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1.
中国南方灯影峡期(晚前寒武纪)是白云岩广泛发育的海洋碳酸盐沉积时期,在灯影组中部发育从海水直接沉积沉淀的原生白云岩,目前仍保留其原始组构特征。从40个原生白云石(岩)中测得:泥晶白云石的δ13C值为3.64‰,δ18O值为-1.17‰(n=6);白云岩的13C值为3.52‰,δ18O值为-1.86‰(n=15);海水纤状白云石胶结物δ13C值为2.90‰,δ18O值2.65‰(n=8);海水刃状白云石胶结物的δ13C值为2.96‰,δ18O值为-2.41‰(n=8);晶纹层和海水纤状白云石胶结物的δ13C值为2.79‰,δ18O值为-3.13‰。40个岩样的δ13C平均值为3.25‰±0.44‰,δ18O平均值为-2.12‰±0.98‰(均以PDB标准)。对于灯影峡期海相云岩的原始δ13C和δ18O值,不采用所有样品的平均值,而是采用原生白云石沉积物与海水白云石结物δ13C值和δ18O值两个图示分布区重叠部分的最重同位素值,即：δ1C值为4.43‰(PDB标准),δ18O值为-0.62‰(PDB标准),将其作为灯影峡期海洋碳酸盐岩的原始同位素组成。对海水原生白云石胶结物包裹体盐度进行了测定,海水δ18O计算值为2.90(SMOW标准),用原始δ18O值计算的原生白云石形成时的海水温度为40.8 ℃。这说明中国南方灯影峡的海洋为炎热的较高的海水温度环境。 相似文献
2.
河南栾川三道沟铅锌银矿床是豫西铅锌银矿集区的重要组成部分。矿床成矿作用划分为早、中、晚3个成矿阶段,即石英-黄铁矿阶段、石英-铅锌银硫化物阶段和石英-方解石阶段。各成矿阶段石英中流体包裹体主要有液体包裹体、气体包裹体、含CO2包裹体3种类型。成矿早、中、晚阶段成矿温度依次降低,分别为260~360 ℃、200~320 ℃、160~260 ℃,成矿流体盐度先升高后降低,分别为4%~10%、6%~12%、4%~8%,密度为0.58~1.06 g/cm3,平均0.86 g/cm3,即成矿流体为高-中温、低盐度、低密度流体。成矿早阶段δD=-67.5‰~-75.1‰,δ18O水=6.4‰~11.1‰;成矿中阶段δD=-106.8‰,δ18O水=5.0‰;成矿晚阶段δD=-86.4‰~ -100‰,δ18O水=-0.7‰~2.2‰,综合研究表明成矿流体为岩浆水或变质水,成矿中-晚阶段有大气降水的加入。初步认为三道沟铅锌银矿床属于中温热液脉型铅锌银矿床,是燕山期岩浆期后含矿热液充填成矿作用的产物。 相似文献
3.
河南省老湾金矿床地球化学特征及矿床成因 总被引：3，自引：0，他引：3
在详细分析河南省老湾金矿床成矿地质背景、矿床地质特征的基础上,研究该矿床流体包裹体和氢、氧、硫、铅同位素,结果表明该金矿床的成矿流体为中低温、低盐度的富CO2的K+-Na+ -Cl--SO 2-4体系。氧、氢同位素分析显示,成矿流体δ18O值变化于-5.25‰～+5.37‰,δD变化于-67‰～-76‰,表明成矿流体主要来源于岩浆水和大气降水;硫化物的δ34S值变化于-0.1‰～+5.3‰,平均值为+3.98‰,显示深源硫的特征;Pb同位素组成显示铅主要来源于地幔,有少量地壳铅的加入。综合研究表明,老湾金矿床为受韧性剪切带控制的中-低温热液构造蚀变岩型金矿床。
相似文献
4.
