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黄陵地区新元古代侵入杂岩可为研究扬子板块北缘新元古代构造演化过程及其深部动力学机制提供关键信息。依据岩石组合及分布特征，可将黄陵杂岩划分为黄陵庙岩套、三斗坪岩套、大老岭岩套和晓峰岩套四个单元。本文以黄陵杂岩的围岩崆岭杂岩中花岗片麻岩、黄陵庙黑云母花岗岩和三斗坪闪长岩为研究对象，在系统的野外地质和岩石学研究基础上，开展了LA- ICP- MS锆石U- Pb年代学分析。结果表明，崆岭杂岩花岗片麻岩原岩年龄为1978±13 Ma，且记录了2.5 Ga的构造- 热事件。黄陵庙黑云母花岗岩和三斗坪闪长岩分别形成于815±9 Ma和813±6 Ma，与黄陵庙岩套和三斗坪岩套的侵位时限基本一致。综合分析本次研究结果与前人资料，认为黄陵杂岩主要形成于863~794 Ma，为新元古代早期岩浆活动的产物。通过综述区域地质和地球化学研究资料，认为黄陵杂岩形成于新元古代早期活动大陆边缘的构造环境，提出扬子板块北缘在新元古代早期经历了长期的俯冲- 增生造山过程。 相似文献
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北大巴山凤凰山岩体锆石U Pb LA ICP MS年龄及其构造意义 总被引：1，自引：0，他引：1
北大巴山凤凰山岩体是扬子陆块北缘典型的新元古代侵入岩群,对采自岩体的6个花岗岩(闪长岩)样品进行了LA-ICP-MS锆石U-Pb同位素定年分析。定年数据显示,岩浆活动可分为早期(797±6Ma)、中期(770±6Ma、774±5Ma)、晚期(755±6Ma、750±13Ma和743±6Ma)三个阶段,证实凤凰山岩体为多期岩浆侵入形成。这几期岩浆活动在扬子陆块具同步性和普遍性,广泛被记录在黄陵、汉南等其它新元古代杂岩中。凤凰山花岗岩完整记录了扬子陆块北缘南华纪初期的区域拉张—裂陷事件,其形成可能与导致Rodinia超大陆裂解作用的幕式地幔柱活动有关。本次研究对认识扬子陆块新元古代地壳生长与再造过程及Rodinia超大陆裂解机制具有重要意义。 相似文献
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鄂西黄陵花岗岩基同位素年龄谱 总被引：14，自引：0，他引：14
采用Isoplot程序重新计算了鄂西黄陵花岗岩基主要岩套的Rb-Sr等时线年龄和锆石U-Pb一致曲线年龄,测定了各种类型脉岩的侵入年龄,最后获得该岩基岩浆活动的年龄谱是主体太平溪英云闪长岩岩套和黄陵庙花岗闪长岩岩套的侵位年龄分别是(833±29)Ma和(819±7)Ma,大老岭石英二长花岗岩岩套是(786±54)Ma,脉岩套侵入年龄从花岗闪长斑岩的813 Ma开始,到770Ma的辉绿岩和772Ma的石英脉侵入,整个岩基抬升作用完成,岩浆活动基本结束.在印支期(217±7)Ma时,岩基上NNW和NNE向大断裂发生了强烈的再次活动.Nd,Sr同位素证据表明,除大老岭岩套外,其他三个岩套的岩浆演化是连续的,这些岩浆起源于晋宁期扬子板块北缘发生的大洋板块消减作用. 相似文献
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南秦岭铁瓦殿岩体的成岩时代及地质意义 总被引：4，自引：0，他引：4
铁瓦殿岩体位于陕西省南部汉阴县、石泉县和紫阳县交界部位,大地构造位置属于南秦岭构造带南部,主要由闪长岩、石英闪长岩、石英二长闪长岩、石英二长岩和二长花岗岩组成。LA-ICP-MS锆石U-Pb同位素定年结果表明铁瓦殿岩体存在3阶段的岩浆侵位:早期阶段的石英二长岩形成于742±5Ma,中期阶段的石英闪长岩、石英二长闪长岩及二长花岗岩形成于～722Ma;晚期阶段的石英闪长岩形成于704±4Ma。通过与扬子北缘汉南杂岩中的中酸性火山岩及侵入岩的岩石组合和形成时代对比,发现铁瓦殿深成侵入岩与扬子克拉通北缘汉南杂岩中中酸性侵入岩具有相似的岩石组合和形成时代,表明它们经历了相似的构造-岩浆演化。铁瓦殿岩体是南秦岭地区新元古代俯冲作用相关的重要地质记录。 相似文献
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黄陵花岗岩基的成因 总被引：18，自引：0，他引：18
黄陵花岗岩基位于扬子地台北缘，它连同汉南和鲤鱼寨岩基一起构成扬子地台北缘的低钾花岗岩等，形成于晋宁晚期扬子地台北侧的“秦岭洋”壳向南俯冲导致的大陆边缘造山运动过程中。黄陵花岗岩基可解体为三斗坪、黄陵庙、大老岭、晓峰4个岩套和14个单元，侵位于832－750Ma之间。三斗坪和黄陵庙两个岩套主要由英云闪长岩、奥长花岗岩花岗闪地组成，是在近南北向区域挤压下于约16km深部塑性域定位的同构造花岗岩，前者主要依靠岩浆在构造弱面逐次强力楔入创造定位空间，后者主要在处于活动状态的韧性拉张剪切带内定位。钙碱性系列的大老岭和晓峰岩套则是在本区地壳迅速隆起过程中分别在5km和＜1．5km深度的脆性域定位的构造晚期花岗岩。根据岩石化学和同位素组成推断，三斗坪岩套的源岩主要是晚太古代大陆拉斑玄武岩，母岩浆相当于英安质，岩套内的成分变化主要受角闪石分离结晶作用控制；黄陵庙岩套除受分离结晶作用影响外，成分变化主要与英安质母岩浆和某种长英质岩浆的混合有关；大老岭岩套的源岩亦为早前寒武纪火山岩。 相似文献
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扬子陆块新元古代地层发育完整并广泛分布,三峡地区南沱组冰碛岩是扬子北部南华纪的冰成杂砾岩,不整合地覆盖在新元古代黄陵花岗岩之上.南沱组冰碛岩成分复杂,分选性差,缺乏可对比的标志,其沉积时代和物源组成研究较少且存在争议.对南沱组冰碛岩开展锆石U-Pb定年工作,得到最年轻的锆石年龄为706±7 Ma,印证了南沱组沉积时代应不早于700 Ma的说法,并可与Marinoan冰期对应.所获得锆石U-Pb年龄谱峰值主要分为~3.0 Ga,2.5~2.3 Ga,2.05~1.95 Ga和900~700 Ma,反映了扬子陆块4次地壳再造事件,其中古元古代和太古代年龄与崆岭杂岩相似,900~800 Ma和800~700 Ma的锆石年龄与附近黄陵花岗岩和扬子北缘岩体一致.冰碛砂岩的微量元素和同位素组成分异明显,可能是扬子北缘岩体、黄陵花岗岩和崆岭杂岩不同程度混合的结果.南沱组冰碛岩中包裹的花岗质砾石表现出不同的微量元素特征,具有偏低的稀土含量和亏损的重稀土组成,结合其锆石U-Pb年龄和Sr-Nd同位素特征,这些花岗质砾石主体可能来自于附近黄陵花岗岩和崆岭岩基.南沱组冰碛岩的物质组成特征反映了新元古时期,扬子地区强烈的裂谷岩浆作用所导致的北高南低的地势环境. 相似文献
