喜马拉雅造山带核部的变质作用与部分熔融:亚东地区高压泥质麻粒岩的岩石学与年代学研究

喜马拉雅造山带核部的高喜马拉雅结晶岩系是印度大陆深俯冲到欧亚板块之下经历了高压变质作用的产物,记录了喜马拉雅造山带的形成与演化历史。本文对喜马拉雅造山带中段亚东地区高喜马拉雅结晶岩系中的泥质麻粒岩进行了岩石学和锆石U-Pb年代学研究,结果表明泥质麻粒岩经历了复杂的变质演化和部分熔融,可识别出三期变质矿物组合。早期进变质矿物组合为石榴石+斜长石+钾长石+黑云母+白云母+石英,峰期变质矿物组合为石榴石+斜长石+钾长石+黑云母+蓝晶石+石英,晚期退变质矿物组合为石榴石+斜长石+钾长石+夕线石+黑云母+白云母+石英。相平衡模拟表明,该泥质麻粒岩经历了高温、高压的峰期变质条件为800~835℃和12.8~14kbar,在进变质和峰期变质过程中经历了白云母和黑云母脱水熔融,所形成的熔体量至少为5%~8%。麻粒岩的晚期退变质条件为720~740℃和7.6~8.3kbar。这表明泥质麻粒岩经历了一条以高压麻粒岩相峰期变质和降温、降压退变质为特征的顺时针P-T轨迹。锆石U-Pb定年结果表明,麻粒岩相变质和深熔作用发生在28.5~17.0Ma。本研究表明高喜马拉雅结晶岩系的上部构造层位经历了高压麻粒岩相变质作用,而不是以前认为的以高温、低压变质作用为特征,并为喜马拉雅造山带构造演化的研究提供了新的见解。     

阿尔泰超高温变泥质麻粒岩的锆石U-Pb年龄及其地质意义

最近我们通过岩相学观察和矿物温压计算,首次确定了在阿勒泰喀拉苏附近存在超高温变泥质麻粒岩,其矿物组合为石榴石+斜方辉石+夕线石+堇青石+尖晶石+黑云母+斜长石+石英等。斜方辉石成分具有高铝特点,其Al₂O₃含量高于8.0%,指示了其峰期变质作用达到了超高温(>900℃)的条件。P-T计算结果显示其峰期变质条件为:P=~8.0kb, T=~960℃。初步P-T估算结果表明了一个峰期后近等压冷却的逆时针P-T轨迹。我们对其中锆石进行了LA-ICP-MS U-Pb年龄测定,年龄结果主要分布于260~280Ma之间,具有峰值年龄271±5Ma,个别年龄为380~390Ma,继承锆石主要分布于450~500Ma之间。该年龄结果表明阿尔泰超高温变质事件发生于二叠纪,在时间上与二叠纪塔里木地幔柱活动的时间(~275Ma)高度一致,且也和该区广泛的二叠纪(260~280Ma) 后造山或非造山的基性岩和花岗岩侵入是同时的。因此,阿尔泰二叠纪超高温变泥质麻粒岩的形成,可能与由二叠纪塔里木地幔柱活动引起的岩浆底侵和下地壳伸展加热密切相关,这也与该超高温变泥质麻粒岩的逆时针P-T轨迹所反映的构造背景一致。     