新疆若羌县红柳沟Ⅰ号剖面出露厚约300 m的新元古界成冰系冰沟南组的细粒沉积物和碳酸盐岩等,并发现有沥青油气显示。通过厚160 m左右硅质岩剖面实测以及岩石学、地球化学等研究表明: 红柳沟Ⅰ号剖面中的硅质岩主要由石英、黏土构成,有微量的含铁、锰、磷的独立矿物;具有隐晶质、微晶石英和粗-巨晶石英“镶嵌结构”3种结构类型;硅质岩中SiO2、Fe2O3、Ba和δEun值相对较高,Al2O3、MnO、MnO/TiO2、U/Th和Sr/Ba值较低,∑REE、Sr/Ba、MnO2/TiO2和δCen值等呈现有规律的变化;δ30Si值平均为-0.43‰(-0.8‰~0.3‰),$\delta^{18}O_{Snow}$值平均为20.42‰(16.0‰~26.0‰),估算的平均温度为90 ℃(52~127 ℃),指示了硅质岩具有多个沉积旋回,在海水与热水参与的大陆边缘盆地中沉积,并经历了早成岩期、浅埋藏期以及与多期走滑断裂活动有关的热流体与大气淡水的叠加改造。 相似文献
5.
《矿物岩石地球化学通报》2016,(5)
为研究滇西小龙河锡矿床和来利山锡矿床的成矿流体演化特征和矿床成因,采用等离子质谱法(ICP-MS)对2个矿床中的脉石矿物萤石和方解石进行了微量元素和稀土元素分析测试。结果表明,小龙河矿床萤石的稀土元素总量(ΣREE)为12.86×10-6~2275.96×10-6,具有弱的负Ce异常和强的负Eu异常,相对富集Rb、Th、U、Pr、Nd和Sm等元素。来利山矿床方解石的ΣREE值低,为3.18×10-6~29.16×10-6,具有弱的负Ce异常,相对富集Rb、Ba、Th、U、Sr和Eu等元素。2个矿床的Y/HoLa/Ho图解和Tb/Ca-Tb/La图解指示萤石和方解石均为热液成因。小龙河矿床成矿物质主要来源于岩浆热液,随着成矿流体的演化,后期明显带有沉积地层物质加入,而来利山矿床成矿物质主要来源于围岩地层。 相似文献
6.
为研究皖北新元古界望山组灰岩地球化学特征及地质背景,对该地区灰岩进行了系统的岩石学和微量元素地球化学测试。研究结果表明：望山组灰岩中,元素U、Pb、Sr、Sm富集,Nb、Pr、Zr、Hf明显亏损;稀土总量偏低（6.68～42.78 μg/g）,轻稀土略亏损,NdSN/YbSN值在0.65～0.91之间变化,轻重稀土分异微弱,灰岩样品均具有程度不同的La和Y正异常。U、Th、Ce等元素特征反映了研究区望山组形成于缺氧的水体环境,Sr/Ba、Sr/Cu值反映了望山组灰岩形成于盐度较大的海水环境和干旱的气候条件;La-Th-Sc和Th-Sc-Zr/10图解指示望山组灰岩可能形成于大陆岛弧环境。 相似文献
7.
