The research on the correlation between hydrocarbon accumulations and magmatic activities has always attracted aroused much wide attention.Existing research has primarily the hydrocarbon generations capability of sour...The research on the correlation between hydrocarbon accumulations and magmatic activities has always attracted aroused much wide attention.Existing research has primarily the hydrocarbon generations capability of source rocks and the quality of reservoirs by diabase intrusions.whereas,rare systematic research has been conducted on the oiliness and enrichment mechanism.To be specific,the diabase intrusive zone,the contact metamorphic zone and the normal shale zone of the Funing Formation in the Gaoyou Sag,Subei Basin were taken as the object of this study.Moreover,in this study,the hydrocarbon generation quality,reservoir quality,and oil-bearing quality of diabase-metamorphic zone-normal shale were evaluated using X-ray diffractions,argon ion polishing-field emission scanning electron microscope,energy spectrum,rock slice/light-sheet microscopic observations,organic geochemical tests,N_(2) gas adsorption and 2D NMR tests.The results indicated that the intrusive zone,the metamorphic zone,and the normal zone were formed in order by the degree of effect of diabase intrusions.Secondly,the oil content of different parts exhibited significant heterogeneity due to the baking effect of diabase,and the metamorphic zone had the significantly better oil-bearing nature than the intrusive zone.Lastly,a distribution model was proposed for the diabase intrusive zone-metamorphic zone-normal surrounding rock zone.展开更多
Widely distributed in Gyangzê-Chigu area, southern Tibet, NW- and nearly E-W-trending diabase（gabbro）-gabbro diorite dykes are regarded as the product of the large-scale spreading of the late Neo-Tethys Ocean. ...Widely distributed in Gyangzê-Chigu area, southern Tibet, NW- and nearly E-W-trending diabase（gabbro）-gabbro diorite dykes are regarded as the product of the large-scale spreading of the late Neo-Tethys Ocean. In order to constrain the emplacement age of these dykes, zircons of two samples from diabases in Nagarzê were dated by using the U-Pb SHRIMP method. Two nearly the same weighted mean ^206pb/^23SU ages were obtained in this paper, which are 134.9±1.8 Ma （MSWD=0.65） and 135.5 ± 2.1 Ma （MSWD=1.40）, respectively. They not only represent the crystallization age of the diabase, but also documented an important spreading event of the Neo-Tethys Ocean during the late Jurassic and early Cretaceous. This dating result is of great significance to reconstruct the temporal framework of the late Neo-Tethys Ocean in the Qinghai-Tibet Plateau.展开更多
The Luxi-Xianrenzhang diabase dikes were emplaced into the eastern part of the Guidong composite granitoids in northern Guangdong Province at the end of the Early Cretaceous. They show tholeiitic features, enrichment ...The Luxi-Xianrenzhang diabase dikes were emplaced into the eastern part of the Guidong composite granitoids in northern Guangdong Province at the end of the Early Cretaceous. They show tholeiitic features, enrichment in large ion lithophile elements, slight enrichment in light rare earth elements, depletion in Zr and Hf, and basically no depletion in Nb and Ta and no Eu anomaly. They are similar to intraplate basalt in terms of trace element characteristics. They have high εNd（t） values （3.6-4.9）, initial ^87Sr/^86Sr ratios （0.70530-70641） and δ^18O values and Dupal anomaly of Pb isotope compositions. Their Sr-Nd, Pb-Sr, Pb-Nd and Pb-Pb isotopes plot between DMM and EMII, with Pb similar to EMII, Nd relatively close to DMM and Sr in between. This profile suggests that the diabase dikes studied were derived from partial melting of a mantle source that had been subjected to metasomatism by fluids originated from a subduction zone under a tectonic environment of crustal extension and lithosphere thinning in the late Yanshanian.展开更多
Diabase dyke swarms are widespread in the East Tianshan and Beishan regions. LA-ICP-MS zircon U-Pb ages of these diabase vary from 305 Ma to 278 Ma, showing that these dykes were formed during Late Carboniferous-Early...Diabase dyke swarms are widespread in the East Tianshan and Beishan regions. LA-ICP-MS zircon U-Pb ages of these diabase vary from 305 Ma to 278 Ma, showing that these dykes were formed during Late Carboniferous-Early Permian magmatism. All diabase samples are subalkali calc-alkali, characterized by slight LREE and LILEs enrichment, and weak negative Ti, Nb and Ta anomalies. The diabase samples have positive ＊＇Nd（t）values （〉＋3）, high Sr isotopic compositions （initial 87Sr/S6Sr values=0.7030-0.7097）, and large variation of Pb isotopic compositions, indicating they were derived from a deplete mantle source. Regional geology and geochemistry evidences indicate that these diabase dyke swarms were generated in a lithosphere extensional setting and had the same magma sources. Initial magmas may be a mixture of depleted asthenosphere mantle and enriched lithospheric mantle during rapid magma ascending.展开更多
The southeastern Alxa Block(i.e.,the Hexi Corridor)is a tectonic junction between the North China Block(NCB)to the east,the Alxa Block to the north,and the western Qinling–North Qilian Orogenic Belt to the southwest(...The southeastern Alxa Block(i.e.,the Hexi Corridor)is a tectonic junction between the North China Block(NCB)to the east,the Alxa Block to the north,and the western Qinling–North Qilian Orogenic Belt to the southwest(Fig.1).The southeastern Alxa Block had undergone展开更多
Objective The Shiquanhe ophiolite is an important tectonic belt in western Tibet. It has been debated whether the Shiquanhe ophiolite represents an allochthonous nappe derived from the Bangong-Nujiang suture zone to t...Objective The Shiquanhe ophiolite is an important tectonic belt in western Tibet. It has been debated whether the Shiquanhe ophiolite represents an allochthonous nappe derived from the Bangong-Nujiang suture zone to the north or the展开更多
