geochemistry of tertiary igneous rocks of northern luzon philippines evidence for a back arc setting for alkalic porphyry copper gold deposits and a case for slab roll back oligocene to early miocene volcanic rocks are preserved in the central cordillera range and cagayan valley of northern luzon philippines basaltic and andesitic rocks of the pugo formation in the baguio district of the central cordillera were intruded by the 27 to 20 ma calc alkaline central cordillera diorite complex in the southern cagayan valley the subalkaline to alkaline late oligocene mamparang formation overlies the cretaceous caraballo formation and has been intruded by the didipio igneous complex the cordon syenite complex and the palali batholith the didipio complex comprises an early suite of diorites which were intruded by the strongly mineralized stocks of the dinkidi cu au porphyry deposit whole rock geochemical data for intrusive and extrusive rocks of the baguio district range from low k calc alkaline to shoshonitic basalts to dacites with rare earth element ree and high field strength element hfse characteristics of suprasubduction zone magmas and are all interpreted to have been sourced from the same parent melt samples from didipio display higher alkali contents but similar trace element characteristics new age dates for the didipio area range from 25 7 to 24 8 ma the potassic magmas of the cagayan valley are interpreted to have formed in a back arc coeval to the mainarc sequence that is preserved in the baguio miocene rocks this contradicts earlier models which invoke an early miocene arc reversal in the northern luzon archipelago with the switch from early westward subduction to later eastward subduction attributed to a variety of causes the lack of a single compelling trigger for arc reversal combined with the coeval emplacement of arc magmas in the west and back arc magmas in the east in northern luzon is best interpreted as the result of eastward subduction since the late oligocene the presence of 20 ma adakitic magmas in the baguio district may indicate that flattening of the downgoing slab resulted in a hiatus in magmatism and termination of back arc rifting

microbially induced cementation of carbonate sands are micritic meniscus cements good indicators of vadose diagenesis characteristic fabrics such as micrite envelopes calcified filaments and micritic grain to grain bridges are observed in a modern subtidal firmground wood cay bahamas and in a variety of firm and hardgrounds of lower cretaceous and upper jurassic platform carbonates swiss and french jura mountains their similarity to microbial fabrics described in grapestones and in intertidal to continental vadose environments suggests that microbial activity played an important role in the initial stabilization and cementation of carbonate sands meniscus type cements to distinguish them from vadose meniscus cements which clearly formed in subtidal environments are related to filament calcification trapping of percolating micrite and microbially induced carbonate formation such meniscus type cements are commonly micritic but meniscus shaped precipitation of fibrous aragonite or sparitic calcite around organic filaments is also observed therefore an interpretation of vadose early diagenesis should not be based on meniscus cements alone similarly subtidally formed filamentous structures can strongly resemble alveolar septal structures and be interpreted incorrectly as related to subaerial exposure

meteoric like fabrics forming in marine waters implications for the use of petrography to identify diagenetic environments petrographic fabrics have long been used to identify meteoric diagenesis of carbonate sediments however on the basis of oxygen isotopic data we document similar fabrics forming in marine pore fluids in the shallow subsurface of great bahama bank therefore petrographic fabrics alone are not reliable indicators of diagenetic environments even for shallow water sediments in our study skeletal grainstones show two distinct diagenetic assemblages either dissolution of aragonitic grains and minimal cementation high permeability intervals or abundant blocky spar cement and neomorphism of aragonitic skeletal grains low permeability intervals these marine burial fabrics are present as shallow as 110 m below sea level well above the aragonite compensation depth a feature that must be considered for models of diagenesis in ancient carbonate sediments marine burial diagenesis may be important in ancient carbonate sediments deposited in moderate water depths or in shallow water during rising sea level where meteoric diagenesis is suppressed

glaucony and sequence stratigraphy a conceptual framework of distribution in siliciclastic sequences abstract detailed analysis of recent literature on glaucony and selected case studies eocene isle of wight miocene northern apennines shows that the presence of glaucony alone is not diagnostic of a specific systems tract of a depositional sequence a reliable sequence stratigraphic interpretation of glaucony bearing units requires additional information on glaucony including 1 spatial distribution 2 maturity distinction between nascent slightly evolved evolved and highly evolved glaucony and 3 genetic attributes differentiation of autochtonous from allochthonous and intrasequential from extrasequential glaucony autochthonous glaucony is common at various stratigraphic levels in the transgressive systems tract tst and the lower highstand systems tract hst showing an upward increase tst and then decrease hst in abundance and maturity the condensed section can be distinguished from the overlying and underlying deposits by the higher concentration and maturity of glaucony allochthonous intrasequential parautochthonous glaucony can be present in the entire tst hst and lowstand systems tract lst generally showing lower concentration and maturity than its autochthonous counterpart allochthonous extrasequential detrital glaucony is present mainly in the lst its concentration and composition depending on the characteristics of the source horizon the associa ion between autochthonous and allochthonous intrasequential and extrasequential glaucony commonly exists in the lst and in the lower tst

tetrapod localities from the triassic of the se of european russia abstract fossil tetrapods amphibians and reptiles have been discovered at 206 localities in the lower and middle triassic of the southern urals area of european russia the first sites were found in the 1940s and subsequent surveys from the 1960s to the present day have revealed many more broad scale stratigraphic schemes have been published but full documentation of the rich tetrapod faunas has not been presented before the area of richest deposits covers some 900 000 km 2 of territory between samara on the river volga in the nw and orenburg and sakmara in the sw continental sedimentary deposits consisting of mudstones siltstones sandstones and conglomerates deposited by rivers flowing off the ural mountain chain span much of the lower and middle triassic induan olenekian anisian ladinian the succession is divided into seven successive svitas or assemblages kopanskaya induan staritskaya kzylsaiskaya gostevskaya and petropavlovskaya all olenekian donguz anisian and bukobay ladinian this succession comprising up to 3 5 km of fluvial and lacustrine sediments documents major climatic changes at the beginning of the early triassic arid zone facies were widely developed aeolian piedmont and proluvium these were replaced by fluvial facies with some features indicating aridity at the end of the middle triassic deltaic and lacustrine marsh formations were dominant indicating more humid conditions the succession of early to mid triassic tetrapod faunas documents the recovery of life after the end permian mass extinction the earliest faunas consist only of small aquatic tetrapods in low diversity low abundance assemblages climbing the succession through the early triassic more terrestrially adapted tetrapods appear and larger herbivorous and carnivorous reptiles come to dominate in the mid triassic as ecosystems were rebuilt

endolithic biodegradation of cool water skeletal carbonates on scott shelf northwestern vancouver island canada abstract biodegradation of shell material is widespread in the cool water skeletal carbonate deposits on scott shelf northwestern vancouver island and is especially evident in the large aragonitic bivalves glycymeris and humilaria major primary sediment contributors ten types of endolithic microborings have been identified in the shells including representatives of green algae e g ostreobium quekettii blue green algae e g plectonema terebrans scytonema sp fungi bacteria and clionid sponges as well as macroborings of phoronids polychaetes and naticid gatropods microcrystalline carbonate is not precipitated in vacated bores boring physically weakens the shells rendering them more prone to mechanical abrasion during sediment transport and bioturbation and to biological abrasion by grazing benthos tumbling experiments demonstrate that the rate of carbonate mud production is much greater for bored as compared to fresh bivalve shells and that mud production rates decrease with tumbling time because most endolithic microborings are confined to the periphery of grains boring also increases significantly the porosity and surface area of skeletal grains and destroys their organic matrix making them susceptible to maceration and dissolution on cool water shelves fostered by the generally low rates of carbonate production and accumulation many aragonitic bivalve shells on scott shelf have become thoroughly degraded through a combination of endolithic microboring maceration and dissolution within about 1000 years in ambient sea water in geologic terms such selective taphonomic loss of skeletal material may be considerable in ancient temperate shelf limestones and should be evaluated when interpreting their paleoecology and paleoenvironments

in situ elemental and sr isotope characteristics of magmatic to hydrothermal minerals from the black mountain porphyry deposit baguio district philippines at the black mountain porphyry cu au deposit in the baguio district northern luzon philippines pre and synmineralized rocks preserve magmatic and hydrothermal minerals e g plagioclase amphibole titanite and epidote spanning the complete paragenesis of the deposit strontium isotope values in early crystallized plagioclase phenocrysts from all felsic porphyries can be divided into two types the type i plagioclase crystals show relatively homogeneous sr isotope values 0 7035 0 7038 1 0 0001 indicating crystallization from a relatively stable and long lived felsic magma chamber the type ii plagioclase grains have a wider range of sr isotope compositions 0 7032 0 7039 1 0 0001 indicating mafic and or felsic magma recharge in magmatic titanite nb ta values are higher than those in the whole rock while zr hf and y ho values are lower in hydrothermal titanite and epidote the ratios are similar to those in the whole rock these patterns reflect crystallization effects imposed during the magmatic stage but an absence of differentiation during the hydrothermal stage the consistent gradual decrease in total rare earth element y zr and u contents in both hydrothermal titanite and epidote from early to late stages indicates the effect of hydrothermal fluid evolution with decreasing temperature the variation of 87sr 86sr values in magmatic amphibole plagioclase and hydrothermal epidote in felsic and mafic rocks indicates the addition of mafic magma derived fluid into the felsic magma derived fluid one extra source of fluid probably derived from wall rock limestone was required to generate the highly radiogenic 87sr 86sr values of some epidote 0 7038 0 7053 thus in situ elemental and sr isotope variation in minerals from different paragenetic stages can be used to interpret formation process and source for both magmas and hydrothermal fluids

stream analysis of small drainage basins in an ancient landform korean peninsula abstract much of the topography of korea is ancient but many quaternary fault outcrops and marine terraces have been observed in the southeastern part of the korean peninsula sufficient evidence of a quaternary fault is lacking in the geological features of the commercially developed jukbyun and uljin areas knickpoints that develop on streams can be formed by tectonic activity such as faulting and folding or can result simply from the differential erosion rates of bedrock in this study we investigated the relationship between stream steepness and faults in the jukbyun area stream profile analyses of the bugu and namdae basins were performed using a digital elevation model to estimate quaternary tectonic movements stream parameters obtained from analysis of the longitudinal stream profiles of the bugu and namdae drainage basins in the northeastern part of the korean peninsula indicated neotectonic movement thirty of the thirty nine knickpoints that developed in the downstream areas of the fluvial channels corresponded to fault zones it is thought that fault activity results in knickpoints in river systems the normalized relative slope k sn value 54 9 of the bs1 stream in the bugu drainage basin was higher than that 28 8 36 3 of the other streams in both basins despite a similar lithology to ns1 and ns2 therefore we concluded that stream steepness might be a result of tectonic forcing rather than a product of rock strength in the study area and that stream parameters could provide indirect evidence of quaternary tectonics in ancient landforms

along strike segmentation of the abanico basin central chile new chronological geochemical and structural constraints the andes of central chile are composed mostly of cenozoic volcanic rocks erupted during the opening and subsequent inversion of the intra arc volcano tectonic abanico basin until recently the internal segmentation of this inverted basin was poorly understood based on a combination of u pb geochronology u th he thermochronology whole rock geochemistry and structural data we propose that the abanico basin can be divided into two main segments separated by the nw striking piuquencillo fault and conjugate ne striking faults stratigraphic units defined in the northern segment abanico and farellones formations cannot be correlated with the rocks of the southern segment coya machali formation and teniente volcanic complex in terms of lithofacies depositional ages and geochemistry the northern and southern segments also show temporal differences in their tectonic evolution an early deformation event beginning at 22 ma affected only the northern segment and is associated with the formation of progressive unconformities between the abanico and farellones formations and also with crustal thickening as reflected in the geochemistry of the farellones formation a second stage of crustal thickening and exhumation began at 12 ma as suggested by a sharp increase of the la yb ratios in the northern segment in the southern segment this event is reflected by only a moderate increase of la yb ratios and by the transition between the coya machali formation and the teniente volcanic complex finally a third stage of exhumation and crustal thickening beginning at 7 ma affected both the northern and southern segments this last stage was the main exhumation event affecting the rocks of the andes of central chile and is recorded in the geochemistry of igneous rocks by a sharp increase in the la yb ratios in the southern segment

