evidence of earthquake triggering by the solid earth tides article i nfo clearevidence forearthquake triggeringbythe earth tides hasremained elusive for morethan a century using the largest global earthquake catalog available the neic catalog with 442412 events we observe a clear correlation with 99 confidence between the phase of the solid earth tide and the timing of seismic events earthquakes occur slightly more often at the time of ground uplift by the earth tide i e when normal stresses are reduced within the lithosphere we observe that this phase distribution anomaly is larger for smaller and shallowerearthquakes although earthquakes inregionswithdominantlynormalandstrike slip faulting seem to exhibit more tidal triggering than regions dominated by thrust faulting there is no statistically significant evidence for a focal mechanism dependence on earthquake triggering finally we show here that it is highly probablethat the observedtriggeringiscaused bythe solid earth tide ratherthan byloading fromthe oceanor atmospheric tides although an additional impact due to loading from ocean tides is possible and probable we cannot detect it here because the earthquake database is not sufficiently complete and homogeneous more smallmagnitudeearthquakesinoceanicareasareneeded ourresultsareconsistentwiththeideaofadamped

foredeeps versus subduction zones the geologic characteristics of foredeeps and accretionary wedges suggest that these features are distinguishable on the basis of the direction of the associated subduction east north east dipping subduction related accretionary wedges show high relief and broad outcrops of metamorphic rocks they are associated with shallow foredeeps with low subsidence rates in contrast west dipping subduction related accretionary wedges show low relief and involve mainly sedimentary cover the related foredeeps are deep and have high subsidence rates this differentiation is useful both for oceanic and continental subductions e g eastern vs western pacific subductions or east dipping alpine vs west dipping apenninec subductions in a cross section of the alps the ratio of the area of the orogen to the area of the foredeeps is at least 2 1 whereas this ratio is 0 22 1 for the apennines these ratios explain why foredeeps related to east or northeast dipping subduction are quickly filled and are bypassed by clastic rocks whereas foredeeps related to west dipping subduction maintain a deep water environment longer these differences support the presence of an eastward asthenospheric counterflow relative to the westward drift of the lithosphere detected in the hot spot reference frame even in the mediterranean where no hot spots are present in this interpretation the apennines foredeep was caused by the eastward push of the mantle acting on the subducted slab whereas the foredeeps in the alps were caused by the load of the thrust sheets and the downward component of movement of the upper adriatic plate these forces contrast with the upward component of the eastward mantle flow

asymmetric dynamics at subduction zones derived from plate kinematic constraints abstract the lithospheric sinking along subduction zones is part of the mantle convection therefore computing the volume of lithosphere recycled within the mantle by subducting slabs quantifies the equivalent amount of mantle that should be displaced for the mass conservation criterion the rate of subduction is constrained by the convergence rate between upper and lower plates and the motion of the subduction hinge h that may either converge or diverge relative to the upper plate here starting from the analysis of the slab hinge kinematics we evaluate the subduction rate at 31 subduction zones worldwide useful to compute volumes of sinking lithosphere into the mantle our results show that 190 km3 yr and 88 km3 yr of lithospheric slabs are currently subducting below h divergent and h convergent subduction zones respectively we also propose supporting numerical models providing asymmetric volumes of the subducted lithosphere using the subduction rate instead of plate convergence as boundary condition furthermore h divergent subduction zones appear to be coincident with subductions having westward directed slabs whereas h convergent subduction zones are mostly compatible with those that have eastward to northeastward directed slabs on the basis of this geographical polarity our lithospheric volume estimation gives 214 km3 yr and 88 km3 yr of subducting lithosphere respectively this entails that w directed subduction zones contribute more than twice in lithospheric sinking into the mantle with respect to e to ne directed ones in accordance with the conservation of mass principle this volumetric asymmetry in the mantle suggests a displacement of 120 km3 yr of mantle material from west to east providing a constraint for global asymmetric mantle convection

subduction kinematics and dynamic constraints the kinematics of subduction zones shows a variety of settings that can provide clues for dynamic understandings two reference frames are used here to describe the simple 2d kinematics of subduction zones in the first the upper plate is assumed fixed whereas in the second frame upper and lower plates move relative to the mantle relative to a fixed point in the upper plate u the transient subduction hinge h can converge diverge or be stationary similarly the lower plate l can converge diverge or be stationary the subduction rate vs is given by the velocity of the hinge h minus the velocity of the lower plate l vs vh vl the subduction rate 1 increases when h diverges and 2 decreases when h converges combining the different movements at least 14 kinematic settings can be distinguished along the subduction zones variable settings can coexist even along a single subduction zone as shown for the 5 different cases occurring along the apennines subduction zone apart from few exceptions the subduction hinge converges toward the upper plate more frequently along e or ne directed subduction zone whereas it mainly diverges from the upper plate along w directed subduction zones accompanying backarc extension before collision orogen growth occurs mostly at the expenses of the upper plate shortening along e ne directed subduction zones whereas the accretionary prism of w directed subduction zones increases at the expenses of the shallow layers of the lower plate the convergence shortening ratio is 1 along e or ne directed subduction zones whereas it is 1 along accretionary prisms of w directed subduction zones backarc spreading forms in two settings along the w directed subduction zones it is determined by the hinge divergence relative to the upper plate minus the volume of the accretionary prism or in case of scarce or no accretion minus the volume of the asthenospheric intrusion at the subduction hinge since the volume of the accretionary prism is proportional to the depth of the decollement plane the backarc rifting is inversely proportional to the depth of the decollement on the other hand along e or ne directed subduction zones few backarc basins form e g aegean andaman and can be explained by the velocity gradient within the hangingwall lithosphere separated into two plates when referring to the mantle the kinematics of subduction zones can be computed either in the deep or in the shallow hotspot reference frames the subduction hinge is mostly stationary being the slab anchored to the mantle along w directed subduction zones whereas it moves w or sw ward along e or ne directed subduction zones surprisingly along e or ne directed subduction zones the slab moves out of the mantle i e the slab slips relative to the mantle opposite to the subduction direction kinematically this subduction occurs because the upper plate overrides the lower plate pushing it down into the mantle as an example the hellenic slab moves out relative to the mantle i e sw ward opposite to its subduction direction both in the deep and shallow hotspot reference frames in the shallow hotspot reference frame upper and lower plates move westward relative to the mantle along all subduction zones this kinematic observation casts serious doubts on the slab negative buoyancy as the primary driving mechanism of subduction and plate motions w directed subduction zones rather provide about 2 3 times larger volumes of lithosphere re entering into the mantle and the slab is pushed down this opposite behavior is consistent with the down dip extension seismicity along e ne directed subduction zones and the frequent down dip compression along the w directed subduction zones subduction kinematics shows that plate velocity is not dictated by the rate of subduction along the w directed subduction zones the rate of subduction is rather controlled i by the hinge migration due to the slab interaction with the easterly trending horizontal mantle wind along the global tectonic mainstream ii by the far field plate velocities and iii by the value of negative buoyancy of the slab relative to the country mantle alternatively e ne nne directed subduction zones have rates of sinking chiefly determined i by the far field velocity of plates and ii by the value of negative buoyancy of the slab relative to the country mantle along this type of subduction the subduction hinge generally advances e ne ward toward the upper plate decreasing the subduction rate but it moves w sw ward relative to the mantle all this indicates that subduction zones have different origin as a function of their geographic polarity and the subduction process is more a passive feature rather than being the driving mechanism of plate motions a rotational component combined with mantle density and viscosity anisotropies seems more plausible for generating the global tuning in the asymmetry of subduction zones

