submarine fan characteristics and dual sediment provenance lower carboniferous bragdon formation eastern klamath terrane california the carboniferous bragdon formation comprises sandstone argillite and conglomerate which were deposited in a hybrid submarine fan setting the bragdon formation contains a crudely progradational succession of sand rich turbidites and intercalated channel fill and debris flows apparent paucity of fine grained rocks and relatively high sedimentation rates may suggest deposition within a small rapidly subsiding ponded basin three end member petrologic sandstone types include i quartz rich chert rich and sedimentary lithic rich sandstone ii volcanic lithic and feldspar rich sandstone and iii crystal rich sandstone and tuffaceous argillite the compositions reflect basement uplift arc dissection and the persistence of volcanism respectively interbedded strata of differing provenance together with little or no provenance mixing within beds indicate multicomponent source terranes line source sediment dispersal pattern and limited transport distances facies associations and provenance to

mesozoic cenozoic tectonic relationships between the kuqa subbasin and tian shan northwest china constraints from depositional records abstract stratigraphic profiles in the kuqa subbasin located along the southern flank of the tian shan northwest china display similar mesozoic cenozoic evolutionary sequences of compositional maturity exist in conglomerate clasts sandstone framework grains and detrital heavy minerals the similarity of these time series profiles resulted from orogenesis and intracontinental deformation of the provenance area the ancestral tian shan mineralogical maturities of conglomerates and sandstones increase from triassic to middle jurassic and decrease from upper jurassic lower cretaceous to tertiary this trend parallels a similar decrease in maturity in detrital heavy minerals zircon rutile and tourmaline dominate in middle upper triassic to middle jurassic sandstone whereas unstable hornblende and pyroxene dominate the heavy mineral suites in the tertiary especially in miocene and pliocene strata these compositional trends are coeval with gradual southward migration of alluvial depositional fronts and depositional depocenters from cretaceous to miocene since the pliocene large scale southward migration of alluvial depositional systems occurred while depositional depocenters migrated northward based on the mesozoic cenozoic depositional records the tectonic evolution of the tian shan kuqa subbasin may be divided into five phases 1 in early triassic following compression and uplift since permian gravelly braided river alluvial plain depositional systems developing in the kuqa subbasin characterized by sands of mixed orogenic provenance type derived from the ancestral tian shan 2 from middle triassic to middle jurassic sediment composition of the kuqa subbasin reflects arc orogen and mixed orogenic sand types with extensive planation of the ancestral tian shan and the development of relatively stable coal bearing depositional environments 3 renewed compression uplift of the tian shan occurred in late mesozoic especially in cretaceous with most detrital modes of the kuqa subbasin indicating provenance attributes akin to the south tian shan 4 further intensive compression uplift and probably southward basinward propagation of the south tian shan occurred during miocene and 5 supracrustal gravity gliding and collapse occurred in the tian shan kuqa subbasin probably due to intensive deep compression with rejuvenated uplift and probable southward basinward structural propagation of the south tian shan developing since pliocene observed changes in sediment composition and depositional environment since pliocene time were also controlled by frequent and abrupt climate changes in addition to intensive uplift of the tian shan moreover all depositional records in the kuqa subbasin seem to reflect west to east differences in provenance along the tian shan probably indicating greater exhumation depth in the western tian shan than that in the eastern tian shan since early cretaceous

mineralogically mature sandstones in accretionary prisms abstract plate tectonic interpretations of sandstone composition are made in the hope that detrital framework modes of sandstone suites provide information about the tectonic setting of basins of deposition and associated provenances dickinson et al 1983 the underlying assumption that provenance tectonics are directly associated with tectonics of depositional and post depositional sedimentary settings is not however universally true as sandstones from two contemporary accretionary prism complexes nias island indonesia and barbados west indies illustrate mineralogically immature sandstones rich in feldspar and volcanic lithic fragments are expected in such tectonic settings but both nias island and barbadian sandstones are mineralogically very mature dominated by quartz in b th cases this discrepancy between inferred and actual tectonic setting has been explained by postulating that sands from a provenance petrogenetically unrelated to the arc trench system e g continental or recycled orogen sands have been introduced into the accretionary prism by sedimentary or tectonic processes sandstones which are transported sedimentologically or tectonically across the boundaries of sedimentary tectonic provinces and which therefore occur in tectonic settings petrogenetically unrelated to the tectonics of the sediment source area are important components of at least some active accretionary complexes the possibility of trans boundary sedimentary and or tectonic transport must be allowed for in making plate tectonic interpretations based on sandstone petrog aphy especially in reconstructions of ancient orogenic belts

age of emplacement of massif type anorthosites in the eastern ghats belt india constraints from u pb zircon dating and structural studies abstract massif type anorthosites in the proterozoic eastern ghats belt of india occur as complexes of varying size within a strongly deformed high to ultra high grade assemblage of metasedimentary and metaigneous rocks recently discovered dikes and sheets of exceptionally hfse and ree enriched ferrodiorites at the immediate contacts of three anorthosite complexes chilka lake bolangir and turkel contain ubiquitous magmatic zircon suitable for u pb dating due to the coeval and comagmatic nature of the ferrodiorites the u pb zircon data provide reliable constraints on the time of anorthosite emplacement zircons from three ferrodiorite samples were analysed applying the conventional multi grain isotope dilution method zircon grains in the bolangir ferrodiorites d4 and b2012 are long prismatic and show the faint fine scale oscillatory zoning typical for magmatic crystallisation with some poorly luminescent thin overgrowths of metamorphic origin the data points obtained for abraded grain fractions are slightly discordant and yield an upper intercept age of 933 32 ma with a lower intercept at 515 20 ma defined by previously published concordant u pb titanite data from calc silicate rocks of the border zone of the anorthosite zircon grains in the chilka lake ferrodiorite ok 76 2 are prismatic and show zoned igneous interiors that are overgrown by irregular poorly luminescent rims presumably of metamorphic origin the u pb ages obtained for abraded grain fractions are concordant and define an age of 792 2 ma the u pb zircon ages for the chilka lake and bolangir ferrodiorites disprove the often quoted mesoproterozoic age of anorthosite emplacement in the egb which was based on a four point rb sr whole rock isochron for the chilka lake anorthosite complex 1404 89 ma sarkar et al 1981 combined with field and geochemical evidence the new u pb zircon ages indicate that the data array in the rb sr evolution diagram should be interpreted as a mixing line resulting from marginal contamination of the ascending hot anorthosite pluton with felsic melts generated in its thermal aureole the u pb zircon ages provide new insights in the deformation history of the eastern ghats belt as structural studies indicate intrusion of the bolangir anorthosite while its country rocks underwent a thrust shear dominated deformation in contrast emplacement of the considerably younger chilka lake anorthosite occurred previous to or at the beginning of a regionally intense transpressive deformation

