magnetism and transmission electron microscopy of fe ti oxides and pyroxenes in a granulite from lofoten norway granulites from southwest lofoten norway often carry intense and stable components of natural remanent magnetization nrm coercivities in excess of 100 mt and blocking temperatures up to 580 645 c are common several phases in these rocks can carry stable components of nrm clinopyroxenes augite with exsolved pigeonite and orthopyroxene usually contain abundant fe ti oxides the majority of which are too small to be studied conclusively with visible light additionally these rocks typically contain coarse grained 100 1000 m exsolution intergrowths of rhombohedral fe ti oxides and coarse grained magnetite we have studied the magnetism and mineralogy of the titanohematite and the inclusion bearing augites in one granulite sample using transmission electron microscopy tem and magnetic experiments to understand better the remanence properties of naturally occurring fe ti oxides and their relationships to silicate minerals the coarse grained titanohematite has a coercivity of 350 mt and a laboratory saturation remanence that unblocks at 570 600 c the hysteresis characteristics of this titanohematite are typical of much smaller 10 m sized single domains which apparently reflects the presence of exsolved ilmenite lamellae as small as 10 nm in thickness these lamellae presumably inhibit 1 domain wall nucleation and 2 movement of walls that manage to nucleate the inclusions in the augites serve as carriers of lower coercivity remanence with blocking temperatures less than about 560 c magnetite hematite and ilmenite are present in the augite and intergrowth of the rhombohedral phases revealed by tem persists down to the 20 nm scale the distribution of the magnetite inclusions in the augite appears to be unrelated to any silicate microstructure while that of the rhombohedral fe ti oxides is strongly controlled by silicate microstructure with intergrowths of these oxides commonly decorating lamellae of pigeonite orthopyroxene and clinoamphibole within the augite the nrm of this sample possibly dates from the amphibolite facies metamorphism that the region experienced about 1000 m y ago paleomagnetic studies of these rocks could readily recover virtual geomagnetic poles dating from this event in addition to the included oxides the augites display a number of unusual features that probably result from the protracted polymetamorphic history of these granulites pigeonite lamellae are not parallel to the b crystallographic axis pigeonite lamellae cut across those of orthopyroxene and numerous included minerals occur rare earth elements are concentrated within inclusions that reside in the augite

inversion of fluvial channels for paleorock uplift rates in taiwan the transient response of erosion to changes in rock uplift rate leads to the preservation of rock uplift history in the long profiles of rivers however extracting this information is nontrivial as changes in channel steepness are the result of both spatial and temporal changes in rock uplift rate as well as other factors such as climate and rock type we exploit an analytical linear solution for river channel profile evolution in response to erosion and tectonic uplift to investigate the rock uplift history of taiwan the analytical approach allows us to solve the linear inverse problem efficiently extracting rock uplift as a function of space and time from digital elevation data we assess the potential of fluvial topography to resolve rock uplift rates using three approaches 1 a synthetic resolution test 2 analysis of the forward model to demonstrate where in space and time the fluvial topography constrains rock uplift rate and 3 interpretation of the model resolution matrix furthermore the potential to analyze large data sets reduces the influence of stochastic processes such as landslides small scale river network reorganization and also local lithological variability in taiwan our analysis suggests that current rock uplift rates exceed erosion rates across much of the island and that there has been an increase in rock uplift rates since 0 5 ma across the central range

2003 mw6 8 chengkung earthquake and its related seismogenic structures abstract the mw 6 8 chengkung earthquake on december 10 2003 in eastern taiwan was associated with abundant aftershocks to explore the seismogenic mechanism and its causative fault system we relocated the aftershocks determined the focal mechanisms from p wave polarities and used the finite dimension source model method to identify the fault plane based on our results the earthquake can be divided into three seismic clusters one is located in the east of the southern longitudinal valley one on the chihshang fault and the other on the western side of the luyeh fault to the south both the seismic distribution and finite dimension source model method show that east dipping fault planes with thrust mechanisms coincide with previous studies based on background seismicity the third seismic cluster suggests thrust mechanism along west dipping fault plane that was not recognized by background seismicity this seismic cluster occurred along the central range fault previously proposed as active by geomorphic and geologic evidence

beyond threshold hillslopes channel adjustment to base level fall in tectonically active mountain ranges numerous empirical and model based studies argue that in general hillslopes and river channels increase their gradients to accommodate high rates of base level fall to date however few data sets show the dynamic range of both these relationships needed to test theoretical models of hillslope evolution and river incision here we utilize concentrations of 10 be in quartz extracted from river sand on the eastern margin of the tibetan plateau to explore relationships among short term 10 2 10 5 a erosion rate hillslope gradient and channel steepness our data illustrate nonlinear behavior and a threshold in the relationship between erosion rate and mean hillslope gradient confi rming the generalization that hillslopes around the world are limited by slope stability and cease to provide a metric for erosion at high rates 0 2 mm a the relationship between channel steepness index and erosion rate is also nonlinear but channels continue to steepen beyond the point where threshold hillslopes emerge up to at least 0 6 mm a demonstrating that channel steepness is a more reliable topographic metric than mean hillslope gradient for erosion rate and that channels ultimately drive landscape adjustment to increasing rates of base level fall in tectonically active settings

seismogenic structure in a tectonic suture zone with new constraints from 2006 mw6 1 taitung earthquake 1 a mw 6 1 earthquake occurred on april 1st 2006 near taitung eastern taiwan it produced significant coseismic ground displacements and a large number of aftershocks in the ensuing month this event provides an opportunity to diagnose the seismogenic structure in the southern longitudinal valley lv of eastern taiwan long viewed as one of the collision sutures between the philippine sea and the eurasian plates with precisely relocated main and aftershock hypocenters focal mechanisms for m 3 8 events and coseismic ground displacements from strong motion records we determine a main shock dislocation model our results indicate that the main shock occurred on a high angle fault azimuth 198 dip 77 the model comprises a fault with two segments the main shock and a large number of aftershocks are associated with the northern segment that exhibited predominantly left lateral strike slip motion in agreement with p wave first motions and waveform usgs solutions the southern segment exhibits a slightly larger thrust component in agreement with cmt solutions tectonically this event highlights a nne trending fault on the west side of the lv which is predominantly strike slip the aftershocks clustered to the east of the main shock which exhibit mainly thrust mechanisms indicate that shortening is still acting on the sedimentary materials deposited between the coastal and central ranges prior to collision as a result the southern lv is undergoing slip partitioning along different faults which has never been specified before

how fast is the denudation of the taiwan mountain belt perspectives from in situ cosmogenic 10be quantifying denudation rates in a wide range of climatic and tectonic settings at various time and space scales is a critical step in calibrating and validating landscape evolution models focusing on taiwan we quantified centennial rates of denudation at the scale of the whole orogen using in situ 10be concentrations measured in stream sediments collected at the outlets of major rivers to assess denudation rates that are statistically significant we applied both the mean square weighted deviation approach and the bootstrap technique for the central segment of the belt where the collision is considered to be near mature the orogen scale pattern of denudation shows a two fold pattern 1 higher denudation values on the order of 4 5 mm yr characterize the eastern side of the belt i e retro wedge with a slight increase towards the south and 2 lower denudation values on the order of 1 3 mm yr on the western side of the belt pro wedge with a minimum value centered on the main recess of the deformation front to the north and to the south of the central segment the denudation rates converge towards lower values on the order of 2 3 mm yr at the scale of the mountain belt drainage basin metrics such as relief hypsometric index and slope values seem to explain the observed variance in the data population conversely to the first order average precipitation pattern suggesting a strong tectonic control on the regional pattern of denudation rates applied to the whole orogen such field based approach thus provides important input data to validate and calibrate the parameters to be supplied to landscape evolution models

holocene tectonic uplift on the hua tung coast eastern taiwan abstract we used radiometric dates from 19 sites to determine the holocene uplift rates of the 140 km long hua tung coast in eastern taiwan these rates ensure that the formation of major marine terraces on the coast several tens of meters in height is related to the deglacial relative sea level cycle with which the uplift rates were further constrained by the elevations of the marine terrace elements uplift rates are less than 4 mm yr in the northernmost 30 km long coast and are 4 7 mm yr in the adjacent 30 km long coast the rest of the coast is generally uplifted 7 9 mm yr with local troughs 700 m and high 40 m mudstone platforms are observed to slope below the sea level these changes in uplift rate or style are all accommodated on the surface by warping most of them are irrelevant to the known bedrock structures suggesting a change in uplift style and perhaps also mechanics of the coast during the holocene

transient fluvial incision in the headwaters of the yellow river northeastern tibet china 1 we utilize topographic analysis of channel profiles combined with field measurements of erosion rates to explore the distribution of channel incision in the anyemaqen shan a broad mountainous region in the northeastern tibetan plateau tributary channels to the yellow river display systematic downstream increases in channel gradient associated with convex upward longitudinal profiles steep lower reaches of channels are associated with rapid 1 m ka incision rates along the yellow river while upstream reaches are associated with relatively slow 0 05 0 1 m ka erosion of soil mantled uplands covariance between erosion rates and channel steepness indices suggest that channels are adjusted to match long wavelength differential rock uplift across the range geologic constraints indicate that rapid incision downstream of the range is associated with excavation of basin fill driven by changes in relative base level farther downstream the upstream limit of this wave of transient incision is marked by a series of knickpoints that are found at nearly the same elevation throughout the watershed consistent with knickpoint migration as a kinematic rather than diffusional wave tributary channel gradients downstream of knickpoints however display a progressive adjustment to increased incision rates that may reflect the influence of increased sediment flux comparison of observed channel profiles to a stream power model of fluvial behavior reveals that the rate of knickpoint propagation can only be explained if the erosional efficiency coefficient k increases during incision our results thus highlight the utility of channel profile analysis to reconstruct the fluvial response to both active tectonism and external changes in base level

