mesoproterozoic arc magmatism in se india petrology zircon u pb geochronology and hf isotopes of the bopudi felsic suite from eastern ghats belt abstract the southern segment of the eastern ghats mobile belt egmb in india was an active convergent margin during mesoproterozoic prior to the final collision in neoproterozoic during the assembly of the rodinia supercontinent here we present mineralogical whole rock geochemical zircon u pb and hf isotopic data from a granitoid suite in the bopudi region in the eggb the granitoid complex comprises quartz monzodiorite with small stocks of rapakivi granites the monzodiorite locally porphyritic contains k feldspar megacrysts plagioclase quartz biotite and ortho amphibole the presence of mantled ovoid megacrysts of alkali feldspar embaying early formed quartz and the presence of two generations of the phenocrystic phases in the rapakivi granites indicate features typical of rapakivi granites the k feldspar phenocrysts in the rapakivi granite are mantled by medium grained aggregates of microcline ab7 or93 which is compositionally equivalent to the rim of kfs phenocryst and pl an23 24 ab75 the geochemistry of both the granitoids shows arc like features for ree and trace elements la icp ms zircon analyses reveal 207pb 206pb ages of 1582 mswd 1 4 for the rapakivi granite 1605 3 ma mswd 3 9 for the monzodiorite the zircons from all the granitoid samples show high ree contents prominent hree enrichment and a conspicuous negative eu anomaly suggesting a common melt source the zircons from the monzodiorite have a limited variation in initial 176hf 177hf ratios of 0 28171 0 28188 with ehf t values of 2 2 to 2 8 correspondingly their two stage hf isotope model ages tdm2 ranging from 2 15 to 2 47 ga probably suggest a mixed source for the magma involving melting of the paleoproterozoic basement and injection of subduction related juvenile magmas the prominent mesoproterozoic ages of these granitoids suggest subduction related arc magmatism in a convergent margin setting associated with the amalgamation of the columbia derived fragments within the neoproterozoic rodinia assembly

structural architecture of the northern composite terrane the eastern ghats mobile belt india implications for gondwana tectonics abstract new data from structural mapping and tectonic evaluation in the northern parts of the eastern ghats mobile belt egmb north involving the interpretation of satellite images field traverses critical outcrop mapping and kinematic studies of macro as well as microstructures of the shear zone rocks together with the geometry and disposition of gondwana basins led to for the first time the elucidation of post grenvillian structural architecture of the terrane this helps in assessing the sequence of successive tectonothermal events that were responsible for the origin and progressive evolution of the permo carboniferous coal bearing sediments along the mahanadi rift that forms significant in the reconstruction models of east gondwana the composite terrane of high grade metamorphic rocks egmb north strikes e w in contrast to the regional ne sw trend of the egmb the structural architecture obtained from this study is controlled by the boundary shear zones and associated link shear zones the dextral kinematic displacements along the northern boundary shear zone nbsz as well as the mahanadi shear zone msz and koraput sonapur rairakhol shear zone ksrsz were derived from multi scale field based structural observations a n s structural cross section presents a crustal scale flower structure across the composite terrane exposing different domains displaying distinctive internal structures with widely varying different geological evolution history and strain partitioning separated by crustal scale shear zones deep seismic imaging and gravity signatures support flower structure model the pervasive first formed gneissic fabrics were continuously reworked and partitioned into a series of e w crustal scale shear zones the neoproterozoic regional dextral transpressional tectonics along the shear zones and their repeated reactivation could be responsible for initiation and successive evolution of gondwana basins and different episodes of sedimentation available geochronological data shows that the structural architecture presented here is post grenvillian which has been repeatedly reactivated through long lived transpressional tectonics the composite terrane is characterized by all the typical features of an oblique convergent orogen with transpressional kinematics in the middle to lower crust the kinematic changes from transpression to transtensional stresses were found to be associated with global geodynamics related to the transformation from rodinia to gondwana configuration

precambrian ophiolites and related rocks developments in precambrian geology 13 t m kusky editor pp 800 elsevier 2004 isbn 0 444 50923 2 price 198 the purpose of this collection of papers is to address the still controversial question as to the continuity of modern plate tectonic processes back through earth s early geologic history by cataloguing worldwide precambrian ophiolite sequences for the economic geologist and explorationist this volume provides an opportunity to acquaint themselves with geological and geochemical characteristics of precambrian ophiolite assemblages and of phanerozoic analogues this in turn will allow them to recognize this distinctive type of sea floor assemblage in the field and from geochemical study as well as the implications of its presence within certain precambrian volcano sedimentary terranes the editors organized the series of 22 papers into four sections proterozoic ophiolites and related rocks archean ophiolites and related rocks models for the evolution of oceanic crust with time and analogies to precambrian ophiolites the editor s introduction to these sections is somewhat lengthy and repetitious but at the same time it is a good summary of the different ophiolite settings and their characteristics and also serves as a volume synopsis

palaeoproterozoic 1 9 ga extension and breakup along the eastern margin of the eastern dharwar craton se india new sm nd isochron age constraints from anorogenic mafic magmatism in the neoarchean nellore greenstone belt abstract the neoarchean nellore greenstone belt located along the eastern margin of the eastern dharwar craton was the site for younger igneous activity the timing of this magmatism and the host metabasalt critical for constraining extensional events along the deformed southeast margin of the eastern dharwar craton was conducted by the sm nd method samples from the large differentiated gabbroic kandra igneous complex a subset kandra group a define an isochron age of 1926 110 ma nd i 0 51006 12 mswd 0 98 n 5 e nd 1 7 and the kandra group b subset yielded a model 3 isochron age of 1882 120 ma nd i 0 50994 14 mswd 1 8 n 4 e nd 5 1 whereas the three samples from north pamuru gabbro anorthosite yielded an isochron age of 1882 160 nd i 0 51012 18 mswd 0 064 e nd 1 7 the kandra group a and north pamuru samples regressed together yielded a preferred isochron age of 1911 88 ma nd i 0 51008 10 mswd 0 62 n 8 e nd 1 6 for the emplacement of gabbros in contrast host greenstone belt metabasalt from chundi yielded a sm nd isochron age of 2693 94 ma nd i 0 50920 8 mswd 1 4 n 4 e nd 1 2 whereas regressing the chaganam and chundi samples yielded an isochron age of 2654 100 ma nd i 0 50923 9 mswd 1 5 n 11 e nd 0 7 basal metapelite underlying the metabasalt yields old nd model ages between 2888 and 3054 ma the results of this study show that the 2 7 ga nellore greenstone belt was intruded by enriched morb type gabbros at 1911 ma it is proposed that this palaeoproterozoic magmatism formed in response to a major extensional event along the eastern dharwar craton margin that likely initiated breakup from the southeastern margin of the north china craton this exposed craton margin later evolved as the site for collisional events during the late palaeoproterozoic to early mesoproterozoic

seismically imaged shallow and deep crustal structure and potential field anomalies across the eastern dharwar craton south indian shield possible geodynamical implications abstract the time bound crustal evolution and subsequent deformation of the cuddapah basin nellore schist belt and eastern ghats terrain of eastern dharwar craton which have undergone sustained geodynamic upheavals since almost 2 0 billion years remain enigmatic an attempt is made here to integrate newly available potential field data and other geophysical anomalies with deep seismic structure to examine the generative mechanism of major crustal features associated with this sector our study indicates that the initial extent of the cuddapah basin sedimentation may have been much larger extending by almost 50 60 km west of tadipatri during paleoproterozoic period which subsequently shrank due to massive erosion following thermal uplift caused by sw cuddapah mantle plume below this region crust is still quite warm with moho temperatures exceeding 500 c similarly nallamalai fold belt rocks bounded by two major faults and extremely low gravity may have occupied a large terrain in western cuddapah basin also before their abrasion no geophysical signatures of thrusting are presently seen below this region and thus it could not be an alien terrain either in contrast nellore schist belt is associated with strikingly high positive gravity possibly caused by a conspicuous horst structure and up dipping mafic crustal layers underneath that resulted due to india east antarctica collision after the cessation of prolonged subduction 1 6 0 95 ga further the crustal seismic and gravity signatures would confirm presence of a totally distinct geological terrain east of the cuddapah basin but the trace of eastern ghats belt is all together missing instead all the geophysical signatures point out to presence of a proterozoic sedimentary terrain east of nellore schist belt it is likely that the extent of prorerozoic sedimentation was much larger than thought today in addition presence of a seismically detected gondwana basin over nellore schist belt apart from some recently discovered similar subsurface gondwana occurrences in intracratonic parts would indicate that dharwar craton was rifting even during gondwana period thereby challenging the long held view of cratonic stability

