Middle Triassic volcaniclastic depositsin the External Dinarides of Croatia and Bosnia and Herzegovina are related to the rifting of the Tethyan Ocean. Three localities in the External Dinarides： Donje Pazariste, Bos...Middle Triassic volcaniclastic depositsin the External Dinarides of Croatia and Bosnia and Herzegovina are related to the rifting of the Tethyan Ocean. Three localities in the External Dinarides： Donje Pazariste, Bosansko Grahovo and Zelovo were biostratigraphically analysed in this study. The Middle Triassic carbonate deposits with volcaniclastic interlayers in Donje Pazariste were defined by means of conodonts. Rare ammonoid specimens were collected.Recovered conodont and ammonoid taxa suggest these sections are of Early Illyrian to Early Fassanian Age. The section studied in Bosansko Grahovo is dominantly composed of volcanic and volcaniclastic rocks. Limestone peperites were collected for conodont analysis. Two conodont zones were defined, suggesting volcanic activity in the same, from Lower Illyrian to Fassanian, time interval. The Zelovo Section was biostratigraphically investigated by several authors. The pietra verde deposits from Zelovo are referred as late Fassanian to Early Longobardian Age. Biostratigraphic correlation from mentioned three localities imply that the magmatic activity in the External Dinarides, and formation of different volcaniclastic facies lasted from Illyrian to Longobardian, similar as in the surrounding western Tethyan territories.展开更多
The Fossil Hill Formation of the type section composed chiefly of the sedimentary-volcaniclastic breccia and tuffites can be divided into two cycles of sedimentation. The thermal fluid was active in the coarse volcani...The Fossil Hill Formation of the type section composed chiefly of the sedimentary-volcaniclastic breccia and tuffites can be divided into two cycles of sedimentation. The thermal fluid was active in the coarse volcaniclastic deposits of the lower cy-cle, it led to the formation of laumontite,analcite,albite and regularly hybrid mineral of interlayered chlorite and montmorillonite .which are absent from the upper cycle, and to the transportation and concentration of some of trace elements between the coarser tuffites and the overlying fine tuffite bed at the upper part of this cycle. So-called 'rainprint' and 'mud crack' actually are non-sedimentary originally, they were formed respectively by sheddillg of the small zeolitized concretions on the bedding plane and tectonic pressed stress. The evidences indicate that the Fossil Hill Formation of the Fossil Hill section was deposited in an intermontane lake affected by both volcanic action andseasonal flail under the condition of worm and moist climate.展开更多
Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undivided sedimentary rock unit of the Bagh complex which is the mélange zone beneath the Muslim Bagh ophiolite. The presence of...Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undivided sedimentary rock unit of the Bagh complex which is the mélange zone beneath the Muslim Bagh ophiolite. The presence of Middle Triassic grey radiolarian chert within the upper and lower horizon of the conglomerates suggests that the lavas, from which these conglomerates were principally derived, were eroded and re-deposited in the Middle Triassic. The Wulgai conglomerate contains several textural and mineralogical varieties of volcanic rocks, such as porphyritic, glomerophyric, intersertal and vitrophyric basalts. The main minerals identified in these samples are augite, olivine, plagioclase（An35–78） leucite and nosean, with apatite ilmenite, magnetite and hematite occurring as accessory minerals. These rocks are mildly to strongly-alkaline with low Mg~# and low Cr, Ni and Co contents suggesting that their parent magma had undergone considerable fractionation prior to eruption. Trace element-enriched mantle-normalized patterns with marked positive Nb anomalies are consistent with 10%–15% melting of an enriched mantle source in a within-plate tectonic setting. It is proposed that this Middle Triassic intra-plate volcanism may represent mantle plume-derived melts related to the Late Triassic rifting of micro-continental blocks（including Afghan, Iran, Karakorum and Lhasa） from the northern margin of Gondwana.展开更多
The study area is located in the entrance of Wadi Girshah in Ablah area, Assir terrain, southwestern Saudi Arabia. The present study aims to shed light on the field, mega- and microscopic description of the volcanicla...The study area is located in the entrance of Wadi Girshah in Ablah area, Assir terrain, southwestern Saudi Arabia. The present study aims to shed light on the field, mega- and microscopic description of the volcaniclastic red beds and the associated scoriaceous basalts of Wadi Al Roaian. It is based mainly up on the field works augmented by petrographic description. The present study revealed that, the succession of the upper part of Girshah Formation comprises three main horizons: 1) lower unit of epidotized and silicified basaltic and andesitic tuffs;2) middle unit of volcaniclastic red beds-scoriaceous basalts of successive cycles (each of these cycles begins by reddish tuffaceous mudstone and sandstone and is terminated by the calcite-bearing scoriaceous basalt). This unit indicated the deposition in lacustrine environments and the red iron oxyhydroxides minerals were formed either by the direct hematitization of the deposited tuffs or by the diagenetic hematitization of the green clays formed instead of the precursor tuffaceous materials;3) upper scoriaceous basalt unit composed from hematitized and calcitized basalt. The unit was formed by basic volcanic eruptions in subaerial condition which was predominated by the formation of calcium carbonate lakes associated with the progressive and subsequent calcitization of the Ca-plagioclase minerals of the basalt and the associated glassy tuffaceous material. The scoriaceous basalts of Wadi Al Roaian area represent subaerial basic volcanic eruption in continental situation and are associated with subsequent events of mineral alteration and formation of secondary minerals i.e. calcite, hematite and goethite.展开更多