from submarine continental accretion to arc continent orogenic evolution the thermal record in southern taiwan constraining the timing of initial collision is critical for understanding how long term plate convergence is accommodated at collisional plate boundaries reevaluation of the age of collision from orogenic thermal evolution requires distinguishing the onset of submarine continental accretion from earlier oceanic subduction and subsequent subaerial orogenic evolution we present new thermochronological constraints from the first age elevation relationship transect in taiwan and zircon and apatite fission track ages from sediments in the western foreland our data reveal the onset of cooling from at least 7 1 1 3 ma at a minimum rate of 21 c m y in the submarine sedimentary wedge followed by a marked acceleration of subaerial exhumation after ca 3 2 0 6 ma at an average rate of 1 7 km m y our data reflect the effect of margin architecture as taiwan evolved from submarine accretion of the distal extremely thinned continental margin to crustal thickening of the proximal margin and orogenic development

temporal evolution of a long lived syenitic centre the kangerlussuaq alkaline complex east greenland abstract we present new mineral and whole rock compositions and sr nd hf pb o h isotope data on samples from the kangerlussuaq alkaline complex 1000 km2 in central east greenland part of the north atlantic igneous province this complex mainly consists of the kangerlussuaq intrusion but includes at least 13 separate satellite intrusions emplaced in the uppermost crust close to the unconformity between archaean gneisses and overlying palaeogene flood basalts the complex is divided into i older satellite intrusions 55 53 ma composed of multiple syenites and granites and minor gabbros and peridotites ii the voluminous kangerlussuaq intrusion 50 ma which displays a gradual transition from quartz syenites nordmarkites at the margin to nepheline syenites foyaites in the centre and iii younger satellite intrusions 47 45 ma of minor syenites granites and diorites concentrated southeast of the kangerlussuaq intrusion the complex displays a temporal evolution in which sio2 decreases 74 56 wt and total alkalis 6 16 wt amphibole na k content 206pb 204pbmeas endi and ehfi 3 to 11 increase from the older intrusions through the nepheline syenites this is followed by a reversal to higher silica 62 73 wt and lower total alkalis 9 12 wt amphibole na k content 206pb 204pbmeas endi and ehfi 13 to 2 in the younger satellite intrusions temporal changes in the location of magma plumbing systems and in magma production rates played a profound role in controlling silica content alkalinity and degree of crustal contamination during development of the complex phonolitic magma was only generated after prolonged magmatism had shielded the conduits from interaction with country rock the parental magmas were probably basanitic to alkali olivine basaltic in composition the older satellite intrusions and the kangerlussuaq intrusion have low 18o magma values 1 to 6 compared to the younger more crustally contaminated satellite intrusions 4 5 to 7 it appears that the magmas only had sufficient over pressure to intrude the basalt cover when larger volumes of less contaminated trachyte magma were produced resulting in the generation of low 18o magmas due to dehydration of hydrothermally altered basalt xenoliths

comment on resentini et al 2020 ongoing exhumation of the taiwan orogenic wedge revealed by detrital apatite thermochronology the impact of effective mineral fertility and zero track grains abstract the interpretation of modern river apatite fission track aft data of taiwan by resentini et al 2020 presents some fundamental inaccuracies that call in question the main conclusions of the paper the study aims at approximating source rock cooling histories by analysing erosional products but ignores existing bedrock data in their maps and discussions the allegedly new southern extension of the aft reset zone is largely unconstrained by the presented data and ignores the local geology and stratigraphy of individual drainage basins notably low grain counts median 9 and catchment with various geological provinces including orogenic derived sediments question the significance of the dataset to characterise single geological domains as explained in the paper overall the new data do not provide discriminating evidence for an earlier collision in the north of the island and thus do not support a southwardly propagation of collision

geomorphology of the southernmost longitudinal valley fault implications for evolution of the active suture of eastern taiwan in order to understand fully the deformational patterns of the longitudinal valley fault system a major structure along the eastern suture of taiwan we mapped geomorphic features near the southern end of the longitudinal valley where many well developed fluvial landforms record deformation along multiple strands of the fault our analysis shows that the longitudinal valley fault there comprises two major strands the luyeh strand on the west has predominantly reverse motion the peinan strand on the east has a significant left lateral component between the two strands late quaternary fluvial sediments and surfaces exhibit progressive deformation the luyeh strand dies out to the north where it steps to the east and joins the peinan strand to become the main strand of the reverse sinistral longitudinal valley fault to the south the luyeh strand becomes an e w striking monocline this suggests that the reverse motion on the longitudinal valley system decreases drastically at that point the longitudinal valley fault system is therefore likely to terminate abruptly there and does not seem to connect to any existing structure further to the south this abrupt structural change suggests that the development of the longitudinal valley suture occurs through discrete structural jumps rather than by a continuous northward maturation

incision and channel morphology across active structures along the peikang river central taiwan implications for the importance of channel width river morphology and dynamics are strongly influenced by active tectonics we report channel dynamics for the peikang river which flows through the hsuehshan range in central taiwan using a digital elevation model and field surveys we constrain channel morphology for an 90 km stretch of river to calculate unit stream power and boundary shear stress along the river path incision rates are estimated with optically stimulated luminescence dating of sand deposited on strath terraces we find a strong correlation between unit stream power shear stress and incision rate but only if variation in channel width is considered a calibrated river incision rule implies river incision rates of 9 13 5 mm yr upstream of the meiyuan and tili faults and suggests that one or both of these structures are presently active our results indicate that the shuilikeng fault is also actively deforming as incision rates increase to 6 10 mm yr across it compared to 1 4 mm yr in adjacent reaches prominent narrowing across the shuilikeng fault and the absence of significant gradient variation indicate that channel width is a first order morphological adjustment to differential incision only when the channel width to depth ratio reaches a minimum does the channel slope significantly adjust to local changes in base level as is the case upstream of the meiyuan and tili faults

the climatic signature of incised river meanders climate controls landscape evolution but quantitative signatures of climatic drivers have yet to be found in topography on a broad scale here we describe how a topographic signature of typhoon rainfall is recorded in the meandering of incising mountain rivers in the western north pacific spatially averaged river sinuosity generated from digital elevation data peaks in the typhoon dominated subtropics where extreme rainfall and flood events are common and decreases toward the equatorial tropics and mid latitudes where such extremes are rare once climatic trends are removed the primary control on sinuosity is rock weakness our results indicate that the weakness of bedrock channel walls and their weakening by heavy rainfall together modulate rates of meander propagation and sinuosity development in incising rivers

uht metamorphism peaking above 1100 c with slow cooling insights from pelitic granulites in the jining complex north china craton

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

ongoing exhumation of the taiwan orogenic wedge revealed by detrital apatite thermochronology the impact of effective mineral fertility and zero track grains abstract in clastic detritus derived from the erosion of young active orogens the geologic interpretation of apatite fission track aft data is hampered by the occurrence of grains without spontaneous tracks and by contributions from multiple eroding sources with different apatite fertilities here we use the taiwan orogen as a test case to illustrate how to overcome these problems and deal with zero track grains in detrital aft studies following long established principles of fission track statistics our results support the effectiveness of raman spectroscopy for a reliable identification of apatite grains we found that zero track grains are dominant in taiwan modern sands and generally contain enough u to provide useful aft age constraints to exhumation the absence of spontaneous tracks in most of these grains is due to a short residence time below the temperature of total aft annealing rather than to low u concentration detrital aft data shows that the extent of the taiwan aft reset zone previously inferred from bedrock data was partly underestimated the revised aft reset zone includes the southernmost part of the island and when combined with published zft data supports a scenario of southward progressing exhumation during arc continent collision the application of the taiwan lesson to clastic detritus derived from the himalaya resolves paradoxical interpretations of detrital fission track data sets recently published in the framework of iodp expedition 354 pointing to a major role of the namche barwa syntaxis as a source of apatite grains shed to the bengal fan

impacts of arc collision on small orogens new insights from the coastal range detrital record taiwan taiwan is considered the archetypical orogen in the development of critical wedge models of mountain building however the issue of how arc collision progressed along the margin remains poorly understood to resolve this the detrital archive of orogenesis preserved in coastal range rocks of eastern taiwan was used to reconstruct the erosional response of arc collision the spatial and temporal distribution of exhumation recorded in this detrital record is consistent with southwards progression of arc continent collision in a punctuated rather than sequential manner with deposition confined to segmented foredeep basins apparent increases in sedimentation rates in taiwan during the pleistocene may not reflect increased erosion but instead may be due to the collisional margin architecture supplementary materials analytical details and dating results are available at www geolsoc org uk sup18693

formation of positive end t granitoids from the alataw mountains xinjiang china by mixing and fractional crystallization implication for phanerozoic crustal growth abstract syn collisional granitic plutons intruded into devonian and carboniferous sedimentary and volcanic rocks along the southern slope of the alataw mountains in the north tianshan fold belt these intrusions are 307 290 ma in age granitoids in the eastern part of the mountain show characteristics similar to i type affinity while those in the western part show s type affinity carboniferous volcanic rocks andesite to rhyolite cover the eastern part of the region they share many common geochemical characteristics with the eastern granitoids intermediate and acid igneous rocks show positive e nd t values ranging from 7 to about 0 and initial sr isotopic ratios of 0 702 0 711 carboniferous basalts exposed in the region give 87 sr 86 sr t 0 701 0 704 and e nd t 7 12 country rock and basement gneisses show 87 sr 86 sr t 0 707 0 715 and e nd t 5 to 8 the positive e nd t suggests that mantle derived material play an important role in petrogenesis of the alataw granitoids a common mantle derived component is much likely to be involved in the petrogenesis of the granites from northern xinjiang since the positive e nd t granites with early paleozoic ages are widespread in the entire central asia mongolia granitic belt our data provide a constraint on the sr and nd isotopic ratios of this mantle derived mafic component which may be similar to those of the carboniferous basalts but can also have lower e nd t of 3 7 positive e nd t values suggest large mantle input representing a contribution of mantle derived materials to the continental crust it is very likely that this event of continental growth took place in very late proterozoic or early paleozoic