once again once again tidal friction topex poseidon t p altimetry has reopened the problem of how tidal dissipation is to be allocated there is now general agreement of a m2 dissipation by 2 5 terawatts 1 tw 1012 w based on four quite separate astronomic observational programs allowing for the bodily tide dissipation of 0 1 tw leaves 2 4 tw for ocean dissipation the traditional disposal sites since jeffreys 1920 have been in the turbulent bottom boundary layer bbl of marginal seas and the modern estimate of about 2 1 tw is in this tradition but the distribution among the shallow seas has changed radically from time to time independent estimates of energy flux into the marginal seas are not in good agreement with the bbl estimates t p altimetry has contributed to the tidal problem in two important ways the assimilation of global altimetry into laplace tidal solutions has led to accurate representations of the global tides as evidenced by the very close agreement between the astronomic measurements and the computed 2 4 tw working of the moon on the global ocean second the detection by ray and mitchum 1996 of small surface manifestation of internal tides radiating away from the hawaiian chain has led to global estimates of 0 2 to 0 4 tw of conversion of surface tides to internal tides measurements of ocean microstructure yields 0 2 tw of global dissipation by pelagic turbulence away from topography we propose that pelagic turbulence is maintained by topographic scattering of barotropic into baroclinic tidal energy via internal tides and internal waves previous estimates by baines 1974 baines 1982 of this conversion along 150 000 km of continental coastlines gave a negligible 0 02 tw evidently the important conversion takes place along mid ocean ridges the maintenance of the abyssal global stratification requires a much larger expenditure of power 2 tw versus 0 2 tw this is usually attributed to wind forcing if tidal power is to play a significant role here then the bbl estimates need to be reduced the challenge is to estimate dissipation from the energy flux divergence in the t p adjusted tidal models without prior assumptions concerning the dissipation processes

the sylvester allochthon upper paleozoic marginal basin and island arc terranes in northern british columbia the sylvester allochthon is a composite klippe of upper paleozoic ophiolitic island arc and pericratonic assemblages which rests directly on the cassiar terrane a displaced sliver of ancestral north america each tectonic assemblage occurs at a distinct and consistent structural level within the allochthon they are assigned respectively to the slide mountain harper ranch and yukon tanana terranes the sylvester allochthon provides a view of the structural relationships between these terranes prior to early cretaceous early tertiary strike slip dismemberment as well as possible sedimentological links to late paleozoic north america slide mountain terrane assemblages designated divisions i and ii form the lowest structural panels chert quartz sandstones are interbedded with lower mississippian deep water sediments in division i and ocean floor basalts and deep water sediments in division ii they are similar in age and character to sandstones in the autochthonous earn group division ii as

eclogite from central yukon a record of subduction at the western margin of ancient north america eclogite occurring in central yukon at faro and near last peak as lenses interleaved with muscovite quartz blastomylonite has the chemical and field characteristics of group c rocks from sigmoidal inclusion trails in garnet from geothermometry and geobarometry and from mineral parageneses the eclogite is inferred to have a crustal protolith and to have followed a hysteretic subduction cycle p t trajectory transformation of basic igneous rock into schist was followed by eclogite metamorphism during which pressure was at least 1000 mpa and temperature was between 600 and 700 c uplifting involved passage through the stability field of glaucophane the eclogite and its host rocks were then subjected to greenschist fades metamorphism and deformation with temperature at approximately 400 c the rocks were emplaced as thrust sheets against or onto the western north american cratonal margin the tectonic boundary ranges from nearly vertical where it is outlined by a zone of steeply dipping melange t

devonian mississippian sinistral transcurrent faulting along the cratonic margin of western north america a hypothesis in the northern canadian cordillera three major proterozoic assemblages show a distinct sinistral separation along the long lived richardson hess fault zone it is suggested that this separation resulted from displacements along a mid paleozoic sinistral fault system connecting the devonian mississippian ellesmerian orogen of the arctic with the antler orogen of the western united states composite displacement of possibly hundreds of kilometres along this fault system created transpressional and transtensional deformation along the western outer margin of the north american craton deformation was accompanied by eastward progradation of turbiditic chert quartz arenites local igneous activity and exhalative ore deposition extensive late mesozoic and cenozoic compression and extension probably greatly modified mid paleozoic fault related deformation patterns

tectonic affinity of nisutlin and anvil assemblage strata from the teslin tectonic zone northern canadian cordillera constraints from neodymium isotope and geochemical evidence we present geochemical and isotopic data for nisutlin assemblage metasedimentary rocks and anvil assemblage greenstones from the teslin tectonic zone of the northern canadian cordillera this study aims to establish the tectonic setting of formation for the sedimentary and basaltic protoliths of these highly deformed and metamorphosed rocks and thereby place constraints on the origin of these enigmatic rocks for which differing tectonic models have been proposed for the nisutlin assemblage metasedimentary rocks the geochemical and isotopic data show that two widely different source regions contributed detritus to the original sediments one source region was felsic upper crustal material with nd isotopic compositions compatible with ultimate derivation from the north american continent depleted mantle model age tdm 2 5 2 8 ga the second source region is deduced to be chemically primitive crust basaltic andesitic with a short crustal residence history 0 9 ga for the anvil assemblage greenstones immobile trace element abundances are dissimilar to within plate oceanic arc and normal mid ocean ridge basalts and similar to calc alkaline basalts in active continental margin settings we interpret the paleosetting for the nisutlin assemblage to be at the outermost margin of the ancestral north american continent in an area which received detrital input from the distal north american craton in the early paleozoic however this area also received detritus from a chemically and isotopically juvenile magmatic arc source a source type not known from paleozoic metasedimentary rocks from the miogeoclinal sequence on the basis of similar nd isotopic relationships recorded elsewhere in deformed paleozoic rocks of the orogen we infer that these geochemical signals reflect tectonic processes of regional extent the trace element geochemistry of the anvil assemblage greenstones does not support a correclation with known paleozoic greenstones of the slide mountain terrane which some tectonic models have advocated