茂租铅锌矿床位于扬子地台西南缘,是滇东北矿集区内的一个大型矿床,矿体主要呈似层状产于震旦系灯影组白云岩中;矿石矿物以闪锌矿为主,次为方铅矿;脉石矿物主要为白云石、方解石和萤石。本文对该矿床中与铅锌矿密切共生的团块状白云石、方解石和萤石以及围岩灯影组白云岩的REE地球化学特征和C、O、Sr同位素进行了对比研究。结果表明:团块状白云石和方解石的稀土配分模式、C同位素和Sr同位素比值与围岩灯影组白云岩比较接近,表明形成团块状白云石和方解石的成矿流体主要来源于围岩灯影组白云岩的溶解;但这两种矿物的稀土总量ΣREE高于灯影组白云岩,说明成矿流体除了主要由围岩提供REE外,还有部分其他富含REE流体的加入。萤石则具有LREE亏损和分配曲线相对平缓的稀土配分模式特征,表明萤石形成于成矿的晚阶段,有更多的外部流体的加入。团块状白云石、方解石和萤石表现出明显的Eu正异常,且团块状白云石和方解石的O同位素低于灯影组白云岩,反映了存在较高温度的流体活动,这3种脉石矿物是由高温热液流体形成的。灯影组白云岩和3种脉石矿物都具有明显的Ce负异常,说明成矿流体可能主要来源于地层循环水,继承了围岩的Ce负异常特征。方解石和萤石的Sr同位素比值高于围岩震旦系灯影组白云岩和峨眉山玄武岩,但小于基底岩石昆阳群和会理群,说明成矿流体主要由赋矿围岩等沉积地层中的循环流体与流经了基底岩石的深部流体混合形成。 相似文献
8.
藏南沙拉岗锑矿稀土和微量元素地球化学示踪及成矿物质来源 总被引：7，自引：1，他引：6
藏南沙拉岗锑矿赋存于下白垩统甲不拉组碳质板岩、泥质粉砂岩、硅质岩及燕山期辉绿岩和喜山期辉长岩中,受近东西向层间破碎带和近南北向构造破碎带控制。围岩蚀变较弱,围绕矿体呈对称性的面状、带状分布。稀土和微量元素测试结果表明碳质板岩和硅质岩具有与上地壳和太古宙后页岩非常相似的稀土配分模式。喜山期辉长岩以轻稀土相对亏损、重稀土相对富集和Eu轻度亏损的平坦型稀土配分模式有别于以轻稀土轻度富集、Eu无异常的稀土配分模式为特征的藏南燕山期辉绿岩。锑矿石具有轻稀土强烈富集、分馏程度高、Eu中度亏损、Ce强烈亏损的配分模式,与洋中脊黑烟囱-白烟囱中热液流体和喷流沉积物的Eu强正异常、海水的Ce中等负异常和重稀土富集的稀土配分模式及沃西Sedex型W-Sb-Au矿的稀土配分模式明显不同,但与喜山期辉长岩的稀土配分模式具有明显的互补关系。此外,锑矿石以其强Nb负异常及Ce和Ba正异常的微量元素特征,展示出与喜山期辉长岩的弱Nb负异常和强Rb正异常及碳质板岩-硅质岩的Nb、Ba负异常和轻度Ce、Rb、Th正异常的异同点,矿石δ34S除个别样品为10.3‰和-41.6‰外,均分布在-2.6‰~-4.1‰区间,反映成矿物质主要来源于岩浆的特点。前人测定的流体包裹体氢、氧同位素值分别为δD=-151‰~-166‰,δ18O=9.4‰~12.3‰,显示岩浆水和地下水的混合性质。因此沙拉岗锑矿是形成于中新世、与藏南拆离系有关的浅成低温热液型矿床,成矿物质主要来源于喜山期辉长岩岩浆,少量来源于围岩,成矿流体部分来源于岩浆期后热液,部分来源于地下水。 相似文献
9.
黔东北沿河大竹园萤石矿赋存于下奥陶统桐梓组及红花园组碳酸盐岩内,受NW向断裂构造控制。该类萤石矿床在黔东北及渝东南一带广泛分布。本文对该萤石矿床的萤石单矿物及围岩进行了微量元素及稀土元素地球化学分析,结果显示萤石的微量元素仅Pb、Zn、Co、Ni等元素含量相对较高,Rb、Sr、Ta、Zr、Nb、V、Cr、U、Th、Hf等元素含量仅为地壳值的0.01~0.05倍。稀土元素含量很低(∑REE=2.35×10–6~4.80×10–6),相对富集轻稀土元素(LREE/HREE=3.12~6.33),具有Eu正、负异常(δEu=0.59~1.59)和Ce负异常(δCe=0.80~0.96)。萤石与赋矿围岩具有相近的微量元素配分型式,均明显亏损Nb、Zr、Hf等元素,富集Ba、U、Sr等元素。萤石与赋矿碳酸盐岩都具有轻稀土相对富集、重稀土相对亏损,明显右倾的REE配分型式。综合分析认为该萤石矿的成矿物质Ca主要来源于碳酸盐岩围岩;而碳酸盐岩围岩的F元素含量很低,结合萤石的微量元素及δEu、δCe值特征,暗示形成萤石的成矿流体经过了深部演化,成矿物质F可能主要来自深部富F地层。 相似文献
10.
