Lower crustal melting via magma underplating: Elemental and Sr–Nd–Pb isotopic constraints from late Mesozoic intermediate–felsic volcanic rocks in the northeastern North China Block     

CHAOWEN LI  FENG GUO  WEIMING FAN 《Island Arc》2011,20(4):477-499

Ar–Ar dating, major and trace element analyses, and Sr–Nd–Pb isotope results of two groups of Lower Cretaceous (erupted at 126 and 119 Ma, respectively) intermediate–felsic lava from the northeastern North China Block (NCB) suggest their derivation from melting of mixtures between the heterogeneous lower crust and underplated basalts. Both groups exhibit high‐K calc‐alkaline to shoshonitic affinities, characterized by light rare earth element (LREE) and large ion lithophile element (LILE) enrichment and variable high field strength element (HFSE, e.g. Nb, Ta and Ti) depletion, and moderately radiogenic Sr and unradiogenic Nd and Pb isotopic compositions. Compared with Group 2, Group 1 rocks have relatively higher K₂O and Al₂O₃/(CaO + K₂O + Na₂O) in molar ratio, higher HFSE concentrations and lower Nb/Ta ratios, and higher Sr–Nd–Pb isotope ratios. Group 1 rocks were derived from a mixture of an enriched mantle‐derived magma and a lower crust that has developed radiogenic Sr and unradiogenic Nd and Pb isotopic compositions, whereas the Group 2 magmas were melts of another mixture between the same mantle‐derived component and another type of lower crust having even lower Sr, Nd, and Pb isotopic ratios. Shift in source region from Group 1 to Group 2 coincided with a change in melting conditions: hydrous melting of both the underplated basalt and the lower crust produced the earlier high‐Nb and low‐Nb/Ta melts with little or no residual Ti‐rich phases; while the younger low‐Nb and high‐Nb/Ta magmas were melted under a water‐deficient system, in which Ti‐rich phases were retained in the source. Generation of the two groups of intermediate–felsic volcanic rocks was genetically linked with the contemporaneous magma underplating event as a result of lithospheric thinning in the eastern NCB.  相似文献   

Crustally-derived granites in the Panzhihua region,SW China: Implications for felsic magmatism in the Emeishan large igneous province     

J. Gregory Shellnutt  Bor-Ming Jahn  Mei-Fu Zhou 《Lithos》2011,123(1-4):145-157

In the Panxi region of the Late Permian (~ 260 Ma) Emeishan large igneous province (ELIP) there is a bimodal assemblage of mafic and felsic plutonic rocks. Most Emeishan granitic rocks were derived by differentiation of basaltic magmas (i.e. mantle-derived) or by mixing between crustal melts and primary basaltic magmas (i.e. hybrid). The Yingpanliangzi granitic pluton within the city of Panzhihua intrudes Sinian (~ 600 Ma) marbles and is unlike the mantle-derived or hybrid granitic rocks. The SHRIMP zircon U–Pb ages of the Yingpanliangzi pluton range from 259 ± 8 Ma to 882 ± 22 Ma. Younger ages are found on the zircon rims whereas older ages are found within the cores. Field relationships and petrography indicate that the Yingpanliangzi pluton must be < 600 Ma, therefore the older zircons are interpreted to represent the protolith age whereas the younger analyses represent zircon re-crystallization during emplacement. The Yingpanliangzi granites are metaluminous and have negative Ta–Nb_PM anomalies, low εNd_{(260 Ma)} values (? 3.9 to ? 4.4), and high I_Sr (0.71074 to 0.71507) consistent with a crustal origin. The recognition of a crustally-derived pluton along with mantle-derived and mantle–crust hybrid plutons within the Panxi region of the ELIP is evidence for a complete spectrum of sources. As a consequence, the types of Panxi granitoids can be distinguished according to their ASI, Eu/Eu*, εNd_(T), εHf_(T), T_Zr(°C) and Nb–Ta_PM values. The diverse granitic magmatism during the evolution of the ELIP from ~ 260 Ma to ~ 252 Ma demonstrates the complexity of crustal growth associated with LIPs.  相似文献   

Identification of C₂₄ and C₂₅ lanostanes in Tertiary sulfur rich crude oils from the Jinxian Sag, Bohai Bay Basin, Northern China     

Hong Lu  Guoying ShengPing’an Peng  Qinglin MaZhenhuan Lu 《Organic Geochemistry》2011,42(2):146-155