This study undertook a comprehensive sedimentological and grain-size analysis of two previously uncharacterized volcanoclastic deposits exposed in the northwestern sector of Chihuahua City, Mexico. The primary objecti...This study undertook a comprehensive sedimentological and grain-size analysis of two previously uncharacterized volcanoclastic deposits exposed in the northwestern sector of Chihuahua City, Mexico. The primary objective was to propose a systematic genetic classification for these deposits, employing traditional sedimentological techniques and an advanced computerized granulometric analysis technique based on orthogonal images to discern their grain size distribution. Through these studies, evidence was sought to classify them genetically, presenting arguments to define them either as a lahar or a volcanic debris avalanche. Results were critically compared against existing literature data pertaining to lahars and debris avalanches, yielding moderate success. The analysis identified one of the deposits as a non-eruptive or post-eruptive lahar. This identification was substantiated by the delineation of distinct overbank and transition facies within the deposit, providing compelling evidence for its genetic classification.展开更多
ECLOGITE occurs in different metamorphic rocks in the Dabie Mountains. Some dike-likeeclogite and garnet amphibolite were discovered when we investigated the newly founded low-greenschist facies volcaniclastic rocks i...ECLOGITE occurs in different metamorphic rocks in the Dabie Mountains. Some dike-likeeclogite and garnet amphibolite were discovered when we investigated the newly founded low-greenschist facies volcaniclastic rocks in Changpu, Yuexi County and Siqian, Taihu County(fig.1). Coesite and quartz pseudomorphs exist in garnet and omphacite. By studying the oc-currence and petrography-mineralogy characteristic, we believe that the eclogite is of展开更多
High abundance gas reservoirs were discovered in the volcaniclastic sedimentary rocks of Wangfu faulted depression in Songliao Basin,but the distribution pattern and formation mechanism of this type of high-quality re...High abundance gas reservoirs were discovered in the volcaniclastic sedimentary rocks of Wangfu faulted depression in Songliao Basin,but the distribution pattern and formation mechanism of this type of high-quality reservoirs were not clear.In the Shahezi Formation of Well Block CS6 in Wangfu faulted depression,the void space type,reservoir property,pore throat and pore diameters were studied by means of the casting thin section,helium intrusion porosimetry,mercury intrusion porosimetry(MIP)and nuclear magnetic resonance(NMR)methods,moreover,formation mechanism and main controlling factors of the high-quality reservoirs were discussed.Results showed that lithology of high-quality reservoirs consisted of the volcaniclastic sedimentary agglomerate and the volcaniclastic sedimentary breccia,and exhibited the coarsening-upward characteristics.Furthermore,three types(seven subtypes)of void spaces were identified,among which the intragranular vesicles with primary abundant pores were uniquely developed in the high-quality reservoirs of volcaniclastic sedimentary rocks,indicating this high-quality reservoir belonged to the large-pore and small-throat reservoir;porosity and permeability of volcaniclastic sedimentary agglomerate were slightly higher than those of volcaniclastic sedimentary breccia,and both were significantly higher than those of sedimentary rock in the Shahezi Formation,the porosity was closely related with the burial depth.Formation mechanisms of reservoirs in the volcaniclastic sedimentary rocks were release of volatile matters in parent rocks,grain support,dissolution and tectonic modification,among which the former two were the main controlling factors.The high-quality reservoirs over the study area were mainly distributed in the central part of the fan of volcaniclastic sedimentary rocks,among which the grain-supported,coarse-grained volcaniclastic sedimentary rocks with high content of intragranular vesicular detritus and burial depth less than 3000 m were the most favorable area for development of the high-quality reservoirs.展开更多
Recently,a high-yield gas flow of 22.5×10^(4)m^(3)/d was achieved in the wildcat well Yongtan 1,deployed by PetroChina Southwest Oil and Gasfield Company,and an extrusive facies volcaniclastic gas reservoir was f...Recently,a high-yield gas flow of 22.5×10^(4)m^(3)/d was achieved in the wildcat well Yongtan 1,deployed by PetroChina Southwest Oil and Gasfield Company,and an extrusive facies volcaniclastic gas reservoir was first discovered in the Sichuan Basin,which is a major breakthrough in the exploration of volcanic rock gas reservoirs.In order to further evaluate the exploration potential in Permian volcanic rock gas reservoirs in this basin,we systematically reviewed and summarized the exploration process of volcanic rocks in this study area,as well as the characteristics of gas reservoirs of well Yongtan 1,the controlling factors and modes of hydrocarbon accumulation.The following findings were obtained.(1)Over the past five decades of gas exploration of volcanic rocks,the change of exploration thought and progress in seismic prediction contribute to a major discovery in this study area,i.e.,the well location deployment of Yongtan 1 was determined in the Jianyan area,where the volcanic anomalies of the Permian developed outbursts are well developed and the gas reservoir conditions are favorable.This also proves that another new gas exploration area in this basin was found.(2)From the data of Yongtan 1,we found high-quality volcanic porous reservoirs with a thickness of over 100 m developed in the Permian strata,the effusive volcanic rock types dominated by breccia and tuffaceous breccia,reservoir space composed of dissolution pores,interbreccia dissolution pores,and other pores,the porosity of which is 6.68%-13.22%and 10.26%on average,the permeability 0.01-4.43 mD and 2.35 mD on average.