petrochemical evolution of the white mfolozi granite pluton evidence for a late palaeoarchaean a type granite from the se kaapvaal craton south africa abstract one of the major limitations in understanding the geochemical evolution of the kaapvaal craton south africa is the scarcity of whole rock trace element data of the granitoid and other rocks compared to the vastness of this cratonic block here we present new xrf major oxide and icp ms trace element analyses of the white mfolozi granitoid wmg pluton se kaapvaal craton which suggest that the 3 25 ga u pb zircon age old wmg pluton is a peraluminous a type granite and could be equivalent to the intrusive potassic granite phase of the anhalt granitoid suite occurring to the north of the wmg pluton the pluton was generated by batch partial melting of a pre existing ttg source in two major phases under relatively anhydrous conditions and the heat of partial melting could have been provided by a voluminous mantle derived mafic magma which intruded into mid crustal levels c 17 km perhaps during a period of crustal extension the estimated pressure and temperature of generation of the wmg parent magma with average molar or or ab 0 48 could be 500 mpa and close to 1000 c respectively when compared with the results of experimental petrology interstitial occurrence of relatively iron rich biotite mg mg fe 0 41 0 45 suggests that the final temperature of crystallization of the pluton was close to 800 c an important magmatic event following the main phase of partial melting was limited mixing between the intrusive mafic magma and co existing newly generated granitic melt this magma mixing resulted in distinct variations in sio 2 and a low initial sr isotopic ratio 0 7013 of the wmg pluton although both the models of partial melting of quartzo feldspathic sources and fractional crystallization of basaltic magmas with or without crustal assimilation have been proposed for the origin of a type granites the model of magmatic evolution of the wmg pluton presented here can also be an alternative model for the generation of a type granites in this model post partial melting magma mixing is perhaps critical in explaining the daly gap in composition and extreme variations in chemical e g sio 2 and isotopic compositions observed in many bimodal a type granite suites the emplacement of the oldest known a type granitoid suite in the kaapvaal craton the wmg pluton marks a period of stabilization of the craton before erosion and deposition of the overlying volcano sedimentary succession of the pongola supergroup

evidence of isotopic equilibration between microgranitoid enclaves and host granodiorite warburton granodiorite lachlan fold belt australia abstract microgranitoid enclaves in the s type warburton granodiorite lachlan fold belt australia display a range in mineralogical and isotopic compositions many show obvious similarities to the host granodiorite they contain biotite as the sole ferromagnesian phase and have isotopic signatures similar to the host other enclaves contain cummingtonite actinolite and rare orthopyroxene mainly in the core of the enclaves these enclaves typically have higher nd i and lower sol 87 sr 86 sr i than the host rocks reversely zoned plagioclase megacrysts in some enclaves contain anhedral cores which are similar in composition to an poor plagioclase crystals in the host rock an45 these megacrysts are jacketed by an rich plagioclase an70 an80 the enclaves are interpreted to be globules of a more mafic magma which mingled with the host while it was still partially liquid megacrysts within the enclaves are thought to have been derived from the granodioritic magma the mafic enclave magma is likely to have been derived from a mantle source but equilibration between enclaves and host rock has changed the mineralogy and isotope geochemistry of all enclaves the equilibration process was incomplete for some enclaves resulting in mineralogical zoning and distinctions in isotopic signature between these enclaves and the host rock this equilibration process is likely to have been arrested as a result of rapid cooling of the pluton due to its small size and shallow emplacement level it is uncertain whether the compositions of the least equilibrated enclaves are truly representative of the original mafic enclave magma or whether their trace element signature has been affected by diffusional processes within a stratified magma chamber

an isotopic mixing model for the origin of granitic rocks in southeastern australia a simple mixing process was a significant element in the genesis of many southeastern australian granitic rocks major and trace element abundances are near linearly correlated nd and sr initial isotopic compositions define a simple hyperbolic trend and many initial 87sr 86sr ratios are a regular function of rb sr ratios geological arguments and regression of geochemical variation diagrams place limits on the nature of the end members the high si end member is meta sedimentary derived magma comparable in composition to the cooma granodiorite the one pluton in the region surrounded by and clearly derived from regional metamorphic rocks the low si end member is basaltic material with similarities to rare gabbros also found in the area isotope dilution calculations based upon initial sr and nd isotopic compositions deduced for the end members yield realistic hypothetical sr and nd concentrations for the end members in a demonstration of the internal consistency of the model all of the granitic rocks from hornblende tonalites to cordierite granodiorites are a single broad family products of variable mixing between distinct batches of basaltic material and a uniform partial melt of the regional basement

the origin of rapakivi texture by sub isothermal decompression abstract the rapakivi texture plagioclase mantled k feldspar ovoids rounded quartz megacrysts and euhedral plagioclase megacrysts in a more fine grained granitic matrix has been studied in five proterozoic 1 64 1 55 ga anorogenic rapakivi granite batholiths in the fennoscandian shield with emphasis on mineral stability and inherited cores k feldspar ovoids and rounded quartz megacrysts with deep embayments consist principally of a core zone and an outer melted and recrystallized zone when the k feldspar ovoids are mantled by plagioclase the outermost part of the mantle is homogeneous but towards the k feldspar a skeletal texture develops intensive parameters obtained from different textural positions show that mineral inclusions in cores of the k feldspar ovoids and quartz megacrysts were formed at low t 680 720 c and high p 5 6 kbar conditions while inclusions in the periphery of ovoids and the plagioclase mantles display high t 780 c and intermediate to low p 3 5 1 kbar the lowest p is comparable to that during solidification of the matrix the total water equivalent of the volatile content in the magma has been calculated as 2 5 the amount of solids in the magma at 1 kbar has been estimated as 40 theoretical calculations and experimental data for mineral stabilities in granitic systems suggest that the texture formed when a crystal saturated kfsp qtz pl 60 and volatile undersaturated a type granite magma was transported under approximately constant temperature 760 780 c from the lower middle crust 5 6 kbar to upper crustal levels according to phase stabilities in the eutectoid granite system quartz and k feldspar were resorbed but plagioclase remained stable and precipitated during this sub isothermal rise of magma textural presence of disequilibrium textures and mineralogical presence of different mineral assemblages including relics evidence of a sub isothermal rise of the rapakivi magmas is better preserved in subvolcanic and contact varieties of rapakivi granites than in the more deep seated rapakivi granites formed by slow cooling

petrology geochemistry and geochronology of the meta mafic rocks in the north sulu ultrahigh pressure belt implications for their petrogenetic diversity and complex tectonic evolution abstract the ultrahigh pressure uhp eclogite and country rocks of the north sulu uhp metamorphic belt have traditionally been considered the products of the deep subduction of the yangtze block yb beneath the north china block ncb however widely distributed non uhp meta mafic rocks appearing as irregular lenses and thin layers together with uhp eclogite in the haiyangsuo wuji weihai area along the northwestern margin of the north sulu uhp belt prompted investigation of the petrogenetic diversity and complex tectonic evolution of these rocks the uhp index mineral assemblage of garnet omphacite rutile phengite coesite is common in the matrix of uhp and retrograde eclogites or as inclusions preserved in metamorphic zircons indicating uhp metamorphism in contrast with previous studies herein high pressure and medium pressure hp mp granulite facies index mineral assemblage of garnet clinopyroxene plagioclase quartz orthopyroxene ilmenite was commonly identified in the matrix of non uhp mafic granulites and amphibolites indicating that these rocks underwent hp mp granulite facies metamorphism rather than uhp metamorphism the whole rock geochemical data revealed multiple origins for the uhp and retrograde eclogites with protoliths derived from heterogeneous mantle or lower upper crust sources with weak fractional crystallization in contrast the protolith of the non uhp meta mafic rocks may have derived from a depleted or primitive mantle origin source with varying degrees of crustal contamination during emplacement the uhp and retrograde eclogites exhibited neoproterozoic 803 760 ma protolith ages and underwent uhp eclogite facies metamorphism in the middle triassic 233 225 ma with subsequent late triassic 219 210 ma amphibolite facies retrogression in contrast the non uhp meta mafic rocks exhibited older paleoproterozoic 1944 ma protolith ages the two distinct metamorphic events that occurred in the paleoproterozoic 1944 1825 ma and middle late triassic 226 201 ma are related to the paleoproterozoic jiao liao ji orogeny and the triassic collisional event between the yb and ncb respectively a combined study of petrography whole rock geochemistry and zircon u pb ages revealed that the uhp and retrograde eclogites show a close affinity to the neoproterozoic continental crust on the northern margin of yb whereas the non uhp meta mafic rocks show a close affinity to the paleoproterozoic jiaobei terrane both the uhp and non uhp meta mafic rocks together with their country rocks form an approximately 200 km long melange zone rather than a single uhp belt which extends from the haiyangsuo through the wuji to the weihai area along the northwestern margin of the north sulu uhp belt