Unusual short chain lanostanes (C₂₄ and C₂₅) and C₃₀ lanostane were identified in sulfur rich crude oils from the Jinxian Sag, Bohai Bay Basin, northern China. Besides the regular steranes (C_27-30), a series of 4-methyl steranes (C₂₂₋₂₃, C₂₇₋₃₀), 4,4-dimethyl steranes (C₂₂₋₂₄, C₂₈₋₃₀), short chain steranes (C₂₃₋₂₆), abundant pregnanes (C₂₁₋₂₂) and androstanes (C₁₉₋₂₀), together with sulfur containing steroids (20-thienylpregnanes and thienylandrostanes) were detected in the aliphatic and branched-cyclic hydrocarbon fraction of these crude oils. A literature survey of some long chain sterane analogues (e.g., A-nor-steranes, norcholestanes, C₃₀ steranes, lanostanes) and pregnanes seems to point to a sponge and/or dinoflagellate source. 4-Methyl, 4,4-dimethyl steroids and lanosterols (4,4,14-trimethyl steroids as the basic skeleton of lanostanes) can be derived from methanotrophic bacteria. Thus, a biological origin from a prokaryotic methylotroph can be used to explain the common source of abundant short chain steranes (C_23-26), 4-methyl (C_22-23) and 4,4-dimethyl steranes (C_22-24), as well as lanostanes (C_24-25 and C₃₀ analogues) in our oil samples. Generally, the steroids appear to have been extensively sulfurized with sulfur substitution at the C-22 position in the side chain during the early stage of diagenesis, which was readily subject to attack by bacterial degradation (enzymatic cleavage) and/or abiotic oxidation. As a consequence, short chain sterane analogues (e.g., abundant pregnanes and androstanes in this study) and short chain lanostanes (C₂₄−C₂₅) might later be released through cleavage of weak C-S bonds at the C-22 carbon in the sulfurized steroids and lanostane sulfides. Finally, the formation of the short chain C₂₄−C₂₅ lanostanes and distinctive occurrence of short chain steranes in this study can be well explained by microbial biodegradation of sulfurized lanostanoids and steroids in the reservoir.  相似文献   

Separation of total nitrogen from sediments into organic and inorganic forms for isotopic analysis   总被引：3，自引：0，他引：3  

Zhiyang Li  Guodong Jia   《Organic Geochemistry》2011,42(3):296-299

Nitrogen isotopic (δ¹⁵N) analysis is widely applied in palaeoceanography, palaeolimnology and soil science. Most measurements are performed on untreated bulk samples containing both organic and inorganic nitrogen (ON and IN), which could sometimes confound isotopic signals. Here we propose a sample pretreatment method to physically and quantitatively separate the total nitrogen into ON and IN for subsequent concentration and isotopic measurements. In the method, the sediment is first demineralized with HCl and HCl-HF, adsorbed and bound IN being liberated into the acid solutions during the demineralization. Then, organic matter (OM) dissolved in the acid solutions is recovered by a sorbent of styrene divinyl benzene polymer (Bond Elut PPL, Varian) and is then combined with the acid-resistant OM to obtain the total OM. Finally, IN in the acid solutions passing through the PPL sorbent is recovered by way of steam distillation. Total nitrogen recovery with the method is 92.4% and isotopic mass balance calculations show that the δ¹⁵N value of total nitrogen can be quantitatively partitioned into the organic and inorganic forms. The δ¹³C values of the separated OM show a small positive excursion of 0.2‰ relative to those of bulk OM, ruling out significant loss of ON during the pretreatment. By comparison, the KOBr method, widely used to remove ON from bulk samples for isotope measurements, gives lower IN concentration and higher δ¹⁵N_IN values, attributed to the partial loss of IN and escape of some oxidation-resistant ON.  相似文献   

The role of metal sulfates in thermochemical sulfate reduction (TSR) of hydrocarbons: Insight from the yields and stable carbon isotopes of gas products     

Hong LuPaul Greenwood  Tengshui ChenJinzhong Liu  Ping’an Peng 《Organic Geochemistry》2011,42(6):700-706

The mechanism of thermochemical sulfate reduction (TSR) was investigated by separately heating n-C₂₄ with three different sulfates (CaSO₄, Na₂SO₄, MgSO₄) in sealed gold tubes at 420 °C and measuring the stable carbon isotope values of hydrocarbon (C₁-C₅) and non-hydrocarbon (CO₂) products. Extensive TSR was observed with the MgSO₄ reactant as reflected by increasing concentrations of H₂S, ¹³C depleted CO₂ and relatively low concentrations of H₂ (compared to the control). H₂S yields were already very high at the first monitoring time (12 h) when the temperature had just reached 420 °C, suggesting that TSR had commenced well prior to this temperature. Only trace amounts of n-C₂₄ and secondary C₃-C₅ alkanes were detected at 12 h, reflecting the efficient TSR utilization of the reactant and lower molecular weight alkane products. Ethane levels were still relatively high at 12 h, but declined thereafter as it was subject to TSR in the absence of higher molecular weight alkanes which had already been utilized. Methane yields were consistently high throughout the 48 h MgSO₄ treatment. The temporal decrease in the concentrations of alkanes available for TSR may also contribute to the sharp enhancement of CO₂ after 36 h. Absence or dampening of the molecular and isotopic trends of MgSO₄ TSR was observed with Na₂SO₄ and CaSO₄ respectively, directly reflecting the levels of TSR reached using these sulfate treatments.For all treatments, the δ¹³C values of C_1-5n-alkanes showed an increase with both molecular weight and treatment time. MgSO₄ TSR led to a 5-10‰ increase in the δ¹³C values of the C₁-C₅ hydrocarbons and a 20‰ decrease in the δ¹³C value of CO₂. The significant ¹³C depletion of the CO₂ may be due to co-production of ¹³C enriched MgCO₃, although this remains unproven as the δ¹³C of MgCO₃ was not measured. The difference in the δ¹³C values of ethane and propane (Δδ¹³C_EP) increased in magnitude with the degree of TSR, and this trend could be used to help evaluate the occurrence and extent of TSR in subsurface gas reservoirs.  相似文献   

