the role of earthquakes in inducing sediment mass movements in the eastern korinthiakos gulf an example from the february 24 march 4 1981 activity abstract korinthiakos gulf is a narrow arm of the sea connecting the ionian and the aegean seas through the rion antirion strait and the korinth canal respectively the eastern part of korinthiakos was surveyed by the marine geology department of the institute of geology and mineral exploration of greece using a 3 5 khz subbottom profiler the survey was carried out a short time after intensive earthquake activity which occurred in the area from february 24 to march 4 1981 during this activity three major shocks of magnitudes ranging from 6 4 to 6 7 took place the subbottom profiles reveal a sediment mass which was deposited by submarine slumping in the alkyonides basin which lies at the eastern end of the studied area the slump is about 10 km long 1 5 to 2 0 km wide and its areal extent is about 16 km2 the scarp area occurs at a bathymetric depth of about 100 to 250 m in the northeastern part of the basin the scarp faces are from 10 to 15 m high and have a total areal extent of about 4 km2 the destruction of fishing nets of trawling boats and other evidence indicates that the triggering of the mass flow was effected by the earthquake activity and probably by the first major shock scarp areas and scarp faces from which sediment masses have been removed were detected in other shallow and deep sectors of the studied area indicating that mass transport processes are very common in this area of high seismicity

oscillatory zoned crystals of pyrochlore group minerals from the guaniamo kimberlites venezuela abstract oscillatory zoned crystals of pyrochlore group minerals are found in the la ceniza diamondiferous kimberlites guaniamo region venezuela this is the first known occurrence of the pyrochlore group minerals in kimberlites worldwide the minerals occur in the kimberlite groundmass in association with olivine zoned spinel phlogopite carbonates dolomite calcite magnesite apatite tetraferriphlogopite fe ni cu sulfides and serpentine they form discrete octahedral crystals or intergrowths up to 50 m with a red brown core and light brown rim individual zones in the cores are remarkably enriched in tio 2 up to 14 3 wt ta 2 o 5 up to 10 1 wt zro 2 up to 23 7 wt tho 2 up to 22 3 wt and uo 2 up to 8 0 wt at moderate nb 2 o 5 contents whereas the outer regions contain significant cao up to 17 5 wt na 2 o up to 5 7 wt nb 2 o 5 up to 58 9 wt and f up to 4 6 wt approaching the ideal formula na ca 2 nb 2 o 6 f following the ima recommendations and the 50 rule the interior is classified as uranoan zr rich thoriobetafite thoriopyrochlore or thorian zr rich betafite pyrochlore and the outer part as pyrochlore or thorian pyrochlore strong compositional zoning is consistent with two substitutions 2 th u 4 ti zr 4 o 2 3ca 2 nb 5 f oh and 2 th u 4 2 ti zr 4 o 2 2ca 2 na 2nb 5 f oh the zoning patterns and the absence of perovskite indicate the dominant role of f among fluid components and relatively high alkalinity during crystallization of the silicate carbonate groundmass of the la ceniza kimberlite the composition and zoning of the la ceniza pyrochlore group minerals are very specific but in general strongly resemble those of some pyrochlores from carbonatites

unusual paired pattern of radiohaloes on a diamond crystal from guaniamo venezuela abstract an octahedral diamond crystal from guaniamo venezuela shows a multitude of round radiocolouration spots that indicate a remarkable formation history spots always occur in pairs with similar spacing and intensity ratio between the two spots of each pair we interpret this pattern to be the result of long term irradiation of the stone emanating from a multitude of radioactive point sources at some point during the irradiation the stone must have experienced a translational movement which shifted it ca 50 m relative to the adjacent material i e the 111 crystal face was a fault plane after which irradiation continued the neoproterozoic age of the guaniamo kimberlites and the high degree of radiation damage suggest that both of the two irradiation periods lasted over hundreds of millions of years this interpretation is supported by results of he irradiation experiments

