submerged tidal notches in the rijeka bay ne adriatic sea indicators of relative sea level change and of recent tectonic movements abstract the rijeka bay coast is formed predominately in carbonate rocks due to relatively sheltered position processes of bioerosion dominate while mechanical wave action has low impact biological zone limits in rijeka bay are well expressed and they reflect the local biological mean sea level bmsl therefore they were used as referent levels for measurement of submerged tidal notch position these in situ biological indicators could be more useful than sea level mareograph data well developed tidal notches are permanently submerged and quite ubiquitous in the whole rijeka bay area that is they are situated in the infralittoral zone they have elongated asymmetric shape inasmuch as the roof top of the notches is well preserved they were correlated with well defined biological zone limit upper limit of white we zone sensu schneider j 1976 biological and inorganic factor in the destruction of limestone coast contributions to sedimentology 6 1 11 results of survey showed that in most of the area tidal notches are located 50 60 cm below bmsl however within the bakar bay notches are from 103 to 115 cm below bmsl regional occurrence of well preserved tidal notches at 0 5 0 6 m below bmsl indicates their possible coseismic origin rapid tectonic subsidence deeper positions of tidal notches in the northeastern part of rijeka bay and within bakar bay indicate enhanced subsidence of that zone which is assumed to be the most seismotectonicaly active

tectonics and geodynamics of south china an introductory note highlights the neoproterozoic jiangnan collision of cathaysia and yangtze is responsible for the formation of the south china block scb during the early paleozoic the scb was welded to the north china block along the qinling belt and also experienced an intracontinental orogeny that partly reworked the jiangnan belt during the middle triassic the scb was welded to indochina the qinling belt was reworked by n directed intracontinental subduction the xuefengshan belt is also a middle triassic intracontinental orogen

tectonic effects on late holocene sea level changes in the gulf of trieste ne adriatic sea italy abstract a multidisciplinary approach has been used to evaluate late holocene relative sea level change along the eastern coast of the gulf of trieste published data together with new 14 c dating have been compared with predicted curves in order to evaluate the tectonic behaviour of the studied area observations derived from precise geomorphological archaeological and sedimentological measurements dated from 10 ka cal sampled at elevations ranging between 25 and 0 10 m tectonic rates range from 1 01 mm y gulf of trieste and 1 99 mm y villaggio del pescatore but are probably higher in the northwestern sector where the elevation of post roman geomorphological markers is lower a detailed surveying of notches beachrocks submerged shore platforms and the geological setting of the coastal area highlight the variability of tectonic subsidence indicated by geophysical data collected in the central part of the gulf analyzed data indicate active tectonism the tectonic setting of the northernmost sector is affected by the presence of strike slip faults which cause differential downdrop of the shoreline as suggested by significant increases of notch depths ranging between 1 0 m and 2 7 m

tin metallogenesis associated with granitoids in the southwestern sanjiang tethyan domain nature deposit types and tectonic setting article i nfo tin mineralization in the southwestern sanjiang tethys sn metallogenic domain extends from the southeast asia tin belt in the south the eastern part of the domain does not contain significant sn deposits whereas the central part of the domain composed of the changning menglian sn belt and related to ca 239 178 ma s type granitoids generated by the collision between tengchong baoshan and simao blocks carries wide spread the hydrothermal vein type mineralization the western part of the domain composed of the tengchong baoshan sn metallogenic belt is related to both 136 113 ma and 89 52 ma s type granitoids the former granitoids resulted from the collision between western burma and tengchong baoshan blocks and generated skarn type tin deposits the younger groups correspond to the india asia continental collision and are associated with the xiaolonghe and lailishan greisen type sn deposits

age and duration of the emeishan flood volcanism sw china geochemistry and shrimp zircon u pb dating of silicic ignimbrites post volcanic xuanwei formation and clay tuff at the chaotian section abstract the age and duration of the emeishan basalts sw china remain poorly constrained largely due to the severe thermo tectonic overprinting of the ar ar system and failure to obtain zircon separates from erupted basalts in an attempt to solve this problem geochemical analyses and shrimp zircon u pb dating have been carried out on rare felsic ignimbrite in the uppermost of the emeishan lava succession the xuanwei formation which immediately overlies the emeishan basalts and a clay tuff at the middle late permian boundary at the chaotian section clastic rocks of the lowermost xuanwei formation group 1 in eastern emeishan large igneous province lip have a geochemical affinity to the emeishan felsic volcanic rocks whereas the overlying sediments group 2 are compositionally more akin to mafic components of the emeishan traps this is the reverse of volcanic sequence of the central emeishan lip where the felsic extrusives sit above predominant mafic rocks it is likely that the clastic rocks are water transported sediments resulting from erosion of the volcanic rocks in the center of the emeishan lip this interpretation is further supported by the general agreement between the age of the lowermost xuanwei formation 257 4 ma 260 5 ma and that of the silicic ignimbrite 263 4 ma and the clay tuff at the middle late permian boundary at chaotian 260 5 ma these ages interpreted as the termination age of the emeishan volcanism are indistinguishable within error from the middle late permian boundary age 260 4 0 4 ma and the main stage 259 262 3 ma of the emeishan volcanism inferred from dating of mafic and alkaline intrusions in the emeishan lip all these suggest that the emplacement of the emeishan volcanism took place over a very short interval moreover the temporal link and geochemical analyses suggest that the chaotian clay at the middle late permian boundary was genetically related to the emeishan silicic volcanism this together with the fact at that both the emeishan basalts and the chaotian clay rest on the maokou formation leads us to infer that the emeishan basalt was emplaced at the middle late permian boundary in this sense the emeishan volcanism can be regarded as a boundary event and its age is presumed at 260 ma although more precise dating is required both stratigraphic correlation and chronologic data presented in this paper lend supports to the notion that the emeishan volcanism was one of likely causes of the end guadalupian mass extinction

geological and geochemical characteristics in the paleo weathering crust sedimentary type ree deposits western guizhou china abstract a supergene ree deposit closely interrelated with the weathering of the emeishan basalt formation was produced in the xuanwei formation the overlying stratum of the late permian emeishan basalt formation in west guizhou china the host strata consist primarily of offwhite kaolinite clay rock and or grayish black carbonaceous shale mineralogical analyses reveal that kaolinites are the major minerals in ree ores with small amounts of smectite illite boehmite hornblende pyrophyllite calcite dolomite and or iron bearing minerals with a certain proportion of feldspar quartz crystal debris and noncrystal debris geochemical analyses reveal high enrichment of trace elements like cu nb ta zr and hf the host strata feature considerable lithological variability close interrelation of the ree grade with the lithology and uneven spatial distribution of the ree ores which are mostly found in lufang maojiaping and zhangsigou profiles of weining county and can be as thick as 20 m of the five stratigraphic profiles 48 have their whole rock ree higher than 1000 ppm the ree in this framework consists primarily of ion adsorbed phases and ree rich residual independent mineral phases comprehensive analyses suggest that the source may not only include the emeishan basalt but the intermediate acid volcanic rocks evolved from the emeishan basalt in the later periods the hydrothermal alteration subsequently imposed on the host strata might have boosted the mineralization of the rare earth the preliminary genetic model should have been the denudation product from the weathering of the parent rock was migrated to the sea continental margin at the continent side carrying huge quantities of ree with it and was preserved by the quick marine transgression the host strata consist primarily of kaolinite clay rock and or carbonaceous shale which are so far believed to be a sedimentary type ree deposit closely interrelated with weathering effect

terrestrial deposition processes of quaternary gibbsite nodules in the yongjiang basin southeastern margin of tibet and implication for the genesis of ancient karst bauxite abstract the terrestrial deposition process for karst bauxite is difficult to constrain due to its allochthonous origin multiple controls and the difficulty in geodynamic reconstruction this ambiguity has been clarified from investigation of the provenance and geologic geographic conditions for the formation of quaternary gibbsite nodules in the yongjiang basin this karst basin located at the southeastern propagation front of the tibet plateau was affected by the se asia monsoon climate developed since the late oligocene and a later quaternary glaciation a thick blanket of quaternary laterite is located on paleozoic carbonate bedrock and covers an area about 1000 km2 along the east flowing river systems in the basin the laterite profiles are well layered with a layer of iron rich gibbsite nodules overlying on a basal clay zone and irregularly covered by a thin clayey topsoil gibbsite nodules from most localities yield detrital zircons with age peaks at ca 1000 ma 450 ma and 250 ma corresponding to those of the mesozoic clastic and magmatic rocks exposed on the western and southern surrounding highlands nevertheless those from the pingtianshan area produce an exclusive spike at ca 100 ma consistent with the emplacement age of nearby granites apatite fission track modeling for the mesozoic clastic rocks and darongshan granites shows a rapid cooling since the early miocene and that for the pingtianshan cretaceous granite reveals fast exhumation since the late miocene these data indicate differential erosion reshaped the topography and consequently a low relief karst basin was developed allowing a diverse material supply from the surrounding and local highlands via sheet flow and east flowing rivers under a monsoon influenced subtropical climate aluminum and iron oxides hydroxides were accumulated as nodules or concretions which were cemented by and coated with fe oxides due to variations in redox potential and alternating consolidation and swelling while silica was leached at greater depth groundwater solutions preferentially removed and brought upward fe under a reducing environment during the wet seasons while an underlying clay layer occurred due to the reduced solubility of silica later this bauxitization process was probably hindered by the quaternary glaciation which could have promoted the formation of the top clay layer this terrestrial deposition process of quaternary gibbsite nodules serves as one analogue for ancient karst bauxite in which the following submergence would improve the quality via further precipitation of alumina hydroxide and leaching of extra fe

distinct phases of relative sea level changes in the central adriatic during the last 1500 years influence of climatic variations abstract we present a new sea level reconstruction for the past 1500 years based on biological indicators from the central adriatic islands biogenic littoral rims built by the coralline rhodophyte lithophyllum byssoides were found on the particularly exposed sites on the rocky coasts of the islands of vis ravnik and bisevo in croatia the presence of thick and well developed lithophyllum rims considered to be precise 10 cm sea level indicators points directly to the rising sea level environment biogenic rims were mapped measured and sampled for 14c dating the obtained results point to four phases of sea level changes the sea level was near stable from around 550 till 770 cal ad in the dark ages cold period dacp then during the medieval climate anomaly mca 770 till 1330 cal ad the sea level increased at a rate of 0 71 mm yr during the little ice age lia 1330 till 1640 cal ad it was near stable again later the sea level started to rise at a much higher rate particularly during the current warm period cwp these data were compared with local predictions derived from a glacio hydro isostatic models associated with the last glacial cycle if the isostatic eustatic component is separated this area seems to have almost stable tectonic conditions during the past 1500 years our results show that the large algal rims most likely grew during near stable sea level conditions that occurred during two relatively colder periods in the past 1500 years they also reveal that well developed up to 1 8 m wide upper levels of algal rims were formed during 300 years of stabilisation throughout the lia

