along arc lateral variation of rb sr and k ar ages of cretaceous granitic rocks in southwest japan cretaceous granitic rocks were emplaced over a distance of 700 km along arc in southwest japan rb sr and k ar ages of a major group of these granitic rocks with ilmenite series ore mineralogy were examined rb sr whole rock ages of 92 8 4 0 ma and rb sr and k ar biotite ages of 80 88 ma were obtained on one group of these granitic rocks from kamo sera area of central hiroshima prefecture the k ar ages of various minerals combined with the rb sr whole rock age give a smooth cooling curve which suggests a 5 to 10 ma time lag between intrusion and cooling at 300 c for the cretaceous granitic rocks the rb sr whole rock and rb sr k ar biotite ages of these granitic rocks become younger eastward along the southwest japan arc and the time lag between the two systems remains constant at 5 to 10 ma over the entire area the along arc age variation does not support the genetical relationship of the cretaceous granitoids with steady state subduction the cretaceous granitic province at the eastern margin of eurasian continent was at least partly formed by an episodic event such as ridge subduction

igneous microstructures in migmatites clear differences between the microstructures of leucosomes and mesosomes occur in some nebulitic migmatites in the proterozoic arunta block central australia the leucosomes show crystal faces of k feldspar microcline microperthite cordierite andalusite and plagio clase against quartz indicating crystallization of a melt in contrast the mesosomes show predominantly polygonal grain shapes modified by 001 crystal faces of biotite and rare crystal faces in some porphyroblasts of garnet cordierite and orthopyroxene indicating re crystallization in the solid state the occurrence of abundant crystal faces in minerals such as feldspar cordierite and andalusite which typically grow crystal faces in magmas but generally not in metamorphic rocks is evidence of former melt therefore igneous microstructures can be preserved in leucosomes that have not undergone penetrative subsolidus deformation and recrystallization the cores of many of the crystals of cordierite and k feldspar have small locally oriented inclusions similar to those in the same minerals in the mesosomes these indicate that the cores remained solid during crystallization of the leucosome which produced inclusion free euhedral rims these crystals provide criteria for recognizing possible restite in granitoid magmas

a high relative sea level stand in the middle holocene of southeastern tunisia abstract study of the marine holocene deposits in southeastern tunisia shows bioclastic beaches at elevations ranging between 0 and 100 cm above high tide level a h t l depending on the elevation of these fossilized shorelines the ages obtained are different the age of the older deposits ranges between 5900 and 4000 14cc yr b p 6400 4300 calendar yr b p there deposits consist of bioclastic beaches attaining an elevation of about 40 to 100 cm a h t l the younger deposit is dated at around 2100 14c years ago 1850 calendar yr b p and is found today at the same elevation as the present sea level this deposit also consists of bioclastic beach material and contains pottery fragments postglacial melting should not be responsible for this observed higher relative sea level stand because deglaciation ended about 7000 6000 14c years ago fairbanks 1989 furthermore the regularity of the paleobeach deposit elevation over a broad area in southeastern tunisia suggests that tectonics cannot explain the emergence the emergence of up to 1 m of marine deposits dating back to between 5900 and 4000 14c yr b p should rather be interpreted as the result in the region of a postglacial hydro isostatic rebound as predicted in the theological models of continental margins by for example clark et al 1978 and lambeck 1993 the present situation was reached 2100 14c years ago

origin of beach ridges comment on tanner w f 1995 origin of beach ridges and swales mar geol 129 149 161 author s reply

formation of distinct granitic magma batches by partial melting of hybrid lower crust in the izu arc collision zone central japan the miocene kofu granitic complex kgc occurs in the izu collision zone where the izu bonin mariana ibm arc has been colliding with the honshu arc since the middle miocene the kgc includes rocks ranging in compositions from biotite bearing granite the shosenkyo and mizugaki plutons and hornblende biotitebearing granodiorite tonalite quartz diorite and granite the shiodaira sanpo hirose and sasago plutons to hornblende bearing tonalite and trondhjemite the ashigawa tonogi pluton indicating that it was constructed from multiple intrusions of magma with different bulk chemistry the sr isotopic compositions corrected to sensitive high resolution ion microprobe shrimp zircon ages sri suggest that the primary magmas of each pluton were formed by anatexis of mixed lower crustal sources involving both juvenile basalt of the ibm arc and shimanto sedimentary rocks of the honshu arc after the primary magmas had formed the individual plutons evolved by crystal fractionation processes without significant crustal assimilation or additional mantle contribution shrimp zircon u pb ages in the kgc range from 16 8 to 10 6ma and overlap the resumption of magmatic activity in the ibmand honshu arcs at c 17ma and the onset of ibm arc honshu arc collision at c 15ma the age of the granite plutons is closely related to the episodic activity of arc magmatism and distinct granitic magma batches could be formed by lower crustal anatexis induced by intrusion of underplated mantle derived arc magmas based on pressures determined with the al in hornblende geobarometer the kgc magmas intruded into the middle crust thus the kgc could represent an example of the middle crust layer indicated throughout the ibm arc by 6 0 6 5 km s seismic velocities this granitic middle crust layer acted buoyantly during the ibm arc honshu arc collision leading to accretion of buoyant ibmarc middle crust to the honshu arc

hydrological changes in the mediterranean sea over the last 30 000 years sea surface temperatures were reconstructed over the last 30 000 years from alkenone paleothermometry sst alk and planktonic foraminifera assemblages using the modern analog technique mat sst foram along two cores of the mediterranean sea md84 632 levantine basin and md04 2797 siculo tunisian strait oxygen isotope of planktonic foraminifera g bulloides for core md04 2797 and g ruber for core md84 632 were also determined sst alk in the levantine basin indicate colder values at the last glacial maximum lgm 14 c than earlier established from mat and a cooling amplitude of 6 7 c comparable to the central mediterranean sea climatic events such as the younger dryas yd and heinrich events 1 and 2 h1 and h2 were times of significant cooling in the two cores in the eastern basin values of local seawater oxygen isotope w indicate relatively saltier waters during the lgm and deglaciation than today with increasing w values higher salinity in the eastern basin and decreasing ones lower salinity in the central mediterranean sea during cold stadials the observed alterations of surface water properties t and w in the central and eastern mediterranean at the lgm are consistent with model experiments showing slightly lower evaporation in the mediterranean than today except for the eastern basin

beach ridge development and sediment supply examples from west africa abstract beach ridges form the dominant mode of holocene coastal progradation in west africa they vary from minor accumulations to massively prograded plains over 100 km long variations in the patterns and morphological expression of these sandy deposits record spatial and temporal changes in various environmental parameters among these sediment supply stands out the importance of this factor is illustrated by the morphological patterns and the current sediment dynamics of minor and major beach ridge plains in this region the simplest beach ridges are related to just one or two sources of sand supply from a nearby source in these examples sand has been supplied by the nearshore zone or by eroding cliffs in many areas beach ridge formation ceased as the sediment supply dwindled because of cliff stabilization or establishment of an equilibrium nearshore profile major beach ridge plains in southern sierra leone and in the bight of benin exhibit complex patterns of development related to a bigger sediment supply from nearshore sources and rivers in southern sierra leone the beach ridge plains have been constructed essentially from sands derived from the nearshore zone locally as in the proximal part of sherbro island shallow nearshore shoals encroached upon by the beach ridge front have led to more massive progradation while engendering complex patterns of beach ridge development the sediment supply has been locally supplemented by sands drifting alongshore from the sewa and moa rivers the sediment supply involved in beach ridge development in the bight of benin highlights the role of longshore drift of sands from the volta delta early stages of progradation were characterized by the development of segmented inner beach ridge barriers separated by still infilling coastal re entrants nearshore sources were particularly important in these early stages of beach ridge progradation as coastal re entrants and their estuaries became infilled following the middle holocene eustatic highstand the longshore drift system evolved from a segmented to a unicellular one the resulting conditions of through drift east of the volta delta allowed for longshore transport of sands from this river for the construction of outer beach ridge barriers over a distance of over 250 km while rivers still actively supply sand to the coast current patterns of beach ridge development depend essentially on the coastal sand transport system which determines either the confinement of incoming sand to the vicinity of the very source area itself its regular delivery to the beach ridge front or its through drift to the local downdrift terminus

dayside and nightside segments of a polar arc the particle characteristics 1 using multiple satellites and a ground based radar network the physical characteristics of a polar arc and its evolution are investigated under quiet solar wind conditions the average electron energy is higher at the near midnight segment than at the sunward extension of the polar arc both polar arc segments are positioned primarily on closed magnetic field lines the convection reversal boundary in the fitted convection pattern was located close to the transition region in the average electron energy seen by the satellites the topside plasma density at an altitude of 680 km is clearly enhanced around the polar arc although the enhancement boundary does not coincide precisely with that of the precipitation the temporal sequence of auroral images suggests that the polar arcs emerged from a double oval structure this suggestion is supported by the observed physical characteristics of the polar arc which are quite similar to those of double oval structures that have been reported previously

transformation of juvenile izu bonin mariana oceanic arc into mature continental crust an example from the neogene izu collision zone granitoid plutons central japan abstract granitic rocks sensu lato are major constituents of upper continental crust recent reviews reveal that the average composition of phanerozoic upper continental crust is granodioritic although oceanic arcs are regarded as a site producing continental crust material in an oceanic setting intermediate to felsic igneous rocks occurring in modern oceanic arcs are dominantly tonalitic to trondhjemitic in composition and have lower incompatible element contents than the average upper continental crust therefore juvenile oceanic arcs require additional processes in order to get transformed into mature continental crust enriched in incompatible elements neogene granitoid plutons are widely exposed in the izu collision zone in central japan where the northern end of the izu bonin mariana ibm arc juvenile oceanic arc has been colliding with the honshu arc mature island arc since middle miocene the plutons in this area are composed of various types of granitoids ranging from tonalite to trondhjemite granodiorite monzogranite and granite three main granitoid plutons are distributed in this area tanzawa plutonic complex kofu granitic complex and kaikomagatake granitoid pluton tanzawa plutonic complex is dominantly composed of tonalite and trondhjemite and characterized by low concentration of incompatible elements and shows geochemical similarity with modern juvenile oceanic arcs in contrast kofu granitic complex and kaikomagatake granitoid pluton consists mainly of granodiorite monzogranite and granite and their incompatible element abundances are comparable to the average upper continental crust previous petrogenetic studies on these plutons suggested that 1 the tanzawa plutonic complex formed by lower crustal anatexis of juvenile basaltic rocks occurring in the ibm arc 2 the kofu granitic complex formed by anatexis of hybrid lower crust comprising of both basaltic rocks of the ibm arc and metasedimentary rocks of the honshu arc and 3 the kaikomagatake granitoid pluton formed by anatexis of hybrid lower crust consisting of k rich rear arc crust of the ibm arc and metasedimentary rocks of the honshu arc these studies collectively suggest that the chemical diversity within the izu collision zone granitoid plutons reflects the chemical variation of basaltic sources i e across arc chemical variation in the ibm arc as well as variable contribution of the metasedimentary component in the source region the petrogenetic models of the izu collision zone granitoid plutons suggest that collision with another mature arc continent hybrid lower crust formation and subsequent hybrid source anatexis are required for juvenile oceanic arcs to produce granitoid magmas with enriched compositions the izu collision zone granitoid plutons provide an exceptional example of the collision induced transformation from a juvenile oceanic arc to the mature continental crust