阿吾拉勒山琼布拉克铜矿床流体包裹体及碳氧同位素研究   总被引：1，自引：1，他引：0  

罗勇  廖思平  杨武斌  单强  周昌平 《矿床地质》2011,30(3):547-556

琼布拉克铜矿床位于新疆伊宁县境内,前人对该矿床的成因一直存在争议.文章通过对琼布拉克铜矿床方解石中的流体包裹体进行系统的岩相学、显微测温学和碳氧稳定同位素分析研究,探讨了成矿流体的来源及演化.研究表明:琼布拉克铜矿床的流体包裹体主要为气-液两相包裹体,另有少量的气相包裹体,未见富CO2和含子矿物的流体包裹体,显示出张性...  相似文献   

四川盆地江油厚坝油砂有机地球化学特征与成因研究   总被引：5，自引：3，他引：2  

罗茂  耿安松  廖泽文  单玄龙 《地球化学》2011,40(3):280-288

四川江油厚坝油砂产出于侏罗系沙溪庙组下段,含油砂层沿北东方向延伸约25 km.露头和岩芯油砂样抽提得到氯仿沥青“A”含量为0.4％～33％.抽提物饱和烃GC-MS分析得到的分子有机地球化学特征表明,油砂油遭受严重生物降解,饱和烃分布呈现双大鼓包,正构烷烃和异构烷烃基木被降解;三环萜烷含量丰富,孕甾烷和升孕甾烷含最也较高...  相似文献   

试论南中国海盆地新生代板块构造及盆地动力学   总被引：2，自引：0，他引：2       下载免费PDF全文

张功成  王良书  唐显春  张开均  刘绍文  赵志刚  王鹏  钟锴 《地质科学》2011,46(3):638-652

南海地处欧亚、印度—澳大利亚和菲律宾海板块的交互带,是西太平洋地区面积最大的边缘海之一,其成因机制和演化过程对探讨特提斯构造域和太平洋构造域相互作用及油气勘探等问题具有重要意义,虽备受关注但仍存争议.综合目前该区及外围已有的大地构造等方面的资料,本文从探讨南海外围的构造格架及中-新生代演化过程入手,分析了南海及外围板块...  相似文献   

鄂西白垩纪远安盆地的变形带构造   总被引：1，自引：0，他引：1       下载免费PDF全文

乔彦波  单业华  田野  聂冠军 《地质科学》2011,46(1):181-193

鄂西白垩纪远安盆地中大量发育变形带及其密切相关的断层,主要分为两期,早期为带有正断性质的北北东向组变形带及简单的正断层,形成在同沉积或早成岩阶段,而晚期为带走滑性质的北-南向组和北东向组变形带及复活断层,形成在白垩纪以后.根据实测的共轭变形带和断层滑动数据,古应力分析的结果表明,早期为北西西-南东东向拉张的伸展状态,而...  相似文献   

新疆阿尔泰康布铁堡组钾质和钠质流纹岩的成因及同位素年代学研究   总被引：10，自引：2，他引：8  

单强  曾乔松  罗勇  杨武斌  张红  裘瑜卓  于学元 《岩石学报》2011,27(12):3653-3665

阿尔泰南缘康布铁堡组酸性火山岩分布在麦兹、克朗、冲呼尔以及阿舍勒等火山-沉积盆地.本文对其中的钾质流纹岩(TM1,铁木尔特地区)和钠质流纹岩(KK7,可可塔勒地区)进行了SHRIMP锆石U-Pb定年以及地球化学的研究.钾质流纹岩的年龄为400.8±8.4Ma(加权平均年龄为394.8±7.9Ma),钠质流纹岩的年龄为402.2±6Ma(加权平均年龄为396.8±5.1Ma).主元素分析结果证明研究区在时间和空间上紧密共生的高钾流纹岩和高钠流纹岩同属于高碱、高硅、低钙、过铝质的钙碱性岩系.相似的稀土元素分配模式和同样亏损高场强元素(Ti、Nb、Ta)的地球化学特征暗示二者的原始岩浆源于上地壳部分熔融.钾质流纹岩富集Rb,Ba、Pb,钠质流纹岩则富集Sr,这种元素分相富集的特征符合在岩浆液态不混溶条件下微量元素在共轭钠质熔体和钾质硅酸盐熔体中的分配原则.由此推论,本区产出的钾质流纹岩和钠质流纹岩可能是上地壳部分熔融形成的高挥发分酸性岩浆液态不混溶的产物.  相似文献