trace and rare earth elements constraints on the sources of the yunfeng paleo karstic bauxite deposit in the xiuwen qingzhen area guizhou china abstract a number of carboniferous paleo karstic bauxite deposits occur in the xiuwen qingzhen area central guizhou province which constitute an important part of the central guizhou southern chongqing bauxite belt in southwestern china these deposits consist of lenticular and stratiform orebodies hosted in the lower carboniferous jiujialu formation which lies unconformably above carbonate rocks mainly dolomite of the middle and upper cambrian loushanguan group shilengshui formation and lower cambrian qingxudong formation although it is generally agreed that the bauxite resulted from weathering of cambrian rocks below the unconformity it remains unclear whether the carbonates alone can provide sufficient material for the formation of the deposits in this study we examined the mineralogy and major trace and rare earth elements geochemistry of bauxite and bauxitic clays from the yunfeng deposit in the xiuwen qingzhen area and compared them to previously published data of a paleo weathering profile consisting of loushanguan dolomite underlying the sub carboniferous unconformity and the black rock sequence of the lower cambrian niutitang formation in order to evaluate the sources of the bauxite the bauxite ores are composed of diaspore as the main ore mineral along with small amounts of pyrite arsenopyrite galena stibnite xenotime and uranium bearing minerals and are characterized by high contents of uranium and phosphorus chondrite normalized ree patterns and various bivariant diagrams commonly used to study the provenance of bauxite including eu eu vs tio2 al2o3 eu eu vs sm nd tio2 vs al2o3 tio2 th th vs ta th vs nb and nb vs ta suggest that the loushanguan dolomite and the niutitang black rock sequence are both potential source rocks however a comparison in u and th contents between the paleo weathering profile of the loushanguan dolomite and the bauxite samples suggests that the dolomite alone cannot provide the materials for the bauxite ores instead the black rock sequence may have contributed most of the ore forming materials which are mainly transported from source regions where the niutitang formation was exposed weathered and eroded therefore the yunfeng bauxite deposit is of mixed autochthonous and allochthonous origin

ni cu pge magmatic sulfide deposits in the yangliuping area permian emeishan igneous province sw china the ni cu pge sulfide deposits in the yangliuping area sw china are hosted in mafic ultramafic sills the four mineralized sills are located in the yangliuping tectonic dome and intrude devonian carbonaceous marble graphitic schist the sills are 200 300 m thick and 1 000 2 000 m in strike length and now consist chiefly of serpentinite talc schist tremolite schist and meta gabbro disseminated ni cu sulfide mineralisation occurs in the serpentinite in the lower parts of the sills massive sulfide mineralisation is located in the base of the sills and in the footwall along fractures beneath the mineralized serpentinite although the sulfide ores have been modified by hydrothermal activity there are relict cumulate textures in the disseminated sulfides indicating a magmatic origin for the ores the yangliuping intrusions and the dashibao formation have similar primitive mantle normalized trace element and platinum group element pge patterns indicating that they are derived from a common parental magma type the positive correlation between cu concentrations and cu zr ratios of the dashibao formation basalts indicates that the chalcophile elements were removed before eruption we propose that fractional crystallization of the yangliuping magma accompanied by the introduction of s and co2 from the wall rocks caused the magma to become s saturated leading to the segregation of magmatic sulfides that became enriched in ni cu pge the sills acted as conduits for the overlying dashibao formation basalts with the sulfide liquid along with early crystallizing olivine and pyroxene segregating from the magma as it passed through the conduits prior to eruption

mineralogical control and characteristics of rare earth elements occurrence in carboniferous bauxites from western henan province north china a xrd sem eds and la icp ms analysis abstract high concentrations of rare earth elements ree are found in the bauxite deposits in the songqi area of henan province north china however no studies have been carried out on the occurrences of ree in these bauxite ores in this study we explored the ree occurrence and their possible enrichment mechanism in the songqi bauxite deposits using petrographic observation x ray diffraction xrd scanning electron microscope with energy dispersive spectroscopy sem eds and la icp ms techniques the major aluminum rich ore mineral in the songqi bauxite deposits is diaspore and other coexisting minerals include clay mineral aggregates with minor amounts of hematite pyrite anatase and zircon the bauxite ores are rich in ree and also some other critical metals li zr nb and ga most of the ree are adsorbed in the form of ions on the surface of clay minerals and diaspore and some heavy rare earth elements hree exist in the form of xenotime the sem eds and la icp ms analyses show that ree is closely related to the content of p and therefore it is possible that other dispersed and minor p bearing rare earth minerals may occur in the bauxite deposits except for the possible co adsorption of p and ree in the clays and diaspore

climatic and hydrologic controls on upper paleozoic bauxite deposits in south china abstract the late paleozoic era was an interval of major tectonic and climatic changes including formation of the supercontinent pangea and the 60 myr long late paleozoic ice age lpia although bauxite formation declined globally from the carboniferous to the permian in conjunction with global cooling it was an interval of widespread bauxite formation in china in south china 1 the jiujialu formation bauxite deposits in central and northern guizhou zunyi area are of early middle visean age 2 the dazhuyaun formation bauxite deposits in northern guizhou wuchuan zheng an daozheng area to southern chongqing nanchuan area and southeastern guizhou fuquan kaili area are of late pennsylvanian early permian age and 3 the heshan formation bauxite deposits in western guangxi to yunnan are of middle late permian age in north china the benxi formation bauxite deposits are of late mississippian middle pennsylvanian age the contrasting trends in bauxite metallogenesis between china and the rest of the world imply different climatic patterns in the eastern tethys high annual humidity with seasonal dryness and pangea aridification this hypothesis is further supported by differences in the chemical index of alteration or cia 80 in the eastern tethys vs 50 in western pangea and in paleotemperatures mean annual temperature or mat 20 c in the eastern tethys vs 4 c in western pangea determined from permo carboniferous siliciclastic deposits permo carboniferous bauxite deposits in south china formed in coastal plain and coastal karstic depression environments in which the position of the groundwater table was related to sea level changes during the late paleozoic high frequency eustatic fluctuations caused by waxing and waning of gondwana icesheets controlled sedimentation in these coastal depositional systems leading to cyclic accumulation of coal and bauxite deposits and cycles of vadose and phreatic type bauxite formation the results of the present study show that during interglacial stages lateritization resulted from high pco2 high sea level and groundwater table elevations low precipitation and limited vegetation cover whereas during glacial stages bauxitization of these ferralitic weathering products was promoted by low pco2 low sea level and groundwater table elevations high precipitation and more extensive vegetation cover thus a unique combination of geographic climatic and eustatic factors accounted for widespread formation of bauxite in south china during the lpia

relative sea level change in western istria croatia during the last millennium relative sea level change occurred along the western coast of the istrian peninsula in croatia sediments from two cores located in the bay of santa marina and soline bay have been analyzed for microfaunal and sedimentological investigations chronostratigraphical evidence was obtained from 14c dating of lagoonal shells gastropods from the sedimentological and paleo environmental analysis 4300 years of continuous deposition in a shallow marine environment was determined at around 550 cal bp marine sedimentation changed to continental consequently the initial sedimentation rate of 0 7 mm y changed to 2 36 mm y after 550 cal bp those upper deposits of continental origin are today partly submerged the data were further compared with a geophysical model which allows the prediction of the local sea level curve as the results from the cores are largely below the curve tectonic subsidence of the area is confirmed radiocarbon analysis allowed the age of the shells to be related to the age of the submerged tidal notch that occurs almost continuously some hundreds of meters south eastwards from the gulf of trieste to the dalmatian coast

petrography and detrital zircon study of late carboniferous sequences in the southwestern north china craton implications for the regional tectonic evolution and bauxite genesis abstract the north china craton ncc has been flanked by the north qilian and north qinling arc accretionary belts to the south and southwest since 400 ma the part of the ncc to the east of the alax terrane e ncc experienced a long sedimentary hiatus and tectonic quiescence between the middle ordovician and the late carboniferous the northern margin of the e ncc was reactivated and uplifted with contemporaneous volcanism during the late carboniferous an event that partly induced the transformation of the e ncc from an erosional platform to a continental sedimentary basin however the factors controlling this transformation are still not fully understood a series of sedimentary rocks overlying ordovician carbonates in the southwestern e ncc contains a lower iron oxide layer and an upper phyllosilicate layer detrital zircons from different parts of the profile from the base to the top of the two layers have similar u pb ages these zircons have a minimum age of ca 300 ma and a prominent peak at ca 450 ma with subordinate peaks at ca 1000 and 2500 ma the near identical minimum age for the two layers suggests they were semi simultaneously deposited in the late carboniferous after the long hiatus in sedimentation detrital zircons with ages of 450 ma have initial hf isotopic compositions that vary from large negative to elevated positive these data together with the trace element compositions of these zircons indicate that these minerals formed in a continental arc environment samples from the upper sedimentary layer contain mica group minerals that are weakly buckled and fractured and have weathered to form clay minerals including chlorite and illite this suggests that the protolith of this sedimentary layer was dominated by mica schist or mica bearing granitoid that most likely located near the adjoined part between the north qilian and north qinling arc accretionary belts detrital zircons with the youngest ages ca 300 ma were considered to derive from the northern marginal region of the e ncc an area characterized by contemporaneous volcanism the co existence of the 450 and 300 ma groups of detrital zircons also suggests that the northern and southern marginal regions of the e ncc underwent almost simultaneous late carboniferous tectonic uplift and denudation a tectonic change that led to the formation of the sedimentary basins within the e ncc late carboniferous phyllosilicate layers within the profile are likely to be the equivalent of economically important diaspore and clay dominated bauxites within the e ncc suggesting that the diaspore in these bauxites was derived from mica group minerals by resolution precipitation processes

sedimentation and lithofacies paleogeography in southwestern china before and after the emeishan flood volcanism new insights into surface response to mantle plume activity abstract investigations into permian sedimentation and reconstruction of paleogeography in sw china are aimed at characterizing sedimentary responses to the emeishan mantle plume in addition to erosional features on the sediments underlying the uplifted emeishan basalts unusual depositions of permian age are also present in the emeishan large igneous province lip specifically carbonate gravity flows and submarine incised canyon fillings were developed in the western margin of the postulated uplifted area and rifting trenches were developed along the eastern margin alluvial fan deposits occur at the boundary between the inner and intermediate zones these depositions all rest on the maokou formation and are in turn covered by the emeishan basalts implying synchronism between crustal uplift and depositional events these deposits and the associated extension and normal faulting along the margin of and within the lip represent sedimentary features resulting from dynamic behavior of mantle plume com

