paragenesis of sodic pyroxene bearing quartz schists implications for the p t history of the sanbagawa belt sodic pyroxene jadeite content x jd 0 1 0 3 occurs locally as small inclusions within albite porphyroblasts and in the matrix of hematite bearing quartz schists in the sanbagawa sambagawa metamorphic belt central shikoku japan the sodic pyroxene bearing samples are characteristically free from chlorite and their typical mineral assemblage is sodic pyroxene subcalcic or sodic amphibole phengitic mica albite quartz hematite titanite epidote spessartine rich garnet occurs in mn rich samples sodic pyroxene in epidote bearing samples tends to be poorer in acmite content average x acm 0 26 0 50 than that in the epidote free samples x acm 0 45 0 47 x jd shows no systematic relationship to metamorphic grade and is different among the three sampling regions saruta gawa asemi gawa and bessi besshi the average x jd of the saruta gawa samples 0 21 0 29 is higher than that of the asemi gawa 0 13 0 17 and bessi 0 14 0 23 the p t conditions of the asemi gawa and bessi regions are estimated at 5 5 6 5 kbar 360 c in the chlorite zone 7 8 5 kbar 440 15 c in the garnet zone and 8 9 5 kbar 520 25 c in the albite biotite zone metamorphic pressure of the saruta gawa region is systematically 1 1 5 kbar higher than that of the asemi gawa and bessi regions and materials of the saruta gawa region have been subducted to a level 3 5 km deeper than materials that underwent metamorphism at equivalent temperatures and are now exposed in the asemi gawa and bessi regions pressure slightly increases toward the north structurally high levels through the sanbagawa belt of central shikoku two types of zonal structure were observed in relatively coarse grained sodic pyroxenes in the matrix one type is characterized by increasing x jd from core to rim the other type by decreasing x jd from core to rim both types of zoned pyroxenes show an increase in x fe 2 fe2 fe2 mg from core to rim the first type of zoning was observed in a sample from the chlorite zone of lowest grade whereas the latter occurs in the garnet and albite biotite zones of higher grade the contrast in zonal structure implies that dp dt during prograde metamorphism decreased with increasing metamorphic grade and may have been negative in some samples from the higher grade zones the estimated dp dt of the prograde stage of the chlorite zone is 3 2 kbar 100 c and that of the garnet and albite biotite zones is 1 8 to 0 9 kbar 100 c the variation of dp dt at shallow and deep levels of a subduction system probably reflects the difference of heating duration and or change in thermal gradient of the subduction zone by continuous cooling of the surrounding mantle

pumpellyites and coexisting minerals in different low grade metamorphic facies of liguria italy pumpellyite from four phase assemblages pumpellyite epidote prehnite chlorite pumpellyite epidote actinolite chlorite pumpellyite epidote na amphibole chlorite together with common excess phases considered to be low variance in a cao mgo feo al2o3 fe2o3 na2o sio2 h2o system have been examined in areas which underwent metamorphism in the prehnite pumpellyite pumpellyite actinolite and low temperature blueschist facies respectively the analysed mineral assemblages are compared for nearly constant basaltic chemical composition at varying metamorphic grade and for varying chemical composition basic intermediate acidic at constant metamorphic conditions low temperature blueschist facies in the studied mineral assemblages coexisting phases approached near chemical equilibrium at constant basaltic bulk rock composition the mgo content of pumpellyite increases and the xfe3 of both pumpellyite and epidote decreases with increasing metamorphic grade the fe3 being preferentially concentrated in epidote both pumpellyite and epidote compositions vary with the bulk rock composition at isofacial conditions pumpellyite becomes progressively enriched in fe and depleted in mg from basic to intermediate and acidic bulk rock compositions the compositional comparison of pumpellyites from high variance 1 3 phases assemblages in various bulk rock compositions basic intermediate acidic rocks greywackes gabbros shows that the compositional fields of both pumpellyite and epidote are wide and variable broadly overlapping the compositional effects observed at varying metamorphic grade in low variance assemblages the intrinsic stability of both fe and al rich pumpellyites extends across the complete range of the considered metamorphic conditions element partitioning between coexisting phases is the main control on the mineral composition at different p t conditions

