Shoulder uplift of the Western Ghats passive margin,India: a denudational model

The paper presents a denudational rift flank uplift model of the Western Ghats of Karnataka, India. The Cenozoic denudation of the Deccan plateau was constrained by relative dating of regional planation surface levels, in combination with preliminary apatite fission track results. The denudational history of the Western Ghats escarpment coastal foreland was constrained both by onshore fission track and offshore sediment data. Methods are briefly described. Results were used as reference data to elaborate a computer simulation model of both flexural rift flank upwarp and escarpment retreat from the K/T boundary to the present. Depending on the assumptions concerning the attributes of the thin elastic lithospheric sheet (infinite or semi-infinite), the shape and elevation of the initial Deccan topography (flat-lying, or affected by lithospheric updoming due to the Reunion mantle plume) and the position of the continental divide upon rifting, the flexural response to denudational unloading is shown to yield either a concave-up flexure of the Dharwar craton, or a convex, monoclinal downwarp of the margin. The relative merits of each model are discussed in the light of auxiliary field evidence, particularly from the neighbouring Deccan traps. However, the diverse assumptions on boundary conditions fail to entirely avoid geomorphological equifinality. © 1998 John Wiley & Sons, Ltd.     

Denudation history of the Kiso Range,central Japan,and its tectonic implications: Constraints from low‐temperature thermochronology

Fission‐track (FT) and (U–Th–Sm)/He (He) analyses are used to constrain the denudation pattern and history of the Kiso Range, a Japanese fault‐block mountain range which has been uplifted since ca 0.8 Ma. We obtained nine zircon FT ages ranging 59.3–42.1 Ma, 18 apatite FT ages ranging 81.9–2.3 Ma, and 13 apatite He ages ranging 36.7–2.2 Ma. The apatite FT and He ages are divided into an older group comparable to the zircon FT age range and a younger group of <18 Ma. The younger ages are interpreted as a reflection of uplift of the Kiso Range because they were obtained only to the east of the Seinaiji‐touge Fault, and the event age estimated from apatite FT data is consistent with the timing of the onset of the Kiso Range uplift. On the basis of the distribution of the younger ages, we propose westward tilting uplift of the Kiso Range between the boundary fault of the Inadani Fault Zone and Seinaiji‐touge Fault, which implies a model of bedrock uplift that is intermediate between two existing models: a pop‐up model in which the Kiso Range is squeezed upward between the two faults and a tilted uplift model which assumes that the Kiso Range is uplifted and tilted to the west by the Inadani Fault Zone. The original land surface before the onset of uplift/denudation of the Kiso Range is estimated to have been uplifted to an elevation of 2700–4900 m. We estimated denudation rates at 1.3–4.0 mm/y and maximum bedrock uplift rates at 3.4–6.1 mm/y since ca 0.8 Ma. The Seinaiji‐touge fault is interpreted as a back thrust of the west‐dipping Inadani Fault Zone. The older group of apatite FT and He ages is interpreted to reflect long‐term peneplanation with a probable denudation rate of <0.1 mm/y.     

Episodic post‐rift deformation in the south‐eastern Australian passive margin: evidence from the Lapstone Structural Complex