the scale invariant nature of migmatite from the oberpfalz ne bavaria and its significance for melt transport abstract four examples of migmatite from the moldanubian zone in western bohemia which formed during the late carboniferous display fractal patterns of melt bodies over more than 1 5 orders of magnitude net type migmatites have a fractal dimension of 1 80 1 85 in two orthogonal planes while that of a cross stromatic migmatite is 1 60 this fractal quality allows the migmatitic structures to be simply quantified and modelled for modelling purposes the net type migmatites are compared analogously to a menger sponge using a published theoretical model of magma flow in vertical channels it is shown that melt with viscosities less than 106 108 pa s can escape from the menger sponge under the influence of gravity alone

mid and late holocene fluvial chronology of tunisia abstract regarding fluvial response to recent climate change it is important to identify and understand previous changes of fluvial dynamics related to past climatic shifts in this paper periods of increased flood activity in central tunisian river systems are presented changes in holocene flood dynamics are reconstructed through a comprehensive analysis of 195 radiocarbon dates from alluvial archives holocene floodplain deposits in central tunisia normally consists of cohesive overbank fines which exhibit excellent preservation conditions against lateral erosion and therefore permit chronostratigraphic records of the entire holocene at most based on published radiocarbon dates two 14 c cumulative probability density plots are created for central tunisia the former represents activity dates indicating phases of increased fluvial dynamics the latter documents stability dates showing periods of soil formation and enhanced landscape stability within the floodplain and the catchment due to geomorphological considerations activity dates and stability dates should be mutually exclusive there is a good match for the mid holocene with increased periods of flooding from 6 2 to 6 0 4 8 to 4 5 4 1 to 3 7 and 3 3 to 3 0 ka these flood periods coincide with low soil formation signals on the other hand periods of increased alluvial soil formation from 6 8 to 6 6 5 9 to 4 8 4 5 to 4 1 3 7 to 3 3 3 0 to 2 8 and 1 8 to 1 6 ka coincide with periods of low flood plain aggradation the data reveal a coupling with north atlantic cooling short term periods of enhanced fluvial dynamics in central tunisia match well with north atlantic cooling the findings indicate a strong climatic link from 4 7 ka until today compared to the holocene floodplain dynamics in tunisian drylands the temperate mid latitudes show mid holocene switches in fluvial dynamics with opposite signs especially after 5 ka north atlantic driven flooding in the temperate central european river systems contrast sharply to flood dynamics in arid to semiarid mediterranean tunisia while under temperate climate conditions floodplain sedimentation decreases it increases under more arid conditions this may indicate that fluvial archives of dissimilar climatic zones reveal different threshold values and sedimentation patterns and therefore different responses to climatic shifts

basin evolution in the arc arc izu collision zone mio pliocene miura group central japan a comparative study of the present collision zone between the izu bonin ridge island arc with mainland japan honshu arc and the mio pliocene of onshore se japan suggests that arc arc collision processes and the resulting stratigraphic successions may be repetitious and predictable arc arc collision has led to the incremental accretion of segments of delaminated izu bonin arc crust onto the honshu arc associated with the sequential southward migration in jumps of the plate boundary and trench prior to accretion of a segment of izu bonin arc crust the leading edge underwent uplift to generate an approximately trench parallel topographic high the zenisu ridge being the present example with the hayama mineoka uplift zone as a mio pliocene example the ridge separated a northern trench or trough from a southern intra oceanic arc basin during collision accretion the trench received both honshu arc derived terrigenous and izu bonin arc derived volcaniclastic sediments whereas the arc basin tended to receive only arc deposits during the final stages of accretion the arc basin began to receive ever increasing volumes of terrigenous honshu arc derived detritus fed through basement controlled canyons the accretionary process was accompanied by intense deformation and the residual deep marine basin was then infilled above an angular unconformity

assessing bulk assimilation in cordierite bearing granitoids from the central system batholith spain experimental geochemical and geochronological constraints

origin of cordierite bearing granites by assimilation in the central iberian massif cim spain abstract the central iberian massif cim is characterized by the great abundance and variety of granitoids emplaced during hercynian times one of the most conspicuous is cordierite bearing biotite granite cg which in the western part of the cim is associated with other granites lacking cordierite amphibole bearing biotite granite ag and biotite granite bg and with anatectic host rocks cordierite rich nebulites nb major trace and rare earth element data for ag and bg show that these granites have chemical affinities and parallel or overlapping differentiation trends suggesting two different granite magmas with a common or similar deep seated source cg show two extreme facies a marginal cordierite rich facies mcg in direct contact with host rocks schists migmatites and an internal cordierite poor facies icg farther away from the host rocks gradual transitions between mcg and icg are commonly observed as well as between icg and bg an anatectic hypothesis for cg is difficult to accept because a cg have higher cao contents relative to nb or other country rocks a smaller eu eu ratio and similar sr contents and b the similar ree absolute contents and patterns in cg bg and nb and the absence of ree fractionation with respect to country rocks simple mixing equations are computed to test assimilation processes involving bg as a primary magma and nb as the contaminant in producing cg cao and mgo data have been used for this purpose since they are the most discriminating elements between bg and nb the results of the computation indicate that a assimilation is possible for nearly the whole cao range in nb if cao in the bg ranges between 1 91 and 2 86 and mgo is between 0 93 and 1 18 these extreme values are comprised within the observed range for cao and mgo in bg b cao and mgo data for mcg are compatible with assimilation for nearly the whole range of data observed and c the percentage of assimilation is

petrogenesis of the kaikomagatake granitoid pluton in the izu collision zone central japan implications for transformation of juvenile oceanic arc into mature continental crust the miocene kaikomagatake pluton is one of the neogene granitoid plutons exposed in the izu collision zone which is where the juvenile izu bonin oceanic arc is colliding against the mature honshu arc the pluton intrudes into the cretaceous to paleogene shimanto accretionary complex of the honshu arc along the itoigawa shizuoka tectonic line which is the collisional boundary between the two arcs the pluton consists of hornblende biotite granodiorite and biotite monzogranite and has sio2 contents of 68 75 wt it has high k series compositions and its incompatible element abundances are comparable to the average upper continental crust major and trace element compositions of the pluton show well defined chemical trends the trends can be interpreted with a crystal fractionation model involving the removal of plagioclase biotite hornblende quartz apatite and zircon from a potential parent magma with a composition of 68 wt sio2 the sr isotopic compositions together with the partial melting modeling results suggest that the parent magma is derived by 53 melting of a hybrid lower crustal source comprising 30 shimanto metasedimentary rocks of the honshu arc and 70 k enriched basaltic rocks of the izu bonin rear arc region together with previous studies on the izu collision zone granitoid plutons the results of this study suggest that the chemical diversity within the parental magmas of the granitoid plutons reflects the chemical variation of basaltic sources i e across arc chemical variation in the izu bonin arc as well as a variable contribution of the metasedimentary component in the lower crustal source regions in addition the petrogenetic models of the izu collision zone granitoid plutons collectively suggest that the contribution of the metasedimentary component is required to produce granitoid magma with compositions comparable to the average upper continental crust the izu collision zone plutons provide an exceptional example of the transformation of a juvenile oceanic arc into mature continental crust

new insights on the relative sea level change during holocene along the coasts of tunisia and western libya from archaeological and geomorphological markers new data of sea level changes for the mediterranean region along the coasts of northern africa are presented data are inferred from archaeological sites of punic roman age located along the coast of tunisia between tunis and jerba island and along the western coast of libya between sabratha and leptis magna data are based on precise measures of presently submerged archaeological markers that are good indicators of past sea level elevation nineteen selected archaeological sites were studied in tunisia and four in libya all aged between 2 0 and 1 5 ka bp the functional elevations of significant archaeological markers were measured with respect to the sea level at the time of measurements applying corrections for tide and atmospheric pressure values the functional elevations of specific architectural parts of the sites were interpreted related to sea level at the time of their construction providing data on the relative changes between land and sea observations were compared against sea level change predictions derived from the glacio hydro isostatic model associated with the last glacial cycle the results indicate that local relative sea level change along the coast of tunisia and libya has increased 0 2 0 5 m since the last 2 ka besides minor vertical tectonic movements of the land the observed changes are produced by eustatic and glacio hydro isostatic variations acting in the mediterranean basin since the end of the last glacial maximum

holocene palaeoclimate in the northern sahara margin jefara plain northwestern libya the palaeoclimatic evolution of northwestern libya has been deduced from the study of the palustrine and aeolian sediments the holocene environmental variations have been recognized through geological and stratigraphic surveys and by pollen analysis and malacofauna content of the sediments some organic rich horizons have been dated using the radiocarbon method the data show that in general the presence of marshes is linked with the period of higher humidity which began around 9 4 ka bp and ended around 5 0 ka bp from c 5 0 ka bp up to about 4 4 ka bp there was a simultaneous presence of marshes and vegetation of arid climate as a consequence of rainfall in the mountains and or a decrease in temperatures the holocene wet period was interrupted by two arid spells dated about 8 2 and 5 5 5 4 ka bp the end of the wet phase must have been gradual the climatic events that occurred in the jefara plain seem to be well correlated with those identified in saharan africa even if the mediterranean is only