genesis of the permian karstic pingguo bauxite deposit western guangxi china more than 0 5 billion tons of late permian bauxite overlies the karstic topography of the maokou formation of western guangxi in china here we provide new mineralogical geochemical sr nd pb isotopic and pyrite s isotope and trace element compositional data for the pingguo bauxite deposit aiming to further our understanding of the genesis of permian bauxite the pingguo bauxite contains three distinct layers a lower layer dominated by ferric clay or weathered iron ore a middle layer of cryptocrystalline and oolitic bauxite ore and an upper layer dominated by argillaceous bauxite the bauxite ore is mainly diaspore pyrite chamosite and anatase whereas the argillaceous bauxite contains diaspore kaolinite pyrophyllite pyrite and anatase two types of pyrite have been identified within the bauxite fine grained and framboidal pyrite py1 occurring in aggregates and coarse grained and euhedral pyrite py2 py1 is enriched in trace elements and is thought to have a diagenetic origin whereas py2 is deficient in trace elements and is considered to have formed by later recrystallization the s isotopic composition of pyrite 34 11 to 18 91 and visible ovoid microorganisms within the bauxite provide evidences of microbial activity during bauxite formation the sr nd pb isotopic composition of the bauxite indicates that these ores were generated by the weathering of basalts belonging to the emeishan large igneous province lip and limestones of the maokou formation microorganisms were likely to have enhanced the dissolution and weathering of the parent rock and facilitated the precipitation of diaspore under near surface conditions

the south china block indochina collision where when and how this study uses new field observations and existing studies to shed new light on the origin and significance of two nw se striking orogens in nw and ne vietnam we conclude that the architecture of each belt is a stack of ne directed nappes formed either under deep ductile synmetamorphic conditions or under shallow depth in the sw and ne parts respectively the song ma zone and song chay ophiolitic melange represent two ophiolitic sutures however the late permian song da and babu mafic rocks are not ophiolites but intraplate basalts related to the emeishan plume a late triassic unconformity the 225 205 ma postorogenic plutonism and the 250 230 ma syntectonic metamorphism support an early to middle triassic age for these tectonic events both nw and ne belts are due to sw directed subduction with arc magmatism ocean closure and continental collision though two contemporary s dipping subduction zones might explain the structural evolution of the two belts a single convergent system offset by the tertiary red river fault is preferred as this s directed subduction better accounts for the late permian intraplate magmatism this scenario is discussed in the general geodynamic framework of se asia

discovery of the ree minerals and its geological significance in the quyang bauxite deposit west guangxi china most of the karstic bauxite deposits in china are enriched in ree and the ree has commonly been considered to be adsorbed on the surface of clay or diaspore minerals as ion state however occurrence of ree minerals in the bauxite deposits has not been reported by far in the quyang bauxite deposit from guangxi province we find ree minerals the minerals are parisite and churchite parisite is widely distributed in the ooids and matrix inducing positive ce anomaly of the ores whereas churchite is rare and occurred in the core of ooid the compositions of the ree minerals show the eu anomaly can change gently during the weathering and the eu anomaly analyses suggest that the ree in the ores are mostly derived from the underlying carbonates the parisite is formed in an alkaline condition while churchite in an acidic situation the co existence of the two minerals in the ores suggests the permian environment for bauxite formation is complex with great change of ph value moreover parisite is inferred to be formed earlier than the churchite

importance of hydrogeological conditions during formation of the karstic bauxite deposits central guizhou province southwest china a case study at lindai deposit abstract karstic bauxite deposits are widespread in central guizhou province sw china and high grade ores are frequently sandwiched with overlying coal and underlying iron rich layers and form a special coal bauxite iron structure the lindai deposit which is one of the most representative karstic bauxite deposits in central guizhou province was selected as a case study based on textural features and iron abundances bauxite ores in the lindai deposit are divided into three types of ores i e clastic compact and high iron the bauxite ores primarily comprise diaspore boehmite kaolinite illite and hematite with minor quartz smectite pyrite zircon rutile anatase and feldspar the al 2 o 3 53 76 8 wt is the main chemical contents of the bauxite ore samples in the lindai district followed by sio 2 fe 2 o 3 tio 2 cao mgo s and p etc our geological data on the lindai deposit indicated that the ore bearing rock series and its underlying stratum have similar rare earth elements distribution pattern and similar y ho zr hf and eu eu values additionally all ore bearing rock samples are rich in mgo range from 0 16 wt to 0 68 wt and the plots of the dolomites and laterites lie almost on or close to the weathering line fit by the al bearing rocks in zr vs hf and nb vs ta diagrams suggesting that the underlying middle cambrian shilengshui formation dolomite is the parent rock of bauxite resources in the lindai district simulated weathering experiments on the modern laterite from the shilengshui formation dolomite in the lindai bauxite deposit show that hydrogeological conditions are important for karstic bauxite formation si is most likely to migrate its migration rate is several magnitudes higher than those of al and fe under natural conditions the reducing inorganic acid condition is the most conducive to al enrichment and si removal fe does not migrate easily in groundwater al enrichment and fe removal can occur only in acidic and reducing conditions with the presence of organic matter the geological and experimental studies show that coal bauxite iron structure in lindai deposit is formed under certain hydrogeological conditions i e since lateritic bauxite or al rich laterite deposited upon the semi closed karst depressions si can be continuously removed out under neutral acidic groundwater conditions the coal carbonaceous rock overlying the bauxitic materials were easily oxidized to produce acidic h 2 s h 2 so 4 etc and reductant groundwater with organic materials that percolated downward resulting in enrichment of al in underlying bauxite it also reduced fe 3 to its easily migrating form fe 2 moving downward to near the basal carbonate culminated in precipitating of ferruginous fes 2 feco 3 etc strata of the coal bauxite iron structure thus the bauxitic materials experienced al enrichment and si and fe removal under above certain hydrogeological conditions forming the high quality bauxite

zircon u pb and hf isotope constraints on crustal melting associated with the emeishan mantle plume abstract shrimp zircon u pb dates combined with in situ hf isotopic data provide new constraints on the petrogenesis and protolith of peralkaline metaluminous and peraluminous intrusions and rhyolitic tuffs in the emeishan large igneous province with significant bearing on crustal melting associated with mantle plumes syenite and a type granitic intrusions from huili miyi and taihe in the center of this large igneous province yield u pb dates at 260 ma consistent with the ages obtained for mafic layered intrusions in the same province zircon from these rocks exhibits a wide range of initial hf isotope ratios ehf t 1 4 to 13 4 with corresponding tdm1 of 400 900 ma the highest ehf t value is only marginally lower than that of depleted mantle reservoir at 260 ma suggesting that their source is primarily juvenile crust added during emeishan volcanism with incorporation of variable amounts of neoproterozoic crust the trigger of crustal melting is most likely related to advective heating associated with magmatic underplating in contrast the 255 251 ma peraluminous granites from ailanghe and 238 ma rhyolitic tuff from binchuan have negative initial ehf values of 1 3 to 4 4 and of 7 7 to 14 respectively hf isotopic model ages and presence of inherited zircons indicate their derivation from mesoproterozoic and paleoproterozoic crust respectively given the time lag relative to the plume impact 260 ma and insignificant mantle contribution to 255 238 ma magmatism conductive heating is suggested as the trigger of crustal melting that resulted in formation of delayed felsic magmas the involvement of older crust in younger felsic magmas is consistent with upward heat transfer to the lithosphere during plume impregnation if the age of crust is inversely stratified i e changes from paleoproterozoic to mesoproterozoic to neoproterozoic to permian with increasing depth such crust may have resulted from episodic downward crustal growth during the evolution of the western yangtze craton

geochronological geochemical and sr nd hf isotopic studies of the baiyanghe a type granite porphyry in the western junggar implications for its petrogenesis and tectonic setting abstract zircon u pb dates sr nd hf isotopic compositions and major element and trace element geochemistry were determined for the baiyanghe granite porphyry in the western junggar nw china the porphyry has a zircon u pb age of 313 4 2 3 ma is high in sio 2 76 34 78 30 wt and k 2 o na 2 o 8 04 8 85 wt relatively low in mgo 0 01 0 03 wt and cao 0 29 0 39 wt and shows characteristics typical of a type granites because its y nb ratio 0 33 0 51 is lower than 1 2 it can be classified into a 1 group moreover due to its positive values of end t 4 06 5 29 and ehf t 8 18 11 07 and high concentrations of incompatible elements including rb th u and nb the baiyanghe granite porphyry is suggested to have been derived from an oceanic island basalt like mantle source their extremely high initial 87 sr 86 sr ratios 0 7143 0 7469 and high la sm n values 5 13 8 44 could be caused by the involvement of marine sediments the low ba sr and eu concentrations and high values of di 97 3 98 0 of the granite porphyry suggest that its magma had undergone a high degree of fractional crystallization characterized by the features of within plate granites a back arc basin tectonic setting is favored for the petrogenesis of the baiyanghe granite porphyry such a setting indicates that the subduction of the irtysh zaysan oceanic lithosphere beneath the zharma saur arc was still active during the late carboniferous and the collision between the siberia and kazakhstan blocks probably occurred between ca 316 ma and 307 ma

genesis of ree minerals in the karstic bauxite in western guangxi china and its constraints on the deposit formation conditions abstract karstic bauxites in western guangxi china comprise two subtypes permian bauxite and quaternary bauxite the quaternary bauxite originated from the breaking up rolling and accumulating of permian bauxite in karstic depressions in quaternary various types of rare earth element ree minerals were discovered during the formation of the permian and quaternary bauxites from the xinxu longhe and tianyang bauxite deposits in this study five types of ree minerals including bastnasite parisite cerianite rhabdophane and churchite were identified bastnasite and parisite are the most abundant and they are widely developed in the permian ore and also present in the quaternary ore obvious variations in bastnasite and parisite ree compositions were observed which is ascribed to distinctions in the source materials in the primary weathering profile from different areas the mode of occurrence of bastnasite and parisite suggests they were mainly precipitated under alkaline and reducing conditions during the permian bauxite forming stage and underwent intensive corrosion in the quaternary churchite was formed during the permian weathering stage under acidic condition both cerianite and rhabdophane occur in fractures within the permian bauxite ore indicating that both formed during the quaternary weathering stage it is considered that the rhabdophane enriched in ce have formed locally in the process of that the ce3 released from bastnasite rapidly entered the rhabdophane lattice before being oxidized to ce4 cerianite was mainly found in association with mn al hydroxides suggesting that the released ce3 was oxidized into ce4 and precipitated cerianite in fractures within the permian bauxite ore mass balance equations reveal a depletion in nearly all rees during the transformation from the permian to the quaternary bauxite ore mainly caused by the dissolution of bastnasite and parisite the genesis of the ree minerals together with the occurrence of other minerals indicates that intensively acidic and oxidizing conditions developed before the formation of the permian bauxite ore towards the end of the permian the conditions became reducing and alkaline favorable for the large scale bauxitization the quaternary bauxite forming stage was characterized by variable ph and eh conditions with acidic ph 4 6 and oxidizing eh 2 conditions at the surface of the exposed permian bauxite ore

