Petrogenesis and geotectonic setting of early Svecofennian arc cumulates in the Roslagen area,east‐central Sweden     

ke Johansson  ULF B. Andersson  Ulf Hlenius 《Geological Journal》2012,47(6):557-593

Several intrusions of ultrabasic to basic composition occur in the Roslagen area of east‐central Sweden in close spatial and temporal association with the surrounding 1.90–1.87 Ga old early orogenic Svecofennian granitoids. An imprecise Sm‐Nd WR errorchron yields an age of 1895 ± 71 Ma. In spite of the penetrative deformation in the granitoids, the basic–ultrabasic rocks mostly appear undeformed and largely preserve magmatic textures with plagioclase, olivine (in some rock types), orthopyroxene and clinopyroxene, and amphibole as major constituents. The plagioclase is typically very anorthitic (ca. An₉₀). The Roslagen intrusions range in composition from primitive to evolved (Mg# 80 to 49) but contain only 40–50 wt% SiO₂. Many samples are highly elevated in Al₂O₃ (up to 30 wt%), CaO (up to 16 wt%) and Sr (up to 800 ppm), with strongly positive Eu and Sr anomalies, in line with being plagioclase cumulates. Although masked by cumulus effects, the relative trace element contents indicate a volcanic arc signature. The initial Nd isotope composition is homogeneously ‘mildly depleted’, with ε_Nd of +0.3 to +1.1, and the initial Sr isotope composition ‘mildly enriched’, with ε_Sr of +8 to +15. Non‐cumulus rocks with small Eu and Sr anomalies can be used to deduce the composition of the parental magma. This LILE‐ and LREE‐enriched and HFSE‐depleted high‐alumina basalt magma, with Mg# of ca. 50–60 and Ca# of ca. 80, most likely formed by partial melting of mantle material, enriched by fluids in a subduction environment, at 1.9 Ga. The cumulate rocks apparently crystallized from a somewhat more evolved water‐rich magma with Mg# of ca. 40. Crystallization was followed by the development of late‐magmatic to post‐magmatic coronas between olivine and plagioclase in the presence of H₂O‐rich fluids. The subduction‐related setting would make these intrusions Palaeoproterozoic counterparts of Alaskan‐type ultramafic intrusions, but they differ from those in being plagioclase enriched, possibly reflecting different levels of exposure. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Hugoniot equation of state of anorthite glass and lunar anorthosite     

Mark B. Boslough  Sally M. Rigden  Thomas J. Ahrens 《Geophysical Journal International》1986,84(3):455-473

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内蒙古阿拉善庆格勒图黑云斜长片麻岩的单颗粒锆石U-Pb法年龄   总被引：3，自引：0，他引：3  

周红英  莫宣学  李俊建  李惠民 《矿物岩石地球化学通报》2007,26(3):221-223

内蒙古阿拉善庆格勒图地区出露地层以片麻岩为主,夹斜长角闪岩。但其归属尚无确切的同位素年龄资料。本文最近获得的黑云斜长片麻岩的单颗粒锆石U-Pb法年龄为1826±13 Ma,这是迄今获得的较为可靠的直接测年数据。结合前人研究成果,提出该区出露的主要变质岩石——黑云斜长片麻岩的形成时代应为古元古代。  相似文献   

福建平潭角闪辉长岩结晶过程的矿物学记录   总被引：10，自引：1，他引：10  

董传万  徐夕生 《矿物学报》1997,17(3):285-290

福建平潭角闪辉长岩中具成分环带的斜长石由钙质斜长石核和膜状中长石两部分组成，它是钙碱性高铝玄武岩浆结晶过程中岩浆上升和吸回作用的记录。  相似文献   

“北祁连蛇绿岩及其构造背景野外研讨会”在甘肃举行     

张旗 《岩石学报》1997,13(4):528-528

别鲁阿嘎希花岗闪长岩－石英闪长岩带与金矿化有十分密切的关系。锆石Ｕ－Ｐｂ法测得别鲁阿嘎希石英闪长岩年龄为３６９Ｍａ。斜长石环带成分振荡，与黑云母共生的角闪石成分显示为富镁。岩石地球化学特征表明，这些岩石为幔源的拉斑玄武岩岩浆和地壳部分熔融形成岩浆混合后的产物。  相似文献   

