Abundant porphyritic granites, including Grt-bearing and Bt-bearing porphyritic granites, and porphyritic potash-feldspar granite (trondhjemite-granitic composition) are widely distributed within the Kovela granitic c...Abundant porphyritic granites, including Grt-bearing and Bt-bearing porphyritic granites, and porphyritic potash-feldspar granite (trondhjemite-granitic composition) are widely distributed within the Kovela granitic complex Southern Finland, which associated with monazite-bearing dikes (strong trondhjemite composition). The investigated monazite-bearing dikes are dominated by a quartz + K-feldspar + plagioclase + biotite + garnet + monazite assemblage. The monazite forms complexly zoned subhedral to euhedral crystals variable in size (100 - 1500 μm in diameter) characterized by high Th content. The chemical zoning characterised as: 1) concentric, 2) patchy, and 3) intergrowth-like. Textural evidence suggests that these accessory minerals crystallized at an early magmatic stage, as they are commonly associated with clusters of the observed variations in their chemical composition are largely explained by the huttonite exchange , and subordinately by the cheralite exchange with proportions of huttonite (ThSiO4) and cheralite [CaTh(PO4)2] up to 20.4% and 9.8%, respectively. Textural evidence suggests that these monazites and associated Th-rich minerals (huttonite/thorite) crystallized at an early magmatic stage, rather than metamorphic origin. The total lanthanide and actinide contents in monazite and host dikes are strongly correlated. Mineral compositions applied to calculate P-T crystallization conditions using different approaches reveal a temperature range of 700°C - 820°C and pressure 3 - 6 kbars for the garnet-biotite geothermometry. P-T pseudo-section analyses calculated using THERMOCALC software for the bulk compositions of suitable rock types, constrain the PT conditions of garnet growth equilibration within the range of 5 - 6 kbars and 760°C - 770°C respectively. Empirical calculations and pseudo-section approaches indicate a clockwise P-T path for the rocks of the studied area. 207Pb/206Pb dating of monazite by LA-MC-ICPMS revealed a recrystallization period at around 1860 - 1840 Ma. These ages are related to the tectonic-thermal event associated with the intense crustal melting and intra-orogenic intrusions, constraining the youngest time limit for metamorphic processes in the Kovela granitic complex.展开更多
New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase m...New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase metamorphic history, with peak Barrovian metamorphism at (32 2±0 4)Ma and a later high\|temperature, low\|pressure event (620℃, 400MPa) at (22 7±0 2)Ma.. Emplacement and crystallization of the Everest granite subsequently occurred at 20 5～21 3Ma. The monazite crystallization ages that differ by 10Ma are recorded in two structurally adjacent rocks of different lithology, which have the same post collisional p—T history.. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armoured within silicate minerals. During the low\|pressure metamorphic event, the armouring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite\|producing reactants, and spots within monazite that are rich in Ca, Fe, Al and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence.展开更多
Eastern Qinling,China is one of the important rare metal metallogenic provinces with extensively distributed granite pegmatite dikes.The No.5 granite pegmatite intruded into the granitic gneiss of the Qinling Group,an...Eastern Qinling,China is one of the important rare metal metallogenic provinces with extensively distributed granite pegmatite dikes.The No.5 granite pegmatite intruded into the granitic gneiss of the Qinling Group,and the major minerals are quartz(39.8%),K-feldspar(18.8%),albite(36.3%),muscovite(3.4%),and garnet(1.1%).Monazite U–Pb isotopic dating indicates that the No.5 pegmatite from the Eastern Qinling was emplaced at ca.420.2±2.2 Ma,which confirms that highpurity quartz mineralization probably formed during the Early Devonian.In-situ laser ablation inductively coupled plasma mass spectrometry analysis of quartz show that quartz samples from Eastern Qinling have total trace element concentrations(Al,Ti,Sc,Li,B,Cr,Mn,and Fe)ranging from 23.2 to 52.8 ppm,slightly higher than the quartz(impurity element content from 13.4 to 25.9 ppm)of the Spruce Pine high-purity quartz deposit in western North Carolina.The No.5 pegmatite of Eastern Qinling could be defined as one high-purity quartz deposit of China.展开更多
Understanding the mechanisms of parent-daughter isotopic mobility at the nanoscale is key to rigorous interpretation of Ue The Pb data and associated dating. Until now, all nanoscale geochronological studies on geolog...Understanding the mechanisms of parent-daughter isotopic mobility at the nanoscale is key to rigorous interpretation of Ue The Pb data and associated dating. Until now, all nanoscale geochronological studies on geological samples have relied on either Transmission Electron Microscope(TEM) or Atom Probe Microscopy(APM) characterizations alone, thus suffering from the respective weaknesses of each technique. Here we focus on monazite crystals from a ~1 Ga, ultrahigh temperature granulite from Rogaland(Norway). This sample has recorded concordant UeP b dates(measured by LA-ICP-MS) that range over 100 My, with the three domains yielding distinct isotopic Ue Pb ages of 1034 ± 6 Ma(D1; Srich core), 1005 ± 7 Ma(D2), and 935 ± 7 Ma(D3), respectively. Combined APM and TEM characterization of these monazite crystals reveal phase separation that led to the isolation of two different radiogenic Pb(Pb*) reservoirs at the nanoscale. The S-rich core of these monazite crystals contains Cae Srich clusters, 5 -10 nm in size, homogenously distributed within the monazite matrix with a mean interparticle distance of 40 -60 nm. The clusters acted as a sink for radiogenic Pb(Pb*) produced in the monazite matrix, which was reset at the nanoscale via Pb diffusion while the grain remained closed at the micro-scale. Compared to the concordant ages given by conventional micro-scale dating of the grain,the apparent nano-scale age of the monazite matrix in between clusters is about 100 Myr younger, which compares remarkably well to the duration of the metamorphic event. This study highlights the capabilities of combined APM-TEM nano-structural and nano-isotopic characterizations in dating and timing of geological events, allowing the detection of processes untraceable with conventional dating methods.展开更多