a hybrid origin for lachlan s type granites the murrumbidgee batholith example the murrumbidgee batholith is typical of other composite s type granite batholiths in the lachlan fold belt lfb of southeastern australia consisting of discrete peraluminous cogenetic granite suites however it contains a unique suite murrumbucka at its southern extremity that has chemical and petrological features transitional with metaluminous i type granites previous detailed structural and metamorphic studies have shown that the batholith is tilted northward exposing subvolcanic plutons in the north and root zones in the south originally located at depths of not vert similar10 km a transition from mafic foliated sheet like granites in the south to felsic generally less foliated homogeneous granites in the north is consistent with magma ascent via subvertical structurally controlled sheets to emplacement in an overlying magma chamber in the inferred root zones the murrumbucka suite hosts migmatitic metasedimentary and gabbroic rocks both of which have transitional contacts and show evidence for mafic felsic interaction with the murrumbucka suite the migmatites extend southward to become part of the high t low p cooma metamorphic complex which contains a core of heterogeneous remobilised diatexitic granite cooma suite lenses of which also occur throughout the southern deeper parts of the murrumbidgee batholith the composition of the most mafic rocks from the batholith lies on a chemical tie line between cooma suite granites and the gabbros for almost all elements this chemical coincidence is interpreted to reflect derivation of parental murrumbidgee s type granite magmas by bulk mixing between a felsic crustal and mafic mantle derived component consistent with sr and nd isotopic results and field observations based on the tie lines and simple numerical modelling the murrumbucka suite is estimated to be a 50 50 mix of mantle and crustal derived magmas whereas the more peraluminous and widespread clear range suite which is very typical of lachlan s type granites is modelled as a 40 60 mix chemical variation trends diverge from the mixing lines and suggest that much of the fractionation process operated after mixing mixing occurred within sheets during the ascent of the magmas whereas fractionation was the dominant process generating chemical diversity during emplacement in the magma chamber generation of the s type granites probably occurred in an extensional tectonic environment

sea level change along the french mediterranean coast for the past 30 000 years abstract observational evidence for sea level change along the french mediterranean coast has been examined and compared with glacio hydro isostatic models to predict the spatial and temporal patterns of change for about the past 30 000 14c years these predictions are pertinent to discussions of changing ocean volumes during this interval the tectonic stability or otherwise of the coastal areas mantle rheology and the timing of possible human occupation of the now submerged coastal plain and caves such as cosquer cave near marseille the principal results from the analysis are i sea levels along this section of the coast have risen continually since the time of the last glacial maximum lgm and at no time during the holocene has the mean sea level been higher than that of today ii the coast has been tectonically stable between marseille and nice as well as further to the west in roussillon western corsica may have experienced a slow tectonic uplift of between 0 15 0 3 mm year for the past 3000 years but northernmost corsica appears to have been stable during this same interval iii during the lgm sea levels along the coast and immediate off shore areas stood at between 105 115 m below present level the range reflecting the importance of the isostatic contributions during oxygen isotope stage 3 sea levels do not appear to have risen locally above about 60 m iv the rebound parameters describing the mantle rheology and ice sheets required to match the limited observational evidence are consistent with the results of similar analyses carried out for other parts of europe because of its distance from the former northern ice sheets the isostatic factors are particularly sensitive to the value of the lower mantle viscosity v the model predictions for sea level change at the cosquer cave site and for its immediate environments indicate that the cave was last readily accessible before about 10 700 500 14c years about 12 500 500 cal years bp and that the cave entrance was completely flooded by 9000 200 radiocarbon years bp between about 9800 and 10 300 calibrated years bp the cave was above sea level throughout the oxygen isotope stage 3

stability of andalusite and sillimanite and the al_ 2 sio_ 5 triple point constraints from the ballachulish aureole scotland andalusite and and sillimanite sil occur in well defined zones in the ballachulish aureole in most of the aureole s sillimanite bearing rocks sillimanite grain diameters range from 2 m to 10 m the boundary between prograde andalusite and prograde sillimanite is constrained to a zone of max 30 m width upgrade of the muscovite quartz andalusite k feldspar h 2 o reaction isograd this boundary is interpreted to correspond to the and sil equilibrium the common occurrence of andalusite well upgrade of the first occurrence of sillimanite is ascribed to sluggish kinetics of the polymorphic inversion the p t position of the and sil equilibrium in the aureole is estimated as 645 20 c and 3 0 0 4 kbar based on a combination of 1 location of the ms qtz and kfs h 2 o reaction corrected for non end member fluid and mineral compositions and 2 independent pressure estimates obtained from equilibria in metapelites marbles calcsilcates and granitoids all in exce

trace element and isotopic sr nd pb o arguments for a mid crustal origin of pan african garnet bearing s type granites from the damara orogen namibia geochronological data major and trace element abundances nd and sr isotope ratios 18o whole rock values and pb isotope ratios from leached feldspars are presented for garnet bearing granites locality at oetmoed and outcrop 10 km north of omaruru from the damara belt namibia for the granites from outcrop 10 km n omaruru reversely discordant u pb monazite data give 207pb 235u ages of 511 2 ma and 517 2 ma similar to previously published estimates for the time of regional high grade metamorphism in the central zone based on textural and compositional variations garnets from these granites are inferred to be refractory residues from partial melting in the deep crust because p t estimates from these xenocrystic garnets are significantly higher 800 c 9 10 kbar than regional estimates 700 c 5 kbar the monazite ages are interpreted to date the peak of regional metamorphism in the source of the granites sm nd garnet whole rock ages are between 500 and 490 ma indicating the age of extraction of the granites from their deep crustal sources for the granites from oetmoed both sm nd and pb pb ages obtained on igneous garnets range from 500 to 490 ma these ages are interpreted as emplacement ages and are significantly younger than the previously proposed age of 520 ma for these granites based on rb sr whole rock age determinations major and trace element compositions indicate that the granites are moderately to strongly peraluminous s type granites high initial 87sr 86sr ratios 0 716 high 18o values of 13 8 negative initial end values between 4 and 7 and evolved pb isotope ratios indicate formation of the granites by anatexis of mid crustal rocks similar to the exposed metapelites into which they intruded the large range of pb isotope ratios and the lack of correlation between pb isotope ratios and nd and sr isotope ratios indicate heterogeneity of the involved crustal rocks evidence for the involvement of isotopically highly evolved lower crust is scarce and the influence of a depleted mantle component is unlikely the crustal heating events that produced these granites might have been caused by crustal thickening and thrusting of crustal sheets enriched in heat producing elements very limited fluxing of volatiles from underthrust low to medium grade metasedimentary rocks may have also been a factor in promoting partial melting furthermore delamination of the lithospheric mantle and uprise of hot mantle could have caused localized high t regions the presence of coeval a type granites at oetmoed that have been derived at least in part from a mantle source supports this model

hybridization of a shallow i type granitoid pluton and its host migmatite by magma chamber wall collapse the tokuwa pluton central japan the miocene tokuwa pluton of i type granitoid affinity was emplaced discordantly into a cretaceous to paleogene accretionary complex and induced a contact aureole in which various thermally metamorphosed rocks were developed including hornfels metatexite diatexite and cordierite bearing tonalite crd tonalite of s type granite affinity the thermally metamorphosed rocks show low pressure reaction textures culminating in partial melting peak p t conditions of 3 kbar at 7808c are estimated on the basis of the twq thermobarometer for the garnet bearing rocks the rocks in the contact aureole exhibit a gradual transition from hornfels through metatexite and diatexite to crd tonalite the sr isotopic composition at the time of tokuwa pluton emplacement at 12 ma decreases systematically from metatexite 0 7100 0 7112 through diatexite 0 7078 0 7094 to crd tonalite 0 7067 0 7068 this trend is interpreted in terms of mixing between the tokuwa magma and the aureole migmatites the field relationships geochemical data and isotopic data collectively suggest that the emplacement of the tokuwa pluton triggered partial melting of the surrounding metasedimentary rocks subsequent hybridization of the tokuwa magma with the metatexite in variable proportions produced the crd tonalite and diatexite the hybridization was caused by invasion of the tokuwa magma into the migmatite zone accompanied by gravitational collapse of the previously crystallized wall of the magma chamber the data presented demonstrate that even a relatively low temperature shallow i type granitoid pluton can induce contact anatexis and hybrid s type granitoid formation at the intrusive contact

sea level markers identified in ground penetrating radar data collected across a modern beach ridge system in a microtidal regime sea level rise has been related to global warming the modern system on the northern coast of anholt denmark may well be analogous to other beach ridge systems formed in microtidal regimes and our results should have impact on estimation of past sea level variation ground penetrating radar data collected across the modern 30 years old berm beach ridge and swale deposits resolve downlapping reflections interpreted to mark sea level at the time of deposition existing time series of sea level data constrain actual sea level variation nineteen readings of sea level markers made along our profile fluctuate within 0 42 and 0 57 m above present mean sea level consistent with 95 of the sea level data these fluctuations reflect tidal effects and meteorological conditions main data uncertainties are well known and the sea level markers may be identified with a high degree of confidence

metamorphic discontinuities in the pennsylvania delaware piedmont evidence for early paleozoic assembly interpretation of the early paleozoic tectonic history of the appalachian piedmont is commonly complicated by post taconian deformation that has disrupted and obscured early paleozoic structure blocks that lie between zones where later deformation has been concentrated however may preserve evidence of taconian high grade metamorphism in these cases analysis of metamorphism allows an interpretation of the early paleozoic tectonic history of the block and its surrounding region a block of this type in the pennsylvania delaware piedmont includes three tectonic units 1 the basement cored massifs of southeastern pennsylvania with grenvillian gneiss unconformably overlain by the setters formation and cockeysville marble 2 the wilmington complex arc terrane and 3 the wissahickon group and associated metaigneous rocks a metamorphic gradient and inferred temperature inversion within the wissahickon group and a metamorphic discontinuity at the wissahickon group cockeysville marble contact are used t

