active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

quaternary palaeolakes in the evolution of semidesert basins with special emphasis on lake bonneville and the great basin u s a abstract this paper reviews attributes of quaternary lakes and lake basins which are often important in the environmental prehistory of semideserts basin floor and basin closure morphometry have set limits on palaeolake sizes lake morphometry and basin drainage patterns have influenced lacustrine processes and water and sediment loads have influenced basin neotectonics information regarding inundated runoff producing and extra basin spatial domains is acquired directly from the palaeolake record including the littoral morphostratigraphic record and indirectly by reconstruction increasingly detailed hypotheses regarding lake bonneville the largest late pleistocene palaeolake in the great basin are subjects for further testing and refinement oscillating transgression of lake bonneville began about 28 ka the highest stage occurred about 15 ka and termination occurred abruptly about 13 ka a final resurgence of perennial lakes probably occurred in many subbasins of the great basin between 11 and 10 ka when the highest stage of great salt lake successor to lake bonneville developed the gilbert shoreline and when the russell shoreline formed 500 600 km away in the carson desert of the lake lahontan basin the highest post gilbert stage of great salt lake which has been one of the few permanent lakes in the great basin during holocene time probably occurred between 3 and 2 ka a set of eighteen general observations regarding geologic aspects of the palaeolake record in semidesert basins is helping to guide quaternary studies in the great basin

late pleistocene and early holocene rivers and wetlands in the bonneville basin of western north america abstract field investigations at dugway proving ground in western utah have produced new data on the chronology and human occupation of late pleistocene and early holocene lakes rivers and wetlands in the lake bonneville basin we have classified paleo river channels of these ages as gravel channels and sand channels gravel channels are straight to curved digitate and have abrupt bulbous ends they are composed of fine gravel and coarse sand and are topographically inverted i e they stand higher than the surrounding mudflats sand channels are younger and sand filled with well developed meander scroll morphology that is truncated by deflated mudflat surfaces gravel channels were formed by a river that originated as overflow from the sevier basin along the old river bed during the late regressive phases of lake bonneville after 12 500 and prior to 11 000 14c yr b p dated samples from sand channels and associated fluvial overbank and wetland deposits range in age from 11 000 to 8800 14c yr b p and are probably related to continued sevier basin overflow and to groundwater discharge paleoarchaic foragers occupied numerous sites on gravel channel landforms and adjacent to sand channels in the extensive early holocene wetland habitats reworking of tools and limited toolstone diversity is consistent with theoretical models suggesting paleoarchaic foragers in the old river bed delta were less mobile than elsewhere in the great basin

the new england batholith constraints on its derivation from nd and sr isotopic studies of granitoids and country rocks abstract nd and sr isotopic compositions are reported for the granitic suites which comprise the late palaeozoic to earliest mesozoic new england batholith of eastern australia some of the granitic suites are typically i type in their mineralogy chemistry and isotopic compositions implying a derivation from igneous infracrustal source rocks whereas other suites have characteristics consistent with a derivation from a protolith which was predominantly sedimentary and relatively felsic s types the i type granitoids of the nundle suite have nd values 3 3 to 6 1 that are amongst the most primitive yet documented for a relatively felsic sio 2 65 plutonic suite and these values imply a derivation from either a depleted upper mantle source or more probably a complex source region involving both volcanic arc rocks and detrital material their compositions are distinctly more primitive than those of the new england super suite which constitutes the permian core of the batholith this extensive super suite comprising granitoids traditionally designated as i type has an overall range in initial nd and sr isotopic compositions of 1 7 to 4 6 and 0 70458 to 0 70624 respectively although the majority of plutons have initial nd isotopic compositions which fall into a very narrow range 1 0 1 5 units this limited range is remarkable considering the extreme lithological diversity and range in chemical composition of the analysed samples sio 2 47 74 and implies a source region of considerable volume having reasonably uniform isotopic compositions but variation in chemistry a similarly uniform source isotopically is also indicated for the s type granitoids of the carboniferous hillgrove suite and carboniferous permian bundarra suite with initial nd values of 0 8 to 2 3 and initial 87 sr 86 sr compositions of 0 70474 to 0 70577 showing only limited ranges five pelites three felsic and four mafic greywackes representing typical country rocks from different stratigraphic levels have initial nd values 1 7 to 6 6 and initial 87 sr 86 sr compositions 0 70378 to 0 70585 which essentially mirror the compositional variation in the granitoids a chemical mineralogical and isotopic bimodality in these sediments indicates two very distinctive sources one felsic rhyodacitic the other relatively mafic andesitic which were separated spatially and temporally in many but not all areas of early to mid palaeozoic new england a model is presented in which the s type granitoids are derived from a predominantly felsic source i e pelites and felsic greywackes whereas some of the granitoids belonging to the new england super suite may have been derived from source rocks consisting of both felsic and mafic sedimentary components the distinction between many s type and i type granitoids in new england is unclear for two principal reasons a because the granitoids and their respective source rocks are relatively young geologically so that their isotopic systems have not evolved to any considerable extent and b because of the intrinsic igneous chemical compositions of any sedimentary component that may be involved in their genesis

the 87sr 86sr ratios of lacustrine carbonates and lake level history of the bonneville paleolake system lakes in the bonneville basin have fluctuated dramatically in response to changes in rainfall temperature and drainage diversion during the quaternary we analyzed tufas and shells from shorelines of known ages in orderto develop a relation between 8 7 sr 8 6 sr ratio of carbonates and lake level which then can be used as a basis for constraining lake level from similar analyses on carbonates in cores carbonates from the late quaternary shorelines yield the following average 8 7 sr 8 6 sr ratios 0 71173 for the stansbury shoreline 22 20 1 4 c ka 1350 m 0 71153 for the bonneville shoreline 15 5 14 5 1 4 c ka 1550 m 0 71175 for the provo shoreline 14 4 14 0 1 4 c ka 1450 m 0 71244 for the gilbert shoreline 10 3 10 9 1 4 c ka 1300 m and 0 71469 for the modern great salt lake 1280 m these analyses show that the 8 7 sr 8 6 sr ratio of lacustrine carbonates changes substantially at low to mid lake levels but is invariant at mid to high lake levels sr isotope mixing models of great salt lake and the bonneville paleolake system were constructed to explain these variations in 8 7 sr 8 6 sr ratios with change in lake level our model of the bonneville system produced a 8 7 sr 8 6 sr ratio of 0 71193 very close to the observed ratios from high shoreline tufa and shell the model verifies that the integration of the southern sevier and beaver rivers with the bear and others rivers in the north is responsible for the lower 8 7 sr 8 6 sr ratios in lake bonneville compared to the modern great salt lake we also modeled the 8 7 sr 8 6 sr ratio of lake bonneville with the upper bear river diverted into the snake river basin and obtained an 8 7 sr 8 6 sr ratio of 0 71414 coincidentally this ratio is close to the observed ratio for great salt lake of 0 71469 this means that 8 7 sr 8 6 sr ratios of 0 714 for carbonate can be produced by climatically induced low lake conditions or by diversion of the upper bear river out of the bonneville basin this model result also demonstrates that the upper bear river had to be flowing into the bonneville basin during highstands of other late quaternary lake cycles carbonates from the little valley 130 160 ka and cutler dam 59 5 ka lake cycles returned 8 7 sr 8 6 sr ratios of 0 71166 and 0 71207 respectively and are too low to be produced by a lake without the upper bear river input