新疆薄克土巴依铁锰矿床赋存于下泥盆统康布铁堡组变质火山-沉积岩系中。本研究利用流体包裹体显微测温、氢和氧同位素以及年代学数据,探讨该矿床的成矿流 体性质及来源、成矿时代和成矿作用。结果表明,矿体呈层状,与地层产状一致,矿石具有块状、条带状、条纹状、细脉状和浸染状构造,矿化具有喷流沉积特征。成矿流体属中温(集中在200~320 ℃) 、低盐度(1.05%~4.49%)、中低密度的Na2O-H2O体系。重晶石的δD值为-129‰~-116‰,δ18O值变化于10.4‰~11.6‰,δ18OH2O值为5.7‰~10.3‰,表明成矿流体来自深循环的海水与岩浆水的混合。矿体围岩变质安山岩的锆石LA-ICP-MS U-Pb年龄为(398.8±1.3) Ma,限定成矿时代在399 Ma左右,即为早泥盆世成矿。 相似文献
11.
Associated with the Cretaceous Okorusu carbonatite complex (Namibia) is a hydrothermal fluorite mineralization hosted in Pan-African country rock marbles, which resulted from fluid-rock reaction between the marbles and orthomagmatic, carbonatitic fluids expelled from the carbonatite. Yellow fluorite I was deposited in veins up to 5 cm away from the wallrock contact, followed by purple and colorless fluorite II, smoky quartz and barite, a Mn-rich crust on early calcite, and pure calcite. This clear-cut sequence of mineral growth allows an investigation into fluid-rock interaction processes between the marble and the migrating carbonatitic fluid, and element fractionation patterns between the fluid and subsequent hydrothermal precipitates.Fluorite I shows a progressive change in color from dark yellow to colorless with purple laminations over time of deposition. Subsequent fluorite I precipitates show an increase in Ca, and a continuous decrease in F, Sr, REE, Y, Th, U and Pb contents. The ratios (Eu/Eu*)cn, Th/Pb and U/Pb increase whereas Y/Ho, Th/U and (La/Yb)cn decrease. The Sr-isotopic composition remains constant at 87Sr/86Sr = 0.70456-0.70459, but with varying, highly radiogenic Pb (206Pb/204Pb = 32-190, 238U/204Pb = 7-63). Fluorite II has 87Sr/86Sr = 0.70454-0.70459, 206Pb/204Pb = 18.349, and 207Pb/204Pb = 15.600, and a chemical composition similar to youngest fluorite I. The Mn-rich crust on early calcite accumulated REE, Ba, Pb, Zr, Cs, Th and U, developing into pure calcite with a prominent negative Ce anomaly and successively more radiogenic Sr. The calculated degrees of fluid-rock interaction, f = weight fraction of fluid/(fluid + marble), decrease from fluorite I and most fluorite II (f = 0.5) to calcite (f = 0.2-0.3) and hydrothermal quartz (f ? 0.1). A crush-leach experiment for fluid inclusions in the hydrothermal quartz yielded a Rb-Sr isochron age of 103 ± 12 Ma. Crush-leach analysis for the carbonatitic fluid trapped in the wallrock yielded a trend from the fluid leachate to the host quartz (206Pb/204Pb = 18.224 and 18.602, 207Pb/204Pb = 15.616 and 15.636, respectively) extending from carbonatite towards crustal rocks.Calculated trace element distribution coefficients fluorite/fluid are below unity throughout, and increase from La to Yb. Elements largely excluded from fluorite (Ba, Pb, LREE relative to HREE) were incorporated later into the Mn-rich crust on calcite. The trace element patterns of the hydrothermal minerals are related to changing aCO2 and aF− in the fluid during continued fluid-marble reaction. A predominance of carbonate over fluoride complexing in the fluid as reactions proceeded controlled the Y/Ho, Th/U and REE patterns in the fluid and the crystallizing phases. Deviations from these trends indicate discontinuous processes of fluid-rock reaction. 相似文献
12.
