We report the discovery of TiO_(2)-Ⅱ in the unmelted rock of the shocked Suizhou L6 chondrite.Natural TiO_(2)-Ⅱ was previously found in ultrahigh-pressure metamorphic and mantle-derived rocks,terrestrial impact stru...We report the discovery of TiO_(2)-Ⅱ in the unmelted rock of the shocked Suizhou L6 chondrite.Natural TiO_(2)-Ⅱ was previously found in ultrahigh-pressure metamorphic and mantle-derived rocks,terrestrial impact structures,and tektite.Our microscopic,Raman spectroscopic,electron microprobe and transmission electron microscopic investigations have revealed:(1) All observed TiO_(2)-Ⅱ grains are related with ilmenite and pyrophanite;(2) TiO_(2)-Ⅱ occurs as needle-and leaf-shaped inclusions in llmenite and patch-,tape-shaped body in pyrophanite;(3)The composition of TiO_(2)-Ⅱ is identical with that of its precursor rutile;(4) The Raman spectrum of TiO_(2)-Ⅱ is in good agreement with that of natural and synthesized α-PbO_(2)-type TiO_(2);(5) TiO_(2)-Ⅱ occurs mainly in the form of well-ordered nano-domains and small mis-orientation among the domains can be observed.(6) All electron diffraction reflections from TiO_(2)-Ⅱ can be indexed to α-PbO_(2)structure in space group Pbcn with lattice parameters of a=4.481 ?,b=5.578 A and c=4.921 A;(7) The exsolution inclusions of rutile from host ilmenite are mostly connected with an alternation process along the lamellar twinning plane of ilmenite induced by shockinduced high pressure and high temperature;(8) The P-T regime of 20-25 GPa and 1000 ℃ estimated for the Suizhou unmelted rock is suitable for phase transition of rutile into TiO_(2)-Ⅱ phase.展开更多
The Suizhou meteorite is a heavily shocked and melted vein-containing L6 chondrite.It contains a minor amount of diopside with a(Ca_(0.419)Mg_(0.466)Fe_(0.088))SiO_(3)composition,and a shock-metamorphosed diopside gra...The Suizhou meteorite is a heavily shocked and melted vein-containing L6 chondrite.It contains a minor amount of diopside with a(Ca_(0.419)Mg_(0.466)Fe_(0.088))SiO_(3)composition,and a shock-metamorphosed diopside grain associated with ringwoodite and lingunite was found in a melt vein of this meteorite.Our electron microprobe,transmission electron microscopic and Raman spectroscopic analyses revealed four silicate phases with different compositions and structures inside this shock-metamorphosed diopside grain,termed phase A,B,C and D in this paper.Phase A is identified as orthorhombic(Ca_(0.663)-Mg_(0.314))SiO_(3)-perovskite which is closely associated with phase B,the vitrified(Mg_(0.642)Ca_(0.290)Fe_(0.098))SiO_(3)perovskite.Phase D is assigned to be(Mg_(0.578)Ca_(0.414))SiO_(3)majorite which is associated with phase C,the vetrified Carich Mg-perovskite with a(Mg_(0.853)Ca_(0.167))SiO_(3)composition.Based on high-pressure and high-temperature experiments,the diopside grain in the melt vein of the Suizhou meteorite would have experienced a P–T regime of 20–24GPa and 1800–>2000℃.Such P–T conditions are high enough for the decomposition of the diopside and the formation of four different silicate phases.The orthorhombic(Ca_(0.663)Mg_(0.314))SiO_(3)perovskite found in the Suizhou L6 chondrite might be considered as the third lower-mantle silicate mineral after bridgmanite and davemaoite after the detailed analyses of its crystal structure and physical properties being completed.展开更多
The Suizhou meteorite is an L6 chondrite. This meteorite is consisted of olivine, low-Ca pyroxene, plagioclase, FeNi metal, troilite, whitlockite, chlorapatite, chromite and ilmenite. Olivine and pyroxene grains displ...The Suizhou meteorite is an L6 chondrite. This meteorite is consisted of olivine, low-Ca pyroxene, plagioclase, FeNi metal, troilite, whitlockite, chlorapatite, chromite and ilmenite. Olivine and pyroxene grains display shock-induced mosaic texture, and most plagioclase grains were melted and transformed to maskelynite. This meteorite contains a few very thin shock-produced melt veins ranging