weathering of the oporto granite geotechnical and physical properties abstract this paper characterizes the weathering products of the two mica oporto granite in terms of its mineralogical chemical geotechnical and physical properties this information is used to identify a physical property that can be used as an index of the degree of weathering and to estimate other properties in outcrop the oporto granite is always weathered and weathering profiles frequently exceed 20 m within these profiles granitic saprolites are composed of quartz feldspars and some mica with kaolinite and gibbsite as final weathering products the average percentage of secondary minerals determined by bulk x ray diffraction xrd is low in both weathered rock 2 4 and saprolite 8 7 geotechnically the saprolites exhibit no or low plasticity plasticity index pi 12 the skeleton character of the saprolites is reflected in the significant proportion of fines 29 5

engineering and geological characteristics of granite weathering profiles in south china granite weathering profiles are widely distributed in south china their engineering and geological characteristics are major geotechnical subjects that are important in the design and construction of civil engineering projects this paper presents a summary of the weathering characteristics and zoning of granite weathering profiles in south china and discusses their engineering and geological properties a five grade scheme has been adopted in the zoning of a granite weathering profile studies have shown that the completely weathered granites cwg in south china have the following characteristics low moisture content low to medium plasticity w l 22 5 39 0 i p 6 5 11 8 medium void ratio 0 36 1 29 weak shrinkage and medium compressibility a 1 2 0 24 0 8 mpa 1 and high shear strength phi 20 30degrees c 20 40 kpa the cwgs are usually at a low or high plastic state and most of them are over consolidated soils a majority of the physical and mechanical properties have good statistical correlations with the degree of weathering the data presented in the paper are important in geotechnical engineering projects such as slope stability evaluation in china c 2002 elsevier science ltd all rights reserved

paleozoic tectonic evolution of the northern xinjiang china geochemical and geochronological constraints from the ophiolites 1 the northern xinjiang of china is a composite orogenic belt in the south central part of the altaids formed by subduction accretion mainly during the paleozoic geochronologic and geochemical data from the paleozoic ophiolites and associated assemblages are reported here to place constrains on the tectonic evolution of this region and to reconstruct its history using a model of subduction accretion plus large scale map view strike slip faulting geologic and geochronologic review indicates that the paleozoic ophiolites and associated assemblages of the western and eastern junggar regions are tectonically related occurring as a pattern with the early paleozoic tangbale mayile hongguleleng aermantai complexes in the center the late paleozoic darbut karamaili and the northern tianshan complexes in the south and the late paleozoic kekesentao qiaoxiahala kuerti complexes in the north available geochemical data suggest that the paleozoic ophiolites of the northern xinjiang are mainly oceanic fragments of these three types mid ocean ridge basalt oceanic island basalts and island arc basalts the paleozoic subduction accretion complexes grew mainly along different segments of the kipchak arc and in associated with migration of magmatic arc the paleozoic ophiolite associated sedimentary sequences and subduction related volcanic rocks exhibit an evolution history from intraoceanic early paleozoic to marginal settings late paleozoic implying coeval strike slip stacking with subduction accretion processes and by which to transport the respective complexes together and further to amalgamate with neighboring units of the altaids subduction accretion processes terminated in the mid carboniferous in this region in the late permian early triassic a counterclockwise rotation of fault blocks in a giant sinistral strike slip and extension domain between altay and tianshan lastly generated present configuration of the paleozoic subduction accretion complexes in the northern xinjiang

palaeozoic collisional tectonics and magmatism of the chinese tien shan central asia abstract the chinese tien shan range is a palaeozoic orogenic belt which contains two collision zones the older southern collision accreted a north facing passive continental margin on the north side of the tarim block to an active continental margin on the south side of an elongate continental tract the central tien shan collision occurred along the qinbulak qawabulak fault southern tien shan suture the time of the collision is poorly constrained but was probably in in the late devonian early carboniferous we propose this age because of a major disconformity at this time along the north side of the tarim block and because the youshugou ophiolite is imbricated with middle devonian sediments a younger probably late carboniferous early permian collision along the north tien shan fault northern tien shan suture accreted the northern side of the central tien shan to an island arc which lay to its north the north tien shan arc this collision is bracketed by the middle carboniferous termination of arc magmatism and the appearance of late carboniferous or early permian elastics in a foreland basin developed over the extinct arc thrust sheets generated by the collision are proposed as the tectonic load responsible for the subsidence of this basin post collisional but palaeozoic dextral shear occurred along the northern suture zone this was accompanied by the intrusion of basic and acidic magmas in the central tien shan late palaeozoic basic igneous rocks from all three lithospheric blocks represented in the tien shan possess chemical characteristics associated with generation in supra subduction zone environments even though many post date one or both collisions rocks from each block also possess distinctive trace element chemistries which supports the three fold structural division of the orogenic belt it is unclear whether the chemical differences represent different source characteristics or are due to different episodes of magmatism being juxtaposed by later dextral strike slip fault motions because the southern collision zone in the tien shan is the older of the two the tarim block sensu stricto collided not with the eurasian landmass but with a continental block which was itself separated from eurasia by at least one ocean the destruction of this ocean in late carboniferous early permian times represented the final elimination of all oceanic basins from this part of central asia

age and paleoclimatic significance of the stansbury shoreline of lake bonneville northeastern great basin abstract the stansbury shoreline one of the conspicuous late pleistocene shorelines of lake bonneville consists of tufa cemented gravel and barrier beaches within a vertical zone of about 45 m the lower limit of which is 70 m above the modern average level of great salt lake stratigraphic evidence at a number of localities including new evidence from crater island on the west side of the great salt lake desert shows that the stansbury shoreline formed during the transgressive phase of late pleistocene lake bonneville sometime between about 22 000 and 20 000 yr b p tufa cemented gravel and barrier beaches were deposited in the stansbury shorezone during one or more fluctuations in water level with a maximum total amplitude of 45 m we refer to the fluctuations as the stansbury oscillation the stansbury oscillation cannot have been caused by basin hypsometric factors such as stabilization of lake level at an external overflow threshold or by expansion into an interior subbasin or by changes in drainage basin size therefore changes in climate must have caused the lake level to reverse its general rise to drop about 45 m in altitude reducing its surface area by about 18 5000 km2 and later to resume its rise if the sizes of great basin lakes are controlled by the mean position of storm tracks and the jetstream which as recently postulated may be controlled by the size of the continental ice sheets the stansbury oscillation may have been caused by a shift in the jetstream during a major interstade of the laurentide ice sheet

accelerator mass spectrometer ams radiocarbon dating of pleistocene lake sediments in the great basin abstract pleistocene lake sediments in the great basin typically contain little organic carbon and thus are difficult to date reliably by conventional radioccarbon methods paleoenvironmental data are abundant in these sediments but are of limited value without adequate age controls with the advent of accelerator mass spectrometer ams radiocarbon dating it is now possible to date these paleolacustrine sediments ams dates were obtained on sediment cores from the bonneville franklin and lahontan basins in the bonneville basin the ams based chronology compares well with other chronologies constructed from dated shore zone features in the bonneville and franklin basins ams dates delimit unconformities not apparent by other means we found that dispersed organic carbon from sediments deposited during relatively freshwater intervals provided apparently reliable ams radiocarbon dates carbonate microfossils from the lahontan basin also produced results that appear reasonable while bulk carbonate yielded erroneous results

