Apatite and zircon fission-track dating from the Hirabayashi-NIED borehole, Nojima Fault, Japan: Evidence for anomalous heating in fracture zones

Fission-track (FT) analysis using apatite and zircon was performed on samples from two fracture zones (FZ) at the depths of 1140 and 1310 m within the 1838 m borehole core penetrating the Ryoke Granitic Rocks in the Nojima Fault at Nojima-Hirabayashi, Awaji Island, Japan, drilled just after the 1995 Hyogo-ken Nanbu earthquake. Clear discordance in apatite and zircon FT age was found for two samples located at  2 m below the central part of each FZs where the presence of pseudotachylyte and/or fault gouge would predict the largest amount of slip. Asymmetric distribution was identified by discordant ages with respect to the central part of FZs. These very local discordant ages in the fault reflect thermal anomalies caused by secondary heating with an inferred maximum temperature in the region between apatite and zircon closure temperatures at a time post-48 Ma. As a source of the secondary heating, heat transfer or dispersion via geothermal fluids caused presumably the observed similarity in asymmetric distribution of discordant FT ages at two different FZs. Other samples yield concordant FT zircon and apatite ages and these indicate rapid cooling within the bounds of two closure temperatures of these minerals at  60 Ma of the Ryoke Granitic Rocks.     

Thermobarometric data from a fossil zircon partial annealing zone in high pressure–low temperature rocks of eastern and central Crete, Greece

A fossil partial annealing zone of fission tracks in zircon is described from high pressure–low temperature (HP–LT) rocks of the Phyllite–Quartzite Unit (PQ) on the island of Crete, Greece. Correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data, and with new experimental annealing results, allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples.The zircon fission track (FT) ages of samples from the PQ across Crete range from original detrital signature through reduced to completely reset. The annealing is the result of a single heating period related to the HP–LT metamorphism with near-peak temperatures lasting for only a few million years some time between 24±1 and 20±1 Ma. In eastern Crete, where rocks have experienced temperatures of 300±50 °C and pressures of 0.8±0.3 GPa, zircon FT ages range from 414±24 to 145±10 Ma. Ages above 300 Ma occur mostly near the east coast of the island in rocks which have not been heated to above ca. 280 °C and probably represent a pre-Variscan source. Track lengths are already indicative of a substantial annealing at this temperature. Most of the zircon FT ages from eastern Crete scatter within error around the stratigraphic age. Samples with apparent zircon FT ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca. 320 °C. Towards the west, a sudden decrease to very young ages ranging from 17±2 to 18±1 Ma reflects a complete resetting at ca. 350 °C. Short tracks, however, are still observed. Throughout the central and western part of the island, ages are consistently below 22 Ma. Thermobarometric data for this area indicate maximum temperatures of 400±50 °C and pressures of 1±0.3 GPa. Only samples from western Crete, which have been exposed to 400±50 °C, show exclusively long tracks. Consequently, the high temperature limit of the zircon partial annealing zone (ZPAZ) appears to be between 350 and 400 °C.A significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0.5 GPa and at different temperatures, which fit the curves previously obtained by other authors at ambient pressure.     

Integration of zircon color and zircon fission-track zonation patterns in orogenic belts: application to the Southern Alps, New Zealand

An exhumed crustal section of the Mesozoic Torlesse terrane underlies the Southern Alps collision zone in New Zealand. Since the Late Miocene, oblique horizontal shortening has formed the northeastern–southwestern trending orogen and exhumed the crustal section within it. On the eastern side, rocks are zeolite- to prehnite–pumpellyite-grade greywacke; on the western side rocks, they have the same protolith, but are greenschist to amphibolite facies of the Alpine Schist. Zircon crystals from sediments in east-flowing rivers (hinterland) have pre-orogenic fission-track ages (>80 Ma) and are dominated by pink, radiation-damaged grains (up to 60%). These zircons are derived from the upper 10 km crustal section (unreset FT color zone) that includes the Late Cenozoic zircon partial annealing zone; both fission tracks and color remain intact and unaffected by orogenesis. Many zircon crystals from sediments in west-flowing rivers (foreland) have synorogenic FT ages, and about 80% are colorless due to thermal annealing. They have been derived from rocks that originally lay in the reset FT color zone and the underlying reset FT colorless zone. The reset FT color zone occurs between 250 and 400 °C. In this zone, zircon crystals have color but reset FT ages that reflect the timing of orogenesis.     