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

rocas verdes ophiolites southernmost south america remnants of progressive stages of development of oceanic type crust in a continental margin back arc basin

northeast basin and range province active tectonics an alternative view slip rates and slip vector azimuths on major active oblique normal faults are used to investigate whether circulation associated with the yellowstone upwelling plume is driving tectonic deformation in the northeast basin and range province observed deformation is consistent with this suggestion the plume is sheared to the southwest by motion of the north american plate testable predictions are made for structure and evolution of the region

proterozoic to mesozoic east gondwana the juxtaposition of india sri lanka and antarctica jurassic and cambro ordovician paleomagnetic pole positions deduced from rocks of sri lanka and antarctica generally conform when sri lanka is juxtaposed with the coast of lutzow holm bay east antarctica in a manner similar to a current gondwana reassembly the highland and southwest groups mostly proterozoic of sri lanka are correlated with the ongul and skallen groups of east antarctica on the basis of similar lithology structural characteristics structural trend tectonothermal history ranging from early proterozoic to mesozoic and the pressure temperature time path of the main metamorphism some neighboring lithotectonic units are also comparable between the two areas fracture lineament systems of sri lanka and antarctica formed after the latest silurian and during or before the jurassic conform in this reconstruction an improved fit of the 2000 m isobaths of india sri lanka antarctica and continuation of the latest archaean mobile belt from enderby land to peninsular india is obtained by fitting sri lanka into lutzow holm bay and enderby land into the embayment in the east coast of peninsular india this juxtaposition of peninsular india to east antarctica involves about 80 km northward movement and about 30 clock wise rotation of sri lanka relative to india the reassembly thus obtained accords well with data supporting the idea that east gondwana existed from the earliest proterozoic to middle mesozoic although some disruption collision events of limited scale are considered possible

new shrimp age and microstructures from a deformed a type granite kanigiri southern india constraining the hiatus between orogenic closure and postorogenic rifting abstracta new u pb zircon shrimp age of 1284 ma from the kanigiri granite india is reported to help constrain the middle to late mesoproterozoic tectonic evolution of the nellore schist belt nsb the kanigiri granite has whole rock chemical characteristics of a type granites and is marked by light rare earth element enrichment a strong negative eu anomaly and negative ba sr p ti and yb anomalies indicating feldspar apatite and ilmenite magnetite fractionation samples show y nb versus yb ta ratios in the range for granites associated with ocean island basalts this two mica granite is peraluminous and alkali calcic to calc alkalic and it has high annite to phlogopite proportions 92 98 strong alignment of flattened mafic microgranular enclaves in the granite together with relatively high to moderate temperature crystal plastic deformation fabric in shear zones within the granite suggest overprinting of subsolidus deformation over a relict magmatic fabric a feature not very common in

ophiolite genesis and global tectonics geochemical and tectonic fingerprinting of ancient oceanic lithosphere ophiolites and discussions on their origin and significance in earth s history have been instrumental in the formulation testing and establishment of hypotheses and theories in earth sciences the definition tectonic origin and emplacement mechanisms of ophiolites have been the subject of a dynamic and continually evolving concept since the nineteenth century here we present a review of these ideas as well as a new classification of ophiolites incorporating the diversity in their structural architecture and geochemical signatures that results from variations in petrological geochemical and tectonic processes during formation in different geodynamic settings we define ophiolites as suites of temporally and spatially associated ultramafic to felsic rocks related to separate melting episodes and processes of magmatic differentiation in particular tectonic environments their geochemical characteristics internal structure and thickness vary with spreading rate proximity to plumes or trenches mantle temperature mantle fertility and the availability of fluids subduction related ophiolites include suprasubduction zone and volcanic arc types the evolution of which is governed by slab dehydration and accompanying metasomatism of the mantle melting of the subducting sediments and repeated episodes of partial melting of metasomatized peridotites subduction unrelated ophiolites include continental margin mid ocean ridge plume proximal plume distal and trench distal and plume type plume proximal ridge and oceanic plateau ophiolites that generally have mid ocean ridge basalt morb compositions subduction related lithosphere and ophiolites develop during the closure of ocean basins whereas subduction unrelated types evolve during rift drift and seafloor spreading the peak times of ophiolite genesis and emplacement in earth history coincided with collisional events leading to the construction of supercontinents continental breakup and plume related supermagmatic events geochemical and tectonic fingerprinting of phanerozoic ophiolites within the framework of this new ophiolite classification is an effective tool for identification of the geodynamic settings of oceanic crust formation in earth history and it can be extended into precambrian greenstone belts in order to investigate the ways in which oceanic crust formed in the archean

source parameters of the cache valley logan utah earthquake of 30 august 1962 abstract the cache valley utah earthquake of 30 august 1962 m s 5 7 has been reexamined our revised focal mechanism with dip 43 strike 193 and rake 101 confirms oblique normal faulting with nodal planes striking approximately north and south this mechanism is based mainly on polarities from records at u s air force lrsm stations which are a valuable scientific resource inversion of long period teleseismic body waveforms indicates centroid focal depth 10 km and seismic moment 3 1 10 24 dyne cm 0 31 10 18 nm corresponding to m w 5 6 the cache valley like other north south trending extensional features in the epicentral region is bounded on its east side by a major active normal fault the east cache fault which has several km of neogene throw however our revised source coordinates for the cache valley earthquake indicate it occurred too far east to have involved slip on this fault its hypocenter was near a downdip projection of the subparallel temple ridge fault a less prominent feature with only 500 m of neogene throw oriented subparallel to the west dipping nodal plane of our focal mechanism we suggest that this fault is continuous and approximately planar between 10 km depth and the earth9s surface with 40 dip and moved in the cache valley earthquake with a component of right lateral strike slip with slip vector azimuth n 65 w

seismic imaging across the eastern ghats belt cuddapah basin collisional zone southern indian shield and possible geodynamic implications abstract the evolutionary nature of the area encompassing cuddapah basin nellore schist belt and the ongole domain of eastern ghats belt south india which contains paleo neoproterozoic imprints of thick sedimentation intense magmatism subduction accretion and possible collision between eastern dharwar craton and east antarctica is still being debated an attempt has been made here to decipher the deep crustal structure and tectonics of this region by reprocessing deep seismic sounding data acquired earlier through the modeling of first arrival refraction and wide angle reflection travel times the derived crustal seismic velocity structure reveals that the intracratonic proterozoic cuddapah basin containing only 4 km thick sediment is bounded by two major faults the moho reaching fault detected on its eastern boundary demarcates cuddapah basin from the nellore schist belt although a deep normal fault is mapped within the nallamalai fold belt but no thrusting signatures are apparent almost all the crustal layers beneath nellore schist belt and the ongole domain of eastern ghats belt show distinct eastward dipping trend conforming to an upthrusted feature suggesting possible presence of a collisional suture besides the areas lying east of cuddapah basin appear to be an accreted orogenic terrain beneath which lower crust has upwarped substantially the entire stretch of the studied region is underplated by unprecedently thick 20 km high velocity 7 0 7 4 km s magma layer above the moho indicating strong crust mantle thermal perturbation and massive subcrustal erosion further an expression of a deep seated mantle thermal anomaly has also been found below the parnapalle region of the sw cuddapah basin beneath which deeper crustal layers have exhumed

dismembered ophiolites in paleoproterozoic nappe complexes of kandra and gurramkonda south india abstract the constitution and structural architecture of ophiolites is important in the understanding of cratonic growth through subduction collision accretion history in the precambrian terrains the nellore schist belt nsb sandwiched between the eastern ghats belt egb and the eastern dharwar craton south india is known to have deformed remnants of ocean plate stratigraphy ops as at kanigiri and kandra suggesting multiple cycle of ocean opening and closure in the paleoproterozoic mesoproterozic interval the outcrop details and structural architecture of the paleoproterozoic kandra complex with geochemical character of subduction related ophiolites is described and analyzed to better constrain the accretion collision history along the southeastern margin of the indian craton imbricate thrust slices between kandra and arimanupadu host slivers of hornblende metagabbro thick massive to pillowed metabasalt sheets sheeted meta dolerite dykes and thin metapsammite and metapelite interstratified with metabasalt comparable to layer 2a of oceanic crust contractional deformation in interlayered metabasalt and quartzite around kandra is accommodated by south dipping imbricate thrust systems and n ne vergent folds the wnw trending thrust system with dominant tectonic transport toward northeast is oblique to overall n s trend of the nsb or the egb further east intercalated metabasalts deep water turbidites and thin metacherts around gurramkonda are deformed into sw vergent imbricate thrust system here occurrence of metabasalt sheets along individual thrusts suggest syntectonic emplacement of some basalts as the subducted and scraped upper oceanic crust was incorporated in the acrcetionary prism the rock sequences around kandra and gurramkonda comprising incomplete ops are tectonically stacked over granites of the eastern dharwar craton margin bivergent thrust systems around kandra possibly root into a detachment separating layers 1 2 from more rigid deeper layers cf layer 3 of oceanic crust as indicated by absence of significant volume of ultramafic rocks at the current outcrop level

ocean plate stratigraphy in east and southeast asia abstract ancient accretionary wedges have been recognised by the presence of glaucophane schist radiolarian chert and melange recent techniques for the reconstruction of disrupted fragments of such wedges by means of radiolarian biostratigraphy provide a more comprehensive history of ocean plate subduction and successive accretion of ocean floor materials from the oceanic plate through offscraping and underplating reconstructed ocean floor sequences found in ancient accretionary complexes in japan comprise from oldest to youngest pillow basalt limestone radiolarian chert siliceous shale and shale and sandstone similar lithologies also occur in the melange complexes of the philippines indonesia thailand and other regions this succession is called ocean plate stratigraphy ops and it represents the following sequence of processes birth of the oceanic plate at the oceanic ridge formation of volcanic islands near the ridge covered by calcareous reefs sedimentation of calcilutite on the flanks of the volcanic islands where radiolarian chert is also deposited deposition of radiolarian skeletons on the oceanic plate in a pelagic setting and sedimentary mixing of radiolarian remains and detrital grains to form siliceous shale in a hemipelagic setting and sedimentation of coarse grained sandstone and shale at or near the trench of the convergent margin radiolarian biostratigraphy of detrital sedimentary rocks provides information on the time and duration of ocean plate subduction the ages of detrital sediments becomes younger oceanward as younger packages of ops are scraped off the downgoing plate ops reconstructed from ancient accretionary complexes give us the age of subduction and accretion direction of subduction and ancient tectonic environments and is an important key to understanding the paleoenvironment and history of the paleo oceans now represented only in suture zones and orogenic belts