geochemical modeling of low melt fraction anatexis in a peraluminous system the pena negra complex central spain abstract a study was made of the chemical fractionation associated with four cases of anatectic segregation of low melt fraction cordieritic granites from migmatized meta greywackes the aims of the study were to 1 reveal the fractionation patterns of major and trace elements 2 compare the major element chemistry of leucogranites and the quantitative behavior of source minerals during anatexis inferred by mass balance adjustment with available experimental data for peraluminous systems and 3 discuss the behavior of trace elements in crustal melting by comparing the chemically determined composition of leucogranites with the results of three fractionation models two of these assume a perfect diffusive behavior of trace elements within residual solids but they use a different set of distribution coefficients the third assumes a perfect nondiffusive behavior in relation to their source rocks the leucogranites are strongly depleted in li transition elements and light rare earth elements but enriched in k2o sio2 and ba the k rb ratio in leucogranites is higher than in sources and reaches values typical of high grade metamorphism mass balance analysis using the anatexis mixing model shows that the chemistry of cordierite leucogranites is compatible with its having originated by closed system water undersaturated anatexis on previously migmatized meta greywackes leaving a residue enriched in cordierite plus biotite and exhausted in k feldspar biotite melts congruently unless important amounts of sillimanite were also present in the source compared with experimental melts obtained from sources with the same chemical composition but with a different femic mineralogy biotite sillimanite instead of cordierite biotite the pena negra leucogranites are richer in k2o and mgo with a lower fe fe mg ratio the differences in magnesium are believed to result from the changes in the mineral assemblage of the source rocks however the differences in potassium contents are still not well understood the behavior of trace elements during anatexis cannot be modeled by trace element fractionation equations because of the sluggish diffusion kinetics of trace elements at the temperature of anatexis making the melting rate of minerals greater than the diffusion rate of trace elements within minerals the behavior of trace elements essentially consists in following that of the minerals containing them

origin of beach ridges and swales abstract sandy beach ridges occur in four main categories 1 swash built 2 settling lag 3 eolian 4 storm surge ridges in the first two classes are geometrically regular only a few tens of centimeters above adjacent swales and commonly in ridge sets and systems tens to hundreds of ridges each individual sets of 5 25 ridges tend to stand 0 5 m to 2 m above or below adjacent sets ridges in the third and fourth classes do not have these characteristics do not occur in sets and are generally not suitable for detailed historical studies no one of these ridges is the same as the storm built berm which is almost never preserved swash built sandy beach ridges have diagnostic 1 map spacing 2 accretion rate 3 periodicity 4 crossbedding and 5 granulometry the last two indicate fair weather waves on a sandy beach in contrast with settlinglag ridges postma style which have the same external geometry but which were deposited without important wave work and in contrast with storm built berms generally seen on eroding coasts but rarely or never in beach ridge plains the grain size kurtosis of beach sand is an excellent index to near shore wave energy density changes in kurtosis at ridge set boundaries mark changes in long term wave energy density hence in sea level the latter can be deduced also from set height differences and from spacing differences periodicity is typically 30 60 years map spacing 25 50 m and accretion rate fairly close to 1 m yr a few ridge sets with intervals of 3 7 10 12 or 18 19 years have smaller spacings this is not what can be done if each ridge is built by one storm if each ridge had been built by one storm wide beach ridge plains like one in denmark dating from about 11 700 yr b p would have been formed in the last 30 50 years at accretion rates of hundreds of meters per year instead each swash type sandy beach ridge was made by a sea level rise and fall couplet amplitude 5 30 cm the swale marks the lower position this mechanism reflects the fact that the transverse profile from beach to sea is gently concave upward with maximum curvature close to shore this is a shape which is out of adjustment with the shoaling wave system shortly after a small sea level change settling lag ridges were built without waves hence the ridge and swale sequence in this case cannot be attributed to waves either fair weather or storm these ridges show the same historical pattern as do swash built ridges this fact suggests that both were controlled by the same mechanism sea level change

solar wind dependence of the occurrence and motion of polar auroral arcs a statistical study 1 polar uv images from a 3 month period in winter 1998 1999 are used for a statistical study of polar arcs the study covers all auroral arcs that are located poleward of the northern auroral ova

a continuous view of the dawn dusk polar cap continuous monitoring of airglow and auroral emissions over eureka 89 magnetic latitude through each winter has shown that the dusk and dawn boundaries of the polar cap can be routinely seen when the imf b 2 is northward when this condition prevails the auroral oval shrinks poleward and the polar boundaries are clearly and continuously seen in photometric dusk dawn meridian scans of oi 630 nm emission brightness this fact is illustrated with two 24 hr days of records on december 19 1996 and january 19 1998 these examples show and others similarly that polar arcs emerge from the dusk or dawn flanks of the auroral oval depending on the sign of b y and thus occur on closed field lines in a few cases polar arcs emerge from the midnight or noon sector of the oval and extend along the sun earth line to cross the eureka meridian bifurcating the polar cap this new technique for monitoring the polar cap dusk dawn extent and all auroral activity within promises to be valuable for diagnostic studies of both polar auroral activity and magnetospheric topology during solar wind changes and major sun earth events

on the pseudomorphing of melt filled pores during the crystallization of migmatites pseudomorphs of melt filled pores recognized by their generally cuspate shape are used as diagnostic for the former presence of partial melt they are commonly observed in migmatites from the mid to deep crust although they occur in the smaller pores in migmatites from shallower levels 1 2 kbar the pseudomorphing of meltfilled pores is controlled by the kinetics of nucleation and is a consequence of the greater supersaturation required for nucleation in a small pore compared with a larger one we examine three migmatites in detail a contact metamorphosed cherty band from an iron formation an archaean regional granulite from an accretionary prism and an amphibolite facies sample from the roots of an archaean mountain chain the greater undercooling required for nucleation in progressively smaller pores is recorded by the composition of plagioclase pseudomorphs a study of dihedral angles at the corners of pseudomorphed pores demonstrates that melt solid textural equilibrium was probably attained only in the contact aureole the regional granulite preserves an almost unmodified reaction controlled melt distribution with little evidence for either melt solid textural equilibration or solid solid re equilibration whereas the reactioncontrolled melt distribution in the regional amphibolite facies example has been modified by a partial approach to solid solid textural equilibrium it is not clear whether the differences in dihedral angle population are due to differences in uplift and exhumation rates or due to the presence of h2o on grain boundaries

rb sr and u pb isotope studies on migmatites from the schwarzwald germany constraints on isotopic resetting during variscan high temperature metamorphism mineral and isotope studies were undertaken on migmatites from the schwarzwald moldanubian zone of the variscan belt the aims of the study were to date the migmatite formation and to determine the processes involved in migmatization in order to evaluate their influence on isotopic resetting textural evidence and the comparison of mineral compositions from leucosomes and mesosomes of two centimetre scale migmatite profiles respectively suggest that migmatitic textures and mineral assemblages were formed by metamorphic segregation deformation enhanced mass transport rather than by partial melting anatexis the results of rb sr thin slab dating on these profiles indicate that sr isotopes were not completely reset during migmatization no true isochron ages but ages of approximate isotopic homogenization were obtained on the thin slabs by calculating 87sr 86sr ratios back to various stages in their evolution the coincidence of these rb sr data with u pb ages of monazites from migmatites and non migmatitic gneisses shows that gneisses and migmatites were formed during the same high temperature event in the carboniferous 330 335 ma the observation that high temperature metamorphism failed to equilibrate sr isotopes on the centimetre scale imposes limitations on the use of conventional whole rock isochron techniques in dating migmatites

partial melting of the appin quartzite driven by fracture controlled h sub 2o infiltration in the aureole of the ballachulish igneous complex scottish highlands the ballachulish igneous complex consists of an outer quartz diorite and an inner granite emplaced at about 300 mpa initially at 1000 to 1050 c the contact aureole 0 5 2 km wide occurs in metapelites and metapsammites plus minor graphitic slates carbonate rocks and metaquartzites a textural examination of the arkosic appin quartzite which was previously believed to have melted only within a few metres of the intrusion demonstrates that partial melting occurred up to 500 m away from the vertical eastern contact coupling petrographic observations with qtz ab or h2o phase relations we determined both the amounts of actual melt and the maximum possible amounts of melt in the samples melting efficiency was everywhere less than 100 and decreased with distance from the intrusion though perhaps not the only possible source of fluid throughout the aureole simple models demonstrate that h2o evolution from the pluton would have been volumetrically sufficient and persisted long enough to account for the observed partial melting a time integrated fluid flux of 7000 kg m2 from the pluton is necessary to account for the observed amounts of partial melt in the appin quartzite from its inefficiency we infer that infiltration of the appin quartzite cannot have occurred along interconnected grain edge channels rather it was controlled by hydraulic fracturing with fracture density determining melting efficiency bulk rock permeability is calculated to be 10 20 m2 an order of magnitude lower than that necessary to permit pervasive flow of all the fluid exsolving from the pluton there is little difference between the calculated time integrated fluid flux through the appin quartzite on the eastern flank and an estimate of the infiltrating flux through the pelitic leven schist on the western flank in the time interval during which both rock types were above their solidus temperature despite differences in their equilibrium quartz h2o dihedral angles at temperatures immediately below the solidus and differences in the attitude of the contact the rates of h2o expulsion from the cooling pluton are consistent with highly efficient fracture dominated flow allowing insufficient time for textural equilibration

structure and development of the sagami trough and the boso triple junction abstract the sagami trough is located at the particular plate margin where the izu forearc is subducted underneath the honshu forearc at its southeastern end the world s only known ttt type triple junction boso triple junction has developed several different kinds of basins occur in different segments along the sagami trough and at the triple junction the bathymetric geologic and geophysical data obtained during the kaiko project and from additional studies are summarized together with our onland studies we suggest that the right lateral oblique plate motion formed an eduction margin in the sagami basin while a normal subduction margin and an oblique subduction margin have been formed in the middle sagami trough basin these tectonic phenomena resulted from the long lasting compressional covergence between the philippine sea plate and eurasian plate since the early or middle miocene the north basin on the northeasternmost margin of the philippine sea plate near the boso triple junction has developed as a stretched basin due to the westward motion of the philippine sea plate with respect to the eurasian plate

