Uplift Events Research Articles

Uplift events of the Qinghai–Tibetan Plateau and environmental evolution of the southwest monsoon since 2.7 Ma, recorded in a long lake sediment core from Heqing, China

The tectonic-sedimentary cycles and environmental evolution in the southwest monsoon area since 2.7 Ma were reconstructed, based on the analysis of lithology, grain size, carbonate content, loss-on-ignition (LOI) and pollen in a 737.72 m sediment core from Heqing Basin, China. The results indicated that the lake basin was formed in about 2.7 Ma. Continuous lacustrine sediment was preserved since 2.7 Ma. Three stages of tectonic-sedimentary cycle were revealed: 2.7–1.5 Ma, 1.5–0.9 Ma and 0.9–0 Ma. The environmental evolution in Heqing area was influenced by the uplift of the Qinghai–Tibetan Plateau, the resulting variation of southwest monsoon and the earth orbital-scale periodicity.

Evidence for large Holocene earthquakes on the Compton thrust fault, Los Angeles, California

We demonstrate that the Compton blind thrust fault is active and has generated at least six large‐magnitude earthquakes (Mw 7.0–7.4) during the past 14,000 years. This large, concealed fault underlies the Los Angeles metropolitan area and thus poses one of the largest deterministic seismic risk in the United States. We employ a methodology that uses a combination of high‐resolution seismic reflection profiles and borehole excavations to link blind faulting at seismogenic depths directly to near‐surface fault‐related folding. Deformed Holocene strata record recent activity on the Compton thrust and are marked by discrete sequences that thicken repeatedly across a series of buried fold scarps. We interpret the intervals of growth as occurring after the formation of now‐buried paleofold scarps that formed during uplift events on the underlying Compton thrust ramp. Minimum uplift in each of the scarp‐forming events, which occurred at 0.7–1.75 ka (event 1), 0.7–3.4 ka or 1.9–3.4 (event 2), 5.6–7.2 ka (event 3), 5.4–8.4 ka (event 4), 10.3–12.5 ka (event 5), and 10.3–13.7 ka (event 6), ranged from ∼0.6 to ∼1.9 m, indicating minimum thrust displacements of ≥1.3 to 4.2 m. Such large displacements are consistent with the occurrence of large‐magnitude earthquakes (Mw ≥ 7). This multidisciplinary methodology provides a means of defining the recent seismic behavior, and therefore the hazard, for blind thrust faults that underlie other major metropolitan regions around the world.

Scales of transient convective support beneath Africa

Beneath sub-equatorial Africa, there is convincing evidence for a gigantic, slow, velocity anomaly within the lower mantle that is inferred to be a thermochemical superplume. Here, we define the spatial and temporal pattern of uplift across the northern edge of this putative superplume by analyzing stratal geometries and stacking velocities of Neogene sedimentary rocks. These marine deposits are imaged on a dense grid of seismic reflection profiles that straddle the southwest African coastal shelf. Inverse modeling of stacking velocity profiles demonstrates that there have been at least two significant phases of uplift. A post-Pliocene uplift event increases from 0 to ~500 m elevation over a distance of ~1000 km, in close agreement with geophysical estimates of the present-day variation of dynamic topography. An earlier phase of uplift occurred in middle Oligocene time (ca. 30–35 Ma ago). We propose a two-stage development of epeirogeny in which a Middle Oligocene phase of uplift may be related to initiation and growth of the African superplume. Post-Pliocene denudation records rapid (100–250 m/Ma) vertical motions generated by upper mantle convection, which vary on length scales of 500–1000 km. Our results support the existence of a convective circulation system that has operated on different temporal and spatial scales beneath the African plate.

