Oxygen isotopes in the Cretaceous-Paleogene granites of Primorye and some problems of their genesis     

G. A. Valui  E. Yu. Moskalenko  A. A. Strizhkova  G. R. Sayadyan 《Russian Journal of Pacific Geology》2008,2(2):150-157

The Cretaceous-Paleogene granites of the Eastern Sikhote Alin volcanic belt (ESAVB) and Late Cretaceous granitoids of the Tatibin Series (Central Sikhote Alin) are subdivided into three groups according to their oxygen isotope composition: group I with δ¹⁸O from +5.5 to +6.5‰, group II with δ¹⁸O from +7.6 to +10.2‰, and group III with less than +4.5‰. Group I rocks are similar in oxygen isotope composition to that of oceanic basalts and can be derived by melting of basaltic crust. Group II (rocks of the Tatibin Series) have higher δ¹⁸O, which suggests that their parental melts were contaminated by sedimentary material. The low ¹⁸O composition of group III rocks can be explained by their derivation from ¹⁸O-depleted rocks or by subsolidus isotopic exchange with low-¹⁸O fluid or meteoric waters. The relatively low δ¹⁸O and ⁸⁷Sr/⁸⁶Sr in the granitoids of Primorye suggest their derivation from rocks with a short-lived crustal history and can result from the following: (1) melting of sedimentary rocks enriched in young volcanic material that was accumulated in the trench along the transform continental margin (granites of the Tatibin Series) and (2) melting of a mixture of abyssal sediments, ocean floor basalts, and upper mantle in the lithospheric plate that subsided beneath the continent in the subduction zone (granites of the ESAVB).  相似文献   

Fe-Cu-Zn-Mo同位素示踪氧化还原过程     

黄思民  张贵宾 《岩石矿物学杂志》2024,43(2):469-494

非传统稳定同位素（Fe-Cu-Zn-Mo）理论与数据相结合提高了科研工作者对地质体系氧化还原过程的理解。本文对这一相对较新的领域进行了综述,包括与氧化还原过程相关的同位素分馏理论和实验约束、时空尺度下的氧逸度以及同位素示踪氧化还原过程。稳定同位素理论预测,Fe-Cu-Zn-Mo同位素应该对氧化还原状态的变化能够做出响应。结果表明,Fe同位素作为岩浆过程、表生过程、俯冲带流体性质"氧逸度计"应用前景广阔;Cu同位素在岩浆、热液、陆地系统可以很好地示踪氧化还原过程;Zn同位素由于络合过程分馏已经被用在许多不同环境中作为含硫/碳流体迁移的敏感示踪剂;Mo同位素作为古氧逸度计可有效重建古海洋-大气氧化还原状态。  相似文献   

Carbon, sulfur and O₂ across the Permian–Triassic boundary     

Robert A. Berner   《Journal of Geochemical Exploration》2006,88(1-3):416

A model for the carbon and sulfur cycles across the Permian–Triassic boundary has been constructed from carbon and sulfur isotopic data. Results indicate a drop in global organic matter burial, the formation of an anoxic deep ocean, and a large drop in atmospheric oxygen over the time span 270 to 240 Ma. Much of these changes were probably due to a drop in terrestrial productivity and preservation and an increase in global aridity.  相似文献   

Integrated stratigraphy and paleoenvironmental reconstruction of the Miocene series of the Chateauredon Dome, S.E. France     

Anne Bialkowski  Jean-Jacques Chateauneuf  Isabelle Cojan  Hugues Bauer 《Eclogae Geologicae Helvetiae》2006,99(1):1-15

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水环境容量的影响因素及分析研究     

孙秀喜  冯耀奇 《地下水》2005,27(5):389-391

本文采用流量级频率分析和统计分析方法,对黄河下游流量及泥沙含量对水环境容量的影响进行了研究分析.分析结果:河流在平滩流量时不仅输沙能力最大[8],而且输运污染物能力也最大,黄河下游水环境容量萎缩是平滩流量降低的必然结果.  相似文献   

许家窑泥河湾沉积物的环境磁学特征   总被引：3，自引：3，他引：3       下载免费PDF全文

王喜生  Lovlie Reidar  苏朴 《第四纪研究》2002,22(5):451-458

许家窑泥河湾河-湖相沉积物磁化率(k)、天然剩磁(NRM)、饱和等温剩磁(SIRM_4T)、非磁滞剩磁(ARM)及S比率(IRM_-0.3T/IRM_4T)等磁学参数与深海氧同位素的对比分析结果显示:1)许家窑泥河湾层从布容/松山界线到氧同位素阶段5(0.13MaB.P.)基本上是连续沉积,沉积速率保持在约2.45cm/103a左右;2)与同期形成的黄土高原黄土-古土壤序列类似,许家窑河-湖相层也很好地记录了当时中国北方的第四纪气候和环境特征,其典型特征为冰期时高矫顽力赤铁矿含量的显著增加,而间冰期则以低矫顽力的磁铁矿及磁赤铁矿为主要载磁矿物;3)由尝试建立的S比率时间标尺所确定的许家窑古人类遗址处的地层年代约0.5MaB.P.,与先前报道的化石的UTh绝对年龄(0.1MaB.P.)不一致;4)与k相比,S比率与SIRM更适合作为河-湖相沉积物的古气候替代性指标;5)以2.45cm/10³a的沉积速率来推算,沉积物的主要物质来源为正常的河-湖相沉积,而直接接受的类似于黄土状的粉尘并不占主导地位  相似文献   