New metamorphic petrology and geochronology from the Loe Sar dome in the Swat region of northern Pakistan place refined constraints on the pressure, temperature and timing of metamorphism and deformation in that part ...New metamorphic petrology and geochronology from the Loe Sar dome in the Swat region of northern Pakistan place refined constraints on the pressure, temperature and timing of metamorphism and deformation in that part of the Himalayan orogen. Thermodynamic modelling and monazite petrochronology indicate that metamorphism in the area followed a prograde evolution from ～525 ± 25 ℃and 6 士 0.5 kbar to ～610 ± 25 ℃ and 9 士 0.5 kbar, between ca. 39 Ma and 28 Ma. Partitioning of heavy rare earth elements between garnet rims and 30-28 Ma monazite are interpreted to indicate coeval crystallization at peak conditions. Microtextural relationships indicate that garnet rim growth post-dated the development of the main foliation in the area. The regional foliation is folded about large-scale N-S trending fold axes and overprinting E-W trending folds to form km-scale domal culminations. The textural relationships observed indicate that final dome development must be younger than the 30-28 Ma monazite that grew with garnet rims post-regional foliation development, but pre-doming-related deformation. This new timing constraint helps resolve discrepancy between previous interpretations,which have alternately suggested that N-S trending regional folds must be either pre-or post-early Oligocene. Finally, when combined with existing hornblende and white mica cooling ages, these new data indicate that the study area was exhumed rapidly following peak metamorphism.展开更多
Gravity, magnetic and electrostatic separation methods allowed to obtain different titanium oxide concentrates (ilmenite, leucoxene, rutile) and different varieties of zircon concentrates (premium zircon, standard zir...Gravity, magnetic and electrostatic separation methods allowed to obtain different titanium oxide concentrates (ilmenite, leucoxene, rutile) and different varieties of zircon concentrates (premium zircon, standard zircon, medium grade zircon standard) from Senegal’s heavy mineral sands. During mining separation, monazite, which is a paramagnetic mineral, was found in a non-negligible concentration of 0.57 wt% on average in the medium grade zircon standard which also contains 37.96 wt% zircon and 44.46 wt% titanium oxides. Magnetic and gravity separation tests were carried out on the Medium grade zircon standard (MGZS) to produce a monazite concentrate at Eramet Ideas laboratory. Magnetic separation at 1.5 teslas intensity resulted in the recovery of 94.8% of the monazite from the MGZS. Gravity separation also recovered 76.6% of the monazite from the MGZS. The combination of these two treatment methods can thus produce three concentrates from MGZS (a monazite concentrate, a zircon concentrate, and a titanium oxide concentrate).展开更多
The Mushgai khudag volcanic-plutonic complex consists of four REE mineralization zones: carbonatite zone, apatite zone, magnetite zone, and monazite zone. REE mineralization occurs within peripheries of alkaline magma...The Mushgai khudag volcanic-plutonic complex consists of four REE mineralization zones: carbonatite zone, apatite zone, magnetite zone, and monazite zone. REE mineralization occurs within peripheries of alkaline magmatic rocks which consist of porphyritic syenite, microsyenite and quartz syenites. Three types of LREE-rich apatite can be found in the carbonatite, apatite, and monazite zones. Crystal-1 type of apatite exists as hexagonal prismatic shape and is mostly found in the apatite zone, and in syenite. Crystal-2 type of apatite can be exposed also at the apatite zone, and carbonatite zone as brecciated massive crystalline aggregate. Crystal-3 type of apatite demonstrates the compositional zoning texture with monazite as inter-zoning, and is only found in monazite zone. The LREE-bearing apatites from the Mushgai khudag complex are mostly fluorapatite to hydroxyl-bearing fluorapatite with variable REE content. Apatites from the monazite zone present individual sulfur-rich monazite grain, and are formed by comprehensive substitutions.展开更多
The behavior of monazite concentrate reduced by carbon, especially the decomposed procedure of rare earth phosphates, was investigated by X ray diffraction , electron probe, TG method and chemical analysis. The result...The behavior of monazite concentrate reduced by carbon, especially the decomposed procedure of rare earth phosphates, was investigated by X ray diffraction , electron probe, TG method and chemical analysis. The results show that rare earth phosphates in monazite concentrate can be reduced to their oxides, among them the decomposition processes of cerium phosphate are not in step with lanthanum phosphate, neodymium phosphate and so on, and the phosphorus was volatilized into air in simple form.展开更多
The Madi rare metal granite is a complex massif,which contains a variety of rare metals,such as Nb,Ta,Li,and Be.In this paper,the geochemical characteristics of the granite were obtained by multi-collector inductively...The Madi rare metal granite is a complex massif,which contains a variety of rare metals,such as Nb,Ta,Li,and Be.In this paper,the geochemical characteristics of the granite were obtained by multi-collector inductively coupled mass spectrometry(MC-ICP-MS).The precise crystalline age of the granite was obtained from monazite U-Pb dating,and the source of the granite was determined using Li-Nd isotopes.The Madi rare metal granite is a high-K(calc-alkaline),peraluminous,S-type granite.The U-Pb monazite age indicates that the crystalline age of the granite is 175.6 Ma,which is Early Jurassic.The granite is characterized by a relatively wide range ofδ7 Li values(+2.99‰to+5.83‰)and high lithium concentrations(181 ppm to 1022 ppm).The lithium isotopic composition of the granite does not significantly correlate with the degree of magmatic differentiation.An insignificant amount of lithium isotope fractionation occurred during the granitic differentiation.The lithium isotopic composition of the granite significantly differs from that of the wall rock,but it is very similar to that of a primitive mantle peridotite xenolith(meanδ7 Li value+3.5‰).The plot of Li concentration versusδ7 Li indicates that the Li isotopic composition of the granite is similar to that of island arc lavas.Based on the above-described evidence,the granite was mainly derived from the crust,but it was contaminated by a deep granitic magma.展开更多
