With mineral-melt thermobarometers,reconstruction of P-T-depth history of magmas can be established for vol-canic rocks.The pillow lava of Hantangang River Basalt is suitable for the study as it bears narrow compositi...With mineral-melt thermobarometers,reconstruction of P-T-depth history of magmas can be established for vol-canic rocks.The pillow lava of Hantangang River Basalt is suitable for the study as it bears narrow compositional range resulting from little or no fractional crystallization or crustal assimilation and shows evidence of rapid magma ascent.The established thermodynamic model covers the pathway from the magma source depth to the eruption.The model shows that the pillow lava originated at the depths of~85-100 km by fluid ascent from a stagnant slab.This range corresponds to the depth that encompasses the uppermost asthenosphere to the lowermost lithosphere corresponding to the upper garnet to the lower spinel sta-bility fields of the mantle.Subsequently,the melt rose to~66-71 km depth where a primary magma reservoir was generated possibly due to existence of a possible local discontinuity within the upper mantle.The magma uprose rapidly from~61 to~20 km or even to a shallower depth with crystallization of dendritic clinopyroxene and titano-magnetite,due to dehydration of magma.Magma ascent slowed down near the surface possibly due to the volcanic channel split into two or more toward the vents.The model can be applied to other volcanic areas composed of less evolved rocks.展开更多
The size of basalt fragments in Chang’E-5(CE-5)regolith are small(<6 mm^(2)),resulting in large variation on the estimated bulk composition of CE-5 basalt.For example,the estimated TiO_(2) content of CE-5 basalt r...The size of basalt fragments in Chang’E-5(CE-5)regolith are small(<6 mm^(2)),resulting in large variation on the estimated bulk composition of CE-5 basalt.For example,the estimated TiO_(2) content of CE-5 basalt ranges from 3.7 wt% to 12.7 wt% and the Mg#(molar percentage of Mg/[Mg+Fe])also shows a wide range(26.2-42.4).Preliminary experimental studies have shown that these geochemical characteristics of CE-5 basalt are critical for investigating the crystallization sequence and formation mechanism of its parent magma.This study presents new experimental data on the distribution coefficient of titanium between pyroxene and lunar basaltic magma(D_(Ti)^(Px/melt)).Combining with available literature data,we confirm that D_(Ti)Px/melt is affected by crystallization conditions such as pressure and temperature,but it is mainly controlled by the CaO content of pyroxene.Comparing with previous experimental results under similar conditions,we parameterized the effect as D_(Ti)^(Px/Melt)=D_(Ti)^(Px/Melt)=-0.0005X_(Cao)^(2)+0.0218X_(CaO)+0.0425(R^(2)=0.82),where X_(CaO) is the CaO content in pyroxene in weight percentage.The new experimental results suggest that pyroxene with high TiO_(2) content(>2.5 wt%)in CE-5 basalt is not a product of equilibrium crystallization,and the CaO content in pyroxene is also affected by cooling rate of its parent magma.The TiO_(2) content in the CE-5 parent magma is estimated to be about 5 wt% based on the Mg# of pyroxene and its calculated CaO content,which is consistent with those estimated from olivine grains.展开更多
Basalt is a major component of the earth and moon crust.Mineral composition and temperature influence frictional instability and thus the potential for seismicity on basaltic faults.We performed velocitystepping shear...Basalt is a major component of the earth and moon crust.Mineral composition and temperature influence frictional instability and thus the potential for seismicity on basaltic faults.We performed velocitystepping shear experiments on basalt gouges at a confining pressure of 100 MPa,temperatures in the range of 100-400℃ and with varied obsidian mass fractions of 0-100%under wet/dry conditions to investigate the frictional strength and stability of basaltic faults.We observe a transition from velocity-neutral to velocity-weakening behaviors with increasing obsidian content.The frictional stability response of the mixed obsidian/basalt gouges is characterized by a transition from velocitystrengthening to velocity-weakening at 200℃ and another transition to velocity-strengthening at temperatures>300℃.Conversely,frictional strengths of the obsidian-bearing gouges are insensitive to temperature and wet/dry conditions.These results suggest that obsidian content dominates the potential seismic response of basaltic faults with the effect of temperature controlling the range of seismogenic depths.Thus,shallow moonquakes tend to occur in the lower lunar crust due to the corresponding anticipated higher glass content and a projected temperature range conducive to velocity-weakening behavior.These observations contribute to a better understanding of the nucleation mechanism of shallow seismicity in basaltic faults.展开更多
The experimental results of the reactions between an alkaline basaltic melt and mantle orthopyroxenes under high-temperature and high-pressure conditions of 1300–1400℃ and 2.0–3.0 GPa using a six-anvil apparatus ar...The experimental results of the reactions between an alkaline basaltic melt and mantle orthopyroxenes under high-temperature and high-pressure conditions of 1300–1400℃ and 2.0–3.0 GPa using a six-anvil apparatus are reported in this paper.The reactions are proposed to simulate the interactions between melts from the asthenospheric mantle and the lithospheric mantle.The starting melt in the experiments was made from the alkaline basalt occurring in Fuxin,Liaoning Province,and the orthopyroxenes were separated from the mantle xenoliths in Damaping,Hebei Province.The results show that clinopyroxenes were formed in all the reactions between the alkaline basaltic melt and orthopyroxenes under the studied P–T conditions.The formation of clinopyroxene in the reaction zone is mainly controlled by dissolution–crystallization,and the chemical compositions of the reacted melt are primarily infl uenced by the diff usion eff ect.Temperature is the most important parameter controlling the reactions between the melt and orthopyroxenes,which has a direct impact on the melting of orthopyroxenes and the diff usion of chemical components in the melt.Temperature also directly controls the chemical compositions of the newly formed clinopyroxenes in the reaction zone and the reacted melt.The formation of clinopyroxenes from the reactions between the alkaline basaltic melt and orthopyroxenes can result in an increase of CaO and Al_(2)O_(3) contents in the rocks containing this mineral.Therefore,the reactions between the alkaline basaltic melt from the asthenospheric mantle and orthopyroxenes from the lithospheric mantle can lead to the evolution of lithospheric mantle in the North China Craton from refractory to fertile with relatively high CaO and Al 2 O 3 contents.In addition,the reacted melts in some runs were transformed from the starting alkaline basaltic into tholeiitic after reactions,indicating that tholeiitic magma could be generated from alkaline basaltic one via reactions between the latter and orthopyroxene.展开更多
As one of the micro-blocks dispersed in the South China Sea(SCS), the basement of the Xisha Islands has rarely been drilled because of the thick overlying Cenozoic sediments, which has led to a confused understanding ...As one of the micro-blocks dispersed in the South China Sea(SCS), the basement of the Xisha Islands has rarely been drilled because of the thick overlying Cenozoic sediments, which has led to a confused understanding of the pre-Cenozoic basement of the Xisha Islands. Well CK-1, a kilometer-scale major scientific drill in the Xisha Islands in the northwestern SCS, penetrated thick reefal limestone(0–888.4 m) and the underlying basement rocks(888.4–901.4 m). In this study, we present the zircon U-Pb ages of basement basaltic pyroclastic rocks from Well CK-1 in the Xisha Islands of the northwestern SCS to investigate the basement nature of the Xisha microblock. The basement of Well CK-1 consists of basaltic pyroclastic rocks on the seamount. The zircon grains yielded apparent ages ranging from ca. 2 138.9 Ma to ca. 36 Ma. The old group of zircon grains from Well CK-1 was considered to be inherited zircons. Two Cenozoic zircons gave a weighted mean 206Pb/238U age of(36.3 ± 1.1) Ma,Mean Squared Weighted Deviations(MSWD) = 1.2, which may represent the maximum age of the volcano eruption. The Yanshanian inherited zircons(116.9–105.7 Ma and 146.1–130.2 Ma) from Well CK-1 are consistent with the zircons from Well XK-1, indicating that the basement of Chenhang Island may be similar to that of Well XK-1. We propose that the Xisha micro-block may have developed on a uniform Late Jurassic metamorphic crystalline basement, intruded by Cretaceous granitic magma.展开更多