东南极拉斯曼丘陵镁铁质麻粒岩的变质作用演化

拉斯曼丘陵（Larsemann Hills）位于东南极普里兹构造带的中部,研究该区麻粒岩的变质作用演化对于理解普里兹带的构造属性至关重要。通过对该区含石榴石镁铁质麻粒岩转石详细的岩相学观察表明,峰期前进变质阶段矿物组合（M1）由角闪石+斜方辉石+单斜辉石+斜长石+黑云母+钛铁矿±石英±磁铁矿组成,其峰期矿物组合（M2）为石榴石+斜方辉石+单斜辉石+角闪石+钛铁矿±磁铁矿±石英,而代表后期与降压有关的叠加变质组合（M3）为斜方辉石+斜长石+单斜辉石+黑云母+钛铁矿±磁铁矿。矿物化学分析,结果显示其中石榴子石和斜方辉石具有弱的成分环带特征。利用THERMOCALC软件在NCFMASHTO体系下对该麻粒岩进行了详细的热力学模拟,结合传统温压计和平均温压计算结果,得出不同阶段温压条件分别为650~750℃/5.5~6.5kb （M1）,850~950℃/8~8.5kb （M2）,800~900℃/5.5~7.5kb （M3）。其变质作用演化为典型的峰期后近等温减压的（ITD）顺时针P-T轨迹。通过区域上镁铁质麻粒岩的对比分析,我们认为该镁铁质麻粒岩可能来源拉斯曼丘陵基岩露头。结合已有的年代学资料,表明该镁铁质麻粒岩的峰期变质事件可能对应于晚元古代格林威尔期构造事件,而后期退变质作用与早古生代的泛非期构造事件有关,意味着泛非期普里兹带可能是陆内造山带。     

浙西南八都杂岩早中生代泥质麻粒岩变质作用及构造意义

遂昌-大柘泥质麻粒岩出露于华夏地块东北部的浙西南八都杂岩中,该岩石保留了典型的减压反应结构.但其变质演化特点、变质作用时代及构造意义目前尚不明确.通过系统的岩相学、矿物化学和同位素年代学分析,结果表明遂昌-大柘泥质麻粒岩记录了4个阶段的变质矿物组合,其中早期进变质阶段M₁的矿物组合为石榴石+黑云母+石英;压力峰期变质阶段M₂的矿物组合为石榴石+铝绿泥石+金红石+蓝晶石+刚玉+黑云母+石英±十字石,该矿物组合可能预示着岩石曾经历了超高压变质作用过程;峰期变质阶段M₃的矿物组合为石榴石+黑云母+夕线石+石英±钾长石±斜长石±钛铁矿;峰后近等温降压M_4-1阶段的矿物组合为石榴石+黑云母+夕线石+堇青石+石英+钛铁矿±尖晶石±斜长石±钾长石;M_4-2阶段的矿物组合为石榴石+堇青石+夕线石+斜长石+黑云母+石英±钾长石.相平衡模拟结合传统地质温压计限定其峰期变质阶段的温压条件为T=780~810 ℃、P=8.0~9.2 kbar;峰期后近等温降压的M_4-1阶段的温压条件为T=780~860 ℃和P=5.7~6.0 kbar,M_4-2阶段的温压条件为T=~700 ℃和P=~4.4 kbar,具有典型的顺时针近等温减压型P-T轨迹特征.LA-ICP-MS U-Pb定年结果表明其麻粒岩相变质作用时代为233.5~238.9 Ma.变质作用历史说明浙西南地体可能卷入了古特提斯洋域内印支-华南-华北板块之间的俯冲-碰撞过程,并经历了早中生代的麻粒岩相变质作用后快速折返至地表.      