geochemistry and origin of early proterozoic dongargarh rapakivi granite complex central india an example for magma mixing and differentiation abstract early proterozoic dongargarh granite complex of central india intruding the tonalitic to granodioritic amgaon gneisses and the nandgaon group bimodal volcanic suite comprises three different textural and compositional types viz porphyritic granodiorite pg coarse equigranular granite eg and microgranite mg synplutonic mafic dykes are common in the granite complex the pg is characterised by rapakivi texture and the eg is the dominant facies and exhibits sporadically developed rapakivi texture microgranular enclaves are common in the eg while they are rare in pg major and trace element geochemistry of pg shows marked i type and some occasional a type granite characters unusual for a rapakivi granite while the eg shows a type granite signatures the field petrographic chemical and isotopic data of these granites suggest their derivation by mixing of mantle derived basic magma with a crustal derived partly crystalline granitic magma episodic mafic magma underplating caused the anatexis of the archaean lower continental crust in a continental margin tectonic setting resulting first in the formation of the i type granodiorite followed by a type granite the i type granodiorite is mixed with the basic magma synplutonic dykes while the eg is formed by mingling of a type granite magma and the intruding basic magma

ultrahigh pressure metamorphic rocks from the chinese continental scientific drilling project i petrology and geochemistry of the main hole 0 2 050 m the main hole mh of the chinese continental scientific drilling project ccsd in southern sulu has penetrated into an ultrahigh pressure uhp metamorphic rock slice which consists of orthogneiss paragneiss eclogite ultramafic rock and minor schist recovered eclogites have a uhp metamorphic mineral assemblage of garnet omphacite rutile phengite kyanite coesite epidote ultramafic rocks contain garnet olivine clinopyroxene orthopyroxene ti clinohumite phlogopite gneisses and schists contain an amphibolite facies paragenesis but their zircons have coesite garnet omphacite or jadeite and phengite inclusions indicating that eclogites and gneisses have been subjected to in situ uhp metamorphism using available geothermobarometers p t estimates of 3 1 4 4 gpa and 678 816 c for eclogites were obtained if surface outcrops and neighboring shallow drill holes are considered together we suggest that a huge supracrustal rock slab 50 km long 100 km wide 5 km deep was subducted to a depth 100 km and then exhumed to the surface the depth interval 0 2 050 m of the ccsd mh can be divided into six lithological units unit 1 consists of alternating layers of quartz rich and rutile rich eclogites with thin interlayers of gneiss and schist eclogites of unit 1 are characterized by nb ta sr and ti depletions low mg number and general lree enrichment unit 2 comprises rutile and ilmenite rich eclogite and minor normal eclogite and is characterized by high tio2 total fe v co and sr and very low sio2 alkali zr ba nb ta and total ree contents and lree depleted ree patterns with slightly positive eu anomalies unit 3 contains ultramafic rock and minor mgo rich eclogite protoliths of uhp rocks from units 1 2 and 3 represent a layered mafic to ultramafic intrusion at crustal depth units 4 and 6 consist of interlayered eclogite and paragneiss the eclogites are characterized by th u nb ta and ti depletion and k enrichment and lree enriched ree patterns paragneisses show nb ta sr and ti depletions and lree enriched ree patterns occasionally with slightly negative eu anomalies indicating that their protoliths represent metamorphic supracrustal series unit 5 consists mainly of orthogneisses showing distinct nb ta sr and ti depletions and lree enriched ree patterns with pronounced negative eu anomalies suggesting granitic protoliths in conclusion it is proposed that the southern sulu uhp belt consists of a series of meta supracrustal rocks a layered mafic ultramafic complex and granites

experimental investigation of morphological characteristics of rill evolution on loess slope abstract the development of rill is the result of a complex interaction of soil properties with high spatial and temporal variability the rill morphology may act as a determinant as well as a stochastically driven process the description of their complex morphology requires geostatistics and nonlinear theories a study of the morphological characteristics of rill evolution was performed via indoor soil pan rainfall simulations experiments were run with loessial soil bulk density of 1 25 g cm 3 under a rainfall intensity of 90 mm h with a 20 slope gradient a detailed scan of the slope topographic analysis and statistical analyses were the main methods utilized in the study statistical analyses showed that characteristic parameters exhibited differences in the expression of the dynamic change of soil loss according to the comparison of quantitative methods we found that the fractal dimension can reflect the complexity of rill network but it is not able to reflect the dynamic changes of the erosion process perfectly in contrast geomorphologic comentropy is sensitive to the dynamic changes of soil erosion intensity and its variation can reflect the dynamic changes of erosion perfectly the topological parameters can reflect the degree of stability in the rill network structure but it is not suitable for reflecting the dynamic changes of erosion intensity the geomorphologic comentropy was evaluated as the most appropriate characterization parameter for the rill morphology description

petrology geochemistry and geochronology of the chilka lake igneous complex orissa state india abstract the chilka lake igneous complex of orissa the largest known anortosite massif of the indian shield occurs in a catazonal environment of high grade metamorphics of the eastern ghats precambrian orogenic province the syntectonic massif consists of the anorthositic balugaon dome leuconoritic rambha lobe and quartz mangeritic kallikota cover a completely gradational suite comprising anorthosite leuconorite norite minor jotunite the anorthositic suite constitutes most of the complex the subordinate of suite of acid rocks spatially associated with this is of a broad quartz mangeritic lithology with minor granitic rocks the acidic suite geochemical evolution of the complex in the sequence anorthosite leuconorite norite jotunite acidic rocks shows moderate iron enrichment in the noritic jotunitic stage and is marked by an overall decrease in al 2 o 3 cao mgo ni co sr ba k rb and increase in sio 2 k 2 o v ni k ba and rb sr such progressive variation in geochemical parameters appears i essentially gradual and frequently overlapping in rock members of the intergradational anorthositic suite and ii rather abrupt across transition zones between the anorthositic suite and the acidic suite due to near absence of intervening intermediate lithologies rb sr whole rock isochron studies indicate that the complex was emplaced ca 1400 ma ago the initial 87 sr 68 sr 0 70661 implies limited hybridisation of the parent magma prior to emplacement a critical appraisal of all the available evidence suggests that i the anorthositic suite of rocks form a perfectly consanguinous and comagmatic assemblage and ii the spatially associated acidic suite emerged through a convergence of magmatic and metasomatic processes the latter brought about by contact anatexis of the host rocks the complex as well as the host metamorphics are intruded by an atectonic suite of noritic dykes emplaced ca 850 ma ago