Identifying the influence of neotectonics on the morphology of elevated passive margins is complicated in that major morpho‐structural patterns might plausibly be explained by processes related to late Mesozoic to early Cenozoic rifting and/or differential erosion induced by Cenozoic epeirogenic uplift. The proportional contribution of each process can vary from continent to continent, and potentially even within the same passive margin. In the passive margin setting of the southeast Australian highlands the documented occurrence of neotectonic deformation is rare, and accordingly its role in landscape evolution is difficult to establish. The results of investigations within the Lapstone Structural Complex, which forms the eastern range front of the Blue Mountains Plateau, provide evidence for two periods of Cenozoic neotectonic uplift in this part of the highlands. The first, demonstrated by seismic and structural evidence, is suggested to have occurred in the Paleogene, and is thus unrelated to Cretaceous rifting. The second period, demonstrated by evidence from the Kurrajong Fault (presented herein) suggests that uplift occurred in both the Mio‐Pliocene and the Middle Pleistocene. The cumulative Neogene and younger uplift of ~15 m determined for the Kurrajong Fault is less than 10% of the 130 m of total measured throw across the fault. The apparently minor contribution of neotectonism to the current elevation of the Blue Mountains Plateau supports a predominantly erosional exhumation origin for the topographic relief at the plateau's eastern edge. This finding contrasts with evidence from fault complexes associated with similar topographic relief elsewhere in the south‐eastern highlands, indicating that present‐day topography cannot be directly related to relief generated by Neogene and younger uplift, even from relatively closely‐spaced (< 150 km) structures within the same passive margin. These findings have implications for understanding the spatio‐temporal variability of post‐rift faulting in continental passive margin settings and the evolution of landscapes therein. © Commonwealth of Australia. Earth Surface Processes and Landforms © 2014 John Wiley & Sons, Ltd.     

Erosion rates and mechanisms of knickzone retreat inferred from 10Be measured across strong climate gradients on the northern and central Andes Western Escarpment

A steep escarpment edge, deep gorges and distinct knickzones in river profiles characterize the landscape on the Western Escarpment of the Andes between ~5°S and ~18°S (northern Peru to northern Chile). Strong north–south and east–west precipitation gradients are exploited in order to determine how climate affects denudation rates in three river basins spanning an otherwise relatively uniform geologic and geomorphologic setting. Late Miocene tectonics uplifted the Meseta/Altiplano plateau (~3000 m a.s.l.), which is underlain by a series of Tertiary volcanic‐volcanoclastic rocks. Streams on this plateau remain graded to the Late Miocene base level. Below the rim of the Meseta, streams have responded to this ramp uplift by incising deeply into fractured Mesozoic rocks via a series of steep, headward retreating knickzones that grade to the present‐day base level defined by the Pacific Ocean. It is found that the Tertiary units on the plateau function as cap‐rocks, which aid in the parallel retreat of the sharp escarpment edge and upper knickzone tips. ¹⁰Be‐derived catchment denudation rates of the Rio Piura (5°S), Rio Pisco (13°S) and Rio Lluta (18°S) average ~10 mm ky^?1 on the Meseta/Altiplano, irrespective of precipitation rates; whereas, downstream of the escarpment edge, denudation rates range from 10 mm ky^?1 to 250 mm ky^?1 and correlate positively with precipitation rates, but show no strong correlation with hillslope angles or channel steepness. These relationships are explained by the presence of a cap‐rock and climate‐driven fluvial incision that steepens hillslopes to near‐threshold conditions. Since escarpment retreat and the precipitation pattern were established at least in the Miocene, it is speculated that the present‐day distribution of morphology and denudation rates has probably remained largely unchanged during the past several millions of years as the knickzones have propagated headward into the plateau. Copyright © 2011 John Wiley & Sons, Ltd.     

Small-scale convection induced by passive rifting: the cause for uplift of rift shoulders

Areas adjacent to rifts, or rift shoulders, are often observed to be uplifted as much as a kilometer or more. In some of these regions geologic data indicate a passive origin for the rifting itself (i.e. there was no anomalous heating of the regions before rifting). Purely conductive heat transport between the rift, where the lithosphere has been thinned, and the rift flanks cannot account for the magnitude of the uplift. Small-scale convection will be induced in the mantle beneath a rift due to the lateral temperature gradients there. Numerical experiments show that convection increases the amount of heat transported vertically into the rift and laterally out of it. In these calculations, the viscosity is taken to be dependent on temperature and pressure and, in some cases, stress. The mantle flow results in thinning of the adjacent lithosphere causing flanking uplift as well as slowing of the subsidence of the middle of the rift. The magnitude of the uplift is dependent on the geometry of the rift and the importance of stress-dependence in the rheology of the mantle. For viscosity parameters which are consistent with the pre-rift temperature structure small-scale convection can produce uplift at least twice as great as would be produced by lateral conduction alone.     