In order to understand the dynamic background,the mantle source region characteristic and magma evolution of the diabase in Henan Songshan region and the mineral composition in the area,we have done a systematic study...In order to understand the dynamic background,the mantle source region characteristic and magma evolution of the diabase in Henan Songshan region and the mineral composition in the area,we have done a systematic study about the mineralogical characteristics and geochemical characteristics of the diabase.Mineralogy research of the diabase in the studied area shows that the diabase have complex mineral compositions,the main rock forming minerals are plagioclase and augite,other minerals in the展开更多
The number of good quality paleomagnetic data of the Mesoproterozoic supercontinent Nuna(e.g.Columbia,Hudsonland)has increased in recent years enabling more reliable global continental reconstructions(e.g Hoffman
Northern part of Eastern Dharwar Craton (EDC) in Karnataka is essentially a granitoid country, frequently intruded by diabase dykes of varied dimensions. Compositionally, majority of them are constituted by pyroxene a...Northern part of Eastern Dharwar Craton (EDC) in Karnataka is essentially a granitoid country, frequently intruded by diabase dykes of varied dimensions. Compositionally, majority of them are constituted by pyroxene and plagioclase and less frequently they are olivine-bearing types. One of the major dykes near Thinthini is intensely altered and contains sulfide mineralization brought out by episodic hydrothermal process. Geochemically they are slightly on the higher side of silica content, except the olivine bearing dykes. Their sulfur endowment is also higher. Various discrimination diagrams suggest that they are broadly tholeiitic in composition formed from the less differentiated magma derived from mantle at relatively greater depth and intruded into the granitic rocks which in turn were formed in a subduction setting. The structural deformation prior to and post dating dyke intrusion as deciphered from detailed field studies, alteration of country rocks and hydrothermal activity in the area provide a good background to explore sulfide and other associated metals and also to understand the likely extension of the known mineralized zones.展开更多
Two suites of mafic dykes,T1193-A and T1194-A,outcrop in Gyangze area,southeast Tibet.They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze,T0902 dyke with 137....Two suites of mafic dykes,T1193-A and T1194-A,outcrop in Gyangze area,southeast Tibet.They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze,T0902 dyke with 137.7±1.3 Ma zircon age and T0907 dyke with 142±1.4 Ma zircon age reported by Wang YY et al.(2016),indicating coeval formation time.Taking all the four diabase dykes into consideration,two different types,OIB-type and weak enriched-type,can be summarized.The“OIB-type”samples,including T1193-A and T0907 dykes,show OIB-like geochemical features and have initial Sr-Nd isotopic values similar with most mafic products in Comei Large Igneous Provinces(LIP),suggesting that they represent melts directly generated from the Kerguelen mantle plume.The“weak enriched-type”samples,including T1194-A and T0902 dykes,have REEs and trace element patterns showing withinplate affinity but have obvious Nb-Ta-Ti negative anomalies.They show uniform lowerεNd(t)values(−6‒−2)and higher 87Sr/86Sr(t)values(0.706‒0.709)independent of their MgO variation,indicating one enriched mantle source.Considering their closely spatial and temporal relationship with the widespread Comei LIP magmatic products in Tethyan Himalaya,these“weak enriched-type”samples are consistent with mixing of melts from mantle plume and the above ancient Tethyan Himalaya subcontinental lithospheric mantle(SCLM)in different proportions.These weak enriched mafic rocks in Comei LIP form one special rock group and most likely suggest large scale hot mantle plume-continental lithosphere interaction.This process may lead to strong modification of the Tethyan Himalaya lithosphere in the Early Cretaceous.展开更多
This paper presents a synthetic U-Pb and Hf isotopic study of zircons and a whole-rock geochemical study on diabase swarms that were emplaced into the Proterozoic formations in the Xuzhou-Huaibei area,the southeast ma...This paper presents a synthetic U-Pb and Hf isotopic study of zircons and a whole-rock geochemical study on diabase swarms that were emplaced into the Proterozoic formations in the Xuzhou-Huaibei area,the southeast margin of North China Craton.Zircons from the diabase dykes display weak oscillatory zoning in the cathodoluminescence(CL) images and show high Th/U ratios(0.91-6.90),both of which are typical of a magmatic origin.The SHRIMP and Q-ICP-MS U-Pb zircon dating results indicate that the diabase swarms were emplaced at ca.890 Ma.Hf isotopic analysis on these zircons gives Hf(t) values ranging from 2.26 to 14.74 and Hf model age t DM1 and t DM2 ranging from 843 to 1321 Ma and from 808 to 1779 Ma,respectively.Geochemically,the diabase swarms are characterized by a relative enrichment in LREE and LILE(Rb,Ba and La),a comparative enrichment in Cr and Ni,but a slight depletement in HFSE(Th,Nb,Ta,Zr and Hf).They are plotted in the within-plate tholeiite series on the tectonic discrimination diagrams.Taken together,these geochemical and isotopic data suggest that the primary magmas to form the diabase dykes in the Xuzhou-Huaibei area could have been derived from a transitional mantle in the Mesoproterozoic,and were most probably emplaced under a continental margin extensional setting at ca.890 Ma.The results of this study demonstrate that the Neoproterozoic(800-900 Ma)magmatism was not restricted to the Yangtze Block,but also occurred at the southeast margin of the North China Craton.展开更多