mesoproterozoic ophiolitic melange from the se periphery of the indian plate u pb zircon ages and tectonic implications abstract the kanigiri melange within the proterozoic nellore khammam schist belt in southern peninsular india includes ophiolitic fragments that represent the remnants of an oceanic plate the ophiolitic units were accreted along a ne trending suture that juxtaposes the proterozoic eastern ghats granulite belt eggb against the archean nellore schist belt of the dharwar craton the ophiolite components in the kanigiri melange include plagiogranites and gabbros which show mutually intrusive relations indicating their coeval nature we report laser ablation icp ms age data and ree geochemistry of zircons from the gabbro and granite the zircons from both gabbro and granite show high ree contents prominent hree enrichment and a conspicuous negative eu anomaly suggesting a common melt source zircon ree abundances and normalized patterns show little intersample and intrasample variations u pb dating of the zircons reveals prominent mesoproterozoic ages for the plagiogranite with the ca 1 33 ga age of the kanigiri ophiolitic melange offering important clues for arc continent collision during the final stages of amalgamation of the columbia derived fragments within the neoproterozoic supercontinent assembly

geologic setting of the 1884 bear lake idaho earthquake rupture in the hanging wall of a basin and range normal fault revealed by historical and geological analyses analysis of historical accounts of the m 6 3 1884 earthquake in northern utah reveals that the earthquake had an epicenter near 42 3 n 111 4 w approximately 30 km northwest of the event s original location we use detailed reports of damage to structures and the consequences of ground shaking to define a felt area of approximately 70 000 km2 and estimate the peak ground accelerations as 100 300 cm sec2 analysis of the geologic structure of the area indicates that the epicentral area is a half graben bounded on the east by the listric bear lake fault and on the west by the steeply dipping west bear lake fault the earthquake epicenter was on the west side of the basin and we interpret the event to have been the result of slip on the west bear lake fault zone at a depth of 4 5 km this zone consists of steeply dipping antithetic faults in the hanging wall of the east bear lake fault these data suggest that moderate magnitude earthquakes on antithetic or small displacement faults pose a significant if local seismic hazard in the northeastern basin and range province we also demonstrate the utility of combining geological and historigraphic analyses to examine pre instrument era earthquakes online material felt reports and town summaries manuscript received 16 july 2002

palaeoproterozoic assembly of the napier complex southern india and western australia implications for the evolution of the cuddapah basin abstract a detailed examination of lithostratigraphic tectonothermal geochronologic and palaeomagnetic database of the dharwar bastar cratons of south india the yilgarn craton of western australia and the east antarctic shield has shown broad similarity two palaeomagnetic key poles of 2400 ma age from the dharwar and yilgarn cratons suggest near neighbor positions matching patterns of craton outlines orientation of mafic dyke swarms and palaeo north direction for 2400 ma have established a continental assembly of siwa an acronym for south india si and western australia wa at 2400 ma in this assembly the yilgarn craton fits against the bastar craton and the singhbhum craton the available geological data from the napier complex of the eastern antarctica and the dharwar craton of south india were used to prepare the barcode style reconstruction of archaean tectonostratigraphic events of both the cratons the method of matching continental outlines the internal features of two continental blocks and the palaeomagnetic data demonstrate that the napier complex was also a part of siwa during the period 2200 1900 ma and was located at the position of the cuddapah basin of india adjacent to the dharwar craton and the yilgarn craton the separation of the napier complex from the south indian block led to the development of the cuddapah basin at 1950 ma

the tripoli libya earthquake of september 4 1974 implications for the active tectonics of the central mediterranean source parameters have been determined for the earthquake ms 5 6 that occurred offshore of tripoli libya on september 4 1974 one nodal plane of its focal mechanism has dip 37 strike 297 and rake 141 indicating oblique normal faulting this nodal plane is subparallel to many west northwest striking normal faults in the epicentral area and is most likely the fault plane indicating a component of right lateral strike slip with slip vector azimuth n84 e inversion of long period teleseismic body waves indicates 12 km centroid depth and 0 4 1018 n m seismic moment a much larger earthquake ms 7 0 on april 19 1935 that occurred in the same zone of active oblique normal faults 400 km farther southeast near sirte probably involved similar slip sense this zone for which the name tunisia libya seismic zone appears appropriate has overall northwest southeast extent 1000 km from northern libya to between tunisia and sicily it takes up a change in motion direction relative to stable europe from west of north inside the african plate to between n30 e and n50 e in the ionian sea between sicily southernmost peninsular italy southwest greece and libya this suggested motion direction of sicily relative to stable europe agrees with independent estimates from fault slip rates and senses elsewhere in italy

shallow marine to pelagic sediments from a dismembered ophiolite kandra southern india glimpses of ancient subduction zone related sedimentation abstract a suprasubduction zone oceanic back arc setting for the paleoproterozoic kandra ophiolite complex koc in southern india has been suggested from geochemical signatures the telescoped segments of thin deformed sedimentary successions of shallow marine to pelagic affinity overlying a basaltic substrate and preserved within thrust slices of the koc are tectonically juxtaposed against the eastern dharwar craton margin in the northern thrust slice kandra village succession about 150 m of sedimentary strata show intercalation of quartz arenite and basaltic flow in the lower part grading upwards to heterolithic sandstone mudstone deposited above the storm wave base in the southeastern part of the koc gurramkonda succession deep water greywacke turbidite pelagic chert mafic tuff and volcaniclastics and quartz arenite deposited below the storm wave base are preserved as thrust bound packets intermittent basaltic outpourings punctuated deeper water deposition as evidenced by alternate metachert and metabasalt layers and emplacement of basaltic rocks along small thrusts which transpose stratification craton margin sediments consists of immature coarse terrigenous clastics intercalated with thin mafic tuff suggesting influence of mass flow processes giving way to fluvial sedimentation in the lower part of the udaigiri group further up fine grained plane laminated siltstone shale with rippled sandstone lenses grade upward to compositionally mature quartz arenite deposited close to the craton margin with signatures of tidal and wave reworking the association of stratigraphic successions of two contrasting depositional environments in the koc adds to the spectrum of variation of sedimentary collage of the ocean plate stratigraphy the kandra village and gurramkonda successions of the koc possibly represent ancient arc trench milieu and shallower part of oceanic marginal basin respectively paleoproterozoic subduction accretion process led to collapse of these basins and tectonic emplacement of the koc against the eastern dharwar craton margin which hosted near shore sedimentary succession of the udaigiri group occurring west of the koc

proterozoic orogens in southern peninsular india contiguities and complexities abstract the precambrian terranes of southern peninsular india have been central to discussions on the history of formation and breakup of supercontinents of particular interest are the proterozoic high grade metamorphic orogens at the southern and eastern margins of the indian shield skirting the 3 4 ga dharwar craton which not only preserve important records of lower crustal processes and lithospheric geodynamics but also carry imprints of the tectonic framework related to the assembly of the major neoproterozoic supercontinents rodinia and gondwana these proterozoic orogens are described as southern granulite terrane sgt in the southern tip and the eastern ghats mobile belt egmb in the eastern domains of the peninsula the contiguity of these orogens is broken for a distance of 400 km and disappears in the bay of bengal these orogens expose windows of middle to lower crust with well preserved rock records displaying multiple tectonothermal events and multiphase exhumation paths recent studies in these orogens have led to the recognition of discrete crustal blocks or terranes separated by major shear zone systems some of which represent collisional sutures the sgt and egmb carry several important features such as fold thrust tectonics regional granulite facies metamorphism of up to ultrahigh temperature conditions in some cases multiple p t paths development of lithospheric shear zones emplacement of ophiolites presence of alkaline and anorthositic complexes development of crustal scale flower structures transpressional strains and reactivation tectonics a heterogeneous distribution of different metamorphic and magmatic assemblages with distinct spatial and temporal strain variations in shaping the fabric elements in different blocks is identified both egmb and sgt share a common transpressional deformation history during the latest neoproterozoic characterized by the steepening of the initial low angle crustal scale structures leading to a subvertical grain conducive to reactivation tectonics our synthesis of the spatial distribution geometry kinematics and the transpressional strain of the shear zone systems provides insights into the tectono metamorphic history of the proterozoic orogens of southern india and their contiguity and complexities recent understanding of subduction accretion and collisional history along these zones together with a long lived transpressional tectonic regime imply that these orogens witnessed identical tectonic regimes at different times in earth history although the major and common structural architecture was built during the final assembly of the gondwana supercontinent

