Mantle Driven Early Eocene Magmatic Flare-up of the Gangdese Arc, Tibet: A Case Study on the Nymo Intrusive Complex

Magmatic periodicity is recognized in continental arcs worldwide, but the mechanism responsible for punctuated arc magmatism is controversial. Continental arcs in the Trans-Himalayan orogenic system display episodic magmatism and the most voluminous flare-up in this system was in early Eocene during the transition from subduction to collision. The close association of the flare-up with collision is intriguing. Our study employs zircon Lu-Hf and bulk rock Sr-Nd isotopes, along with mineral geochemistry, to track the melt sources of the Nymo intrusive complex and the role of mantle magma during the early Eocene flare-up of the Gangdese arc, Tibet. The Nymo intrusive complex is composed of gabbronorite, diorite, quartz diorite, and granodiorite which define an arc-related calc-alkaline suite. Zircon U-Pb ages reveal that the complex was emplaced between ~50–47 Ma. Zircon Hf isotopes yield εHf(t) values of 8.2–13.1, while whole-rock Sr and Nd isotopes yield εNd(t) values of 2.7–6.5 indicative of magmatism dominated by melting of a juvenile mantle source with only minor crustal assimilation(~15%–25%) as indicated by assimilation and fractional crystallization modeling. Together with published data, the early Eocene magmatic flare-up was likely triggered by slab breakoff of subducted oceanic lithosphere at depths shallower than the overriding plate. The early Eocene magmatic flare-up may have contributed to crustal thickening of the Gangdese arc. This study provides important insights into the magmatic flare-up and its significant role in the generation of large batholiths during the transition from subduction to collision.

Geology and mineralization of the Hongqiling large magmatic nickel-copper-cobalt deposit(22×10^(4)t)in Jilin Province,China:A review

The Hongqiling large nickel-copper-cobalt deposit(hereafter referred to as the Hongqiling deposit),a typical mafic-ultramafic copper-nickel deposit in China,boasts proven Ni(Ni)resources of approximately 22×10^(4)t,associated copper resources of 2×10^(4)t,and associated cobalt(Co)resources of 0.5×10^(4)t,with Ni reserves ranking 10th among China's magmatic nickel deposits.Geotectonically,the Hongqiling deposit is situated in the superimposed zone between the Xing'an-Mongolian orogenic belt and the circum-Western Pacific's active continental margin belt.Its ore-bearing plutons occur within the metamorphic rocks of the Ordovician Hulan Group,with the emplacement of plutons and the locations of orebodies governed by the deep-seated Huifahe fault and its secondary NW-trending Fujia-Hejiagou-Beixinglong-Changsheng fault zone.In the deposit,the rock assemblages of ore-bearing plutons predominantly encompass gabbro-pyroxenite-olivine pyroxenite-pyroxene peridotite(pluton No.1)and norite-orthopyroxenite-harzburgite(pluton No.7),with ore-bearing lithofacies consisting primarily of olivine pyroxenite and pyroxenite facies.The Hongqiling deposit hosts stratoid,overhanging lentoid,veined,and pure-sulfide veined orebodies.Its ores principally contain metallic minerals including pyrrhotite,pentlandite,chalcopyrite,violarite,and pyrite.Despite unidentified magma sources of ore-bearing mafic-ultramafic rocks,it is roughly accepted that the magmatic evolution in the Hongqiling deposit primarily involved fractional crystallization and crustal contamination.The ore-forming materials were primarily derived from the upper mantle,mixed with minor crustal materials.The ore-bearing mafic-ultramafic rocks in the deposit,primarily emplaced during the Indosinian(208-239 Ma),were formed in an intense extension setting followed by the collisional orogeny between the North China Plate and the Songnen-Zhangguangcai Range Block during the Middle-Late Triassic.From the perspective of the metallogenic geological setting,surrounding rocks,ore-controlling structures,and rock assemblages,this study identified one favorable condition and seven significant indicators for prospecting for Hongqiling-type nickel deposits and developed a prospecting model of the Hongqiling deposit.These serve as valuable references for exploring similar nickel deposits in the region,as well as the deep parts and margins of the Hongqiling deposit.