paleothermal structure of the point san luis slab of central california effects of late cretaceous underplating out of sequence thrusting and late cenozoic dextral offset late cretaceous shale and sandstone turbidites of the point san luis slab are isoclinally folded locally sheared and faulted but their severity of stratal disruption is relatively mild when compared to adjacent polymictic melange of the franciscan complex we tested the interpretation of a trench slope basin origin for these strata by documenting their paleothermal structure including contacts between turbidites and melange values of mean random vitrinite reflectance rm from turbidites are 0 9 1 7 estimates of maximum paleotemperature are 135 200 c melange matrix samples yield rm values of 1 1 2 5 with an average of 1 5 and peak temperatures between 160 and 240 c the turbidite over melange contact is locally cooler over warmer and was folded after peak heating the relatively high paleotemperatures cast doubt on a shallow slope basin model i e 1 2 km burial depth we suggest instead that thermal maturation of the point san luis slab occurred much deeper in an accretionary prism 10 15 km where offscraped trench wedge deposits were faulted against underplated melange the paleothermal structure was offset and tilted after peak heating by two out of sequence faults late oligocene to pliocene strata rest unconformably above the franciscan and there is a significant gap in thermal maturity across this unconformity with no evidence to show that franciscan rocks were reset thermally following the main episode of uplift and erosion three dimensional orientations of isoreflectance surfaces on opposite sides of the san gregorio san simeon hosgri fault system also can be used to test interpretations of strike slip neotectonics the failure to match these geometries among suspected piercing points at point san luis cambria and point sur favors a suggestion that differential post thermal peak dextral offset of franciscan basement has not exceeded 10 15 km

provenance mixing in an intraoceanic subduction zone tonga trench louisville ridge collision zone southwest pacific abstract dredging on the lower slope of the tonga forearc at the intersection between the louisville ridge hotspot chain and the trench yielded both late tertiary volcaniclastic sediments and late cretaceous slightly tuffaceous pelagic sediments petrography and phase chemistry of volcanic debris of tertiary age samples indicates derivation from a low k tholeiitic arc volcanic glass has a low k2o content and shows an fe enrichment trend plagioclase grains are high in an and low in or components pyroxene grains calcic clinopyroxene orthopyroxene and pigeonite have low tio2 contents and show an fe enrichment trend alkali feldspar and biotite are absent the composition of the tertiary samples is similar to other tonga forearc sediments and is consistent with their derivation from the adjacent magmatic arc the character and composition of volcanogenic debris in cretaceous age samples indicates derivation from an intraplate alkali igneous source plagioclase compositions show an increasing or component with increasing ab alkali feldspar is a rare additional component of these samples calcic clinopyroxene has high tio2 contents and is titanaugite amphibole is also rich in tio2 and is kaersutite minor volcanic glass is rich in alkalis samples were dredged from the seaward slope of a small terrace on the lower trench slope a planar reflector located 2 6 km below the terrace is marked by an abrupt jump in seismic velocity and is interpreted as the top of an essentially undamaged late cretaceous guyot of the louisville chain that was subducted at the tonga trench about 0 5 ma this guyot is the likely source of the late cretaceous intraplate igneous detritus collected at the dredge site some dredge samples yielded a mixed volcanic arc intraplate provenance and or late tertiary late cretaceous ages this probably represents the mixing of the cretaceous seamount and tertiary magmatic arc sources during post collision slumping of the wedge of lower slope material as it re establishes its critical taper

provenance of franciscan graywackes in coastal california a systematic comparison of available detrital modes for graywacke sandstones of the franciscan subduction complex and for coeval sandstones of the great valley sequence in the california coast ranges indicates that both were apparently derived from the same general sources the inferred provenance terrane was the ancestral sierran klamath magmatic arc from which mixed volcanic and plutonic detritus readily entered the adjacent great valley forearc basin at intervals along the trend of the arc trench system arc derived detritus also bypassed the forearc region through submarine canyons that fed the franciscan trench longitudinal flow along both the great valley trough and the franciscan trench achieved wide dispersal of the turbidite sediment suites of both franciscan and great valley samples include an array of subquartzose compositions ranging from feldspatholithic to lithofeldspathic mean framework modes of 17 franciscan suites comprising 203 individual samples and of 23 great valley suites comprising 410 individual samples range from 14 to 44 quartz grains 15 to 54 feldspar grains and 7 to 71 total lithic fragments the ratio of quartz to feldspar remains relatively constant as the proportion of lithic fragments changes the compositional variations reflect differences mainly in the admixture of lithic fragments derived principally from volcanic cover with quartz and feldspar derived principally from erosion of underlying plutons despite major overlap in the compositions of the two sets of samples some franciscan sandstones are somewhat more feldspathic and less lithic than any known great valley counterparts and were probably derived from segments of the arc terrane where exposures of plutons were more extensive than within typical great valley sources higher proportions of non volcanic to volcanic lithic fragments in some franciscan sandstones probably reflect complex recycling processes on the trench slope diagenetic effects in many franciscan suites include apparent wholesale replacement of k feldspar by albite present age control is inadequate to test fully for time dependent trends in the compositions of franciscan sandstones analogous to the known stratigraphic variations in the composition of great valley sandstones this question ought to be investigated in future studies

sediment provenance within subduction complexes an example from the aleutian forearc abstract the ultimate composition of any sandstone is affected by a host of primary and secondary factors including the lithologies present in source terranes climate depositional environment and diagenesis in the case of a subduction complex however unequivocal identification of detrital provenance may be impossible because of the cumulative effects of tectonic and sedimentary transport long distance sedimentary transport 1000 km is common within trenches and abyssal plain turbidites can be tectonically transported for long distances as the underlying oceanic basement drifts towards a subduction front post accretionary displacement can occur as a consequence of strike slip faulting and the total distance of tectonic dislocation may reach several thousand kilometers the present day aleutian forearc region north pacific ocean illustrates many of the problems which typify subduction zones several petrologic suites can be identified and there are significant variations in detrital modes in both time and space the aleutian region serves as a sobering modern analog for accreted rock units such as the franciscan complex of california where intercalations of discrete sandstone suites have been noted in the absence of paleomagnetic control interpretations of sediment provenance within ancient subduction complexes probably should be restricted to the generic level

composition of modern deep sea sands from arc related basins summary petrographic and chemical examination of modern deep sea sands shows a clear distinction between active and passive plate tectonic settings among active settings sands from forearc basins of island arcs and basins from strike slip continental margins can be distinguished but those from other arc related settings overlap considerably in composition in particular sands from continental margin subduction zones and those from the backarc of island arcs appear to be indistinguishable chemically arc related sands are very close in composition to ancient greywacke sandstones for instance sodium almost always exceeds potassium thus it is not necessary for sodium to be added to sands diagenetically to make greywackes as has been suggested the influence of tectonics on the composition of sandstones has long been a central feature of sandstone petrology the geosynclinal model of global tectonics stimulated much thought on this subject probably the best known ideas are those of krynine e g 1942 subsequently such research declined but the plate model for global tectonics has produced a new wave of interest e g crook 1974 schwab 1975 potter 1978 dickinson suczek 1979 much of this work has relied on data from ancient sediments where diagenetic changes and difficulty in de ciphering the tectonic setting limit the useful ness of the conclusions much more work is needed on recent sediments to establish a base line against which ancient sediments can be compared we have previously reported valloni maynard 1981 the results of our work on the petrography of a set of recent deep sea sands from piston cores in this paper we shall com pare this petrographic information with bulk chemistry and attempt to relate these to tecto nics in arc related settings

