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1.
The rare-earth element （REE） concentrations of representative granite samples from the southeast of the Obudu Plateau, Nigeria, were analyzed with an attempt to determine the signatures of their source, evolutionary history and tectonic setting. Results indicated that the granites have high absolute REE concentrations （190×10^-6-1191×10^-6; av.=549×10^-6） with the chondrite-normalized REE patterns characterized by steep negative slopes and prominent to slight or no negative Eu anomalies. All the samples are also characterized by high and variable concentrations of the LREE （151×10^-6-1169×10^-6; av.= 466×10^-6）, while the HREE show low abundance （4×10^-6-107×10^-6; av.=28×10^-6）. These are consistent with the variable levels of REE fractionation, and differentiation of the granites. This is further supported by the range of REE contents, the chondrite-normalized patterns and the ratios of LaN/YbN （2.30-343.37）, CeN/YbN （5.94-716.87）, LaN/SmN （3.14-11.68） and TbN/YbN （0.58-1.65）. The general parallelism of the REE patterns, suggest that all the granites were comagmatic in origin, while the high Eu/Eu＊ ratios （0.085-2.807; av.=0.9398） indicate high fo2 at the source. Similarly, irregular variations in LaN/YbN, CeN/YbN and Eu/Eu＊ ratios and REE abundances among the samples suggest behaviors that are related to mantle and crustal sources.  相似文献   

2.
The trace elements characteristics of the migmatitic gneisses (biotite-garnetand hornblende-biotite), granulite facies rocks (charnockitic gneisses) and meta-peridotite in the area of Southwest Obudu Plateau indicate that the area exhibits a high degree of geochemical variability. Compatible trace elements (Ni and Cr) are comparatively high in the granulite facies rocks and meta-peridotite. Ni ranges from 28×10-6 to 266×10-6 whilst Cr ranges from 62×10-6 to 481×10-6 for the granulite facies rocks (charnocki...  相似文献   

3.
太行山南段矿山杂岩体主要由闪长岩、石英闪长岩及二长闪长岩组成,LA-ICP-MS锆石U-Pb测年显示,闪长岩形成于125.2Ma±1.4Ma—126.9 Ma±1.3 Ma,说明该岩体形成于早白垩世。矿山杂岩体具有高w(Sr)(557×10~(-6)～985×10~(-6))和w(Sr)/w(Y)(30.9～61.8)值,低w(Y)(11.52×10~(-6)～22.10×10~(-6))和w(Yb)(1.30×10~(-6)～2.00×10~(-6))值的特征,这和埃达克岩相似。Th、U和大离子亲石元素(Rb、Ba、K)富集,高场强元素(Nb、Ta、Zr、Hf)亏损。稀土元素配分曲线近乎一致,均显示为轻稀土富集、弱正铕异常的右倾型的特点。综合岩性组合、岩相特点、地球化学特征和锆石年代学特征认为,矿山杂岩体是在下地壳大规模拆沉基础上,经过连续俯冲的影响,拆沉下来的物质诱发软流圈上涌而部分熔融,并交代上覆亏损地幔岩体使其发生部分重熔为高Mg的类似埃达克岩浆而形成的。  相似文献   

4.
内蒙古乌兰沟埃达克岩锆石U-Pb年龄及构造环境   总被引：2，自引：1，他引：1  
王金芳  李英杰  李红阳  董培培 《地质通报》2018,37(10):1933-1943
内蒙古中部贺根山缝合带的梅劳特乌拉蛇绿岩中,新发现乌兰沟埃达克岩,岩性为花岗闪长岩。LA-ICP-MS锆石UPb测年结果表明,乌兰沟埃达克岩的侵位年龄为279.3±1.4Ma,其形成时代为早二叠世。乌兰沟埃达克岩SiO_2含量为65.92%~69.65%,MgO为1.34%~2.16%,Al_2O_3为15.30%~17.33%,Na_2O/K_2O值为3.95~14.09,Sr=359.60×10~(-6)~734.00×10~(-6),Yb=0.83×10~(-6)~2.02×10~(-6),Y=6.65×10~(-6)~12.84×10~(-6);富集K、Rb、Sr等大离子亲石元素,亏损Nb、Ta、Ti、P等高场强元素;稀土元素总量为32.18×10~(-6)~65.41×10~(-6),明显较低,轻、重稀土元素分馏明显,(La/Yb)N值为2.84~7.56,无明显Eu异常,显示出高硅埃达克岩(HSA)的地球化学特征。该埃达克岩具有岛弧型岩浆岩特征,形成于俯冲带岛弧环境,可能为洋内俯冲洋壳+俯冲深积物部分熔融并与上覆地幔楔橄榄岩反应成因。根据乌兰沟埃达克岩与梅劳特乌拉蛇绿岩的时空分布与演化特征,贺根山缝合带在早二叠世可能存在洋内俯冲作用。  相似文献   