东南极茹尔群岛超高温麻粒岩的研究进展

茹尔群岛(又称赖于尔群岛)位于东南极普里兹构造带的东部边缘,是一个由太古宙和中元古代岩石组成的复合高级变质地体。中元古代岩石是含有富Fe-Al的含石榴子石-矽线石的费拉副片麻岩组合,经历了格林维尔和泛非两期变质作用。太古宙正片麻岩是含有富Mg-Al的含假蓝宝石的超高温泥质麻粒岩组合(梅瑟副片麻岩组合),主要由经历超高温变质作用的含假蓝宝石的泥质麻粒岩、富Mg的石榴子石-矽线石泥质片麻岩、斜方辉石-矽线石石英岩、含石榴子石镁铁质麻粒岩和钙硅酸盐麻粒岩等组成。其中,含假蓝宝石泥质麻粒岩中石榴子石变斑晶和矽线石集合体(蓝晶石假象)周围分别发育峰期后由假蓝宝石+斜方辉石和假蓝宝石+堇青石后成合晶组成的典型减压结构。含石榴子石镁铁质麻粒岩中石榴子石变斑晶周围则发育峰期后由斜方辉石+斜长石后成合晶组成的典型白眼圈减压结构。不同研究者得出了具有不同超高温峰期条件、峰期前及峰期后演化历史、不同形式的顺时针变质P-T轨迹。对超高温变质事件发生的时间和构造背景的认识也存在较大分歧,有认为超高温变质事件发生于格林维尔期(~1000 Ma)并与碰撞造山和弧岩浆作用有关,也有研究认为发生于泛非期(~590 Ma或~530 Ma)并与普里兹造山及冈瓦纳大陆聚合有关。因此,为理清该区超高温麻粒岩的变质演化历史和构造背景,需要对其进一步进行详细深入的矿物组合-变质结构分析、P-T轨迹重建及高精度的锆石-独居石U-Pb年代学研究,并进行区域上对比。      

西藏定结高压基性麻粒岩(退变榴辉岩)的变质P-T轨迹及构造意义

定结（Dinggye）位于藏南高喜马拉雅结晶岩系的中部,研究该区域麻粒岩的变质P-T轨迹对于理解青藏高原的碰撞和抬升过程至关重要.通过对该地区的高压基性麻粒岩（退变榴辉岩）的岩相学观察,确定了4期矿物组合:（1）峰期榴辉岩相矿物组合（M₁）由石榴子石（核部）+绿辉石（假象）+石英+金红石组成;（2）高压麻粒岩相矿物组合（M₂）主要由石榴子石（幔部）+单斜辉石+斜长石+钛铁矿+角闪石+黑云母组成;（3）中压麻粒岩相矿物组合（M₃）由石榴子石（边缘）+斜方辉石+斜长石+钛铁矿+黑云母组成;（4）角闪岩相矿物组合（M₄）主要由角闪石+斜长石组成.在NCFMASHTO体系下,用THERMOCALC软件对该高压基性麻粒岩进行了热力学模拟.结合传统温压计和平均温压计计算结果,求得M₂、M₃、M₄阶段的温压条件分别为786~826 ℃、0.78~0.96 GPa;798~850 ℃、0.71~0.75 GPa;610~666 ℃、0.51~0.60 GPa,这指示了一条以峰期后近等温降压（ITD）为特征的顺时针P-T轨迹.结合已有地质资料,表明定结高压基性麻粒岩（退变榴辉岩）是喜马拉雅碰撞造山的产物,峰期后经历了近等温降压的构造抬升过程.      

藏南吉隆地区大喜马拉雅结晶杂岩的新生代变质作用和构造意义

大喜马拉雅结晶杂岩位于喜马拉雅造山带的核部,其变质作用的研究是揭示碰撞造山作用和动力学的关键。本文对喜马拉雅造山带中部吉隆地区的大喜马拉雅结晶杂岩中的片麻岩和片岩进行了岩石学和锆石U-Pb年代学的研究,表明这些高级变质岩经历了高角闪岩相的变质作用和部分熔融,以及近等温降压的退变质过程。片麻岩和片岩的峰期变质矿物组合为斜长石+钾长石+黑云母+白云母+石英±石榴子石±钛铁矿和石榴子石+蓝晶石+斜长石+黑云母+白云母+钛铁矿+石英,晚期退变质矿物组合为斜长石+钾长石+黑云母+白云母+夕线石+石英±石榴子石和石榴子石+夕线石+斜长石+黑云母+白云母+钛铁矿+石英。相平衡模拟研究表明,岩石的峰期变质条件为685~755℃和9.5~12kbar,退变质作用条件为675~685℃和6~7.4kbar。锆石U-Pb年代学表明,高级变质岩的部分熔融时间为38~16Ma,熔体结晶时间为17~15Ma。本次研究表明,大喜马拉雅结晶杂岩中、上部并没有普遍经历高压麻粒岩相变质作用,部分地区包括吉隆地区经历的是高角闪岩相变质作用。此外,本文在吉隆地区高级变质的大喜马拉雅结晶杂岩中识别出较低级变质的特提斯喜马拉雅岩系单元。结合已发表的藏南拆离断裂的主要活动时间,本文认为构造楔模型更适用于研究区喜马拉雅造山过程的解释。     