asthenosphere rheology inferred from observations of the 2012 indian ocean earthquake the concept of a weak asthenospheric layer underlying earth s mobile tectonic plates is fundamental to our understanding of mantle convection and plate tectonics however little is known about the mechanical properties of the asthenosphere the part of the upper mantle below the lithosphere underlying the oceanic crust which covers about 60 per cent of earth s surface great earthquakes cause large coseismic crustal deformation in areas hundreds of kilometres away from and below the rupture area subsequent relaxation of the earthquake induced stresses in the viscoelastic upper mantle leads to prolonged postseismic crustal deformation that may last several decades and can be recorded with geodetic methods the observed postseismic deformation helps us to understand the rheological properties of the upper mantle but so far such measurements have been limited to continental plate boundary zones here we consider the postseismic deformation of the very large moment magnitude 8 6 2012 indian ocean earthquake to provide by far the most direct constraint on the structure of oceanic mantle rheology in the first three years after the indian ocean earthquake 37 continuous global navigation satellite systems stations in the region underwent horizontal northeastward displacements of up to 17 centimetres in a direction similar to that of the coseismic offsets however a few stations close to the rupture area that had experienced subsidence of up to about 4 centimetres during the earthquake rose by nearly 7 centimetres after the earthquake our three dimensional viscoelastic finite element models of the post earthquake deformation show that a thin 30 200 kilometres low viscosity having a steady state maxwell viscosity of 0 5 10 1018 pascal seconds asthenospheric layer beneath the elastic oceanic lithosphere is required to produce the observed postseismic uplift

absence of earthquake correlation with earth tides an indication of high preseismic fault stress rate because the rate of stress change from the earth tides exceeds that from tectonic stress accumulation tidal triggering of earthquakes would be expected if the final hours of loading of the fault were at the tectonic rate and if rupture began soon after the achievement of a critical stress level we analyze the tidal stresses and stress rates on the fault planes and at the times of 13 042 earthquakes which are so close to the san andreas and calaveras faults in california that we may take the fault plane to be known we find that the stresses and stress rates from earth tides at the times of earthquakes are distributed in the same way as tidal stresses and stress rates at random times while the rate of earthquakes when the tidal stress promotes failure is 2 higher than when the stress does not this difference in rate is not statistically significant this lack of tidal triggering implies that preseismic stress rates in the nucleation zones of earthquakes are at least 0 15 bar h just preceding seismic failure much above the long term tectonic stress rate of 10 4 bar h

rift asymmetry and continental uplift 1 the topography of ocean ridges and rifts show a distinct asymmetry the eastern sides of the east pacific rise the mid atlantic ridge and the nw indian ridge are on average 100 300 m more elevated than the conjugate flank to the west the asymmetry is maintained when bathymetry is plotted versus the square root of crustal age a comparable topographic asymmetry occurs in the red sea and baikal rifts where the eastern continental shoulders are more elevated we suggest that depleted and lighter asthenosphere generated below the ocean ridge was shifted eastward relative to the lithosphere determining a density deficit below the eastern flank the eastward migration of the lighter atlantic asthenosphere below the african continent could eventually have contributed to the anomalous postrift uplift of africa this model suggests that the westward drift of the lithosphere relative to the underlying mantle might be a global phenomenon

the behaviour of so called immobile elements in hydrothermally altered rocks associated with volcanogenic submarine exhalative ore deposits evidence is available that some elements notably zr tio2 y sc ce and nb are largely immobile during the alteration of volcanic rocks owing to metamorphism hydrothermal events and weathering e g floyd and winchester 1978 however it is shown by reference to analyses of rocks from the environment of five volcanogenic massive sulphide bodies that while zr tio2 and ce are mostly immobile even during intense hydrothermal alteration y and particularly sc and nb may be extremely mobile when elements are removed by solution in a hydrothermal fluid it seems that reaction rates are such that these elements are almost totally removed from the rock therefore of the so called immobile trace elements only zr and tio2 may be used with any reliability to identify the degree of magmatic differentiation in an hydrothermally altered rock however if an element has been mobile it is usually readily identified as having moved

evolution of the yukon tanana terrane evidence from southeastern yukon territory the yukon tanana terrane ytt in southeastern yukon consists predominantly of a mid paleozoic volcanic plutonic arc assemblage built on continental crust the ytt had experienced strong deformation and metamorphism by late triassic time by mid cretaceous the metamorphic complex and late triassic clastic rocks derived from it were imbricated with middle and upper paleozoic ophiolitic sheets the ytt differs markedly from adjacent parts of the north american continental margin in both its depositional and tectonic histories the composition and tectonic history of the ytt is comparable to that of the kootenay and barkerville terranes of southern and central british columbia from which the ytt may have been displaced

space geodesy validation of the global lithospheric flow summary space geodesy data are used to verify whether plates move chaotically or rather follow a sort of tectonic mainstream while independent lines of geological evidence support the existence of a global ordered flow of plate motions that is westerly polarized the terrestrial reference frame trf presents limitations in describing absolute plate motions relative to the mantle for these reasons we jointly estimated a new plate motions model and three different solutions of net lithospheric rotation considering the six major plate boundaries and variable source depths of the main pacific hotspots we adapted the trf plate kinematics by global space geodesy to absolute plate motions models with respect to the mantle all three reconstructions confirm i the tectonic mainstream and ii the net rotation of the lithosphere we still do not know the precise trend of this tectonic flow and the velocity of the differential rotation however our results show that assuming faster pacific motions as the asthenospheric source of the hotspots would allow the best lithospheric net rotation estimate is 13 4 0 7 cm yr 1 this superfast solution seems in contradiction with present knowledge on the lithosphere decoupling but it matches remarkably better with the geological constraints than those retrieved with slower pacific motion and net rotation estimates assuming faster pacific motion it is shown that all plates move orderly westward along the tectonic mainstream at different velocities and the equator of the lithospheric net rotation lies inside the corresponding tectonic mainstream latitude band 7 defined by the 1 confidence intervals