emeishan large igneous province sw china in recent years there have been major advances in our understanding of the emeishan large igneous province lip of sw china following publication of a number of lip focused investigations of the terrain and associated rocks this paper reviews the current state of knowledge the volcanic and upper intrusive portion of the province is relatively small 0 3 106 km3 even when offset fragments eroded sections and buried portions are included in the volume calculation the most reliable radiometric age dates zircon u pb shrimp from an associated layered intrusive body several kilometers in area indicate generation at 259 ma consistent with the end guadalupian end middle permian stratigraphic age in addition several ar ar dating studies have been carried out mainly on the volcanic rocks with a number of reported dates 253 251 ma late permian but a consensus is emerging that these ages are problematic because they are in conflict with the stratigraphic data possibly due to a monitor standard miscalibration the ar ar investigations have also yielded a large number of secondary ages which are clustered at 175 142 98 and 42 ma and these are inferred to record sub regional tectonic events that affected the western yangtze block as east asia was assembled and later deformed by india s collision indentation into asia magnetostratigraphic data and field observations suggest that the bulk of the volcanic sequence formed within 1 2 my the geochemistry of the volcanic rocks and bio lithostratigraphic studies of the underlying maokou formation suggests a mantle plume generated the province the basalts can be classified into low and high ti groups with different parental magmas the low ti basalts are confined to the western part of the province and are overlain by the high ti basalts the low ti magmas formed at shallow mantle depths in the spinel garnet field transition zone 60 80 km whereas the high ti magmas formed by low degrees of partial melting within the deeper garnet stability field this observation suggests a deepening of the melting column as the lithosphere thickened due to under plating and a transition from peak basalt generation to the waning stage outstanding issues which might focus future studies are also outlined

comparison between coastal and inland karst limestone lowering rates in the northeastern adriatic region italy and croatia a comparison among lowering rates collected in the limestones of the northeastern adriatic region italy and croatia gives a picture of the erosion patterns in the inland and coastal classical karst and istrian karst erosion rates were measured using either a micro erosion meter or a traversing micro erosion meter beginning from a large dataset spread over a maximum of 26 years significant differences in limestone lowering rates have been recognized in the surveyed area the mean lowering rate for the inland classical karst area is 0 018 mm yr whereas in the inland istrian karst it is 0 009 mm yr in the coastal sectors the mean erosion rate varies between 0 14 mm yr in the gulf of trieste and 0 04 mm yr in the sites located along the istrian shoreline these differences are probably due to the climatic setting of the classical karst area mediterranean continental to sub alpine climate and istrian peninsula mediterranean climate moreover along the coasts of the gulf of trieste there are many submarine springs which are absent along the istrian coast it is hypothesized that these underwater springs stress the effect of rainfall along the coast which is both direct rain on the measurement site and mainly indirect freshwater outflow from submarine springs higher lowering rates were surveyed during autumn rainfall therefore also freshwater outflow from submarine springs is particularly high at the end of the summer and in autumn

genesis of the guangou karstic bauxite deposit in western henan china abstract the guangou bauxite deposit in western henan china is located in the north china block and to the north of the north qinling orogenic belt the orebody is hosted within the lower member of the carboniferous benxi formation which overlies unconformably upon the ordovician majiagou formation in the lower member of the benxi formation the bauxite orebody with a diaspore illite anatase mineral assemblage is sandwiched between underlying ferric clay illite hematite goethite and overlying top clay kaolinite quartz goethite according to field observations and geochemical evidence including trace and rare earth element ree compositions especially zr hf ratios the ferric clays were weathered from the underlying argillaceous limestones in the majiagou formation during this weathering process trace elements s zn ni cr v sc f ba and be are depleted li rb and b are enriched and zr hf bi ta ga nb and th are relatively immobile rees exhibit evident differentiation with enrichment of la ce pr and nd and depletion of gd tb dy ho er tm yb and lu the bauxite formed in weak reducing slightly basic water conditions according to the geneses of coexisting diaspore and anatase and it was altered during the epigenetic and second exposure periods forming kaolinite and goethite respectively interelemental relationship analyses of the ores suggest that the elemental behaviors of trace elements and rees in the bauxitization process are mainly controlled by the mineral compositions in bauxite ore and chemical properties of the elements for instance zircon rutile and anatase contain zr hf nb ta w and u based on geochemical evidence together with age data and chemical compositions of the detrital minerals both distant igneous rocks in the plate margin and paleozoic carbonates and precambrian rocks inside north china block provide the miscellaneous material for the bauxite ore and the top clay

tidal notches in vinodol channel and bakar bay ne adriatic sea indicators of recent tectonics abstract detailed mapping of coastline in vinodol channel and adjacent bays in the kvarner area northern adriatic sea revealed the existence of well expressed submerged notches ranging in their elevation from 45 to 115 cm below mean sea level noticeable difference in the height of these presumably coeval tidal notches is attributed to neotectonic movements since the roman times the difference of 0 1 m on opposite parts of vinodol channel is in accordance with the presumed thrusting tectonics in the adjacent vinodol valley the deeper position of coeval tidal notches in bakar bay the drowned part of vinodol valley indicates it is the tectonically most active zone investigation of tidal notches in this case complements information from the solid rock geology and measurements of recent tectonic movements revealed by gps positioning moreover it indicates the potential of detailed mapping of tidal notches for neotectonic research in some coastal areas

a high resolution late holocene palaeo environmental record from the central adriatic sea a multi proxy study of a holocene sediment core rf 93 30 from the western flank of the central adriatic in 77 m of water reveals a sequence of changes in terrestrial vegetation terrigenous sediment input and benthic fauna as well as evidence for variations in sea surface temperature spanning most of the last 7000 yr the chronology of sedimentation is based on several lines of evidence including ams 14c dates of foraminifera extracted from the core palaeomagnetic secular variation pollen indicators and dated tephra the temporal resolution increases towards the surface and for some of the properties measured is sub decadal for the last few centuries the main changes recorded in vegetation sedimentation and benthic foraminiferal assemblages appear to be directly related to human activity in the sediment source area which includes the po valley and the eastern flanks of the central and northern appenines the most striking episodes of deforestation and expanding human impact begin around 3600 bp late bronze age and 700 bp medieval and each leads to an acceleration in mass sedimentation and an increase in the proportion of terrigenous material reflecting the response of surface processes to widespread forest clearance and cultivation although human impact appears to be the proximal cause of these changes climatic effects may also have been important during these periods signs of stress are detectable in the benthic foram morphotype assemblages between these two periods of increased terrigeneous sedimentation there is smaller peak in sedimentation rate around 2400bp which is not associated with evidence for deforestation shifts in the balance between terrigenous and authigenic sedimentation or changes in benthic foraminifera the mineral magnetic record provides a sensitive indicator of changing sediment sources during forested periods of reduced terrigenous input it is dominated by authigenic bacterial magnetite whereas during periods of increased erosion anti ferromagetic minerals haematite and or goethite become more important as well as both paramagnetic minerals and super paramagnetic magnetite analysis of the alkenone u37k record provides an indication of possible changes in sea surface temperature during the period but it is premature to place too much reliance on these inferred changes until the indirect effects of past changes in the depth of the halocline and in circulation have been more fully evaluated the combination of methods used and the results obtained illustrate the potential value of such high resolution near shore marine sedimentary sequences for recording wide scale human impact documenting the effects of this on marine sedimentation and fauna and potentially disentangling evidence for human activities from that for past changes in climate

voluminous silicic eruptions during late permian emeishan igneous province and link to climate cooling abstract silicic eruptive units can constitute a substantive component in flood basalts dominated large igneous provinces but usually constitute only a small proportion of the preserved volume due to poor preservation thus their environmental impact can be underestimated or ignored establishing the original volume and potential climate sensitive gas emissions of silicic eruptions is generally lacking for most large igneous provinces we present a case study for the 260 ma emeishan province where silicic volcanic rocks are a very minor component of the preserved rock archive due to extensive erosion during the late permian modal and geochemical data from late permian sandstones derived from the province suggest that silicic volcanic rocks constituted some 30 by volume of the total eroded emeishan volcanic source rocks this volume corresponds to 3 10 4 km 3 on the basis of two independent estimate methods detrital zircon trace element and hf isotopic data require the silicic source rocks to be formed mainly by fractional crystallization from associated basaltic magmas based on experimental and theoretical calculations these basalt derived 104 km3 silicic eruptions released 1017 g sulfur gases into the higher atmosphere and contribute to the contemporaneous climate cooling at the capitanian wuchiapingian transition 260 ma this study highlights the potentially important impact on climate of silicic eruptions associated with large igneous province volcanism

impact of holocene tsunamis detected in lagoonal environments on corfu ionian islands greece geomorphological sedimentary and microfaunal evidence abstract in this paper we present for the first time geomorphological sedimentary and microfaunal evidence of palaeotsunami impact on corfu ionian islands greece the island of corfu is located in an area of exceptional tectonic stress towards the south the african oceanic plate is being subducted underneath the aegean plate whereas towards the north the adriatic and european plates form a continental collision zone recent publications provide evidence of earthquake related co seismic movements that potentially trigger extreme wave events as well as relative sea level fluctuations in this context we investigated two selected near coast geological archives the chalikiopoulou lagoon in the east and the korission lagoon in the southwest of corfu island our results clearly document that the eastern as well as the southwestern coasts of corfu were repeatedly affected by palaeotsunami impact during the holocene with regard to the local topographical constellation and the recent geomorphodynamic potential of each study area evidence of high energy wave impact is based on the stratigraphical and microfaunal record of selected vibracoring sites as well as on numerical modelling results it is concluded that the eastern coast of corfu is preferably affected by high energy wave impacts from a southern direction such impacts are most likely related to teletsunamis from the major seismical zone of the hellenic trench in contrast the southwestern coast of corfu is endangered by impacts from both western and southern directions such impacts may comprise teletsunamis triggered in the hellenic trench or the etna regions but may also be caused by local submarine landslides at the steeply sloping continental shelf directly west of corfu our study builds a bridge between palaeotsunami research conducted in the southern ionian sea and the adriatic sea and allows to better discriminate between the effects of teletsunamis and locally triggered events within one of the seismically most active regions in the eastern mediterranean