from 20 to 100 μm in width. They are chondritic in composition and contain abundant high-pressure minerals in two assemblages. One is the coarse-grained assemblage of ringwoodite, majorite, lingunite with minor amount of tuite, xieite, the CF-phase, akimotoite and amorphized perovskite, and the fine-grained assemblage (the melt vein matrix) composed of majorite-pyrope garnet, magnesiowüstite. FeNi metal and troilite in the Suizhou shock veins were molten and occur as small intergrowth grains or veinlets filling the interstices of garnet crystals or cracks in the vein matrix. It was revealed that olivine, pyroxene and plagioclase in the Suizhou shock veins have transformed in solid state to their high-pressure polymorphs ringwoodite, majorite, and lingunite, respectively, without change in their chemical compositions.展开更多
The mineralogy of shock vein matrix in the Suizhou meteorite has been investigated by optical and transmission electron microscopy. It was revealed that the vein matrix is composed of majorite-pyrope garnet, magnesiow...The mineralogy of shock vein matrix in the Suizhou meteorite has been investigated by optical and transmission electron microscopy. It was revealed that the vein matrix is composed of majorite-pyrope garnet, magnesiowüstite, and ringwoodite, with FeNi–FeS intergrowths. The observation and character of ring-like selected electron diffraction(SAED) patterns indicate that the idiomorphic garnet crystals in the vein matrix have different orientations. The polycrystalline nature of magnesiowüstite is also confirmed by a ring-like SAED pattern.Both garnet and magnesiowüstite crystals showed sharp diffraction spots, signifying the good crystallinity of these two minerals. The SAED pattern of cryptocrystalline ringwoodite shows only diffuse concentric diffraction rings. FeNi metal and troilite(FeS), which were molten during the shock event, occur in the matrix as fine eutectic FeNi–FeS intergrowths filling the interstices between garnet and magnesiowüstite grains. Based on the phase diagram of the Allende chondrite and the results of this TEM study, it is inferred that majorite-pyrope garnet first crystallized from the Suizhou chondritic melt at 22–26 GPa,followed by crystallization of magnesiowüstite at 20–24 GPa, and then ringwoodite at 18–20 GPa. The eutectic intergrowths of FeNi-metal and troilite are proposed to have crystallized during meteorite cooling and solidified at the last stage of vein formation.展开更多
The synchrotron radiation X-ray diffraction technique developed for in situ study ahigh pressure and temperature has also been used to investigate microscopic mineral inclusionsin ultrahigh-pressure metamorphic rocks ...The synchrotron radiation X-ray diffraction technique developed for in situ study ahigh pressure and temperature has also been used to investigate microscopic mineral inclusionsin ultrahigh-pressure metamorphic rocks and deep-mantle samples. Present study added twomore examples of successful utilization of synchrotron radiation X-ray diffraction technique for insitu investigations of fine-grained (0.5―30 μm in size) minerals in very thin shock melt veins othe Suizhou meteorite: ( i ) X-ray diffraction measurement of extremely small-sized vein matrixminerals, and (ii) identification of the micron-sized new mineral tuite embedded in the vein matrixIt has been revealed that the fine-grained vein matrix consists of well crystallized garnet, kamacite and troilite, and the powder diffraction pattern consisting of 17 lines with d-values, intensities( I ), relative intensities (I/Io) and Miller indices, as well as the cell parameters for the new mineratuite has also been successfully obtained. The result of present investigations has enriched thecontent of dynamic high-pressure mineralogy and that of Earth’s mantle geochemistry.展开更多