Compositionally and texturally zoned diabase dykes and sills occur in the outer zone of the Emeishan large igneous province(ELIP) in the southern Guizhou Province,Southwest China. Based on the detailed petrology,whole...Compositionally and texturally zoned diabase dykes and sills occur in the outer zone of the Emeishan large igneous province(ELIP) in the southern Guizhou Province,Southwest China. Based on the detailed petrology,whole rock geochemistry,zircon U-Pb geochronology and Hf isotopes and clinopyroxene mineral compositions studies,we investigate a representative diabase sill in the Luodian region with a view to understanding its petrogenesis and tectonic implications. Formed as composite zoned sub-volcanic intrusion,the diabase sill is characterized by gabbros and diabases in the inner zone and amygdaloidal diabases sporadically in the chilled zone within the upper sill margin. The diabasic and gabbroic rocks are composed of quartz-free and quartz-bearing groups. The quartz-free group rocks have low Si O2(45.7 wt.%–49.5 wt.%),moderate Mg O(5.66 wt.%–7.88 wt.%),high Ti O2(2.54 wt.%–3.65 wt.%),and Ti/Y values(536–747),corresponding to high-Ti type rocks. The quartz-bearing group rocks have higher Si O2(49.8 wt.%–51.7 wt.%) and lower Mg O(4.23 wt.%–4.74 wt.%),higher Ti O2(3.16 wt.%–3.63 wt.%),but lower Ti/Y values(399–419) than the quartz-free group ones,and thus belong to the low-Ti type. Both groups of rocks are enriched in LREE and LILE with negative Nb-Ta anomalies,and show broad tholeiitic affinity. The precursor magma of the high-Ti rocks might have originated from a source composed of mantle plume and subcontinental lithosphere mantle components,with minor crustal contamination during ascending. The magma of the low-Ti rocks was produced by mingling of the high-Ti diabasic rocks with minor injected intermediate-acidic magma plugs or blebs,suggesting magma mingling as one of the effective ways to change the high-Ti to low-Ti rocks of the ELIP. The diabasic sill underwent a rapid cooling event probably in response to a rapid tectonic uplift event,which probably occurred in the waning stage of ELIP during transition between the Middle and Late Permian after the domal uplift induced by the mantle-plume or in the Late Jurassic.展开更多
The tectonic evolution of SE China block since late Paleozoic remains debated. Here we present a new set of zircon U-Pb geochronological, Lu-Hf isotopic data and whole-rock geochemistry for two stages of basicintermed...The tectonic evolution of SE China block since late Paleozoic remains debated. Here we present a new set of zircon U-Pb geochronological, Lu-Hf isotopic data and whole-rock geochemistry for two stages of basicintermediate dykes from the southwestern Fujian. The samples were collected from the NE-trending （mainly diabases） and NW-trending （mainly diabasic diorites） dykes and yielded zircon U-Pb ages of 315 and 141 Ma, with eHf（t） values of -8.90 to 7.49 and -23.39 to -7.15 （corresponding to TDM2 values of 850 to 1890 Ma and 737 to 2670 Ma）, respectively. Geochemically these rocks are characterized by low TiO2 （0.91-1.73 wt.%） and MgO （3.04-7.96 wt.%）, and high A1203 （12.5-16.60 wt.%） and K20 （0.60-3.63 wt.%）. Further they are enriched in LREEs and LILEs （Rb, Ba, Th and K）, but depleted in HFSEs （Nb, Ta and Zr）. The tectonic discrimination analysis revealed that the dykes were formed in an intraplate extensional envi- ronment. However, the NW trending dykes show crust-mantle mixed composition, which indicate an extensional tectonic setting with evidence for crustal contamination. The SE China block experienced two main stages of extensional tectonics from late Carboniferous to early Cretaceous. The tectonic evolution of the SE China block from late Devonian to Cretaceous is also evaluated.展开更多
Discontinuous ophiolite suites along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet representing remnants of the Neo-Tethyan oceanic lithosphere are considered to be formed between Late Jurassic and Early Creta...Discontinuous ophiolite suites along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet representing remnants of the Neo-Tethyan oceanic lithosphere are considered to be formed between Late Jurassic and Early Cretaceous.Older ophiolite or ophiolitic mélange(e.g.Triassic)to reveal the initial evolution the Neo-Tethyan ocean within the YZSZ have rarely been documented so far.The western YZSZ extending from the Saga to Ladakh area are composed of the northern ophiolitic subbelt,the Zhongba terrane and the southern ophiolitic sub-belt.In this study,we document structural,petrological and geochronological data of mafic intrusions from the Mayoumu massif in the southern ophiolitic sub-belt of the western YZSZ.Two lithos-tectonic sub-units,the southern ophiolitic complex and the northern ophiolitic mélange,are recognized in the Mayoumu massif in terms of structural pattern and petrology.LA-ICP-MS zircon U-Pb dating of gabbro from the ophiolitic mélange yields an age of 243±1 Ma with zirconεHf(t)values of+7.9 to+13.2.Two samples of diabase samples from the ophiolite yield ages of 131±1 Ma and 124±1 Ma with zirconεHf(t)values ranging from+10.8 to+15.0 and+12.3 to+15.4,respectively.Geochemically,rare earth elements(REEs)patterns show that these mafic intrusions are similar to those of the normal mid-ocean-ridge basalt(N-MORB).Enrichment of fluidmobile elements(e.g.Rb and Ba)and depletion of Nb,and Ta suggest that these intrusions were possibly originated from melting of a depleted mantle source influenced by subducted slab.Our data strongly confirms that the Neo-Tethyan ocean between the Lhasa terrane and Gondwana had been existed since the Middle Triassic at least.The ages of the two diabases from the ophiolitic complex reveal that mafic magma activities within the Neo-Tethyan ocean could be as a continuing process during 120–130 Ma.Emplacement and preservation of older ophiolitic recorder during evolution of the Neo-Tethyan Ocean may be closely related to the occurrence of the Zhongba micro-terrane within the western YZSZ.展开更多