ESR detection of seismic frictional heating events in the Nojima fault drill core samples, Japan

We have analyzed the Nojima fault NIED 1800 m drill core samples by ESR (Electron Spin Resonance) to detect seismic frictional heating events, especially during the 1995 Kobe Earthquake. Dark gray fault gouge with foliation > 10 cm away from the fault plane at about 1140 m in depth, which was produced by ancient fault movements, has a FMR (ferrimagnetic resonance) signal. Heating experiments show that this FMR signal is derived from ferrimagnetic trivalent ion oxides (γ-Fe₂O₃: maghemite) with imperfect crystallinity, which is produced by thermal dehydration of γ-FeOOH (lepidocrocite) or Fe(OH)₃ (limonite). The existence of the FMR signal means that dry heating such as frictional heating once occurred, and that the frictional heat temperature along the dark gray fault gouge may have risen to over 350 °C during ancient seismic fault slip. In order to detect frictional heating events in fault zones, the increase of the FMR signal and the color change of fault gouge into dark gray or black are important indexes. On the other hand, no FMR signal is detected from the fault gouges just on two fault planes at about 1140 m and 1300 m in depth, which are considered to be possible main fault planes in the 1995 Kobe Earthquake. These two fault planes may not have played an important role of fault slip in the Earthquake.     

Temporal change in permeability of the Nojima fault zone by repeated water injection experiments

Three boreholes were drilled near the Nojima fault, which the 1995 Hyogoken–Nanbu earthquake occurred on. In order to research the properties and the healing process of the fault, water injection experiments were conducted every 3 years. In this report, we researched the permeability of the fault as a measurement of crack density or porosity of the fault zone. Pore water pressure changes in rock due to the water injections at one borehole were observed as discharge changes or groundwater level changes at the other borehole. Using numerical calculations, the permeability of the fault fracture zone was estimated for each experiment. The permeability has been decreasing as time passed, which is thought to show the fault healing process of the Nojima fault after the 1995 Hyogoken–Nanbu earthquake.     

Fission track analysis and thermotectonic history of the main borehole of the Chinese Continental Scientific Drilling project

The Chinese Continental Scientific Drilling (CCSD) project, part of the International Continental Drilling Program (ICDP), has completed drilling a 5158 m hole in the eastern part of the Dabie-Sulu ultrahigh-pressure metamorphic belt. This study reports on an apatite fission track analysis of core samples from 0 to 4000 m depth in the CCSD main hole (CCSD-MH). We determined the fission track ages of 38 apatite samples from different depths. The ages range between 98.6 ± 17.0 and 3.2 ± 1.3 Ma, showing a general decreasing trend with depth, from 87.1 ± 11.2 Ma at the surface to 3.2 ± 1.3 Ma at 3899 m depth. As a first approximation, an average uplift rate of ~ 35 m/Ma is calculated for the period 90-30 Ma. The trend in ages within the borehole shows some fluctuations, and indicates movements along major faults. It is inferred that the highest-level major normal fault occurs at a depth of ~ 350 m, recording a vertical displacement of ~ 400 m. Movement along another prominent normal fault at a depth of ~ 2150 m occurred subsequent to ~ 25 Ma. Three major reverse faults occur at about 2450, 3050 and 3250 m depth. Testing geological constrains against the fission track data set indicated an agreement with a reheating of the area during the late Cretaceous and Eocene, followed by cooling to ~ 80 °C during the Eocene and a low cooling until the samples reached their present-day position in the Donghai area.     