ams radiocarbon dating and varve chronology of lake soppensee 6000 to 12000 14c years bp for the extension of the radiocarbon calibration curve beyond 10000 14c y bp laminated sediment from lake soppensee central switzerland was dated the radiocarbon time scale was obtained using accelerator mass spectrometry ams dating of terrestrial macrofossils selected from the soppensee sediment because of an unlaminated sediment section during the younger dryas 10000 11000 14c y bp the absolute time scale based on counting annual layers varves had to be corrected for missing varves the soppensee radiocarbon verve chronology covers the time period from 6000 to 12000 14c y bp on the radiocarbon time scale and 7000 to 13000 calendar y bp on the absolute time scale the good agreement with the tree ring curve in the interval from 7000 to 11450 cal y bp cal y indicates calendar year proves the annual character of the laminations the ash layer of the vasset killian tephra massif central france is dated at 8230 140 14c y bp and 9407 44 cal y bp the boundaries of the younger dryas biozone are placed at 10986 69 cal y bp younger dryas preboreal and 1212 86 cal y bp allerod younger dryas on the absolute time scale the absolute age of the laacher see tephra layer dated with the radiocarbon method at 10 800 to 11200 14c y bp is estimated at 12350 135 cal y bp the oldest radiocarbon age of 14190 120 14c y bp was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile for the late glacial the offset between the radiocarbon 10000 12000 14c y bp and the absolute time scale 11400 13000 cal y bp in the soppensee chronology is not greater than 1000 years which differs from the trend of the u th radiocarbon curve derived from corals

lake sediments record cycles of sediment flux driven by large earthquakes on the alpine fault new zealand large earthquakes in mountain regions commonly trigger extensive landsliding and are important drivers of erosion but the contribution of this landsliding to long term erosion rates and seismic hazard remains poorly understood here we show that lake sediments record postseismic landscape response as a sequence of turbidites that can be used to quantify erosion related to large moment magnitude m w 7 6 earthquakes on the alpine fault new zealand alpine fault earthquakes caused a threefold increase in sediment flux over the 50 yr duration of each postseismic landscape response this represents considerable delayed hazard following earthquake induced strong ground motion earthquakes were responsible for 27 of the sediment flux from the lake catchment over the past 1100 yr leading us to conclude that alpine fault earthquakes are one of the most important drivers of erosion in the range front of the southern alps

prehistoric earthquake history revealed by lacustrine slump deposits five strong paleoseismic events were recorded in the past 15 k y in a series of slump deposits in the subsurface of lake lucerne central switzerland revealing for the first time the paleoseismic history of one of the most seismically active areas in central europe although many slump deposits in marine and lacustrine environments were previously attributed to historic earthquakes the lack of detailed three dimensional stratigraphic correlation in combination with accurate dating hampered the use of multiple slump deposits as paleoseismic indicators this study investigated the fingerprint of the well described a d 1601 earthquake i vii viii mw 6 2 in the sediments of lake lucerne the earthquake triggered numerous synchronous slumps and megaturbidites within different subbasins of the lake producing a characteristic pattern that can be used to assign a seismic triggering mechanism to prehistoric slump events for each seismic event horizon the slump synchronicity was established by seismic stratigraphic correlation between individual slump deposits through a quasi three dimensional high resolution seismic survey grid four prehistoric events dated by accelerator mass spectrometry 14c measurements and tephrochronology on a series of long gravity cores occurred at 2420 9770 13 910 and 14 560 calendar yr ago these recurrence times are essential factors for assessing seismic hazard in the area the seismic hazard for lakeshore communities is additionally amplified by slump induced tsunami and seiche waves numerical modeling of such tsunami waves revealed wave heights to 3 m indicating tsunami risk in lacustrine environments