implications of the shear stress river incision model for the timescale of postorogenic decay of topography 1 the reason for the survival of mountainous topography in ancient orogenic belts is a long standing problem in geomorphology and geodynamics we explore the geomorphologic controls on the timescale for the postorogenic decay of topography to address the question of whether there is a viable geomorphologic explanation for the persistence of topography in ancient orogenic belts or whether alternative geodynamic explanations must be sought using both approximate analytical solutions and numerical simulations we show that the standard detachment limited stream power river incision model predicts for reasonable initial topographies relatively short postorogenic decay times of 1 10 myr additional layers of complexity are introduced to this simplest model including isostasy and flexural strength a transition to transport limited conditions during decline and the incorporation of the combined effects of a critical threshold for erosion and the stochastic variability of flood magnitudes each of these additional factors acts to lengthen the decay timescale pure airy isostatic rebound of a thick crustal root results in decay times that are at most a factor of 6 longer than the detachment limited result the transition to transport limited conditions involves partial protection of the bed by a thin layer of alluvium which inhibits erosion and therefore increases decay times by a factor of 2 3 in our analysis finally including critical shear stress results increases decay time by approximately a factor of 20 for the parameter values in our example calculation more importantly however a significant portion of topography remains after predicted lowering rates have dropped to values less than measured rates of denudation in weathering limited low relief environments thus a model combining isostasy a transition to transport limited conditions and a critical shear stress for erosion could account for the presence of residual topography for hundreds of million years all three of these factors can be expected to play a role in natural settings

rapid exhumation since at least 13 ma in the himalaya recorded by detrital apatite fission track dating of bengal fan iodp expedition 354 and modern himalayan river sediments abstract apatite fission track analysis of middle bengal fan sediments iodp expedition 354 and modern himalayan river sediments shows that most of the detrital apatites are very young compared to their depositional ages independent of their uranium content bengal fan apatites display an average central age lag time as short as 2 26 1 6 myr since at least 13 ma such lag times reflect a mean exhumation rate on the order of at least 1 3 km myr the occurrence of detrital apatites with relatively short aft lag times since at least 13 ma indicates that there have always been areas of rapid erosional exhumation supplying detrital apatites to the fluvial system and delivering them to the paleo ganges and or brahmaputra plains and finally to the bengal fan it also supports that temporary storage of detrital apatites in the floodplains or delta has always been negligible since at least 13 ma comparison of the aft data of the bengal fan with those of the central and eastern proximal neogene himalayan foreland basin shows that both paleo ganga and brahmaputra catchments provided apatites with similar short lag time to the distal bengal fan basin in the modern drainage system of the bengal fan the apatites with young fission track cooling ages are principally derived from areas where the topography has a sharp relief controlled by threshold hillslope processes and stream power resulting in landslide erosion as a coupled response to tectonic and fluvial forcing by analogy with the modern erosion processes in the himalayan range we suggest that over the past 13 ma apatites were mainly derived from areas of sharp relief where river stream power was high and hill slopes close to the threshold angle as the exhumation signal is rather consistent since the late miocene the detrital apatite fission track data are either not sensitive enough to detect rapid climatically controlled changes in exhumation rates or overall long term erosion rates on the orogen scale are not strongly affected by climatic variations such as the variability of the indian summer monsoon given the already rapid exhumation rates controlled by tectonics the impact of climate variability on surface erosion rates cannot be detected with our data especially in the case of erosion processes dominated by threshold hillslope model

knickpoint initiation and distribution within fluvial networks 236 waterfalls in the waipaoa river north island new zealand if knickpoints transmit signals of base level fall in river networks then improvements in our understanding of their retreat rate and basin wide distribution helps constrain the transient response following perturbation many studies of knickpoint retreat focus on the response of trunk streams to base level fall here we examine the response of an entire fluvial network as recorded by 236 active knickpoints distributed within the waipaoa river on the north island of new zealand base level fall within the waipaoa catchment initiated 18 000 years ago in response to a climatically triggered and tectonically exacerbated pulse of incision using observations from field work aerial photo analysis and a digital elevation model dem we study the knickpoint positions within the network we find that 70 of the knickpoints are located at drainage areas between 1 10 5 m 2 and 1 10 6 m 2 and more than half are b1 km upstream of a large change in drainage area for the knickpoints b1 km upstream of large tributary junctions we find that the retreat distances were well correlated with the tributaries drainage areas in order to determine how a pulse of incision distributes itself throughout a fluvial network we develop two simple end member models and compare their behavior to the observed knickpoint distribution in the waipaoa in the first model we propose that a knickpoint initiated at the basin outlet retreats upstream and distributes the signal throughout the network at a rate that is a power law function of drainage area in the second model we propose that knickpoints form near a threshold drainage area below which channels cannot incise with the same efficiency as possible in downstream reaches though neither model addresses the along stream variability in substrate or knickpoint form the misfit between the modeled and the observed knickpoints along stream positions are surprisingly low b1 km 1 25 of the total stream length for knickpoints with drainage areas b1 10 6 m 2 large misfits up to 3 5 km are observed for knickpoints with present day drainage areas greater than 1 10 6 m 2 the large single step in channel elevation that characterizes knickpoints presently observed in tributaries of the waipaoa river may not characterize the base level fall signal that propagated through the trunk streams evidence for progressive rather than instantaneous incision in the trunk streams the knickpoints vicinities to tributary junctions and the equivalent success of the two end member models lead us to conclude that the present positions of the 236 observed knickpoints are largely a consequence of thresholds in channel incision at low drainage areas

erosion rates driven by channel network incision in the bolivian andes the bolivian andes flank one of earth s major topographic features and dominate sediment input into the amazon basin millennial scale erosion rates and dominant controls on erosion patterns in this range are poorly known to define these patterns we present 48 erosion rate estimates derived from analysis of in situ 10 be in quartz bearing alluvium collected from the upper beni river basin erosion rates corrected for the non uniform distribution of quartz in the sample basins range from 0 04 mm a 1 to 1 35 mm a 1 and thus integrate over 10 2 10 4 years mean and modal values are 0 42 standard deviation 0 29 and 0 2 0 4 mm a 1 respectively within the range of long term average erosion rates in this area derived from apatite fission track thermochronology 0 1 0 6 mm a 1 hence our data do not record any significant variation in erosion rate over the last several million years mean and modal short term erosion rates for the andes are an order of magnitude lower than rates in the ganges river headwaters in the high himalaya and an order of magnitude greater than rates typical of the european alps in the upper beni river region of the bolivian andes short term basin averaged erosion rates correlate with normalized channel steepness index a metric of relative channel gradient corrected for drainage area neither normalized channel steepness index nor basin averaged erosion rate shows strong correlation with mean basin hillslope gradient or mean basin local relief because many hillslopes in the upper beni river region are at threshold values of slope and local relief patterns of normalized channel steepness index appear primarily to reflect tectonic patterns and transient adjustment to those patterns by channel networks climate and lithology do not appear to exert first order controls on patterns of basin averaged erosion rates in the bolivian andes copyright 2005 john wiley sons ltd

crust mantle boundaries in the taiwan luzon arc continent collision system determined from local earthquake tomography and 1d models implications for the mode of subduction polarity reversal abstract in order to better understand the mode of subduction polarity reversal in the taiwan luzon arc continent collision zone we mapped its crust mantle boundaries using local earthquake tomography by contouring surfaces of constant vp 7 5 km s 1 we identified three moho discontinuities and the plate interface that juxtaposes eurasian lower crust against mantle lithosphere of the philippine sea plate the plate interface dips to the east under southeastern taiwan and steepens progressively towards north until it becomes vertical at 23 7 n from there it continues northward in a vertical orientation until the limit of the tomographic model inhibited further mapping for the moho additional depth constraints were derived from 1d models using p wave arrivals of local earthquakes the mohos of the eurasian and philippine sea plates are disconnected across the plate interface beneath southern taiwan the eurasian moho dips to the east at 50 60 following the orientation of the plate boundary and continuous with the benioff zone towards north the eurasian moho steepens into subvertical again together with the plate boundary the philippine sea plate moho exhibits a synform like crustal root interpreted as the base of the magmatic luzon arc towards the north this root deepens from 30 to 70 km underneath the ryukyu trench in northernmost taiwan the hinge of the vertically subducting eurasian slab steps westward out of the thrust belt leaving the deformation front to the east inactive and giving way to the north dipping philippine sea plate a subhorizontal moho at 30 35 km depth overlies the north dipping philippine sea slab and is interpreted as a newly formed moho established after westward rollback and delamination of the subducting eurasian slab in combination these data support a model of progressive subduction polarity reversal in which a tear within the eurasian lithosphere propagated southwestward deactivating the deformation front

active back thrust in the eastern taiwan suture revealed by the 2013 rueisuei earthquake evidence for a doubly vergent orogenic wedge rapid exhumation of 3 10 mm yr of the taiwan metamorphic range is often explained as the unroofing of the retrowedge of a doubly vergent mountain belt yet to date the central range fault forming the boundary of the retrowedge has displayed no definitive evidence for recent seismic activity and no unambiguous geomorphic expression over much of the fault the 2013 m6 4 rueisuei reverse faulting earthquake nucleated at the eastern boundary of the retrowedge and appears to illuminate the west dipping central range fault we estimate the fault geometry and coseismic slip distribution using a uniform stress drop slip inversion and surface displacements derived from gps and strong motion data we identify a 42 dipping blind reverse fault consistent with the previously proposed buried central range fault beneath the highly active longitudinal valley fault this earthquake may be the first indication that rapid exhumation and uplift occur along a distinct fault structure bounding the eastern margin of the taiwan retrowedge