In order to reveal the strength deterioration law of rock mass under an acidified environment, a series of experiments on strength deterioration and the environmental effect on marble and diabase under the conditions ...In order to reveal the strength deterioration law of rock mass under an acidified environment, a series of experiments on strength deterioration and the environmental effect on marble and diabase under the conditions of three kinds of acids （H2SO4, HNO3 and HC1） with three contents （1.0%, 5.0% and 10.0%） in a static fluid surrounding were carried out by single factor simulation. After the stones had been saturated in the above solutions for 90 days, an indoor weathering simulation had been observed for 300 days and its strength characteristics were measured under static/dynamic load and that results were compared with those under the natural condition. It is evident that the strength is emaciated greatly after the stones eroded by the liquids, whether under the static or dynamic load.展开更多
The end-Permian to Early–Middle Triassic magmatic rocks in Inner Mongolia can provide valuable insights into the relationships between the collisional processes and the magmatic responses during the final orogenic ev...The end-Permian to Early–Middle Triassic magmatic rocks in Inner Mongolia can provide valuable insights into the relationships between the collisional processes and the magmatic responses during the final orogenic evolution of Xing-Meng orogenic belt(XMOB). This paper presents zircon U-Pb ages and Hf isotopes, whole rock geochemical and Sr-Nd-Pb isotopic data for the Early–Middle Triassic diabases and monzogranites from the Langshan area, southwestern XMOB. Our results suggest that the studied diabases and monzogranites were respectively formed during Early Triassic and Middle Triassic. The Early Triassic diabases are characterized by "arc-like" geochemical signatures, including enrichment in Rb, U and K, and depletion in Nb, Ta, P and Ti. They have negative to weak positive εNd(t) values(-3.1 to +1.5) and relatively high initial ratios of 208 Pb/204 Pb(35.968–37.346), 207 Pb/204 Pb(15.448–15.508) and 206 Pb/204 Pb(16.280–17.492), indicating a subduction-metasomatized enriched lithospheric mantle source. Their low Ba/Rb(2.72–6.56), Ce/Y(0.97–1.39) and(Tb/Yb)N ratios(1.31–1.45) suggest that the parental magma was likely originated from low degree partial melting of the phlogopite-bearing lherzolite in a spinel-stability field. The Middle Triassic monzogranites show high Sr/Y ratios, low Mg O, Cr and Ni contents, high Zr/Sm ratios(40–64), negative zircon εHf(t) values(-25.8 to-8.8), as well as relatively flat heavy rare earth element patterns. They were likely derived from low degree partial melting of a moderately thickened ancient lower crust. The diabases and the slightly postdated high Sr/Y granites in this study represent the magmatic responses to the final orogenic evolution in the southwestern XMOB. Together with regional works, we propose that the slab break-off of the Paleo-Asian oceanic lithosphere following the terminal collision between the North China Craton and the South Mongolia terranes triggered asthenospheric upwelling, and the ongoing convergence further initiated moderately crustal thickening and uplift in the XMOB.展开更多
Mafic dyke swarm is widely developed in Proterozoic continental lithosphere.The Gangou diabase dyke from the Xixia area,intruded into the Douling complex of the South Qinling belt,yields zircon UPb age of 731 Ma.It ha...Mafic dyke swarm is widely developed in Proterozoic continental lithosphere.The Gangou diabase dyke from the Xixia area,intruded into the Douling complex of the South Qinling belt,yields zircon UPb age of 731 Ma.It has low SiO2 content(49.02 wt.%-49.37 wt.%)and Mg^#(34.0–37.7)and shows characteristics of subalkaline tholeiite series.They show highΣREE(155.5×10^-6–184.7×10^-6),weak negative Eu anomaly(δEu=0.88-0.93),slight depletion of Nb and Ta,and enrichment of LILE.Their major and trace element,Sr-Nd-Pb isotope and clinopyroxene compositions indicate that it originated from the partial melting of the asthenospheric mantle within-plate extension setting and was slightly contaminated by crust compositions.The similarities of formation age,petrogenesis,source characteristic and tectonic setting for Gangou diabase with mafic dykes in Wudang Block and mafic volcanic rocks in Yaolinghe Group indicate that the South Qinling belt underwent strong continental extension in Neoproterozoic during 796–685 Ma most likely correspondence to the breaking-up of the Rodinia supercontinent.展开更多
The Noorabad-Harsin ophiolite is a part of the eastern Mediterranean-Zagros-Oman Tethyan ophiolites. This area is located in the south-southwest of the main Zagros thrust zone. This ophiolite consists of peridotites, ...The Noorabad-Harsin ophiolite is a part of the eastern Mediterranean-Zagros-Oman Tethyan ophiolites. This area is located in the south-southwest of the main Zagros thrust zone. This ophiolite consists of peridotites, serpentinites and pegmatite gabbros as mantle sequence whereas crustal sequence is composed of locally layered gabbros, isotropic gabbros, sheeted dike complex, basaltic to andesitic lavas and sedimentary rocks （radiolarites and Late Cretaceous pelagic limes- tones）. The diabase dikes are enriched in LREE relative to HREE （La（n）/Yb（n）=1.7-3.3）. Also, the andesites are enriched in LREE relative to HREE （La（n）/Yb（n）=3.1-5.37） and the pillow lavas are enriched in LILE （Th（n）/La（n）=2.1） while show a depletion in HFSE （Nb（n）/La（n）=0.07-0.2）. The basaltic-andesitic lavas exhibiting mainly calc-alkaline, with minor island-arc tholeiitic affinities, are characterized by enrichment in LILE and LREE and depletion in HFSE. These geochemical characteristics compared with other Tethyan ophiolites along the Bitlis-Zagros suture zone reveal a supra- subduction zone environment for the genesis of the Noorabad-Harsin ophiolites.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.42072150).