Spatiotemporal mapping of(ultra‐)mafic magmatic mine areas:Implications of economic and political realities in China

The spatiotemporal extension/expansion of mine areas is affected by multiple factors.So far,very little has been done to examine the interaction between mine areas and political or economic realities.The(ultra‐)mafic magmatic mines in China played a specific role in supporting national development and providing an ideal research subject for monitoring their interrelationship.In this study,remote sensing and mining‐related GIS data were used to identify and analyze 1233(ultra‐)mafic magmatic mine area polygons in China,which covered approximately 322.96 km2 of land and included a V–Ti–Fe mine,a copper–nickel mine,a chromite mine,an asbestos mine,and a diamond mine.It was found that(1)the areal expansion of mines is significantly related to the mine types,perimeter,topography,and population density.(2)The mine area variation also reflects market and policy realities.The temporal expansion of the mine area from 2010 to 2020 followed an S‐shaped pattern(with the turning point occurring in 2014),closely related to iron overcapacity and tightened mining policies.(3)The complexity(D)of the mine area may reflect mine design and excavation practices.To be specific,lower D indicates early‐stage or artisanal/small‐scale mining,whereas higher D represents large‐scale mining.This study demonstrates that the detailed mapping of mine land can serve as an indicator to implement miningrelated market and policy changes.The(ultra‐)mafic mines area data set can be accessed at https://zenodo.org/record/7636616#.Y-p0uXaZOa0.

Coherent Chemical Variation Trends of the 55-25 Ma Magmatic Rocks in SE Tibet:N-S Direction Lithospheric Stretching of Eurasia during Early Stage of India-Eurasia Collision

The progressive indentation of India into Eurasia generated an E-W-trending orthogonal collision belt and a N-S-trending oblique collision belt.Compiling available data reveals that~70%of the Cenozoic igneous rocks in eastern and southeastern Tibet are concentrated within an ENE-trending,~550-km long and~250-km wide magmatic zone(CMZ)that once separated the orthogonal and oblique collision belts.The Latitude 26°N Line is now its southern boundary.The onset timing of magmatism of the CMZ varies gradually from~55 Ma in the westernmost part to~27 Ma in the easternmost.Then the magmatism successively occurred and suddenly stopped at~25 Ma.The segmented and coherent chemical variation trends found suggest that the CMZ magmatic rocks were formed due to partial melting of the heterogeneous upper mantle and crusts of Eurasia.Subduction of Paleo-and Neotethyan oceanic plates generated this compositional and mineralogical heterogeneity.Combined with available geophysical data,the CMZ was diachronously formed in response to asthenosphere upwelling induced by NNW-SSE-direction lithosphere stretching.The difference in responses of the orthogonal and oblique collision belts to the indentation of the Indian continent has led to this lithosphere stretching.

Neoarchean Magmatic Events in the Western Songnen Massif,Central Asian Orogenic Belt:Timing and Tectonic Significance

Whether a Neoarchean basement existing in the Songnen massif is currently debated.Identification of Archean magmatism from the Songnen Massif is helpful to resolve this issue.Here,we report newly discovered Neoarchean Shanquan pluton in the Western Songnen Massif.These Neoarchean Shanquan pluton are mainly composed of granites that are exposed near the town of Shanquan in Heilongjiang Province.LA-ICP-MS zircon U-Pb dating reveals that the sample 2015TW1 has an upper intercept age of 2801±69 Ma and a weighted mean age of 2708±18 Ma,while samples LJ27QY1 and LJ27QY2 have upper intercept ages of 2677±57 Ma and 2653±18 Ma,and weighted mean ages of 2649±10 Ma and 2653±15 Ma,respectively.This indicates that these granites were formed at~2.7 Ga.Most of the~2.7 Ga zircons have older TDM2 ages of 2762–3326 Ma with positiveεHf(t)values ranging from 0 to 6.4,while a few of the zircons have negativeεHf(t)values ranging from-8.1 to-11.5 and older TDM2 ages varying from 3158 to 3264 Ma.The zircon Hf isotopes indicate that Paleo-Mesoarchean crusts might once existed in the Songnen Massif,and the studied Neoarchean magmas were principally derived from partial melting of these Paleo-Mesoarchean ancient crust.Based on the geochronological spectrum of magmatic and detrital zircons,the Songnen,Erguna,Jiamusi,Bureya massifs may have a common basement prior to the Neoproterozoic and may even be linked with the Triam Craton.