Erosion of a high‐altitude,low‐relief area on the Korean Peninsula: implications for its development processes and evolution

The processes involved in the development of high‐altitude, low‐relief areas (HLAs) are still poorly understood. Although cosmogenic nuclides have provided insights into the evolution of HLAs interpreted as paleo‐surfaces, most studies focus on estimating how slowly they erode and thereby their relative stability. To understand actual development processes of HLAs, we applied several techniques of cosmogenic nuclides in the Daegwanryeong Plateau, a well‐known HLA in the Korean Peninsula. Our denudation data from strath terraces, riverine sediments, soils, and tors provide the following conclusions: (1) bedrock incision rate in the plateau (~127 m Myr^?1) is controlled by the incision rate of the western part of the Korean Peninsula, and is similar to the catchment‐wide denudation rate of the plateau (~93 m Myr^?1); (2) the soil production function we observed shows weak depth dependency that may result from highly weathered bedrock coupled with frequent frost action driven by alpine climate; (3) a discrepancy between the soil production and catchment‐wide denudation rates implies morphological disequilibrium in the plateau; (4) the tors once regarded as fossil landforms of the Tertiary do not reflect Tertiary processes; and (5) when compared with those of global paleo‐surfaces (<20 m Myr^?1), our rapid denudation rates suggest that the plateau cannot have maintained its probable initial paleo landscape, and thus is not a paleo‐surface. Our data contribute to understanding the surface processes of actively eroding upland landscapes as well as call into question conventional interpretations of supposed paleo‐surfaces around the world. Copyright © 2015 John Wiley & Sons, Ltd.     

Contrasting rifted margin styles south of Greenland: implications for mantle plume dynamics

We present new and reprocessed seismic reflection data from the area where the southeast and southwest Greenland margins intersected to form a triple junction south of Greenland in the early Tertiary. During breakup at 56 Ma, thick igneous crust was accreted along the entire 1300-km-long southeast Greenland margin from the Greenland Iceland Ridge to, and possibly 100 km beyond, the triple junction into the Labrador Sea. However, highly extended and thin crust 250 km to the west of the triple junction suggests that magmatically starved crustal formation occurred on the southwest Greenland margin at the same time. Thus, a transition from a volcanic to a non-volcanic margin over only 100–200 km is observed. Magmatism related to the impact of the Iceland plume below the North Atlantic around 61 Ma is known from central-west and southeast Greenland. The new seismic data also suggest the presence of a small volcanic plateau of similar age close to the triple junction. The extent of initial plume-related volcanism inferred from these observations is explained by a model of lateral flow of plume material that is guided by relief at the base of the lithosphere. Plume mantle is channelled to great distances provided that significant melting does not take place. Melting causes cooling and dehydration of the plume mantle. The associated viscosity increase acts against lateral flow and restricts plume material to its point of entry into an actively spreading rift. We further suggest that thick Archaean lithosphere blocked direct flow of plume material into the magma-starved southwest Greenland margin while the plume was free to flow into the central west and east Greenland margins. The model is consistent with a plume layer that is only moderately hotter, 100–200°C, than ambient mantle temperature, and has a thickness comparable to lithospheric thickness variations, 50–100 km. Lithospheric architecture, the timing of continental rifting and viscosity changes due to melting of the plume material are therefore critical parameters for understanding the distribution of magmatism.     