文摘The research on the correlation between hydrocarbon accumulations and magmatic activities has always attracted aroused much wide attention.Existing research has primarily the hydrocarbon generations capability of source rocks and the quality of reservoirs by diabase intrusions.whereas,rare systematic research has been conducted on the oiliness and enrichment mechanism.To be specific,the diabase intrusive zone,the contact metamorphic zone and the normal shale zone of the Funing Formation in the Gaoyou Sag,Subei Basin were taken as the object of this study.Moreover,in this study,the hydrocarbon generation quality,reservoir quality,and oil-bearing quality of diabase-metamorphic zone-normal shale were evaluated using X-ray diffractions,argon ion polishing-field emission scanning electron microscope,energy spectrum,rock slice/light-sheet microscopic observations,organic geochemical tests,N_(2) gas adsorption and 2D NMR tests.The results indicated that the intrusive zone,the metamorphic zone,and the normal zone were formed in order by the degree of effect of diabase intrusions.Secondly,the oil content of different parts exhibited significant heterogeneity due to the baking effect of diabase,and the metamorphic zone had the significantly better oil-bearing nature than the intrusive zone.Lastly,a distribution model was proposed for the diabase intrusive zone-metamorphic zone-normal surrounding rock zone.
文摘Widely distributed in Gyangzê-Chigu area, southern Tibet, NW- and nearly E-W-trending diabase（gabbro）-gabbro diorite dykes are regarded as the product of the large-scale spreading of the late Neo-Tethys Ocean. In order to constrain the emplacement age of these dykes, zircons of two samples from diabases in Nagarzê were dated by using the U-Pb SHRIMP method. Two nearly the same weighted mean ^206pb/^23SU ages were obtained in this paper, which are 134.9±1.8 Ma （MSWD=0.65） and 135.5 ± 2.1 Ma （MSWD=1.40）, respectively. They not only represent the crystallization age of the diabase, but also documented an important spreading event of the Neo-Tethys Ocean during the late Jurassic and early Cretaceous. This dating result is of great significance to reconstruct the temporal framework of the late Neo-Tethys Ocean in the Qinghai-Tibet Plateau.
基金This study was supported by National Natural Science Foundation of China(grants 4022 1301 and 40132010).
文摘The Luxi-Xianrenzhang diabase dikes were emplaced into the eastern part of the Guidong composite granitoids in northern Guangdong Province at the end of the Early Cretaceous. They show tholeiitic features, enrichment in large ion lithophile elements, slight enrichment in light rare earth elements, depletion in Zr and Hf, and basically no depletion in Nb and Ta and no Eu anomaly. They are similar to intraplate basalt in terms of trace element characteristics. They have high εNd（t） values （3.6-4.9）, initial ^87Sr/^86Sr ratios （0.70530-70641） and δ^18O values and Dupal anomaly of Pb isotope compositions. Their Sr-Nd, Pb-Sr, Pb-Nd and Pb-Pb isotopes plot between DMM and EMII, with Pb similar to EMII, Nd relatively close to DMM and Sr in between. This profile suggests that the diabase dikes studied were derived from partial melting of a mantle source that had been subjected to metasomatism by fluids originated from a subduction zone under a tectonic environment of crustal extension and lithosphere thinning in the late Yanshanian.
基金supported by the National Natural Science Foundation of China (No. 40973028)the Central Public-interest Scientific Institution Basal Research Fund (K1107)
文摘Diabase dyke swarms are widespread in the East Tianshan and Beishan regions. LA-ICP-MS zircon U-Pb ages of these diabase vary from 305 Ma to 278 Ma, showing that these dykes were formed during Late Carboniferous-Early Permian magmatism. All diabase samples are subalkali calc-alkali, characterized by slight LREE and LILEs enrichment, and weak negative Ti, Nb and Ta anomalies. The diabase samples have positive ＊＇Nd（t）values （〉＋3）, high Sr isotopic compositions （initial 87Sr/S6Sr values=0.7030-0.7097）, and large variation of Pb isotopic compositions, indicating they were derived from a deplete mantle source. Regional geology and geochemistry evidences indicate that these diabase dyke swarms were generated in a lithosphere extensional setting and had the same magma sources. Initial magmas may be a mixture of depleted asthenosphere mantle and enriched lithospheric mantle during rapid magma ascending.
