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1.
Abstract Chloritoid-bearing metasedimentary rocks occur in close proximity to blueschists and eclogites in the Tertiary high-pressure metamorphic belt of northern New Caledonia. The typical assemblage of chloritoid-bearing rocks in the epidote zone is quartzchlorite-muscovite-garnet-chloritoid. In the omphacite zone, epidote is an additional member of the chloritoid-bearing assemblage. Paragonite is rare, plagioclase was not detected, and rutile and ilmenite are the Fe-Ti oxide phases. Chloritoid-glaucophane is not a common assemblage. Chloritoid-bearing rocks have relatively low (Ca+K+Na)/Al ratios and the chloritoids are relatively Mg-rich with Mg/ (Mg+Fe) up to about 0.4. A comparison of the mineral assemblages and mineral chemistry with experimental and computed phase equilibria suggest an upper temperature limit near 560° C in the omphacite zone and a minimum temperature limit near 450° C at 10 kbar. An empirical garnet-chlorite Fe-Mg exchange thermometer does not yield consistent results for the higher-grade rocks, suggesting T s ranging from 390 to 535° C in the omphacite zone and 420–465° C in the epidote zone. The distribution coefficient K D = (Fe/Mg)ctd/(Fe/Mg)chl for chloritoid and chlorite ranges from 3.9 to 6.4, values which are lower than those (=10) from lower greenschist facies rocks, but are near those of upper greenschist facies and albite-epidote amphibolite facies.  相似文献   

2.
Ferric iron solid solution in synthetic orthopyroxene has been studied along the joins MgSiO3-Al2O3 · Fe2O3 and MgSiO3-Fe2O3. The partially reduced synthetic orthopyroxenes showed that major incorporation of ferric iron can only occur together with a concomitant incorporation of Al. Maximum solid solution of ferric iron along the join MgSiO3-Fe2O3 was found to be only 0.63 wt% Fe2O3 at 1000°C and 2 kb total pressure. From the observed Mössbauer parameters octahedral ferric iron can be assigned to the MI position in orthopyroxene. Incorporation of Fe3+ and/or Al will increase the disorder of Fe2+ and Mg between the M1 and M2 sites, which is also observed in a ferric iron-containing aluminous orthopyroxene of metamorphic origin. In the assemblage orthopyroxene + sillimanite + quartz the ferric iron content of orthopyroxene is directly related to oxygen fugacity.  相似文献   

3.
鄂西南利川二叠纪吴家坪组硅质岩成因及沉积环境   总被引：3，自引：1，他引：2  
鄂西南利川吴家坪组硅质岩与海相石煤及多层火山粘土岩共生,产海绵骨针及放射虫化石,放射虫组合以泡沫虫类为主,内射球虫类次之,隐管虫类很少,代表外陆棚沉积环境。硅质岩的陆源元素Al、Ti含量较高,热水来源元素Fe、Mn含量较低,Al/(Al+Fe+Mn)值在0.64~0.83之间,平均值0.73。在Al-Fe-Mn三角图中,样品位于或紧邻非热水沉积区,在 SiO2- (K2O+Na2O)、SiO2-Al2O3, (K2O+Na2O)-Al2O3 图解中大多数样品落在火山成因区,少数位于火山成因与生物成因区之间。相对于沉积岩的微量元素丰度,生命元素Mo、V富集,指示热水沉积的特征元素Ba、As、Sc亏损。∑REE较低,∑LREE/∑HREE平均值为3.02,Ce、Eu均轻度负异常（δCe:0.75~0.83,平均值0.79;δEu:0.61~0.95, 平均值0.84）,经北美页岩标准化后稀土元素配分曲线近水平。以上地球化学特征表明研究区硅质岩属火山成因,并伴有生物作用。氧化还原判别指标U/Th、V/(V+Ni)及Ceanom,沉积环境判别指标MnO/TiO2,LaN/YbN 与判别图解100×TFe2O3/SiO2-100 Al2O3/SiO2、TFe2O3/(100-SiO2)-Al2O3/(100-SiO2)、TFe2O3/TiO2-Al2O3/(Al2O3+TFe2O3)、LaN/CeN-Al2O3/(Al2O3+TFe2O3)与∑LREE/∑HREE-100×Eu/∑REE一致表明硅质岩形成于大陆边缘缺氧环境。  相似文献   