Seafloor extension and associated rifting in the North Atlantic Area, which started in Early Paleogene (from −62 Ma), resulted in a few micro-continents being isolated and submerged below sea levels. Published isotopi...Seafloor extension and associated rifting in the North Atlantic Area, which started in Early Paleogene (from −62 Ma), resulted in a few micro-continents being isolated and submerged below sea levels. Published isotopic data for sunken offshore continental materials (basement) in the North Atlantic area are quite sparse, but a few do exist for the Rockall Plateau, or more precisely the Rockall Bank. Isotopic data for Early Paleogene basaltic materials, covering basement rocks of the Rockall Plateau, have hitherto only been publicised for the NW margin of the Hatton bank. The Early Paleogene basaltic archipelago of the Faroe Islands, on which some isotopic data do exist, rests on an ancient sunken continental crust of unknown geochemical and isotopic compositions. The objective of this contribution is to assess potential lead isotopic relationships between the Rockall Plateau and the Faroese sub-basaltic basement, based on the sparse available isotopic data existing for the former and using available isotopic data for slightly contaminated Faroese basaltic rocks. The results reached in this contribution point to a likely association between the Faroese sub-basaltic basement and the basement of the Rockall Bank and hence the Rockall Plateau and potentially also between Faroese basaltic rocks and contemporaneous counterparts from the Hatton Bank.展开更多
The importance of this study is to identify the newly reordered and recognized basaltic intrusion for the first time in Maasser El Chouf in Lebanon. The recorded basaltic intrusion cut the Jurassic-Lower Cretaceous ro...The importance of this study is to identify the newly reordered and recognized basaltic intrusion for the first time in Maasser El Chouf in Lebanon. The recorded basaltic intrusion cut the Jurassic-Lower Cretaceous rock in this area. Necessary field inspection, geology, mineralogy and chemical tests were carried out on 8 basalt samples to determine their mineralogy, petrography and chemical composition. Representative samples have been tested with polarizing microscope, X-ray diffraction (XRD) and X-ray fluorescence (XRF). Petrographic and mineralogical studies show that the basalt is characterized by presence mainly of calcic-plagioclase feldspar, pyroxene-augite and olivine minerals. Secondary minerals of iron oxides also present (ilmenite and magnetite). The most appeared property is the alteration of olivine mineral to iddingsite that indicated highly weathered process. The composition of the basaltic samples reflects ultrabasic-basic type (Basanite-Tholeiitic basalt). The existence of volcanic activity occurred mostly with Pliocene age (< 2 Ma) as indicated by previous studies for similar basalt in Lebanon. Possibly, these boulders have been carried up from some deeper intrusive magmatic body under very active tension zones. Volcanism of Lebanon basalts belong to the alkaline olivine basalt, suite generally associated with tension, rifting and block faulting movements of the continental crust. Most of the volcanisms in Lebanon and in Harrat Ash Shaam Basalt from Syria and Palestine through Jordan to Saudi Arabia are related and connected to the opening of the Red Sea Rift System, making the area with tremendous volcanic tectonic activities.展开更多
Fifteen basaltic rock samples were collected from central Jordan at the Atarous volcanism basaltic flow area. The samples cover about 8 km2 from the Atarous Basalt flow (AB). The AB flow was introduced in the Miocene ...Fifteen basaltic rock samples were collected from central Jordan at the Atarous volcanism basaltic flow area. The samples cover about 8 km2 from the Atarous Basalt flow (AB). The AB flow was introduced in the Miocene to Pleistocene periods. The samples analyze major and trace elements by using XRF. Petrography, Geochemistry and Petrogensis have investigation to carried out for the AB. The petrography analyses of the AB rocks show they are composed of plagioclase (labradorite and bytownite), pyroxene (augite), and olivine (forsterite);accessory minerals include apatite and secondary minerals magnetite, ilmenite, spinel and iddingsite. The AB is classified within alkaline to sub-alkaline and tholeiitic to Calc-Alkaline basalt. The Mg# range between 0.39 and 0.49 of basalt samples exhibits different degrees of fractionation with a low degree of melting < 15% as indicated from the varying concentration of incompatible trace elements Ba, Rb, Sr. Trace elements of primary magna show low variable abundances of compatible and incompatible elements, which reflecs a homogenous source. Geochemical parameters such as Mg# and high Ti contents indicate that the corresponding magmas are of primary origin. The tectonic setting of AB is explained by using discrimination diagrams, Ti-Zr-Sr and Nb-Zr-Y and Ti-Zr-Y, the AB plotted within the plate basalt, alkali basalt and Calk alkaline basalt field, respectively. The spider diagram shows the samples AB enrichment of the Ba, K, Nb and Ce, depletion of Nb and Y. The AB exhibited positive Nb, Ce and Ti anomalies, and negative anomalies of Ba, Sr, and P. It is attributed to the fractionation of feldspar for Ba and Sr and apatite for P depletion. The spider diagram showed a positive Nb peak, which conforms to the tertiary and to recent continental alkali basalt provinces and indicates that the AB is the product of lithosphere from upwelling asthenosphere mantle.展开更多
Holocene basaltic rocks of the Jingpohu area are located in the “Crater Forest” and Hamatang districts to the northwest of the Jingpohu Lake. Although there is only a distance of 15 km between the two districts, the...Holocene basaltic rocks of the Jingpohu area are located in the “Crater Forest” and Hamatang districts to the northwest of the Jingpohu Lake. Although there is only a distance of 15 km between the two districts, their petrological characteristics are very different: alkaline olivine basalt without any megacrysts in the former, and leucite tephrite with Ti-amphibole, phlogopite and anorthoclasite megacrysts in the latter. On the basis of their geochemical characteristics, the two types of basaltic rocks should belong to weakly sodian alkaline basalts. But leucite tephrite is characterized by higher Al2O3, Na2O and K2O, higher enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), lower MgO and CaO, compatible elements and moderately compatible elements and lower Mg*values and Na/K ratios in comparison with alkaline olivine basalt. However, the two types of basaltic rocks have similar Sr, Nd, Pb isotopic compositions, which suggests that the mantle beneath the Jingpohu area was homogeneous before undergoing some geological processes about 3490 years ago. As the activity of the mantle plume led to different degrees of metasomatism, extreme mantle source heterogeneities occurred beneath the Jingpohu area. In comparison with alkaline olivine basalt, the leucite tephrite was derived from the more enriched mantle source region and resulted from strong metasomatism.展开更多