5.
The host rocks of the porphyry tin deposits in the Yangbin area are principally topaz-bearing porphyry dikes about 2 km long and 2–20m wide. Three lithologie types are identified for the dikes: topaz-bearing potassium feldspar granitic porphyry, topaz-bearing monzonitic granitic porphyry and topaz-bearing quartz porphyry. The content of topaz in the rocks ranges from 10 to 20 vol.%. Porphyritic texture is characteristic, with quartz, potassium feldspar and albite as main phenocryst minerals. The phenocryst occupies 10–20 vol% of the rocks. The rock groundmass consists of subhedral topaz, quartz and protolithionite. Topaz has a unit-cell parameter b=8.797 (Å), and F:OH=1.92:0.18, indicating a F-rich variety formed at high temperature. The topaz-bearing porphyries occurring in this area are strongly peraluminous (A/NKC=1.574–12.94), with high ratios of F/Cl (146–303) and Rb/Sr (5–122). They are rich in incompatible elements (Sn, 313 × 10?6–1042 × 10?6; W, 6 × 10?6–218 × 10?6; Nb, 27 × 10?6–54 × 10?6), but poor in compatible elements (Sr, 10 × 10?6–28 × 10?6; Ba, 58 × 10?6–73 × 10?6; V, 3 × 10?6–12 × 10?6, Cl, 150 × 10?6–226 × 10?6). The rocks are also characterized by high total REE amount (281.69 × 10?6–319.76 × 10?6), with strong Eu depletion (δEu=0.01–0.03) and low ratio of LREE/HREE (0.78–0.84). In summary, the authors propose an idea of S-type genesis for the topaz-bearing porphyries with tin mineralization, instead of I-type.  相似文献   

6.
The X-ray fluorescence and ICP methods were used to analyze 60 outcrop samples of black shale, of which 15 were collected from Belait, 15 from the Setap Shale, 15 from Temburong, and 15 from the Trusmadi formations. The average compositions of the shales from the study area are 64.62%, 63.95%, 62.32%, 63.84% SiO2, 1.84%, 2.14%, 2.04%, 1.99% MgO, 2.55%, 3.12%, 2.89%, 2.72% K2O, 0.32%, 0.30%, 0.32%, 0.53% CaO, 5.86%, 6.06%, 7.14%, 6.60% Fe2O3, 207×10^-6, 180×10^-6, 213×10^-6, 200×10^-6 Rb, and 56×10^-6, 49×10^-6, 50×10^-6, 32×10^-6 Sr for the Setap Shale, Temburong, Belait and Trusmadi samples, respectively. The high Rb/Sr ratios of 3.8, 3.7, 4.2, and 6.1 are attributed to the lowest contents of Sr due to reducing conditions prevailing. The high Rb/K ratio sug- gests either brackish marine or rapid deposition that prevented equilibrium between Rb and K in the shales and marine waters.  相似文献   