迅速抬升剥蚀山区大地热流的地形校正

在大地热流评估中，经常要对接近地表的实测值进行校正，然而在迅速抬升剥蚀的崎岖山区，在抬升剥蚀校正基础上进一步作地形校正时，没有剥蚀静态条件下的地形校正是否仍然适用是一个没有讨论过的问题．本文以新西兰的南阿尔卑斯山地区为例，通过有限单元法数值计算，探讨了迅速抬升剥蚀的山区剥蚀和地形二者对近地表不同深度地热流量影响的综合效应．结果表明，虽然迅速抬升地区大地热流密度的地形校正与不考虑剥蚀情况下的校正在较大深度处会略有差别，但总的来说差别甚微．因此，可以沿用传统的地形校正方法，根据钻孔所处地形和测温深度作地形校正．     

Back-arc rifting in the Izu-Bonin Island Arc: Structural evolution of Hachijo and Aoga Shima Rifts

Abstract Multi- and single-channel seismic profiles are used to investigate the structural evolution of back-arc rifting in the intra-oceanic Izu-Bonin Arc. Hachijo and Aoga Shima Rifts, located west of the Izu-Bonin frontal arc, are bounded along-strike by structural and volcanic highs west of Kurose Hole, North Aoga Shima Caldera and Myojin Sho arc volcanoes. Zig-zag and curvilinear faults subdivide the rifts longitudinally into an arc margin (AM), inner rift, outer rift and proto-remnant arc margin (PRA). Hachijo Rift is 65 km long and 20–40 km wide. Aoga Shima Rift is 70 km long and up to 45 km wide. Large-offset border fault zones, with convex and concave dip slopes and uplifted rift flanks, occur along the east (AM) side of the Hachijo Rift and along the west (PRA) side of the Aoga Shima Rift. No cross-rift structures are observed at the transfer zone between these two regions; differential strain may be accommodated by interdigitating rift-parallel faults rather than by strike- or oblique-slip faults. In the Aoga Shima Rift, a 12 km long flank uplift, facing the flank uplift of the PRA, extends northeast from beneath the Myojin Knoll Caldera. Fore-arc sedimentary sequences onlap this uplift creating an unconformity that constrains rift onset to ～1-2Ma. Estimates of extension (～3km) and inferred age suggest that these rifts are in the early syn-rift stage of back-arc formation. A two-stage evolution of early back-arc structural evolution is proposed: initially, half-graben form with synthetically faulted, structural rollovers (ramping side of the half-graben) dipping towards zig-zagging large-offset border fault zones. The half-graben asymmetry alternates sides along-strike. The present ‘full-graben’ stage is dominated by rift-parallel hanging wall collapse and by antithetic faulting that concentrates subsidence in an inner rift. Structurally controlled back-arc magmatism occurs within the rift and PRA during both stages. Significant complications to this simple model occur in the Aoga Shima Rift where the east-dipping half-graben dips away from the flank uplift along the PRA. A linear zone of weakness caused by the greater temperatures and crustal thickness along the arc volcanic line controls the initial locus of rifting. Rifts are better developed between the arc edifices; intrusions may be accommodating extensional strain adjacent to the arc volcanoes. Pre-existing structures have little influence on rift evolution; the rifts cut across large structural and volcanic highs west of the North Aoga Shima Caldera and Aoga Shima. Large, rift-elongate volcanic ridges, usually extruded within the most extended inner rift between arc volcanoes, may be the precursors of sea floor spreading. As extension continues, the fissure ridges may become spreading cells and propagate toward the ends of the rifts (adjacent to the arc volcanoes), eventually coalescing with those in adjacent rift basins to form a continuous spreading centre. Analysis of the rift fault patterns suggests an extension direction of N80°E ± 10° that is orthogonal to the trend of the active volcanic arc (N10°W). The zig-zag pattern of border faults may indicate orthorhombic fault formation in response to this extension. Elongation of arc volcanic constructs may also be developed along one set of the possible orthorhombic orientations. Border fault formation may modify the regional stress field locally within the rift basin resulting in the formation of rift-parallel faults and emplacement of rift-parallel volcanic ridges. The border faults dip 45–55° near the surface and the majority of the basin subsidence is accommodated by only a few of these faults. Distinct border fault reflections decreases dips to only 30° at 2.5 km below the sea floor (possibly flattening to near horizontal at 2.8 km although the overlying rollover geometry shows a deeper detachment) suggesting that these rifting structures may be detached at extremely shallow crustal levels.     

