criteria for interpreting kimberlite as coherent insights from the muskox and jericho kimberlites nunavut canada the jurassic muskox and jericho kimberlites northern slave province nunavut canada contain a variety of facies exhibiting different geometries contact relationships internal organisation country rock abundance and olivine shapes although many have similar matrix groundmass mineralogies and textures five facies are examined that either have characteristics consistent with coherent rocks in general i e intrusive and extrusive non fragmental rocks or are mineralogically and texturally similar to kimberlite described as coherent or apparent coherent three facies are interpreted as coherent on the basis of 1 geological setting 2 apparent porphyritic texture 3 sharp contacts with fragmental kimberlite 4 relative abundance of elongate and unbroken olivine crystals and 5 paucity of country rock xenoliths while the remaining two facies are interpreted as fragmental on the basis of 1 the gradational contacts with demonstrably fragmental kimberlite 2 relative abundance and range of sizes of country rock lithic clasts and 3 numerous broken olivine crystals comparisons are made with coherent and apparent coherent kimberlite from the literature our three coherent facies are similar to literature reported coherent kimberlite dykes hosted in country rock ckd in terms of internal organisation low abundance of country rock xenoliths and apparent porphyritic texture conversely our two fragmental facies share attributes with previously described pipe filling coherent and apparent coherent kimberlite ckpf in terms of geometry internal organisation and abundance of country rock xenoliths we conclude that ckd and most ckpf although similar in matrix groundmass mineralogy and texture can be distinguished on the basis of internal organisation country rock lithic clast abundance texture e g apparent porphyritic texture and possibly olivine crystal shapes and suggest that fragmental kimberlite is more common than reported

silurian s type granite related w mo mineralization in the nanling range south china a case study of the pingtan w mo deposit abstract the pingtan deposit in southwestern hunan province is a newly discovered large sized w mo deposit this deposit is situated in the northwestern part of the miao ershan granite batholith western nanling range the tungsten mineralization is mainly hosted in biotite monzogranite and the alteration related to mineralization is controlled by a ne trending fault zone in this paper we present new molybdenite re os and zircon u pb ages zircon lu hf isotope and ree geochemical data aiming to constrain the w mo mineralization age and ore hosting granite petrogenesis in the pingtan w mo deposit molybdenite re os dating of eight ore samples yielded a weighted average model age of 427 0 5 4 ma mswd 0 24 the la icp ms zircon u pb analysis of two biotite monzogranite yielded 206pb 238u ages of 430 8 2 4 ma and 431 0 1 8 ma respectively suggesting that the w mo mineralization is spatial temporally associated with the biotite monzogranite the ore related granites have high contents of sio2 and k2o belong to weakly to strongly peraluminous a cnk 1 00 1 30 and geochemically classified as s type affinity molybdenite re contents 2 262 7 297 g g zircon ehf t 10 34 5 87 and 176hf 177hf 0 282241 0 282376 values of the biotite monzogranite suggest that the ore forming materials are predominantly derived from the crust this is the first identification of tungsten mineralization related to silurian s type granites caledonian granites in the miao ershan granite intrusion indicating caledonian is an important mineralization period of w in the western part of nanling range south china

reconstruction of a multi vent kimberlite eruption from deposit and host rock characteristics jericho kimberlite nunavut canada abstract the jericho kimberlite 173 1 1 3 ma is a small 130 70 m multi vent system that preserves products from deep 1 km portions of kimberlite vents pit mapping drill core examination petrographic study image analysis of olivine crystals grain size distributions and shape studies and compositional and mineralogical studies are used to reconstruct processes from near surface magma ascent to kimberlite emplacement and alteration the jericho kimberlite formed by multiple eruptions through an archean granodiorite batholith that was overlain by mid devonian limestones 1 km in thickness kimberlite magma ascended through granodiorite basement by dyke propagation but ascended through limestone at least in part by locally brecciating the host rocks after the first explosive breakthrough to surface vent deepening and widening occurred by the erosive forces of the waxing phase of the eruption by gravitationally induced failures as portions of the vent margins slid into the vent and in the deeper portions of the vent 1 km by scaling as thin slabs burst from the walls into the vent at currently exposed levels coherent kimberlite ck dykes

geological setting and timing of the chah zard breccia hosted epithermal gold silver deposit in the tethyan belt of iran the breccia hosted epithermal gold silver deposit of chah zard is located within a high k calc alkaline andesitic to rhyolitic volcanic complex in the central part of the urumieh dokhtar magmatic arc udma west central iran the total measured resource for chah zard is 2 5 million tonnes of ore at 12 7 g t ag and 1 7 g t au 28 6 t ag 3 8 t au making it one of the largest epithermal gold deposits in iran magmatic and hydrothermal activity was associated with local extensional tectonics in a strike slip regime formed in transtensional structures of the dehshir baft strike slip fault system the host rocks of the volcanic complex consist of eocene sedimentary and volcanic rocks covered by miocene sedimentary rocks la icp ms u pb zircon geochronology yields a mean age of 6 2 0 2 ma for magmatic activity at chah zard this age represents the maximum age of mineralization and may indicate a previously unrecognized mineralization event in the udma breccias and veins formed during and after the waning stages of explosive brecciation events due to shallow emplacement of rhyolite porphyry detailed systematic mapping leads to the recognition of three distinct breccia bodies volcaniclastic breccia with a dominantly clastic matrix gray polymict breccia with a greater proportion of hydrothermal cement and mixed monomict to polymict breccia with clay matrix the polymictic breccias generated bulk mineable ore whereas the volcaniclastic breccia is relatively impermeable and largely barren precious metals occur with sulfide and sulfosalt minerals as disseminations as well as in the veins and breccia cements there is a progression from pyrite dominated stage 1 to pyrite base metal sulfide and sulfosalt dominated stages 2 and 3 to base metal sulfide dominated stage 4 breccias and veins hydrothermal alteration and deposition of gangue minerals progressed from illite quartz to quartz adularia carbonate and finally gypsum dominated assemblages free gold occurs in stages 2 and 4 principally intergrown with pyrite quartz chalcopyrite galena sphalerite and ag rich tennantite tetrahedrite and also as inclusions in pyrite high rb sr ratios in ore grade zones are closely related to sericite and adularia alteration positive correlations of au and ag with cu as pb zn sb and cd in epithermal veins and breccias suggest that all these elements are related to the same mineralization event

the importance of vein selvaging in controlling the intensity and character of subsurface alteration in hydrothermal systems the identity and abundance of secondary minerals produced when a hydrothermal fluid initially in equilibrium with its host formation convects or is otherwise propelled down a temperature gradient toward the surface are calculated with and without boiling the calculations show that the mass of secondary minerals produced by a unit throughput of hydrothermal water is surprisingly dependent on selvaging mineral precipitation is over 1 000 times greater when chemical contact is maintained with the host formation than when the upwelling fluid is chemically isolated from the host rock by selvages this means for example that a selvaged vein with only one tenth the hydrothermal mineral alteration of a nonselvaged vein formed in a similar environment may nevertheless have transmitted over 100 times more hydrothermal fluid and precipitated 100 times the mass of ore minerals these conclusions are for end member equilibrium models the magnitude of the effect suggests however that selvage formation will remain an important consideration in cases between the two end member extremes and for cases subject to kinetic control

evolution and facies architecture of paleogene surtseyan volcanoes on chatham islands new zealand southwest pacific ocean abstract this paper reports for the first time phreatomagmatic deposits and preserved surtseyan tuff cones in the chatham islands new zealand fieldwork has located the relicts of at least six closely spaced paleogene surtseyan cones and associated volcaniclastic sediments within the red bluff tuff formation the complete stratigraphic section of the cones consists of two parts 1 the lower part represents volcanic aggradational processes that constructed tuff cones in a short period of time and is composed of a bedded interval of explosively fragmented vesicular glassy basaltic pyroclasts ash and lapilli sizes as well as feeder dykes pillow lavas and pillow sills and 2 the upper part represents the rapid denudation of these cones by shallow marine currents or gravity flows reflecting the instability of the tephra pile forming the cones and a much later marine faunal colonization stage e g corals brachiopods molluscs etc erosion could have occurred almost immediately after or even during the emplacement of the volcanic pile similar to what occurred at surtla vent a satellite submerged cone of the basaltic island volcano surtsey iceland the waiareka deborah volcanics bridge point aorere point and lookout bluff surtseyan cones otago new zealand and marion and prince edward islands southwest indian ocean amongst others by contrast the complete faunal colonization and stabilization of a diverse marine community could have taken hundreds or perhaps even thousands of years to reach their acme following the volcanic pulses the structural textural and compositional characteristics of the red bluff tuff formation support a phreatomagmatic mode of fragmentation similar to that at surtsey volcano iceland the red bluff tuff sequence represents one of the most complete marine tuff cones described in the geologic record