polyphase deformation in a fore arc back arc basin salin subbasin myanmar burma the salin subbasin of myanmar part of the larger central basin is a fore arc back arc basin couplet situated between an oblique subduction zone to the west and a major right lateral strike slip fault to the east surface and subsurface expressions of folds and faults suggest that the basin experienced north northwest directed extensional deformation in the miocene followed by east northeast directed pliocene pleistocene transpressional deformation resulting in a variety of structural styles including thrust faults oblique reverse faults strike slip faults and normal faults fault propagation folds cored by west dipping thrust faults in the basin center are located above steps in the top of basement surface most likely fault controlled unconformities at the base of and within the pliocene pleistocene synorogenic section indicate that the thrust faults were active during the pliocene pleistocene the southeastern region contains broad north northwest trending uplifts and east northeast striking normal faults associated with thickened miocene synorogenic deposits pliocene pleistocene sedimentary rocks lie unconformably above the miocene section and are folded above the uplifts reflecting pliocene pleistocene compression in the southern part of the basin miocene sedimentary rocks thicken dramatically over the 20 n uplift and the yedwet uplift suggesting that the north northwest striking faults that bound them represent pliocene pleistocene inversion of miocene normal faults during the miocene the burma plate acted as a fore arc sliver coupled with the india plate subducting obliquely underneath it and moved northward relative to asia along the sagaing fault normal faulting and local basin formation took place at this time when the northern part of the burma plate collided with eastern asia in the pliocene transpressional deformation predominated creating thrust and reverse faults positive flower structures and inverted basins

regional tectonics of myanmar burma and adjacent areas analysis of 38 contiguous landsat multispectral scanner scenes acquired over myanmar burma reveals numerous large scale features associated with margins of the burman plate previously unidentified northeast southwest trending discontinuities important extensions of previously mapped fault trends and numerous structural features that appear favorable for petroleum exploration a mosaic of these scenes at 1 1 000 000 scale shows a large number of tectonic elements and their spatial relationships within the area of investigation are portions of the indian burman lhasa and shan thai plates and perhaps other smaller plates the himalayan front and indo burman ranges manifest effects of current and recently past plate movement the complexity of the kinematic history accounts for the diversity of structural features in the area the last major event in this long and violent saga which began in middle miocene approximately 11 ma time and continues to the present is the recent change from a collisional to a right lateral strike slip transform margin between the indian and burman plates the complexity of the structures visible is the product of multiple plate collisions rotation of the indian plate and parts of the asian plate and long continued convergence that changed velocity and direction tbrough time the most obvious evidence of this complexity which ismore immediately apparent on geologic maps or the landsat mosaic of the region is the almost right angle relationship of the folds of the indo burman ranges and the frontal thrusts and suture zones of the himalaya these two sets of compressive features imply maximum compressive stress axes that lie at right angles to each other the implications are either that the orientation of the stress field changes rapidly over a short distance or that the stress field has changed through time both occurrences seem to be true less

transcurrent movements in the burma andaman sea region the drag produced by the northward movement of the indian plate has caused the indoburman ranges an accretionary prism to decouple from the burma plate along the kabaw fault and the burma plate itself has decoupled from the eastern highlands of burma along the sagaing fault the indoburman ranges have probably been dragged north slightly ahead of the burma plate although at times the two plates may have locked together to move as one unit it is suggested that the double arc formed by the indoburman ranges and the andaman nicobar sumatra islands was formerly one large single arc northward translation of this larger single arcuate structure has caused the tail end of the arc i e the andaman nicobar sumatra section to rotate into the burma plate causing a bending of the arc to form the present double arc and compression within the burma plate to form the pegu yoma folding northward movement of the burma plate has also resulted in offset by over 400 km of the irrawaddy river from its former connection through the channel of what is now the chindwin river

tectonics of the western margin of the shan plateau central myanmar implication for the india indochina oblique convergence since the oligocene abstract we present new data and interpretations on the neogene tectonics of the shan scarp area central myanmar and its relationship with the india indochina oblique convergence we describe ductile and brittle fabrics associated with the major features in this area the mogok metamorphic belt mmb the shan scarp and the sagaing fault from these data we identify a succession of two tectonic regimes first a dominant nnw sse trending extension marked by ductile stretching that characterizes the mmb and associated n70e brittle normal faults later from middle or upper miocene to the present these structures were cross cut by brittle right lateral faults among which the most important are the n20w transpressive shan scarp fault zone and the n s sagaing fault to explain this transition from a dominant transtensive to a transpressive stress regime that occurred during miocene we place our data within a larger geodynamic context we suggest that like the intraplate deformation in the indian ocean the end of spreading in the south china sea the opening of the andaman basin or the end of subduction within the indo burma range the change in the tectonic regime in central myanmar could be in response to a major miocene regional plate kinematic reorganization