7.
The Duolanasayi gold deposit, 60 km NW of Habahe County, Xinjiang Uygur Autonomous Region, is a mid-large-scale gold deposit controlled by brittle-ductile shearing, and superimposed by albitite veins and late-stage magma hydrothermal solutions. There are four types of pyrite, which are contained in the light metamorphosed rocks (limestone, siltstone), altered-mineralized rocks (chlorite-schist, altered albite-granite, mineralized phyllite), quartz veins and carbonatite veinlets. The pyrite is the most common ore mineral. The Au-barren pyrite is present mainly in a simple form and gold-bearing pyrite is present mainly in a composite form. From the top downwards, the pyrite varies in crystal form from {100} and {210} {100} to {210} {100} {111} to {100} {111}. Geochemical studies indicate that the molecular contents of pyrite range from Fe1.057S2 to Fe0.941S2. Gold positively correlates with Mn, Sr, Zn, Te, Pb, Ba and Ag. There are four groups of trace elements: Fe-Cu-Sr-Ag, Au-Te-Co, As-Pb-Zn and Mn-V-Ti-Ba-Ni-Cr in pyrite. The REE characteristics show that the total amount of REE (ΣREE) ranges from 32.35×10 -6 to 132.18×10 -6; LREE/HREE, 4.466-9.142; (La/Yb)N, 3.719-11.133; (Eu/Sm)N, 0.553-1.656; (Sm/Nd)N, 0.602-0.717; La/Yb, 6.26-18.75; δEu, 0.628-2.309; δCe, 0.308-0.816. Sulfur isotopic compositions (δ 34S=-2.46‰--7.02‰) suggest that the sulfur associated with gold mineralization was derived from the upper mantle or lower crust.  相似文献   

8.
Summary The F-rich Hongshan pluton in the eastern Nanling Range, southern China, is a topaz-bearing albite leucogranite. It is distinctive from other topaz-bearing felsic rocks in South China with respect to age, size, geochemical evolution and topaz mode and morphology. The Hongshan granites are highly peraluminous and characterized by high K2O/Na2O, Si, Rb, Cs, Nb, Ta and F, and low Ca, Ba, Sr, Zr, Hf, P, K/Rb, Zr/Hf and Eu/Eu*. The granites show significant trace-element variations with magma evolution, with increasing Rb, Cs, Nb, Ta, Sn, W and decreasing Sr, Ba, Zr, Hf, Y, REE, Pb, Th, K/Rb, Zr/Hf, Th/U and Eu/Eu*. These changes dominantly reflect fractional crystallization of plagioclase, biotite and accessory minerals such as zircon and monazite. The granites also exhibit a decrease in ɛNd(t = 225 Ma) from −7.9 to −11.7 with magma evolution. Modeling shows that the Nd isotopic variation could result from assimilation of the Taoxi Group wall rocks during fractional crystallization. The Hongshan pluton also shows spatial geochemical variations; the most evolved parts are located in the southeastern part of the pluton, which would be the most likely target area for rare-metal mineralization commonly associated with other topaz-bearing granites. Zircon grains from two rock types in the Hongshan body were analyzed in situ for U–Pb ages and Hf isotopic values. The concordant zircon grains mostly range from 218 to 230 Ma with an average of 224.6 ± 2.3 Ma (Indosinian). Some zircons with different internal structures and Hf isotope compositions, as well as monazite fragments, yield U–Pb ages of ca. 280 to 240 Ma, suggesting older thermal events in the studied area. The ɛHf(t) of these older zircons is strongly negative (−12.3), implying a crustal source with a Paleoproterozoic model age, similar to that for the Proterozoic Zhoutan Group. The main (∼225 Ma) zircon population exhibits less negative ɛHf(t) (−3.0 to −7.6) and Mesoproterozoic model ages, suggesting that the original magma of the Hongshan granite was generated from deeper Mesoproterozoic crust.  相似文献   