The Okinawa Trough（OT） is a back-arc basin at an initial spreading stage that is under the influence of subduction of the Philippine Sea Plate. In this study, we analyzed the geochemical compositions of basaltic gla...The Okinawa Trough（OT） is a back-arc basin at an initial spreading stage that is under the influence of subduction of the Philippine Sea Plate. In this study, we analyzed the geochemical compositions of basaltic glass in the OT and discussed the effects of different magmatic sources, evolution, and subducted components in basalts. Our results showed that the middle and southern regions of the OT exhibit characteristics consistent with an iron-rich tholeiite series. Trace element proportions conform to the typical spider diagram pattern characteristic of back-arc basin basalts, rich in large ion lithophile elements（LILEs） including Rb, Ba, Pb, U, and Th, while depleted in high field-strength elements（HFSEs） including Nb, Ta, Zr, Hf, and Ti. The distribution of rare earth elements（REEs） is also consistent with enrichment by right-leaning light rare earth elements（LREEs）.The addition of enriched mantle type I（EMI） materials as well as mantle heterogeneity may have led to variable degrees of enrichment in different regions. The magma source of the middle trough has undergone crystallization towards pyroxene, while development of plagioclase was restricted partly, and the crystallization of spinel and olivine ceased altogether. At the same time, crystallization of the southern OT magma source was dominated by olivine and including the formation of plagioclase, pyroxene, and magnetite（or titanomagnetite）. Finally, the results of this study showed that 90% Th, 95% Ba in the southern basalt, 50%–70% Th and 70%–90% Ba in the middle basalt originated from subducted component. Different subducted component influence may be due to different subduction zone structural feature.展开更多
Most basaltic shergottites are too Mg-rich to represent parent melt compositions because they contain some cumulus pyroxenes. However, basaltic shergottite Northwest Africa(NWA) 8656 with subophitic texture can be use...Most basaltic shergottites are too Mg-rich to represent parent melt compositions because they contain some cumulus pyroxenes. However, basaltic shergottite Northwest Africa(NWA) 8656 with subophitic texture can be used as the parent melt composition in petrogenetic studies because it contains no or rare cumulus pyroxenes. Its pyroxene cores(Mg# 66-68, the most magnesian) are in equilibrium with the bulk rock composition based on major(Fe-Mg) and trace elements(REE—rare earth elements).The patchy zoning of pyroxenes has been interpreted as reflecting a two-stage crystallization history: 1) crystallization of Mg-rich pyroxene cores at depth(50 km, the base of Martian crust), 2) crystallization of Fe-rich pyroxene rims at the shallow depth near the Martian surface with a fast cooling history. The crystallization of Fe-rich pyroxenes and the existence of different symplectites indicate that NWA 8656 underwent eruption. The oxygen fugacity of NWA 8656(QFM –0.9±0.5) suggests an oxidized condition at the late-stage crystallization process, and the CI-normalized REE patterns of different minerals show enrichment in LREE, compared to that of depleted shergottites. Both of these observations suggest a relatively ITE(incompatible trace elements)-enriched signature of NWA 8656, similar to those of other enriched shergottites. The REE compositions of augite core and rim and plagioclase can be successfully reproduced by progressive crystallization without exogenous components, which indicates a closed magmatic system for NWA 8656. Consequently, we conclude that the ITE-enriched signature of NWA 8656 is inherited from an enriched mantle source rather than caused by crustal assimilation. Moreover, partial melting of depleted Martian mantle could not directly yield magmas that have geochemical characteristics similar to enriched shergottite parent magmas, so the enriched and depleted shergottites are derived from distinct mantle sources, and the mantle source of enriched shergottites would be expected to contain ilmenite.展开更多
Based on five types of conventional logging curves including GR,RLLD,CNL,DEN and AC,and 39 core samples from 30 representative boreholes,the logging characteristics and lithofacies and sub-facies of the basaltic rocks...Based on five types of conventional logging curves including GR,RLLD,CNL,DEN and AC,and 39 core samples from 30 representative boreholes,the logging characteristics and lithofacies and sub-facies of the basaltic rocks were studied.Three basaltic facies and four sub-facies are recognized from the well logs,includ-ing volcanic conduit facies(post intrusive sub-facies),explosive facies,and effusive lava flow facies(tabular flow,compound flow and hyaloclastite sub-facies).The post intrusive,tabular flow and compound flow sub-facies logging curves are mainly controlled by the distribution of vesiculate zones and vesiculate content,which are characterized by four curves with good correlation.Post intrusive sub-facies are characterized by high RLLD,high DEN,with a micro-dentate logging curve pattern,abrupt contact relationships at the top and base.Tabular flow sub-facies are characterized by high RLLD,high DEN,with a bell-shaped log curve pattern,abrupt contact at the base and gradational contact at the top.Compound flow sub-facies are characterized by medium-low RLLD,with a micro-dentate or finger-like logging curve pattern,abrupt contact at the base and gradational contact at the top.Explosive facies and hyaloclastite sub-facies logging curves are mainly controlled by the distribution of the size and sorting of rock particles,which can be recognized by four kinds of logging curves with poor cor-relation.Explosive facies are characterized by low RLLD,medium-low CNL and low DEN,with a micro-dentate logging curve pattern.Hyaloclastite sub-facies are characterized by low RLLD,high CNL,low DEN and high AC,with a micro-dentate logging curve pattern.The present research is beneficial for the prediction of basaltic reser-voirs not only in the Liaohe depression but also in the other volcanic-sedimentary basins.展开更多
Volcanism along the northwest boundary of the Arabian Plate found in the Gaziantep Basin, southeast Turkey, is of Miocene age and is of alkaline and calc-alkaline basic composition. The rare earth element data for bot...Volcanism along the northwest boundary of the Arabian Plate found in the Gaziantep Basin, southeast Turkey, is of Miocene age and is of alkaline and calc-alkaline basic composition. The rare earth element data for both compositional series indicates spinel-peridotite source areas. The rare earth and trace elements of the alkaline lavas originate from a highly primitive and slightiy contaminated asthenospheric mantle; those of the calc-alkaline lavas originate from a highly heterogeneous, asthenospheric, and lithospheric mantle source. Partial melting and magmatic differentiation processes played a role in the formation of the petrological features of these volcanics. These rocks form two groups on the basis of their 87Sr[S6Sr and 143Nd/lI4Nd isotopic compositions in addition to their classifications based on their chemical compositions （alkaline and calc-alkaline）. These isotopic differences indicate a dissimilar parental magma. Therefore, high Nd isotope samples imply a previously formed and highly primitive mantle whereas low Nd isotope samples may indicate comparable partial melting of an enriched heterogeneous shallow mantle. Other isotopic changes that do not conform to the chemical features of these lavas are partly related to the various tectonic events of the region, such as the Dead Sea Fault System and the Bitlis Suture Zone.展开更多
1 Introduction Generally,we can observe varying degree of ophitic texture or sub-ophitic texture in unbrecciated basaltic eucrites.However,a few unbrecciated basaltic eucritespossess the special characteristic of crys...1 Introduction Generally,we can observe varying degree of ophitic texture or sub-ophitic texture in unbrecciated basaltic eucrites.However,a few unbrecciated basaltic eucritespossess the special characteristic of crystalloblastic texture by high metamorphism,which are called as granoblastic textured basaltic eucrites(Mayne et al.2009,展开更多