The origin and timing of multiphase cementation in carbonates: Impact of regional scale geodynamic events on the Middle Jurassic Limestones diagenesis (Paris Basin, France)

The Middle Jurassic carbonates of the eastern part of the Paris Basin display surprisingly low values of porosity and permeability ( Φ < 15‰ and K < 0.5 mD). The main objective of this study is to determine the causes and timing of the cementation that altered the petrophysical properties of these carbonates thereby destroying their potential as oil reservoirs; a fate that did not befall their equivalents in deeper, central parts of the Paris Basin. Using petrographic and geochemical analyses (stable O and C isotopes, Sr isotopes, major elements), we identify six calcitic spar stages, two dolomite stages, and several episodes of fracturing and stylolitization ordered in paragenetic sequence. Cement quantification shows the predominance of two blocky calcite cement stages (75% of total cementation). O and Sr isotopes from these calcite cements suggest that the parent fluids resulted either from a mixing of trapped Jurassic seawater and meteoric water, or from buffered meteoric waters. In the geological history of the Paris Basin, major meteoric water inputs were possible during the Early Cretaceous, when the Middle Jurassic carbonates cropped out at its northern and eastern borders. Lateral meteoric recharge may have occurred as a result of two separate uplift events (Late Cimmerian Unconformity and Late Aptian Unconformity) and the related exposures of carbonates to the north of the study area. This palaeohydrological circulation brought about a significant reduction of porosity (from 40% to 10%) through calcite cement precipitation. The Early Cretaceous events are of great importance in the diagenetic evolution of the sedimentary basins bordering the London-Brabant Massif across all of northwestern Europe. A subsequent dolomite and calcite cementation stage accounts for about 5% of the total cement volumes. This late cementation may have been caused by hydrothermal fluids ascending along permeable fractures during the Late Oligocene extension episode.

Origin of the Gangdise (Transhimalaya) Permian arc in southern Tibet: Stratigraphic and volcanic geochemical constraints

AbstractThe well‐studied Mesozoic and Cenozoic volcanic rocks of the Gangdise Terrane, southern Tibet, are widely interpreted to have resulted from subduction of the Neotethys; however, Late Paleozoic volcanic rocks and their tectonic setting remain poorly studied. Based on new geological data, we carried out stratigraphical and geochemical analyses of Permian volcano‐stratigraphic sequences within an east–west‐trending, fault‐bounded zone of uplift in the central Gangdise Terrane. Sedimentary rocks in this area consist of platform carbonates and terrigenous clastic rocks that represent widespread shallow‐marine sedimentary basins developed around northern Gondwana. A regression or tectonic uplift event is recorded in Permian sedimentary rocks that show the local development of fluvial environments. The sedimentary succession contains evidence of two volcanic stages: a period of basaltic extrusions and younger explosive felsic magmatism. The first volcanic stage is Early and Middle Permian in age. Tholeiitic basaltic lavas are exposed around Maizhokunggar (Tangjia) and Lhunzhub in central Gangdise. The Lower Permian basalts are relatively enriched in MgO (4.58–12.19%), whereas the Middle Permian basalts are characterized by high Al2O3 contents (11.75–21.22%). Rocks of both ages are enriched in large‐ion lithophile elements (LILE) and light rare earth elements (LREE), and show pronounced negative Nb and Ta anomalies. Total REE contents and light (LREE)/heavy (HREE) ratios increased from the Early to Middle Permian. Observed variations in initial Sr, Nd, and Pb isotopes (87Sr/86Sri = 0.7013–0.7066, 207Pb/204Pbi = 15.53–15.63, and 208Pb/204Pbi = 38.04–38.64 for a given 206Pb/204Pbi; εNd = +0.69 to −11.55) can be explained by crustal interaction with mantle sources, as is characteristic of metasomatism by slab‐derived fluids or assimilation and fractional crystallization (AFC) processes during magmatic evolution. The observed geochemical signatures, coupled with stratigraphic constraints, support the hypothesis that an initial arc formed during the Permian due to southward subduction of the Paleotethys, predating the well‐known Mesozoic arc preserved in the Gangdise Terrane.

