排序方式： 共有150条查询结果，搜索用时 312 毫秒
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通过1∶5万区域水文地质和环境地质调查,利用物探、钻探等手段研究江西景德镇城区岩溶塌陷地质特征及其发育规律。景德镇城区覆盖型碳酸盐岩基岩面起伏大,浅部岩溶发育,土洞较多,第四系岩性结构复杂,覆盖层厚度一般20m,地下水埋藏浅。通过分析该区岩溶塌陷分布特征、形成条件和诱发控制因素,确定抽排地下水是该区岩溶塌陷的主要诱发因素。在预测岩溶塌陷发展趋势的基础上,对可能发生岩溶塌陷的区域进行初步预测,并针对性提出相应的保护和防治措施,为城市工程建设和环境保护提供参考。 相似文献
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Post-collisional, potassic magmatic rocks widely distributed in the eastern Lhasa terrane provide significant information for comprehensive understanding of geodynamic processes of northward subduction of the Indian lithosphere and uplift of the Tibetan Plateau. A combined dataset of whole-rock major and trace elements, Sr–Nd–Pb isotopes, and in situ zircon U–Pb dating and Hf–O isotopic analyses are presented for the Yangying potassic volcanic rocks (YPVR) in the eastern part of the Lhasa terrane, South Tibet. These volcanic rocks consist of trachytes, which are characterized by high K2O (5.46–9.30 wt.%), SiO2 (61.34–68.62 wt.%) and Al2O3 (15.06–17.36 wt.%), and relatively low MgO (0.47–2.80 wt.%) and FeOt (1.70–4.90 wt.%). Chondrite-normalized rare earth elements (REE) patterns display clearly negative Eu anomalies. Primitive mantle-normalized incompatible trace elements diagrams exhibit strong enrichment in large ion lithophile elements (LILE) relative to high field strength elements (HFSE) and display significantly negative Nb–Ta–Ti anomalies. Initial isotopic compositions indicate relatively radiogenic Sr [(87Sr/86Sr)i = 0.711978–0.712090)] and unradiogenic Nd [(143Nd/144Nd)i = 0.512121–0.512148]. Combined with their Pb isotopic compositions [(206Pb/204Pb)i = 18.615–18.774, (207Pb/204Pb)i = 15.708–15.793, (208Pb/204Pb)i = 39.274–39.355)], these data are consistent with the involvement of component from subducted continental crustal sediment in their source region. The whole-rock Sr–Nd–Pb isotopic compositions exhibit linear trends between enriched mantle-derived mafic ultrapotassic magmas and relatively depleted crustal contaminants from the Lhasa terrane. The enrichment of the upper mantle below South Tibet is considered to result from the addition of components derived from subducted Indian continental crust to depleted MORB-source mantle during northward underthrusting of the Indian continental lithosphere beneath the Lhasa terrane since India–Asia collision at ~ 55 Ma. Secondary Ion Mass Spectrometry (SIMS) U–Pb zircon analyses yield the eruptive ages of 10.61 ± 0.10 Ma and 10.70 ± 0.18 Ma (weighted mean ages). Zircon Hf isotope compositions [ƐHf(t) = −4.79 to −0.17], combined with zircon O isotope ratios (5.51–7.22‰), imply an addition of crustal material in their petrogenesis. Clinopyroxene-liquid thermobarometer reveals pressure (2.5–4.1 kbar) and temperature (1029.4–1082.9 °C) of clinopyroxene crystallization, suggesting that depth of the magma chamber was 11.6–16.4 km. Energy-constrained assimilation and fractional crystallization (EC–AFC) model calculation indicates depth of assimilation and fractional crystallization in the region of 14.40–18.75 km underneath the Lhasa terrane, which is in consistent with depth of the magma chamber as suggested by clinopyroxene-liquid thermobarometer. Based on the whole-rock major and trace elements and Sr–Nd–Pb isotope compositions, combined with EC–AFC modeling simulations and zircon Hf–O isotope data, we propose that the YPVR resulted from assimilation and fractional crystallization (AFC) process of the K-rich mafic primitive magmas, which were caused by partial melting of the Indian continental subduction-induced mélange rocks. 相似文献