This research was conducted to investigate the mineralogy, petrography, geochemistry and petrogensis of the basaltic flows in Jurf Ed Darawish (JDB) area of central Jordan. Sexton representative basalt rock samples we...This research was conducted to investigate the mineralogy, petrography, geochemistry and petrogensis of the basaltic flows in Jurf Ed Darawish (JDB) area of central Jordan. Sexton representative basalt rock samples were selected from the studied JDB outcrops. Modally, JDB consists of plagioclase, olivine, pyroxene (diopside), opaque’s, calcite and iddingsite minerals. Petrographically, basalt is holocrystalline, hypidiomorphic fine to medium grained and exhibited aphanitic to porphyritic texture. The common textures of the JDB rock samples were aphanitic, porphyritic, trachytic, glomeroporphyritic, sub ophitic, vesicular, and amygdaloidal. Geochemically, all of the inspected samples of JDB are located within Trachy basalt and plate alkaline basalt. The tectonic setting of JDB was plotted within the calcalkaline basalt and continental basaltic field. The rare-earth elements showed enrichment of the Ba and K, depletion of Ce relative to K, and enrichment of Nb and Pb with depletion of Y and positive Nb, Zr and Ti anomalies. Negative anomalies of Ba, Sr, Ti and P may be attributed to the fractionation of feldspar for Ba and Sr depletion apatite for P depletion. The positive Nb peak conforms to the tertiary as well as to recent continental alkali basalt provinces and acts as an indicator to the JDB product for the lithosphere from upwelling of the asthenosphere mantle.展开更多
Electric DC and AC measurements and dielectric investigations have been carried out on some Plio-Qaternary basalt of Hemat Madam volcano from Sana’a-Amran volcanic field (SAVF). In this article we focus primarily on ...Electric DC and AC measurements and dielectric investigations have been carried out on some Plio-Qaternary basalt of Hemat Madam volcano from Sana’a-Amran volcanic field (SAVF). In this article we focus primarily on the field aspects and the main characteristic mineralogical and petrographic features of this inactive volcano. Using DC and AC experimental arrangements we discovered excellent electrical characteristics for this inactive volcano. The results of DC electrical resistivity versus a temperature reveal that all the samples have semiconductor characters. Moreover, the measurements showed that these samples have high resistive extrinsic semiconductors (ρDC ~ 109 Ω·m). AC and dielectric measurements were ensured the semi-conductivity and normal dielectric behavior of these samples. AC measurements reveal that the classical barrier hopping model (CBH) is the predominant conduction mechanism, while at low temperature region small polarons may contribute to the conduction in the samples. The samples have low values for dielectric constant ε' and low loss factor tanδ (ε' ~ 27 and tanδ ~ 0.7 at 200 Hz for the sample BA7). Then, the semicodutor behavior, the high values of DC/AC resistivity and low loss dissipation factor considered a very good characterization for magnetic semiconductor materials. So, we can predict that, the studied natural materials represent newborn promising material sciences for many more technological applications.展开更多
The petrogenetic age of Tunchang basaltic komatiites in Hainan Island has never been solved for a long time.Five samples of the basaltic komatiites are taken to be measured by Sm－ Nd radioactive isotope method in thi...The petrogenetic age of Tunchang basaltic komatiites in Hainan Island has never been solved for a long time.Five samples of the basaltic komatiites are taken to be measured by Sm－ Nd radioactive isotope method in this study.The Sm－ Nd whole rock isochron age of 1 687± 10 Ma with INd=0.510796± 0.000006 (2σ ) and ε Nd(T)=＋ 6.64 has been obtained.Meanwhile the basaltic komatiites give Nd model age of 1637～ 1 756 Ma which correspond basically to the isochron age of 1 687 Ma.These indicate that Tunchang basaltic komatiites were formed in the Palaeoproterozoic (about 1 687 Ma) and its primary magma would be derived from a depleted mantle.展开更多
Based on the temporal-spatial distribution and geochemical characteristics,the Emeishan basalts can be divided into two types: high-P_2O-TiO_2 basalt (HPT) andlow-P_2O_5-TiO_2 basalt (LPT), which differ distinctly in ...Based on the temporal-spatial distribution and geochemical characteristics,the Emeishan basalts can be divided into two types: high-P_2O-TiO_2 basalt (HPT) andlow-P_2O_5-TiO_2 basalt (LPT), which differ distinctly in geochemistry: the LPTs are characterizedby relatively high abundances of MgO, total FeO and P_2O_5 and compatible elements (Cr, Ni, Sc), andrelatively low contents of moderately compatible elements (V, Y, Yb, Co), LREE and otherincompatible elements compared with the HPT. On the diagrams of trace element ratios, they areplotted on an approximately linear mixing line between depleted and enriched mantle sources,suggesting that these two types of basalts resulted from interactions of varying degrees betweenmantle plume and lithospheric mantle containing such volatile-rich minerals as amphibole andapatite. The source region of the LPT involves a smaller proportion of lithospheric components,while that of the HTP has a larger proportion of lithospheric components. Trachyte is generated bypartial melting of the basic igneous rocks at the base of the lower continental crust. Both the twotypes of magmas underwent certain crystal fractionation and contamination of the lower crest athigh-level magma chambers and en route to the surface.展开更多
The composition of mantle-derived basalts reflects the nature of their mantle source regions,which constrain magma generation and composition.Here we present a new whole rock major and trace elements and phenocryst co...The composition of mantle-derived basalts reflects the nature of their mantle source regions,which constrain magma generation and composition.Here we present a new whole rock major and trace elements and phenocryst composition of the basaltic lava in the central Mariana Trough.These data provide insights into the mantle source characteristics affected by subduction components.The rocks range from basalts to basaltic andesites,which have high subduction-mobile element contents(e.g.,K,U,Th,LREE)related to N-MORB.The calculated temperature and depth of magma generation are about 1300℃and 30 km,respectively.Although the results above suggest that the addition of hydrous fluid and/or a melt derived from a slab decreases the temperature of mantle partial melting and mildly modifies the composition of a mantle source,the mantle source lithology from which primary magma is generated remains to be peridotite.展开更多
A series of crystallization experiments have been carried out by using natural Emeishan Ti-rich hydrous basalts as starting materials at a pressure of 0.5 GPa and temperatures of 800-1000℃to constrain the origin of F...A series of crystallization experiments have been carried out by using natural Emeishan Ti-rich hydrous basalts as starting materials at a pressure of 0.5 GPa and temperatures of 800-1000℃to constrain the origin of Fe-Ti-V oxide ore deposits.Our experimental results demonstrate that the sandwich-and trellis-type ilmenite lamellae in titanomagnetite of layered intrusions can be formed by the reaction of earlier crystallized ilmenite and the evolved parental magma.During evolution of parental basaltic magma,the Fe-Ti oxide should be composed of titanomagnetite+ilmenite in the earlier stage,but changed to titanomagnetite+titanomagnetite-ilmenite intergrowth±ilmenite at the later stage.Accordingly,the Panzhihua Fe-Ti oxide ores,which are mainly composed of titanomagnetite,should be formed earlier than the adjacent gabbro,in which titanomagnetite-ilmenite intergrowth is the major form of the Fe-Ti oxide.展开更多
基金supported by the 2021 Research Project for UNESCO Hantangang River Global Geopark supported by Gyeonggi Provincial Office(Grant No.20210606641-00)Basic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(No.2019R1A6A1A03033167).