Cenozoic palaeocanyon evolution, Ancestral Cascades arc volcanism, and structure of the Hope Valley–Carson Pass region, Sierra Nevada, California

We use new geologic mapping, geochronological, and geochemical data on Tertiary volcanic, volcaniclastic, and intrusive rocks to investigate the volcanic, stratigraphic, and structural evolution of the Carson Pass region south of Lake Tahoe in the central Sierra Nevada. Volcanic and volcaniclastic rocks were deposited in east–west-trending palaeocanyons carved into Mesozoic granitic and metamorphic basement rocks; sediments were transported westwards towards the present-day Central Valley of California. In the Carson Pass–Hope Valley area, two palaeotributaries are preserved in faulted terrane east of the present-day Sierran crest (Hope Valley area); these merge at the crest to form one large, >7 km wide palaeocanyon that is undisrupted by faults west of the crest (Carson Pass–Kirkwood area). This single, large palaeocanyon roughly coincides with the present-day Mokelumne River drainage. New 40Ar/39Ar dates and stratigraphic data east of the crest, integrated with previously published data west of the crest, constrain the ages of strata and unconformities within the Hope Valley–Carson Pass–Kirkwood palaeocanyon system. We interpret three major erosional unconformities to record uplift events at ca. 23–16, 13.5–11, and 10–7 Ma. In other parts of the central Sierra, these uplift events are inferred to correspond to range-front faulting events. We propose the term ‘Hope Valley Graben’ for the structural feature mapped immediately east of the Sierran crest at Carson Pass. It is a nearly symmetrical full graben that offsets volcanic rocks as young as 6 Ma at least 400 m (1300 ft) on each of its bounding faults – herein named the Red Lake Fault on the west and the Hope Valley Fault on the east. However, we infer that faulting began before eruption of the 6 Ma volcanic rocks for three reasons: (1) the graben-localized emplacement of one of the largest volcanic centres in the Sierra, the 6.34 ± 0.14–6.18 ± 0.14 Ma Markleeville Peak Center; (2) andesite lava flows erupted at 6.22 ± 0.14 Ma from the Red Lake Fault, and abut it within the graben; and (3) brecciated granite along the Red Lake Fault is intruded by altered andesite, indicating that the fault started slipping before magmatism ceased. Our stratigraphic and geochronologic data do not permit an estimate of the amount of pre-6 Ma displacement in the Hope Valley graben. The geometry of the palaeocanyon system indicates that a dextral component of slip demonstrated for transtensional faults in other parts of the region did not operate in the Hope Valley graben.

Island-like radiation of Saussurea (Asteraceae: Cardueae) triggered by uplifts of the Qinghai-Tibetan Plateau

Increasing evidence suggests that geological or climatic events in the past triggered the radiative diversification of both animals and plants on islands as well as continents. The Qinghai–Tibetan Plateau (QTP) has been extensively uplifted since the Miocene, but there is little information on possible links between these events and biological diversification in this and adjacent regions. Partly to explore such links, we have examined the diversification of Saussurea (Asteraceae: Cardueae), a species-rich genus that is mostly endemic to QTP, but also occurs in arid highlands elsewhere in the Northern Hemisphere. The phylogenetic analyses were conducted on the basis of the nuclear (internal transcribed spacer, ITS) and plastid (trnL-F and psbA-trnH) sequences from 55 species, representing 19 sections from all six subgenera of Saussurea, and species from 15 genera of the Cardueae. The results suggest that the currently circumscribed genus Saussurea (s.l.) is a polyphyletic group and that five sections should be excluded from the genus. Samples from the other 14 sections (representing five subgenera) clustered as a monophyletic group (here designated the Saussurea s.s. lineage, SSSL) with high statistical support. However, none of the analyses (nuclear, plastid or combined) resolved SSSL's infrageneric phylogeny, and the parallel clades of the lineage indicate that island-like adaptive radiation occurred. Furthermore, this radiation appears to have occurred 14–7 Mya, during the period of the major uplift events of QTP. Thus, our results support the hypothesis that geological events may play important roles in driving biological diversification through continental radiation.

