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1.
A flight of marine terraces along the Cuban coast records Quaternary sea‐level highstands and a general slowly uplifting trend during the Pleistocene. U/Th dating of these limestone terraces is difficult because fossil reef corals have been affected by open system conditions. Terrace ages are thus often based on geological and geomorphological observations. In contrast, the minimum age of the terraces can be constrained by dating speleothems from coastal mixing (flank margin) caves formed during past sea‐level highstands and carving the marine limestones. Speleothems in Santa Catalina Cave have ages >360 ka and show various cycles of subaerial–subaqueous corrosion and speleothem growth. This suggests that the cave was carved during the MIS 11 sea‐level highstand or earlier. Some stalagmites grew during MIS 11 through MIS 8 and were submerged twice, once at the end of MIS 11 and then during MIS 9. Phreatic overgrowths (POS) covering the speleothems suggest anchialine conditions in the cave during MIS 5e. Their altitude at 16 m above present sea level indicates a late Pleistocene uplift rate of <0.1 mm/ka, but modelling also shows uplift to have been insignificant over a long timespan during the middle Pleistocene since the cave was carved. Our study shows that some flank margin caves in the region of Matanzas are older than commonly believed (i.e. MIS 11 rather than MIS 5). These caves not only can be preserved but are good markers of interglacial sea‐level highstands, more reliable than marine abrasion surfaces. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

2.
Located at the west of the Linfen basin, the Luoyunshan piedmont fault zone controls the western boundary of the basin. According to the measurements of the terraces in eight gullies along the Luoyunshan fault zone, five levels of terraces, namely T1～T5 have developed in these gullies. The heights of terraces T1, T2, T3, T4 and T5 are about 3m, 8～10m, about 20m, about 30m and 40～50m, respectively. The dating data of the terraces and investigation of the faulted landforms show that the Luoyunshan fault zone has experienced much activity since the Late Quaternary. The uplift rate of the terraces was 0.41mm/a since the Middle-Late Pleistocene, and 0.75mm/a since the Holocene. The increasing trend of uplift rate of the terraces along the Luoyunshan fault zone from the Middle-Late Pleistocene to Holocene indicates the tendency of gradual tectonic uplift of the fault zone since the late Quaternary. This is in good agreement with the increasing trend of subsidence rate of the Linfen basin from the Late Pleistocene to Holocene.  相似文献   

3.
A detailed survey of morphological and biological markers of paleo-shorelines has been carried out along the coastal sector of Mt. Etna volcano (eastern Sicily, Italy), in order to better define causes and timing of vertical deformation. We have mapped markers of raised Holocene shorelines, which are represented by beach rocks, wave-cut platforms, balanid, vermetid and algal rims. The timing of coastal uplift has been determined by radiocarbon dating of shells collected from the raised paleo-shorelines and, to correctly assess the total amount of tectonic uplift of the coast during the Late Holocene, we have compared the elevation-age data of sampled shells to the local curve of Holocene sea-level rise. Taking into account the nominal elevation of the associated paleo-shorelines, an uplift rate of 2.5–3.0 mm/year has been estimated for the last 6–7 ka. This general process of uplifting is only locally interrupted by subsidence related to flank sliding of the volcanic edifice, measured at docks and other manmade structures, and by acceleration along the hinge of an active anticline and at the footwall of an active fault. Based on this new data we suggest more precise time–space constraints for the dynamics of the lower eastern flank of Mt. Etna volcano.  相似文献   