effects of lithospheric viscoelastic relaxation on the contemporary deformation following the 1959 mw 7 3 hebgen lake montana earthquake and other areas of the intermountain seismic belt 1 the 1959 mw 7 3 hebgen lake mt normal faulting earthquake occurred in an extensional stress regime near the yellowstone volcanic field time dependent crustal deformation data following this major earthquake were acquired by precise trilateration and gps surveys from 1973 to 2000 around the hebgen lake fault zone modeling the changes of baseline lengths across and near the fault reveals a lateral variation of transient rheology in which the lithosphere is stronger near the hebgen lake fault zone than in the vicinity of the yellowstone volcano system the models also imply that the lower crust is stronger than the upper mantle in agreement with results from studies of postseismic and post lake filling relaxations 100 years in addition evaluations of the postseismic motion produced by the hebgen lake and the 1983 mw 6 9 borah peak id earthquakes indicate that horizontal transient motion of up to 1 mm yr contribute significantly to the contemporary regional crustal deformation near the epicentral areas for the eastern basin and range 500 km south of the hebgen lake fault similar rheologic models were derived from the observed uplift associated with the lake bonneville rebound and were used to evaluate the postseismic deformation associated with six most recent paleoearthquakes of the wasatch fault zone and three m 5 6 historic earthquakes of northern utah the results show 0 1 mm yr of horizontal postseismic motion at present time that are within the horizontal uncertainties of continuous gps velocity from the basin and range and significantly smaller than the contemporary extension of 1 3 mm yr in the wasatch front

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

regional structural synthesis wyoming salient of western overthrust belt surface geologic mapping regional and high density reflection seismic data and information from approximately 370 wells have been combined to describe geometrically that area of the western overthrust belt between the snake river plain and the uinta uplift particular care has been taken to verify two dimensional interpretations of multiple thrust sheets by linear restoration by establishing equivalence of pre thrust lengths of affected beds one can gain confidence in interpreted structural geometries as well as generate data in regard to internal shortening and deformation intensity because of irresoluable geometric problems within sections 47 cross sections were developed at roughly 6 mi 10 km spacing to help verify changes in displacement or placement of key st uctural elements displacements of 0 to 32 mi 0 to 51 km have been demonstrated jurassic to paleocene sevier thrusts were active across a previously deformed cratonic shelf terrane and interacted with active structural elements such as the uinta uplift gros ventre range and moxa arch thrusts are progressively younger to the east except for the darby prospect pair in which the darby system is younger

new insight into a subduction related orogen a reappraisal of the geotectonic framework and evolution of the japanese islands abstract the geotectonic framework and the evolutionary history of the japanese islands need revision in accordance with the various geophysical geological evidence gathered by new methodologies in the recent years including seismic tomography vibroseis ground breaking seismic experiments and detrital zircon chronology these investigations have addressed various themes such as 1 seismic profile of the crust and mantle beneath the japanese islands 2 high precision ages of the protoliths of high p t metamorphic rocks and 3 provenance of terrigenous clastics the results have led to a number of important findings including 1 detection of a large mass of slab around the mantle boundary layer suggesting the long term oceanic subduction beneath japan 2 confirmation of the subhorizontal piled nappe structure for the entire crust of japan 3 finding a new high p t metamorphosed accretionary complex unit that represents the youngest blueschist in japan 4 finding of the oldest early cambrian arc batholith and cover sediments and 5 the identification of plural arc batholiths which have already been erased from the surface based on a synthesis of these new data this article presents a re evaluation of the conventional geotectonic subdivision of the subduction related orogen in japan re definition of the elements and their mutual boundaries and re consideration of the geotectonic evolution of the japanese islands in particular the historical change in provenance suggests that proto japan has experienced large scale tectonic erosion in multiple stages and the corresponding large amounts of continental crust materials were subducted for understanding the orogenic growth of japan during the last ca 500 million years the significance of tectonic erosion coupled with continental contraction as well as the oceanward accretionary growth requires further attention

petrological and geochemical characterization of proterozoic ophiolitic melange nellore khammam schist belt se india abstract the ophiolitic melange occurs close to a major fault within the metavolcanics of kanigiri area in the western margin of the khammam nellore schist belt andhra pradesh india the unique feature of kanigiri melange is the occurrence of ophiolitic bodies of various sizes most of which display petrological and geochemical characteristics typical of supra subduction zone oceanic crust the ophiolitic melange is composed mainly of blocks of variably deformed and metamorphosed pillow basalts serpentinized ultramafic rocks meta gabbros cherts and pelagic sediments in a pervasive scaly argillite matrix the melange has a tectonic contact with a granite intrusion and numerous thrust faults cut across the melange exposures primary magmatic features such as drainage cavities in pillow basalts magmatic layering in gabbros and clinopyroxene cumulates in ultramafic rocks are well preserved in low strain domains mafic components enclosed in the melange are characterized by low pressure secondary mineral assemblages retrograded from amphibolite down to greenschist facies as commonly observed in subducted and exhumed orogens all amphiboles in the studied fragments are calcic and cluster in the range from winchite actinolite to hornblende amphibole compositions are characterized by al 2 o 3 2 4 13 8 feo 5 13 k 2 o 0 04 0 7 and x mg 0 67 0 77 the metabasalt and wherlite samples exhibit light rare earth element lree enriched patterns and negative high field strength element hfse zr and ti consistent with a suprasubduction zone geodynamic setting a notable feature of both metabasalt and wherlite samples is their pronounced negative ce anomaly and a positive eu anomaly as observed in a number of modern island arc suites as the petrological features and the geochemical characteristics of the remnant fragments we analyzed in this study are reminiscent of their phanerozoic ophiolite counterparts we suggest that these rocks were derived from a proterozoic oceanic plate belonging to a suprasubduction ophiolite assemblage subduction zone geochemical signatures and ophiolite like crustal lithologies in the study region are consistent with the accretion of juvenile oceanic fragments to the pre existing continental blocks through a forearc continent collision

cleavage duplexes in the marcellus shale of the appalachian foreland abstract cleavage duplexes are zones of platy spaced cleavage that either parallel bedding or ramp through shale sections examples are 2 60 m thick the cleavage within the zones is generally subperpendicular to the zone boundaries but sigmoidally dragged against floor roof and internal thrusts between the well developed floor thrust and the more obscure roof thrusts of the duplexes the shale has been shortened 30 perpendicular to cleavage the thrusts are sharp strain discontinuities because both overlying and underlying shale is uncleaved and less deformed

emplacement and deformation of the vinukonda meta granite eastern ghats india implications for the geological evolution of peninsular india and for rodinia reconstructions abstract the u pb and rb sr systematics of zircon populations from two samples and biotite white mica pairs from four samples constrain the time of emplacement and deformation of the vinukonda meta granite eastern ghats india sm nd and lu hf systematics of whole rock samples provide information on the magma source and its evolution the granitic magma intruded into granitic gneisses of the vinjamuru domain krishna province andhra pradesh india which were already deformed and metamorphosed at epidote amphibolite facies peak conditions consistent sm nd and lu hf whole rock model ages suggest an isotopically homogeneous crustal source and a multi stage evolution of the granitic magma u pb analyses of prismatic zircon multi grain fractions define two discordias with identical upper intercepts at 1588 4 7 1 and 1589 7 5 7 ma interpreted to date magma emplacement rb sr ages of strongly annitic biotite xmg 0 07 0 20 and phengitic white mica 3 13 3 23 si pfu show a complex age pattern due to low temperatures during deformation the rb sr system only partly re equilibrated in biotite synkinematically grown phengitic white mica evidence a low grade metamorphic overprint at 501 474 ma the deformation was associated with w nw directed nappe stacking which caused the actual geological configuration of southern andhra pradesh with the arcuate nallamalai fold belt as most prominent feature regional considerations lead to the proposition that thrusting in the krishna province is the expression of intracratonic deformation in response to the amalgamation of the eastern ghats rayner province terrane with subcontinental india in early palaeozoic time

on merging high and low resolution dems from topsar and srtm using a prediction error filter high resolution digital elevation models dems are often limited in spatial coverage they also may possess systematic artifacts when compared to comprehensive low resolution maps here we correct artifacts and interpolate regions of missing data in airborne topographic synthetic aperture radar topsar dems using a low resolution shuttle radar topography mission srtm dem we use a prediction error pe filter to interpolate and fill missing data so that the interpolated regions have the same spectral content as the valid regions of the topsar dem the srtm dem is used as an additional constraint in the interpolation we use cross validation methods to obtain the optimal weighting for the pe filter and srtm dem constraints

comparison of seismic and geodetic scalar moment rates across the basin and range province scalar moment rates estimated from a 146 year seismicity catalog agree within uncertainties with the deformation rate of the basin and range province determined by using space geodesy seismic moment rates have been estimated from a new catalog of earthquakes complete for m 5 the catalog was compiled from 15 preexisting catalogs supplemented by the review of 44 journal articles throughout the catalog compilation care was taken to obtain the moment magnitude or a reasonable and not inflated equivalent seventy six percent of the moment release occurred during 10 earthquakes of magnitude m w 6 79 the spatial distribution of earthquakes and their moment release matches the geodetic pattern of deformation all three are concentrated in a 200 km wide zone along the western boundary of the great basin with this zone widening to the north several techniques ultimately traceable to kostrov and brune are used to translate the geodetic strain rates into rates of seismic moment release the agreement between geodetic and seismic moment rate suggests that within uncertainties the rate of historic earthquakes within the basin and range province taken as a whole provides a reasonable estimate for the future rate of seismicity these results support the hypothesis that even a few years of detailed geodetic monitoring can provide a good constraint on earthquake occurrence rate estimates for large enough regions