tsunami induced sediment transport in the abyssal mediterranean sea an unusual stratigraphic unit nicknamed homogenite fills topographic lows in the complex ridge and trough bathymetry at two survey sites on the western mediterranean ridge and the calabrian ridge on near bottom 4 khz seismic reflection profiles this unit us an acoustically transparent near surface flat lying layer whereas in cores it is a homogeneous gray marl as much as 7 m thick grain size decreases upcore within the unit implying that it was deposited in a single event controlled by gravitational settling the stratigraphic position of the homogenite relative to a firmly dated sapropel bed suggests emplacement between 4400 and 3100 yr b p the source of the homogenite is inferred to be the nearby basin walls farther east two other sites with similar rugged topography lack homogenite entirely a triggering mechanism is required which is capable of initiating massive sediment transport simultaneously in many separate basins at the western two survey sites but which is not effective at the eastern sites a large archeologically recorded earthquake of the correct age is considered and rejected because its epicenter is closer to the nonhomogenite bearing sites than to the sites where this sediment type was observed and because several other earthquakes of comparable magnitude have since been recorded in the area whereas the homogenite is unique the 3 500 yr b p collapse of the caldera of the volcano of santorini caused a huge tsunami which is recorded archeologically and geologically around the eastern mediterranean because of refraction of the tsunami by the bathymetry and because the caldera collapsed in its southwest corner a disproportionate amount of tsunami energy was directed toward the western area where homogenite is observed in contrast the homogenite free sites were relatively sheltered an order of magnitude calculation shows that the near bottom oscillating currents accompanying the santorini tsunami were at or above the threshold erosion velocity at the homogenite bearing sites in addition the near bottom pressure pulse under the tsunami at the homogenite bearing sites was sufficient to cause liquefaction of sediments neither mechanism was adequate to cause sediment transport or slope failure at the homogenite free sites

sedimentary features of seismoturbidites triggered by the 1983 and older historical earthquakes in the eastern margin of the japan sea abstract both mass failure deposits and turbidites are widely distributed in the epicentral area of the 1983 earthquake mw 7 9 in the eastern margin of the japan sea this basin is semi enclosed with no active conduits for the entrance of coarse detrital sediments seismic reflection surveys and sediment cores reveal that mass failure deposits which are distributed on the continental slopes merge into turbidites in the basin plain hence the mass wasting process is a major transportation process in this region one gravity core gh93 816 was recovered from the southeastern margin of the japan basin close to the epicentral area of the 1983 japan sea earthquake sedimentological results show that five turbidite beds are intercalated in the top 68 cm of the column occurrence of the b tm tephra at the depth of 68 71 cm indicates that these turbidite beds were developed during the last 1000 years the high 137cs concentration in the top 20 cm of the core implies that the uppermost turbidite bed was deposited after 1954 based on these age limits for the top and the bottom of the studied interval we estimate the recurrence intervals of turbidites as 160 330 years we suggest that these turbidites were generated by submarine slides which were triggered by the 1983 and older historical earthquakes in this region these seismoturbidites are characterized by amalgamated beds irregular structure sequences grain size breaks fluctuations abrupt changes in composition within bed and variable composition among beds from these features we infer that deposition resulted from a series of turbidity currents associated with multiple or line sources for example multiple shallow slides that were regionally initiated by the same earthquake the sedimentary features described herein may be useful as criteria for identifying modern seismoturbidites in other settings as well as seismoturbidites in the geologic record however further study is needed for the distinction of this type of turbidites from other types e g tempestites reflected turbidites

evidence for jericho earthquakes from slumped sediments of the jordan river delta in the dead sea seismic reflection data and historical accounts suggest that a large submarine slump in the dead sea was produced by the most recent large earthquake along the dead sea jordan transform plate boundary the m l 6 25 jericho earthquake of july 11 1927 the correlation supports the use of seismically triggered slump landslide and other sediment failures in lakes to infer the timing of paleoearthquakes furthermore the location of the submarine slump adds to evidence that the 1927 earthquake was caused by rupture on a fault segment beneath the north basin of the dead sea this fault rupture implies that the strain accumulation on the jordan fault north of the dead sea is higher than previously recognized older seismically triggered slumps buried beneath the 1927 slump show that a record of ancient jericho earthquakes can also be found in the sedimentary record the estimated number and age range of these slumps suggest a long average earthquake recurrence time

