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| 1 | 大陆碰撞造山带榴辉岩相的熔体活动:来自南阿尔金基性麻粒岩中长英质脉体的证据显示文摘本文通过对南阿尔金巴什瓦克基性麻粒岩中长英质脉体的岩相学、锆石U-Pb年代学、Lu-Hf同位素及全岩主微量地球化学的综合研究,首次限定了该区基性麻粒岩中长英质脉体的形成时代为491±2 Ma (MSWD=0.91),此年龄与寄主麻粒岩高压—超高温阶段(榴辉岩相)的变质时代在误差范围内近一致,表明长英质脉体形成于榴辉岩相的变质阶段。由于长英质脉体中锆石明显不同于寄主基性麻粒岩中变质锆石的形态特征,基本排除了长英质脉体中的锆石为捕获锆石的可能性。此外,该长英质脉体中的锆石具有少量的长石、石英包裹体和较低的Th/U比值(0.05-0.41),锆石稀土元素配分模式图显示其具有重稀土富集和Eu负异常的特征,这些证据表明长英质脉体中的锆石可能结晶于变质熔体之中。长英质脉体的全岩地球化学特征显示其该脉体具有相对较低的K2O值,基本上排除了其来源于围岩长英质麻粒岩的可能,而且这些锆石的Hf同位素特征与寄主岩石的锆石Hf同位素特征具有相似性,表明形成长英质脉体的熔体为内部来源。结合全岩地球化学特征,推测其可能为基性麻粒岩发生部分熔融所致。 | 郭晶 李云帅 张建新 | 2021 | 地质学报2021，95，3： | 1 |
| 2 | Preface: Metamorphism and Orogenic Belts——Response from Micro-to Macro-Scale显示文摘The geological toolbox for the analysis of orogenic processes has seen substantial additions over the recent decades.Major advances have been made in the ability to simulate geological conditions and processes by computer modeling,we have a much improved knowledge of geochemical processes(trace elements and isotopes in particular),and,last but not least,the range and versatility of micro-analytical methods and instrumentation available to us has been expanded dramatically.The latter aspect has had a particular impact on metamorphic petrology as the conventional tools to determine pressure-temperaturetime paths via rock and mineral analysis combined with isotope geochronology have generally gained in precision and accuracy through a much improved resolution.Geochronology has moved from whole-grain analysis to spot analyses on zoned single grains while analyzing trace elements and isotopes at the same time.It is therefore possible to recognize complex multi-stage orogenic events in single samples or single grains.Diffusion profiles in minerals provide us with time-scales of metamorphic and magmatic processes.Major and trace elements as well as isotope profiles of mineral grains give us insight into changing ambient conditions during mineral growth.This special issue focuses on pressure-temperature conditions and geochronology of metamorphic rocks,isotope studies of magmatic rocks,partial melting and metasomatic processes,all with a view at tectonic implications and orogeny.Much of the evidence has been gained from small-scale observation and analysis.Diligent field work and detailed microscopic examination remain indispensable,though,as demonstrated clearly by the'expansion'of the P-T space as applicable to crustal metamorphic processes towards extreme pressures and temperatures.As a consequence,much interest has thus focused on UHP and UHT rocks and the orogenic processes that generate them.There is petrological evidence for subduction to,and subsequent exhumation from,depths in excess of 250 km.While this impacts substantially on the large-scale geodynamic models of orogenic processes,the evidence is gathered primarily from small-scale petrological observation.The same applies in principle to UHT granulites.To generate temperatures in the 900 to 1100℃range within the sillimanite stability field in orogenic heat budget models remains a serious challenge,however.The large overlap of solid-state metamorphism,partial anatexis and magmatic crystallization in P-T space suggests close interrelationships,and the role and contribution of the diverse magmatic activities in forming orogenic belts,from the onset of subduction to late-orogenic delamination or slab-break-off is crucial for our understanding of geodynamics,with focus on geochemistry and geochronology.Aspects of metasomatism in the framework of orogeny are given some special consideration in this issue.The topics include the formation of sagvandite,pyrope quartzite(or whiteschist),jadeitite and rodingite.One of the key questions addressed is the source and the nature of the fluids that triggered the different types of metasomatic events.Finally,it is shown how small-scale methods contribute to a better understanding of the formation of deep-seated mantle xenoliths. | Xu-Ping Li Hans-Peter Schertl Jürgen Reinhardt | 2019 | Journal of Earth Science2019，30，6： | 1 |
| 3 | Trace Elements of Multi-stage Minerals and Titanite U-Pb Dating for the Gneisses from Liansan Island,Sulu UHPM Belt显示文摘Gneisses with anatectic characteristics from the Liansan island in the Sulu UHPM(ultra-high pressure metamorphic)belt were studied for petrography,titanite U-Pb dating and mineral geochemistry.Three origins of garnets are distinguished:metamorphic garnet,peritectic garnet and anatectic garnet,which are formed in the stages of peak metamorphism,retrograde anatexis and melt crystallization,respectively.The euhedral titanite has a high content of REE and high Th/U ratios,which is interpreted as indicating that it was newly-formed from an anatectic melt.The LA-ICP-MS titanite U-Pb dating yields 214-217 Ma ages for the titanite(melt)crystallization.The distribution of trace elements varies in response to the different host minerals at different stages.At the peak metamorphic stage,Y and HREE are mainly hosted by garnet,Ba and Rb by phengite,Sr,Nb,Ta,Pb,Th,U and LREE by allanite and Y,U and HREE by zircon.During partial melting,Y,Pb,Th,U and REE are released into the melt,which causes a dramatic decline of these element contents in the retrograde minerals.Finally,titanite absorbs most of the Nb,U,LREE and HREE from the melt.Therefore,the different stages of metamorphism have different mineral assemblages,which host different trace elements. | SONG Lihao CAO Yuting XIE Tianhe CHEN Yuyao GAO Yuan WANG Songjie LI Xuping | 2023 | Acta Geologica Sinica(English Edition)2023，97，6： | 0 |
| 4 | Crystal Structure,Thermal Expansivity and High-Temperature Vibrational Spectra on Natural Hydrous Rutile显示文摘A natural rutle sample was measured by in situ high-temperature X-ray diffraction(XRD)patterns,as well as Raman and Fourier transform infrared(FTIR).Crystal structure is refined on the sample with 1.4 mol.%Fe and 510±120 ppmw.H2 O.The unit-cell and Ti O6 octahedral volumes are expanded by 0.7%–0.8%for Fe3+incorporation,as compared with the reported Ti-pure samples.The volumetric thermal expansion coefficient(α,K-1)could be approximated as a linear function of T(K):4.95(3)×10-9×T+21.54(5)×10-6,with the averaged valueα0=30.48(5)×10-6 K-1,in the temperature range of 300–1500 K.The internal Ti-O stretching(A1 g and B2 g)and O-Ti-O bending(Eg)modes show‘red shift',whereas the multi-phonon process exhibits‘blue shift'at elevated temperature.The rotational mode(B1 g)for Ti O6 octahedra is nearly insensitive to temperature variations.The OH-stretching bands at 3279 and 3297 cm-1 are measured by high-temperature spectroscopy experiments.Both the IR-active and Raman-active OH-stretching modes shift to lower frequencies at higher temperature,with the signal intensities decreasing.And after quenching,we expect about 43%dehydration around 873 K,and 85%dehydration at 1273 K for this hydrous sample. | Sha Wang Jinhua Zhang Joseph R.Smyth Junfeng Zhang Dan Liu Xi Zhu Xiang Wang Yu Ye | 2020 | Journal of Earth Science2020，31，6： | 0 |
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