东南沿海分布大面积的白垩纪晚期侵入岩。这些岩石可分为两期:其中115~100Ma以钙碱性系列岩石为主,岩石组合为辉长岩-闪长岩-花岗闪长岩-二长花岗岩-碱性长石花岗岩;而100~86Ma的岩石为碱性系列,岩石组合为石英二长斑岩-正长斑岩-碱性长石花岗岩。115~100Ma的辉长岩以角闪辉长岩为主,具有极高的CaO、MgO和Al_(2)O_(3)含量,具有极低的SiO_(2)(42.9%~53.8%)、全碱(K_(2)O+Na_(2)O:0.86%~5.28%)、Ba、Nb、Th、Rb和Zr含量,也具有极低的FeO^(T)/MgO、La/Yb和Zr/Hf比值,较高的Eu/Eu^(*)、Sr/Y比值和Sr含量,为基性-超基性堆晶岩。与辉长岩同期的闪长岩和细粒暗色包体具有较高的SiO_(2)(50.34%~63.68%),较低的CaO、P_(2)O_(5)、MgO、Al_(2)O_(3)含量,相对低的Eu/Eu^(*)和Sr/Y比值,变化较大的La/Yb和Zr/Hf比值,代表了从基性岩浆储库中抽取的富硅熔体。115~100Ma的花岗闪长岩和二长花岗岩类岩石为准铝质岩石,SiO_(2)含量变化较大(61.7%~75.3%),具有较低的FeO^(T)/MgO、Ga/Al比值和Nb、Zr及Nb+Zr+Ce+Y元素含量,显示出典型I型花岗岩的特征。这些花岗岩具有相对高的La/Yb、Eu/Eu^(*)和Zr/Hf比值和高的Sr、Ba和Zr含量。结合岩相学特征,这些花岗岩为堆晶花岗岩。而115~100Ma的碱性长石花岗岩具有极高的SiO_(2)含量(大于75%),低的Eu/Eu^(*)、La/Yb、Zr/Hf和Sr/Y比值,具有低的Ba、Sr和Zr含量和高的Rb、Nb、Y和Th含量和Rb/Sr比值,表明这些花岗岩是由富硅岩浆储库中抽离的高硅熔体侵入地壳形成。100~86Ma期间形成的二长斑岩和正长斑岩具有极高的全碱含量,可以达到8%~12%,其SiO_(2)主要集中在60%~70%,具有极高的Zr、Sr和Ba含量和Eu/Eu^(*)、La/Yb和Sr/Y比值,显示出堆晶花岗岩的特征。而100~86Ma期间形成的大部分碱性长石花岗岩具有极高的SiO_(2)含量(大于75%),并显示出A型花岗岩的特征,具有高的Rb/Sr比值和高的Rb、Y和Th和低的Ba、Sr含量和低的Zr/Hf、La/Yb、Eu/Eu^(*)和Sr/Y比值,表明它们是由富硅岩浆储库抽离的高硅熔体侵入浅部地壳形成。东南沿海高硅花岗岩的形成和穿地壳岩浆系统密切相关,高硅花岗岩是由浅部地壳内晶体-熔体分异产生的熔体侵入地壳所形成,而高硅花岗岩的地球化学特征与岩浆储库的水及挥发份含量密切相关。115~100Ma期间,从富水的岩浆储库抽离的熔体形成具有低高场强元素含量和低Rb/Sr比值的高硅花岗岩,这一过程与古太平洋板块俯冲有关;100~86Ma期间,从富挥发份的岩浆储库抽离的熔体形成碱性特征、富含高场强元素和具有高的Rb/Sr比值的高硅花岗岩,这一过程和古太平洋板块回撤软流圈上涌有关。 相似文献
13.