evolution of waning subduction related magmatism northern sierra madre occidental mexico the stratigraphic record at the tomochic volcanic center chihuahua documents a change from andesitic to rhyolite dominated volcanism with late extrusion of mafic lavas during the final 10 m y of subduction related activity in the northern sierra madre occidental andesitic volcanism which started before 38 ma and continued until 35 ma was followed by eruption of large volume rhyolite ash flows from the las varas 34 1 ma and tomochic 31 8 31 4 ma calderas basaltic andesite the most mafic rock type in the area was extruded near the end of calcalkalic volcanism at 30 ma the change in style of volcanism at the tomochic volcanic center also occurred in other parts of the northern sierra madre occidental and is interpreted to reflect the evolution of waning subduction related magmatism as convergence between the north american and farallon plates slowed before it eventually ceased slowed plate convergence resulted in a decreased flux of mafic melts from the mantle to the crust leading in turn to the stagnation and coalescence of intermediate composition magmas similar to those that fed early andesitic eruptions subsequent differentiation led to growth of zoned magma reservoirs from which the rhyolite ash flows were extruded slowed convergence was accompanied by the onset of crustal extension which possibly aided the coalescence of andesitic magmas and which allowed the ascent and eruption of mafic melts near the end of silicic volcanic activity although minor differences exist the history of mid tertiary magmatism and tectonism in the northern sierra madre occidental was broadly similar to that in parts of the south western united states

nature and origin of proterozoic a type granitic magmatism in the southwestern united states of america the mountain ranges of arizona and adjacent california and nevada contain large areas underlain by proterozoic anorogenic granites comprising the southwesternmost portion of a transcontinental belt of 1 4 1 5 ga old anorogenic complexes that extends across north america northeast into labrador of these a two mica monazite bearing granitic suite resides in central and southeastern arizona as part of a peraluminous subprovince that is bordered on the south southern arizona to sonora and west western arizona and adjacent portions of california and nevada by marginally metaluminous granites bearing biotite sphene hornblende and fluorite all of these 1 4 ga granites are distinctly more potassic iron enriched relative to mg and depleted in ca mg and sr in contrast to typical orogenic granitoids in general the large ion lithophile element enriched composition is a consequence of limited melting of a water deficient crustal source at depths greater than 25 37 km for the peraluminous granites this contrast is less extreme perhaps resulting from a larger degree of melting as a consequence of a greater metasedimentary component and water in its crustal source the anorogenic granitic magmas intruded into the upper crust at depths of 8 17 km or shallower at temperatures up to 790 c the most dramatic variation in the crystallization intensive parameters resides in the oxygen fugacity which spans three orders of magnitude relative to other anorogenic suites all of the magmas crystallized at elevated levels of o2 as reflected in their assignment to the anorogenic magnetite series yet a regionally significant rise in primary o2 levels unmatched elsewhere in the transcontinental belt occurs for plutons in western arizona including the holy moses and hualapai granites the most extreme case is the hualapai granite whose biotite fe fe mg ratios drop due to high o2 to a low of 0 27 down from more typical levels of 0 54 to 0 75 such extreme variations in primary levels of oxygen fugacity must be an indirect imprint of regional changes of the level of oxidation of the lower crust the high fo2 holy moses and hualapai plutons have intruded near the regional boundary between the metaluminous and peraluminous granites and appear to be imaging a major change in the level of oxidation of the lower crust this boundary is also approximately equivalent to significant changes in the nd and pb isotopic compositions of these granites and the metamorphic and magmatic character of the older orogenic terrane on a global scale the crust forming orogenies ended by 1 6 ga ago and the continents entered a long lived era dominated by localized extension and transcontinental intrusion of anorogenic potassic rapakivi granite mafic dike swarms charnockite and anorthosite the absence of orogenic deformation implies that plate consumption became intraoceanic during this time the profuse and widespread nature of the igneous activity has no phanerozoic analogue and is considered to be unique to the proterozoic a crustal overturn model ties the magmatism to heating within a largely undepleted subcontinental mantle the eventual rise of mantle plumes and the transfer of heat into the youthful undifferentiated proterozoic crust subsequent melting and rise of potassic granitic magmas from the lower crust leads to considerable crustal reorganization a process that would continue until both the mantle and crust reached a stable configuration

a gold and platinum mineralized layer in gabbros of the kap edvard holm complex field petrologic and geochemical relations the lower layered series a cumulates of the kap edvard holm complex contain a stratiform layer 1 to 20 m thick and 6 km long that is mineralized with gold and platinum group elements pges the lower layered series a cumulates 650 m thick are dominated by modally layered gabbro with lesser volumes of granular anorthosite and troctolite that together form 2 to 30 m thick layers that are most abundant above the mineralized layer minor volumes of poikilitic wehrlite form a few 1 to 2 m thick layers throughout the section field and petrographic relations as well as cryptic variations in cumulus mineral compositions indicate that the lower layered series a formed in an open system magma chamber from repeated magma injections within the mineralized layer average concentrations over 3 m thickness are 250 ppb pt 40 ppb pd and 50 ppb au with individual samples containing up to 5 ppm pt and 6 ppm au the concentrations of ir os ru and rh are uniformly low 20 ppb stratigraphic zoning of pt pd and au is consistent along strike with peak au concentrations overlying pt and pd peaks platinum minerals are primary pt fe alloy sperrylite and moncheite with secondary pt sulfide overgrowths gold occurs as alloys with ag and cu these minerals are found in contact with primary and secondary silicates and oxides and with intercumulus base metal sulfides that consist of the assemblage bornite chalcopyrite digenite deposition of the mineralized layer is associated in space and time with injections of plagioclase saturated primitive magma that mixed with more evolved resident magma these events caused efficient partitioning of au and pge into sulfides derived from a large volume of magma deposition of these sulfides to form the mineralized layer and subsequent deposition of the overlying anorthosite layers the wehrlite layers however were formed by postcumulus reactions between gabbro cumulates and hydrous intercumulus melts probably derived from the compacting cumulus pile subsolidus reactions between primary minerals and meteoric hydrothermal solutions caused extensive alteration of the mineralized gabbro oxidation and desulfurization of cu fe sulfides and local recrystallization of pge minerals

laboratory characterization and discrete element modeling of shrinkage and cracking in clay layer the performance of a variety of geostructures such as compacted clay liners earth dams and pavement embankments is compromised by soil cracking experiments are set up to monitor the drying pro

rapakivi granites and related rocks an introduction abstract this article is an introductory chapter for the proceedings of the last seventh meeting of the international geological correlation programme igcp project 315 correlation of rapakivi granites and related rocks on a global scale 1991 1996 based on current knowledge progress made during the six years of the project and the seven papers published in this special issue a synthesis of the age distribution geotectonic environment petrogenesis geochemistry and metallogeny of the rapakivi granites and related rocks is presented

desiccation of a sensitive clay field experimental observations an excavation with three different levels was exposed to continuous evaporation during 35 days in order to observe and document the formation of shrinkage cracks in an intact and weathered sensitive marine clay desiccation of the intact saint alban clay under restrained conditions at an average evaporation rate of 0 018 cm h and an initial moisture content of 103 produced visible primary cracks after 17 h with an average spacing of 20 to 24 cm secondary cracks within each original polygon appeared after about 70 h of evaporation subhorizontal cracks at a depth of 6 to 8 cm were also created owing to differential strains induced by differential shrinkage of the soil polygons further evaporation resulted in the formation of a new set of vertical cracks after about 150 h of evaporation in the soil below the subhorizontal shear plane the shrinkage induced volume change associated with these different sets of cracks produced polygons with a protuberance at their bottom part indicating that the depth of crack propagation below the subhorizontal shear plane was about 3 to 4 cm in weathered clay at an initial moisture content of about 50 the average spacing was 10 to 12 cm indicating that spacing between primary cracks is related to soil type in the cohesionless topsoil no cracks were observed

syneresis cracks subaqueous shrinkage in argillaceous sediments caused by earthquake induced dewatering abstract syneresis cracks often confused with subaerial desiccation phenomena are traditionally ascribed to subaqueous shrinkage whereby salinity changes caused deflocculation of clay this and other previously proposed mechanisms fail to account for their occurrence in low energy typically non evaporitic facies stratigraphically sporadic distribution intrastratal formation under shallow burial depths variation in morphology degree of contraction generation of sedimentary dikelets as crack fills and deformation of dikelets and enclosing layers instead it is suggested that ground motion from strong synsedimentary earthquakes caused argillaceous sediments to dewater interbedded sands and silts to be almost simultaneously liquefied and injected into the resulting fissures and then these dikelets to be distorted comparative rarity of syneresis cracks in phanerozoic versus precambrian marine strata is considered to be primarily an evolutionary consequence of theological changes caused by increased organic binding of clay flocs in the water column greater input of organic matter into the sediment and the diversification of sediment dwelling bacteria and meiofauna in phanerozoic deposits

