Experimental study on reactions between alkaline basaltic melt and orthopyroxenes: constraints on the evolution of lithospheric mantle in the North China Craton

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.

U-Pb zircon geochronology of basaltic pyroclastic rocks from the basement beneath the Xisha Islands in the northwestern South China Sea and its geological significance

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.

Mineralogy and Chemistry Characterization of the New Basaltic Intrusion at Maasser El Chouf/Lebanon

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.

Logging curves characteristics and response mechanisms of basaltic facies and sub-facies: A case study from eastern sag of Liaohe depression, Northeast China

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.

Mineralogical and Geochemical Constraints on the Mantle Source Characteristics of Basaltic Lavas from the Central Mariana Trough

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.

Petrography, Geochemistry and Petrogensis of Pleistocene Basaltic Flow from Northwest Atarous Area, Central Jordan

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.

Extreme Mantle Heterogeneity beneath the Jingpohu Area,Northeastern China-Geochemical Evidence of Holocene Basaltic Rock

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.

Geochemical characteristics of major and trace elements in the Okinawa Trough basaltic glass

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.

Petrogenesis of basaltic shergottite NWA 8656

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.

Geochemistry and Petrogenesis of Intracontinental Basaltic Volcanism on the Northwest Arabian Plate,Gaziantep Basin,Southeast Anatolia,Turkey

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.

A special unbrecciated granoblastic textured basaltic eucrite meteorite

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,

Characterization of Mineralogy, Petrography, Geochemistry and Petrogensis of Basaltic Outcrops in Jurf Ed Darawish Area, Central Jordan

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.

Semi-Conducting Behavior of Plio-Quaternary Basaltic Lava Flows from Hemat Madam Volcano, Sana’a-Amran Volcanic Field, Yemen

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.

SM-ND AGE OF TUNCHANG BASALTIC KOMATIITES AND ITS GEOLOGICAL SIGNIFICANCE ON HAINAN ISLAND

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.

Geochemistry of Two Types of Basalts in the Emeishan Basaltic Province: Evidence for Mantle Plume-Lithosphere Interaction

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.

Stability investigation of road cut slope in basaltic rockmass,Mahabaleshwar,India

Slope failures along hill cut road slopes are the major nuisance for commuters and highway planners as they put the human lives at huge risk,coupled with immense monetary losses.Analysis of these vulnerable cut slopes entails the assessment and estimation of the suitable material strength input parameters to be used in the numerical models to accomplish a holistic stability examination.For the present study a 60 m high,basaltic and lateritic road cut hill slope in Mahabaleshwar,India,has been considered.A number of samples of both basalt and laterite,in their natural state were tested in the laboratory and the evaluated maximum,minimum and mean strength parameters were employed for the three cases in a distinct element numerical model.The Mohr-Coulomb failure criterion has been incorporated in the numerical model for the material as well as the joints.The numerical investigation offered the factor of safety and insights into the probable deformational mechanism for the three cases.Beside,several critical parameters have also been judged from the study viz.,mode of failure,factor of safety,shear strain rate,displacement magnitudes etc.The result of this analysis shows that the studied section is prone to recurrent failures due to the capping of a substantially thick layer of weaker lateritic material above the high strength basaltic rock mass.External triggering mechanisms like heavy precipitation and earthquake may also accelerate the slope failure in this area.The study also suggests employing instant preventive measures to avert the further risk of damage.

Reaction between basaltic melt and orthopyroxene at 3.0–4.5 GPa:Implications for the evolution of ocean island basalts in the mantle