metamorphic evolution of the susunai metabasites in southern sakhalin russian republic the susunai complex of southeast sakhalin represents a subduction related accretionary complex of pelitic and basic rocks two stages of metamorphism are recognized 1 a local low p t event characterized by si poor calcic amphiboles 2 a regional high p t event characterized by pumpellyite actinolite epidote sodic amphibole sodic pyroxene stilpnomelane and aragonite the major mineral assemblages of the high p t susunai metabasites contain pumpellyite epidote actinolite chlorite epidote actinolite chlorite epidote na amphibole na pyroxene chlorite haematite the na amphibole is commonly magnesioriebeckite the na pyroxene is jadeite poor aegirine to aegirine augite application of empirically and experimentally based thermobarometers suggests peak conditions of t 250 300c p 4 7 6 kbar textural relationships in susunai metabasite samples and a petrogenetic grid calculated for the fe3 rich basaltic system suggest that pressure and temperature increased during prograde metamorphism

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

blueschist facies metamorphism shear heating and p t t paths in subduction shear zones the low temperatures recorded by blueschist facies metamorphic rocks place upper bounds on the magnitude of shear stresses in subduction zones at depths of 15 50 km in this paper steady state and transient pressure temperature time p t t paths followed by subducted material are calculated using analytical expressions presented by molnar and england 1990 supplemented by two dimensional numerical calculations in the absence of shear heating calculated steady state p t t paths are very cold intersecting 1 gpa 10 kbar at t 200 c for a wide range of subduction parameters for the case of constant shear stress in the subduction shear zone and typical thermal parameters steady state p t t paths intersect the blueschist facies for 10 60 mpa and 0 100 mpa for convergence rates of 10 and 3 cm yr 1 respectively blueschist facies metamorphism will not occur in rapid subduction zones if shear stresses exceed 60 mpa for the case of shear stress increasing linearly with depth steady state p t t paths intersect the blueschist facies when 1 9 p and 0 14 p for convergence rates of 10 and 3 cm yr 1 respectively subduction zone shear stresses may be considerably lower and possibly zero if blueschist terrains represent material metamorphosed during the early stages of subduction first 5 10 m y while the thermal structure is still evolving or if maximum temperatures in blueschist terrains are achieved during exhumation subduction zone shear stresses of several tens of mpa at 35 km depth or a few percent of lithostatic pressure are consistent with a steady state model of franciscan metamorphism a progressive underplating model for the formation of the pelona schist inverted metamorphic gradient and surface heat flow measurements in the ne japan subduction zone

water transportation from the subducting slab into the mantle transition zone using a recently developed petrogenetic grid for morb h2o we propose a new model for the transportation of water from the subducting slab into the mantle transition zone depending on the geothermal gradient two contrasting water transportation mechanisms operate at depth in a subduction zone if the geothermal gradient is low lawsonite carries h2o into mantle depths of 300 km with further subduction down to the mantle transition depth approximately 400 km lawsonite is no longer stable and thereafter h2o is once migrated upward to the mantle wedge then again carried down to the transition zone due to the induced convection at this depth hydrous phase olivine is stable and plays a role as a huge water reservoir in contrast if the geothermal gradient is high the subducted slab may melt at 700 900 c at depths shallower than 80 km to form felsic melt into which water is dissolved in this case h2o cannot be transported into the mantle below 80 km between these two endmember mechanisms two intermediate types are present in the high pressure intermediate type the hydrous phase a plays an important role to carry water into the mantle transition zone water liberated by the lawsonite consuming continuous reaction moves upward to form hydrous phase a in the hanging wall which transports water into deeper mantle this is due to a unique character of the reaction because phase a can become stable through the hydration reaction of olivine in the case of low pressure intermediate type the presence of a dry mantle wedge below 100 km acts as a barrier to prevent h2o from entering into deeper mantle 2006 published by elsevier b v on behalf of international association for gondwana research

diachronous cooling along the mogok metamorphic belt shan scarp myanmar the trace of the northward migration of the indian syntaxis abstract we present new observations and new mineral ages eight by the 40 ar 39 ar and nine by the 40 k 40 ar methods from high grade metamorphic and foliated intrusive rocks collected along the mogok metamorphic belt of central myanmar that complete preliminary results we previously published all 30 ages presented here confirm the oligocene to middle miocene age of the mogok metamorphism moreover the ages are young from the gulf of martaban in the south to the china myanmar border in the north showing a clear diachronism these results confirm a northward migration of the tectonic event responsible for the cooling of our samples at a velocity similar to the india relative to indochina velocity at the same period in addition intensive field work along a 800 km long section of the mogok metamorphic belt has revealed the numerous ductile structures that resulted from a strong nnw sse trending extension from the analogy between the present day local extrusion around the eastern indian syntaxis and the extension observed along the mogok metamorphic belt and from the diachronism we document we suggest that the central part of myanmar has recorded the northward passage of the eastern indian syntaxis with respect to indochina from oligocene to middle miocene