4.
The island of Crete in the forearc of the Hellenic subduction zone has a rugged topography with local relief exceeding 2 km. Based on the elevation of marine shorelines, rates of rock uplift during the Late Holocene were previously estimated to range between 1 and 4 mm/a in different parts of the island. These rates may, however, not be representative for longer timescales, because subduction earthquakes with up to 9 m of vertical coseismic displacement have affected Crete in the Late Holocene. Here we use a well preserved sequence of marine terraces near Kato Zakros in eastern Crete to determine the rate of rock uplift over the last ∼600 ka. Field investigations and topographic profiles document a flight of more than 13 marine bedrock terraces that were carved into limestones of the Tripolitza unit. Preliminary age constraints for the terraces were obtained by 10Be exposure dating of rare quartz-bearing sandstone clasts, which are present on some terraces. The 10Be ages of these samples, which have been corrected for an inherited nuclide component, yielded exposure ages between ∼100 ka and zero. Combined with geomorphologic evidence the two oldest 10Be ages suggest that the terraces T4 and T5, with shoreline angles at an elevation of ∼68 and ∼76 m above sea level, respectively, formed during the marine isotope stage 5e about 120 ka ago. The correlation of the higher terraces (T6 to T13) with regional sea-level highstands indicates sustained rock uplift at a rate of ∼0.5 m/ka since at least ∼600 ka. As normal faulting has dominated the tectonics of Crete during the last several million years, upper crustal shortening can be ruled out as a cause for rock uplift. We argue that the sustained uplift of the island results from the continuous underplating of sediments, which are transferred from the subducting African plate to the base of the crust beneath Crete.  相似文献   

5.
Pleistocene uplift of the Chilean coast is recorded by the formation of wave-cut platforms resulting from marine erosion during sea-level highstands. In the Altos de Talinay area (~ 31°S), we have identified a sequence of 5 wave-cut platforms. Using in situ produced 10Be exposure ages we show that these platforms were formed during interglacial periods at 6, 122, 232, 321 and 690 ka. These ages correspond to marine isotopic stages (MIS) or substages (MISS) 1, 5e, 7e, 9c and 17. Shoreline angle elevations used in conjunction with our chronology of wave-cut platform formation, illustrate that surface uplift rates vary from 103 ± 69 mm/ka between 122 and 6 ka, to 1158 ± 416 mm/ka between 321 and 232 ka. The absence of preserved platforms related to the MIS 11, 13 and 15 highstands likely reflects slow uplift rates during these times. We suggest that since 700 ka, the Altos de Talinay area was predominantly uplifted during 2 short periods following MIS 17 and MISS 9c. This episodic uplift of the Chilean coast in the Pleistocene may result from subduction related processes, such as pulses of tectonic accretion at the base of the forearc wedge.  相似文献   

6.
Many earthquakes have been recorded from the coastal margin of the Indian peninsular shield during the last 200 years. Largely made up of Precambrian assemblages with variable cover of Jurassic to Quaternary sedimentary rocks and Cretaceous-Eocene volcanics, the peninsular shield was long held to be aseismic. Recent measurements, however, show that this continental fragment is being pushed northeastward by the Carlsberg and Central Indian ridges; and the Indo-Myanmar subduction zone is exerting vigorous slab pull towards the east. Repeated cycles of sea level change during the Quaternary have also induced continuing hydro-isostatic adjustment due to variable melt water loading in the Bay of Bengal and the Arabian sea. All these forces produce space-time fluctuations of strain around many small to large faults, which occur in the upper crust of the shield. Some of the faults have been intermittently active (during the past 100 kyr); others were active earlier. Although the Shillong plateau and the associated hill ranges of northeastern India and Myanmar are subject to the maximum seismic hazard, the peninsular coast is also vulnerable to intermittent seismicity. We present illustrative evidence of some active faults, which are recognisable (a) on coastal land by displaced Pleistocene weathered cover, hot springs, leakages of native mercury and allochthonous geochemical anomalies of base metals and (b) offshore below the inner shelf by horst-shaped uplifted segments and intra-formational slump folds on and below the top shallow seismic (3.5 kHz) reflector. On the other hand, there are long stretches of the east coast at Vishakhapatnam and Manappad Point, which do not show active faults. Step-like marine terraces, which occur up to+6 m above the low tide level (LTL) preserve records of relative sea level fluctuations during the Holocene and the Last Interglacial. In such sectors, absence of tectonic disturbance during the last 100 ka is also corroborated by lateral continuity of shallow seismic reflectors below the inner shelf over many kilometers. Since authentic historical (200–1000 years B.P.) records of seismicity along the Peninsular coast are virtually unavailable, the likely recurrence interval between earthquakes in each sector cannot be gauged. We, therefore, propose a scale of seismic risk, based on geometry of the mappable faults and available seismic records of the last two centuries. These could be used in combination to rank the densely populated coastal tracts sector-wise.  相似文献   