Relationship model of sediment grain size and Tibetan Plateau uplift in middle-west parts of Qilian Mountain

By observing, measuring the fluvial sediment grain size of mid-western segment of the Qilianshan Range and studying the correlation between the grain size and uplift of the plateau, we model the correlation. These models are applied to the Laojunmiao section and the process curve of the uplift of the northern Tibetan Plateau against age from 8.35 Ma is illustrated here. The process curve shows that the northern Tibetan Plateau surface has uplifted from the mean altitude of 900–3700 m since 8.35 MaBP. From 8.35 to 3.1 MaBP, the Tibetan Plateau uplifted slowly, uplifted amplitude is small, the total range is 420 m. From 3.1 MaBP up to now, the Tibetan Plateau uplifted tempestuously, showing that the uplift accelerated obviously later. It uplifted totally 2400 m. About 0.9 Ma ago, the northern Tibetan Plateau surface had uplifted to over 3000 m a.s.l., showing that the Tibetan Plateau surface had reached the cryosphere; and the mountain peaks had uplifted to more than 4000 m altitude, suggesting that there was a glacier developed on the mountains.     

Pre-deccan trap topography in central India and crustal warping in relation to Narmada rift structure and volcanic activity

A study of the geology of the Dhar Forest, the Pachmarhi plateau and the area around Bari in Central India has led to the conclusion that the pre-Deccan Trap topography which was completely covered by the lava flows and is being exposed with spectacular clarity by the process of exhumation, had much the same relief as the present land surface. The geomorphological studies of the Vindhyan and Pachmarhi plateau suggest a characteristic rise and increasing separation of different planation surfaces towards the edges of the Narmada rift valley and indicate upwarping movements in several distinct stages. In considering the possible causes of the upwarping movements special significance is attached to epeirogenic movements probably representing the various stages of Himalayan orogeny. The succession of events in Peninsular India suggests that these upwarping movements were caused by rising magma which led to the fissure eruptions of the Deccan Trap lavas; which presumably took place during a period of tension in the upwarped area. The problem of the origin of the Narmada rift structure is discussed and evidence is adduced to show that the final sinking of the crest of the upwarped area has caused the out-pouring of the Deccan Trap lavas. The individual lava flow with their typical field and microscopic characteristics maintaining their interflow differences have been traced over long distances. These studies have led to the correlation of the flows between the measured sections. Further, as regards the cause of the higher elevation of the base of the basal flow in Katangi (1950), the possibility of a post-Deccan Trap upwarping movement is briefly considered.     

Widening of the Krafla fissure swarm during the 1975–1981 volcano-tectonic episode

Frequent distance measurements across the Krafla fissure swarm, North Iceland, recorded the extension accompanying the sequence of rifting events which started in December, 1975, and lasted for 6 years.An 80 to 90 km long section of the fissure swarm extended during this sequence of rifting and volcanic events. Maximum widening of about 8 m occurred 10 to 12 km north of Leirhnjúkur. which is located above the center of the Krafla magma reservoir. From that location, the amount of widening decreased north-wards and is estimated to exceed 2 m where the seismicity indicated the northern termination of the present rifting, off the north coast, about 70 km north of Leirhnjúkur. The amount of widening also decreased southwards and approached zero at 15 to 20 km south of Leirhnjúkur.The ground deformation associated with these rifting events can be summarised as:A narrow strip, 1 to 2 km wide, along the fissure swarm is heavily fractured with numerous open cracks parallel to the fissure swarm. This fractured strip has subsided 2 to 3 m relative to its flanks.The flanks of the fractured zone have been uplifted relative to regions farther away. The uplift is not well constrained, but tilt observations at several locations indicate about 1 m uplift. The flanks of the rift zone have contracted, perpendicular to the fissure swarm. The maximum contractional strain exceeds 300 mm per km.The amount of areal expansion (windening of the fissure swarm times the length of the fractured zone) associated with these rifting events is estimated to be about 0.30 km². For individual events, the area of expansion has been roungly proportional to the volume of subsidence above the Krafla magma reservoir.If the width of a new dike is equal widening of surface fissures, the ratio of the subsidence volume to the area of expansion for the best observed events indicated a height of a new dike system as 2.4 to 2.8 km. This ratio is significantly less for events of large lava production, but even during these events, the majority of magma leaving the Krafla reservoir was apparently emplaced in subsurface fissures.     