文摘The southeastern Alxa Block(i.e.,the Hexi Corridor)is a tectonic junction between the North China Block(NCB)to the east,the Alxa Block to the north,and the western Qinling–North Qilian Orogenic Belt to the southwest(Fig.1).The southeastern Alxa Block had undergone
基金financially supported by the National Natural Science Foundation (grants No. 41102065 and 41872110)the Sichuan Science and Technology Program (grant No. 2018JY0465)
文摘Objective The Shiquanhe ophiolite is an important tectonic belt in western Tibet. It has been debated whether the Shiquanhe ophiolite represents an allochthonous nappe derived from the Bangong-Nujiang suture zone to the north or the
文摘In order to understand the dynamic background,the mantle source region characteristic and magma evolution of the diabase in Henan Songshan region and the mineral composition in the area,we have done a systematic study about the mineralogical characteristics and geochemical characteristics of the diabase.Mineralogy research of the diabase in the studied area shows that the diabase have complex mineral compositions,the main rock forming minerals are plagioclase and augite,other minerals in the
文摘The number of good quality paleomagnetic data of the Mesoproterozoic supercontinent Nuna(e.g.Columbia,Hudsonland)has increased in recent years enabling more reliable global continental reconstructions(e.g Hoffman
文摘Northern part of Eastern Dharwar Craton (EDC) in Karnataka is essentially a granitoid country, frequently intruded by diabase dykes of varied dimensions. Compositionally, majority of them are constituted by pyroxene and plagioclase and less frequently they are olivine-bearing types. One of the major dykes near Thinthini is intensely altered and contains sulfide mineralization brought out by episodic hydrothermal process. Geochemically they are slightly on the higher side of silica content, except the olivine bearing dykes. Their sulfur endowment is also higher. Various discrimination diagrams suggest that they are broadly tholeiitic in composition formed from the less differentiated magma derived from mantle at relatively greater depth and intruded into the granitic rocks which in turn were formed in a subduction setting. The structural deformation prior to and post dating dyke intrusion as deciphered from detailed field studies, alteration of country rocks and hydrothermal activity in the area provide a good background to explore sulfide and other associated metals and also to understand the likely extension of the known mineralized zones.
基金supported by National Science Foundation of China(42102059 and 92055202)the China Geological Survey(DD20221817 and DD20190057)+1 种基金the basic scientific research funding in CAGS(J2204)the Second Tibetan Plateau Scientific Expedition and Research(2019QZKK0702).
文摘Two suites of mafic dykes,T1193-A and T1194-A,outcrop in Gyangze area,southeast Tibet.They are in the area of Comei LIP and have indistinguishable field occurrences with two other dykes in Gyangze,T0902 dyke with 137.7±1.3 Ma zircon age and T0907 dyke with 142±1.4 Ma zircon age reported by Wang YY et al.(2016),indicating coeval formation time.Taking all the four diabase dykes into consideration,two different types,OIB-type and weak enriched-type,can be summarized.The“OIB-type”samples,including T1193-A and T0907 dykes,show OIB-like geochemical features and have initial Sr-Nd isotopic values similar with most mafic products in Comei Large Igneous Provinces(LIP),suggesting that they represent melts directly generated from the Kerguelen mantle plume.The“weak enriched-type”samples,including T1194-A and T0902 dykes,have REEs and trace element patterns showing withinplate affinity but have obvious Nb-Ta-Ti negative anomalies.They show uniform lowerεNd(t)values(−6‒−2)and higher 87Sr/86Sr(t)values(0.706‒0.709)independent of their MgO variation,indicating one enriched mantle source.Considering their closely spatial and temporal relationship with the widespread Comei LIP magmatic products in Tethyan Himalaya,these“weak enriched-type”samples are consistent with mixing of melts from mantle plume and the above ancient Tethyan Himalaya subcontinental lithospheric mantle(SCLM)in different proportions.These weak enriched mafic rocks in Comei LIP form one special rock group and most likely suggest large scale hot mantle plume-continental lithosphere interaction.This process may lead to strong modification of the Tethyan Himalaya lithosphere in the Early Cretaceous.
基金supported by National Natural Science Foundation of China (Grant Nos. 40772037,90814003)
文摘This paper presents a synthetic U-Pb and Hf isotopic study of zircons and a whole-rock geochemical study on diabase swarms that were emplaced into the Proterozoic formations in the Xuzhou-Huaibei area,the southeast margin of North China Craton.Zircons from the diabase dykes display weak oscillatory zoning in the cathodoluminescence(CL) images and show high Th/U ratios(0.91-6.90),both of which are typical of a magmatic origin.The SHRIMP and Q-ICP-MS U-Pb zircon dating results indicate that the diabase swarms were emplaced at ca.890 Ma.Hf isotopic analysis on these zircons gives Hf(t) values ranging from 2.26 to 14.74 and Hf model age t DM1 and t DM2 ranging from 843 to 1321 Ma and from 808 to 1779 Ma,respectively.Geochemically,the diabase swarms are characterized by a relative enrichment in LREE and LILE(Rb,Ba and La),a comparative enrichment in Cr and Ni,but a slight depletement in HFSE(Th,Nb,Ta,Zr and Hf).They are plotted in the within-plate tholeiite series on the tectonic discrimination diagrams.Taken together,these geochemical and isotopic data suggest that the primary magmas to form the diabase dykes in the Xuzhou-Huaibei area could have been derived from a transitional mantle in the Mesoproterozoic,and were most probably emplaced under a continental margin extensional setting at ca.890 Ma.The results of this study demonstrate that the Neoproterozoic(800-900 Ma)magmatism was not restricted to the Yangtze Block,but also occurred at the southeast margin of the North China Craton.
