Retrogressive Microstructures:A Key to Post Collisional Uplift and Extension Tectonics of Ultrahigh-Pressure Metamorphic Rocks from Dabie Orogenic Belt,China

ThereisanunanimousunderstandingthattheUHPmetamorphisminDabie-SuluareaswasformedduringtheTri-assiccollisioneventbetweentheYangtzeandNorthChinacratons(Congetal.,l994$Zhouetal-,l996;Liouetal.,l994)-Eclogiteisthemostimportantrocktypeamongtheul-trahigh-pressure(UHP)metamorphicrocks.Accordingtotheiroccurrencethereare3typesofeclogites:typeIisen-clavesinultramaficintrusionsandasmembersinthelayeredmafic-ultramaficcomplex(Jahnl998);typeIispodsorlay-ersinthehighlymetamorphicsupracrustals(mainlying…     

多硅白云母压力计在退变质作用中的稳定性探讨

探讨多硅白云母地质压力计在低温退变质过程中的稳定性，在对大别山东缘和苏鲁造山带西缘郯庐左旋走滑韧性剪切带糜棱岩中的多硅白云母残斑由中心向两侧边缘进行电子探针分析后发现：由中心向两侧边缘Si减少,Al增加,Fe，Mg略有降低，部分样品中K，Na有不同程度的增加．而Ti则显示不活动富集。这是由于退变质过程中流体的活动常会改变残斑白云母的成分．并且在流体活动过程相对短暂的情况下，使残斑白云母的成分不能发生充分变化．最终会导致白云母不同部位具有不同的成分。因而,经历了富流体活动的退变质作用后,岩石中的多硅白云母残斑已不能完全保存其形成时的压力信息。     

新疆艾维尔沟煤变质作用研究

新疆艾维尔沟矿区是侏罗纪天山褶皱带中的一个小型山间含煤盆地。多项煤变质指标的分析结果表明:该区煤级在横向上分带明显,垂向上煤级突变,煤岩组份中出现热变显微组份,煤晶核指标(La/Lc)大于1,矿区广泛发育热液石英脉和方解石脉,煤层围岩也具有中低温热液蚀变现象。所有这些特征都充分表明,艾维尔沟的煤变质属区域热变质类型。推测其附加热源位于该煤盆地西部,地下水热液的对流为主要热传导方式。矿区及其外围的构造、地层结构、地势、水文等条件均有利于地下水热液循环。     

羌塘地区榴辉岩中矿物出溶体及其成因机制探讨

西藏羌塘地区榴辉岩石榴子石和磷灰石中均发育矿物出溶体,结合电子探针和扫描电镜分析及能谱分析,确定了石榴子石中的出溶体有金红石、石英和角闪石,指示其可能经历了高压/超高压变质作用。本研究在磷灰石中发现了金红石出溶,并认为其可能是在高压/超高压条件下元素相互置换的结果,置换方式为Ti~(4+)(Fe~(2+)、Si~(4+))=2Ca~(2+),这些出溶体的形成为榴辉岩曾经历高压/超高压变质作用提供了矿物学证据。     

硼及硼同位素地球化学在地质研究中的应用

总结了硼及硼同位素的地球化学特征：（１）硼是易溶元素,主要赋存在地球表层,尤其是海水、海相沉积物及海水交代岩石中。其同位素组成δ１１Ｂ值按顺序变化,封闭盐湖卤水（＞４０‰）＞海水（３９５‰）＞海相硼矿物（１８２‰～３１７３‰）＞海相沉积物（１３９‰～２５２‰）＞海水交代岩石（４５１‰～１０８５‰）。大陆水及陆相沉积物硼含量及硼同位素组成变化极大,并多以负值为主。海陆过渡构造带则具有过渡的硼丰度值和硼同位素组成。（２）１１Ｂ较１０Ｂ具有更活跃的地球化学性质,因此在水岩作用中具有明显的同位素交换。硅化交代作用中,岩石被硅化交代,释放硼,并优先释放重硼,同位素组成变轻;在脱硅反应中,岩石释放硅吸收硼,并优先吸收重硼,同位素组成变重。在封闭体系中,水溶液淋滤岩石中部分的硼,即可大量富集,并富集１１Ｂ;在开放体系中,岩石硼被大量淋滤流失,δ１１Ｂ值明显降低。由于水岩作用的结果,从新鲜海底玄武岩到正常海水,硼同位素值从－２９５‰到３９５‰逐渐升高。（３）变质脱水反应中硼被大量排出,并优先排出重硼同位素,进入流体相,因此随着变质程度由低到高,岩石中硼含量及同位素组成δ１１Ｂ值由高变低。（４）在成矿研究中?     