7.
Marine terrace flights resulting from the interaction of Quaternary glacio-eustatic fluctuations and tectonic uplift are a typical feature of the Tyrrhenian coast of Calabria in Southern Italy; in particular a térrace flight with four orders of terraces is evident in the Diamante area. The lowest terrace levels (fourth order: Diamante-Cirella terrace) are typified by a calcarenitic deposit with Cladocora caespitosa which give a Th/U age > 300,000 years. The third order terrace has a sedimentary cover formed of a basal discontinuous level of well rounded pebbles which underlies a deeply weathered coarse-grained sand horizon. The deposit ends with a paleosol locally cut by erosional scours filled by yellowish tuff deposits. The formation of this terrace dates from the Middle Pleistocene. The second order terrace presents a sedimentary cover composed of two generations of soils and is attributed to Middle Pleistocene age. The first order terrace (M. Carpinoso terrace) presents a wave-cut platform covered by a clastic deposit of marine and continental origin; this deposit consists of superimposed depositional events separated by unconformities, bounded by two diachronous surfaces. The formation of the wave-cut platform could be related to several sea-level stands during a long-lasting slow subsidence phase of the coastal area during the Lower Pleistocene. The uplift following terrace formation displaced the first order terrace most markedly; tectonic lineations controlled the hydrographic pattern and erosion of the surfaces.  相似文献   

8.
With enhanced rates of sea‐level rise predicted for the next century, the upstream extent of sea‐level influence across coastal plains is a topic of public importance. Australian coastal rivers provide a testing ground for exploring this issue because the area is tectonically stable, was not glaciated, and experienced a Holocene highstand between 7.4 and 2 ka of up to 1.5 m above Australian Height Datum (AHD). In the Shoalhaven River of New South Wales, investigation of a confined bedrock reach at Wogamia, 32 km inland, has identified a unit of dark, cohesive silt and sand with marine diatoms, shell fragments, and enhanced pyrite content, interpreted as estuarine. The unit is up to 13 m thick, thickens downstream, and is overlain by fluvial channel and floodplain deposits. The estuarine unit on‐laps a remnant Pleistocene terrace and extends to approximately +2.2 m AHD. Optically stimulated luminescence (OSL) and radiocarbon ages suggest that estuarine deposition commenced prior to 7.8 ka cal bp , predating the highstand by ~ 500 years, and that marine influence in the area continued to 5.3 ± 0.7 ka. During this period, a delta probably persisted at Wogamia, where a narrow upstream reach opens out, and subsequently advanced to fill the broad Shoalhaven coastal embayment. Although the effect of sea‐level rise depends on many factors, the results suggest that, during a highstand at or above present sea level, a strong marine influence may extend for tens of kilometres inland and penetrate confined bedrock reaches landward of coastal embayments. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

9.
通过对河曲县城一带出露较好的黄河阶地剖面进行研究,认为河曲一带黄河三、四级阶地形成于中更新世时期,晚更新世早期形成二级阶地,全新世形成一级阶地。本区中更新世抬升速率为0．14mm／a,晚更新世抬升速率为0．18mm／a,全新世抬升速率为0．70mm／a,晚更新世和全新世抬升速率的突然加大,可能与黄河下游三门湖的贯通、区域侵蚀基准面突然降低、河流侵蚀加大有关。  相似文献   