deformation of the ne basin and range province the response of the lithosphere to the yellowstone plume summary tectonic deformation in the ne basin and range province of the western united states is concentrated in two zones the n s trending northern part of the intermountain seismic belt in northern utah se idaho and sw wyoming and the e w trending central idaho seismic zone which converge at yellowstone in nw wyoming accepting the popular view that the yellowstone volcanic field is above an upwelling plume from the deep mantle i explore the possibility that deformation of the brittle upper crust in these two seismic zones may be caused by return flow from this plume this return flow is assumed sheared sw in the direction of motion of the north american plate relative to yellowstone the snake river plain srp a linear outcrop of neogene and quaternary basalt that trends sw from yellowstone for more than 400 km bisecting the angle between the two seismic zones may be a trail formed as the plate moves sw across the upwelling plume beyond 150 km from yellowstone slip vectors on active normal faults in both deforming zones are oriented inwards at 45 towards the sw azimuth along the srp normal slip rates on these faults are typically 1 mm yr 1 implying extensional strain rate 10 15 s 1 proportions of normal slip and strike slip suggest faults in the intermountain seismic belt are rotating anticlockwise at 2 myr 1 around vertical axes and faults in the central idaho seismic zone are rotating clockwise at similar rates within 100 km of yellowstone observed sense of rotation around vertical axes in both zones appears reversed tilt rates of hanging wall beds suggest most faults in both zones are rotating at 2 myr 1 also 10 15 s 1 around horizontal axes oriented nw the relative size of rotation rate around vertical axes and horizontal extensional strain rate is shown to imply that velocity in the underlying deforming fluid is small in the direction perpendicular to the axis of the srp in an initial model this velocity is set to zero enabling the two dimensional pattern of flow at the horizontal upper boundary of this deforming fluid to be solved straightforwardly this approximation enables observed rates and senses of horizontal extension and rotation around a vertical axis to be explained as consequences of the pattern of horizontal gradients of velocity parallel to the axis of the srp in the deforming fluid beneath the brittle layer a refinement suggests that velocity perpendicular to the srp near the upper boundary of the deforming fluid is small but inward towards the srp from both sides and is accompanied by downwelling beneath the srp beyond 100 km sw of yellowstone this pattern of flow will act to move magma in the uppermost mantle beneath the srp from its sides it may thus reconcile petrological observations that srp basalts do not show deep mantle characteristics expected had they been extruded from the yellowstone plume with the existence of this plume nearby conservation of angular momentum around horizontal axes perpendicular to the srp for the combined system of the plume interacting with the north american plate leads to the deduction that the plume radius is 50 km consistent with results of other investigations and its upwelling velocity is 60 mm yr 1

the cuddapah salient a tectonic model for the cuddapah basin india based on landsat image interpretation abstract analysis of geologic geophysical data and lineaments derived from landsat image interpretation has revealed a pattern of tectonic inheritance of archean structural elements by the folded and thrusted eastern margin of the middle late proterozoic cuddapah basin in india a structural pattern set by deep crustal faults in the archean and intracratonic basin fabric is apparent in both sedimentary and tectonic trends in the basin the lineaments represent broad zones of en echelon and parallel alignments that appear to have nucleated on deep crustal faults which were reactivated as structural uplifts lateral and frontal ramps and transverse tear faults the major zones recognized are the northeast trending veldruti guntur lateral ramp to the north and the northwest trending cuddapah nellore transverse tear fault to the south east west directed compression during the eastern ghats latest proterozoic orogeny was apparently confined within these converging lineament zones that effectively buttressed the west verging thrust fronts block uplift along the ne trending veldruti guntur lateral ramp acted as a boundary to east to west thrust translation the northeastern ends of folds and thrusts were pinned down with relative displacement being clockwise and greater increasing to the southwest the lack of a lateral ramp or basement buttress to the south resulted in the development of the left lateral cuddapah nellore transverse tear fault steep imbricate thrust ramps in the foreland resisted further movement westward the resulting convex to the west arcuate nallamalai and vellikonda thrust fronts broadly paralleled by the east coast gravity high anomaly kaila and bhatia 1981 is herein named the cuddapah salient

geologically constraining india in columbia the age isotopic provenance and geochemistry of the protoliths of the ongole domain southern eastern ghats india abstract the ongole domain in the southern eastern ghats belt of india formed during the final stages of columbia amalgamation at ca 1600 ma yet very little is known about the protolith ages tectonic evolution or geographic affinity of the region we present new detrital and igneous u pb hf zircon data and in situ monazite data to further understand the tectonic evolution of this columbia forming orogen detrital zircon patterns from the metasedimentary rocks are dominated by major populations of palaeoproterozoic grains ca 2460 2320 2260 2200 2100 2080 2010 1980 1920 1850 and 1750 ma and minor archaean grains ca 2850 2740 2600 and 2550 ma combined u pb ages and lu hf zircon isotopic data suggest that the sedimentary protoliths were not sourced from the adjacent dharwar craton instead they were likely derived from east antarctica possibly the same source as parts of proterozoic australia magmatism occurred episodically between 1 64 and 1 57 ga in the ongole domain forming felsic orthopyroxene bearing granitoids isotopically the granitoids are evolved producing ehf values between 2 and 12 the magmatism is interpreted to have been derived from the reworking of archaean crust with only a minor juvenile input metamorphism between 1 68 and 1 60 ga resulted in the partial to complete resetting of detrital zircon grains as well as the growth of new metamorphic zircon at 1 67 and 1 63 ga in situ monazite geochronology indicates metamorphism occurred between 1 68 and 1 59 ga the ongole domain is interpreted to represent part of an exotic terrane which was transferred to proto india in the late palaeoproterozoic as part of a linear accretionary orogenic belt that may also have included south west baltica and south eastern laurentia given the isotopic geological and geochemical similarities the proposed exotic terrane is interpreted to be an extension of the napier complex antarctica and may also have been connected to proterozoic australia north australian craton and gawler craton

neoproterozoic massif type anorthosites and related magmatic suites from the eastern ghats belt india implications for slab window magmatism at the terminal stage of collisional orogeny abstract the jugsaipatna massif type anorthosite complex jac in the eastern ghats belt of india comprises anorthosite leuconorite norite in the central part and gabbros gabbronorites and porphyritic granites in the periphery in this study we report laser ablation icp ms zircon u pb data and ree geochemistry from the anorthosites gabbros and porphyritic granites from the jac the zircon data yield weighted mean 207 pb 206 pb ages of 918 33 ma mswd 2 2 for the anorthosite and 931 38 ma mswd 2 2 and 928 35 ma mswd 0 99 for two leuconorites the gabbros bordering the anorthosite body yield weighted mean 207 pb 206 pb ages of 984 10 ma mswd 0 41 and 969 12 ma mswd 1 5 zircons from the associated porphyritic granites define two concordant age groups an older group with 207 pb 206 pb weighted mean age of 996 11 ma mswd 2 1 and a younger group with an age of 964 29 ma mswd 2 1 zircons from another granite sample yield an age of 957 17 ma mswd 1 1 identical to the neoproterozoic age data obtained from the zircons in the anorthosites and gabbros of the jac the zircons from anorthosites show moderate ree contents prominent hree enrichment and a conspicuous positive eu anomaly the zircons from the granites show high ree contents prominent hree enrichment and a conspicuous positive eu anomaly suggesting a common melt source the ages reported in study correlate well with similar ages of 983 2 5 ma for the anorthosites from chilka lake complex and the ca 930 ma for bolangir anorthosite in the eastern ghats belt the early neoproterozoic ages reported from the magmatic suite in this study remarkably coincide with the timing of ultrahigh temperature metamorphism reported from various localities in the eastern ghats belt in recent studies the coeval nature of mantle derived magmatism and ultrahigh temperature metamorphism in a collisional orogen following a prolonged subduction accretion history along the eastern periphery of the indian lithosphere suggests asthenospheric upwelling probably through a slab window mechanism we correlate the geodynamic setting to post collisional slab break off at the terminal stages of the orogeny