A fission-track and (U–Th)/He thermochronometric study of the northern margin of the South China Sea: An example of a complex passive margin

Zircon fission track (ZFT), apatite fission track (AFT) and (U–Th)/He thermochronometric data are used to reconstruct the Cenozoic exhumation history of the South China continental margin. A south to north sample transect from coast to continental interior yielded ZFT ages between 116.6 ± 4.7 Ma and 87.3 ± 4.0, indicating that by the Late Cretaceous samples were at depths of 5–6 km in the upper crust. Apatite FT ages range between 60.9 ± 3.6 and 37.3 ± 2.3 Ma with mean track lengths between 13.26 ± 0.16 µm and 13.95 ± 0.19 µm whilst AHe ages are marginally younger 47.5 ± 1.9–15.3 ± 0.5 Ma. These results show the sampled rocks resided in the top 1–1.5 km of the crust for most of the Cenozoic. Thermal history modeling of the combined FT and (U–Th)/He datasets reveal a common three stage cooling history which differed systematically in timing inland away from the rifted margin. 1) Initial phase of rapid cooling that youngs to the north, 2) a period of relative (but not perfect) thermal stasis at ~ 70–60 °C which increases in duration from the south to the north; 3) final-stage cooling to surface temperatures that initiated in all samples between 15 and 10 Ma. The timing and pattern of rock uplift and erosion does not fit with conventional passive margin landscape models that require youngest exhumation ages to be concentrated at or close to the rifted margin. The history of South China margin is more complex aided by weakened crust from the active margin period that immediately preceded rifting and opening of the South China Sea. This rheological inheritance created a transition zone of steeply thinned crust that served as a flexural filter disconnecting the northern margin of the South China block and site of active rifting to the south. Consequently whilst the South China margin displays many features of a rifted continental margin its exhumation history does not conform to conventional images of a passive margin.     

Fracture-zone conditions on a recently active fault: insights from mineralogical and geochemical analyses of the Hirabayashi NIED drill core on the Nojima fault, southwest Japan, which ruptured in the 1995 Kobe earthquake

An 1800-m-deep borehole into the Nojima fault zone was drilled at Nojima-Hirabayashi, Japan, after the 1995 Hyogo-ken Nanbu (Kobe) earthquake. Three possible fracture zones were detected at depths of about 1140, 1300, and 1800 m. To assess these fracture zones in this recently active fault, we analyzed the distributions of fault rocks, minerals, and chemical elements in these zones. The central fault plane in the shallowest fracture zone was identified by foliated blue-gray gouge at a depth of 1140 m. The degree of fracturing was evidently greater in the hanging wall than in the footwall. Minerals detected in this zone were quartz, orthoclase, plagioclase, and biotite, as in the parent rock (granodiorite), and also kaolinite, smectite, laumontite, stilbite, calcite, ankerite, and siderite, which are related to hydrothermal alteration. Biotite was absent in both the hanging wall and footwall across the central fault plane, but it was absent over a greater distance from the central fault plane in the hanging wall than in the footwall. Major element compositions across this zone suggested that hydrothermal alteration minerals such as kaolinite and smectite occurred across the central fault plane for a greater distance in the hanging wall than in the footwall. Similarly, H₂O+ and CO₂ had higher concentrations in the hanging wall than in the footwall. This asymmetrical distribution pattern is probably due to the greater degree of wall–rock fracturing and associated alteration in the hanging wall. We attributed the characteristics of this zone to fault activity and fluid–rock interactions. We analyzed the other fracture zones along this fault in the same way. In the fracture zone at about 1300 m depth, we detected the same kinds of hydrothermal alteration minerals as in the shallower zone, but they were in fewer samples. We detected relatively little H₂O+ and CO₂, and little evidence for movement of the major chemical elements, indicating little past fluid–rock interaction. In the fracture zone at about 1800 m depth, H₂O+ and CO₂ were very enriched throughout the interval, as in the fracture zone at about 1140 m depth. However, smectite was absent and chlorite was present, indicating the occurrence of chloritization, which requires a temperature of more than 200 °C. Only smectite can form under the present conditions in these fracture zones. The chloritization probably occurred in the past when the fracture zone was deeper than it is now. These observations suggest that among the three fracture zones, that at about 1140 m depth was the most activated at the time of the 1995 Hyogo-ken Nanbu (Kobe) earthquake.     