tectonic and geologic implications of the zodiac fan aleutian abyssal plain northeast pacific the zodiac fan a large body of upper eocene through at least lower oligocene turbidities underlies the aleutian abyssal plain and lies just south of the aleutian trench and the alaskan peninsula in the northeastern north pacific the fan deposits cover an area of more than 1 10 6 km 2 and contain at least 280 000 km 3 of terrigenous sediment the most striking feature of the fan is its well developed channel distributary system which persists nearly to the plain limits levee overbank deposits associated with the channels are the dominant sedimentary style a process believed to predominate on fans receiving primarily fine grained detritus four major channels have been identified on the fan with the following relative age relation older than sagittarius aquarius taurus and sagittarius seamap recently obtained seismic information implies that seamap channel may be older than aquarius channel if seamap is the youngest channel a depositional interval of 8 m y 40 32 m y b p is indicated for the fan as a whole if taurus is the youngest as we believe the interval of deposition is greater than 8 m y but is probably less than 16 m y 40 24 m y b p nanno flora pollen and spores obtained from deep sea drilling site 183 near the northern margin of the fan indicate that the fan formed in a nontropical northern environment and that the source terrane had a climate similar to or slightly cooler than that recorded from coeval onshore deposits in the eastern gulf of alaska on the basis of the interval of deposition the volume of the fan and sediment yield from climatically similar modern drainages a minimum drainage of 500 000 km 2 is believed necessary to have supplied the sediment to form the fan assuming no sediment was deposited before it reached the fan tertiary plate motion models requiring large amounts of relative convergence along the aleutian trench are judged unworkable as such reconstructions require the zodiac fan to have formed 1 500 to 3 000 km from the nearest continental landmass and separated from it by topographic barriers requiring that the drainage be inflated in size manyfold to overcome anticipated sediment losses during such a lengthy transport as the minimum drainage 500 000 km 2 is already equal to one half of the state of alaska any major expansion is judged unreasonable this requires that relative convergence at the aleutian trench be limited to less than 500 km from 40 m y b p to present a possible method by which this limitation can be satisfied is to allow a significant portion of southern alaska to move in concert with the pacific plate since the upper eocene

origin of the torlesse terrane and coeval rocks south island new zealand the carboniferous to lower cretaceous torlesse terrane and haast schist derivatives constitute the major part of the complexly deformed facies of the eastern province of new zealand strata consist mainly of quartzofeldspathic graywacke and mudstone intercalated with minor but widely distributed conglomerate and volcanics with associated chert and limestone clastic rocks were deposited largely by sediment gravity flow mechanisms in a deep marine environment also present are a few highly fossiliferous shallow marine and terrestrial deposits of limited areal extent which rest unconformably on or in fault contact with torlesse flysch several periods of deformation are recognized and melange is present on both local and regional scales metamorphism ranges from zeolite to greenschist facies the bulk of the rocks fall into five areally extensive and mutually exclusive fossil zones of the following ages permian atomodesma middle triassic early late triassic torlessia late triassic monotis and late jurassic early cretaceous contacts between major fossil zones are mainly tectonic petrographic analysis permits subdivision of torlesse sandstones into five major petrofacies that correspond in age to the five major fossil zones the sandstone petrofacies mainly arkosic together with the composition of conglomerate clasts mainly indurated torlesse rocks indicate that the source terrane was a continental volcano plutonic arc probably part of gondwanaland coupled with autocannibalistic reworking of older uplifted torlesse rocks in contrast to the quartzofeldspathic nature of the torlesse coeval sedimentary rocks of the eastern province are volcanogenic they are thought to represent related forearc basin maitai murihiku terranes and trench complex caples terrane deposits derived from a volcanic island arc brook street terrane three petrofacies are established for maitai murihiku and caples sandstones the petrofacies indicate a common evolving immature to submature volcanic island arc source for these terranes a reconstruction of new zealand s eastern and western provinces is proposed in permian and triassic times the torlesse was deposited in trench slope or borderland basins along a trench transform margin fronting a continental volcano plutonic arc source western province gondwanaland deposition was spasmodic but voluminous and was accompanied by concurrent deformation and accretion resulting in parallel belts of torlesse rock younging outward from the gondwanaland margin at the same time the brook street terrane volcanic arc and associated terranes were forming to the west of the torlesse site separated from gondwanaland by a marginal sea in latest triassic or early jurassic times the torlesse was rafted into the volcanic arc system via transform faulting approximately parallel to the gondwana margin the collision event resulted in tectonic thickening of torlesse and caples rocks at the plate interface and metamorphism to haast schist the source was then dominated by older partly metamorphosed torlesse terrane newly uplifted along the collision front closing of the marginal sea behind the brook street terrane in late jurassic early cretaceous times resulted in juxtapositioning with the western province gondwanaland along the median tectonic line

tectonic history of the kyrgyz south tien shan atbashi inylchek suture zone the role of inherited structures during deformation propagation 1 multimethod chronology was applied on intrusives bordering the kyrgyz south tien shan suture stss to decipher the timing of 1 formation and amalgamation of the suturing units and 2 intracontinental deformation that built the bordering mountain ranges zircon u pb data indicate similarities between the tien shan and tarim precambrian crust caledonian 440 410 ma and hercynian 310 280 ma zircon u pb ages were found at the edge of the stss related to subduction and closure of the turkestan ocean and the formation of the suture itself permian triassic 280 210 ma titanite fission track and zircon u th he data record the first signs of exhumation when the stss evolved into a shear zone and the adjacent tarim basin started to subside low temperature thermochronological apatite fission track zircon and apatite u th he analyses reveal three distinct cooling phases becoming younger toward the stss center 1 jurassic cretaceous cooling ages provide evidence that a mesozoic south tien shan orogen formed as a response to the cimmerian orogeny 2 early paleogene 60 45 ma data indicate a renewed pulse of stss reactivation during the early cenozoic 3 neogene ages constrain the onset of the modern tien shan mountain building to the late oligocene 30 25 ma which intensified during the miocene 10 8 ma and pliocene 3 2 ma the cenozoic signals may reflect renewed responses to collisions at the southern eurasian border i e the kohistan dras and india eurasia collisions this progressive rejuvenation of the stss demonstrates that deformation has not migrated steadily into the forelands but was focused on pre existing basement structures

