Journal of Asian Earth Sciences

Published by Elsevier
Online ISSN: 1367-9120
Publications
Article
A large mafic dyke from the NNW-trending dyke swarms in the Eastern Block of the North China Craton was dated by SHRIMP U-Pb age analysis. This dyke occurs near Mt. Taishan in Shandong Province; it cuts Neoarchean tonalite, adamellite and diorite plutons. Two types of zircons were found in the dyke. Type 1 zircons were inherited from the host rocks and gave a SHRIMP U-Pb age of 2544±24 Ma with a weighted mean 207Pb/206Pb age of 2523±18 Ma. Type 2 zircons were crystallized from the dyke magma and yielded a concordant SHRIMP U-Pb age of 1830±17 Ma with a weighted mean 207Pb/206Pb age of 1837±18 Ma, indicating that the large dyke at Taishan was emplaced at ∼1830 Ma. The mafic dyke swarm provides evidence of a phase of extension in the Eastern Block of the North China Craton at ∼1.8 Ga. This dyke has a similar age to dyke swarms in the Western Block and in the Central Orogen Belt of the North China Craton. This lithospheric extension, led to the opening of the Yanliao and Zhongtiao aulacogens. The similar ages and orientations of ∼1.8 Ga dyke swarms throughout the North China Craton demonstrate that at that time the Eastern and Western blocks were united and that the amalgamated craton experienced widespread extension.
 
Article
The Neoarchean Nellore greenstone belt, located along the eastern margin of the Eastern Dharwar Craton, was the site for younger igneous activity. The timing of this magmatism and the host metabasalt, critical for constraining extensional events along the deformed southeast margin of the Eastern Dharwar Craton, was conducted by the Sm–Nd method.Samples from the large differentiated gabbroic Kandra igneous complex, a subset Kandra group a, define an isochron age of 1926 ± 110 Ma, Ndi = 0.51006 ± 12, MSWD = 0.98 (n = 5), εNd = −1.7, and the Kandra group b subset yielded a Model 3 isochron age of 1882 ± 120 Ma, Ndi = 0.50994 ± 14, MSWD = 1.8 (n = 4), εNd = −5.1. Whereas the three samples from north Pamuru gabbro-anorthosite yielded an isochron age of 1882 ± 160, Ndi = 0.51012 ± 18, MSWD = 0.064, εNd = −1.7, the Kandra group a and north Pamuru samples regressed together yielded a preferred isochron age of 1911 ± 88 Ma, Ndi = 0.51008 ± 10, MSWD = 0.62 (n = 8), εNd = −1.6, for the emplacement of gabbros. In contrast host greenstone belt metabasalt from Chundi yielded a Sm–Nd isochron age of 2693 ± 94 Ma, Ndi = 0.50920 ± 8, MSWD = 1.4 (n = 4), εNd = +1.2, whereas regressing the Chaganam and Chundi samples yielded an isochron age of 2654 ± 100 Ma, Ndi = 0.50923 ± 9, MSWD = 1.5 (n = 11), εNd = +0.7. Basal metapelite, underlying the metabasalt yields old Nd model ages between 2888 and 3054 Ma.The results of this study show that the ∼2.7 Ga Nellore greenstone belt was intruded by enriched MORB-type gabbros at ∼1911 Ma. It is proposed that this Palaeoproterozoic magmatism formed in response to a major extensional event along the Eastern Dharwar Craton margin that likely initiated breakup from the southeastern margin of the North China Craton. This exposed craton margin later evolved as the site for collisional events during the Late Palaeoproterozoic to Early Mesoproterozoic.
 
Article
Was the abrupt climate cold reversal called the Younger Dryas (YD) a global climate excursion? This study presents the first evidence for YD glacial advances on the Tibetan Plateau, derived from 10Be, 26Al, and 21Ne exposure ages of two erratics with a weighted mean age of about 11,600 years bp from a moraine at the eastern margin of the Tibetan Plateau. This implies that the YD climate signal, commonly thought to be initiated by decreased North Atlantic Deep Water Formation and transferred by ocean circulation, was even recorded at the inner-continental, high-altitude site of Tibet, implying atmospheric transport and thus a global character for this abrupt climatic change.
 
Article
Variations of orbital-driven insolation, ice volume, and greenhouse gas effects have been proposed as major controlling factors in determining the timing and amplitude of Quaternary cyclic climate changes. However, it remains to be determined how the internal feedback in the tropical atmosphere and ocean and the coupling between the low- and high-latitude systems may have produced instability or non-cyclic changes in the long-term climate evolution. Such “abnormalities” have been reported increasingly from paleoclimatic reconstructions in East Asia and the western Pacific for a prolonged warm and humid climate interval during marine isotope stage (MIS) 13–15, ∼475–610 kya. To better address the climate abnormality in MIS 13–15 that has been observed in the western Pacific, here we report high-resolution late Quaternary planktic foraminifer faunal abundance and faunal sea surface temperature (SST) records from the International Marine Past Global Change (IMAGES) program core MD972142, which was retrieved from the southeastern South China Sea (SCS). Our results indicate that the faunal assemblages and SSTs in the southeastern SCS express a substantially prolonged, unusual warm interglacial-type climate condition in MIS 13–15. The climate was abnormally warm during the cold MIS 14. Our study also suggests a lowering of sea surface salinity (SSS) during MIS 13–15. While the western Pacific climate experienced a persistently warm and humid period at MIS 14, a “normal” cooling (∼2 °C) condition on the surface of the eastern equatorial Pacific existed concomitantly. While assessing possible interpretations of this “abnormal” climate interval in MIS 13–15, our study indicates that an enhanced interhemispheric and/or longitudinal temperature gradient across the basin-wide Pacific cannot be ruled out. A change in the sensitivity of the East Asian Monsoon (EAM) that controlled temperature and precipitation patterns in East Asia and the western Pacific is probably also important or responsible for this climate abnormality. Based on our evidence, we suggest that the tropical dynamics would have played a role in the climate abnormality in MIS 13–15, through maintaining or even increasing the longitudinal SST gradient in the equatorial Pacific, which may have intensified the low-latitude trade winds in the eastern component of the Walker Circulation that drove a longer duration and/or stronger intensity of the summer vs. winter EAM.
 
Article
The background concentrations of 13 soil trace elements, copper (Cu), lead (Pb), zinc (Zn), cadmium (Cd), nickel (Ni), chromium (Cr), mercury (Hg), arsenic (As), selenium (Se), cobalt (Co), vanadium (V), manganese (Mn), and fluorine (F), from approximately 205 pedons in Tibet, China are reported here for the first time. The 13 trace element concentrations follow an approximately log–normal distribution. While the mean concentrations of Hg and Se are lower and As is higher than the average concentration for all of China, concentrations of the other trace elements are similar to the national average. Trace element concentrations are related to vegetation and human activity also played a notable role on the contents of trace elements in Tibet. The parent material relationship for all 13 soil trace element concentrations follows the pattern: shale>sandstone≅igneous rock≅limestone>alluvial sediment>glacial deposits>lake sediments; while for vegetation and human activity the concentration pattern is farmland=shrub>forests>meadow>prairie>marsh and others. The soil trace element concentrations on the Tibetan Plateau are related primarily to the parent material, but were also affected by vegetation and human activity.
 
Article
An earthquake of Mw 5.1 occurred on March 14, 2005, in the seismically active Koyna–Warna region in western India, the site known for the largest reservoir triggered seismicity (RTS) in the world. For more than four decades, earthquakes with M ⩾ 4.0 have occurred in this region at regular intervals. Impoundment of reservoirs and changes in lake levels can trigger earthquakes by two processes of stress modifications, namely direct loading effect of the reservoir and diffusion through various faults and fractures. In this paper we analysed the reservoir water level data at Koyna and Warna reservoirs prior to the occurrence of the March 14, 2005 earthquake, to explain the dominant mechanism behind its occurrence and its correlation with the observed coseismic changes. We conclude that the diffusion process, not the reservoir load effect, is the dominating mechanism triggering earthquakes in the region. The coseismic changes in deep well water levels sensitive to earth tides are found to be to the order of 1–12 cm.
 