viscosity of oceanic asthenosphere inferred from remote triggering of earthquakes a sequence of large interplate earthquakes from 1952 to 1965 along the aleutian arc and kurile kamchatka trench released accumulated stresses along nearly the entire northern portion of the pacific plate boundary the postseismic stress evolution across the northern pacific and arctic basins calculated from a viscoelastic coupling model with an asthenospheric viscosity of 5 x 10 17 pascal seconds is consistent with triggering of oceanic intraplate earthquakes temporal patterns in seismicity at remote plate boundaries and space based geodetic measurements of anomalous velocity over an area 7000 by 7000 kilometers square during the 30 year period after the sequence

influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions the influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions has been investigated by performing a series of high temperature triaxial compression experiments samples with melt fractions of 0 02 0 12 were deformed under water saturated conditions at temperatures between 1373 and 1473 k and a confining pressure of 300 mpa in a gas medium apparatus at constant differential stress and temperature the rate of deformation increased rapidly but systematically with increasing melt fraction in the diffusion creep regime at a given differential stress samples with melt fractions of 0 02 and 0 12 deformed a factor of 2 and 20 respectively faster than a melt free sample in the dislocation creep regime a sample with a melt fraction of 0 12 deformed a factor of 40 faster than a melt free sample for partially molten olivine basalt aggregates deformed under hydrous conditions the dependence of creep rate on melt fraction can be expressed in the form 0 exp where 26 for diffusion creep and 31 for dislocation creep the results of this study combined with reasonable estimates for the spatial variation in the concentrations of water and melt as well as for the geotherm and the activation volume for creep provide constraints on the viscosity structure of earth s upper mantle as an example we present a viscosity profile for the mantle wedge above a subducting plate demonstrating that the viscosity in that region can vary by 3 orders of magnitude over a depth of 60 km due to the combined effects of water and melt weakening

atmospheric pressure loading corrections applied to gps data at the observation level 1 space geodetic techniques can detect elastic deformation of the earth caused by atmospheric pressure loading atml however it has not yet been demonstrated whether these surface displacements should be accounted for at the time of reduction of the observations or by applying time averaged values to the coordinates after the analysis of the observations an analysis of the power spectral density of the atml predicted vertical deformation shows that aside from the diurnal and semi diurnal periods there is very little power in the sub daily frequencies the present tidal atml models improve the analysis at sites near the equator but seem to degrade the height estimates elsewhere the majority of the non tidal deformation can be modelled by applying a daily averaged correction to daily estimates of coordinates but a greater improvement in height rms is found if non tidal atml is applied at the observation level

blueschist and eclogite in mylonitic allochthons ross river and watson lake areas southeastern yukon two new occurrences of eclogite associated with mylonitic rocks are documented the first near ross river is in a quartz rich metasedimentary host that includes glaucophane schist the host forms part of a belt of high pressure rocks more than 50 km long and several kilometres wide between ross river and faro in the second occurrence north of watson lake eclogite is associated with mafic and ultramafic rocks occurring in a klippe more than 100 km2 in area that rests on unmetamorphosed triassic rocks of the north american miogeocline geothermobarometry shows that the eclogites were metamorphosed at 10 15 kb 1 kb 100 mpa between 470 and 750 c these peak conditions are comparable to those for other eclogites in the yukon and adjacent alaska the age of metamorphism and mylonitization is triassic or older the high pressure rocks occur at the leading edge of the most inboard accreted terrane along its boundary with north american miogeoclinal strata over a length of several hundred kilometres t

high resolution stratigraphy and sedimentary evolution of coarse grained canyon filling turbidites from the upper cretaceous transgressive megasequence campos basin offshore brazil abstract coniacian to lower maastrichtian coarse grained turbidites fill intra slope fault controlled canyons in the campos basin off shore brazil they form part of an upper albian to lower paleocene transgressive succession characterized by onlapping deepening upward sedimentation throughout the eastern brazilian margin in the carapeba and pargo crp pg oil fields the turbidites consist mainly 95 of graded beds without any other sedimentary structures individual beds are up to 12 m thick and are composed of small pebble 2 cm to granule rich sandstones and medium to very coarse sandstones the finer grained portions of these graded beds show better sorting and higher porosity and these characteristics can be recognized in density logs use of 92 density logs calibrated w th 13 cores permitted the mapping of 198 coarse grained turbidites in the crp pg turbidite system the turbidites form eight thinning and fining upward facies successions some bounded by regional unconformities or local erosion surfaces the successions are 27 140 m thick and contain 7 58 turbidites their durations are estimated to be between 0 4 0 9 m y they form 1 12 km wide tabular or linguoid sandstone bodies in which the younger or more distal turbidites become finer grained thinner bedded and more discontinuous upsection and downcanyon the successions are stacked in an overall retrogradatioual pattern for at least 20 km recording the backfilling of the crp pg canyon turbidites in the crp pg area were probably deposited during falls of relative sea level that punctuated the overall transgressive setting of the late cretaceous and early tertiary there is a mismatch between the number of successions eight and the number of time equivalent third order fluctuations of relative sea level four and part of a fifth haq et al 1988 suggesting that eustatic sea level fluctuation was not the dominant control on most of the successions cross sections and isopach maps of the successions do not suggest internal channeling and a channel fill origin for the fining and thinning upward successions seems unlikely we therefore suggest that episodic tectonic reactivation in the uplifted precambrian source area and faulted basin margin led to relatively abr pt increases in the volume of sediment supplied to the head of the canyon across a narrow shelf steady denudation and decreasing supply of sediment led to formation of the fining and thinning upward successions

the slide mountain terrane and the structural evolution of the finlayson lake fault zone southeastern yukon the finlayson lake fault zone forms a fundamental but little studied tectonic boundary between strata of autochthonous north america and the accreted slide mountain and yukon tanana terranes in southeastern yukon a structural and petrologic study was undertaken to examine the depositional environment of the slide mountain terrane its tectono thermal evolution in the fault zone and its relationship with the yukon tanana terrane the slide mountain and yukon tanana terranes are divisible into units dominated by metavolcanic and metasedimentary rocks field observations and whole rock geochemistry indicate that slide mountain greenstone is ocean floor basalt deposited in a deep submarine basin with a proximal terrigenous sediment influx either a marginal or ocean basin setting is supported by the data slide mountain greenstone is thrust northeastward over metasedimentary rocks of slide mountain terrane and southwestward over rocks of the yukon tanana terrane regional metamorphic grade ranges from su