melting kinetics of a plagioclase feldspar partial melting experiments on plagioclase feldspar have been carried out to investigate textures and kinetics of the melting a labradorite single crystal was heated at one atmosphere pressure and temperatures within its melting interval as a function of time so called honeycomb fingerprint or sieve textures were produced except for the runs just below the liquidus the melting was initiated by heterogeneous nucleation of melt at the surface and or interior cracks and possively dislocations of the crystal the pattern of the melt is dendritic with a few m arm spacing after the melt develops throughout the crystal the volumes of melt and residual crystal become larger and smaller respectively without changing the arm spacings the melt is homogeneous and has the approximate temperature dependent liquidus composition irrespective of the time there are compositional gradients in the residual crystal after short periods of melting the an content of the crystals increases with increasing time until it finally reaches equilibrium with the melt after several thousands minutes of heating it is concluded that the enlargement of the melt the main process of the melting is controlled by diffusion in the crystal the fact that partial melts have the composition of the equilibrium liquidus even from the first several minutes strongly suggests that the local equilibrium at the crystal liquid interface is satisfied during the melting some of the honeycomb fingerprint and sieve textures found in xenoliths and phenocrysts of sodic plagioclase in volcanic rocks would be caused by heating events such as magma mixing during which temperatures of magmas were temporarily higher than the solidus of some of the minerals

ground penetrating radar profiles of holocene raised beach deposits in the kujukuri strand plain pacific coast of eastern japan abstract ground penetrating radar gpr profiles of holocene beach deposits were documented from the kujukuri strand plain pacific coast of japan to examine a marker of past sea level recognized in these profiles the kujukuri strand plain has been uplifted over the last 6000 years with a total relative sea level fall of about 5 m suggested by seaward lowering of the lithologic boundary between the foreshore and upper shoreface facies a gpr survey was performed on a modern aeolian dune and beach ridges of the strand plain using a pulseekko100 system with 100 mhz antennae the profiles obtained contain five vertically stacked radar units r1 r5 with characteristic reflections ground truthing using sediment cores and the morphology of the modern beach suggest that these radar units correspond to aeolian dune r1 small scale swale r2 backshore and foreshore r3 upper shoreface r4 and lower shoreface r5 deposits in descending order the backshore and foreshore radar unit shows a sequence of continuous reflections dipping seaward at an angle consistent with the modern beach whereas the underlying upper shoreface radar unit represents complicated and less continuous reflections the boundary between these two units is a downlap surface of the foreshore reflections and is thought to have formed at about 1 m below the mean sea level at the time of deposition the lateral tracing of the boundary in radar profiles across the strand plain indicates a total fall in relative sea level of 5 m which is consistent with the drill core results radar profiles of the foreshore and upper shoreface deposits in the kujukuri strand plain thus provide a past sea level indicator that is available without drilling sediment cores

tracing sea level changes during the mid holocene in the southern mediterranean coast an example from the gulf of gabes abstract mid holocene sea level emergence was recorded along a mid latitude coastal site in the gulf of gabes tunisia in beach rock deposits however the post emergence sea level curve and associated hydro sedimentary processes have rarely been documented this study presents new records of sea level changes along the tunisian coast since the mid holocene each phase of the sea level curve was evidenced and supported by lithostratigraphic morphological and archaeologic markers post emergence sea level fall due to postglacial isostatic rebound was recognized in regressive sequences which vary depending on available accommodation space from a small pocket beach to a well developed dune system sea level stabilization following isostatic rebound has promoted the end phase deposits of the regressive sequences however this stability was interrupted during the late holocene by a high energy storm event that accumulated a transgressive boulder unit at 2 m above present shape and disposition of the boulder ridge behind a prograding modern shoreline suggests that sea level has not changed during the late holocene the existence of a roman fish pond on the upper foreshore confirms stability of sea level during the last two millennia the combination of lithostratigraphic morphological and archaeologic markers represents a tool for improving the accuracy of dating of erosional and depositional periods in mid coastal sections

a beach ridge progradation complex reflecting periodical sea level and climate variability during the holocene gulf of almeria western mediterranean detailed mapping based on aerial photographs at various scales analysis of morpho sedimentary units and radiocarbon dating of the prograding beach ridge complex of campo de dalias almeria allow the differentiation of six prograding units these are called h1 7400 6000 cal bp h2 5400 4200 cal bp h3 4200 3000 cal bp h4 2700 1900 cal bp h5 1900 1100 cal bp and h6 500 cal bp present h units are deposited during periods of high relative sea level and increased sediment input to the coast they are bounded by large swales or erosional surfaces associated with lower sea levels and reduced input of sediment to the coast these correspond to short periods of increased aridity inside the general arid trend recorded in the western mediterranean since 5 4 ka changes in the flux of atlantic superficial waters into the mediterranean sea and relative strength of the w sw winds account for the recorded oscillations of relative sea level we deduce a decadal periodicity for the deposition of a beach ridge and the adjacent swale and suggest that it is related to fluctuations of the north atlantic oscillation nao index and to variations of solar activity the duration of h units shows a quasi millennial periodicity punctuated by short hundred years episodes of reduced progradation or erosion representing events of increased aridity likely to be related to bond s holocene cold events

geochemical characteristics of crustal anatexis during the formation of migmatite at the southern sierra nevada california we provide data on the geochemical and isotopic consequences of nonmodal partial melting of a thick jurassic pelite unit at mid crustal levels that produced a migmatite complex in conjunction with the intrusion of part of the southern sierra nevada batholith at ca 100 ma field relations suggest that this pelitic migmatite formed and then abruptly solidified prior to substantial mobilization and escape of its melt products hence this area yields insights into potential mid crustal level contributions of crustal components into cordilleran type batholiths major and trace element analyses in addition to field and petrographic data demonstrate that leucosomes are products of partial melting of the pelitic protolith host compared with the metapelites leucosomes have higher sr and lower sm concentrations and lower rb sr ratios the initial 87sr 86sr ratios of leucosomes range from 0 7124 to 0 7247 similar to those of the metapelite protoliths 0 7125 0 7221 however the leucosomes have a much wider range of initial end values which range from 6 0 to 11 0 as compared to 8 7 to 11 3 for the metapelites sr and nd isotopic compositions of the leucosomes migmatites and metapelites suggest disequilibrium partial melting of the metapelite protolith based on their sr nd and other trace element characteristics two groups of leucosomes have been identified group a leucosomes have relatively high rb pb ba and k2o contents rb sr ratios 0 15 rb sr 1 0 and initial end values group b leucosomes have relatively low rb pb ba and k2o contents rb sr ratios 0 15 and initial end values the low rb concentrations and rb sr ratios of the group b leucosomes together suggest that partial melting was dominated by water saturated or h2o fluxed melting of quartz feldspar assemblage with minor involvement of muscovite breakdown of quartz and plagioclase with minor contributions from muscovite resulted in low rb sr ratios characterizing both group a and group b leucosomes in contrast group a leucosomes have greater contributions from k feldspar which is suggested by 1 their relatively high k concentrations 2 positive or slightly negative eu anomalies and 3 correlation of their pb and ba concentrations with k2o contents it is also shown that accessory minerals have played a critical role in regulating the partitioning of key trace elements such as sm nd nb and v between melt products and residues during migmatization the various degrees of parent daughter fractionations in the rb sr and sm nd isotopic systems as a consequence of nonmodal crustal anatexis would render melt products with distinct isotopic signatures which could profoundly influence the products of subsequent mixing events this is not only important for geochemical patterns of intracrustal differentiation but also a potentially important process in generating crustal scale as well as individual pluton scale isotopic heterogeneities

missing oligocene crust of the izu bonin arc consumed or rejuvenated during collision the 50 myr old izu bonin mariana ibm arc consists mostly of oligocene middle and lower crust that underlies the upper crust these units are in turn covered by quaternary volcanic rocks seismic imaging forearc geology ocean drilling program drilling and magnetic anomalies suggest that most ibm arc crust was created in eocene oligocene times however remnants of this old crust have never been found at the northern end of the arc where it is colliding with the honshu arc izu collision zone two batholiths in this collision zone thetanzawa tonalites and the kofu granitic complex were emplaced during the miocene 4 17 ma major elements zr y rare earth element ratios and normalized abundance patterns and sr nd isotopic data indicate that these plutonic bodies are compositionally similar to the oligocene ibm volcanic rocks and that they are dissimilar to the miocene pliocene and quaternary ibm lavas and volcaniclastic rocks we suggest that the miocene plutonic rocks in the izu collision zone were derived from partially melted oligocene middle crust a model is proposed in which ibm arc middle crust in the collision zone was partially melted during the collision and then intruded into the overlying upper crust of the honshu and ibm arcs this resulted in the complete loss of chronological information related to their original source

u series evidence for two high last interglacial sea levels in southeastern tunisia abstract pleistocene raised marine deposits in southeastern tunisia consist of a siliciclastic unit that culminates at 3 m asl overlain by a carbonate rich unit with strombus bubonius that culminates at 5 m asl 234 u 238 u ratios on fossil ostraea shells from both units are compatible with a marine origin from the uranium incorporated into the shells and show narrowly clustered 230 th ages respectively between 147 and 110 ka and 141 and 100 ka the two units were therefore developed during marine isotopic substage 5e miss 5e last interglacial their heights are comparable to those of contemporaneous marine deposits found in many tectonically stable areas of the world such as in the bahamas and in bermuda and can therefore be used as indicators of eustatic changes during the last interglacial it is argued that on the basis of this evidence the last interglacial was characterised by two eustatic maxima

in situ migmatite and hybrid diatexite at mt stafford central australia metasedimentary gneisses show a rapid change in grade within a 10 km wide low p high t regional aureole at mt stafford arunta block central australia migmatites occur in all but the lowermost of five metamorphic zones which are characterized by 1 muscovite quartz schist 2 andalusite cordierite k feldspar granofels with small melt segregations 3 spinel sillimanite cordierite k feldspar migmatite 4 garnet orthopyroxene cordierite migmatite and minor diatexite and 5 biotite cordierite plagioclase diatexite that shows a transition to granite a subsolidus unit comprising interbedded sandstone and siltstone is equivalent to bedded migmatite the main rock type in zones 2 4 mesoscopic textures and migmatite classification of this unit vary with grade in zone 2 metatexite is developed in siltstone layers that are separated by quartz rich unmelted metapsammite layers melt segregation was less efficient in zones 3 and 4 where the dominant migmatite layering is a modified bedding high proportions of melt were present in zone 4 in which schlieren migmatite is transitional between bedded migmatite and metapelite sourced diatexite the preservation of sedimentary structures and coexistence of melt reactants and products in zone 4 metapelite imply that melting proceeded insitu without substantial migration of melt zone 5 biotite cordierite plagioclase diatexite carries rafts of bedded migmatite with strongly resorbed edges as well as large k feldspar and quartz augen this unit of comparatively ca rich migmatites is inferred to have been formed by the mixing of locally derived and injected granitic melt