Post-rift landscape development of north-east Brazil

The evolution of the landscape of north-east Brazil in relation to the burial and exhumation history of both onshore and offshore areas is the focus of a research project carried out for StatoilHydrodo Brasil and Petrobras from 2007 to 2009 by the Geological Survey of Denmark and Greenland in collaboration with Geotrack International. In hydrocarbon exploration it is important to understand the regional tectonic framework and thus also to consider the volumes of rocks that may have been present and then removed during the geological past. For example, the timing of hydrocarbon generation and changes in migration routes can be assessed when the timing and magnitude of uplift and erosion is known. Studies in West Greenland have demonstrated the usefulness of large-scale, low-relief, high-level landscapes as markers of uplift events, and in particular the strength of combining the denudation history from landscape analysis with the cooling history from apatite fission-track analysis (AFTA) data and the stratigraphic record (Bonow et al. 2006, 2007; Japsen et al. 2006, 2009). In the study area, there are two plateaux with elevations up to c. 1300 m above sea level (a.s.l.). The plateaux are currently being dissected by deeply incised fluvial valleys, and escarpments separate the two plateaux. The lowlands cut across Early Cretaceous rift systems along the Atlantic margin, including the intracontinental Recôncavo–Tucano–Jatobá (RTJ) Rift and also the Camamu Basin, of which the western margin is exposed onshore (Fig. 1). The RTJ Rift is a mature hydrocarbon province, whereas the deep-water parts of the Camamu Basin are the target of frontier exploration (e.g. Magnavita et al. 1994; Davison 1999; Cobbold et al. 2008). The post-rift sequence in the RTJ Rift and the inshore Camamu Basin is thin or absent. However, it has been estimated that up to 2000 m of sedimentary cover once was present, but has now been removed (Magnavita et al. 1994).

Relocating Odysseus' homeland

Homer's Ithaca had been viewed as a work of poetic licence and imprecise geography. However, as recent research shows the island's form may have been disguised over the past two millennia by catastrophic rockfalls, co-seismic uplift events and relative sea-level change.

Miocene evolution of the western edge of the Nevadaplano in the central and northern Sierra Nevada: palaeocanyons, magmatism, and structure

The Sierra Nevada of California is the longest and tallest mountain range in the co-terminus USA, and has long been regarded as topographically very young ( < 6 Ma); however, recent work has provided evidence that the range is very old (>80 Ma), and represents the western shoulder of a Tibetan-like plateau (the Nevadaplano) that was centred over Nevada. A great deal of effort has been invested in applying modern laboratory and geophysical techniques to understanding the Sierra Nevada, yet some of the most unambiguous constraints on the Sierran landscape evolution are derived from field studies of dated strata preserved in the palaeochannels/palaeocanyons that crossed the range in Cenozoic time. Our work in the Sierra Nevada suggests that neither end-member model is correct for the debate regarding youth vs. antiquity of the range. Many features of the Cenozoic palaeocanyons and palaeochannels reflect the shape of the Cretaceous orogen, but they were also affected by Miocene tectonic and magmatic events. In the central Sierra Nevada, we infer that the inherited Cretaceous landscape was modified by three Miocene tectonic events, each followed by ∼2–5 Myr of subduction-induced magmatism and sedimentation during a period of relative tectonic quiescence. The first event, at about 16 Ma, corresponds to the westward sweep of the Ancestral Cascades arc front into the Sierra Nevada and adjacent western Nevada. We suggest that this caused thermal uplift and extension. The second event, at about 11–10 Ma, records the birth of the ‘future plate boundary’ by transtensional faulting and voluminous high-K volcanism at the western edge of the Walker Lane belt. The third event, at about 8–7 Ma, is associated with renewed range-front faulting in the central Sierra, and rejuvenation and beheading of the palaeocanyons. Volcanic pulses closely followed all three events, and we tentatively infer that footwall uplift of the Sierra Nevada occurred during all three events. By analogy with the ∼11 Ma event, we speculate that high-K volcanic rocks in the southern part of the range mark the inception of yet a fourth pulse of range-front faulting at 3–3.5 Ma, which resulted in a fourth tilting and crestal uplift event. Cenozoic rocks along the western edge of the Nevadaplano record the following variation, from the central to the northern Sierra: decrease in crustal thickness (and presumably palaeoelevation), decrease in palaeorelief and attendant decrease in coarse-grained fluvial- and mass-wasting deposits, and greater degree of encroachment by Walker Lane-related faults beginning at 10–11 Ma. By mapping and dating Cenozoic strata in detail, we show that what is now the Sierra Nevada was, at least in part, shaped by the Miocene structural and magmatic events.

