High-temperature annealing of amoeboid olivine aggregates: Heating experiments on olivine–anorthite mixtures     

Mutsumi Komatsu  Takashi Mikouchi  Masamichi Miyamoto 《Polar Science》2009,3(1):31-55

Amoeboid olivine aggregates (AOAs) are composed of forsteritic olivine, Fe,Ni-metal, and Ca,Al-rich nodules consisting mainly of Al-diopside, spinel, and anorthite. Although the textures, shapes, and mineralogy of AOAs are consistent with their being aggregates of nebular condensates, some textures are in conflict with equilibrium condensation calculations, indicating that AOAs were not produced by a simple one-stage condensation. To examine the origin of the constituent minerals within AOAs and their textural relationships, we performed heating experiments using mineral mixtures analogous to those in AOAs. Isothermal and cooling experiments on forsterite + anorthite mixtures reveal that a high-Ca pyroxene phase forms via the incipient melting of the two minerals. Comparative studies of heating experiments performed using the mineralogy of AOAs suggest that Al-diopside in AOAs can be produced from a small degree of melting of forsterite and anorthite. The formation of Al-diopside in this way is consistent with the annealing textures observed in AOAs, and it may account for the discrepancy between the observed mineralogy of AOAs and the results of equilibrium condensation calculations, the occurrence of two types of diopside (Al,Ti-rich diopside and Al-diopside), and the variable Al₂O₃ content of Al-diopside.  相似文献   

Seismic evidence for a metastable olivine wedge in the subducting Pacific slab under Japan Sea   总被引：4，自引：0，他引：4  

Guoming Jiang  Dapeng Zhao  Guibin Zhang 《Earth and Planetary Science Letters》2008,270(3-4):300-307

We apply a forward-modeling approach to high-quality arrival time data from 23 deep earthquakes greater than 400 km depth to investigate the detailed structure of the subducting Pacific slab beneath the Japan Sea. Our results show that a finger-like anomaly exists within the subducting Pacific slab below 400 km depth, which has a P-wave velocity 5% lower than the surrounding slab velocity (or 3% lower than that of the normal mantle), suggesting the existence of a metastable olivine wedge (MOW) in the slab. The MOW top and bottom depths are 400 and 560 km, respectively. The MOW is estimated to be about 50 km wide at 400 km depth and close to the slab upper boundary. At 560 km depth the MOW is located at about 25 km below the slab upper boundary. Most of the deep earthquakes are located in the MOW. Our results favor transformational faulting as the mechanism for deep earthquakes.  相似文献   

Determination of cation distribution in (Co,Ni,Zn)2SiO4 olivine by synchrotron X-ray diffraction     

K. Tsukimura  S. Sasaki 《Physics and Chemistry of Minerals》2000,27(4):234-241

 The cation distribution of Co, Ni, and Zn between the M1 and M2 sites of a synthetic olivine was determined with a single-crystal diffraction method. The crystal data are (Co_0.377Ni_0.396Zn_0.227)₂SiO₄, M _r  = 212.692, orthorhombic, Pbnm, a = 475.64(3), b = 1022.83(8), and c = 596.96(6) pm, V = 0.2904(1) nm³, Z = 4, D _x  = 4.864 g cm⁻³, and F(0 0 0) = 408.62. Lattice, positional, and thermal parameters were determined with MoKα radiation; R = 0.025 for 1487 symmetry-independent reflections with F > 4σ(F). The site occupancies of Co, Ni, and Zn were determined with synchrotron radiation employing the anomalous dispersion effect of Co and Ni. The synchrotron radiation data include two sets of intensity data collected at 161.57 and 149.81 pm, which are about 1 pm longer than Co and Ni absorption edges, respectively. The R value was 0.022 for Co K edge data with 174 independent reflections, and 0.034 for Ni K edge data with 169 reflections. The occupancies are 0.334Co + 0.539Ni + 0.127Zn in the M1 sites, and 0.420Co + 0.253Ni + 0.327Zn in the M2 sites. The compilation of the cation distributions in olivines shows that the distributions depend on ionic radii and electronegativities of constituent cations, and that the partition coefficient can be estimated from the equation: ln [(A/B)_M1/(A/B)_M2] = −0.272 (IR _A -IR _B ) + 3.65 (EN _A −EN _B ), where IR (pm) and EN are ionic radius and electronegativity, respectively. Received: 8 April 1999 / Revised, accepted: 7 September 1999  相似文献   

橄榄石原位高温拉曼光谱研究   总被引：2，自引：0，他引：2  

马艳梅  崔启良  周强  黄伟军  刘冶  彭刚  邹广田 《吉林大学学报(地球科学版)》2006,36(3):342-345

利用微型电阻丝加热装置产生高温, 采用镍铬热电偶探测样品的温度, 在273～1 113 K温度范围,对橄榄石晶体进行了原位高温拉曼光谱研究。拉曼光谱数据显示：Si-O伸缩振动模高于800 cm^-1,Si-O弯曲振动模为400～700 cm^-1,SiO₄四面体旋转振动模和金属-氧的平移振动模低于400 cm^-1;得到了橄榄石拉曼振动频率随温度的变化关系,首次发现了橄榄石常温频率为541 cm^-1的Si-O反对称弯曲振动的A_g模,比其它的振动频率有较弱的温度效应。  相似文献   