文摘With mineral-melt thermobarometers,reconstruction of P-T-depth history of magmas can be established for vol-canic rocks.The pillow lava of Hantangang River Basalt is suitable for the study as it bears narrow compositional range resulting from little or no fractional crystallization or crustal assimilation and shows evidence of rapid magma ascent.The established thermodynamic model covers the pathway from the magma source depth to the eruption.The model shows that the pillow lava originated at the depths of~85-100 km by fluid ascent from a stagnant slab.This range corresponds to the depth that encompasses the uppermost asthenosphere to the lowermost lithosphere corresponding to the upper garnet to the lower spinel sta-bility fields of the mantle.Subsequently,the melt rose to~66-71 km depth where a primary magma reservoir was generated possibly due to existence of a possible local discontinuity within the upper mantle.The magma uprose rapidly from~61 to~20 km or even to a shallower depth with crystallization of dendritic clinopyroxene and titano-magnetite,due to dehydration of magma.Magma ascent slowed down near the surface possibly due to the volcanic channel split into two or more toward the vents.The model can be applied to other volcanic areas composed of less evolved rocks.
基金funded by National natural Science Foundation of China(41973058 and 42473052)the B-type Strategic Priority Research Program of Chinese Academy of Sciences(XDB41020305)National Key and Development Program of China(2024YFF0807500).
文摘The size of basalt fragments in Chang’E-5(CE-5)regolith are small(<6 mm^(2)),resulting in large variation on the estimated bulk composition of CE-5 basalt.For example,the estimated TiO_(2) content of CE-5 basalt ranges from 3.7 wt% to 12.7 wt% and the Mg#(molar percentage of Mg/[Mg+Fe])also shows a wide range(26.2-42.4).Preliminary experimental studies have shown that these geochemical characteristics of CE-5 basalt are critical for investigating the crystallization sequence and formation mechanism of its parent magma.This study presents new experimental data on the distribution coefficient of titanium between pyroxene and lunar basaltic magma(D_(Ti)^(Px/melt)).Combining with available literature data,we confirm that D_(Ti)Px/melt is affected by crystallization conditions such as pressure and temperature,but it is mainly controlled by the CaO content of pyroxene.Comparing with previous experimental results under similar conditions,we parameterized the effect as D_(Ti)^(Px/Melt)=D_(Ti)^(Px/Melt)=-0.0005X_(Cao)^(2)+0.0218X_(CaO)+0.0425(R^(2)=0.82),where X_(CaO) is the CaO content in pyroxene in weight percentage.The new experimental results suggest that pyroxene with high TiO_(2) content(>2.5 wt%)in CE-5 basalt is not a product of equilibrium crystallization,and the CaO content in pyroxene is also affected by cooling rate of its parent magma.The TiO_(2) content in the CE-5 parent magma is estimated to be about 5 wt% based on the Mg# of pyroxene and its calculated CaO content,which is consistent with those estimated from olivine grains.
基金funded by the National Natural Science Foundation of China(Nos.42320104003 and 42107163)the Funda mental Research Funds for the Central Universities.Derek Elsworth acknowledges support from the G.Albert Shoemaker endowment.
文摘Basalt is a major component of the earth and moon crust.Mineral composition and temperature influence frictional instability and thus the potential for seismicity on basaltic faults.We performed velocitystepping shear experiments on basalt gouges at a confining pressure of 100 MPa,temperatures in the range of 100-400℃ and with varied obsidian mass fractions of 0-100%under wet/dry conditions to investigate the frictional strength and stability of basaltic faults.We observe a transition from velocity-neutral to velocity-weakening behaviors with increasing obsidian content.The frictional stability response of the mixed obsidian/basalt gouges is characterized by a transition from velocitystrengthening to velocity-weakening at 200℃ and another transition to velocity-strengthening at temperatures>300℃.Conversely,frictional strengths of the obsidian-bearing gouges are insensitive to temperature and wet/dry conditions.These results suggest that obsidian content dominates the potential seismic response of basaltic faults with the effect of temperature controlling the range of seismogenic depths.Thus,shallow moonquakes tend to occur in the lower lunar crust due to the corresponding anticipated higher glass content and a projected temperature range conducive to velocity-weakening behavior.These observations contribute to a better understanding of the nucleation mechanism of shallow seismicity in basaltic faults.
基金supported by the National Natural Science Foundation of China(Nos.41472065 and 42073059).
文摘The experimental results of the reactions between an alkaline basaltic melt and mantle orthopyroxenes under high-temperature and high-pressure conditions of 1300–1400℃ and 2.0–3.0 GPa using a six-anvil apparatus are reported in this paper.The reactions are proposed to simulate the interactions between melts from the asthenospheric mantle and the lithospheric mantle.The starting melt in the experiments was made from the alkaline basalt occurring in Fuxin,Liaoning Province,and the orthopyroxenes were separated from the mantle xenoliths in Damaping,Hebei Province.The results show that clinopyroxenes were formed in all the reactions between the alkaline basaltic melt and orthopyroxenes under the studied P–T conditions.The formation of clinopyroxene in the reaction zone is mainly controlled by dissolution–crystallization,and the chemical compositions of the reacted melt are primarily infl uenced by the diff usion eff ect.Temperature is the most important parameter controlling the reactions between the melt and orthopyroxenes,which has a direct impact on the melting of orthopyroxenes and the diff usion of chemical components in the melt.Temperature also directly controls the chemical compositions of the newly formed clinopyroxenes in the reaction zone and the reacted melt.The formation of clinopyroxenes from the reactions between the alkaline basaltic melt and orthopyroxenes can result in an increase of CaO and Al_(2)O_(3) contents in the rocks containing this mineral.Therefore,the reactions between the alkaline basaltic melt from the asthenospheric mantle and orthopyroxenes from the lithospheric mantle can lead to the evolution of lithospheric mantle in the North China Craton from refractory to fertile with relatively high CaO and Al 2 O 3 contents.In addition,the reacted melts in some runs were transformed from the starting alkaline basaltic into tholeiitic after reactions,indicating that tholeiitic magma could be generated from alkaline basaltic one via reactions between the latter and orthopyroxene.
