Paleoproterozoic Nb-enriched meta-gabbros in the Quanji Massif,NW China:Implications for assembly of the Columbia supercontinent

Diverse models have been proposed for the role of the Tarim Craton within the Paleoproterozoic Columbia supercontinent assembly. Here we report a suite of-1.71 Ga Nb-enriched meta-gabbro lenses in the eastern Quanji Massif, within the Tarim Craton in NW China. The meta-gabbroic rocks have Nb contents of 11.5-16.4 ppm with Nb/La ratios varying from 0.84 to 1.02((Nb/La)_N = 0.81-0.98) and Nb/U ratios from 38.0 to 47.2. They show low SiO_2(45.1-48.5 wt.%) and MgO(5.96-6.81 wt.%) and Mg#(Mg# = Mg/(Mg + Fe) = 43.5-47.7), high FeO^t(13.0-15.7 wt.%) and moderate Ti02(1.70-2.51 wt.%).with tholeiitic affinities. These rocks possess low fractionated REE patterns without obvious Eu anomalies(Eu/Eu~* = 0.87-1.02). Their primitive mantle-normalized elements patterns display significant Zr-Hf troughs, positive Nb anomalies, weak negative Ti and P anomalies, and high contents of Rb and Ba,resembling Nb-enriched basalts generated in arc-related tectonic settings. Their arc-like geochemical signatures together with whole rock εNd(t) values of 0.4-2.1 and corresponding old T_(DM)(2.22-2.37 Ga)as well as(^(143)Nd/^(144)Nd)_t and(^(87)Sr/^(86)Sr)t(t = 1712 Ma) values of 0.5104-0.5105 and 0.7030-0.7058,respectively, suggest that their precursor magma originated from mantle wedge peridotite metasomatised by subduction-derived melts. The results from our study reveal subduction along the eastern periphery of the Tarim Craton and marginal outgrowth continuing to ~1.7 Ga within the Columbia supercontinent.

全吉地块前寒武纪地层学研究进展

青藏高原北部全吉地块的全吉群和小高炉群记录了“新元古代冰期事件”、“超大陆循环”和“大不整合事件”等一系列意义重大的地质事件,并以此作为探索全吉地块前寒武纪地质演化史的重要窗口。近年来,关于全吉地块的前寒武纪生物地层学、年代地层学和事件地层学研究取得了一系列重要进展:(1)在全吉地块发现的埃迪卡拉型宏体生物化石以及共生的管状动物化石,为探索现代型海洋生态系统起源提供了新的视角,同时将小高炉群的时代上限进一步限定为埃迪卡拉纪晚期(551~543 Ma)。(2)全吉地块缺失寒武系纽芬兰统,其埃迪卡拉纪—寒武纪界限的地层缺失大致为25~50 Ma,与华北克拉通西缘-西南缘的“大不整合事件”尺度具有相似性。(3)全吉群红藻山组与上覆地层小高炉群黑土坡组之间存在一个较大的不整合,年代地层学研究显示红藻山组的形成时代为古元古代末期(1640~1646 Ma),而不是之前认为的埃迪卡拉纪(635~539 Ma)。(4)全吉地块仅存在一期新元古代冰碛岩,即埃迪卡拉纪红铁沟组冰碛岩,其与华北克拉通西缘-西南缘分布的罗圈组和正目观组冰碛岩时代大致相当。(5)全吉地块与华北克拉通在埃迪卡拉纪—寒武纪过渡时期具有相似的构造-沉积演化史,二者在埃迪卡拉纪末期同处于中高纬度,而不是之前认为的低纬度地区。

法相威仪:《吴全节十四像并赞卷》法服像研究

美国波士顿美术博物馆藏《吴全节十四像并赞卷》表现了元代玄教第二代掌教吴全节一生中的14个重要场景,其中六幅描绘了举行道教仪式时穿着道服的法衣像。这些画像忠实反映了元代玄教高道的法服制度,其中玉环、如意莲花冠和织金法服体现了吴全节与蒙元帝王的交往细节,填补了今人对元大都道教服饰传统的认知空白,对于服饰史和道教史研究均具有重要价值。

Zircon Hf Isotope of Yingfeng Rapakivi Granites from the Quanji Massif and ～2.7 Ga Crustal Growth