基金supported by the Guizhou Scientific and Technology Planning Project (Nos. QKHZDZX [2014]6003, QKHPTRC[2018]5626 and QKH[2016]PTRC5401)
文摘Compositionally and texturally zoned diabase dykes and sills occur in the outer zone of the Emeishan large igneous province(ELIP) in the southern Guizhou Province,Southwest China. Based on the detailed petrology,whole rock geochemistry,zircon U-Pb geochronology and Hf isotopes and clinopyroxene mineral compositions studies,we investigate a representative diabase sill in the Luodian region with a view to understanding its petrogenesis and tectonic implications. Formed as composite zoned sub-volcanic intrusion,the diabase sill is characterized by gabbros and diabases in the inner zone and amygdaloidal diabases sporadically in the chilled zone within the upper sill margin. The diabasic and gabbroic rocks are composed of quartz-free and quartz-bearing groups. The quartz-free group rocks have low Si O2(45.7 wt.%–49.5 wt.%),moderate Mg O(5.66 wt.%–7.88 wt.%),high Ti O2(2.54 wt.%–3.65 wt.%),and Ti/Y values(536–747),corresponding to high-Ti type rocks. The quartz-bearing group rocks have higher Si O2(49.8 wt.%–51.7 wt.%) and lower Mg O(4.23 wt.%–4.74 wt.%),higher Ti O2(3.16 wt.%–3.63 wt.%),but lower Ti/Y values(399–419) than the quartz-free group ones,and thus belong to the low-Ti type. Both groups of rocks are enriched in LREE and LILE with negative Nb-Ta anomalies,and show broad tholeiitic affinity. The precursor magma of the high-Ti rocks might have originated from a source composed of mantle plume and subcontinental lithosphere mantle components,with minor crustal contamination during ascending. The magma of the low-Ti rocks was produced by mingling of the high-Ti diabasic rocks with minor injected intermediate-acidic magma plugs or blebs,suggesting magma mingling as one of the effective ways to change the high-Ti to low-Ti rocks of the ELIP. The diabasic sill underwent a rapid cooling event probably in response to a rapid tectonic uplift event,which probably occurred in the waning stage of ELIP during transition between the Middle and Late Permian after the domal uplift induced by the mantle-plume or in the Late Jurassic.
基金supported by projects from the China Geological Survey(Grant Nos.12120113089600,12120114028701 and 1212011085472)
文摘The tectonic evolution of SE China block since late Paleozoic remains debated. Here we present a new set of zircon U-Pb geochronological, Lu-Hf isotopic data and whole-rock geochemistry for two stages of basicintermediate dykes from the southwestern Fujian. The samples were collected from the NE-trending （mainly diabases） and NW-trending （mainly diabasic diorites） dykes and yielded zircon U-Pb ages of 315 and 141 Ma, with eHf（t） values of -8.90 to 7.49 and -23.39 to -7.15 （corresponding to TDM2 values of 850 to 1890 Ma and 737 to 2670 Ma）, respectively. Geochemically these rocks are characterized by low TiO2 （0.91-1.73 wt.%） and MgO （3.04-7.96 wt.%）, and high A1203 （12.5-16.60 wt.%） and K20 （0.60-3.63 wt.%）. Further they are enriched in LREEs and LILEs （Rb, Ba, Th and K）, but depleted in HFSEs （Nb, Ta and Zr）. The tectonic discrimination analysis revealed that the dykes were formed in an intraplate extensional envi- ronment. However, the NW trending dykes show crust-mantle mixed composition, which indicate an extensional tectonic setting with evidence for crustal contamination. The SE China block experienced two main stages of extensional tectonics from late Carboniferous to early Cretaceous. The tectonic evolution of the SE China block from late Devonian to Cretaceous is also evaluated.
基金granted by the National Key Basic Research Program from the Chinese Ministry of Science and Technology(Grant No.2015CB856101)Foundation of Research Center for Tibetan Plateau Geology(21201010000150014-29)the China Geological Survey(No.1212011221066)
文摘Discontinuous ophiolite suites along the Yarlung Zangbo suture zone(YZSZ)in southern Tibet representing remnants of the Neo-Tethyan oceanic lithosphere are considered to be formed between Late Jurassic and Early Cretaceous.Older ophiolite or ophiolitic mélange(e.g.Triassic)to reveal the initial evolution the Neo-Tethyan ocean within the YZSZ have rarely been documented so far.The western YZSZ extending from the Saga to Ladakh area are composed of the northern ophiolitic subbelt,the Zhongba terrane and the southern ophiolitic sub-belt.In this study,we document structural,petrological and geochronological data of mafic intrusions from the Mayoumu massif in the southern ophiolitic sub-belt of the western YZSZ.Two lithos-tectonic sub-units,the southern ophiolitic complex and the northern ophiolitic mélange,are recognized in the Mayoumu massif in terms of structural pattern and petrology.LA-ICP-MS zircon U-Pb dating of gabbro from the ophiolitic mélange yields an age of 243±1 Ma with zirconεHf(t)values of+7.9 to+13.2.Two samples of diabase samples from the ophiolite yield ages of 131±1 Ma and 124±1 Ma with zirconεHf(t)values ranging from+10.8 to+15.0 and+12.3 to+15.4,respectively.Geochemically,rare earth elements(REEs)patterns show that these mafic intrusions are similar to those of the normal mid-ocean-ridge basalt(N-MORB).Enrichment of fluidmobile elements(e.g.Rb and Ba)and depletion of Nb,and Ta suggest that these intrusions were possibly originated from melting of a depleted mantle source influenced by subducted slab.Our data strongly confirms that the Neo-Tethyan ocean between the Lhasa terrane and Gondwana had been existed since the Middle Triassic at least.The ages of the two diabases from the ophiolitic complex reveal that mafic magma activities within the Neo-Tethyan ocean could be as a continuing process during 120–130 Ma.Emplacement and preservation of older ophiolitic recorder during evolution of the Neo-Tethyan Ocean may be closely related to the occurrence of the Zhongba micro-terrane within the western YZSZ.