deep bedded ultramafic diatremes in the missouri river breaks volcanic field montana usa 1 km of syn eruptive subsidence the ultramafic eocene missouri river breaks volcanic field mrbvf montana usa includes over 50 diatremes emplaced in a mostly soft substrate the current erosion level is 1 3 1 5 km below the pre eruptive surface exposing the deep part of the diatreme structures and some dikes five representative diatremes are described here they are 200 375 m across and have sub vertical walls their infill consists mostly of 55 90 bedded pyroclastic rocks fine tuffs to coarse lapilli tuffs with concave upward bedding and 45 10 non bedded pyroclastic rocks medium lapilli tuffs to tuff breccias the latter zones form steep columns 15 135 m in horizontal dimension which cross cut the bedded pyroclastic rocks megablocks of the host sedimentary formations are also present in the diatremes some being found 1 km or more below their sources the diatreme infill contains abundant lithic clasts and ash sized particles indicating efficient fragmentation of magma and country rocks the spherical to sub spherical juvenile clasts are non vesicular they are accompanied by minor accretionary lapilli and armored lapilli the deposits of dilute pyroclastic density currents are locally observed our main interpretations are as follows 1 the observations strongly support phreatomagmatic explosions as the energy source for fragmentation and diatreme excavation 2 the bedded pyroclastic rocks were deposited on the crater floor and subsided by 1 0 1 3 km to their current location with subsidence taking place mostly during the eruption 3 the observed non bedded pyroclastic columns were created by debris jets that punched through the bedded pyroclastic material the debris jets did not empty the mature diatreme occupying only a fraction of its width and some debris jets probably did not reach the crater floor 4 the mature diatreme was nearly always filled and buttressed by pyroclastic debris at depth there was never a 1 3 1 5 km deep empty hole with sub vertical walls otherwise the soft substrate would have collapsed inward which it only did near the surface to create the megablocks we infer that syn eruptive subsidence shifted down bedded pyroclastic material and shallow sedimentary megablocks by 0 8 1 1 km or more after which limited post eruptive subsidence occurred this makes the mrbvf diatremes an extreme end member case of syn eruptive subsidence in the spectrum of possibilities for maar diatreme volcanoes worldwide

rock type variability and impact fracture formation working towards a more robust macrofracture method investigations into the development of weapon systems are increasingly important in archaeological debates about human evolution and behavioural variability diagnostic impact fractures are key but controversial lines of evidence commonly used in such investigations in 2009 a series of experiments was initiated to investigate the processes associated with macrofracture formation specifically focussing on the taphonomic factors affecting the formation of diagnostic impact fractures difs this paper adds to that experimental data set with macrofracture results from recent knapping experiments investigating rock type variability and dif formation these results show that rock type variation plays less of a role in dif formation than variables related to use and lithic taphonomy the collective results of this experimental series show that the location co occurrence type and proximity to retouch on a tool are all important means of distinguishing between weapon and non weapon related difs collectively these macrofracture patterns are more important in diagnosing weapon components than any one diagnostic impact fracture is alone overall these experimental studies are showing that background noise in the form of non hunting related impact fractures exists in many macrofracture results and that much work remains in securing the analytical robusticity of the method the paper concludes that the macrofracture method is not a stand alone method but when used with caution and in conjunction with other lines of evidence it is a useful time efficient tool for generating assemblage level use trace data

quartz backed tools as arrowheads and hand cast spearheads hunting experiments and macro fracture analysis the invention of the bow and arrow was a milestone in late pleistocene technological evolution preservation biases and methodological problems imped our ability to detect its presence in the archaeological record currently south africa has the earliest suggested evidence for arrowheads amongst others small quartz backed tools dating 65 60 ka these artefacts inferred function is based on their small size micro and macro wear traces and micro residues recorded on quartz segments from sibudu cave experimental support for these inferences or to show that similar artefacts are associated with bow hunting are however lacking here we describe breakage patterns on 150 quartz backed tools hafted as transverse arrowheads and hand cast spearheads in simulated hunting experiments these experiments controlled for hafting variability to test the effects of propulsion velocity on the types patterns and area of diagnostic impact fractures difs our results show step terminating bending fracture spin off fracture and impactburination frequencies dif locations and ventrally situated dif frequencies to be robust means of distinguishing arrowheads from spearheads our experiments verify previous observations that overall dif frequencies differentiate between these weapon types importantly we confirm that dif size is linked to weapon propulsion velocity but that fracture area is affected by tool area these findings provide methods for future testing of the hypothesis that bow and arrow technology was in use at least 65 ka in southern africa and in other regions where quartz was used to tip weapons

molybdenite re os and u pb zircon dating and genesis of the dayana w mo deposit in eastern ujumchin inner mongolia abstract the dayana w mo deposit in eastern ujumchin of inner mongolia is a quartz vein type deposit in the mid western part of the central asian orogenic belt caob biotite monzogranite quartz porphyry and hornfels host w mo in quartz veins based on spatial relationships molybdenite was deposited first followed by wolframite this contribution presents precise laser ablation inductively coupled plasma mass spectroscopy la icp ms u pb zircon dating and geochemical analysis of the biotite monzogranite the u pb dating shows that the monzogranite is 134 1 ma major and trace element geochemistry shows that the monzogranite is characterized by high sio 2 and k 2 o contents a right inclined shape of the chondrite normalized ree patterns enrichment of large ion lithophile elements liles and depletion of high field strength elements hfses such as nb p ba the monzogranite is high k calc alkaline has a strong negative eu anomaly eu eu 0 04 0 45 low p 2 o 5 content high a cnk of 1 2 enriched in large ion lithophile elements liles such as rb th u nd and hf and notably depleted in ba sr p ti and nb these characteristics define the dayana monzogranite as a highly fractionated peraluminous granite re os isotopic analysis of seven molybdenite samples from the deposit yield an isochron age of 133 3 ma mswd 2 2 which indicates that the monzogranite and ore have the same age within error are probably genetically related and related to a major early cretaceous mineralizing event in china known as the yanshanian

eruption processes and facies architecture of the orion central kimberlite volcanic complex fort a la corne saskatchewan kimberlite mass flow deposits in a sedimentary basin abstract the fort a la corne diamondiferous kimberlite field consists of at least 70 bodies of volcaniclastic kimberlite hosted within a contemporaneous non volcanic sedimentary succession this study of the three dimensional stratigraphy and facies architecture across the orion central kimberlite volcanic complex highlights the variations in upper and extra vent processes the sedimentary succession consists of continental to marginal marine quartz sandstones and mudstones overlain by marginal to deep marine dark mudstone and muddy sandstones and siltstones relatively thin conformable volcaniclastic kimberlite packages are interbedded throughout the host rock stratigraphy extremely thick up to at least 211 m thick discordant to concordant volcaniclastic packages series infill at least three elongate northwest trending craters 145a 145b and 219 craters and contain laterally equivalent conformable extra crater deposits bound by marine mudstones indicative of a prevailing dominantly marine environment the volcaniclastic deposits within the 145a and 145b craters respectively are separated by a considerable hiatus whereas the deposit infilling the 219 crater was formed around the same time as 145b crater deposit multiple depositional units of massive to stratified olivine rich sand to pebble sized volcaniclastic facies infill craters and were emplaced by megaturbidite pulses fed by crystal rich eruption fountains which interacted with the crater relief stacked normally graded thick to very thick bedded matrix supported olivine rich facies characterized by brief depositional breaks between some beds represent syn to post eruptive turbidite pulses associated with the early eruptive event in the 145a crater thin layers of light grey kimberlitic mudstone underlie or occur near the base of and above the main volcaniclastic packages associated with the 145b and 219 eruptions crater infilling volcaniclastic deposits were later reworked by storm induced currents into thin to medium graded moderately sorted fine to coarse olivine rich sandstone with intercalated discontinuous muddy laminae laminated to cross laminated olivine rich silt to sand sized volcaniclastic facies constitutes a small volume volcaniclastic turbidite which marks the last preserved kimberlite emplacement event at orion central