paleoseismicity of the cascadia subduction zone evidence from turbidites off the oregon washington margin cores from cascadia deep sea channel contain sequences of turbidites that can be correlated and dated by the first occurrence of volcanic glass from the mount mazama eruption 6845 50 radiocarbon yrbp turbidity currents from the tributaries appear to have occurred synchronously to form single deposits in the main channel there being only 13 turbidite deposits in the lower main channel since the mazama eruption instead of the twice as many expected if the tributaries had behaved independently in addition to the cascadia channel 13 post mazama turbidites have been deposited in the astoria canyon and at two sites off cape blanco sample locations that span 580 km of the oregon washington margin pelagic intervals deposited between the turbidites suggest that in each place the turbidity currents occurred fairly regularly every 590 170 years on average the best explanation of the spatial and temporal extent of the data is that the turbidity currents were triggered by 13 great earthquakes on the cascadia subduction zone the variability of turbidite timing is similar to that for great earthquake cycles the thickness of the topmost pelagic layer suggests the last event was 300 60 years ago from three places along the margin but this number may be a biased underestimate it is however consistent with the youngest sudden subsidence event on the washington coast the turbidite data demonstrate that the near term hazard of a great earthquake on the cascadia subduction zone is of the order of 2 10 in the next 50 years

evidence for an earthquake triggered basin collapse in saguenay fjord canada abstract on february 5 1663 perhaps the largest earthquake ever witnessed in eastern north america struck the saguenay fjord basin with such force that landslides and submarine slides were triggered over a wide region over 3 km 3 of clayey holocene sediments collapsed from the margins of the fjord resulting in amalgamated debris flow and slide deposits that covered much of the basin floor these deposits reached thicknesses of up to 100 m and extended over an area of 100 km 2 the ambient seafloor was compressed under the impact and load of these debris masses and or liquefied under the cyclic stress of the seismic wave a 0 2 km 3 landslide also occurred at this time blocking the saguenay river and possibly facilitating an extra large spring freshet discharge biotracers planktonic and benthic foraminifera arcellaceans pollen and wood in conjuction with mass physical properties of sediment cores and high resolution seismic and sidescan profiler data have been used to identify local and distal sediment sources including their original water depth of deposition and their subsequent mode of mass gravitational transport the landslide material was eroded by the river and super elevated sediment concentrations are considered responsible for a long lasting 28 days turbidity current that entered the saguenay fjord depositing a single 0 3 km 3 turbidite the 2 to 10 m thick turbidite is considered to have been self igniting having eroded into the surface of the collapsed basin debris paleo hydraulic calculations suggest that this turbid flow averaged 0 45 m s and reached a flow thickness of 30 m

earthquakes as a triggering mechanism for debris flows and turbidites on the calabrian ridge abstract debris flows and turbidites have been described in piston cores bottom photographs and side looking sonar records from basin floors amid the rugged irregular topography of the calabrian ridge a sediment transport process is inferred which began with a rotational slump on the steep basin wall subsequently transformed into a debris flow and turbid cloud such events occurred approximately every 1500 years because the debris flow turbidite deposits are correlative between basins some relatively widespread mechanism such as an earthquake is required to initiate the slope failure the estimated intensity of ground shaking as a result of historical earthquakes on the nearby calabrian and hellenic arcs has been used to develop a relationship between frequency of occurrence and intensity of ground shaking extrapolation of this relation to infrequent large magnitude events shows that the 1500 yr event is small enough to be geologically plausible but large enough to cause slope failure on basin walls it is possible that the historical record fortuitously contains one of these large magnitude long repeat time events which may have caused the most recent of the observed debris flows in 1903