This study presents a re-examination of historical specimens(DG136 and DG167)from the Monashee complex in the southeastern Canadian Cordillera that are critical to the current understanding of rare earth element(REE)d...This study presents a re-examination of historical specimens(DG136 and DG167)from the Monashee complex in the southeastern Canadian Cordillera that are critical to the current understanding of rare earth element(REE)distribution between garnet and monazite(and other accessory minerals)during metamorphism.Nine-hundred and fifty-one new monazite petrochronology spot analyses on 29 different grains across two specimens outline detailed(re)crystallization histories.Trace element data collected from the same ablated volume,interpreted in the context of new phase equilibria modelling that includes monazite,xenotime and apatite,link ages to specific portions of the pressure-temperature(P-T)paths followed by the specimens.These linkages are further informed by garnet Lu-Hf geochronology and xenotime petrochronology.The clockwise P-T paths indicate prograde metamorphism was ongoing by ca.80 Ma in both specimens.The structurally deeper specimen,DG136,records peak P-T conditions of~755-770℃and 8.8-10.4 kbar,interpreted to coincide with(re-)crystallization of low Y monazite at~75-70 Ma.Near-rim garnet isopleths from DG167 cross in the observed peak assemblage field at~680℃ and 9.3 kbar.These conditions are interpreted to correspond with low Y monazite(re-)crystallisation at~65 Ma.Both specimens record decompression along their retrograde path coincident with high Y 70-55 Ma and 65-55 Ma monazite populations in DG136 and DG167,respectively.These findings broadly agree with those initially reported~20 years ago and confirm early interpretations using trace elements in monazite as generally reliable markers of metamorphic reactions.Modern phase equilibria modelling and in situ petrochronological analysis,however,provide additional insight into monazite behaviour during anatexis and the effects of potential trace element buffering by REE-bearing phases such as apatite.展开更多
The poly-phase orogeny information included in one orogenic belt is the key for studying the regional tectonic evolution at different time period.It also has important significance of understanding the rock association
The monazite deposit at Andoharano is 7 km NE of Ambatofinandrahana.It is in the form of filons of hydrothermal chalcedony origin both with monazite and barite,which intersects the small syenitic post-tectonic massif,...The monazite deposit at Andoharano is 7 km NE of Ambatofinandrahana.It is in the form of filons of hydrothermal chalcedony origin both with monazite and barite,which intersects the small syenitic post-tectonic massif,aged 550 to 510 Ma.The syenite is part of the Ambalavao-Kiangara-Maevaranomagmatic suite located in the Itremo sub-domain.The mineralized filon’s length is approximately 100 meters with an average thickness of 2 to 5 meters,direction N75 and a subvertical dip.It is characterized by the mineralogical association of monazite,chalcedony,barite,quartz and magnetite.Two deformation phases affect the emplacement of the deposit.The first phase corresponds to the crystallization of the automorphic monazites,while the second phase affects the filon which leads to the fracturing of the first through silicification and which leads to the formation of the small xenomorphic monazite crystals.The monazite appears as brownish spots scattered in the rocks.It is rich in ceric earth(32%to 33%)and low in thorium.It constitutes ceric earth ore in the region.展开更多
The Mushgai khudag volcanic-plutonic complex consists of four REE mineralization zones: carbonatite zone, apatite zone, magnetite zone, and monazite zone. REE mineralization occurs within peripheries of alkaline magma...The Mushgai khudag volcanic-plutonic complex consists of four REE mineralization zones: carbonatite zone, apatite zone, magnetite zone, and monazite zone. REE mineralization occurs within peripheries of alkaline magmatic rocks which consist of porphyritic syenite, microsyenite and quartz syenites. Three types of LREE-rich apatite can be found in the carbonatite, apatite, and monazite zones. Crystal-1 type of apatite exists as hexagonal prismatic shape and is mostly found in the apatite zone, and in syenite. Crystal-2 type of apatite can be exposed also at the apatite zone, and carbonatite zone as brecciated massive crystalline aggregate. Crystal-3 type of apatite demonstrates the compositional zoning texture with monazite as inter-zoning, and is only found in monazite zone. The LREE-bearing apatites from the Mushgai khudag complex are mostly fluorapatite to hydroxyl-bearing fluorapatite with variable REE content. Apatites from the monazite zone present individual sulfur-rich monazite grain, and are formed by comprehensive substitutions.展开更多
The Late Cenozoic strata are 313 m thick, revealed by the drilling core PD-99 in the south Changjiang delta. Monazite chemical dating shows that 350-500-Ma monazites predominate in the Pliocene and 100-275-Ma monazite...The Late Cenozoic strata are 313 m thick, revealed by the drilling core PD-99 in the south Changjiang delta. Monazite chemical dating shows that 350-500-Ma monazites predominate in the Pliocene and 100-275-Ma monazites in the Quaternary, indicating a great change of their provenance. The first presence horizon of monazites younger than 25 Ma is just above the Matruyama/Gauss boundary (~2.58 Ma), whch is exactly when uplift of the Tibetan Plateau began to influence deposition in the East China Sea. Variations in contents of monazites younger than 25 Ma can be divided into two sections. The Early-Middle Pleistocene with less <25 Ma monazites corresponds with rapid uplift of the Tibetan Plateau, and the Late Pleistocene with more <25 Ma monazites parallels the peak uplift of the Tibetan Plateau. This study demonstrates that chemical dating of monazites in the river-mouth strata is a useful method to explore changes of river drainage basins, and deconvolute multistage tectonic and magmatic activity histories in the provenance areas.展开更多
Electron probe microanalysis(EPMA) dating of monazite has been developed over decades. However, limited by the detectability and analytical sensitivity of dating-related elements(Th, Pb, U and Y), the EPMA dating has ...Electron probe microanalysis(EPMA) dating of monazite has been developed over decades. However, limited by the detectability and analytical sensitivity of dating-related elements(Th, Pb, U and Y), the EPMA dating has been restricted to geological research. In this study, various probe currents, beam diameters and counting times have been utilized on a JEOL JXA-8230 electron microprobe to determine the optimal experimental conditions for measuring Th, Pb, U and Y in monazite. The optimal conditions are:(1) accelerating voltage is 15 k V;(2) probe current is 100 n A;(3) beam diameter is 1 μm;(4) the peak and background counting time of U and Pb are 200 and 100 s;and(5) the peak and background counting time of Th and Y are 100 and 50 s. We apply this method to monazite from garnet-bearing biotite gneiss in the Zanhuang area of the Central Orogenic Belt of the North China Craton. The Pb O-Th O2* isochron age calculated by EPMA data is 1 812±17 Ma(MSWD=2.06), which is similar to the weighted mean 207 Pb/206 Pb age(1 805±12 Ma, MSWD=1.07) obtained by LA-ICP-MS. This study suggests that EPMA dating of monazite as a powerful dating technique can be widely used in geochronological study.展开更多