the stability of ca na pyroxene in low grade metabasites of high pressure intermediate facies series minor metamorphic ca na pyroxene occurs as minute crystals and as thin rims around primary augites in metabasites intermediate between the prehnite pumpellyite pp and pumpellyite actinolite pa facies in the sanbagawa belt shikoku japan their compositions vary systematically with mineral paragenesis from augite to acmite with a constant jadeite component of about 20 molvo the ca na pyroxenes in the pumpellyite bearing assemblages contain a very low acmite component acaaugssjd2s which increases through ac25aug55jd2s in the alkali amphibole bearing and ac66augzsjdrs in the hematite bearing assemblages finally attaining an aegirine composition ac65aug1sjd25 in the magnetite bearing assemblages they are distinguished from relict igneous augites chemically by very low opx and tio2 contents and morphologically by fibrous crystal habit the pyroxene bearing metabasites contain assemblages of chlorite pyroxene pumpellyite epidote actinolite alkali amphibole stilpnomelane hematite and magnetite which are incompatible with the higher grade and widely developed pumpellyiteactinolite facies assemblage epidote chlorite xr 0 50 actinolite pumpellyite the reaction augite chlorite pumpellyite actinolite h2o has been suggested for such a transition the stability relations of augite chlorite pumpellyite were analyzed from comparative mineral parageneses in low grade metabasites from new caledonia new zealand and the appalachians the assemblage may have a wedge shaped p t space bounded against the high tpumpellyite actinolite facies by the above reaction and against the low t prehnite pumpellyite facies by the reaction prehnite actinolite augite chlorite with probable negative slope from the mineral parageneses in the metabasites of the sanbagawa belt and elsewhere it is concluded that the ca na pyroxenes occur within a restricted p t space between the prehnite pumpellyite and pumpellyite actinolite facies

low pressure and low temperature k bearing kosmochloric diopside from the osayama serpentinite melange sw japan kosmochloric diopside with high k content up to 0 56 wt 0 026 k atom per formula unit was discovered from the osayama serpentinite melange in the chugoku mountains sw japan k bearing clinopyroxene fills microcracks 5 150 m in wide together with uvarovite within albite vein of a tremolite rock compositions of analyzed clinopyroxene consist mainly ofkosmochlor augite 92 98 mol ko 1 9 3 8 aug 5 6 7 6 components and minor amounts of jadeite 0 6 mol aegirine 0 5 mol ca tschermak 0 3 mol and k kosmochlor 0 2 mol although the k content in clinopyroxene is also variable and heterogeneous even in a single vein clinopyroxene with higher k content occurs in ko rich part higher magnification secondary electron images confirmed that exsolution and inclusion are essentially absent in the analyzed clinopyroxenes the good negative correlation between cr na k and ca mg fe 2 indicates the cr incorporation into the octahedral site furthermore k correlates with na and cr indicating a simultaneous enrichment of k for na and cr during pyroxene growth textual relations and parageneses and compositions of minerals suggest that the k cpx precipitated together with uvarovite in brittle microcracks directly from a ca and cr rich hydrothermal fluid at approximately p 4 gpa environment permits to host relatively large k cation into the clinopyroxene structure our finding indicates that the incorporation of k into the kosmochlor diopside series solid solution with at least 0 2 cr cation p f u is possible even at low p conditions

tertiary diachronic extrusion and deformation of western indochina structural and 40ar 39ar evidence from nw thailand the wang chao and three pagodas fault zones cut the western part of the indochina block and run parallel to the red river fault evidence of intense ductile left lateral shear is found in the lansang gneisses which form a 5 km wide elongated core along the wang chao fault zone dating by 40 ar 39 ar shows that such deformation probably terminated around 30 5 ma the wang chao and three pagodas faults offset the north striking lower mesozoic metamorphic and magmatic belt of northern thailand 40 ar 39 ar results suggest that this belt suffered rapid cooling in the tertiary probably around 23 ma these results imply that the extrusion of the southwestern part of indochina occurred in the upper eocene lower oligocene it probably induced rifting in some basins of the gulf of thailand and in the malay and mekong basins in the oligo miocene the continuing penetration of india into asia culminated with the extrusion of all of indochina along the ailao shan red river fault this occurred concurrently with the onset of e w extension more to the south plotting in a geographical reference frame the diachronic time spans of movement on left lateral faults east and southeast of tibet implies that the northward movement of the indian indenter successively initiated new strike slip faults located farther and farther north along its path