metabasites from the ktb oberpfalz target area bavaria geochemical characteristics and examples of mobile behaviour of immobile elements abstract major trace and rare earth element chemistry studies of metabasite intercalations within different tectonic units of the east bavarian crystalline basement leads to the following geochemical classification the flaser amphibolites of the erbendorf vohenstrauss zone zev exhibit an enriched e morb or intraplate like tholeiitic character whereas the schistose and striped amphibolites of the zev and of the tirschenreuth mahring zone show n morb compositions the metagabbros of the zev are transitional between these two types the metabasites of the erbendorf greenschist zone are similar to modern island arc basalts tholeiitic to calc alkaline the fichtelgebirge crystalline complex contains amphibolites of enriched tholeiitic to alkaline i e intraplate character in most of the investigated metabasites a post basaltic post gabbroic mobilization of the trace elements cannot be recognized an exception is ba which is generally enriched this may be due to pre metamorphic hydrothermal alteration processes and or to a synmetamorphic chemical exchange with adjacent metasediments the contact metamorphic overprint of some flaser amphibolites from the zev by the intrusion of the variscan falkenberg granite led to enrichment in li rb k and w a simultaneous depletion in ca sr cr and ni and a decrease in the k rb ratio nb ce p zr ti and v scatter in a much wider range than in the unaffected flaser amphibolites although with no clear tendency for enrichment or depletion a mobilization of p and the lree s in some schistose and striped amphibolites of the zev and in the contact metamorphosed flaser amphibolites is presumably a result of post granitic hydrothermal alteration which is indicated by enrichment of as as a pathfinder element

tidal modulation of plate motions abstract while mantle convection is a fundamental ingredient of geodynamics the driving mechanism of plate tectonics remains elusive are plates driven only from the thermal cooling of the mantle or are there further astronomical forces acting on them gps measurements are now accurate enough that on long baselines both secular plate motions and periodic tidal displacements are visible the now 20 year long space geodesy record of plate motions allows a more accurate analysis of the contribution of the horizontal component of the body tide in shifting the lithosphere we review the data and show that lithospheric plates retain a non zero horizontal component of the solid earth tidal waves and their speed correlates with tidal harmonics high frequency semidiurnal earth s tides are likely contributing to plate motions but their residuals are still within the error of the present accuracy of gnss data the low frequency body tides rather show horizontal residuals equal to the relative motion among plates proving the astronomical input on plate dynamics plates move faster with nutation cyclicities of 8 8 and 18 6 years that correlate to lunar apsides migration and nodal precession the high frequency body tides are mostly buffered by the high viscosity of the lithosphere and the underlying mantle whereas low frequency horizontal tidal oscillations are compatible with the relaxation time of the low velocity zone and can westerly drag the lithosphere over the asthenospheric mantle variable angular velocities among plates are controlled by the viscosity anisotropies in the decoupling layer within the low velocity zone tidal oscillations also correlate with the seismic release

geology of the hazelton volcanic belt in british columbia implications for the early to middle jurassic evolution of stikinia the hazelton group is an early to middle jurassic volcanic and sedimentary succession that was deposited on the stikine terrane stikinia of the canadian cordillera the group is distributed across the entire width of stikinia a distance of about 300 km prior to post hazelton contractional deformation the width across which volcanism had occurred was at least 450 km a review of chronologic and stratigraphic information corroborates an earlier suggestion that the hazelton group formed as a pair of coeval partly subaerial volcanic chains separated by a subsiding mainly sedimentary marine basin hazelton trough the trough developed in response to extension of stikinia during the latest triassic and or earliest jurassic and remained the locus of moderate extension during deposition of the hazelton group volcanic rocks of the group are diverse comprising subaerially and subaqueously deposited lavas and volcaniclastic rocks of mafic to felsic composition calc alkaline to tholeiitic characteristics and depletion of high field strength elements relative to alkali and alkaline earth elements indicate a subduction related origin the degree of alkalinity medium to high k is fairly consistent throughout the group the original width across which volcanism occurred is two to five times greater than widths of modern volcanic arcs the anomalous width cannot be accounted for by time transgression of a single volcanic arc because the two volcanic chains were coeval extremely low angle subduction of a single oceanic plate is also rejected as an explanation because alkalinity does not differ significantly between the two volcanic chains genesis of the hazelton group above a single subduction zone is therefore considered unlikely we propose a model in which a pair of oceanic plates were subducted beneath stikinia from opposite sides in a manner analagous to the tectonic regime of the philippine archipelago subduction angles of the two downgoing plates are postulated to be 30 to a depth of 150 km a configuration consistent with a postulated forearc width of about 175 km on each side stikinia is thereby considered to have been an 800 km wide microplate on which two island arcs developed the hazelton trough was a back arc region common to both volcanic arcs during deposition of the hazelton group stikinia was not part of the intermontane superterrane an amalgam composed of more inboard terranes rather it belonged to an oceanic microplate that accreted to the inboard terranes in late early jurassic to early middle jurassic time during which hazelton volcanism waned and ended

evidence for tidal triggering of earthquakes as revealed from statistical analysis of global data 1 we observe tidal triggering of earthquakes by measuring the correlation between the earth tide and earthquake occurrence we used the times locations and focal mechanisms of the 9350 globally distributed earthquakes with magnitude 5 5 or larger from the harvard centroid moment tensor catalog the tidal stress was theoretically computed by using the preliminary reference earth model and a recent ocean tide model nao 99b we considered the shear stress on the fault plane and the trace of stress tensor j1 defining the tidal phase angle at the occurrence time for each earthquake we statistically tested the phase selectivity using the schuster s method for all the earthquakes no significant correlation is found between the earth tide and earthquake occurrence both for the shear stress and for j1 by classifying the data set according to fault types however we find a high correlation with the shear stress for reverse fault type the correlation is particularly clear for shallow and smaller earthquakes of this type significant correlation with j1 also appears for larger earthquakes of reverse fault type and for shallow and larger ones of normal fault type we find no correlation for strike slip type for all the cases of high correlation earthquakes tend to occur when the tidal stress accelerates the fault slip indicating that high correlation is not coincidental but is physically justified this result strongly suggests that a small stress change due to the earth tide encourages earthquake occurrence when the stress in the future focal area is near a critical condition