The Suizhou L6 chondrite contains a few very thin shock melt veins of 0.02-0.09 mm in width. In spite of small width of the veins, shock-induced high-pressure phases, such as coarse-grained NaAlSi3O8-hollandite, ringw...The Suizhou L6 chondrite contains a few very thin shock melt veins of 0.02-0.09 mm in width. In spite of small width of the veins, shock-induced high-pressure phases, such as coarse-grained NaAlSi3O8-hollandite, ringwoodite, majorite and fine-grained matrix majorite-pyropess have been discovered in these veins. NaAlSi3O8-hollandite, the high-pressure phase of plagioclase, in Suizhou shock veins occurs as a single phase mineral, no silicate glassy phase, such as albitic glass, was incorporated with it. The presence of above-mentioned high-pressure phases constrains the high pressure (up to 23-24 GPa) and high temperature (up to 1900-2000℃) regime in Suizhou shock veins, and indicates that the duration of high-pressure regime in the veins should be long enough (a few seconds) for phase transformation and crystallization of minerals under pressure. The discovery of the first natural single-phase crystalline NaAlSi3O8- holland-ite in Suizhou meteorite is of important significance in understanding the Earth’展开更多
In this study, we present systematic petrological, geochemical, LA-ICP-MS zircon U-Pb ages and Nd isotopic data for the A-type granites and syenites from Suizhou-Zaoyang region. The results show that the peralkaline A...In this study, we present systematic petrological, geochemical, LA-ICP-MS zircon U-Pb ages and Nd isotopic data for the A-type granites and syenites from Suizhou-Zaoyang region. The results show that the peralkaline A-type granites and syenites were episodically emplaced in Suizhou-Zaoyang region between 450±3 and 441±7 Ma which corresponds to Late Ordovician and Early Silurian periods, respectively. Petrologically, the syenite-peralkaline granite association comprises of nephefine normative-syenite and alkaline granite in Guanzishan and quartz normative syenite and alkafine granite in Huangyangshan. The syenite-granite associations are ferroan to alkali in composition. They depict characteristics of typical OIB (oceanic island basalts) derived A-type granites in multi-elements primitive normalized diagram and Ybffa vs. Y/Nb as well as Ce/Nb vs. Y/Nb binary plots. Significant depletion in Ba, Sr, P, Ti and Eu indicates fractionation of feldspars, biotite, amphiboles and Ti-rich augite. The values of eNd(t) in Guanzishan nepheline syenite and alkaline granite are +1.81 and +2.26, respectively and the calculated two-stage model age for these rocks are 1 040 and 1 003 Ma, respectively. On the other hand, the Huangyangshan alkaline granite has eNd(t) values ranging from +2.61 to +3.46 and a relatively younger two-stage Nd model age values ranging from 906 to 975 Ma, respectively. Based on these data, we inferred that the Guanzishan nepheline syenites and granites were formed from fractional crystallization of OIB-like basic magmas derived from upweliing of metasomatized lithospheric mantle. The Huangyangshan quartz syenite and granite on the other hand, were formed from similar magmas through fractional crystallization with low input from the ancient crustal rocks. Typically, the rocks exhibit Al-type granite affinity and classified as within plate granites associated with the Ordovician crustal extension and the Silurian rifting.展开更多
An average ancient track density of(7.6±1.1)×10~3/cm^2 has been obtained for pyroxene in Suizhou meteorite based on ancient and neutron-induced fission-track density measurements. The result is consistent wi...An average ancient track density of(7.6±1.1)×10~3/cm^2 has been obtained for pyroxene in Suizhou meteorite based on ancient and neutron-induced fission-track density measurements. The result is consistent with the ancient track density of 8.4×10~3/cm^2展开更多
A chondrite shower occurred on April 15, 1986 in the vicinity of Dayianpo Village, Suizhou City, Hubei Province. It is the second large scale meteorite shower following the Jilin Meteorite Shower.
