【摘 要】
：
Discontinuous chains of ultramafic rock bodies form part of the 3800-3700 Ma Isua Supracrustal Belt(ISB),hosted in the ltsaq Gneiss Complex of southwestern Greenland.These bodies are among the world\'s oldest outcrops of ultramafic rocks and hence an in
【机 构】
：
Graduate School of Natural Science & Technology,Kanazawa University,Japan;School of Environmental Sc
论文部分内容阅读
Discontinuous chains of ultramafic rock bodies form part of the 3800-3700 Ma Isua Supracrustal Belt(ISB),hosted in the ltsaq Gneiss Complex of southwestern Greenland.These bodies are among the world\'s oldest outcrops of ultramafic rocks and hence an invaluable geologic record.Ultramafic rocks from Lens B in the northwestern limb of ISB show characteristics of several stages of serpentinization and deserpen-tinization forming prograde and retrograde mineral assemblages.Ti-rich humite-group minerals such as titanian chondrodite (Ti-Chn) and titanian clinohumite (Ti-Chu) often occur as accessory phases in the metamorphosed ultramafic rocks.The Ti-rich humite minerals are associated with metamorphic olivine.The host olivine is highly forsteritic (Fo96-98) with variable MnO and NiO contents.The concentrations of the rare-earth elements (REE) and high-field strength elements (HFSE) of the metamorphic olivine are higher than typical mantle olivine.The textural and chemical characteristics of the olivine indicate meta-morphic origin as a result of deserpentinization of a serpentinized ultramafic protolith rather than pri-mary assemblage reflecting mantle residues from high-degrees of partial melting.The close association of olivine,antigorite and intergrown Ti-Chn and Ti-Chu suggests pressure condition between ～1.3-2.6 GPa within the antigorite stability field (＜700 ℃).The overall petrological and geochemical features of Lens B ultramafic body within the Eoarchean ISB indicate that these are allochthonous ultramafic rocks that recorded serpentine dehydration at relatively lower temperature and reached eclogite facies condi-tion during their complex metamorphic history similar to exhumed UHP ultramafic rocks in modern sub-duction zone channels.
其他文献
Ground-level ozone (O3) is a primary air pollutant,which can greatly harm human health and ecosys-tems.At present,data fusion frameworks only provided ground-level O3 concentrations at coarse spatial(e.g.,10 km) or temporal (e.g.,daily) resolutions.As pho
The Duolong mineral district in western Tibet is one of the largest porphyry Cu-Au deposit fields with significant metallogenic potential in China.Its tectonic environment relevant to Early Cretaceous Cu-Au mineralization remains controversial.Here we rep
The Zhuxi deposit is a recently discovered W-Cu deposit located in the Jiangnan porphyry-skarn W belt in South China.The deposit has a resource of 3.44 million tonnes of WO3,making it the largest on Earth,however its origin and the evolution of its magmat
The sub-arc mantle that experienced hydrous melting is commonly characterized by refractory geochem-ical compositions.Nevertheless,minor lherzolites with fertile compositions have also been reported for mantle peridotites from subduction zone.The petrogen
We present major and trace element compositions of mineral concentrates comprising garnet xenocrysts,ilmenite,phlogopite,spinel,zircon,and uncommon minerals (titanite,calzirtite,anatase,baddeleyite and pyrochlore) of a newly discovered Late Cretaceous kim
This paper presents a confidence ellipse-based method to evaluate the similarity of soil parametric data using the database from the site investigation reports.Then,the obtained similarity assessment results of parametric data are used to further estimate
The early Albian Oceanic Anoxic Event 1b (OAE 1b) is well documented in the Tethys,Pacific and North Atlantic,but few studies have evaluated whether or not terrestrial records of OAE 1b exist.In order to identify terrestrial records of the early Albian OA
The Marwar Supergroup (NW Peninsular India) is thought to be of Ediacaran-Cambrian age,based on pre-vious paleontological and geochronological studies.However,direct constraints on the onset of sedimen-tation within the Marwar basin are still scarce.In th
Glaciological mass balance (MB) is considered the most direct,undelayed and unfiltered response of the glaciers to climatic perturbations.However,it may inherit errors associated with stake under-representation,averaging over the entire glacier and human
The higher concentration of PM10 and PM2.5 in the lower atmosphere is severely harmful for human health and it also makes visibility diminution along with weather and climate modifications.The main objective is to find out the spatiotemporal variation and