40ar 39ar dating of volcanism and subsequent very low grade metamorphism in a subsiding basin example of the cretaceous lava series from central chile abstract 40ar 39ar geochronological method is applied to date both emplacement and subsequent very low grade metamorphism of a thick lava series the veta negra formation from the cordon de chacana area in the coastal range of central chile on the same lava series and even on the same rock sample it was possible to measure apparently valid ages of both the emplacement of lava flows by dating transparent plagioclase and the very low grade metamorphic event by dating sericite and or adularia sericite was dated on step heated single grains of strongly altered plagioclases the radiogenic argon from remaining fresh plagioclase appearing as negligible on most part of the age spectrum the concordance between one plateau age of 118 7 0 6 ma displayed by fresh plagioclase and a previously measured plateau age on plagioclase from one lava flow from a region due west from santiago bustamante hill aguirre l feraud g morata d vergara m robinson d 1999 time interval between volcanism and burial metamorphism and rate of basin subsidence in a cretaceous andean extensional setting tectonophysics 313 433 447 may indicate that the volcanic activity of the veta negra formation was synchronous along the 80 km long latitudinal segment studied ages of 96 8 0 2 and 97 0 1 6 ma displayed by adularia and sericite respectively are slightly older than ages of 93 94 ma given by adularia from the bustamante hill these data allow to define a period of about 22 ma between volcanism and metamorphism because of the contemporaneity of some metamorphic minerals and cretaceous plutons of the region the very low grade metamorphic event may be the result of the additional effect of burial and a regional thermal event nevertheless a significant effect of burial relatively to the contribution of high thermal gradient event s seems revealed by an apparent age gradient on very low grade minerals with the stratigraphic depth

assessing the macrofracture method for identifying stone age hunting weaponry abstract macrofracture analysis is an experimentally derived method used as an initial step in investigating the hunting function of stone artefacts diagnostic impact fractures which can only develop as a result of longitudinal impact underpin this method macrofracture analysis recently gained favour in middle stone age studies supporting hypotheses for effective hunting during the late pleistocene in southern africa however the factors affecting diagnostic impact fracture formation and the interpretation of these fracture frequencies are not yet fully understood this paper outlines a set of experiments designed to test macrofracture formation under human and cattle trampling and knapping conditions the results show that a macrofractures occur frequently when stone artefacts are trampled by cattle and humans and in knapping debris b diagnostic impact fractures occur on some of the trampled flakes and knapping debris 3 but significantly less often than in previous hunting experiments c when they do occur they are likely produced by longitudinal forces similar to those experienced during hunting d considering artefact morphology is important during macrofracture analysis and e macrofracture analysis is not a standalone method but is most useful as part of a multi analytical approach to functional analysis these experiments help to establish a significant baseline diagnostic impact fracture frequency for the interpretation of archaeological macrofracture frequencies

the initiation and development of a caldera forming plinian eruption 172 ka lower pumice 2 eruption santorini greece the rhyodacitic 172 ka lower pumice 2 lp2 eruption terminated the first magmatic cycle at santorini greece producing a proximal 50 m thick succession of pyroclastic fall deposits diffusely stratified to massive ignimbrites and multiple lithic breccias the eruption commenced with the development of a short lived precursory eruption column depositing a 15 cm blanket of 1 2 cm sized pumice fragments at near vent localities lp2 a1 the precursor deposits are conformably overlain by a 30 m thick sequence of reversely graded ungraded pumice fall deposits that reflect opening and widening of a point source vent increasing mass discharge rates up to 108 kg s 1 and the development of a 36 km high plinian eruption column lp2 a2 a3 the progressive increase in maximum vesicle number density nvf in rhyodacitic pumice from 3 2 109 cm 3 in the basal fall unit of lp2 a2 1 to 9 2 109 cm 3 in lp2 a3 translates to an increase in magma decompression rate from 18 to 29 mpa s 1 over the course of the initial plinian phase this is interpreted to be a consequence of progressive vent widening and a deepening of the fragmentation surface such interpretations are supported by the increase in lithic clast abundance vertically through lp2 a and the occurrence of basement derived deep lithic components in lp2 a3 the increasing lithic clast content and the inability to effectively entrain air into the eruption column due to vent widening resulted in column collapse and the development of pyroclastic density currents pdcs lp2 b a major vent excavation event or the opening of new vents possibly associated with incipient caldera collapse facilitated the ingress of water into the magmatic system the development of widespread pdcs and the deposition of a 20m thick massive phreatomagmatic tuff lp2 c the eruption cumulated in catastrophic caldera collapse the enlargement of a pre existing flooded caldera and the discharge of lithic rich pdcs depositing proximal 9 m thick lithic lag breccias lp2 d

tuffisitic kimberlites from the wesselton mine south africa mineralogical characteristics relevant to their formation abstract tuffisitic kimberlites from the wesselton mine consist in order of formation of the following primary components chloritized olivine macrocrysts and phenocrysts magmaclasts cryptocrystalline diopside phlogopite rich mantles and a smectite chlorite interclast matrix magmaclasts consist of one to several crystals of chloritized olivine set in a microcrystalline groundmass of diopside apatite perovskite spinel and chloritized and fresh phlogopite the latter commonly rimming chloritized olivines magmaclasts have some similarities to holocrystalline hypabyssal kimberlite but lack monticellite carbonate carbonate serpentine segregations and atoll spinels spinels in the magmaclasts show only a limited compositional evolution relative to spinels in spatially associated hypabyssal kimberlite pre existing solids including discrete olivine grains magmaclasts and most xenoliths are mantled by acicular diopside and phlogopite the interclast matrix is now represented by mixed layer phyllosilicates chlorite smectites that are poorer in alumina and iron than chlorite pseudomorphing olivine and microlitic phlogopite and diopside the interclast chlorite smectite is considered to represent former phlogopite which has undergone late stage deuteric hydrothermal like modification the interclast matrix crystallized from the volatile rich remnants of the magma none of the constituents of tuffisitic kimberlites including the chlorite or chlorite smectites represent material formed from externally derived fluids these primary textures are unique to kimberlites and only form in certain circumstances tuffisitic kimberlites formed by progressive crystallization and volatile exsolution induced segregation and or disruption within a kimberlite magma magmaclasts mantles interclast matrix during a continuum of rapidly changing conditions in a subsurface subvolcanic magmatic system this continuum represents a transition from a degassing magmatic system to a magmatic derived hydrothermal like fluid rapid drops in temperature with extensive exsolution of co 2 and incorporation of large amounts of locally derived country rock xenoliths resulted in explosive diatreme formation and within diatreme modification of the crystallization and deuteric replacement sequence of typical kimberlite magma resulting in a distinctive mineralogy and texture

the basalt pipes of the tunguska basin siberia russia high temperature processes and volatile degassing into the end permian atmosphere abstract a number of mechanisms have been proposed to explain the end permian crisis many of them explore the link between this catastrophe and the siberian traps we test the hypothesis that eruption of thermogenic gas generated in contact aureoles around igneous sills intruded into evaporite sequences of the tunguska basin triggered the crisis in particular we test the idea that the aspect that breccia pipes represent conduits for voluminous gas migration from the deep basins to the atmosphere this contribution sheds new light on the pipe formation based on new field and borehole observations and electron microscopy analyses of more than three hundred mapped magnetite bearing basalt pipes 43 are classified as diatremes the diatremes are usually circular or elliptical with multiple zones of brecciation reaching the surface sometimes with preserved in filled crater lakes the pipe diameter on the surface varies from a few tens of meters for small single diatremes to about a kilometer the largest crater lake area is 2 7 km 2 we have conducted a detailed study of the breccias in the sholokhovsk basalt pipe located within the nepa potash deposit in the tunguska basin siberia russia about n 59 and e 107 and find that the breccias are cemented by carbonate matrix calcite dolomite and halite breccia clasts are altered at various temperatures evidenced by growth of albite and garnet from basaltic glass and diopside garnet magnetite and chlorine bearing amphibole up to 1 8 cl in altered magmatic clasts these mineral assemblages suggest high temperature interactions with evaporites within the pipe conduits the large number of pipes support that degassing of halogen rich volatiles was a widespread and violent process with implications for the end permian crisis