Shock-produced akimotoite was identified in the Suizhou chondritic meteorite, which occurs in two kinds of occurrence. The first is the irregular layers of akimotoite up to 4 ?m in thickness occurring in fractures and...Shock-produced akimotoite was identified in the Suizhou chondritic meteorite, which occurs in two kinds of occurrence. The first is the irregular layers of akimotoite up to 4 ?m in thickness occurring in fractures and cracks of low-Ca pyroxene enclosed in the shock veins. The second is the zonal polycrystalline aggregates of akimotoite in shocked pyroxene grains close to the shock vein, where akimotoite occurs in a zonal area in between pyroxene and Mg Si O3-glass as irregular small clumps up to 5 ?m in size. This investigation suggests a solid-state transformation mechanism of pyroxene to akimotoite, and that akimotoite should have nucleated and grew in the area with abundant defects caused by shock deformation because the defect significantly enhances the solid-state reactivity and the kinetics of nucleation of high-pressure phase. The spatial relationship among the composed grains of pyroxene, akimotoite and Mg Si O3-glass(possibly vitrified perovskite) demonstrates a temperature gradient from the vein wall to the unmelted chondritic meteorite.展开更多
The occurrence andmineral chemistry of chromite and its high-pressure phase xieite in the Suizhou meteorite were studied by different modern micromineralogical techniques.Three types of occurrences for chromite were o...The occurrence andmineral chemistry of chromite and its high-pressure phase xieite in the Suizhou meteorite were studied by different modern micromineralogical techniques.Three types of occurrences for chromite were observed in the Suizhou L6 chondrite:coarse chromite grains,cluster of chromite fragments in molten plagioclase,and exsolution lamellar chromite in olivine.All the chromite grains of the first two types are remarkably similar in chemical compositions,but the composition of exsolution chromite is inhomogeneous and variable in Al 2 O 3 content.Xieite is a post-spinel CT-phase of chromite firstly found in the Suizhou meteorite.Three types of occurrences of xieite have also been revealed in this meteorite:coarse xieite grains,complex three-zone-grains consisting of the inner xieite,the intermediate lamellae-like CF-phase and the outer chromite phase,and two-phase-grains consisting of xieite and one of the high-pressure silicateminerals lingunite,ringwoodite or majorite.The curved boundary between xieite and the silicate half in two-phase grains is indicative of some partial or even full melting of the silicate phase.EPMA and EDS results show that the compositions of xieite inside/contacting the shock veins are also identical to that of chromite outside the veins.However,some element diffusion appeared in between the xieite and the silicate half in the two-phase grains,namely,some of Al 3+ from lingunite,or Fe 2+ from ringwoodite migrated to xieite,and some of Cr 3+ migrated from xieite to lingunite or ringwoodite.Majorite in two-phase grains shows remarkable decrease of SiO 2 and MgO,and notable increase of Al 2 O 3 and CaO,indicating that its hostmineral pyroxene was fully molten and mixed with the surrounding silicate melt of the vein matrix.The complexity inmineral chemistry of these two-phase grains in shock veins can be explained by the much higher shock peak temperature in shock veins (1800-2000°C) than in unmelted main body (~1000°C),and by the much lower density of the silicateminerals (2.6-3.3 g/cm 3) than that of chromite (4.43 g/cm 3).Being a refractory and a relatively high-impedance material,chromite is chemically more stable and easier to reflect shock wave into the silicate half causing the partial or even full melting of silicate phases,upon which some diffusion of elements between the two phases themselves,or even mixing of molten pyroxene and the surrounding silicate melt.展开更多
文摘We report the discovery of TiO_(2)-Ⅱ in the unmelted rock of the shocked Suizhou L6 chondrite.Natural TiO_(2)-Ⅱ was previously found in ultrahigh-pressure metamorphic and mantle-derived rocks,terrestrial impact structures,and tektite.Our microscopic,Raman spectroscopic,electron microprobe and transmission electron microscopic investigations have revealed:(1) All observed TiO_(2)-Ⅱ grains are related with ilmenite and pyrophanite;(2) TiO_(2)-Ⅱ occurs as needle-and leaf-shaped inclusions in llmenite and patch-,tape-shaped body in pyrophanite;(3)The composition of TiO_(2)-Ⅱ is identical with that of its precursor rutile;(4) The Raman spectrum of TiO_(2)-Ⅱ is in good agreement with that of natural and synthesized α-PbO_(2)-type TiO_(2);(5) TiO_(2)-Ⅱ occurs mainly in the form of well-ordered nano-domains and small mis-orientation among the domains can be observed.(6) All electron diffraction reflections from TiO_(2)-Ⅱ can be indexed to α-PbO_(2)structure in space group Pbcn with lattice parameters of a=4.481 ?,b=5.578 A and c=4.921 A;(7) The exsolution inclusions of rutile from host ilmenite are mostly connected with an alternation process along the lamellar twinning plane of ilmenite induced by shockinduced high pressure and high temperature;(8) The P-T regime of 20-25 GPa and 1000 ℃ estimated for the Suizhou unmelted rock is suitable for phase transition of rutile into TiO_(2)-Ⅱ phase.