Article
The Longgang volcanic field, located in northeastern China, is volcanically active with a number of eruptions during the Quaternary but the chronology of the eruptions is poorly defined. Some tephra layers are well preserved in the annually laminated sediments of maar lakes in the region, and facilitate the construction of a much improved chronological framework for the volcanic history of the area. The results of our investigations reveal that three basaltic explosive eruptions occurred at AD 460, 11460 cal yr BP and 14000 cal yr BP, respectively. The largest explosive basaltic eruption (AD 460) produced a thick black scoria layer in the Longgang volcanic field, including lakes. The tephra distribution and chronological data suggest that this eruption is likely to be from the Jinlongdingzi volcano. Two basaltic flood eruptions occurred at Jinlongdingzi. The earlier basaltic eruption produced a lava flow that spread over a forest and encased standing trees. Two radiocarbon ages obtained from charcoal samples collected from the burned remains of these trees are 1828–1989 cal yr BP and 2164–2359 cal yr BP. In the most recent stage of volcanism, the lava flow extended only ca. 2 km, and flowed into Lake Dalongwan. From the present status of the forest ecosystem, which has not yet reached the fully mature successional stage, we estimate that this lava is very young (ca. a few hundreds years old). Jinlongdingzi is a potentially dangerous volcano. Monitoring and assessment of the potential hazards in the Longgang volcanic field should be carried out in the future.
 
Article
The Dauki Fault, which is inferred to go through the southern margin of the Shillong Plateau, is an E–W trending reverse one inclined towards the north. The Dauki Fault was believed to be active during the Late Quaternary time by the geomorphic features of the Shillong Plateau, the gravity anomaly data, and uplifted Tertiary and Quaternary deposits on the southern foothills of the Shillong Plateau. However, previous studies did not show any specific evidence that the Dauki Fault is active, since active fault survey such as satellite photo interpretation and trench investigation was not performed hitherto. We carried out CORONA satellite photo interpretation and trench investigation across the Dauki Fault at Gabrakhari Village for the first time. Consequently small fault strands and clear unconformity accompanied with faulting were confirmed in the trench. However, these small fault strands may be secondary ones branched from a main fault which may be concealed under the trench. The time of seismic event, which is inferred from unconformity, is dated back to A.D. 1500–1630. The seismic event during A.D. 1500–1630 may correspond with the 1548 earthquake which is currently a first recorded large earthquake in Bangladesh. Furthermore, sand dikes due to paleo-liquefaction, which reach near the ground surface, were confirmed at the trench. According to radiocarbon age, the sand dikes were formed during the 1897 Ms. 8.0 Great Assam earthquake.Highlights► We conducted active fault survey on the southern margin of the Shillong Plateau. ► The Dauki Fault was first confirmed by trench investigation. ► The Dauki Fault has ruptured during 16th century. ► The seismic event may correspond with the 1548 earthquake.
 
Article
Seismo-electromagnetic phenomena refers to the electric and magnetic field perturbations that may be caused due to geophysical activities like earthquakes and volcanic eruptions. Due to the existence of such phenomena before earthquakes they may be regarded as short term precursors to earthquakes. Keeping in mind the in situ measurements for detection of such phenomena, the satellite based techniques are of great interest because they keep a constant track of the seismically active zones globally. With the objective of detecting the electromagnetic emissions in the ionosphere, the DEMETER satellite has been launched on 29th June 2004 from Baikonour in order to study the ionospheric perturbations associated with seismic activities. In this paper, we discuss some interesting results of electromagnetic emissions that are observed before a series of recent Indonesian earthquakes in the Jawa region with a major shock measuring 7.7 magnitude on Richter scale which occurred on 17 July 2006. The emissions have been observed in the Ultra Low Frequency (ULF)/Extremely Low Frequency (ELF) range of electromagnetic spectra.
 
Article
The eastern margin of the Tibetan Plateau is bounded by a N–S-trending active fault zone, including the Zemuhe Fault, which is an important tectonic boundary in studies of continental dynamics and deformation modes. Here, we present the kinematic mechanism and deformation features of co-seismic surface ruptures caused by a large historic earthquake that occurred upon the Zemuhe Fault. Field investigations and interpretations of aerial photographs reveal a NNW–SSE-trending surface rupture zone, less than 100 m wide, defined by en echelon fractures, mole tracks, and fault scarps over a length of 60 km. Trench excavations and radiocarbon age data confirm that the surface rupture zone was produced by the 1850 M 7.5 Xichang earthquake. Gullies preserved on the youngest alluvial fans and the lowest terrace risers in the area record systematic left-lateral offsets of 1.4–6.0 m and vertical offsets of 0.2–0.65 m resulting from the 1850 earthquake. Topographic and geologic evidence reveals that the spatial distribution of the 1850 co-seismic surface rupture was controlled by pre-existing geological structures of the Zemuhe Fault. The present results confirm that the Zemuhe Fault plays an important role as a major strike-slip fault in the southeastward motion of the southeastern Tibetan Plateau, and that the southern segment of the Zemuhe Fault has high seismic potential.
 
Article
During a 42 year period (1893–1935), the Swedish explorer Sven Hedin led and co-ordinated four expeditions to remote and inhospitable parts of Central Asia (Tibet, Xinjiang, Pamir). Along with collaborators he collected a diverse collection of just under 3100 petrological specimens. Petrographic examples of high pressure metamorphic blueschists, mantle peridotites and serpentinites, granitoids, K-rich alkaline lavas, mylonites, and a range of clastic and fossil rich carbonate sedimentary rocks are present. This collection is a major asset for scientists studying the history of continental collision between India and Asia, and the uplift of the Tibetan plateau.A spreadsheet listing all the samples collected during Hedin's first three expeditions into Tibet (commencing 1893, 1899, 1906) includes a brief description and location of each specimen, with additional information on the availability of thin sections. Samples are cross-referenced with the geographical position of Hedin's campsites indicated on maps published with his extensive reports. Most samples, and a number of thin sections, are available for loan from the Swedish Museum of Natural History, Stockholm. We also describe a smaller collection of specimens and thin sections from Hedin's fourth (1927–35, Sino-Swedish) expedition, currently housed at the Institute of Earth Sciences, Uppsala University. Hedin's career as an explorer, highlighting the geological significance of his work and the reasons that it has remained largely ignored by the majority of Himalayan and Central Asian researchers for so many years, is outlined.
 
Article
The earthquakes of November 1951 constitute the most destructive seismic episode in the recorded history of the Longitudinal Valley, eastern Taiwan. However, information about their source parameters is sparse. To understand the relationship between the 1951 ruptures and new interpretations of the regional neotectonic architecture of the Longitudinal Valley, we re-evaluated the November 1951 ruptures by analyzing old documents, reports and photographs, and by interviewing local residents who experienced the earthquake. As a result, we have revised significantly the rupture map previously published. We divide the surface ruptures from south to north into the Chihshang, Yuli, and Rueisuei sections. The first shock of the 1951 series probably resulted from the Chihshang rupture, and the second shock probably resulted from the Yuli and Rueisuei ruptures. The lengths of these ruptures indicate that the two shocks had similar magnitudes. The Chihshang and Rueisuei ruptures are along segments of the Longitudinal Valley fault, a left-lateral oblique fault along which the Coastal Range thrusts westward over the Longitudinal Valley. The Yuli rupture, on the other hand, appears to be part of a separate, left-lateral strike-slip Yuli fault, which traverses the middle of the Longitudinal Valley. The complex behavior of these structures and interaction between them are important in understanding the future seismic hazard of the area.
 
Article
The 80-km-long surface rupture of the Chelungpu fault in the 21 September 1999, Chichi, Taiwan Mw=7.6 earthquake resulted in a surface scarp with vertical throws of 2–9 m, and horizontal heaves of 4–8 m. Few major thrust faults have broken the surface in the past century, and the Chelungpu surface rupture is of interest in that it provides a morphological template for the identification of paleo-surface thrusts in similar neotectonic environments such as the Himalaya. The toe of the thrust is found emplaced gently over underlying hanging-wall materials, partly by prograde hanging-wall rotation and partly by simple shear, leaving few overt clues as to the total amount or sense of slip. Despite the large surface slip near the toe of the Chelungpu thrust its emplacement appears to have been relatively slow. MSK (the Medvedev–Sponheuer–Karnik 1981 revision of the Seismic Intensity Scale MSK81 supersedes the Mercalli Intensity scale for the description of acceleration-induced damage to modern buildings) Intensity VIII accelerations were imposed on buildings on the hanging-wall, and Intensity VII on the footwall, decaying in both directions by perhaps one intensity unit a few hundred meters from the rupture. The somewhat moderate amplitude of these accelerations, for a rupture with several meters of slip, is attributed to non-linear dissipative deformation near the toe of the rupture. The partitioning of thrusting into basal slip and hillside steepening in some locations on the Chelungpu fault suggests that the estimation of paleoseismic slip from the offset of piercing points crossing historic thrust faults elsewhere may result in underestimates of fault slip.
 