10.
Detailed mapping of geomorphological and biological sea-level markers around the Capo Vaticano promontory (western Calabria, Italy), has documented the occurrence of four Holocene paleo-shorelines raised at different altitudes. The uppermost shoreline (PS1) is represented by a deeply eroded fossiliferous beach deposit, reaching an elevation of ∼2.2 m above the present sea-level, and by a notch whose roof is at ∼2.3 m. The subjacent shoreline PS2 is found at an elevation of ∼1.8 m and is represented by a Dendropoma rim, a barnacle band and by a wave-cut platform. Shoreline PS3 includes remnants of vermetid concretions, a barnacle band, a notch and a marine deposit, and reaches an elevation of ∼1.4 m. The lowermost paleo-shoreline (PS4) includes a wave-cut platform and a notch and reaches an elevation of ∼0.8 m. Radiocarbon dating of material from individual paleo-shorelines points to an average uplift rate of 1.2–1.4 mm/yr in the last ∼6 ka at Capo Vaticano. Our data suggest that Holocene uplift was asymmetric, with a greater magnitude in the south-west sector of the promontory, in a manner similar to the long-term deformation attested by Pleistocene terraces. The larger uplift in the south-western sector is possibly related to the additional contribution, onto a large-wavelength regional signal, of co-seismic deformation events, which are not registered to the north-east. We have recognized four co-seismic uplift events at 5.7–5.4 ka, 3.9–3.5 ka, ∼1.9 ka and <1.8 ka ago, superposed on a regional uplift that in the area, is occurring at a rate of ∼1 mm/yr. Our findings places new constrains on the recent activity of border faults south of the peninsula and on the location of the seismogenic source the 1905 destructive earthquake.  相似文献   

11.
The Qilian Mountains, as a major orogenic belt in the northeastern margin of the Tibetan plateau, is the forefront of the expansion of the plateau to the northeast, where thrusts and folds dominate tectonic deformation. The Baiyang River starts from the inner Qilian Mountains, flowing northward across various structures, and finally into the Jiuxi Basin. This work focused on exhaustive investigations to the terraces on this river to characterize the Late Quaternary tectonic deformation in this region. The results show that (1)these river terraces on the Baiyang River are segmented, of which multiple levels developed at steep terrains and anticlines in the basin. Bounded by the Niutou Mountains, mainly 2-3 and 4-5 levels of terraces formed in the upper and lower reaches, respectively. (2)The longitudinal profiles along the river suggest a vertical motion rate of the Changma fault as (0.32±0.09)mm/a and crustal shortening rate (0.12±0.09)mm/a. There was no vertical activity since the formation of T5 surface (13ka)on the Hanxia-Dahuanggou fault. At the terrace T5 (9ka)on the Laojunmiao anticline, fold uplift amounts (6.55±0.5)m and shortening amounts (3.47±0.5)m, yielding uplift and shortening rates (1.23±0.81)mm/a and (0.67±0.44)mm/a, respectively. The Baiyang River anticline began to be active about 300ka with uplift and shortening rates (0.21±0.02)mm/a and (0.14±0.03)mm/a, respectively since 170ka. (3)In the Qilian Mountains, there were two different deformation characteristics in response to the expansion of the Tibetan plateau. Shear deformation dominates the inner Qilian Mountains, which is manifested as lateral extrusion of blocks. In the northern margin of Qilian Mountains and Jiuxi Basin, the deformation is dominated by compression, expressing crustal shortening and uplift, and the shortening within the basin accounts about half of the total deformation.  相似文献   

12.
A flight of Holocene marine terraces on the southwestern coast of Cape Omaezaki of central Japan provides evidence of recurrent millennium‐scale uplift events. We reconstructed the uplift history of these terraces by using facies analysis of drill core and geoslicer samples, environmental analysis of trace fossils, and 14C age determinations. Coastal uplift can be identified by the displacement of beach deposits such as foreshore deposits, which represent the intertidal swash zone of a wave‐dominated sandy coast. Three levels of former beach deposits facing the Nankai Trough were identified near the coast in the Omaezaki area. The highest of these, dated at about 3020–2880 BC, records a maximum of 2.2–2.7 m of emergence. The middle beach surface, of minimum age 370–190 BC, shows 1.6–2.8 m of emergence. The lowest beach surface, which is older than 1300–1370 AD, records 0.4–1.6 m of emergence. Our analysis of vertical crustal deformation data during the Holocene in this region suggests that rapid and strong uplift was restricted to the southwestern coast of the Omaezaki area and was probably caused by high‐angle thrusting on subsidiary faults branching from the underlying plate boundary megathrust.  相似文献   