文摘The Suizhou meteorite is a heavily shocked and melted vein-containing L6 chondrite.It contains a minor amount of diopside with a(Ca_(0.419)Mg_(0.466)Fe_(0.088))SiO_(3)composition,and a shock-metamorphosed diopside grain associated with ringwoodite and lingunite was found in a melt vein of this meteorite.Our electron microprobe,transmission electron microscopic and Raman spectroscopic analyses revealed four silicate phases with different compositions and structures inside this shock-metamorphosed diopside grain,termed phase A,B,C and D in this paper.Phase A is identified as orthorhombic(Ca_(0.663)-Mg_(0.314))SiO_(3)-perovskite which is closely associated with phase B,the vitrified(Mg_(0.642)Ca_(0.290)Fe_(0.098))SiO_(3)perovskite.Phase D is assigned to be(Mg_(0.578)Ca_(0.414))SiO_(3)majorite which is associated with phase C,the vetrified Carich Mg-perovskite with a(Mg_(0.853)Ca_(0.167))SiO_(3)composition.Based on high-pressure and high-temperature experiments,the diopside grain in the melt vein of the Suizhou meteorite would have experienced a P–T regime of 20–24GPa and 1800–>2000℃.Such P–T conditions are high enough for the decomposition of the diopside and the formation of four different silicate phases.The orthorhombic(Ca_(0.663)Mg_(0.314))SiO_(3)perovskite found in the Suizhou L6 chondrite might be considered as the third lower-mantle silicate mineral after bridgmanite and davemaoite after the detailed analyses of its crystal structure and physical properties being completed.
文摘The Suizhou meteorite is an L6 chondrite. This meteorite is consisted of olivine, low-Ca pyroxene, plagioclase, FeNi metal, troilite, whitlockite, chlorapatite, chromite and ilmenite. Olivine and pyroxene grains display shock-induced mosaic texture, and most plagioclase grains were melted and transformed to maskelynite. This meteorite contains a few very thin shock-produced melt veins ranging from 20 to 100 μm in width. They are chondritic in composition and contain abundant high-pressure minerals in two assemblages. One is the coarse-grained assemblage of ringwoodite, majorite, lingunite with minor amount of tuite, xieite, the CF-phase, akimotoite and amorphized perovskite, and the fine-grained assemblage (the melt vein matrix) composed of majorite-pyrope garnet, magnesiowüstite. FeNi metal and troilite in the Suizhou shock veins were molten and occur as small intergrowth grains or veinlets filling the interstices of garnet crystals or cracks in the vein matrix. It was revealed that olivine, pyroxene and plagioclase in the Suizhou shock veins have transformed in solid state to their high-pressure polymorphs ringwoodite, majorite, and lingunite, respectively, without change in their chemical compositions.
基金financially supported by National Natural Science foundation of China under Grant 41172046 and 40972044 in part
文摘The mineralogy of shock vein matrix in the Suizhou meteorite has been investigated by optical and transmission electron microscopy. It was revealed that the vein matrix is composed of majorite-pyrope garnet, magnesiowüstite, and ringwoodite, with FeNi–FeS intergrowths. The observation and character of ring-like selected electron diffraction(SAED) patterns indicate that the idiomorphic garnet crystals in the vein matrix have different orientations. The polycrystalline nature of magnesiowüstite is also confirmed by a ring-like SAED pattern.Both garnet and magnesiowüstite crystals showed sharp diffraction spots, signifying the good crystallinity of these two minerals. The SAED pattern of cryptocrystalline ringwoodite shows only diffuse concentric diffraction rings. FeNi metal and troilite(FeS), which were molten during the shock event, occur in the matrix as fine eutectic FeNi–FeS intergrowths filling the interstices between garnet and magnesiowüstite grains. Based on the phase diagram of the Allende chondrite and the results of this TEM study, it is inferred that majorite-pyrope garnet first crystallized from the Suizhou chondritic melt at 22–26 GPa,followed by crystallization of magnesiowüstite at 20–24 GPa, and then ringwoodite at 18–20 GPa. The eutectic intergrowths of FeNi-metal and troilite are proposed to have crystallized during meteorite cooling and solidified at the last stage of vein formation.