sr z sbnd nd isotopic record of multi stage interactions between mantle derived magmas and crustal components in a collision context the ultramafic granitoid association from vivero hercynian belt nw spain late stage epizonal calc alkaline granitoids of the hercynian belt are often associated with coeval more basic rocks such granitoids have been the focus of special attention when studying the role of mantle derived magmas in granitoid genesis these studies conclude that basic magmas are involved in granitoid production but their contribution to the chemical composition of granitoids is often controversial the vivero massif nw spain includes calc alkaline granitoids and coeval ultramafic and mafic rocks but these granitoids are syntectonic and intruded into middle crustal levels during an early stage scattered major and trace element chemistry together with heterogeneous sr nd isotopic results preclude an origin of this ultramafic to granitoid association by any closed system fractionation process ultramafic rocks include peridotites pyroxenites and homblendites with endi from 3 5 to 1 3 and 87sr86sr i ratio from 0 7059 to 0 7080 they are interpreted as cumulates formed by in situ fractional crystallization from contaminated basaltic magmas particularly by interaction with 87sr enriched fluids mafic rocks comprise biotite amphibole diorites quartz diorites and tonalites with ndi from 3 8 to 0 0 and 87sr86sr i ratio from 0 7058 to 0 7073 they represent either cumulates or more evolved magmas of calc alkaline affinity these rocks display an inverse correlation between the degree of differentiation and the degree of contamination inferred from isotope data this points to wall rock assimilation by thermal erosion during ascent of basic magmas up to the middle crust and supports the participation of mantle sources with positive end and 87sr86sr i 0 7058 granitoids range from amphibole biotite tonalites through biotite granodiorites to monzonitic granites they show an isotopic trend which diverges from that of ultramafic and mafic rocks endi 6 0 to 1 9 decreases while 87sr86sr i ratio 0 7061 to 0 7082 increases from tonalites to monzonitic granites reflecting an increasing contribution of crustal components in more differentiated rocks assimilation and fractional crystallization mixing included account for such an evolution contamination of basic magmas by this process occurring at deeper crustal level produced hybrid tonalites and related mafic magmatic enclaves only monzonitic granites are interpreted as pure crustal melts their hree fractionated patterns gd yb 4 5 suggest equilibrium with a garnet rich residuum partial melting of moderate time integrated rb sr protolith such as greywackes and or meta igneous rocks of intermediate acid composition could account for the isotopic composition of these monozogranites this example shows that at least some calc alkaline granitoids of collisional setting are not produced by pure intra crustal melting they are formed through a complex multi stage hybridization process involving mantle derived magmas crustal components and several concomitant magmatic processes

identifying a reference frame for calculating mass change during weathering a review and case study utilizing the c program assessing element immobility and critical ratio methodology abstract the first step in calculating mass changes that occur during the transformation of plutonic rock to saprock involves the determination of a reference frame i e an immobile element whose mass was conserved during the alteration process procedures for identifying the statistical properties of immobile elements have been available since 1990 but have not generally been applied we therefore developed the c program assessing element immobility aei that allows for rapid assessment of those elements possessing the statistical properties of immobility aei utilizes algorithms that test for equal distributions and unchanging means of ratios subcompositional independence and subcompositional invariance following discussion of the general mathematical and statistical procedures implemented in aei we utilize it in a case study involving three sites in an 30 m thick section of regolith zr i is located near the base of the regolith while zr ii and zr iii are located at depths of 20 m and 5 m respectively from each site previous workers chemically analyzed a number of samples from saprock and adjacent unweathered corestones in addition xrd work showed that from zr i to zr ii to zr iii biotite was altered to vermiculite vermiculite kaolinite and vermiculite mixed layer biotite vermiculite kaolinite respectively at zr iii the most dominant clay mineral is kaolinite aei performs a series of tests to assess whether or not a given set of elements possess the statistical properties for immobility it identified the following elements as a potential reference frame al na fe mg ti and p at zr i si al fe mn mg ti and p at zr ii and mg and mn at zr iii however critical ratio methodology indicated that the precision as measured by the smallest 95 confidence interval is greatest for al2o3corestone al2o3saprock and na2ocorestone na2osaprock at zr i for sio2corestone sio2saprock at zr ii and for mgocorestone mgosaprock at zr iii mass balance results using al2o3 and na2o at zr i were nearly identical and as a result only the results derived from al2o3 are reported here using al2o3 sio2 and mgo as reference frame elements for zr i zr ii and zr iii respectively revealed the following statistically significant losses of k mass 14 9 8 at zr i 28 11 9 at zr ii and 33 8 7 at zr iii in addition at zr iii the statistically significant loss of 36 13 11 p mass is attributed to the dissolution of apatite and the small nominal loss of 6 5 5 ca mass may reflect incongruent leaching of plagioclase and or apatite in contrast the small additions of 5 5 4 al 5 2 2 fe and 4 2 2 ti mass at zr iii are likely the result of the translocation of kaolinite and kaolinitized biotite particles into the crack system by downward percolating fluids and the exchange and adsorption of al fe and ti ions onto the illuviated clay lining as it evolved over time overall the interplay between eluviation and illuviation at zr iii translates into a statistically significant 5 3 3 increase in bulk mass

chemical weathering in granitic environments abstract factors controlling chemical weathering in granitic environments are deduced using an extensive database from the literature based on a transition state theory model we evaluated the effects on chemical weathering of runoff temperature and ph the dependence between temperature and runoff and chemical weathering is complicated by other factors such as the presence depth of soil cover soil cover favors chemical weathering when it is thin and rich in weatherable minerals in contrast it reduces chemical weathering when is thick and poor in primary minerals processes that increase the contact time and the surface of the water rock interactions such as physical denudation increase chemical weathering rates in granitic environments the effect of temperature can be quantified assuming an apparent activation energy value of 48 7 kj mol to describe chemical weathering of silica in granitic crystalline environment under high runoff conditions

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

crustal thickening and deformation sequence in the footwall to the suture of the variscan belt of northwest spain abstract the sequence of formation and propagation of structures as well as the evolution of crustal thickening in the variscan belt of northwest spain are proposed in this paper the foreland of this mountain belt shows thin skinned tectonics a polyphase deformation with associated regional metamorphism is recognized in the hinterland zones two important culminations the narcea and lugo antiforms are present in an e w cross section through the footwall to the suture of this orogen such culminations are derived from the stacking of several thrust systems generated during two successive periods the sequence of thrust emplacement helps to clarify the formation of different types of structures at the same time in different places in the orogen