deposition of sand in a trench slope basin by unconfined turbidity currents abstract site 181 of the deep sea drilling project is located on the seaward margin of a small basin which formed on the accretionary lower slope of the eastern aleutian trench sand layers recovered from this basin display an unexpected degree of compositional heterogeneity evidently all of the detritus was not derived from a single point source or submarine channel instead unconfined turbidity currents must have converged on the site of deposition from initiation points which were widely spaced across the hinterland of the gulf of alaska most of the unconfined flows probably were deflected around larger bathymetric obstacles however the bathymetric relief associated with many ridges appears to be insufficient for complete blockage of turbidity currents ridge bypassing can also occur by direct upslope flow over the ridge crests and we believe this mechanism represents an important element of forearc sedimentation

phase relations of epidote blueschists phase diagrams have been computed for minerals in the system ncmash using the optimised thermodynamic data base of berman 1988 augmented by data on glaucophane and pumpellyite to illustrate the relationships between rocks containing epidote and sodic amphibole and those containing assemblages characteristic of neighbouring metamorphic facies the stoichiometries of stable bounding equilibria yield a simple list of mineral parageneses that serves to define an epidote blueschist facies and surrounding metamorphic facies the calculations suggest that when iron free the pairs zoisite glaucophane and clinozoisite glaucophane do not possess a stability field the natural fe bearing paragenesis of epidote sodic amphibole occupies a closed field in the pt diagram whose size increases dramatically as the ratio fe3 al in the minerals is increased where garnet is involved in bounding reactions such as with respect to eclogite and garnet bearing albite epidote amphibolite the epidote blueschist field decreases in size as the ratio fe2 mg is increased the classic blueschist to greenschist transition reaction is best developed in rocks with large fe3 and fe2 contents and is possibly metastable in mgal rich rocks in the latter a wedge of albite epidote actinolite barroisite amphibolite separates the epidote blueschist from the greenschits paragenesis field a first occurrence of garnet divides the epidote blueschist field into a lower temperature garnet free zone and a higher temperature garnet bearing zone although the temperatures calculated for this garnet isograd seem high the locations of all the facies boundaries are influenced by h2o activity however even minor amounts of co2 in the fluid phase x co2 0 005 render the epidote sodic amphibole paragenesis metastable so that facies boundaries cannot be shifted by varying the co2 content of the fluid phase below 600 c no mutual boundaries exist between the amphibolite facies and the epidote blueschist and eclogite facies respectively the calculated low pressure limit for the eclogite paragenesis pyralspite omphacite jd 50 quartz typical metabasite compositions is 12 to 14 kbars with h2o activity 0 9 or 1 5 to 2 kbar lower for jd 30

detrital modes of recent deep sea sands and their relation to tectonic setting a first approximation complete petrographic analyses of modern deep sea sands are surprisingly rare but are needed if problems such as the influence of tectonics on petrology or changes in petrology due to diagenesis are to be understood in ancient sandstones this paper is a first attempt using data from our own study of 80 sands plus data from the literature to establish a baseline for modern deep sea sands with which ancient sandstones can be compared we assigned sands to five plate tectonic categories each of which has a distinct average petrologic composition 1 basins associated with trailing edge continental margins q62f26l12 2 with leading edge continental margins either subduction q16f53l31 or 3 strike slip q34f39l27 4 back arc basins q20f29l51 5 fore arc basins q8f17l75 the amount and type of lithic fragments and the type of feldspar are particularly important discriminators the amount of quartz less so trailing edge and fore arc basins have quite distinctive compositions but back arc basins and basins near the two types of leading edge margins show some overlap and thus may be hard to differentiate in ancient sandstones

post grenvillean transpression in the chilka lake area eastern ghats belt implications for the geological evolution of peninsular india abstract results of a combined structural and geochronological study of the area around the 0 79 ga chilka lake anorthosite complex in the eastern ghats belt of india place important constraints on the geological history of peninsular india th u pb epma dating of monazites from the outer margin of the anorthosite complex and from country rocks reveals that the emplacement of the anorthosite occurred at the beginning of a protracted middle neoproterozoic tectono magmatic event encompassing leucogranite emplacement and or cooling in the aureole of the anorthosite between 762 and 743 ma and a fabric defining transpressional deformation at 690 662 ma the progressive deformation was accompanied by granulite facies metamorphism a thermal event at 520 505 ma led to local resetting of the th u pb systematics in some monazites ages of 964 921 ma obtained from metapelitic granulites constituting the oldest lithological component imply that the chilka lake area was involved in the global grenvillean orogenesis which was the fabric defining tectonothermal event in most parts of the eastern ghats belt in combination with additional data from these authors and published data from other domains of the eastern ghats belt these results indicate that the post grenvillean evolution of the eastern ghats belt is characterized by a sequence of neoproterozoic tectonothermal events between 792 and 662 ma and a pan african thermal event at 520 505 ma it further implies slow cooling of the entire granulite terrain in view of appreciably different metamorphic conditions between the low grade proterozoic supracrustal cover of the archean cratons east dharwar and bastar and the neighbouring proterozoic granulites of the eastern ghats belt it is suggested that final thrusting of the eastern ghats belt over the archean forelands took place in early phanerozoic time

geometry and kinematics of mykonos detachment cyclades greece evidence for slip at shallow dip 1 the eastern part of mykonos island cyclades greece shows the detailed internal structure of a two branch shallow dipping extensional detachment system of miocene age this paper shows that the last stage of slip along the detachment during the deposition of syn rift sediments occurred with a very low dip and proposes that this geometry prevailed since the initiation of extension extensional deformation during and after a 13 ma old granite intrusion is taken up by two main shallow dipping shear zones 1 the lower livada detachment which extends laterally across tinos island is a ductile structure located at the interface between the granite and the upper cycladic nappe metabasites a pervasive top to the ne shearing deformation is observed throughout the granite in this island with a strong gradient toward the intrusive contact later brittle faults shallowly and steeply dipping rework the ductile deformation with the same overall shear sense 2 the upper mykonos detachment is brittle and separates the metabasites from late miocene sandstones and conglomerates the detachment fault dips 12 15 toward the nne and its sense of shear is consistent with that of the livada detachment soft sediment deformation during the time of detachment faulting and the presence of steep normal faults that root into the detachment gouge indicate a shallow depth of deformation rotations about vertical and horizontal axes can be reconstructed within and below the detachment zone indicating that the overall direction of extension is nne ssw with a sense of shear toward the nne and the dip of the fault is throughout very low the two detachments have accommodated several tens of kilometers of horizontal extension during the formation of the aegean sea which emphasizes the importance of low angle extensional faults and shear zones in extensional tectonics