characterizing nutrient pathways in quebec canada vineyards insight from stable and radiogenic strontium isotopes abstract soils are a crucial interface of earth s critical zone responsible for the biogeochemical cycling of mineral nutrients while the sources of essential nutrients such as ca and sr in plants have been widely studied the processes by which these nutrients are transferred from the soil to the plants is less clear we present new evidence for systematic nutrient fractionation between soils grapes and wines from five vineyards from the quebec terroir canada using the novel stable sr 88 86sr isotope system we coupled this approach with traditional radiogenic 87sr 86sr measurements on the same samples bulk soils labile fraction of these soils whole grapes and wines from five vineyards from the quebec terroir canada to ensure that variations in 88 86sr values were provoked by processes involved in sr transfer instead of mixing between different sources the 88 86sr values generally decrease from the bulk to the labile fractions of the soils to the grapes a decrease in the difference between the soil fractions 88 86srbulk labile with increasing 88 86sr values in the labile fraction is interpreted to reflect increasing pedogenic mineral precipitation and higher soil fertility the depleted 88 86sr values of the grapes are consistent with a preferential uptake of lighter isotopes by plants this effect is magnified in soils showing higher secondary mineral precipitation an increase in the 88 86sr values from the grapes to the wines reflects the separation of the skin seeds and the juice pulp enriched in 88sr in the winemaking process this mixing relationship is supported by a correlation between the sr concentrations and the 88 86sr values of the wines and grapes these findings suggest promising new applications of stable sr isotopes values for studying soil fertility and the impact of nutrient availability for plant growth in agricultural ecosystems as well as the impact of the maceration processes in the production of wine the overall similarity of 87sr 86sr ratios of the labile soil fractions grapes and wines from the same vineyard support the hypothesis of a same sr source from the soil solution to its transfer to the grape and wine and confirm the potential of the 87sr 86sr ratios as a proxy for geographic provenance of wine however slightly lower 87sr 86sr ratios in the grape pulps by 0 00040 on average compared to the skins and seeds suggest that the sources of nutrients available for plant uptake vary during the vegetative cycle the grape seeds and skins formed in the early growth cycle are characterized by rapid growth due to enhanced rhizosphere activity enhanced mineral dissolution providing higher nutrient levels the enhanced mineral solubility results in higher 87sr 86sr ratios in the skin and seeds derived from enhanced dissolution of 87sr enriched silicate minerals in contrast the pulp develops later in the growth cycle when rhizosphere activity and mineral solubility is reduced resulting in a lesser contribution from silicate minerals and thus reflect a higher proportion of dissolved carbonate contributing to the lower 87sr 86sr ratios of the pulps

epigenetic gorges in fluvial landscapes epigenetic gorges form when channels that have been laterally displaced during episodes of river blockage or aggradation incise down into bedrock spurs or side walls of the former valley rather than excavating unconsolidated fills and reinhabiting the buried paleovalley valley filling events that promote epigenetic gorges can be localized such as a landslide dam or an alluvial debris flow fan deposit at a tributary junction or widespread such as fluvial aggradation in response to climate change or fluctuating base level the formation of epigenetic gorges depends upon the competition between the resistance to transport strength and roughness of valley filling sediments and a river s ability to sculpt and incise bedrock the former affects the location and lateral mobility of a channel incising into valley filling deposits the latter determines rates of bedrock incision should the path of the incising channel intersect with bedrock that is not the paleovalley bottom epigenetic gorge incision by definition post dates the incision that originally cut the valley strath terraces and sculpted bedrock walls that form in relation to epigenetic gorges should not be used to directly infer river incision induced by tectonic activity or climate variability rather they are indicative of the variability of short term bedrock river incision and autogenic dynamics of actively incising fluvial landscapes the rate of bedrock incision associated with an epigenetic gorge can be very high 1 cm yr typically orders of magnitude higher than both short and long term landscape denudation rates in the context of bedrock river incision and landscape evolution epigenetic gorges force rivers to incise more bedrock slowing long term incision and delaying the adjustment of rivers to regional tectonic and climatic forcing copyright 2008 john wiley sons ltd

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

characterization of topographic steady state in taiwan abstract the arc continent collision in taiwan has resulted in surface uplift high relief and high rates of erosion because the collision is older in the north and has propagated southward taiwan offers the opportunity to study the evolution of topography as it evolves towards a large scale steady state in this paper we analyze a 40 m digital elevation model of taiwan to determine how topographic steady state is expressed in the landscape particular attention is paid to the eastern central range where major drainage basins are approximately aligned in the direction of the collision propagation analyses of orogen size regional topographic slope drainage basin hypsometry and local topographic slope reveal a geomorphological transition 100 125 km north of the southern tip of the island to the south of this transition topographic characteristics change with distance along the island to the north these characteristics are relatively constant which we interpret as representing large scale topographic steady state assuming that the collision has propagated southward at a rate of 55 mm yr the time to topographic steady state is 1 8 2 3 myr after emergence above sea level within the steady state region we evaluate regional variability in the topography and find that the most prominent deviations from a steady form are associated with large scale structures though our analyses of local topographic slope and river profile form suggest that spatial variations in rock strength and rock uplift rate also contribute to regional topographic variability

pleistocene onset of rapid punctuated exhumation in the eastern central range of the taiwan orogenic belt the taiwan orogenic belt is often treated as a steady southward propagating orogenic system with an essentially constant erosion rate of 4 6 mm yr over the past 5 m y we present 4 new age elevation transects from the central range based on 19 new and 86 previously published fission track and u th he dates of completely reset detrital zircon and apatite grains the age elevation curves and thermal models imply slow cooling prior to ca 2 1 5 ma at exhumation rates of 0 1 mm yr an increase in exhumation rates from ca 2 1 5 ma to ca 0 5 ma 2 4 mm yr and possibly a further acceleration in exhumation from ca 0 5 ma to present 4 8 mm yr three transects from three different latitudes in the eastern central range yield similar results each showing punctuated exhumation with progressively faster rates

provenance evolution and unroofing history of a modern arc continent collision evidence from petrography of plio pleistocene sandstones eastern taiwan abstract plio pleistocene sandstones from the coastal range of eastern taiwan provide a record of shifting source areas and unroofing events in adjacent arc and accretionary wedge terranes during the early stages of are continent collision in latest miocene and early pliocene time arc derived sediments were deposited in a precollisional forearc basin between the luzon volcanic arc and the manila trench sandstones of this age are rich in zoned plagioclase volcanic lithic fragments and pelagic foraminifera and contain only minor quartz and sedimentary metasedimentary lithic fragments in contrast lower pliocene to lower pleistocene sandstones are poor in feldspar and volcanic fragments and contain abundant sedimentary and metasedimentary lithic fragments this reflects a provenance shift f om the volcanic arc to the uplifted meta sedimentary accretionary wedge of proto taiwan which resulted from the early pliocene onset of arc continent collision a refined classification of sedimentary and metasedimentary lithic fragments is introduced here and used to interpret the early evolution of the collisional orogen lithic fragments are rich in pelitic minerals and are divided into 1 sedimentary ls mudstone shale siltstone chert and argillite 2 low grade metamorphic lm1 slate slatey siltstone and quartzite and 3 medium grade metamorphic lm2 phyllite schist phyllitic quartzite and quartz mica albite aggregate a good correlation is observed between these lithic fragment types and bedrock lithologies exposed in the present day central range of taiwan based on this correlation the change in relative abundance of sedimentary and metasedimentary lithic fragments through time has been used to interpret an unroofing sequence for the collisional fold and thrust belt lower pliocene taiwan derived sandstones are rich in sedimentary lithic fragments ls which were shed from the accretionary wedge during the earliest stages of arc continent collision from early pliocene to early pleistocene time sandstones became progressively depleted in ls lithic fragments and enriched first in lm1 and later in lm2 fragments as deeper levels in the metamorphic complex were uplifted and exposed to erosion regional metamorphism of biotite grade rocks lm2 occurred at about 4 5 ma at depths of 12 15 km ernst 1983 and were uplifted to the surface by about 1 4 ma this study these ages give an uplift rate of 4 to 5 km m y which is in good agreement with independent estimates based on fission track studies raised coral reefs quaternary elevation changes and present day denudation rates thus it appears that sandstone detrital modes of clastic orogenic sequences can be used to interpret specific aspects of unroofing and tectonic evolution in nearby active mountain belts

petrogenesis of coexisting sio2 undersaturated to sio2 oversaturated felsic igneous rocks the alkaline complex of itatiaia southeastern brazil abstract the itatiaia alkaline complex is a late cretaceous intrusion 72 myr made up of felsic differentiates with syenitic rocks dominant throughout and with presence of both nepheline and quartz rich varieties dykes with phonolitic or trachytic composition cross cut the coarse grained facies the rocks are arranged concentrically with the core of the complex being formed by sio 2 oversaturated syenites with a small outcrop of granites and are radially displaced by faults related to regional tectonic lineaments the minerals show gradual but significant changes in composition salitic and augitic to aegirine rich pyroxenes hastingsite and actinolite to richterite and arfvedsonite amphiboles sodic plagioclase to orthoclase feldspars and so on and the whole rock trends are broadly consistent with fractional crystallization processes dominated by alkali feldspar removal sr isotopic data indicate more radiogenic ratios for the sio 2 oversaturated rocks 0 7062 0 7067 against 0 7048 0 7054 for the sio 2 undersaturated syenites consistent with small amounts of crustal input the favored hypothesis for the petrogenesis of the different syenitic groups is the prolonged differentiation starting from differently sio 2 undersaturated mafic parental magmas potassic alkali basalts to ankaratrites present in the late cretaceous dyke swarms of the area accompanied by variable crustal contamination prior to the final emplacement the lack of carbonatite as a significant lithotype the potassic affinity of the itatiaia complex and the relatively high sr isotopic ratios match the characteristics of the other complexes of the rio de janeiro sa o paulo states coastline and confirm the ultimate derivation of these differentiated rocks from an enriched lithospheric mantle source