the permian huangshanxi cu ni deposit in western china intrusive extrusive association ore genesis and exploration implications the permian huangshanxi cu ni deposit is the second largest magmatic sulfide deposit discovered to date in a major ni cu province related to protracted basaltic magmatism in eastern xinjiang china it is hosted by a small mafic ultramafic intrusion comprised predominantly of lherzolites olivine websterites gabbronorites and gabbros the huangshanxi intrusion is coeval with permian basalts of tholeiitic and alkaline affinities in the tuha and tarim basins respectively to evaluate a possible genetic relationship between the huangshanxi intrusion and a specific type of coeval basalt in the region as well as ore genesis in the intrusion we have carried out an integrated mineralogical petrological and geochemical study our data reveal that the huangshanxi intrusive rocks are characterized by relatively flat chondrite normalized ree patterns depletion in nb and ta and elevated end values varying between 6 and 10 these features are similar to those of coeval tholeiitic basalts in the nearby tuha basin but are significantly different from those of coeval alkaline basalts in the relatively remote tarim basin the geochemical similarities and differences suggest that the huangshanxi intrusion is genetically related to the tholeiitic basalts in the tuha basin not to the alkaline basalts in the tarim basin as suggested previously by some researchers this implies that regional exploration for the huangshanxi type cu ni deposits should be centered in the tuha basin instead of the tarim basin more specifically the uplifted areas around the tuha basin where similar intrusions may have been brought close to the surface should be carefully examined for mineralization potential intrusive relations and mass balance constraints from incompatible trace elements and sulfide abundances suggest that the huangshanxi intrusion represents a dynamic magma conduit through which multiple pulses of magma ascended to higher levels or to the surface numerical simulation of magma evolution and mixing calculations using sr nd isotopes indicate that selective assimilation of s bearing crustal materials is important for sulfide saturation during the early stages of magma evolution when lherzolites formed fractional crystallization may have also played a role in the attainment of sulfide saturation during the later stages of magma evolution when olivine websterites and gabbronorites formed in both cases immiscible sulfide droplets were retained in the conduit to form disseminated sulfide lenses while the fractionated silicate liquids and buoyant phases such as plagioclase continued to ascend extremely low pge tenors in the sulfide ores of the huangshanxi deposit suggest that the parental magma was highly depleted in chalcophile elements possibly due to previous sulfide segregation at depth

the composite nature of the provo level of lake bonneville great basin western north america abstract deposits of a transgressive phase lake bonneville stillstand or oscillation are found just below the elevation of the regressive phase provo shoreline at numerous exposures throughout the bonneville basin existence of these subprovo shoreline deposits provides a new explanation for the massive size of provo depositional and erosional landforms which can no longer be explained by a long stillstand at the provo shoreline provo coastal landforms are large because they are superimposed on subprovo landforms results also help to clarify divergent interpretations regarding the relative age of the provo shoreline and the number of times it was occupied by the water plane occupation of approximately the same level during both the transgressive and the regressive phase of lake bonneville may be coincidental or it may indicate that a bedrock sill controlled outflow at subprovo as well as provo time rise to the bonneville level could have occurred after massive slope failure plugged the outlet pass

surface subsidence induced by groundwater drainage tunneling in granite residual soils burata railway tunnel spain abstractunderground tunneling besides raising geotechnical challenges can often modify the hydrological regime around an excavated area this fact entails not only the modification of superficial aquifers but also the appearance of subsidence phenomena as a consequence of the decrease in pore pressure in the end this may jeopardize the structural integrity of the construction leading to delays and undesirable secondary effects this paper documents the problems arising from the construction of a railway tunnel for a high speed train in the province of orense in the northwest of spain the tunnel was excavated through a highly weathered granitic massif using conventional methods the drawdown in the water table caused by the tunnel advance was analyzed and monitored the initial lowering of the water level was followed by a period of soil subsidence with deflections reaching up to 104 mm these differential settlements happened along a 150 m strip on both sides of the tunnel axes which affected urban

lake size variations in the lahontan and bonneville basins between 13 000 and 9000 14c yr b p abstract recessions of lakes lahontan and bonneville that commenced 13 500 14 c yr b p were interrupted at 11 500 14 c yr b p in the lahontan basin and 12 200 14 c yr b p in the bonneville basin by relatively large perturbations in lake level that persisted for 2000 years minor glacial readvances in the sierra nevada and white mountains of california nevada occurred during the latter half of this interval between 11 000 and 9700 14 c yr b p the hydrologic response of lakes lahontan and bonneville and the mountain glacial advances were concurrent with the allerod younger dryas climatic intervals recorded in vegetational and glacial records of western and central europe

grouting experiment in a completely weathered granite dam abutment case study on grouting technique and test analysis anti seepage grouting of earth rock dams is an important aspect of dam construction projects completely weathered granite is a typical porous granular soil traditional grouting techniques cannot meet the requirements of completely weathered granite grouting therefore pulsating grouting which combines drilling and grouting is proposed and grouting experiments were performed on a completely weathered granite reservoir abutment in combination with traditional clay cement slurry materials the results show that single row 1 m hole spacing of the permeability after grouting was less than 10 lu the acoustic wave velocity increased by 17 3 52 5 moreover the core sample was relatively complete and the compressive strength of the core reached 7 3 mpa on average the proposed technique significantly reduces the unit cost is applicable to completely and strongly weathered granite and similar formations thus this work provides an engineering reference for these formations

smectite formation produced by weathering in a coarse granite saprolite in galicia nw spain abstract weathering of a calcalkaline granite was studied in the south of galicia nw spain where the average annual precipitation is 1400 mm and the average annual temperature is 12 c the original rock contains perthitic k feldspars plagioclases with inclusions of muscovite and opaque minerals quartz and chloritized biotite with apatite zircon sphene and opaques as accessories in the saprolite the structure of the rock is preserved the plagioclases show up to grade 4 weathering and the biotites between 2 and 3 weathering in quartz and potassium feldspar crystals is manifested only by fracturing biotite changes following the parallel linear model and its weathering products are interstratified biotite vermiculite and iron oxyhydroxides the plagioclases change to a microgranular material by pseudomorphic transformation this material which substitutes the plagioclase includes small clearly delimited units which retain zones with the optic characteristics of muscovite x ray diffraction analyses of microsamples show that they are formed by 1 1 diocthaedral phyllosilicate smectite and a small quantity of mica from these facts we concluded that smectite is formed inside the plagioclase crystals and probably originates from the inclusions of muscovite contained in these crystals as it is suggested by the microscopic study which shows the increase in volume which occurs when the crystals of muscovite are transformed

isotopic studies bearing on the tectonics of the west junggar region xinjiang china isotopic investigations from the hercynian age fold belt between the kazakhstan and siberian cratons in the west junggar region determine the timing of tectonic evolution and the petrogenesis of the granitic rocks of the region sphene from the leucogabbro phase of the tangbale ophiolite melange the oldest member of the ophiolite sequences in the fold belt yields an isotopic pb pb age of 523 2 7 2 ma zircon from a postcollision alkali granite yields slightly discordant isotopic u pb ages that indicate magma crystallization at 321 4 6 7 ma dating it in the lower carboniferous period radiometric dating thus documents a time span of circa 200 ma for igneous activity in the area petrogenetic studies were made to test whether precambrian crustal rocks might underlie the junggar sedimentary basin initial lead isotope ratios determined from potassium feldspars from five alkali granites show clear affinity with ratios from mid ocean ridge basalts in pb isotope correlation diagrams sm nd data from sphene and apatite from one of the granites yield an initial end t 6 1 the granite sources are depleted mantle rocks of oceanic affinity that show no involvement of recycled aged granitic crustal rocks

late quaternary environments in ruby valley nevada abstract palynological data from sediment cores from the ruby marshes provide a record of environmental and climatic changes over the last 40 000 yr the modern marsh waters are fresh but no deeper than 3 m a shallow saline lake occupied this basin during the middle wisconsin followed by fresh and perhaps deep waters by 18 000 to 15 000 yr b p no sediments were recovered for the period between 15 000 and 11 000 yr b p possibly due to lake desiccation by 10 800 yr b p a fresh water lake was again present and deeper than modern conditions lasted until 6800 yr b p the middle holocene was characterized by very shallow water and perhaps complete desiccation the marsh system deepened after 4700 yr b p and fresh water conditions persisted until modern times vegetation changes in ruby valley were more gradual than those seen in the paleolimno logical record sagebrush steppe was more widespread than at present through the late pleistocene and early holocene giving way somewhat to expanded shadscale vegetation between 8500 and 6800 yr b p shadscale steppe contracted by 4000 yr b p but had greater than modern coverage until 1000 to 500 yr ago pinyon juniper woodland was established in the southern ruby mountains by 4700 yr b p

