俯冲带硫的地球化学行为及硫循环SCIEI北大核心CSCD

俯冲带是全球最大的物质循环系统,控制着硫(S)在地球内部圈层及表层的循环,影响着大气圈、水圈、生物圈、岩石圈的稳定性以及地球的宜居性。厘清S在俯冲带中的地球化学行为和循环特征对理解地球各储库的氧化还原状态、岩浆作用与演化、成矿物质聚集、以及地球大气成分等具有重要意义。本文首先总结了进入俯冲带之前的大洋岩石圈的S结构模型,对S在大洋板片中的分布状态和地球化学特征进行了系统归纳。随后,系统阐述了俯冲带高压-超高压变质岩记录的板片变质及脱水过程中硫的地球化学行为。岩石学研究表明俯冲板片中的S多以硫化物相存在,硫酸盐矿物在弧前深度就已被释放或分解。相较于熔体,俯冲带流体中S的溶解度更高,是运移硫的更有效方式。DEW模型计算结果显示,流体中S含量总体较低,但在俯冲板片~90km处其含量有一个峰值(浓度0.5%~1.0%)。岩相学证据、地球化学测试结果、磷灰石S近边吸收结构(S-XANES)特征以及模拟结果都显示俯冲深部流体中S多以HS^(-)及H_(2)S形式存在,不含大量的SO_(4)^(2-)及硫酸盐;中f_(S_(2))流体有利于S迁移出俯冲板片,从而促进俯冲带大规模S循环,而高f_(S_(2))流体在流-岩交换过程沿流体通道发生S的锁固作用而不利于俯冲带S循环。质量平衡计算显示全球俯冲带S输入通量为4.65×10^(13)g/yr,弧下深度板片S输出通量为2.91×10^(12)g/yr,板片-岛弧S循环效率仅6.3%。俯冲板片在弧下深度可能存在一个短暂高效的S释放窗口,释放流体的δ^(34)S值为-2.1±3.0‰。基于高压-超高压变质岩中硫化物的研究,初步厘清了俯冲板片中S的地球化学行为,首次从板片角度全面、定量地限定了俯冲带的脱硫通量、效率、种型和同位素特征,提出俯冲带循环的S不是岛弧岩浆的氧化剂,与岛弧环境的正δ^(34)S值也无直接因果联系,对解析俯冲带S循环和理解地球长期的S循环具有重要意义。最后,本文还展望了俯冲带S循环的未来发展方向,应在俯冲带流体氧化还原性质(硫酸盐的命运)、俯冲沉积物对S循环的制约、俯冲带环境下多硫同位素的分馏效应、S循环与其它挥发分(如C等)循环之间的耦合关系、地球历史上深部S循环等方向做出探索,更深入地理解俯冲带及全球S循环过程。     

Myojin Rift, Izu–Bonin Arc as the Modern Analog of Hokuroku Basin, Northeast Japan: Geotectonic Significance of the New Hydrothermal Deposit in the Back-Arc Rift

A huge hydrothermal field, named the "Hakurei Sulfide Deposit" (HSD) was discovered in the North Myojin Rift (NMR), Izu–Bonin Back-Arc Rift (BAR) during the 2003 survey cruise of R/V Hakurei-maru No.2 . This paper investigates the geotectonic features and the tectonic setting of ore deposits between the NMR and the Hokuroku Basin, which is representative of kuroko fields in Japan. The topographic features of the NMR and the Hokuroku Basin are similar. Both have a clear ring structure surrounded by faults and the east–west width is almost the same. Many kuroko deposits were formed on the extrusion centers of the five pre-mineral acidic volcanic complexes, located in a loop inside the Hokuroku Basin. In the case of the NMR, seven submarine volcanoes are also located in a loop, and the HSD formed inside the summit caldera of Bayonnaise Knoll, which is one of the seven volcanoes. These topographic similarities highlight that the NMR is a modern analog of the Hokuroku Basin. Identifying such similarities is extremely useful when prospecting kuroko deposits on land equivalents as well as on the other segments of the Izu–Bonin BAR. The probability of finding kuroko deposits on land is expected to increase when the following are identified: (i) location of back-arc rift and the volcanic front; (ii) direction of the arc–trench system and intra-rift faults (and/or fracture zone); (iii) position of submarine volcanoes surrounding a back-arc rift; and (iv) intersections of a caldera fault and intra-rift fault (and/or fracture zone) inside the summit caldera of submarine volcanoes. Within these aforementioned points a ring structure, acidic volcanic complexes that circle the circuit and submarine calderas along the volcanic front, are an important indication of submarine hydrothermal deposits.     