4.
Granulite facies relics are found in the early Paleozoic kyanite-bearing melanocratic metagabbro from the Fuko Pass metacumulate mass of the Oeyama belt, southwestern Japan. The granulite facies assemblage consists of relict Al-rich clinopyroxene (up to 8.5 wt.% Al2O3) and pseudomorphs of spinel and plagioclase. The spinel pseudomorphs consist mainly of symplectic intergrowth of corundum and magnetite with minor gahnitic spinel. The plagioclase pseudomorphs are composed mainly of clinozoisite with minor kyanite. The symplectite suggests oxidation and Mg-depletion of the original spinel: hercynite (3FeAl2O4)+(O) = corundum (3Al2O3)+magnetite (Fe3O4). This oxidation reaction may have taken place at 700-900°C temperature. The melanocratic metagabbro has later been hydrated to form the epidote amphibolite assemblage represented by clinozoisite+kyanite+paragonite. The clinozoisite+kyanite assemblage has further reacted to form margarite at a lower temperature. The first granulite facies assemblage implies that the metacumulate has originally constituted a basal part of thick oceanic crust, and then has experienced the high-P/T type metamorphism in a subduction zone. This indicates that the thick oceanic crust has been formed and accreted to the Circum-Pacific orogenic belt in the early Paleozoic time.  相似文献   

5.
青海省东昆仑造山带洪水河铁矿床为一中型铁矿床,其含铁建造产于狼牙山组千枚岩中,矿石类型主要为块状磁铁石英岩型,少量为条带状磁铁石英岩型,前人一般认为其属于沉积变质型铁矿床。本文在前人研究基础上,对洪水河铁矿区含铁建造中块状铁矿石进行了铁同位素、主量元素、稀土元素和微量元素分析。结果显示：除1件样品外,其余含铁建造样品的铁同位素δ56FeIRMM014均介于0.97‰~1.97‰之间,和全球典型新元古代含铁建造的Fe同位素特征基本一致;铁矿石的SiO2+Fe2O3质量分数高达78.56%~98.06%,具有极低的Al/(Al+Fe+Mn)值（0.00~0.06）,为典型的化学沉积岩;总稀土元素（w (∑REE)）变化范围为(16.49~80.89)×10-6,没有明显的Ce异常(Ce/Ce*为0.93~1.05),轻稀土元素轻微亏损,显示出类似新元古代含铁建造型的特点。综合对比洪水河铁矿区含铁建造的Fe同位素组成、沉积时代和地球化学特征,推断洪水河铁矿区含铁建造的沉积环境为新元古代柴达木—东昆北陆块的被动大陆边缘构造环境,铁等成矿物质主要来源于海相热液流体;富含Fe2+的海相热液流体上涌并逐渐演变为低温热液后在亚氧化水体环境中与含氧海水混合,最后导致Fe2+被部分氧化并形成氢氧化铁,氢氧化铁逐渐沉积在大陆斜坡上最终形成含铁建造。洪水河铁矿的成因类型可划归为拉皮坦型新元古代含铁建造。  相似文献   