diffusion creep and partial melting in high temperature mylonitic gneisses hope valley shear zone new england appalachians usa field petrographic microstructural and isotopic studies of mylonitic gneisses and associated pegmatites along the hope valley shear zone in southern rhode island indicate that late palaeozoic deformation c 275 ma in this zone occurred at very high temperatures 650 c high energy cuspate lobate phase boundary microstructures a predominance of equant to sub equant grains with low internal lattice strain and mixed phase distributions indicate that diffusion creep was an important and possibly predominant deformation mechanism field and petrographic evidence are consistent with the presence of an intergranular melt phase during deformation some of which collected into syntectonic pegmatites rb sr isotopic analyses of tightly sampled pegmatites and wall rocks confirm that the pegmatites were derived as partial melts of the immediately adjacent isotopically heterogeneous mylonitic gneisses the presence of syntectonic interstitial melts is inferred to have permitted a switch from dislocation creep to melt enhanced diffusion creep as the dominant mechanism in these relatively coarse grained mylonitic gneisses 200 500 lm syn deformational grain size a switch to diffusion creep would lead to significant weakening and may explain why the hope valley shear zone evolved into a major regional tectonic boundary this work identifies conditions under which diffusion creep operates in naturally deformed granitic rocks and illuminates the deformation processes involved in the development of a tectonic boundary between two distinct late proterozoic avalonian basement terranes

magma recharge and reactive bulk assimilation in enclave bearing granitoids tonglu south china national nature science foundation of china 41530211 mlr special funds for public welfare projects 201211013 2 state administration of foreign expert affairs of china b07039 most special funds of the state key laboratory of geological processes and mineral resources msfgpmr01

microstructural investigation of naturally deformed leucogneiss from an alpine shear zone southern calabria italy in order to reveal any correlation between the preferred orientation of quartz and progressive intensity of strain a suite of deformed leucogneiss collected within a ductile shear zone outcropping in calabria southern italy was investigated based on the microstructural approach and matrix clast relationships the method applied here may be useful for appraising the connection between deformation mechanisms of constituent minerals and bulk textural properties of naturally sheared rocks accordingly quartz c axis orientation patterns were determined by image assisted analysis results revealed a correlation between finite strain and textural features as strain increases the matrix develops at the expense of the clast counterpart which is instead progressively reduced in both size and amount

evolution of structurally contrasting anatectic migmatites in the 3 kbar ballachulish aureole scotland anatectic migmatites of contrasting structural style are found adjacent to the contacts of the ballachulish igneous complex argyllshire scotland on the east flank evidence for migmatization is largely restricted to the local development of millimetre centimetre scale kfs qtz rich leucocratic segregations which accompany fragmentation of brittle hornfels layers and ductile deformation of mm cm scale semipelitic layers large volumes of semipelitic rock rich in feldspar and quartz on the east flank show no migmatitic features and bedding is usually preserved undisturbed right up to the contact on the west flank in contrast similar semipelitic rocks show widespread migmatitic features and disruption of layering is substantial and widespread over a 400 m wide zone within the west flank migmatites 1 100 cm scale rigid bedding fragments schollen may be suspended and disoriented in a semipelitic matrix that underwent ductile deformation the p t conditions on both flanks are in the same range 3 kbar and 650 700 c the contrast in gross structural style is believed to result from differences in the volumes of melt produced and differences in the proportion of rock in which the critical melt fraction of the rocks was exceeded on the east flank only on a mm cm scale was enough melt locally accumulated to cause disruption of some layers and segregation of melt on the west flank melting proceeded substantially in a broad tract of semipelitic rocks resulting in larger scale contrasts in rheology that led to the present chaotic structures in this zone because migmatization occurred at a pressure too low for muscovite dehydration melting and at temperatures too low for substantial biotite dehydration melting the different amounts of melting on the east and west flanks most probably resulted from the introduction of differing amounts of externally derived water on the east flank and throughout most of the aureole the absence of melting even in quartzofeldspathic protoliths indicates that there was no substantial movement of fluid towards or away from the igneous complex during migmatization the contrasting situation on the west flank may have resulted from devolatilization of underlying quartz diorite magma 690 710 c which released heat and fluids into the overlying quartz and feldspar rich semipelites solidus temperature 650 680 c

origin of peraluminous granites and granodiorites iberian massif spain an experimental test of granite petrogenesis the discrimination between potential source materials involved in the genesis of iberian granites and granodiorites as well as the role of mantle crust inter actions are examined using constraints imposed by melting experiments melting assimilation experiments and sr nd isotope systematics the sr nd isotope re lationships indicate the existence of diaerent genetic trends in which juvenile mantle materials are involved by diaerent mechanisms 1 a source trend traced by a particular evolution of the pre hercynian basement and indicating mantle participation at the time of sedimen tation 2 a set of magmatic trends traced by gabbro tonalite enclave granodiorite associations implying the incorporation of new mantle material at the time of granite generation these relationships strongly support a pure crustal origin for the peraluminous leucogranites derived from partial melting of crustal protoliths and a hybrid origin for the peraluminous granodiorites these granodiorites are the most abundant granitic rocks of the central iberian zone ciz of the iberian massif implying that processes of hybridisation by assimilation and or magma mixing played an important role in granitoid production during the hercynian orogeny these hypotheses have been tested by means of melting and assimilation experiments melting experiments in the range 800 900 c and at pressures of 3 6 10 and 15 kbar indicate that 1 several potential source materials such as bt ms gneisses and metagreywackes are suitable for the production of peraluminous leucogranite melts 2 the melt compositions are always leucogranitic re gardless of pressure 3 pressure exerts a strong influ ence on the fertility of the source experiments at 3 kbar produce more than 20 vol of melt compared with less than 5 vol of melt produced at 10 and 15 kbar and at the same temperature the melting assimilation experi ments carried out at 1000 c and 4 7 and 10 kbar and using a proportion of 50 gabbro and 50 gneiss give high melt proportions more than 50 vol and noritic residues these melts have the composition of le ucogranodiorites and overlap with part of the compo sitional range of peraluminous granodiorites of the iberian massif the generation of more mafic granodiorites may be explained by the incorporation of some residual orthopyroxene to the granodiorite mag mas the low solubility of fe mg prevents the gen eration of granodiorite melts with more than 3 wt of mgo feo at all crustal pressures the large volumes of peraluminous hybrid granodiorites produced by assimilation of crustal rocks by mantle magmas imply that an important episode of crustal growth took place during the late palaeozoic hercynian orogeny in the iberian massif

tourmaline breakdown in the migmatite zone of the ryoke metamorphic belt sw japan a sharp line delimitating the distribution of tourmaline termed as a tourmaline out isograd is defined in the migmatite zone of the ryoke metamorphic belt japan the trend of the tourmaline out isograd closely matches that of the isograds formed through the regional metamorphism suggesting that it represents the breakdown front of tourmaline during regional metamorphism this is confirmed by the presence of the reaction textures of tourmaline to sillimanite and cordierite near the tourmaline out isograd the breakdown of tourmaline would release boron into associated melts or fluids and be an important factor in controlling the behaviour of boron in tourmaline bearing high temperature metamorphic rocks near the tourmaline out isograd large tourmaline crystals occur in the centre of interboudin partitions containing leucosome in the melanosome of the intervening matrix reaction textures involving tourmaline are locally observed these observations imply that tourmaline breakdown is related to a melting reaction and that the boron in the leucosome is derived from the breakdown of tourmaline in the melanosome during prograde metamorphism boron released by tourmaline breakdown lowers both the solidus temperature of the rock and the viscosity of any associated melt considering that the tourmaline out isograd lies close to the schist migmatite boundary these effects might have enhanced melt generation and segregation in the migmatite zone of the ryoke belt the evidence for the breakdown of tourmaline and the almost complete absence of any borosilicates throughout the migmatite zone suggest that boron was effectively removed from this region by the movement of melt and or fluid this implies that the tourmaline out isograd can reflect a significant amount of mass transfer in the anatectic zones

temperature and salinity records of the tyrrhenian sea during the last 18 000 years abstract we have used the modern analogue technique to derive sea surface temperature sst records of the last 18 000 years from two well dated deep sea cores recovered in the tyrrhenian sea results show two major cooling events synchronous with the european and north atlantic oldest and younger dryas events a later cooling of lower amplitude is observed between about 8000 and 4500 yr bp tyrrhenian ssts were similar to those of the upper holocene only during the bolling allerod event and at the beginning of the holocene we compared the sst and the planktonic foraminiferal oxygen isotope records to estimate the surface salinity variations our reconstruction shows that salinity decreased in the tyrrhenian sea during the three cold events whereas high ssts correlate with high salinities during most of the last 18 000 years tyrrhenian sea salinity variations were similar to those of the north atlantic ocean near the entrance of the mediterranean sea the salinity gradient between the two basins was thus constant indicating that the western mediterranean circulation pattern and the freshwater budget were not significantly different from the modern one the case was however different during the middle holocene when the strong salinity decrease associated with the sapropel deposit in the eastern mediterranean basin had no equivalent in the north atlantic ocean this peculiar event can only be explained by a local climatic change and an increase of precipitation

glass rich cordierite biotite rhyodacite valle ninahuisa puno se peru petrological evidence for hybridization of lachlan s type and potassic mafic magmas

nd isotope disequilibrium during crustal anatexis a record from the goat ranch migmatite complex southern sierra nevada batholith california geological and geochemical studies of a pelitic migmatite complex within the isabella pendant of the southern sierra nevada batholith california suggest that the leucosomes represent the products of partial melting of the metapelite host driven by the emplacement of the adjacent goat ranch pluton ca 100 ma the leucosomes preserve a record of largemagnitude nd isotope disequilibrium with respect to their pelitic source the leucosomes have a wide range of nd 100 ma from 26 0 to 211 0 as compared to 28 7 to 211 3 for the source they can be subdivided into two groups based on their major elements and sr and nd isotope geochemistry group i leucosomes have higher p2o5 contents and nd 100 ma values than those of group ii the nd 100 ma values of group i leucosomes are significantly higher than those of metapelites and migmatites by two to four epsilon units suggesting that group i leucosomes are in nd isotope disequilibrium with their sources correlations among p2o5 contents nd 100 ma values and sm nd ratios in the leucosomes suggest that apatite or monazite has played a dominant role in fractionating sm from nd and generating nd isotope disequilibrium dissolution of apatite or monazite might play a critical role in regulating the behavior of the sm nd isotope systems and thus the nd isotope compositions of melts generated during crustal anatexis especially in metasedimentary protoliths

