In-reservoir mixing of mantle-derived CO2 and metasedimentary CH4–N2 fluids – Noble gas and stable isotope study of two multistacked fields (Pannonian Basin System,W-Hungary)

Several multistacked gas fields, located in very different parts of Hungary, display a large variation in their gas composition. The shallow position of the mantle beneath the basement of the PBS is responsible for the high heat flux. It facilitates that the CO₂ – intensely released from the ascending upper-mantle derived melts – could reach the basin system. In this work the results of a geochemical study of the main components and noble gases of the multistacked Répcelak (CO₂–HC–N₂) and Mihályi (CO₂) fields are presented and discussed. The vertical variations of gas composition in the Répcelak and Mihályi fields fit well with in-reservoir mixing of two end-members, a mantle-related magmatic CO₂ fluid and a N₂-rich HC-gas fluid of crustal origin. However, it is very likely that other processes modified to some extent the gas composition of the two fields. Carbon isotopic composition of the CO₂ of the samples studied agrees with both the carbonate decomposition and mantle degassing origins. It is very likely that the marked difference in helium isotopic composition between the neighbouring Répcelak and Mihályi fields also reflects this heterogeneity.     

东乌旗中铁陨石硅酸盐地球化学特征及对成因的启示

东乌旗中铁陨石为1995年在内蒙发现的、为数不多的降落型中铁陨石,由金属—硫化物和硅酸盐相紧密混合而成。硅酸盐相由角砾部分（主要为角砾状橄榄石和辉长岩岩屑）和非角砾部分组成。岩相学特征、主量元素成分及REE地球化学特征表明角砾状橄榄石、非角砾橄榄石和辉长质硅酸盐（辉长岩岩屑和除橄榄石外的非角砾部分）三者可能分别结晶自不同的岩浆源区。进一步的分析表明Mg含量非常高的角砾状橄榄石可能来自一个分异小行星的橄榄岩质地幔,非角砾橄榄石和辉长质硅酸盐可能和HED陨石具有相同的母体Vesta小行星。冲击碰撞导致两个小行星的物质发生了混合。冲击作用产生的高温（约1200℃—1450℃）使得被撞击小行星表壳玄武质和辉长质岩石发生混合重熔,熔体结晶后形成中铁陨石的辉长质硅酸盐。该温度下非角砾橄榄石和角砾状橄榄石均未发生重熔。该模型较好地解释了角砾状橄榄石、非角砾橄榄石和辉长质硅酸盐三者之间的不平衡现象。     

Transport process of sand grains from fluvial to deep marine regions estimated by luminescence of feldspar: example from the Kumano area,central Japan

Using the concept of bleaching in optical dating, a new index of sediment sample bleaching percentage (BLP‐2) was developed and applied to evaluate sand grain transport from riverine to deep‐marine environments. As bleached grains in modern sediments have no optically stimulated luminescence (OSL)/infrared stimulated luminescence (IRSL) signal, bleached and unbleached feldspar grains are distinguished by IRSL intensity. The BLP‐2 distribution of present deposits around the Kumano area, on the Pacific coast of central Japan, suggests that sand grains in surface turbidites obtained from the bottom of the Kumano Trough are of flood/storm origin rather than seismogenic origin. The distribution of BLP‐2 tentatively suggests sand grain erosion–transport–depositional processes; for example, origin and transport agencies of shelf sand, and influence of coastal erosion on the beach deposit. Although the present BLP analysis is not yet supported by a rigorous statistical test, it is useful to distinguish recent deposition and remobilization of sand grains. Furthermore, if the depositional age and the luminescence age of sand grains are accurately estimated, sand grain transport processes of old (late Quaternary) sediments may be estimated by the methodology similar to that of the present study.     

辽宁丹东四道沟金矿床叠生成因的流体包裹体证据

四道沟金矿床为辽东南地区一重要蚀变岩型矿床,其空间产出受构造、盖县组变质地层及区内岩浆活动的联合制约。矿化分3种类型、4个成矿阶段。流体包裹体研究表明,成矿早期流体为一中温、低盐度且富含CO2及CH4等挥发份的热液;矿区主成矿阶段成矿流体为一中温高盐度类型热液。综合分析认为,四道沟金矿床是燕山晚期不同来源及性质的热液先后叠加成矿作用的产物,矿床属叠生成因类型。     

Discussion on geologic characteristics and genesis of the Yuansha lead-zinc deposit in Qitao coal deposit in Datian county, Fujian province

大田元沙矿区位于闽西南坳陷带中北部,大田一龙岩坳陷的东北边缘,成矿地质条件较好,区内矿产资源丰富。铅锌矿床产于倒转翼林地组砾岩与楱霞组石灰岩接触带中,严格受层位和构造控制。矿区F0断裂为矿液运移提供了通道,并在有利部位富集成矿。矿床成因类型为沉积一热液改造型。     

福建大田元沙铅锌矿床地质特征及其成因探讨

大田元沙矿区位于闽西南坳陷带中北部,大田一龙岩坳陷的东北边缘,成矿地质条件较好,区内矿产资源丰富。铅锌矿床产于倒转翼林地组砾岩与楱霞组石灰岩接触带中,严格受层位和构造控制。矿区F0断裂为矿液运移提供了通道,并在有利部位富集成矿。矿床成因类型为沉积一热液改造型。     