13.
Raised marine terraces and submerged insular shelves are used through an integrated approach as markers of relative sea level changes along the flanks of the Salina volcanic island (Aeolian Arc, southern Italy) for the purpose of evaluating its crustal vertical deformation pattern through time. Paleo sea level positions are estimated for the terrace inner margins exposed subaerially at different elevations and the erosive shelf edges recognized offshore at different depths. Compared with the eustatic sea levels at the main highstands (for the terraces) and lowstands (for the shelf edges) derived from the literature, these paleo sea level markers allowed us to reconstruct the interplay among different processes shaping the flanks of the island and, in particular, to quantify the pattern, magnitudes and rates of vertical movements affecting the different sectors of Salina since the time of their formation. A uniform uplift process at rates of 0.35 m ka−1 during the Last Interglacial is estimated for Salina (extended to most of the Aeolian Arc) as evidence of a regional (tectonic) vertical deformation affecting the sub-volcanic basement in a subduction-related geodynamic context. Before that, a dominant subsidence at rates of 0.39–0.56 m ka−1 is instead suggested for the time interval between 465 ka (MIS 12) and the onset of the Last Interglacial (MIS 5.5, 124 ka). By matching the insular shelf edges with the main lowstands of the sea level curve, a relative age attribution is provided for the (mostly) submerged volcanic centres on which the deepest (and oldest) insular shelves were carved, with insights on the chronological development of the older stages of Salina and the early emergence of the island. The shift from subsidence to uplift at the Last Interglacial suggests a major geodynamic change and variation of the stress regime acting on the Aeolian sub-volcanic basement. © 2019 John Wiley & Sons, Ltd.  相似文献   

14.
Deposits of late‐Holocene beach sand buried conifer forests episodically emerge on beaches of the Oregon coast. Simultaneously, sand dunes buried late‐Holocene forests growing on marine terraces landward of the beaches. Dune ramps, up to 60 m in elevation, connected the beach and dune deposits. The average age of wood samples from stumps rooted on the shore platforms is 3·07 ± 1·45 ka. The average age of wood and charcoal samples embedded in forest soil on the marine terraces is 3·27 ± 1·46 ka. Between 1994 and 2006, winter storm waves exposed more than 4·5 km2 of late‐Holocene forest soil on shore platforms at 19 localities. Rooted stumps without soil were uncovered at an additional 14 localities. Once exposed, wave action eroded the soil rapidly (one to two years). The intact forest soil and roots on the shore platforms must have been nearly continuously buried, protected and preserved prior to recent exposure. The late‐Holocene buried forest provides the basis for a conceptual model of coastal evolution. A three stage reversal of erosion and sand supply must have occurred: (1) wave erosion switched to seaward advancement of forests, (2) forest growth and soil development switched to burial beneath beach and dune sand and (3) burial and preservation switched to wave erosion, truncation of dune ramps and landward retreat of sea cliffs. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

15.
We present new data about the morphological and stratigraphic evolution and the rates of fluvial denudation of the Tavoliere di Puglia plain, a low‐relief landscape representing the northernmost sector of the Pliocene‐Pleistocene foredeep of the southern Apennines. The study area is located between the easternmost part of the southern Apennine chain and the Gargano promontory and it is characterized by several orders of terraced fluvial deposits, disconformably overlying lower Pleistocene marine clay and organized in a staircase geometry, which recorded the emersion and the long‐term incision history of this sector since mid‐Pleistocene times. We used the spatial and altimetric distribution of several orders of middle to late Pleistocene fluvial terraces in order to perform paleotopographic reconstruction and GIS‐aided eroded volumes estimates. Then, we estimated denudation rates on the basis of the terraces chronostratigraphy, supported by published OSL and AAR dating. Middle to upper Pleistocene denudation rates estimated by means of such an approach are slightly lower than 0.1 mm yr‐1, in good agreement with short‐term data from direct and indirect evaluation of suspended sediment yield. The analysis of longitudinal river profiles using the stream power erosion model provided additional information on the incision rates of the studied area. Middle to late Quaternary uplift rates (about 0.15 mm yr‐1), calculated on the basis of the elevation above sea level of marine deposits outcropping in the easternmost sector of the study area, are quite similar to the erosion rates average value, thus suggesting a steady‐state fluvial incision. The approach adopted in this work has demonstrated that erosion rates traditionally obtained by quantitative geomorphic analysis and ksn estimations can be successfully integrated to quantify rates of tectonic or geomorphological processes of a landscape approaching steady‐state equilibrium. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