tertiary mineralization and magmatism east greenland lead isotope evidence for remobilization of continental crust abstract well defined lead isotope signatures of sulphides from mineral occurrences associated with tertiary igneous rocks in east greenland fall in two distinct groups 1 sulphide samples from the region south of scoresby sund kangerlussuaq igneous complex have lead characterized by retarded uranogenic evolution and slightly elevated thorogenic isotopic ratios 2 sulphide samples from the region north of scoresby sund werner bjerge kap simpson and kap broer ruys igneous complexes have lead compositions typical of modern average terrestrial lead these distinct signatures in both conventional and 208 pb 204 pb 207 pb 204 pb diagrams lie within linear trends defined by previously published lead isotope data for unmineralized tertiary basalts and intrusive rocks the linear trends are mixing lines between the lead in the tertiary mantle derived magmas and lead remobilized from continental crust tertiary magmas in the region south of scoresby sund remobilized and incorporated lead from low high 208 pb 204 pb crustal sources similar in isotope composition to archaean high grade metamorphic gneisses exposed in the area non to sub parallel distinct lead mixing lines in the 208 pb 204 pb 206 pb 204 pb diagram for the tertiary igneous complexes in this region suggest strong heterogeneity of the remobilized crust more than one half of the lead from sulphide mineral occurrences within the kangerlussuaq alkaline intrusive complex may be derived from local continental crust in the region north of scoresby sund the tertiary magmas remobilized moderately radiogenic lead from local basement and sedimentary basins palaeoproterozoic mesoproterozoic gneisses neoproterozoic ordovician sediments caledonian granites and palaeozoic mesozoic sediments these crustal rocks lack the very low 206 pb 204 pb and 207 pb 204 pb ratios typical of the gneisses from the kangerlussuaq region and mixing trends between mantle derived and crustal lead are therefore much less extensive however because the mantle derived magmas had very low total lead contents even small additions of crustal lead are traceable sulphide mineralized alkaline intrusive complexes are shown to be highly contaminated with crustal lead and it is further shown that the pre tertiary rocks of north east greenland are likely local crustal sources of lead for contaminated tertiary plateau basalts many stratabound sediment hosted hydrothermal base metal occurrences in the palaeozoic mesozoic jameson land basin are thought to be tertiary in age but do not appear to contain tertiary igneous derived lead on the contrary the hydrothermal alteration zones associated with several of the mineralized tertiary igneous complexes attest to extensive fluid rock mass transfer lead and other base metals were leached from the country rocks homogenized and incorporated into sulphide minerals

rapakivi texture an indication of the crystallization of hydrosilicates ii rapakivi granites have puzzled all who have seriously studied them typical rapakivi texture is a mixture of variously mantled non mantled or partly mantled concentrically zoned plastically distorted fragmented reaggregated large and small ovoids commonly they are potash feldspar often mantled by and having a variable content of plagioclase some display remarkable sphericity in form composition zoning sequence and crystallization pattern each ovoid reflects an individual development up to five concentric internal plagioclase rims have been observed and some ovoids may be isolated in autoliths and wall rocks anomalies and contradictions arise from any assumption of genesis from a cooling melt the recorded objective data imply that the magma from which rapakivi textures develop had similar diffusive and rheological properties to those of a partly dewatered macromolecular paste or a mixture of gelatinous hydrosilicates as indicated by deep oil wells this system is found at somewhat elevated temperatures at considerable depths within accumulated sediments in addition to the very specific diffusive and rheological properties of such partly dewatered sediments the system has as its major components normal solvated macromolecules of mixed clays silica gels and hydrous ferromagnesian minerals which are characterised by distinctive particle sizes and geometric shapes platelets spheres and rods respectively thixotropic liquefaction and intrusion of such concentrated gelatinous magma or sediment paste introduces relative movement between the component macromolecules whereby they can reduce surface energy by interaction to assume a close packed condition and aggregate during laminar flow into macro accretions comprised essentially of their respective particle shapes syneresis of these precursor accretions desorbs ions including the small montmorillonite particles behaving as a colloidal electrolyte these diffuse from the illitic cores to form a montmorillonite rich rim which it is suggested crystallizes together with the illitic cores to form mantled or polymantled feldspar ovoids crystallization of the rapakivi massif is associated with strong temperature rise stemming from exothermic crystallization of the close packed metastable colloids this follows the development of the characteristic texture the rounded and rimmed precursor accretions are formed during earlier lower temperature episodes of thixotropic liquefaction which are isothermal the fluidity is an earlier event there is high temperature dependent on the rate of water loss but no molten stage forty six typical features of rapakivi texture are described and illustrated each of which is directly attributable to specific interactions in an alternately dynamic and static colloidal system individual correlation between each observed distinctive feature of the rapakivi texture and the well documented physico chemical process is complete for sediment derived granites therefore the rapakivi texture can confidently be assumed to be an indication of the crystallization of their sedimentary hydrosilicate precursors

image analysis and fractal geometry to characterize soil desiccation cracks the rapid transport of water and solute through desiccation soil cracks can lead to crop water and nutrient stress as well as ground and surface water contamination the objectives of this research were to determine 1 soil surface crack area 2 fractal dimension of crack edges d1 and 3 mass fractal dimension d2 and lacunarity of soil surface cracks photographs were used to record in situ soil cracking in a mexico silt loam fine smectitic mesic vertic epiaqualf at two locations for three sampling dates photographs of the cracks were digitized and an algorithm was developed to determine crack area and the fractal dimension and lacunarity of the digitized images location 1 produced 7 crack area a mass fractal dimension d2 of 1 44 and a crack edge fractal dimension d1 of 1 08 location 2 produced 25 crack area a mass fractal dimension d2 of 1 64 and a crack edge fractal dimension of 1 08 d1 lacunarity curves as a function of box size for crack boundary fractal dimension were more variable at location 2 soil profile moisture content and texture analysis indicated the presence of an argillic horizon at the 20 cm depth at location 1 while at location 2 the argillic horizon was exposed to the soil surface photographic image analysis techniques and fractal analysis appear to distinguish differences in crack area and patterns which may be useful in characterizing soil cracking

syn tectonic emplacement of the late mesozoic laojunshan granite pluton in the eastern qinling central china an integrated fabric and geochronologic study abstract the porphyritic monzogranite of laojunshan eastern qinling in central china forms a w e elongated pluton characterized by a varying abundance of cm scale potassium feldspar kfs megacrysts with or without plagioclase mantles mafic microgranular enclaves mmes and associated mafic dykes the measurements of the shape preferred orientation of kfs megacrysts and the tiling of megacrystic pairs throughout the pluton suggest that these megacrysts constitute magmatic foliations subparallel to the pluton s margin possibly resulting from eastward non coaxial magmatic flow felsic mafic magma mixing and mingling were important during magma emplacement as indicated by abundant mmes coeval mafic dykes and disequilibrium textures within kfs megacrysts quantitative analyses of the crystal size distribution and the in situ chemistry of kfs megacrysts revealed that the temperature fluctuation in the deep magma chamber and the resultant textural coarsening are the most likely important mechanisms for the growth of kfs megacrysts the syn tectonic and two main stage emplacement of the pluton in a sinistral transtensional regime is inferred by the mechanical coupling between magmatic submagmatic solid state fabrics in the pluton and wall rock deformations as well as zircon u pb dating results which produce eastward younging emplacement ages spanning from 122 ma to 119 ma combined with other studies our work supports the idea that the qinling dabie orogen was in a sinistral transtensional regime during the early cretaceous which may correspond to the eastward extrusion tectonics in eastern china