The Quanji （全吉） Massif is located in the Northwest China, which is interpreted as a micro-continent that is composed of metamorphic basement and stable cover strata. There are some controversies of genetic relationship between the Quanji Massif and the major cratons in China. In this study, we obtained in situ zircon U-Pb and Hf isotopic compositions of the Yingfeng （鹰峰） rapakivi granites from the northwest Quanji Massif by application of LA-MC-ICP-MS technique. Twenty U-Pb age measurements points are concordant or near concordant, and their weighted mean 207pb/206pb age is 1 793.9±6.4 Ma （MSWD= 1.09）, yields an upper intercept age of 1 800±17 Ma （MSWD=0.41）; 19 Hf isotope measurements yield a two-stage Hf model ages （TDM2） of 2.63 to 2.81 Ga, with a weighted average age of about 2.70±0.02 Ga and till（t）values variate between -8.91 to -5.35. This indicates that magma source of the Yingfeng rapakivi granites were produced from partial melting of late stage of Neoarchean juvenile crust, and suggests a significant crustal growth event occurred in the Quanji Massif at that time. The Quanji Massif might be an ancient continental segment detached from the Tarim Craton based on the crustal growth history and other geological records. The Tarim Craton （including the Quanji Massif） and the North China Craton had a similar or homological early crustal evolution around -2.7 Ga, which implies that Tarim Craton might be one of the component parts of North China Craton. of the Yingfeng rapakivi granites were produced from partial melting of late stage of Neoarchean juve- nile crust, and suggests a significant crustal growth event occurred in the Quanji Massif at that time. The Quanji Massif might be an ancient continental segment detached from the Tarim Craton based on the crustal growth history and other geological records. The Tarim Craton （including the Quanji Massif） and the North China Craton had a similar or homological early crustal evolution around -2.7 Ga, which implies that Tarim Craton might be one of the component parts of North China Craton.

Zircon Hf Isotopes and Geochemistry of the Early Paleoproterozoic High-Sr Low-Y Quartz-Diorite in the Quanji Massif,NW China:Crustal Growth and Tectonic Implications

The metamorphosed Early Paleoproterozoic granitoids in the Quanji massif, Northwest- ern China provide constraints for relationship between the Tarim Craton and North China Craton. Among granitoids batholiths, rocks of the Mohe quartz-diorite show typically adakitic geochemical characteristics, with medium K2O/Na2O ratios （0.56-1.17） and high Sr （519-619 ppm） low Y （9.37-20.40 ppm） and Yb （0.97-1.77 ppm） concentrations. The rocks have εNd（t） values between ＋2.4 and ＋4.4 and depleted mantle Nd model ages of 2.43-2.59 Ga. The magmatic zircons have positive εHf（t） values ranging from ＋0.40 to ＋7.60 and depleted mantle Hf model ages of 2.43-2.70 Ga, with major peaks at -2.54 and -2.65 Ga. The geochemical and Nd-Hf isotopic characteristics indicate that the Mohe quartz-dioritic rocks might be formed by partial melting of high-pressure metamorphosed juve- nile crustal rocks in post-orogenic extensional regime in the Early Paleoproterozoic. It suggests that important crustal growth occurred in the Quanji massif and the Tarim Craton at -2.4 and 2.5-2.7 Ga. The Quanji massif and Tarim Craton might share a similar crustal evolution history with the North China Craton in the Neoarchean.

Cambrian Ichnofossils from the Zhoujieshan Formation(Quanji Group) Overlying Tillites in the Northern Margin of the Qaidam Basin, NW China

The Quanji Group is composed of siliciclastics and carbonates and was deposited on a relatively stable block, in the northern margin of the Qaidam Basin, NW China. It is one of the research hotspots in the Qilian-Qinling-Kunlun tectonic zones. However, it has long been argued whether the up- per Qnanji Group should be assigned to the Precambrian or the Cambrian for lack of convincing fossil evidence. The discovery of ichnofossils, including Rusophycus, Cruziana, Dimorphichnus, Treptichnus, Skolithos, Arenicolites, Palaeophycus, and Helminthopsis, indicates that the upper member of the Zhou- jieshan Formation （top Quanji Group） is Cambrian in age, and at least above the Treptichnus （Phycodes） pedum Biozone, the lowermost biozone in the Cambrian. The lower member of the Zhoujieshan Forma- tion should belong to the Cambrian. During the time when the upper member of the Zhoujieshan For- mation was deposited, the northern margin of the Qaidam Basin was dominated by the Cruziana Ichnofacies, characterizing a lower-energy shelf （shallow） sea environment with moderate-rich oxygen con- tents. In addition, the conglomerates in the Hongtiegou Formation of the Quanji Group underlying the Zhoujieshan Formation were generally regarded as tillites. However, the dolostones of the lower member of the Zhoujieshan Formation are, in lithology and geochemistry, different from the typical cap-dolostones of the Doushantuo Formation in South China, so it is necessary to further study the origins of the lower member of the Zhoujieshan Formation and the conglomerates of the Hongriegou Formarion.