16.
The Tan-Lu Fault Zone(TLFZ), a well-known lithosphere fault zone in eastern China, is a boundary tectonic belt of the secondary block within the North China plate, and its seismic risk has always been a focus problem. Previous studies were primarily conducted on the eastern graben faults of the Yishu segment where there are historical earthquake records, but the faults in western graben have seldom been involved. So, there has been no agreement about the activity of the western graben fault from the previous studies. This paper focuses on the activity of the two buried faults in the western graben along the southern segment of Yishu through combination of shallow seismic reflection profile and composite drilling section exploration. Shallow seismic reflection profile reveals that the Tangwu-Gegou Fault(F4)only affects the top surface of Suqian Formation, therefore, the fault may be an early Quaternary fault. The Yishui-Tangtou Fault(F3)has displaced the upper Pleistocene series in the shallow seismic reflection profile, suggesting that the fault may be a late Pleistocene active fault. Drilling was implemented in Caiji Town and Lingcheng Town along the Yishui-Tangtou Fault(F3)respectively, and the result shows that the latest activity time of Yishui-Tangtou Fault(F3)is between(91.2±4.4)ka and(97.0±4.8)ka, therefore, the fault belongs to late Pleistocene active fault. Combined with the latest research on the activity of other faults along TLFZ, both faults in eastern and western graben were active during the late Pleistocene in the southern segment of the Yishu fault zone, however, only the fault in eastern graben was active in the Holocene. This phenomenon is the tectonic response to the subduction of the Pacific and Philippine Sea Plate and collision between India and Asian Plate. The two late Quaternary active faults in the Yishu segment of TLFZ are deep faults and present different forms on the surface and in near surface according to studies of deep seismic reflection profile, seismic wave function and seismic relocation. Considering the tectonic structure of the southern segment of Yishu fault zone, the relationship between deep and shallow structures, and the impact of 1668 Tancheng earthquake(M=8(1/2)), the seismogenic ability of moderate-strong earthquake along the Yishui-Tangtou Fault(F3)can't be ignored.  相似文献   

17.
海南岛北西部新构造特征及其演化研究   总被引：3，自引：1，他引：2  
张军龙  田勤俭  李峰  高站武  苏刚 《地震》2008,28(3):85-94
利用DGPS系统测量海南岛西部阶地, 绘制地质地貌综合剖面, 将西部阶地分为海成阶地和河流阶地两种。 其中海成地貌包括一条砂堤和四级阶地: 砂堤宽2～10 m, 高程约10 m, 形成于5 ka以来; 海成一级阶地发育较好, 阶地面高程21～22 m, 形成于晚更新世至全新世之间; 海成二级阶地顶面高程约32 m左右, 形成于晚更新世晚期; 海成三级阶地较为发育, 阶地面高程40～42 m, 形成于121.8 ka; 海成四级阶地零星分布, 阶地面高程约57 m, 形成于中更新世晚期。 河流阶地也可分出四级: 一级阶地高程约20 m, 局部发育, 形成于11.4 ka; 二级阶地高程约34 m, 形成于47.2 ka; 三级阶地高约50 m, 其基座顶面标高约41 m, 形成于晚更新世早期; 四级阶地高程约71 m, 基座面标高约60 m, 形成于中更新世晚期。 这些阶地中均以二级最为发育。 晚更新世以来全区处于整体加速抬升的状态。 依据阶地面的综合剖面特征, 认为王五-文教断裂晚更新世以来的活动性较弱。  相似文献   