geochronology and petrogenesis of miocene granitic intrusions related to the zhibula cu skarn deposit in the gangdese belt southern tibet abstract the zhibula cu skarn deposit 19 5 mt ore 1 64 near the qulong porphyry cu mo deposit is located in the gangdese porphyry copper belt in southern tibet the deposit is a typical metasomatic skarn that is related to the interaction of magmatic hydrothermal fluids and calcareous host rocks stratiform skarn orebodies are mainly distributed in the contact between tuff and marble in the lower part of the jurassic yeba formation endoskarn zonations for an outward trend are observed in the granodiorite which grade from a fresh granodiorite to a weakly chlorite altered granodiorite a green diopside bearing granodiorite and a dark red brown garnet bearing granodiorite the zhibula granodiorite and monzogranite have similar secondary ion mass spectrometry sims zircon u pb ages of 16 9 0 3 ma and 17 0 0 2 ma respectively they exhibit different fractional crystallization from granodiorite sio 2 64 8 69 3 wt to monzogranite sio 2 72 3 76 8 wt both the granodiorite and monzogranite are characterized by high al 2 o 3 12 6 16 7 wt and k 2 o 1 5 5 5 wt contents high sr y 35 151 and la yb 19 48 ratios and variable mgo 0 16 3 91 and mg 31 61 values they display features of enrichment in large ion lithophile elements liles e g rb ba sr and k depletion in high field strength elements hfses e g nb ta ti and p and moderate negative eu anomalies eu 0 58 0 98 they show restricted in situ zircon hf isotopic compositions 6 7 to 8 8 only one sample is 4 5 and consistent 18 o values 6 0 to 6 6 the geochemical data indicated that the miocene zhibula granitic intrusions formed by the magma that were characterized by high sr y ratios and were derived from the partial melting of the thickened juvenile lower crust which may have been metasomatized by the slab melts during subduction of the neo tethyan oceanic crust and were induced by the convective removal of the thickened lithosphere in addition the zhibula cu skarn deposit and the qulong cu mo deposit form a significant porphyry skarn ore system

kelvin and the age of the earth kelvin s estimate of about 10 8 years for the age of the earth based on the time required for an initially uniform and hot thermal structure to decay to the presently observed surface temperature gradient is briefly reviewed the later realization that the earth was at least several billion years old 4 5 times 10 9 years posed a dilemma how to reconcile thermal evolution with this great age radiogenic heat production alone is demonstrably insufficient to effect the reconciliation and in the end it is mantle convection with its ability to exploit the entire internal heat of the earth that provides the way out the present usefulness of thermal structure as a measure of age age now taken to mean local as opposed to global age is reviewed for oceanic and continental regions as for kelvin he was quite right in arguing that the earth s age was not only finite but measurable measurable however by methods he did not anticipate

mineralogical and geochemical indicators of the polygenetic nature of terra rossa in istria croatia abstract terra rossa in istria is situated on the jurassic cretaceous paleogene carbonate plain and is considered a polygenetic reddish soil which bears typical terra rossa fe oxide characteristics e g fe d and fe d fe t the difference in particle size mineralogy and geochemistry observed between terra rossa and the insoluble residue of limestones and dolomites clearly indicates that the additions of external materials might have diminished the influence of insoluble residue of limestones and dolomites as the primary parent material of terra rossa in istria terra rossa is clay and silty clay composed of quartz plagioclase k feldspar micaceous clay minerals illitic material and mica kaolinites kl d and kl chlorite vermiculite low charge vermiculite or high charge smectite mixed layer clay minerals other than illitic material hematite goethite and xrd amorphous inorganic compound calcite dolomite and boehmite are sporadically present and are of local importance kaolinites and illitic material are dominant clay mineral phases in the clay fraction of all terra rossa from istria kaolinite which does not form intercalation compounds with dimethylsulfoxide dmso is the dominant mineral phase in fine clay and is considered predominantly authigenic rather then inherited from parent materials neither the content and particle size distribution nor the bulk and clay mineralogy of the insoluble residue of limestone and dolomite support development of terra rossa entirely by dissolution of carbonate rock if terra rossa has developed only from the insoluble residue of limestone and dolomite its clay content due to weathering should be higher than that in the insoluble residues which is not the case plagioclase was found only in one insoluble residue while all terra rossa samples contain this mineral moreover insoluble residues do not contain vermiculite which was observed in small amounts in clay fraction of all terra rossa samples na 2 o k 2 o 100 zr nb and zr ti 1000 ratios in the majority of terra rossa samples are much higher than in the insoluble residue of limestones and dolomites which also supports external material influence in the genesis of terra rossa materials other than the insoluble residue of limestones and dolomites which might have contributed to terra rossa are loess sediments whose deposition was very important recurrent process in istria probably since the early middle pleistocene and flysch sediments which extended much more southwards from its present position analyses performed indicate that both loess older than that of the upper pleistocene age and flysch might have contributed in the genesis of terra rossa

morpho sedimentary characteristics and holocene evolution of the emergent part of the ombrone river delta southern tuscany abstract the holocene evolution of the ombrone river delta has been investigated using morphological and sedimentological evidence the delta had a lagoon like prehistoric evolution while seawards the growth occurred mainly in historical times the data obtained together with the available historical and archeological documentation enable a quantitative evaluation of the volume of the emerged part of the delta to be made moreover for the apical area it has been possible to calculate the annual average increase in the volume of deposition during etruscan and roman times as well as during the middle ages and since the renaissance up to now it has been possible to estimate the periods during which wind exerted a more important role in shaping the delta morphology the volume of sediments deposited during the last 6000 years has been estimated at 1766 10 6 m 3 a combination of climatic conditions littoral dynamics and human action appears to have driven the dynamics of the delta growth which however was not continuous but active especially during the last 3000 years during this period about the 80 of the whole delta volume seems to have deposited high rates of sedimentation occurred between the 16th and the 19th centuries a cold and moist period coinciding with the little ice age when the delta took the typical shape of microtidal wave dominated deltas

sea level change during the holocene in sardinia and in the northeastern adriatic central mediterranean sea from archaeological and geomorphological data abstract we provide new data on relative sea level change from the late holocene for two locations in the central mediterranean sardinia and ne adriatico they are based on precise measures of submerged archaeological and tide notch markers that are good indicators of past sea level elevation twelve submerged archaeological sites were studied six aged between 2 5 and 1 6 ka bp located along the sardinia coast and a further six dated 2 0 ka bp located along the ne adriatic coast italy slovenia and croatia for sardinia we also use beach rock and core data that can be related to holocene sea level the elevations of selected significant archaeological markers were measured with respect to the present sea level applying corrections for tide and atmospheric pressure values at the time of surveys the interpretation of the functional heights related to sea level at the time of their construction provides data on the relative changes between land and sea these data are compared with predictions derived from a new glacio hydro isostatic model associated with the last glacial cycle sardinia is tectonically relatively stable and we use the sea level data from this island to calibrate our models for eustatic and glacio hydro isostatic change the results are consistent with those from another tectonically stable site the versilia plain of italy the northeast adriatic italy slovenia and croatia is an area of subsidence and we use the calibrated model results to separate out the isostatic from the tectonic contributions this indicates that the adriatic coast from the gulf of trieste to the southern end of istria has tectonically subsided by 1 5 m since roman times

geochemistry and secular trends in the middle late permian karst bauxite deposits northwestern iran abstract this study focuses on the middle late permian bauxite deposits found within karstic depressions and sinkholes of carbonates of the ruteh and nessen formations northwestern iran data concerning five karst bauxite deposits each related to a different stratigraphic position within the bedrock were selected to address the chemical distribution and inter elemental relationships especially for critical elements factors that control bauxite formation and the parental affinity the analyzed samples mainly clayey bauxite and bauxitic clay are characterized by large compositional fluctuations involving both major and trace elements the major element composition is dominated by sio2 tio2 al2o3 and fe2o3 among the critical elements compositional fluctuations induce the occurrence of outliers for co nb ta lree and hree similar to other trace elements such as ba sr cr u and zr elemental mobility indicates that most of elements are generally depleted among the critical elements co is enriched only in several samples of the older deposits and ree are enriched in some samples of the younger deposits factor analysis suggests that due to the observed al ga covariance fairly acidic conditions were never attained during bauxitization and that detrital resistant minerals concentrated during a bauxitization stage promoting al ti accumulation furthermore the u co variance with low soluble elements nb ta and th suggests that u was mostly conservative during the formation of deposits cobalt co varies with cr and these elements accumulated during later bauxitization stages when the massive leaching of silica occurred the cia ciw and pia paleo weathering proxies indicate an upward weathering increase which suggests a trend toward more extreme weathering conditions in a wetter and warmer climate according to the permian global warming this is consistent with an upward increasing ba sr ratio and the inspection of the a cn k plot where the younger deposits fall close to the a k edge involving a clayey precursor requires a rainfall increase interestingly the upward trend toward a warmer and wetter climate was also coupled with paleo redox conditions promoting cerium oxidation as depicted by the ce ce values finally the eu anomaly and the sm nd ratio indicate that the studied bauxite deposits were mainly derived from a mafic protolith that formed in the middle late permian as a consequence of the volcanism that affected the entire iranian platform a cluster of karst bauxites however has eu eu values lower than the average standard deviation range of the mafic rocks suggesting a possible contribution of a more differentiated and less mafic protolith similarly the u th ratio at large supports the hypothesis of a mafic protolith for the middle late permian bauxite deposits although some samples show the u th values well above the average standard deviation range of the mafic rocks likely indicating that processes promoting the accumulation of resistant minerals with high u th ratios cannot be excluded this means that in this case the u th ratio does not necessarily reflect the protolith of karst bauxites and that more in general this proxy needs to be carefully interpreted when used to assess the parental affinity of residual rocks

geochemistry of the apulian karst bauxites southern italy chemical fractionation and parental affinities article i nfo this study focuses on a late cretaceous karst bauxite deposit in the murge area of the apulia district southern italy the first analysis of the vertical distributions of a wide range of elements including rees and selected trace elements throughout the deposit was shown in order to identify the processes determining element frac tionation during the evolution of the bauxite the studied karst bauxite deposit exhibits an ooidal texture is mineralogically homogeneous and contains higher abundances of boehmite than of hematite kaolinite and anatase the major element composition of the bauxite is dominated by elevated concentrations of sio2 t io2 a l2o3 a nd fe2o3 and analyses of element mo bility within the bauxite indicate that all elements except for nb and ni and to a lesser extent cr are depleted relative to the immobile element ti r mode factor analysis revealed a number of key findings i some low solubility elements e g zr th ti v ga were concentrated in detrital zircon and monazite zr th in anatase ti v and possibly in boehmite and hematite ga during the later stages of bauxitisation ii fe and cr were concentrated during wet conditions whereas al and co accumulated during dry conditions iii distributions of the light rees lrees and the heavy rees hrees are controlled by the same processes suggesting that little lree hree fractionation occurred during bauxite formation and iv the behaviour of cerium is different from that of the other rees and highly variable cerium anomalies are observed across the deposit with three characteristic ce ce maxima with values ofn2 parisite was the only authigenic cerium mineral detected during this study thus we propose a three step model to explain the distribution of ce cerianite is dissolved by cerium reduction is transported by downward moving meteoric water per descensum and finally parisite is precipi tated this cycle was repeated several times in the apulian karst bauxite in response to eh decreases under alka line conditions promoted by fluctuations in the groundwater level finally we used the value of the eu anomaly todiscuss theparental affinity or protolith of thebauxite the value of the eu anomaly min eu eu 0 76 max eu eu 0 89 indicates that the bauxite was not derived from carbonates but rather that the majority of the bauxite was influenced by intermediate to mafic magmatic sources eu eu vs sm nd diagram suggests that the parental material for the bauxite was derived from a combination of a distant magmatic source and clastic material derived from a continental margin northern africa to the south