late precambrian volcaniclastic deposits of the avalonian eastport basin newfoundland appalachians petrofacies detrital clinopyroxene geochemistry and palaeotectonic implications abstract the eastport basin contains over 5 km of well preserved marine volcaniclastic deposits that comprise parts of the late precambrian avalonian connecting point and love cove groups of the eastern newfoundland appalachians basin infilling was dominated by deep sea resedimentation of pyroclastic and epiclastic sediments four petrographically and texturally distinct petrofacies have been designated viz tuffs tuffaceous sandstones and conglomerates feldspathic sandstones and conglomerates polymict sandstones and conglomerates a broad compositional spectrum of volcanogenic detritus a copious supply of pyroclastic basaltic andesitic dacitic and rhyolitic ejecta and the ubiquity of trace plutonic and metamorphic rock fragments are diagnostic provenance attributes of the basin fill and these indicate derivation from an evolved magmatic arc developed on a transitional or possibly continental crust detrital calcic clinopyroxenes and calcic amphiboles from the upper part of the connecting point group are low in ti and al display calc alkaline and calc alkaline to tholeftic affinity of the parental magma and plot in the field of orogenic basalts discriminant function analysis demonstrates that basalts and andesites were the main source of the detrital clinopyroxene the clinopyroxene major element chemistry is consistent with the evolved volcanic arc provenance suggested by petrographic data both datasets independently support other sedimentological and stratigraphic evidence that the eastport basin records sedimentation adjacent to an active avalonian cadomian volcanic arc the remnants of which are preserved in part within the presently adjacent predominantly volcanic love cove group

pacific basin tsunami hazards associated with mass flows in the aleutian arc of alaska abstract we analyze mass flow tsunami generation for selected areas within the aleutian arc of alaska using results from numerical simulation of hypothetical but plausible mass flow sources such as submarine landslides and volcanic debris avalanches the aleutian arc consists of a chain of volcanic mountains volcanic islands and submarine canyons surrounded by a low relief continental shelf above about 1000 2000 m water depth parts of the arc are fragmented into a series of fault bounded blocks tens to hundreds of kilometers in length and separated from one another by distinctive fault controlled canyons that are roughly normal to the arc axis the canyons are natural regions for the accumulation and conveyance of sediment derived from glacial and volcanic processes the volcanic islands in the region include a number of historically active volcanoes and some possess geological evidence for large scale sector collapse into the sea large scale mass flow deposits have not been mapped on the seafloor south of the aleutian islands in part because most of the area has never been examined at the resolution required to identify such features and in part because of the complex nature of erosional and depositional processes extensive submarine landslide deposits and debris flows are known on the north side of the arc and are common in similar settings elsewhere and thus they likely exist on the trench slope south of the aleutian islands because the aleutian arc is surrounded by deep open ocean mass flows of unconsolidated debris that originate either as submarine landslides or as volcanic debris avalanches entering the sea may be potential tsunami sources to test this hypothesis we present a series of numerical simulations of submarine mass flow initiated tsunamis from eight different source areas we consider four submarine mass flows originating in submarine canyons and four flows that evolve from submarine landslides on the trench slope the flows have lengths that range from 40 to 80 km maximum thicknesses of 400 800 m and maximum widths of 10 40 km we also evaluate tsunami generation by volcanic debris avalanches associated with flank collapse at four locations makushin cleveland seguam and yunaska sw volcanoes which represent large to moderate sized events in this region we calculate tsunami sources using the numerical model topics and simulate wave propagation across the pacific using a spherical boussinesq model which is a modified version of the public domain code funwave our numerical simulations indicate that geologically plausible mass flows originating in the north pacific near the aleutian islands can indeed generate large local tsunamis as well as large transoceanic tsunamis these waves may be several meters in elevation at distal locations such as japan hawaii and along the north and south american coastlines where they would constitute significant hazards

nd isotopic mapping of crustal domains in the eastern ghats belt of india implications for the indo antarctic terrane assembly within rodinia and gondwana

exhumation of basement cored uplifts example of the kyrgyz range quantified with apatite fission track thermochronology 1 the kyrgyz range the northernmost portion of the kyrgyzstan tien shan displays topographic evidence for lateral propagation of surface uplift and exhumation the highest most deeply dissected segment lies in the center of the range to the east topography and relief decrease and preserved remnants of a cretaceous regional erosion surface imply minimal amounts of bedrock exhumation the timing of exhumation of range segments defines the lateral propagation rate of the range bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology new multicompositional apatite fission track aft data from three transects from the eastern kyrgyz range combined with published aft data demonstrate that the range has propagated over 110 km eastward over the last 7 11 myr on the basis of the thermal and topographic evolutionary history we present a model for a time varying exhumation rate driven by rock uplift and changes in erodability and the timescale of geomorphic adjustment to surface uplift easily eroded cenozoic sedimentary rocks overlying resistant basement control early rapid exhumation and exhibit slow surface uplift rates as increasing amounts of resistant basement are exposed exhumation rates decrease while surface uplift rates are sustained or increase thereby growing topography as the range becomes high enough to cause ice accumulation and to develop steep river valleys fluvial and glacial erosion becomes more powerful and exhumation rates once again increase independently determined range normal shortening rates also varied over time suggesting a feedback between erosional efficiency and shortening rate

tectonic evolution of the south tianshan orogen and adjacent regions nw china geochemical and age constraints of granitoid rocks geochemical and geochronological evidence was obtained from granitoids of the south tianshan orogen and adjacent regions which consist of three individual tectonic domains the kazakhstan yili plate the central tianshan terrane and the tarim plate from north to south the central tianshan terrane is structurally bounded by the early paleozoic nikolaev line north nalati fault and late paleozoic atbashy inyl chek south nalati qawabulak fault zones against the kazakhstan yili and tarim plates respectively the meta aluminous to weakly peraluminous granitic rocks which are exposed along the kekesu river and the bikai river across the central tianshan terrane have a tholeiitic calc alkaline or high potassium calc alkaline composition i type geochemical trace element characteristics and the y versus rb nb or y versus nb discrimination diagrams favor a continental arc setting for these granitoid rocks shrimp u pb and la icp ms u pb zircon age data indicate that the magmatism started at about 480 ma continued from 460 to 330 ma and ended at about 275 ma the earlier magmatism 470 ma is considered to be the result of a simultaneous southward and northward subduction of the terskey ocean beneath the northern margin of the tarim plate and the kazakhstan yili plate respectively the later magmatism 460 330 ma is related to the northward subduction of the south tianshan ocean beneath the southern margin of the kazakhstan yili central tianshan plate the dataset presented here in conjunction with previously published data support a late paleozoic tectonic evolution of the south tianshan orogen not a triassic one as recently suggested by shrimp u pb zircon dating for eclogites