基金The National Natural Science Foundation of China under contract Nos 42030502, 42090041 and 42166003the Guangxi Scientific Projects under contract Nos AD17129063 and AA17204074+1 种基金the Guangxi Youth Science Fund Project under contract 2019GXNSFBA185016the Ph.D. Research Start-up Foundation of Guangxi University under contract No. XBZ170339。
文摘As one of the micro-blocks dispersed in the South China Sea(SCS), the basement of the Xisha Islands has rarely been drilled because of the thick overlying Cenozoic sediments, which has led to a confused understanding of the pre-Cenozoic basement of the Xisha Islands. Well CK-1, a kilometer-scale major scientific drill in the Xisha Islands in the northwestern SCS, penetrated thick reefal limestone(0–888.4 m) and the underlying basement rocks(888.4–901.4 m). In this study, we present the zircon U-Pb ages of basement basaltic pyroclastic rocks from Well CK-1 in the Xisha Islands of the northwestern SCS to investigate the basement nature of the Xisha microblock. The basement of Well CK-1 consists of basaltic pyroclastic rocks on the seamount. The zircon grains yielded apparent ages ranging from ca. 2 138.9 Ma to ca. 36 Ma. The old group of zircon grains from Well CK-1 was considered to be inherited zircons. Two Cenozoic zircons gave a weighted mean 206Pb/238U age of(36.3 ± 1.1) Ma,Mean Squared Weighted Deviations(MSWD) = 1.2, which may represent the maximum age of the volcano eruption. The Yanshanian inherited zircons(116.9–105.7 Ma and 146.1–130.2 Ma) from Well CK-1 are consistent with the zircons from Well XK-1, indicating that the basement of Chenhang Island may be similar to that of Well XK-1. We propose that the Xisha micro-block may have developed on a uniform Late Jurassic metamorphic crystalline basement, intruded by Cretaceous granitic magma.
文摘Seafloor extension and associated rifting in the North Atlantic Area, which started in Early Paleogene (from −62 Ma), resulted in a few micro-continents being isolated and submerged below sea levels. Published isotopic data for sunken offshore continental materials (basement) in the North Atlantic area are quite sparse, but a few do exist for the Rockall Plateau, or more precisely the Rockall Bank. Isotopic data for Early Paleogene basaltic materials, covering basement rocks of the Rockall Plateau, have hitherto only been publicised for the NW margin of the Hatton bank. The Early Paleogene basaltic archipelago of the Faroe Islands, on which some isotopic data do exist, rests on an ancient sunken continental crust of unknown geochemical and isotopic compositions. The objective of this contribution is to assess potential lead isotopic relationships between the Rockall Plateau and the Faroese sub-basaltic basement, based on the sparse available isotopic data existing for the former and using available isotopic data for slightly contaminated Faroese basaltic rocks. The results reached in this contribution point to a likely association between the Faroese sub-basaltic basement and the basement of the Rockall Bank and hence the Rockall Plateau and potentially also between Faroese basaltic rocks and contemporaneous counterparts from the Hatton Bank.
文摘The importance of this study is to identify the newly reordered and recognized basaltic intrusion for the first time in Maasser El Chouf in Lebanon. The recorded basaltic intrusion cut the Jurassic-Lower Cretaceous rock in this area. Necessary field inspection, geology, mineralogy and chemical tests were carried out on 8 basalt samples to determine their mineralogy, petrography and chemical composition. Representative samples have been tested with polarizing microscope, X-ray diffraction (XRD) and X-ray fluorescence (XRF). Petrographic and mineralogical studies show that the basalt is characterized by presence mainly of calcic-plagioclase feldspar, pyroxene-augite and olivine minerals. Secondary minerals of iron oxides also present (ilmenite and magnetite). The most appeared property is the alteration of olivine mineral to iddingsite that indicated highly weathered process. The composition of the basaltic samples reflects ultrabasic-basic type (Basanite-Tholeiitic basalt). The existence of volcanic activity occurred mostly with Pliocene age (< 2 Ma) as indicated by previous studies for similar basalt in Lebanon. Possibly, these boulders have been carried up from some deeper intrusive magmatic body under very active tension zones. Volcanism of Lebanon basalts belong to the alkaline olivine basalt, suite generally associated with tension, rifting and block faulting movements of the continental crust. Most of the volcanisms in Lebanon and in Harrat Ash Shaam Basalt from Syria and Palestine through Jordan to Saudi Arabia are related and connected to the opening of the Red Sea Rift System, making the area with tremendous volcanic tectonic activities.
文摘Fifteen basaltic rock samples were collected from central Jordan at the Atarous volcanism basaltic flow area. The samples cover about 8 km2 from the Atarous Basalt flow (AB). The AB flow was introduced in the Miocene to Pleistocene periods. The samples analyze major and trace elements by using XRF. Petrography, Geochemistry and Petrogensis have investigation to carried out for the AB. The petrography analyses of the AB rocks show they are composed of plagioclase (labradorite and bytownite), pyroxene (augite), and olivine (forsterite);accessory minerals include apatite and secondary minerals magnetite, ilmenite, spinel and iddingsite. The AB is classified within alkaline to sub-alkaline and tholeiitic to Calc-Alkaline basalt. The Mg# range between 0.39 and 0.49 of basalt samples exhibits different degrees of fractionation with a low degree of melting < 15% as indicated from the varying concentration of incompatible trace elements Ba, Rb, Sr. Trace elements of primary magna show low variable abundances of compatible and incompatible elements, which reflecs a homogenous source. Geochemical parameters such as Mg# and high Ti contents indicate that the corresponding magmas are of primary origin. The tectonic setting of AB is explained by using discrimination diagrams, Ti-Zr-Sr and Nb-Zr-Y and Ti-Zr-Y, the AB plotted within the plate basalt, alkali basalt and Calk alkaline basalt field, respectively. The spider diagram shows the samples AB enrichment of the Ba, K, Nb and Ce, depletion of Nb and Y. The AB exhibited positive Nb, Ce and Ti anomalies, and negative anomalies of Ba, Sr, and P. It is attributed to the fractionation of feldspar for Ba and Sr and apatite for P depletion. The spider diagram showed a positive Nb peak, which conforms to the tertiary and to recent continental alkali basalt provinces and indicates that the AB is the product of lithosphere from upwelling asthenosphere mantle.
文摘Holocene basaltic rocks of the Jingpohu area are located in the “Crater Forest” and Hamatang districts to the northwest of the Jingpohu Lake. Although there is only a distance of 15 km between the two districts, their petrological characteristics are very different: alkaline olivine basalt without any megacrysts in the former, and leucite tephrite with Ti-amphibole, phlogopite and anorthoclasite megacrysts in the latter. On the basis of their geochemical characteristics, the two types of basaltic rocks should belong to weakly sodian alkaline basalts. But leucite tephrite is characterized by higher Al2O3, Na2O and K2O, higher enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE), lower MgO and CaO, compatible elements and moderately compatible elements and lower Mg*values and Na/K ratios in comparison with alkaline olivine basalt. However, the two types of basaltic rocks have similar Sr, Nd, Pb isotopic compositions, which suggests that the mantle beneath the Jingpohu area was homogeneous before undergoing some geological processes about 3490 years ago. As the activity of the mantle plume led to different degrees of metasomatism, extreme mantle source heterogeneities occurred beneath the Jingpohu area. In comparison with alkaline olivine basalt, the leucite tephrite was derived from the more enriched mantle source region and resulted from strong metasomatism.