remobilization of metasomatized mantle lithosphere a new model for the jiaodong gold province eastern china the 120 ma jiaodong province in the north china craton composed of abundant mesozoic granites that intrude precambrian metamorphic basement is bordered by the sulu orogenic belt which formed through the collision between the north china and yangtze cratons in the triassic insights on the geodynamic setting and source of gold and fluids in the jiaodong gold province are based on a detailed study of the sanshandao deposit the 13cpdb and 18o values of hydrothermal calcite from this deposit range from 4 3 to 6 5 and 11 4 to 15 1 respectively which are compatible with a mantle source pre ore mafic dykes in the deposit show typical arc like geochemical features suggesting that the mantle source was metasomatized prior to the basic magmatism the 34s values of gold related pyrite from sanshandao and other large deposits in the province range from 10 9 to 11 5 and are higher than those of the country rocks but consistent with the signature of orogenic gold deposits sourced from a neoproterozoic sedimentary reservoir these high positive 34s values are interpreted to be inherited from auriferous neoproterozoic sedimentary rocks of the northern yangtze craton which were subducted into the mantle lithosphere beneath the north china craton during the formation of eclogite in the adjacent sulu orogenic belt in the triassic the syn ore lower cretaceous mafic dykes display oceanic island basalt like geochemical features suggesting that asthenosphere upwelling triggered the release of gold and sulfur from an enriched and fertilized mantle lithosphere contributing to the auriferous fluid which formed the widespread gold mineralization in the jiaodong province at ca 120 ma

genetic relationship between the emeishan plume and the bauxite deposits in western guangxi china constraints from u pb and lu hf isotopes of the detrital zircons in bauxite ores abstract the formation processes and alumina sources of the large and super large bauxite deposits that have developed in west guangxi in the yangtze block have been debated for a long time shrimp zircon u pb dates combined with in situ hf isotopic data of the detrital zircons from permian bauxite ores in the western guangxi province china provide new constraints on the genesis of the bauxites in west guangxi u pb dating ages of the detrital zircons cluster around 256 ma and 261 ma this is consistent with the emplacement age of the emeishan plume thus it has been determined that the detrital zircons come from magmatic rocks related to the emeishan plume and that the emeishan plume has significant control on the formation of bauxites in addition this work presents new evidence for the evolution of the emeishan plume most of the e hf t values of the zircons around 256 ma and 261 ma are negative varying widely from 1 3 to 16 1 this data indicates the melting of yangtze block basement rocks and the mixing of magmas generated both from the mantle and from the crust occurred at the periphery of the plume in the main phase of emeishan lip magmatism this study verified that the plume induced uplift exposed carbonates as well as the mafic and felsic rocks generated by the emeishan plume to long periods of intense weathering under humid tropical conditions the weathering remnants of the high alumina magmatic rocks and carbonates were deposited on or transported to the paleokarst surface and converted to bauxites

sequence of late jurassic early cretaceous magmatic hydrothermal events in the xiong ershan region central china an overview with new zircon u pb geochronology data on quartz porphyries recent investigations have revealed several large au and mo deposits in the xiong ershan region central china most quartz porphyries associated with the mineralization occur as dikes and apophyses or as rubbles cemented in mineralized breccia pipes three types of quartz porphyries were sampled from the leimengou mo deposit the qiyugou au deposit and the niutougou au deposit la icp ms zircon u pb analysis was performed in zircons from two quartz porphyries the results yielded ages of 125 4 0 77 ma for leimengou mo deposit and 150 1 1 1 ma for qiyugou au deposit the magma source of leimengou quartz porphyry is similar to that of the mineralized cementing material in breccia pipes of the qiyugou au deposit whereas the magma source of qiyugou quartz porphyry is the same as that of quartz porphyries in niutougou au deposit based on the new u pb isotopic ages of granitic plutons reported in this study together with the age data in the literature we identify distinct magmatic pulses in the xiong ershan region at ca 160 150 143 133 125 and 115 ma during the late jurassic early cretaceous the ages of au and mo mineralization coincide with the thermal events at about 115 125 133 and 143 ma are considered to be co eval with granitic magmatism no mineralization ages of 150 and 160 ma thermal events have been previously reported our study demonstrates late jurassic early cretaceous multiple magmatic pulses and mineralization in the xiong ershan region

combined tectonic and paleogeographic controls on the genesis of bauxite in the early carboniferous to permian central yangtze island abstract two bauxite horizons with a total reserve of 1 29 bt occur in the lower carboniferous and lower permian in the central south china block different from other intracontinental bauxites in china which are genetically linked to the orogenesis along the continental margin these bauxites were generated in the absence of marginal orogenesis the genesis of these bauxites were studied based on tectonic paleogeographic and paleoclimatic controls the orebody in huofengchong hfc region is hosted within the lower carboniferous which overlies upon the cambrian dolomite unconformably the orebody in the regions of yanfengba yfb and baiyantou byt occurs in lower permian which overlies upon the silurian shale or devonian dolomite unconformably the mineral assemblages in the carboniferous hfc bauxite consist of diaspore illite anatase and in permian yfb and byt bauxite the minerals are diaspore anatase illite clinochlore and kaolinite the data from the u pb isotope measurements of detrital zircons from these bauxites provide two main ages 1 a maximum u pb age peak of ca 800 ma from the carboniferous hfc and 2 a maximum age peak of ca 1100 ma for the permian byt and yfb the ca 800 ma detrital zircons from the carboniferous bauxite are dominating in the paleozoic sedimentary units which likely derive from the erosion of the mid to neo proterozoic felsic volcanic and intrusive rocks panxi hannan arc occurring in the western margin of the south china block by contrast the zircons with ages of ca 1100 ma are prevalent in the paleozoic sediments from the center of the block the above results indicate that the lower carboniferous and lower permian bauxites are sourced from the sedimentary rocks in the western and central parts of the south china block respectively despite the difference in the provenance these two episodes of deposits were both deposited in a tidal flat restricted platform attached to an ew trending yangtze island occupies the western to central parts of the south china block this indicates that the shift from a marginal to central uplift within the paleo island from early carboniferous to early permian has induced the transition in the provenance of the source material in addition the weathered materials from the two provenances both accumulated in the coastal region receiving further bauxitization the bauxitization was boosted by the persistent preferable tepid and humid paleoclimate defined by the equatorial position of south china block and the drop of global temperature during the metallogenic period

challenging an ice core paleothermometer temperatures measured in a borehole in the greenland ice sheet can offer clues about the past history of the earth9s surface temperature and climate macayeal in his perspective provides background and commentary to accompany a research report by cuffey et al which challenges previous climate histories derived from ice core oxygen isotope data and offers a new calibration of this paleothermometer based on a climate history derived from borehole temperatures

the age of the inner core abstract the energy conservation law when applied to the earth s core and integrated between the onset of the crystallization of the inner core and the present time gives an equation for the age of the inner core in this equation all the terms can be expressed theoretically and given values and uncertainties of all relevant physical parameters the age of the inner core can be obtained as a function of the heat flux at the core mantle boundary and the concentrations in radioactive elements it is found that in absence of radioactive elements in the core the age of the inner core cannot exceed 2 5 ga and is most likely around 1 ga in addition to have an inner core as old as the earth concentrations in radioactive elements needed in the core are too high to be acceptable on geochemical grounds

delayed cooling of the earth s mantle due to variable thermal conductivity and the formation of a low conductivity zone abstract the thermal conductivity of mantle materials decreases with higher temperatures and increases with greater pressure due to phonon mechanism but increases with temperature for radiative transfer this trade off attribute allows for the formation of a low conductivity zone lcz within the top thermal boundary layer in mantle convection we have studied with a two dimensional 2 d cartesian model the potential of this low conductivity zone in retarding secular cooling of the mantle for a longer period of time than models with constant thermal conductivity using a recently proposed model for thermal conductivity and an adiabatic boundary condition for the bottom of the mantle we have carried out a set of numerical experiments within the framework of the extended boussinesq approximation for constant viscosity depth dependent thermal expansivity and variable thermal conductivity with surface rayleigh numbers between around 106 and around 107 we have employed internal heating between two and four times the chondritic level and half life time values of 2 5 ga and 5 ga the cooling rate of the mantle can be decreased by the feedback interaction between mantle conductivity and internal heating which gives rise to slower sinking cold currents the retardation time increases with the strength of radiogenic heating and can be as long as a couple of billion years for high initial heating rates four times the chondritic value however increasing the radiative contribution of the conductivity speeds up the cooling process the less the radiative contribution is the more mantle cooling would be retarded in the course of adiabatic cooling we find the paradoxical situation in which the effective rayleigh number of the mantle can actually increase with time we suggest then that because of the possibilities for the formation of low conductivity zones adjacent to the thermal boundary layers which bring forth unexpected consequences mantle thermal conductivity should be considered as a fundamentally important factor in constraining the thermal evolution of both the core and mantle

mineralogical characteristics of the superlarge quaternary bauxite deposits in jingxi and debao counties western guangxi china abstract in recent decades more than 0 5 billion tons of ores scattered in the quaternary laterite in western guangxi china have been explored the ores were derived from a bauxite horizon in permian via physical break up and re sediment process utilizing various test methods i e xrd dta tg dtg sem eds and epma the mineralogical characteristics of the quaternary bauxite ores in jingxi and debao counties were investigated xrd was used together with tg dtg to obtain relatively accurate ore mineral abundance diaspore is the major phase whereas hematite kaolinite anatase chamosite gibbsite goethite illite and rutile are minor diaspore is characterized by a small particle size low degrees of crystallinity and complex chemical composition both gibbsite and goethite have a varied particle size and goethite crystals contain high al substitution and si it is clarified that diaspore chamosite and anatase were formed in a mildly reduced and alkaline depositional environment in permian while gibbsite hematite goethite and part kaolinite were precipitated from al 3 si 4 and fe 3 enriched solutions within an quaternary oxidized environment the ions al 3 si 4 and fe 3 are mostly released from chamosite in its dissolution process the different physicochemical conditions between the permian depositional and the quaternary weathering periods resulted in a complex mineral assemblage in the quaternary bauxite