Magmatic Network Structure of Volcanic Rocks in the Shengli Oilfield, Eastern China

Abstract: Types of polymerized molecular network structure and degree of bond breakdown for glass phases of magmatic inclusions and glassy matrix in volcanic rocks from the Shengli oilfield have been defined by the laser Raman spectroscopic investigation. There are significant differences in types of polymerized molecular network structure and degree of bond breakdown of the magmatic glass phases between the non-CO2 and CO2 gas pools: magmatic glass phases of fluid inclusions and matrix in volcanic rocks from the CO2 gas pool contain more sheet network molecules and have a greater degree of bond beakdown than those from the non-CO2 gas pool; and when gas bubbles occur in evolving magma, magma saturated with volatile components has more sheet network molecules. The results suggest the magmadegassing mechanism of the formation of CO2 gas pools in the Shengli oilfield.

A Preliminary Research on Skarns of Magmatic Origin

Skarns of magmatic origin, or magmatic skarns as called, are formed by crystallization of skarnic magma injecting into structural fissures. They occur in various rocks (rock formations), mainly in form of veins. Usually, they possess massive structure and cumulative texture. They mainly consist of calc silicate, without or with minor water bearing silicates. The typical minerals in it include alkali feldspar, calcite and anhydrite. Some silicate melt inclusions and high temperature, high salinity poly phase inclusions can be seen in the crystals of their host minerals. The particular members of the magmatic skarns are transitional skarn and skarnic pegmatite. The magmatic skarn and the congenetic alkali rich diorite usually collaborate in a conjugating and complementary manner. They probably are the products of calcic contamination, degassing, desilicification and separation in melt state of deep seated (high level magma chamber) alkali rich intermediate acid magma.

Magmatic Event at the End of the Archean in Eastern Hebei Province and Its Geological Implication

By using the SHRIMP U-Pb and single zircon stepwise evaporation methods, the authors have obtained some results for granitoids from eastern Hebei Province. The Yuhuzhai hyperthene tonalitic granite was formed 2550 Ma ago, the Qingyangshu gabbroic gneiss 2536 Ma, the Yinmahe granodioritic gneiss near Lücao, Lulong County, 2533 Ma, the gabbro-dioritic gneiss near Longwan, Qianxi County, 2518-2515 Ma, the Qiuhuayu trondjemitic gneiss at Zunhua 2515 Ma, the Xiaoguanzhuang tonalitic gneiss at Zunhua 2495 Ma, and the Cuizhangzi gneiss in Qianxi County 2492 Ma. These geochronilogical data demonstrate that, though diverse in composition, type and origin, the granitic gneisses in eastern Hebei Province were emplaced and crystallized in a rather short period of magmatic activity. The formation of such a great amount of gneisses in this small time gap suggests that it was a critical crust accretion stage at the end of Neoarchean. The fact that granitoids of various types occurred at the same time implies a large-scale underplating （mantle plume） activity, which was then responsible for the crust accretion.

Magmatic Ni-Cu-(PGE) deposits in magma plumbing systems:Features,formation and exploration

The three most crucial factors for the formation of large and super-large magmatic sulfide deposits are： （1） a large volume of mantle-derived mafic-ultramafic magmas that participated in the formation of the deposits; （2） fractional crystallization and crustal contamination, particularly the input of sulfur from crustal rocks, resulting in sulfide immiscibility and segregation; and （3） the timing of sulfide concentration in the intrusion. The super-large magmatic Ni-Cu sulfide deposits around the world have been found in small mafic-ultramafic intrusions, except for the Sudbury deposit. Studies in the past decade indicated that the intrusions hosting large and super-large magmatic sulfide deposits occur in magma conduits, such as those in China, including Jinchuan （Gansu）, Yangliuping （Sichuan）, Kalatongke （Xinjiang）, and Hongqiling （Jilin）. Magma conduits as open magma systems provide a perfect environment for extensive concentration of immiscible sulfide melts, which have been found to occur along deep regional faults. The origin of many mantle-derived magmas is closely associated with mantle plumes, intracontinental rifts, or post-collisional extension. Although it has been confirmed that sulfide immiscibility results from crustal contamination, grades of sulfide ores are also related to the nature of the parental magmas, the ratio between silicate magma and immiscible sulfide melt, the reaction between the sulfide melts and newly injected silicate magmas, and fractionation of the sulfide melt. The field relationships of the ore-bearing intrusion and the sulfide ore body are controlled by the geological features of the wall rocks. In this paper, we attempt to demonstrate the general characteristics, formation mechanism,tectonic settings, and indicators of magmatic sulfide deposits occurring in magmatic conduits which would provide guidelines for further exploration.