thermal history of an early paleozoic epithermal deposit constraints from 40ar 39ar and u th he thermochronology at zhengguang eastern central asian orogenic belt abstract the zhengguang epithermal au zn deposit located in heilongjiang province ne china is an early paleozoic intermediate sulfidation epithermal deposit which is adjacent to the duobaoshan and tongshan porphyry cu deposits in the duobaoshan magmatic arc eastern central asian orogenic belt caob our new 40ar 39ar dating presents plateau ages of 276 9 1 2 ma mswd 1 5 for adularia and 265 7 1 2 ma mswd 3 5 for illite these ages are clearly younger than the mineralization age of zhengguang 480 ma and therefore represent a post ore event which reset the adularia and illite argon systems the resetting event could be related to post collision of xing an block and songliao xilinhot block the weighted mean of zircon u th he ages zhe and apatite u th he ages ahe from the same dacite porphyry with illite dating sample are 192 10 ma mswd 2 2 and 98 8 5 3 ma mswd 2 1 respectively the zhe age 190 ma indicates a tectonothermal resetting event possibly related to the development of tongshan fault whereas the ahe age 100 ma likely reflects 3 km deep burial at zhengguang the intra sample variations of u th he ages for zircon grains are mainly due to radiation damage while those for apatite are unknown we argue that the post ore volcanic eruption and slow uplift and exhumation rate caused by rollback of the paleo pacific plate could facilitate burial and preservation of the epithermal and by inference porphyry deposits in ne china considering the complex collisional and amalgamation history in this area we believe that there is exploration potential for ancient porphyry and epithermal deposits within the eastern section of the caob

a segment is not a monolith evidence from the howiesons poort of sibudu south africa segments from the howiesons poort of sibudu south africa can be separated into at least three populations based on quartz hornfels and dolerite rocks used for their production length breadth thickness and tip cross sectional areas are significantly different between segments made on the three rock types segments are not monoliths and they were not intended as a single tool type they were flexible enough to be mounted to shafts in a variety of ways several hafting strategies are evident including the use of different adhesive recipes most segments were probably parts of hunting weapons based on use trace analysis but weapon types varied quartz segments have standardized shapes short and deep perhaps because they were hafted as transverse arrowheads while hornfels and dolerite segments may on occasion also have been parts of projectiles the large dolerite segments could sometimes have served as parts of spearheads with two segments hafted back to back howiesons poort segment technology is sophisticated its makers appreciated distinct properties of rocks their flaking wear and impact possibilities further they recognized the best sizes and shapes for use with each kind of weapon they understood the qualities and applications of various adhesive recipes and they knew how to make a variety of hafts from materials that included bone and wood

a techno functional perspective on quartz micro notches in sibudu s howiesons poort indicates the use of barbs in hunting technology abstract in this paper we present the results of a use wear study of quartz micro notches identified during a technological analysis of lithics from the howiesons poort layers of sibudu cave building on the technological analysis and preliminary functional screening of the archaeological material a series of experiments was designed to evaluate different hypotheses for notch formation blank production intentional notching hafting projectile use and trampling the experimental reference collection was compared with archaeological micro notches and a large sample of other archaeological quartz pieces including bladelets bipolar blanks flakes and retouched pieces this allowed us to evaluate the causes of micro notch formation in the studied assemblage results indicate two novelties in the howiesons poort hunting technology at sibudu the use of quartz barbs and non retouched quartz blanks it seems that in addition to backed pieces segments obliquely backed points etc unretouched pieces were mounted as elements in hunting weapons during the howiesons poort techno tradition seven probable and 29 tentative barbs were identified we thus present one of the strongest and oldest bodies of evidence for the use of barbs as projectile elements

a new approach to kimberlite facies terminology using a revised general approach to the nomenclature of all volcanic rocks and deposits descriptive to genetic although kimberlite pipes bodies are usually the remains of volcanic vents in vent deposits and subvolcanic intrusions the terminology used for kimberlite rocks has largely developed independently of that used in mainstream volcanology existing kimberlite terminology is not descriptive and includes terms that are rarely used used differently and even not used at all in mainstream volcanology in addition kimberlite bodies are altered to varying degrees making application of genetic terminology difficult because original components and depositional textures are commonly masked by alteration this paper recommends an approach to the terminology for kimberlite rocks that is consistent with usage for other volcanic successions in modern terrains the eruption and emplacement origins of deposits can often be readily deduced but this is often not the case for old variably altered and deformed rock successions a staged approach is required whereby descriptive terminology is developed first followed by application of genetic terminology once all features including the effects of alteration on original texture and depositional features together with contact relationships and setting have been evaluated because many volcanic successions consist of both primary volcanic deposits as well as volcanic sediments terminology must account for both possibilities

middle stone age bone tools from the howiesons poort layers sibudu cave south africa abstract recently discovered bone implements from middle stone age msa deposits at sibudu cave south africa confirm the existence of a bone tool industry for the howiesons poort hp technocomplex previously an isolated bone point from klasies river provided inconclusive evidence this paper describes three bone tools two points and the end of a polished spatula shaped piece from unequivocal hp layers at sibudu cave with ages greater than 61 ka comparative microscopic and morphometric analysis of the sibudu specimens together with bone tools from southern african middle and later stone age lsa deposits an iron age occupation nineteenth century bushman hunter gatherer toolkits and bone tools used experimentally in a variety of tasks reveals that the sibudu polished piece has use wear reminiscent of that on bones experimentally used to work animal hides a slender point is consistent with a pin or needle like implement while a larger point reminiscent of the single specimen from peers cave parallels large un poisoned bone arrow points from lsa iron age and historical bushman sites additional support for the sibudu point having served as an arrow tip comes from backed lithics in the hp compatible with this use and the recovery of older larger bone and lithic points from blombos cave interpreted as spear heads if the bone point from the hp layers at sibudu cave is substantiated by future discoveries this will push back the origin of bow and bone arrow technology by at least 20 000 years and corroborate arguments in favour of the hypothesis that crucial technological innovations took place during the msa in africa

a practical guide to terminology for kimberlite facies a systematic progression from descriptive to genetic including a pocket guide kimberlite terminology remains problematic because both descriptive and genetic terms are mixed together in most existing terminology schemes in addition many terms used in existing kimberlite terminology schemes are not used in mainstream volcanology even though kimberlite bodies are commonly the remains of kimberlite volcanic vents and edifices we build on our own recently published approach to kimberlite facies terminology involving a systematic progression from descriptive to genetic the scheme can be used for both coherent kimberlite i e kimberlite that was emplaced without undergoing any fragmentation processes and therefore preserving coherent igneous textures and fragmental kimberlites the approach involves documentation of components textures and assessing the degree and effects of alteration on both components and original emplacement textures this allows a purely descriptive composite component textural and compositional petrological rock or deposit name to be constructed first free of any biases about emplacement setting and processes then important facies features such as depositional structures contact relationships and setting are assessed leading to a composite descriptive and genetic name for the facies or rock unit that summarises key descriptive characteristics emplacement processes and setting flow charts summarising the key steps in developing a progressive descriptive to genetic terminology are provided for both coherent and fragmental facies deposits rock units these can be copied and used in the field or in conjunction with field e g drill core observations and petrographic data because the approach depends heavily on field scale observations characteristics and process interpretations only the first descriptive part is appropriate where only petrographic observations are being made where field scale observations are available the progression from developing descriptive to interpretative terminology can be used especially where some petrographic data also becomes available