(3)This abnormally high pressure gas reservoir was buried 4500-6000 m deep underground with the middle formation pressure being 125.625 MPa and the pressure coefficient being up to 2.22.Methane content in the minor H_(2)S-bearing produced gas flow reached up to 99.03%.(4)Volcanic rocks in the Jianyang-Zhongjiang-Santai area are developed,and they are adjacent to the Cambrian high-quality source rocks in the Deyang-Anyue rifting.The early extensional deep faults play a role in connecting source and storage.There are many sets of caprocks,such as the Upper Permian Longtan Formation and Lower Triassic layered thick paste rocks,providing conditions for forming large-scale tectonic-lithologic composite trap gas reservoirs,and the favorable exploration area reaches up to 6000 km^(2).In conclusion,this major discovery not only proves that Permian volcanic rocks in the Sichuan Basin has large potential for oil and gas exploration,but reaffirms the confidence in changing our exploration thought,speeding up new exploration zones and areas,and discovering more and bigger gas fields.展开更多
The Early–mid Cretaceous marks the confluence of three major continental-scale events in eastern Gondwana:(1)the emplacement of a Silicic Large Igneous Province(LIP)near the continental margin;(2)the volcaniclastic f...The Early–mid Cretaceous marks the confluence of three major continental-scale events in eastern Gondwana:(1)the emplacement of a Silicic Large Igneous Province(LIP)near the continental margin;(2)the volcaniclastic fill,transgression and regression of a major epicontinental seaway developed over at least a quarter of the Australian continent;and(3)epeirogenic uplift,exhumation and continental rupturing culminating in the opening of the Tasman Basin c.84 Ma.The Whitsunday Silicic LIP event had widespread impact,producing both substantial extrusive volumes of dominantly silicic pyroclastic material and coeval first-cycle volcanogenic sediment that accumulated within many eastern Australian sedimentary basins,and principally in the Great Australian Basin system(>2 Mkm^(3)combined volume).The final pulse of volcanism and volcanogenic sedimentation at c.105–95 Ma coincided with epicontinental seaway regression,which shows a lack of correspondence with the global sea-level curve,and alternatively records a wider,continental-scale effect of volcanism and rift tectonism.Widespread igneous underplating related to this LIP event is evident from high paleogeothermal gradients and regional hydrothermal fluid flow detectable in the shallow crust and over a broad region.Enhanced CO_(2)fluxing through sedimentary basins also records indirectly,large-scale,LIP-related mafic underplating.展开更多
The eastern part of the Caucasus orogen,termed the Georgian segment,is mainly underlain by highly deformed Lower-Middle Jurassic shales,sandstones,and volcaniclastic rocks,and cut by numerous intrusive bodies of vario...The eastern part of the Caucasus orogen,termed the Georgian segment,is mainly underlain by highly deformed Lower-Middle Jurassic shales,sandstones,and volcaniclastic rocks,and cut by numerous intrusive bodies of various compositions.All units contain a variety of mineral deposit types and their surrounding zones of hydrothermal alteration.Detailed geological and metallogenic research,after 30 years stagnation,has led to important new information regarding the evolution of this region.Three main stages of magmatic activity are now clearly distinguished.The oldest magmatism comprises early Jurassic events,related to extensional tectonism,with volcanism and subvolcanic plutonism that ranged from rhyolitic,through dacitic and andesitic,and to basaltic.Additional extensional processes(in Bajocian times)were characterized by intrusion of a gabbro and diorite dike system into slightly older late Early Jurassicearly Middle Jurassic formations.The final magmatic event was associated with Middle Jurassic folding and uplift during which multiphase diorite plutons were emplaced.Intense hydrothermal activity related to this latest magmatism was responisble for important polymetallic mineralization including more than 100 historically recognized outcropping occurrences.A detailed study of 11of the more significant of these occurrences has indicated anomalous concentrations of base metals as well as gold,thorium,yttrium,cobalt,cadmium,and bismuth.In addition,several new and potentially significant mineral occurrences were discovered,including two designated here as Gelia and Lechuri.展开更多
The Lachlan Orogen of New South Wales,Victoria and eastern Tasmania is the best understood element of the eastern Australian Tasmanides.The Tasmanides encompass continental growth in a Neoproterozoic passive margin se...The Lachlan Orogen of New South Wales,Victoria and eastern Tasmania is the best understood element of the eastern Australian Tasmanides.The Tasmanides encompass continental growth in a Neoproterozoic passive margin setting and a Paleozoic–Mesozoic active margin in east Gondwana,bounded to the east by the Pacific Ocean.In the Ordovician,the supra-subduction zone element in the Lachlan Orogen is the Macquarie Arc.This comprises one minor and three major belts of mafic to intermediate volcanic and volcaniclastic rocks,limestones and intrusions that,with two hiatuses in magmatism,span the Ordovician and extend into the Early Silurian.The three major belts in central New South Wales are separated by Silurian–Devonian rift basins and are therefore,inferred to have been rifted apart during crustal extension.Chemical and isotopic data suggest the Macquarie Arc is intraoceanic,developed on primitive oceanic crust.Despite this,key features such as its longevity,stacked magmatic phases,little deformation and flanking coeval craton-derived turbidites and black shales with no provenance mixing indicate differences from modern intraoceanic arcs.Paleogeographic setting and magmatic evolution of the Macquarie Arc provided perfect conditions for mainly porphyry-related,rich Au-Cu deposits,in the Ordovician,and especially in the Early Silurian after amalgamation of the arc with its flanking terranes.展开更多