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

bivergent thrust wedges surrounding oceanic island arcs insight from observations and sandbox models of the northeastern caribbean plate at several localities around the world thrust belts have developed on both sides of oceanic island arcs e g java timor panama vanuatu and the northeastern caribbean in these localities the overall vergence of the backarc thrust belt is opposite to that of the forearc thrust belt for example in the northeastern caribbean a north verging accretionary prism lies to the north of the eastern greater antilles arc hispaniola and puerto rico whereas a south verging thrust belt called the muertos thrust belt lies to the south researchers have attributed such bivergent geometry to several processes including reversal of subduction polarity subduction driven mantle fl ow stress transmission across the arc gravitational spreading of the arc and magmatic infl ation within the arc new observations of deformational features in the muertos thrust belt and of fault geometries produced in sandbox kinematic models along with examination of published studies of island arcs lead to the conclusion that the bivergence of thrusting in island arcs can develop without reversal of subduction polarity without subarc mantle fl ow and without magmatic infl ation we suggest that the eastern greater antilles arc and comparable arcs are simply crustalscale bivergent or doubly vergent thrust wedges formed during unidirectional subduction sandbox kinematic modeling suggests in addition that a broad retrowedge containing an imbricate fan of thrusts develops only where the arc behaves relatively rigidly in such cases the arc acts as a backstop that transmits compressive stress into the backarc region further modeling shows that when arcs behave as rigid blocks the strike slip component of oblique convergence is accommodated entirely within the prowedge and the arc the retrowedge hosts only dip slip faulting frontal thrusting the existence of large retrowedges and the distribution of faulting in an island arc may therefore be evidence that the arc is relatively rigid the rigidity of an island arc may arise from its mafi c composition and has implications for seismic hazard analysis

sm nd and rb sr dating of amphibolite from the nellore khammam schist belt se india constraints on the collision of the eastern ghats terrane and dharwar bastar craton the nellore khammam schist belt se india is sandwiched in between the proterozoic eastern ghats terrane and the archaean dharwar bastar craton we report sm nd and rb sr mineral isochron ages of amphibolite from the schist belt the sm nd and rb sr ages are 824 43 ma and 481 16 ma respectively the sm nd age indicates the timing of peak metamorphism whereas the rb sr age indicates the pan african thermal overprint the peak metamorphism was related to collision of the eastern ghats terrane with the dharwar bastar craton which occurred during early neoproterozoic time

dynamics of earthquake normal faulting two dimensional lattice particle model a 2d lattice particle model is used to simulate the dynamic rupture process of a normal fault the system equations for the particle motions are solved numerically by the finite difference method under a given block boundary condition the flexibility of the implementation of a 2d lattice particle model to simulate an earthquake dynamic process was demonstrated in previous modeling of a shallow angle thrust fault shi et al 1998 numerical results indicate that the particle motions displacement velocity and acceleration along the fault are discontinuous both in the fault parallel and fault normal directions with a localized slip rupture and localized fault separation in the vicinity of the fault outcrop the position at which the fault intersects with the free surface the particle velocity and acceleration increase rapidly both on the hanging wall and the footwall the particle motions on the hanging wall are larger than those on the footwall these motions are amplified as the fault scarp develops rupture breaks out at the surface with strong asymmetry between the hanging wall and the footwall along the free surface as the distance from the fault outcrop increases the particle velocity and acceleration decrease rapidly on the footwall and less rapidly on the hanging wall the asymmetrical particle motion results from the geometrical effect of the dip of the fault the free surface and the dynamic source rupture the combination of all of these effects causes a strong asymmetry in stress when the rupture pulse approaches the free surface the dynamically propagating rupture is characterized by a ramp slip time function accompanied with fault opening the slip pulse becomes sharper when the rupture approaches the free surface consequentially the hanging wall in the vicinity of the fault exhibits a large vibration which generates a strong surface wave propagating along the free surface away from the fault scarp on the hanging wall side this result is similar but significantly different from the numerical simulation of a normal fault with a moving double couple dislocation source benz and smith 1988 in addition the numerical result is qualitatively in agreement with recent foam rubber experiments brune and anooshehpoor 1999 and similar to results from a finite element simulation oglesby et al 1998 oglesby 1999 comparing with a 2d strike slip fault and thrust fault the particle motions in the vicinity of the normal fault on the free surface are smaller for a same size rupture pulse

block rotation in western turkey 1 observational evidence western turkey is a region of rapid continental extension where extension rate increasing westward causes counterclockwise vertical vorticity and hence counterclockwise rotation around vertical axes on a regional scale field observations and seismicity of the past century are used to deduce positions and slip senses of major active oblique normal faults in this region which take up extension in the upper crustal brittle layer and allow fault bounded blocks to rotate around vertical axes the principal active normal faults in western turkey strike roughly east west near the aegean coast turning gradually toward westnorthwest eastsoutheast strike across 200 km distance inland to the east slip vector azimuths indicate typical extension direction on these faults is s18 8w they truncate a second set of faults with smaller displacement and roughly orthogonal strike and slip vector azimuth as well as subdividing the brittle layer into blocks that show little internal deformation some major oblique normal faults subdivide it into domains that show different neogene rotation around vertical axes some domains contain sets of major active oblique normal faults that bound blocks that are elongated angular and shaped like tilted dominoes these faults take up extension and can also take up rotation around vertical axes provided they and the blocks between them rotate around vertical axes at the same rate where adequate paleomagnetic observations are available they indicate these domains have rotated counterclockwise as expected by up to 40 roughly equal to the change in strike of the principal set of active faults between the aegean coast and the eastern edge of the actively extending zone however evidence is scarce for the right lateral strike slip expected in some kinematic models on a set of oblique normal faults that takes up extension and counterclockwise rotation instead each fault appears to have the component of strike slip necessary to enable it given its local strike to slip in ue direction in which the region is extending two domains that have rotated clockwise are approximately circular in plan view with diameter 90 km and are bounded by faults with variable orientation each comprises a single block with no internal major active faults

multi stage deformation in the nallamalai fold belt cuddapah basin south india implications for mesoproterozoic tectonism along southeastern margin of india abstract the common occurrence of small scale refolded folds deformed lineations and overprinting of foliation in the northern nallamalai fold belt nfb within the intracratonic cuddapah basin south india suggest three phases of deformation d 1 d 2 and d 3 during the late paleoproterozoic to neoproterozoic d 1 structures are represented by tight to isoclinal folds a slaty cleavage and local development of mylonites d 2 structures include ne trending tight to open folds f 2 with variable plunge indicating control of large domal structures and a steep crenulation cleavage developed in phyllites and other schistose rocks the above structures are overprinted by e w trending d 3 folds and cleavage which affect mesoproterozoic rocks of the srisailam formation uppermost nallamalai group in the e w trending vami konda range and metasediments of the palnad area thought to be equivalent of the neoproterozoic kurnool group taking into account the ages of intrusive vellaturu granite 1575 ma which is post d 2 deformation in the nfb and the chelima lamproite 1400 ma which intrudes the folded nallamalai rocks we suggest that the earlier episodes of multiple deformation in the nfb represent either late paleoproterozoic or early mesoproterozoic nw se compression in this part of the east gondwana the e w fold thrust structures affecting the srisailam quartzite and adjacent metasediments in the palnad area represent late mesoproterozoic and or neoproterozoic event the granite gneisses and schists of the nellore schist belt bordering the nfb are affected by both early and later events and thrust over rocks of the nallamalai group we propose that early deformation in the nfb lying southwest of the eastern ghats and roughly parallel to the present southeastern coast of india was unrelated to and occurred prior to the main deformation in the eastern ghats which is generally correlated with the 1000 ma old grenville event alternatively in view of the complex protracted evolution of the eastern ghats and published geochronological data supporting pre grenvillian tectonism particularly in the western charnockite zone of the eastern ghats d 1 and d 2 deformation in the nfb may be linked to this older 1600 1400 ma tectonic disturbance in the eastern ghats

shrimp u pb zircon provenance of the sullavai group of pranhita godavari basin and bairenkonda quartzite of cuddapah basin with implications for the southern indian proterozoic tectonic architecture abstract proterozoic basins in cratonic india referred to as purana basins cover about 20 of the archean basement of the subcontinent although the stratigraphy of most of these basins has been well established it is only recently that radiometric age constraints have been obtained for some of the sedimentary sequences this study provides new data for two of the purana basins in southern india using shrimp u pb analysis of detrital zircons for the pranhita godavari basin an age limit of 709 ma is provided for the age of deposition of the sullavai group this prolongs the duration of proterozoic sedimentation to approximately one billion years ca 1700 709 ma and establishes the venkatpur sandstones of sullavai group as the youngest purana basin succession identified in india so far a major zircon provenance age peak at about 1000 ma and zircon ages between 800 and 750 ma are correlated with major tectonothermal events in the eastern ghats mobile belt egmb and intrusion of granites and associated pegmatites at that time the main provenance area of the venkatpur sandstones is interpreted to be the egmb with subordinate supply of sediments from the eastern dharwar craton it is suggested that portions of the egmb must have been an integral part of peninsular india at the time of deposition of these sediments for the cuddapah basin new u pb detrital zircon age constraints are provided for the nallamalai group sediments bairenkonda quartzites within the nallamalai fold belt the youngest population of which yielded an age of ca 1550 ma this age is similar to the emplacement age of the vinukonda granite 1589 4 4 ma in the nellore schist belt this suggests that the nellore schist belt was a source region for the bairenkonda quartzites and that deposition continued until at least 1550 ma a high precision archean age ca 3366 ma for a detrital zircon grain indicates the presence of paleoarchean components within the sediment source region provided that paleoarchean rocks are as yet unknown from the largely juvenile neoarchean eastern dharwar craton there exists a possibility that the nallamalai group was sourced from the ongole domain of the egmb