the magma mixing origin of mantled feldspars the key to mantled feldspar genesis is epitaxial nucleation of plagioclase on k feldspar or k feldspar on plagioclase once this nucleation takes place there is a relatively straightforward process of crystal growth yielding rapakivi and antirapikivi textures the most common mantling is plagioclase on k feldspar which occurs in both volcanic and plutonic environments in the volcanic environment the morphology of the plagioclase overgrowth typically is dendritic though in subvolcanic and shallow plutonic environments dendritic growth is followed by a more or less continuous non cellular shell of plagioclase in the plutonic environment early stages of plagioclase overgrowth also tend to be dendritic although with coarser grained characteristics dendritic morphology is thus a common denominator in rapakivi genesis since growth of dendritic plagioclase is clearly related to marked undercooling in silicate melt systems its occurrence in many volcanic rocks is to be expected equivalent quenching in the plutonic environment requires a cooling mechanism independent of conductive heat transfer to wallrock and also independent of effective cooling related to sudden loss of volatile phases that could only occur late in the crystallization of most magmas and therefore after much dendritic plagioclase had already formed internal quenching of portions of magma systems must occur if mafic magma is abruptly mixed with felsic magma such magma mixing yields a heterogeneous system at first one that is in a drastic state of disequilibrium and tending to force nucleation of one feldspar type on the surface of another resulting in epitaxial crystallization of dendritic plagioclase on k feldspar mantling of one feldspar type by another during magma mixing is paralleled by dendritic growth zones in coexisting plagioclase crystals

plagioclase xenocrysts and mafic magmatic enclaves in some granitoids of the sierra nevada batholith california plagioclase phenocrysts from mafic magmatic enclaves and plagioclase crystals from host granitoids of some plutons of the central part of the sierra nevada batholith are complexly zoned and commonly divided into three neatly distinct parts an oscillatory locally patchy zoned andesine or more calcic core a ring with dusty calcic plagioclase and a normally zoned rim of sodic plagioclase although aspect of the calcic rings and width and zoning of the rims may slightly vary from the enclaves to the hosts cores of both phenocrysts and large plagioclase crystals show similar zoning and composition the andesine or more calcic cores are interpreted to have crystallized in the felsic or the mafic magma respectively and been incorporated into the coeval magma when the two magmas mixed introduction of the xenocrystic cores into a magma where they were not in equilibrium resulted in partial dissolution development of abundant patchy zoning and coating with dusty calcic plagioclase in both granitoids and mafic magmatic enclaves composition and zoning contrast between cores and rims of the plagioclase crystals reflect drastic changes in conditions of crystallization before and after the mechanical mixing event mixing of two magmas with contrasted compositions is suggested to be the major mechanism for generating complexly zoned plagioclase xenocrysts in granitoids and mafic magmatic enclaves this hypothesis is consistent with many recent models in which mixing of two contrasting components is proposed to play a fundamental part in the generation of calc alkaline granitoids and mafic magmatic enclaves of the sierra nevada batholith plagioclase xenocrysts may also provide information on the timing of the different mixing processes and on the magmatic evolution of the plutons

mechanical behavior and fracture spatial propagation of coal injected with liquid nitrogen under triaxial stress applied for coalbed methane recovery abstract fracturing technology through liquid nitrogen ln2 injection alters the physical properties of coal and rock masses because of the thermal and pressure effects in order to investigate heat transfer and fracture propagation behaviors under in situ geological condition with ln2 injections experimental work was conducted to study the ln2 induced rock coal failures under true triaxial stress conditions during the experiments the temperature ultrasonic waves and acoustic emission location detection were monitored to determine the intensity and complexity of specimen failure under singular or cyclic ln2 injections the results show that a single ln2 injection mainly transfers heat through the solid skeleton and only damages areas adjacent to the injection tube however cyclic injections formed a propagated fracture network and the heat can sequentially transfer further along the induced fractures moreover plastic deformation occurred in the entire volume of the sample and the main fractures coalesced until the sample failed based on the spatial locations of the acoustic emission sources the dynamic fracturing within the sample progressed after ln2 injection was clarified the experimental results can provide evidences for the proposed crack propagation model for the coal masses the research revealed that high pressure nitrogen gas transferring liquid water to the tips of new fractures is essential for cyclic ln2 injection to form effective frost heaving forces and fracturing therefore the fracturing efficiency of the cyclic ln2 injection is far higher than that of singular ln2 injections

p t conditions of crystallization and origin of plagioclase mantled alkali feldspar megacrysts in the mesozoic granitoids in the qinling orogen china abstract the qinling orogen between the north china and south china cratons was intruded at 211 217 ma by calc alkaline quartz monzonitic to monzogranitic plutons characterized by i to a type geochemistry and in many places contain plagioclase mantled alkali feldspar megacrysts rapakivi texture sensu lato the felsic rocks contain mafic to intermediate magmatic enclaves suggestive of mingling and mixing of mafic and felsic magmas the p t conditions of crystallization have been determined for early mineral assemblages inner parts of alkali feldspar megacrysts and their plagioclase quartz amphibole and biotite inclusions and late assemblages matrix minerals of the rapakivi textured granitoids al contents in amphibole from the early and late mineral assemblages yield pressures of 1 2 3 0 and 0 7 3 0 kbar respectively and indicate only minor pressure change between the crystallization of the early and late assemblages amphibole plagioclase thermometry gives temperatures mainly of the order of 900 to 1000 c for both the early and late assemblages indicating nearly isothermal conditions feldspar thermometers yield lower temperatures relative abundances of minerals and their chemical compositions indicate that the late mineral assemblages tend to be richer in mgo na 2 o and cao than the early assemblages rapakivi texture is interpreted in this case mainly as a result of compositional changes related to the hybridization between granitic and more mafic magmas small release of pressure during crystallization of the magmas may have contributed to the origin of the mantled alkali feldspar megacrysts

magma mixing in granitic rocks of the central sierra nevada california abstract the el capitan alaskite exposed in the north american wall yosemite national park was intruded by two sets of mafic dikes that interacted thermally and chemically with the host alaskite comparisons of petrographic and compositional data for these dikes and alaskite with published data for sierra nevada plutons lead us to suggest that mafic magmas were important in the generation of the sierra nevada batholith specifically we conclude that 1 intrusion of mafic magmas in the lower crust caused partial melting and generation of alaskite rhyolitic magmas 2 interaction between the mafic and felsic magmas lead to the observed linear variation diagrams for major elements 3 most mafic inclusions in sierra nevada plutons represent chilled pillows of mafic magmas related by fractional crystallization and granitoid assimilation that dissolve into their felsic host and contaminate it to intermediate granodioritic compositions 4 vesiculation of hydrous mafic magma upon chilling may allow buoyant mafic inclusions and their disaggregation products to collect beneath a pluton s domed ceiling causing the zoning mafic margins to felsic core that these plutons exhibit

fractal analysis of temperature induced cracking in clays and rocks because of their low hydraulic conductivity clays have been used as a hydraulic barrier to the flow of rainwater into landfills similarly rocks have been used as depository sites for nuclear waste high temperatures resulting from climatic fluctuations for clays or from heat generated by nuclear waste for rocks can have detrimental effects on their hydro mechanical properties causing cracking in clays this is the result of desiccation in rocks it is the result of varying expansion between mineral grains the present study deals with the evolution and interconnectivity of cracks in clays and rocks as a result of high temperatures evaluated using the fractal dimension concept