郯庐断裂带中桃源韧性剪切带剪切温压条件及锆石U-Pb分析

郯庐断裂带西侧的桃源韧性剪切带位于合肥市肥东县浮槎山的东麓,是郯庐断裂带的重要组成部分。左旋平移现象十分经典,走向北北东,垂直于大别造山带展布,带内大量发育高温糜棱岩。综合剪切带内基质的矿物组合、变形机制及电子探针分析结果,本文得出该韧性剪切带的变形温度为550~650℃,压力在0.5GPa左右,属高温中压变质环境,剪切深度大概在20km左右,后期抬升至地表。剪切带内不同岩石分别给出了~0.8Ga、~2.0Ga、~2.5Ga的锆石U-Pb基底年龄。推断0.8Ga和2.0Ga年龄具有华南板块的特征,而2.5Ga年龄岩石兼具有华南和华北板块的属性,仍无法判断其具体来自哪个板块。此外,剪切带内发育的同构造弱变形伟晶岩脉测得年龄为129Ma,指示郯庐断裂带肥东段在129Ma仍在进行左行剪切活动,但剪切强度已大幅衰减。     

Mesozoic thermal history of the Prebetic continental margin (southern Spain): Constraints from apatite fission-track analysis

Apatite fission-track analysis was applied to Triassic and Cretaceous sediments from the South-Iberian Continental Margin to unravel its thermal history. Apatite fission-track age populations from Triassic samples indicate partial annealing and point to a maximum temperature of around 100–110 °C during their post-depositional evolution. In certain apatites from Cretaceous samples, two different fission-track age populations of 93–99 and around 180 Ma can be distinguished. Track lengths associated with these two populations enabled thermal modelling based on experimental annealing and mathematical algorithms. These thermal models indicate that the post-depositional thermal evolution attained temperatures ≤ 70 °C, which is consistent with available vitrinite-reflectance data. Thermal modelling for the Cretaceous samples makes it possible to decipher a succession of cooling and heating periods, consisting of (a) a late Carboniferous–Permian cooling followed by (b) a progressive heating episode that ended approximately 120 Ma at a maximum T of around 110 °C. The first cooling episode resulted from a combination of factors such as: the relaxation of the thermal anomaly related to the termination of the Hercynian cycle; the progressive exhumation of the Hercynian basement and the thermal subsidence related to the rifting of the Bay of Biscay, reactivated during the Late Permian. Jurassic thermal evolution deduced from the inherited thermal signal in the Cretaceous sediments is characterized by progressive heating that ended around 120 Ma. This heating episode is related to thermal subsidence during Jurassic rifting, in agreement with the presence of abundant mantle-derived tholeiitic magmas interbedded in the Jurassic rocks. The end of the Jurassic rifting is well marked by a cooling episode apparently starting during Neocomiam times and ending at surface conditions by Albian times.     

Tectonic implications of damage zone-related fault-fracture networks revealed in drill core through the Nojima fault, Japan

1800 m of drill core through the Nojima fault zone, Japan, reveals subsidiary fault and fracture networks that developed in the fault zone that triggered the 1995 Ms 7.2 Kobe earthquake. The subsidiary fault zones contain a fault gouge of < 1 cm bounded by thin zones of foliated cataclasite or breccia. Fractures are filled with calcite veins, calcite-cemented breccias, clay, and iron-oxide and carbonate alternation of the granitic host rock. These features are typical of extensional fractures that form the conduit network for fluid flux close to a major fault zone. The zone of distributed deformation surrounding the main fault is 50 m in width, and the dip of the Nojima fault at > 1 km depth is 75°. The fault-fracture networks associated with the Nojima fault zone are coseismic and were filled with carbonate and fine-grained material during repeated seismic-related infiltration of the fault zone by carbonate-bearing subsurface water. This study shows that fault-related fracture networks plays an important role as fluid flow conduits within seismically active faults, and can change in character from zones of high permeability to low permeability due to cementation and/or pore collapse.     