从CAD到ArcGIS格式数据转换的精度改进

针对直接利用空间数据操作引擎将CAD注记数据转换成ArcGIS数据与原CAD图文字注记数据存在一定差异的问题,提出了一种新的转换注记方法。利用Arc Map提取CAD原图注记层数据,较好的减少了FME转换的注记的差异,为地形图的转换提供了可行的方案。以某市的地形图为数据源进行实例论证,实验结果显示所提的方法不仅能够更好地保持数据的精度和完整性,还有利于数据的入库。研究结果对从事地理信息系统开发的技术人员具有一定的参考价值。     

Porphyry fertility in the Northparkes district: indicators from whole-rock geochemistry

Abstract

Four economic porphyry Cu–Au deposits and several prospects have been investigated in the Northparkes district, part of the Ordovician to early Silurian Junee–Narromine Belt of the Macquarie Arc, New whole-rock geochemical data from the Northparkes porphyry Cu–Au district, NSW, indicate that the mineralising intrusive complexes exhibit distinct arc signatures that are transitional from high-K calc-alkaline to silica-saturated alkalic. Based on ratios of Sr/Y vs Y (e.g. Sr/Y > ～20 and Y < ～17?ppm) the mineralising intrusions are interpreted to have crystallised from fractionated hydrous melts indicating the suppression of plagioclase crystallisation in favour of hydrous mineral phases. This interpretation is supported by listric-shaped rare earth element curves and the presence of primary hornblende phenocrysts indicating elevated magmatic water contents. There is an association of mineralising intrusions with a low Zr trend both in the mineralised Northparkes district intrusive rocks and in mineralised porphyry-related intrusive rocks globally. A newly developed fertility indicator ratio Zr/Y ～10% is more accurate at identifying the mineralised rocks at Northparkes than the conventional Sr/Y vs Y fertility indicator diagram, successfully identifying 92% of the mineralising intrusions, mainly owing to the fact that it is less affected by hydrothermal alteration. The insensitivity of Zr–Y to alteration makes this indicator a useful new tool that may lead to enhanced probabilities for future discoveries in the Northparkes district, broader Macquarie Arc and altered rocks globally.

1. KEY POINTS

2. Mineralising intrusions in the Northparkes district have distinct Zr vs Y concentrations.

3. The Zr vs Y indicator of magmatic fertility is less sensitive to alteration than Sr-based indicators.

4. The Zr vs Y magmatic fertility indicator identified at Northparkes is not unique and identifies mineralising intrusions in other porphyry fields.

     

Plio-Quaternary segmentation of the south Tyrrhenian forearc basin

The structural elements constituting the forearc basin of the Calabrian Arc–Sicily orogenic system are recognizable on land and in the Tyrrhenian offshore. The Plio–Pleistocene retreat of the Ionian subduction hinge, coeval with the roll-back of the Africa continental crust, leads to segmentation of the forearc basin and southeastward migration of the Calabrian Arc due to its higher degree of mobility compared to Sicily, where, on the contrary, continental collision takes place. The analysis of geological data collected in three areas of the orogenic belt and the integration with offshore geophysical data show evidence of two phases of subduction hinge retreat: (1) Late Pliocene–Early Pleistocene southeastward migration accompanied by the development of N120°E trending tear-faults and NE–SW-trending extensional systems, (2) Middle–Late Pleistocene SSE-ward migration with development of NNW–SSE-trending tear-faults and N70°E-trending collapse systems. The data presented here provide an innovative framework for the interpretation of this most seismically active area of the Mediterranean. In particular, in the Messina Strait area, the more recent N70°E lineaments could be associated with the faults that generated the 1783 Calabria earthquake and are coherent with the focal mechanism of the 1908 Messina earthquake, confirmed also by the analysis of frequency diagrams of the elongation directions of the isoseists.     