compositions of sandstones in circum pacific subduction complexes and fore arc basins arc trench systems of the circum pacific orogenic belt contain voluminous sandstones within fore arc terranes that include complexly deformed subduction complexes and relatively undeformed fore arc basins of several types turbidites incorporated within subduction complexes include not only axially transported trench fill but also abyssal plain sediments deposited on the sea floor beyond the trench and slope basin deposits perched on the accretionary trench slope mean framework modes of circum pacific sandstone suites can be expressed adequately by the use of qfl and qmflt plots supplementary qmpk and qplvls plots depict partial modes of mineral grains alone and polycrystalline lithic fragments respectively source rocks were mainly volcanic and plutonic terranes of he circum pacific magmatic arcs although some recycled sedimentary and metasedimentary debris is also present analysis of point counts for 2 587 rocks grouped into 104 suites from california the pacific northwest southern alaska southwest japan and new zealand indicates that the characteristic fore arc sandstones display similar compositional ranges everywhere and can be termed the circum pacific volcano plutonic graywacke suite knowledge of their petrology may aid the recognition of analogous tectonic settings in the geologic past frameworks vary across a compositional spectrum that ranges chiefly from feldspatholithic sands derived mainly from volcanic cover in undissected magmatic arcs to lithofeldspathic sands derived largely from plutonic batholiths in dissected magmatic arcs quartz contents are typically intermediate and the feldspar to quartz ratio is semiconstant plagioclas is the dominant feldspar and volcanic rock fragments are commonly the most abundant lithic fragments interpretations of compositional trends within subduction complexes and adjacent fore arc basins imply that simple transverse delivery of sediment from the arc orogene to the fore arc region is not the rule instead sand evidently is distributed along subduction zones by longitudinal turbidity currents initiated at widely spaced sediment delivery points where sediment derived from tectonic culminations along the arc trench system can bypass the sediment traps of fore arc basins moreover turbidites shed from dormant or transform segments of arc orogenes are locally spread far into the ocean basin as abyssal plains which are later rafted bodily into the subduction zone finally no sedimentologic explanations of compositional contrasts across fore arc graywacke terranes can be acce ted without considering the alternative of postdepositional tectonic transport by strike slip

the saint daniel melange evolution of an accretionary complex in the dunnage terrane of the quebec appalachians the saint daniel melange is part of a series of melanges located along the baie verte brompton line in the northern appalachians this line marks the suture between rocks of oceanic affinities and those of the ancient passive margin of north america with which they collided during the taconian middle to late ordovician orogeny the saint daniel melange contains a wide variety of lithologies including well bedded to dismembered sedimentary sequences pebbly mudstone olistostromes and slivers of igneous and metamorphic rocks black shales with interbeds of green shale calcareous siltstone or sandstone are the dominant units they exhibit various stages of melange formation such as those present in shallow parts of an accretionary complex units of oceanic origin include sediments derived from the forearc basin and slivers of an ophiolite and of a magmatic arc units derived from sediments of the passive margin of north america are also present the ratio between these various lithologies changes greatly within the melange on a kilometric scale along strike the saint daniel melange is a structural complex in which the various units were assigned a sequential order mimicking a stratigraphic order the saint daniel melange is interpreted as the relict of an accretionary complex because of its actual structural position within the northern appalachians and because all its lithologies and their structural fabric can be found in modern accretionary complexes

dome and basin refolding and transpressive inversion along the karatau fault system southern kazakstan the karatau fault system of southern kazakstan forms a crustal scale zone of strike slip dominated transpressional tectonics which has undergone multiple phases and styles of deformation during a protracted history of reactivation from the neoproterozoic to the cenozoic ductile fabrics associated with dextral kinematic indicators are present in amphibolites along the main karatau fault the ages of the possibly ophiolitic protoliths and the ductile fabrics are not well constrained but they are plausibly pre late riphean late ordovician granites stitch thrusts and folds which deform late riphean to llanvirn clastics preserved beneath a regional late devonian angular unconformity this deformation may be related to a contemporary continental collision ne of the karatau two phases of late palaeozoic deformation affected the upper devonian and carboniferous carbonate succession the first phase is related to sinistral transpression along the karatau fault system the second to dextral transpressional reactivation the combination of these events produced a regional scale dome and basin fold interference pattern similar polyphase deformation appears to have affected large areas of central asia and was possibly caused by the late palaeozoic orogenies at asia s margins such as the accretion of tarim and the east european craton to asia and the closure of the kazakstan orocline normal faults in the karatau are related to the formation of the leontiev graben south turgay basin and the yarkand fergana basin in the early to mid jurassic during renewed dextral slip along the karatau talas fergana fault late cenozoic deformation is minor and resulted in the uplift and incision of a cretaceous palaeogene peneplain without a major tectonic overprint reversals in the sense of strike slip dominated transpressive deformation across major fault systems results in transpressive inversion this represents an ideal process with which to generate overprinting orthogonal fold systems resulting in classic dome and basin interference patterns on a regional scale

sandstone detrital modes in the makran accretionary wedge southwest pakistan implications for tectonic setting and long distance turbidite transportation detrital modes of early miocene to early pliocene sandstones from the makran accretionary wedge in southwest pakistan show a mainly quartzolithic composition with an evolution from the transitional recycled to quartzose recycled the lithic types however indicate two distinct petrofacies accreted abyssal plain turbidites have qp11lvm27lsm62 and lm39lv27ls34 showing a predominant supply from sedimentary and metasedimentary source terranes whereas slope and shelf facies sediments deposited on the accretionary wedge have qp7lvm47lsm47 and lm22lv48ls30 due to an increase of volcanic detritus the detrital modes of the abyssal plain sediments suggest a recycled orogenic source probably the himalayan collision zone the facies and longitudinal dispersal pattern suggest deposition in an oligo miocene analogue of the present indus fan the sediment must have been transported across strike parallel to the transform structure linking the makran wedge to the himalayas chaman ornach nal fault system and fed into the fan at the western end of the subduction zone the detrital modes also show an increase in volcanic detritus with time lv l 0 27 for the early miocene abyssal plain sediments to 0 47 for the slope sequences this may have been derived from late mesozoic volcanic terrains in northern baluchistan or the ladakh himalayas or more probably from the early to middle miocene andesitic volcanic centre in the northern makran