Low thermal conductivity, matched thermal expansion coefficient and good compatibility are general requirements for the environmental/thermal barrier coatings(EBCs/TBCs) and interphases for Al2O3 f/Al2O3 composites. I...Low thermal conductivity, matched thermal expansion coefficient and good compatibility are general requirements for the environmental/thermal barrier coatings(EBCs/TBCs) and interphases for Al2O3 f/Al2O3 composites. In this work, a novel high-entropy(HE) rare-earth phosphate monazite ceramic (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 is designed and successfully synthesized. This new type of HE rare-earth phosphate monazite exhibits good chemical compatibility with Al2O3, without reaction with Al2O3 as high as 1600℃ in air. Moreover, the thermal expansion coefficient(TEC) of HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4(8.9 × 10^-6/℃ at 300–1000℃) is close to that of Al2O3. The thermal conductivity of HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 at room temperature is as low as 2.08 W·m^-1·K^-1, which is about 42% lower than that of La PO4. Good chemical compatibility, close TEC to that of Al2O3, and low thermal conductivity indicate that HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 is suitable as a candidate EBC/TBC material and an interphase for Al2O3 f/Al2O3 composites.展开更多
Monazite((Ce,La)PO_(4))is one of the major types of light rare earth minerals from which the light rare earth elements cerium(Ce)and lanthanum(La)are economically extracted.Flotation is extensively used to recover fin...Monazite((Ce,La)PO_(4))is one of the major types of light rare earth minerals from which the light rare earth elements cerium(Ce)and lanthanum(La)are economically extracted.Flotation is extensively used to recover fine-grained monazite.Sodium oleate(NaOL)is considered as the collector with strong collecting ability for monazite flotation.However,this study shows that its collecting ability is still limited.In this paper,a phosphonic acid,nonane-1,1-bisphosphonic acid(C9-BPA),was employed as the novel collector in place of NaOL.Flotation experiments show that even when the C9-BPA dosage is less than one-fifth of the NaOL dosage,the monazite recove ry using C9-BPA as the collector is approximately 22 wt%higher than that using NaOL.The mechanism by which C9-BPA adsorbs on monazite was investigated using zeta potential,infrared(IR)spectroscopy and X-ray photoelectron spectroscopy(XPS)measurements as well as first-principles calculations.Zeta potential measurements show a more significant decrease in the zeta potentials of monazite after the addition of C9-BPA compared to those after the addition of NaOL.For C9-BPA-treated monazite,the characteristic peaks of C9-BPA are observed in the IR and C 1 s XPS spectrum,whereas for monazite treated by NaOL,no characteristic peak of NaOL was observed.Experimental results show that C9-BPA has a stronger affinity towards the monazite surface than NaOL as confirmed by the higher adsorption energy of CP-BPA on the monazite surface(-204.22 kJ/mol)than NaOL(-48.48 kJ/mol).This study demonstrates an extensive application value and prospect of C9-BPA in monazite flotation and helps design novel collectors with strong collecting ability for monazite flotation.展开更多
Monazite is an important accessory mineral in the pelitic granulites(Weihai area,Sulu orogen),and is also a powerful monitor for understanding the metamorphic evolution of the granulites.The pelitic granulites incongr...Monazite is an important accessory mineral in the pelitic granulites(Weihai area,Sulu orogen),and is also a powerful monitor for understanding the metamorphic evolution of the granulites.The pelitic granulites incongruously occur as lenses in granitic gneisses.The lithologies of the lenses gradually change from core to margin:The undeformed coarse-grained granulite,the foliated fine-grained granulite,the garnet-biotite-gneiss,and the migmatized granulite.The lens cores mostly preserve a peak granulite-facies metamorphic mineral assemblage of garnet+plagioclase(antiperthite)+quartz+sillimanite+biotite with accessory minerals of rutile,zircon,and monazite.The lens margins display a fluid-induced retrogression.In order to decipher the metamorphic processes of the pelitic granulites,a combined study of BSE imaging,U-Pb dating,and trace element composition for the monazites from the metapelitic lens were conducted.Monazites from the undeformed coarse-grained granulite only record a Paleoproterozoic age(1832±7 Ma,n=40).Monazites from the other lithologies yield the inherited Paleoproterozoic age and Triassic overgrowth age.For example,monazites from the migmatite yield intercept ages of 1818±10 and 211±22 Ma(n=56)with Triassic concordant age of 223.8±2.9 Ma.The Paleoproterozoic monazites are characterized by remarkable depletion in HREE and Y with obviously negative Eu anomalies,indicating their formation equilibrated with garnet and feldspar under granulite-facies conditions.During Triassic fluid modification,the monazite bright rims assimilated Th and Si but released U,HREE,Y,and P.This process resulted in that the Triassic overgrowth monazites have higher HREE and Y contents,and lower Th and U contents with relatively low Th/U ratios.Thus,the monazites in the pelitic granulites recorded a Paleoproterozoic metamorphic event and Triassic fluid modification.The Weihai pelitic granulites might have a tectonic affinity with the North China Craton.Therefore,the Paleoproterozoic pelitic granulites were mechanically drawn into the orogen during the Triassic continental collision,and subsequently were remoulded by the fluids during its exhumation.展开更多
The West Kunlun orogenic belt(WKOB) along the northern margin of the Tibetan Plateau is important for understanding the evolution of the Proto-and Paleo-Tethys oceans. Previous investigations have focused on the igneo...The West Kunlun orogenic belt(WKOB) along the northern margin of the Tibetan Plateau is important for understanding the evolution of the Proto-and Paleo-Tethys oceans. Previous investigations have focused on the igneous rocks and ophiolites distributed mostly along the Xinjiang-Tibet road and the China-Pakistan road, and have constructed a preliminary tectonic model for this orogenic belt. However, few studies have focused on the so-called Precambrian basement in this area. As a result, the tectonic affinity of the individual terranes of the WKOB and their detailed evolution process are uncertain. Here we report new field observations, zircon and monazite U-Pb ages of the "Precambrian basement" of the South Kunlun terrane(SKT) and the Tianshuihai terrane(TSHT), two major terranes in the WKOB. Based on new zircon U-Pb age data, the amphibolite-facies metamorphosed volcanosedimentary sequence within SKT was deposited during the late Neoproterozoic to Cambrian(600-500 Ma), and the flysch-affinity Tianshuihai Group, as the basement of the TSHT, was deposited during the late Neoproterozoic rather than Mesoproterozoic. The rock association of the volcano-sedimentary sequence within SKT suggests a large early Paleozoic accretionary wedge formed by the long-term lowangle southward subduction of the Proto-Tethys Ocean between Tarim and TSHT. The amphibolitefacies metamorphism in SKT occurred at ca. 440 Ma. This ca. 440 Ma metamorphism is genetically related to the closure of the Proto-Tethys Ocean between Tarim and the Tianshuihai terrane, which led to the assembly of Tarim to Eastern Gondwana and the final formation of the Gondwana. Since the late Paleozoic to early Mesozoic, the northward subduction of the Paleo-Tethys Ocean along the HongshihuQiaoertianshan belt produced the voluminous early Mesozoic arc-signature granites along the southern part of NKT-TSHT. The Paleo-Tethys ocean between TSHT and Karakorum closed at ca. 200 Ma, as demonstrated by the monazite age of the paragneiss in the Kangxiwa Group. Our study does not favor the existence of a Precambrian basement in SKT.展开更多