climate driven bedrock incision in an active mountain belt measurements of fluvial bedrock incision were made with submillimeter precision in the east central range of taiwan where long term exhumation rates and precipitation driven river discharge are independently known they indicate that valley lowering is driven by relatively frequent flows of moderate intensity abrasion by suspended sediment is an important fluvial wear process and channel bed geometry and the presence of widely spaced planes of weakness in the rock mass influence erosion rate and style

polyphase history and kinematics of a complex major fault zone in the northern taiwan mountain belt the lishan fault abstract the lishan fault is a major fault zone in the taiwan collision belt it separates two major units the hsuehshan range and the backbone range which differ in lithology ages of sediments metamorphic grades and deformation styles despite the importance of the lishan fault its evolution and tectonic behaviour remained poorly known and controversial we therefore carried out a tectonic study which includes both the identification of structures in and along the fault zone and the palaeostress analysis aiming at reconstructing the succession of fault mechanisms the lishan fault zone underwent polyphase evolution with reactivations under different tectonic regimes consistent with the cenozoic history of taiwan 1 1 on the hsuehshan range the earliest events reflect the palaeogene miocene extension of the chinese continental margin 2 2 serial cross sections and observation of ductile brittle structures show east vergent folding indicating that for the most recent compressional evolution related to late cenozoic taiwan collision the lishan fault was a steeply dipping east vergent back thrust the compression occurred along nw se trends inducing thrusting but also along n s ones inducing transpression with reverse sinistral slip the lishan fault thus underwent contraction as well as strike slip during the mountain building of the taiwan orogeny reverse and strike slip fault systems alternated because of permutations 2 3 under the same compressional stress regime of nw se 1 minor compressional events also occurred 3 3 a late extension accommodated by normal faulting reveals the influence of both the n s extension in the okinawa trough northeast off taiwan

a thermomechanical wedge model of taiwan constrained by fission track thermochronometry abstract we present 31 new apatite fission track aft ages for the island of taiwan that when combined with existing aft and zircon fission track zft data provide regional spatial coverage of the island with respect to low temperature thermochronometry the overall pattern of zft and aft ages in taiwan exhibits unreset ages in the southern and western portions of the island and reset ages predominantly in the central range and eastern taiwan this pattern supports interpretations of the orogen kinematics as reflecting a crustal scale wedge with a southward propagating collision zone in this model new material is accreted to the wedge from the west and is transferred to the east with the greatest exhumation occurring along the eastern margin as recorded in the reset ages in the east and unreset ages in the west the southward propagating collision is consistent with reset ages in the north where erosional exhumation has been ongoing for longer and unreset ages in the south where the younger collision implies less time for erosional exhumation despite the variation in the age of the collision along the strike of the island the widths of the aft and zft reset age zones remain nearly constant between 23 00 n to 24 00 n and 23 20 n to 24 00 n respectively suggesting that the orogen is in an exhumational steady state over these regions with respect to the aft and zft thermochronometers we use the fission track data in conjunction with observations of crustal structure crustal fabric and heat flow measurements to constrain a time dependent two dimensional thermomechanical model of orogen evolution by accounting for the heat transfer tectonic and erosion processes needed to predict aft and zft ages we are able to investigate the relationship between the measured ages and the tectonic characteristics of the orogen with our model we conclude that 1 roughly half of the material accretion in taiwan occurs through underplating over an approximately 40 km wide region 2 current average erosion rates are 3 3 mm yr in the eastern central range and 2 3 mm yr over the whole island 3 the collision has been propagating southward at a rate between 20 and 51 km ma over the past 2 3 ma and 4 central taiwan is in a topographic thermal and exhumational steady state

production of cosmogenic radionuclides at great depth a multi element approach abstract for the last two decades in situ produced cosmogenic nuclides are increasingly applied in earth sciences to quantify surface processes in parallel significant reduction of the analytical uncertainties linked to advances in accelerator mass spectrometry ams allows more precise measurements however among all the published works on cosmogenic nuclides only few studies are dedicated to a better understanding of their production systematic or to a better constrain of the physical parameters involved in their production thus an approach to investigate in situ produced cosmogenic nuclides 10 be 26 al and 36 cl along a single 11 meter long core drilled from the surface and composed of carbonates and quartzose conglomerates has been launched these measurements have been used to quantify muon induced productions based on natural samples for each studied nuclide contrary to the current most oftenly used calculation of muon induced production parameters which are based on irradiation experiments at discrete energies productions based on natural samples are considering the entire energy range of particles reaching the ground surface the evolution of 36 cl concentrations with depth needs to agree with those parameters deduced from 10 be and 26 al data this is optimized when considering a fast muon induced 36 cl production contribution and a spallation production rate at sea level high latitude slhl of 42 0 2 0 atoms 36 cl g ca 1 a 1 1 sigma uncertainty

dynamic reorganization of river basins river networks evolve as migrating drainage divides reshape river basins and change network topology by capture of river channels we demonstrate that a characteristic metric of river network geometry gauges the horizontal motion of drainage divides assessing this metric throughout a landscape maps the dynamic states of entire river networks revealing diverse conditions drainage divides in the loess plateau of china appear stationary the young topography of taiwan has migrating divides driving adjustment of major basins and rivers draining the ancient landscape of the southeastern united states are reorganizing in response to escarpment retreat and coastal advance the ability to measure the dynamic reorganization of river basins presents opportunities to examine landscape scale interactions among tectonics erosion and ecology

late quaternary landscape evolution and genesis of the 2009 catastrophic landslide in the hsiao lin area southwestern taiwan abstract with cumulative rainfall of 1700 mm typhoon morakot triggered a catastrophic landslide at hsiao lin 9 august 2009 which dammed the river buried the village and killed 400 people we conducted a geomorphic study to understand the origin of this landslide in the context of the long term evolution of the hillslope the landslide originated from a broad poorly drained slope 21 23 and ran down along two first order channels the erosion up to 80 m thick has created a concave shape slope and exposed mostly loose debris which implies that the landslide was mainly the reworking of ancient colluviums the genesis of the concave shape slope where the source sediments of the landslide resided reflects the weakness of the mudstone shale bedrock underlying this slope in contrast to the sandstone based transport area the two channels in the transport area also follow old faults or joints given that the source area has been subject to erosion during large landslides the subsequent deposition here was likely achieved by minor colluvial processes this deposition continued until the catastrophic failure in 2009 which could be controlled by 1 the amount of sediments deposited which determined the slope angle and 2 the headward expansion of the channels from the transport area which enhanced groundwater convergence and later provided routes for the landslide materials to run downslope extensive mass wasting motions had occurred in the area as shown by the prevalence of 20 m thick landslide debris flow sequences on the lower part of the hillslope which are dated 21 14 9 13 7 and 12 0 ka by the radiocarbon method these mass wasting events had hindered the long term incision of the trunk river in response to the rapid tectonic uplift at least the 12 0 ka event which caused extensive mud flow deposition had dammed the river overall this study shows how bedrock lithology and structures controlled the shape of a hillslope and caused extremely unsteady mass wasting transport in the active mountains of taiwan

modern vertical deformation rates and mountain building in taiwan from precise leveling and continuous gps observations 2000 2008 1 to characterize the present day vertical displacement field in the active taiwan orogenic belt 1843 precise leveling and 199 continuous gps measurements from 2000 to 2008 are collected and analyzed in this study vertical velocities derived from the leveling data are placed in a reference frame of the chinese continental margin using continuous gps observations at nearby sites the leveling and gps vertical velocities generally reveal a dome shaped pattern with uplift of 0 2 18 5 mm yr in the interior of the mountain range and subsidence on the flanks of the mountains and coastal plains modern uplift rates in the active fold and thrust belt are generally consistent with geologic uplift rates however present day uplift rates in the central range are faster than the million years averaged exhumation rates the modern subsidence rates are generally consistent with geologic rates except for the rates in western coastal areas due to groundwater pumping present day subsidence in the southern central range and northern coastal range is however inconsistent with long term uplift which may reflect interseismic elastic strain accumulation across faults present day subsidence in northern taiwan occurs in a region of postcollisional orogenic collapse we model the present day and geologic vertical velocities and published gps horizontal velocity data across southern taiwan using a 2 d lithospheric model the model suggests a combined slip rate of 40 mm yr on the frontal thrusts and 45 mm yr on the longitudinal valley fault the model requires an additional source of crustal thickening under the central range to match the observed present day uplift rates

geomorphic analysis of the central range fault the second major active structure of the longitudinal valley suture eastern taiwan numerous landforms along the longitudinal valley suture of eastern taiwan indicate that two opposing reverse faults currently dominate the suturing process between the luzon volcanic arc and the central range of taiwan the east dipping longitudinal valley fault on the eastern flank of the valley is well known the west dipping central range reverse fault on the western flank of the valley is more obscure nonetheless it has produced many uplifted lateritic fluvial terraces along the eastern flank of the central range in the central reach of the valley from just north of the wuhe tableland to near chihshang the fault appears to be active but blind south of chihshang and inactive along the northern part of the longitudinal valley the late quaternary slip rate of the fault is less than 12 8 mm yr this constraint means that the fault is absorbing far less than half of the horizontal shortening across the longitudinal valley suture however the late quaternary slip rate along the fault may be comparable to the uplift and exhumation rate of the central range this suggests that localized brittle slip along the central range fault is an important component of crustal thickening and uplift of the range even though additional shortening and crustal thickening may be occurring because of pervasive deformation beneath the range

millennial slip rate of the longitudinal valley fault from river terraces implications for convergence across the active suture of eastern taiwan the longitudinal valley fault is a key element in the active tectonics of taiwan it is the principal structure accommodating convergence across one of the two active sutures of the taiwan orogeny to understand more precisely its role in the suturing process we analyzed fluvial terraces along the hsiukuluan river which cuts across the coastal range in eastern taiwan in the fault s hanging wall block this allowed us to determine both its subsurface geometry and its long term slip rate the uplift pattern of the terraces is consistent with a fault bend fold model our analysis yields a listric geometry with dips decreasing downdip from about 50 to about 30 in the shallowest 2 5 km the holocene rate of dip slip of the fault is about 22 7 mm yr this rate is less than the 40 mm yr rate of shortening across the longitudinal valley derived from gps measurements the discrepancy may reflect an actual difference in millennial and decadal rates of convergence an alternative explanation is that the discrepancy is accommodated by a combination of slip on the central range fault and subsidence of the longitudinal valley floor the shallow listric geometry of the longitudinal valley fault at the hsiukuluan river valley differs markedly from the deep listric geometry illuminated by earthquake hypocenters near chihshang 45 km to the south we hypothesize that this fundamental along strike difference in geometry of the fault is a manifestation of the northward maturation of the suturing of the luzon volcanic arc to the central range continental sliver