Evaluating thermal history models for the Otway Basin, southeastern Australia, using (U-Th)/He and fission-track data from borehole apatites

New apatite helium and fission-track data from the Otway Basin are consistent with previously published borehole ages, confirming earlier suggestions that existing thermal models for basin evolution should be reevaluated. Analysis of the relationship between helium ages and grain size in newly analyzed samples, as well as in samples previously reported, reveals that grain size variations may contribute to the previously reported scatter in helium ages among aliquots of the same sample. In addition, systematic variations in apatite grain size with borehole depth or temperature may also have a significant effect on the interpretation of borehole helium age data. Incorporation of the observed grain size variations in Otway borehole apatites into forward models based on published thermal histories, principally based on vitrinite reflectance and fission-track data, suggests that existing models for the eastern Otway Basin are broadly consistent with the helium data. In contrast, thermal histories for western basin boreholes, now thought to be at maximum temperatures, predict helium ages that are generally older than the observed ages, implying that basin temperatures were hotter than indicated by the models. This discrepancy is consistent with a Cenozoic heating event in parts of the western Otway Basin similar to that documented for the eastern basin. The relatively wide spread of apparent apatite fission-track (AFT) ages and compositions compared to the restricted age range of helium measurements on coexisting grains, although not conclusive, supports previous suggestions that composition does not appear to affect the sensitivity of the He closure temperature in apatite.     

Numerical analysis of overburden soil subjected to strike-slip fault: Distinct element analysis of Nojima fault

A distinct element method analysis is carried out to examine the development of shear bands in overburden soil subjected to a strike-slip fault. About 2.3 million spherical particles are used in the analysis and the results are compared with the shears observed at the Nojima earthquake fault during the 1995 Hyogoken Nanbu earthquake. En echelon shears and secondary shears which strike at lower angles to the basement fault – typical in strike-slip faults – are observed in the numerical analysis. Simple shear in the horizontal plane and drag due to the dependence of velocity on depth are confirmed to control the helicoidal shape of Riedel shears. Rotation of the compressional direction toward the fault strike as a result of slip along Riedel shears is also verified. It is found that the compressional direction is more horizontal within the area enclosed by Riedel shears than in outside areas and that these compressional directions produce secondary lower-angle shears that are less helicoidal. It is shown that the formation of column-like structures of particles and their subsequent buckling play significant micromechanical roles in three-dimensionally wrenched shears. The results of the numerical analysis, such as shear intervals and striking angles, show a resemblance to observational results at sites where sediment contains coarse grains and is subjected to strike slip with a small dip component, although they are not exactly the same as those observed at locations with similar overburden thicknesses.     

The thermo-tectonic history of the Song-Kul plateau, Kyrgyz Tien Shan: Constraints by apatite and titanite thermochronometry and zircon U/Pb dating

The Song-Kul Basin sits on a plateau at the Northern and Middle Kyrgyz Tien Shan junction. It is a lacustrine basin, occupied by Lake Song-Kul and predominantly developed on igneous basement. This basement was targeted for a multi-method chronological study to identify the different magmatic episodes responsible for basement formation and to constrain the timing of the development of its present-day morphology. Zircon U/Pb dating by LA-ICP-MS revealed four different magmatic episodes: a Late Cambrian (~ 500 Ma) island arc system, a Late Ordovician (~ 450 Ma) subduction related intrusion, an Early Permian (~ 290 Ma) collisional stage, and a Middle to Late Permian (~ 260 Ma) post-collisional magmatic pulse. Middle to Late Triassic (~ 200–230 Ma) titanite fission-track ages and Late Triassic – Early Jurassic (~ 180–210 Ma) apatite fission-track ages and thermal history modeling indicate the Song-Kul basement was already emplaced in the shallow crust at that time. An exhumed fossil apatite fission-track partial annealing zone is recognized in the bordering Song-Kul mountain ranges. The area experienced only minor post-Early Mesozoic denudation. The igneous basement was slowly brought to apatite (U–Th)/He retention temperatures in the Late Cretaceous–Palaeogene. Miocene to present reactivation of the Tien Shan does not manifestly affect this part of the orogen.     