文摘Abundant porphyritic granites, including Grt-bearing and Bt-bearing porphyritic granites, and porphyritic potash-feldspar granite (trondhjemite-granitic composition) are widely distributed within the Kovela granitic complex Southern Finland, which associated with monazite-bearing dikes (strong trondhjemite composition). The investigated monazite-bearing dikes are dominated by a quartz + K-feldspar + plagioclase + biotite + garnet + monazite assemblage. The monazite forms complexly zoned subhedral to euhedral crystals variable in size (100 - 1500 μm in diameter) characterized by high Th content. The chemical zoning characterised as: 1) concentric, 2) patchy, and 3) intergrowth-like. Textural evidence suggests that these accessory minerals crystallized at an early magmatic stage, as they are commonly associated with clusters of the observed variations in their chemical composition are largely explained by the huttonite exchange , and subordinately by the cheralite exchange with proportions of huttonite (ThSiO4) and cheralite [CaTh(PO4)2] up to 20.4% and 9.8%, respectively. Textural evidence suggests that these monazites and associated Th-rich minerals (huttonite/thorite) crystallized at an early magmatic stage, rather than metamorphic origin. The total lanthanide and actinide contents in monazite and host dikes are strongly correlated. Mineral compositions applied to calculate P-T crystallization conditions using different approaches reveal a temperature range of 700°C - 820°C and pressure 3 - 6 kbars for the garnet-biotite geothermometry. P-T pseudo-section analyses calculated using THERMOCALC software for the bulk compositions of suitable rock types, constrain the PT conditions of garnet growth equilibration within the range of 5 - 6 kbars and 760°C - 770°C respectively. Empirical calculations and pseudo-section approaches indicate a clockwise P-T path for the rocks of the studied area. 207Pb/206Pb dating of monazite by LA-MC-ICPMS revealed a recrystallization period at around 1860 - 1840 Ma. These ages are related to the tectonic-thermal event associated with the intense crustal melting and intra-orogenic intrusions, constraining the youngest time limit for metamorphic processes in the Kovela granitic complex.
文摘New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase metamorphic history, with peak Barrovian metamorphism at (32 2±0 4)Ma and a later high\|temperature, low\|pressure event (620℃, 400MPa) at (22 7±0 2)Ma.. Emplacement and crystallization of the Everest granite subsequently occurred at 20 5～21 3Ma. The monazite crystallization ages that differ by 10Ma are recorded in two structurally adjacent rocks of different lithology, which have the same post collisional p—T history.. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armoured within silicate minerals. During the low\|pressure metamorphic event, the armouring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite\|producing reactants, and spots within monazite that are rich in Ca, Fe, Al and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence.
基金the National Natural Science Foundation of China(42062006 and 41962007)the National Key Research and Development Program of China(2016YFC0600207)+1 种基金the Project of China Geological Survey(DD20190186 and 12120114034501)the science and technology research project of Jiangxi Provincial Department of Education(GJJ190379)。
文摘Eastern Qinling,China is one of the important rare metal metallogenic provinces with extensively distributed granite pegmatite dikes.The No.5 granite pegmatite intruded into the granitic gneiss of the Qinling Group,and the major minerals are quartz(39.8%),K-feldspar(18.8%),albite(36.3%),muscovite(3.4%),and garnet(1.1%).Monazite U–Pb isotopic dating indicates that the No.5 pegmatite from the Eastern Qinling was emplaced at ca.420.2±2.2 Ma,which confirms that highpurity quartz mineralization probably formed during the Early Devonian.In-situ laser ablation inductively coupled plasma mass spectrometry analysis of quartz show that quartz samples from Eastern Qinling have total trace element concentrations(Al,Ti,Sc,Li,B,Cr,Mn,and Fe)ranging from 23.2 to 52.8 ppm,slightly higher than the quartz(impurity element content from 13.4 to 25.9 ppm)of the Spruce Pine high-purity quartz deposit in western North Carolina.The No.5 pegmatite of Eastern Qinling could be defined as one high-purity quartz deposit of China.
基金Both UJM and CNRS (INSU TelluS-SYSTER) are thanked for financial support for AMSG and ATL. The Australian Resource Characterisation Facility (ARCF), under the auspices of the National Resource Sciences Precinct (NRSP) - a collaboration between CSIRO, Curtin University and The University of Western Australia e is supported by the Science and Industry Endowment Fund (SIEF RI13-01)
文摘Understanding the mechanisms of parent-daughter isotopic mobility at the nanoscale is key to rigorous interpretation of Ue The Pb data and associated dating. Until now, all nanoscale geochronological studies on geological samples have relied on either Transmission Electron Microscope(TEM) or Atom Probe Microscopy(APM) characterizations alone, thus suffering from the respective weaknesses of each technique. Here we focus on monazite crystals from a ~1 Ga, ultrahigh temperature granulite from Rogaland(Norway). This sample has recorded concordant UeP b dates(measured by LA-ICP-MS) that range over 100 My, with the three domains yielding distinct isotopic Ue Pb ages of 1034 ± 6 Ma(D1; Srich core), 1005 ± 7 Ma(D2), and 935 ± 7 Ma(D3), respectively. Combined APM and TEM characterization of these monazite crystals reveal phase separation that led to the isolation of two different radiogenic Pb(Pb*) reservoirs at the nanoscale. The S-rich core of these monazite crystals contains Cae Srich clusters, 5 -10 nm in size, homogenously distributed within the monazite matrix with a mean interparticle distance of 40 -60 nm. The clusters acted as a sink for radiogenic Pb(Pb*) produced in the monazite matrix, which was reset at the nanoscale via Pb diffusion while the grain remained closed at the micro-scale. Compared to the concordant ages given by conventional micro-scale dating of the grain,the apparent nano-scale age of the monazite matrix in between clusters is about 100 Myr younger, which compares remarkably well to the duration of the metamorphic event. This study highlights the capabilities of combined APM-TEM nano-structural and nano-isotopic characterizations in dating and timing of geological events, allowing the detection of processes untraceable with conventional dating methods.