formation of wehrlites through dehydration of metabasalt xenoliths in layered gabbros of the noe nygaard intrusion southeast greenland the noe nygaard intrusion is a 4 2 5 km stock composed of layered gabbros and wehrlites within the precambrian basement of the coastal mountains west of the kialineq plutonic complex transgressive relationships to tertiary mafic dykes and the occurrence of abundant metabasaltic xenoliths signify a tertiary age for the intrusion the intrusion is characterized by alternating zones of gabbro and wehrlite gabbro is both intruded and replaced by wehrlite and the wehrlite zones are characterized by abundant metabasaltic xenoliths based on 87 sr 86 sr ratios mica olivine and oxide gabbros are all cumulates crystallized at different differentiation stages from a common parental magma field relations together with similarities in strontium isotope ratios and in the major and rare earth element ree mineral chemistry between gabbros and wehrlites indicate that the wehrlite bodies were formed by the dissolution of plagioclase from a gabbro cumulate mush by h 2 o derived from dehydration and the partial assimilation of metabasaltic xenoliths in terms of their ree characteristics melts from which the noe nygaard intrusion crystallized are within the compositional range of melts for other early tertiary mafic ultramafic complexes of east greenland however they were generated at a greater mean melting pressure and have less radiogenic strontium isotope ratios than the nearby imilik mafic ultramafic complex supporting existing models for mantle heterogeneity at the time of continental break up the abundance of metabasaltic xenoliths in the noe nygaard intrusion provides further evidence for the lateral extent of the north atlantic flood basalt province which onshore has been mostly removed by glacial erosion south of 68 n in greenland

resurfacing time of terrestrial surfaces by the formation and maturation of polygonal patterned ground 1 to help interpret the polygonal patterned ground on mars we present recent findings about a similar form of patterned ground in a particularly cold and arid region on earth the dry valleys of antarctica in this region distinct arrays of interconnected polygons which we refer to herein simply as patterned ground characterize many surfaces reflecting a subsurface network of interconnected subvertical wedges of sand that grow incrementally as sand progressively fills soil fractures the fractures form initially as thermoelastic stresses arise during periods of rapid cooling of frozen ground and they continue to open and close in response to thermal cycles we describe the initiation and maturation of the patterned ground using data for the growth of sand wedges and for the evolution of crack patterns and microrelief over time scales ranging up to 106 years

cracking and vertical preferential flow through landfill clay liners abstract cracking is a major concern in the long term performance of landfill clay liners cracking of clay liners is affected by the roots of the vegetation planted to control erosion while vegetation roots may restrict cracking they may introduce preferential flow through the liners the impact of vegetation roots on the hydraulic properties of clay liners remains unclear this study investigates the effect of vegetation roots on crack formation and preferential flow through clay liners three experimental soil columns were used to observe crack formation by exposure to the weather and to measure the flow through them caused by artificial rainfall the clay in each column was compacted to 90 relative compaction the first column was not vegetated and no crack developed in it the second column was vegetated and underwent drying wetting cycles outdoor the third column did not have vegetation but underwent drying wetting cycles outdoor cracks developed in the second and third columns due to the exposure to the weather image analysis in the experimental soil columns revealed that vegetation roots restricted crack formation especially in the early stages of drying wetting cycles infiltration tests performed on the experimental soil columns showed that the unsaturated hydraulic conductivity of the vegetated soil in the second column was respectively about two orders and one order of magnitude larger than those of the soils in the first and third columns the experimental results imply that the effect of vegetation roots on the preferential flow through landfill clay liners should be considered in practical designs

origin of mantle rapakivi feldspars experimental evidence of a dissolution and diffusion controlled mechanism experiments designed to simulate the dissolution of alkali feldspar during magma mixing produced plagioclase mantles that are texturally and compositionally similar to those in some hybrid volcanic rocks in hydrous dacite melt 69 sio2 at 0 8 gpa 850 c orthoclase or93 and sanidine or30 partially dissolved and were mantled by sodic plagioclase an25 30 although plagioclase nucleated epitaxially as a thin shell on the alkali feldspar surface near the time of initial resorption plagioclase subsequently grew inward mostly in the form of parallel blades toaard the receding dissolution surface orthoclase dissolved at a rate approximately proportional to the square root of run duration indicating diffusional control plagioclase grew inward within a static boundary zone of melt that formed between the original crystal dacite interface and the dissolution surface during orthoclase dissolution this boundary zone rapidly and simultancously gained na by diffusion from dacite and lost k by diffusion into dacite ca diffused more slowly into this zone from which non feldspar species were mostly excluded plagioclase was stable where sufficient ca had diffused in that the boundary zone melt intersected the plagioclase saturation liquidus plagioclase subsequently grew toward the receding dissolution surface as the ca compositional gradient and hence the site of plagioclase saturation stepped inward crystallization of plagioclase in the form of parallel blades allowed continued diffusive exchange of melt components between the dissolution surface and the host melt bladed growth also served to maintain at blade tips proximity of plagioclase to the dissolution surface thereby apparently preserving locally a thin zone of low variance melt in natural systems mantling of alkali feldspar by plagioclase will occur in a similar manner when a p t or x are changed to induce alkali feldspar dissolution b sufficient ca is available in the host melt to drive by diffusion boundary zone melt compositions to plagioclase saturation and c temperatures are low enough to stabilize sodic plagioclase and to maintain a coherent boundary zone these reqjirements are satisfied in volcanic systems when alkali feldspar is juxtaposed during mixing with hybrid melts of dacitic composition mantled feldspars in some intrusive systems i e rapakivi granites may form by a similar dissolution and diffusion controlled mechanism textural evidence of a similar origin may be obscurred in intrusive rocks however by products of late stage magmatic and subsolidus processes

separation and fracturing in overlying strata disturbed by longwall mining in a mineral deposit seam abstract mining induced fractures influence the stability of overburden and may provide pathways for transferring heat and mass in underground environment a novel approach was proposed to quantify the separation and fracture evolution in the undermined overburden consisting of 1 theoretical distribution models of the void ratios of fractures vrfs based on analytical evaluation of key strata subsidence and 2 numerical modeling using the universal distinct element code and a sequence of image post processing procedures for a longwall mining panel both theoretical calculations and numerical simulations indicated that vrf first increased rapidly then gradually decreased and finally stabilized to a minimum from the surrounding edges of disturbed strata to their centers and gradually decreased from deep to shallow strata the fractures exhibited a fracture rich arch distribution type along a vertical section numerous fractures occurred around the arch feet near the perimeters of mined out area and or arch crown near the center of disturbed strata the distributions of vrfs show the heights shapes and damage intensities of fractured zones and can also be used as porosity parameters to determine the permeabilities of mining disturbed overburdens therefore the vrf models can be used as a quantitative parameter to assess the extent of possible risk zones e g for water inflow into the mine or escape of hazardous fluids to the surface

40ar39ar geochronology of tertiary mafic intrusions along the east greenland rifted margin relation to flood basalts and the iceland hotspot track abstract the east greeland tertiary igneous province includes the largest exposed continental flood basalt sequence within the north atlantic borderlands more than ten layered gabbro complexes including the 55 ma skaergaard intrusion and a large dolerite sill complex are the plutonic equivalents of flood basalts both lavas and intrusions have been regarded as synchronous with continental breakup at 57 54 ma we report ten new ages of the mafic intrusions determined by40ar 39ar incremental heating experiments demonstrating that the mafic intrusions formed in two distinct time windows only intrusion ii of the imilik gabbro complex the skaergaard intrusion and the sorgenfri glestcher sill complex formed at 57 55 ma coeval with the eruption of regional flood basalts and continental breakup other layered gabbro intrusions at imilik intrusion iii kruuse fjord igtutarajik nordre aputite q kap edvard holm and lilloise are distinctly younger and formed between 50 and 47 ma plate kinematic models indicate the axis of the ancestral iceland mantle plume was located under central greenland at 60 ma and subsequently crossed the east greenland rifted continental margin we propose that tholeiitic magmatism along the east greenland rifted margin largely occurred in three distinct pulses at 62 59 ma lavas and dykes 57 54 ma lavas dykes sills and some gabbros and 50 47 ma gabbros dykes and rare lavas related to discrete mantle melting episodes triggered by plume impact continental breakup and passage of the plume axis respectively this model implies northwestward continental drift of greenland relative to the plume axis by 3 9 5 0 cm yr between 60 and 49 ma consistent with estimates from seismic studies of submerged flood basalts