Surplus Space Method: A New Numerical Model for Prediction of Shallow-seated Magmatic Bodies

Based on the data of field measurement and drilling in the Tongling area, a series of numerical simulations are carried out by using the 'Surplus Space Method' (SSM), which is first put forward in this paper and applied to predict the shallow-seated magmatic bodies. The results of the numerical simulations show the existence and the 3-D shape of a conical magmatic structure at a depth of-1000 m beneath the center of the area: its top offsets southwards and bifurcates to several branches, while its lower part stretches northeastwards and contracts rapidly to a point at about -1000 m depth. This point is reckoned to be a 'sink' of magma system, transferring ore materials and heat energy from the deep magma chamber to the sub-surface apophyses. The preliminary application of the SSM proves that it may be developed as a new detection means for determining the existence of shallow-seated magmatic bodies and analyzing their three-dimensional features.

Petrogenesis of Middle-Eocene granitoids and their Mafic microgranular enclaves in central Urmia-Dokhtar Magmatic Arc(Iran): Evidence for interaction between felsic and mafic magmas

Whole rock major and trace element geochemistry together with zircon U-Pb ages and Sr-Nd isotope compositions for the Middle Eocene intrusive rocks in the Haji Abad region are presented. The granitoid hosts, including granodiorite and diorite, yielded zircon U-Pb ages with a weighted mean value of 40.0 ± 0.7 Ma for the granodiorite phase. Mafic microgranular enclaves(MMEs) are common in these plutons, and have relatively low SiO_2 contents(53.04-57.08 wt.%) and high Mg#(42.6-60.1), probably reflecting a mantle-derived origin. The host rocks are metaluminous(A/CNK = 0.69-1.03), arc-related calc-alkaline, and I-type in composition, possessing higher SiO_2 contents(59.7-66.77 wt.%) and lower Mg#(38.6-52.2); they are considered a product of partial melting of the mafic lower crust. Chondritenormalized REE patterns of the MMEs and granitoid hosts are characterized by LREE enrichment and show slight negative Eu anomalies(Eu/Eu* = 0.60-0.93). The host granodiorite samples yield(^(87)Sr/^(86)Sr);ratios ranging from 0.70498 to 0.70591,positive eNd(t) values varying from +0.21 to +2.3, and TDM2 ranging from 760 to 909 Ma, which is consistent with that of associated mafic microgranular enclaves(^(87)Sr/^(86)Sr)i = 0.705111-0.705113, ε_(Nd)(t)= +2.14 to +2.16, T_(DM2) = 697-785 Ma). Petrographic and geochemical characterization together with bulk rock Nd-Sr isotopic data suggest that host rocks and associated enclaves originated by interaction between basaltic lower crust-derived felsic and mantlederived mafic magmas in an active continental margin arc environment.

Advances in Research of Mineral Chemistry of Magmatic and Hydrothermal Biotites

Biotite is an important hydrated ferromagnesian silicate mineral in igneous rocks and porphyry deposits.The determination of chemical compositions of biotite plays an important role in both igneous petrology and ore forming processes.This paper summarizes research results of magmatic and hydrothermal biotites exemplified by the Lakange porphyry Cu–Mo deposit and the Qulong porphyry Cu deposit in the Gangdese porphyry–skarn metallogenic belt,Tibet.Biotite mineral chemistry can provide critical insights into classification,geothermometer,geothermobarometry,oxygen fugacity,petrogenesis and tectonic setting,evaluating magmatic-hydrothermal process by halogen and halogen fugacity ratios,and distinguishing between barren and mineralized rocks.Biotite provides the latest mineralogical evidence on metallogenic prognosis and prospecting evaluation for porphyry Cu polymetallic deposits or magmatic hydrothermal deposits.

Classification of Magmatic Sulphide Deposits in China and Mineralization of Small Intrusions

Many important metal resources, such as Ni （Cu, Co）, PGE, exist in magmatic sulfide deposits, are a hot spot in geological research. We divide the magmatic sulphide deposits in China into four types according to their tectonic setting, intruding mode, ore deposit mode, main metallogenic elements. The four types are as follows： （1） Small-intrusion deposits in paleo-continent; （2） Smallintrusion deposits in continental flood basalt; （3） Small-intrusion deposits in orogenic belt; and （4） The deposits associated with ophiolites. On the basis of the classification, we put forward that the main magmatic metallogenic type in China is small-intrusion metallogeny, and describe its characteristics from small intrusions related concept, three geologic settings, three volcanic-intrusive assemblages and metallogenic key factors. According to the experiences of prospecting at home and abroad, we point out that there is big potential in prospecting small-intrusion deposits, which need further study. At last, we indicate that small-intrusion metallogeny not only widely distributes in mafic-ultramafic intrusions, but also has an important economic value and scientific significance in intermediate-acid intrusions.