南海新生代碱性玄武岩中斜长石矿物的化学成分及意义   总被引：1，自引：0，他引：1  

鄢全树  石学法  刘季花  常丽华  尹京武 《矿物学报》2008,28(2):135-142

南海新生代碱性玄武岩中存在两种不同粒径的斜长石矿物.其一为斜长石斑晶,常见熔蚀麻点,是岩浆上升、压力降低时发生熔蚀作用并在骤冷条件下形成的;其二斜长石微晶,半定向或杂乱分布于火山玻璃中,其中空骸晶结构表明斜长石微晶是在淬冷条件下迅速结晶形成的.斜长石斑晶具弱成分环带,斑晶边部的An值稍高或接近于斜长石微晶.微晶斜长石An值与岩浆喷出后的水深以及喷发位置距离岩浆主通道的远近存在一定联系.本区的斜长石斑晶形成温度明显低于冲绳海槽地区,而类似于东海陆架地区;斜长石微晶的结晶温度类似于冲绳海槽,表明两地区在岩浆喷出海底后淬火结晶的物理化学条件相似.结合同样品中橄榄石斑晶研究结果以及已有的地球物理学和岩石学方面的资料,可能反映了地幔柱快速上涌使早期部分熔融及结晶分异作用较弱,岩浆本身温度高提供了早期结晶形成的斑晶与寄主岩浆进一步充分反应的热量.计算的斜长石斑晶温度不能反映源区温度特征,后者应高于本文所计算的斜长石斑晶的结晶温度.  相似文献   

玲珑花岗岩斜长石的费氏台研究及岩体形成时代问题的初步探讨     

Sang Longkang 《地球科学》1986,(1)

作者在地质调查基础上,对取自玲珑花岗岩、包体和胶东群变质岩的25个有代表性的样品,用费氏台测定了113个斜长石颗粒。本文根据测定资料的统计分析,探讨了玲珑花岗岩斜长石成分、有序度、双晶类型、演化规律及其成因意义,并将玲珑花岗岩与金喆佑、舟桥三男（1972）建立的不同时代花岗岩模式进行了对比。上述研究的初步结果认为玲珑花岗岩属于元古代交代-深熔成因。  相似文献   

Alteration at the Olympic Dam IOCG–U deposit: insights into distal to proximal feldspar and phyllosilicate chemistry from infrared reflectance spectroscopy     

A. J. Mauger  K. Ehrig  A. Kontonikas-Charos  C. L. Ciobanu  N. J. Cook  V. S. Kamenetsky 《Australian Journal of Earth Sciences》2016,63(8):959-972

Twenty thousand metres of diamond drill core representing a 14 km cross-section from weakly to intensely altered Roxby Downs Granite through the Olympic Dam Breccia Complex, host to the Olympic Dam iron-oxide–copper–gold–uranium deposit in South Australia, was analysed using the HyLogger-3 spectral scanner. Thermal and shortwave infrared spectroscopy results from 30 drill holes provide insight into the spatial relationships between quartz, orthoclase–microcline, albite–oligoclase and progressively changing sericite and chlorite compositions. The relative proportions of quartz, feldspars and phyllosilicates were mapped with thermal infrared spectroscopy. Variations in the chemistry of sericite and chlorite were extracted by proxy from their shortwave infrared spectral response, together with their relative spatial distribution. HyLogger scanning has revealed four deposit-scale mineralogical trends, progressing from least-altered Roxby Downs Granite into mineralisation where most of the feldspar has been replaced by sericite + hematite + quartz: (1) a progressive Al–OH wavelength shift of 2205 nm to 2210 nm for sericite, followed by a spatially rapid reversal corresponding to lower phengite/muscovite abundance ratios; (2) progressive Mg/Fe–OH wavelength shift of 2248 nm to 2252 nm reflecting an increase in the Fe:Mg ratio of chlorite; (3) increasing ratio of microcline to orthoclase followed by a rapid decrease; and (4) slightly decreasing ratio of albite to oligoclase followed by plagioclase destruction prior to albite replacement by sericite. The HyLogger feldspar results support recent petrographic evidence for hydrothermal albite and K-feldspar at the Olympic Dam deposit, not previously reported. The spectral results from continuous HyLogger scans also show that the microscopic observations and proposed feldspar replacement reactions are not locally isolated phenomena, but are applicable at the deposit and regional-scale. A modified quartz–K-feldspar–plagioclase ternary diagram utilising mineralogy interpreted from HyLogger thermal infrared spectra (QAP_TIR) diagram along with supporting data on the abundance ratios of orthoclase/microcline and albite/plagioclase, and the wavelength shifts in characteristic absorption features for sericite and chlorite, can be used as empirical vectors towards mineralisation within the Olympic Dam mineral system, with potential application to other IOCG ore-forming systems. Intrusion of Gairdner Dyke Swarm dolerite dykes into sericite ± hematite altered Roxby Downs Granite results in retrograde albite–chlorite–magnetite alteration envelopes (up to tens of metres thick) overprinting the original sericite ± hematite alteration zone and needs to be carefully evaluated to ensure that such areas are not falsely downgraded during exploration.  相似文献   