利用XRD法探讨邢台隆东井田煤变质规律

邢台隆东井田煤变质情况复杂,直接影响煤的工业利用。利用X-射线衍射(XRD)法探讨了区内不同变质程度煤的基本结构单元特征及煤变质规律。结果显示:垂向上,随着煤层埋藏深度的增加,层片间距d₀₀₂值逐渐减小,层片堆积高度L_c和层片直径L_a值逐渐增大;平面上,离岩浆侵入体越近,煤层的层间距d₀₀₂值越小,反之d₀₀₂值越大。在煤种分布上,因受岩浆热源的影响,井田内煤种以旧城为中心向外呈带状分布,旧城附近为无烟煤,向外逐渐过渡为贫煤、瘦煤、焦煤、肥煤和气煤。区内煤变质作用主要受区域变质作用影响,并叠加了岩浆热变质作用。      

Contact-metamorphic effect on parameters for kerogen maturation

This study examines the effect of contact metamorphism by an igneous dyke on parameters for kerogen maturation, such as elemental composition (H/C, O/C, N/C), ¹H-NMR T₁, vitrinite reflectance and infrared spectra. Although elemental composition and ¹H-NMR T₁ of the kerogen changed only within 1.5 and 5.0 m from the dyke respectively, vitrinite reflectance of the kerogen was thermally affected beyond 10.0 m from the intrusion. It is concluded that vitrinite reflectance is the most sensitive of the parameters evaluated to assess thermal stress of kerogens.     

青藏高原羌塘中部榴辉岩Ar-Ar定年

羌塘榴辉岩产于红脊山-双湖高压变质带中段的片石山地区,是目前青藏高原内部唯一的榴辉岩产地。榴辉岩多硅白云母~(40)Ar-~(39)Ar年龄 t_p=219.3±1.5Ma;榴辉岩围岩的多硅白云母~(40)Ar-~(39)Ar 年龄 t_p=217.2±1.8Ma,定年结果表明,榴辉岩与围岩经历了相同的高压变质作用,与红脊山-双湖地区蓝闪片岩的高压变质时间是一致的。根据已有高压变质年代学资料,从羌塘的红脊山到双湖、那曲地区的巴青以北、昌都的酉西,直到滇西地区,断续分布长达2000余公里的高压变质带为同一期构造事件的产物,是龙木错-双湖板块缝合带向南延伸到滇西的重要依据。榴辉岩的定年数据进一步揭示,冈瓦纳板块与欧亚(扬子)板块的主体碰撞时间在220Ma 左右,同时也是古特提斯洋消亡的时间记录。     

Petrology and geochemistry of prograde deserpentinized peridotites from Happo-O’ne, Japan: Evidence of element mobility during deserpentinization