Quantifying river incision into low‐relief surfaces using local and catchment‐wide 10Be denudation rates

Relief generation in non‐glaciated regions is largely controlled by river incision into bedrock but datable fluvial terraces that allow quantifying incision rates are not always present. Here we suggest a new method to determine river incision rates in regions where low‐relief surfaces are dissected by streams. The approach consists of three steps and requires the ¹⁰Be concentrations of a stream sediment sample and a regolith sample from the low‐relief surface. In the first step, the spatial distribution of ¹⁰Be surface concentrations in the given catchment is modelled by assuming that denudation rates are controlled by the local hillslope angles. The slope–denudation rate relation for this catchment is then quantified by adjusting the relation between slope angle and denudation rate until the average ¹⁰Be concentration in the model is equal to the one measured in the stream sediment sample. In the second step, curved swath profiles are used to measure hillslope angles adjacent to the main river channel. Third, the mean slope angle derived from these swath profiles and the slope–denudation relation are used to quantify the river incision rate (assuming that the incision rate equals the denudation rate on adjacent hillslopes). We apply our approach to two study areas in southern Tibet and central Europe (Black Forest). In both regions, local ¹⁰Be denudation rates on flat parts of the incised low‐relief surface are lower than catchment‐wide denudation rates. As the latter integrate across the entire landscape, river incision rates must exceed these spatially averaged denudation rates. Our approach yields river incision rates between ~15 and ~30 m/Ma for the Tibetan study area and incision rates of ~70 to ~100 m/Ma in the Black Forest. Taking the lowering of the low‐relief surfaces into account suggests that relief in the two study areas increases at rates of 10–20 and 40–70 m/Ma, respectively. Copyright © 2018 John Wiley & Sons, Ltd.     

Ar/Ar geochronology of the West Greenland Tertiary volcanic province

Paleocene volcanic rocks in West Greenland and Baffin Island were among the first products of the Iceland mantle plume, forming part of a larger igneous province that is now submerged beneath the northern Labrador Sea. A ⁴⁰Ar/³⁹Ar dating study shows that volcanism commenced in West Greenland between 60.9 and 61.3 Ma and that 80% of the Paleocene lava pile was erupted in 1 million years or less (weighted mean age of 60.5±0.4 Ma). Minimum estimates of magma production rates (1.3×10⁻⁴ km³ year⁻¹ km⁻¹) are similar to the present Iceland rift, except for the uppermost part of the Paleocene volcanic succession where the rate decreases to <0.7×10⁻⁴ km³ year⁻¹ km⁻¹ (rift). The timing of onset of volcanism in West Greenland coincides with the opening of the northern Labrador Sea and is also strikingly similar to the age of the oldest Tertiary volcanic rocks from offshore SE Greenland and the British–Irish province. This is interpreted as manifesting the impact and rapid (>1 m/year) lateral spreading of the Iceland plume head at the base of the Greenland lithosphere at 62 Ma. We suggest that the arrival, or at least a major increase in the flux, of the Iceland mantle plume beneath Greenland was a contributing factor in the initiation of seafloor spreading in the northern Labrador Sea. Our study has also revealed a previously unrecognised Early Eocene volcanic episode in West Greenland. This magmatism may be related to movement on the transform Ungava Fault System which transferred drifting from the Labrador Sea to Baffin Bay. A regional change in plate kinematics at 55 Ma, associated with the opening of the North Atlantic, would have caused net extension along parts of this fault. This would have resulted in decompression and partial melting of the underlying asthenosphere. The source of the melts for the Eocene magmatism may have been remnants of still anomalously hot Iceland plume mantle which were left stranded beneath the West Greenland lithosphere in the Early Paleocene.     