Article
We summarize the structural characteristics of the surface ruptures of the 1999 Mw 7.6 Chi-Chi earthquake in western Taiwan and discuss the geological interaction of the Chelungpu fault with adjacent faults. Based on geological investigations, seismological analyses, and GPS measurements of surface co-seismic displacements, we describe the regional 3-D fault plane and slip distribution of the Chi-Chi earthquake and compare these to the geological features of the Chelungpu fault. We find that one key feature of the Chelungpu fault is the stratigraphy-controlled slip surface: at the level of the uppermost few kilometers, the Chelungpu fault slip plane generally follows the bedding plane of the Pliocene Chinshui shale. The second key feature of the Chelungpu fault is the difference in structurally geometric configuration between its northern and southern segments. The northern Fengyuan segment shows a bedding-parallel thrust fault within east-dipping strata in both footwall and hanging wall. In contrast, the southern Tsaotun segment exhibits east-dipping strata are overthrust onto flat-lying recent alluvial deposits. These two features not only explain a hinterland imbricate thrusting on the hanging-wall of the Fengyuan segment, but also explain the change in strike of the Chi-Chi surface ruptures at the northern end. The southern end of the 1999 Chi-Chi rupture is interpreted to be linked to a series of NW-trending strike-slip faults. In particular, we propose that the Luliao strike-slip fault served as the lateral ramp of the Chelungpu fault, and the Gukeng strike-slip fault acted as a barrier to end the southern propagation of the 1999 rupture. Geomorphic features and paleoseismological data indicate that the range-front Chelungpu fault has generated large earthquakes during the last several thousand years. Alternatively, in the Miaoli area to the north and the Chiayi area to south, historical earthquakes as well as active geomorphic features are not restricted on the range-front thrust faults. Instead, more complicated structures, including tightly spaced folds, duplex structures, and strike-slip faults are involved in seismogenic processes. A more detailed investigation of regional structural characteristics is needed for mitigation against the seismic hazards in the 300-km-long active fold belt in western Taiwan, where several damaging large earthquakes have been documented during the last century.
 
Article
The 21 September 1999 earthquake (MW 7.6) produced a surface rupture that extended for 100-km in a general north–south direction in front of the Western Foothills, central Taiwan. The study area, located in a segment of the fold–thrust belt of central Taiwan, provides an important natural laboratory to study the relationship between active thrust deformation and fluvial terrace development. We recognize, from west to east, three subparallel thrusts, the Sanyi, Houli, and Shihkang faults in the northern part of the earthquake disaster area. The 1999 earthquake rupture occurred only along the Shihkang fault, whereas the other two faults were inactive. Along the Tachia River in the hanging wall of the Shihkang fault, eight well-developed terrace levels are observed, and can be subdivided into lateritic (Lt5–Lt1) and non-lateritic terraces (Ft3–Ft1). Five levels of lateritic terrace (Lt5–Lt1) are located in the hanging wall of the Houli fault, and a lateritic terrace (Lt5) is present in the hanging wall of the Sanyi fault. Stratigraphic and elevation correlations between these well-developed fluvial terraces in relationship to nearby geologic structures show that the Sanyi fault is the oldest structure. Lateritic terraces of at least 10,000 yr bp, for example, overlie the Sanyi fault, but correlative terraces associated with the Houli fault are offset. These types of terrace correlations allow us to define the progressive development of the thrust system within the Western Foothills.
 
Article
Palynological and sedimentological studies of a series of slimes collected from a 284 m-long drill-well from the Kathmandu Basin reveal paleoclimatic records and environmental changes within the Kathmandu Valley during the last 2.5 myr. The slimes are composed of fluvio-deltaic and lacustrine sediments comprising sand beds of 66.3 m and mud beds of 218 m in length. Pollen analyses show Quercus and Cyclobalanopsis are predominant, with frequencies exceeding 70%. Pinus, Alnus and Gramineae are the next dominant taxa. Three fossil pollen zones were discriminated; each zone reflects major climatic change: Zone I, the oldest stage, indicates a cool and rather wet climate during 400 kyr from ca. 2.5 to 2.1 Ma; Zone II, the middle stage, reflects a warm and relatively dry climate without remarkable fluctuation; Zone III is characterized by seven cycles of warm-and-wet and cold-and-dry climate, which reflect the alternation of glacial and interglacial periods. The last cold maximum, 11 m deep, corresponds to the last glacial age around 20 kyr bp, judging from the 14C dating of the uppermost part of the lacustrine sediments.The Paleo-Kathmandu Lake is likely to have been initiated at around 2.1 Ma and to have been filled with black organic mud, the Kalimati Clay. The top of the Kalimati Clay is eroded and was overlain by fluvial sand after the last glacial age. The abrupt appearance of a 4 m-thick fossiliferous sand bed at the top of the middle member suggests a lowering of water level at around 1 Ma.
 
Article
We investigated the characteristics of the precursory seismicity changes associated with the M=6.8 Nemuro Peninsula earthquake, January 28, 2000 by applying the RTL (Region–Time–Length) algorithm to the earthquake catalogue of the Japan Meteorological Agency (JMA). The RTL parameters at the epicentre indicated that a seismic quiescence started in 1995 and reached its minimum during October 1996. An activation stage with a duration of about eight months followed. Our detailed investigations indicated that the RTL anomaly around 1996 was not an artificial effect due to the changes of the model parameters, the upgrade of the JMA seismic network or the process of aftershock elimination. The spatial distribution of quiescence in 1996 revealed a significant anomaly in a broad region around the epicentre of the Nemuro Peninsula earthquake. Following the quiescence stage, an activation zone, which was on the order of the rupture length of this earthquake, was obtained around the epicentre during October 1996–July 1997. The consistency of the rupture region and the anomalous activation zone that appeared after the seismic quiescence stage may provide useful information for determining the future risk zones. This study may strengthen the understanding of the seismogenic process of strong earthquakes.
 
Article
In this paper, we examine pre-earthquake ionospheric anomalies by the total electron content (TEC) derived from a ground-based receiver of the global positioning system (GPS). A network of eight GPS receivers is used to construct daily latitude-time-TEC (LTT) plots to monitor the crest of equatorial ionization anomaly (EIA) in the Taiwan area. Three parameters of the strength, location, and formation time of the EIA crest are extracted. A 15-day running medians of the three parameters and the associated upper and lower quartiles are utilized as the references for identifying abnormal signals for all of the 150 M ≧ 5.0 earthquakes in the Taiwan area during 2001–2007. Results show that the EIA crest significantly moves equatorward (poleward) and appears in an earlier (later) time of the afternoon period a few days before (after) the earthquakes along the Taiwan longitude. The two parameters of the EIA crest location and occurrence time can be employed to detect ionospheric earthquake precursors. The results further imply that atmospheric electric fields generated around the epicenter of a forthcoming earthquake during the preparation period are essential.
 
Article
Mistakenly perceived as safe from the hazards of tsunami, Malaysia faced a rude awakening by the 26 December 2004 Andaman tsunami. Since the event, Malaysia has started active research on some aspects of tsunami, including numerical simulations of tsunami and the role of mangrove as a mitigation measure against tsunami hazards. An in-house tsunami numerical simulation model TUNA has been developed and applied to the 26 December 2004 Andaman tsunami to simulate the generation, propagation and inundation processes along affected beaches in Malaysia. Mildly nonlinear bottom friction term in the deeper ocean is excluded, as it is insignificant to the simulation results, consistent with theoretical expectation. On the other hand, in regions with shallow depth near the beaches, friction and nonlinearity are significant and are included in TUNA. Simulation results with TUNA indicate satisfactory performance when compared with COMCOT and on-site survey results.
 
Article
The May 12, 2008, Mw 7.9 Wenchuan earthquake was induced by failure of two of the major faults of the Longmen Shan thrust fault zone along the eastern margin of Tibet Plateau. Our study focused on trenches across the Yingxiu–Bichuan fault, the central fault in the Longmen Shan belt that has a coseismic surface break of more than 200 km long. Trenching excavation across the 2008 earthquake rupture on three representative sites reveals the styles and amounts of the deformation and paleoseismicity along the Longmen Shan fault. Styles of coseismic deformation along the 2008 earthquake rupture at these three sites represent three models of deformation along a thrust fault. Two of the three trench exposures reveal one pre-2008 earthquake event, which is coincident with the pre-existing scarps. Based on the observation of exposed stratigraphy and structures in the trenches and the geomorphic expressions on ground surface, we interpret the 2008 earthquake as a characteristic earthquake along this fault. The interval of reoccurrence of large earthquake events on the Central Longmen Shan fault (the Yingxiu–Beichuan fault) can be inferred to be about 11,000 years according to 14C and OSL dating. The amounts of the vertical displacement and shortening across the surface rupture during the 2008 earthquake are determined to be 1.0–2.8 m and 0.15–1.32 m, respectively. The shortening rate and uplift rate are then estimated to be 0.09–0.12 mm/yr and 0.18–0.2 mm/yr, respectively. It is indicated that the deformation is absorbed mainly not by shortening, but by uplift along the rupture during the 2008 earthquake.
 