Evidence for Holocenic uplift at Somma-Vesuvius

Detailed stratigraphical, archaeological, micropalaeontological, archaeometrical and petrochemical analyses of samples from trenches and boreholes at insula of Casti Amanti, in Pompeii, allowed a faithful reconstruction of the recent environmental evolution of the site. The present data clearly indicate the alternation of both subaerial and shallow marine conditions during Holocene times. Taking into account the relative local sea level variations, a ~ 30 m ground uplift event in the last 6 kyr (with an average vertical uplift rate of ~ 5 mm/yr) was inferred for the first time.

Constraints on continued episodic inflation at Long Valley Caldera, based on seismic and geodetic observations

Long Valley Caldera, a large and potentially explosive silicic system, has experienced highly anomalous continued inflation since late 1970s. We characterize an episode of rapid episodic uplift occurring between 2002 and 2003 following similar episodes of 1979–1980, 1983, 1989–1990, and 1997–1998. This most recent episode was the first to be observed by a dense array of 13 continuous Global Positioning System (GPS) stations. Similar to previously observed episodes of deformation, uplift is quasi‐radially symmetric and is mostly explained by a compact pressure source located ∼3 km west of the resurgent dome. The maximum uplift during the 2002–2003 episode is ∼35 ± 8 mm, about 1/3 the magnitude but with a similar time‐dependent behavior as the 1997–1998 episode. The horizontal source location is well constrained at −118.930°, 37.678°, for a small spherical source, and indistinguishable from the location of a vertically dipping prolate spheroidal source. A trade‐off between depth and volume change is observed for both spherical and prolate models, with depth between 7.5 and 13.5 km and a volume change of 0.01–0.03 km3 at 95% confidence. For prolate spheroidal models, depth and volume change are additionally affected by the source axis ratio (b/a), which is greater than 0.55. Though the background seismicity remained low during the 2002–2003 episode, we identified a significant spike in activity during the maximum rate of uplift, similar to observations in both the much larger episodes in 1989–1990, and 1997–1998. More interestingly, we additionally find that all three episodes begin immediately after a short period of seismic quiescence, with background seismicity falling to levels below background levels following the prior uplift event. With the dense GPS coverage, we also identify increased opening of the Mono‐Inyo volcanic chain after the 2002–2003 episode suggesting potential interaction of magmatic fluids between the two systems.

Carbon monoxide distributions from the upper troposphere to the mesosphere inferred from 4.7 μm non-local thermal equilibrium emissions measured by MIPAS on Envisat