temporal constraints and pulsed late cenozoic deformation during the structural disruption of the active kashi foreland northwest china 1 in response to the ongoing indo asian collision structural deformation has encroached into the tian shan foreland in western china since the early miocene in order to reconstruct a detailed history of foreland deformation along the southern margin of the tian shan we have synthesized extensive mapping analysis of seismic sections magnetostratigraphy of the foreland fill and associated growth strata apatite fission track dating changes in sediment accumulation rates and geodetic surveys of deformed fluvial terraces across an area exceeding 6500 km2 that spans the kashi foreland in the northwestern tarim basin we use these data to place temporal constraints on individual structures that delineate at least 4 distinct stages of deformation stage 1 involved initial uplift of hinterland structures beginning at 20 25 ma stage 2 began at 16 3 ma when the basement involved deformation front stepped south to the kashi basin thrust that bounds the foredeep strata stage 3 occurred from 13 5 to 4 ma as the deformation front migrated south in episodic steps above thin skinned detachment and ramp flat folding finally stage 4 began after 4 ma with growth of the keketamu anticline followed by rapid southward migration of the deformation front to the atushi and then kashi detachment anticlines on the basis of the deformed tertiary strata and available seismic data calculations of the minimum magnitude of shortening yield totals ranging from 10 to 32 km since the early miocene of which 7 12 km occurred since 4 ma although average shortening rates since 16 3 ma were 0 8 1 3 mm a rates were faster from 16 3 to 13 5 ma 1 1 3 2 mm a after which they decreased to 0 5 mm a between 13 5 and 4 ma before increasing to 2 2 2 7 mm a after 4 ma similarly the rate of southward propagation of the deformation front was initially 3 7 mm a for the first 10 ma of basin development slowed to 1 5 mm a between 13 5 and 4 ma and increased to more than 10 mm a since 4 ma these changes in shortening and structural migration rates over time suggest that the loci of orogenic deformation shifted in and out of the foreland during the neogene surveyed stream terraces suggest that although most current deformation is located along the southern front of the foreland modest deformation and shortening continue in the hinterland structural style within the foreland has also changed over time from imbricate thrust faults with hanging wall folds along the northern margin to ramp flat faults and detachment folds along the southern margin where the basement rocks are previously deformed such as in the hinterland of the kashi foreland thick skinned fault ramps and related fault propagation folds dominate the structural style as syntectonic sedimentation within the foreland produced thick subhorizontal stratigraphy the structural style evolved to detachment and fault bend folding above these footwall flats within the neogene strata

sedimentation and deformation in the amlia fracture zone sector of the aleutian trench abstract a wedge shaped landward thickening mass of sedimentary deposits composed chiefly of terrigenous turbidite beds underlies the west south west trending amlia sector 172 20 173 30 w of the aleutian trench pacific oceanic crust dips northward beneath the sector s sedimentary wedge and obliquely underthrusts 30 off normal the adjacent aleutian ridge the trench floor and subsurface strata dip gently northward toward the base of the inner trench slope the dip of the trench deposits increases downsection from about 0 2 at the trench floor to as much as 6 7 just above basement the wedge is typically 2 2 5 km thick but it is thickest 3 7 4 0 km near the base of the inner slope overlying the north trending amlia fracture zone and also east of this structure slight undulations and relatively abrupt offsets of the trench floor reflect subsurface and generally west trending structures within the wedge that are superimposed above ridges and swales in the underlying oceanic basement the southern or seaward side of some of these structures are bordered by high angle faults or abrupt flexures across these offsets the northern side of the trench floor and underlying wedge is typically upthrown west flowing turbidity currents originating along the alaskan segment of the trench 1200 km to the east probably formed the greater part of the amlia wedge during the past 0 5 m y the gentle northward or cross trench inclination of the trench floor and underlying wedge probably reflects regional downbending of the oceanic lithosphere and trench floor basement faulting and rotation much of the undulatory flexuring of the trench wedge can be attributed to differential compaction over buried basement relief however abrupt structural offsets attest to basement faulting faulting is associated with extensional earthquakes in the upper crust the west trending basement offsets are probably normal faults that dip steeply south or antithetic to the north dip of the subducting oceanic crust up to arc extensional faulting can be attributed to the downbending of the pacific plate into the aleutian subduction zone the rupturing direction and dip is controlled by zones of crustal weakness that parallel north pacific magnetic anomalies which were formed south of a late cretaceous early tertiary spreading center kula pacific ridge the strike of these anomalies is fortuitously nearly parallel to the amlia sector the up to arc fracturing style may locally assist in elevating blocks of trench deposits to form the toe of the trench s landward slope which is in part underlain by a compressionally thickened accretionary mass of older trench deposits compressional structures that can be related to underthrusting are only indistinctly recorded in the turbidite wedge that underlies the trench floor

paleogene accretion of upper cretaceous oceanic limestone in northern california blocks of pelagic limestone tectonically incorporated into coastal terrane melange contain planktonic foraminifers of early campanian to middle maestrichtian age 82 69 ma typical of low latitudes between 20 n and 20 s carbonate concretions from the sheared terrigenous matrix of the melange yield temperate middle latitude planktonic foraminifers and dinoflagellates of middle to late eocene age 49 41 ma the pelagic limestone and the basaltic substrate presumably formed on the eastern flank of the pacific farallon spreading ridge in a low latitude zone of high productivity and migrated northward on the farallon plate until about 40 ma when they initially encountered terrigenous turbidites north of lat 30 n northward translation and final accretion were completed by about 25 ma

exceptions to the relationship between plate tectonics and sandstone composition abstract routine use of qfl qplsmlvm and lmlslv plate tectonic provenance diagrams has led to the recognition of error populations for these sandstones the interpretation of tectonic setting based on data exclusive of petrography does not coincide with the interpretation of tectonic setting based on their location on compositional diagrams the anomalous sandstones can be separated into at least four categories i sandstones deposited during the transition between tectonic regimes may be derived in part from relict source rocks ii the relative enrichment of sandstones in detrital quartz by weathering and or depositional reworking may lead to an inaccurate interpretation of tectonic setting from compositional data iii sandstones deposited in tectonic settings as yet unrepresented on he provenance diagrams may plot between the provenance fields or overlap existing fields iv the role of detrital carbonate rock fragments directly affects the location of data points on provenance diagrams and is an unresolved problem the first two categories represent permanent problems in the use of sandstone composition as an indicator of plate tectonic setting whereas the last two may only be temporary problems that can be solved by more data and a consensus on determining detrital modes recognition of anomalous sandstones in the rock record will reduce the probability of erroneous interpretations of tectonic setting and enhance the use of sandstone petrology as an indicator of plate tectonic setting

permian bimodal dyke of tarim basin nw china geochemical characteristics and tectonic implications abstract this study reports for the first time the occurrence of bimodal dyke in the shuigongtuan area of bachu county tarim basin nw china here quartz syenite porphyry and diabase dykes occur in direct contact showing bimodal feature the quartz syenitic porphyry is metaluminous enriched in k2o na2o 10 11 wt and total rare earth elements ree with low mg mg fe ratios high lree hree and negative eu anomalies the chemical characteristics and tectonic discriminative diagrams show that the rocks have geochemical affinity with a type granites the diabase dyke shows 45 52 wt sio2 and mg mg fe ratio in the range of with high total ree high lree hree ratios and lack of eu anomalies broadly corresponding to tholeiitic composition based on low y nb as low as 0 4 and less than 1 2 enrichment in lile and hfse and uniform nb enrichment patterns in spider diagram for the quartz syenitic porphyry together with the geochemical patterns of the diabases this biomodal association is interpreted to be derived from a mantle source and formed under typical within plate environment the quartz syenitic porphyry and diabase have daly gap of 46 wt 67 wt in sio2 which is explained through formation under bimodal rifting the quartz syenitic dyke probably formed during early permian 277 ma and has geochemical affinity with the xiaohaizi syenitic body we propose that magmas sourced from the mantle intruded into middle upper crust and were emplaced as dykes which indicate large scale extension during the permian in tarim basin the bimodal dyke has genetic affinity with the huge volume of permian basalts and igneous rocks 248 292 ma that occur in the tarim basin the magmatism manifests the culmination of the major thermal event in the tarim basin