seismically derived gondwana and proterozoic sediments east of cuddapah basin south indian shield and its possible geotectonic implications the study area situated east of the intracratonic proterozoic cuddapah basin that covers nellore schist belt ongole domain of the eastern ghats belt and adjacent east coast terrain forms a geodynamically important segment of the dharwar craton this region came into focus due to proposition that during paleoproterozoic to mesoproterozoic era it underwent persistent oceanic subduction continent continent collision and multi stage accretional growth in view of this we have reprocessed in detail the deep seismic sounding data over this region and integrated the obtained results with other geophysical studies to decipher the deep subsurface crustal structure underneath the derived shallow seismic section across this region showed the presence of a thin layer 250 m of gondwana sediments with a distinct velocity of 4 20 km s and a lateral dimension of about 40 km around vinjamuru region of the nellore schist belt another important finding has been the depiction of 5 3 and 5 5 km s velocity sediments comparable to upper and lower cuddapah sediments between nellore schist belt and the east coast indicating the possible presence of an additional proterozoic sedimentary terrain named here as east coast sedimentary basin overlying the concealed archean crystalline basement the presence of this sedimentary terrain which is separated from the cuddapah basin by an exhumed horst like feature situated below nellore schist belt would indicate proterozoic sedimentation in a much larger area during columbia and rodinia supercontinental assembly periods than hitherto known importantly no seismic trace of the eastern ghats belt has been found between nellore schist belt and the east coast it appears that during the gondwana period entire eastern segment of the east dharwar craton has been persistently rifting uplifting and eroding together with other gondwana grabens in india thereby leaving behind only a thin veneer of gondwana sediments at many places in view of the presence of number of gondwana occurrences all along the east coast it is felt that the rifting during the gondwana period may have been a prelude to india antarctica breakup with final separation between the two taking place much later during early cretaceous

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

structure and tectonics of a mesoproterozoic ophiolite insight from kanigiri ophiolite with a melange zone southern india abstract the 1334 ma kanigiri ophiolite ko occurring within the nellore schist belt nsb at the eastern dharwar craton edc margin india provides clues to tectonics of the paleo ocean outboard of mesoproterozoic indian craton the ko shows a diverse assemblage of fragmentary remains of the then oceanic crust including massive gabbro anorthosite from the lower part through a tectonic melange to 2 3 km thick slivers of upper oceanic crust with vesicular to pillowed basalt mafic agglomerate and mafic to felsic tuff with thin sedimentary intercalation the melange consists of up to meter size blocks of mafic igneous rocks and larger rafts of pelagic chert set in a fine grained weakly foliated mafic matrix showing low grade metamorphism and hydrothermal alteration the volcanic components of the ko are ultrapotassic to potassic while the gabbroic rocks show high ti v high th nb ratios high y and enrichment in th compared to hf and ta suggesting suprasubduction zone oceanic arc setting restricted to n s elongated fault bounded block the ko shows internal deformation with two sets of folds and tectonic foliation in the upper part and common block in matrix structure with gabbroic blocks in the middle part possibly representing an accretionary wedge the ko is tectonically juxtaposed against multiply deformed shallow marine succession of the udaigiri group nsb where second generation folds and crenulation cleavage compare with those in the ko metavolcanics post tectonic granitic stocks of 1284 ma age intrude the ophiolitic melange and adjoining rocks of the nsb suggesting ocean closure and accretionary growth of the edc margin during the mesoproterozoic components of the edc margin were fused together during the 1100 900 ma rodinia amalgamation with collisional suturing between india and antarctica the earlier supercontinent build up namely columbia or nuna probably left traces of an archipelago like paleogeographic scenario outboard of the edc

the north aegean region a tectonic paradox in the past two decades several publications have been presented concerning the recent and active fault geometry kinematics and geodynamics of the aegean region and particularly of the northern sector data and results are often contradictory and because of the complexity of the area most hypotheses and models should be considered carefully the right lateral movement of the north anatolia fault continues into some branches of the north aegean fault system there strike slip motion along ne sw trending faults coexists with dip slip e w trending faults in the frame of an extensional regime related to n s crustal stretching if we take into account the geodynamic environment of the region several mechanical problems arise to the east the aegean is compressed by the westward convergence of anatolia while to the south and west along the hellenic arc a hemiradial compression occurs due to subduction although the north anatolia north aegean trough fault system resembles a restraining bend the whole area is in fact affected by pure extension and local transtension along ne sw trending structures accordingly the major paradox of the area and especially in the western sector fault termination is the occurrence of extension where compression should regionally or at least locally predominate

neogene evolution of the denizli region of western turkey the denizli region contains one of the easternmost neogene sedimentary basins in the part of western turkey that takes up ssw extension this isolated active normal fault zone which contains closely spaced en echelon normal fault branches is investigated using field measurements of fault exposures and tilted sediments and seismological observations as a case study to address its style of extension the denizli basin is no more than 1 km thick and has accommodated up to 4 km of extension substantial 20 sediment dips are readily explicable assuming extension is accompanied by distributed vertical simple shear with initial and present day dips of the main normal faults that control extension most likely 54 57 and 45 50 other aspects of the form of this basin require regional uplift at 0 1 mm yr 1 providing the first indication of major tectonic elevation changes in this actively extending region that are not directly related to throw on normal faults

collision tectonics in the late precambrian eastern ghats mobile belt mesoscopic to satellite scale structural observations regional mapping of a section across the eastern ghats mobile belt egmb north of the godavari graben in eastern peninsular india by using landsat thematic mapper data enables recognition of a number of shear zones lineaments and structural domes and basins a conspicuous megashear occurs at the western boundary of the granulite facies rocks of the egmb adjacent to the archean granite greenstone craton the confinement of a suite of alkaline igneous rocks to this shear zone is a notable feature the strike extensions of this shear belt extend through to the elchuru alkaline complex prakasam district andhra pradesh and the syenite plutons of koraput district orissa the contrasting lithologies metamorphism and structural history on either side of the shear zone suggests that it might be a precambrian suture zone the mesoscopic structural features in the egmb include prominent foliation with moderate to steep dips folds faults shears s c fabrics pinch and swell structures and other linear fabric elements these observations favour the consideration of drastic crustal shortening and thickening and a complex deformational sequence the major rock units in this part of egmb comprise garnetiferous sillimanite gneisses quartzites and calc granulites forming the khondalitic suite of rocks and a wide variety of charnockitic rocks the contact of the two rock units is generally sheared and often migmatised the structural fabric suggests two major tectonic events an essentially horizontal tectonic regime resulting in thrust systems and associated structures subsequently followed by strike slip tectonics characterized by high shear strains features such as westward verging thrusts large scale recumbent folds major shear zones structural domes and basins indications of tectonic crustal shortening extensive calc alkali magmatism and widespread migmatization in the region are attributed to collisional processes during proterozoic times the spatial disposition of the egmb and its linkage with the distribution of similar rock units during the late precambrian time in a global tectonic scenario are discussed

the central sudetic ophiolites sw poland petrogenetic issues geochronology and palaeotectonic implications abstract the central sudetic ophiolites cso including the largest and best studied leza ophiolite are relatively well preserved complete palaeozoic ophiolitic sequences at the ne margin of the bohemian massif near the eastern edge of the variscan belt in central europe despite a detailed study and a well documented morb type affinity the geochemical complexity of these ophiolites has only recently been appreciated allowing construction of petrogenetic models we review here petrological and geochemical data indicating a contrast between the plutonic and volcanic members of the leza ophiolite this contrast was previously interpreted in terms of a model of two stage incremental melting of a depleted asthenospheric source producing basaltic magmas and subsequent melts crystallizing as gabbros however we argue that the geochemical differences between the plutonic and volcanic members can be explained by differentiation and cumulation processes of broadly similar parental magmas preliminary interpretation of new shrimp zircon age data from plutonic and volcanic members are consistent with earlier u pb zircon ages and provide evidence for magmatic crystallization of the leza ophiolite at c 400 ma the cso interpreted as traces of the rheic ocean are key for reconstructing the early to mid palaeozoic rifting processes distinct similarities exist with time equivalent ophiolitic units in the western variscan segment of the nw iberian massif the cso represent c 400 ma oceanic crust fragments and their structural position delineates likely major variscan tectonic sutures and tectonic mosaic domains within the variscan accretionary prism

plate margin paleostress variations and intracontinental deformations in the evolution of the cuddapah basin through proterozoic abstract the sedimentary basins are often influenced by adjoining mobile belts as is the case of the proterozoic cuddapah basin in southern india lying in proximity of the eastern ghats granulite belt egb and the southern granulite terrain sgt two major faults gani kalva and kona faults in the western part of the cuddapah basin have been examined in this work to comment on the changes in paleostress conditions affecting the basin evolution punctuated by several stages of extensional and compressional regimes in the time interval 1 9 0 5 ga the tensor solutions were obtained for the mesoscale faults and fault striae using the improved right dihedron method followed by the rotational optimization method tensor delvaux and sperner 2003 combining the paleostress field reconstruction and other structural stratigraphic attributes we propose a possible scenario of punctuated evolution of the cuddapah basin and its inversion the stress regimes are tentatively correlated with multiple stages of basin opening and deformation of basin in fill representing the pre grenvillian through the pan african orogeny the paleostress conditions derived from various stratigraphic horizons provide an opportunity to comment on the changes in tectonic stresses including several stages of extensional and compressive regimes in the cuddapah basin the tensor solutions were obtained for the mesoscale faults and fault striae in the neighborhood of above two fault lines using the improved right dihedron method followed by the rotational optimization method tensor delvaux and sperner 2003 the most prominent stress states recorded around the two fault lines can be classified into those affecting 1 the paleoproterozoic lower cuddapah successions 2 the younger kurnool group and 3 both the groups integrating the stress states of the fault slip analysis obtained from different unconformity bounded rock groups of lower cuddapah and other geologic data we suggest extensional to transtensive pure strike slip regime to be active during the first phase of basin opening and c 1 89 ga mafic igneous activity late compressional to transpressive pure strike slip regimes are well recorded from the younger kurnool group representing late neoproterozoic deformations the tensor solutions from different unconformity bound stratigraphic horizons constrain different states of deformation we relate the extensional to transtensive pure strike slip regimes from lower cuddapah successions to the ongoing basin opening events and the associated palaeoproterozoic igneous activities the late neoproterozoic to early paleozoic compressional to transpressive strike slip regime present the possible effects of compressional activities happening around the cratonic margin the present analysis lends further support to the idea that estimation of paleostress states from fault slip data even in regions of relatively weak deformation in continental interior are important while assessing influence of plate margin stresses on the continental interior