A recalibration of the garnet-olivine geothermometer and a new geobarometer for garnet peridotites and garnet-olivine-plagioclase-bearing granulites   总被引：1，自引：0，他引：1  

C. M. WU  G. C. ZHAO 《Journal of Metamorphic Geology》2007,25(5):497-505

The garnet-olivine Fe-Mg exchange geothermometer and the garnet-olivine-plagioclase geobarometer have been simultaneously calibrated using reversed experimental data based on the model reactions and between 900 and 1500 °C at 9.1–95.0 kbar and between 4.7 and 7.0 kbar at 750–1050 °C, respectively. The resulting garnet-olivine thermometer reproduces experimental temperatures mostly within ±75 °C and the garnet-olivine-plagioclase barometer reproduces experimental pressures well within ±0.19 kbar. These new thermobarometers use the same garnet and olivine activity models and are thermodynamically consistent. Application of these thermobarometers to garnet peridotites from mantle xenoliths, orogenic garnet peridotites over the world and the Adirondack olivine-bearing metagabbros yielded reasonable P–T results. The present garnet-olivine thermometer can be used to measure medium-high-grade to ultrahigh-grade, low-pressure to ultrahigh–high-pressure garnet peridotites and metagabbros, whereas the garnet-olivine-plagioclase barometer has limited application to garnet-olivine-plagioclase-bearing granulites.  相似文献   

Mechanism of Crystal Redistribution in a Sheet-like Magma Body: Constraints from the Nosappumisaki and Other Shoshonite Intrusions in the Nemuro Peninsula, Northern Japan     

SIMURA  RAYKO; OZAWA  KAZUHITO 《Journal of Petrology》2006,47(9):1809-1851

Processes of crystal separation in a magma heavily laden withcrystals without phase change are investigated from observationson frozen magma systems: Nosappumisaki and other shoshoniteintrusions in the Nemuro peninsula, Japan, for which the originof the crystals and the initial conditions are well constrained.The Nosappumisaki intrusion is 120 m in thickness and extendsfor more than 1·5 km. It exhibits a wide range of lithologicalvariation, principally as a result of crystal redistributionafter intrusion. Crystals in each lithology can be clearly dividedinto two kinds according to their composition and texture: thosepresent before the intrusion of the magma (‘phenocrysts’)and those that crystallized in situ after intrusion. From thevertical change in mode and size of ‘phenocrysts’,it is shown that (1) augite ‘phenocrysts’ were rapidlydeposited, with little overgrowth after intrusion, by significantcoagulation or clustering on a time-scale of more than a fewyears, and (2) plagioclase ‘phenocrysts’, definitelydenser than the melt but concentrated in the upper level, floatedby counter flow of massive deposition of augite ‘phenocrysts’.These results indicate that in a magma heavily laden with crystalsof a few millimeters in size (>20 vol. %), crystal–crystaland crystal–melt interaction play an important role inthe separation of crystals from the host melt. KEY WORDS: magma chamber; sill; crystal settling; plagioclase flotation; Nosappumisaki  相似文献