The age range of the major intra-plate volcanic event that affected the northern Indian margin in the Early Cretaceous is here defined precisely by detrital zircon geochronology. U-Pb ages of Early Cretaceous detrital...The age range of the major intra-plate volcanic event that affected the northern Indian margin in the Early Cretaceous is here defined precisely by detrital zircon geochronology. U-Pb ages of Early Cretaceous detrital zircons found in the Cretaceous to the Paleocene sandstones cluster mainly between 142 Ma and 123 Ma in the northern Tethys Himalayan unit, and between 140 Ma and 116 Ma in the southern Tethys Himalayan unit. The youngest and oldest detrital zircons within this group indicate that volcanism in the source areas started in the latest Jurassic and ended by the early Albian. Stratigraphic data indicate that volcaniclastic sedimentation began significantly earlier in southern Tibet （Tithonian） than in Nepal （Valangin- ian）, and considerably later in Spiti and Zanskar （Aptian/AIbian） to the west. This apparent westward migration of magmatism was explained with progressive westward propagation of extensional/transtensional tectonic activity and development of fractures cutting deeply across the Indian continental margin crust. However, detrital zircon geochronology provides no indication of heterochroneity in magmatic activity in the source areas from east to west, and thus lends little support to such a scenario. Westward migration of volcaniclastic sedimentation may thus reflect instead the westward progradation of major drainage systems supplying volcanic detritus sourced from the same volcanic centers in the east. Development of multiple radial drainage away from the domal surface uplift associated with magmatic upwelling, as observed for most large igneous provinces around the world, may also explain why U-Pb ages of detrital zircons tend to cluster around 133-132 Ma （the age of the Cornel igneous province） in Tethys Himalayan units, but around 118-117 Ma （the age of the Rajmahal igneous province） in Lesser Himalayan units.展开更多
The North Tianshan Orogenic Belt contains the youngest ophiolites in the Tianshan and provides some information on timing of the last closure of the Junggar-Balkhash Ocean. LA-ICP-MS zircon U-Pb dating was conducted t...The North Tianshan Orogenic Belt contains the youngest ophiolites in the Tianshan and provides some information on timing of the last closure of the Junggar-Balkhash Ocean. LA-ICP-MS zircon U-Pb dating was conducted to define the formation age of the Arbasay Formation in the Shichang Region of North Tianshan, which is exposed near the suture zone but its age remains debated. The Arbasay Formation is mainly composed of volcanic and volcaniclastic rocks with tuft interlayers. The zircons from the tufts yield two age populations of 315 ± 3 Ma and 304 ± 2 Ma, constraining the commencement and demise timings of volcanism, respectively. Furthermore, zircon U-Pb age spectra of the tuffaceous sandstones display the youngest peak age at 308 Ma, indicating a 〈 308 Ma age for the depositional age of volcaniclastic rocks. The volcaniclastic rocks therefore were likely to deposit together with the syn-sedimentary volcanism during Late Carboniferous. This means that the Arbasay Formation in Shichang Region should be re-assigned to Late Carboniferous in age. Given that the Arbasay Formation was likely to be formed during the tectonic transition from compression to extension, the Junggar-Balkhash Ocean possibly closed during Late Carboniferous.展开更多
The use of mineral interfaces, in sand-sized rock fragments, to infer the influence exerted by mechanical durability on the generation of siliciclastic sediments, has been determined for plutoniclastic sand. Conversel...The use of mineral interfaces, in sand-sized rock fragments, to infer the influence exerted by mechanical durability on the generation of siliciclastic sediments, has been determined for plutoniclastic sand. Conversely, for volcaniclastic sand, it has received much less attention, and, to our knowledge, this is the first attempt to make use of the volcaniclastic interfacial modal mineralogy of epiclastic sandy fragments, to infer mechanical durability control at a modern beach environment. Volcaniclastic sand was collected along five beaches developed on five islands, of the southern Tyrrhenian Sea(Alicudi, Filicudi, Salina, Panarea and Stromboli) from the Aeolian Archipelago, and one sample was collected near the Stromboli Island volcanic crater. Each sample was sieved and thin sectioned for petrographic analysis. The modal mineralogy of the very coarse, coarse and medium sand fractions was determined by point-counting of the interfacial boundaries discriminating 36 types of interfaces categories, both no-isomineralic and/or no iso-structural(e.g., phenocrystal/glassy groundmass or phenocrystal/microlitic groundmass boundaries) and iso-mineralic interfaces, inside volcanic lithic grains with lathwork and porphyric textures. A total of 47,386 interfacial boundaries have been counted and, the most representative series of interfaces, from the highest to the lowest preservation, can be grouped as: a) ultrastable interfaces, categorized as Pl(Plagioclase)/Glgr(Glassy groundmass) > > Px(Pyroxene)/Glgr > > Ol(Olivine)/Glgr > > Op(Opaque)/Glgr > > Hbl(Hornblende)/Glgr> > Bt(Biotite)/Glgr > > Idd(Iddingsite)/Glgr > > Rt(Rutile)/Glgr;b) stable interfaces, categorized as Pl/Migr(Microlitic groundmass) > > Op/Migr > > Px/Migr > > Ol/Migr;c) moderately stable interfaces, categorized as Op/Px > > Op/Hbl > > Px/P > > Ol/Pl> > Bt/Op;and d) unstable interfaces, categorized as Pl/Pl > > Px/Px > > Ol/Ol > >Op/Op > > Hbl/Hbl > > Bt/Bt. Grains, eroded from the volcanic bedrock, if affected solely by abrasion, developed a rounded and smoothed form, with prevailing no-isostructural interfaces such as Plagioclase/Glassy groundmass,Pyroxene/Glassy groundmass and Olivine/Glassy groundmass interfaces. Grains that during transport suffered fracturing and percussion have a sharp and angular form: these combined transport mechanisms produce mainly volcanic sandy grains with iso-structural interfaces, such as Pl/Pl, Px/Px, Hbl/Hbl, and, to a lesser extent, Bt/Op and Bt/Glgr interfaces.展开更多