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湖北红安群的原岩形成时代一直是个有争议的问题。笔者对红安群中两个不同类型的花岗质侵入体进行了锆石U-Pb定年,在位于红安群之下的双峰尖岩体中获得岩浆侵位年龄为(813±6)Ma,在侵入于红安群中的高格岩体获得岩浆侵位年龄为(638±142)Ma,高压变质年龄为(229±22)Ma。结合目前在扬子板块和大别造山带内部获得的一系列新元古代年代学数据,认为红安群变质杂岩中沉积地层的形成时代应限制在825～630Ma之间,是扬子大陆基底在新元古代裂解的产物。这套岩石在印支期(约230Ma)华北与扬子板块碰撞过程中经历了低温高压蓝片岩—榴辉岩相变质作用。 相似文献
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扬子克拉通广泛存在太古宙-古元古代的结晶基底,但关于扬子克拉通早前寒武纪基底形成和演化的基本问题尚未完全解决,特别是基底是由多个块体拼合而成还是一个统一的结晶基底尚无定论.对扬子北缘张八岭隆起内肥东杂岩的片麻岩、斜长角闪岩及侵入其中的花岗岩进行了同位素地质年代学和地球化学研究,发现片麻岩具有相似的原岩年龄,分别为2 449±17 Ma、2 444±15 Ma、2 495±23 Ma、2 478±24 Ma,斜长角闪岩和A型花岗岩的原岩年龄分别为2 032±35 Ma和747±4 Ma,表明肥东杂岩出露有扬子克拉通晚太古-古元古代的结晶基底.片麻岩锆石Hf同位素组成相似,εHf（t）平均值为-3.6±0.5,两阶段Hf模式年龄（TDM2）范围主要在3.3~3.0 Ga,平均值为3 185±31 Ma,说明这一期约为2.45~2.50 Ga的岩浆活动主要是对扬子北缘古-中太古代地壳的再造.扬子北缘的鱼洞子群和陡岭杂岩都经历了相同性质的岩浆事件,同时扬子克拉通广泛出现约2.50 Ga的碎屑锆石和捕获锆石,表明扬子克拉通结晶基底是统一的. 相似文献
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西秦岭造山带北缘古元古界变质杂岩中新识别出新元古代元龙花岗质片麻岩和新阳花岗质片麻岩。花岗质片麻岩中锆石Th/U比值较高,阴极发光图象显示锆石内部发育振荡环带,具岩浆成因特点。LA-ICP-MS锆石U-Pb同位素206Pb/238U加权平均年龄分别为914.7±7.6Ma(MSWD=4.8)、978.5±4.8Ma(MSWD=1.5)和935.5±3.1Ma(MSWD=1.3),表明花岗岩岩体形成于新元古代,反映了新元古代早期西秦岭北缘存在一次俯冲碰撞事件,与Rodinia超大陆的汇聚事件具有一致性。 相似文献
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KIEFFER BRUNO; ARNDT NICHOLAS; LAPIERRE HENRIETTE; BASTIEN FLORENCE; BOSCH DELPHINE; PECHER ARNAUD; YIRGU GEZAHEGN; AYALEW DEREJE; WEIS DOMINIQUE; JERRAM DOUGAL A.; KELLER FRANCINE; MEUGNIOT CLAUDINE 《Journal of Petrology》2004,45(4):793-834
The Ethiopian plateau is made up of several distinct volcaniccentres of different ages and magmatic affinities. In the NE,a thick sequence of 30 Ma flood basalts is overlain by the 30Ma Simien shield volcano. The flood basalts and most of thisshield volcano, except for a thin veneer of alkali basalt, aretholeiitic. In the centre of the province, a far thinner sequenceof flood basalt is overlain by the 22 Ma Choke and Guguftu shieldvolcanoes. Like the underlying flood basalts, these shieldsare composed of alkaline lavas. A third type of magma, whichalso erupted at 30 Ma, is more magnesian, alkaline and stronglyenriched in incompatible trace elements. Eruption of this magmawas confined to the NE of the province, a region where the lavaflows are steeply tilted as a result of deformation contemporaneouswith their emplacement. Younger shields (e.g. Mt Guna, 10·7Ma) are composed of