9.
The 1.86 Ga Liangtun-Kuangdonggou complex (LKC) is one of the oldest alkaline syenite bodies so far discovered in China. This syenite suite has elevated contents of total alkali (K2O Na2O), with an average of 10.50%, and a mean Rittmann Index (σ) of 6.48. The intrusions have slightly higher concentrations of K2O than those of Na2O on a weight percent basis, indicating the rocks belong to potassium-rich alkaline syenite series. Total rare-earth element concentrations (∑REE ) of the rocks are relatively high, ranging from 324×10 -6 to 1314×10 -6, with a mean value of 666×10 -6. The REE patterns are subparallel and rightward steep with (La/Yb)N >33, showing mild negative to positive Eu anomalies (δEu: 0.63-1.15). All samples exhibit strong LILE and LREE enrichments and TNT (Nb, Ta, Ti) and P depletions in multi-element spidergrams. On the εSr(t)-εNd(t) correlation diagram, most analytical data points plot within the enriched mantle field with low ( 87Sr/86Sr)i ratios (0.7045-0.7051) and negative εNd(t) values (-3.72--3.97), falling among those kimberlites from Fuxian County, Liaoning Provinve, from Mengyin County, Shandong Province and the Ⅱ-type kimberlites from South Africa. These characteristics imply that the LKC-rocks may have the same source as the above-mentioned kimberlites, i.e., they have close connections to the materials derived from enriched mantle reservoirs, further revealing that the upper mantle beneath the northeastern part of the North China Plate had been highly enriched before 1.86 Ga. Geodynamically, the LKC-rocks were formed in a within-plate environment with close genetic connections to rift-related alkaline magma activities possibly controlled by ancient mantle plumes.  相似文献   

10.
《China Geology》2018,1(2):225-235
For the first time, we present the rare earth element (REE) and sulfur isotopic composition of hydrothermal precipitates recovered from the Tangyin hydrothermal field (THF), Okinawa Trough at a water depth of 1206 m. The natural sulfur samples exhibit the lowest ΣREE concentrations (ΣREE= 0.65×10–6–4.580×10–6) followed by metal sulfides (ΣREE=1.71×10–6–11.63×10–6). By contrast, the natural sulfur-sediment samples have maximum ΣREE concentrations (ΣREE=11.54×10–6–33.06×10–6), significantly lower than those of the volcanic and sediment samples. Nevertheless, the δEu, δCe, (La/Yb)N, La/Sm, (Gd/Yb)N and normalized patterns of the natural sulfur and metal sulfide show the most similarity to the sediment. Most hydrothermal precipitate samples are characterized by enrichments of LREE (LREE/HREE=10.09–24.53) and slightly negative Eu anomalies or no anomaly (δEu=0.48–0.99), which are different from the hydrothermal fluid from sediment-free mid-oceanic ridges and back-arc basins, but identical to the sulfides from the Jade hydrothermal field. The lower temperature and more oxidizing conditions produced by the mixing between seawater and hydrothermal fluids further attenuate the leaching ability of hydrothermal fluid, inducing lower REE concentrations for natural sulfur compared with metal sulfide; meanwhile, the negative Eu anomaly is also weakened or almost absent. The sulfur isotopic compositions of the natural sulfur (δ34S=3.20‰–5.01‰, mean 4.23‰) and metal sulfide samples (δ34S=0.82‰–0.89‰, mean 0.85‰) reveal that the sulfur of the chimney is sourced from magmatic degassing.  相似文献   

11.
内蒙古东部马鞍山地区发育早石炭世高镁安山岩,其LA-ICP-MS锆石U-Pb测年结果为346.4±1.4Ma,指示其形成于早石炭世。马鞍山高镁安山岩属于钙碱性岩石系列,SiO_2含量为53.22%~54.22%,MgO为7.21%~10.03%,Al_2O_2为14.37%~15.94%,CaO为4.81%~5.94%,富Na、贫K(Na_2O为3.87%~4.34%、K_2O为0.49%~0.93%)、低TFeO/MgO(1.5)、高Cr(364×10~(-6)~429×10~(-6))、Ni(204×10~(-6)~211×10~(-6))。所有样品均显示轻稀土元素富集,具轻微的负Eu异常,富集大离子亲石元素Rb、K、Ba、Sr,亏损高场强元素Nb、Zr、Ti、Y、Yb、Lu等,地球化学特征与赞岐岩相似。由此可知,马鞍山地区早白垩世高镁安山岩是由地幔橄榄岩与消减洋壳板片部分熔融产生的富Si质熔体平衡反应的产物,暗示其形成于与俯冲消减有关的构造背景,是古亚洲洋闭合过程中洋陆转化的产物。  相似文献   