Asymmetric extension associated with uplift and subsidence in the Transantarctic Mountains and Ross Embayment

Apatite fission track data combined with regional geological observations indicate that the uplift of the Transantarctic Mountains has been coeval with thinning and subsidence of the crust beneath the Ross Embayment. In the Dry Valleys region of south Victoria Land, the mountains have been uplifted about 5 km since the early Cenozoic at an average rate of about 100 m/Ma. During uplift, the crust remained at constant thickness or was slightly thickened by magmatic underplating. In contrast, the crust beneath the Ross Embayment has been extended and consequently thinned beginning in the Late Cretaceous but mainly during Cenozoic times. We suggest here that the uplift of the Transantarctic Mountains and the subsidence of the Ross Embayment are a result of passive rifting governed by a fundamental structural asymmetry defined by a shallow crustal penetrative detachment zone that dips westward beneath the Transantarctic Mountain Front. The localization and asymmetry of this detachment and its unusually deep level expression are attributed to a profound crustal anisotropy inherited from an early Palaeozoic collision along the present site of the mountain range.     

TECTONIC FEATURE OF QINGHAI-XIZANG PLATEAU AND ITS STRESSED STATE

This paper deals with the uplift mechanism and the uplift form of Qinghai-Xizang (Tibet) plateau and the deformation regularity of its surrounding region caused by this uplifting. It is shown that the insertion of Indian plate with the wedge-like frontal margin beneath Qinghai-Xizang plateau made the plateau compressed and uplifted; at same time along several pre-existing large faults, striking NE and NW, the strike-slip movement took place. It is of great significance to study Asian     

辽河裂谷的深部构造与裂谷活动的侧向迁移

对横穿辽河裂谷的闾阳－海城－东沟剖面的深部地震探测、重力测量、大地电磁测深、大地热流测量资料做了进一步分析,发现辽河裂谷地带壳幔间具有多个薄层过渡的特征,与东西两侧的辽东台隆和燕山台褶带明显不同。壳幔过渡带的薄层结构、速度结构、温度结构以及壳内低速层和软流圈顶面构造特点表明辽河裂谷的构造演化过程自西向东侧向迁移,当前上地幔物质运动的前锋不在裂谷之下,而是向东移至金州地震带附近的析木一带,深部物质运动是辽河裂谷形成及其活动性侧向迁移的主要动力学因素     

