (Grant No. 49671012)  相似文献   

17.
沂沭断裂带古应力值的探讨   总被引：2，自引：0，他引：2       下载免费PDF全文
本文侧重于利用变形矿物显微构造估算断裂带古应力值的一些理论分析和方法介绍。并以变形石英晶内自由位错密度ρ和方解石变形双晶百分比分别估算了沂沭断裂带西支北段的沂水-汤头断裂及鄌郚-葛沟断裂燕山晚期(K_1后)构造活动的应力值,其结果分别为1000—1500巴和700—1100巴量级。断裂带显微构造可能表明在地质时期的构造应力场作用中,稳态位错蠕变既可发生于韧性变形,又可发生于脆—韧性变形过程中。考虑到断层带“水”的因素,估算中采用McCormick关系式较Weathers关系式可能更接近实际  相似文献   

18.
Zircon U-Pb results of basalt from the Dashizhai Town in Inner Mongolia, NE China, shows that the basaltic lava was erupted at 439±3 Ma, much older than the “Permian basalts” as previously thought. These rocks show arc-type trace element patterns (i.e., Nb-Ta depletion and light REE and large ion lithophile element enrichment) and unradiogenic Sr and highly radiogenic Nd and Hf isotope compositions. They can be subdivided into two petrogenetic groups: Group 1 basalts have relatively high TiO2, MgO and compatible elements and low Sr and Th, characterized by mid-oceanic ridge basalt (MORB)-type Sr-Nd-Hf isotope compositions (87Sr/86Sr(i)=0.7028−0.7032, εNd(t)=+9.8−+11.2, εHf(t)=+16.1−+18.4). Group 2 has lower TiO2, MgO and compatible elements and higher Sr and Th, and relatively evolved Sr-Nd-Hf isotope compositions (87Sr/86Sr(i)=0.7037−0.7038, εNd(t)=+5.7−+7.3, εHf(t)=+12.6−+13.0). Both groups were interpreted as melts derived from a metasomatized mantle wedge formed during the subduction of Paleo-Asian Ocean. The mantle source for Group 1 was probably a highly isotopically depleted oceanic mantle modified by predominant slab fluids; whereas subducted sediments had an important contribution to the melting source for Group 2. The petrogenesis of the Dashizhai basalts provides clear evidence for early Paleozoic subduction of the Paleo-Asian Ocean, and the highly radiogenic Nd and Hf compositions in these rocks suggest that these lavas and their possible intrusive counterparts were one of the important components for Phanerozoic crustal growth. Our and previous studies on the “Dashizhai Formation” volcanic rocks yield an unrealistic eruption range of 440-270 Ma for different rock types, we thus advise to disassemble the previously defined “Dashizhai Formation” into multiple lithologic units and to reinterpret the spatial and temporal distributions of different volcano-sedimentary associations. Supported by National Basic Research Program of China (Grant No. 2006CB403504)  相似文献   

19.
Immersed tunnels are particularly sensitive to tensile and compressive deformations such as those imposed by a normal seismogenic fault rupturing underneath, and those generated by the dynamic response due to seismic waves. The paper investigates the response of a future 70 m deep immersed tunnel to the consecutive action of a major normal fault rupturing in an earthquake occurring in the basement rock underneath the tunnel, and a subsequent strong excitation from a different large-magnitude seismic event that may occur years later. Non-linear finite elements model the quasi-static fault rupture propagation through the thick soil deposit overlying the bedrock and the ensuing interaction of the rupture with the immersed tunnel. It is shown that despite imposed bedrock offset of 2 m, net tension or excessive compression between tunnel segments could be avoided with a suitable design of the joint gaskets. Then, the already deformed (“injured”) structure is subjected to strong asynchronous seismic shaking. The thick-walled tunnel is modelled as a 3-D massive flexural beam connected to the soil through properly-calibrated nonlinear interaction springs and dashpots, the supports of which are subjected to the free-field acceleration time histories. The latter, obtained with 1-D wave propagation analysis, are then modified to account for wave passage effects. The joints between tunnel segments are modeled with special non-linear hyper-elastic elements, properly accounting for their 7-bar longitudinal hydrostatic pre-stressing. Sliding is captured with special gap elements. The effect of segment length and joint properties is explored parametrically. A fascinating conclusion emerges in all analysed cases for the joints between segments that were differentially deformed after the quasi-static fault rupture: upon subsequent very strong seismic shaking, overstressed joints de-compress and understressed joints re-compress—a “healing” process that leads to a more uniform deformation profile along the tunnel. This is particularly beneficial for the precariously de-compressed joint gaskets. Hence, the safety of the immersed tunnel improves with “subsequent” strong seismic shaking!  相似文献   

20.
Strongly mylonitic rocks associated with the regionally extensive Norumbega fault zone in south-central Maine provide an excellent opportunity for testing the effects of mylonitization on argon isotopic systems in muscovite. 40Ar/39Ar muscovite age spectra from samples outside the zone of mylonitization are relatively undisturbed and have well defined Early Carboniferous plateau ages. In contrast to these nonmylonitized samples, all age spectra for muscovite from the mylonites are highly discordant. They are characterized by young ages at low extraction temperatures, which systematically increase to ages that equal the plateau ages for muscovite collected outside the mylonite zone. Detailed petrographic observations suggest that these systematic discordances reflect a mixing of argon components from older, relict, muscovite porphyroclasts and fine-grained white mica aggregates that recrystallized during mylonitic deformation.

Total gas ages of five different grain size fractions separated from the same mylonite sample become progressively younger with decreasing grain size; indicating a larger component of the recrystallized grains in the finer grain size fractions. Although the three finest grain size fractions give different total gas ages and do not overlap in age for most of their release spectra, their initial increments do coincide, at approximately 290 Ma. This indicates a minimal older age contribution from the relict porphyroclasts in the initial increments and suggests the 290 Ma age provides a good estimate for the time of mineral growth associated with mylonitic deformation. These data, combined with kinematic analysis, reveal that the segment of the Norumbega fault zone studied, the Sandhill Corner fault, is a Late Carboniferous-Early Permian dextral strike-slip fault. A lack of significant offset in regional Early Carboniferous mineral age patterns across the fault suggests that displacement was probably less than 30 km.

This study demonstrates that 40Ar/39Ar dating methods can be used to date deformational events effectively, as long as several important criteria are met. First and foremost, samples must be well characterized prior to analysis. Dynamic recrystallization must have occurred at or below the closure temperature of the mineral to be analyzed. Regional cooling patterns must also be established through detailed thermochronology so that mineral ages and age spectra from the deformed rocks can be compared to regional cooling ages of the same mineral. Finally, the effects of excess argon must be negligible.  相似文献   


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