bonneville basin shoreline records of large lake intervals during marine isotope stage 3 and the last glacial maximum abstract lacustrine shoreline depositional features in the bonneville basin western north america were investigated to chronicle paleolake expansion and contraction in response to climate change based on stratigraphy sedimentology geomorphology and radiocarbon dating this study identifies multiple intermediate to large lake intervals during marine isotope stage 3 and the last glacial maximum timing and magnitude of the bonneville basin lake size change are compared with those of hemispheric scale climate change events reported from the greenland ice sheet southwestern north america winter precipitation and east asian monsoon 18 o records the amount of precipitation received by surface water systems in the bonneville basin appears to have increased significantly during the greenland stades throughout the last half of mis 3 and early mis 2 the lake also underwent rapid large amplitude oscillations during the last glacial maximum

stratigraphy and chronology of offshore to nearshore deposits associated with the provo shoreline pleistocene lake bonneville utah abstract stratigraphic descriptions and radiocarbon data from eleven field locations are presented in this paper to establish a chronostratigraphic framework for offshore to nearshore deposits of lake bonneville based on key marker beds and geomorphic position the deposits are interpreted to have accumulated during the period from the late transgressive phase through the overflowing phase into the regressive phase of the lake radiocarbon ages of sediments associated with the provo shoreline indicate that lake bonneville dropped rapidly from the provo shoreline at about 12 600 14c yr bp 15 000 cal yr b p the presence of one or more sand beds in the upper part of the provo aged marl indicates rapid lowering of lake level or storm events at the end of the provo episode an accurate understanding of the timing and nature of lake bonneville s climate driven regression from the provo shoreline is critical to correlations with records of regional and hemispheric climate change the rapid descent of the lake from the provo shoreline correlates with the decline of lakes lahontan and estancia and with the onset of the b o lling aller o d warming event

transgressive stratigraphic record and possible oscillations of late pleistocene lake bonneville northern hogup mountains utah u s a abstract distinct mappable facies changes make the stratigraphic record of the shorezone of late pleistocene lake bonneville the most robust indicator for past lake level oscillations unfortunately clear stratigraphic evidence of transgressive and regressive deposits has been generally lacking new stratigraphic and chronological data within the lacustrine shorezone sediments of the hogup mountains of northwestern utah provide some of the best evidence yet for oscillations within the overall transgressive phase of the lake this study documents two previously unknown oscillations hereby named the lower hogup 22 cal ka and upper hogup 20 6 cal ka oscillations and provides further evidence for the previously proposed u2 oscillation 21 3 cal ka the study suggests that the water level of the lake changed dramatically up to 25 of the lake s total volume during the transgressive phase 30 15 cal ka with the additional oscillations documented in this study there are seven proposed oscillatory events during the transgressive phase of the lake these events likely correlate to rapid but short term regional climatic fluctuations during the broader climatic trends of the last glacial maximum however it is still unknown what specific climatic drivers are causing these oscillations and if these events can be correlated to other global climatic events

nd sr isotopic mapping of the chinese altai and implications for continental growth in the central asian orogenic belt article i nfo the chinese altai orogen is a typical domain of the central asian orogenic belt and in previous syntheses was divided into six tectonic units or terranes in this paper 41 new and 36 published whole rock nd and sr isotopic data for granitoid intrusions and mafic dykes within units 2 and 3 of the central altai and units 4 to 6 of the southern altai were used for isotopic mapping the age of the samples used is known from u pb zircon dating end t values range from 4 to 2 in the central altai units 2 and 3 and from 1 4 to 6 in the southern altai units 4 and 5 and up to 8 4 in unit 6 correspondingly nd model ages tdm decrease from 1 6 1 1 ga in the central altai to 1 0 0 5 ga in the southern altai except for a continental fragment in unit 4 isr is elevated in the central units decreasing to b0 705 in the southern units 5 and 6 these results demonstrate that the central altai contains widespread old crustal components in its basement whereas the southern altai comprises a higher proportion of juvenile crust when integrated with published u pb zircon ages our data show that new crust grew southwards in the chinese altai in addition our data suggest that units 2 and 3 are a single tectonic unit whereas the southern altai unit 4 which previously was regarded as a single young accretionary terrane should be subdivided into two units a younger arc and an older continental fragment the granitoids in the chinese altai can be divided into syn and post non orogenic groups the syn orogenic granitoids have ca 50 80 mantle derived component whereas the post non orogenic granitoids contain ca 70 90 the generation of syn and post non orogenic granitoids represents horizontal lateral and vertical crustal growth which contributed ca 18 28 and 7 8 respectively to the area of the chinese altai this work shows that isotopic mapping is an effective approach to elucidate terrane composition in the central asian orogenic belt and thereby better constrain palaeozoic crustal growth

a generalized 3 d geological and hydrogeological conceptual model of granite aquifers controlled by single or multiphase weathering summary the weathered layers of crystalline rocks form aquifers that are of prime interest for water supply in hard rock areas these weathering profiles generally develop under both stable geodynamic conditions weathering rate erosion rate and a hydrolysing climate they are composed of thick stratiform layers that follow the paleo landscape paleotopography and thus present a gently dipping sequence at a regional scale the structure and the hydrodynamic properties of the weathering profile of a granitic area 53 km 2 maheshwaram catchment state of andhra pradesh india were characterized in detail and mapped from observations on outcrops 80 vertical electric soundings and lithologs from 45 borewells in which flowmeter measurements and injection tests were also performed to characterize the hydraulic conductivities of the conductive fissure zones the structure of the weathering profile results from a multiphase process an ancient weathering profile was partly eroded down to its fissured layer it was later re weathered more or less parallel to the current topographic surface this peculiar structure is linked to the geodynamic history of the indian peninsula that underwent alternate weathering and erosion dominated phases the profile is thus composed from top to bottom up to a total depth of 35 m of sandy regolith saprolite 1 3 m 10 15 m of laminated saprolite containing unusual preserved fissures and a 15 20 m thick fissured layer by comparing various case studies in similar terrain a generalized 3 d geological and hydrogeological conceptual model of granite type aquifers granites gneisses etc is proposed in granite type rocks single weathering or multiphase weathering and erosion processes induce similar geological structures a few main geological differences arise from the comparison of single phase and multiphase weathering profiles i in the later the respective thicknesses of the various layers can be deeply modified ii the ancient fissured layer can be re weathered and the resulting new laminated layer may contain quite well preserved and conductive ancient fissures and iii the upper part of the fissured layer is more densely fissured as a result of the same weathering processes the fissures from the fissured layer of single phase or multi phase profiles exhibit very similar hydraulic conductivities and show both a higher density of conductive fissures at the top of the layer the preserved ancient fissures within the laminated layer of a multiphase profile are partly obliterated by the recent weathering their hydraulic conductivity is thus significantly reduced nevertheless they do significantly contribute to borewell yield these weathering induced fissures provide most of the aquifer permeability the use of such a conceptual model for the precise geological mapping of the weathering structure appears to be a prerequisite for groundwater development and management in hard rock areas as it answers to several key issues