1822 earthquake triggered homogenite in lake le bourget nw alps high resolution textural signatures of an earthquake induced historical homogenite layer are presented as well as its 3d distribution this homogeneous deposit is correlated with the ad 1822 event vii viii msk intensity the main historical earthquake of the french outer alps using 210pb dating and historical chronicles during this earthquake a violent lake water oscillation was reported seiche effect in the present study we discuss the influence of lake water oscillations during earthquake induced subaqueous slide through a pluridisciplinary analysis of subbottom sediments including high resolution seismic sidescan sonar and short gravity coring

extreme crustal oxygen isotope signatures preserved in coesite in diamond the anomalously high and low oxygen isotope values observed in eclogite xenoliths from the upper mantle beneath cratons have been interpreted as indicating that the parent rock of the eclogites experienced alteration on the ancient sea floor1 recognition of this genetic lineage has provided the foundation for a model of the evolution of the continents whereby imbricated slabs of oceanic lithosphere underpin and promote stabilization of early cratons2 early crustal growth is thought to have been enhanced by the addition of slab derived magmas leaving an eclogite residuum in the upper mantle beneath the cratons3 but the oxygen isotope anomalies observed in eclogite xenoliths are small relative to those in altered ocean floor basalt and intermediate stage subduction zone eclogites and this has hindered acceptance of the hypothesis that the eclogite xenoliths represent subducted and metamorphosed ocean floor basalts we present here the oxygen isotope composition of eclogitic mineral inclusions analysed in situ in diamonds using an ion microprobe secondary ion mass spectrometer the oxygen isotope values of coesite a polymorph of sio2 inclusions are substantially higher than previously reported for xenoliths from the subcratonic mantle but are typical of subduction zone meta basalts and accordingly provide strong support for the link between altered ocean floor basalts and mantle eclogite xenoliths

neoproterozoic anomalous kimberlites of guaniamo venezuela mica kimberlites of isotopic transitional type in venezuela kimberlites have so far only been found in the guaniamo region where they occur as high diamond grade sheets in massive to steeply foliated paleoproterozoic granitoid rocks the emplacement age of the guaniamo kimberlites is 712f6 ma i e neoproterozoic the guaniamo kimberlites contain a high abundance of mantle minerals with greater than 30 olivine macrocrysts the principal kimberlite indicator minerals found are pyrope garnet and chromian spinel with the overwhelming majority of the garnets being of the peridotite association chrome diopside is rare and picroilmenite is uncommon chemically the guaniamo kimberlites are characterized by high mgo contents with low al2o3 and tio2 contents and higher than average feo and k2o contents these rocks have above average ni cr co th nb ta sr and lree concentrations and very low p yand particularly zr and hf contents the nb zr ratio is very distinctive and is similar to that of the aries australia kimberlite the guaniamo kimberlites are similar in petrography mineralogy and mantle mineral content to ilmenite free group 2 mica kimberlites of south africa the nd sr isotopic characteristics of guaniamo kimberlites are distinct from both kimberlite group 1 and group 2 being more similar to transitional type kimberlites and in particular to diamondiferous kimberlites of the arkhangelsk diamond province russia the guaniamo kimberlites form part of a compositional spectrum between other standard kimberlite reference groups they formed from metasomatised subcontinental lithospheric mantle and it is likely that subduction of oceanic crust was the source of this metasomatised material and also of the eclogitic component which is dominant in guaniamo diamonds d 2004 published by elsevier b v

documentation of earthquake induced disturbance of lake sediments using subbottom acoustic profiling subbottom acoustic profiling in lakes on the canadian shield and in the canadian cordillera has revealed disruptions in deltaic and lacustrine sediments that can be attributed to large historical earthquakes the timiskaming earthquake of 1935 magnitude 6 25 and the vancouver island earthquake of 1946 magnitude 7 2 triggered extensive slumping and flow of postglacial sediments in lakes located within a few tens of kilometres of the epicentres of these events there is some evidence in one of the surveyed lakes for in situ mobilization of sediment on relatively gentle slopes with minimal horizontal displacement this may be a product of liquefaction induced by coseismic shaking or displacements along faults beneath the basin in another lake widespread coseismic slumping resuspended large amounts of fine sediment which then settled out onto the lake floor to produce a texturally anomalous layer features similar to those produced by the 1935 and 1946 earthquakes can also result from a variety of non