云南腾冲地块北部空树河组一个菱铁矿结核中的C、O同位素变化特征     

金小赤 《地球学报》2002,23(1):37-41

空树河组是滇西腾冲地块北部的石碳－二叠纪冈瓦纳相沉积。菱铁矿结核见于该组顶部的黑色泥岩中。将一个结核通过中心切开，在切面上由中心向边缘用牙钻等间隔提取10个样品。同位素测试结果显示，δ^13C自中心向边缘逐渐由－8．09％减为－16．12％，最外一个样例外（－15．39‰），而δ^18O自中心向边缘逐渐由－10．64‰增加为0‰左右。δ^13C的变化情况表明，菱铁矿结核可能形成于硫酸盐还原带。在解释δ^18o的变化情况时，推测在结核开始生长时可能有δ^18O亏损的大气降水掺入，随着埋藏深度的逐渐加大，孔隙水的O同位素逐渐趋近正常海水的值（0‰）。  相似文献   

Dissolved silica budget in the North basin of Lake Lugano     

Annette Hofmann  Didier RoussyMontserrat Filella 《Chemical Geology》2002,182(1):35-55

We studied the dissolved silica cycle in the water column of the North basin of Lake Lugano, Switzerland/Italy. Lake Lugano is a meromictic, eutrophic lake, permanently stratified below 100-m depth. A one-box model was used to calculate a silica mass-balance over 1993, based on various lake measurements, such as sediment traps, sediment cores, water analysis and biota countings. We found that the North basin of Lake Lugano is at steady state as far as dissolved silica is concerned. The primary source of dissolved silica in the lake is river input (about 80%), with diffusion from bottom sediments and groundwater input also playing a role. Atmospheric input is negligible. The main export of dissolved silica occurs via biogenic uptake by diatoms and final burial of their frustules in the bottom sediment. Loss of dissolved silica through the lake outflow only represents 15% of the total output. Of the total amount of Si exported to the lake bottom through diatom sinking, less than 20% is re-supplied to the surface water by diffusion. Thus, the lake acts as an important permanent sink for silica. The long residence time of dissolved silica in the lake (7 years) is related to the strong physical stratification of the lake. Only about 10% of the standing stock are available to phytoplankton uptake.  相似文献   

Negative Ce Anomaly in the Indian Banded Iron Formations: Evidence for the Emergence of Oxygenated Deep-Sea at 2.9-2.7 Ga     

Yasuhiro KATO  Takashi KANO  Keitaro KUNUGIZA 《Resource Geology》2002,52(2):101-110

Abstract: Major and rare earth element contents are reported for Late Archean banded iron formations (BIFs) in the Bababudan Group of the Dharwar Craton, South India. The BIFs are mostly composed of SiO₂ (average1ρ = 54.88.1 wt%) and Fe₂O₃* (44.38.2 wt%). The Al₂O₃ and TiO₂ contents are remarkably low, suggesting that detrital components were starved during the BIF deposition. The BIFs have a LREE-enriched pattern with a relatively high (La/Yb)_N (6.644.07). Total REE concentrations (RE) vary from 5.2 to 65.3 ppm. The REE patterns are characterized by the presence of a very large negative Ce anomaly (Ce/Ce*: 0.13-0.83) and a positive Eu anomaly (Eu/Eu*: 0.96-2.45). The Eu/Eu* decreases and (La/Yb)_N increases with a increase of RE. These correlations of REE indices are similar to those of modern hydrothermal iron-rich sediments near a mid-ocean ridge (MOR). Greenstones associated with the BIFs have MORB-like geochemical features. These geochemical and geological lines of evidence indicate that the depositional site of the BIFs was remote from a continent and/or island arc and that the BIFs were in situ hydrothermal sediments near a MOR. A striking negative Ce anomaly in the BIFs indicates that oxygenated deep-sea environments emerged at 2.9-2.7 Ga. The existence of contemporaneous Mn deposits in the Dharwar Craton supports this assertion. Our scenario of oxygen in the Earth's surface of the Late Archean is different from long-held notion that the atmosphere and ocean were persistently anoxic throughout the Archean.  相似文献   

极地冰雪氢氧同位素指标及其指示意义   总被引：1，自引：0，他引：1       下载免费PDF全文

张小伟  康建成  周尚哲 《极地研究》2002,14(1):73-80

本文综述了水汽来源状况、降水季节变化、火山喷发、太阳活动等气候环境因素对极地冰雪中同位素含量的可能影响及其程度 ,以及降水区域不均衡性、降水年际不均衡性、逆温层和同位素在冰雪中的扩散迁移作用等几种不稳定因素可能对冰雪同位素分析造成的干扰 ;在此基础上 ,综述了极地冰雪中δ1 8O、δD和其差值d(d =δD - 8δ1 8O)与局部或全球气温之间的一些线性关系 (包括全球尺度 ,格陵兰地区 ,南极地区等 )及它们在空间分布上的变化规律  相似文献