the westward drift of the lithosphere a rotational drag net westward rotation of the lithosphere relative to the underlying mantle is a controversial phenomenon fi rst attributed to tidal effects and later to the dynamics of mantle convection in spite of a number of independent geological and geophysical arguments for westward tectonic drift this phenomenon has received little recent attention we suggest that this differential rotation is a combined effect of three processes 1 tidal torques act on the lithosphere generating a westerly directed torque decelerating earth s spin 2 the downwelling of the denser material toward the bottom of the mantle and in the core slightly decreases the moment of inertia and speeds up earth s rotation only partly counterbalancing the tidal drag 3 thin 3 30 km layers of very low viscosity hydrate channels occur in the asthenosphere it is suggested that shear heating and the mechanical fatigue self perpetuate one or more channels of this kind which provide the necessary decoupling zone of the lithosphere

plate tectonics and net lithosphere rotation over the past 150 my we have developed an improved model of global digital palaeo plate boundaries and plate motion to describe the distribution and history of plates since the late jurassic from this history we computed net lithospheric rotation nr through time confirming the so called westward drift but only for the past 30 myr the nr has significantly smaller magnitudes 0 13 my past 5 my than for some other plate models it averages to 0 11 0 03 my for the past 50 my with a small but systematic increase toward the present the westward drift seen only for the past 30 my is attributed to the increased dominance of a steadily growing and accelerating pacific plate nr shows peaks with time but only an early tertiary peak of 0 33 my when the indian plate was undergoing the largest known acceleration deceleration can be interpreted with some confidence we find a linear decreasing trend in net rotation over the past 150 my but attribute this trend to increasing reconstruction uncertainties back in time as subduction consumed more than half of the oceanic crust since the jurassic after removing a linear time trend we find a nr average of about 0 12 my for the past 150 my

melanges through time life cycle of the world s largest archean melange compared with mesozoic and paleozoic subduction accretion collision melanges abstract melanges represent a significant component of collisional and accretionary orogenic belts we present a comparison of subduction accretion melanges of different ages to test how melange forming processes at convergent margins changed through time we describe the mesozoic mchugh melange in alaska and the paleozoic proto tethyan laohushan melange of the qilian orogenic belt of the alpine himalayan chain together with documentation of a neoarchean melange that marks the suture between the eastern block and central orogenic belt of the north china craton ncc the mchugh is a classic accretionary melange that has not yet experienced a collision and the laohushan is an accretionary collisional melange with structures related to both stages of its evolution we compare the characteristics of these melanges with the world s largest archean melange the newly documented circa 2 5 ga 1600 km long jianping zunhua zanhuang dengfeng jzzd melange of the north china craton the jzzd is a classical melange in terms of map patterns lithological relations structural characteristics including mixed rock types of different ages origins and metamorphic histories and preserves both paired metamorphic features and local blocks preserving ultra high pressure uhp assemblages it shows high stratal disruption with both block in matrix and highly mixed thrust bounded tectonic slices types of map patterns the melange is part of an arc accretionary complex that was emplaced over a 2 7 2 5 ga passive margin sequence on the western edge of the eastern block of the ncc at 2 5 ga the frontal zone of the accretionary complex marks the suture between the eastern block and an oceanic arc terrane in the central orogenic belt cob and exhibits significant along strike n s variations in the north the jianping pyroxenite melange contains blocks of 2 52 ga metapyroxenite metabasalt tonalite trondhjemite granodiorite diorite ttgd gneisses in a metasedimentary and serpentinite matrix intruded by 2 49 2 47 ga plutons metamorphosed to amphibolite granulite conditions at 2 47 ga the zunhua shangying ophiolitic melange contains relatively intact 2 5 ga ophiolitic sheets in a 2 5 ga metasedimentary melange intruded by 2 48 ga granitic dikes the zunhua ultra high pressure uhp podiform chromite melange has blocks of pillow basalt bif dikes gabbros pyroxenite harzburgite some with 2 55 ga podiform chromites in dunite envelopes enclosed in a 2 52 2 46 ga metasedimentary matrix metamorphosed and intruded by granitic dikes at 2 46 ga the chromites and dunite pods formed through reaction of a boninitic melt and harzburgite during subduction initiation bewtween 2 6 2 55 ga uhp conditions are documented by tio2 ii inclusions in chromites indicating subduction to at least 270 km depth the zanhuang melange includes blocks of metapsammites metagabbros metabasalts and ultramafic rocks in a metapelitic matrix intruded by 2 49 2 54 ga granites then imbricated with 2 65 ga marble metapelite quartzite of the passive margin of the eastern block the dengfeng melange includes upper plate blocks of metagabbro metabasalt bif and felsic rocks in a sandy to pelitic matrix thrust over a turbiditic broken formation melange unit in the east circa 2 5 ga metamorphic conditions record a relatively high t p anatexis 950 c gpa in the west whereas the central part of the belt records intermediate t p metamorphism

mantle updrafts and mechanisms of oceanic volcanism convection in an isolated planet is characterized by narrow downwellings and broad updrafts consequences of archimedes principle the cooling required by the second law of thermodynamics and the effect of compression on material properties a mature cooling planet with a conductive low viscosity core develops a thick insulating surface boundary layer with a thermal maximum a subadiabatic interior and a cooling highly conductive but thin boundary layer above the core parts of the surface layer sink into the interior displacing older colder material which is entrained by spreading ridges magma characteristics of intraplate volcanoes are derived from within the upper boundary layer upper mantle features revealed by seismic tomography and that are apparently related to surface volcanoes are intrinsically broad and are not due to unresolved narrow jets their morphology aspect ratio inferred ascent rate and temperature show that they are passively responding to downward fluxes as appropriate for a cooling planet that is losing more heat through its surface than is being provided from its core or from radioactive heating response to doward flux is the inverse of the heat pipe mantle plume mode of planetary cooling shear driven melt extraction from the surface boundary layer explains volcanic provinces such as yellowstone hawaii and samoa passive upwellings from deeper in the upper mantle feed ridges and near ridge hotspots and others interact with the sheared and metasomatized surface layer normal plate tectonic processes are responsible both for plate boundary and intraplate swells and volcanism

lead isotopic fingerprinting of tectono stratigraphic terranes east central alaska common lead isotopic compositions have been determined on feldspars from meta igneous rocks from nine tectono stratigraphic terranes or subterranes in east central alaska most of the terranes have distinct and well defined signatures in terms of isotopic composition thus most can be distinguished on conventional lead isotopic diagrams lead isotopic ratios provide evidence for 1 possible sources for the igneous rocks 2 time of metamorphism 3 correlation of terrane fragments and 4 delineation of juxtaposed terranes determination of lead isotopic ratios from igneous rocks can be useful in characterizing tectono stratigraphic terranes as to mantle or crustal origin and in correlation particularly where terrane relationships are enigmatic