Article
The Ms 8.0 Wenchuan earthquake of May 12, 2008 is one of the most disastrous earthquakes in China. The earthquake triggered tens of thousands of landslides over a broad area, including shallow, disrupted landslides, rock falls, deep-seated landslides, and rock avalanches, some of which buried large sections of some towns and dammed the rivers. The purpose of this study is to investigate correlations between the occurrence of landslides with geologic and geomorphologic conditions, and seismic parameters. Over 56,000 earthquake-triggered landslides, with a total area of 811 km2, are interpreted using aerial photographs and remote sensing images taken following the earthquake. The spatial distribution of these landslides is analyzed statistically using both landslide-point density (LPD), defined as the number of landslides per square kilometer, and landslide-area density (LAD), the percentage of the area affected by landslides, to determine how the occurrence of landslides correlates with distance from the epicenter, distance from the major surface rupture, seismic intensity and peak ground acceleration (PGA), slope angle, slope aspect, elevation, and lithology. It is found that both LAD and LPD have strong positive correlations with slope steepness, distance from the major surface rupture and seismic intensity, and that Pre-Sinian schist, and Cambrian sandstone and siltstone intercalated with slate have the most concentrated landslide activities, followed by the Permian limestone intercalated with shale, and Devonian limestone. Statistical analyses also indicate that the major surface rupture has influence on the spatial distribution of landslides, because LAD and LPD are relatively higher on the hanging wall than on the footwall. However, the correlation between the occurrence of landslides with distance from the epicenter of the earthquake is complicated, rather than a relatively simple negative correlation as found from other reported cases of earthquakes. This is possibly due to complicated rupture processes of the earthquake.
 
Article
Bad weather conditions usually limit the acquisition of optical remote sensing images, while all day and all weather synthetic aperture radar (SAR) shows the ability of providing timely remote sensing data for emergency response and rescue works after earthquake. Because SAR is sensitive to the surface changes caused by earthquake, the modified electromagnetic behaviour by geological disasters and the collapse of buildings can be recorded in SAR images as backscattering intensity changes. Absolute radiometric calibration was performed to SAR products to derive backscattering coefficient sigma nought from image digital number (DN). Based on change detection methods, Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) data and TerraSAR-X data acquired for the Ms 8.0 Wenchuan earthquake were used to extract earthquake damage information. This study revealed that landslides showed stronger backscattering and barrier lakes showed lower backscattering in post-earthquake 10 m ALOS PALSAR images comparing to pre-earthquake, and collapsed buildings showed lower backscattering compared to un-collapsed buildings in 1 m TerraSAR-X image. Results showed that SAR data with different spatial resolutions are useful for different earthquake damage information extraction: medium spatial resolution SAR data, e.g. 10 m ALOS PALSAR data, were efficient for secondary geological disaster extraction; high-resolution SAR data, e.g. 1 m TerraSAR-X data, with the help of ancillary GIS data or high-resolution optical data, could be used to extract building collapse information in urban areas. This study indicates that SAR remote sensing data can provide earthquake damage information at early emergency stage and assist the field surveying, further damage assessment and post-earthquake reconstruction.
 
Article
A Mw 6.3 magnitude earthquake occurred on October 6, 2008 in southern Damxung County within the N–S trending Yangyi graben, which forms the northern section of the Yadong-Gulu rift of south-central Tibet. The earthquake had a maximum intensity of IX at the village of Yangyi (also Yangying) (29°43.3′N; 90°23.6′E) and resulted in 10 deaths and 60 injured in this sparsely populated region. Field observations and focal mechanism solutions show normal fault movement occurred along the NNE-trending western boundary fault of the Yangyi graben, in agreement with the felt epicenter, pattern of the isoseismal contours, and distribution of aftershocks. The earthquake and its tectonic relations were studied in detail to provide data on the seismic hazard to the nearby city of Lhasa.
 
Article
This study attempts to analyse paleoceanographic changes in the Central Indian Ocean (Deep Sea Drilling Project Site 237), linked to monsoon variability as well as deep-sea circulation during the Plio-Pleistocene. We used factor and cluster analyses of census data of the 34 most dominant species of benthic foraminifera that enabled us to identify five biofacies: Astrononion umbilicatulum–Uvigerina proboscidea (Au–Up), Pullenia bulloides–Bulimina striata (Pb–Bs), Globocassidulina tumida–Nuttallides umbonifera (Gt–Nu), Gyroidinoides nitidula–Cibicides wuellerstorfi (Gn–Cw) and Cassidulina carinata–Cassidulina laevigata (Cc–Cl) biofacies. Knowledge of the environmental preferences of modern deep-sea benthic foraminifera helped to interpret the results of factor and cluster analyses in combination with oxygen and carbon isotope values. The biofacies indicative of high surface productivity, resulting from a stronger South Equatorial Current (Au–Up and Pb–Bs biofacies), dominate the early Pliocene interval (5.6–4.5 Ma) of global warmth. An intense Indo-Pacific ‘biogenic bloom’ and strong Oxygen Minimum Zone extended to intermediate depths (∼1000–2000 m) over large parts of the Indian Ocean in the early Pliocene. Since 4.5 Ma, the food supply in the Central Indian Ocean dropped and fluctuated while deep waters were corrosive (biofacies Gt–Nu, Gn–Cw). The Pleistocene interval is characterized by an intermediate flux of organic matter (Cc–Cl biofacies).
 
Geological and Tectonic map of Narmada-Son lineaments with locations of DSS profiles and heat flow sites (modified after Sridhar and Tewari, 2001).
(a) Crustal layers with V p-velocity distribution (km/s) and distribution of heat generation (mW/m 3 ) values (in bracket) along Profile II. Crosses represent the Narmada North Fault (NNF) and Narmada South Fault (NSF); (b) Crustal layers with V p-velocity distribution (km/s) and distribution of heat generation (mW/m 3 ) values (in bracket) along profile III. Crosses represent the Narmada North Fault (NNF) and Narmada South Fault (NSF).
Calculated (a) surface heat flow density and (b) isotherms (8C) (solid line) along with crustal structure (dotted line) for profile II.
Calculated temperature-depth distribution at 220 km near Multai on profile II.
Calculated (a) surface heat flow density and (b) isotherms (8C) (solid line) along with crustal structure (dotted line) for Profile III.
Article
This work deals with 2D thermal modeling in order to delineate the crustal thermal structure of central India along two Deep Seismic Sounding (DSS) profiles, namely Khajuriakalan–Pulgaon and Ujjan–Mahan, traversing the Narmada-Son-Lineament (NSL) in an almost north–south direction. Knowledge of the crustal structure and P-wave velocity distribution up to the Moho, obtained from DSS studies, has been used for the development of the thermal model. Numerical results reveal that the Moho temperature in this region of central India varies between 500 and 580 °C. The estimated heat flow density value is found to vary between 46 and 49 mW/m2. The Curie depth varies between 40 and 42 km and is in close agreement with the Curie depth (40±4 km) estimated from the analysis of MAGSAT data. Based on the present work and previous work, it is suggested that the major part of peninsular India consisting of the Wardha–Pranhita Godavari graben/basin, Bastar craton and the adjoining region of the Narmada Son Lineament between profiles I and III towards the north and northwest of the Bastar craton are characterized with a similar mantle heat flow density value equal to ∼23 mW/m2. Variation in surface heat flow density values in these regions are caused by variation in the radioactive heat production and fluid circulation in the upper crustal layer.
 
Article
The Precambrian geologic history of Peninsular India covers nearly 3.0 billion years of time. India is presently attached to the Eurasian continent although it remains (for now) a separate plate. It comprises several cratonic nuclei namely, Aravalli–Bundelkhand, Eastern Dharwar, Western Dharwar, Bastar and Singhbhum Cratons along with the Southern Granulite Province. Cratonization of India was polyphase, but a stable configuration between the major elements was largely complete by 2.5 Ga. Each of the major cratons was intruded by various age granitoids, mafic dykes and ultramafic bodies throughout the Proterozoic. The Vindhyan, Chhattisgarh, Cuddapah, Pranhita–Godavari, Indravati, Bhima–Kaladgi, Kurnool and Marwar basins are the major Meso to Neoproterozoic sedimentary repositories. In this paper we review the major tectonic and igneous events that led to the formation of Peninsular India and provide an up to date geochronologic summary of the Precambrian. India is thought to have played a role in a number of supercontinental cycles including (from oldest to youngest) Ur, Columbia, Rodinia, Gondwana and Pangea. This paper gives an overview of the deep history of Peninsular India as an introduction to this special TOIS volume.
 