Time scales and length scales in magma ?ow pathways and the origin ofmagmatic Ni-Cu-PGE ore deposits

Ore forming processes involve the redistribution of heat, mass and momentum by a wide range of processes operating at different time and length scales. The fastest process at any given length scale tends to be the dominant control. Applying this principle to the array of physical processes that operate within magma flow pathways leads to some key insights into the origins of magmatic Ni-Cu-PGE sulfide ore deposits. A high proportion of mineralised systems, including those in the super-giant Noril'sk-Talnakh camp, are formed in small conduit intrusions where assimilation of country rock has played a major role. Evidence of this process is reflected in the common association of sulfides with varitextured contaminated host rocks containing xenoliths in varying stages of assimilation. Direct incorporation of S-bearing country rock xenoliths is likely to be the dominant mechanism for generating sulfide liquids in this setting. However, the processes of melting or dissolving these xenoliths is relatively slow compared with magma flow rates and, depending on xenolith lithology and the composition of the carrier magma, slow compared with settling and accumulation rates. Chemical equilibration between sulfide droplets and silicate magma is slower still, as is the process of dissolving sulfide liquid into initially undersaturated silicate magmas. Much of the transport and deposition of sulfide in the carrier magmas may occur while sulfide is still incorporated in the xenoliths, accounting for the common association of magmatic sulfide-matrix ore breccias and contaminated "taxitic" host rocks. Effective upgrading of so-formed sulfide liquids would require repetitive recycling by processes such as reentrainment, back flow or gravity flow operating over the lifetime of the magma transport system as a whole. In contrast to mafic-hosted systems, komatiite-hosted ores only rarely show an association with externally-derived xenoliths, an observation which is partially due to the predominant formation of ores in lava flows rather than deep-seated intrusions, but also to the much shorter timescales of key component systems in hotter, less viscous magmas. Nonetheless, multiple cycles of deposition and entrainment are necessary to account for the metal contents of komatiite-hosted sulfides. More generally, the time and length scale approach introduced here may be of value in understanding other igneous processes as well as non-magmatic mineral systems.

Rare Earth Element Geochemistry on Magmatic Rocks and Gold Deposits in Shizishan Ore-Field of Tongling, China

REE geochemical characteristics of the magmatic rocks and gold deposits in Shizishan ore-field of Tongling were studied. Three types of the magmatic rocks have almost the same chondrite-normalized REE patterns, Eu and Ce anomalous values, and ∑REE, ∑LREE/∑HREE regular changes, which indicates that their magmas come from the same source and their digenetic mechanism is fractional crystallization. In three gold deposits, the mineral ores and related altered rocks have similar chondrite-normalized REE patterns and sharp Eu positive anomalous values. The REE contents reduced from the magmatic rocks to skamization or alteration magmatic rocks, skam type ores, sulphide type ores, wall-rocks limestone or marble. The REE geochemical characteristics of the ores and related rocks show that primary fluids originated from magmatic differentiation in lower pressure of shallow crust, ore-forming hydrothermal solutions gained REE and mineralization elements further from leaching the magmatic rocks, then superimposed and reformed the limestones or marbles and deposited ore-forming material.

Dynamic disaster control of backfill mining under thick magmatic rock in one side goaf:A case study

In order to explore the control effect of backfill mining on dynamic disasters under special geological mining conditions of overlying thick magmatic rock(TMR),a three-dimensional numerical model of a panel of one side goaf in Yangliu coal mine with double-yield backfill material constitutive model was developed.The simulation results were then compared with field monitoring data.The dynamic disaster control effect of both caving and backfill mining was analyzed in three different aspects,i.e.,displacement field,stress field and energy field.The results show that in comparison to the full caving mining method,the bearing capacity of the goaf after backfilling was enhanced,the backfill mining can effectively reduce the stress and energy accumulated in the coal/rock body,and the backfill mining eliminates the further moving space of TMR and prevents its sudden rupture.Before TMR fracture,the subsidence displacement of TMR was reduced by 65.3%,the front abutment stress of panel decreased by 9.4%on average and the high energy concentration zone around panel was also significantly reduced.Overall,the results of this study provide deeper insights into the control of dynamic disasters by backfill mining in mines.