no net rotation model of current plate velocities incorporating plate motion model nuvel 1 we present nnr nuvel1 a model of plate velocities relative to the unique reference frame defined by requiring no net rotation of the lithosphere while constraining relative plate velocities to equal those in global plate motion model nuvel 1 demets et al 1990 differences between nnr nuvel1 and no net rotation plate motion model am0 2 minster and jordan 1978 are as large as 15 mm yr in nnr nuvel1 the pacific plate rotates in a right handed sense relative to the no net rotation reference frame at 0 67 m y about 63 s 107 e this rotation nearly parallels but is 32 slower than the pacific hotspot euler vector of hs2 nuvel1 which is a global model of plate hotspot velocities constrained to consistency with nuvel 1 gripp and gordon 1990 at hawaii the pacific plate moves relative to the no net rotation reference frame at 70 mm yr which is 25 mm yr slower than the pacific plate moves relative to the hotspots differences between nnr nuvel1 and hs2 nuvel1 are described completely by a right handed rotation of 0 33 m y about 49 s 65 e the 99 confidence ellipsoids for plate hotspot motion in model hs2 nuvel1 exclude the corresponding euler vectors from model nnr nuvell thus the no net rotation reference frame differs significantly from the hotspot reference frame if the difference between reference frames is caused by motion of the hotspots relative to a mean mantle reference frame then hotspots beneath the pacific plate move with coherent motion towards the east southeast alternatively the difference between reference frames may show that the uniform drag no net torque reference frame which is kinematically equivalent to the no net rotation reference frame is based on a dynamically incorrect premise possible exceptions to the assumption of uniform drag include a net torque on the lithosphere due to attached subducting slabs and greater resistance to plate motion beneath continents than beneath oceans

geological evidence for a global tectonic polarity inferences about plate motions over the past 40 ma based on structural and geodetic data suggest that there is a coherent movement direction on a global scale moreover a westward drift of the lithosphere relative to the asthenosphere is indicated by plate motions in the hot spot reference frame independent geological observations such as the different styles of deformation in thrust belts associated with subduction following or opposing the relative eastward or northeastward mantle flow also support this global tectonic polarity unfortunately most hot spot reference frames are based on assumptions which strongly limit their validity for example many combine magmatic sources originating from different depths in the mantle including hot spots located along oceanic ridges which are not fixed relative to one another using a hot spot reference frame filtered to exclude shallow hot spots and anomalous wet spots we would predict a much higher relative westward drift of the lithosphere plate motions are not random rather that they are controlled by the relative motion between lithosphere and asthenosphere and by gradients in lithospheric thickness and composition triangular shaped plates may experience rotations resulting from differential drag at the base of the lithosphere with respect to the asthenosphere e g the clockwise rotation of south america plates appear to follow an undulatory pattern of motion on a global scale and their poles of rotation fall into a main cone located near the earth s rotation poles plate rotations induced by triangular shape differential basal drag or lithospheric anisotropies along subduction zones may generate the scattered distribution of euler poles this might have inhibited the recognition of a coherent global tectonic pattern

review of radiometric data from the yukon crystalline terrane alaska and yukon territory the results of more than 20 years of geochronological studies in the yukon crystalline terrane in east central alaska and the western yukon territory suggest at least six igneous and thermal metamorphic events plutonism during mississippian early jurassic mid cretaceous late cretaceous and early tertiary times is indicated evidence also indicates that mississippian early jurassic late early cretaceous and late cretaceous thermal metamorphic events have affected parts of the terrane the western part of the terrane was affected by a significant regional metamorphic event in late early cretaceous time followed by a terrane wide mid cretaceous plutonic event the pattern of k ar ages allows division of the terrane into domains bounded by northeast trending lineaments

tectonic significance of the kootenay terrane southeastern canadian cordillera an alternative model new field observations from the northern termination of the kootenay arc show that lower paleozoic rocks assigned to the kootenay terrane are depositionally linked to and conformable with underlying rocks that form part of the north american cordilleran miogeocline accordingly models involving an allochthonous origin for the kootenay terrane should be reevaluated the presence of coarse clastic rocks and mafic volcanic rocks within the lower paleozoic sequence of the kootenay arc is explained in terms of intermittent early paleozoic extensional deformation such as is well documented elsewhere along the cordilleran margin of the north american craton

seasonal and long term vertical deformation in the nepal himalaya constrained by gps and grace measurements 1 we analyze continuous gps measurements in nepal southern side of the himalaya and compare gps results with grace observations in this area we find both gps and grace show significant seasonal variations further comparison indicates that the observed seasonal gps height variation and grace derived seasonal vertical displacement due to the changing hydrologic load exhibit very consistent results for both amplitude and phase for continuous gps stations whose observation time span are longer than 3 years the average wrms reduction is 45 when we subtract grace derived vertical displacements from gps observed time series the comparison for annual amplitudes between gps observed and grace derived seasonal displacements also shows consistent correlation the good seasonal correlation between gps and grace is due to the improved gps processing strategies and also because of the strong seasonal hydrological variations in nepal besides the seasonal signal grace also indicates a long term mass loss in the himalaya region assuming no gia effect this mass loss therefore will lead to crustal uplift since the earth behaves as an elastic body we model this effect and remove it from gps observed vertical rates with a 2d dislocation model most gps vertical rates especially in the central part of nepal can be interpreted by interseismic strain from the main himalayan thrust and several exceptions may indicate the complexity of vertical motion in this region and some potential local effects

hierarchical geocellular facies modelling of a turbidite reservoir analogue from the eocene of the ainsa basin ne spain geocellular models of outcrop analogues can provide useful insights into modelling strategies for the subsurface reservoirs a model of the outcropping ainsa slope turbidite system was built to test the effects of different scales of heterogeneity on production in deep water systems the modelling began with a structural reconstruction based primarily upon the outcrop data to remove the post depositional structural relief of the reservoir analogue the facies modelling workflow consisted of three nested stages each corresponding to a different scale a the first scale addressed the deterministic reconstruction of surfaces that bound sedimentary bodies b the second scale related to the modelling of the interfingering at the gradational boundaries of the sedimentary bodies c the third scale reproduced the internal heterogeneity within the sandstone dominated sedimentary bodies flow simulation was used as a dynamic test of the differences in recovery efficiency for the different scales at which the geological heterogeneity was modelled