Abstract. We present global distributions of carbon monoxide (CO) from the upper troposphere to the mesosphere observed by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat. Vertically resolved volume mixing ratio profiles have been retrieved from 4.7 μm limb emission spectra under consideration of non-local thermodynamic equilibrium. The precision of individual CO profiles is typically 5–30 ppbv (15–40% for altitudes greater than 40 km and lower than 15 km and 30–90% within 15–40 km). Estimated systematic errors are in the order of 8–15%. Below 60 km, the vertical resolution is 4–7 km. The data set which covers 54 days from September 2003 to March 2004 has been derived with an improved retrieval version including (i) the retrieval of log(vmr), (ii) the consideration of illumination-dependent vibrational population gradients along the instrument's line of sight, and (iii) joint-fitted vmr horizontal gradients in latitudinal and longitudinal directions. A detailed analysis of spatially resolved CO distributions during the 2003/2004 Northern Hemisphere major warming event demonstrate the potential of MIPAS CO observations to obtain new information on transport processes during dynamical active episodes, particularly on those acting in the vertical. From the temporal evolution of zonally averaged CO abundances, we derived extraordinary polar winter descent velocities of 1200 m per day inside the recovered polar vortex in January 2004. Middle stratospheric CO abundances show a well established correlation with the chemical source CH4, particularly in the tropics. In the upper troposphere, a moderate CO decrease from September 2003 to March 2004 was observed. Upper tropospheric CO observations provide a detailed picture of long-range transport of polluted air masses and uplift events. MIPAS observations taken on 9–11 September 2003 confirm the trapping of convective outflow of polluted CO-rich air from Southeast Asia into the Asian monsoon anticyclone, which has been described in previous studies. Upper tropospheric CO plumes, observed by MIPAS on this day, were predominantly located in the Northern Hemisphere. Most of these plumes could be related to Southeast Asian pollution by means of backward trajectory calculations. During 20–22 October, southern hemispheric biomass burning was the most likely source of the major CO plumes observed over the Southern Atlantic and Indian Ocean.

Evidence for Tibetan plateau uplift in Qaidam basin before Eocene-Oligocene boundary and its climatic implications

Geometry analysis of the Hongsanhan (红三旱) Section in the northwestern Qaidam basin illustrates the typical growth strata in the Xiaganchaigou (下干柴沟) Formation. The age and sedi-mentation rates of the Xiaganchaigou and the Shangganchaigou (上干柴沟) formations were determined by the high-resolution magnetostratigraphy. This result shows that the growth strata began to form at ca. 38.0 Ma and increased sedimentation rates occurred at ca. 37.0 Ma. The uplift of the Tibetan plateau before the Eocene-Oligocene boundary is confirmed, which enables us to better understand the relationship between climatic changes and the tectonic uplift. This uplift event could have resulted in the regional drying by blocking the moisture and contributed to the Eocene-Oligocene boundary global cooling event due to the declining atmospheric CO2 concentrations by increased weathering of the mountains.

Active tectonics in and around Kimin-Ziro area, Lower Subansiri District, Arunachal Pradesh, NE India

Summary. The paper presents neotectonically-evolved landforms along the foothills of Arunachal Himalaya as well as within the Outer and Lesser Himalayan domains, along the Kimin-Ziro valley section, where tectonic activity is dated to 22-14 ka by OSL technique. High-resolution satellite data suggest the presence of a highly mature, almost flat Brahma­ putra floodplain evolved during the recent geological past, in which palaeochannels had a very high sinuosity. Subsequent events of uplift resulted in the formation of entrenched meanders due to incision of the valley floor. As the process of incision was unable to keep pace with the rate of uplift, after initial attempts to incise the major channels abandoned their sinuous courses and instead followed a straight braided course from near the point of emergence of Himalayan Frontal Thrust (HFT). The data suggest that tectonic activity along the Main Boundary Thrust (MBT) and HFT during the Holocene have played significant role in geomorphic evolution.