glacier change on axel heiberg island nunavut canada historical records are valuable for assessing glacier change in the canadian high arctic ommanney s 1969 detailed inventory of axel heiberg island glaciers based on photography from 1958 59 has been revisited converted into digital format and compared to glacier extents mapped from 1999 2000 satellite imagery our results show that the island wide ice coverage decreased by 15 92 km 2 in the 42 year period a loss of 2 if the contributions to ice advance of only three surging glaciers are removed then the island wide ice loss approaches 60 km 2 furthermore it is notable that 90 of ice masses smaller than 0 2 km 2 disappeared entirely during the 42 year study period an observation confirmed by field studies successful predictions from the original inventory are highlighted and the likely mechanisms driving the observed advances and retreats are discussed

the active tectonics of the eastern himalayan syntaxis and surrounding regions source parameters of 53 moderate sized earthquakes obtained from the joint inversion of regional and teleseismic distance long period body waves provide the data set for an analysis of the style of deformation and kinematics in the region of the eastern himalayan syntaxis focal mechanisms of eastern himalayan events show oblique thrust consistent with the n ne directed movement of the indian plate as it underthrusts a boundary that strikes at an oblique angle to the direction of convergence earthquakes near the sagaing fault show strike slip mechanisms with right lateral slip earthquakes on its northern splays however indicate predominant thrusting evidence that the dextral motion on the sagaing fault which accommodates a portion of the lateral motion between india and southeast asia terminates in a zone of thrust faulting at the eastern himalayan syntaxis remaining motion between india and southeast asia is accommodated in a zone of distributed shear in east burma and yunnan manifested by strike slip and oblique normal faulting east west extension crustal thinning and clockwise rotation of crustal blocks we determined strain rates throughout the region with a moment tensor summation using 25 years modern and 85 years modern and historic of earthquake data we matched the observed strains with a fifth order polynomial function and from this we determined both the velocity field and rotations with respect to a specified region velocities calculated relative to south china stationary show that the entire area extending from 20 n 36 n within deforming asia yunnan western sichuan and east tibet constitutes a distributed dextral shear zone with clockwise rotations up to 1 7 m y maximum in the region of the eastern syntaxis proper integrated strains across this zone relative to south china stationary show 38 mm yr 12mm yr of north directed motion at the himalaya remaining plate motion relative to south china fixed must be taken up by the underthrusting of india beneath the lesser himalaya strike slip motion on the sagaing fault and intraplate ne directed shortening within ne india as well as ne directed shortening within the eastern syntaxis proper 10 mm yr 2 mm yr of relative right lateral motion between india and southeast asia is absorbed in the region between the sagaing and red river faults 94 e 100 e it is the clockwise vorticity relative to south china associated with the deformation in yunnan east tibet and western sichuan that provides the relative north directed motion of 38 12 mm yr at the himalaya not all of the deformation is accommodated in right lateral shear between india and south china and between east tibet and south china velocity gradients exist that are parallel to the trend of the shear zone relative to a point within western sichuan 32 n 100 e the velocity field shows that the yunnan crust is moving s se at rates of 8 10 mm yr relative to south china there is no eastward expulsion of crustal material beyond the eastern margin of the tibetan plateau

parageneses and compositions of amphiboles from franciscan jadeite glaucophane type facies series metabasites at cazadero california sodic amphiboles are common in franciscan type ii and type iii metabasites from cazadero california they occur as 1 vein fillings 2 overgrowths on relict augites 3 discrete tiny crystals in the groundmass and 4 composite crystals with metamorphic ca na pyroxenes in low grade rocks they become coarse grained and show strong preferred orientation in schistose high grade rocks in the lowest grade only riebeckite to crossite appears with increasing grade sodic amphibole becomes first enriched in glaucophane component later coexists with actinolite and finally at even higher grade becomes winchite actinolite first appears in foliated blueschists of the upper pumpellyite zone it occurs 1 interlayered on a millimetre scale with glaucophane prisms and 2 as segments of composite amphibole crystals actinolite is considered to be in equilibrium with other high pressure phases on the basis of its restricted occurrence in higher grade rocks textural and compositional characteristics and fe mg distribution coefficient between actinolite and chlorite detailed analyses delineate a compositional gap for coexisting sodic and calcic amphiboles at the highest grade winchite appears at the expense of the actinolite glaucophane pair compositional characteristics of franciscan amphiboles from ward creek are compared with those of other high p t facies series the amphibole trend in terms of major components is very sensitive to the metamorphic field gradient na amphibole appears at lower grade than actinolite along the higher p t facies series e g franciscan and new caledonia whereas reverse relations occur in the lower p t facies series e g sanbagawa and new zealand available data also indicate that at low temperature conditions such as those of the blueschist and pumpellyite actinolite facies large compositional gaps exist between ca and na amphiboles and between actinolite and hornblende whereas at higher temperatures such as in the epidote amphibolite greenschist and eclogite facies the gaps become very restricted common occurrence of both sodic and calcic amphiboles and ca na pyroxene together with albite quartz in the ward creek metabasites and their compositional trends are characteristic of the jadeite glaucophane type facies series in new caledonia blueschists ca na pyroxenes are also common na amphiboles do not appear alone at low grade in metabasites instead na amphiboles coexist with ca amphiboles throughout the progressive sequence however for metabasites of the intermediate pressure facies series such as those of the sanbagawa belt japan and south island new zealand ca na pyroxene and glaucophane are not common sodic amphiboles are restricted to crossite and riebeckite in composition and clinopyroxenes to acmite and sodic augite and occur only in fe2o3 rich metabasites the glaucophane component of na amphibole systematically decreases from ward creek new caledonia through sanbagawa to new zealand this relation is consistent with estimated pressure decrease employing the geobarometer of maruyama et al 1986 similarly the decrease in tschermakite content and increase in nam4 of ca amphiboles from new zealand through sanbagawa to new caledonia is consistent with the geobarometry of brown 1977b therefore the difference in compositional trends of amphiboles can be used as a guide for p t detail within the metamorphic facies series