Geochemical and Sr-Nd isotopic evidence for origin and evolution of the Miocene Pangeon granitoids,Southern Rhodope,Greece

The Sr-Nd isotopic ratios of selected post-collisional, calc-alkaline, I-type granitoids from the Pangeon pluton, intruding the lower tectonic unit (LTU) in the Southern Rhodope in the Miocene, support the existence of two types of granitoids (PTG porphyritic tonalite granodiorite and MGG biotite granodiorite to two-mica granite) unrelated by crystal fractionation and likely derived by partial melting of the same source under different P-T conditions. The Sr-Nd isotopic ratios of mafic enclaves in the granitoids as well as metamorphic rocks from the LTU have also been determined. At 22 Ma, the IR_Sr range between 0.706850 and 0.708381, whereas the ε_Nd(22) range from –3.86 to –1.05, with no relationship to granitoid types. The relationships between Sr and Nd isotopes as well as these isotopes and SiO₂ provide evidence of contamination of mafic melts by interaction with crust during magma differentiation. Both partial melting and AFC processes (r = 0.2) may account for compositional variations in the Pangeon magmas. The mafic enclaves display IR_Sr from 0.706189 to 0.707139, and ε_Nd(22) from –2.29 to –1.94, similar to the granitoids, supporting the hypothesis of a common origin. Amphibolites inferred to be subduction-enriched metabasalts under-plated crust during old subduction can represent the source of the Pangeon melts. The T_DM of the Pangeon granitoids is in the range 0.7–1.1 Ga for the inferred extraction age of the LILE-enriched subcontinental lithospheric mantle source. The upper crustal geochemical signatures and the relatively small isotopic composition of the Pangeon granitoids make these rocks similar to the coeval eastern-Mediterranean lamproites emplaced within the same geodynamic setting; this prompts similar melt sources. Lastly, the Pangeon granitoids display geochemical characteristics, isotopic ratios, and T_DM also similar to other Tertiary magmatic rocks from the Southern Rhodope and Biga peninsula, western Anatolia, suggesting a similar tectonic environment and co-magmatic evolution throughout the area.     

Mantle origin of the Dexing porphyry copper deposit,SE China

The Dexing ore deposit, Jiangxi Province, is the largest porphyry copper deposit in China. Controversies exist regarding the ore-forming source of this deposit. We have conducted Pb isotope analyses of pyrites from the Tongchang and Fujiawu mines. Our results document consistent Pb isotopes from these two orebodies, with ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of 17.954–18.320, 15.407–15.517, and 37.888–38.153, respectively. These Pb isotope ratios are consistent with those of ore-bearing adakitic porphyries but distinctly different from those of the Neoproterozoic metamorphic wall rocks, which indicates that the metals were derived from the porphyries. Based on previous S and Os isotopic data and comparisons with more than 20 Mo-bearing deposits worldwide, we further attribute the narrow range of δ³⁴S values of sulphide minerals and high Re–¹⁸⁷Os concentrations of associated molybdenites to a mantle origin. This large-scale copper deposit was evidently emplaced in a continental arc setting attending westward subduction of the palaeo-Pacific plate. Partial melting of the downgoing oceanic slab generated the adakitic magmas. The associated metals were extracted from the lithospheric mantle by these magmas during ascent through the mantle wedge.     

花岗岩及其成矿作用的研究进展

近年来,随着大陆动力学研究的不断深入以及现代分析技术的应用,花岗岩成因与地壳演化、花岗岩成矿作用等问题成为新一轮地质科学研究的重点和热点,并取得了重大的进展。本文系统阐述了花岗岩成因、花岗岩浆源区性质及岩浆作用过程、构造背景以及花岗岩成矿作用的研究进展。     

东营凹陷不同超压成因的有效应力特征

利用实测流体压力(DST)测试结果,结合声波和密度测井资料,对超压段所识别的不均衡压实作用和生烃作用两种超压成因机制下的实测压力和有效应力随深度的变化特征进行了分析,结果表明:①两种不同成因机制下的实测压力和有效应力特征具有明显的差异性,不均衡压实作用在压实过程中导致流体排出受阻,地层流体承担上覆岩层压力形成超压,表现为阻止了地层有效应力增大,因此其实测压力增大段和静岩压力增大趋势大体一致,而有效应力随深度基本保持不变;生油作用在地层正常压实之后形成超压,发育程度不受上覆岩层压力的影响,因此超压的增大在深度上与上覆岩层压力增大不具有一致性,且超压对有效应力的影响要小于不均衡压实作用;②这两种不同的超压成因使得有效应力的变化随着声波速度而出现加载和卸载两种趋势,从而可以用来判断超压成因,利用实测资料计算的有效应力结果说明东营凹陷超压成因机制包括不均衡压实作用和生油作用,但不均衡压实作用形成超压的范围和规模较小,生油作用对深部大规模超压和强超压的形成至关重要.