12.
The Liuyuan area,which is located on the southern margin of the Beishan orogenic belt,develops abundant Early Paleozic granitoids.SHRIMP zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 421±8 Ma for the Liuyuan granodiorite(Zhao Zehui et al.,2007),implying its Late Silurian intrusion.Geochemical compositions showed that the Liuyuan granodiorite is characterized by high SiO2(65.01%-67.31%),A12O3(17.17%-18.05%) and Na2O(Na2O/K2O=1.67-1.87) but low Mg# contents calculated as 100×Mg2+/(Mg2++∑Fe2+) from 28.77 to 31.15,as well as being enriched in Sr(472×10-6-517×10-6) but depleted in Yb(1.2×10-6-1.42×10-6) and Y(12.8×10-6-14×10-6).The REEs are characterized by right-inclined patterns with LREE enrichment,HREE depletion and slightly negative Eu anomalies(Eu/Eu*=0.91-0.97).Major and trace elements indicate that the granodiorite is an adakite.The Nb/Ta values of the granodiorite vary from 10.80 to 18.01 and Nb/U from 6.32 to 10.09,both lying between the values of the crust and the mantle.The rock has low εNd(t) values(-2.5--0.8) and high ISr(0.706321-0.706495).Geochemical and Sr-Nd isotopic compositions indicate that the Liuyuan granodiorite is possibly derived from partial melting of thickening lower crust,related to mantle underplating.The Yb-Ta and Y+Nb-Rb discriminant diagrams imply the Liuyuan granodiorite intruded in a local extensional tectonic setting during late collision.Combined with previous studies on geochronology,geochemistry and tectonic setting of granitoids,we interprete that the constraint of this adakite in the Liuyuan area indicates that the tectonic setting may have transformed from collision to extension during the Early Devonian.  相似文献   

13.
安徽牯牛降A型花岗岩的年代学、地球化学和构造意义   总被引：9，自引：6，他引：3  
谢建成  陈思  荣伟  李全忠  杨晓勇  孙卫东 《岩石学报》2012,28(12):4007-4020
皖南地区牯牛降岩体位于扬子板块东南缘,江南隆起带内。本文报道了牯牛降花岗岩体新的锆石U-Pb年龄和地球化学数据,并对岩体成因及其构造意义进行了探讨。锆石原位LA-ICP-MS U-Pb定年表明牯牛降岩体的形成年龄为130.1±1.3Ma (95% confidence, MSWD=0.55)。结合己发表的其他高质量锆石U-Pb同位素年龄数据表明皖南地区花岗岩的形成年龄主要集中在125~130Ma。牯牛降花岗岩为高钾钙碱性、准铝质岩石,SiO2 含量为72.21%~74.85%,具有高K2O含量(>5.11%)、高铁值(FeOT/(FeOT+MgO)>0.91)和K2O/Na2O比值(>1.61),低MgO和CaO含量的特征。微量元素地球化学性质上表现为强烈亏损Ba、Sr、Eu(Eu*/Eu=0.29~0.30),富集REE(>419×10-6)、Rb、Th 和U,较高的高场强元素Zr、Nb、Y和Ga含量。主量和微量元素均表现为A型花岗岩的特征。非常低的Mg#值(0.14~0.16)和较低Cr含量(Cr=10×10-6),高Yb(7.08×10-6~9.02×10-6)、Y(78.7×10-6~90.8×10-6)含量和较高的Th/U比值(5.17~7.79)说明古老地壳物质的部分熔融可能是牯牛降岩体主要形成机制。牯牛降A2型花岗岩特征代表了拉张的碰撞后构造环境。  相似文献   