initiation of subduction and the generation of slab melts in western and eastern mindanao philippines adakite found in both the eastern and western parts of mindanao island philippines is a rare rock type characterized by low heavy rare earth elements and y contents together with high sr y ratios and is considered to be the result of the melting of young subducted oceanic crust which leaves an eclogite residue pliocene quaternary adakites from western mindanao zamboanga peninsula are probably derived from the melting of the young miocene sulu sea crust which is currently subducting beneath zamboanga associated nb enriched basalts are thought to come from mantle metasomatized through interaction with adakitic melts in eastern mindanao pliocene quaternary cones and plugs of typical adakitic composition mark the trace of the philippine fault in surigao and north davao the underlying philippine sea crust is of eocene age and therefore cannot melt under normal subduction thermal conditions thermal models indicate that melting at the start of subduction can occur subduction of the philippine sea plate began 3 to 4 ma beneath eastern mindanao and probably accounts for the presence of adakites along the philippine fault

marine cements in mid tertiary cool water shelf limestones of new zealand and southern australia large areas of southern australia and new zealand are covered by mid tertiary limestones formed in cool water shelf environments the generally destructive character of sea floor diagenesis in such settings precludes ubiquitous inorganic precipitation of carbonates yet these limestones include occasional units with marine cements 1 within rare in situ biomounds 2 within some stacked cross bedded sand bodies 3 at the top of metre scale subtidal carbonate cycles and 4 most commonly associated with certain unconformities the marine cements are dominated by isopachous rinds of fibrous to bladed spar interstitial homogeneous micrite and interstitial micropeloidal micrite often precipitated sequentially in that order internal sedimentation of microbioclastic micrite may occur at any stage the paradox of marine cemented limestone units in an overall destructive cool water diagenetic regime may be explained by the precipitation of cement as intermediate mg calcite from marine waters undersaturated with respect to aragonite in some of the marine cemented limestones aragonite biomoulds may include marine cement sediment internally suggesting that dissolution of aragonite can at times be wholly marine and not always involve meteoric influences we suggest that marine cementation occurred preferentially but not exclusively during periods of relatively lowered sea level probably glacio eustatically driven in the mid tertiary at times of reduced sea level there was a relative increase in both the temperature and the carbonate saturation state of the shelf waters and the locus of carbonate sedimentation shifted towards formerly deeper shelf sites which now experienced increased swell wave and or tidal energy levels fostering sediment abrasion and reworking reduced sedimentation rates and freer exchange of sediment pore waters energy levels were probably also enhanced by increased upwelling of cold deep waters onto the southern ocean margins of the australasian carbonate platforms where water mass mixing warming and loss of co2 locally maintained critical levels of carbonate saturation for sea floor cement precipitation and promoted the phosphate glauconite mineralization associated with some of the marine cemented limestone units

burial dominated cementation in non tropical carbonates of the oligocene te kuiti group new zealand abstract cementation of bryozoan echinoid benthic foraminiferal temperate shelf carbonates of the oligocene te kuiti group north island new zealand occurred mainly during subsurface burial the calcite cements in the limestones are dominated by equant and syntaxial rim spar which typically becomes ferroan given an iron supply and compared to the skeletal material with normal marine 18o values from 2 to 1 more depleted in 18o with depth of burial the 18o composition of bulk cement samples ranging from 1 to 7 these trends reflect the establishment in pore waters during sediment burial of reducing conditions and gradually increasing temperatures 20 50 c respectively the 13c values 0 to 3 of the cements remain the same as the host marine shells suggesting the source of carbon in the cements was simply redistributed marine carbonate derived from shell dissolution two gradational burial diagenetic environments influenced by marine derived porewaters are arbitrarily distinguished shallow burial phase and moderate burial phase during the shallow burial phase down to 500 600 m sub bottom depth the carbonates lost at least 25 of their original porosity by mechanical compaction and were selectively cemented by non ferroan or usually ferroan variably luminescent slightly 18o depleted sparry calcite cement 18o 2 to 4 mainly as syntaxial rims about echinoid grains these shallow burial cements form less than about 10 of total cement in the majority of the limestones and their source was probably mainly mild intergranular dissolution of calcitic skeletal fragments accompanying the onset of chemical compaction during the moderate burial phase between about 600 and 1100 m sub bottom depth porosity loss continued typically to about 70 of its original value as a result of pressure solution of calcitic bioclasts associated with more advanced stages of chemical compaction this involved development of a wide variety of non sutured and microstylolitic solution seams including both single and composite wispy or continuous bedding parallel types and non parallel reticulate forms the released carbonate was precipitated as ferroan or non ferroan where iron supply was negligible dull luminescent strongly 18o depleted 18o 4 to 7 mainly equant calcite spar cement occluding available pore space in the limestones

large scale porphyry type mineralization in the central asian metallogenic domain a review abstract a series of porphyry type cu mo au deposits including some giant world class deposits such as kounrad aktogai kal makyr oyu tolgoi and chalukou occur in the central asian metallogenic domain camd the outline of the camd almost overlaps with that of the central asian orogenic belt caob which is located between the east europe siberia tarim and north china cratons the camd comprises sparsely exposed tectonic slices of precambrian high grade metamorphic basement rocks that are sandwiched between phanerozoic accretionary complexes and arc rocks according to geological metallogenic geochronological and tectonic setting characteristics the camd comprises three metallogenic provinces 1 the kazakhstan cu au mo 2 the mongolia cu au and 3 the northeast china mo cu metallogenic provinces early paleozoic 490 to 440 ma and late paleozoic 330 to 295 ma large scale porphyry type mineralization in the kazakhstan metallogenic province is intimately associated with the evolution of the central tianshan yili northern tianshan kokchetav chingiz paleozoic arc system which was terminated by the late permian closure of the western segment of the paleo asian ocean in contrast the 370 ma and 240 ma porphyry type mineralization of the mongolia metallogenic province is related to the tuva mongolia arc collage system that was formed during the evolution of the paleo asian ocean in the paleozoic and the mongol okhotsk ocean in the early mesozoic furthermore the northeast china metallogenic province was affected by three distinct geodynamic processes that were associated with the paleo asian mongol okhotsk and paleo pacific oceans during the paleozoic 250 ma the early mesozoic 200 ma and the late mesozoic 200 90 ma respectively except for the early paleozoic cu mineralization at duobaoshan 480 ma and bainaimiao 440 ma the porphyry type mineralization of this metallogenic province is predominantly characterized by widespread mesozoic mo mineralization in general porphyry type deposits of the camd have geological structural metallogenic alteration and fluid characteristics which are consistent either with those related to the oceanic subductional arc settings of the circum pacific metallogenic domain or with those of the continental collisional environment in the tethyan metallogenic domain the involvement of highly oxidized intermediate to felsic magmas is fundamental for the formation of porphyry deposits even though the prevalent mash and slab melting models can be employed to interpret the genesis of some porphyry cu deposits in the camd a here newly suggested model which is based on pre enriched mafic lower crust and the subduction of a relictic mid oceanic ridge is thought to explain the large scale copper mineralization in the balkhash west junggar metallogenic belt of the kazakhstan metallogenic province nevertheless most of the porphyritic suites associated with the mo deposits in the northeast china metallogenic province have relatively depleted mantle like neodymium and hafnium isotopic compositions suggesting that the ore forming granitic magma may have predominantly been derived from juvenile lower crust upwelling of asthenosphere may have triggered the melting of the lower crust during post collisional extension subsequent to the closure of the paleo asian ocean in the triassic the subduction of the paleo pacific ocean in the jurassic and the thinning of the lithosphere caused by rollback of the paleo pacific plate in the cretaceous ancient crustal components were only locally found to have been involved in the magma source of several medium large mo deposits

plate kinematics origin and tectonic emplacement of supra subduction ophiolites in se asia abstract a unique feature of the circum pacific orogenic belts is the occurrence of ophiolitic bodies of various sizes most of which display petrological and geochemical characteristics typical of supra subduction zone oceanic crust in se asia a majority of the ophiolites appear to have originated at convergent margins and specifically in backarc or island arc settings which evolved either along the edge of the sunda eurasia and australian cratons or within the philippine sea plate these ophiolites were later accreted to continental margins during the tertiary because of fast relative plate velocities tectonic regimes at the active margins of these three plates also changed rapidly strain partitioning associated with oblique convergence caused arc trench systems to move further away from the locus of their accretion we distinguish relatively autochthonous ophiolites resulting from the shortening of marginal basins such as the present day south china sea or the coral sea and highly displaced ophiolites developed in oblique convergent margins where they were dismantled transported and locally severely sheared during final docking in peri cratonic mobile belts i e the philippine mobile belt we find a series of oceanic basins which have been slightly deformed and uplifted varying lithologies and geochemical compositions of tectonic units in these basins as well as their age discrepancies suggest important displacements along major wrench faults we have used plate tectonic reconstructions to restore the former backarc basins and island arcs characterized by known petro geochemical data to their original location and their former tectonic settings some of the ophiolites occurring in front of the sunda plate represent supra subduction zone basins formed along the australian craton margin during the mesozoic the philippine sea basin the huatung basin south of taiwan and composite ophiolitic basements of the philippines and halmahera may represent remnants of such marginal basins the portion of the philippine sea plate carrying the taiwan philippine arc and its composite ophiolitic continental crustal basement might have actually originated in a different setting closer to that of the papua new guinea ophiolite and then have been displaced rapidly as a result of shearing associated with fast oblique convergence

regional geochemistry of tertiary igneous rocks in central chile implications for the geodynamic environment of giant porphyry copper and epithermal gold mineralization the giant porphyry copper molybdenum deposits of central chile formed within a thick sequence of cretaceous to pliocene volcanic rocks the predominantly calc alkaline basaltic andesites of the cretaceous las chilcas formation are characterized by la smn ratios of 1 8 to 2 5 and sm ybn of 1 8 to 2 8 the upper oligocene to lower miocene abanico formation variously defined as the los pelambres abanico or coya machali formations ranges from basalt to rhyolite in composition and exhibits a broad southward transition from calc alkaline to tholeiitic all samples from this formation are characterized by lree enrichment and moderately or locally strongly fractionated hree la smn 1 3 4 1 sm ybn 1 5 5 8 the basaltic andesites and andesites of the middle miocene salamanca formation have ree chemistry similar to that of the upper cretaceous strata la smn 1 5 2 7 sm ybn 1 6 2 7 the overlying middle miocene farellones formation ranges from tholeiitic to calc alkaline and from basalt to andesitic and has a similar lree enrichment and fractionated hree la smn 1 7 2 5 sm ybn 1 7 3 3 the pliocene la copa rhyolite complex however is strongly lree enriched and hree depleted la smn 3 8 3 9 sm ybn 4 2 4 7 overall the trace element geochemistry of the cretaceous to middle miocene volcanic rocks is characterized by enriched lree and negative nb anomalies consistent with an arc setting with only minor differences in the abundance of most elements crustal thickening during the miocene in central chile has been suggested to have been responsible for a transition from an amphibole to garnet dominated residual mineralogy resulting in the release of fluids that enabled the formation of giant copper porphyry deposits however the gradual increase in la yb through the early middle and late miocene reported in earlier studies and interpreted to be a response to crustal thickening is not observed in the regional data instead a rapid change in the geochemical signature between the end of the eruption of the farellones formation and the eruption of the high la yb la copa rhyolite complex implies a more abrupt change in the tectonic environment isotopic data broadly support this although lower epsilon nd values in the farellones formation imply a greater role for crustal contamination in younger suites in the absence of gradual crustal thickening it is suggested that the subduction of the juan fernandez ridge may have been the key geodynamic process responsible for the genesis of the three middle miocene to lower pliocene giant porphyry copper deposits in central chile possibly by promoting crustal scale faulting and even acting as a source of metals