In progressing from a granitoid mylonite to an ultramylonite in the Brevard shear zone in North Carolina, Ca and LOI (H2O) increase, Si, Mg, K, Na, Ba, Sr, Ta, Cs and Th decrease, while changes in Al, Ti, Fe, P, Sc, Rb, REE, Hf, Cr and U are relatively small. A volume loss of 44% is calculated for the Brevard ultramylonite relative to an Al–Ti–Fe isocon. The increase in Ca and LOI is related to a large increase in retrograde epidote and muscovite in the ultramylonite, the decreases in K, Na, Si, Ba and Sr reflect the destruction of feldspars, and the decrease in Mg is related to the destruction of biotite during mylonitization. In an amphibolite facies fault zone separating grey and pink granitic gneisses in the Hope Valley shear zone in New England, compositional similarity suggests the ultramylonite is composed chiefly of the pink gneisses. Utilizing an Al–Ti–Fe isocon for the pink gneisses, Sc, Cr, Hf, Ta, U, Th and M-HREE are relatively unchanged, Si, LOI, K, Mg, Rb, Cs and Ba are enriched, and Ca, Na, P, Sr and LREE are lost during deformation. In contrast to the Brevard mylonite, the Hope Valley mylonite appears to have increased in volume by about 70%, chiefly in response to an introduction of quartz. Chondrite-normalized REE patterns of granitoids from both shear zones are LREE-enriched and have prominent negative Eu anomalies. Although REE increase in abundance in the Brevard ultramylonites (reflecting the volume loss), the shape of the REE pattern remains unchanged. In contrast, REE and especially LREE decrease in abundance with increasing deformation of the Hope Valley gneisses. Mass balance calculations indicate that ≥95% of the REE in the Brevard rocks reside in titanite. In contrast, in the Hope Valley rocks only 15–40% of the REE can be accounted for collectively by titanite, apatite and zircon. Possible sites for the remaining REE are allanite, fluorite or grain boundaries. Loss of LREE from the pink gneisses during deformation may have resulted from decreases in allanite and perhaps apatite or by leaching ofy REE from grain boundaries by fluids moving through the shear zone. Among the element ratios most resistant to change during mylonitization in the Brevard shear zone are La/Yb, Eu/Eu*, Sm/Nd, La/Sc, Th/Sc, Th/Yb, Cr/Th, Th/U and Hf/Ta, whereas the most stable ratios in the Hope Valley shear zone are K/Rb, Rb/Cs, Th/U, Eu/Eu*, Th/Sc, Th/Yb, Sm/Nd, Th/Ta, Hf/Ta and Hf/Yb. However, until more trace element data are available from other shear zones, these ratios should not be used alone to identify protoliths of deformed rocks. 相似文献
14.