transformation from permian to quaternary bauxite in southwestern south china block driven by superimposed orogeny a case study from sanhe ore deposit abstract permian karstic bauxite and its quaternary derivative in western guangxi southwestern south china block possess a total tonnage greater than 0 5 billion tons the primary late permian karstic bauxite formed in reduced environment in the background of tethyan accretionary orogenesis and as one consequence of cenozoic convergence of the indian and eurasia continents the primary orebody was uplifted eroded and re sedimented within quaternary laterite the geochemical variation and its controls during the ore transformation from permian to quaternary remain poorly understood quaternary ore blocks comprise an inner zone of fresh ore and then it gradually transited through a middle zone to a margin with extensive weathering one such bauxite block was selected and further subdivided into twenty three samples for geochemical and mineralogical analysis the inner and middle zones contain similar mineralogical compositions dominated by diaspore and amesite with minor illite anatase goethite pyrite zircon and rutile the margin is composed of diaspore with small amounts of amesite boehmite illite goethite anatase kaolinite zircon rutile and barite bauxite in all three zones is composed of mainly al si fe and ti and high contents of zr cr li f s zn v sr nb ba and ree variations in fe2 and fe3 between the three zones were observed the elements si al fe2 mg ba cr f li ni zn and ree decrease from the core of the ore block outwards corresponding to an increase in s and fe3 depletions in si al fe2 mg ba and cr were caused by the dissolution of amesite most of the al and si in amesite were lost during the weathering and minor retained to form kaolinite depletions in li ni and zn resulted from changes in the depositional environment between the late permian and quaternary dissolution of ree bearing fluorocarbonates resulted in depletions of ree and f the enrichment of fe3 and s was related to the precipitation of goethite hematite and barite in an oxidizing environment while local enrichment of ce resulted from the redox change of ce3 ce4 under the same condition this shows that the chemical composition of laterite enwrapping the bauxite also took part in quaternary bauxite transformation this study shows that the elements migrations during bauxite transformation were influenced by multiple independent factors except for the elemental attributes

jabuka island central adriatic sea earthquakes of 2003 we present analyses of one of the strongest earthquake sequences ever recorded within the adriatic microplate which occurred near the jabuka island in the very centre of the adriatic sea the mainshock 29 march 2003 17 42 ml 5 5 was preceded by over 150 foreshocks and followed by many aftershocks over 4600 of which were recorded on the closest station hvar about 90 km to the east as the epicentre was in the open sea and due to the absence of nearby stations we were able to confidently locate only 597 events hypocentral locations were computed by a grid search algorithm after seven iterations of refining hypocentres and adjusting station corrections epicentres lie in a well defined area of about 300 km 2 just to the w and nw of the jabuka island the vertical cross sections reveal that hypocentres dip to the ne closely matching faults from the jabuka andrija fault system as identified on the available reflection profiles in the area the fault plane solution of the main shock based on the first motion polarity readings agrees well with the cmt solutions and indicates faulting caused by a s n directed tectonic pressure on a reverse dip slip fault this is in very good agreement with the seismotectonic framework of the area these earthquakes are important as they identify the jabuka andrija fault system as an active one which can significantly influence seismic hazard on the islands in the central adriatic archipelago and on the croatian coast between zadar and split along with several other sequences which occurred in the last two decades they force us to change our notion of adria as nearly aseismic compact and rigid block in fact it turns out that recent seismicity of the central adriatic sea is comparable to the seismicity of several well known earthquake prone areas in the circum adriatic region d 2005 elsevier b v all rights reserved

evolution of the adriatic carbonate platform palaeogeography main events and depositional dynamics abstract the adriatic carbonate platform adcp is one of the largest mesozoic carbonate platforms of the perimediterranean region its deposits comprise a major part of the entire carbonate succession of the croatian karst external or outer dinarides which is very thick in places more than 8000 m and ranges in age from the middle permian or even upper carboniferous to the eocene however only deposits ranging from the top of the lower jurassic toarcian to the top of the cretaceous can be attributed to the adcp defined as an isolated palaeogeographical entity although the entire carbonate succession of the karst dinarides was deposited within carbonate platform environments there were different types of carbonate platforms located in different palaeogeographical settings carboniferous to middle triassic mixed siliciclastic carbonate deposits were accumulated along the gondwanian margin on a spacious epeiric carbonate platform after tectonic activity culminating by regional middle triassic volcanism recorded throughout adria the african promontory a huge isolated carbonate southern tethyan megaplatform abbreviated as stm was formed with the area of the future adcp located in its inner part tectonic disintegration of the megaplatform during the middle to late early jurassic resulted in the establishment of several carbonate platforms including the adriatic apenninic and apulian separated by newly drowned deeper marine areas including the adriatic basin as a connection between the ionian and belluno basins lagonero basin and the area of the slovenian and bosnian troughs the adcp was characterised by predominantly shallow marine deposition although short or long periods of emergence were numerous as a consequence of the interaction of synsedimentary tectonics and eustatic changes also several events of temporary platform drowning were recorded especially in the late cretaceous when synsedimentary tectonics became stronger leading up to the final disintegration of the adcp the thickness of deposits formed during the 125 my of the adcp s existence is variable between 3500 and 5000 m the end of adcp deposition was marked by regional emergence between the cretaceous and the palaeogene deposition during the palaeogene was mainly controlled by intense synsedimentary tectonic deformation of the former platform area some carbonates mostly eocene in age were deposited on irregular ramp type carbonate platforms surrounding newly formed flysch basins and the final uplift of the dinarides reached its maximum in the oligocene miocene the adriatic carbonate platform represents a part although a relatively large and well preserved one of the broader shallow water carbonate platform that extended from ne italy to turkey although its continuity is somewhat debatable in the area near albanian greece boundary this large carbonate body which was deformed mostly in the cenozoic including a significant reduction of its width needs a specific name and the central mediterranean carbonate platform is proposed abbreviated to cmcp although the local names such as adcp for its nw part should be kept to enable easier communication and to facilitate description of local differences in platform evolution

geological and isotopic evidence for magmatic hydrothermal origin of the ag pb zn deposits in the lengshuikeng district east central china the lengshuikeng ore district in east central china has an ore reserve of 43 mt with an average grade of 204 53 g t ag and 4 63 pb zn based on contrasting geological characteristics the mineralization in the lengshuikeng ore district can be divided into porphyry hosted and stratabound types the porphyry hosted mineralization is distributed in and around the lengshuikeng granite porphyry and shows a distinct alteration zoning including minor chloritization and sericitization in the proximal zone sericitization silicification and carbonatization in the peripheral zone and sericitization and carbonatization in the distal zone the stratabound mineralization occurs in volcano sedimentary rocks at 100 400 m depth without obvious zoning of alterations and ore minerals porphyry hosted and stratabound mineralization are both characterized by early stage pyrite chalcopyrite sphalerite middle stage acanthite native silver galena sphalerite and late stage pyrite quartz calcite the 34s values of pyrite sphalerite and galena in the ores range from 3 8 to 6 9 with an average of 2 0 the c o isotope values of siderite calcite and dolomite range from 7 2 to 1 5 with an average of 4 4 v pdb and from 10 9 to 19 5 with an average of 14 8 v smow respectively hydrogen oxygen and carbon isotopes indicate that the hydrothermal fluids were derived mainly from meteoric water with addition of minor amounts of magmatic water geochronology employing la icp ms analyses of zircons from a quartz syenite porphyry yielded a weighted mean 206pb 238u age of 136 3 0 8 ma considered as the emplacement age of the porphyry rb sr dating of sphalerite from the main ore stage yielded an age of 126 9 7 1 ma marking the time of mineralization the lengshuikeng mineralization classifies as an epithermal ag pb zn deposit

global and regional factors controlling changes of coastlines in southern iberia spain during the holocene the interaction between global glacio eustatic sea level rise and regional factors oceanographic and tectonic has controlled the evolution of coastline during the holocene in southem iberia at ca 10 000 14c years bp a deceleration of relative sea level rise took place both in the atlantic and mediterranean littorals with a maximum transgression at 6450 14c years bp in subsiding areas present tidal flats estuaries illustrate a clear marine influence recorded both in sediments and the fauna while in uplifting areas prograding spit bar systems developed two phases of major progradation are distinguished in these systems the first one between 6450 and 3000 14c years bp with a sedimentary gap at ca 4000 14c years bp and the second one from 2750 14c years bp up to present with an intervening gap between 1200 and 1050 14c years bp these progradation phases develop during stillstands followed by relative sea level fall while the sedimentary gaps represent relative high sea level in the mediterranean areas with a higher uplift rate marine terraces almost coeval to those gaps occur the most pronounced modifications in littoral dynamics occurred at between 3000 and 2750 14c years bp represented by changes in the direction of longshore drift and prevailing winds and in the predominance of progradation over aggradation processes at ca 1000 14c years bp the estuaries record a greater fluvial than marine influence and at 500 years ago an extraordinary increase in coastal progradation took place in all littoral zones the european medieval warm period is characterized at least during its initial phase by low pressure climate conditions while during the little ice age anticyclonic conditions gave rise to a strong coastal progradation

permian peralkaline peraluminous and metaluminous a type granites in the panxi district sw china their relationship to the emeishan mantle plume abstract numerous permian granitic intrusions plutons in the panxi region sw china are spatially and temporally associated with the emeishan large igneous province elip granites from the 260 ma panzhihua and taihe plutons are peralkaline asi 0 76 1 12 na k al 0 78 1 2 and have high fe values 0 92 0 99 with negative eu anomalies eu eu 0 22 0 98 contrasted with the peralkaline plutons syenites from the 260 ma woshui pluton are metaluminous asi 0 84 1 0 na k al 0 91 1 01 and have moderately high fe 0 79 0 81 and positive eu anomalies eu eu 0 82 1 91 both the peralkaline and metaluminous rocks have mantle isotopic signatures end t 1 3 3 2 and were derived from the elip mantle plume source the peralkaline rocks were likely derived by fractional crystallization of the temporally spatially and chemically associated layered mafic intrusions which host giant magmatic fe ti v oxide deposits the metaluminous granitic rocks although spatially related to the peralkaline granites and layered gabbros were likely generated by partial melting of underplated mafic rocks granites from the 251 ma ailanghe pluton are peraluminous asi 0 97 1 29 and have high fe 0 82 0 91 values and negative eu anomalies eu eu 0 10 0 37 their crustal isotopic signature end t 5 7 to 6 7 indicates possible derivation from melting of yangtze block basement rocks the ailanghe pluton is contemporaneous with other a type granites in the region supporting the view that elip magmatism was sporadic for at least 9 million years the coexistence of three chemically exclusive a type granites in the elip suggests that a variety of a type granites can be generated in the same tectonic setting

content and mode of occurrences of rare earth elements in the zagrad karstic bauxite deposit niksic area montenegro abstract three vertical sections through the zagrad deposit of jurassic karst bauxite in central montenegro have provided knowledge of the vertical distribution of major and some selected trace elements including rare earth elements ree variations in the mineralogy particularly those hosting ree have been studied this has revealed the presence of authigenic mineral phases such as xenotime mottramite and monazite best proved using raman microprobe analysis as well as residual phases such as zircon titanite and monazite the mobility of the elements during bauxitization processes has been studied to show that the ree minerals ensure progressive concentration of these elements during removal of major elements through weathering the similarity of normalized ree in the bauxite to the typical post archean australian shales paas and upper continental crust ucc profile and the preserved eu anomaly are evidence that the bauxite was not derived from carbonates and represents alteration of shale marly limestone and volcanogenic or proximal igneous sourced detritus that accumulated in the original karst landform mass change during bauxitization using ti as index element and compared to paas composition revealed almost 100 depletion of si and weak enrichment in al deeper parts of the deposit with authigenic minerals exhibit very strong enrichment in all ree the bauxite ores have high ree contents 693 5 6953 4 ppm especially lree contents 582 8 4882 9 ppm while hree contents 106 6 2070 5 ppm are much lower