Interactions between basaltic melt and orthopyroxenite(Opx)were investigated to gain a better understanding of the consequences of the residence and transport of ocean island basalts(OIBs)within the mantle.The experiments were conducted using a DS-3600 six-anvil apparatus at 3.0–4.5 GPa and 1300–1450℃.The basaltic melt and Opx coexisted at local equilibrium at these pressures and temperatures;the initial melts dissolved Opx,which modified their chemical composition,and clinopyroxene(Cpx)precipitated with or without garnet(Grt).The trace-element contents of Grt,Cpx,and melt were measured and the mineral–melt distribution coefficients(D)of Cpx–melt and Grt–melt were calculated,which can be used to assess the distribution of trace elements between basalt and minerals in the mantle.Two types of reaction rim were found in the experimental products,Cpx,and Cpx+Grt;this result indicates that residual rocks within the mantle should be pyroxenite or garnet pyroxenite.Both rock types are found in mantle xenoliths from Hawaii,and the rare-earth-element(REE)pattern of Cpx in these mantle pyroxenites matches those of Cpx in the experimental reaction rims.Furthermore,residual melts in the experimental products plot in similar positions to Hawaiian high-SiO_(2)OIBs on major-element Harker diagrams,and their trace-element patterns show the signature of residual Grt,particularly in runs at1350℃ and 4.0–4.5 GPa.Trace-element concentrations of the experimental residual melts plot in similar positions to the Hawaiian OIBs on commonly used discrimination diagrams(Ti vs.Zr,Cr vs.Y,Cr vs.V,Zr/Y vs.Zr,and Ti/Y vs.Nb/Y).These results indicate that reaction between basaltic melt and pyroxenite might contribute to the generation of Hawaiian high-SiO2 OIBs and account for their chemical variability.

Characterization and Origin of the Miocene Mudawwara-Quwayra Basaltic Dike, Southern Jordan

Petrographic, mineralogical and geochemical investigations were carried out on representative?samples from the Mudawwara-Quwayra Dike (MQD) in southernJordan. The MQD intruded Paleozoic and Cretaceous rocks as sub-vertical basaltic plugs, striking NW-SE along a fault zone and extending for more than 100 km. The MQD forms irregularly positive features, and is represented by symmetrical, elliptical, elongated or circular hills. It comprises thin basaltic layers intercalated?with pyroclastics and inclusions of different size and lithology, including limestone, sandstone, phosphate, quartzite, and marble. Petrographically, the rock exhibits phyric, porphyritic, vitrophyric and locally glomerophyritic textures manifested by plagioclase, clinopyroxene and rare?olivine and set in a matrix of plagioclase, pyroxene, brown glass and opaque phases. Clinopyroxene?and olivine phenocyrsts show disequilibrium textures such as reaction/resorbed rims in the?forms of corroded ends. The paragenetic sequence shows that olivine is the first phase to be crystallized and coexisting with pyroxene at sometime, while pyroxene continues crystallization. Plagioclase might have crystallized in contemporaneous later than the pyroxene. The MQD rocks are classified?as basalt and exhibit a narrow range of silica with a unique subalkaline affinity. This is most?probably attributed to assimilation of the abundant siliciclastic inclusions by the ascending magma. Emplacement of the MQD is attributed to regional phase of magmatism in Jordan and Saudi Arabia, which is probably the peripheral extension of a large magmatic event widely exposed in the Red Sea realm.

Evidences for Late Paleozoic and Mesozoic Basaltic Magmatism in Southwestern Cameroon and Implications for Correlations between the Gulf of Guinea in Africa and Northeast Brazil

Late Paleozoic and Mesozoic basaltic dikes were recently identified in Southwestern Cameroon in a ca.200km corridor of NE-SW trend that includes the Cameroon Line and corresponds,in a prebreak-up reconstitution of

Origin and evolution of alkali basaltic magma in the Okinawa Trough

The contents of major element composition of the phenocrysts and the matrix glass as well as the spinel inclusions and the melt inclusion in the phenocrysts of the basalt dredged from Station 133 of the Okinawa Trough are determined by electron microprobe. The results show that the basalt is a dor- galite consisting of phenocrysts of bytownite, chrysolite, clinopyroxene and magnetite as well as labradorite microcrystal, matrix glass and a few bits of broken vein quartz. Glassy melt inclusion and chromohercynite or chrompleonaste exist in bytownite and chrysolite. The formation of the spinels is re- lated to partial melting of mantle. The melt inclusions stand for a primary alkali dorgalitic magma, whose composition corresponds to olivine gabbro. The basaltic magma was generated from partial melting of spinel-lherzolite of the upper mantle and evolved in a process of 'alkali dorgalitic magma-trachy- basaltic magma-basdaltic trachytic magma-trachytic magma'. Assimilation and hybridization of crustal material may exist during magma upwelling in every evolutionary stage.