基金financed by the Croatian Ministry of Science and EducationUniversity of Zagreb financial support founds
文摘Middle Triassic volcaniclastic depositsin the External Dinarides of Croatia and Bosnia and Herzegovina are related to the rifting of the Tethyan Ocean. Three localities in the External Dinarides： Donje Pazariste, Bosansko Grahovo and Zelovo were biostratigraphically analysed in this study. The Middle Triassic carbonate deposits with volcaniclastic interlayers in Donje Pazariste were defined by means of conodonts. Rare ammonoid specimens were collected.Recovered conodont and ammonoid taxa suggest these sections are of Early Illyrian to Early Fassanian Age. The section studied in Bosansko Grahovo is dominantly composed of volcanic and volcaniclastic rocks. Limestone peperites were collected for conodont analysis. Two conodont zones were defined, suggesting volcanic activity in the same, from Lower Illyrian to Fassanian, time interval. The Zelovo Section was biostratigraphically investigated by several authors. The pietra verde deposits from Zelovo are referred as late Fassanian to Early Longobardian Age. Biostratigraphic correlation from mentioned three localities imply that the magmatic activity in the External Dinarides, and formation of different volcaniclastic facies lasted from Illyrian to Longobardian, similar as in the surrounding western Tethyan territories.
文摘The Fossil Hill Formation of the type section composed chiefly of the sedimentary-volcaniclastic breccia and tuffites can be divided into two cycles of sedimentation. The thermal fluid was active in the coarse volcaniclastic deposits of the lower cy-cle, it led to the formation of laumontite,analcite,albite and regularly hybrid mineral of interlayered chlorite and montmorillonite .which are absent from the upper cycle, and to the transportation and concentration of some of trace elements between the coarser tuffites and the overlying fine tuffite bed at the upper part of this cycle. So-called 'rainprint' and 'mud crack' actually are non-sedimentary originally, they were formed respectively by sheddillg of the small zeolitized concretions on the bedding plane and tectonic pressed stress. The evidences indicate that the Fossil Hill Formation of the Fossil Hill section was deposited in an intermontane lake affected by both volcanic action andseasonal flail under the condition of worm and moist climate.
文摘Basaltic volcanic conglomerates near the Wulgai village in Balochistan occur in the undivided sedimentary rock unit of the Bagh complex which is the mélange zone beneath the Muslim Bagh ophiolite. The presence of Middle Triassic grey radiolarian chert within the upper and lower horizon of the conglomerates suggests that the lavas, from which these conglomerates were principally derived, were eroded and re-deposited in the Middle Triassic. The Wulgai conglomerate contains several textural and mineralogical varieties of volcanic rocks, such as porphyritic, glomerophyric, intersertal and vitrophyric basalts. The main minerals identified in these samples are augite, olivine, plagioclase（An35–78） leucite and nosean, with apatite ilmenite, magnetite and hematite occurring as accessory minerals. These rocks are mildly to strongly-alkaline with low Mg~# and low Cr, Ni and Co contents suggesting that their parent magma had undergone considerable fractionation prior to eruption. Trace element-enriched mantle-normalized patterns with marked positive Nb anomalies are consistent with 10%–15% melting of an enriched mantle source in a within-plate tectonic setting. It is proposed that this Middle Triassic intra-plate volcanism may represent mantle plume-derived melts related to the Late Triassic rifting of micro-continental blocks（including Afghan, Iran, Karakorum and Lhasa） from the northern margin of Gondwana.
文摘The study area is located in the entrance of Wadi Girshah in Ablah area, Assir terrain, southwestern Saudi Arabia. The present study aims to shed light on the field, mega- and microscopic description of the volcaniclastic red beds and the associated scoriaceous basalts of Wadi Al Roaian. It is based mainly up on the field works augmented by petrographic description. The present study revealed that, the succession of the upper part of Girshah Formation comprises three main horizons: 1) lower unit of epidotized and silicified basaltic and andesitic tuffs;2) middle unit of volcaniclastic red beds-scoriaceous basalts of successive cycles (each of these cycles begins by reddish tuffaceous mudstone and sandstone and is terminated by the calcite-bearing scoriaceous basalt). This unit indicated the deposition in lacustrine environments and the red iron oxyhydroxides minerals were formed either by the direct hematitization of the deposited tuffs or by the diagenetic hematitization of the green clays formed instead of the precursor tuffaceous materials;3) upper scoriaceous basalt unit composed from hematitized and calcitized basalt. The unit was formed by basic volcanic eruptions in subaerial condition which was predominated by the formation of calcium carbonate lakes associated with the progressive and subsequent calcitization of the Ca-plagioclase minerals of the basalt and the associated glassy tuffaceous material. The scoriaceous basalts of Wadi Al Roaian area represent subaerial basic volcanic eruption in continental situation and are associated with subsequent events of mineral alteration and formation of secondary minerals i.e. calcite, hematite and goethite.