文摘In order to reveal the strength deterioration law of rock mass under an acidified environment, a series of experiments on strength deterioration and the environmental effect on marble and diabase under the conditions of three kinds of acids （H2SO4, HNO3 and HC1） with three contents （1.0%, 5.0% and 10.0%） in a static fluid surrounding were carried out by single factor simulation. After the stones had been saturated in the above solutions for 90 days, an indoor weathering simulation had been observed for 300 days and its strength characteristics were measured under static/dynamic load and that results were compared with those under the natural condition. It is evident that the strength is emaciated greatly after the stones eroded by the liquids, whether under the static or dynamic load.
基金supported by the Geological Survey of China (No. 1212011085490)the National Natural Science Foundation of China (No. 41421002)
文摘The end-Permian to Early–Middle Triassic magmatic rocks in Inner Mongolia can provide valuable insights into the relationships between the collisional processes and the magmatic responses during the final orogenic evolution of Xing-Meng orogenic belt(XMOB). This paper presents zircon U-Pb ages and Hf isotopes, whole rock geochemical and Sr-Nd-Pb isotopic data for the Early–Middle Triassic diabases and monzogranites from the Langshan area, southwestern XMOB. Our results suggest that the studied diabases and monzogranites were respectively formed during Early Triassic and Middle Triassic. The Early Triassic diabases are characterized by "arc-like" geochemical signatures, including enrichment in Rb, U and K, and depletion in Nb, Ta, P and Ti. They have negative to weak positive εNd(t) values(-3.1 to +1.5) and relatively high initial ratios of 208 Pb/204 Pb(35.968–37.346), 207 Pb/204 Pb(15.448–15.508) and 206 Pb/204 Pb(16.280–17.492), indicating a subduction-metasomatized enriched lithospheric mantle source. Their low Ba/Rb(2.72–6.56), Ce/Y(0.97–1.39) and(Tb/Yb)N ratios(1.31–1.45) suggest that the parental magma was likely originated from low degree partial melting of the phlogopite-bearing lherzolite in a spinel-stability field. The Middle Triassic monzogranites show high Sr/Y ratios, low Mg O, Cr and Ni contents, high Zr/Sm ratios(40–64), negative zircon εHf(t) values(-25.8 to-8.8), as well as relatively flat heavy rare earth element patterns. They were likely derived from low degree partial melting of a moderately thickened ancient lower crust. The diabases and the slightly postdated high Sr/Y granites in this study represent the magmatic responses to the final orogenic evolution in the southwestern XMOB. Together with regional works, we propose that the slab break-off of the Paleo-Asian oceanic lithosphere following the terminal collision between the North China Craton and the South Mongolia terranes triggered asthenospheric upwelling, and the ongoing convergence further initiated moderately crustal thickening and uplift in the XMOB.
基金We are grateful to three anonymous reviewers for their constructive comments and suggestionsThis study was financially supported by the National Nature Science Foundation of China(Nos.41572049,41902050,41430209,41421002)+1 种基金the Major State Basic Research Development Projects(No.2015CB856103)the State Key Laboratory of Continental Dynamics,Northwest University.
文摘Mafic dyke swarm is widely developed in Proterozoic continental lithosphere.The Gangou diabase dyke from the Xixia area,intruded into the Douling complex of the South Qinling belt,yields zircon UPb age of 731 Ma.It has low SiO2 content(49.02 wt.%-49.37 wt.%)and Mg^#(34.0–37.7)and shows characteristics of subalkaline tholeiite series.They show highΣREE(155.5×10^-6–184.7×10^-6),weak negative Eu anomaly(δEu=0.88-0.93),slight depletion of Nb and Ta,and enrichment of LILE.Their major and trace element,Sr-Nd-Pb isotope and clinopyroxene compositions indicate that it originated from the partial melting of the asthenospheric mantle within-plate extension setting and was slightly contaminated by crust compositions.The similarities of formation age,petrogenesis,source characteristic and tectonic setting for Gangou diabase with mafic dykes in Wudang Block and mafic volcanic rocks in Yaolinghe Group indicate that the South Qinling belt underwent strong continental extension in Neoproterozoic during 796–685 Ma most likely correspondence to the breaking-up of the Rodinia supercontinent.
文摘The Noorabad-Harsin ophiolite is a part of the eastern Mediterranean-Zagros-Oman Tethyan ophiolites. This area is located in the south-southwest of the main Zagros thrust zone. This ophiolite consists of peridotites, serpentinites and pegmatite gabbros as mantle sequence whereas crustal sequence is composed of locally layered gabbros, isotropic gabbros, sheeted dike complex, basaltic to andesitic lavas and sedimentary rocks （radiolarites and Late Cretaceous pelagic limes- tones）. The diabase dikes are enriched in LREE relative to HREE （La（n）/Yb（n）=1.7-3.3）. Also, the andesites are enriched in LREE relative to HREE （La（n）/Yb（n）=3.1-5.37） and the pillow lavas are enriched in LILE （Th（n）/La（n）=2.1） while show a depletion in HFSE （Nb（n）/La（n）=0.07-0.2）. The basaltic-andesitic lavas exhibiting mainly calc-alkaline, with minor island-arc tholeiitic affinities, are characterized by enrichment in LILE and LREE and depletion in HFSE. These geochemical characteristics compared with other Tethyan ophiolites along the Bitlis-Zagros suture zone reveal a supra- subduction zone environment for the genesis of the Noorabad-Harsin ophiolites.