last glacial to holocene palaeoenvironmental evolution at lago di pergusa sicily southern italy as inferred by pollen microcharcoal and stable isotopes abstract sediments of last glacial and holocene age from two different locations in the basin of lago di pergusa have been palynologically and isotopically investigated new data have been integrated with those available from previous researches carried out by the authors this study indicates once more that lago di pergusa was and still is very sensitive to climate changes in particular during the last glacial it played an important role in preserving the biodiversity as thermophilous and mesophilous taxa never completely disappeared in particular zelkova pollen indicates that the distribution area of this tree still living as a relic plant in south eastern sicily was wider during the last glacial where its last spread is found around 20 000 years bp the 18 o record mirroring the arboreal concentration trend confirms the climate inferences based on vegetation features both the late glacial and the postglacial reforestation periods show slower vegetation dynamics and forest development than expected with trends mirroring the slow and sustained decline of 18 o record the younger dryas oscillation is not pronounced in any of the lacustrine palaeoenvironmental proxies its termination occurring around 11 100 cal years bp the opening of the woodland recorded by a slow trend ranging from the neolithic around 8000 cal years bp to the eneolithic few centuries before 4000 cal years bp seems to be a natural forest clearance and not due to human impact anomalies in pollen microcharcoals and positive correlations between 18 o and ap curves are found after a climate change occurring at 4500 years bp and interpreted as a signal of human impact the new 18 o data presented in this paper throws new light to propose this hypothesis confirming an early aridification trend detected from pollen and a relatively late human impact inferred from fire dynamics in this central and montane region of sicily

the evolution of a precambrian arc related granulite facies gold deposit evidence from the glenburgh deposit western australia abstract gold deposits are rare in upper amphibolite to granulite facies environments known examples commonly attract debate about whether they formed under these conditions or instead represent metamorphosed metasomatic or superimposed retrograde mineralization the glenburgh gold deposit is located in the paleoproterozoic upper amphibolite to granulite facies glenburgh terrane in the southern gascoyne province of western australia gold at the glenburgh deposit is free and disseminated within quartz biotite garnet gneiss amphibolite and post gold quartz chlorite veins no clear association with a specific host lithology has been identified and mineralization does not have a visually distinct proximal alteration assemblage the rocks hosting the deposit represent a distinct sedimentary package that was deposited mineralized buried and metamorphosed all during arc magmatism features within the internal structure of gold grains such as high purity gold veinlets incoherent twinning and low silver content suggest the gold has been through post depositional processes such as metamorphism and deformation abundant sulfide minerals are interpreted to have formed by sulfidation of the host rock contemporaneously with gold mineralization and the presence of rounded sulfide inclusions within garnet porphyroblasts illustrates the presence of a sulfide phase prior to peak metamorphism geochronology of zircon and monazite constrains the timing of mineralization to be younger than c 2035 ma the maximum depositional age of the metasedimentary host rocks but older than c 1991 ma the peak of m1 metamorphism during the glenburgh orogeny these events were synchronous with arc magmatism rocks at the glenburgh deposit were likely deposited in a fore arc or accretionary wedge a favourable setting for porphyry cu mo au epithermal au polymetallic sn w skarn and orogenic au mineralization phase equilibria modelling of a pelitic migmatite constrains peak p t conditions to be 865 885 c 6 8 7 6 kbar consistent with elevated thermal gradients within the arc followed by conductive cooling of arc magmas partial melting during peak m1 metamorphism possible caused gold remobilization the lack of an alteration assemblage further suggests that the alteration assemblage and mineralization were recrystallized during deformation and metamorphism however increases in ca and k abundance and magnetic susceptibility decreases toward mineralization suggesting that they may constitute ore vectors

scale of pluton wall rock interaction near may lake yosemite national park ca usa interaction of magma with wall rock is an important process in igneous petrology but the mechanisms by which interactions occur are poorly known the western outer granodiorite of the cretaceous tuolumne intrusive suite of yosemite national park california intruded a variety of metasedimentary and igneous wall rocks at 93 1 ma the may lake metamorphic screen is a metasedimentary remnant whose contact zone exhibits a variety of interaction phenomena including xenolith incorporation disaggregation and partial melting the chemical contrast of these metasedimentary rocks with the invading pluton provides an excellent measure of pluton wall rock interactions wall rock xenoliths mostly pelitic quartzite are predominantly located in an elongate horizon surrounded by a hybridized fine grained granodiorite initial sr and nd isotopic ratios of the hybridized granodiorite indicate significant local incorporation of crustal material major and trace element geochemical data indicate that contamination of the granodiorite occurred via selective assimilation of both high k and low k high silica partial melts derived from pelitic quartzite although the hybridized granodiorite shows significant amounts of contamination adjacent to xenoliths the proportion of contamination is undetectable more than a meter away these results indicate that the chemical and isotopic variability of the tuolumne intrusive suite is not caused by magma contamination via in situ wall rock assimilation

evolution of ptygmatic folds in migmatites from the type area s finland abstract it is proposed that ptygmatic folds in migmatites form during leucosome melanosome differentiation volume loss by depletion of quartz and feldspar takes place in the interlimb domains of folds leaving a residual melanosome buckling leucosomes increase in volume due to this process and are protected from substantial thinning concurrent with tectonic segregation albeit at a lower rate the leucosome expands by replacing the melanosome this process is induced by fluid activity at the leucosome boundary as suggested by the occurrence of secondary offshoot veinlets segregation and growth causes the most typical aspect of ptygmatic folds preservation of an overall buckle shape during the stage when the folds become isoclinal and devoid of interlimb matrix

mid holocene emergence of southern tunisian coasts abstract we present new sea level data from the coasts of southern tunisia between the gulf of gabes and the libyan border the work tests previously published evidence on holocene shorelines and confirmed that a distinct emergence has occurred in this area during this time the emergence peak lies at least 186 11 cm above present and is inferred from 1 ams radiocarbon dates of subtidal vermetids and boring shells collected in growth position and 2 careful assessment of tidal heights maximum emergence took place between about 6000 and 5000 14c years bp it cannot be ascribed to tectonics and is probably related to post glacial hydro isostatic effects it challenges the inference of a 3 m global sea level rise since 6000 years bp due to residual antarctic melting

aeolian beach ridges and their significance for climate and sea level concept and insight from the levant coast east mediterranean abstract relict beach ridges of aeolian origin and associated soils are often used for inferring relative sea level and climate with contrasting results most studies link the aeolian coastal deposits to regressive phases some to high sea level stands and a few to intermediate relative sea level positions we interpret the apparent contradictions as indicating the lack of an over arching concept and the inconsistent usage of sea level related terms in this paper we present an integrated morpho sedimentological concept for a microtidal mid latitudinal coast and review existing data from the levant east mediterranean coast to evaluate the concept and to eliminate nomenclatural confusion a coastal depositional environment in a semi arid environment consists of shallow marine aeolian and alluvial facies which together form an aeolian beach ridge complex as a package of strata which respond simultaneously to sea level change a transgressive complex forms through reworking or overstepping of the coastal foredune and a regressive complex forms by downstepping under transgression the aeolian beach ridge represents the highstand deposit and its adjacent shallow marine sediment is the transgressive deposit under regression the complex represents the falling stage and the associated downdip surface marks the lowstand on the levant coast we find chronologically well constrained offlapping aeolian beach ridges as parts of six downstepping beach ridge complexes formed between 200 ka and 10 ka the complexes represent the falling stage systems tract fsst of a short lived 5th order depositional sequence when the shoreline shifted from a position close to the modern coastline to the shelf or below the shelf edge three of these fssts and their up dip and down dip super bounding surface together form the 4th order 100 ka sequence of the last interglacial glacial cycle the absence of transgressive highstand and lowstand systems tract is explained by the poor preservation potential due to the small sediment budget of the complex the falling stage complex has a high preservation potential because sediment source area increases while the sand drift potential remains above the local threshold on the levant coast sand delivery to the backshore continued during relative sea level falls for distances of up to 10 km between dune and coastline which is unprecedented in most modern analogues the significance of the dune soil succession for climate is limited because the dunes are governed by relative sea level change the vegetation response to changes in precipitation is non linear and the dune dynamics are characterised by low resilience and hysteresis

paleohydrologie isotopique de l oued el akarit sud tunisie au pleistocene superieur et a l holocene previous data from gobert and howe coque and page on the upper quaternary deposits from wadi el akarit are expanded through radiocarbon and stable isotope measurements 18c and 13c from carbonates 18o and 34s from sulphates these new results report on detailed stratigraphic profiles and indicate fluviatile and palustrine environments during the late pleistocene vegetal dams linked to spring activity caused water stagnation fine grained sediments were deposited with appreciable amounts of organic matter which locally developed into some peaty levels in the upper part of the typical cross section located on the left bank about 100 m upstream of the railway bridge pleistocene deposits show a palustrine carbonate crust this formation is attributed to the drainage induced by the major marine regression at glacial maximum during the holocene stagnation periods still occurred interrupted by flood episodes marked by bottom transport and coarse deposits in the typical cross section deposits are well drained and oxidized however downstream a stagnation episode takes place with a rich malacofauna dominated by cerastoderma cardium the uneven distribution of rainfall is documented by the alternation of fine and coarse deposits and it is accentuated by the climatic evolution toward aridity which results in the formation of a gypsum crust after 4000 yr bp later exceptional floods removed sediments from the wadi channel cutting the upper quaternary deposits for about 13 m along the central course of the wadi radiocarbon ages on carbonates are discussed according to various possible origins of total dissolved carbon atmospheric co2 organic activity in the basins and aquifer supply a simple exchange mixing model between aquifer bicarbonate and atmospheric co2 is used for calculations of initial carbonate activities chemical isotopic and hydraulic steady states are assumed in this treatment present day 14c and 13c contents of aquifer bicarbonate are thus adopted for past values the model leads to acceptable corrected ages for pleistocene carbonate samples corrected ages are younger than apparent ages by a few thousands of years and become consistent with ages given by organic matter from nearby levels however holocene samples appear overcorrected their crystallization appears to be controlled by modern organogenic co2 holocene 14c ages are probably correct 18o contents of carbonate indicate a continental origin for environmental water nodules and carbonate concretions crystallized in bottom sediments through upward leakage of confined aquifers they show 18o contents compatible with present day stable isotope compositions of artesian springs this supports the concept of a good time constancy in stable isotope contents shell carbonate values indicate a variable evaporation rate from the same initial waters 18o and 34s contents of gypsums are also compatible with aqueous sulphates from springs the data set falls within the range of permo triassic sulphate and suggests deep hydraulic connections within aquifer systems the entire formation appears to be of continental origin the occurence of cardium rich basins can only be attributed to the initial salinity of springs waters 7 9 g 1 1 sightly increased by evaporation this signifies that one can not deduce any tectonic uplift from their location with respect to sea level