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

neotectonic characteristics along the eastern flank of the central range in the active taiwan orogen inferred from fluvial channel morphology the tectonic activity of the taiwan orogenic belt has been studied by different methods over various timescales constraints on tectonic characteristics over timescales of 103 105 years however are rather limited to further understand the tectonic forcing over this timescale we analyzed 20 major river basins along the eastern flank of the central range the mountainous core of the orogen the results of river steepness index ksn values and the distribution patterns of knickpoints are consistent with the patterns of tectonic evolution in taiwan on both ends of the orogen the rivers have low ksn values that indicate low uplift rates throughout the area in the central part of the island where the orogen is under rapid collisional processes the rivers are steeper and are characterized by many tectonic knickpoints our results show different patterns from both short term and long term uplift and denudation rate patterns this suggests that these rates change temporally and spatially moreover the steepness indexes of rivers in the taiwan orogen show the same increasing trend with erosion rates as those in other active orogens but correspond to significantly higher erosion rates this is likely produced by the frequent debris flow and landslide events in taiwan a character that makes the island distinctive from other active orogens in the world

extensional collapse of the northern taiwan mountain belt as an active collision zone between the luzon arc and the china continental margin the taiwan mountain belt particularly its south central part is undergoing crustal shortening and rapid uplift the northern part of the orogen is however subjected to crustal stretching and rifting as a result of flipping of subduction from the northwest facing luzon arc system to the south facing ryukyu arc system taiwan and its neighboring southern ryukyu used to be part of the rifted china continental margin before the collision started in late miocene time engineered by the northwest movement of the philippine sea plate in the past 5 m y the north south trending luzon arc obliquely overrode the northeast southwest trending continental margin and tectonized it into a collision orogen that progressively enlarged and migrated from northeast to southwest following the southwest propagating collision the north dipping philippine sea plate which was subducting beneath the ryukyu arc also extended westward and caused flipping of subduction in the northern part of the collision orogen in consequence the orogen lost the compressive support by the colliding plates and became subjected to lithospheric stretching induced by the trench suction the collision orogen collapsed as a result of crustal thinning and its central part foundered into a deep submerged basin a whole spectrum of active tectonic scenarios ranging from orogenic buildup by collision to orogenic collapse by rifting and subsidence can be readily observed in the taiwan ryukyu area and provides a vivid example for the process of orogenic collapse

late cenozoic metamorphism and mountain building in taiwan a review abstract the orogenic wedge of taiwan results from the late miocene collision of the chinese passive margin and the luzon volcanic arc because of the southward propagation of the collision over time and because of its extreme rates of deformation and erosion it has appeared as an ideal place to investigate mountain building processes here we review existing metamorphic and thermochronological data on late cenozoic burial and exhumation most of the island has been extensively investigated in particular in terms of zircon or apatite fission track and u th he thermochronology peak metamorphic temperatures have also been quantified from the raman spectroscopy of carbonaceous material along three transects in central taiwan the different datasets appear consistent and indicate that cooling rates and exhumation are more intense within the hsueshan range and within the tananao complex lateral variations from south to north are also observed and they can be interpreted in terms of different stages of exhumation and mountain building existing models provide a framework to analyze the data and discuss the limits of some previous interpretations in particular in terms of exhumational steady state or of recent acceleration of uplift and exhumation these models are also discussed in light of available data it appears that all of them fit thermochronological data within the tananao complex whatever the kinematics the depth of the wedge or the mechanism responsible for exhumation and that exhumation of the hsueshan range has been ignored in most models future models need therefore to consider the taiwan wedge as a whole additional constraints on peak metamorphic conditions on kinematics of shortening and exhumation or on the geometry of the wedge at depth need to be gathered to further unravel mountain building processes at the scale of the whole orogen

the tsaoling landslide triggered by the chi chi earthquake taiwan insights from a discrete element simulation article i nfo in the village of tsaoling in yunlin county taiwan a major landslide was triggered by the chi chi earthquake in 1999 with more than 125 10 6 m 3 of rock displaced the kinematic behaviour of this landslide is simulated using a 2d discrete element model pfc2d code our numerical model is composed of discs bonded together the initial boundary conditions are applied along the ball wall contacts by using derived velocities integrated from the strong motion data with a duration of 160 s including the peak acceleration near tsaoling the constraints are mainly issued from the final geometry of the landslide including its capacity to cross the river valley and reach a significant elevation on the opposite mountain flank they also result from a variety of geological and hydrological observations including the local levels of material disruption and the location of survivors our modelling thus indicates that a low friction coefficient about 0 15 and a medium strength are required to account for the actual landslide characteristics a self lubrication mechanism probably accounts for the low residual friction our model also suggests that the maximum velocity of sliding reached 50 m s a result that cannot be checked in the absence of actual measurements in addition to friction the strength of sliding block is of special importance because it controlled the possibility for the upper layer fragments to roll and get buried and hence the probability of survival

catastrophic landslide induced by typhoon morakot shiaolin taiwan abstract typhoon morakot induced the catastrophic and deadly shiaolin landslide in southern taiwan on 9 august 2009 resulting in more than 400 casualties we undertook a geological and geomorphological investigation with the aim of reconstructing the events leading up to this landslide and to clarify factors that contributed to its development cumulative rainfall reached up to 1676 5 mm in about three days under the influence of the typhoon and the shiaolin landslide with a volume of 25 106 m3 occurred one day after the peak in rainfall intensity the landslide occurred on a dip slope overlying late miocene to early pliocene sedimentary rocks consisting of silty shale massive mudstone and sandstone it started as a rockslide in the upper third of the landslide area and transformed into a rock avalanche that crossed a series of terraces and displaced or buried the village below it buried the riverbed of the chishan river and ran up the opposite slope creating a landslide dam 60 m high which was breached about 1 h and 24 min later flooding the village the velocity of the landslide is estimated to have been 20 4 to 33 7 m s 1 and its apparent friction angle was 14 which indicates its high mobility the detachments in the source area consist of combinations of bedding planes and joints or faults the landslide was preceded by gravitational deformation which appeared as hummocky landforms before the landslide and as buckle folds exposed after the event the landslide deposits consist of fragments of mudstone shale and sandstone as well as clayey material at its base this clayey material consisting of illite chlorite quartz feldspar and calcite is assumed to have strongly influenced the long rapid runout

the origin of magnetic anomalies in lower crustal rocks labrador mid to lower crustal granulites near wilson lake in central labrador exhibit pronounced aeromagnetic anomalies areas characterized by high and low field strength correlate with the wilson lake allochthon and the surrounding autochthon respectively the induced magnetization in both units has mean values of 0 34 a m allochthon and 0 33 a m autochthon however the mean values of remanent magnetizations are 9 2 a m allochthon and 3 3 a m autochthon in directions contributing to the present geomagnetic field therefore the remanent magnetization plays the main role in generating the observed magnetic anomaly thermal demagnetizations indicate that titanhematite is stable to 585 600 c the absence of significant verwey transitions indicates that titanhematite is the predominant carrier in some rocks and a significant carrier along with magnetite in others any interpretation of the magnetic anomalies above these rocks must consider magnetic remanence as the principle anomaly source

solutions of the stream power equation and application to the evolution of river longitudinal profiles 1 erosion by bedrock river channels is commonly modeled with the stream power equation we present a two part approach to solving this nonlinear equation analytically and explore the implications for evolving river profiles first a method for non dimensionalizing the stream power equation transforms river profiles in steady state with respect to uniform uplift into a straight line in dimensionless distance elevation space second a method that tracks the upstream migration of slope patches which are mathematical entities that carry information about downstream river states provides a basis for constructing analytical solutions slope patch analysis explains why the transient morphology of dimensionless river profiles differs fundamentally if the exponent on channel slope n is less than or greater than one and why only concave up migrating knickpoints persist when n 1 at migrating knickpoints slope patches and the information they carry are lost a phenomenon that fundamentally limits the potential for reconstructing tectonic histories from bedrock river profiles stationary knickpoints which can arise from spatially varying uplift rates differ from migrating knickpoints in that slope patches and the information they carry are not lost counterparts to migrating knickpoints called stretch zones are created when closely spaced slope patches spread to form smooth curves in distance elevation space these theoretical results are illustrated with examples from the california king range and the central apennines

uplift histories from river profiles 1 longitudinal river profiles where elevation of a river bed is plotted as a function of distance along the river bed contain information about uplift rate when a region adjacent to a reference level e g sea level is uplifted a rapid change in gradient occurs near the river mouth the erosional process causes this change in gradient to migrate upstream thus a river profile is effectively a tape recording of the uplift rate history provided that the erosional process can be adequately parameterized here we use a non linear equation to relate the shape of a river profile z x to uplift rate history u t if erosion is assumed to be dominated by knickpoint retreat an inverse model can be formulated and used to calculate uplift rate histories our model builds upon standard stream profile analysis which focuses on the relationship between profile slope and drainage area we have applied this analytical approach to river profiles from the bie dome angola calculated uplift rate histories agree with independent geologic estimates