6.
Jian-Jun Yang   《Lithos》2003,70(3-4):359-379
A garnet–pyroxene rock containing abundant Ti-clinohumite (ca. 40 vol.%) occurs along with eclogites as small blocks in quartzo-feldsparthic gneiss in the southern end of the Chinese Su-Lu ultrahigh-pressure (UHP) metamorphic terrane. It consists of three aggregates: (1) Ti-clinohumite-dominated aggregate with interstitial garnet and pyroxene, (2) garnet+pyroxene aggregate with Ti-clinohumite inclusions, and (3) Ti-clinohumite-free aggregate dominated by garnet. Apatite, phlogopite, zircon, hematite, pentlandite, and an unknown Ni-Fe-volatile-Si (NFVS) mineral, which is replaced by Ni-greenalite, occur as accessories. Serpentine is the major secondary mineral. Garnet (Prp63.9–64.6Alm25.8–26.9Grs1.4–7.9Uva0.5–7.6Sps1.0) in all three aggregates is pyrope-rich with very low grossular component, with that in the aggregate (2) most enriched in Cr (Cr2O3=2.55 wt.%). Orthopyroxene is depleted in Al (Al2O3=0.16 wt.% in the cores) and Ca (CaO=0.06–0.09 wt.% in the cores), with XMg (Mg/(Mg+Fe)) values at ca. 0.900. Clinopyroxene is chromian diopside with Fe3+≥Fe2+. Matrix clinopyroxene has a lower XMg (0.862) than that (0.887) included in Ti-clinohumite. The rock contains modest amount of heavy rare earth elements (HREE) (10 to 12×C1 chondrite), with significant enrichment in Cr, Co, Ni, V, Sr, and light rare earth elements (LREE) (22 to 33×C1 chondrite). The clinopyroxene is very enriched in Cr (Cr2O3 is up to 2.09 wt.% in the cores) and Sr (ca. 350 ppm) and LREE (CeN/YbN=157.7). Ti-clinohumite is enriched in Ni (1981 ppm), Co (123 ppm), and Nb (85 ppm).

While it is possible to enrich ultramafites in incompatible elements in a subducted slab, the high Al, Fe, Ti, and low Si, Ca, and Na contents in the Ti-clinohumite rock are difficult to account for by crustal metasomatism of an ultramafite. On the other hand, the similarity in major and trace element compositions and their systematic variations between the Ti-clinohumite-garnet-pyroxene rock of this study and those of Mg-metasomatised Fe–Ti gabbros reported in the literature suggest that crustal metasomatism occurred in a gabbroic protolith, which resulted in addition of Cr, Co, Ni, and Mg and removal of Si, Ca, Na, Al, and Fe. This implies that the rock was in contact with an ultramafite at low pressure. During subsequent subduction, the metagabbro was thrust into the country gneiss, where gneiss-derived hydrous fluids caused enrichment of Sr and LREE in recrystallised clinopyroxene. P–T estimates for the high-pressure assemblage are ca. 4.2 GPa and ca. 760 °C, compatible with those for the eclogites and gneisses in this terrane. It is possible that the Ti-clinohumite-garnet-pyroxene rock and associated eclogites represent remnants of former oceanic crust that was subducted to a great depth.  相似文献   


7.
通过对内蒙古阿拉善右旗雅干地区好比如、杭乌拉剖面二叠系埋汗哈达组硅质岩岩石学特征、主量元素、稀土元素地球化学研究,探讨了硅质岩的成因及其沉积环境。地球化学测试结果显示：好比如剖面硅质岩SiO2质量分数为89.83%~94.16%,平均值为92.01%,Al/（Al+Fe+Mn）值为0.49~0.65,平均值为0.56,δCe值为0.87~0.92,平均值为0.89;杭乌拉剖面硅质岩SiO2质量分数为75.93%~90.14%,平均值为86.70%,Al/（Al+Fe+Mn）值为0.68~0.78,平均值为0.73,δCe值为0.89~0.94,平均值为0.90;在Al-Fe-Mn三角图上,样品全部落入生物成因硅质岩区,指示研究区硅质岩为海水生物沉积成因。好比如剖面硅质岩Al2O3/（Al2O3+Fe2O3）值为0.59~0.78,平均值为0.71,MnO/TiO2值为0.17~0.88,平均值为0.41,（La/Ce）N值为1.07~1.25,平均值为1.16,Ceanom值为-0.059~-0.026,平均值为-0.043;杭乌拉剖面硅质岩Al2O3/（Al2O3+Fe2O3）值为0.78~0.86,平均值为0.83,MnO/TiO2值为0.04~0.40,平均值为0.16,（La/Ce）N值为1.02~1.15,平均值为1.10,Ceanom值为-0.041~-0.001,平均值为-0.029;在硅质岩沉积环境判别图上,样品落在大陆边缘型硅质岩区域内,指示研究区硅质岩沉积于大陆边缘缺氧的水体环境。综合分析认为研究区早二叠世为大陆边缘滨海-浅海相沉积环境。  相似文献   