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《Chemical Geology》2002,182(2-4):293-300
Our previously reported lithium isotope data for the least enriched members of the Central American Volcanic Arc were in error due to problems in ion extraction from high MgO rocks. This paper presents reanalyses of the entire suite of the CAVA lavas after a systematic investigation of the elution behavior of Li as a function of the rock composition. The most significant correction pertains to the mantle end members of the Nicaragua and Costa Rica series, which now display MORB-like δ6Li values (−4.5‰) and not much lighter (+1‰ to +3‰) as previously reported. Also revised is the composition of a peridotite from Zabargad Island (Red Sea), considered to represent undepleted upper mantle, whose corrected δ6Li also resembles MORB. These new data therefore remove the speculation that Earth's primitive mantle has extremely light Li isotopic composition and that the mantle beneath CAVA contains such isotopically light domains. The δ6Li range for the arc segment from Costa Rica to Guatemala has now been reset to −4.5‰ to −6.4‰. Despite the narrower range, Li isotopic values remain well correlated with other subduction-related properties, including LILE and fluid-mobile elements. Model calculations show that the isotopic compositions of the lavas are consistent with small additions of slab-derived fluids to the enriched and depleted domains of the subarc mantle. 相似文献
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江西省铅山县篁碧铅锌矿区同位素年代学和稳定同位素组成 总被引：7，自引：4，他引：3
江西省铅山县篁碧铅锌矿区位于华南扬子板块与华夏板块结合的北武夷地区,该地区是钦杭结合带的重要组成部分,以发育一系列的中生代火山岩盆地为主要特征.篁碧铅锌矿之西侧冷水坑地区,东侧的梨子坑、仙霞岭都已有了同位素年代学研究成果.本次研究选取了篁碧矿石中闪锌矿进行同位素年代学测试;Rb-Sr法和Sm-Nd法两种同位素年龄测试,得到其等时线年龄分别为135.4±4.4Ma( SMWD =0.52)和139±15Ma (SMWD =0.118).结果表明该矿床系形成于早白垩世,另一方面也显示了闪锌矿可以作为测年的理想矿物.V5号矿脉的铅锌矿石和方解石脉的C、S、O同位素分析结果:铅锌矿的34SV-CDT为2.5％ ～5.1‰,方解石脉的13 CV-PDB为-2.6％ ～ -4.7％,18 OV-PDB为-23.9‰～ -27.7％,18 OV-SMOW为2.3‰～6.2％.以上数据显示矿石中S主要为岩浆热液来源,方解石脉中C、O显示其来源比较复杂,指示源于基性岩或地幔源,并有大气降水.综上说明该矿床为早白垩世的岩浆热液矿床.上述研究丰富了北武夷地区的成矿年代学研究成果.结合前人资料,认为中生代成矿时代由西往东渐新.岩浆源方解石脉的发现暗示北武夷隐伏基底断裂可能深达地幔,为钦杭结合带南界的厘定提供了新的依据. 相似文献
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江西省鄱阳湖及周边经济区土壤有机碳储量分布特征 总被引：3，自引：2，他引：1
土壤是陆地生态系统的重要组成部分,土壤碳储量研究在碳循环和全球变化中具有重要意义。本文利用江西省鄱阳湖及周边经济区多目标区域地球化学调查取得的土壤碳数据,计算了研究区表层、中层、深层土壤的全碳储量和有机碳储量,分析其有机碳储量和有机碳密度的分布特征。结果表明：研究区总体碳储量是以有机碳储量为主;表层土壤（0~0.2 m）的有机碳密度为3512 t/km2,有机碳储量为1.38亿吨;中层土壤（0~1.0 m）的有机碳密度为11156 t/km2,有机碳储量为4.39亿吨;深层土壤（0~1.8 m）的有机碳密度为15617 t/km2,有机碳储量为6.14亿吨。与全国农业地质调查数据进行对比,研究区表层土壤的有机碳密度高于全国农业地质调查区内表层土壤有机碳密度的10.86%,中层及深层土壤的有机碳密度与全国农业地质调查区平均水平接近,显示研究区土壤的有机碳储量巨大。进一步分析研究区不同土壤类型、不同土地利用类型、不同地貌单元、不同行政单元的土壤有机碳密度及有机碳储量,系统查明了土壤有机碳的分布和分配特征。研究认为,区域内各层土壤有机碳密度空间分布具有同一性特征,与所处区域的成土地质背景和植被覆盖率密切相关。土壤有机碳密度高值区均分布在山地和丘陵区,包括江西丰城市北部、高安市南部、乐平市周边地区等古生代炭质岩和煤系地层区,其中乐平市表层土壤的有机碳密度最高;低值区均分布在湖区和水系河谷地区。该成果可为江西省的碳循环和碳排放研究提供可靠的数据基础。 相似文献
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多目标区域地球化学调查结果显示,江西龙南地区表层土壤Se 平均含量为0.34 mg/kg,总体足硒,局部富硒,且土壤中重金属元素含量处于安全水平?异常查证结果表明,富含硒的基岩是富硒土壤分布的控制因素?在研究区发现天然富硒水稻?富硒大豆优质农产品,其中大豆的富硒率达100%?土壤中有效Se 与总Se 呈极显著的正相关,总Se 含量增大可增加有效Se 量;有效Se 与阳离子交换量(CEC)?N?P呈较显著的正相关,土壤中粘土矿物及有机质对Se 有较强的吸附?络合作用,且土壤中有效Se 主要以亚硒酸盐形式存在?水稻?大豆中Se 的生物富集系数均与土壤Se?N呈显著负相关,与土壤K2O呈显著正相关? 相似文献
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铜陵—池州地区水系沉积物测量地球化学特征及找矿方向 总被引：2，自引：0，他引：2
在长江中下游铁、铜、金多金属成矿带1∶20万水系沉积物测量的基础上,对铜陵—池州地区的地球化学异常特征进行初步总结。通过对区内元素进行因子分析,得出多种与成矿有关的异常组合,利用成矿元素异常组合划分地球化学分区,进而圈定地球化学异常。通过对比成矿地质背景和地球化学条件,对铜陵地区典型矿床进行相似度分析,预测池州地区的找矿远景区。结果表明:综合区域上的地层、构造、岩浆岩和区域矿产等资料,对成矿元素异常组合进行地球化学分区是可行的,能有效反映致矿异常,突出矿化信息;根据样点相似度值的计算结果与典型矿床相似度图的耦合情况分析,池州市南部的梅街镇、青阳县东侧、铜山铜矿外围是区域上最为有利的铜多金属找矿远景区。 相似文献
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