inner core differential motion confirmed by earthquake waveform doublets we analyzed 18 high quality waveform doublets with time separations of up to 35 years in the south sandwich islands region for which the seismic signals have traversed the inner core as pkp df the doublets show a consistent temporal change of travel times at up to 58 stations in and near alaska and they show a dissimilarity of pkp df coda using waveform doublets avoids artifacts of earthquake mislocations and contamination from small scale heterogeneities our results confirm that earth s inner core is rotating faster than the mantle and crust at about 0 3 degrees to 0 5 degrees per year

influence of tidal forces on the triggering of seismic events tidal stresses are generated in any three dimensional body influenced by an external inhomogeneous gravity field of rotating planets or moons in this paper as a special case stresses caused within the solid earth by the body tides are discussed from viewpoint of their influence on seismic activity the earthquake triggering effects of the moon and sun are usually investigated by statistical comparison of tidal variations and temporal distribution of earthquake activity or with the use of mathematical or experimental modelling of physical processes in earthquake prone structures in this study the magnitude of the lunisolar stress tensor in terms of its components along the latitude of the spherical surface of the earth as well as inside the earth up to the core mantle boundary were calculated for the prem dziewonski and anderson in phys earth planet inter 25 4 297 356 1981 results of calculations prove that stress increases as a function of depth reaching a value around some kpa at the depth of 900 1500 km well below the zone of deep earthquakes at the depth of the overwhelming part of seismic energy accumulation around 50 km the stresses of lunisolar origin are only 0 0 1 0 103 pa despite the fact that these values are much smaller than the earthquake stress drops 1 30 mpa kanamori in annu rev earth planet sci 22 207 237 1994 this does not exclude the possibility of an impact of tidal forces on outbreak of seismic events since the tidal potential and its derivatives are coordinate dependent and the zonal tesseral and sectorial tides have different distributions from the surface down to the cmb the lunisolar stress cannot influence the break out of every seismological event in the same degree the influencing lunisolar effect of the solid earth tides on earthquake occurrences is connected first of all with stress components acting parallel to the surface of the earth the influence of load tides is limited to the loaded area and its immediate vicinity

petrology and tectonic significance of augen gneiss from a belt of mississippian granitoids in the yukon tanana terrane east central alaska an approximately east west trending belt of porphyritic peraluminous granitoids metamorphosed and deformed to augen gneiss is exposed for 400 km across the yukon tanana terrane this belt consists of compositionally texturally and isotopically similar concordant intrusions of augen gneiss in the big delta eagle and tanacross quadrangles of east central alaska in the fiftymile batholith of west central yukon territory and in two batholiths in the offset part of the yukon tanana terrane northeast of the tintina fault in southeastern yukon territory chemical analyses of augen gneiss from widely separated localities within the big delta intrusion suggest that the various samples are related by crystal fractionation comparison of major and trace element data from concordant layers of augen poor gneiss and aplitic gneiss with similar data from adjacent augen gneiss suggests that the layers represent co magmatic sills of more highly differentiated filter pressed melt similarities between elemental abundances particularly those of rare earth elements in augen gneiss from the large bodies in the big delta eagle and tanacross quadrangles alaska and southeastern yukon territory suggest a common origin for these bodies the peraluminous composition of the gneiss its high initial 87 sr 86 sr ratio and high th concentration indicate that the augen gneiss protolith contains a large component of crustal material geochronologic studies of augen gneiss in east central alaska and southeastern yukon territory indicate a mississippian intrusive age and an early proterozoic age for the crustal component the augen gneiss bodies were intruded late in a middle paleozoic volcanic plutonic episode and they may represent a deeply eroded continental magmatic arc regional amphibolite facies metamorphism and mylonitization may have occurred late during the tectonic episode that resulted in intrusion of the porphyritic granitoid protoliths

can earth s rotation and tidal despinning drive plate tectonics abstract we re evaluate the possibility that earth s rotation contributes to plate tectonics on the basis of the following observations 1 plates move along a westerly polarized flow that forms an angle relative to the equator close to the revolution plane of the moon 2 plate boundaries are asymmetric being their geographic polarity the first order controlling parameter unlike recent analysis the slab dip is confirmed to be steeper along w directed subduction zones 3 the global seismicity depends on latitude and correlates with the decadal oscillations of the excess length of day lod 4 the earth s deceleration supplies energy to plate tectonics comparable to the computed budget dissipated by the deformation processes 5 the gutenberg richter law supports that the whole lithosphere is a self organized system in critical state i e a force is acting contemporaneously on all the plates and distributes the energy over the whole lithospheric shell a condition that can be satisfied by a force acting at the astronomical scale assuming an ultra low viscosity layer in the upper asthenosphere the horizontal component of the tidal oscillation and torque would be able to slowly shift the lithosphere relative to the mantle

trace element geochemistry of metabasaltic rocks from the yukon tanana upland and implications for the origin of tectonic assemblages in east central alaska we present major and trace element geochemical data for 27 amphibolites and six greenstones from three structural packages in the yukon tanana upland of east central alaska the lake george assem

on the increasing size of the orogens moving from the alps to the himalayas in the frame of the net rotation of the lithosphere abstract the tectonic equator represents the great circle of the non random mainstream of plate motions and it is inclined about 30 relative to the geographic equator divergence or convergence rates among plates are in average faster along the tectonic equator and they tend to decrease toward the polar areas moving from western europe to eastern asia the mainstream is roughly oriented southwest northeast here we show how this pattern may have played a role in determining the dimension of the alpine himalayas orogenic belt which is increasing in size and thickness moving from west northwest to east southeast i e moving from high latitude to low latitude of the tectonic mainstream of plates the alps are in average 200 250 km wide whereas the himalayas are regularly 1000 km wide moreover due to the westerly polarization of the lithospheric mainstream relative to the mantle either the net rotation or the westward drift of the lithosphere the subduction zones can be differentiated into two types 1 increasing or 2 decreasing the lithospheric thickness the alpine himalayas system pertains to type 1 and it may represent a prototype of the continental lithosphere growth since the archean the increasing size of the orogens moving from the alps to the himalayas is presently concentrated in the northern hemisphere of the tectonic mainstream because subduction type 2 dominated the western margin of the pacific ocean hence preventing continental growth in the southern hemisphere in that longitude range therefore the largest growth of continental crust and mantle lithosphere should have occurred along the tectonic equator but only where type 1 subduction was generated