Source and magmatic evolution of ocean island basalts from the Pohnpei Island,Northwest Pacific Ocean: Insights from olivine geochemistry     

Tong Zong  Zhenggang Li  Xuping Li  Yanhui Dong  Jihao Zhu 《海洋学报(英文版)》2021,40(12):27-38

The compositional variability of ocean island basalts (OIBs) is thought to reflect partial melting of a lithologically-heterogeneous mantle source dominated by either pyroxenite or peridotite. The Pohnpei Island in Micronesia, which is associated with the Caroline hotspot, is suggested to have been generated from partial melting of a pyroxenite-rich mantle. To examine this hypothesis, we present new major- and trace-element compositions of olivine phenocrysts in basalts from the island. The olivines exhibit large systematic inter- and intra-crystalline compositional variability. In Sample DS1, olivines record compositional zonation, in which cores have relatively high Fo (77–85), Ni (550×10?6–2 392×10?6), and Fe/Mn ratios (66–82), whereas rims have lower Fo (71–78), Ni (526×10?6–1 537×10?6), and Fe/Mn ratios (51–62). By contrast, olivines within other samples preserve no clear compositional zonation, exhibiting similar or slightly lower Fo values (66–78), Ni contents (401×10?6–1 268×10?6), and Fe/Mn ratios (53–69) as the rims of zoned crystals. The distinct chemical contrast between the two different types of olivine suggests they formed in magma chambers at different depths. Analysis using forward petrological modeling and multi-element indicators (Fe/Mn, Zn/Fe, FC3MS (FeOT/CaO?(3×MgO/SiO₂)), Mn/Zn, and Ni/(Mg/Fe)) of whole-rock samples and high-Fo olivines is inconsistent with a pyroxenite-rich mantle source. We suggest these inconsistencies reflect an influence on the partition coefficients of Ni and Mn between olivine and liquid during melting at variable pressures and temperatures. In addition, magma recharge and mixing within the magmatic plumbing system can change the composition of olivine. We suggest that identification of the mantle source of OIBs in volcanic islands such as the Pohnpei Island using olivine geochemistry should be treated with caution.  相似文献   

Subdivision of petrologic type of unequilibrated ordinary chondrites from Antarctica     

蒋云  徐伟彪 《极地研究(英文版)》2009,20(2):135-150

We report results of petrologic and mineralogical studies of 25 unequilibrated ordinary chondrites (19 Chinese Antarctic meteorites) using electron microprobe, scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS) techniques. With increasing degree of thermal metamorphism, chemical zoning of olivine was erased; plessite was transformed into intergrowths of coarser-grained kamacite and Ni-rich metal; Cr exsolved from ferroan olivine, produced needle-like crystals and coarsened into equant chromite grains; and feldspar crystallized during devitrification of glass and recrystallization of matrix. These features can help to identify different metamorphic grades. Based on the scheme by Sears et al (1982), we subdivided type 3 Chinese Antarctic ordinary chondrites into petrologic type 3.3 to 4 (3 type 3.3, 3 type 3.4, 1 type 3.5, 2 type 3.6, 2 type 3.7, 5 type 3.8, 3 type 4). This classification scheme is a quite effective way to subdivide Antarctic meteorites. Additionally, we propose to revise the chemical groups of GRV 020032 and GRV 020104 to L and H, respectively.  相似文献   

亚稳态橄榄石相变与深源地震研究进展     

刘雷  杜建国  易丽 《地震》2007,27(3):41-49

由于岩石圈俯冲板块内部温度低, 在400km左右的深度橄榄石不发生相变, 低压相的橄榄石便以亚稳态的形式进入更深的深度。 高温高压实验研究表明, 亚稳态橄榄石相变机制以相变形成的超塑性透镜状尖晶石反裂纹破裂为深源地震的触发机制, 能很好的解释深源地震的特征。 亚稳态橄榄石在俯冲带中存在的范围,是制约亚稳态相变机制的重要因素。 然而亚稳态橄榄石在俯冲带存在的范围尚存争议, 不同模型给出结果相差较大, 文中给出一些解决这个问题的建议。  相似文献   

对一类相变体积分数计算公式的修正   总被引：2，自引：2，他引：0       下载免费PDF全文

王曙光  叶国扬  宁杰远  楼小挺  刘平江 《地球物理学报》2007,50(6):1794-1801

考虑了相变过程中生成相晶核的真实形状,对1956年Cahn给出的颗粒边界成核情况下成核长大型相变的相变体积分数计算公式进行了修正;当初始实验数据是成核率、长大率时,两种相变体积分数计算公式的计算结果差别很大. 当初始实验数据是相变体积分数随时间变化的实验点时,两种相变体积分数计算公式所给出的计算结果的差别主要由拟合误差所致. 无论从哪种实验数据开始计算,两种不同的计算模型给出的生成相的颗粒大小都存在很大区别,这将影响对俯冲带流变结构的认识.  相似文献   