大别山东缘郯庐断裂带造山后左行平移活动时间：锆石LA-ICP-MS U-Pb定年结果的限定

郯庐断裂带在造山阶段之后发生了明显的左行平移活动,但到目前为止对于其发生时间仍存在较大争议。大别山东缘郯庐断裂带内存在一系列花岗质、基性岩脉,其形成与郯庐断裂带左行平移活动密切相关,因而对其形成年龄的测定可以为断裂带左行平移时间提供限定。本次工作在大别山东缘郯庐断裂带内糜棱岩及岩脉中采集了6个样品开展锆石LA-ICP-MS年龄测定。两个花岗质糜棱岩样品均得到了新元古代和印支期两组年龄结果,但并未得到早白垩世年龄结果,可能指示了强烈的构造变形抑制了锆石的生长。与断裂带左行平移活动同期的基性岩墙侵位时间为128 Ma左右;斜切糜棱岩面理的基性岩墙侵位于127 Ma 左右;发生韧性变形形成糜棱岩的二长花岗岩侵位时间为128 Ma左右;仅出现NE向劈理的钾长花岗岩侵位于126 Ma。综合以上结果,大别山东缘郯庐断裂带与下扬子地区存在类似的构造背景,其早白垩世左行平移事件的发生时间为128 Ma之前,之后断裂带在区域伸展背景下转变为正断层活动。     

Deep structure of the Nojima Fault, southwest Japan, estimated from borehole observations of fault-zone trapped waves

To estimate the deep structure of the southern part of the Nojima Fault, southwest Japan without the influence of near-surface structures, we analyzed the Love-wave-type fault-zone trapped waves (LTWs) recorded by a borehole seismometer at 1800 m depth. We examined the polarization, dispersion, and dominant frequency of the wavetrain following the direct S-wave in each seismogram to identify the LTW. We selected eight candidates for typical LTWs from 462 records. Because the duration of the LTW increases with hypocentral distance, we infer that the low velocity fault-zone of the Nojima Fault continues towards the seismogenic depth. In addition, since the duration of the LTW increases nonlinearly with hypocentral distance, we infer that the S-wave velocity of the fault-zone increases with depth. The location of events showing the LTW indicates that the fault-zone dips to the southeast at 75° and continues to a depth of approximately 10 km. We assumed a uniform low-velocity waveguide to estimate the average structure of the fault-zone. We estimated the average width, S-wave velocity, and Q_s of the fault-zone by comparing an analytical solution of the LTW with measured data. The average width, S-wave velocity, and Q_s of the fault-zone are 150 to 290 m, 2.5 to 3.2 km/s, and 40 to 90, respectively. Hence the fault-zone structure with a larger width and smaller velocity reduction than the fault-zone model estimated by previous surface observation is more suitable to represent the average fault-zone structure of the Nojima fault. The present study also indicated that the shallow layers and/or a shallow fault-zone structure drastically changes the characteristics of the LTW recorded at the surface, and therefore cause a discrepancy in the fault-zone model between the borehole observation and surface observation.     

Dating pseudotachylyte of the Asuke Shear Zone using zircon fission-track and U–Pb methods

Zircon fission-track (FT) and U–Pb analyses were performed on zircon extracted from a pseudotachylyte zone and surrounding rocks of the Asuke Shear Zone (ASZ), Aichi Prefecture, Japan. The U–Pb ages of all four samples are  67–76 Ma, which is interpreted as the formation age of Ryoke granitic rocks along the ASZ. The mean zircon FT age of host rock is 73 ± 7 (2σ) Ma, suggesting a time of initial cooling through the zircon closure temperature. The pseudotachylyte zone however, yielded a zircon FT age of 53 ± 9 (2σ) Ma, statistically different from the age of the host rock. Zircon FTs showed reduced mean lengths and intermediate ages for samples adjacent to the pseudotachylyte zone. Coupled with the new zircon U–Pb ages and previous heat conduction modeling, the present FT data are best interpreted as reflecting paleothermal effects of the frictional heating of the fault. The age for the pseudotachylyte coincides with the change in direction of rotation of the Pacific plate from NW to N which can be considered to initialize the NNE–SSW trending sinistral–extensional ASZ before the Miocene clockwise rotation of SW Japan. The present study demonstrates that a history of fault motions in seismically active regions can be reconstructed by dating pseudotachylytes using zircon FT thermochronology.     