the bastar craton central india a window to archean paleoproterozoic crustal evolution abstract the bastar craton in central india surrounded by cratonic blocks and paleoproterozoic to neoproterozoic orogenic belts is a window to investigate the archean paleoproterozoic crustal evolution and tectonic processes here we propose a new tectonic classification of the craton into the western bastar craton wbc eastern bastar craton ebc and the intervening central bastar orogen cbo we present petrologic geochemical and zircon u pb ree and lu hf data from a suite of rocks from the cbo and along the eastern margin of the wbc including 1 volcanic successions comprising meta andesite and fine grained amphibolite representing arc related volcanics along a convergent margin 2 ferruginous sandstone in association with rhyolite representing a volcano sedimentary succession deposited in an active trench and 3 metamorphosed mafic ultramafic suite including gabbro pyroxenite and dunite invaded by trondhjemite representing the section of sub arc mantle and arc root adjacent to a long lasting subduction system petrologic studies indicate that the mafic ultramafic suite crystallized from an island arc tholeiitic parental magma in a suprasubduction zone environment the chondrite normalized and primitive mantle normalized diagrams of the mafic and ultramafic rocks suggest derivation from morb magma the mixed characters from n morb to e morb of the studied samples are consistent with subduction modification of a morb related magma involving partial melting of the metasomatized mantle wedge our zircon u pb age data suggest that the cratonic nuclei was constructed as early as paleoarchean we present evidence for active subduction and arc magmatism through mesoarchean to neoarchean and early paleoproterozoic with the trench remaining open until at least 2 3 ga two major crust building events are recognized in the bastar craton during mesoarchean recycled paleoarchean subduction related as well as juvenile depleted mantle components and neoarchean accretion of juvenile oceanic crust arc magmatism including granite batholiths and related porphyry mineralization the final cratonization occurred during latest paleoproterozoic followed by collisional assembly of the craton and its incorporation within the peninsular indian mosaic during mesoproterozoic in the global supercontinent context the craton preserves the history of ur the earliest supercontinent followed by the paleo mesoproterozoic columbia as well as minor thermal imprints of the neoproterozoic rodinia and associated grenvillian orogeny

magma mixing and the production of compositional variation within granite suites evidence from the granites of southeastern australia granite suites are groups of plutons possessing characteristic features that are a result of their derivation from source material of a specific composition variation within suites has been ascribed to a variety of processes magma mixing or mingling is a popular hypothesis generally proposed in terms of blending between a crustal melt and mafic material from the mantle that caused that melting when the compositions of pain of suites from the bega batholith of southeastern australia are compared any differences seen at either end of the range in composition are also seen at the other limit so that both the most mafic and mostfelsic rocks show similar relative abundances of particular elements similar relationships are seen for other granites in the region these observations are not consistent with largescale magma mixing or mingling and although those processes may operate on a small scale they cannot have been responsible for the major compositional variations likewise assimilation of country rocks had no significant role in producing variation in the granites of southeastern australia the production of variation by differential separation of melt from residual solid source material or restite must be favoured for many of the granite suites of this region

petrology and geochemistry of the kruuse fjord gabbro complex east greenland the kruuse fjord gabbro complex is a composite intrusion of layered gabbro and troctolite with subordinate ultramafic rocks and minor trondhjemitic bodies it was emplaced into archaean continental crust of east greenland during early tertiary rifting of greenland from eurasia the work to date has identified an outer gabbro series and an inner troctolite series and these are separated by a narrow zone of trondhjemitic intrusions in the southeast the partially crystallized cumulates of the gabbro series were intruded by a lenticular ultramafic pluton 800 m in thickness volumetrically minor syenite trachyandesite net veined dykes and later diabase dykes cross cut the plutonic rocks structural and topographic features suggest that the layered rocks were affected by synmagmatic subsidence and deformation but not by monoclinal coastal flexure the gabbro series is composed of a marginal gabbro unit about 20 m wide bordering more than a 2 km thickness of layered olivine and magnetite gabbro cumulates the marginal gabbro is interpreted to be chilled magma the layered cumulates are the product of repeated injections of magma that fractionated in an open system magma chamber anorthositic and troctolitic layers in the lower part of the sequence may represent inputs of magma and suggest that the order of cumulus mineral crystallization was 1 plagioclase an 39 85 2 olivine fo 46 82 3 augite wo 28 47 en 39 58 fs 8 18 and 4 magnetite the disappearance of cumulus magnetite and a reversal in mineral compositions at 1 5 km from the base of the succession suggests a major input of magma occurred at this height in the troctolite series the composition of cumulus minerals mineral crystallization sequence and style of emplacement are similar to those in the gabbro series the ultramafic pluton is composed of coarse grained wehrlite olivine melagabbro and troctolite that were formed by at least three injections of magma the typical mineral crystallization sequence was 1 cumulus chromite and olivine fo 84 88 2 poikilitic chrome diopside wo 29 51 en 43 63 fs 3 13 and 3 intercumulus plagioclase an 75 90 phlogopite apatite and localized disseminated sulphides containing au and platinum group elements comparison of crystallization sequences and the major and trace element compositions of clinopyroxene suggests that the gabbroic and troctolitic rocks formed from a magma represented by the chilled marginal gabbro a tholeiitic basalt magma similar to e morb whereas the ultramafic rocks formed from a magma that was relatively enriched in incompatible trace elements and volatiles the association of these two magma types is an example of bimodal mafic ultramafic magmatism in a rifting environment

comparative petrogenesis and tectonics of paleoproterozoic malanjkhand and dongargarh granitoids central india abstract the malanjkhand granitoid mg and two units of dongargarh granitoids dgs represent contemporaneous episodes of paleoproterozoic felsic magmatism in the bastar craton central india a comparative geochemical study is carried out between the mineralized malanjkhand granitoid mg and barren dongargarh granitoids dgs that occur adjacent to each other separated by the dongargarh group of rocks major element oxides geochemistry reveals that mg is granite granodiorite whereas dg is strictly granite in composition and both plutons show calc alkaline affinity geochemical discrimination indicates that mg is an i type whereas an a type affinity can only be suspected in case of dg and both can be labeled as peraluminous trace element data from these paleoproterozoic granitoids indicate that they evolved in a tectonic environment similar to continental rift setting hfse ratios suggest variable degree of fractionation of highly differentiated granitic magma was a very complex crystallization process results in the formation of these two granitoids by common mechanism possibly fluid separation might be involved highly fractionated ree and depleted mree patterns with eu anomaly absent in mg and negative in dg inferred that the parental magma derived by low degree partial melting of heterogeneous mafic source probably amphibolitic in nature followed by progressive differentiation zircon saturation temperature and zr content reveals that mg crystallized from wet melt whereas dg crystallized from relatively dry melt but both are classify as hot granites thermobarometric calculations indicates that mg has emplaced at upper level whereas dg at relatively deeper or middle upper level in the continental crust the origin of palaeoproterozoic granitoids in central india has attributed to the magma mixing process between crustal derived felsic and mafic magma contributed by basaltic underplating in a continental rift environment

textural evolution of the rapakivi granites south greenland sr o and h isotopic investigations the development of rapakivi texture in feldspars from the ketilidian granitoids of south greenland has been investigated using sr o and h isotopes a low temperature signature is found in the sr and o data which seemingly contradicts some textural features that point to a magmatic origin of the plagioclase mantles around the k feldspar ovoids an origin for these mantles involving exsolution from an original alkali feldspar solid solution is proposed which involves growth of mantles over a range of conditions determined by the mobility of the exsolving sodic feldspar this mobility may be enhanced at high temperatures in the presence of melts or increased fluid pressures and at lower temperatures by the processes responsible for the transformation of k feldspar to microcline rapakivi granites with both white and dark green feldspar occur in south greenland but show no major isotopic differences although the dark alkali feldspars contain significantly more fluid equivalent fluids in the white alkali feldspars may have escaped during plagioclase exsolution