18.
Elevated erosional notches and emergent marine deposits developed on limestone headlands along the Taormina coastline of northeastern Sicily testify to recent shoreline uplift. Although located at the southern prolongation of the Calabrian seismogenic belt, a zone of active extensional tectonics and rapid late Quaternary uplift, the study area lacks historical and instrumental evidence for significant earthquakes. A prominent notch level at an elevation of +4.5 and +5.0 m at Mazzaro and Capo Sant'Alessio, respectively, is dated by 14C assay of associated marine boring molluscs (Lithophaga) to be coincident with the 5000 yr BP deceleration of global eustatic rise, the mid-Holocene quasi-stillstand. These first radiometric dates of Holocene emergence along the northeastern Sicily coast indicate time-averaged uplift rates of 1.1 – 1.8 mm/yr. Well-defined erosional notches postdating the mid-Holocene quasistillstand, however, imply coastal uplift was not gradual but instead involved occasional abrupt crustal movements, probably the result of large paleoseismic earthquakes along the coastal-bounding normal faults. The results support a need for a re-evaluation of the earthquake potential of the Sicilian sector of the Apenninic seismogenic belt.  相似文献   

19.
焉耆盆地北缘和静逆断裂-褶皱带中晚第四纪变形速率   总被引：4，自引：4，他引：0  
焉耆盆地为南天山内部的一个山间盆地,盆地北缘发育1排第四纪新生褶皱带,即和静逆断裂-褶皱带。中晚第四纪以来,由于和静逆断裂-褶皱带的持续活动使得在褶皱生长过程中形成的多期洪积地貌面发生反向掀斜变形。利用高精度差分GPS,对褶皱带中部哈尔莫敦背斜区内的多期变形地貌面的地形形态进行了测绘,判定背斜的生长主要以翼旋转为主。利用背斜北翼不同地貌面的反向掀斜角度,分别计算了不同期次地貌面的隆升和缩短变形量。结合原地宇宙成因核素深度剖面法和光释光测年法,对背斜区内的F4,F3b,F2洪积台地面和T1阶地面的形成年龄进行了测定,发现背斜在距今约550ka、428.3+57.6-47.2ka和354.3+34.2-34.8ka不同时段的平均隆升速率从0.31±0.24mm/a下降至0.15±0.02mm/a,同时背斜北翼的翼旋转速度也呈逐渐减小的趋势。但背斜自起始变形开始,缩短速率却大致保持恒定为约0.3mm/a。而这一恒定的缩短速率与现今横跨和静逆断裂-褶皱带所观测的GPS速率具有很好的一致性,说明在天山内部的哈尔莫敦背斜区,短尺度的GPS速率可以代表长尺度的地壳应变速率,同时反映出山体内部一系列断层和褶皱构造在吸收和调节整体变形量时也起到一定的作用。  相似文献   

20.
Sedimentary deposits in the foreland basin of the northeastern Qilian Mountains are crucial documents recording tectonic activity and climate changes on the Tibetan Plateau. In this study, luminescence dating was used to date alluvial conglomerates and fluvial terrace sediments collected from the Beida River in the Jiuquan Basin, a foreland basin in the Hexi Corridor, northeastern Qilian Mountains. Detailed sedimentology and luminescence ages reveal that alluvial conglomerates accumulated from before 620 ka to 12 ka and that sediment accumulation rates increased at ∼330 ka and ∼35 ka, coinciding with the dates of two tectonic events (∼350 and ∼50 ka) and followed by climate cooling (from marine isotope stage (MIS) 9 to MIS 8 and from MIS 3 to MIS 2). This reveals that variations in the sediment accumulation rates are controlled by the coupling of tectonic uplift and climate cooling. The highest terrace (T7) that developed on the alluvial conglomerate base formed at ∼ 12 ka. The incision rate in the early Holocene was ∼2.1 mm/yr and increased to ∼14.6 mm/yr during the middle and late Holocene. The variations in the river incision rate provide geomorphic evidence for Holocene climate patterns in arid and semiarid areas. Luminescence dating offers a credible temporal framework for the deposits and reveals climate and tectonic effects on the evolution of the foreland basin, northeastern Qilian Mountains.  相似文献   

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