8.
Cordierite samples from pegmatites and metamorphic rocks have been analysed for major [electron microprobe analysis (EMPA)] and trace elements [inductively coupled plasma mass spectrometry (ICP-MS), secondary ion mass spectrometry analyses (SIMS)] as well as for H2O and CO2 (coulometric titration), and the results evaluated in conjunction with published data in order to determine which exchange mechanisms are significant. Apart from the homovalent substitutions FeMg−1 and MnMg−1 on the octahedral site, some minor KNa−1 on the Ch0 channel site, and Fe3+Al−1 on the T11 tetrahedral site, the three most important substitution mechanisms are those for the incorporation of Li on the octahedral sites (NaLi□−1Mg−1), and of Be and other divalent cations on the tetrahedral T11 site (NaBe□−1Al−1 and Na(Mg,Fe2+)□−1Al−1). The dominant role of the last vector is clearly demonstrated. We propose a new generalized formula for cordierite: Ch(Na,K)0–1 VI(Mg,Fe2+,Mn,Li)2 IVSi5 IVAl3 IV(Al, Be, Mg, Fe2+, Fe3+)O18 *xCh(H2O, CO2…). Our results show that the population of (Mg, Fe2+) on the T11-site is limited to about 0.08 a.p.f.u. Other exchange mechanisms that were encountered in experiments operate only under P–T conditions or in bulk compositions that are rarely realized in nature. Routine analyses by electron microprobe in which Li and Be are not determined can be plotted as (Mg+Fe+Mn) versus (Si+Al) to assess whether significant amounts of Li and Be could be present. These amounts can be calculated as Li (a.p.f.u.)=Al+Na–4 and Be (a.p.f.u.)=10–2Al–M2+–Na.  相似文献   

9.
A series of granitoids from Proterozoic to Cenozoic age occurred in the western Kunlun orogenic belt, Xinjiang, northwestern China. Several intrusions such as the West Datong (Middle Caledonian age), North Kuda (Late Caledonian age) and Kuzigan, Karibasheng, Zankan (Himalayan age) plutons have shoshonitic affinity. Their rock assemblages include (quartz) monzodiorite–(quartz) monzonite–quartz syenite (Middle Caledonian) or monzonitic granite–granite (Late Caledonian) or biotite (monzonitic) granite–diopside granite–diopside syenite (Himalayan). Generally, biotite is iron–phlogopite, with some eastonite and high Mg/(Mg+FeT) and Fe3+/Fe2+ ratio. Amphibole is mainly edenitic hornblende and magnesian hastingsitic hornblende, with some edenite and higher Mg/(Mg+FeT) and Fe3+/Fe2+ ratio. The rocks show SiO2 contents of 52.77–71.85% and high K2O+Na2O (mostly >8%, average 9.14%), K2O/Na2O (mostly >1, average 1.50) and Fe2O3/FeO (0.85–1.51, average 1.01) and low TiO2 contents (0.15–1.12%, average 0.57%). Al2O3 contents (13.01–19.20%) are high but variable. The granitoids are prominently enriched in LILE, LREE and volatiles such as F. However, the studied shoshonitic granitoids among the three intrusive periods also show differences in isotopic compositions and trace element concentrations, suggesting their different geneses: the origin of the West Datong pluton is probably related to the involvement of subducted oceanic crust sediments into the mantle source; the North Kuda and Himalayan plutons could have been generated by partial melting of subducted oceanic crust sediments or metasediments of thickened continental lower crust in the process of late-orogenic slab break-off or lithospheric thinning.  相似文献   

10.
竹山地区位于扬子陆块北缘,寒武纪早期发育一套深水硅质岩系。该岩系由纯硅质岩夹少量白云岩、页岩所组成。硅质岩中微晶石英含量均超过85%,还含有少量碳质、燧石及微量绢云母。地球化学分析表明,该硅质岩的SiO2含量较高,平均为93.4%;Al2O3和TiO2含量较低,分别为0.19%~1.45%和0.01%~0.09%,TFe2O3为0.053%~0.342%,Al/(Al+Fe+Mn)比值为0.58~0.83,平均为0.71,Eu/Eu*为0.74~3.61,平均为1.65,表明其硅质主要来源于生物本身或其生命活动产物,海底热液活动亦提供了一部硅质物质;同时,硅质岩具有较低的TFe2O3/TiO2比值(2.16~12.56,平均值为5.86)和Al2O3/(Al2O3+Fe2O3)比值(0.65~0.87,平均值为0.78),Y的正异常(Y/Ho值为34.81~60.19,平均为47.0)及Ce的负异常(Ce/Ce*值为0.28~0.92),表明它们形成于远离陆源物质干扰的边缘海盆环境,且Ce负异常从底部到顶部有逐渐减小的趋势,记录了寒武纪时期扬子北缘被动陆缘裂谷盆地不断扩大,水体逐渐变深的过程。  相似文献   