基金supported by a Higher Education Commission of Pakistan Post-Doctoral Scholarship to A. Ali, NSERC Discovery Grant and Canada Foundation for Innovation grants to K. Larson, and NSF grant NSF-EAR-1119380 to J. Cottle. D. Arkinstall is thanked for his assistance in the FiLTER
文摘New metamorphic petrology and geochronology from the Loe Sar dome in the Swat region of northern Pakistan place refined constraints on the pressure, temperature and timing of metamorphism and deformation in that part of the Himalayan orogen. Thermodynamic modelling and monazite petrochronology indicate that metamorphism in the area followed a prograde evolution from ～525 ± 25 ℃and 6 士 0.5 kbar to ～610 ± 25 ℃ and 9 士 0.5 kbar, between ca. 39 Ma and 28 Ma. Partitioning of heavy rare earth elements between garnet rims and 30-28 Ma monazite are interpreted to indicate coeval crystallization at peak conditions. Microtextural relationships indicate that garnet rim growth post-dated the development of the main foliation in the area. The regional foliation is folded about large-scale N-S trending fold axes and overprinting E-W trending folds to form km-scale domal culminations. The textural relationships observed indicate that final dome development must be younger than the 30-28 Ma monazite that grew with garnet rims post-regional foliation development, but pre-doming-related deformation. This new timing constraint helps resolve discrepancy between previous interpretations,which have alternately suggested that N-S trending regional folds must be either pre-or post-early Oligocene. Finally, when combined with existing hornblende and white mica cooling ages, these new data indicate that the study area was exhumed rapidly following peak metamorphism.
文摘Gravity, magnetic and electrostatic separation methods allowed to obtain different titanium oxide concentrates (ilmenite, leucoxene, rutile) and different varieties of zircon concentrates (premium zircon, standard zircon, medium grade zircon standard) from Senegal’s heavy mineral sands. During mining separation, monazite, which is a paramagnetic mineral, was found in a non-negligible concentration of 0.57 wt% on average in the medium grade zircon standard which also contains 37.96 wt% zircon and 44.46 wt% titanium oxides. Magnetic and gravity separation tests were carried out on the Medium grade zircon standard (MGZS) to produce a monazite concentrate at Eramet Ideas laboratory. Magnetic separation at 1.5 teslas intensity resulted in the recovery of 94.8% of the monazite from the MGZS. Gravity separation also recovered 76.6% of the monazite from the MGZS. The combination of these two treatment methods can thus produce three concentrates from MGZS (a monazite concentrate, a zircon concentrate, and a titanium oxide concentrate).
文摘The Mushgai khudag volcanic-plutonic complex consists of four REE mineralization zones: carbonatite zone, apatite zone, magnetite zone, and monazite zone. REE mineralization occurs within peripheries of alkaline magmatic rocks which consist of porphyritic syenite, microsyenite and quartz syenites. Three types of LREE-rich apatite can be found in the carbonatite, apatite, and monazite zones. Crystal-1 type of apatite exists as hexagonal prismatic shape and is mostly found in the apatite zone, and in syenite. Crystal-2 type of apatite can be exposed also at the apatite zone, and carbonatite zone as brecciated massive crystalline aggregate. Crystal-3 type of apatite demonstrates the compositional zoning texture with monazite as inter-zoning, and is only found in monazite zone. The LREE-bearing apatites from the Mushgai khudag complex are mostly fluorapatite to hydroxyl-bearing fluorapatite with variable REE content. Apatites from the monazite zone present individual sulfur-rich monazite grain, and are formed by comprehensive substitutions.
文摘The behavior of monazite concentrate reduced by carbon, especially the decomposed procedure of rare earth phosphates, was investigated by X ray diffraction , electron probe, TG method and chemical analysis. The results show that rare earth phosphates in monazite concentrate can be reduced to their oxides, among them the decomposition processes of cerium phosphate are not in step with lanthanum phosphate, neodymium phosphate and so on, and the phosphorus was volatilized into air in simple form.
基金the project of“Comprehensive integration and service of mineral geology and its metallogenic regularity in China”from China Geological Survey(Grant No.DD20160346)
文摘The Madi rare metal granite is a complex massif,which contains a variety of rare metals,such as Nb,Ta,Li,and Be.In this paper,the geochemical characteristics of the granite were obtained by multi-collector inductively coupled mass spectrometry(MC-ICP-MS).The precise crystalline age of the granite was obtained from monazite U-Pb dating,and the source of the granite was determined using Li-Nd isotopes.The Madi rare metal granite is a high-K(calc-alkaline),peraluminous,S-type granite.The U-Pb monazite age indicates that the crystalline age of the granite is 175.6 Ma,which is Early Jurassic.The granite is characterized by a relatively wide range ofδ7 Li values(+2.99‰to+5.83‰)and high lithium concentrations(181 ppm to 1022 ppm).The lithium isotopic composition of the granite does not significantly correlate with the degree of magmatic differentiation.An insignificant amount of lithium isotope fractionation occurred during the granitic differentiation.The lithium isotopic composition of the granite significantly differs from that of the wall rock,but it is very similar to that of a primitive mantle peridotite xenolith(meanδ7 Li value+3.5‰).The plot of Li concentration versusδ7 Li indicates that the Li isotopic composition of the granite is similar to that of island arc lavas.Based on the above-described evidence,the granite was mainly derived from the crust,but it was contaminated by a deep granitic magma.
文摘This study presents a re-examination of historical specimens(DG136 and DG167)from the Monashee complex in the southeastern Canadian Cordillera that are critical to the current understanding of rare earth element(REE)distribution between garnet and monazite(and other accessory minerals)during metamorphism.Nine-hundred and fifty-one new monazite petrochronology spot analyses on 29 different grains across two specimens outline detailed(re)crystallization histories.Trace element data collected from the same ablated volume,interpreted in the context of new phase equilibria modelling that includes monazite,xenotime and apatite,link ages to specific portions of the pressure-temperature(P-T)paths followed by the specimens.These linkages are further informed by garnet Lu-Hf geochronology and xenotime petrochronology.The clockwise P-T paths indicate prograde metamorphism was ongoing by ca.80 Ma in both specimens.The structurally deeper specimen,DG136,records peak P-T conditions of~755-770℃and 8.8-10.4 kbar,interpreted to coincide with(re-)crystallization of low Y monazite at~75-70 Ma.Near-rim garnet isopleths from DG167 cross in the observed peak assemblage field at~680℃ and 9.3 kbar.These conditions are interpreted to correspond with low Y monazite(re-)crystallisation at~65 Ma.Both specimens record decompression along their retrograde path coincident with high Y 70-55 Ma and 65-55 Ma monazite populations in DG136 and DG167,respectively.These findings broadly agree with those initially reported~20 years ago and confirm early interpretations using trace elements in monazite as generally reliable markers of metamorphic reactions.Modern phase equilibria modelling and in situ petrochronological analysis,however,provide additional insight into monazite behaviour during anatexis and the effects of potential trace element buffering by REE-bearing phases such as apatite.