Article
Left-lateral motion along the Ailao Shan–Red River (ASRR) Shear Zone has been widely advocated to be the result of the collision between the Indian and Eurasian plates and to account for sea-floor spreading in the South China Sea. Our new 40Ar/39Ar data on the south-easternmost outcrop of the Day Nui Con Voi metamorphic massif, northern Vietnam, suggest that the exhumation of metamorphic massif by shearing along the ASRR zone began ∼27 Ma and lasted until ∼22 Ma. A perfect correlation between location and cooling path for the samples along the shear zone suggests that the transtensional deformation may have propagated northwestward at a rate of ∼6 cm y−1. Such a good correlation also indicates that the onset of the left-lateral movement of the shear zone may have occurred later than ∼27.5 Ma. This conclusion is consistent with our previous interpretation that collision-induced southeastward extrusion of Indochina along the ASRR Shear Zone postdates the opening of the South China Sea, and that extrusion tectonics in SE China may not be responsible for the opening of the South China Sea.
 
Article
Four K-feldspar samples from the Yidun Arc, eastern Tibetan Plateau, were analysed by the 40Ar/39Ar method with the aim of recovering information on their thermal history using multiple diffusion domain (MDD) theory. Arrhenius plots for each of the samples reveal low retentivity early in the heating experiments, a property that is attributed to their recrystallised nature. This low argon retentivity appears to violate the MDD assumption that volume diffusion is the only mechanism for argon transport within the crystals, thus the thermal histories derived from these analyses are considered suspect. Nevertheless, the age spectra themselves suggest that the majority of samples had cooled below ∼200 °C prior to the Eocene collision of India with Asia. Thermal history modelling from apatite fission track analyses from the same and nearby samples shows slow cooling through the apatite fission track partial annealing zone during the Cenozoic in samples from the high elevation, low relief areas of the Yidun Arc, while samples from the major Jinsha River valley show rapid cooling through the partial annealing zone beginning in the Miocene. These results suggest that significant Cenozoic denudation has been localised and that most parts of the Yidun Arc have experienced very little denudation during the Cenozoic.
 
Article
In the Lesser Caucausus the Sevan-Akera ophiolites of N Armenia have lithological features of a slow-spreading oceanic lithosphere: serpentinites are frequently exposed and hydrothermalized at sea-floor level, plutonic rocks and dykes are rare. A complete differentiation trend is observed from mafic norites evolving to diorites and plagiogranites. Normal faults have exposed some of the deep magmatic rocks at sea-floor level. Geochemically, two distinct lava flow series have been distinguished: (1) a contaminated Mid-Oceanic Ridge Basalt (MORB) series evolving from gabbros to plagiogranites and from basalts to basaltic andesites, exhibiting slight calc-alkaline features (enrichments in Large Ion Lithophile Elements (LILE); negative anomalies in Nb–Ta and Ti relative to N-MORB); (2) an alkaline series evolving from basanites to trachy-andesites (on anhydrous basis). 40Ar/39Ar age on amphibole-bearing gabbros evidence a Middle Jurassic age (165.3 ± 1.7 Ma, 2σ) for oceanic crust formation. Structural data, including geological cross-sections and logs of the ophiolite along the northern part of Sevan Lake allow discussing the geodynamic evolution of that segment of the Amassia-Sevan-Akera ophiolitic suture zone.
 
Article
The Simav detachment fault in the northern part of Menderes Core Complex in western Turkey, separates cover sequence rocks with brittle deformation, from high-grade metamorphic (core) rocks and young granitoid intrusions. The timing of shear zone formation and the intrusion of syn-tectonic granitoids is constrained by 40Ar/39Ar geochronology on muscovite from mylonitic gneiss, and biotite from the Egrigöz granitoid. 40Ar/39Ar data indicate that mylonitic deformation occurred at 22.86±0.47 Ma, whilst the cooling age of the granitoid is 20.19±0.28 Ma. The intrusion and cooling of the Egrigöz granitoid occurred between ∼23–20 Ma. These data demonstrate that extensional deformation in the northern Menderes Core Complex began before Early Miocene times and represents an early stage in the Tertiary extensional tectonics of western Turkey.
 
Article
40Ar/39Ar and fission track thermochronological results from two granitoid suites in the mountain ranges along the northern and southern edges of Qaidam basin constrain the timing of a Tertiary denudation event and their tectonic association in northern Tibet. The cooling histories based upon 40Ar/39Ar and fission track ages suggest a rapid cooling event (7.5–10.7 °C/Ma) during Oligocene–early Miocene time. This cooling event is thought to reflect an increasing denudation rate associated with the rapid uplift and denudation of the North Qaidam and Kunlun Shan mountain ranges. With consideration to the field evidence, sedimentation rate of the Qaidam basin, and the propagation rate along the Altyn Tagh fault, the rapid uplifting and denudation are probably due to crustal thickening associated with Cenozoic propagation of the Altyn Tagh fault in accommodating the collision of India with Asia.
 
Article
Dolerite sills are the dominant type of mafic intrusions within the Siberian traps province. Their total volume is comparable to the volume of effusive magmas. Six large dolerite sills are known on basis of geological survey data within the Angara-Taseevskaya syncline at the southeastern part of the Siberian traps. We obtained 40Ar/39Ar ‘plateau’ ages of 240.1 ± 1.0/2.5/5.4 Ma and 241.6 ± 1.3/2.6/5.5 Ma for Tulunskii and Padunskii sills, respectively (errors are reported as x/y/z, where x, y and z are analytical, internal and external errors, respectively). The obtained ages are indistinguishable from each other at level of analytical errors and suggest emplacement of the sills during the same Middle Triassic pulse of magmatism. Samples from Tolstomysovskii and Chuna-Biryusinskii sills did not yield statistically acceptable plateau ages, though their 40Ar/39Ar spectra and K/Ca versus apparent age diagrams suggest that they were emplaced in the Middle Triassic too. The dolerites are characterized by uniform trace element and platinum group element patterns typical for low-Ti tholeiites of the Noril’sk area, although the Noril’sk low-Ti tholeiites were erupted at Permo-Triassic boundary about 9 Ma earlier. The low-Ti tholeiites make up the greatest volume of the flood basalts and possess a distinctive chemical signature. Our data suggests that low-Ti tholeiitic magma was emplaced at more than one locality in the Siberian traps province, and in more than one temporal pulse.
 
Article
The Neogene Yamadağ volcanics occupy a vast area between Sivas and Malatya in eastern Anatolia, Turkey. These volcanic rocks are characterized by pyroclastics comprising agglomerates, tuffs and some small outcrops of basaltic–andesitic–dacitic rocks, overlain upward by basaltic and dacitic rocks, and finally by basaltic lava flows in the Arapkir area, northern Malatya Province. The basaltic lava flows in the Arapkir area yield a 40Ar/39Ar age of 15.8 ± 0.2 Ma, whereas the dacitic lava flows give 40Ar/39Ar ages ranging from 17.6 through 14.7 ± 0.1 to 12.2 ± 0.2 Ma, corresponding to the Middle Miocene. These volcanic rocks have subalkaline basaltic, basaltic andesitic; alkaline basaltic trachyandesitic and dacitic chemical compositions. Some special textures, such as spongy-cellular, sieve and embayed textures; oscillatory zoning and glass inclusions in plagioclase phenocrysts; ghost amphiboles and fresh biotite flakes are attributable to disequilibrium crystallization related to magma mixing between coeval magmas. The main solidification processes consist of fractional crystallization and magma mixing which were operative during the soldification of these volcanic rocks. The dacitic rocks are enriched in LILE, LREE and Th, U type HFSE relative to the basaltic rocks. The basaltic rocks also show some marked differences in terms of trace-element and REE geochemistry; namely, the alkaline basaltic trachyandesites have pronounced higher HFSE, MREE and HREE contents relative to the subalkaline basalts. Trace and REE geochemical data reveal the existence of three distinct magma sources – one subalkaline basaltic trachyandesitic, one alkaline basaltic and one dacitic – in the genesis of the Yamadağ volcanics in the Arapkir region. The subalkaline basaltic and alkaline basaltic trachyandesitic magmas were derived from an E-MORB type enriched mantle source with a relatively high- and low-degree partial melting, respectively. The magmatic melt of dacitic rocks seem to be derived from an OIB-type enriched lithospheric mantle with a low proportion of partial melting. The enriched lithospheric mantle source reflect the metasomatism induced by earlier subduction-derived fluids. All these coeval magmas were generated in a post-collisional extensional geodynamic setting in Eastern Anatolia, Turkey.
 