radiation damage to kokchetav uhpm diamonds in zircon variations in raman photoluminescence and cathodoluminescence spectra abstract we conducted detailed in situ raman photoluminescence pl and cathodoluminescence cl studies on microdiamonds in a tourmaline rich quartzofeldspathic rock from the kokchetav massif kazakhstan the microdiamonds occur as inclusions in the cores of k tourmaline and in zoned zircons with varying u contents the results of 2d raman mapping of zircon showed that the u rich parts were more metamictized than the u poor parts all the diamonds showed a strong raman band at approximately 1332 cm 1 however the features of the raman bands were distinctly different depending on the host minerals on the one hand diamonds in tourmaline had a sharp raman band that is similar to that of kimberlite diamonds full width at half maximum fwhm 2 3 cm 1 on the other hand diamonds in zircon had a broad and downshifted band compared to those in tourmaline in particular diamonds in u rich cores of zircons up to 0 15 wt uo 2 showed broader and more downshifted raman bands fwhms and peak positions varied up to 9 3 cm 1 and 1328 cm 1 respectively with additional small bands at approximately 1490 cm 1 and 1630 cm 1 a negative correlation was observed between the peak position and the fwhm of the principal raman band of microdiamonds furthermore the pl and cl spectra showed systematic variations diamonds in zircons with low to moderate u concentrations had very strong pl and cl compared to diamonds in u rich zircons and in tourmalines several characteristic peaks appeared in the pl and cl spectra indicating the presence of irradiation and or nitrogen related point defects in the diamonds pl and cl of microdiamonds in high u zircon were weak but still showed irradiation related peaks the relationship between the occurrence of microdiamonds i e corresponding to the estimated total dose since crystallization and the raman pl and cl spectral characteristics of microdiamonds strongly suggests that radiation damage predominantly caused by particle emission from radioactive decay of actinides mainly u in zircon is a principal factor for the spectral variations radiation damage metamictization is probably a common phenomenon among microdiamonds in zircons in various diamond bearing rocks from the kokchetav massif to discuss the genesis of diamonds based on their raman pl or cl spectra it is highly recommended that microdiamonds included in actinide bearing minerals e g zircon should be treated with the most careful attention because post crystallization radiation damage significantly influences the spectra

structural control of tertiary au ag bearing breccias in an extensional environment nelson area southern nevada usa gold silver mineralization in the nelson area of southern nevada was controlled by structures associated with intrusion of an east west oriented pluton flatlying breccias formed during intrusion have allowed passive flooding of highly permeable zones and deposition of mineralized quartz and calcite steep fractures were formed in the pluton and immediate country rock during cooling and later reactivated by north south extension these fractures have channelled fluids and some have been the sites of hydrothermal eruptions which produced further brecciation and deposition of mineralized quartzcalcite veins the mineralizing fluid was water which was boiling at or near 100 c the calcite deposited by this water has 13c 5 4 to 7 1 and 18o 5 8 to 11 3 and the water was probably meteoric in origin mineralization had an epithermal style with strong local structural control rather than deep sourced regional detachment related hydrothermal origin