Rare Earths of Magmatic Rocks in Yanshanian Stage in Adjacent Region of Anhui and Jiangxi Provinces, Jiangnan Uplift

The geochemical characteristics of rare earth elements of magmatic rocks of Yanshanian stage were studied in the south of Anhui Province and northeast of Jiangxi Province, Jiangnan Uplift. The result shows that the magmatic rocks of Yanshanian stage in the south of Anhui Province are the typical crust source type and those in the northeast of Jiangxi Province have the characteristics of mantle source type. So the polymetal deposits having relation to the magmatic rocks of Yanshanian stage in the northeast of Jiangxi Province were developed better than those in the south of Anhui Province. The research results of the rare earth elements are confirmed by the studies of geophysics,tectonic setting and stable isotope at the same time. It also indicates that the rare earth elements are the effective approach to tracing the material sources of magmatic rocks.

Platinum-group Elements Geochemistry of the Yangliuping Magmatic Ni-Cu-PGE Sulfide Deposit:Implications of Its Genetic Link with the Extrusive Basalts

Primitive mantle normalized Platinum group elements (PGE) concentration patterns for the Zhengziyanwo intrusion and Dashibao Formation basalts are of positive slope, similar to most of the world class magmatic Ni Cu PGE sulfide deposits. Characters of this intrusion and its related ores and Dashibao Formation basalts are their negative Pt anomaly and high concentration of Rh relative to Pt and Pd, facts being interpreted to be the results of crystallization and fractionation of Pt alloys and spinel phase free crystallization history for the magma, respectively. PGE parameters of the Dashibao Formation basalts are consistent with the general trend of those found for the Zhengziyanwo intrusion, and this might infer a genetic link between them.

Source Lithology and Magmatic Processes Recorded in the Mineral of Basalts from the Parece Vela Basin

Since the Early Cenozoic,the Philippine Sea Plate(PSP)has undergone a complex tectonic evolution.During this period the Parece Vela Basin(PVB)was formed by seafloor spreading in the back-arc region of the proto-Izu-Bonin-Mariana(IBM)arc.However,until now,studies of the geological,geophysical,and tectonic evolution of the PVB have been rare.In this study,we obtained in situ trace element and major element compositions of minerals in basalts collected from two sites in the southern part of the PVB.The results reveal that the basalts from site CJ09-63 were likely formed via~10%partial melting of spinel-garnet lherzolite,while the basalts from site CJ09-64 were likely formed via 15%–25%partial melting of garnet lherzolite.The order of mineral crystallization for the basalts from site CJ09-64 was olivine,spinel,clinopyroxene,and plagioclase,while the plagioclase in the basalts from site CJ09-63 crystallized earlier than the clinopyroxene.Using a plagioclase-liquid hygrometer and an olivine-liquid oxybarometer,we determined that the basalts in this study have high H2O contents and oxygen fugacities,suggesting that the magma source of the Parece Vela basalts was affected by subduction components,which is consistent with the trace element composition of whole rock.

Geochemical Features of Trace and Rare Earth Elements of Pumice in Middle Okinawa Trough and Its Indication of Magmatic Process

Pumice,the most widely distributed volcanic rock in Okinawa Trough,is loose and porous.Since its formation,it has definitely suffered from the denudation of the sea to different degrees.In order to truly reveal the geochemical features of pumice,we choose the method of mineral separation.Firstly,the phenocryst is separated from glass.Then the phenocryst is divided into light and heavy mineral compositions.By ICP-MS(inductively coupled plasma mass spectrometry) analytical technology,the contents of trace and rare earth elements in the whole pumice,the glass and the heavy and light mineral compositions are determined respectively.By researching the elemental geochemical features,the magma dynamic processes are found.It shows that the initial magma for the pumice in Okinawa Trough came from the depleted mantle,from which the N-MORB(normal type of mid-ocean ridge basalt) is formed,homologous with the local basalts.But they are formed in different periods of magma crystal fractionation.Featured with sufficient crystal fractionation for pumice,it is found that the earlier crystallizing minerals are olivine,plagioclase and pyroxene.The pumice magma,formed from the depleted mantle,was mixed with additional subduction-related materials(components),and contaminated with the mass from upper crust when it rose up into the crust.As the Okinawa Trough is a back-arc basin in its early back-arc spreading stage,its magmatism has a series of its own unique characteristics,different from not only the mid-ocean ridge expansion,but also the mature back-arc basin.