isotopic evidence for channeled fluid flow in low grade metamorphosed jurassic accretionary complex in the northern chichibu belt western shikoku japan the low grade metamorphosed jurassic accretionary complex of the northern chichibu belt hijikawa area western shikoku is divided into two units the hijikawa and kanogawa units that are separated by an out of sequence thrust oost the ozu kawabegawa fault the kanogawa unit south of the ozu kawabegawa fault consists mainly of sandstone shale broken formation of alternating sandstone and shale greenstone chert and pelitic melange while the hijikawa unit is characterized by a stack of subunits separated by small scale thrusts the subunits are mainly made up of basic pelitic and psammitic semischists schistose pelitic melange and chert petrological and mineralogical constraints suggest peak metamorphic conditions of 204 247 c at 1 3 kbar in the kanogawa unit and 228 289 c at 3 5 6 kbar in the hijikawa unit quartz and quartz calcite veins are widely developed in the study area especially in the hijikawa unit regional variations in stable isotopic data show that the 18oquartz and 18ocalcite values in veins tend to increase towards the ozu kawabegawa fault the 18owhole rock values are remarkably high in some subunits close to oosts within the hijikawa unit oxygen isotopic compositions from vein quartz indicate that a higher 18o fluid migrated upward from depth along the ozu kawabegawa fault within the accretionary prism during prehnite pumpellyite facies metamorphism the fluid source is inferred to be pelitic rocks at higher temperatures and greater depths within the accretionary prism

evolution of the illecillewaet glacier glacier national park b c using historical data aerial photography and satellite image analysis the iliecillewaet glacier british columbia has been surveyed in a variety of ways since the end of the 19th century a summary of the different information archive photographs field surveys photo interpretation and remote sensing reveals that between 1887 and 1962 the glacier had retreated more than one kilometre however since 1972 it has advanced about 100 m the techniques used and the results are discussed

canada and the world glacier inventory this paper reviews the origins of the world glacier inventory program and canada s participation it tracks the program of the canadian federal government from its initiation to its demise today progress is geared towards the international glims and globglacier programs to which scientists from several canadian universities are making contributions achievements during the past decade towards providing data on canada s glacierized areas in the arctic and in western canada are documented

a newly discovered high pressure terrane in eastern hokkaido japan the upper jurassic nikoro greenstone complex of eastern hokkaido suffered high pressure intermediate type metamorphism characteristic minerals include lawsonite aragonite sodic pyroxene of the aegirinejadeite series winchite sodic amphibole of the glaucophane riebeckite series pumpellyite epidote and actinolite high pressure metamorphism of the nikoro greenstone complex is related to subduction of the kula plate toward the palaeo okhotsk land during cretaceous time