Evolution of hydrocarbon generation of Jurassic source rock of the Lenke-1 well in Lenghu tectonic belt of Qaidam basin, China

The Lenghu tectonic belt is located at or near the northern margin in the Qaidam Basin, which is an intracontinental composite basin evolved during the Mesozoic and Cenozoic epochs. The Lower Jurassic is considered a good source rock with a wide distribution. Since the deposit of the Lower Jurassic hydrocarbon source rock, the basin has undergone many tectonic events of subsidence and uplift. The source rocks in the Lengke-1 well, have experienced a complicated tectonic-burial history during which different hydrocarbon generation (HG) evolutions have taken place. We have investigated the history of burying, heating and hydrocarbon generation of the Lower Jurassic source rocks, not just on the basis of tectonic disturbance and deep burial, but also from new studies in fluid inclusion measurements and the application of numerical simulation with EASY% R o. Our study reveals the evolution process, tectonic episodes and the strength of the HG of the Jurassic source rock. We conclude that twice HG processes have taken place since the Lower Jurassic formation and infer from that the important conclusion that more HG of the Lower Jurassic source rock took place during the Eocene-Miocene epochs. Finally, we discuss the oil and gas tarp formation and destruction in the Lenghu tectonic belt and point out that more attention should be paid to the thrust faults, which formed during the late Himalayan epoch.

Formation, uplift and dissection of planation surfaces at passive continental margins – a new approach

AbstractThe usefulness of large‐scale, low‐relief, high‐level landscapes as markers of uplift events has become a subject of disagreement among geomorphologists. We argue that the formation of low‐relief surfaces over areas of large extent and cutting across bedrock of different age and resistance must have been guided by distinct base levels. In the absence of other options the most likely base level is sea level. We have analysed West Greenland landscapes in a recent study by combining the cooling history from apatite fission‐track analysis (AFTA) data with the denudation history from landscape analysis and the stratigraphic record. An important difference between our approach and that of classical geomorphology is that we now have the ability to document when thick sections of rocks have been deposited and then removed. The present‐day high‐level plateau in West Greenland is the remnant of a planation surface that was formed by denudation that lasted c. 20 million years during which up to 1 km of cover was removed after maximum burial at the Eocene–Oligocene transition. Here we present additional AFTA data to show that the planation surface is the end‐product of Cenozoic denudation even in basement areas and argue that Phanerozoic sediments – most likely of Cretaceous–Palaeogene age – must have been present prior to denudation. The planation surface was offset by reactivated faults and uplifted to present‐day altitudes of up to 2 km. The uplift occurred in two late Neogene phases that caused incision of valleys below the planation surface and their subsequent uplift. We therefore find that the elevated and deeply dissected plateau is evidence of episodic post‐rift uplift that took place millions of years after cessation of sea‐floor spreading west of Greenland. We suggest that other margins with similar morphology may also be characterized by episodic post‐rift uplift unrelated to the processes of rifting and continental separation, rather than being permanently uplifted since the time of rifting, as is commonly assumed. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Miocene mass-transport sediments, Troodos Massif, Cyprus

Sediment mass-transport layers of submarine origin on the northern and southern flanks of the Troodos ophiolitic massif are dated biostratigraphically as early Miocene and late Miocene, respectively and therefore represent different seismogenic events in the uplift and erosional history of the Troodos terrane. Analysis of such events has potential for documenting Miocene seismic and uplift events regionally in the context of changing stress field directions and plate vectors through time.

Earthquakes generated from bedding plane-parallel reverse faults above an active wedge thrust, Seattle fault zone