华北克拉通清原地体新太古代和古元古代两期麻粒岩相变质作用

对华北克拉通新太古代和古元古代的构造模式有多种不同认识,有必要进行深入的变质作用研究。本文选取了辽北清原地区中性麻粒岩、石榴方辉石岩和变质基性岩墙,开展系统的岩相学观察、矿物化学分析、相平衡模拟和锆石-独居定年研究,以阐明其变质演化过程和大地构造意义。中性麻粒岩和石榴方辉石岩均发育两期麻粒岩相组合。中性麻粒岩第一期斜长石发育复杂成份环带,从核到幔部其钙长石含量(X_An)降低,然后再向边部升高;石榴方辉石岩中第一期石榴石与斜方辉石互相包裹。第一期麻粒岩相变质作用P-T轨迹为逆时针型,包含峰期前升压至峰期和峰后降温降压至固相线两个变质阶段。依据两个样品中观测的峰期矿物组合在P-T视剖面图中的稳定范围,并结合斜长石幔部成份,确定峰期温压条件为1.0～1.2GPa/890～1000℃。石榴方辉石岩在峰前升压过程,斜方辉石转变为石榴石,形成石榴石包裹斜方辉石的结构;在峰后降温降压过程中,石榴石又转变为斜方辉石,导斜方辉石包裹石榴石。中性麻粒岩和石榴方辉石岩的第二期组合以形成石榴石+石英和黑云母+石英±单斜辉石±钾长石后成合晶和冠状体为特征。变质基性岩墙只发育第二期矿物组合,...     

Constraints from phase equilibrium modeling and in -situ U-Pb dating of monazite.SCIEI北大核心CSCD

西秦岭天水北道地区位于西秦岭造山带北缘,地处秦岭造山带和祁连造山带的结合部位。近来,我们在该地区秦岭杂岩中识别出一套麻粒岩相岩石(石榴夕线黑云片麻岩),峰期矿物组合为石榴子石+钛铁矿+金红石+夕线石+钾长石+石英,相平衡模拟计算结果显示其峰期温压条件为P=1.02GPa,T=820℃,经历了进变质阶段以升温升压为特征,峰期之后以大致近等温降压为特征的顺时针P-T轨迹。独居石原位LA-ICP-MS U-Pb年代学结果显示石榴夕线黑云片麻岩经历了~421Ma、~388Ma和368~362Ma三期构造热事件。结合独居石的产出位置,我们推测421Ma代表了麻粒岩相变质作用的时代,这与天水花庙地区获得的麻粒岩峰期年龄一致;388Ma近似代表了峰期之后大致近等温降压至固相线附近的年龄;368~362Ma与区域韧性剪切作用的时代一致,可能记录了与新阳-元龙韧性剪切变形作用相关的热事件的时代。结合区域地质资料和本研究成果(矿物演化特征、顺时针的P-T演化轨迹和独居石原位定年结果),我们推测西秦岭造山带北缘天水北道地区的麻粒岩可能是早古生代陆-陆碰撞造山过程的产物。     