complex variations during a caldera forming plinian eruption including precursor deposits thick pumice fallout co ignimbrite breccias and climactic lag breccias the 184 ka lower pumice 1 eruption sequence santorini greece the 184 ka lower pumice 1 eruption sequence records a complex history of eruption behaviours denoted by two significant eruptive phases 1 a minor precursor lp1 pc and 2 a major plinian phase lp1 a b c the precursor phase produced 13 small volume pyroclastic fallout surge and flow deposits which record the transition from a dominantly magmatic to a phreatomagmatic eruptive style and exhibit a normal dacite to andesitic dacite to reverse andesitic dacite to dacite compositional zonation of juvenile pyroclasts in the stratigraphy incipient bioturbation and variability in unit thickness and lithology reflect multiple time breaks and highlight the episodic nature of volcanism prior to the main plinian eruption phase the plinian magmatic eruption phase is defined by three major stratigraphic divisions including a basal pumice fallout deposit lp1 a an overlying valley confined ignimbrite lp1 b and a compositionally zoned rhyodacite to basaltic andesite lithic rich lag breccia lp1 c which caps the sequence this sequence records the initial development of a buoyant convective eruption column and the transition to eruption column and catastrophic late stage caldera collapse events similarities in pyroclast properties i e chemistry density between the plinian fallout lp1 a and pyroclastic flow lp1 b deposits indicate that changes in magma properties exerted no influence on the dynamics and temporal evolution of the lp1 eruption conversely lithic breccias at the base of the lp1 b ignimbrite suggest that the transition from a buoyant convective column to column collapse was facilitated by mechanical erosion of the conduit system and or the initiation of caldera collapse leading to vent widening an increase in magma discharge rate and the increased incorporation of lithics into the eruption column causing mass overload lithic rich lag breccia deposits lp1 c which cap the eruption sequence record incremental high energy caldera collapse events whereby downfaulting occurred in discrete jumps resulting in variable magma discharge rates and the development of a fissure vent system

kimberlite wall rock fragmentation processes venetia k08 pipe development current kimberlite pipe development models strongly advocate a downward growth process with the pipe cutting down onto its feeder dyke by means of volcanic explosions evidence is presented from the k08 kimberlite pipe in venetia mine south africa which suggests that some pipes or sub components of pipes develop upwards the k08 pipe in pit exposure comprises 90 vol chaotic mega breccia of country rock clasts gneiss and schist and 10 vol coherent kimberlite sub horizontal breccia layers tens of metres thick are defined by lithic clast size variations and contain zones of shearing and secondary fragmentation textural studies of the breccias and fractal statistics on clast size distributions are used to characterize sheared and non sheared breccia zones and to deduce a fragmentation mechanism breccia statistics are compared directly with the statistics of fragmented rock produced from mining processes in order to support interpretations results are consistent with an initial stage of brecciation formed by upward moving collapse of an explosively pre conditioned hanging wall into a sub terranean volcanic excavation our analysis suggests that the pre conditioning is most likely to have been caused by explosions either phreatic or phreatomagmatic in nature with a total energy output of 2 7 109 kj 656 t of tnt a second stage of fragmentation is interpreted as shearing of the breccia caused by multiple late kimberlite intrusions and possible bulk movement of material in the pipe conduit related to adjacent volcanism in the k02 pipe

sedimentologic and stratigraphic constraints on emplacement of the star kimberlite east central saskatchewan abstract diamond bearing kimberlites in the fort a la corne region east central saskatchewan consist primarily of extra crater pyroclastic deposits which are interstratified with lower cretaceous albian and cenomanian marine marginal marine and continental sediments approximately 70 individual kimberlite occurrences have been documented the star kimberlite occurring at the southeastern end of the main fort a la corne trend has been identified as being of economic interest and is characterized by an excellent drill core database integration of multi disciplinary data sets has helped to refine and resolve models for emplacement of the star kimberlite detailed core logging has provided the foundation for sedimentological and volcanological studies and for construction of a regionally consistent stratigraphic and architectural framework for the kimberlite complex micropaleontologic and biostratigraphic analysis of selected sedimentary rocks and u pb perovskite geochronology on kimberlite samples have been integrated to define periods of kimberlite emplacement radiometric age determination and micropaleontologic evidence support the hypothesis that multiple kimberlite eruptive phases occurred at star the oldest kimberlite in the star body erupted during deposition of the predominantly continental strata of the lower mannville group cantuar formation kimberlites within the cantuar formation include terrestrial airfall deposits as well as fluvially transported kimberlitic sandstone and conglomerate successive eruptive events occurred contemporaneous with deposition of the marginal marine upper mannville group pense formation kimberlites within the pense formation consist primarily of terrestrial airfall deposits fine to medium grained cross stratified kimberlitic olivine dominated sandstone in this interval reflects reworking of airfall deposits during a regional marine transgression the location of the source feeder vents of the cantuar and pense kimberlite deposits has not been identified the youngest and volumetrically most significant eruptive events associated with the star kimberlite occur within the predominantly marine lower colorado group joli fou and viking formations kimberlite beds which occur at several horizons within these units consist of subaerial and marine fall deposits the latter commonly exhibiting evidence of wave reworking black shale encased resedimented kimberlite beds likely deposited as subaqueous debris flows and turbidites are particularly common in the lower colorado group during its multi eruptive history the star kimberlite body is interpreted to have evolved from a feeder vent and overlying positive relief tephra ring into a tephra cone initial early joli fou volcanism resulted in formation of a feeder vent 200 m diameter and tephra ring subsequent eruptions dominated by subaerial deposits partly infilled the crater and constructed a tephra cone a late joli fou eruption formed a small 70 m diameter feeder pipe slightly offset to the nw of the early joli fou feeder vent deposits from this event further infilled the crater and were deposited on top of early joli fou kimberlite proximal to the vent and sediments of the joli fou formation distal to the vent the shape of the tephra cone was modified during multiple marine transgression and regression cycles coeval with deposition of the lower colorado group resulting in wave reworked kimberlite sand along the fringes of the cone and kimberlitic event deposits tempestites turbidites debris flows in more distal settings

the internal geology and emplacement history of the renard 2 kimberlite superior province quebec canada abstract the renard 2 kimberlite is located in the otish mountains region of quebec canada and is one of the largest pipes in the renard cluster the cluster consists of nine kimberlite bodies and was discovered in 2001 by ashton mining of canada inc and its joint venture partner soquem inc renard 2 was emplaced into archean meta greywacke derived migmatite gneiss and granite of the opinaca subprovince of the eastern superior province at approximately 640 5 2 8 ma an undetermined amount of erosion has occurred since emplacement with the present surface expression of the pipe estimated to be 0 75 ha this kimberlite is interpreted as a steep sided diatreme with minor irregularities in the external shape the dominant infill is a massive volcaniclastic kimberlite mvk that is classified as tuffisitic kimberlite breccia tkb and is characterized by a high proportion of granitoid country rock xenoliths a second dominant infill is a texturally complex less diluted coherent kimberlite ck characterized locally by a transitional textures between ck and tkb surrounding the diatreme is a significant zone of variable width comprised of extensively brecciated country rock kimberlite and referred to as marginal breccia in addition to the two main rock types infilling the pipe a number of hypabyssal kimberlite hk dykes and irregular shaped intrusions occur throughout the body along the pipe contacts within the marginal breccia and in the surrounding country rock geological features displayed by renard 2 are similar to those described from class 1 kimberlites of the kimberley area of south africa the gahcho kue cluster of canada and the pimenta bueno kimberlite field of brazil the economic evaluation of renard 2 is in progress and to date has included extensive diamond and reverse circulation drilling as well as the collection of an underground bulk sample results from material sampled from renard 2 including a 2449 tonne bulk sample suggest renard 2 has an estimated diamond content of 83 cpht carats per hundred tonnes a three dimension geology model of the pipe has been developed following the investigation of drill cores subsurface mapping and petrography combined with diamond studies and geophysics the model produced is being used to guide and direct the evaluation of the kimberlite and unravel the emplacement history of the pipe

adularia in epithermal veins queensland morphology structural state and origin four types of adularia i e sub rhombic rhombic tabular and pseudo acicular are recognised from examination of samples from ten epithermal vein deposits and prospects in queensland based on morphology of the individual crystals further investigation of the structural state of adularia reveals that each group has some specific features in terms of the degree of al si disordering which can be related to various crystallisation conditions and the thermal history sub rhombic adularia is commonly 2 4 mm in size and subhedral with more or less rhombic outlines and has a relatively ordered al si distribution 2t1 0 84 reflecting slow crystallisation conditions adularia of this type in association with coarse grained quartz is predominant at deep levels of epithermal systems where boiling is initiated in an environment of low permeability and the fluid is slightly supersaturated with respect to adularia and quartz tabular adularia characterised by its lath shape and disordered structure 2t1 values ranging from 0 64 to 0 74 is likely to have formed when the fluid moves up to a more permeable environment and starts boiling violently relatively high temperatures and rapidly changing conditions account for its special morphology and disordered structure rhombic adularia showing very small crystal size 0 2 mm with euhedral rhombic form has an intermediate degree of al si ordering pseudo acicular adularia is interpreted as pseudomorphs after carbonate and its high al si ordered structure is attributed to the presence of a carbonate precursor these two types of adularia commonly occur within crustiform and colloform bands in association with high grade ore and chalcedony or fine grained quartz which often displays various recrystallisation textures it is most likely that adularias of these two types are formed when extensive boiling is protracted microprobe analyses indicate the composition of all adularia types close to pure kalsi3o8 sericite and or carbonate altered adularias consistently display more ordered structures suggesting that the post crystallisation thermal regime affects the structural state of altered adularia even at temperatures as low as in epithermal environments