11.
认识渝湘黔地区南华系的沉积构造背景可以为该地区锰矿勘探提供新的依据,基于此,文中对重庆秀山小茶园锰矿ZK0606钻孔的南华系千子门组和大塘坡组开展了系统的沉积环境和地球化学分析。沉积相分析结果表明,该套地层共可划分出冰水浅海、局限边缘盆地和浅水陆棚3种沉积环境。地球化学分析结果表明,研究区大塘坡组稀土元素总量较高、富轻稀土元素、具Eu负异常,结合Al2O3/(Al2O3+Fe2O3)、Al/(Al+Fe+Mn)值等,推测其形成于被动大陆边缘背景。根据微量元素含量及其比值(U、V、Mo、V/Cr)等推测,大塘坡组一段沉积于缺氧—贫氧沉积环境,而大塘坡组二段逐渐过渡到氧化沉积环境;根据Al/Ca值、化学蚀变指数(CIA)等指标分析,该套地层自下而上化学风化强度逐渐增大、陆源碎屑供给增多,这可能与Sturtian冰期结束、气候变暖和海平面迅速升高有关。综合上述分析结果认为,重庆秀山小茶园锰矿主要产出于大塘坡组一段下部相对深水厌氧的局限边缘盆地环境中。  相似文献   

12.
The proposed geothermobarometer is based on an empirical calibration which takes account of two equilibria involving the tremolite, edenite, pargasite and hastingsite components in amphiboles. It has applications to assemblages found in metabasic rocks of widely different chemical compositions (magnesian to Fe-rich metabasalts), and for metamorphism ranging from lower greenschist to highest amphibolite facies. Knowing the Si(T1), Aliv, Alvi, Fe3+, Fe2+, Mg, Ca, NaM4, NaA and A vacancy in an amphibole, and the Al3+ and X Mg in coexisting epidote and chlorite, it is possible to calculate two values of In K d for this assemblage. These equilibria involve edenite-tremolite and (pargasite/hastingsite)-tremolite end-members in amphibole (the calculation program is given). For these equilibria, the isopleths (iso-values of K d) have been calculated for 0.27 < X Mg < 0.75 and 0 < X Fe3+= Fe3+/(Fe3++ Alvi) < 0.8. It is then possible to determine pressure and temperature directly when X Mg, X Fe3+, In K d for tremoliteedenite and In K d for (pargasite/hastingsite)-tremolite are known. Application of this geothermobarometer is limited to Ca-free plagioclase assemblages, and complete P–T paths can be drawn only if all the minerals are considered together. Phase relations at successive stages of crystallization can be constrained by studying the relationships between the coexisting minerals, their zoning and the metamorphic fabrics.  相似文献   