内蒙古集宁三岔口夕线堇青石榴二长片麻岩变质作用及年代学研究

三岔口夕线堇青石榴二长片麻岩出露于华北克拉通孔兹岩带东部的集宁变质杂岩中,该岩石保留了典型的减压反应结构。系统的岩相学观察和矿物化学研究结果表明,三岔口地区夕线堇青石榴二长片麻岩保存了两个阶段变质作用的矿物组合及相应的变质反应结构,其中峰期变质阶段M1的矿物组合为石榴石+夕线石+黑云母+石英+斜长石+钾长石+钛铁矿±磁铁矿;峰后减压的M2-1变质阶段矿物组合为石榴石+堇青石+夕线石+石英+斜长石+钾长石+钛铁矿±尖晶石,M2-2阶段的矿物组合为石榴石+堇青石+黑云母+石英+斜长石+钾长石+钛铁矿+磁铁矿±尖晶石。自峰期变质阶段到峰后减压阶段,典型的转变(减压)反应包括:Grt+Sil+Melt→Crd+Bt+Fe-oxide和Grt+Sil→Crd+Spl。相平衡模拟结合传统地质温压计限定峰期变质阶段的温压条件为T=852~862℃,P=9.3~10.2kbar;峰期后近等温减压的M2-1和M2-2阶段的温压条件分别为854~880℃和7.0~7.4kbar,820~848℃和5.3~6.4kbar。三岔口夕线堇青石榴二长片麻岩记录了典型的近等温减压型的顺时针P-T轨迹。阴极发光图像特征显示夕线堇青石榴二长片麻岩存在大量变质锆石,LA-ICP-MS U-Pb定年结果表明,所有变质锆石记录了十分一致的207Pb/206Pb年龄,其变质时代为1912±11Ma。变质作用历史说明内蒙古孔兹岩带东段的集宁地体卷入了华北克拉通西部的阴山陆块和鄂尔多斯陆块之间的俯冲-碰撞,并经历了古元古代(~1912Ma)的麻粒岩相变质作用后快速折返至地表的过程。     

Teredolites Leymerie in the Lower Greensand Group (Cretaceous) of the Isle of Wight and the problematic ichnology of reworked clasts

Nineteenth-century references to clavate borings in woody substrates in the Lower Greensand of the Isle of Wight used a variety of names, but Teredo (a wood-boring bivalve, not a boring), Teredolithes (a junior synonym of Teredolites) and Gastrochaena (a bivalve borer of rock and shelly substrates, not a boring in wood) are all nomenclatorially incorrect. Borings in a beach clast derived from the Lower Greensand Group and recently collected from Sandown Bay, Isle of Wight, are referred to Teredolites isp. cf. T. longissimus Kelly and Bromley. This specimen confirms the presence of Teredolites in the Lower Greensand Group and demonstrates a common ichnological problem of beach clasts; borings, either fossil or modern, are incompletely preserved, making confident classification below the level of ichnogenus problematic.     

New palaeontological data from the organic-rich layers of the Bathonian of the Grands Causses (France)

The palaeontological content (charophytes and vertebrates) of organic-rich layers from the Middle Jurassic (Bathonian) of the Grands Causses at Mostuéjouls (Aveyron, France) has been examined. It is rich in gyrogonites of Porochara douzensis. The vertebrates of the lower layer include a single hybodontiform tooth, “semionotiform” teeth and scales, and one pycnodontiform tooth whereas the upper layer has yielded one hybodontiform tooth, a variety of actinopterygian remains (mostly Caturus sp. and indeterminate pycnodontiforms) and a few possible reptile remains. The variation in fauna between the two layers is ascribed to a different degree of marine influence.     

Vegetation and climate change on the Bolivian Altiplano between 108,000 and 18,000 yr ago

A 90,000-yr record of environmental change before 18,000 cal yr B.P. has been constructed using pollen analyses from a sediment core obtained from Salar de Uyuni (3653 m above sea level) on the Bolivian Altiplano. The sequence consists of alternating mud and salt, which reflect shifts between wet and dry periods. Low abundances of aquatic species between 108,000 and 50,000 yr ago (such as Myriophyllum and Isoëtes) and marked fluctuations in Pediastrum suggest generally dry conditions dominated by saltpans. Between 50,000 yr ago and 36,000 cal yr B.P., lacustrine sediments become increasingly dominant. The transition to the formation of paleolake “Minchin” begins with marked rises in Isoëtes and Myriophyllum, suggesting a lake of moderate depth. Similarly, between 36,000 and 26,000 cal yr B.P., the transition to paleolake Tauca is also initiated by rises in Isoëtes and Myriophyllum; the sustained presence of Isoëtes indicates the development of flooded littoral communities associated with a lake maintained at a higher water level. Polylepis tarapacana-dominated communities were probably an important component of the Altiplano terrestrial vegetation during much of the Last Glacial Maximum (LGM) and previous wet phases.     