new knapping methods in the howiesons poort at sibudu kwazulu natal south africa abstract the lithic technology study of layer grey sand at sibudu reveals a large number of cores on flakes varying knapping methods of core reduction are presented here most of the core reduction techniques can be attributed to bladelet or small flake production also we point to a new type of blade production from prismatic cores revealed by the study of debitage these innovative knapping methods demonstrate the technological variability associated with howiesons poort lithic assemblages

experimental tests of middle palaeolithic spear points using a calibrated crossbow abstract controlled experiments using a calibrated crossbow to thrust stone tipped spears into animal carcasses reveal a relationship between levallois point morphology and their performance as spear points a comparative study of morphometric variation of levallois points from levantine mousterian contexts supports the hypothesis that the demand for stone spear points was an important factor in levallois point production

gold mineralization in the northern margin of the north china craton influence of alkaline magmatism and regional tectonic during middle paleozoic mesozoic abstract the northern margin of north china craton nncc has undergone multiple tectonic and magmatic episodes associated with numerous gold mineralization during devonian to cretaceous the origin of gold mineralization is a subject of debate in the nncc but there is a consensus on a metamorphic hydrothermal origin and a magmatic hydrothermal origin for this study we focused on four gold districts including the daqingshan zhangjiakou west liaoning and changbaishan from west to east we specifically constrain the link between the hadamengou dongping jinchanggouliang erdaogou and haigou gold deposits and their magmatic episodes the dahuabei and haigou granites and dongping syenite rocks have an alkaline affinity in contrast the xitaizi jinchanggouliang and xiaoxigou granites as well as the duimiangou quartz monzonites are calc alkaline with high alkaline rocks they are predominantly metaluminous and high fractionated i type granites except the xiaoxigou granite which is a type granites with peraluminous nature this indicates a variable mixing between depleted mantle derived mafic magma and ancient crust derived magma the magmatic events overlap the gold mineralization episodes in the nncc we have identified four magmatic episodes during middle paleozoic to mesozoic at 400 320 ma 245 221 ma 199 161 ma and 143 125 ma on the other hand gold mineralization was emplaced from carboniferous to cretaceous 390 110 ma with a peak in the middle jurassic 170 160 ma the available sulfur oxygen and carbon isotopic data from the studied nncc gold deposits suggest that the ore forming fluids were derived from a mixture of magmatic fluids and meteoric waters that flow in the wall rocks except for the hadamengou and jinchanggouliang gold deposits both late deposits present a multi source involving organic matter and other regional crustal rocks as shown by their positive 34s values 0 6 18 5 the intrusive rocks and sulfides in the nncc display similar lead isotope data suggesting that the lead isotopes might have similar origin the gold forming materials resulting from the mixing of these fluids are the product of several alkaline magmatism activities in this region hence this study has proved that gold mineralization is spatially and temporally related to the alkaline magmatism in the nncc the dominant tectonic events in the nncc are marked by post collisional or anorogenic geodynamical setting which is characterized by high alkaline features and andean type arc related to subduction geodynamical setting and characterized by calc alkaline features of the studied rocks both tectonic events are controlled by 1 the collision between the ncc and the bainaimiao arc 2 the subduction of the paleo asian ocean plate beneath the ncc 3 the collision between the siberian craton and the ncc and 4 the subduction of the western paleo pacific beneath the ncc these tectonic regimes are expressed by a transitional regime changing from compression to extension at western and an extensional regime at western and eastern parts of the nncc respectively

characteristics and alteration origins of matrix minerals in volcaniclastic kimberlite of the muskox pipe nunavut canada abstract the matrix of volcaniclastic kimberlite vk from the muskox pipe northern slave province nunavut canada is interpreted to represent an overprint of an original clastic matrix muskox vk is subdivided into three different matrix mineral assemblages that reflect differences in the proportions of original primary matrix constituents temperature of formation and nature of the altering fluids using whole rock x ray fluorescence xrf whole rock x ray diffraction xrd microprobe analyses back scatter electron bse imaging petrography and core logging we find that most matrix minerals serpentine phlogopite chlorite saponite monticellite fe ti oxides and calcite lack either primary igneous or primary clastic textures the mineralogy and textures are most consistent with formation through alteration overprinting of an original clastic matrix that form by retrograde reactions as the deposit cools or in the case of calcite by precipitation from ca bearing fluids into a secondary porosity the first mineral assemblage consists largely of serpentine phlogopite calcite fe ti oxides and monticellite and occurs in vk with relatively fresh framework clasts alteration reactions driven by deuteric fluids derived from the juvenile constituents promote the crystallisation of minerals that indicate relatively high temperatures of formation 400 c lower temperature minerals are not present because permeability was occluded before the deposit cooled to low temperatures thus shielding the facies from further interaction with fluids the other two matrix mineral assemblages consist largely of serpentine phlogopite calcite diopside and chlorite they form in vk that contains more country rock which may have caused the deposit to be cooler upon emplacement most framework components are completely altered suggesting that larger volumes of fluids drove the alteration reactions these fluids were likely of meteoric provenance and became heated by the volcaniclastic debris when they percolated into the vk infill most alteration reactions ceased at temperatures 200 c as indicated by the absence or paucity of lower temperature phases in most samples such as saponite recognition that muskox vk contains an original clastic matrix is a necessary first step for evaluating the textural configuration which is important for reconstructing the physical processes responsible for the formation of the deposit

projectile impact fractures and launching mechanisms results of a controlled ballistic experiment using replica levallois points abstract identifying the use of stone tipped projectile weapons in prehistory is important for understanding hominin strategic behavior and cognitive capacities such identifications are based on diagnostic impact fractures difs assumed to form as a result of collisions between the tips and organic materials in the prey body however demonstrating weapon use requires documenting an impact speed and or kinetic energy beyond those likely to occur accidentally or as a by product of other tasks we present a new experiment aimed at investigating the influence of speed on impact fracture formation in controlled conditions using an air gun we fired 234 nearly identical spears tipped with copies of a levallois point cast in soda lime glass into a composite target made of polyurethane bone like plates ballistic gelatin and leather the impact speed ranged from 7 to 30 m s and the impact angle ia varied in increments of 15 from 90 to 45 we show that realistic difs can be produced under these controlled conditions the frequency of longitudinal tip macrofractures is directly proportional to the impact speed but inversely proportional to the ia the relationship between the tip fracture type and the type of damage left on the target explains the contact conditions for the formation of different difs no relationship between either initiation or termination type and speed could be established therefore we conclude that step terminating bending fractures should not be considered diagnostic of weapon use without further supporting evidence further although fracture length increases with speed when ia is held constant a great deal of overlap exists between trials with different ias given the expected high variance in ia in real hunting situations large longitudinal macrofractures on the tips of archaeologically recovered lithics should not automatically be interpreted as resulting from the use of high speed projectiles we discuss the study s implications for the differentiation of prehistoric weapon delivery systems especially regarding recognizing stonetipped weapon use by neandertals

experimental use and quantitative performance analysis of triangular flakes levallois points used as arrowheads the invention and widespread use of projectile weaponry is a characteristic presumed to exist only with homo sapiens however as finds of wooden material during the early development of projectile weapons are extremely rare this remains a contentious topic recent work has proposed a series of ballistically significant morphological characteristics of stone points that yield information about their potential use here we report on initial experimental approaches to quantifying the performance of relatively simple stone points as arrow armatures two experimental trials were performed using a series of 51 levallois points the first against a uniform density target was designed to give an overall indication of performance the second against a simulated animal carcass demonstrated the durability of these points the results of this study suggest that small levallois points could have functioned as arrowheads albeit ones likely to break after limited use they also suggest that these points penetrating power is strongly controlled by their morphometric characteristics most notably their perimeter this latter finding refines a method for assessing hypothetical paleolithic stone points on the basis of tip cross sectional area previously proposed by others