Si-undersaturated lavas. The three maintypes of magma have very different major and trace element characteristicsranging from compositions low in incompatible elements in thetholeiites [e.g. 10 ppm La at 7 wt % MgO (=La7), La/Yb = 4·2],moderate in the alkali basalts (La7 = 24, La/Yb = 9·2),and very high in the magnesian alkaline magmas (La7 = 43, La/Yb= 17). Although their Nd and Sr isotope compositions are similar,Pb isotopic compositions vary considerably; 206Pb/204Pb variesin the range of 相似文献
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J. E. Ortiz T. Torres Y. Yanes C. Castillo J. De La Nuez M. Ibez M. R. Alonso 《第四纪科学杂志》2006,21(3):287-306
Aminochronological and aminostratigraphical methods have been used to study the Quaternary aeolian deposits from the islands located east of the Canary Archipelago (Fuerteventura and Lanzarote islands and La Graciosa, Montaña Clara and Alegranza islets). The extent of racemisation/epimerisation of four amino acids (isoleucine, aspartic acid, phenylalanine and glutamic acid) was measured in land snail shells of the genus Theba. The age calculation algorithms of these amino acids have been determined to permit the numerical dating of these deposits. Eight Aminozones, each defining dune/palaeosol‐formation episodes, have been distinguished and dated at 48.6 ± 6.4, 42.5 ± 6.0, 37.8 ± 4.6, 29.4 ± 4.8, 22.4 ± 4.5, 14.9 ± 3.6, 11.0 ± 4.0 and 5.4 ± 1.1 ka BP, the first five of them defining cycles of 5–7 ka. The alternation of palaeosols and aeolian deposits, which are related to abrupt transitions from humid to arid conditions, are the reflection of globally induced changes in North Africa palaeoenvironmental conditions linked to the effect of African palaeomonsoons on the trade winds and the Saharan Air Layer. Probably these aeolian cycles, with a recurrence period of 5–7 ka, are the expression of multiples of the ～2.4 ka solar‐cycle. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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A paleomagnetic, rock-magnetic and paleointensity study has been carried out on 14 basaltic lava flows from two Pliocene (K–Ar age between 3.09 ± 0.10 Ma and 4.00 ± 0.15 Ma) sequences (Apnia and Korxi) from the eastern Djhavakheti Highland in southern Georgia (Caucasus).Measurement of strong-field magnetisation versus temperature curves yielded three types of thermomagnetic curves: (i) Reversible curves with magnetite as only remanence carrier (type H); (ii) irreversible curves with magnetite as only carrier of remanence (type H−) and (iii) irreversible curves showing a low Curie-temperature