对华北克拉通重力梯度带东西两侧的河北承德袁家庄和内蒙古四子王旗白脑包出露的晚中生代火山岩进行了地球化
学对比研究。全岩主量元素、微量元素和Sr-Nd-Hf同位素数据表明,袁家庄火山岩和白脑包火山岩具有相似的地球化学特
征。这些火山岩轻、重稀土强烈分异,富集大离子亲石元素(如Rb,Ba,Th,U,K等),亏损高场强元素(如Nb,Ta,Zr,
Hf,Ti等);其同位素具有高(87Sr/86Sr)i,低εNd(t)和低εHf(t)的特征,因此认为袁家庄和白脑包火山岩具有相似的源区,即均来
源于被交代的古老岩石圈地幔的部分熔融。结合文献资料,作者认为,这些晚中生代火山岩是华北克拉通岩石圈减薄的直
接产物,中生代时期华北克拉通岩石圈的减薄不仅仅局限于重力梯度带以东地区,以西的部分地区也有发生。 chengxu 相似文献
学对比研究。全岩主量元素、微量元素和Sr-Nd-Hf同位素数据表明,袁家庄火山岩和白脑包火山岩具有相似的地球化学特
征。这些火山岩轻、重稀土强烈分异,富集大离子亲石元素(如Rb,Ba,Th,U,K等),亏损高场强元素(如Nb,Ta,Zr,
Hf,Ti等);其同位素具有高(87Sr/86Sr)i,低εNd(t)和低εHf(t)的特征,因此认为袁家庄和白脑包火山岩具有相似的源区,即均来
源于被交代的古老岩石圈地幔的部分熔融。结合文献资料,作者认为,这些晚中生代火山岩是华北克拉通岩石圈减薄的直
接产物,中生代时期华北克拉通岩石圈的减薄不仅仅局限于重力梯度带以东地区,以西的部分地区也有发生。 chengxu 相似文献
15.
Geochemistry of eocene calc-alkaline volcanic rocks from the Kastamonu area,Northern Turkey 总被引：294，自引：3，他引：294
Analytical data for Sr, Rb, Cs, Ba, Pb, rare earth elements, Y, Th, U, Zr, Hf, Sn, Nb, Mo, Ni, Co, V, Cr, Sc, Cu and major elements are reported for eocene volcanic rocks cropping out in the Kastamonu area, Pontic chain of Northern Turkey. SiO2% versus K2O% relationship shows that the analyzed samples belong to two major groups: the basaltic andesitic and the andesitic ones. High-K basaltic andesites and low-K andesites occur too. Although emplaced on continental type basement (the North Anatolian Crystalline Swell), the Pontic eocene volcanics show elemental abundances closely comparable with typical island arc calc-alkaline suites, e.g. low SiO2% range, low to moderate K2O% and large cations (Cs, Rb, Sr, Ba, Pb) contents and REE patterns with fractionated light and almost flat heavy REE patterns. REE and highly charged cations (Th, U, Hf, Sn, Zr) are slightly higher than typical calc-alkaline values. Ferromagnesian elements show variable values. Within the basaltic andesite group the increase of K%, large cations, REE, La/Yb ratio and high valency cations and the decrease of ferromagnesian element abundances with increasing SiO2% content indicate that the rock types making up this group developed by crystalliquid fractionation of olivine and clinopyroxene from a basic parent magma. Trace element concentration suggest that the andesite group was not derived by crystal-liquid fractionation processes from the basaltic andesites, but could represent a distinct group of rocks derived from a different parent magma. 相似文献
16.
塔里木盆地北部下奥陶统碳酸盐岩孔洞充填物特征及其成岩环境分析 总被引：2，自引：0，他引：2
为了正确分析和评价碳酸盐岩溶蚀孔洞在埋藏成岩环境中的发育和保存条件,对塔里木盆地北部露头剖面中下奥陶统白云岩及其溶蚀孔洞的充填物进行了详细的矿物学和地球化学研究,试图对这类孔洞充填物沉淀时的成岩环境进行恢复。大型洞穴充填物的矿物学特征和微孔洞充填物扫描电镜的分析表明,此类孔洞的环带状充填物具有明显的世代性,由基岩向孔洞中心,至少可识别出4期充填物,即第1期的乳白色白云石,第2期的铁质浸染的杂色高镁方解石,第3期的无色透明白云石和第4期的自形石英。碳、氧同位素分析结果表明,孔洞充填物形成于高温条件,结合微量元素、稀土元素所示的成岩信息可进一步推断其形成于高温埋藏环境,而非现代表生暴露期的充填物;第1期和第3期白云石充填物形成在相对还原且高盐度的流体性质条件下,而第2期高镁方解石充填物沉淀时相对偏氧化,盐度也偏低。据下奥陶统此类4期充填物的特征分析可知,第2期高镁方解石充填物的发育可能与构造抬升导致成岩环境的改变有关。 相似文献
17.