西藏拉萨地块北部白垩纪火山岩及其对冈底斯岛弧构造演化的制约

拉萨地块北部广泛分布着白垩纪火山岩。本文及已有年代学研究表明,这些火山岩主要形成于早白垩世中期(140～110Ma)和晚白垩世早期(100～80Ma)两个阶段。早白垩世中期火山岩主要为则弄群和多尼组地层中的火山岩夹层,岩性组合包括玄武岩、玄武安山岩、安山岩、英安岩和流纹岩,主体为高钾钙碱和钾玄质系列,具有初始87Sr/86Sr比值(0.7068～0.7102)较高、εNd(t)(-9.3～-1.5)较低和δ18OV-SMOW(7.2‰～9.8‰)较高等同位素组成特征,源区为受消减沉积物和/或蚀变玄武质洋壳的含水流体/熔体交代的富集岩石圈地幔楔。晚白垩世早期火山岩零星分布在拉萨地块北部和羌塘地块南部,岩石类型以玄武岩、玄武安山岩、安山岩为主,有少量的酸性火山岩(英安岩),主体为典型的钙碱性系列组合(低钾拉斑+中钾钙碱),具有较高的Mg(Mg#可高达59)和相容元素Cr(162×10-6)、V(216×10-6)和Ni(80×10-6)含量以及更为原始的Sr-Nd同位素组成,(87Sr/86Sr)t=0.7041～0.7048,εNd(t)=0.9～2.2,指示源区可能为受到上涌软流圈地幔熔体二次交代的交代富集岩石圈地幔,本文将其命名为尼玛火山岩。综合以上白垩纪火山岩和拉萨地块南部叶巴组、桑日群和林子宗群火山岩的时空分布特征,认为中生代至早第三纪冈底斯岛弧的演化发生了两次大的空间迁移:中生代早侏罗世以来由南向北变新,从最南部的叶巴组(早侏罗世,193～174Ma)和桑日群火山岩(J3—K1),到北部的则弄群和多尼组火山岩(早白垩世中期,140～110Ma),最后到最北部的尼玛火山岩(晚白垩世早期,100～80Ma);早第三纪由北向南跃迁回南部,从北部的尼玛火山岩迁移到南部的林子宗群火山岩(70～40Ma)。冈底斯岛弧火山岩的时空分布特征和成分演化规律,揭示了新特提斯洋板块的俯冲历史,即早期新特提斯洋壳由南向北低角度俯冲,然后再高角度反向旋转,直至最后发生拆沉。     

Crystal retention,fractionation and crustal assimilation in a convecting magma chamber,Nisyros Volcano,Greece

Nisyros island is a calc-alkaline volcano, built up during the last 100 ka. The first cycle of its subaerial history includes the cone-building activity with three phases, each characterized by a similar sequence: (1) effusive and explosive activity fed by basaltic andesitic and andesitic magmas; and (2) effusive andextrusive activity fed by dacitic and rhyolitic magmas. The second eruptive cycle includes the caldera-forming explosive activity with two phases, each consisting of the sequence: (1) rhyolitic phreatomagmatic eruptions triggering a central caldera collapse; and (2) extrusion of dacitic-rhyolitic domes and lava flows. The rocks of this cycle are characteized by the presence of mafic enclaves with different petrographic and chemical features which testify to mixing-mingling processes between variously evolved magmas. Jumps in the degree of evolution are present in the stratigraphic series, accompanied by changes in the porphyritic index. This index ranges from 60% to about 5% and correlates with several teochemical parameters, including a negative correlation with Sr isotope ratios (0.703384–0.705120). The latter increase from basaltic andesites to intermediate rocks, but then slightly decrease in the most evolved volcanic rocks. The petrographic, geochemical and isotopic characteristics can be largely explained by processes occurring in a convecting, crystallizing and assimilating magma chamber, where crystal sorting, retention, resorption and accumulation take place. A group of crystal-rich basaltic andesites with high Sr and compatible element contents and low incompatible elements and Sr isotope ratios probably resulted from the accumulation of plagioclase and pyroxene in an andesitic liquid. Re-entrainment of plagioclase crystals in the crystallizing magma may have been responsible for the lower ⁸⁷Sr/⁸⁶Sr in the most evolved rocks. The gaps in the degree of evolution with time are interpreted as due to liquid segregation from a crystal mush once critical crystallinity was reached. At that stage convection halted, and a less dense, less porphyritic, more evolved magma separated from a denser crystal-rich magma portion. The differences in incompatible element enrichment of pre-and post-caldera dacites and the chemical variation in the post-caldera dome sequence are the result of hybridization of post-caldera dome magmas with more mafic magmas, as represented by the enclave compositions. The occurrence of the quenched, more mafic magmas in the two post-caldera units suggests that renewed intrusion of mafic magma took place after each collapse event.     

一次强降水系统的演变和细结构分析

文章分析1992年7月23日河北省东部平原地区一次突发性暴雨过程，研究了产生特大暴雨的中-α尺度对流系统的演变及其细结构，讨论了该系统内部中心暖区形成的物理机制，并指出几种不同尺度的天气系统相互作用对这次暴雨系统的重要影响。     

Seismicity and stress field in Okinawa Trough and Ryukyu regions

（黄培华）（苏维加）（陈金波）ＳｅｉｓｍｉｃｉｔｙａｎｄｓｔｒｅｓｓｆｉｅｌｄｉｎＯｋｉｎａｗａＴｒｏｕｇｈａｎｄＲｙｕｋｙｕｒｅｇｉｏｎｓ￥Ｐｅｉ－ＨｕａＨＵＡＮＧ；Ｗｅｉ－ｊｉａＳＵａｎｄＪｉｎ－ＢｏＣＨＥＮ（ＤｅｐａｒｔｍｅｎｔｏｆＥａｒｔｈａ...