evidence for magmatic hydrothermal fluids and ore forming processes in epithermal and porphyry deposits of the baguio district philippines the baguio district contains a diverse array of epithermal porphyry and skarn deposits together with a large broadly strata bound advanced argillic lithocap magmatism mineralization and alteration occurred in response to subduction of the south china sea plate and the scarborough ridge beneath northern luzon over the past 3 m y rapid uplift and exhumation resulted in epithermal veins overprinting several porphyry cu au deposits most of the epithermal au ag deposits of the baguio district including antamok and acupan the two largest au deposits are intermediate sulfidation state quartz carbonate adularia illite base metal sulfide veins that contain electrum and minor au ag tellurides in contrast high sulfidation mineralization at kelly includes enargite tennantite electrum and precious metal tellurides and is associated with advanced argillic alteration although the mineralizing fluids that formed the porphyry and epithermal deposits had distinct temperatures and salinities stable and radiogenic data provide evidence for direct magmatic contributions into each deposit type the epithermal mineralizing fluids were dilute generally 600 c hypersaline brines 30 to 70 wt nacl equiv and low density vapor sulfur isotope compositions of sulfides in the porphyry skarn and intermediate sulfidation epithermal veins of the southern and central baguio district are mostly between 1 and 6 per mil consistent with a predominance of h2s in the mineralizing fluids i e reducing conditions in contrast sulfides from the high sulfidation porphyry and intermediate sulfidation deposits located adjacent to the baguio lithocap mostly have negative sulfur isotope values 6 9 to 0 8 consistent with oxidizing so42 predominant mineralizing fluids intermediate sulfidation epithermal veins at acupan have crosscut a well mineralized porphyry cu au stock work at ampucao the two deposits cannot be distinguished on the basis of radiometric age determinations ampucao 0 51 0 26 ma acupan 0 65 0 07 ma and are interpreted to be cogenetic with telescoping of the two environments caused by the rapid uplift and exhumation associated with ridge subduction measured 34ssulfide 1 1 to 6 6 34ssulfate 10 4 to 31 8 values and initial strontium ratios of anhydrite 0 70378 0 70385 are consistent with identical and predominantly magmatic sources of these components for the ampucao porphyry and acupan epithermal veins helium isotopes provide further evidence of mantle derived components in the epithermal veins r ra values of 6 0 and 6 7 oxygen deuterium and carbon isotopes provide evidence for predominantly magmatic water at ampucao and for hybrid magmatic meteoric waters at acupan that precipitated precious metals due to boiling the proportion of magmatic water relative to meteoric water and precious metal grades both decreased with time during epithermal vein formation at acupan the common observation of cross cutting relationships between porphyry and epithermal veins observed throughout the baguio district imply that the evolution of porphyry style to intermediate sulfidation style mineralization was a common phenomenon in this region and contributed significantly to its rich metal endowment

trace element geochemistry of enargite in the mankayan district philippines we report the first laser ablation inductively coupled plasma mass spectroscopy la icp ms study of trace element substitution in enargite results indicate significant variability in the composition of enargite samples from a single ore system samples come from the mankayan district philippines which hosts the lepanto high sulfidation cu au deposit now mined out and the adjacent far southeast porphyry cu au deposit the genetic relationship between these deposits has been documented in previous studies la icp ms analyses indicate significant incorporation of sb and fe in enargite locally exceeding 1 wt other elements such as bi sn se te ag and zn occur at concentrations exceeding 0 1 wt percent the distribution of selected trace elements in enargite correlates with previously published variations in fluid inclusion homogenization and melting temperatures and gas compositions the spatial distribution of data indicates enargite is enriched in au and te close to the far southeast porphyry enargite is enriched in silver fe and pb in the center of lepanto and zn cd is enrich the ore distal to the far southeast porphyry locally elevated sb contents occur in samples from subsidiary branch vein structures and may indicate that mineralizing fluids along these structures were modified compared to those that formed the main orebody

dupuit ghyben herzberg analysis of strip island lenses dupuit ghyben herzberg analysis follows from combination of the continuity equation and darcy s law with the ghyben herzberg principle and the dupuit assumptions of horizontal flow the analysis is used to derive the position of the water table and salt water interface in island lenses in terms of island geometry distribution of hydraulic conductivity k and distribution of recharge r for small islands and cases for which the salt water head is zero application of dupuit ghyben herzberg analysis gives good results because the low r k ratios of natural lenses assure that height width ratios of natural lenses are extremely low 1 30 to 1 100 in earlier publications the dupuit ghyben herzberg differential equation has been integrated with the boundary condition that the water table and interface meet at sea level at the shoreline that is no outflow face the dimensions of an outflow face however are known from results of potential theory analysis integration of the dupuit ghyben herzberg equation with a boundary condition consistent with the potential theory outflow face a places the interface indistinguishably close to its position given by potential theory and b allows calculation of ghyben herzberg ratios interface depth to water table elevation which in this case depart from their usual value of 40 because equipotentials are curved close to the outflow face for natural sized lenses however such analysis is necessary only within a narrow strip within 1 to 5 of the island width of the shoreline outside this strip the regular analysis that ignores the presence of the outflow face positions the interface indistinguishably close to that of the potential theory solution analytical solutions are developed for a number of infinite strip islands it is shown by analysis of the homogeneous rectangular island case that an island can be considered an infinite strip to 0 1 accuracy if its length width ratio is larger than 4 4 asymmetric lenses occur if the island is composed of strips of different k or different r with the greater asymmetry occurring with differences in k a high k basement compresses the root of the lens and thereby decreases the water table in the island a lens perched on impermeable basement has a higher water table than would otherwise occur in the island but the volume of the lens is less

controls of facies and sediment composition on the diagenetic pathway of shallow water heterozoan carbonates the oligocene of the maltese islands relatively few studies have so far addressed diagenetic processes in heterozoan carbonates and the role that sediment composition and depositional facies exert over diagenetic pathways this paper presents a study of oligocene shallow water heterozoan carbonates from the maltese islands we investigate stratigraphic distribution abundance and timing of diagenetic features and their relationship to sediment composition and depositional facies the studied carbonate rocks comprise rud to packstones of the heterozoan association predominantly containing coralline red algae bryozoans echinoids and benthic foraminifers xrd analyses show that all high mg calcite has been transformed to low mg calcite and that no aragonite is preserved diagenetic processes include dissolution of aragonitic biota neomorphism of high mg calcitic biota to low mg calcite and cementation by fibrous bladed epitaxial and blocky cements stable isotopes on bulk rock integrated with petrographic data suggest that the study interval was not exposed to significant meteoric diagenesis we interpret early cementation to have taken place in the marine and marine burial environment the distribution and abundance of early diagenetic features determining the diagenetic pathway can be related to the primary sediment composition and depositional texture sorting and micrite content are important controls over the abundance of diagenetic features

regional cementation from unconformity recharged aquifer and burial fluids mississippian newman limestone kentucky abstract the mississippian newman limestone in kentucky was studied to assess the effects of unconformities within and above the sequence on calcite cementation early cements are low in fe and show a nonluminescent to dull to nonluminescent zonation early nonluminescent cement mainly formed in updip areas from oxidizing meteoric waters in a regional paleoaquifer that formed during regional regression in the late mississippian during late mississippian transgression waters became reducing to form early dull cement up to 600 ppm mn up to 2 700 ppm fe but averaging 570 ppm the aquifer underwent later recharge during mississippian pennsylvanian regression to form a second nonluminescent cement this event continued into the pennsylvanian when the sequence underwent increasing burial earl cements have 13o values that become lighter downdip perhaps reflecting a downdip temperature increase due to burial 13c values are lightest in the north postulated recharge area and reflect input of organically derived co2 in waters there most calcite cementation appears to have been associated with two post newman unconformities which generated regional aquifers and reflects a shift to a wetter climate in late mississippian pennsylvanian time early cement abundance decreases away from postulated recharge areas later iron rich burial cements up to 2 200 ppm mn up to 11 000 ppm fe fill remaining pore spaces compaction induced fractures spalled cement rims and tectonic fractures lined with saddle dolomite and pyrite they formed above 60 c at depths of 1 to 3 km 13o values are compatible with derivation by pressure solution of preexisting calcites in isotopically heavy waters highly modified by burial diagenesis light 13c values reflect isotopically light organic carbon in the deltaic waters entering the subsurface or being expelled from shales or buffering of waters by light c early calcite cements the 13c calcite cements become heavier downdip by equilibration of waters with host limestone newman sediments may have been subjected to late postcementation migration of warm fluids based on secondary fluid inclusions these late stage fluids most likely were chemically complex warm brines 7 17 equiv wt naci 50 to 160 c that resided in the formation for sufficiently short times that conodont cai values were not affected

diagenetic alterations in temperate shelf carbonates from southeastern australia abstract temperate shelf carbonates form in cool marine waters and have skeletal and mineralogical compositions which are different from their tropical counterparts they commonly lack non skeletal grains and are often composed of low and high magnesium calcite with subordinate aragonite many of the aragonitic components found in tropical carbonates such as corals ooids blue green algae and lime mud are absent temperate shelf carbonates undergo diagenesis in marine waters with lower carbonate saturation than do tropical carbonates and are exposed to cool climates with moderate to low rainfall marine cementation is rare because of low carbonate saturations in the surrounding waters however aragonite and high magnesium calcite cements have been reported forming under specialized conditions associated with biogenic precipitation submarine methane and sulphate reducing bacteria and more commonly in the intertidal environment where evaporation has increased carbonate concentrations in pleistocene and tertiary temperate shelf carbonates from southeastern australia evidence of marine diagenesis is rare to absent diagenetic stabilization of aragonite and high magnesium calcite has taken from 80 000 y to 1 my or longer during subaerial exposure this is slower than rates reported from tropical climates a general lack of aragonite in some facies within these temperate carbonates leads to a lack of secondary porosity and only sparse low magnesium calcite cement even after prolonged fresh water diagenesis however with lengthy exposure and under the right climatic conditions karstic solution and calcrete precipitation can occur in sequences containing siliciclastic clays pyrite and glauconite abundant iron is present in interstitial waters leading to the precipitation of ferroan calcite cements in the phreatic and shallow burial environments and to the substitution of iron for magnesium in stabilizing high magnesium calcite skeletal material a unique void filling micritic internal sediment occurs in discrete layers in many of the tertiary temperate shelf carbonate sequences in southeastern australia this internal sediment is localized as a pore filling material above permeability barriers such as fine grained sediments or volcanics and above paleo water tables which formed during periods of subaerial exposure it is a feature of the vadose zone and lithifies to form a dense micritic low magnesium calcite cement with characteristic pink brown coloration often associated with erosion surfaces and nodule beds dolomite is uncommon in the southeastern australian temperate shelf carbonates it forms associated with preferential fluid pathways or mixing zones ferroan dolomite forms in siliciclastic clay rich carbonates in the shallow burial environment the ubiquitous fine evaporite related dolomite so common in tropical carbonates is absent

the diagenesis of the late dinantian derbyshire east midland carbonate shelf central england carbonate cements in late dinantian asbian and brigantian limestones of the derbyshire carbonate platform record a diagenetic history starting with early vadose meteoric cementation and finishing with burial and localized mineral and oil emplacement the sequence is documented using cement petrography cathodoluminescence trace element geochemistry and c and o isotopes the earliest cements pre zone 1 are locally developed non luminescent brown sparry calcite below intrastratal palaeokarsts and calcretes they contain negligible fe mn and sr but up to 1000 ppm mg their isotopic compositions centre around 18o 8 5 13c 5 0 calcretes contain less 13c subsequent cements are widespread as inclusion free low mg low fe crinoid overgrowths and are described as having a dead bright dull cathodoluminescence the dead cements zone 1 are mostly non luminescent but contain dissolution hiatuses overlain by finely detailed bright subzones that correlate over several kilometres across dead bright subzones there is a clear trend in mg 500 900 ppm mn 100 450 ppm and fe 80 230 ppm zone 1 cements have isotopic compositions centred around 18o 8 0 and 13c 2 5 zone 2 cement is bright thin and complexly subzoned it is geochemically similar to bright subzones of zone 1 cements dull zone 3 cement pre dates pressure dissolution and fills 70 or more of the pore space it generally contains little mn fe and sr but can have more than 1000 ppm mg increasing stratigraphically upwards the 18o compositions range from 5 5 to 15 and the 13c range is 1 to 3 20 00 zone 4 fills veins and stylolite seams in addition to pores it is synchronous with pb ba f ore mineralization and oil migration zone 4 is ferroan with around 500 ppm fe up to 2500 ppm mg and up to 1500 ppm mn isotopic compositions range widely 15o 2 7 to 9 and 13c 3 8 to 2 50 unaltered marine brachiopods suggest a dinantian seawater composition around 15o 0 smow but vital isotopic effects probably mask the original 13c pdb value pre zone 1 calcites are meteoric vadose cements with light soil derived 13c and light meteoric 18o an unusually fractionated pluvial 15o smow value of around 6 is indicated for local dinantian meteoric water calcrete 18o values are heavier through evaporation zone 1 textures and geochemistry indicate a meteoric phreatic environment fe and mn trends in the bright subzones indicate stagnation and precipitation occurred in increments from widespread cyclically developed shallow meteoric water bodies meteoric alteration of the rock body was pervasive by the end of zone 1 with a general resetting of isotopic values zone 3 is volumetrically important and external sources of water and carbonate are required emplacement was during the namurian early westphalian by meteoric water sourced at a karst landscape on the uplifted eastern edge of the derbyshire east midland shelf the light 18o values mainly reflect burial temperatures and an unusually high local heat flow but an input of highly fractionated hinterland derived meteoric water at the unconformity is also likely relatively heavy 13c values reflect the less altered state of the source carbonate and aquifer zone 4 is partly vein fed and spans burial down to 2000 m and the onset of tectonism light organic matter derived 13c and heavy 18o values suggest basin derived formation water combined with textural evidence of geopressures this relates to local high temperature ore mineralization and oil migration low water to rock ratios with host rock buffering probably affected the final isotopic compositions of zone 4 masking extremes both of temperature and organic matter derived co2