low grade metamorphism of the mikabu and northern chichibu belts in central shikoku sw japan implications for the areal extent of the sanbagawa low grade metamorphism in central shikoku sw japan the mikabu belt is bounded to the north by the sanbagawa belt and to the south by the northern n chichibu belt the n chichibu belt can be further subdivided into northern and southern parts there is no apparent difference in the overall geology structure or fossil and radiometric ages between the mikabu belt and the northern part of the n chichibu belt greenstones from the mikabu belt and the northern part of the n chichibu belt show evidence for similar low grade metamorphism and include the following mineral assemblages with albite chlorite in excess metamorphic aragonite sodic pyroxene quartz epidote actinolite pumpellyite glaucophane pumpellyite quartz and lawsonite not with actinolite or glaucophane these similarities suggest that the mikabu belt and the northern part of the n chichibu belt belong to the same geological unit the mb nnc complex the mineral assemblages also indicate that the mb nnc complex belongs to a different metamorphic facies from the low grade part of the sanbagawa belt that is the former represents lower temperature higher pressure conditions than the latter structural and petrological continuity between the mb nnc complex and sanbagawa belt has not yet been confirmed but both have similar radiometric ages it is therefore most likely that the mb nnc complex and sanbagawa belt belong to the same subduction complex and were metamorphosed under similar but distinct conditions these two units were juxtaposed during exhumation in contrast the southern part of the n chichibu belt is distinct in lithology and structure and includes no mineral assemblages diagnostic of the mb nnc complex and the sanbagawa belt thus the southern part of the n chichibu belt may represent a different geological unit from the mb nnc complex and sanbagawa belt

active faulting and tectonics of burma and surrounding regions this study of the active tectonics of burma and surrounding regions is based mostly on an interpretation of landsat imagery and on fault plane solutions for shallow and intermediate earthquakes fold axes in the indoburman ranges and an east dipping inclined zone of intermediate depth earthquakes suggest that a slab of oceanic lithosphere was recently subducted to the east under the indoburman ranges fault plane solutions of shallow earthquakes however do not show underthrusting at the present time instead p axes are oriented roughly north south parallel not perpendicular to the fold axes in the ranges p axes for fault plane solutions of intermediate shocks also trend north south parallel to the strike of the subducted slab and may indicate that the hanging slab is being dragged north by india through the surrounding asthenosphere the sagaing fault probably accommodates most of the right lateral slip of india past indochina but india s northward movement also causes internal deformation within burma thailand and yunnan differences between the tectonic fabric seen on the landsat images and the tectonic regime compatible with the fault plane solutions throughout the region imply major changes in the directions of relative motion in the orientations of strain and in the style of deformation in the late cenozoic presumably these changes reflect the transition from subduction to collision and strike slip motion as india penetrated into eurasia past burma large parts of burma and thailand may have rotated several tens of degrees clockwise in this process

cenozoic metamorphism along the shan scarp myanmar evidences for ductile shear along the sagaing fault or the northward migration of the eastern himalayan syntaxis the mogok metamorphic belt exposed along the n s trending shan scarp and sagaing fault in the eastern part of myanmar has been regarded as paleozoic to precambrian for a long time new observations in the shan scarp area close to the sagaing fault from thaton in the south to mandalay in the north allowed us to collect samples of high grade metamorphic and intrusive rocks that have been analyzed by 40ar 39ar step heating method the 13 samples we analyzed provide oligocene to lower miocene ages for this metamorphism oriented thin sections and field observations suggest that this metamorphism was caused by a nnw sse to n s ductile extension therefore we suggest that this metamorphism is not directly related to the sagaing fault but could be instead related to the northward migration of the eastern himalayan syntaxis characterized by crustal thinning resulting from the india asia oblique collision

clinopyroxene a mineral telescoped through the processes of blueschist facies metamorphism textural evolution and compositional variation of clinopyroxenes in ward creek metabasites are described pyroxenes change with increasing grade from finegrained aggregates through fan shaped medium grained prisms to blocky coarse crystals characteristic features of metamorphic pyroxenes include 1 the occurrence of coexisting pyroxene pairs the compositions of which are used to delineate compositional gaps 2 the existence of large compositional variations of pyroxenes within a single specimen which record a considerable span of p and or t for crystallization and 3 the development of compositional trends in single specimens and in three metamorphic zones which are progressive in nature the first formed clinopyroxene jd20aug65ac15 in the lower lawsonite zone mimics the composition of relict igneous augite it changes continuously with increasing grade at nearly constant low xjd content towards acmite at a composition around jd20aug30ac50 the trend turns towards jadeite and intersects a solvus to form two coexisting clinopyroxenes in the middle lawsonite zone at higher grade the compositional gap becomes restricted towards the jadeite omphacite join and clinopyroxene increases in xjd toward jadeite a reversed compositional trend occurs at higher grade clinopyroxenes decrease in jadeite component at nearly constant aug ac ratio of 50 50 and finally become omphacite in the uppermost pumpellyite and epidote zones the na ca pyroxenes close to the binary join jd ac occur in the lawsonite and pumpellyite zones ranging from xjd 1 0 0 30 together with ab and qz the ubiquitous occurrence of aragonite at temperature estimates of 170 240 c by taylor coleman 1968 for these zones does not support the low temperature extrapolation of the jd ab qz curve by holland 1980 the estimated metamorphic field gradient indicates an inflection point at 7 kbar 200 c below this blueschist facies metamorphism proceeded under dominant pressure increase from 4 to 7 kbar at nearly constant temperature about 150 200 c whereas at higher grade recrystallization above the inflection point the metamorphic temperature increased from 200 to 350 c at nearly constant pressure about 7 8 kbar such an inflection point suggests the depth of underplating of either seamounts or accretionary packages in a subduction zone