基金The National Basic Research Program of China under contract No.2013CB429702the open fund project supported by the Laboratory for Marine Geology,Qingdao National Laboratory for Marine Science and Technology under contract No.MGQNLM-KF201707+4 种基金the National Natural Science Foundation of China under contract Nos 41476044,41325021 and 41306053the Special Fund for the Taishan Scholar Program of Shandong Province under contract No.ts201511061the AoShan Talents Program supported by Qingdao National Laboratory for Marine Science and Technology under contract No.2015ASTP-0S17the Innovative Talent Promotion Program under contract No.2012RA2191the Science and Technology Development Program of Shandong Province under contract No.2013GRC31502
文摘The Okinawa Trough（OT） is a back-arc basin at an initial spreading stage that is under the influence of subduction of the Philippine Sea Plate. In this study, we analyzed the geochemical compositions of basaltic glass in the OT and discussed the effects of different magmatic sources, evolution, and subducted components in basalts. Our results showed that the middle and southern regions of the OT exhibit characteristics consistent with an iron-rich tholeiite series. Trace element proportions conform to the typical spider diagram pattern characteristic of back-arc basin basalts, rich in large ion lithophile elements（LILEs） including Rb, Ba, Pb, U, and Th, while depleted in high field-strength elements（HFSEs） including Nb, Ta, Zr, Hf, and Ti. The distribution of rare earth elements（REEs） is also consistent with enrichment by right-leaning light rare earth elements（LREEs）.The addition of enriched mantle type I（EMI） materials as well as mantle heterogeneity may have led to variable degrees of enrichment in different regions. The magma source of the middle trough has undergone crystallization towards pyroxene, while development of plagioclase was restricted partly, and the crystallization of spinel and olivine ceased altogether. At the same time, crystallization of the southern OT magma source was dominated by olivine and including the formation of plagioclase, pyroxene, and magnetite（or titanomagnetite）. Finally, the results of this study showed that 90% Th, 95% Ba in the southern basalt, 50%–70% Th and 70%–90% Ba in the middle basalt originated from subducted component. Different subducted component influence may be due to different subduction zone structural feature.
文摘Most basaltic shergottites are too Mg-rich to represent parent melt compositions because they contain some cumulus pyroxenes. However, basaltic shergottite Northwest Africa(NWA) 8656 with subophitic texture can be used as the parent melt composition in petrogenetic studies because it contains no or rare cumulus pyroxenes. Its pyroxene cores(Mg# 66-68, the most magnesian) are in equilibrium with the bulk rock composition based on major(Fe-Mg) and trace elements(REE—rare earth elements).The patchy zoning of pyroxenes has been interpreted as reflecting a two-stage crystallization history: 1) crystallization of Mg-rich pyroxene cores at depth(50 km, the base of Martian crust), 2) crystallization of Fe-rich pyroxene rims at the shallow depth near the Martian surface with a fast cooling history. The crystallization of Fe-rich pyroxenes and the existence of different symplectites indicate that NWA 8656 underwent eruption. The oxygen fugacity of NWA 8656(QFM –0.9±0.5) suggests an oxidized condition at the late-stage crystallization process, and the CI-normalized REE patterns of different minerals show enrichment in LREE, compared to that of depleted shergottites. Both of these observations suggest a relatively ITE(incompatible trace elements)-enriched signature of NWA 8656, similar to those of other enriched shergottites. The REE compositions of augite core and rim and plagioclase can be successfully reproduced by progressive crystallization without exogenous components, which indicates a closed magmatic system for NWA 8656. Consequently, we conclude that the ITE-enriched signature of NWA 8656 is inherited from an enriched mantle source rather than caused by crustal assimilation. Moreover, partial melting of depleted Martian mantle could not directly yield magmas that have geochemical characteristics similar to enriched shergottite parent magmas, so the enriched and depleted shergottites are derived from distinct mantle sources, and the mantle source of enriched shergottites would be expected to contain ilmenite.
文摘Based on five types of conventional logging curves including GR,RLLD,CNL,DEN and AC,and 39 core samples from 30 representative boreholes,the logging characteristics and lithofacies and sub-facies of the basaltic rocks were studied.Three basaltic facies and four sub-facies are recognized from the well logs,includ-ing volcanic conduit facies(post intrusive sub-facies),explosive facies,and effusive lava flow facies(tabular flow,compound flow and hyaloclastite sub-facies).The post intrusive,tabular flow and compound flow sub-facies logging curves are mainly controlled by the distribution of vesiculate zones and vesiculate content,which are characterized by four curves with good correlation.Post intrusive sub-facies are characterized by high RLLD,high DEN,with a micro-dentate logging curve pattern,abrupt contact relationships at the top and base.Tabular flow sub-facies are characterized by high RLLD,high DEN,with a bell-shaped log curve pattern,abrupt contact at the base and gradational contact at the top.Compound flow sub-facies are characterized by medium-low RLLD,with a micro-dentate or finger-like logging curve pattern,abrupt contact at the base and gradational contact at the top.Explosive facies and hyaloclastite sub-facies logging curves are mainly controlled by the distribution of the size and sorting of rock particles,which can be recognized by four kinds of logging curves with poor cor-relation.Explosive facies are characterized by low RLLD,medium-low CNL and low DEN,with a micro-dentate logging curve pattern.Hyaloclastite sub-facies are characterized by low RLLD,high CNL,low DEN and high AC,with a micro-dentate logging curve pattern.The present research is beneficial for the prediction of basaltic reser-voirs not only in the Liaohe depression but also in the other volcanic-sedimentary basins.
基金the University of Firat Scientific Research Projects Unit(FUBAP)for research support(Project number MF-13.06)
文摘Volcanism along the northwest boundary of the Arabian Plate found in the Gaziantep Basin, southeast Turkey, is of Miocene age and is of alkaline and calc-alkaline basic composition. The rare earth element data for both compositional series indicates spinel-peridotite source areas. The rare earth and trace elements of the alkaline lavas originate from a highly primitive and slightiy contaminated asthenospheric mantle; those of the calc-alkaline lavas originate from a highly heterogeneous, asthenospheric, and lithospheric mantle source. Partial melting and magmatic differentiation processes played a role in the formation of the petrological features of these volcanics. These rocks form two groups on the basis of their 87Sr[S6Sr and 143Nd/lI4Nd isotopic compositions in addition to their classifications based on their chemical compositions （alkaline and calc-alkaline）. These isotopic differences indicate a dissimilar parental magma. Therefore, high Nd isotope samples imply a previously formed and highly primitive mantle whereas low Nd isotope samples may indicate comparable partial melting of an enriched heterogeneous shallow mantle. Other isotopic changes that do not conform to the chemical features of these lavas are partly related to the various tectonic events of the region, such as the Dead Sea Fault System and the Bitlis Suture Zone.