tectonic evolution and continental crust growth of northern xinjiang in northwestern china remnant ocean model abstract the northern xinjiang region is located in the southwestern part of the central asian orogenic belt caob also known as the altaid tectonic collage despite extensive research aimed at understanding the crustal growth of the caob and the evolution of the paleo asian ocean the tectonic evolution mechanism of continental crust growth in northern xinjiang remains controversial the geology of northern xinjiang is characterized by widespread ophiolites granitoids intermediate basic dikes most of the ophiolites were generated in the early paleozoic the ophiolites are widely spread around the junggar basin but their distribution does not indicate a well defined band their outcrops are generally related to various faults the basic rocks widespread in northern xinjiang are grouped into two categories i gabbros diabases basalts of the ophiolites and ii basic dikes that intrude into the paleozoic strata granite plutons the basic rocks associated with the early paleozoic ophiolites were reworked by later geothermal events with a peak 40ar 39ar age of 310 290 ma the basic dikes intruded into paleozoic strata and granite plutons during the carboniferous jurassic displaying three peaks of emplacement at 260 250 ma 220 ma and 200 190 ma these two types of basic rocks and the documented variscan magmatic rocks were derived from the same source their isotope geochemical characteristics and widespread distribution suggest that since the paleozoic a large geochemical province has existed in northern xinjiang with an affinity to mid ocean ridge basalts morb and ocean island basalts oib which is related to a long lived remnant ocean and the underlying early paleozoic oceanic crust the existence of remnant oceanic crust in northern xinjiang was confirmed by seismic gravity and aeromagnetic data therefore we propose the following remnant ocean model for the paleozoic tectonic evolution of northern xinjiang it consists of three stages 1 oceanic crust formation and deposition of the overlying volcanic sedimentary rocks during the early paleozoic 2 retaining of the remnant ocean with marine sediments deposited during the early stage of the late paleozoic and 3 widespread and pervasive emplacement of variscan granites intermediate basic dikes and their volcanic equivalents during the late carboniferous and early permian and termination of marine sedimentation at the end of the early permian the tectonic evolution of northern xinjiang has been in a state of intracontinental deformation since the mesozoic the variscan granitoids and basic dikes of northern xinjiang originated from the partial melting of the remnant oceanic crust formed in the early paleozoic these variscan intrusive rocks represent the production of continental crust transferred from the basic crust the phanerozoic continental growth of northern xinjiang was completed by mass transfer from the early paleozoic remnant oceanic crust this approach may considerably change our views of continental growth

geochemistry and petrogenesis of 270 ma ni cu pge sulfide bearing mafic intrusions in the huangshan district eastern xinjiang northwest china implications for the tectonic evolution of the central asian orogenic belt abstract the central asian orogenic belt caob is composed of remnants of microcontinents island arcs and ophiolites the presence of voluminous phanerozoic a type granites suggest that continental growth occurred through addition of juvenile crust and the presence of mafic ultramafic intrusions provides direct evidence for a mantle contribution the origin of the mafic ultramafic intrusions in the huangshan area eastern xinjiang has been debated because of the lack of precise age data or trace element and isotopic analyses we have studied the geology petrology geochemistry and geochronology of two of the intrusions the huangshanxi and huangshandong intrusions both are typical layered mafic ultramafic intrusions composed of diorite troctolite norite gabbronorite gabbro wehrlite websterite and lherzolite with systematic geochemical variations that are consistent with the following crystallization sequence ol chr ol pyx chr cpx pl and hbl bt igneous zircons separated from a diorite in the huangshanxi intrusion yield a 269 2 ma shrimp u pb age the rocks are enriched in rb ba u k sr relative to th and lree depleted in nb ta relative to th and exhibit positive end values 6 7 to 9 3 ni cu pge sulfide mineralization occurs in the lower parts of the intrusions primarily strata bound within wehrlite or lherzolite and locally stratiform along the margins of the intrusions the parental magmas appear to have been derived from a mantle source that was previously contaminated by subduction of oceanic crust and to have been variably contaminated by upper continental crustal components the intrusions appear to have formed by plume related activity within a continental setting likely related to post orogenic extension following carboniferous amalgamation of arc related terranes in the caob this plume activity was most likely also responsible for providing heat sources to generate large amounts of a type granites across the caob

accretionary orogenesis of the chinese altai insights from paleozoic granitoids zircon u pb dating and whole rock major oxide trace element and nd sr isotope compositions have been determined for four representative granitic intrusions in the sw chinese altai in order to understand the orogenesis and history of crustal growth in the central asian orogenic belt caob the ashile and halatas bodiesare relatively small intrusions formed in the late carboniferous 318 6ma andpermian 267 4ma respectively thelargertarlang tb andkeketuohaibatholiths kb havemagmaticagesof 359 to 412 ma the granitoids consist chiefly of tonalite granodiorite and granite and are metaluminous to weakly peraluminous in composition asi 0 8 1 1 the ashile pluton is characterized by relatively high mgo 2 73 3 54 wt and sr 395 456 ppm contents with low k2o na2o ratios 0 31 0 42 and mantle like nd sr isotopic compositions endt 2 85 to 3 26 initial 87 sr 86 sr 0 7047 0 7051 it probably formed by fractional crystallization of a mantle derived magma with limited assimilation of oldcrustalmaterial theotherintrusionshavenear zeroornegative endtvalues 0 67to 4 41 andhighersrisotopiccompositions initial 87 sr 86 sr 0 7067 0 7092 indicating a mixture of juvenile and old components in their genesis these intrusions are characterized by relatively low k rb cs contents and low rb sr ratios mostly b0 6 and generally exhibit moderate to high heavy rare earth element hree concentrations ybn 8 26 and weak hree fractionation dy ybnb1 5 with or without negative europium anomalies eu eu 0 5 1 0 these characteristics are consistent with an origin by dehydration melting of a hornblendebearing mid crustal source above the garnet stability field dominated by mafic to intermediate rocks this suggests that the deep crust of the chinese altai may contain a considerable proportion of juvenile material mantle derived magmatism probably in an active extensional continental margin setting played an important role in the formation of the chinese altai acting not only as a heat sourceforcrustalmeltingbutasasourceofjuvenilecomponents therelativelysmallvolumesanddistinctgeochemicalcompositions of the ashile and halatas plutons may imply a substantial change in the geodynamic setting in the late paleozoic 2007 elsevier b v all rights reserved

evidence for a shallow early or middle wisconsin age lake in the bonneville basin utah abstract relatively complete stratigraphic records of the bonneville cycle and of at least one and probably two earlier lacustrine are exposed along the bear river below cutler dam in northern utah between altitudes of 1290 and 1365 m in most exposures the unconformity between the bonneville alloformation and the underlying unit herein named the cutler dam alloformation is marked by slight erosional relief and by a weakly to moderately developed buried soil herein named the fielding geosol in truncated profiles the fielding geosol reaches a maximum of stage ii carbonate morphology wood from near the base of the cutler dam alloformation yielded a 14 c date of 36 000 yr b p beta 9845 alloisoleucine isoleucine aile ile ratios of sphaerium shells from the cutler dam beds average 0 15 0 01 in the total hydrolysate which is significantly greater than the average for sphaerium shells of bonneville age elsewhere in the basin therefore the cutler dam alloformation is older than 36 000 yr b p but much younger than deposits of the little valley lake cycle 140 000 yr b p which bear shells having significantly higher aile ile ratios the cutler dam alloformation along the bear river may be broadly correlative with marine oxygen isotope stages 4 or 3 fine grained fossiliferous marginal lacustrine facies of the cutler dam alloformation are exposed at altitudes near 1340 m and are probably the highest exposures of sediments deposited in the early or middle wisconsin lake in the bonneville basin