Article
Between the Qiangtang Block and Yalung-Zangpo Suture Zone in the south-central Tibetan Plateau, the following geological units and suture zones have been identified from south to north: the Gangdese Granitic Belt, the Lhasa Block, the Nyainqentanghla Shear Zone, the Dangxiong–Sangxiong Tectono-granitic Belt and the Bangong–Nujiang Suture Zone. To better constrain the tectonic evolution and cooling histories of these units, 40Ar/39Ar muscovite, biotite and K-feldspar, as well as apatite fission track dating and thermochronological analysis have been carried out. The analytical results indicate that the south-central Tibetan Plateau, with the exception of the Nyainqentanghla Shear Zone, provides a record of three cooling stages at 165–150, 130–110 and ∼45–35 Ma. Fission-track data modelling also indicates that the stages of cooling were different in the different tectonic belts or blocks. Very different cooling phases occurred in the south-central Tibetan Plateau, compared with southern Tibet, as well as along the Yalung–Zangpo Suture Zone. There is no thermochronological evidence to indicate that the south-central part of Tibetan Plateau was influenced by the underthrusting of Indian Plate.The three-stage cooling history and the stages of tectonic exhumation were controlled completely by the closure of the Bangong–Nujiang Suture Zone along its eastern segment during Middle–Late Jurassic (165–150 Ma) and its western segment in the Early–Late Cretaceous (130–110 Ma), as well as by the collision between the Indian and Asian plates in the Paleogene (45–35 Ma).
 
Article
The opening of the South China Sea is one of the most important Cenozoic events in SE Asia. In order to investigate its tectonic evolution, three analogue modeling experiments were compared. The modeling results suggest that rifting pattern and orientation change of the rift zone were related to initial rheological stratification. Affected by the ductile flow of silicone (lower crust) and honey (asthenosphere), the faults became flattened, especially close to the breakup area. We conjecture that the slope area may bear relatively hotter and thinner lithosphere than the shelf area from the beginning of rifting due to stretching and mantle upwelling associated with this regional extension, which in turn lead to the change in initial rheological stratification and therefore the rifting pattern from shelf to slope. In the experiments, breakup developed first at isolated points, which grew and coalesced to become a single spreading area. The conjugate boundaries were either all concave or all convex. Where a rigid massif was located at the divergent boundary, stretching history was different. In this case, the northern and southern areas thinned rapidly and developed into two deep troughs, which may finally evolve into spreading centers. The shape of the massif controls the orientation and boundary shape of the spreading area. It is interpreted that crustal breakup was more viscous in style, and the NW sub sea basin developed along the northern trough of the Zhongsha-Xisha massif (Macclesfield Bank).
 
Article
The secular change in 87Sr/86Sr ratio of the Paleozoic recorded the lowest value below 0.7070 in Late Middle Permian, i.e., the Permian minimum, suggesting that a major reform in oceanography occurred before the Paleozoic–Mesozoic transition. We have detected the correlative lowest 87Sr/86Sr value (0.706914 ± 0.000012) from the Middle-Upper Permian paleo-atoll limestone in Japan, formed primarily on an ancient seamount in mid-Panthalassa. The stratigraphic horizon of the minimum was constrained to the Capitanian interval (265.8–260.4 Ma), Middle Permian, by fusulines. As the mid-oceanic data represent the global average, the present study confirmed the chemostratigraphical utility of the “Capitanian minimum” of 87Sr/86Sr ratio in global correlation. After the long-term (nearly 280 million years) decrease throughout the Paleozoic since the Cambrian, a remarkable turnover of seawater 87Sr/86Sr values appeared in the Capitanian immediately before the Guadalupian–Lopingian (Middle-Late Permian) boundary. A major global change likely appeared in the Capitanian to change the Sr-isotope balance in seawater from a mantle flux-dominated to a continental flux-dominated regime. The initial rifting of Pangea probably started in the Capitanian, and the rifting-induced new connection of many intra-supercontinental drainage systems to the superocean may have caused the overturn in global Sr isotopic trend.
 
Article
A total of 140 polycystine radiolarians (84 nassellarians and 56 spumellarians; called Mn-03 assemblage herein) were identified from a manganese nodule in mudstone of the chert–clastic sequence distributed in the Jurassic accretionary complex of the Kuzumaki–Kamaishi Belt, Northern Kitakami Mountains, Northeast Japan. The horizon yielding this well-preserved assemblage was correlated to the uppermost part of the radiolarian JR4 Zone (the Upper Aalenian, Middle Jurassic) on the basis of the presence of Tricolocapsa tegiminis, the probable decendant of Laxtorum (?) jurassicum, and the absence of L. (?) jurassicum and Tricolocapsa plicarum. The Mn-03A assemblage is of high diversity but shows nearly half of the diversity of the contemporaneous assemblage which was reported from manganese nodules in another Jurassic accretionary complex of the Mino Belt in Japan. Both assemblages are considered to have been derived from the same province due to faunal similarity. The difference between both assemblages is explained by lower productivity in the depositional region of the Mn-03A assemblage. Comparison of the Mn-03A assemblage to the contemporaneous assemblage indicates that the fauna lived in the equatorial to lower latitudinal zone of the Pacific Superocean in late Aalenian time.
 
Article
Folding at the leading edge of the western Taiwan thrust belt is well preserved by a flight of fluvial terraces at Houli. Strain in this region is driven by slip on the north trending Changhua and Sanyi blind wedge thrusts and occurs at the boundary between the Miaoli and Taichung neotectonic domains located respectively to the north and south. In the past century, two large historical earthquakes occurred in these two domains and produced surface ruptures within or close to the study area, indicating Houli is not only tectonically active but also critical for understanding the interaction between the neighboring active systems. Although abundant river terraces and their deformation by active structures have long been well known in the area, a kinematical model for this region has not yet been proposed. We have therefore remapped the geomorphic features using the 40 m DEM and aerial photos to identify often subtle structural features in order to separate the effects of folding interference produced by different active structural systems. Besides the Tuntzuchiao fault (TTCF), which generated the 1935 earthquake, two other active regional scale structural systems have been reported in Houli area: the Tiechanshan (TCS) anticline and the Changhua fault (CHF). Our results demonstrate a number of tectonic scarps and warped surfaces in association with the CHF and its coupled back thrust, indicating that the CHF system is active. In contrast, the flight of fluvial terraces distributed in the middle of the study area cannot be related to the growth of the TCS anticline. Instead, terraces here record growth of another smaller and previously unknown anticline, Yuehmei (tentatively named in this study and shortened to YM in the text). Although it has developed parallel to the TCS anticline, relevant seismic profiles show the YM anticline as a local drag-fold attached to the southern limb of the TCS anticline and restricted in the Houli area. Based on the above observation, the TCS anticline can be interpreted as becoming less active where strain is instead transferred to the more rapidly uplifting YM anticline. This structural switch may be the result of interference between the newly developed southern Taichung system and the preexisting TCS anticline.
 
Article
We conduct shear wave splitting measurements on waveform data from the Hi-net and the broadband F-net seismic stations in Kanto and SW Japan generated by shallow and intermediate-depth earthquakes occurring in the subducting Philippine Sea and Pacific slabs. We obtain 1115 shear wave splitting parameter pairs. The results are divided into those from the shallow (depth < 50 km) and the deep (depth > 50 km) events. The deep events beneath Kanto are further divided into PHS1 and PHS2 (upper and lower planes of the double seismic zone in the Philippine Sea slab, respectively), PAC1 and PAC2 (western and eastern Pacific slab, respectively) events. The results from the shallow events represent the crustal anisotropy, and their fast directions are more or less aligned in the σHmax directions, implying that the anisotropy is produced by the alignment of the vertical cracks in the crust induced by the compressive stresses. In Kanto, Kii Peninsula and Kyushu regions, the results from the deep events suggest a contribution from the mantle wedge anisotropy. Events from all groups beneath Kanto show NW, NE and EW fast directions. This complex pattern seems to be produced by the corner flows induced by both the WNW PAC plate subduction and the oblique NNW PHS slab subduction with the associated olivine lattice-preferred orientations (LPOs), and the anisotropy frozen in the PHS slab. The deep events beneath Kii Peninsula show NE and NW fast directions and may be produced by the corner flow produced by the NNW PHS slab subduction with the associated olivine LPOs. The NE directions might also be produced by the segregated melts in the thin layers parallel to the PHS slab subduction. The deep events beneath N Kyushu show NNW fast directions, which may result from the southeastward flow in the upper mantle inferred from the stresses in the upper plate. Results from the deep events beneath middle-south Kyushu show dominantly E–W fast directions, in both the fore- and back-arcs. They may be produced by the corner flow of the westward PHS slab subduction with the olivine LPOs. Because the source regions with multiple fast directions are not resolved in this study, further detailed analyses of shear wave splitting are necessary for a better understanding of the stress state, the induced mantle flow, and the melt-segregation processes.
 