the geology of kimberlite pipes of the ekati property northwest territories canada abstract this paper reviews key characteristics of kimberlites on the ekati property nwt canada to date 150 kimberlites have been discovered on the property five of which are mined for diamonds the kimberlites intrude archean basement of the central slave craton numerous proterozoic diabase dykes intrude the area the precambrian rocks are overlain by quaternary glacial sediments no phanerozoic rocks are present however mudstone xenoliths and disaggregated sediment within the kimberlites indicate that late cretaceous and tertiary cover likely

cemented ash as a receptacle or work surface for ochre powder production at sibudu south africa 58 000 years ago the white ash of sibudu hearths sometimes became cemented and when this was the case some of these crusts were used as work surfaces or receptacles particularly in occupations dating about 58 000 years ago substantial deposits of red and yellow ochre powder have been found on these crusts this suggests that the ochre was not associated with hearths for heat treatment because yellow ochre readily transforms to red even at low temperatures xrf readings suggest that the ochre used at the site derives from different geological sources micromorphological studies imply that phosphatization caused the cementation of the ashes in some hearths while gypsum growth hardened one of the hearths described here

maar diatreme volcanoes a review maar diatreme volcanoes are produced by explosive eruptions that cut deeply into the country rock a maar is the crater cut into the ground and surrounded by an ejecta ring while the diatreme structure continues downward and encloses diatreme and root zone deposits here we attempt an evenhanded review of maar diatreme volcanology that extends from mafic to kimberlitic varieties and from historical maar eruptions to deeply eroded or mined diatreme structures we conclude that maar diatreme eruptions are episodic ejecta rings provide invaluable insight into eruption processes and sequence but are incomplete records of diatreme formation deposits within the diatreme structure include in varying proportions lower unbedded deposits sometimes typified by subvertical contacts among domains of debris emplaced sequentially and upper bedded deposits formed by sedimentation on surfaces open to the atmosphere a basal root zone comprises the transition from coherent magmatic feeder dike to clastic deposits formed by fragmentation of magma and enclosing country rock root zones are irregular in form and the clastic deposits are typically intruded by contorted dikes irregular root zone like chaotic breccias cut by contorted dikes are also present within diatreme deposits where they represent intra diatreme fragmentation zones and record changes in the location of the explosion locus during eruption

design and performance of microlith implemented projectiles during the middle and the late epipaleolithic of the levant experimental and archaeological evidence abstract the study comprises an experimentally based investigation of interaction between temporal change in the morphology of microlithic tools and transformations in projectile technology during the late pleistocene in the levant archery experiments with differently designed arrows fitted with various types of microliths representing subsequent epipaleolithic cultures of the levant allowed analyzing performance abilities of the arrows identifying projectile damage types characteristic of particular hafting modes detecting factors influencing the frequency of projectile damage and estimating the frequency of projectile damage expected to be found in archaeological samples the data obtained through the experiments applied in the analysis of the archaeological microliths from geometric kebaran and natufian sites in israel indicate different approaches to the design of projectiles fitted with microliths characteristic for these cultures the shift in design associated with such important economic and social transformations as transition to sedentary settlements and a broad spectrum economy may reflect a demand for light flexible and efficient projectile weapons requiring low time and labor investment for preparation and retooling the use of such efficient weapons in conditions of growing population density and restricted areas available for natufian hunter gatherers can be considered as one of the factors that could have affected the subsequent transition to food production that took place in the early holocene

an empirical test of the relative frequency of bipolar reduction in beds vi v and iii at mumba rockshelter tanzania implications for the east african middle to late stone age transition abstract mumba rockshelter tanzania is the only east african site spanning a continuous record of more than 100 000 years including the middle stone age msa to late stone age lsa transition rather than examine the presence or absence of traditional markers of behavioral modernity we have endeavored here to respond to the calls of shea 2011 and basell 2008 by examining the proportional similarity of a trait present throughout the msa lsa sequence at mumba rockshelter the bipolar technique of lithic reduction we use a quantified experimentally derived proxy to track the relative amount of bipolar percussion among mumba s beds vi v and iii namely waste shatter our examination of mehlman s previously unanalyzed collections from mumba demonstrates that in terms of bipolar production bed v is statistically indistinguishable from the late stone age lsa bed iii but significantly different from the middle stone age msa bed vi given that bed v dates to 56 9 4 8 49 1 4 3 ka cal bp this result is consistent with other evidence that the origins of the lsa in east africa began well before 40 kya and that mumba bed v represents one of the earliest manifestations of the lsa in east africa we conclude with a discussion of factors that may have influenced the increased dependence of bipolar production at the site

three dimensional potential field modelling of a multi vent maar diatreme the lake coragulac maar newer volcanics province south eastern australia abstract high resolution gravity and magnetic data have been acquired across lake coragulac a quaternary maar volcano located in the newer volcanics province of south eastern australia a gravity low is observed across the maar crater with several local gravity highs identified in the centre of the crater often with corresponding magnetic anomalies geophysical data has been integrated with geologic observations and subjected to 2d forward and 3d inverse potential field modelling modelling has revealed a complex subsurface maar structure with four coalesced diatremes and several intrusive dykes identified the modelled diatremes are shallow maximum of 290 m deep with the margins having a similar density to the host rock while the diatreme centre is often denser indicating that higher volumes of volcanic debris are present deposits of the maar rim sequence show frequent transitions between phreatomagmatic and magmatic fragmentation styles a result of fluctuations in magma rise rate and interactions with external water the complex nature of the underlying maar diatreme suggests that the maar formed from at least four vents which migrated laterally during the eruption

measuring use related fracture velocity in lithic armatures to identify spears javelins darts and arrows this study employs a brittle fracture mechanics based approach to explore the relationship between lithic fracture velocity and precursory loading rate in fine grained lithic armatures the data demonstrate that only high speed dart and arrow armatures are subject to dynamic loading events whereas spear and javelin armatures are limited to rapid and quasi static loading the data presented were derived from controlled experiments employing spears javelins spearthrower darts and arrows armatures associated with both bow and spearthrower technologies are reliably identified and distinguished from those of low speed technologies such as spears and javelins javelin armatures may also sustain higher velocity fractures than spear armatures thus permitting the further differentiation of these technologies the methodology offers a quantitative non subjective means to identify the delivery technology associated with a lithic armature

some major problems with existing models and terminology associated with kimberlite pipes from a volcanological perspective and some suggestions five significant problems hinder advances in understanding of the volcanology of kimberlites 1 kimberlite geology is very model driven 2 a highly genetic terminology drives deposit or facies interpretation 3 the effects of alteration on preserved depositional textures have been grossly underestimated 4 the level of understanding of the physical process significance of preserved textures is limited and 5 some inferred processes and deposits are not based on actual modern volcanological processes these issues need to be addressed in order to advance understanding of kimberlite volcanological pipe forming processes and deposits the traditional steep sided southern african pipe model class i consists of a steep tapering pipe with a deep root zone a middle diatreme zone and an upper crater zone if preserved each zone is thought to be dominated by distinctive facies respectively hypabyssal kimberlite hk descriptively called here massive coherent porphyritic kimberlite tuffisitic kimberlite breccia tkb descriptively here called massive poorly sorted lapilli tuff and crater zone facies which include variably bedded pyroclastic kimberlite and resedimented and reworked volcaniclastic kimberlite rvk porphyritic coherent kimberlite may however also be emplaced at different levels in the pipe as later stage intrusions as well as dykes in the surrounding country rock the relationship between hk and tkb is not always clear sub terranean fluidisation as an emplacement process is a largely unsubstantiated hypothesis modern in vent volcanological processes should initially be considered to explain observed deposits crater zone volcaniclastic deposits can occur within the diatreme zone of some pipes indicating that the pipe was largely empty at the end of the eruption and subsequently began to fill in largely through resedimentation and sourcing of pyroclastic deposits from nearby vents classes ii and iii canadian kimberlite models have a more factual descriptive basis but are still inadequately documented given the recency of their discovery the diversity amongst kimberlite bodies suggests that a three model classification is an over simplification every kimberlite is altered to varying degrees which is an intrinsic consequence of the ultrabasic composition of kimberlite and the in vent context few preserve original textures the effects of syn to post emplacement alteration on original textures have not been adequately considered to date and should be back stripped to identify original textural elements and configurations applying sedimentological textural configurations as a guide to emplacement processes would be useful the traditional terminology has many connotations about spatial position in pipe and of process perhaps the traditional terminology can be retained in the industrial situation as a general lithofacies mining terminological scheme because it is so entrenched however for research purposes a more descriptive lithofacies terminology should be adopted to facilitate detailed understanding of deposit characteristics important variations in these and the process origins for example every deposit of tkb is different in componentry texture or depositional structure however because so many deposits in many different pipes are called tkb there is an implication that they are all similar and that similar processes were involved which is far from clear