基金funded by the National Science Foundation of China (No. 41572051)the China Geological Survey (No. DD20160022-01)project from Institute of Geology, Chinese Academy of Geological Sciences (J1518)
文摘The poly-phase orogeny information included in one orogenic belt is the key for studying the regional tectonic evolution at different time period.It also has important significance of understanding the rock association
文摘The monazite deposit at Andoharano is 7 km NE of Ambatofinandrahana.It is in the form of filons of hydrothermal chalcedony origin both with monazite and barite,which intersects the small syenitic post-tectonic massif,aged 550 to 510 Ma.The syenite is part of the Ambalavao-Kiangara-Maevaranomagmatic suite located in the Itremo sub-domain.The mineralized filon’s length is approximately 100 meters with an average thickness of 2 to 5 meters,direction N75 and a subvertical dip.It is characterized by the mineralogical association of monazite,chalcedony,barite,quartz and magnetite.Two deformation phases affect the emplacement of the deposit.The first phase corresponds to the crystallization of the automorphic monazites,while the second phase affects the filon which leads to the fracturing of the first through silicification and which leads to the formation of the small xenomorphic monazite crystals.The monazite appears as brownish spots scattered in the rocks.It is rich in ceric earth(32%to 33%)and low in thorium.It constitutes ceric earth ore in the region.
文摘The Mushgai khudag volcanic-plutonic complex consists of four REE mineralization zones: carbonatite zone, apatite zone, magnetite zone, and monazite zone. REE mineralization occurs within peripheries of alkaline magmatic rocks which consist of porphyritic syenite, microsyenite and quartz syenites. Three types of LREE-rich apatite can be found in the carbonatite, apatite, and monazite zones. Crystal-1 type of apatite exists as hexagonal prismatic shape and is mostly found in the apatite zone, and in syenite. Crystal-2 type of apatite can be exposed also at the apatite zone, and carbonatite zone as brecciated massive crystalline aggregate. Crystal-3 type of apatite demonstrates the compositional zoning texture with monazite as inter-zoning, and is only found in monazite zone. The LREE-bearing apatites from the Mushgai khudag complex are mostly fluorapatite to hydroxyl-bearing fluorapatite with variable REE content. Apatites from the monazite zone present individual sulfur-rich monazite grain, and are formed by comprehensive substitutions.
基金supported by the National Natural Science Foundation of China(Grant Nos.40176022,40276018 and 40476028).
文摘The Late Cenozoic strata are 313 m thick, revealed by the drilling core PD-99 in the south Changjiang delta. Monazite chemical dating shows that 350-500-Ma monazites predominate in the Pliocene and 100-275-Ma monazites in the Quaternary, indicating a great change of their provenance. The first presence horizon of monazites younger than 25 Ma is just above the Matruyama/Gauss boundary (~2.58 Ma), whch is exactly when uplift of the Tibetan Plateau began to influence deposition in the East China Sea. Variations in contents of monazites younger than 25 Ma can be divided into two sections. The Early-Middle Pleistocene with less <25 Ma monazites corresponds with rapid uplift of the Tibetan Plateau, and the Late Pleistocene with more <25 Ma monazites parallels the peak uplift of the Tibetan Plateau. This study demonstrates that chemical dating of monazites in the river-mouth strata is a useful method to explore changes of river drainage basins, and deconvolute multistage tectonic and magmatic activity histories in the provenance areas.
基金supported by the National Natural Science Foundation of China(No.41602234)the Fundamental Research Funds for the Central Universities,China University of Geosciences,Wuhan,China(Nos.CUGL180406,CUGCJ1707)Open Fund(No.GRMR201901)from the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Wuhan
文摘Electron probe microanalysis(EPMA) dating of monazite has been developed over decades. However, limited by the detectability and analytical sensitivity of dating-related elements(Th, Pb, U and Y), the EPMA dating has been restricted to geological research. In this study, various probe currents, beam diameters and counting times have been utilized on a JEOL JXA-8230 electron microprobe to determine the optimal experimental conditions for measuring Th, Pb, U and Y in monazite. The optimal conditions are:(1) accelerating voltage is 15 k V;(2) probe current is 100 n A;(3) beam diameter is 1 μm;(4) the peak and background counting time of U and Pb are 200 and 100 s;and(5) the peak and background counting time of Th and Y are 100 and 50 s. We apply this method to monazite from garnet-bearing biotite gneiss in the Zanhuang area of the Central Orogenic Belt of the North China Craton. The Pb O-Th O2* isochron age calculated by EPMA data is 1 812±17 Ma(MSWD=2.06), which is similar to the weighted mean 207 Pb/206 Pb age(1 805±12 Ma, MSWD=1.07) obtained by LA-ICP-MS. This study suggests that EPMA dating of monazite as a powerful dating technique can be widely used in geochronological study.
基金financially supported by the National Natural Science Foundation of China (Nos. 51672064 and U1435206)
文摘Low thermal conductivity, matched thermal expansion coefficient and good compatibility are general requirements for the environmental/thermal barrier coatings(EBCs/TBCs) and interphases for Al2O3 f/Al2O3 composites. In this work, a novel high-entropy(HE) rare-earth phosphate monazite ceramic (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 is designed and successfully synthesized. This new type of HE rare-earth phosphate monazite exhibits good chemical compatibility with Al2O3, without reaction with Al2O3 as high as 1600℃ in air. Moreover, the thermal expansion coefficient(TEC) of HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4(8.9 × 10^-6/℃ at 300–1000℃) is close to that of Al2O3. The thermal conductivity of HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 at room temperature is as low as 2.08 W·m^-1·K^-1, which is about 42% lower than that of La PO4. Good chemical compatibility, close TEC to that of Al2O3, and low thermal conductivity indicate that HE (La0.2Ce0.2Nd0.2Sm0.2Eu0.2)PO4 is suitable as a candidate EBC/TBC material and an interphase for Al2O3 f/Al2O3 composites.