phase and magnetite (type L). Analysis of hysteresis curves showed that samples were characterised by a mixture of single-domain and multi-domain grains.Paleomagnetic experiments allowed determining characteristic components for all flows and normal polarities (6 flows), reversed polarities (7 flows) and intermediate polarities (1 flow) were observed.. Paleomagnetic poles were calculated using only those sites unequivocally showing normal or reversed polarities. The paleomagnetic pole obtained from flows of both combined sequences (latitude λ = 77.9°N, longitude ϕ = 152.1°E, n = 13, A95 = 11.8°, k = 13.4) showed a good agreement with the 5 Ma window of the European synthetic apparent polar wander path of Besse and Courtillot (2002). The paleomagnetic direction of the combined Apnia-Korxi flows agrees well with the expected one, showing no significant tectonic rotation. The latter cannot be however, completely excluded in the Korxi section. In that section, analysis of the angular dispersion of virtual geomagnetic poles yields a much higher value than expected.Paleointensity experiments using the Coe method were performed on 31 specimens from 10 flows. After application of specific selection criteria, 19 samples from 8 flows were observed to provide successful determinations, with mean flow values showing a wide scatter. If only flows with more than one successful paleointensity determination are taken into account, virtual dipole moments (VDMs) vary between 3.5 × 1022 A m2 and 8.3 × 1022 A m2. In intermediate polarity site AP2 no weak transitional paleostrength values were observed. 相似文献
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对芬兰斜长岩中斜长石的宏观和微观观测显示,无晕彩的斜长石包裹体不发育,有晕彩的斜长石发育定向排列的针状包裹体。依据斜长石中包裹体的发育程度,可将包裹体分为两类:密集型包裹体(35～50条/mm)和稀疏型包裹体(25～35条/mm)。发育密集型包裹体的斜长石的晕彩以蓝色为主,发育稀疏型包裹体的斜长石的晕彩以红色或橙红色为主。电子探针、扫描电镜和激光拉曼光谱的分析结果表明,该晕彩斜长石中的所有包裹体在成分上一致,均为磁铁矿,有晕彩的斜长石和无晕彩的斜长石的成分也一致。这表明该斜长岩中的斜长石是否具有晕彩与斜长石的成分、包裹体的成分及斜长石的双晶发育程度无关,而与包裹体的发育程度有关。斜长石和其中定向排列的磁铁矿针状包裹体类似于光学中的光栅效应,斜长石中晕彩的出现可能是光栅衍射和干涉造成的。 相似文献
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Pollen and dinoflagellate cyst assemblages from Core SU 81-18 recovered off Portugal (37°46′N, 10°11′W; 3135-m water depth) have been used to document the short-term environmental changes that occurred in southwest Europe since 25,000 yr B.P. The relationship between the oceanic and continental environments has been further examined by the use of other marine proxies (coarse sedimentary fraction, foraminifera) and by comparison with proximal land pollen records. Heinrich 2 (H2) and Heinrich 1 (H1) events were the most extreme parts