stratigraphic sedimentology of tertiary cool water limestones se australia abstract mid tertiary limestones exposed as sea cliffs along the coast of victoria southeastern australia accumulated on the inner part of a cool water distally steepened ramp or open shelf all sediments are bioclastic dominated by particles of bryozoans echinoderms benthic foraminifers brachiopods and molluscs shallow grainy facies also contain coralline algae quartz and glauconite while deep muddy facies include ahermatypic corals ostracodes sponge spicules planktic foraminifers and terrigenous clays the fundamental depositional unit is a meter scale subtidal cycle or rhythm shallow shelf cycles are shallowing upward cross bedded or burrowed grainstone capped by a marine cemented hardground or quartz granule lag while mid shelf cycles are upward coarsening and thickening proximal to distal tempestites such cycles are interpreted to form by eustatically driven climatically controlled oscillations in abrasion wave base and swell wave base deep shelf rhythms are interbedded bryozoan marl and calcareous clay thought to be generated by climatically influenced fluctuations in carbonate productivity and terrigenous dilution lowstand systems tracts are depositional or erosional sequence boundaries are complex multigeneration mostly submarine surfaces condensed cycle boundaries that can be traced offshore into multiple omission surfaces and conformable contacts basinward facies shifts result in deposition of condensed lowstand wedges of stacked shallowing upward grainstone cycles transgressive systems tracts are thick bryozoan marl calcareous clay rhythms associated with facies backstepping and abrupt deepening such rhythmites typically grade stratigraphically upward into tempestite cycles highstand systems tracts are highly progradational wedge shaped rock bodies of shallowing upward grainy cycles these limestones provide the critical link of stratigraphy between modern cool water carbonate shelf deposits and the older mesozoic and paleozoic record of similar sediments

lowstand carbonates highstand sandstones the sedimentary facies sediment dynamics and sequence architecture of modern high energy shelves in the mid and high latitudes are largely governed by wave abrasion processes cool water carbonates may form there if the influx and or net accretion of siliciclastics is kept at a minimum little dilution of the carbonate produced in situ is generally promoted by a wide epicontinental shelf subdued topography of the adjacent mainland the predominance of limestone outcrops and an arid climate the aforementioned requirements are rarely met and thus will automatically lead to the formation of mixed siliciclastic cool water carbonates such an example is found in the early to mid miocene lagos portimao formation algarve s portugal which formed on a narrow high energy shelf of the atlantic ocean that was bounded by a mountain range the sediments of the formation consist of fossiliferous sandstone fs shell beds and rhodolith blankets along strike the stratification of the formation is monotonous for tens of kilometres and well exposed in coastal cliffs whereas no outcrops of dip sections exist the bulk skeletal composition of the sediments is typical for the warm temperate climatic zone various endo and epibenthic bivalves bryozoans coralline algae echinoderms gastropods and large foraminifers heterostegina in some very rare beds a few isolated not framework forming specimens of zooxanthellate corals porites tarbellastrea indicate temporally elevated surface water temperatures close to the lower threshold of the coral reef ecosystem in sandstones the fauna is well preserved and burrowing bivalves are commonly found in life position in limestone beds the state of preservation of the grains ranges from intact to disintegrated and abraded specimens we infer an accumulation of the shell beds through winnowing of fine materials siliciclastic sand and carbonate mud at wave abrasion depth and concentration of calcareous skeletons associated with the subsequent attraction of new epibiota in a complex shell bed the vertical alternation of fossiliferous sandstone and shell beds and in phase variations of the photo index photic biota vs bryozoans and bryozoan index bivalves vs bryozoans is envisaged to document variations of water depth and sea level sandstone units built up when wave abrasion depth wad rose above the sea floor during tst and early hst whereas the shell beds formed during lst when the wad for sand intersected with the sea floor clastic sediments were probably brought on the outer shelf during early transgression and by longshore currents sea level signatures inferred in the mixed siliciclastic cool water carbonate shelf setting of s portugal therefore significantly deviate from conventional concepts of carbonate sequence stratigraphy which were developed for flat topped platforms successful interpretations of ancient mixed sequences must therefore take into consideration the processes of production concentration and accretion of the carbonate sediments

the trace metal chemistry of deep geothermal water palinpinon geothermal field negros island philippines implications for precious metal deposition in epithermal gold deposits palinpinon geothermal field negros island philippines is a high temperature liquid dominated geothermal system in an active volcanic island arc setting parallels have been drawn between the geologic setting and hydrothermal alteration styles recognized at palinpinon with those that characterize several types of magmatichydrothermal ore deposits e g porphyry skarn and high and intermediate sulfidation epithermal systems the neutral chloride palinpinon reservoir water chemistry is affected by boiling mixing and conductive cooling the occurrence of base and precious metal scale deposits in several geothermal wells demonstrates that the deep reservoir fluid is capable of transporting and depositing base and precious metals however trace metal analysis of the deep reservoir fluids shows they are undersaturated with respect to gold 1 4 ig kg chemical modeling of palinpinon geothermal water predicts that boiling should be the most effective mechanism for base and precious metal deposition producing sulfide assemblages similar to those present in well scale deposits mixing with acid bearing sulfate waters can also produce these sulfide assemblages but less efficiently and with gold and silver deposition occurring at lower temperatures i e 110 c despite indications that modern hydrothermal fluids are capable of metal transportation base and precious metal deposition is not strongly developed at palinpinon base and precious metal concentrations in drill core and drill cuttings are one to two orders of magnitude below ore grade 0 02 wt cu 0 03 wt pb 0 01 wt zn 0 01 wt mo 8 g t ag and 0 05 g t au and important features that characterize high grade ore zones of porphyry i e quartz stockwork veining and epithermal deposits i e residual vuggy quartz massive crustiform veins and or hydrothermal breccia complexes are apparently absent at palinpinon such features intimate that high grade ore deposition is promoted by large volumes of fluid and highly permeable wall rock their absence at palinpinon indicates that permeability fluid flux and or metal transport have been insufficient to form significant zones of base or precious metal enrichment

barnacle dominated limestone with giant cross beds in a non tropical tide swept pliocene forearc seaway hawke s bay new zealand abstract pliocene non tropical widespread and locally thick up to 100 m limestones occur in hawke s bay eastern north island where they are intimately associated with very thick 5 km terrigenous dominated neogene sequences that formed in a tectonically active convergent margin setting the non tropical character of the limestones is shown unequivocally by 1 the complete dominance of skeletal calcarenites and calcirudites 2 the occurrence of oyster banks as the only in situ organic structures 3 the dominance of barnacles epifaunal molluscs bryozoans echinoderms foraminifers brachiopods and calcareous red algae as skeletal components and 4 the preponderance of calcite over aragonite in the mineralogy of the skeletal grains and cements the abundance of barnacle fragments in the limestones and the related exclusive occurrence of only one major organic association a barnacle epifaunal bivalve bryozoan assemblage is striking and unusual given the extent of the limestones pecten and oyster valves acted as substrates for barnacle attachment and their growth was promoted by strong tidal paleocurrents that swept the depositional setting a long 450 km narrow 30 50 km forearc basin seaway which formed between an actively deforming subduction complex to the east and an uplifting structural ridge to the west synsedimentary deformation promoted limestone formation on the margins of the seaway by creating current swept clastic free submarine ridges that acted as the sites of carbonate production tidal flows dispersed the carbonate constituents and organised them into a wide spectrum of tide influenced cross bedded and horizontal structures most spectacular are occurrences of giant tabular cross beds with sets 10 40 m thick and foreset dips of 7 36 some interpreted as the deposits of major sand bars on carbonate deltas marginal to the mouths of saddles traversing the rising antiforms and others analogous to modern linear sand ridges the small to large scale planar and trough cross beds and the horizontal and lenticular beds that are invariably associated with the giant cross beds and dominate most sections represent mainly the deposits of sand waves and sand sheets at inner to mid shelf depths in the seaway

repeated crustal thickening and recycling during the andean orogeny in north chile 21 26 s posttectonic granitoids 2 lower crustal p wave velocities of 7 3 7 7 km s 1 compatible with underplated mafic crust and 3 results from recent experimental petrologic work showing garnet stability in mafic mineralogies 12 kbar 40 km crustal thickness analogous to older andean magmatic episodes in north chile newly underplated basaltic crust may account for the remaining deficit in neogene crustal thickening similar evolutionary patterns in geochemistry and initial sr and nd isotopic characteristics of andean 200 ma to present magmatic rocks suggest that the andean orogeny in this region evolved by a combination of processes of repeated arc migration tectonic and magmatic crustal thickening and igneous recycling which was controlled by periodically changing plate convergence rates and obliquity and corresponding changes in the rheologic behavior of the continental crust index terms 1020 geochemistry composition of the crust 1030 geochemistry geochemical cycles 0330 8159 evolution of the earth rheology crust and lithosphere 9360 information related to geographic region south america keywords andean orogeny continental crust recycling adakite ttg crustal thickening

age and geochemistry of host rocks of the cobre panama porphyry cu au deposit central panama implications for the paleogene evolution of the panamanian magmatic arc abstract the cobre panama porphyry cu au deposit located in the petaquilla district of central panama is hosted by a sequence of medium to high k calc alkaline volcanic and sub volcanic rocks new crystallisation ages obtained from a granodiorite petaquilla batholith and associated mineralised diorite to granodiorite porphyry stocks and dikes at cobre panama indicate that the batholith was emplaced as a multi phase intrusion over a period of 4 million years from 32 20 0 76 ma to 28 26 0 61 ma while the porphyritic rocks were emplaced over a 2 million year period from 28 96 0 62 ma to 27 48 0 68 ma both the volcanic to sub volcanic host rocks and intrusive rocks of the cobre panama deposit evolved via fractional crystallisation processes as demonstrated by the major elements e g al2o3 fe2o3 tio2 and mgo displaying negative trends with increasing sio2 the petaquilla intrusive rocks including the diorite granodiorite porphyries and granodiorite batholith are geochemically evolved and appear to have formed from more hydrous magmas than the preceding host volcanic rocks as evidenced by the presence of hornblende phenocrysts higher degrees of large ion lithophile element lile and light rare earth element lree enrichment and heavy rare earth element hree depletion and higher sr y and la yb values however the degree of lree enrichment hree depletion and la yb values are insufficient for the intrusive rocks to be considered as adakites collectively the volcanic and intrusive rocks have lile ree and mobile trace element concentrations similar to enriched miocene age cordilleran arc magmatism found throughout central and western panama both the petaquilla and cordilleran arc magmatic suites are geochemically more evolved than the late cretaceous to eocene chagres bayano arc magmas from northeastern panama as they display higher degrees of lile and lree enrichment the geochemical similarities between the petaquilla and cordilleran arc magmas suggest that evolved calc alkaline arc magmatism may extend to the late eocene at least 10 million years earlier than previously estimated the crystallisation ages for intrusive rocks associated with mineralisation at cobre panama imply that the deposit formed in the early oligocene between a period of late cretaceous to eocene magmatism ca 66 42 ma chagres bayano arc and cordilleran arc magmatism 22 7 ma similarities in the timing of intrusive suite emplacement and the fingerprinting of magmatic fractionation processes between the cobre panama porphyry deposit and the cerro colorado porphyry deposit in western panama ca 5 3 ma suggest that these features provide favourable geodynamic and geochemical prerequisites for the formation of porphyry deposits along the panamanian magmatic arc during the cenozoic