triassic granitoids of the qinling orogen central china genetic relationship of enclaves and rapakivi textured rocks abstract granitoids varying in composition from biotite amphibole granodiorite to monzogranite with rapakivi textures have recently been recognized in the qinling orogen central china the granitoids are magnesian calc alkalic and metaluminous a cnk 0 71 0 95 they contain many mafic to intermediate microgranular enclaves the enclaves are quenched mafic melts in granitic host magma as evidenced by fine grained sinuous margins against or transitional contacts with the host granitoids as well as disequilibrium textures and mineral assemblages u pb zircon dating of the granitoids yields 209 2 ma and 212 2 ma and the enclaves 210 2 ma and 211 2 ma respectively the host granitoids and enclaves show obvious silica gap but similar ree and trace element patterns the whole rock 87sr 86sr t end t and zircon ehf t values for the granitoids vary from 0 70516 to 0 70634 2 3 to 4 4 and 0 7 to 7 6 and for the enclaves from 0 70467 to 0 70600 1 1 to 4 0 and 1 2 to 8 8 respectively showing overlapped end t and zircon ehf t values all these suggest that the two magmatic systems represented by the host rock and enclave are probably derived from distinct sources with sufficient interaction or common origin but underwent different degrees of crustal contamination mineralogical and geochemical data point to enclave dissolution in silicic magma as a major process accounting for the origin of the rapakivi texture the possible bimodal magmatism suggested by the coeval granitoids and lamprophyre dykes combined with the structural pattern geochemical features and regional tectonics suggest a post collision setting for the qinling rapakivi textured granitoid plutons

structure and porosity of smectitic mudrocks as affected by experimental wetting drying cycles and freezing thawing cycles abstract the erosion rates in the vallcebre basin pyrenees are controlled predominantly by the physical weathering rate of bare regolith i e mudrocks to obtain information on the influence of thermic and moisture regimes on the weathering dynamics laboratory experiments were carried out to investigate how freezing thawing or wetting drying cycles under controlled conditions affect structure and porosity three different clayey mudrocks were selected to represent materials more susceptible to erosion in the studied area the three lithologies identified as ca1r ca2r carr differed mainly in mineral constituents type and quantity of the clay minerals and cation exchange capacity an automated non contact laser profile meter was used to analyse surface microtopography in order to monitor random roughness variations and to calculate bulk density porosity and pore size distribution were carried out with image analysis freezing thawing cycles were the most active in modifying soil surface and bulk structure roughness of ca1r and ca2r was more than doubled at the end of freezing thawing cycles this variation was mostly associated with the whole surface elevation related to the bulk volume increase roughness variations in carr were less pronounced and related to a modification of the microtopography micromorphological observations revealed a platy structure formation induced by repeated ice lensing also porosity was increased by freezing thawing cycles with the formation of a large number of irregular and rounded pores wetting drying cycles did not affect surface roughness and modified bulk density very little in all samples they increased porosity by the formation of large cracks and fissures overall data from wetting drying cycles showed that changes in water content alone did not produce deep structural modifications a mechanism of alteration of soil structure during freezing thawing cycles is proposed

formation of rapakivi feldspar in the deer isle granite complex coastal maine in situ lead isotope and trace element analysis rapakivi and alkali feldspar phenocrysts from the devonian deer isle granite complex maine were investigated to see if magma mixing or isothermal decompression was responsible for their formation pb isotope and trace element analyses of alkali feldspar ovoids and their plagioclase inclusions were obtained by la icp ms to determine the characteristics of the initial magma these were compared with the plagioclase mantles rapakivi grains show a decrease in pb isotopic values and an increase in ba la and ce concentrations from the ovoids and inclusions to the innermost plagioclase mantles adjacent to the ovoids these variations along with cl imagery of quartz phenocrysts indicate an open system with compositional changes in the magma chamber occurring during rapakivi feldspar growth repeated episodes of magma mixing replenishment by ba and lree enriched magmas with lower pb isotopic ratios along with hybridized variations with the host magma created localized dissolution of alkali feldspar and quartz alkali feldspar phenocrysts proximal to these zones of thermal perturbation were first resorbed and then mantled by plagioclase that records the more primitive signature of the more mafic melt pb isotopic values and ba la and ce concentrations trend back to the initial magma composition at the mantle rims as the effects of the mixing event dissipated for grains that were somewhat more distal to these zones of mixing resorption of the alkali feldspar crystals did not occur yet the fresh supply of ba resulted in ba rich alkali feldspar mantles over ba poor alkali feldspar cores other alkali feldspar crystals were too far from the site of mixing hence they lack any evidence of open system crystallization as crystallization of the chamber continued along solidification fronts batches of cooler crystal rich magmas settled en masse to the floor disaggregation of these batches during settling and subsequent accumulation on the reservoir floor brought grains with disparate crystallization histories together filter pressing of the cumulate pile flushed highly evolved melts fluids out from interstitial pores to the high silica upper portions of the chamber the crystallization transportation and juxtaposition of disparate types of feldspar phenocrysts suggest that a relatively large and active magma chamber periodically recharged by localized batches of melt must have existed in this case it is clear that rapakivi mantled feldspars are the result of magma mixing such interpretations may apply to many other occurrences as well

cracks bifurcation and shear bands propagation in saturated clays discontinuities in the form of cracks or fissures and inclusions are often present in natural clays they serve as stress concentrators when loads are applied to the material such concentrations result in cracks advancing often surrounded by and preceded by a propagating damage zone as cracks propagate the damage may be in the form of one or more shear bands which may play the part of new stress concentrators and blunt the action of the original crack this paper examines some of the phenomena associated with cracks in over consolidated clays and normally consolidated clays differences between isotropic and anisotropic materials and the level at which serious modifications take place in the fabric of the material are noted the influence of the cracks and the shear bands on the kinematics and strength of the test specimens is discussed des discontinuites sont souvent presentes sous forme de fractures fissures et inclusions dans les argiles naturelles elles jouent le role de concentrateurs de c

fractal analysis of cracking in a clayey soil under freeze thaw cycles abstract under extreme climate conditions clayey soils experience not only seasonal drying and wetting but also frequent freezing and thawing cracking would also occur in clayey soils under freeze thaw cycles but now less academic attention has been paid on this issue in this study a series of laboratory tests were conducted on a clayey soil to investigate the cracking behaviors under freeze thaw cycles water loss surface crack initiation and propagation processes were monitored after each freeze thaw cycle by using the image processing technique the crack patterns were described and then quantitatively analyzed on the basis of the fractal dimension concept it was found that for the tested clayey soil subjected to freeze thaw cycles the surface crack pattern slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi hexagonal one and the water loss closely related to the sample thickness plays a significant role in the process of the clay cracking upon cyclic freezing thawing the fractal dimension is well correlated to the surface crack ratio in a logarithmic equation fractal dimension concept can offer a new perspective on the quantitative understanding of cracking initiation and propagation in clayey soils under freeze thaw cycles

contrasting sr and nd isotopic behaviour during magma mingling new insights from the mannum a type granite abstract the mannum granite in south australia is a classic a type granite which displays good evidence for magma mingling such as numerous syn plutonic mafic enclaves and rapakivi feldspars in both the granite and enclave study of the sr and nd isotopes show that the systems are dominantly controlled by plagioclase and titanite respectively the contrasting behaviour of these minerals during the development of a bimodal magmatic system has led to a well defined 482 ma isochron across a granite enclave boundary in the sr isotope system but not in the nd isotope system in situ techniques involving the development and production of a new titanite glass standard were developed to resolve this dichotomy inferred repeated interaction with mafic magmas has resulted in the destabilization and restabilization of plagioclase this has produced rapakivi textures and provides an effective mechanism for efficient sr isotope equilibration across the range of bulk rock compositions despite this interaction titanite in the host granite retain a range of initial nd isotope ratios indicating multiple parental magmas were assembled to produce the final pluton decoupling of the sr and nd isotope systems in other magmatic systems could be indicative of magma mixing as opposed to mingling where physical evidence e g enclaves xenocrysts etc is absent