combining sedimentological trace metal mn mo and molecular evidence for reconstructing past water column redox conditions the example of meromictic lake cadagno swiss alps here we present sedimentological trace metal and molecular evidence for tracking bottom water redox state conditions during the past 12 500 years in nowadays sulfidic and meromictic lake cadagno switzerland a 10 5 m long sediment core from the lake covering the holocene period was investigated for concentration variations of the trace metals mn and mo xrf core scanning and icp ms measurements and for the presence of anoxygenic phototrophic sulfur bacteria carotenoid pigment analysis and 16s rdna real time pcr our trace metal analysis documents an oxic intermediate sulfidic redox transition period beginning shortly after the lake formation similar to 12 5 kyr ago the oxic period is characterized by low sedimentary mn and mo concentrations as well as by the absence of any remnants of anoxygenic phototrophic sulfur bacteria enhanced accumulation preservation of mn up to 5 6 wt in the sediments indicates an intermediate mn enriched oxygenation state with fluctuating redox conditions during a similar to 2300 year long transition interval between similar to 12 1 and 9 8 kyr bp we propose that the high mn concentrations are the result of enhanced mn2 leaching from the sediments during reducing conditions and subsequent rapid precipitation of mn oxyhydr oxide minerals during episodic and short term water column mixing events mainly due to flood induced underflows at 9800 130 cal yr bp a rapid transition to fully sulfidic conditions is indicated by the marked enrichment of mo in the sediments up to 490 ppm accompanied by an abrupt drop in mn concentrations and the increase of molecular biomarkers that indicate the presence of anoxygenic photosynthetic bacteria in the water column persistently high mo concentrations 80 ppm provide evidence that sulfidic conditions prevailed thereafter until modern times without any lasting hypolimnetic ventilation and reoxygenation hence lake cadagno with its persistently stable chemocline offers a framework to study in great temporal detail over similar to 12 kyr the development of phototrophic sulfur bacteria communities and redox processes in a sulfidic environment possibly depicting analogous conditions in an ancient ocean our study underscores the value of combining sedimentological geochemical and microbiological approaches to characterize paleo environmental and redox conditions in lacustrine and marine settings

raman study of diamond based abrasives and possible artefacts in detecting uhp microdiamond abstract raman spectral characteristics of a range of diamond based abrasives powders and sprays and drilling and cutting tools originating from preparation laboratories worldwide are presented some abrasives show strong broadening of the main diamond band fwhm full width at half band maximum 5 cm 1 accompanied by strong band downshift 1316 1330 cm 1 others are characterised by moderate band broadening fwhm 1 8 5 cm 1 at rather regular band position 1331 1333 cm 1 in addition we found that a fresh abrasive and its used analogue may in some cases show vast differences in their raman spectra the raman parameters of diamond based abrasives overlap widely with raman parameters of uhp ultra high pressure microdiamond it is hence impossible to assign diamond detected in a geological specimen to either an introduced artefact or a genuine uhp relict from the raman spectrum alone raman is an excellent technique for the detection of minute amounts of diamond however it does not provide conclusive evidence for the identification of uhp microdiamond the latter requires thorough verification for instance by optical microscopy or if doubts cannot be dispelled transmission electron microscopy

unusual upper mantle beneath guaniamo guyana shield venezuela evidence from diamond inclusions the geochemistry of mineral inclusions in diamond is an important source of information about the composition of the continental lithospheric mantle at depths exceeding 120 150 km at these depths two main types of geochemical environment support diamond formation they are ultramafic or peridotitic u type and eclogitic e type environments as shown by minerals that occur as inclusions in diamonds in primary diamond bearing kimberlite or lamproite rock the ratio of diamonds from these two geochemical environments varies widely between localities the u type environment dominates for the majority of diamond occurrences worldwide whereas the e type environment dominates for a very limited number of localities in south africa north america and australia the present study shows that an uncommonly high percentage 99 4 of e type diamonds with extremely variable inclusion assemblages is found in kimberlites in the northwestern part of the guyana shield at guaniamo venezuela these variations range from previously unknown silica undersaturated corundum eclogite to abundant silica rich coesite eclogite assemblages representing 22 of all e type diamonds some of which contain syngenetic ilmenite and magnetite the compositional variations of garnet and omphacite inclusions are extremely broad the wide variability of the eclogitic source in which diamonds formed beneath the guyana shield indicates a broadly basaltic chemistry in this environment which may represent ancient subducted oceanic crust such specific features have not been reported for any other diamond occurrence and reflect an unusual composition of the deep lithospheric mantle in this area