the nature of magmatism at palinpinon geothermal field negros island philippines implications for geothermal activity and regional tectonics the palinpinon geothermal field negros island philippines is a high temperature liquid dominated geothermal system in an active island arc volcanic setting this paper presents a regional context for the palinpinon geology discusses the petrogenetic evolution of magmatism in the district and assesses the genetic relationships between intrusion and geothermal circulation the oldest rock formation the lower puhagan volcanic formation middle miocene is part of a volcanic sequence that is traceable throughout the visayas region and is related to subduction of the sulu sea oceanic basin in a southeasterly direction beneath the sulu arc late miocene to early pliocene times mark a period of regional subsidence and marine sedimentation a thick sequence of calcareous sediments okoy formation was deposited during this period magmatism in early pliocene to recent times coincided with commencement of subduction at the negros sulu arc this produced basaltic andesites and andesites belonging to the southern negros and cuernos volcanic formations during this time the puhagan dikes and the nasuji pluton intruded middle miocene late miocene and early late pliocene formations based on radiogenic 40ar 39ar dating of hornblende the puhagan dikes are 4 1 4 2 ma and the nasuji pluton 0 3 0 7 ma this age difference confirms these intrusions are not genetically related the early pliocene age of the puhagan dikes also confirms they are not the heat source for the current geothermal system and that a much younger intrusion is situated beyond drill depths igneous rock formations in southern negros are the products of regional island arc magmatism with medium k calcalkaline basaltic to dacitic compositions their adakitic affinity implies that the melting of subducted oceanic basalt has influenced magmatism in this region considering the regional tectonic history the most likely scenarios for the generation of slab melts are 1 during the middle miocene by the melting of relatively young less than 20 ma oceanic crust 2 during early pliocene times by the initiation of subduction along the negros sulu trench and 3 during late pliocene times by the melting of young less than 10 20 ma oceanic crust the adakitic composition of the magmas at palinpinon has promoted the formation of a porphyry copper style magmatic hydrothermal system that is comparable to mineralised porphyry deposits elsewhere in the philippines

petrogenetic constraints on magma fertility in the baguio mineral district philippines probing the mineralization potential of the igneous host rocks in the sangilo epithermal deposit abstract in the baguio mineral district bmd porphyry cu au deposition and associated epithermal mineralization are attributed to the highly evolved magmatism during the pliocene it has been well documented that the interaction between silicic crustal melts and primitive mantle melts formed water rich oxidized magmas that resulted to hydrothermal mineralization however there are very few studies on the early to middle miocene calc alkaline magmatism which is considered to be barren of mineralization this magmatic event is represented by phases of the central cordillera diorite complex ccdc which also serve as host rocks to the sangilo epithermal deposit the sangilo quartz carbonate veins in the bmd are hosted by an early miocene hornblende diorite 22 33 0 63 ma intruded by a middle miocene quartz diorite 15 91 0 6 ma which are in turn penetrated by pliocene basaltic andesite dikes the miocene magmatic units with hybrid crust mantle source affinity were formed from varying degrees of interaction within the mash mixing assimilation storage and homogenization zone during the formation of the ccdc the basaltic andesite dikes part of the pliocene mafic dike complex represent direct differentiates of basaltic melts that experienced ponding at the base of the lower crust before ascending to shallow crustal levels based on the assessment of the physico chemical conditions three distinct magmatic events were identified a barren early miocene event a fertile middle miocene event and a fertile pliocene event the middle miocene fertile magmatism is attributed to further development of the mash zone under the luzon arc from the early to middle miocene on the other hand the enhanced fertility during the pliocene is associated with the subduction of the scarborough ridge

magma mixing origin for the aolunhua porphyry related to mo cu mineralization eastern central asian orogenic belt abstract many cu mo au deposits are considered to be related to adakitic porphyries formed in non arc settings e g in collisional orogenic zones and intra plate environments but their genesis is still under discussion the aolunhua porphyry complex and its related mo cu deposit from the eastern central asian orogenic belt caob provide important insights into this issue the porphyries are characterized by high sr 496 705 ppm and sr y and la yb ratios similar to those of typical adakitic rocks and low i sr ratios 0 7049 0 7052 and positive e nd t 0 5 to 1 4 and e hf t 3 5 to 9 8 values these features along with the occurrence of mafic microgranular enclaves mmes compositional and textural disequilibrium of plagioclase phenocrysts and relatively high mg values 45 52 indicate that they were derived from mixing of felsic magma from partial melting of a juvenile arc type lower crust and mafic magma from a lithospheric mantle previously metasomatized by subduction zone fluids melts high sr y and la yb ratios are indicative of contribution from enriched mantle derived materials with high liles e g sr la which were strengthened by subsequent fractionation of ferromagnesian phases such as pyroxene and hornblende mmes hosted by the ore bearing porphyry have zircon u pb ages of ca 132 ma similar to those of the host rocks the enclaves have elevated mg 56 63 liles e g sr 660 891 ppm lree la n 68 150 la sm n 3 0 4 0 la yb n 12 0 19 6 and ratios of radiogenic isotopes of nd and hf e nd 0 7 to 1 6 e hf 3 3 to 10 9 suggesting that their parental magmas were derived from the metasomatized mantle source the mo cu mineralization was probably related to the high water content high oxygen and sulfur fugacity of hybrid magma formation of the adakitic porphyries and related mo cu deposits of the eastern caob could be related to the early cretaceous lithospheric extension caused by the subduction of the paleo pacific plate and its induced reactivation of juvenile arc type lower crust

synsedimentary cemented calcarenite layers in oligo miocene cool water shelf limestones eucla platform southern australia abstract the abrakurrie limestone is a bryozoan rich cool water open shelf unit of oligocene middle miocene age beneath the nullarbor plain the sediments have been in the meteoric diagenetic environment never buried more than a few hundred meters since middle miocene time the unit is composed of meter scale subtidal cycles each of which is capped by an erosion surface the upper several centimeters of most cycles are well lithified forming distinctive hard layers in otherwise friable carbonates intergranular cements in these layers are now isopachous rinds of low magnesium calcite crystals are inclusion rich generally fibrous and have a speckled cathodoluminescence signature cements in intergranular pores at the tops of cycles are overlain by interstitial marine sediment the cem nts are interpreted to have been marine precipitates in the form of magnesium calcite originally containing from 8 12 mole mgco3 and having a 18o value of 1 0 0 5 versus pdb stable carbon and oxygen isotope values in these interpreted marine hardgrounds are distinctly more positive than values from underlying soft sediments reflecting alteration under lower water rock ratio conditions due to reduced permeabilities covariance in stable isotope values from different localities suggests diagenesis in groundwaters of mixed composition fluid inclusions indicate neomorphism in fluids with salinities equal to or slightly greater than seawater alteration is envisaged to have taken place in a paleogroundwater system of variably mixed saline continental waters and seawater occurrence of similar to identical cemented layers and cements in coeval cool water new zealand shelf carbonates suggests that such cementation was a sporadic but widespread phenomenon on mid cenozoic platforms in this area by inference cool water carbonates of all ages may contain units lithified on the seafloor by cements containing low to intermediate amounts of magnesium cool water is not an inhibitor to synsedimentary cementation

trace element and isotope geochemistry of zoned calcite cements lake valley formation mississippian new mexico insights from water rock interaction modelling abstract regionally extensive pre pennsylvanian meteoric zoned calcite cements from the mississippian age lake valley formation new mexico comprise three major zones zones 1 2 and 3 each with a distinct isotope and trace element geochemistry zone 1 has the highest mg 18o and 13c contents zone 2 intermediate values and greatest mn and fe and zone 3 has the lowest trace element 18o and 13c values covariation of c and o isotopes for the three zones define an inverted l shaped trend and covariations of mg mn and mg fe define l shaped trends all suggestive of rock evolution curves resulting from water rock interaction these covariant trends were the impetus for quantitative mass balance modelling of water rock interaction iterative mass balance modelling of covariations of stable isotopes c and o and trace elements mg mn fe of these zoned cements implies that water rock interaction progressively decreased water rock ratios increased during precipitation cementing waters for the oldest cement zone zone 1 resulted from water rock ratios in the range of tens to a few hundred whereas the youngest cement zone 3 resulted from water rock ratios in the 100 s to 1000 s the modelling also implies that differences in geochemistry of the cement zones cannot be explained solely by changes in water rock ratios but require greater 18o and greater ca and mg concentrations in input waters that evolved to zone 1 precipitational waters than those for zones 2 and 3 zones 2 and 3 can reasonably be modelled using input waters with the same isotopic compositions the same ca concentration and for some zone 2 cement the same mg concentrations the minimum mg ca ratios in input waters is constrained by the lower mg plateau in mg mn space and is about the same for all three zones about 1 25 the maximum mg ca ratios about 1 20 occurred in zone 2 input waters mn fe covariations also show an l shaped trend a trend whch fits neither a simple water rock interaction model nor a simple eh model a model is proposed in which eh and limited mn sources determine the amount of fe and mn available in solution to partake in water rock interaction water rock interaction modelling provides one useful approach to quantitatively interpreting isotopic and trace element data from diagenetic carbonates to gain a clearer understanding of evolution of diagenetic fluids

retrodeformation analysis of the quaternary fault in the southeastern korean peninsula abstract the suryum fault f1 with subsidiary branches f2 3 varies in strike from n40 e to n14 e and in dip from

sequence stratigraphic context of syndepositional diagenesis in cool water shelf carbonates pliocene limestones new zealand abstract pliocene limestones in eastern north island new zealand are cool water deposits composed of barnacle epifaunal bivalve bryozoan dominated calcitic biota formed in shoal areas about the margins of a tectonically active forearc basin seaway vertical changes in the thickness and depositional facies of the limestones and fundamentally the position and nature of internal bounding discontinuities within them have enabled identification of high order likely 41 ka transgressive deepening upwards and transgressive regressive deepening then shallowing upwards sequences within the formations syndepositional or sea floor or pre compaction diagenesis in the limestones involves a spectrum of destructive to constructive features including skeletal abrasion bioerosion encrustation dissolution and cementation upward changes in the type and extent of these pre compaction diagenetic features within the discontinuity bounded sequences relate closely to the stacking patterns of depositional facies and their associated skeletal and mineralogical composition consequently it has been possible to develop a series of predictive diagenetic models for cool water shelf carbonates deposited upon and about upthrust antiforms in the forearc that integrate their patterns of syndepositional diagenesis into a sequence stratigraphy based framework driven ultimately by relative sea level changes marine constructive diagenesis characterized by bioencrustation turbid cements and interstratified internal sediments occurs most commonly in those facies close to the sequence bounding discontinuities within the lower levels of transgressive systems tracts tsts and the uppermost levels of regressive systems tracts rsts these sediments equate to the highest energy facies upon antiform tops close to the wave abrasion base where sedimentation rates were low in contrast destructive diagenetic processes typically dominate over constructive ones often exclusively so in the upper part of tsts in highstand systems tracts hsts and in the lower portion of rst carbonates where the sediments were not so influenced by active fluid circulation or strong reworking for prolonged periods but were more rapidly buried within accommodation traps below wave abrasion base about the antiforms the link between the facies motifs and synsedimentary diagenesis in these cool water pliocene limestones helps unlock their otherwise often cryptic high order sedimentary architecture such an interpretive opportunity is not afforded by the subsequent post compaction diagenetic features in the limestones because these are no longer closely related to the sedimentation realm