13.
Pumpellyite from four-phase assemblages (pumpellyite + epidote + prehnite + chlorite; pumpellyite + epidote + actinolite + chlorite; pumpellyite + epidote + Na-amphibole + chlorite, together with common excess phases), considered to be low variance in a CaO-(MgO + FeO)-Al2O3-Fe2O3 (+Na2O + SiO2+ H2O) system, have been examined in areas which underwent metamorphism in the prehnite-pumpellyite, pumpellyite-actinolite and low-temperature blueschist facies respectively. The analysed mineral assemblages are compared for nearly constant (basaltic) chemical composition at varying metamorphic grade and for varying chemical composition (basic, intermediate, acidic) at constant metamorphic conditions (low-temperature blueschist facies). In the studied mineral assemblages, coexisting phases approached near chemical equilibrium. At constant (basaltic) bulk rock composition the MgO content of pumpellyite increases, and the XFe3+ of both pumpellyite and epidote decreases with increasing metamorphic grade, the Fe3+ being preferentially concentrated in epidote. Both pumpellyite and epidote compositions vary with the bulk rock composition at isofacial conditions; pumpellyite becomes progressively enriched in Fe and depleted in Mg from basic to intermediate and acidic bulk rock compositions. The compositional comparison of pumpellyites from high-variance (1–3 phases) assemblages in various bulk rock compositions (basic, intermediate, acidic rocks, greywackes, gabbros) shows that the compositional fields of both pumpellyite and epidote are wide and variable, broadly overlapping the compositional effects observed at varying metamorphic grade in low-variance assemblages. The intrinsic stability of both Fe- and Al-rich pumpellyites extends across the complete range of the considered metamorphic conditions. Element partitioning between coexisting phases is the main control on the mineral composition at different P-T conditions.  相似文献   

14.
刘建清  何利  何平  冉敬  何佳伟  陈风霖 《沉积学报》2021,39(5):1305-1319
云南省昭通市昭阳区锌厂沟位于康滇古陆东缘,在剖面测量及样品系统采集分析基础上,建立了该区下寒武统筇竹寺组泥页岩地球化学剖面,为该区筇竹寺组沉积环境、物源分析提供了定量的地球化学数据。研究结果显示:1）筇竹寺组物源主要来自康滇古陆中元古界东川群、会理群砂泥岩、海相玄武岩,并可能有少许同时代花岗岩,形成于康滇古陆东缘大陆坡或边缘海,自西向东呈康滇古陆—潮坪—浅水陆棚—深水陆棚—水下隆起有序变化,工区位于浅水陆棚相;2）稀土元素δCe值、δEu值及微量元素Mo、V含量、（V）N/（V+Ni）N比值、（Cu）N/（Zn）N比值反映筇竹寺组底部为深水陆棚环境,上部总体为浅水陆棚沉积环境,局部水体加深为深水陆棚沉积环境。总体上该区以浅水陆棚为优势相,并具酸性还原环境特点;3）微量元素Rb、Ba、Ga、V、Zn、Mo、Cd、Sn、Zr有明显的富集。主量元素（SiO2）N/（Al2O3）N比值及微量元素Ba、U含量、Zn-Ni-Co三角图、U/Th比值、Co/Zn比值表明有生物或热水作用的参与。  相似文献   

15.
Almost pure andradite and intermediate members of the andradite-grossular series (gros40–49, and 47–54, py0–3, alm0–3, spess0–2, hydrogarnet0–3), often framboidal in habit, are widespread in metabasites including lavas, minor intrusions, and volcanic sandstones and breccias metamorphosed under prehnite-pumpellyite and pumpellyite-actinolite facies conditions, possibly extending into the zeolite facies. Coexisting phases include iron-rich epidotes (100 Fe*/Fe*+Al=22–34), pumpellyite, prehnite, actinolite, and chlorite, electron microprobe analyses of which are given, as well as quartz, albite, and calcite. Zoisite (100 Fe*/Fe*+Al=1–5) and iron-poor epidote (100 Fe*/Fe*+Al=11–18) occur in 2 rocks in pseudomorphs after plagioclase together with more iron-rich epidote, but not in close association with the garnets. Coexisting pumpellyite is iron-rich (FeO* 9–14%) in the prehnite-pumpellyite facies and iron-poor (FeO* 5%) in the pumpellyiteactinolite facies. Chlorites and actinolites vary widely and sympathetically in FeO/MgO+FeO ratio. Andradite is also described from a stilpnomelane-actinolite-hematite-bearing andradite quartzite of the pumpellyite-actinolite facies. Conditions of formation involved temperatures of 300 to 400 ° or less, at pressures up to a few kilobars. A wide range of oxygen fugacities is possible, but in the fluid phase was low. Grandite and chlorite are incompatible in the pumpellyite-actinolite and greenschist facies in the presence of quartz but the 2 minerals occur together in some pumpellyite-actinolite facies assemblages as a result of incomplete reaction and/or local deficiency in silica. In the greenschist facies the association is replaced by epidote-actinolite±hematite and sodic amphibole. Whereas at medium to high grades of metamorphism andradite and grandite are characteristic of skarns irrespective of , at very low grades they are found in mafic volcanic rocks and volcanogenic sediments as well as in certain cherty rocks of unusual composition, rodingites, and serpentinites, where was very low.  相似文献   