文摘This study undertook a comprehensive sedimentological and grain-size analysis of two previously uncharacterized volcanoclastic deposits exposed in the northwestern sector of Chihuahua City, Mexico. The primary objective was to propose a systematic genetic classification for these deposits, employing traditional sedimentological techniques and an advanced computerized granulometric analysis technique based on orthogonal images to discern their grain size distribution. Through these studies, evidence was sought to classify them genetically, presenting arguments to define them either as a lahar or a volcanic debris avalanche. Results were critically compared against existing literature data pertaining to lahars and debris avalanches, yielding moderate success. The analysis identified one of the deposits as a non-eruptive or post-eruptive lahar. This identification was substantiated by the delineation of distinct overbank and transition facies within the deposit, providing compelling evidence for its genetic classification.
文摘ECLOGITE occurs in different metamorphic rocks in the Dabie Mountains. Some dike-likeeclogite and garnet amphibolite were discovered when we investigated the newly founded low-greenschist facies volcaniclastic rocks in Changpu, Yuexi County and Siqian, Taihu County(fig.1). Coesite and quartz pseudomorphs exist in garnet and omphacite. By studying the oc-currence and petrography-mineralogy characteristic, we believe that the eclogite is of
基金This study was supported by National Key Basic Research Program of China(973 Program)(No.2012CB822002)National Natural Science Foundation of China(No.41472304),and Outstanding Young Teachers Training Program of Jilin University。
文摘High abundance gas reservoirs were discovered in the volcaniclastic sedimentary rocks of Wangfu faulted depression in Songliao Basin,but the distribution pattern and formation mechanism of this type of high-quality reservoirs were not clear.In the Shahezi Formation of Well Block CS6 in Wangfu faulted depression,the void space type,reservoir property,pore throat and pore diameters were studied by means of the casting thin section,helium intrusion porosimetry,mercury intrusion porosimetry(MIP)and nuclear magnetic resonance(NMR)methods,moreover,formation mechanism and main controlling factors of the high-quality reservoirs were discussed.Results showed that lithology of high-quality reservoirs consisted of the volcaniclastic sedimentary agglomerate and the volcaniclastic sedimentary breccia,and exhibited the coarsening-upward characteristics.Furthermore,three types(seven subtypes)of void spaces were identified,among which the intragranular vesicles with primary abundant pores were uniquely developed in the high-quality reservoirs of volcaniclastic sedimentary rocks,indicating this high-quality reservoir belonged to the large-pore and small-throat reservoir;porosity and permeability of volcaniclastic sedimentary agglomerate were slightly higher than those of volcaniclastic sedimentary breccia,and both were significantly higher than those of sedimentary rock in the Shahezi Formation,the porosity was closely related with the burial depth.Formation mechanisms of reservoirs in the volcaniclastic sedimentary rocks were release of volatile matters in parent rocks,grain support,dissolution and tectonic modification,among which the former two were the main controlling factors.The high-quality reservoirs over the study area were mainly distributed in the central part of the fan of volcaniclastic sedimentary rocks,among which the grain-supported,coarse-grained volcaniclastic sedimentary rocks with high content of intragranular vesicular detritus and burial depth less than 3000 m were the most favorable area for development of the high-quality reservoirs.
基金supported by the Major Science&Technology Special Project of PetroChina Company Limited“Research and Application of Key Technologies for 300×10^(8) m^(3) Gas Productivity in Southwest Oil&Gasfield”(No.:2016E-0604).
文摘Recently,a high-yield gas flow of 22.5×10^(4)m^(3)/d was achieved in the wildcat well Yongtan 1,deployed by PetroChina Southwest Oil and Gasfield Company,and an extrusive facies volcaniclastic gas reservoir was first discovered in the Sichuan Basin,which is a major breakthrough in the exploration of volcanic rock gas reservoirs.In order to further evaluate the exploration potential in Permian volcanic rock gas reservoirs in this basin,we systematically reviewed and summarized the exploration process of volcanic rocks in this study area,as well as the characteristics of gas reservoirs of well Yongtan 1,the controlling factors and modes of hydrocarbon accumulation.The following findings were obtained.(1)Over the past five decades of gas exploration of volcanic rocks,the change of exploration thought and progress in seismic prediction contribute to a major discovery in this study area,i.e.,the well location deployment of Yongtan 1 was determined in the Jianyan area,where the volcanic anomalies of the Permian developed outbursts are well developed and the gas reservoir conditions are favorable.This also proves that another new gas exploration area in this basin was found.(2)From the data of Yongtan 1,we found high-quality volcanic porous reservoirs with a thickness of over 100 m developed in the Permian strata,the effusive volcanic rock types dominated by breccia and tuffaceous breccia,reservoir space composed of dissolution pores,interbreccia dissolution pores,and other pores,the porosity of which is 6.68%-13.22%and 10.26%on average,the permeability 0.01-4.43 mD and 2.35 mD on average.(3)This abnormally high pressure gas reservoir was buried 4500-6000 m deep underground with the middle formation pressure being 125.625 MPa and the pressure coefficient being up to 2.22.Methane content in the minor H_(2)S-bearing produced gas flow reached up to 99.03%.(4)Volcanic rocks in the Jianyang-Zhongjiang-Santai area are developed,and they are adjacent to the Cambrian high-quality source rocks in the Deyang-Anyue rifting.The early extensional deep faults play a role in connecting source and storage.There are many sets of caprocks,such as the Upper Permian Longtan Formation and Lower Triassic layered thick paste rocks,providing conditions for forming large-scale tectonic-lithologic composite trap gas reservoirs,and the favorable exploration area reaches up to 6000 km^(2).In conclusion,this major discovery not only proves that Permian volcanic rocks in the Sichuan Basin has large potential for oil and gas exploration,but reaffirms the confidence in changing our exploration thought,speeding up new exploration zones and areas,and discovering more and bigger gas fields.