基金Project supported by the National Key Research and Development Program of China(2019YFC0408300)the Excellent Youth Foundation of IMUST(2017YQL05)+7 种基金the Key Program for International S&T Cooperation Projects of China(2019YFE012999)the Science Fund for Distinguished Young Scholars of Hunan Province(2020JJ2044)the Young Elite Scientists Sponsorship Program of Hunan Province,China(2018RS_(3) 011)Hubei Key Laboratory for Efficient Utilization and Agglomeration of Metallurgic Mineral Resourcesthe National Natural Science Foundation of China(U2067201,51774328,51674045,51404300)the National 111Project of China(B14034)Inner Mongolia Natural Science Foundation(2020LH05027,2019MS05039)。
文摘Monazite((Ce,La)PO_(4))is one of the major types of light rare earth minerals from which the light rare earth elements cerium(Ce)and lanthanum(La)are economically extracted.Flotation is extensively used to recover fine-grained monazite.Sodium oleate(NaOL)is considered as the collector with strong collecting ability for monazite flotation.However,this study shows that its collecting ability is still limited.In this paper,a phosphonic acid,nonane-1,1-bisphosphonic acid(C9-BPA),was employed as the novel collector in place of NaOL.Flotation experiments show that even when the C9-BPA dosage is less than one-fifth of the NaOL dosage,the monazite recove ry using C9-BPA as the collector is approximately 22 wt%higher than that using NaOL.The mechanism by which C9-BPA adsorbs on monazite was investigated using zeta potential,infrared(IR)spectroscopy and X-ray photoelectron spectroscopy(XPS)measurements as well as first-principles calculations.Zeta potential measurements show a more significant decrease in the zeta potentials of monazite after the addition of C9-BPA compared to those after the addition of NaOL.For C9-BPA-treated monazite,the characteristic peaks of C9-BPA are observed in the IR and C 1 s XPS spectrum,whereas for monazite treated by NaOL,no characteristic peak of NaOL was observed.Experimental results show that C9-BPA has a stronger affinity towards the monazite surface than NaOL as confirmed by the higher adsorption energy of CP-BPA on the monazite surface(-204.22 kJ/mol)than NaOL(-48.48 kJ/mol).This study demonstrates an extensive application value and prospect of C9-BPA in monazite flotation and helps design novel collectors with strong collecting ability for monazite flotation.
基金supported by the National Natural Science Foundation of China(Grant Nos.42072058,41772054,41572039)。
文摘Monazite is an important accessory mineral in the pelitic granulites(Weihai area,Sulu orogen),and is also a powerful monitor for understanding the metamorphic evolution of the granulites.The pelitic granulites incongruously occur as lenses in granitic gneisses.The lithologies of the lenses gradually change from core to margin:The undeformed coarse-grained granulite,the foliated fine-grained granulite,the garnet-biotite-gneiss,and the migmatized granulite.The lens cores mostly preserve a peak granulite-facies metamorphic mineral assemblage of garnet+plagioclase(antiperthite)+quartz+sillimanite+biotite with accessory minerals of rutile,zircon,and monazite.The lens margins display a fluid-induced retrogression.In order to decipher the metamorphic processes of the pelitic granulites,a combined study of BSE imaging,U-Pb dating,and trace element composition for the monazites from the metapelitic lens were conducted.Monazites from the undeformed coarse-grained granulite only record a Paleoproterozoic age(1832±7 Ma,n=40).Monazites from the other lithologies yield the inherited Paleoproterozoic age and Triassic overgrowth age.For example,monazites from the migmatite yield intercept ages of 1818±10 and 211±22 Ma(n=56)with Triassic concordant age of 223.8±2.9 Ma.The Paleoproterozoic monazites are characterized by remarkable depletion in HREE and Y with obviously negative Eu anomalies,indicating their formation equilibrated with garnet and feldspar under granulite-facies conditions.During Triassic fluid modification,the monazite bright rims assimilated Th and Si but released U,HREE,Y,and P.This process resulted in that the Triassic overgrowth monazites have higher HREE and Y contents,and lower Th and U contents with relatively low Th/U ratios.Thus,the monazites in the pelitic granulites recorded a Paleoproterozoic metamorphic event and Triassic fluid modification.The Weihai pelitic granulites might have a tectonic affinity with the North China Craton.Therefore,the Paleoproterozoic pelitic granulites were mechanically drawn into the orogen during the Triassic continental collision,and subsequently were remoulded by the fluids during its exhumation.
基金funded by the National 305 Project of China (2018A03004-1, 2015BAB05B01-02)the Fundamental Research Fund for Central Universities(B16020127)
文摘The West Kunlun orogenic belt(WKOB) along the northern margin of the Tibetan Plateau is important for understanding the evolution of the Proto-and Paleo-Tethys oceans. Previous investigations have focused on the igneous rocks and ophiolites distributed mostly along the Xinjiang-Tibet road and the China-Pakistan road, and have constructed a preliminary tectonic model for this orogenic belt. However, few studies have focused on the so-called Precambrian basement in this area. As a result, the tectonic affinity of the individual terranes of the WKOB and their detailed evolution process are uncertain. Here we report new field observations, zircon and monazite U-Pb ages of the "Precambrian basement" of the South Kunlun terrane(SKT) and the Tianshuihai terrane(TSHT), two major terranes in the WKOB. Based on new zircon U-Pb age data, the amphibolite-facies metamorphosed volcanosedimentary sequence within SKT was deposited during the late Neoproterozoic to Cambrian(600-500 Ma), and the flysch-affinity Tianshuihai Group, as the basement of the TSHT, was deposited during the late Neoproterozoic rather than Mesoproterozoic. The rock association of the volcano-sedimentary sequence within SKT suggests a large early Paleozoic accretionary wedge formed by the long-term lowangle southward subduction of the Proto-Tethys Ocean between Tarim and TSHT. The amphibolitefacies metamorphism in SKT occurred at ca. 440 Ma. This ca. 440 Ma metamorphism is genetically related to the closure of the Proto-Tethys Ocean between Tarim and the Tianshuihai terrane, which led to the assembly of Tarim to Eastern Gondwana and the final formation of the Gondwana. Since the late Paleozoic to early Mesozoic, the northward subduction of the Paleo-Tethys Ocean along the HongshihuQiaoertianshan belt produced the voluminous early Mesozoic arc-signature granites along the southern part of NKT-TSHT. The Paleo-Tethys ocean between TSHT and Karakorum closed at ca. 200 Ma, as demonstrated by the monazite age of the paragneiss in the Kangxiwa Group. Our study does not favor the existence of a Precambrian basement in SKT.