The Olduvai buffalo Pelorovis and the origin of Bos

The origin of the genus Bos is a debated issue. From ∼ 0.5 Ma until historic times, the genus is well known in the Eurasian large mammal assemblages, where it is represented by Bos primigenius. This species has a highly derived cranial anatomy that shows important morphological differences from other Plio-Pleistocene Eurasian genera of the tribe Bovini such as Leptobos, Bison, Proamphibos-Hemibos, and Bubalus. The oldest clear evidence of Bos is the skull fragment ASB-198-1 from the middle Pleistocene (∼ 0.6-0.8 Ma) site of Asbole (Lower Awash Valley, Ethiopia). The first appearance of Bos in Europe is at the site of Venosa-Notarchirico, Italy (∼ 0.5-0.6 Ma). Although the origin of Bos has traditionally been connected with Leptobos and Bison, after a detailed anatomical and morphometric study we propose here a different origin, connecting the middle Pleistocene Eurasian forms of B. primigenius with the African Late Pliocene and early Pleistocene large size member of the tribe Bovini Pelorovis sensu stricto. The dispersal of the Bos lineage in Western Europe during middle Pleistocene times seems to coincide with the arrival of the Acheulean tool technology in this continent.     

Geochemistry and metamorphic evolution of the Pohorje Mountain eclogites from the easternmost Austroalpine basement of the Eastern Alps (Northern Slovenia)

Kyanite-rich and quartz-rich eclogites occur as lenses within amphibolite-facies quartzo-feldspathic gneisses in the Pohorje Mountains, Northern Slovenia, that form the easternmost Austroalpine basement. Major and trace elements indicate that the kyanite-rich eclogites were derived from plagioclase-rich gabbroic cumulates, whereas the quartz-rich eclogites represent more fractionated basaltic compositions. Both varieties are characterized by a LREE-depleted N-MORB type REE signature. Geothermobarometry and P-T pseudosections indicate that eclogites equilibrated at 1.8-2.5 GPa and 630-700 °C, consistently with the lack of coesite and with equilibration conditions of the chemically similar eclogites from the adjacent basement units at Koralpe and Saualpe type localities. Decompression reaction textures include (i) clinopyroxene-plagioclase intergrowths after omphacite, (ii) replacement of kyanite by corundum-plagioclase-spinel±sapphirine symplectites, (iii) breakdown of phengite to biotite-plagioclase sapphirine symplectites. The results of this study indicate that Koralpe, Saualpe and Pohorje high-pressure rocks represent former MORB-type oceanic crust that was subducted in the course of the late Cretaceous (approximately 100 Ma ago) collision between the European and the Apulian plates.     

Neoichnology and implications for stratigraphy of reworked Upper Oligocene oysters,Antigua, West Indies

The Late Oligocene oyster Hyotissa antiguensis (Brown) is locally common in the Antigua Formation of Hughes Point, eastern Antigua, Lesser Antilles; it was not commonly bored at that time. Its valves and shells are robust, and reworked into the shallow water near-shore environment in Antigua; it could potentially be incorporated into younger rocks. Its neoichnology includes clues that would facilitate identification of these oysters as reworked fossils. The suite of modern borings found in these specimens includes common Caulostrepsis taeniola Clarke, Gastrochaenolites isp. cf. G. turbinatus Kelly and Bromley and Entobia isp., and rare Oichnus simplex Bromley and Rogerella? isp. The latter three taxa are limited to oyster shell substrates. Of the common ichnotaxa, Caulostrepsis and Gastrochaenolites are particularly prominent in limestone clasts and limestone cemented to oyster shells, which would be an indicator of reworking if found in a post-Oligocene lithified deposit. Caulostrepsis and Gastrochaenolites are relatively less common in oyster shells and valves, and in many specimens are seen to terminate against the shell. Entobia is the only common boring limited to the shell substrate. The fidelity of preservation of modern borings is also superior in limestone clasts. This suite of borings is comparable with those found in the Neogene of the Antillean region.     