新生代阿尔金断裂带的演化:来自沿线盆地沉积记录的启示SCIEI北大核心CSCD

阿尔金断裂带是青藏高原自印度与欧亚大陆碰撞后向北扩展的前缘断裂,其新生代活动性对于研究青藏高原隆升与扩展过程和机制具有重要意义。近些年,运用热年代学、断裂几何学和运动学、沉积学、磁性地层学和地震学等方法对阿尔金断裂带的性质、组成结构、断裂活动时代、走滑断裂运动特征、走滑位移量和走滑速率等进行了细致的研究,而对阿尔金断裂带沿线受其控制的新生代沉积盆地的地层年代、沉积演化特征虽然也有一定研究,但往往仅限于单个盆地,缺乏对沿线盆地整体的对比认识,造成对阿尔金断裂带走滑起始时间及阿尔金山的隆升历史存在不同的认识。本文对近二十年来阿尔金断裂带沿线新生代沉积盆地的磁性地层年代与沉积相演化的研究进展进行综述,建立阿尔金断裂带沿线盆地新生代沉积序列和年代框架;辅助热年代学等资料,提出阿尔金断裂带的三阶段演化模型:始新世-中中新世,阿尔金断裂带以大幅度的走滑运动为主,同时伴随着阿尔金山小范围的隆升;中中新世开始,阿尔金山开始大规模的隆升,伴随着较少量的走滑运动;晚中新世以来,阿尔金断裂带构造活动加强。     

Time evolution of hydraulic and electrokinetic parameters around the Nojima fault, Japan, estimated by an electrokinetic method

The Nojima Fault Zone Probe was designed to study the properties and healing processes of the Nojima fault, which is the surface fault rupture of the Hyogo-ken Nanbu earthquake (M7.2) of 1995 (1995 Kobe earthquake). In this project, water injection experiments were conducted in a borehole of 1800 m depth at the Nojima fault. We set up electrodes around the borehole and observed self-potential variations to investigate the magnitude of electrokinetic and hydraulic parameters around the Nojima fault zone. In the 1997 experiment, self-potential variations were in the range of a few to about 20 mV across 320–450 m electrode dipoles with hydraulic pressure variations from 3.5 to 4 MPa. In the 2000 experiment, self-potential variations were in the range of a few to about 85 mV across 160–260 m electrode dipoles with the hydraulic pressure variations from 3 to 4.5 MPa. In the 2003 experiment, self-potential variations were in the range of a few to about 30 mV across 20–80 m electrode dipoles with hydraulic pressure of 4 MPa. These observed self-potential variations were explained well with an electrokinetic effect due to the underground flow of the injected water. From the observed results, we estimated that the ratio of hydraulic parameters (permeability, porosity, and tortuosity) to electrokinetic parameters (zeta potential and dielectric constant) decreased approximately 40% during eight years after the earthquake. This result suggests that the healing process around the fault zone progress.     

苏鲁超高压变质岩的构造热历史：中国大陆科学钻探工程(CCSD)主孔（MH）和先导孔（PP2）的磷灰石裂变径迹约束

本文包括中国大陆科学钻（CCSD）主孔（MH）0~5000m和先导孔（PP2）0~1000m的磷灰石裂变径迹分折结果,先导孔PP2的裂变径迹表观年龄变化范围为79.5±5.1~50.4±6.2Ma,主孔的裂变径迹表观年龄变化范围为98.6±17.0~2.9±2.0Ma,主孔在4200m以下,磷灰石样品中实际上已不存在自发裂变径迹,表明裂变径迹时钟已经“置零”。实验资料表明,裂变径迹表观年龄值随样品深度的增加而逐渐减少,直到一定深度,即达到磷灰石的裂变径迹封闭温度（~120℃）以后,年龄值为零。根据主孔0~2000m和先导孔0~1000m的裂变径迹年龄剖面,作为一级近似,计算出超高压变质岩体在90~30Ma期间,平均隆升速度为~35m/Ma。对主孔测定了9个样品的约束径迹（Confined track）长度,样品约束径迹平均长度的变化范围约为13.1~7.4μm,总的变化趋势是：约束径迹平均长度随样品深度的增加而逐渐减少。样品的约束径迹长度分布都具有双峰型特征。根据裂变径迹年龄和约束径迹长度的资料,应用计算机模拟得到了样品的时间-温度（t-T）轨迹。结果表明,岩体从早白垩世（~120Ma）快速冷却以后,在晚白垩世和始新世又经历了两次加热作用,始新世末岩体所达到的温度大约是80℃,随后岩体则一直上升和缓慢冷却到现今所处的位置。在最后~30Ma岩体的平均隆升速度为~53m/Ma。