16.
自然状态下土壤中重金属元素是否稳定存在是重金属污染固化修复技术中的核心问题。本文以常见重金属离子Pb2+为例,分析土壤中重金属离子与常见离子基团结合的稳定性。将第一性原理应用于Pb的存在形态和稳定性的分析,计算了PbCO3、PbSO4、PbCl2、Pb3（PO4）2、PbAl2O4和Pb3Fe2（PO4）4的自由能、能带和态密度。首先推断Pb2+和CO32-、SO42-、Cl-、PO43-等土壤中常见阴离子的结合稳定性,再判断加入金属阳离子Al3+和Fe3+对体系稳定性的影响。结果表明：铅化合物自由能从高到低趋势为PbCl2、PbAl2O4、PbCO3、PbSO4、Pb3（PO4）2、Pb3Fe2（PO4）4,其相应的结构稳定性顺序从大到小为Pb3Fe2（PO4）4、Pb3（PO4）2、PbSO4、PbCO3、PbAl2O4、PbCl2。通过对能带和态密度的分析,首先确定了SO42-和PO43-的引入能够增强含Pb体系的稳定性,进一步加入金属阳离子Fe3+会使体系更稳定。推测SO42-、PO43-为治理Pb2+污染合适的官能团,应选择容易释放SO42-、PO43-的物质作为合适的钝化剂。在实际应用中可选择磷酸二氢钠、无水硫酸钠、脱硫石膏等作为钝化剂。  相似文献   

17.
T. Agata 《Lithos》1994,33(4):241-263
The Asama igneous complex comprises layered mafic and ultramafic plutonic rocks exposed over about 500×6000 m in the Mikabu greenstone belt, Sambagawa metamorphic terrain of Mie Prefecture; its margins terminate by faults, and there is no trace of chilled rocks. The exposed layered sequence is about 460 m thick, and includes dunite, plagioclase wehrlite, olivine gabbro and two-pyroxene gabbro. The crystallization sequence of essential cumulus minerals is olivine, followed by plagioclase and clinopyroxene together, and finally the appearance of orthopyroxene. Olivine systematically varies in composition from Fo89 to Fo78 with stratigraphic height in the lower to middle portion of the layered sequence. The composition of clinopyroxene changes from Ca49Mg46Fe5 to Ca40Mg47Fe13 upward in the layered sequence; cumulus orthopyroxene, which occurs at the top of the exposed layered sequence, has a composition of Ca2Mg74Fe24. Cumulus chromite occurs as disseminated grains in peridotitic rocks, and tends to increase its Fe3+/(Cr+Al+Fe3+) ratio with stratigraphic height. The most aluminous chromite [Cr/(Cr+Al) = 0.48] occurs in dunite that crystallized shortly before plagioclase began to separate as an essential phase. The Cr/(Cr+Al) ratio of the most aluminous chromite, coupled with the crystallization order of essential minerals, suggests that the Asama parental magma was moderately enriched in plagioclase and clinopyroxene components in the normative mineral diagram plagioclase-clinopyroxene-orthopyroxene. It was similar to a Hawaiian tholeiite and different from the Bushveld and Great “Dyke” parental magmas that were more enriched in orthopyroxene component; it also differed from mid-oceanic ridge basalts that are more depleted in the orthopyroxene component. The Asama clinopyroxene and chromite show characteristically high TiO2 contents and are also similar to those in Hawaiian tholeiites. The Asama igneous complex probably resulted from the crystallization of a magma of a Hawaiian (oceanic-island) tholeiite composition and formed in an oceanic island regime.  相似文献   

18.
A. D. Paktunc  L. J. Cabri 《Lithos》1995,35(3-4):261-282
Chromian spinels from a number of localities were analyzed by proton and electron microprobes to examine the variation of trace elements in different geological environments. Chromian spinels studied include those representing ophiolitic complexes, layered intrusions in continental areas, Alaskan-type complexes, komatiitic subvolcanic sills, Ni sulfide ores and metamorphosed mafic and ultramafic rocks.