A key question in earthquake hazard analysis is whether individual faults within fault zones represent independent seismic sources. For the Seattle fault zone, an upper plate structure within the Cascadia convergent margin, evaluating seismic hazard requires understanding how north-side-up, bedding-plane reverse faults, which generate late Holocene fault scarps, interact with the north-vergent master-ramp thrust and overlying backthrust of the fault zone. A regional uplift at A.D. 900–930 involved an earthquake that nucleated at depth and included slip on both the master-ramp thrust and the backthrust. This earthquake also included slip on some of the <6-km-deep north-side-up, bedding-plane reverse faults. At locales where the north-side-up reverse faults intersect the Puget Sound coast, an earthquake a few centuries earlier than the A.D. 900–930 regional uplift only uplifted areas within hundreds of meters north of the reverse faults. We infer that the bedding-plane reverse faults are seismogenic because shore platforms near the reverse faults have been abruptly uplifted during earthquakes when other shorelines in the Seattle fault zone were unaffected. Faults of the Seattle fault zone therefore can both produce regional uplift earthquakes, with or without surface displacement on the reverse faults, and produce earthquakes that rupture the bedding-plane reverse faults causing fault scarps and uplift localized to hundreds of meters north of these faults. This latter type of earthquake has occurred at least twice and perhaps three times in the late Holocene, and all these earthquakes preceded the regional coseismic uplift of A.D. 900–930. To account for the paleoseismic observations, we propose that the Seattle fault zone is a wedge thrust, with the leading edge being a fault-bend, wedge thrust fold. The active axial surface of the wedge thrust fold is pinned at the tip of the wedge, and a steeply north-dipping sequence of Tertiary sediment forms the south limb of the wedge thrust fold. Some of these steeply north-dipping, bedding-plane surfaces are seismogenic reverse faults that produce scarps. Earthquakes on the wedge thrust produce the regional coseismic uplift events, and earthquakes within the faultbend fold cause the local uplift earthquakes. Thus, bedding-plane faults can rupture during earthquakes when the wedge thrust does not rupture but instead continues to accumulate seismic energy.

Cenozoic sedimentary records and geochronological constraints of differential uplift of the Qinghai-Tibet Plateau

Geological mapping data (1:250000) in the Qinghai-Tibet Plateau and its adjacent regions reveal the sediment sequences, distribution and tectonic evolution of the 92 Tertiary remnant basins. Southern Tibet and the Yecheng area in Xinjiang, located at southern and northwestern margins of the Qinghai-Tibet Plateau, respectively, were parts of the Neo-Tethys remnant sea in the Paleogene. In southern Tibet, both the subabyssal and abyssal sequences occur at the Gyangze, Saga, Guoyala, and Sangmai areas. The deep-water facies successions outcrop in the west, whereas the shallow-water facies sequences in the east, indicating the east to the west retreat of the Neo-Tethys Ocean. The retreat of the Neo-Tethys Ocean in the east was contributed to the earlier tectonic uplift of the eastern Qinghai-Tibet Plateau. The uplift process of the Plateau from the Late Cretaceous to Pliocene is described as follows: During the Late Cretaceous, tectonic uplift of the Qinghai-Tibet Plateau occurred in the northeastern part and the configuration of the Qinghai-Tibet Plateau was characterized by rise in the northeast and depression in the west. In the Paleocene-Eocene interval, the Tengchong-Baingoin and Kuyake-Golmud areas experienced local tectonic uplifting, the West Kunlun uplift zone broadened easterly, the Qilian uplift zone broadened southerly, and the Songpan-Garze uplift zone shrank easterly. The Oligocene configuration of the Qinghai-Tibet Plateau was characterized by mountain chains rising along its margins and sedimentary basins in the central part because of tectonic uplifts of the Gangdise and the Himalaya blocks. Meanwhile, the Kunlun-Altyn-Qilian uplift zones have also broadened southerly and northerly. In contrast, the great uplift zones of the Gangdise, the Himalaya, the Karakorum, and the Kunlun blocks characterize the paleogeographic contours of the Qinghai-Tibet Plateau during the Miocene-Pliocene. Additionally, the thermochronological data on tectonic uplift events in southern Tibet, West Kunlun Mountains, Altyn Tagh, eastern Tibet, and western Sichuan all suggest that the most intense deformation occurred at 13-8 Ma and since 5 Ma, respectively, corresponding to two great uplift periods in Neogene. As a result, turnover of paleogeographic configuration of the Qinghai-Tibet Plateau occurred during the Neogene, experiencing a change from high contours in the east in the pre-Oligocene to high contours in the west at the end-Pliocene. The uplift of the Qinghai-Tibet Plateau during the Cenozoic was episodic, and the uplifts of various blocks within the Plateau were spatially and chronologically different.