of the highly variable last glacial period, with the maximum extension of dry steppe on land and the occurrence of cool and dilute waters at the core site. Our study shows that H1 and H2 are divided in two distinct phases: one with Neogloboquadrina pachyderma left coiling associated with the maximum input of ice rafted debris, reflecting the in situ release of icebergs and the occurrence of cool and dilute seawater at the core site; the other with dinoflagellate cysts of subpolar affinity, Bitectatodinium tepikiense, reflecting a seasonal control marked by warm summer SST and cold winter SST. 相似文献
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G. N. Baturin 《Lithology and Mineral Resources》2002,37(5):412-428
The behavior of molybdenum and manganese is studied in phosphorite samples from shelves, seamounts, and islands of the ocean. In shelf phosphorites, molybdenum and manganese contents are 2–128 and 12–1915 ppm, respectively, while the Mo/Mn ratio ranges from 0.004 to 4.5. Phosphorites from oceanic seamounts impregnated with ferromanganese oxyhydroxides contain 0.84–14.5 ppm of Mo and 0.1–17% of Mn. The Mo/Mn ratio ranges within 0.0008–0.004. Phosphate-bearing ferromanganese crusts overlying the seamount phosphorites contain 54–798 ppm of Mo and 10–20% of Mn; Mo/Mn ratio varies within 0.002–0.005. Corresponding values for most island phosphorites are 0.44–11.2 ppm, 27–287 ppm, and 0.008–0.20, respectively. Phosphorites from reduced environments are characterized by a relative enrichment in Mo and depletion in Mn, whereas the Mo/Mn ratio reaches maximum values. The ratio decreases with transition to suboxic and oxic conditions. Molybdenum content in recent shelf sediments is commonly higher than that in authigenic phosphorites from these sediments. Recent phosphorite nodules from the Namibian shelf become depleted in Mo and Mn during their lithification, but Pliocene–Pleistocene nodules of similar composition and origin from the same region are enriched in Mo and characterized by a variable Mn content. The higher Mo content in phosphate-bearing ferromanganese crusts is a result of coprecipitation of Mo and Mn from seawater. Nonweathered phosphorites on continents and phosphorites from oceanic shelves are largely enriched in Mo with the Mo/Mn ratio ranging from 0.01 to 1.0. This is an evidence of their formation in reducing conditions. 相似文献
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<正> 过去的天然气成因研究只是指出天然气是属于腐泥型、腐殖型还是混合型。但是天然气既可来源于干酪根裂解气,也可来源于原油(包括胶质和沥青质)的裂解气,而对于腐泥型有机质,天然气绝大部分是来自于干酪根先期生成的原油的裂解气,只有少部分天然气来自于干酪根的裂解。因此,对于母质类型好的有机质,干酪根在成熟阶段生成的油能否 相似文献
19.