基金the National Natural Science Foundation of China(Grant No.40272028).
文摘The synchrotron radiation X-ray diffraction technique developed for in situ study ahigh pressure and temperature has also been used to investigate microscopic mineral inclusionsin ultrahigh-pressure metamorphic rocks and deep-mantle samples. Present study added twomore examples of successful utilization of synchrotron radiation X-ray diffraction technique for insitu investigations of fine-grained (0.5―30 μm in size) minerals in very thin shock melt veins othe Suizhou meteorite: ( i ) X-ray diffraction measurement of extremely small-sized vein matrixminerals, and (ii) identification of the micron-sized new mineral tuite embedded in the vein matrixIt has been revealed that the fine-grained vein matrix consists of well crystallized garnet, kamacite and troilite, and the powder diffraction pattern consisting of 17 lines with d-values, intensities( I ), relative intensities (I/Io) and Miller indices, as well as the cell parameters for the new mineratuite has also been successfully obtained. The result of present investigations has enriched thecontent of dynamic high-pressure mineralogy and that of Earth’s mantle geochemistry.
基金. This work was supported by the National Natural Science Foundation of China (Grant Nos. 49825106 and 49672098) and Guangdong Provincial Natural Science Foundation (Grant No. 960500).
文摘The Suizhou L6 chondrite contains a few very thin shock melt veins of 0.02-0.09 mm in width. In spite of small width of the veins, shock-induced high-pressure phases, such as coarse-grained NaAlSi3O8-hollandite, ringwoodite, majorite and fine-grained matrix majorite-pyropess have been discovered in these veins. NaAlSi3O8-hollandite, the high-pressure phase of plagioclase, in Suizhou shock veins occurs as a single phase mineral, no silicate glassy phase, such as albitic glass, was incorporated with it. The presence of above-mentioned high-pressure phases constrains the high pressure (up to 23-24 GPa) and high temperature (up to 1900-2000℃) regime in Suizhou shock veins, and indicates that the duration of high-pressure regime in the veins should be long enough (a few seconds) for phase transformation and crystallization of minerals under pressure. The discovery of the first natural single-phase crystalline NaAlSi3O8- holland-ite in Suizhou meteorite is of important significance in understanding the Earth’
基金the support from the National Natural Science Foundation of China(No.41502046)partial financial support by the China Geological Survey(No.DD20160030the Fundamental Research Funds for the Central Universities,China University of Geosciences,Wuhan(No.CUGCJ1711)
文摘In this study, we present systematic petrological, geochemical, LA-ICP-MS zircon U-Pb ages and Nd isotopic data for the A-type granites and syenites from Suizhou-Zaoyang region. The results show that the peralkaline A-type granites and syenites were episodically emplaced in Suizhou-Zaoyang region between 450±3 and 441±7 Ma which corresponds to Late Ordovician and Early Silurian periods, respectively. Petrologically, the syenite-peralkaline granite association comprises of nephefine normative-syenite and alkaline granite in Guanzishan and quartz normative syenite and alkafine granite in Huangyangshan. The syenite-granite associations are ferroan to alkali in composition. They depict characteristics of typical OIB (oceanic island basalts) derived A-type granites in multi-elements primitive normalized diagram and Ybffa vs. Y/Nb as well as Ce/Nb vs. Y/Nb binary plots. Significant depletion in Ba, Sr, P, Ti and Eu indicates fractionation of feldspars, biotite, amphiboles and Ti-rich augite. The values of eNd(t) in Guanzishan nepheline syenite and alkaline granite are +1.81 and +2.26, respectively and the calculated two-stage model age for these rocks are 1 040 and 1 003 Ma, respectively. On the other hand, the Huangyangshan alkaline granite has eNd(t) values ranging from +2.61 to +3.46 and a relatively younger two-stage Nd model age values ranging from 906 to 975 Ma, respectively. Based on these data, we inferred that the Guanzishan nepheline syenites and granites were formed from fractional crystallization of OIB-like basic magmas derived from upweliing of metasomatized lithospheric mantle. The Huangyangshan quartz syenite and granite on the other hand, were formed from similar magmas through fractional crystallization with low input from the ancient crustal rocks. Typically, the rocks exhibit Al-type granite affinity and classified as within plate granites associated with the Ordovician crustal extension and the Silurian rifting.