weathering of granites in a temperate climate nw portugal granitic saprolites and arenization abstract saprolites or in situ weathering products from granitoid rocks of northwest portugal were studied by means of x ray diffraction xrd of their clay fraction and observations of polished thin sections combined with transmission electron microscopy tem scanning electron microscopy with energy dispersive spectrometer sem eds microanalyses their principal features are 1 depths of more than 10 m 2 mean material loss of 40 as calculated by an isovolumetric method 3 low clay content mean value of 7 and a high degree of mineralogical evolution the clay fraction is characterized by a predominance of kaolinite and gibbsite with subordinate 2 1 minerals illite chlorite vermiculitic mixed layers vermiculite the significance of the secondary minerals in granitic saprolites from northwest portugal is compared to published data from atlantic europe this allows the definition of a climatic zonality for weathering products and identifies arenization as an important weathering process

assessing volumetric strains and mass balance relationships resulting from biotite controlled weathering implications for the isovolumetric weathering of the boulder creek granodiorite boulder county colorado usa abstract an important process often cited in the development of saprock and saprolite is the isovolumetric weathering of granitic bedrock evidence for isovolumetric weathering includes the observation that the texture of the granitic protolith often remains recognizable in its weathered products in contrast to the above often cited view we present results from a study of two sites located on the 1 65 ga boulder creek granodiorite near boulder colorado usa in which weakly chemically altered saprock derived from tonalitic and granodioritic tonalitic bedrock records volumetric strains on the order of 7 6 8 5 and 7 9 8 2 respectively we show that dilation is likely due to the alteration of biotite to vermiculite during the early stages of weathering and is associated with an expansion normal to the 001 cleavage of 40 theoretical calculations of volumetric strains based on the modal biotite present in the protolith support such an interpretation

deep weathering of granitic rocks a case of tunnelling in nw spain abstract this paper highlights a case of extensive development of saprolith from granitic bedrock in nw spain the weathering front at the study area extends to more than 250 m in depth the drilling of a railway tunnel madrid galicia high speed line through the bedrock and saprolith resulted in significant technical issues and economic losses cross sections revealing the 3d complexity of saprolith development are mainly based on fieldwork boreholes laboratory tests and the excavation works saprock is always observed overlying unweathered igneous bedrock two saprolite facies one clay rich and the other clay poor overlie the saprock the recognition is based on several criteria these deposits gradually thicken from the boundaries between the granitoid and metasedimentary roof pendants factors controlling saprolith development are discussed and the chemical and mineralogical changes and trends that occur are described variations in some geotechnical properties and the loss of quality of the rock masses from an engineering perspective are also quantified

diachronous variscan tectonothermal activity in the nw iberian massif evidence from 40ar 39ar dating of regional fabrics abstract multigrain concentrates of hornblende and muscovite together with whole rock slate phyllite samples have been dated 27 analyses using 40ar 39ar incremental release methods along a systematic traverse across the various lithotectonic structural elements which comprise northwestern sectors of the variscan iberian massif hornblende concentrates from amphibolites in the allochthonous ordenes complex yield plateau isotope correlation ages of 425 ma and 377 ma muscovite concentrates and whole rock slate phyllite from this and the cabo ortegal complex yield plateau ages which range from 367 ma to 295 ma analyses of similar material from the relative autochthon yield plateau ages between 359 ma and 275 ma muscovite concentrates from three late to post kinematic granitic stocks yield plateau ages between 309 ma and 274 ma at least seven of the 40ar 39ar analyses from metamorphic rocks record variable thermal rejuvenation of intracrystalline argon systems associated with emplacement of proximal granitic stocks the remaining analyses may be used to constrain the local age of various variscan tectonothermal events the oldest fabric ages are recorded in allochthonous units whereas the youngest fabric ages occur along the boundary between internal and external zones middle devonian ages are recorded in the allochthon and suggest a chronological continuity with deformational events in the relative autochthon where variscan deformation initiated in the upper devonian and diachronously prograded eastward the first deformational events recorded in the limit within the internal and external zones occured ca 20 25 ma later lower namurian variscan deformation systematically prograded diachronously eastward across the orogen as new crustal material was added along the front of the developing orogenic wedge however the entire orogen remained tectonically active with different structural features forming at different times and at different places an average propagation rate of ca 5 km m y is suggested by consideration of a 20 25 ma difference in correlative fabric ages and present separations

late pleistocene to early holocene lake level and paleoclimate insights from stansbury island bonneville basin utah abstract this paper reports on recent multiproxy research conducted to determine the chronology of lake level fluctuations recorded in sediments from a natural exposure at a classic bonneville basin site grain size carbonate percentage magnetic susceptibility amount of charcoal and diatom community composition data were collected from the 16 lacustrine units that compose the 122 cm stratigraphic column in stansbury gulch trends observed in the measured proxies reveal several significant changes in lake level and thereby effective moisture over the approximately 14 500 yr time span represented by the sediments results 1 verify the effectiveness of the multiproxy approach in bonneville basin studies which has been underutilized in this region 2 reaffirm the double nature of lake bonneville s stansbury oscillation 3 suggest a previously undocumented post gilbert highstand of great salt lake and 4 identify possible teleconnections between climate events in the bonneville basin and events in the north atlantic at about 20 500 and 7500 14c yr bp

genesis of post collisional granitoids and basement nature of the junggar terrane nw china nd sr isotope and trace element evidence the post collisional magmatism of the junggar terrane is characterized by intrusion of large amounts of granitoids and minor basic ultrabasic rocks the granitoids comprise two magmatic suites calc alkaline and alkaline which were emplaced contemporaneously at about 294 ma the calc alkaline rocks are typically sodium rich na2o k2o 1 1 3 5 and metaluminous a nk 1 0 a cnk 0 78 1 04 they show mildly fractionated ree patterns la yb n 15 and spidergrams with strong depletion of nb ti and to a lesser extent sr the alkaline granites have high contents of sio2 75 78 alkalis nb hree y sn f and high feo mgo ratios and huge sr and eu depletion in the spidergrams moreover they display characteristic tetrad ree patterns and non charac trace element behaviour the two rock suites have similar initial nd and sr isotopic compositions with end t in the range 5 2 to 7 1 and isr mostly in the range 0 7031 0 7041 this points to a predominance of juvenile components in their sources the calc alkaline rocks are most probably derived by dehydration melting of a basic lower crust leaving behind a granulite residue the process was probably triggered by underplating of mantle derived basic magmas in an extensional regime the alkaline granites are considered to have formed by differentiation of the calc alkaline granitoids our study argues for a juvenile continental crust for the basement of the junggar terrane which is likely dominated by early paleozoic oceanic crust and arc complex that were deeply buried during the late paleozoic subduction and accretion