Dynamic early Holocene vegetation development on the Faroe Islands inferred from high-resolution plant macrofossil and pollen data

Vegetation dynamics during the earliest part of the Holocene (11,250-10,250 cal yr BP) have been reconstructed from a lacustrine sequence on Sandoy, the Faroe Islands, using detailed plant macrofossil and pollen evidence. The plant macrofossils suggest the initial vegetation was sparse herb and shrub tundra, with Salix herbacea and open-ground species, followed by the development of a denser and more species-rich arctic heathland after 11,150 cal yr BP. Despite high pollen values for Betula nana, macrofossils are rare. The bulk of the macrofossils recorded are S. herbacea and Empetrum leaves with numerous herb taxa and an abundance of Racomitrium moss. Conditions start to change around 10,800 cal yr BP, with increased catchment erosion and sediment delivery to the lake from ca. 10,600 cal yr BP, and a transition to alternating Cyperaceae and Poaceae communities between ca. 10,450 and 10,250 cal yr BP. This vegetation change, which has been recorded throughout the Faroes, has previously been interpreted as a retrogressive shift from woody shrubs to a herbaceous community. The detailed plant macrofossil data show the shift is the replacement of an Empetrum arctic heathland by grassland and moist sedge communities. These taxa dominate the modern landscape.     

缅甸硬玉岩地区的热液型钠长石岩

产于俯冲带内的低温高压带的由单矿物构成的硬玉岩通常伴有钠长石岩,目前对于硬玉岩研究的关注度较高,而对于钠长石岩则相对较低,很少有相关论文报导.产于缅甸翡翠矿区的钠长石岩,经常与硬玉岩相伴而生,是良好的研究样品.钠长石岩的主要矿物成分是低温钠长石,其次含有硬玉、绿辉石、透辉石等辉石类矿物和钠透闪石、蓝透闪石、镁钠闪石等闪石类矿物,此外还有钠沸石等.钠长石沿着解理和裂隙交代硬玉,说明钠长石形成晚于硬玉岩.钠长岩中的主要组成矿物钠长石的形成温度小于300℃,且其形成压力小于0.5kb,推测是在硬玉岩抬升程中通过交代与沉淀作用形成.其内的透辉石有两种类型,一类可能是被交代的硬玉中的透辉石组分会渐进增加,最终形成透辉石.另一类是被绿辉石包裹的透辉石残留,其很有可能是早期来自地幔楔或者俯冲带岩石中的矿物残留,即异剥钙榴岩或辉石岩类,可以视作硬玉化绿辉石岩和硬玉化异剥钙榴岩的矿物学证据.热液型钠长石岩的存在进一步说明缅甸翡翠矿区钠化热液存在现象的普遍性与穿越性.     

First record of the puzosiine ammonite genus Pachydesmoceras from the Middle and Upper Turonian of Poland

Two gigantic individuals of the puzosiine ammonite genus Pachydesmoceras, from uppermost Middle and lower Upper Turonian strata in central and southwest Poland, are described and illustrated as the first examples of this genus to be recorded from Poland. Specific identification is problematic because of internal mould preservation and deformation to various extent; in addition, comparative material from other European localities is lacking. Representatives of Pachydesmoceras are typical of the Tethyan Realm; records from the European and Northwest Pacific provinces in the Boreal Realm are few. Both Polish specimens are referred to as P. cf. pachydiscoide Matsumoto.