基金Project supported by the National Natural Science Foundation of China.
文摘An average ancient track density of(7.6±1.1)×10~3/cm^2 has been obtained for pyroxene in Suizhou meteorite based on ancient and neutron-induced fission-track density measurements. The result is consistent with the ancient track density of 8.4×10~3/cm^2
文摘A chondrite shower occurred on April 15, 1986 in the vicinity of Dayianpo Village, Suizhou City, Hubei Province. It is the second large scale meteorite shower following the Jilin Meteorite Shower.
基金supported by the National Natural Science Foundation of China(Grant Nos.41172046 and 40772030)the Guangdong Key Laboratory of Mineral Physics and Materials
文摘Shock-produced akimotoite was identified in the Suizhou chondritic meteorite, which occurs in two kinds of occurrence. The first is the irregular layers of akimotoite up to 4 ?m in thickness occurring in fractures and cracks of low-Ca pyroxene enclosed in the shock veins. The second is the zonal polycrystalline aggregates of akimotoite in shocked pyroxene grains close to the shock vein, where akimotoite occurs in a zonal area in between pyroxene and Mg Si O3-glass as irregular small clumps up to 5 ?m in size. This investigation suggests a solid-state transformation mechanism of pyroxene to akimotoite, and that akimotoite should have nucleated and grew in the area with abundant defects caused by shock deformation because the defect significantly enhances the solid-state reactivity and the kinetics of nucleation of high-pressure phase. The spatial relationship among the composed grains of pyroxene, akimotoite and Mg Si O3-glass(possibly vitrified perovskite) demonstrates a temperature gradient from the vein wall to the unmelted chondritic meteorite.
基金supported by National Natural Science Foundation of China (Grant No. 40772030)
文摘The occurrence andmineral chemistry of chromite and its high-pressure phase xieite in the Suizhou meteorite were studied by different modern micromineralogical techniques.Three types of occurrences for chromite were observed in the Suizhou L6 chondrite:coarse chromite grains,cluster of chromite fragments in molten plagioclase,and exsolution lamellar chromite in olivine.All the chromite grains of the first two types are remarkably similar in chemical compositions,but the composition of exsolution chromite is inhomogeneous and variable in Al 2 O 3 content.Xieite is a post-spinel CT-phase of chromite firstly found in the Suizhou meteorite.Three types of occurrences of xieite have also been revealed in this meteorite:coarse xieite grains,complex three-zone-grains consisting of the inner xieite,the intermediate lamellae-like CF-phase and the outer chromite phase,and two-phase-grains consisting of xieite and one of the high-pressure silicateminerals lingunite,ringwoodite or majorite.The curved boundary between xieite and the silicate half in two-phase grains is indicative of some partial or even full melting of the silicate phase.EPMA and EDS results show that the compositions of xieite inside/contacting the shock veins are also identical to that of chromite outside the veins.However,some element diffusion appeared in between the xieite and the silicate half in the two-phase grains,namely,some of Al 3+ from lingunite,or Fe 2+ from ringwoodite migrated to xieite,and some of Cr 3+ migrated from xieite to lingunite or ringwoodite.Majorite in two-phase grains shows remarkable decrease of SiO 2 and MgO,and notable increase of Al 2 O 3 and CaO,indicating that its hostmineral pyroxene was fully molten and mixed with the surrounding silicate melt of the vein matrix.The complexity inmineral chemistry of these two-phase grains in shock veins can be explained by the much higher shock peak temperature in shock veins (1800-2000°C) than in unmelted main body (~1000°C),and by the much lower density of the silicateminerals (2.6-3.3 g/cm 3) than that of chromite (4.43 g/cm 3).Being a refractory and a relatively high-impedance material,chromite is chemically more stable and easier to reflect shock wave into the silicate half causing the partial or even full melting of silicate phases,upon which some diffusion of elements between the two phases themselves,or even mixing of molten pyroxene and the surrounding silicate melt.