14.
The Zargat Na’ am ring complex crops out 90 km NW of Shalatin City in the Southeastern Desert of Egypt. The ring complex forms a prominent ridge standing high above the surrounding mafic-ultramafic hills. It is cut by two sets of joints and faults which strike predominantly NNW-SSE and E-W, and is injected by dikes, porphyritic alkaline syenites, and felsite porphyries. It consists of alkali syenites, alkali quartz syenites, and peralkaline arfvedsonite-bearing granitic and pegmatitic dikes and sills. The complex is characterized locally by extreme enrichments in REEs, wolframite and rare, high field strength metals (HFSM), such as Zr and Nb. The highest concentrations (1.5 wt% Zr, 0.25 wt% Nb, 0.6 wt% Σ REEs) occur in aegirine-albite aplites that formed around arfvedsonite pegmatites. Quartzhosted melt inclusions in arfvedsonite granite and pegmatite provide unequivocal evidence that the peralkaline compositions and rare metal enrichments are primary magmatic features. Glass inclusions in quartz crystals also have high concentrations of incompatible trace elements including Nb (750 ￠ 10−6), Zr (2500 × 10−6) and REEs (1450 × 10−6). The REEs, Nb and Zr compositions of the aegirine-albite aplites plot along the same linear enrichment trends as the melt inclusions, and Y/Ho ratios mostly display unfractionated, near-chondritic values. The chemical and textural features of the aegirine-albite aplites are apparently resultant from rapid crystallization after volatile loss from a residual peralkaline granitic melt similar in composition to the melt inclusions.  相似文献   

15.
全球范围内出露的碳酸岩大多为钙质、镁质、铁质碳酸岩,少量为钠质和硅质碳酸岩,极少有富Sr碳酸岩的报道,其岩石成因、资源意义及对碳酸岩岩浆演化的指示意义尚不清楚。本次在四川省牦牛坪稀土矿区南部包子山稀土矿床的露天采坑中发现了超级富Sr的碳酸岩,其呈不规则的脉状侵入到构造角砾岩中。岩石呈紫色-淡紫色,微晶-斑状结构,斑晶主要为萤石,基质主要为菱锶矿、方解石、氟碳铈矿、氟碳钙铈矿、金云母、重晶石并含少量的金属硫化物和氧化物。全岩的微量元素分析表明,其稀土元素总量(∑REE)达3.5%～6.1%,Sr含量达19.0%～27.7%,已超过稀土矿床和锶矿床的工业品位要求。岩石中的中、重稀土元素含量占稀土元素总量的1.14%～1.77%,一些高价值稀土元素含量较高,如Pr(939×10~(-6)～1399×10~(-6))、Nd(2783×10~(-6)～3937×10~(-6))、Gd(237×10~(-6)～320×10~(-6)),因此除轻稀土元素外,中、重稀土和锶元素也具有重要的资源意义。岩石强烈富集REE、Sr、Ba,而明显亏损P、Nb、Ta、Zr、Hf元素,可能与岩浆演化过程中锆石和其它基性矿物的结晶分离有关。全岩的Sr-Nd同位素组成与牦牛坪、里庄稀土矿床的碳酸岩相似,表明它们为同源岩浆产物。笔者认为,富Sr的碳酸岩代表了碳酸岩岩浆演化晚期的产物,REE、Sr、Ba、F和S元素均在岩浆演化晚期的碳酸岩中高度富集。碳酸岩岩浆超浅成侵位至构造角砾岩中,并与下渗的大气水相遇导致岩浆的淬冷和微晶-斑状结构的形成。早期基性矿物(如霓辉石、黑云母)及碳酸盐矿物(如方解石、白云石等)的结晶分离是造成晚期碳酸岩中稀土元素富集的重要原因。富Sr碳酸岩中石英斑晶的发现和其较低的SiO_2含量表明碳酸岩岩浆演化晚期可能是硅饱和的,且这种岩浆具有很低的SiO_2溶解能力。以菱锶矿(体积分数 50%)为主要碳酸盐矿物的稀土碳酸岩可能代表了一种新的碳酸岩类型,明显不同于已知的钙质、镁质、铁质和钠质碳酸岩。  相似文献   