木洛稀土矿床成因上与碳酸岩-碱性杂岩密切相关。碳酸岩主要由方解石组成,CaO/（CaO＋MgO＋FeO＋Fe2O3＋MnO）比值在95.7%～99.6%,为方解石碳酸岩。碳酸岩相对富集大离子亲石元素Ba、Sr、LREE,亏损高场强元素Nb、Ta、Ti、Zr、P,高Zr/Hf和La/Nb值,低Sm/Nd和Rb/Sr值,暗示岩石来自富集地幔EMI。地质、地球化学研究表明,木洛碳酸岩是在峨眉山地幔柱地幔遗存物经喜马拉雅造山运动再次活化的产物,但碳酸岩熔浆在上侵过程中受到地壳物质混染。碳酸岩-碱性岩熔浆带来大量稀土元素,并在喜马拉雅造山期造山运动派生的局部引张部位成矿。 相似文献
18.
Kent C. Condie M. J. Viljoen E. J. D. Kable 《Contributions to Mineralogy and Petrology》1977,64(1):75-89
Major and trace element and modal analyses are presented for unaltered, epidotized, and carbonated tholeiite flows from the Barberton greenstone belt. Au, As, Sb, Sr, Fe+3, Ca, Br, Ga, and U are enriched and H2O, Na, Mg, Fe+2, K, Rb, Ba, Si, Ti, P, Ni, Cs, Zn, Nb, Cu, Zr, and Co are depleted during epidotization. CO2, H2O, Fe+2, Ti, Zn, Y, Nb, Ga, Ta, and light REE are enriched and Na, Sr, Cr, Ba, Fe+3, Ca, Cs, Sb, Au, Mn, and U are depleted during carbonization-chloritization. The elements least affected by epidotization are Hf, Ta, Sc, Cr, Th, and REE; those least affected by carbonization-chloritization are Hf, Ni, Co, Zr, Th, and heavy REE. Both alteration processes can significantly change major element concentrations (and ratios) and hence caution should be used in distinguishing tholeiites from komatiites based on major elements alone. The amount of variation of many of the least mobile trace elements in the altered flows is approximately the same as allowed by magma model calculations. Hence, up to about 10% carbonization and 60% epidotization of tholeiite do not appreciably affect the interpretation of trace-element models for magma generation. 相似文献
19.
New geological, petrochemical, mineralogical, and geochemical data are presented on the Uspensky granitoid massif in Southern
Primorye. The massif consists of the rocks of two associations: (1) the early association (103.3 ± 2.4 Ma) consisting of garnet-bearing
biotite and two-mica granite-leucogranites and (2) the late association (99 ± 2 Ma) represented by biotite (±amphibole) granodiorites,
melanogranites, and granites. The granitoids of both associations have moderate potassic alkalinity and elevated alumina contents
but differ in the proportions of alumina, calcium, and alkalis. The garnet-bearing granite-leucogranites are characterized
by the highest Rb, Th, and U contents and the lowest Sr, Ba, Hf, and Zr contents. The REE distribution patterns have a quasi-symmetric
shape and deep Eu minimums. The melanogranites show higher Sr and Ba contents and, as granites, are characterized by asymmetric
REE spectrums with an insignificant negative Eu anomaly. The porphyraceous granodiorites and granites are peculiar in their
lowered Sr and Ba contents, while the granodiorites have lowered contents of K, REE, Zr, Hf, Th, and U; elevated Nb contents;
and a distinctive Eu minimum. 相似文献