genesis and evolution of a beach ridge plain reflecting relative sea level rise a case study from trab el makhadha gulf of gabes southeastern tunisia abstract the trab el makhadha beach ridge plain presents a progradational shoreline feature on the gulf of gabes tunisia diachronic analysis coupled with a morpho sedimentary approach was applied to elucidate the genesis mode of the beach ridge plain its sedimentary sources and the climatic conditions responsible for the prograding trends in the gulf of gabes shapes dimensions sedimentologic compositions and other textural parameters of the sandy ridges have been analyzed therein we found that the trab el makhdha coast is made up of two distinctive categories of eolian beach ridge complex progradational sequences implying a significant change in climatic and hydrological conditions during the deposition of each ridge in the holocene sequence about 5600 14c years old the predominance of detrital material suggests an important contribution to sediment supply from continental input the preservation of the eolian beach ridge and its adjacent marine sediment has been favored by the postglacial hydro isostatic rebound today the paucity of rainfall is reflected by the decrease in input of terrigenous material therefore the modern sequence which has been emerging since 1987 is made mainly of bioclastic sand supplied by subaqueous shoals due to a rapid rise in sea level the observed decrease of sea level around 2100 14c yr b p largely contributed to the formation of the swale the formation of the beach ridge plain shows that since the middle holocene highstand the coastal segment of trab el makhadha has been governed by equilibrium of sediment abundance

beach ridges definitions and significance abstract beach ridges frequent components of quaternary coastal plains and other coastal landforms have been cited as indicators of the positions of ancient seashores and associated sea levels numerous authors utilized the term beach ridge for active and relict usually wave built supratidal and or intertidal forms wind built ridges have been only occasionally included in the definition the term was applied also to submerged landward shifting eventually stranded bars a consistent redefinition of the term is highly desirable beach ridges should include all relict strandplain ridges whether dominated by wave swash built or by eolian lithosomes all active ridge like shore features regardless of dimensions morphology and origin are excluded because of the resistance of coarse clastic ridges to wave and wind erosion swash built gravel or coarse shell storm ridges may build several meters above the level of high tide swash built high berms even on pure sandy beaches exceed the highest tides during episodes of wind induced record water levels frequently but not always burying underlying low relief berm ridges of berm lithosomes sequences of relatively steep multiple foredunes are commonly named beach ridge plains the narrow subparallel relict foredunes that form these strandplains presently are designated as eolian beach ridges beach ridges thus are defined as relict semiparallel multiple wave and wind built landforms that originated in the inter and supratidal zones until separated from the shoreline by progradation sandy pebbly or shell enriched backshore berm ridges behind an active foreshore should not be considered beach ridges strandplain progradation is either continuous or with the inclusion of subtidal cat s eye ponds discontinuous contrary to claims transgressive cheniers do not represent true cheniers alone within their overall progradational context cheniers a special category of beach ridges bracketed by subtidal intertidal mudflats may be transgressive or regressive in character landward driven transgressive ridges should be designated beach ridges only after they are stabilized on intertidal flats when recognizable between clearly identifiable intertidal and overlying eolian intervals the horizontal interface between these lithosomes in beach ridges may help the reconstruction of ancient tide lake levels diagnostic sedimentary textures structures and fossils however often may be unavailable in the deposits along with various types of elevated terraces composed of raised marine deposits and certain coastal landforms of erosional origin that occur worldwide beach ridges of clearly proven wave built origin may also serve as indicators of ancient higher than present sea levels

accretion of japanese island arcs and implications for the origin of archean greenstone belts the present day region of arc arc collision between the izu bonin arc and mainland japan honshu arc in the western pacific called the izu collision zone or icz provides a useful kinematic model for the development of many archean greenstone belts the compositional assemblage thermal structure and structural style of the crust in the icz are very similar to those inferred for many archean greenstone belts in both cases thick young and flaky arc crust with a high heat flux is in collision with another crustal block the icz has resulted in the imbrication of very thick slices of crust and associated sediments juxtaposed against older accretionary prisms many archean greenstone belts show similar geological features and we suggest that the incremental imbrication of the crust was a common tectonic style in some archean convergent margins

variations in fluid activity across the etive thermal aureole scotland evidence from cordierite volatile contents the h2o and co2 content of cordierite was analysed in 34 samples from successive contact metamorphic zones of the etive thermal aureole scotland using fourier transform infrared spectroscopy ftir the measured volatile contents were used to calculate peak metamorphic h2o and co2 activities total volatile contents are compared with recently modelled cordierite volatile saturation surfaces in order to assess the extent of fluid present v fluid absent conditions across the thermal aureole in the middle aureole prior to the onset of partial melting calculated ah2o values are high close to unity and measured volatile contents intersect modelled h2o co2 saturation curves at the temperature of interest suggesting that fluid present conditions prevailed total volatile contents and ah2o steadily decrease beyond the onset of partial melting consistent with the notion of ah2o being buffered to lower values as melting progresses once free hydrous fluid is exhausted all sillimanite zone samples record total volatile contents that are significantly lower than modelled h2o co2 saturation surfaces implying that fluid absent conditions prevailed the lowest recorded ah2o values lie entirely within part of the section where fluid absent melting reactions are thought to have dominated samples within 30 m of the igneous contact appear to be re saturated possibly via a magmatically derived fluid in fluid absent parts of the aureole cordierite h2o contents yield melt h2o contents that are compatible with independently determined melt h2o contents the internally consistent cordierite volatile data and melt h2o data support the conclusion that the independent p t estimates applied to the etive rocks were valid and that measured cordierite volatile contents are representative of peak metamorphic values the etive thermal aureole provides the most compelling evidence suggesting that the cordierite fluid monitor can be used to accurately assess the fluid conditions during metamorphism and partial melting in a thermal aureole

genesis of the two main types of peraluminous granitoids two mica monzogranites to leucogranites and biotite rich cordierite bearing tonalites to monzogranites form two distinct groups of peraluminous granitoids they can be distinguished by mineral and rock associations and by the variation of their peraluminosity during differentiation except for the rare muscovite bearing granitoids produced by extreme fractionation or local contamination of metaluminous magmas the majority of peraluminous granitoids are produced by partial melting of crustal rocks production of either muscovite bearing granites or biotite rich cordierite bearing granitoids does not depend only on the nature of the sources but is also controlled by the physical parameters of partial melting and consequently by the way anatexis of a thickened crust is enhanced biotite rich cordierite bearing granitoids are generated where mantle derived magmas are injected into or have underplated crustal rocks two mica granites are generated where thickened crust is affected by major crustal shears or thrusts correlations between differentiation and peraluminosity indicate the dominant role of either restite unmixing or fractional crystallization in the production and evolution of the various types of peraluminous granitoids

the iugs systematics of igneous rocks in order to create a sustainable classification of igneous rocks which all geologists might use an international body was set up by the iugs the iugs subcommission on the systematics of igneous rocks in the course of creating the classification the subcommission has established ten principles for its construction and for defining an appropriate nomenclature the principles are 1 use descriptive attributes 2 use actual properties 3 ensure suitability for all geologists 4 use current terminology 5 define boundaries of rock species 6 keep it simple to apply 7 follow natural relations 8 use modal mineralogy 9 if mode not feasible use chemistry 10 follow terminology of other iugs advisory bodies these principles and their rationale have not previously been enunciated the classification separates and individually classifies the pyroclastic carbonatitic melititic lamprophyric and charnockitic rocks before entering the main qapf classification for plutonic and volcanic rocks which is based on the modal mineral proportions of quartz q alkali feldspar a and plagioclase p or of alkali feldspar a plagioclase p and feldspathoids f rocks with mafic content 90 have their own classification if the mineral mode cannot be determined as is often the case for volcanic rocks then a chemical classification of total alkalis versus silica tas is used the nomenclature for these classifications necessitates only 297 rock names out of the c 1500 that exist

the petrogenesis of some migmatites and granites central damara orogen namibia evidence for disequilibrium melting wall rock contamination and crystal fractionation

mediterranean pluvial periods and sapropel formation over the last 200 000 years abstract three mediterranean deep sea cores have been studied to reconstruct the hydrological conditions at the time of deposition of interglacial and glacial sapropels during the time interval 200 60 kyr bp the isotopic and sea surface temperature records of planktonic foraminifera were used to estimate the oxygen isotopic composition of surface water w in the tyrrhenian sea and levantine basin our results show a strong w salinity decrease in both basins associated with each sapropel these w decreases reflect a drastic change in the local freshwater budget and were comparable to that observed during the last sapropel s 1 centred at ca 8 kyr bp a strong precipitation increase transformed the whole mediterranean sea into a non concentration basin the low surface salinity was responsible for the water column stratification while nutrients brought in by the runoff enhanced productivity it resulted in a significant reduction in the rate of deep water oxygenation and sapropel formation in the eastern basin in addition the mediterranean sea 18 o record is very similar to that of the bay of bengal as the latter is very sensitive to the summer monsoon rain this similarity suggests that both glacial and interglacial sapropels result from enhanced monsoon like precipitation due to an increase in summer insolation driven by precession variations

petrogenesis of migmatites in maine usa possible source of peraluminous leucogranite in plutons high t low p facies series conditions during deformation within a devonian crustal scale shear zone system defined by kilometer scale straight belts of apparent flattening strain that anastomose around lozenges of apparent constrictional strain at upper amphibolite facies grade metapelites are partially melted the onset of which is introduction