Article
A 650-m-thick sequence of fluvio-lacustrine sediments from the Yuanmou Basin in southwest China was analyzed at 20-cm intervals for grain-size distribution to provide a high-resolution terrestrial record of Indian summer monsoon variations during the Pliocene. The concentrations of the clay and clay-plus-fine-silt fractions are inferred to reflect the water-level status of the lake basin related to the intensity of the Indian summer monsoon and high concentrations reflect high lake levels resulting from the intensified summer monsoon. The frequency of individual lacustrine mud beds is considered to reveal the frequency of the lakes developed in the basin associated with the variability of the Indian summer monsoon and an increased frequency of the lakes reveals an increased variability of the summer monsoon. The proxy data indicate that the Indian summer monsoon experienced two major shifts at 3.57 and 2.78 Ma and two secondary shifts at 3.09 and 2.39 Ma during the Pliocene. The summer monsoon displayed a general trend of gradual intensification during the period of 3.57–2.78 Ma, coeval with an accelerated uplift of the Tibetan Plateau, implying a close link between the monsoon intensification and the plateau uplift. At 2.78 Ma, the summer monsoon was markedly weakened, synchronous with the formation of extensive Northern Hemisphere ice sheets, denoting a quick response of the monsoon regime to the Northern Hemisphere glaciation. The variability of the summer monsoon decreased at 3.09 Ma and increased at 2.39 Ma, presumably suggesting that variations of the Indian monsoon would be modulated by the initiation and periodic fluctuations of ice-sheet covers in Northern Hemisphere high latitudes.
 
Article
The Abu Ruweis Formation is composed of carbonates, evaporites, and mudstones, with some locally developed pelletic, oolitic and stromatolitic limestones. The lateral persistence of bedding, the purity of the evaporite rocks, the alternating arrangement of marine carbonates and evaporites indicates periodic deposition in subaqueous conditions (salina). Petrographic investigations, X-ray diffraction analysis as well as chemical analysis have shown that the outcropping evaporite beds are mainly composed of secondary gypsum, with rare anhydrite relics. Five microfacies of gypsum were recognized according to their fabrics: porphyroblastic and granoblastic gypsum showing polarization texture, gypsum pseudomorph after anhydrite laths, and satin spar gypsum. The textures they display indicate a hydration origin of precursor anhydrite, which is in turn rehydrated from primary gypsum. Some of these anhydrites were formed as a result of replacement processes of the carbonate sediments associated with the evaporites, as evidenced from the textural relationships of the carbonate and sulfate minerals. The O18 content ranges from 1.45 to 8.38% PDB and the C13 content ranges from −1.52 to 4.73% PDB. Trace elements analysis has shown that the Abu Ruweis dolomites are rich in strontium (up to 600 ppm), and sodium (up to 835 ppm). The isotope composition and trace elements content, as well as the petrographic characteristics point to a penecontemporaneous hypersaline dolomitization origin for the Abu Ruweis dolomites. The evaporites were deposited during a regressive lowstand systems tract, whereas the carbonates were deposited under shallow water marine conditions during a highstand systems tract. The Abu Ruweis succession represents a relatively stable arid climate within a rapidly subsiding basin. Restricted conditions were provided by the development of beach barriers.
 
Article
The predominant clastic rocks of the late Eocene Namunagarh Grit, South Andaman Island are coarse to fine-grained and pebbly immature greywacke sandstones. These rocks have long been known and interpreted as epiclastic deposits formed from the weathering and erosion of accreted ophiolite in a trench-slope setting. This study documents abundant juvenile vesiculated fragments, pumice clasts, shards, unbroken vesicles, cognate lithics of andesite, broken and whole euhedral fresh plagioclase, and chlorite-replaced glassy matrix in these sandstones. The sandstones evidently have a pyroclastic origin. Based on structures and textures, a coarse-grained and massive, and a finer-grained, bedded and graded sandstone facies are identified. The coarse-grained facies occurs in the lower part of the section, while the finer-grained one, interstratified with mudstone, occurs in the upper part. Major element chemistry indicates a predominantly andesitic composition for these rocks.
 
Simplified geologic map showing fission track sample localities and corresponding ages. The oldest ages correspond to either structurally high units of distal parts of the continental margin (Maubisse Formation) or stratigraphically high units (Upper Triassic Babulu Formation) from proximal parts of the continental margin.
Apatite track length distributions for all samples with horizontal confined tracks. Values in upper right are sample number, mean track length ±l r:t. (~lm), standard deviation (~lll1), and number of measured samples.
Article
Paleotemperature indicators and apatite fission track analysis of Australian continental margin cover sequences accreted to the active Banda arc–continent collision indicate little to no heating during rapid late Neogene uplift and exhumation. Thermal maturation patterns of vitrinite reflectance, conodont alteration and illite crystallinity show that peak paleotemperatures (PPT) increase with stratigraphic and structural burial. The highest PPT is found in the northern hinterland of the accretionary wedge, which was beneath progressively thicker parts of the upper plate towards the north. Major discontinuities in the pattern of PPT are associated with the position of major thrust ramps such as those forming the Ramelau/Kekneno Arch (RKA). PPT for Upper Triassic to Neogene strata south of the RKA are 60–80°C, which are similar to, and in many cases lower than, correlative and age equivalent units drilled on the NW Australian Shelf. Permian to Lower Triassic sedimentary strata thrust over younger units within and north of the RKA have PPT of 100–220°C. Thrust sheets accreted beneath the upper plate have PPT approximately 90°C higher than those frontally accreted. Metamorphism of the northernmost units of these sequences yield PPT of >300°C. Thrust stacking yields an inverted thermal profile of PPT decreasing discontinuously downward and to the south (towards the foreland). The timing of PPT is constrained by apatite fission track ages from mostly Triassic continental margin cover sequences. Ages of Upper Triassic units are primarily coeval with deposition and show little evidence of thermal annealing, whereas those of Lower Triassic units are almost completely annealed and range from 1.8±0.5–19.2±9.7 Ma. The clustering of apatite fission track ages into two distinct groups indicates that the upper boundary of the partial annealing zone has remained for some time at a Triassic stratigraphic interval in the slope and rise of the NW Australian continental margin. The position of this zone on the present shelf is higher in the stratigraphic column due to the greater thickness of post-breakup shelf facies units. Thrust stacking of rise, slope and shelf units produces an inverted vertical profile of increasing apatite fission track age with depth. Lack of any long confined track lengths in apatite from all of the units requires rapid and recent exhumation of the thrust stack, which is coincident with rapid phases of Pliocene–Pleistocene exhumation documented throughout Timor. These data preclude pre-Late Miocene tectonic burial or pre-Pliocene exhumation of the NW Australian continental margin.
 
Article
The Saykhandulaan Inlier in South East Mongolia lies within the Central Asian Orogenic Belt (CAOB), and records a complex history of Palaeozoic tectonism and magmatism associated with terrane accretion on the northern margin of the Palaeo-Asian ocean. The inlier spans the boundary between the Gobi Altai back-arc basin terrane in the north and the Mandalovoo and Gurvansayhan island-arc terranes in the south which are notable for their many mineralised intrusions, including the Oyu Tolgoi gold-rich copper porphyry deposit. Results from cross-strike transects within the Saykhandulaan Inlier reveal that it can be subdivided into five parallel east–west striking litho-tectonic domains; (1) the Northern Slate Belt, comprising Devonian greenschist grade pelites and psammites with deep-marine to coastal siliciclastic protoliths; (2) the Saykhandulaan Valley Lineament Zone (SVLZ), a tectonised zone of faulted and lithologically altered volcanic rocks; (3) the High Strain Belt, consisting of tightly folded and flattened metamorphosed clastic sedimentary rocks; (4) the Molasse Succession, consisting of relatively undeformed coarse conglomerates and sandstones and, (5) the Oyut Ulaan Volcanic Group, a nearly 5 km-thick folded Carboniferous volcanic succession that hosts the mid-Carboniferous Oyut Ulaan mineralised granite. The Northern Slate Belt metasedimentary rocks record a northerly cratonic provenance, whereas all rocks to the south of the SVLZ have arc affinities. The SVLZ is thus interpreted to be the boundary between the Gobi Altai and Mandalovoo terranes. Two major deformation events are documented; (1) back-arc basin closure and inversion involving regional scale folding and greenschist grade metamorphism in the Northern Slate and High Strain Belts; (2) contraction associated with Mandalovoo terrane accretion and final closure of the Palaeo-Asian Ocean to the south. Following terrane accretion and cessation of subduction, crustal extension and strike-slip faulting further modified the crustal architecture of the inlier. The results presented here provide a useful framework for understanding the crustal evolution of adjacent regions within the southeast Gobi mineral belt.
 