Nickel concentrations range from 30 to 4690 ppm (proton microprobe), with a mean value of 943 ppm. Nickel, favouring the octahedral sites in the spinel structure, displays an overall increase with a decrease in the Cr/(Cr + Al + Fe3+) ratio. Nickel partitioning between chromian spinel and mantle silicates appears to be primarily dependent upon the major element composition of the chromian spinel.

Zinc concentrations range from 230 to 9810 ppm (proton microprobe), with a cluster around 500 ppm. Ophiolitic chromian spinels display the lowest overall Zn values. Zinc levels appear to discriminate between chromian spinels in chromitite samples from those occurring as accessory chromian spinel in dunites or other rock types. Chromian spinels that are enclosed in or adjacent to sulfide grains display higher concentrations of Zn. Zinc, strongly favouring the tetrahedral sites, displays a crude negative correlation with the Mg/(Mg + Fe2+) ratio and appears to vary as a function of temperature.

All the chromian spinel grains analyzed contain measurable quantities of Ga by proton microprobe, ranging from 10 to 208 ppm. There is a reciprocal relationship between the Ga concentration and the Cr/(Cr +Al + Fe3+) ratio and a crude positive correlation between the Ni and Ga concentrations. Measured Ga concentrations in chromian spinel and whole rock samples are supportive of the experimental mineral-melt partition coefficient of Malvin and Drake (1987). Similar to the peridotite xenoliths, mid-ocean ridge basalts and oceanic-island basalts, Ga correlates well with Al2O3 in the case of the ophiolitic chromian spinels and most of those representing layered complexes. The ophiolitic chromian spinels seem to have crystallized from melts whose compositions are similar to those of partial melts of the upper mantle.  相似文献   


19.
In order to study the sedimentary environment characteristics of the Late Paleozoic in Kala area of Western Sichuan Province, the authors have conducted the petrological and geochemical analyses of the widely distributed silicate in Qiongyi Formation of Lower Carboniferous and Kawenggou Formation of Upper Permian. The results show that the silicate in the study area belongs to the pure siliceous rocks, with a continuous supply of land-based materials during the deposition process. The average Al/(Al+Fe+Mn) ratio is 0.62, and the silicate shows a biogenic origin by the Al-Fe-Mn diagram. The ratios of Al2O3/ (Al2O3+ Fe2O3), Th/U, Th/Sc, (La/Ce)N and (La/Yb)N and tectonic environment discriminant diagram demonstrate that the silicate developed in a shallow-slope depesitional environment in the continental margin. The Ceanom value is -0.04 to 0.07, and it gradually increases from the Carboniferous to the Permian period, indicating the water body is in an anoxic environment with gradually increasing reducibility. The Garz--Litang basin opened in the Carboniferous period, in accordance with the regional geological evolution, and it continued to expand during the Permian period, with the gradually increasing depth of the seawater within the sedimentary basins.  相似文献   

20.
为了研究川西卡拉地区晚古生代沉积环境特征,以该地区下石炭统邛依组和上二叠统卡翁沟组中广泛分布的硅质岩为研究对象,开展了岩石学、地球化学特征等研究。结果表明: 研究区古生代硅质岩属纯硅质岩范畴,在沉积过程中有持续的陆源物质供给; Al/(Al+Fe+Mn)平均值0.62,结合Al-Fe-Mn三角图解,显示它们为生物成因硅质岩; Al2O3/(Al2O3+Fe2O3)、Th/U、Th/Sc、(La/Ce)N、(La/Yb)N等特征比值以及构造环境判别图,反映出硅质岩沉积环境为大陆边缘的浅海-斜坡; Ceanom值为-0.04~0.07,从石炭纪—二叠纪逐渐增大,指示水体为缺氧环境,且还原性逐渐增强。结合区域地质演化,认为甘孜理塘洋在石炭纪时期已经打开,并在二叠纪时期持续扩张,区内沉积盆地的海水逐渐变深。  相似文献   

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