the geodynamic evolution of the alpine orogen in the cyclades aegean sea greece insights from diverse origins and modes of emplacement of ultramafic rocks

high temperature metamorphism in a major strike slip shear zone the ailao shan red river people s republic of china abstract petrographic and thermobarometric analysis provides constraints on thept path of the mylonitic gneisses of the left lateral ailao shan red river shear zone which has accommodated the lateral extrusion of indochina during the tertiary two different paragenesis p1 and p2 are coeval with this deformation and correspond respectively to the amphibolite and greenschist facies microprobe analysis reveals that p1 garnets bear a chemical zonation from core to rim this zonation indicates a temperature increase during garnet growth conditions of formation of garnet rims p1b which are estimated using biotite garnet and plagioclase garnet thermobarometers are close to the granitic solidus 710 70 c and4 5 1 5 kbar p2 conditions are estimated to be approximately 500 c and

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

archean ocean floor metamorphism in the north pole area pilbara craton western australia abstract archean greenstones ca 3 49 3 46 ga in the north pole dome pilbara craton western australia have undergone prograde metamorphism from prehnite pumpellyite facies to greenschist amphibolite facies observations of 3000 thin sections shows that a metamorphic aureole was restricted to within a few kilometers of the contact with the 3459 ma north pole monzogranite three types of alteration were observed carbonate silicic and chlorite types the distribution of the three types of alteration suggests that secondary chemical migration of elements occurred in the whole area but that some samples were unaffected by this alteration the southern north pole area is outside of the contact metamorphic aureole and is composed of five units from north unit i to south unit v dipping south about 30 70 metamorphism of the north pole greenstones corresponds to the low pressure type which is broadly comparable to that inferred for ocean floor metamorphism prehnite pumpellyite pp transitional tr and greenschist gs facies prograde metamorphic zones occur from structural top to bottom within each of units metamorphic grade increases downward through the units and metamorphic isograds never cut unit boundaries

late cretaceous blueschist facies metamorphism in southern thrace turkey and its geodynamic implications a blueschist facies tectonic sliver 9 km long and 1 km wide crops out within the miocene clastic rocks bounded by the strands of the north anatolian fault zone in southern thrace nw turkey two types of blueschist facies rock assemblages occur in the sliver i a serpentinite body with numerous dykes of incipient blueschist facies metadiabase ii a well foliated and thoroughly recrystallized rock assemblage consisting of blueschist marble and metachert both are partially enveloped by an upper eocene wildflysch which includes olistoliths of serpentinite metadiabase upper cretaceous and palaeogene pelagic limestone upper eocene reefal limestone radiolarian chert quartzite and minor greenschist field relations in combination with the bore core data suggest that the tectonic sliver forms a positive flower structure within the miocene clastic rocks in a transpressional strike slip setting and represents an uplifted part of the pre eocene basement the blueschists are represented by lawsonite glaucophane bearing assemblages equilibrated at 270 310 c and 0 8 gpa the metadiabase dykes in the serpentinite on the other hand are represented by pumpellyite glaucophane lawsonite assemblages that most probably equilibrated below 290 c and at 0 75 gpa one metadiabase olistolith in the upper eocene flysch sequence contains the mineral assemblage epidote pumpellyite glaucophane recording p t conditions of 290 350 c and 0 65 0 78 gpa indicative of slightly lower depths and different thermal setting timing of the blueschist facies metamorphism is constrained to c 86 ma coniacian santonian by rb sr phengite whole rock and incremental 40 ar 39 ar phengite dating on blueschists the activity of the strike slip fault post dates the blueschist facies metamorphism and exhumation and is only responsible for the present outcrop pattern and post miocene exhumation 2 km the high p t metamorphic rocks of southern thrace and the biga peninsula are located to the southeast of the circum rhodope belt and indicate late cretaceous subduction and accretion under the northern continent i e the rhodope massif enveloped by the circum rhodope belt the late cretaceous is therefore a time of continued accretionary growth of this continental domain