nd isotopes demonstrate the role of contamination in the formation of coexisting quartz and nepheline syenites at the abu khruq complex egypt the petrogenesis of abu khruq an 89 ma alkaline ring complex of eastern egypt which is composed of alkali gabbros and both silica over and undersaturated syenites has been investigated major and trace element relationships and nd and sr isotope data are consistent with formation of the gabbros from an alkaline mafic magma that experienced extensive fractionation and all syenites from a felsic derivative of this melt the parental magma had an 87sr 86sr of 0 7030 and an 143nd 144nd of 0 512750 nd 4 4 indicating derivation from a depeleted mantle source the initial 143nd 144nd ratios are 0 512721 to 0 512748 for the gabbros 0 512739 to 0 512750 for the alkali syenites and trachytes 0 512717 to 0 512755 for the nepheline syenites and 0 512706 to 0 512732 for the quartz syenites in contrast analyzed precambrian granites from eastern egypt have generally lower 143nd 144nd ratios ranging from 0 51247 to 0 51261 or nd 0 8 to 1 7 for 89ma their nd model ages range from 775 to 935 ma and suggest there was no significant input of pre pan african crust in their formation among abu khruq rocks 143nd 144nd ratios indicate that the quartz syenites formed by open system crustal contamination processes whereas the nepheline syenites experienced little or no contamination modeling shows that contamination occurred at various stages affecting both mafic and more evolved compositions with input of about 20 crustal nd for the most contaminated samples the degree of contamination is related to the silica saturation of the quartz syenites simplified modeling of magma evolution within petrogeny s residua system demonstrates the ability of afc processes to cause a critically undersaturated magma to evolve across the feldspar join and produce oversaturated rocks the oversaturated syenites at abu khruq were produced in this manner whereas the nepheline syenites formed by fractionation without similarly large degrees of contamination the results have broad implications for the formation of subvolcanic complexes in continental settings beyond the important production of silica oversaturated compositions from crustal interaction they underscore the importance of crustal interactions in the formation of the various lithologies such interactions occur at various stages in the evolution of the magmas and as such are not strictly coupled with fractional crystallization while previous study of abu khruq has demonstrated extensive hydrothermal alteration of o and sr isotopes the present work shows that the nd isotope ratios were not significantly affected and thus reflect magmatic signatures this feature combined with relatively small corrections for initial ratios emphasizes the utility of nd isotopes for petrogenetic studies

earthquake triggered increase in sediment delivery from an active mountain belt in tectonically active mountain belts earthquake triggered landslides deliver large amounts of sediment to rivers we quantify the geomorphic impact of the 1999 mw 7 6 chi chi earthquake in taiwan which triggered 20 000 landslides coseismic weakening of substrate material caused increased landsliding during subsequent typhoons most coseismic landslides remained confined to hillslopes downslope transport of sediment into the channel network occurred during later storms the sequential processes have led to a factor of four increase in unit sediment concentration in rivers draining the epicentral area and increased the magnitude and frequency of hyperpycnal sediment delivery to the ocean four years after the earthquake rates of hillslope mass wasting remain elevated in the epicentral area

a quantitative evaluation of playfair s law and its use in testing long term stream erosion models playfair s law j playfair illustrations of the huttonian theory of the earth 1802 requires any two tributaries in a river network to lower at the same rate near their junction although this law holds exactly at the junction it is unclear how well it holds in the vicinity of the junction this issue has practical importance because playfair s law has been used to estimate parameters for detachment limited models of erosion if the incision rate of a stream is modelled as amsn where is an erodibility parameter a is the area drained by the stream and s is the local gradient of the channel then the ratio of the parameters m n can be estimated from junctions by assuming that playfair s law holds over the distance used to determine s for each tributary in this paper playfair s law and associated m n estimates are evaluated for simulated basins with constant and temporally varying uplift rates or baselevel lowering rates the results demonstrate that estimates of m n may be biased for basins with upward concave stream profiles because the local slope must be approximated with an average upstream slope in addition when uplift rate varies temporally knickpoints are shown to travel through the basins with constant vertical velocity because incision rates vary within the basin playfair s law only holds exactly at the junctions these effects are more important when slopes are measured over longer distances finally measurement techniques are presented which address these potential biases copyright 2001 john wiley sons ltd

tandem suturing and disarticulation of the taiwan orogen revealed by its neotectonic elements taiwan s numerous active faults and folds demarcate distinct eastern and western neotectonic belts the western belt results from the attachment and subsequent detachment of a sliver of continental lithosphere to the eurasian continental margin the eastern belt is the product of the same continental sliver docking with and then separating from the luzon volcanic arc thus the active taiwan orogen is a tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the eurasian continental margin this progressive suturing and separation is a superb living demonstration of the fundamental weakness of lithospheric sutures furthermore this neotectonic architecture provides the basis for understanding the taiwan s seismic sources

trace element and nd isotope systematics in detrital apatite of the po river catchment implications for provenance discrimination and the lag time approach to detrital thermochronology abstract detrital thermochronology is often employed to assess the evolutionary stage of an entire orogenic belt using the lag time approach i e the difference between the cooling and depositional ages of detrital mineral grains preserved in a stratigraphic succession the impact of different eroding sources to the final sediment sink is controlled by several factors including the short term erosion rate and the mineral fertility of eroded bedrock here we use apatite fertility data and cosmogenic derived erosion rates in the po river catchment alps apennines to calculate the expected percentage of apatite grains supplied to the modern po delta from the major alpine and apenninic eroding sources we test these predictions by using a cutting edge dataset of trace element and nd isotope signatures on 871 apatite grains from 14 modern sand samples and we use apatite fission track data to validate our geochemical approach to provenance discrimination we found that apatite grains shed from different sources are geochemically distinct apatites from the lepontine dome in the central alps show relative hree enrichment lower concentrations in ce and u and higher 147 sm 144 nd ratios compared to apatites derived from the external massifs derived provenance budgets point to a dominant apatite contribution to the po delta from the high fertility lepontine dome consistent with the range independently predicted from cosmonuclide and mineral fertility data our results demonstrate that the single mineral record in the final sediment sink can be largely determined by high fertility source rocks exposed in rapidly eroding areas within the drainage this implies that the detrital thermochronology record may reflect processes affecting relatively small parts of the orogenic system under consideration a reliable approach to lag time analysis would thus benefit from an independent provenance discrimination of dated mineral grains which may allow to proficiently reconsider many previous interpretations of detrital thermochronology datasets in terms of orogenic wide steady state

reply to comment on resentini et al 2020 ongoing exhumation of the taiwan orogenic wedge revealed by detrital apatite thermochronology the impact of effective mineral fertility and zero track grains abstract in their comment to resentini et al 2020 mesalles et al pointed out supposed fundamental inaccuracies concerning analytical aspects and the tectonic interpretation of fission track data this would invalidate the main conclusions of our study here we demonstrate that their criticism is ill founded

analytical electron microscopy of nanometer scale hornblende lamellae low temperature exsolution in cummingtonite cummingtonite from central massachusetts which has experienced pervasive exsolution of hornblende contains numerous hornblende precipitates lamellae and discs ranging in thickness from 2 5 mm to 4 nm that represent multiple generations of exsolution the smallest precipitates were investigated using transmission electron microscopy and analytical electron microscopy to characterize the coherent cummingtonite hornblende solvus at low temperature in contrast to older coarser generations of exsolution lamellae which are 0 5 2 5 mm in width planar and extend across entire grains the youngest generation consists of nanometer scale discs 4 80 nm thick and 10 1000 nm long that represent exsolution at approximately 300 8c klein et al 1996 quantitative energy dispersive x ray analyses were obtained from discs as small as 20 nm in thickness providing compositional data for coherent exsolution of hornblende at 300 8c surprisingly these tiny discs have a lower ca content and a higher al content than the coarser higher temperature lamellae these compositions appear to lie well within miscibility gaps of the equilibrium and coherent solvi for cummingtonite hornblende in terms of ca fe 21 exchange at low temperatures and may represent a more tschermakitic hornblende coexisting with cummingtonite with excess al relative to ca the composition of the cummingtonite host between nanometer scale discs is very low in both ca and al relative to bulk cummingtonite analyses that were obtained from electron microprobe analyses of 1 2 mm areas compositional profiles across host areas were measured to help interpret the unexpected chemistries of the nanometer scale discs a profile across the precipitate free zone between a coarse hornblende lamella and a group of nanometer scale hornblende discs shows downward concavity for ca and al as expected for incomplete diffusion between the precipitation zone and the pre existing hornblende lamellae a profile measured between two nanometer scale discs shows downward concavity for al and nearly constant to slight upward concavity for the ca content suggesting incomplete al diffusion before completion of the exsolution process but a near equilibrium state for ca however the ca profile could also represent incomplete diffusion if the hornblende discs had started coarsening at the expense of other shrinking discs by means of the gibbs thomson capillary effect the observed profiles suggest that relative to al ca was the faster diffusing element when the exsolution and coarsening processes stopped

coseismic versus interseismic ground deformations fault rupture inversion and segmentation revealed by 2003 mw 6 8 chengkung earthquake in eastern taiwan 1 the 2003 chengkung earthquake mw 6 8 provided diagnostic evidence for a source model showing the deformation process of the seismogenic chihshang fault in eastern taiwan the aftershocks show a fault bend at a depth of 18 km coseismic ground displacements recorded by strong motion records allow us to deduce instant rupturing of this event our resulting model shows a fault length of 33 km and dip slip dominant rupture on fault plane deeper than 18 km estimated coseismic displacements constrain two fault planes one at 5 18 km depth dipping 60 e and 18 36 km depth dipping 45 e the uppermost fault plane of the chihshang fault 0 5 km did not break immediately after the main shock however it may have a major role in after slip and even interseismic ground deformation the taiyuan basin developed in the hanging wall is a geomorphic feature consistent with and adequately explained by coseismic ground displacements