16.
曾维顺  周建波  董策  曹嘉麟  王斌 《岩石学报》2014,30(7):1948-1960
本文对额尔古纳地块西缘八大关杂岩进行了锆石LA-ICP-MS U-Pb定年和岩石地球化学分析,以确定该套杂岩的形成时代及其构造属性。原定义为"佳疙瘩组"的八大关杂岩主要由黑云角闪斜长片麻岩和花岗质糜棱岩组成。LA-ICP MS锆石U-Pb研究表明,3个样品的锆石发育典型的岩浆振荡环带,高Th/U(0.13~1.42),轻稀土元素亏损,重稀土元素富集,具有强烈的正Ce异常和强烈的负Eu异常等特征,表明锆石均属于岩浆成因。测年结果表明2个黑云角闪斜长片麻岩形成时代分别为210±2Ma、214±2Ma,花岗质糜棱岩的原岩年龄为203±3Ma;样品中同时存在~501Ma和~795Ma的捕获/继承锆石。上述结果显示八大关杂岩的形成时代应为晚三叠世而不是前人认为的新元古代,而捕获锆石则显示与东北其它地块具有相同的构造演化历史。地球化学研究显示,八大关杂岩具有高钠、铝等特点,A/CNK=0.86~1.05,A/NK=1.53~1.97,为准铝质到弱过铝质钙碱性系列;轻稀土元素富集、重稀土元素亏损(La/Yb)N=6~31,Eu弱亏损(Eu/Eu*=0.50~1.01),具有较高的Sr含量(在378×10-6~598×10-6之间)及低的Yb含量(在0.71×10-6~3.50×10-6之间);微量元素原始地幔标准化蛛网模式图显示,富集Rb、Ba、K及Sr等大离子亲石元素、强烈亏损Nb、Ta、P、Ce及Ti等高场强元素。这些地球化学特征表明八大关杂岩形成于活动大陆边缘的岛弧环境。因此,八大关杂岩应形成于蒙古-鄂霍茨克洋向额尔古纳地块俯冲的大地构造背景,为蒙古-鄂霍茨克洋在三叠纪晚期南向俯冲提供了关键证据。  相似文献   

17.
陕西省西南部铧厂沟火山岩以英安岩为主(～ 90vol％),夹玄武岩构造透镜体(～ 10vol％).玄武岩SiO2含量为43.6％ ～ 54.7％,具有低K、Ti,高Na、Mg的特征;稀土总量为24×10-6 ～29×10-6,中稀土轻微富集,Eu、Sr轻微正异常;具有正Rb、Ba异常及负Nb、Zr异常,LaN/YbN值为1.81 ～2.87,Th/Yb值为0.19 ～0.23,Th/Nb值为0.11 ～0.20,Nb/La值为0.26～0.70,Hf/Th值为0.50 ～ 0.67,显示亚碱性弧玄武岩的特征.英安岩SiO2含量为59.5％～ 72.3％,稀土总量较低(116×10-6～187 × 10-6),为右倾式配分模式,Eu负异常,富集大离子亲石元素(如Rb、Ba、Th、K等),亏损高场强元素(如Nb、P、Ti、Ta等),显示弧火山岩地球化学特征.获得玄武岩的锆石SHRIMP U-Pb年龄为801.7±4.7Ma (MSWD=1.18;n=12),英安岩的锆石LA-ICP-MS U-Pb年龄为802.1±5.3Ma (MSWD=1.02;n=19),二者在误差范.内一致.因此,铧厂沟火山岩是一套火山弧环境的亚碱性玄武质-英安质火山岩组合,表明新元古代曾有大洋板块向南俯冲到扬子古板块北缘之下;这套火山岩裹挟于泥盆系沉积地层中,与泥盆系地层一起,共同组成了一套由晚古生代-三叠纪勉略洋闭合所致的构造混杂岩带.  相似文献   

18.
This paper determined the fixed-ammonium (NH4 +) contents of lamprophyres in the Zhenyuan gold orefield, Yunnan Province, China. The results show that the NH4 + contents of minettes in the orefield range from 120 × 10−6 to 469 × 10−6 and those of kersantites from 74.3 × 10−6 to 136 × 10−6. These values are higher than those of other mantle-derived rocks (less than 50 × 10−6), but lower than those of carbonaceous wall rocks in the orefield (from 1200 × 10−6 to 1343 × 10−6). Combining with the Sr isotopic composition, this paper suggested that lamprophyres in the orefield with high NH4 + contents relative to other mantle-derived rocks would not have resulted from the primary magma contaminated by crustal materials in the process of rising or in the magma chamber, but from mantel metasomatism. This research project was financially supported jointly by the State Key Basic Research Program of the People’s Republic of China (No. G1999043203) and the Chinese Academy of Sciences Knowledge-Innovation Program (No. KZCX3-SW-125).  相似文献   