thermochronologic insight into late cenozoic deformation in the basement cored terskey range kyrgyz tien shan 1 basement cored ranges formed by reverse faulting within intracontinental mountain belts are often composed of poly deformed lithologies geological data capable of constraining the timing magnitude and distribution of the most recent deformational phase are usually missing in such ranges in this paper we present new low temperature thermochronological and geological data from a transect through the basement cored terskey range located in the kyrgyz tien shan using these data we are able to investigate the range s late cenozoic deformation for the first time displacements on reactivated faults are constrained and deformation of thermochronologically derived structural markers is assessed these structural markers postdate the earlier deformational phases providing the only record of cenozoic deformation and of the reactivation of structures within the terskey range overall these structural markers have a southern inclination interpreted to reflect the decreasing inclination of the reverse fault bounding the terskey range our thermochronological data are also used to investigate spatial and temporal variations in the exhumation of the terskey range identifying a three stage cenozoic exhumation history 1 virtually no exhumation in the paleogene 2 increase to slightly higher exhumation rates at 26 20 ma and 3 significant increase in exhumation starting at 10 ma

franciscan complex calera limestones accreted remnants of farallon plate oceanic plateaus the calera limestone part of the franciscan complex of northern california may have formed in a palaeoenvironment similar to hess and shatsky rises of the present north west pacific1 we report here new palaeomagnetic results palaeontological data and recent plate motion models that reinforce this assertion the calera limestone may have formed on farallon plate plateaus north of the pacific farallon spreading centre as a counterpart to hess or shatsky rises in one model2 the plateaus were formed by hotspots close to the farallon pacific ridge axis on accretion to north america plateau dissection in the late cretaceous to eocene 50 70 myr could explain the occurrence of large volumes of pillow basalt and exotic blocks of limestone in the franciscan complex partial subduction of the plateaus could have contributed to laramide 70 40 myr compressional events3

composition of modern stream sand in a humid climate derived from a low grade metamorphic and sedimentary foreland fore thrust belt of north georgia abstract conditions of tectonics and drainage in north central georgia provide an excellent natural laboratory to study the composition of stream sand derived from a low grade metamorphic and sedimentary foreland fold thurst belt under humid climatic conditions the streams head in a high relief phyllite schist and metasandstone terrain and flow westward across a bounding fault into lower relief paleozoic shales cherty carbonates and quartz arenites the relative abundance of the source rock types in the drainage basin of each sample site was determined and a source rock ratio was calculated as the ratio of the area underlain by metamorphic rock to the total area of the drainage basin low grade metamorphic source rocks supply subequal amounts of monocrystalline quartz polycrystalline quartz and foliated quartz mica rock fragments to stream sediment whereas sand from the sedimentary source terrain consists primarily of monocrystalline quartz a surprisingly large number of pelitic rock fragments and chert mixing of sediment from both source rock types is recognizable on the quartz provenance diagram of young 1976 by a high instability index unstable polycrystalline quartz total polycrystalline quartz and a low polycrystallinity index polycrystalline total quartz this diagram is especially sensitive to the presence of sandstones as source rocks which further decreases the polycrystallinity index the ratio of metamorphic rock fragments to total rock frag ents also is directly related to the source rock ratio modern sand derived from the foreland fold thurst belt of north georgia can be distinguished from neogene subduction complex derived sand and collision orogen derived sand on qfl lmlslv and qplsmlvm provenance diagrams by containing less total feldspar more total quartz and no volcanic rock fragments the concepts developed from the recent sand are applied to the mississippian parkwood formation alabama and the cretaceous muddy formation montana the results suggest that both sandstone units were derived from foreland fold thrust belts but that the parkwood source area contained a greater proportion of low grade metamorphic source rocks than the source area of the muddy

sandstone petrofacies of the yager complex and the franciscan coastal belt paleogene of northern california paleogene strata of the franciscan coastal belt and the yager complex northern california provide a vivid illustration of the problems encountered during studies of detrital provenance along accretionary continental margins the northern portion of the yager complex contains lower percentages of total quartz and higher percentages of feldspar than do correlative stratigraphic units to the south mean q f l modes are q 30 f 54 l 16 n yager and q 49 f 31 l 20 s yager a similar spatial trend is evident within the coastal belt where mean q f l modes are q 33 f 47 l 20 n cb and q 48 f 33 l 19 s cb a third coastal belt petrofacies l cb is dominated by volcanic lithic grains interpretations of generic provenance for each petrofacies are straightforward the arkosic sands probably were eroded from deeply dissected granitic plutons and the more quartzose sands are attributed to recycling from both orogenic backarc terranes and an adjacent magmatic arc the influx of volcanic detritus proves that magmatism was active within the drainage basin during paleogene time identification of specific source areas is more problematic however perhaps the north to south changes in detrital mineralogy were caused by influx from an idaho batholith source arkosic versus a sierra nevada source quartzose the depositional paleolatitude of franciscan sands is unknown and in the absence of latitudinal control potential sources as far south as mexico remain plausible regardless of these uncertainties the variations common to both coastal and yager terranes demonstrate that amalgamation must have preceded any translational events such that differential slip has not occurred between the two terranes

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

crustal scale structure of south tien shan implications for subduction polarity and cenozoic reactivation based on new structural and petrological investigations we present two crustal scale cross sections of the kyrgyz south tien shan and correlations of main faults and units between kyrgyzstan and china the overall structure corresponds to a doubly vergent mountain belt the kyrgyz and chinese areas exhibit identical structural and metamorphic histories to the west the atbashi range comprises high pressure oceanic and continental units stacked by north verging thrusts above a low metamorphic accretionary prism high pressure hp gneisses are bound to their south by a south dipping detachment exhibiting mantle relicts the high pressure oceanic and continental units underwent similar pressure temperature p t paths with peak conditions of around 500 c 20 kbar followed by rapid exhumation the overall south dipping structure and kinematics indicate a south dipping subduction of the central tien shan ocean at 320 310 ma ending with the docking of the tarim block to the kazakh continent to the east the pobeda massif shows a narrow push up structure a major north vergent thrust exhumes deep crustal level granulites constituting the highest summits which were thrust towards the north onto low grade devonian carboniferous schists the southern part of south tien shan is made up of a south verging thrust stack that formed later during ongoing convergence reactivated throughout post 30 ma phases