Article
The Gorny Altai region in southern Siberia is one of the key areas in reconstructing the tectonic evolution of the western segment of the Central Asian Orogenic Belt (CAOB). This region features various orogenic elements of Late Neoproterozoic–Early Paleozoic age, such as an accretionary complex (AC), high-P/T metamorphic (HP) rocks, and ophiolite (OP), all formed by ancient subduction–accretion processes. This study investigated the detailed geology of the Upper Neoproterozoic to Lower Paleozoic rocks in a traverse between Gorno-Altaisk city and Lake Teletskoy in the northern part of the region, and in the Kurai to Chagan-Uzun area in the southern part. The tectonic units of the studied areas consist of (1) the Ediacaran (=Vendian)–Early Cambrian AC, (2) ca. 630 Ma HP complex, (3) the Ediacaran–Early Cambrian OP complex, (4) the Cryogenian–Cambrian island arc complex, and (5) the Middle Paleozoic fore-arc sedimentary rocks. The AC consists mostly of paleo-atoll limestone and underlying oceanic island basalt with minor amount of chert and serpentinite. The basaltic lavas show petrochemistry similar to modern oceanic plateau basalt. The 630 Ma HP complex records a maximum peak metamorphism at 660 °C and 2.0 GPa that corresponds to 60 km-deep burial in a subduction zone, and exhumation at ca. 570 Ma. The Cryogenian island arc complex includes boninitic rocks that suggest an incipient stage of arc development. The Upper Neoproterozoic–Lower Paleozoic complexes in the Gorno-Altaisk city to Lake Teletskoy and the Kurai to Chagan-Uzun areas are totally involved in a subhorizontal piled-nappe structure, and overprinted by Late Paleozoic strike-slip faulting. The HP complex occurs as a nappe tectonically sandwiched between the non- to weakly metamorphosed AC and the OP complex. These lithologic assemblages and geologic structure newly documented in the Gorny Altai region are essentially similar to those of the circum-Pacific (Miyashiro-type) orogenic belts, such as the Japan Islands in East Asia and the Cordillera in western North America. The Cryogenian boninite-bearing arc volcanism indicates that the initial stage of arc development occurred in a transient setting from a transform zone to an incipient subduction zone. The less abundant of terrigenous clastics from mature continental crust and thick deep-sea chert in the Ediacaran–Early Cambrian AC may suggest that the southern Gorny Altai region evolved in an intra-oceanic arc-trench setting like the modern Mariana arc, rather than along the continental arc of a major continental margin. Based on geological, petrochemical, and geochronological data, we synthesize the Late Neoproterozoic to Early Paleozoic tectonic history of the Gorny Altai region in the western CAOB.
 
Article
The blueschist/greenshist Terekta Complex is the only blueschist locality known in the Russian Altai. The Terekta metabasites contain Na and Na–Ca amphibole, actinolite, phengite, epidote, albite, quartz, calcite, magnetite (or hematite). Depending on the amphibole composition, these rocks were subdivided into blueschist, transitional blueschist/greenschist and greenschist. Both blueschists and transitional blueschist/greenschists (glaucophane-bearing and winchite–actinolite schists) have compositions similar to alkaline basalts of oceanic islands, whereas the greenschists correspond to ocean-floor tholeiitic basalts, or MORB. Available geothermobarometry yielded the following estimates of metamorphic conditions: T=350–400 °C and P=6–8 kbar. The different mineral assemblages of the metabasites are believed to be a result of their different lithologies. The presence of matabasalts with ocean island basalt and MORB affinity, as well as the occurrence of layered metachert, marble, metagraywacke, and plates of serpentinized dunites, pyroxenites indicate that the complex was very likely a subduction-accretionary complex. The complex contains rocks of accretionary wedge, and fragments of oceanic crust which are regarded to be a remnant of an Early Paleozoic subduction zone in the Russian Altai.
 
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Middle-Cambrian to Permian subduction-related records are widely distributed in Northern Xinjiang which can be grouped into the Chinese Altay–East Junggar–Eastern Tien Shan, West Junggar, Yili, and Tarim domains. By integrating paleogeographic and geological data, we suppose that the Chinese Altay–East Junggar–Eastern Tien Shan domain was more closely located to Siberia, while the West Junggar and Yili domains occupied an intermediate position near the Kazakhstan block in the early Paleozoic Paleoasian Ocean. Distribution of Andean-type magmatic arcs, island arcs, accretionary wedges, ophiolitic slices, and/or microcontinents shows an archipelago paleogeography forming a huge accretionary active margin sequences. The Tarim domain was on the opposite side of the early Paleozoic Paleoasian Ocean remaining passive margin. These tectonic units drifted northwards and approached the southern active margin of the Siberian craton in the late Paleozoic, leading to termination of the Paleoasian Ocean and formation of a complicated orogenic collage between Siberian craton and the Tarim block between the end-Permian and Triassic. These multiple accretion processes significantly contributed to the lateral growth of central Asia.
 
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The Qilian Shan, located in the northern Tibetan Plateau of NW China, has an excellent record of early to middle Paleozoic subduction–accretion that resulted from convergence between the Alax and Qaidam blocks, but there is no consensus about its detailed tectonic history. This paper summarizes its tectonic divisions and discusses its tectonic evolution from the Cambrian to Devonian. The belt has the following tectonic divisions: In the far north the southern passive margin of the Alax block is juxtaposed against an early Cambrian to Ordovician, Marianan-type intra-oceanic arc (North Qilian). The North Qilian arc is separated from a Japanese-type arc (Central Qilian) to the south by a high-pressure metamorphic belt composed mostly of ophiolitic slices and oceanic crusts. The Central Qilian is bounded to the south by a wide mélange zone (South Qilian), consisting of ophiolitic slices and continental margin sequences. Farther to the south lies the Oulongbuluk microcontinent that is separated from the Qaidam block and farther south by an ultrahigh-pressure metamorphic belt. Tectonostratigraphic analysis, together with geochemical, geochronological, and geophysical data, indicates a complex evolution by subduction–accretion processes from the Cambrian to the Devonian before final amalgamation and docking to the northern Alax block. This model solves the long-lasting discussion on the polarity of subduction in Paleozoic time; this multiple subduction–accretion history sheds light on the continuity of Paleozoic sutures along the Qilian Shan and the nature of the Altyn Tagh fault, and thus contributes to an improved understanding of the tectonic architecture of Central Asia.
 
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The Ba Lat River is the major distributary of the Red River system in North Vietnam. To assess the recent to subrecent depositional processes in the Ba Lat prodelta, a detailed sediment analysis was conducted. Bottom samples were collected during two field surveys, one in the dry season (winter) and one in the wet season (summer). A steep frontal prodelta slope is characterized by very rapid sedimentation (tens of cm per year) of muddy sediments under influence of the turbid river plume. Beyond direct influence of the river plume the bottom slope decreases and bottom transport by the prevailing southward directed currents becomes important. Coarse-grained tempestites alternate with the dominating muddy sediments. Downcore changes in the 234Th activities indicate that the subaqueous delta progrades to the southwest, with erosion and reworking of older sediments occurring north of the present outlet. The southwestward progradation is also encountered in the trend of 210Pb activities indicating that this process has continued for at least 100 years. Avulsion of the Ba Lat outlet in 1973 has led to a decrease in sedimentation rates north of the Ba Lat outlet.
 
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Heavy metal and organic pollutants in sediments along the coastal zone of southeastern China have been investigated. Sediment samples are retrieved from three depositional environments: coast, estuary, and tide-affected river mouth. The relative abundance of heavy metal and organic pollutants is related to their geochemical properties as well as depositional environments and anthropogenic discharge. Based on a sequential extraction method, it is revealed that anthropogenic Pb, Cr, Cu, and Cd are mainly bound to Fe–Mn oxides, suggesting that adsorption and co-precipitation of Fe–Mn oxides are in the control of their transfer processes from water column to sediment. Heavy metal bound to carbonates is also an important pool especially for Cd, Mn, and Pb. The main organic pollutants found in the study area include petroleum-related alkanes, phthalic acid ester, organic silicon, chlorophenol, phenyl ether, and amine. The accumulation of heavy metals and organics in surficial sediments has a decrease tendency from estuarine environment to coastal environment and to tide-affected river mouth.
 
Top-cited authors
M. Santosh
  • China University of Geosciences (Beijing)
Bor-ming Jahn
  • National Taiwan University
Simon Wilde
  • Curtin University
I. Metcalfe
  • University of New England (Australia)
Guochun Zhao 赵国春
  • The University of Hong Kong