numerical earthquake model of the 31 october 2013 ruisui taiwan earthquake source rupture process and seismic wave propagation abstract we build a numerical earthquake model including numerical source and wave propagation models to understand the rupture process and the ground motion time history of the 2013 ml 6 4 ruisui earthquake in taiwan this moderately large event was located in the longitudinal valley a suture zone of the philippine sea plate and the eurasia plate a joint source inversion analysis by using teleseismic body wave gps coseismic displacement and near field ground motion data was performed first the inversion results derived from a western dipping fault plane indicate that the slip occurred in depths between 10 and 20 km the rupture propagated from south to north and two asperities were resolved the largest one was located approximately 15 km north of the epicenter with a maximum slip about 1 m a 3d seismic wave propagation simulation based on the spectral element method was then carried out by using the inverted source model a strong rupture directivity effect in the northern area of the longitudinal valley was found which was due to the northward rupture process forward synthetic waveforms could explain most of the near field ground motion data for frequencies between 0 05 and 0 2 hz this numerical earthquake model not only helps us confirm the detailed rupture processes on the central range fault but also gives contribution to regional seismic hazard mitigation for future large earthquakes

downstream evolution of the thermochronologic age signal in the brahmaputra catchment eastern himalaya implications for the detrital record of erosion the namche barwa massif in the eastern himalayan syntaxis is characterized by very rapid exhumation and provides a significant proportion of the sediment flux carried by the brahmaputra river we present new detrital zircon fission track zft and muscovite 40ar 39ar mar data from modern sediments of rivers draining the eastern himalaya the cooling age populations for both thermochronometers contain a characteristic 2 ma signature related to the rapid exhumation of namche barwa which can be traced hundreds of kilometers downstream from their source into the brahmaputra foreland despite dilution from downstream tributary catchments to estimate present day erosion in the catchments we apply a mixing model based on linear inversion of the binned age distributions the inversion predicts relative erosion rates in the syntaxial region that are an order of magnitude higher than those in upstream catchments and about twice as high as those in the southern himalayan catchments consistent to first order with previous estimates of erosion rate patterns in the eastern himalaya a comparison of the observed downstream evolution of age distributions with a sediment flux model suggests that the zft signal can be explained by dilution from himalayan tributaries only whereas the mar signal is also affected by selective sequestering possibly through winnowing of micas as they are transported downstream nevertheless thermochronological ages 2 ma provide a diagnostic signal of syntaxial exhumation in the sedimentary record of the eastern himalaya this study suggests the most robust signal to be recorded in the most proximal deposits with respect to the syntaxis

three dimensional p velocity structures of the lithosphere beneath taiwan from the analysis of taiger and related seismic data sets 1 the convergence of the philippine sea and the eurasian plates in the taiwan region led to the formation of a young collisional mountain between two subduction zones of nearly orthogonal polarities the geological processes underlying the collision and its relation to subduction are the primary targets of taiger taiwan integrated geodynamic research project newly acquired passive and active sources data on land supplemented by ocean bottom as well as permanent seismic network data are used to derive a new 3 d tomographic velocity model using the 7 5 km sec contour as a marker for crustal deformation two trend parallel roots one under the central range with a maximum depth of 55 km and the other under the coastal range at 40 km are found to extend from southern to central 24 n taiwan between the two roots and lying approximately beneath the longitudinal valley the 7 5 km sec contour rises to 25 km depth in the upper mantle a high velocity zone east dipping and its upper surface coinciding with a wadati benioff zone in the south 22 8 n becomes near vertical and ill defined in the north 23 9 n the crustal deformation as defined by the roots and the along trend variations of the upper mantle structures under taiwan provide key information for the orogeny with the thickening of crust to 55 km or more processes such as eclogitization and delamination may come into play

how rivers react to large earthquakes evidence from central taiwan earthquakes and bedrock river incision are fundamental processes in the evolution of tectonically active landscapes yet little work has focused on understanding how a bedrock river responds to a single large earthquake data from the 1999 m w 7 6 chi chi earthquake in central taiwan show dramatic differences in river response that depend on the proximity to the rupture zone near the fault scarp vertical ground deformation intensifi es river incision on a time scale of years to decades while distal to the fault landslides induced by the earthquake mantle bedrock on the river bed with sediment impeding incision for decades to centuries as the material is evacuated this surprising spatial and temporal variability in bedrock incision caused by earthquakes has implications for the paleoseismic interpretation of bedrock terraces and for the evolution of tectonically active landscapes

spatial and temporal trends in exhumation of the eastern himalaya and syntaxis as determined from a multitechnique detrital thermochronological study of the bengal fan the bengal fan provides a neogene record of eastern and central himalaya exhumation we provide the first detrital thermochronological study apatite and rutile u pb mica ar ar zircon fission track of sediment samples collected during international ocean discovery program iodp expedition 354 to the mid bengal fan our data from rutile and zircon fission track thermochronometry show a shift in lag times over the interval 5 59 3 47 ma the oldest sample with a lag time of 6 m y has a depositional age of 5 59 4 50 ma and the zircon and rutile populations then show a static peak until 12 ma this interval from 5 59 4 50 ma to 12 ma is most easily interpreted as recording passive erosion of the greater himalaya however single grains with lag times of 4 m y but with high analytical uncertainty are recorded over this interval for sediments older than 10 ma these grains were derived from the greater himalaya which was exhuming rapidly until ca 14 ma in sediments younger than 10 ma these grains could represent slower yet still rapid exhumation of the syntaxial antiform to the south of the massif lag times 1 m y are again recorded from 14 5 ma to the base of the studied section at 17 ma reflecting a period of greater himalayan rapid exhumation mica 40ar 39ar and apatite u pb data are not sensitive to syntaxial exhumation we ascribe this to the paucity of white mica in syntaxial lithologies and to high levels of common pb resulting in u pb ages associated with unacceptably high uncertainties respectively

partitioning sediment flux by provenance and tracing erosion patterns in taiwan we critically evaluate the potential and limitations of an alternative way to calculate erosion rates based on petrographic and mineralogical fingerprints of fluvial sediments coupled with gauged sediment fluxes our approach allows us to apportion sediment loads to different lithological units and consequently to discriminate erosion rates in different tectonic domains within each catchment our provenance data on modern taiwanese sands indicate focused erosion in the backbone range and tananao complex of the retrowedge lower rates are inferred for the northern part of the island characterized by tectonic extension and for the western foothills in the prowedge the principal factor of uncertainty affecting our estimates is the inevitably inaccurate evaluation of total sediment load because only the suspended flux was measured another is the assumption that suspended load and bed load are derived from the same sources in fixed proportions additional errors are caused by the insufficiently precise definition of lithologically similar compositional end members and by the temporal variability of sediment composition at the outlet of each catchment related to the spatial variability of erosional processes and triggering agents such as earthquakes typhoons and landslides to evaluate the robustness of our findings we applied a morphometric technique based on the stream power model the results obtained are broadly consistent with local discrepancies ascribed to poorly constrained assumptions and choices of scaling parameters our local erosion estimates are consistent with gps uplift rates measured on a decadal timescale and generally higher than basin wide results inferred from cosmogenic nuclide and thermochronology data

erosion rates and orogenic wedge kinematics in taiwan inferred from fission track thermochronometry new apatite and zircon fission track ages and previously published thermochronometric data are used to evaluate erosion rates and particle paths within the active taiwan arc continent collision we present 20 new apatite fission track ages and 6 new zircon fission track ages apatite and zircon ages are all reset in the northern and eastern parts of taiwan although the region of reset apatite ages is larger we interpret this pattern as resulting from crustal accretion at the western margin of the orogenic wedge combined with southward propagation of the collision zone a onedimensional thermal model including erosion provides prediction of the fission track ages the distribution of reset ages is best explained with an erosion rate of 4 6 mm yr given a propagation velocity of 60 mm yr this erosion rate implies that nearly 25 km of material has been eroded from northern taiwan the lack of reset 40 ar 39 ar ages from muscovite and biotite suggests that rockparticle paths have a large horizontal component a result consistent with an eroding orogenic wedge model

simultaneous mountain building in the taiwan orogenic belt the obliquity of the arc continent collision in taiwan is thought to have produced a southward propagating orogenic system starting as early as 8 ma we combine 62 new zircon fission track ages with timing of rapid subsidence in the foreland basin to identify the timing of the onset of exhumation and orogenesis the oldest completely reset zircon fission track ages and the onset of rapid tectonic subsidence in both the northern and southern parts of the foreland basin are ca 5 6 ma we propose that north south rifting in the south china sea created a north trending continental margin before the collision rather than the commonly assumed northeast trending margin consequently both this north trending continental margin and the luzon arc of the philippine sea plate were subparallel resulting in an initial collision that was simultaneous along strike

neotectonic architecture of taiwan and its implications for future large earthquakes the disastrous effects of the 1999 chi chi earthquake in taiwan demonstrated an urgent need for better knowledge of the island s potential earthquake sources toward this end we have prepared a neotectonic map of taiwan the map and related cross sections are based upon structural and geomorphic expression of active faults and folds both in the field and on shaded relief maps prepared from a 40 m resolution digital elevation model augmented by geodetic and seismologic data the active tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the eurasian continental margin have created two neotectonic belts in taiwan in the southern part of the orogen both belts are in the final stage of consuming oceanic crust collision and suturing occur in the middle part of both belts and postcollisional collapse and extension dominate the island s northern and northeastern flanks both belts consist of several distinct neotectonic domains seven domains kaoping chiayi taichung miaoli hsinchu ilan and taipei constitute the western belt and four domains lutao lanyu taitung hualien and ryukyu make up the eastern belt each domain is defined by a distinct suite of active structures for example the chelungpu fault source of the 1999 earthquake and its western neighbor the changhua fault are the principal components of the taichung domain whereas both its neighboring domains the chiayi and miaoli domains are dominated by major blind faults in most of the domains the size of the principal active fault is large enough to produce future earthquakes with magnitudes in the mid 7 values