structural trends in the cuddapah basin from deep seismic soundings dss and their tectonic implications abstract structural trends in the upper proterozoic cuddapah basin at the basement level and at the moho level have been discussed based on deep seismic sounding dss studies results of dss studies along the alampur koniki profile profile 2 of fig 1 crossing the northern part of the cuddapah basin have been discussed in detail these results combined with the results of the kavali paranpalle section of the kavali udipi dss profile profile 1 of fig 1 kaila et al 1979 crossing the basin on its southern flank along with geological data and earthquake epicentral locations are used to explain the structural trends of the area it has been shown that the cuddapah basin was first created in its western part by downfaulting of the crustal block between faults 7 and 14 towards the west and fault 6 in the east fig 1 subsequently the eastern part was downfaulted against fault 6 before the commencement of upper cuddapah sedimentation further downfaulting towards the north along fault 5 created the srisailam block minor scale downfaulting between faults 7 and 13 in the west and fault 6 in the east and fault 8 in the north gave rise to the kurnool sub basin at a later stage similar downfaulting east of fault 9 and north of fault 5 gave rise to the palnad sub basin both these sub basins received kurnool sediments after the close of kurnool sedimentation the blocks between faults 4 and 6 along profile ii and between 11 and 6 along profile i were uplifted at the basement level thus giving rise to the nallamalai hills and iswarakuppam dome fig 1 the low angle thrust fault 3 on the eastern margin of the cuddapah basin might be a post cuddapah phenomenon the low angle thrust fault 2 probably occurred in the post dharwar period faults 1 17 and 10 near the east coast of india seem to be comparatively younger probably of mesozoic time along which the coastal block is downfaulted giving rise to the sedimentary basins

surface faulting in the southern italian campania basilicata earthquake of 23 november 1980 the campania basilicata earthquake of 23 november 1980 was the largest ms 6 9 and most destructive earthquake that has occurred in this region of southern italy for over 100 years killing more than 3 000 people the consensus among seismologists geologists and earthquake engineers who have studied1 10 this event is in keeping with previous italian earthquakes that it did not produce faulting at the surface this has led to the establishment of a number of models2 3 11 13 requiring an unusual tectonic setting for the southern apennines however on a recent visit to the epicentral region of the earthquake may 1984 we discovered more than 10 km of surface faulting that is consistent with focal mechanisms for this event based on first motion polarities2 4 5 12 and long period waveform studies14 16 which show that it involved normal faulting with one nodal plane dipping at 60 towards the north east our observations of this the first well documented earthquake fault break to be reported in italy suggest that the deformation associated with earthquakes in the southern apennines takes place in the upper 10 15 km of the earth s crust on steep planar normal faults which break the surface as is widely observed in other areas of active extension outside italy

proterozoic evolution of eastern dharwar and bastar cratons india an overview of the intracratonic basins craton margins and mobile belts abstract based on critical analysis of stratigraphic succesions in the proterozoic intracratonic basins geochronological data and possible connections or disconnections with adjacent fold belts and craton margin mobile belts an overview of the proterozoic evolution of the eastern dharwar and bastar cratons in india is presented the chattisgarh and cuddapah basins in these cratons with archean nuclei host sedimentary successions ranging in age from the paleoproterozoic to the ediacaran period and representing several silicilastic and carbonate cycles the proterozoic successions of the pranhita godavari valley pgv basin along the dharwar bastar join record multiple rifting since late neoarchean suturing of the two cratons we postulate a first order stratigraphic correlation across the cratons and their join and discuss how major sea level fluctuations coupled with regional tectonic events shaped the development of unconformity bound successions adjoining fold belts and the mobile belts with supposed global tectonic connections the oldest paleoproterozoic intracratonic sedimentation is preserved in the cuddapah and pgv basins while sedimentation in the bastar craton is largely mesoproterozoic the fluviodeltaic to shallow marine neoproterozoic sedimentation followed emplacement of end mesoproterozoic kimberlites and lamproites indicating thermal rejuvenation of the indian continental crust the allochthonus nallamalai fold belt in eastern cuddapah basin and the early mesoproterozoic fold belt in pgv basin point to craton margin crustal convergences which punctuated the paleoproterozoic sedimentation widespread development of carbonate bearing sequences in the mesoproterozoic to neoproterozoic successions point to peneplanation of the cratons and stable platformal sedimentation the neoproterozoic sedimentation was terminated following the docking of the eastern ghats belt to the eastern margin of the dharwar bastar ensemble and possible final tectonic hiccups in the central indian tectonic zone bordering the bastar craton the available data and their analysis rule out any foreland basin type connection between the eastern ghats belt and cratonic sedimentation in bastar and eastern dharwar

rbsr geochronological studies on the granites of vinukonda and kanigiri prakasam district andhra pradesh india

accreted oceanic materials in japan abstract the phanerozoic circum pacific orogenic belts contain numerous ocean derived materials accreted through plate converging processes japanese islands in particular display various kinds of oceanic materials of different origins including fragments of seamounts oceanic reef limestone morb like rocks and oceanic mantle and pelagic sediments the compilation of these rocks in many subduction complexes of late permian to the present led to following conclusions accretion processes work effectively only for materials primarily composing the upper portion of subducting oceanic crust i e layer 1 and layer 2 many fragments of seamount with alkali basalt 600 hot spot seamount 26 oceanic reef limestone 291 morb like basalt 200 and numerous cherts more than 1000 are recognized as ancient oceanic materials accreted to the japanese islands however gabbros and mantle materials of layer 3 and lower parts of the oceanic lithosphere scarcely occur in subduction accretion complexes except for a few examples of back arc basin or fore arc origin accretion occurs episodically in southwest japan oceanic materials were accreted intermittently in 1 a end permian 2 b middle late jurassic 3 c late cretaceous times 4 d at ca 50 ma and 5 e in miocene times while in northeast japan and hokkaido this occurred in b middle late jurassic c late cretaceous and f early cretaceous times in contrast to the general belief on accretion of younger oceanic plates the majority of japanese subduction accretion complexes were formed during the subduction of plates up to 160 ma old the accretionary events in end permian and middle late jurassic times coincide with northward collision of ancient island arcs oceanic rises or seamount chains of hot spot origin with the asian continent accretion relevant to subduction of older plates may be controlled by the collision subduction process of these topographic reliefs on an oceanic plate in addition the chronological coincidence with the continent collision amalgamation between the sino korean and siberian platforms and between the sino korean and yangtze blocks also implies collision induced voluminous supply of elastics from back arc regions and its contribution to the formation of huge accretionary complexes accreted fragments of ancient seamounts are much smaller than the average size of modern seamounts this implies that most parts of a colliding seamount are not accreted but subducted together with the underlying oceanic crust to much deeper levels with respect to the metamorphic grades for japanese subduction complexes oceanic materials have less than 1 vol in the zeolite facies 15 20 in the prehnite pumpellyite metagraywacke facies and ca 30 in the greenschist glaucophane schist facies and albite epidote amphibolite fades this relationship indicates that the major process for landward accretion of oceanic materials is not off scraping or sedimentary mixing at the trench but underplating subcretion at much deeper levels of a subduction zone

foreshocks and aftershocks of large m 5 5 earthquakes within the western cordillera of the united states source parameters of foreshocks and aftershocks of 27 large m 5 5 earthquake sequences occurring within the western cordillera of the united states between 1915 and 1988 have been used to examine the properties of foreshocks and aftershocks and to determine how foreshocks and aftershocks relate to faulting properties of their main shocks to physiographic province and to heat flow this study examines only the largest foreshocks and aftershocks occurring within 2 months and 40 km of the main shocks results of this study show that nearly 60 per cent of western cordilleran earthquakes have foreshocks and that 58 per cent of the foreshocks occurred within 24 hours of their main shocks most aftershocks appear to be occurring on a fault plane with the same or similar orientation to the fault that ruptured in the main shock at or slightly above the main shock depth the average magnitude difference between main shocks and their largest aftershocks is 1 03 0 47 the difference between main shock and aftershock magnitude appears to decrease with increasing heat flow sixty percent of the aftershocks occurred within 24 hours of their main shocks but nearly one third occurred more than 1 week after their main shocks