基金supported by the National Natural Foundation of China (No. 41173077)
文摘1 Introduction Generally,we can observe varying degree of ophitic texture or sub-ophitic texture in unbrecciated basaltic eucrites.However,a few unbrecciated basaltic eucritespossess the special characteristic of crystalloblastic texture by high metamorphism,which are called as granoblastic textured basaltic eucrites(Mayne et al.2009,
文摘This research was conducted to investigate the mineralogy, petrography, geochemistry and petrogensis of the basaltic flows in Jurf Ed Darawish (JDB) area of central Jordan. Sexton representative basalt rock samples were selected from the studied JDB outcrops. Modally, JDB consists of plagioclase, olivine, pyroxene (diopside), opaque’s, calcite and iddingsite minerals. Petrographically, basalt is holocrystalline, hypidiomorphic fine to medium grained and exhibited aphanitic to porphyritic texture. The common textures of the JDB rock samples were aphanitic, porphyritic, trachytic, glomeroporphyritic, sub ophitic, vesicular, and amygdaloidal. Geochemically, all of the inspected samples of JDB are located within Trachy basalt and plate alkaline basalt. The tectonic setting of JDB was plotted within the calcalkaline basalt and continental basaltic field. The rare-earth elements showed enrichment of the Ba and K, depletion of Ce relative to K, and enrichment of Nb and Pb with depletion of Y and positive Nb, Zr and Ti anomalies. Negative anomalies of Ba, Sr, Ti and P may be attributed to the fractionation of feldspar for Ba and Sr depletion apatite for P depletion. The positive Nb peak conforms to the tertiary as well as to recent continental alkali basalt provinces and acts as an indicator to the JDB product for the lithosphere from upwelling of the asthenosphere mantle.
文摘Electric DC and AC measurements and dielectric investigations have been carried out on some Plio-Qaternary basalt of Hemat Madam volcano from Sana’a-Amran volcanic field (SAVF). In this article we focus primarily on the field aspects and the main characteristic mineralogical and petrographic features of this inactive volcano. Using DC and AC experimental arrangements we discovered excellent electrical characteristics for this inactive volcano. The results of DC electrical resistivity versus a temperature reveal that all the samples have semiconductor characters. Moreover, the measurements showed that these samples have high resistive extrinsic semiconductors (ρDC ~ 109 Ω·m). AC and dielectric measurements were ensured the semi-conductivity and normal dielectric behavior of these samples. AC measurements reveal that the classical barrier hopping model (CBH) is the predominant conduction mechanism, while at low temperature region small polarons may contribute to the conduction in the samples. The samples have low values for dielectric constant ε' and low loss factor tanδ (ε' ~ 27 and tanδ ~ 0.7 at 200 Hz for the sample BA7). Then, the semicodutor behavior, the high values of DC/AC resistivity and low loss dissipation factor considered a very good characterization for magnetic semiconductor materials. So, we can predict that, the studied natural materials represent newborn promising material sciences for many more technological applications.
基金The paper is finicially supported by the key gold and resource environment project(KZ952- J1- 007) of " the Eighth Five Years
文摘The petrogenetic age of Tunchang basaltic komatiites in Hainan Island has never been solved for a long time.Five samples of the basaltic komatiites are taken to be measured by Sm－ Nd radioactive isotope method in this study.The Sm－ Nd whole rock isochron age of 1 687± 10 Ma with INd=0.510796± 0.000006 (2σ ) and ε Nd(T)=＋ 6.64 has been obtained.Meanwhile the basaltic komatiites give Nd model age of 1637～ 1 756 Ma which correspond basically to the isochron age of 1 687 Ma.These indicate that Tunchang basaltic komatiites were formed in the Palaeoproterozoic (about 1 687 Ma) and its primary magma would be derived from a depleted mantle.
文摘Based on the temporal-spatial distribution and geochemical characteristics,the Emeishan basalts can be divided into two types: high-P_2O-TiO_2 basalt (HPT) andlow-P_2O_5-TiO_2 basalt (LPT), which differ distinctly in geochemistry: the LPTs are characterizedby relatively high abundances of MgO, total FeO and P_2O_5 and compatible elements (Cr, Ni, Sc), andrelatively low contents of moderately compatible elements (V, Y, Yb, Co), LREE and otherincompatible elements compared with the HPT. On the diagrams of trace element ratios, they areplotted on an approximately linear mixing line between depleted and enriched mantle sources,suggesting that these two types of basalts resulted from interactions of varying degrees betweenmantle plume and lithospheric mantle containing such volatile-rich minerals as amphibole andapatite. The source region of the LPT involves a smaller proportion of lithospheric components,while that of the HTP has a larger proportion of lithospheric components. Trachyte is generated bypartial melting of the basic igneous rocks at the base of the lower continental crust. Both the twotypes of magmas underwent certain crystal fractionation and contamination of the lower crest athigh-level magma chambers and en route to the surface.
基金the Shandong Provincial Natural Science Foundation,China(Nos.ZR2017PD002 and ZR2019BD010)the Open Fund of the Key Laboratory of Marine Geology and Environment,Chinese Academy of Sciences(Nos.MGE2019KG05 and MG E2021KG01)the Fundamental Research Funds for the Central Universities(No.202051009)。
文摘The composition of mantle-derived basalts reflects the nature of their mantle source regions,which constrain magma generation and composition.Here we present a new whole rock major and trace elements and phenocryst composition of the basaltic lava in the central Mariana Trough.These data provide insights into the mantle source characteristics affected by subduction components.The rocks range from basalts to basaltic andesites,which have high subduction-mobile element contents(e.g.,K,U,Th,LREE)related to N-MORB.The calculated temperature and depth of magma generation are about 1300℃and 30 km,respectively.Although the results above suggest that the addition of hydrous fluid and/or a melt derived from a slab decreases the temperature of mantle partial melting and mildly modifies the composition of a mantle source,the mantle source lithology from which primary magma is generated remains to be peridotite.
基金supported by funds from the National Key Research and Development Program of China (No.2016YFC0600204)the National Natural Science Foundation of China (Nos.41530211 and41872061)+1 种基金the National Key Basic Research Program of China (No.2015CB856101)the MOST Special Fund from the State Key Laboratory of GPMR (No.MSFGPMR02-2)
文摘A series of crystallization experiments have been carried out by using natural Emeishan Ti-rich hydrous basalts as starting materials at a pressure of 0.5 GPa and temperatures of 800-1000℃to constrain the origin of Fe-Ti-V oxide ore deposits.Our experimental results demonstrate that the sandwich-and trellis-type ilmenite lamellae in titanomagnetite of layered intrusions can be formed by the reaction of earlier crystallized ilmenite and the evolved parental magma.During evolution of parental basaltic magma,the Fe-Ti oxide should be composed of titanomagnetite+ilmenite in the earlier stage,but changed to titanomagnetite+titanomagnetite-ilmenite intergrowth±ilmenite at the later stage.Accordingly,the Panzhihua Fe-Ti oxide ores,which are mainly composed of titanomagnetite,should be formed earlier than the adjacent gabbro,in which titanomagnetite-ilmenite intergrowth is the major form of the Fe-Ti oxide.