The prograde deserpentinized peridotites from the talc zone in the Happo-O’ne complex, central Japan, show differences in their field relation and mineral assemblage with the high-P retrograde peridotites of the other part of the complex. They show a mineral assemblage, olivine + talc + antigorite ± prograde tremolite ± chlorite, formed by thermal metamorphism around the granitic intrusion at T, 500-650 °C and P < 7 kbar. The olivine has numerous opaque inclusions and high Fo (91.5-96.5) relative to the retrograde olivine, reflecting its formation by deserpentinization. The prograde tremolite, which is low in Al₂O₃ (<1.0 wt.%), Cr₂O₃ (<0.35 wt.%), and Na₂O (<0.6 wt.%) but high in Mg# (up to 0.98) and SiO₂ (up to 59.9 wt.%), is different in size, shape and chemistry from the retrograde tremolite. The prograde peridotites display a U-shaped REE pattern (0.02-0.5 times PM), similar to diopside-zone retrograde metaperidotites, possible protoliths. They are enriched in LILE (e.g., Cs, Pb, Sr, Rb) relative to HFSE (e.g., Ta, Hf, Zr, Nb), like their protoliths, because of their local re-equilibration with the fluid released during dehydration of the protoliths. They have high contents of REE and some trace elements (e.g., Cs, Th, U, Ta) relative to their protoliths because of an external-element addition from the granitic magma. In-situ analyses of peridotitic silicates confirmed that the prograde tremolite and talc display a spoon-shaped primitive mantle (PM)-normalized REE pattern (0.1-3 times PM) in which LREE are higher than HREE contents. The prograde tremolite is depleted in Al, Na, Cr, Sc, V, Ti, B, HREE and Li, but is enriched in Si, Cs, U, Th, HFSE (Hf, Zr, Nb, Ta), Rb and Ba relative to the retrograde tremolite; the immobile-element depletion in this tremolite is inherited from its source (antigorite + secondary diopside), whereas the depletion of mobile elements (e.g., Li, B, Na, Al) is ascribed to their mobility during the deserpentinization and/or the depleted character of the source of tremolite. The enrichment of HFSE and LILE in the prograde tremolite is related to an external addition of these elements from fluid/melt of the surrounding granitic magma and/or in situ equilibrium with LILE-bearing fluid released during dehydration of serpentinized retrograde metaperidotites and olivine-bearing serpentinites (protoliths). The prograde olivine is higher in REE and most trace-element contents than the retrograde one due to the external addition of these elements; it is enriched in B, Co and Ni, but depleted in Li that was liberated during deserpentinization by prograde metamorphism.     

Disequilibrium in the Ross of Mull Contact Metamorphic Aureole, Scotland: a Consequence of Polymetamorphism

The Ross of Mull pluton consists of granites and granodioritesand intrudes sediments previously metamorphosed at amphibolitefacies. The high grade and coarse grain size of the protolithis responsible for a high degree of disequilibrium in many partsof the aureole and for some unusual textures. A band of metapelitecontained coarse garnet, biotite and kyanite prior to intrusion,and developed a sequence of textures towards the pluton. InZone I, garnet is rimmed by cordierite and new biotite. In ZoneII, coarse kyanite grains are partly replaced by andalusite,indicating incomplete reaction. Coronas of cordierite + muscovitearound kyanite are due to reaction with biotite. In the higher-gradeparts of this zone there is complete replacement of kyaniteand/or andalusite by muscovite and cordierite. Cordierite chemistryindicates that in Zone II the stable AFM assemblage (not attained)would have been cordierite + biotite + muscovite, without andalusite.The observed andalusite is therefore metastable. Garnet is unstablein Zone II, with regional garnets breaking down to cordierite,new biotite and plagioclase. In Zone III this breakdown is welladvanced, and this zone marks the appearance of fibrolite andK-feldspar in the groundmass as a result of muscovite breakdown.Zone IV shows garnet with cordierite, biotite, sillimanite,K-feldspar and quartz. Some garnets are armoured by cordieriteand are inferred to be relics. Others are euhedral with Mn-richcores. For these, the reaction biotite + sillimanite + quartz garnet + cordierite + K-feldspar + melt is inferred. Usinga petrogenetic grid based on the work of Pattison and Harte,pressure is estimated at 3·2 kbar, and temperature atthe Zone II–III boundary at 650°C and in Zone IV asat least 750°C. KEY WORDS: contact metamorphism; disequilibrium