文摘The Early–mid Cretaceous marks the confluence of three major continental-scale events in eastern Gondwana:(1)the emplacement of a Silicic Large Igneous Province(LIP)near the continental margin;(2)the volcaniclastic fill,transgression and regression of a major epicontinental seaway developed over at least a quarter of the Australian continent;and(3)epeirogenic uplift,exhumation and continental rupturing culminating in the opening of the Tasman Basin c.84 Ma.The Whitsunday Silicic LIP event had widespread impact,producing both substantial extrusive volumes of dominantly silicic pyroclastic material and coeval first-cycle volcanogenic sediment that accumulated within many eastern Australian sedimentary basins,and principally in the Great Australian Basin system(>2 Mkm^(3)combined volume).The final pulse of volcanism and volcanogenic sedimentation at c.105–95 Ma coincided with epicontinental seaway regression,which shows a lack of correspondence with the global sea-level curve,and alternatively records a wider,continental-scale effect of volcanism and rift tectonism.Widespread igneous underplating related to this LIP event is evident from high paleogeothermal gradients and regional hydrothermal fluid flow detectable in the shallow crust and over a broad region.Enhanced CO_(2)fluxing through sedimentary basins also records indirectly,large-scale,LIP-related mafic underplating.
基金Rustaveli National Science Foundation of Georgia for funding the project(#GNSF/ST09-1071-5-150)through which the research work was conducted in the eastern Greater Caucasus.
文摘The eastern part of the Caucasus orogen,termed the Georgian segment,is mainly underlain by highly deformed Lower-Middle Jurassic shales,sandstones,and volcaniclastic rocks,and cut by numerous intrusive bodies of various compositions.All units contain a variety of mineral deposit types and their surrounding zones of hydrothermal alteration.Detailed geological and metallogenic research,after 30 years stagnation,has led to important new information regarding the evolution of this region.Three main stages of magmatic activity are now clearly distinguished.The oldest magmatism comprises early Jurassic events,related to extensional tectonism,with volcanism and subvolcanic plutonism that ranged from rhyolitic,through dacitic and andesitic,and to basaltic.Additional extensional processes(in Bajocian times)were characterized by intrusion of a gabbro and diorite dike system into slightly older late Early Jurassicearly Middle Jurassic formations.The final magmatic event was associated with Middle Jurassic folding and uplift during which multiphase diorite plutons were emplaced.Intense hydrothermal activity related to this latest magmatism was responisble for important polymetallic mineralization including more than 100 historically recognized outcropping occurrences.A detailed study of 11of the more significant of these occurrences has indicated anomalous concentrations of base metals as well as gold,thorium,yttrium,cobalt,cadmium,and bismuth.In addition,several new and potentially significant mineral occurrences were discovered,including two designated here as Gelia and Lechuri.
文摘The Lachlan Orogen of New South Wales,Victoria and eastern Tasmania is the best understood element of the eastern Australian Tasmanides.The Tasmanides encompass continental growth in a Neoproterozoic passive margin setting and a Paleozoic–Mesozoic active margin in east Gondwana,bounded to the east by the Pacific Ocean.In the Ordovician,the supra-subduction zone element in the Lachlan Orogen is the Macquarie Arc.This comprises one minor and three major belts of mafic to intermediate volcanic and volcaniclastic rocks,limestones and intrusions that,with two hiatuses in magmatism,span the Ordovician and extend into the Early Silurian.The three major belts in central New South Wales are separated by Silurian–Devonian rift basins and are therefore,inferred to have been rifted apart during crustal extension.Chemical and isotopic data suggest the Macquarie Arc is intraoceanic,developed on primitive oceanic crust.Despite this,key features such as its longevity,stacked magmatic phases,little deformation and flanking coeval craton-derived turbidites and black shales with no provenance mixing indicate differences from modern intraoceanic arcs.Paleogeographic setting and magmatic evolution of the Macquarie Arc provided perfect conditions for mainly porphyry-related,rich Au-Cu deposits,in the Ordovician,and especially in the Early Silurian after amalgamation of the arc with its flanking terranes.