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

mesozoic porphyry cu au mineralization and associated adakite like magmatism in the philippines insights from the giant atlas deposit the atlas porphyry cu au deposit is located in central cebu island in the philippines with a proven mineral reserve of 1420 mt at 0 45 cu 0 24 g t au 0 018 g t mo and 1 8 g t ag it is associated with the lutopan quartz diorite porphyry stock that was emplaced into the cretaceous volcano sedimentary sequences of the cansi formation two stages of hypogene alteration have been identified at atlas stage i quartz magnetite chalcopyrite pyrite veins associated with potassic and propylitic alteration and stage ii anhydrite pyrite chalcopyrite specularite veins associated with phyllic alteration supergene gypsum veins are also present mineralization is mainly associated with the stage i and stage ii veins the lutopan quartz diorite porphyry yielded a zircon u pb age of 108 5 1 6 ma and is characterized by high sr y 54 69 with the corresponding magma having high oxygen fugacity avg fmq 2 7 avg ce4 ce3 of zircon 439 and h2o concentrations presence of amphibole and biotite phenocrysts and low magmatic temperatures avg ti in zircon thermometry 706 c the relatively low la yb ratios 9 11 listric shaped normalized ree patterns with weak or absent eu anomalies together with zircon ehf t values of 3 4 to 10 0 whole rock isr values of 0 70373 0 70382 end t values of 2 4 3 4 and mg numbers of 49 53 suggest that the lutopan quartz diorite porphyry was likely derived from partial melting of young lower continental crust or interaction between asthenospheric melts and lower crust melts that evolved to adakite like trace element compositions through amphibole fractionation stage i veins yielded a pyrite re os isochron age of 110 2 5 6 ma making atlas the only mesozoic porphyry deposit discovered in the philippines

non tropical carbonate deposits on the modern new zealand shelf abstract extensive ca 50 000 km 2 shallow marine platforms 70 caco 3 despite proximity to a tectonically active plate margin in these regions the terrigenous sediment supply is presently low and growth of epibenthos is fostered by firm substrates rock gravels shells seaweeds and the generally energetic nature and high nutrient levels of open shelf waters rapid transition into adjacent terrigenous dominated facies is characteristic irrespective of water depth the carbonates are coarse grained and fragmental carbonate mud is rare calcite dominates over aragonite high mg calcite widespread off northern new zealand is rare in the south skeletal material is dominated by bryozoans and bivalve molluscs with significant local contributions from foraminifers barnacles calcareous red algae and echinoderms the name bryomol is suggested for this distinctive temperate region skeletal carbonate facies which can be usefully subdivided based on dominant zoarial growth forms of the bryozoan component known to be habitat related bioerosion is an important mechanism of skeletal fragmentation and degradation many grains especially aragontic bivalves are infested by endolithic borers and have low preservation potential ages of skeletal material in the surficial deposits range from more than 20 000 years b p to modern which is consistent with both low rates of carbonate production and sediment accumulation and the wide range in preservation state of grains some data suggest that the skeletal carbonates are dispersed and mixed mainly during infrequent movement of sand ribbons sand waves and sand sheets driven by storm assisted tidal flows tracts of modern palimpsest and relict carbonates can occur in juxtaposition the facies characteristics of the new zealand shelf carbonate deposits contrast significantly with those of the classical bahaman type carbonate model however they are similar to those reported from many other mid to high latitude carbonate shelves and afford good analogues for most onland occurrences of new zealand cenozoic limestones

philippine porphyry and epithermal deposits an introduction the philippines is one of the most richly endowed parts of the southwest pacific with many porphyry copper gold and epithermal gold silver deposits scattered along the archipelago e g sillitoe and gappe 1984 mitchell and leach 1991 fig 1 chinese mining artifacts discovered in the baguio and masbate districts suggest that gold and silver mining dates back to at least the 14th century several placer gold mining regions were active during the spanish regime 1521 to 1898 bureau of mines and geosciences 1986 since world war ii gold and silver production has risen fairly steadily from 2 0 t au and 1 4 t ag in 1946 to 37 t au and 34 t ag in 2009 bureau of mines and geosciences 1986 fig 2 between 2005 and 2009 the philippines accounted for approximately 1 5 and 0 1 percent of global gold and silver production respectively when approximately 37 t au and between 14 and 34 t ag were produced each year george 2011 brooks 2011 fig 2 fig 1 a distribution of active copper gold silver zinc chromium and nickel mines in the philippines circa mid 2011 modified from philippines mines and geoscience bureau http www mgb gov ph b study site locations for this special issue fig 2 philippines gold and silver production in tonnes from 1910 to 2009 and copper production in millions of tonnes from 1947 to 2009 data sources wu 1984 bureau of mines and geosciences 1986 lyday 1989 edelstein 1994 1999 2004 2011 lucas 1994 reese 1994 amey 1999 hilliard 1999 brooks 2004 brooks 2011 and george 2011 the first large scale copper mining operations in the philippines commenced at

porphyry and epithermal deposits and 40ar 39ar geochronology of the baguio district philippines the baguio district is located in the central cordillera of northern luzon philippines it contains numerous mineralized porphyry copper gold epithermal gold silver and skarn gold lead zinc deposits the district is floored by cretaceous eocene metavolcanic and metasedimentary rocks which are overlain by marine to terrestrial sedimentary and volcanic rocks of early miocene to pliocene ages tertiary arc magmatism related to east directed subduction of the south china sea plate along the manila trench beneath northern luzon produced a major batholith the central cordillera intrusive complex which defines the eastern boundary of the baguio district the intrusive complex was emplaced in the early miocene based on 40ar 39ar age determinations for the lucbuban gabbro 22 6 0 5 ma and virac granodiorite 20 23 0 38 and 20 2 0 7 ma recent exploration has led to the discovery of several new porphyry copper gold and skarn prospects in the western baguio district mineralization was preceded by the intrusion of a suite of hornblende megacrystic andesite dikes in the central part of the district from 4 55 0 15 to 3 45 0 19 ma porphyry copper gold and skarn deposits at black mountain and mexico on the western side of the district formed between 3 09 0 15 and 2 81 0 24 ma the santo tomas ii cu au pd porphyry deposit was emplaced into the central southern part of the district at about 1 5 ma based on secondary biotite 40ar 39ar ages of 1 48 0 05 ma and 1 47 0 05 ma on the eastern side of the district porphyry style mineralization at the hartwell and ampucao porphyry cu au prospects returned 40ar 39ar ages of 1 09 0 10 and 0 51 0 26 ma respectively quartz carbonate base metal sulfide style epithermal gold silver veins are well developed on the eastern side of the baguio district and crosscut porphyry style mineralization at the acupan baguio gold and nugget hill deposits epithermal veining is inferred to have occurred in the past million years based on a reported k ar age determination of 0 65 0 07 ma from the acupan gold mine a large advanced argillic alteration zone the baguio lithocap crops out in the northwest part of the district and formed between 1 4 and 0 9 ma based on previous k ar dating pliocene pleistocene mineralization in the baguio district was triggered by the east directed subduction of the scarborough ridge ridge subduction caused the subduction angle along the manila trench beneath northern luzon to decrease which facilitated crustal thickening and exhumation ridge subduction also promoted the development of northwest trending faults in the upper plate that interacted with major arc parallel north and arc normal northeast trending fault sets associated with the philippine fault system fertile magmas were emplaced into transtensional strike slip relay basins resulting in the accumulation of more than 35 moz of gold and several million tonnes of copper over approximately 3 m y

forward modelling of the sequence stratigraphic architecture of shelf cyclothems application to late pliocene sequences wanganui basin new zealand we demonstrate a procedure for forward modelling of the sequence stratigraphic architecture i e positions of systems tract boundaries of shelf cyclothems as observed at outcrop sites or in well logs the 1 d model is based on the fact that the deposition of facies within shelf sequences and those defining the key stratigraphic surfaces between systems tracts respond directly to changes in depth between the sea surface and seafloor this accommodation bathymetry model incorporates three reference surfaces sea surface seafloor and lower sequence boundary each of which varies independently as a result of changes in the rates of eustatic sea level sedimentation and subsidence the model input and boundary conditions are an eustatic sea level curve i e late cenozoic deep sea 18o record an independent chronology for the outcrop or well section and a subsidence curve the model outputs are changes in accommodation and palaeobathymetry throughout the sequence and the time missing at erosional sequence boundaries the main variable in the model i e sedimentation rate is established by comparison of a model output bathymetry with the model target palaeobathymetry established from the faunal and facies content of the sequence being modelled when the model output and target are compatible the model sedimentation rate curve is adopted and the theoretical positions of the systems tract boundaries can be read off the model in relation to the lower sequence boundary and compared with independent field based interpretations of their stratigraphic position the model is designed to predict the architecture of sequences as they appear at particular outcrop sites or in well sections its usefulness lies in establishing the timing of accumulation of systems tracts in relation to stages in a eustatic sea level cycle in particular distinguishing between units deposited during highstand versus regressive systems tracts the model is applied to 6th order 41 ka plio pleistocene cyclothems in wanganui basin new zealand where it distinguishes the boundary between highstand systems tracts hst and regressive systems tracts rst the modelling has implications for the definition of systems tracts especially in late cenozoic successions for which the record of eustatic sea level changes is known independently

subduction arc reversal and the origin of porphyry copper gold deposits in island arcs the tertiary quaternary porphyry copper gold deposits of the southwest pacific rim particularly in luzon mainland papua new guinea bougainville guadalcanal and fiji mostly formed after a reversal of arc polarity where this reversal has not occurred e g new zealand and japan porphyry copper gold deposits are absent or scarce hence older porphyry copper gold deposits may be useful clues to tectonic history enrichment of magmas in gold may have resulted from two stage melting the tectonic setting of porphyry copper gold deposits differs from that inferred for volcanic hosted massive sulfide deposits

geodynamic evolution of the baguio mineral district unlocking the cenozoic record from clastic rocks abstract geochemical studies done on the baguio mineral district had dominantly looked at the igneous rocks a major gap is the scarcity of studies dealing with the sedimentary rock geochemistry for this district which this paper intends to address the petrographic data and major and trace element compositions of the siltstones sandstones from the lower member of the late oligocene to early miocene zigzag formation show that they are generally quartz rich and have high k2o th and la sc contents the chondrite normalized ree pattern exhibits a negative eu anomaly enrichment in lrees and flat hrees similar to typical post archean shales taken together the data indicate derivation of the lower member of the zigzag formation from intermediate to acid igneous rock sources generated in an active margin setting a likely candidate source is the cordon syenite complex palali formation in the northern sierra madre caraballo mountains derivation from mafic source rocks in an oceanic island arc setting is inferred for samples of the middle to late miocene klondyke late miocene to early pliocene amlang and late pliocene cataguintingan formations these samples are characterized by low k2o th and la sc but high cr th values unroofing of the pugo metavolcanics and the younger plutons in the central cordillera provided the materials which eventually produced the klondyke and amlang formations continuous uplift and shallowing of the basin resulted in the deposition of the cataguintingan formation the petrography geochemistry and geological features of the sedimentary rocks clearly define the change in sediment provenance from quartz rich during the oligocene to quartz deficit in the miocene this offers additional constraints in understanding the geological evolution of the mineral district