Ultra‐high temperature metamorphism recorded in Fe‐rich olivine‐bearing migmatite from the Khondalite Belt,North China Craton          下载免费PDF全文

Cyril Lobjoie  Wei Lin  Pierre Trap  Philippe Goncalves  Qiuli Li  Didier Marquer  Olivier Bruguier  Arnaud Devoir 《Journal of Metamorphic Geology》2018,36(3):343-368

We document the first occurrence of Fe‐rich olivine‐bearing migmatitic metapelite in the Khondalite Belt, North China Craton. Petrological analyses revealed two exotic assemblages of orthopyroxene+spinel+olivine and orthopyroxene+spinel+cordierite. Phase relation modelling suggests that these assemblages are diagnostic of ultra‐high temperature (UHT) metamorphism in the Fe‐rich system, with temperatures from 1,000 to 1,050°C at 0.6 GPa. U–Th–Pb SIMS analyses on zircon reveal a similar age of c. 1.92 Ga for the olivine‐bearing migmatite and an adjacent gabbronoritic intrusion that is therefore identified as the heat source for the UHT metamorphism. These results, coupled with additional analysis of the famous Tuguiwula sapphirine‐bearing granulite, lead to a re‐appraisal of the P–T path shape and heat source for the UHT metamorphism. We suggest that UHT metamorphism, dated between 1.92 and 1.88 Ga, across the whole Khondalite belt, proceeded from a clockwise P–T evolution with an initial near‐isobaric heating path at ~0.6–0.8 GPa, and a maximum temperature of 1,050°C followed by a cooling path with minor decompression to ~0.5 GPa. Considering our results and previous works, we propose that the orogenic crust underwent partial melting at temperature reaching 850°C and depth of ~20 to ~30 km during a period of c. 30 Ma, between 1.93 and 1.90 Ga. During this time span, the partially molten crust was continuously intruded by mafic magma pulses responsible for local greater heat supply and UHT metamorphism above 1,000°C. We propose that the UHT metamorphism in the Khondalite belt is not related to an extensional post‐collisional event, but is rather syn‐orogenic and associated with mafic magma supplies.  相似文献   

Hydroxyl in mantle olivine xenocrysts from the Udachnaya kimberlite pipe   总被引：6，自引：1，他引：5  

Monika Koch-Müller  Stanislav S. Matsyuk  Dieter Rhede  Richard Wirth  Natasha Khisina 《Physics and Chemistry of Minerals》2006,33(4):276-287

The incorporation of hydrogen in mantle olivine xenocrysts from the Udachnaya kimberlite pipe was investigated by Fourier-transform infrared spectroscopy and secondary ion mass spectrometry (SIMS). IR spectra were collected in the OH stretching region on oriented single crystals using a conventional IR source at ambient conditions and in situ at temperatures down to −180°C as well as with IR synchrotron radiation. The IR spectra of the samples are complex containing more than 20 strongly polarized OH bands in the range 3,730–3,330 cm⁻¹. Bands at high energies (3,730–3,670 cm⁻¹) were assigned to inclusions of serpentine, talc and the 10 Å phase. All other bands are believed to be intrinsic to olivine. The corresponding point defects are (a) associated with vacant Si sites (3,607 cm⁻¹ E || a, 3,597 E || a, 3,571 cm⁻¹ E || c, 3,567 E || c, and 3,556 E || b), and (b) with vacant M1 sites (most of the bands polarized parallel to a). From the pleochroic behavior and position of the OH bands associated with the vacant M1 sites, we propose two types of hydrogen—one bonded to O1 and another to O2, so that both OH vectors are strongly aligned parallel to a. The O2–H groups may be responsible for the OH bands at higher wavenumbers than those for the O1–H groups. The multiplicity of the corresponding OH bands in the spectra can be explained by different chemical environments and by slightly different distortions of the M1 sites in these high-pressure olivines. Four samples were investigated by SIMS. The calculated integral molar absorption coefficient using the IR and SIMS results of 37,500±5,000 L mol H₂O cm⁻² is within the uncertainties slightly higher than the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003) (28,450±1,830 L mol H₂O cm⁻²). The reason for the difference is the different distributions of the absorption intensity of the spectra of both studies (mean wavenumber 3,548 vs. 3,570 cm⁻¹). Olivine samples with a mean wavenumber of about 3,548 cm⁻¹ should be quantified with the absorption coefficient as determined in this study; those containing more bands at higher wavenumber (mean wavenumber 3,570 cm⁻¹) should be quantified using the value determined by Bell et al. (J Geophys Res 108(B2):2105–2113, 2003).

Monika Koch-MüllerEmail: Phone: +49-331-2881492

  相似文献