19.
Zr diffusion in titanite   总被引：2，自引：0，他引：2  
Chemical diffusion of Zr under anhydrous, pO2-buffered conditions has been measured in natural titanite. The source of diffusant was either zircon powder or a ZrO2–Al2O3–titanite mixture. Experiments were run in sealed silica glass capsules with solid buffers (to buffer at NNO or QFM). Rutherford Backscattering Spectrometry (RBS) was used to measure diffusion profiles. The following Arrhenius parameters were obtained for Zr diffusion parallel to c over the temperature range 753–1,100°C under NNO-buffered conditions: D Zr = 5.33 × 10−7 exp(−325 ± 30 kJ mol−1/RT) m2 s−1 Diffusivities are similar for experiments buffered at QFM. These data suggest that titanite should be moderately retentive of Zr chemical signatures, with diffusivities slower than those for O and Pb in titanite, but faster than those for Sr and the REE. When applied in evaluation of the relative robustness of the recently developed Zr-in-titanite geothermometer (Hayden and Watson, Abstract, 16th V.M. Goldschmidt Conference 2006), these findings suggest that Zr concentrations in titanite will be less likely to be affected by later thermal disturbance than the geothermometer based on Zr concentrations in rutile (Zack et al. in Contrib Mineral Petrol 148:471–488, 2004; Watson et al. in Contrib Mineral. Petrol, 2006), but much less resistant to diffusional alteration subsequent to crystallization than the Ti-in-Zircon geothermometer (Watson and Harrison in Science 308:841–844, 2005).  相似文献   

20.
We have analyzed by RNAA 25 aubrite and 9 diogenite samples for 13 to 29 siderophile, volatile, and lithophile trace elements. Both meteorite classes show a typically igneous siderophile element pattern, with Ir, Os, Re, Ge more depleted than Au, Ni, Pd, Sb. But aubrites tend to have about 10 × higher abundances (10?3 ? 10 ? 4 × Cl for the first 4 and 10?2?10?3 × Cl for the last 4 siderophiles), apparently reflecting smaller metal/silicate distribution coefficients at lowerf(O2), or less complete segregation of metal. Se is surprisingly abundant in aubrites (up to 0.4 × Cl), but Te is less so (SeTe ? 5 × Cl), apparently due to its stronger siderophile character. Other volatiles (Ag, Zn, In, Cd, Bi, T1) show depletions intermediate between lunar dunite and the Earth's mantle.Of 7 aubrites analyzed for REE (Ce, Nd, Eu, Tb, Yb, Lu), 6 are depleted in REE (0.08?0.5 × Cl) and 5 show negative Eu anomalies (the exceptions are Bishopville and Mt. Egerton silicate). This supports an igneous origin, as already noted by Boynton and Schmitt (1972). No samples of the complementary, basaltic and feldspathic rocks have been found thus far, but one of our samples of Khor Temiki dark is a candidate for the basalt. It is 5?7 × enriched in REE and only slightly less so in Rb, Cs, and U. Though shocked and enriched in siderophiles to ~0.05 × Cl, it apparently represents a new meteorite class.Three diogenites analyzed for REE show very diverse patterns, from strongly depleted in light REE for Tatahouine (Ce = 0.01 × Cl) to flat for Garland (~2.5 × Cl). The data confirm the trends found by Fukuokaet al. (1977) as well as their interpretations.Factor analysis shows several parallel groupings for aubrites and diogenites: siderophiles (Re, Ir, Os, Pd, Ge), chalcophiles (Se, Te), volatiles (Ag, In, Tl) and incompatibles (U, REE, and Cs or Rb). But there are some differences for elements such as Ni, Sb, Cd, Bi, Au, and Zn, most of which behave more sensibly in aubrites than in diogenites.Several element pairs that differ greatly in volatility (Cs-U, Ge-Ir) correlate closely in aubrites, in approximately Cl-chondrite proportions. These correlations, and other lines of evidence, suggest strongly that aubrites originated by igneous processes in their parent body, not by direct nebular condensation. The source material may have resembled EL chondrites in oxidation state and depletion of refractories, metal, and volatiles.  相似文献   

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