基金financially supported by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (XDB03010100)the Chinese MOST 973 Project (2012CB822001)the NSFC Project (41172092)
文摘The age range of the major intra-plate volcanic event that affected the northern Indian margin in the Early Cretaceous is here defined precisely by detrital zircon geochronology. U-Pb ages of Early Cretaceous detrital zircons found in the Cretaceous to the Paleocene sandstones cluster mainly between 142 Ma and 123 Ma in the northern Tethys Himalayan unit, and between 140 Ma and 116 Ma in the southern Tethys Himalayan unit. The youngest and oldest detrital zircons within this group indicate that volcanism in the source areas started in the latest Jurassic and ended by the early Albian. Stratigraphic data indicate that volcaniclastic sedimentation began significantly earlier in southern Tibet （Tithonian） than in Nepal （Valangin- ian）, and considerably later in Spiti and Zanskar （Aptian/AIbian） to the west. This apparent westward migration of magmatism was explained with progressive westward propagation of extensional/transtensional tectonic activity and development of fractures cutting deeply across the Indian continental margin crust. However, detrital zircon geochronology provides no indication of heterochroneity in magmatic activity in the source areas from east to west, and thus lends little support to such a scenario. Westward migration of volcaniclastic sedimentation may thus reflect instead the westward progradation of major drainage systems supplying volcanic detritus sourced from the same volcanic centers in the east. Development of multiple radial drainage away from the domal surface uplift associated with magmatic upwelling, as observed for most large igneous provinces around the world, may also explain why U-Pb ages of detrital zircons tend to cluster around 133-132 Ma （the age of the Cornel igneous province） in Tethys Himalayan units, but around 118-117 Ma （the age of the Rajmahal igneous province） in Lesser Himalayan units.
基金supported by the National Science and Technology Major Project of China (Grant No. 2017ZX05008-001)
文摘The North Tianshan Orogenic Belt contains the youngest ophiolites in the Tianshan and provides some information on timing of the last closure of the Junggar-Balkhash Ocean. LA-ICP-MS zircon U-Pb dating was conducted to define the formation age of the Arbasay Formation in the Shichang Region of North Tianshan, which is exposed near the suture zone but its age remains debated. The Arbasay Formation is mainly composed of volcanic and volcaniclastic rocks with tuft interlayers. The zircons from the tufts yield two age populations of 315 ± 3 Ma and 304 ± 2 Ma, constraining the commencement and demise timings of volcanism, respectively. Furthermore, zircon U-Pb age spectra of the tuffaceous sandstones display the youngest peak age at 308 Ma, indicating a 〈 308 Ma age for the depositional age of volcaniclastic rocks. The volcaniclastic rocks therefore were likely to deposit together with the syn-sedimentary volcanism during Late Carboniferous. This means that the Arbasay Formation in Shichang Region should be re-assigned to Late Carboniferous in age. Given that the Arbasay Formation was likely to be formed during the tectonic transition from compression to extension, the Junggar-Balkhash Ocean possibly closed during Late Carboniferous.
基金funded by MIUR (Ministero dell’Istruzione,dell’Università e della Ricerca),ex 60% fund (2019 year) to E. Le Pera。
文摘The use of mineral interfaces, in sand-sized rock fragments, to infer the influence exerted by mechanical durability on the generation of siliciclastic sediments, has been determined for plutoniclastic sand. Conversely, for volcaniclastic sand, it has received much less attention, and, to our knowledge, this is the first attempt to make use of the volcaniclastic interfacial modal mineralogy of epiclastic sandy fragments, to infer mechanical durability control at a modern beach environment. Volcaniclastic sand was collected along five beaches developed on five islands, of the southern Tyrrhenian Sea(Alicudi, Filicudi, Salina, Panarea and Stromboli) from the Aeolian Archipelago, and one sample was collected near the Stromboli Island volcanic crater. Each sample was sieved and thin sectioned for petrographic analysis. The modal mineralogy of the very coarse, coarse and medium sand fractions was determined by point-counting of the interfacial boundaries discriminating 36 types of interfaces categories, both no-isomineralic and/or no iso-structural(e.g., phenocrystal/glassy groundmass or phenocrystal/microlitic groundmass boundaries) and iso-mineralic interfaces, inside volcanic lithic grains with lathwork and porphyric textures. A total of 47,386 interfacial boundaries have been counted and, the most representative series of interfaces, from the highest to the lowest preservation, can be grouped as: a) ultrastable interfaces, categorized as Pl(Plagioclase)/Glgr(Glassy groundmass) > > Px(Pyroxene)/Glgr > > Ol(Olivine)/Glgr > > Op(Opaque)/Glgr > > Hbl(Hornblende)/Glgr> > Bt(Biotite)/Glgr > > Idd(Iddingsite)/Glgr > > Rt(Rutile)/Glgr;b) stable interfaces, categorized as Pl/Migr(Microlitic groundmass) > > Op/Migr > > Px/Migr > > Ol/Migr;c) moderately stable interfaces, categorized as Op/Px > > Op/Hbl > > Px/P > > Ol/Pl> > Bt/Op;and d) unstable interfaces, categorized as Pl/Pl > > Px/Px > > Ol/Ol > >Op/Op > > Hbl/Hbl > > Bt/Bt. Grains, eroded from the volcanic bedrock, if affected solely by abrasion, developed a rounded and smoothed form, with prevailing no-isostructural interfaces such as Plagioclase/Glassy groundmass,Pyroxene/Glassy groundmass and Olivine/Glassy groundmass interfaces. Grains that during transport suffered fracturing and percussion have a sharp and angular form: these combined transport mechanisms produce mainly volcanic sandy grains with iso-structural interfaces, such as Pl/Pl, Px/Px, Hbl/Hbl, and, to a lesser extent, Bt/Op and Bt/Glgr interfaces.