GEOMORPHOLOGY OF THE GYARING CO FAULT ZONAL DRAINAGE SYSTEM AND ITS STRUCTURAL IMPLICATIONS

Strike-slip faults and normal faults are dominant active tectonics in the interior of Tibetan plateau and control a series of basins and lakes showing extension since the Late Cenozoic, by contrast with the thrust faulting along the orogenic belts bordering the plateau. The late Neotectonic movement of those faults is key information to understand the deformation mechanism for Tibetan plateau. The Gyaring Co Fault is a major active right-lateral strike-slip fault striking~300° for a distance of~240km in central Tibet, in south of Bangong-Nujiang suture zone. The Gyaring Co Fault merges with the north-trending Xainza-Dinggye rift near the southern shore of Gyaring Co. From NW to SE, Dongguo Co, Gemang Co-Zhangnai Co, Zigui Co-Gyaring Co form the Gyaring Co fault zonal drainage basin. Some scholars have noticed that the formation of lakes and basins may be related to strike-slip faults and rift, but there is no analysis on the Gyaring Co fault zonal drainage basin and its response to regional tectonics. In recent years, a variety of quantitative geomorphic parameters have been widely used in the neotectonic systems to analyze the characteristics of the basin and its response mechanism to the tectonic movement. In this paper, we applied ASTER GDEM data on the ArcGIS platform, extracted the Gyaring Co fault zonal drainage basin based on Google Earth images (Landsat and GeoEye) and field work. We acquired basic geomorphic parameters of 153 sub-basin (such as grade, relief, average slope, area) and Hypsometric Index (HI) value and curve. Statistical results have indicated significant differences in scale(area and river network grade)in north and south sides of the fault. Southern drainage basins' relief, slope, HI value are higher than the northern basins, and the overall shape of hypsometric curve of northern basins are convex compared with southern concavity. Along the strike of the Gyaring Co Fault, average slope, and HI value are showing generally increasing trending and hypsometric curve become convex from west to east. By comparing and analyzing the lithology and rainfall conditions, we found that they have little influence on the basic parameters and HI value of drainage basins. Therefore, the changes of basin topographic differences between northern and southern side of fault and profile reveal the Gyaring Co Fault has experienced differential uplift since the late Cenozoic, southern side has greater uplift compared to the north side, and the uplift increased from NW to SE, thus indicate that normal faulting of the Gyaring Co Fault may enhanced by the Xainza-Dinggye rift. The early uplift of the Gangdise-Nyainqentanglha Mountain in late Cenozoic might provide northward inclined pre-existing geomorphic surfaces and the later further rapid uplift on the Gangdise-Nyaingentanglha Mountain and Xainza-Dinggye rift might contribute to the asymmetrical development of the Gyaring Co fault zonal drainage basin.     

The pre-glacial evolution of Wales

The classical explanation of the development of the Welsh landscape by the effects of a pulsed ‘eustatic’ uplift during the Cenozoic times is challenged by new data on the geology and geomorphology of Wales and the adjacent regions. The post-Caledonian surface developed over most of Wales in the upper Westphalian plays a major role in landform development. Since its emergence before mid-Cretaceous times, the Welsh Massif has suffered a long subaerial evolution which favoured a powerful chemical weathering. In Anglesey and St. David's Land, residual hills were formed by a process of differential weathering, and downwearing in saprolites. The Millstone Grit quartzites have been deeply weathered and dolines or flat-bottomed basins have been developed. From Cretaceous to Miocene times, a morphotectonic equilibrium has existed between uplift and denudation, so that, in the major part of Wales, the original planation surface was constantly maintained by lowering on itself and in some places it is possible to prove that no more than a few dozen metres of rock thickness disappeared during that period. Several main escarpments were produced by the warping of the planation surface along sharp flexures, during Neogene times. The Cenozoic vertical movements were controlled by the Caledonian or pre-Caledonian tectonic pattern which has divided the continental crust into major structural units. Welsh tectonic development is related to the opening of the North Atlantic, associated stresses reactivating ancient lines of weakness in the heterogeneous lower crust or upper mantle.     

剥蚀及地幔作用下青藏高原隆升过程的数值模拟

修改了England和Mckenzie的黏性薄层流变模型中控制大陆形变的连续性方程,将剥蚀作用对高原隆升演化的影响直接引入该方程,并考虑下伏地幔小尺度对流对增厚岩石层的搬离作用对高原隆升演化后期的影响,用有限差分法直接模拟青藏高原隆升过程. 数值模拟结果所显示的高原隆升演化过程与实际观测资料吻合较好,揭示了高原隆升演化过程的非平稳和多阶段的特性;同时还表明上地幔小尺度对流对岩石层底部的搬离作用可能是最近8Ma以来高原快速隆升的主导机制.