南岭东段早侏罗世沉积岩碎屑锆石U-Pb定年及其地质意义——以东坑盆地为例 总被引：1，自引：0，他引：1
印支造山运动是华南早中生代最重要的构造-岩浆事件,它在很大程度上影响了华南现今的地形和地貌特点。本文研究了南岭东段赣南早侏罗世东坑火山岩盆地沉积岩的碎屑锆石U-Pb年代,获得最显著的年龄峰值为196Ma、238Ma、364Ma和427Ma,表明该沉积岩并不是外来的震旦纪-寒武纪变质岩,而是早侏罗世裂谷火山盆地的沉积物。缺乏260～290Ma的锆石年龄,很可能反映物质为近源来源。通过与闽西南晚三叠世和华南内陆中-晚二叠世沉积砂岩中碎屑锆石年龄谱对比,反映华南印支早期(290～260Ma)岩浆活动主体在东南沿海地区,晚期(240～200Ma)主体发育在内陆地区。大量印支期侵入岩锆石的出现也很可能表明华南内陆印支造山带在～190Ma已经经历了相当程度的垮塌。 相似文献
20.
A. I. Efimov I. V. Chashei M. K. Bird L. N. Samoznaev D. Plettemeier 《Astronomy Reports》2005,49(6):485-494
The results of several sets of measurements of the frequency of radio signals during coronal-sounding experiments carried out from 1991 to 2000 using the ULYSSES and GALILEO spacecraft are presented and analyzed. The S-band signals (carrier frequency f = 2295 MHz) were received at the three 70-m widely spaced ground stations of the NASA Deep Space Network. As a rule, the frequency-fluctuation spectra at frequencies above 1 mHz are power-laws. At small heliocentric distances, R < 10R⊙ (R⊙ is the solar radius), the spectral index is close to zero; this corresponds to a spectral index for the one-dimensional turbulence spectrum p1 = 1. The index of the frequency-fluctuation spectra in the region of the supersonic solar wind at distances R > 30 R⊙ is between 0.5 and 0.7 (p1 = 1.5–1.7). The results demonstrate a substantial difference between the turbulence regimes in these regions: in the region of the established solar wind, the power-law spectra are determined by nonlinear cascade processes that pump energy from the outer turbulence scale to the small-scale part of the spectrum, whereas such cascade processes are absent in the solar wind acceleration region. Near the solar minimum, the change in the turbulence regime of the fast, high-latitude solar wind occurs at greater distances than for the slow, low-latitude solar wind. Spectra with a sharp cutoff at high frequencies have been detected for the first time. Such spectra are observed only at R < 10 R⊙ and at sufficiently low levels of the electron density fluctuations. The measured cutoff frequencies are between 10 and 30 mHz; the cutoff frequency tends to increase with heliocentric distance. The variance of the plasma-density fluctuations has been estimated for the slow, low-latitude solar wind. These estimates suggest that the relative fluctuation level at distances 7 R⊙ < R < 30 R⊙ does not depend on heliocentric distance. The cross correlation of the frequency fluctuations recorded at widely spaced ground stations increases with the index of the frequency-fluctuation spectrum. At distances R ≈ 10 R⊙, the rate of temporal changes in irregularities on the scale of several thousand kilometers is less than or comparable to the solar wind velocity. 相似文献