physicochemical processes in the magma chamber under the black mountain porphyry cu au deposit philippines insights from mineral chemistry and implications for mineralization the black mountain porphyry cu au deposit in the baguio district northern luzon philippines is associated with late miocene to pliocene intrusive rocks that retain primary crystallization signatures providing an excellent natural laboratory to study the details of magma chamber processes each igneous phase contains disequilibrium textures including resorptive textures in plagioclase and distinct core rim textures in amphibole high crystallization temperatures and pressures in felsic 880 c and 2 8 kbar and mafic 1 030 c and 7 7 kbar rocks recorded by amphibole phenocrysts reflect crystallization in the magma chamber amphibole in felsic rocks aged 6 39 0 49 to 2 83 0 23 ma have similar crystallization temperatures and pressures suggesting a long lived and hot felsic magma chamber under the black mountain deposit four independent oxybarometers including amphibole coexisting magnetite ilmenite magmatic anhydrite and zircon consistently show a high oxidation state of nno 1 for the felsic magma and nno 0 7 for the mafic magma element profiles across phenocrystic plagioclase display repeated oscillatory variations of ca fe and sr contents with large anorthite variations and a positive correlation between cao and feo the amphibole is classified as group 1 mg hornblende to tschermakite hornblende in felsic rocks and group 2 mg hastingsite in mafic rocks the group 1 amphiboles show a variety of major and trace element variations from core to rim in disequilibrated grains and transitional compositions to group 2 mg hastingsite both mineral textures and chemistry recorded by phenocrysts of plagioclase and amphibole indicate repeated mafic magma recharge in the felsic magma chamber the common occurrence of rounded or elongated sulfide inclusions in the megacrystic amphibole from the mafic rocks 2 81 0 15 ma suggests a greater enrichment of cu in mafic rocks relative to the ore forming porphyries 2 91 2 83 ma this is also consistent with higher cu contents 3 4 0 9 ppm in the megacrystic amphibole from the mafic rocks relative to amphibole in felsic rocks 1 0 0 2 ppm and may indicate up to 3 4 times higher cu in the mafic magma relative to felsic magma therefore large scale mafic magma recharge particularly at 2 8 ma likely introduced ore forming metals to the long lived felsic magma chamber further contributing to the fertility of the felsic rocks and ultimately to cu au mineralization at the black mountain deposit

geology geochronology and fluid inclusion studies of the xiaorequanzi volcanogenic massive sulphide cu zn deposit in the east tianshan terrane china the xiaorequanzi cu zn deposit is in the westernmost part of east tianshan terrane in northwestern china the deposit is unique in the region being a volcanogenic massive sulphide vms deposit loc

transgressive surfaces of erosion as sequence boundary markers in cool water shelf carbonates abstract although sequence stratigraphy was first conceptualized in and applied to siliciclastic successions its methodology and concepts are applicable to the carbonate regimen provided that potential modifications to the existing models are appreciated that take into account the specificities of carbonate systems we demonstrate that some properties inherent to isolated i e continent detached shallow water temperate carbonate systems including their typical low diagenetic potential due to the prevalance of calcitic mineralogies the critical role exerted by storm waves and tidal currents on sediment dynamics e g shedding of sediments at wave abrasion depth during highstand and lowstand conditions and uneven sea bed topographies cause both the genesis and preservation of subaerial unconformities to be uncommon thereby rendering their use as sequence boundaries inappropriate instead transgressive surfaces of erosion tses that formed as wave base shifts upwards during early rise of relative sea level are readily identifiable in the field extensive and by their very nature are preserved in the rock record typically at the base of upward deepening stacked facies in pliocene cool water carbonate successions from new zealand the tses are characterized by starved sedimentation and burrowed network development and are overlain by coarse bioclastic shoreface sediments and shell beds in most cases the surfaces top truncate shoaling upward deposits but also deepening upward stacking facies in places emersive events rarely correspond to actual physical surfaces but diagenetic evidence preserved beneath tses indicates that occasionally subaerial surfaces had previously developed and were later modified into tses therefore we propose that tses are the most adequate unconformities to define high order depositional sequences 20 250 ka in the studied successions because by contrast with emersion surfaces their formation and preservation are not dependent upon cool water sedimentary facies and mineralogy and are favoured by the dynamics of the setting i e wave base shift and accommodation creation during relative sea level rise

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

exploration tools for linked porphyry and epithermal deposits example from the mankayan intrusion centered cu au district luzon philippines the mankayan mineral district of northern luzon philippines hosts several significant ore deposits and prospects of various types within an area of similar to 25 km 2 including the far southeast porphyry cu au deposit the lepanto high sulfidation epithermal cu au deposit the victoria intermediate sulfidation epithermal au ag vein deposit the teresa epithermal au ag vein deposit the guinaoang porphyry cu au deposit and the buaki old palidan porphyry cu au prospects all having formed in a period of about 2 m y from similar to 3 ma the geologic units include 1 a basement composed of late cretaceous to middle miocene metavolcanic rocks volcaniclastic rocks 2 the miocene 12 to 13 ma tonalitic bagon intrusive complex 3 the pliocene similar to 2 2 to 1 8 ma imbanguila dacite porphyry and pyroclastic rocks and 4 postmineralization cover rocks including die similar to 1 2 to 1 0 ma bato dacite porphyry and pyroclastic rocks and the similar to 0 02 ma lapangan tuff extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the imbanguila dacite formation consists of quartz alunite pyrophyllite or diaspore with local zones of silicic alteration and a halo of dickite kaolinite the alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps the northwest striking portion is similar to 4 km long and hosts the lepanto enargite au ore deposit also controlled by the lepanto fault the lepanto epithermal deposit is related to the underlying far southeast porphyry the quartz alunite alteration halo of lepanto is contemporaneous with the similar to 1 4 ma potassic alteration of the porphyry there are also silicic advanced argillic alteration patches similar to 600 m above the far southeast orebody at the present surface these are interpreted to be perched alteration there is no systematic mineralogical or textural zoning in the lepanto lithocap that indicates direction to the intrusive source most surface samples of the lithocap contain less than 50 ppb au despite many being less than a few hundred meters from underground cu au ore this study found that several characteristics of the lepanto lithocap change systematically with distance from the causative intrusion the alunite absorption peak at similar to 1 480 nm in the short wavelength infrared swir spectrum shifts to higher wavelengths where the sample is closer to the intrusive center due to higher na and lower k content in the alunite published experimental studies indicate that high na na k is related to higher formation temperature high ca alunite including huangite also occurs at locations proximal to the intrusive center alunite mineral composition analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that the pb content decreases toward the intrusive center whereas sr la sr ph and la pb increase markedly whole rock compositions using only nonmineralized taken as cu similar to 350 m above the upper extent of the veins an airborne geophysics survey indicates that the far southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite destructive phyllic alteration such low magnetic anomalies on the margin of a large lithocap elsewhere may deserve attention the directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry epithermal districts

giant porphyry deposits characteristics distribution and tectonic controls more than half of the 25 largest known porphyry copper deposits defined in terms of contained copper metal formed during three time periods the paleocene to eocene eocene to oligocene and middle miocene to pliocene these giant deposits are clustered within three provinces central chile northern chile and southwest arizona northern mexico other giant deposits occur in montana utah panama peru argentina irian jaya mongolia and iran compressive tectonic environments thickened continental crust and active uplift and erosion were associated with the formation of many of these deposits calc alkalic magmas are most favorable for the formation of giant porphyry copper deposits although several of the largest systems are associated with high k calc alkalic intrusions the 25 largest gold rich porphyry deposits are concentrated in the southwest pacific and south america with other occurrences in eurasia british columbia alaska and new south wales many of the deposits formed in the last 13 m y the largest of the deposits are associated with high k calc alkalic intrusions many calc alkalic porphyritic intrusions have also produced giant gold rich porphyries in the last 20 m y the formation of giant porphyry copper molybdenum and copper gold deposits in the circum pacific region has been closely associated with subduction of aseismic ridges seamount chains and oceanic plateaus beneath oceanic island and continental arcs in several examples these tectonic perturbations have promoted flat slab subduction crustal thickening uplift and erosion and adakitic magmatism coeval with the formation of well endowed porphyry and or epithermal mineral provinces similar tectonic features are inferred to be associated with the giant porphyry copper molybdenum provinces of northern chile eocene oligocene and southwest united states cretaceous paleocene topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation other factors such as sutures in the overriding plate permeability architecture of the upper crust efficient processes of ore transport and deposition and in some cases formation and preservation of supergene enrichment blankets are also vital for the development of high grade giant ore deposits a low grade geochemical anomaly may be the final product of mineralization if ore forming processes do not operate efficiently even in the most favorable geodynamic settings

geochemistry and tectonic setting of the luzon arc philippines miocene 10 ma to recent volcanism is associated with eastward subduction along the manila trench for some 1 200 km from the coastal range in taiwan south to min doro we suggest calling this the luzon arc there are five distinct segments along this arc mindoro bataan northern luzon babuyan and taiwan the bataan and mindoro segments in the south are separated by a northeast southwest zone of volcanoes the northern luzon segment consists of pliocene to pleistocene necks and plugs that run along the entire western section of northern luzon the babuyan segment 10 ma to recent is made up of a larger number of active volcanoes than are other segments of the luzon arc the taiwan segment is composed entirely of extinct volcanoes in the coastal range and on the islands of lanhsu and lutao late miocene to 1 8 ma the nature of volcanism throughout the luzon are is clearly subduction related with calc alkaline affinities high th la ratios and negative nb ta and ti anomalies the earliest phase of volcanism so far recorded 10 ma however is tholeiitic island of calayan in the babuyan segment with mid oceanic ridge basalt like morb like tight rare earth element and large ion lithophile element concentrations and low th u ratios there are clear differences in sr and nd isotopic ratios among the samples from the luzon are samples from the southern segments mindoro through bataan fall within the mantle array with higher sr and lower nd isotopic values than those of morb pb isotope data indicate sediment involvement the isotopic values have been interpreted to result from source contamination by slab derived fluids bataan segment and by subducted crustal material from collision of the mindoro palawan terrane mindoro segment with the manila trench in contrast babuyan segment samples north have unusual island arc nd and sr isotopic ratios that fall below the mantle array they appear to be the result of sediment source contaminants or a unique mantle composition incorporation of sediments analyzed from eastern china and taiwan into a morb type mantle can explain the nd and sr isotopic ratios of the babuyan segment

a double island arc between taiwan and luzon consequence of ridge subduction analysis of geomorphological geochronological geochemical and geophysical features in the segment of the taiwan luzon arc between taiwan and luzon the bashi segment allows the recognition of a double arc structure the two volcanic chains are separated by 50 km just north of luzon 18 n and converge near 20 n islets in the western chain are older and largely composed of volcanic rocks of miocene to pliocene age they all show low relief lateritic platforms and wave cut terraces and are covered by massive recrystallized limestone in contrast all active volcanoes in this segment of the taiwan luzon arc belong to the eastern chain where most islets are quaternary in age the volcanoes have well developed cone shapes and well preserved deposits of near vent facies magmas of the eastern chain have higher ksi la n la yb n and lowerend than their counterparts at the same latitude in the western chain therefore the magmas erupted in the eastern chain were derived from more enriched mantle sources than the magmas erupted in the western chain moreover the available seismological data seem to suggest an abrupt increase of the dip angle from 30 at 18 n to 80 at 20 n thus the double arc structure is located in the region where the benioff zone suddenly changes in analogy with the lesser antilles arc we propose a geodynamic model in which the double arc in the bashi strait is the tectonic manifestation of the subduction of the aseismic scarborough seamount chain the extinct mid ocean ridge of the south china sea before that ridge reached the manila trench the western chain was the volcanic front when the ridge reached the subduction zone at 5 4 ma its buoyancy temporarily interrupted the subduction thus causing a time gap in magmatic activity furthermore this ridge arc collision was probably also responsible for regional uplift causing extensive sub aerial weathering and erosion as well as massive reef formation in the western chain when subduction started again the dip angle became shallower in response to the extra buoyancy of the downgoing ridge if the depth of magma generation remained constant the shallower dip angle would have naturally led to an eastward shift of the volcanic front thus producing the younger eastern chain moreover we speculate that the abrupt change of the dip angle may have torn the downgoing slab thus allowing more enriched continental lithospheric material to invade the mantle wedge from the northwest thus imprinting a geochemically more enriched signature on the magmas of the eastern chain