diffusion and fluid interaction in itrongay pegmatite madagascar evidence from in situ 40ar 39ar dating of gem quality alkali feldspar and u pb dating of protogenetic apatite inclusions alkali feldspar 40ar 39ar and apatite upb geochronological studies have typically invoked two mechanisms to account for apparent loss of radiogenic 40ar and 206 208pb some studies have suggested that the radiogenic isotopes were lost by volume diffusion and used these dates to constrain temporal variations of rock temperatures others have argued that the radiogenic isotopes were lost due to interaction with fluids and related these dates to chemical alteration these two end member interpretations have fundamentally different implications for tectonic models derived from geochronological data and therefore it is important to reliably identify the principal mechanism for loss of radiogenic isotopes here we revisit the mechanisms of 40ar loss in the famous gem quality alkali feldspar from the itrongay pegmatite in madagascar previous studies have suggested that volume diffusion is the dominant mechanism of 40ar loss providing key evidence to support the use of 40ar 39ar dating of alkali feldspar for thermochronology we attempted to verify these results by obtaining time temperature paths from petrologically characterised cogenetic feldspar and apatite from the itrongay pegmatite and comparing them with each other however our results suggest that only a minor component in the variability of 40ar 39ar dates of itrongay feldspar is related to the diffusive loss of 40ar and that this loss was not compatible with the majority of previously proposed models which hinders quantitative interpretations the crystal studied here grew in five episodes related to the influx initially of co existing dense sio2 rich solution and co2 dominated fluid the first and supposedly the following two episodes and subsequently of h2o rich fluid supposedly the final two episodes much greater component in the variability of the acquired 40ar 39ar dates is interpreted to reflect the differences in the ages of these growth episodes which we estimate to span from 477 ma to 176 ma the first four episodes apatite inclusions in this crystal are interpreted to be xenocrysts derived from the country rocks of the itrongay pegmatite these yield older upb dates than the estimated age of their host feldspar and have apparently experienced diffusive loss of 206 207pb prior to entrapment our 40ar 39ar results indicate that there is a lack of unambiguous evidence for diffusive loss of 40ar from alkali feldspar that can be readily interpreted for thermochronological purposes however in situ 40ar 39ar dating of alkali feldspar appears to be a promising tool for tracking fluid flow events in the earth s crust whose applicability is not restricted to sedimentary rocks our upb results corroborate previous suggestions that upb dating of apatite can be used for thermochronology

gamma ray spectrometry in the field radioactive heat production in the central slovakian volcanic zone we report 62 sets of measurements from central southern slovakia obtained using a modern portable gamma ray spectrometer which reveal the radioactive heat production in intrusive and extrusive igneous rocks of the late cenozoic central slovakian volcanic zone sites in granodiorite of the stiavnica pluton are thus shown to have heat production in the range 2 2 4 9 w m 3 this variability being primarily a reflection of variations in content of the trace element uranium sites in dioritic parts of this pluton have a lower but overlapping range of values 2 1 4 4 w m 3 sites that have been interpreted in adjoining minor dioritic intrusions of similar age have heat production in the range 1 4 3 3 w m 3 the main stiavnica pluton has zoned composition with potassium and uranium content and radioactive heat production typically increasing inward from its margins reflecting variations observed in other granodioritic plutons elsewhere it is indeed possible that the adjoining dioritic rocks hitherto assigned to other minor intrusions of similar age located around the periphery of the stiavnica pluton in reality provide further evidence for zonation of the same pluton the vicinity of this pluton is associated with surface heat flow 40 mw m 2 above the regional background on the basis of our heat production measurements we thus infer that the pluton has a substantial vertical extent our preferred estimate for the scale depth for its downward decrease in radioactive heat production being 8 km nonetheless this pluton lacks any significant negative bouguer gravity anomaly we attribute this to the effect of the surrounding volcanic caldera filled with relatively low density lavas masking the pluton s own gravity anomaly we envisage that emplacement occurred when the pluton was much hotter and thus of lower density than at present its continued uplift evident from the local geomorphology being the isostatic consequence of localized erosion the heat production in this intrusion evidently plays a significant role hitherto unrecognized in the regional geothermics

the history of vein formation determined by 40ar 39ar dating of adularia in the hosen 1 vein at the hishikari epithermal gold deposit japan the hosen 1 vein has a symmetrical banded structure within the hishikari epithermal gold deposit in japan the vein can be divided into four macroscopic bands we used 40ar 39ar dating of adularia by incremental step heating to determine the duration of mineralization in the individual bands of the vein and the history of vein formation plateau ages were obtained from all adularia samples and no significant excess 40ar is recognized from inverse isochrons the derived age spectra suggest that thermal overprinting of the epithermal system did not affect the plateau ages although early bands must have been reheated by the thermal pulses associated with later bands the 40ar 39ar ages of adularia indicate that vein formation occurred episodically in distinct periods separated by intervals of about 30 000 to 110 000 yr the hosen 1 vein grew in at least six increments at the 20 m level and at least four increments at the 62 5 m level the total duration of mineralization from the margin to the center of the hosen 1 vein was about 260 000 yr during which time the temperature of the hydrothermal fluid decreased from 190 to 210 c to less than 170 c

how unique is the udachnaya east kimberlite comparison with kimberlites from the slave craton canada and sw greenland the origin of alkali carbonates and chlorides in the groundmass of unaltered udachnaya east kimberlites in siberia is still controversial contrary to existing dogma that the udachnaya east kimberlite was either contaminated by the crustal sediments or platform brines magmatic origin of the groundmass assemblage has been proposed on the basis of melt immiscibility textures melt inclusion studies and strontium and neon isotope compositions we further tested the idea of alkali and chlorine enrichment of the kimberlite parental melt by studying olivine hosted melt inclusions and secondary serpentine in kimberlites from the slave craton canada gahcho kue jericho aaron and leslie pipes and southern west greenland majuagaa dyke host olivine phenocrysts closely resemble groundmass olivine from the udachnaya east kimberlite in morphology compositions high fo low ca complex zoning with cores of varying shapes and compositions and rims of constant fo melt inclusions in olivine consist of several translucent and opaque daughter phases and vapour bubble s the daughter crystals studied in unexposed inclusions by laser raman spectroscopy and in carefully exposed inclusions by wds eds are represented by na k chlorides calcite dolomite magnesite ca na ca na k and ca mg ba carbonates bradleyite na3mg co3 po4 k bearing nahpoite na2 hpo4 apatite phlogopite and tetraferriphlogopite unidentified sulphates fe sulphides djerfisherite pyrochlore na ca 2nb2o6 oh f monticellite cr spinel and fe ti oxides high abundances of na k e g na k ca 0 15 0 85 and incompatible trace elements in the melt inclusions are confirmed by la icpms analysis of individual inclusions heating experiments show that melting of daughter minerals starts and completes at low temperatures 100oc and 600oc respectively further reinforcing the similarity with the udachnaya east kimberlite serpentine minerals replacing olivine in some of the studied kimberlites demonstrate elevated abundances of chlorine up to 3 4 wt especially in the early generation despite heterogeneous distribution of chlorine such abundances are significantly higher than in the serpentine in abyssal and ophiolitic peridotites 0 5 wt the groundmass of most kimberlites including those studied here and altered kimberlites from the udachnaya pipe contain no alkali carbonates and chlorides and have low na2o 0 2 wt we believe that alteration disturbs original melt compositions with the alkaline elements and chlorine being mostly affected however the compositions of melt inclusions and serpentine are indicative of the chemical signature of a parental kimberlite melt it appears that enrichment in alkalies and chlorine as seen in unaltered udachnaya east kimberlites is shared by other kimberlites and thus can be assigned to deep mantle origin