orebody vertical structure and implications for ore forming processes in the xinxu bauxite deposit western guangxi china abstract the xinxu bauxite orebodies which are contained in quaternary depressions overlying strata of permian to devonian age were formed through the break up oxidation and re sedimentation of a pre existing permian bauxite horizon with progressive karsitification the underlying strata of the quaternary orebodies were eroded out downwards in sequence gradually transiting from permian to devonian thus an older underlying stratum generally infers a higher degree of weathering a total of 47 exploration wells sampled each meter were chosen from several orebodies to evaluate the vertical distribution of four major components al 2 o 3 fe 2 o 3 sio 2 and loss on ignition in the ores the vertical evenness is quantified via a box gliding multifractal model the small width of the multifractal spectrum suggests that the vertical ore quality is even overall indicating an intertwining break up and mixing up processes during evolution of the quaternary orebody although the four components show complex spatial distributions topographic elevation displays a positive relationship with the mean fe 2 o 3 content and a negative correlation with the vertical unevenness of al 2 o 3 and fe 2 o 3 in the wells this is taken to reflect the more uniform oxidizing environment in the higher depressions which facilitates a homogeneous and greater increase of fe 2 o 3 content throughout the orebody in contrast the redox conditions in lower depressions are less oxidizing and varied in space inducing great variation in degree of fe 2 o 3 increase in the ores this study also demonstrates that in the xinxu deposit the ore forming redox environment has more impact on the ore quality than the degree of weathering as the contents show irregular vertical changes in the lower depressions it follows that it is the ancient redox environment rather than the modern conditions which affect the orebody vertical structure this clarifies the fact that the vertical structure of the orebody is jointly constrained by the physical melange accumulation of ores and the differences between the ancient redox environments in the higher and lower locations these factors should be the primary factors affecting the vertical structure of karst bauxite deposits

mineralogical and geochemical studies of boron rich bauxite ore deposits in the songqi region sw henan china the songqi region sw henan is an important bauxite province in china the bauxite ore deposits occur unconformably on the top of middle ordovician argillaceous carbonates the bauxite ores from the songqi region are characterized by unusually high boron contents in this paper we report the mineralogical and chemical compositions of selected bauxite ores from the region these new data together with existing geochemical data of soils in the region are used to evaluate the origin of boron enrichment in the bauxite ores the compositional characteristics of tourmaline in the bauxite ores suggests that this mineral was likely derived from a meta sedimentary protolith mass balance calculation reveals that tourmaline only accounts for a small portion of boron in the bauxite ores the majority of boron in the ores must occur in other forms possibly by ion absorption on the surfaces of diaspore and clay minerals in the songqi region the precambrian meta sedimentary rocks are known to contain abundant tourmalines whereas the cambrian ordovician argillaceous carbonates and the upper proterozoic shales are all enriched in boron in free ion state we suggest that these rocks provided tourmaline and boron ion to the bauxite deposits in the region most known bauxite deposits in the songqi region occur at the margins of boron rich soil domains suggesting that boron in soils is a potential exploration indicator for unknown bauxite deposits in this region

geochemical study of laterites of the jamnagar district gujarat india implications on parent rock mineralogy and tectonics abstract the laterite deposits occur in a linear stretch along the northern arabian sea coast in the jamnagar and porbandar districts of gujarat state india these deposits are characterised by presence of gibbsite kaoline calcite quartz anatase natroalunite goethite and hematite and relicts of mafic minerals and plagioclase on the basis of petro mineralogy and geochemistry these deposits are grouped as aluminous laterites fe2o3 1 45 3 84 av 3 13 al2o3 39 31 57 24 av 45 80 and laterites fe2o3 9 84 32 21 av 25 13 al2o3 34 74 49 59 av 41 27 the major trace and ree characteristics of laterites indicate that these were formed in situ by the alteration of parent rocks of trachytic andesitic composition and the process of bauxitisation followed the path of destruction of kaolinite and deferruginisation the correlation patterns of several trace and rare earth elements and their preferential enrichment have indicated that there is an influence of precursor rock on the distribution of trace elements the jamnagar laterite deposits occur as capping over the deccan trap basaltic lava flows and pyroclasic deposits lateritisation prevailed during palaeocene age when india was separated from the seychelles and passing over the equator during this time climate morphology and drainage conditions were favourable for lateritisation that result in the formation of jamnagar and other laterite deposits within the deccan province flood basaltic provinces of deccan columbia north australia and hawaii appear good location for hosting laterite deposits due to their wide areal extent small geological time span and uniform chemical composition however comparison of the major flood basaltic provinces of the world has indicated that their palaeopositions along with palaeoclimate morphology and drainage are equally important factors for facilitating lateritisation

extreme enrichment of rare earth elements in hard clay rocks and its potential as a resource abstract the xuanwei formation is widely distributed in western guizhou province nw china the lower section of which is primarily composed of gray white kaolinitic claystone interbedded with thin layers of grayish black carbonaceous mudstone that are extremely enriched with rare earth elements in order to determine the distribution patterns and existing status of ore forming elements in these rocks careful field investigations were performed along a selected geological profile and rock samples were collected and studied in terms of mineralogical and geochemical characteristics the results show that 1 rees are primarily enriched in the grayish white kaolinitic clay sediments and grayish black carbonaceous mudstone mineralogical analyses revealed kaolinite as the major mineral in rocks along with smaller amounts of smectite illite boehmite hornblende pyrophyllite calcite dolomite and or iron bearing minerals as well as a certain proportion of feldspar quartz crystal debris and non crystal debris 2 ree contents are 89 0 to 9965 ppm with an average of 1312 ppm the thickness of the host rock with ree higher than 1300 ppm is more than 4 m which is referred to as the ree enriched layer 3 the ree contents of bulk rocks exhibit a negative correlation with kaolinite positive correlations with boehmite hornblende and iron bearing minerals and weak positive correlations with smectite illite and pyrophyllite indicating that the ree might exist in an ion adsorption state in the space between the layers of clay minerals 4 compared with the underlying emeishan basalts the ree patterns of samples are quite similar but are enriched in both lree and hree the degree of enrichment of hree is relatively high based on these results a model is suggested where the ree enriched layers originated from the emeishan basalts and were controlled by the transportation and deposition of detritus from a paleo weathering crust the hard clay rocks have a significant resource potential as the contents of ree ga nb and zr are considerably higher than those in the weathering crust type of ree deposit

updrift river mouth migration on cuspate deltas two examples from the coast of tuscany italy the configuration of the arno and ombrone deltas italy is evaluated the terminal courses of the rivers forming these deltas face the dominant wave orthogonal this configuration came about during rapid delta progradation as a consequence of increased river sediment input due to widespread deforestation within the catchment area a prevailing phenomenon from the early middle ages to the xviii century the rivers attained and maintained their directions as the result of the increased accretion rate on the less exposed downdrift side of the delta on the more exposed updrift side delta growth caused the shoreline to gradually rotate so that it directly faced the waves approaching the coast here due to the lower refraction wave energy per shore unit increased whilst accretion rate decreased this rotation of the shoreline induced longshore inversion on the updrift side whereas today cusp erosion is restoring the original drift direction

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method

new zircon fission track analysis constraints on tectonic mineralization epochs in the ganzi litang gold belt eastern qinghai tibet plateau abstract the ganzi litang gold belt as a part of the sanjiang tethys orogen is located between the yidun block and songpan ganzi block terrane in the eastern qinghai tibetan plateau and experienced oceanic slab subduction continent arc collision and intracontinental convergence since the indosinian orogeny a series of gold ore deposits have been found within the region this paper describes the tectonic evolution and episodes of gold mineralization within this belt using zircon fission track ft thermochronology a total of 15 zircon ft analysis results were obtained that can be divided into four age groups 217 213 ma 190 160 ma 155 93 ma and 72 67 ma representing four distinct episodes of gold mineralization of which the middle two episodes predominate eruption of the auriferous volcanic rocks that comprise the belt started at 217 213 ma when the ganzi litang meso tethys ocean began to subduct the mineralization episode at 190 160 ma corresponds to the formation of auriferous volcanic rocks during intracontinental collisional convergence of the ganzi litang belt finally the episodes at 155 93 ma and 72 67 ma are respectively related to the closing times of the bangong nujiang and yarlung zangbu oceans corresponding to tectonic quiet episodes

recently submerged tidal notches in the wider makarska area central adriatic croatia abstract the active tidal notches in the makarska area which were observed and described in historical records from the beginning of the 20th century andrijasevic 1910 have been reanalysed 107 years later detailed mapping of three locations in the wider makarska area revealed their level of submergence which varied between 30 and 37 5 cm below the recent mean sea level msl according to location this investigation points to the recent acceleration of relative sea level change during the current warm period cwp and also to the past temporary still stand according to data from central adriatic islands of vis ravnik and bisevo this still stand probably lasted around 500 years during the little ice age lia period however the notch in the dubrovnik area which was as stated in historical data suess 1885 1908 active at the end of the 19th century is still active today indicating tectonic uplift of the dubrovnik area

provenance of late carboniferous bauxite deposits in the north china craton new constraints on marginal arc construction and accretion processes abstract the north china craton ncc is bounded by two paleozoic accretionary arc terranes the north qinling terrane to the south and the bainaimiao terrane to the north the timing of arc accretion to the ncc and the architecture of the bainaimiao arc remain unclear during the building and accretion of the arcs along its margins the ncc experienced a long sedimentary hiatus since the ordovician which ended with the deposition of bauxite bearing sediments in the late carboniferous in this paper we report the u pb and hf isotopes of detrital zircons from the late carboniferous bauxite layer and use these data to constrain the tectonic evolution of the margin of the ncc the detrital zircons yield a minimum u pb age of ca 310 ma and a prominent age peak at ca 450 ma zircon crystals with ages of ca 330 ma and ca 1900 ma are more common in the bauxite samples from the northern part of the ncc than in those from the central part the ehf t values of the ca 450 ma detrital zircon crystals of the bauxite samples from the ncc are similar to those of the contemporaneous detrital zircon crystals from the north qinling arc terrane to the south but different from those of the contemporaneous detrital zircon crystals from the bainaimiao arc terrane to the north the ca 450 ma detrital zircon crystals in the ca 310 ma bauxite deposits are therefore interpreted to have been derived from the north qinling arc terrane the source of the ca 330 ma detrital zircon crystals of the bauxite deposits is interpreted to be the northern margin of the ncc where intermediate felsic plutons formed at ca 330 ma are common the results from this study support the interpretation that the paleozoic continental arc terranes and their concomitant back arc basins were developed along the margins of the ncc before ca 450 ma and the arc complexes were subsequently accreted to the craton in the late carboniferous this was then followed by the formation of a walled continental basin within the ncc