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

discussion on giant versus small porphyry copper deposits of cenozoic age in northern chile adakitic versus normal calc alkaline magmatism by oyarzun et al mineralium deposita 36 794 798 2001

mineralization parameters and exploration targeting for gold copper deposits in the baguio luzon and pacific cordillera mindanao mineral districts philippines a review abstract the baguio mineral district in luzon philippines is known to host several world class epithermal gold porphyry copper deposits the interplay of tectonic setting magma composition structural control and hydrothermal systems contributed to the generation of these deposits ridge subduction scarborough seamount resulting to flat subduction and a transpressional regime could also be related to the formation of epithermal gold porphyry copper deposits in baguio subduction processes leading to the formation of calc alkaline rocks associated with high water pressure oxygen fugacity and late sulfur saturation are almost always associated with the gold copper deposits in the district compared to the baguio mineral district less exploration work mine development and production were done in the pacific cordillera mineral district mindanao in southern philippines it is worth noting however that both mineral districts show similarities and overlapping features in terms of geological geophysical and geochemical characteristics this leads one to conclude that the pacific cordillera mineral district has ore deposits waiting to be discovered

the altar porphyry cu au mo deposit argentina a complex magmatic hydrothermal system with evidence of recharge processes altar 31 29 s 70 28 w is a large porphyry cu au mo deposit with associated epithermal au ag cu veins located in the cordillera principal of southwest san juan province argentina altar is a complex magmatic hydrothermal system formed from several magmatic and hydrothermal pulses during the middle late miocene new la icpms u pb ages in zircons from the altar porphyries indicate four discrete events of intrusions over an extended magmatic life time of ca 3 m y it comprises a premineralization porphyry 11 75 0 24 ma three mineralized porphyries 11 62 0 21 and 11 68 0 27 ma 11 13 0 26 ma 10 35 0 32 ma related to hydrothermal breccias two postmineralization intrusions and a postmineralization breccia 8 9 0 4 ma the three mineralized porphyries porphyries 2 3 and 4 were emplaced within 0 7 to 1 3 m y amphibole phenocrysts from the porphyries crystallized from oxidized magmas f o2 nno 1 to 2 at temperatures of 780 to 850 c and pressures between 0 9 and 1 8 kbars corresponding to depths of 4 to 7 km anorthite and fe rich rims in the plagioclase phenocrysts suggest that the magmatic chambers were episodically recharged by a less evolved magma the middle late miocene intrusions are interpreted to have been derived from a deeper and relatively large magmatic reservoir that supplied magmas to smaller chambers located in the upper crust the focused magmatic output to shallow levels during a period of a few million years in the altar area has been a main requirement in the formation of this large porphyry copper deposit

microboring versus recrystallization further insight into the micritization process sem observations of lightly etched thin sections of bahamian sediments reveal an unusual process of micritization that involves carbonate precipitation in microborings concurrent with endolithic activity a coccoid cyanobacterium tentatively identified as solentia sp bores tunnels which initially penetrate just beneath grain surfaces and eventually extend throughout the entire grain these tunnels are filled by radial fibrous aragonite which is precipitated as the microorganism advances extensive multicyclic repetitions of this process result in obliteration of original grain textures with almost complete preservation of grain margins and rare empty bore holes the rapidly filled tunnels cannot be detected by resin cast embedding techniques that are commonly used to study microboring this type of multicyclic boring and concurrent filling of bore holes forms micritized grains that can be difficult or impossible to distinguish from micritized grains formed by recrystallization

insights into magma histories through silicate oxide crystal clusters linking the hiltaba suite intrusive rocks to the gawler range volcanics gawler craton south australia the roxby downs granite rdg host to the supergiant olympic dam deposit and the gawler range volcanics grv in south australia both contain clusters of touching silicate and oxide minerals here we report on the geochemistry and petrography of these rocks and their contained mineral clusters before comparing them to similar occurrences elsewhere in the world to gain a better understand of their genesis and the links between the rdg and other members of the hiltaba suite and the grv crystal clusters in the rdg comprise magnetite apatite titanite biotite zircon which are typically enveloped in a plagioclase crystal matrix in the grv crystal clusters comprise pyroxene titanomagnetite plagioclase apatite zircon display variably glomeroporphyritic equigranular poikilitic and loosely packed habits and are enclosed by texturally varied groundmass of the grv lavas studied pyroxenes and titanomagnetite show systematic trends in major and trace element compositions conformable with the stratigraphic position of their hosts this suggests the lavas are related through differentiation in the upper crust and represent the inversion of a normally zoned reservoir there are no compositional contrasts between phenocrysts and crystals in grv clusters and mg of pyroxenes are consistent with those predicted from whole rock compositions implying that all analysed crystals including those in clusters were formed within or were at least equilibrated to the host lavas precursors rather than entire histories as isolated crystal clusters entrained by melt flow intergrowth textures and mafic magmatic enclaves suggest that the majority of grv crystal clusters were liberated from closely packed crystal masses through magma rejuvenation and associated crystal resorption consistent fe ti oxide apatite zircon plagioclase assemblages and textures in both the grv and rdg suggest a shared genetic scenario although an extended model is needed to account for the transformation of grv type to hs type crystal clusters for hot and dry magmas such as those that formed the grv and rdg cooling causes pyroxene fe ti oxide plagioclase in grv type crystal clusters to react with each other and the melt forming hs type magnetite titanite biotite feldspar crystal clusters rejuvenation events implicated in the liberation of grv type crystal clusters may be important drivers of magmatic hydrothermal iron oxide deposit formation

igneous geochemistry of mineralized rocks of the baguio district philippines implications for tectonic evolution and the genesis of porphyry style mineralization the baguio district of the philippines is one of the world s premier mineral provinces containing 35 million ounces moz of gold and 2 7 million metric tons mt of copper in epithermal porphyry and skarn deposits that formed in the last 3 5 m y pliocene and pleistocene magmatic rocks of the baguio district that are spatially and temporally associated with mineralization can be broadly subdivided into an intermediate to felsic suite of mineralized low to medium k intrusions some of which have adakitic affinities and a suite of mafic to intermediate medium k to shoshonitic hornblende phyric dikes the geochemical and isotopic characteristics of the dikes are consistent with primitive mantle derived melts that underwent minimal crustal contamination as they ascended through the arc crust in contrast the intermediate to felsic suite has been contaminated by young arc crust suggesting ponding and fractionation within shallow crustal magma chambers the philippine arc has formed in a complex tectonic environment and is currently sandwiched between two active subduction zones eastward directed subduction of the scarborough ridge along the manila trench is currently associated with flattening of the downgoing slab the formation of the mafic dike complex is broadly coeval with the onset of subduction of the scarborough ridge and slab flattening the extinct scarborough ridge would have been younger than the downgoing plate and consequently more susceptible to melting these melts can account for the isotopic recharge of the pliocene subarc mantle as well as the generation of the primitive melts and adakitic rocks found within the baguio district the interaction between primitive mafic melts and the more felsic calc alkaline rocks has

age tectonic setting and metallogenic implication of phanerozoic granitic magmatism at the eastern margin of the xing an mongolian orogenic belt ne china abstract the eastern margin of the xing an mongolian orogenic belt is characterised by widespread phanerozoic granitic magmatism some of which is closely related to significant ore mineralisation this paper presents new geochronological petrogenetic and tectonic data for selected intrusions zircon u pb geochronology for five granitoid plutons indicates they were emplaced during the middle late permian 264 255 ma and cretaceous 106 94 ma and thus granitic magmatism occurred throughout the phanerozoic permian 268 252 ma early middle triassic 248 240 ma early jurassic 183 ma and cretaceous 112 94 ma the permian granitoids consist of monzogranite granodiorite tonalite and quartz diorite characterised by enrichment in na2o 3 60 4 72 wt depletion in k2o 0 97 2 66 wt and a negative correlation between p2o5 and sio2 together with the presence of hornblende these geochemical features are indicative of an i type affinity the permian granitic magmatism is associated with quartz vein type tungsten deposits 252 ma unpublished sm nd isochron age which formed in an active continental margin setting related to subduction of the palaeo asian ocean the cretaceous quartz diorites have an adakitic affinity having relatively high sr 374 502 ppm low yb 0 51 0 67 ppm and y 8 7 10 7 ppm and high sr y 39 4 46 8 and la yb n values 16 2 34 7 suggesting that they were related to the partial melting of subducted oceanic crust in addition they are associated with porphyry au cu deposits we conclude that the cretaceous granitic rocks and associated porphyry au cu mineralisation occurred in an extensional tectonic setting related to the subduction of the palaeo pacific plate beneath the eurasian plate in addition the large scale early middle triassic syn collisional granite belt at the eastern margin of the xing an mongolian orogenic belt extends from the middle of jilin province to the wangqing hunchun region constraining the timing of the final collision between the north china craton and the jiamusi khanka massif and suggesting that the xra moron river changchun suture likely extends eastward into the eastern hunchun region this collision caused the middle triassic mesothermal lode gold mineralisation

effects of early sea floor processes on the taphonomy of temperate shelf skeletal carbonate deposits abstract cool water shelf carbonates differ from tropical carbonates in their sources modes and rates of deposition geochemistry and diagenesis inorganic precipitation marine cementation and sediment accumulation rates are absent or slow in cool waters so that temperate carbonates remain longer at or near the sea bed early sea floor processes occurring between biogenic calcification and ultimate deposition thus take on an important role and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool water carbonate deposits the physical breakdown processes of dissociation breakage and abrasion are mediated mainly by hydraulic regime and are always destructive impact damage reduces the size of grains removes structure and therefore information and ultimately may transform skeletal material into anonymous particles abrasion is highly selective amongst and within taxa their skeletal form and structure strongly influencing resistance to mechanical breakdown dissolution and precipitation are the end members of a two way chemical equilibrium operating in sea water in cool waters inorganic precipitation is rare there is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor but test maceration and early loss of aragonite in particular are reported dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter strong bioturbation and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits laboratory experiments demonstrate that surface to volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution biological processes on the sea floor include encrustation and bioerosion encrustation a constructive process may be periodic or seasonal and can be reversed it produces both information and material bioerosion in contrast is destructive and permanent in temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor on the order of hundreds to thousands of years overall processes on the temperate sea floor may combine to destroy more carbonate than they produce and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected where preservation does occur in such a destructive regime the effects of early sea floor processes will be key determinants of the deposit resulting in a taphofacies characteristic of temperate shelf carbonate sediments

a new insight on the geometry of subducting slabs in northern luzon philippines abstract we used hypocentral and focal mechanism data in order to characterize the tectonic configuration of northern luzon and propose a model for describing the geometry of the subducted slab of the eurasian plate beneath the northern segment of the manila trench we took into consideration some of the observed bathymetric features i e the bend in the trench line of the manila trench at 20 n lat and the collision and subduction of an extinct mid oceanic ridge at 16 17 n lat and the intraplate deformation pattern in the north luzon ridge region in depicting a model that is consistent with most of the observed features and phenomena in the study area an earthquake catalog covering the period from 1619 to 1997 was used in studying the distribution of strain energy released while earthquakes covering the instrumental years 1963 1997 were used to analyze vertical distributions of earthquakes in sections we refined the location of some of the historical earthquakes using macroseismic data the inclusion of historical records despite their inaccurate locations could prevent misidentification of some regions as aseismic zones or gaps in seismicity especially along structures with long return periods a focal mechanism database that covers the period from 1963 to 1997 was used to decipher intraplate deformation pattern and subduction process of the slab the focal mechanism database consists of first motion solutions from previous authors and cmt solutions from harvard university seismicity strain energy release and focal mechanism maps and cross sections were drawn in order to have a three dimensional visualization of the geometry and stress regimes of seismogenic zones a new model of the subducted slab of the eurasian plate beneath the manila trench is proposed the model suggests the collision and subsequent partial subduction of a buoyant plateau at around 20 n lat to explain the sharp bend in the trench line the complicated deformation pattern on the overriding plate fronting the bend and the shallow dip of the subducted slab beneath this zone a tear in the slab is also inferred to be present as evidenced by the observed gap in strain energy release and the abrupt change in dip from shallow to steep south of 18 n lat the gap in seismicity and strain energy release 65 300 km depth at around 17 n lat may be used to infer the trajectory and location of the subducted extinct mid oceanic ridge mor the aseismic behavior is probably caused by the subducted ridge which is still hot and is deforming plastically this is supported by the heatflow data which shows high values along the extinct mor the subducted part of the mor may serve as the weakest zone where this tear could be localized the tear may also explain the cause of the abrupt termination of the eastern chain of volcanoes south of 18 n lat the above model which is a refinement of the model introduced by yang et al tectonophysics 258 1996 85 is consistent with the observed seismicity and deformation pattern observed bathymetric features spatial distribution and geochemical character of volcanism in northern luzon