radiocarbon chronology of lake bonneville eastern great basin usa abstract lake bonneville occupied a series of connected topographically closed structural basins in the eastern great basin from about 30 ka to 12 ka the following synthesis of lake bonneville history is based on a critical evaluation of the stratigraphic and geomorphic contexts of 83 radiocarbon ages of a variety of samples including wood charcoal dispersed organic matter mollusk shells and tufa the lake began to rise from levels close to average holocene levels after about 28 ka by 22 ka it had transgressed approximately 100 m between 22 and 20 ka it regressed about 45 m in the stansbury oscillation and the stansbury shoreline was formed transgression after 20 ka proceeded in two phases a rapid phase from 20 to 18 ka and a slower phase from 18 to 15 ka the lake overflowed intermittently at its highest level the bonneville shoreline from about 15 to 14 5 ka then catastrophically dropped 100 m during the bonneville flood to the level of the provo shoreline which it occupied until about 14 ka subsequent closed basin regression was rapid and complete by 12 ka and was followed by a modest transgression to form the gilbert shoreline between 10 9 and 10 3 ka the lake bonneville record is an accurate proxy of the changing water balance in the bonneville basin during the late pleistocene although the nature of the climatic changes during this period are still uncertain

mineralogical variability in weathering microsystems of a granitic outcrop of galicia spain summary several products of weathering have been studied in a granitic outcrop in galicia n w spain spain alteration took place under a humid temperate climate the various materials and the microsystems in which they occur are 1 fissures containing gibbsite and or 1 1 sheet silicates of varying degrees of crystallinity 2 fissures containing 2 1 sheet silicates of beidellite type 3 encrustations of siliceous material showing varying degrees of structural order with or without organic matter and 4 encrustations of non crystalline matter composed chiefly of al p and si the results demonstrate the importance of considering the different microsystems which contribute to the formation of secondary products in a given weathering system

late paleozoic strike slip shear zones in eastern central asia nw china new structural and geochronological data 1 new structural studies and 40ar 39ar dating in northwest china provide information about late paleozoic strike slip motions subsequent to accretional events which built eastern central asia during the paleozoic two principal areas were affected by these large transcurrent motions first in the tianshan range main east west ductile shear zones are dextral and coeval with an eastward decreasing greenschist retrograde metamorphism associated biotites give ages ranging from 290 ma to 245 ma the earlier n110 shearing occurred in western tianshan while the last one dextral in whole tianshan occurred 250 245 myr ago second in the chinese altay region several nw se shear zones structured the area the main motion is sinistral and occurred along the erqishi zone at 280 290 ma it is followed by a complex succession of dextral and sinistral shearing episodes leading to the northwestward structuring dated at 245 ma of a metamorphic zone that was folded during a compressive event

controlling factors of gullying in the maracuja catchment southeastern brazil hundreds of gullies vocorocas of huge dimensions up to 400 500 m long 150 m wide and 50 m deep are very common in the small maracuja catchment in southeastern brazil these erosional features which occur with an uneven intensity throughout the area started due to bad soil management practices at the beginning of european settlement at the end of the 17th century and nowadays are still evolving but at a slower rate as surface soils are usually very resistant to erosion the outcrop of the more erodible basement saprolites seems to be an essential condition for their beginning an analysis of well known erosion controlling factors was performed aiming to explain the beginning and evolution of these gullies and to understand the reasons for their spatial distribution data shows that geology and mainly geomorphology are the main controlling factors since gullies tend to be concentrated in basement rock areas with lower relief domain 2 of maracuja catchment mainly at the fringes of broad and flat interfluves at the detailed scale 1 10 000 gullies are more common in amphitheatre like headwater hollows that frequently represent upper quaternary gullies paleogullies which demonstrate the recurrence of channel erosion so gullies occur in areas of thicker saprolites domain 2 in places with a natural concentration of surface and underground water hollows saprolites of the preserved non eroded hollows are usually pressurized confined aquifer due to a thick seal of quaternary clay layer in a similar configuration to the ones found in hollows of mass movement mudflow sites in southeastern brazil therefore the erosion of the resistant soils by human activities such as road cuts and trenches valos or their mobilization by mudflow movements seem to be likely mechanisms of gullying initiation afterwards gullies evolve by a combination of surface and underground processes such as wash and tunnel erosion and falls and slumps of gully walls copyright 2005 john wiley sons ltd

pseudomorphic transformation of plagioclases during the weathering of granitic rocks in galicia nw spain abstract microscopic study of twelve weathering profiles developed on granitic rocks in galicia nw spain showed that in most cases the transformation of the parent rock into saprolite occurs with pseudomorphic alteration of the plagioclases it was seen that the transformation and the retention of plagioclases in the alteration profile are directly related to the conservation of the general structure of the rock and this in its turn depends on the mineralogical composition and texture the most unstable constituents in the galician environment are biotites and plagioclases there being a clear difference in the rate of alteration between the plagioclases and the k feldspars this implies that a large part of the fabric of the rock remains unaltered when the plagioclases are completely weathered so that the pores caused by the weathering of the plagioclases are filled by their own alteration products with regard to the influence of the texture it was observed that fine grained rocks are altered more easily than coarse grained ones especially if they are rich in biotites in this study we show various examples in which even with high levels of alteration the morphological features of the original plagioclase crystals are preserved twins original zoning myrmekitic textures and perthites the pseudomorphic transformation of plagioclase is independent of the products to which it gives rise and here we show examples where gibbsite 1 1 dioctahedral phyllosilicate or a mixture of both appear as secondary minerals the mineralogical nature of a newly formed product depends mainly on the intensity of the leaching to which the profile is subjected which is influenced by the rainfall in the area where they are found as well as the size of existing voids in the material

pluvial lakes in the great basin of the western united states a view from the outcrop abstract paleo lakes in the western united states provide geomorphic and hydrologic records of climate and drainage basin change at multiple time scales extending back to the miocene recent reviews and studies of paleo lake records have focused on interpretations of proxies in lake sediment cores from the northern and central parts of the great basin in this review emphasis is placed on equally important studies of lake history during the past 30 years that were derived from outcrop exposures and geomorphology in some cases combined with cores outcrop and core records have different strengths and weaknesses that must be recognized and exploited in the interpretation of paleohydrology and paleoclimate outcrops and landforms can yield direct evidence of lake level facies changes that record details of lake level fluctuations and geologic events such as catastrophic floods drainage basin changes and isostatic rebound cores can potentially yield continuous records when sampled in stable parts of lake basins and can provide proxies for changes in lake level water temperature and chemistry and ecological conditions in the surrounding landscape however proxies such as stable isotopes may be influenced by several competing factors the relative effects of which may be difficult to assess and interpretations may be confounded by geologic events within the drainage basin that were unrecorded or not recognized in a core the best evidence for documenting absolute lake level changes lies within the shore nearshore and deltaic sediments that were deposited across piedmonts and at the mouths of streams as lake level rose and fell we review the different shorezone environments and resulting deposits used in such reconstructions and discuss potential estimation errors lake level studies based on deposits and landforms have provided paleohydrologic records ranging from general changes during the past million years to centennial scale details of fluctuations during the late pleistocene and holocene outcrop studies have documented the integration histories of several important drainage basins including the humboldt amargosa owens and mojave river systems that have evolved since the miocene within the active tectonic setting of the great basin these histories have influenced lake levels in terminal basins many pre late pleistocene lakes in the western great basin were significantly larger and record wetter conditions than the youngest lakes outcrop based lake level data provide important checks on core based proxy interpretations we discuss four such comparisons in some cases such as for lakes owens and manix outcrop and core data synthesis yields stronger and more complete records in other cases such as for bonneville and lahontan conflicts point toward reconsideration of confounding factors in interpretation of core based proxies