Geochemistry of Metamafic Dykes from the Quanji Massif: Petrogenesis and Further Evidence for Oceanic Subduction, Late Paleoproterozoic, NW China

A suite of ~1.84-1.92 Ga metamafic dykes within the paragneiss suite（khondalite） of the Quanji massif in NW China, has been chosen in this study for further understanding the tectonic evolution and possible links to the global Columbia supercontinent. Occurrence and field relations suggest that they were formed coevally with a previous studied ~1.83-1.85 Ga metamafic dyke swarms. Whole-rock major and trace elemental geochemistry suggests precursor magma of the amphibolites being generated from a volcanic arc-related tectonic setting rather than a back-arc environment where the metamafic dyke swarms were emplaced. The metamafic dykes show enrichment of LREE and strongly negative anomalies for Ta-Nb, Zr-Hf and Ti, have high SiO_2（49.3 wt.%-52.5 wt.%） but low MgO（6.40 wt.%-7.76 wt.%） contents and Mg~#（Mg~#=[100×（MgO/40.3）]/[MgO/40.3＋FeO/71.8]） values（45.7-52.1）, suggesting evolved precursor magma. The high values of La/Ta（22.2-42.8） and La/Nb（1.71-2.47）, mildly negative εNd（t） values（-2.51-0.15）, with depleted mantle model ages（TDM） of 2.45-2.84 Ga, suggest that their precursor magmas were possibly derived from a subduction-related fluid metasomatized Archean sub-continental lithospheric mantle. This study provides further evidence for oceanic plate subduction prevailing before or around ~1.85 Ga, which confirms a prolonged subduction-accretion-collision history in the NW China which is possibly linked to the assembly of the Columbia supercontinent.

夏译《论语全解》校读札记

黑水城出土的西夏译《论语全解》是现存最早的《论语全解》版本,具有极高的文献价值。之前未被学界大量关注的明抄本与四库本在字句上多有不同,而与西夏译本更为接近。利用西夏译本可以校勘汉文本中的讹舛之处,而明抄本也为解读西夏译本中与四库本龃龉之处提供了坚实的文献依据。

元代文坛与吴全节的“儒仙”印记

元代玄教宗师吴全节不仅以其儒道素养际遇元廷,由主持皇室斋醮、国家祭祀进而参与元廷政治,取得了元代汉人、南人无法企及的功业;而且以其艺文素养参与元代艺文活动,营造了元代最为庞大的艺文交游圈,成为元代文坛的一大盟主,元代文坛与吴全节的交游唱和遂成为元代艺文创作的一道靓丽风景。就留存至今的73位作家的393篇(首)作品加以分析,我们发现,这些唱和题赠之作反映了元代士人对吴全节庙堂功业、江湖情怀的体认与感悟,反映了元代士人对吴全节身份和地位的判断,“儒仙”吴全节也因此成为折射元代士人心态的绝佳窗口,彰显了元代儒士的用世情怀和出世愿景,是元代文学、元代文化“儒道互补”结构的集中体现。吴全节的功业、吴全节与文坛的交游、吴全节的“儒仙”印记,在道教史、文化史、文学史上都是空前绝后的,乃元代特殊的制度使然,值得我们深思。

柴北缘全吉煤田侏罗系构造控煤及找煤方向分析

全吉煤田是柴达木盆地北缘重要的煤炭产地,大煤沟煤矿、绿草山煤矿是煤田内代表性煤矿,侏罗纪含煤地层及煤层出露较好、埋深较浅,已开采多年。多年的勘查和全吉山整装勘查工作,全吉煤田浅部,特别是地表出露地段已基本查明,但大部分地段为隐伏区,加之全吉煤田构造复杂,目前构造控煤是困扰全吉煤田实现找矿突破的问题,需进一步加强对构造的研究,提高构造对煤层赋存及埋藏深度影响的认识。在分析全吉煤田侏罗系沉积演化及聚煤模式研究、构造演化特征的基础上,总结了全吉煤田典型构造控煤样式,并指出了全吉煤田侏罗系今后的找煤方向,以期对全吉煤田,特别是全吉煤田隐伏区找煤工作起到一定的现实指导作用。

青海柴达木盆地北缘全吉群内部存在区域性不整合

通过野外考察和前人资料分析发现,柴达木盆地北缘全吉群红藻山组之上存在一个区域性的不整合,其中发育铁质风化壳、沉积间断、地层的缺失、侵蚀作用特征。不整合面上、下地层存在古生物组合、沉积环境的突变。界面以下为碳酸盐台地沉积,界面之上代表了冰水沉积到海相潮上—潮间带沉积,上覆黑土坡组—红铁沟组—皱节山组,依次沿着不整合面向上超覆,反映了不整合发育之后的又一次海进过程。该不整合界面可能代表了新元古代晚期该地区裂谷盆地的伸展阶段的构造响应。该区域性不整合的发现,改变了以往传统的对全吉群内部整合关系的认识,说明全吉群需要解体。该不整合可能发生于成冰纪—埃迪卡拉纪。该时期的不整合面上、下生物面貌和沉积环境的变化或突变,可能与新元古代晚期罗迪尼亚超大陆的裂解和全球雪球事件相关。

全吉地块花岗片麻岩中镁铁质岩包体的矿物演化和锆石定年与古元古代区域变质作用

全吉地块中段古元古代早期的德令哈二长花岗片麻岩中发育一个来自围岩的变质镁铁质岩包体。该包体的岩性从核部到边缘依次为角闪斜长辉石岩、斜长角闪岩和石榴石角闪片岩。角闪斜长辉石岩的显微结构指示三个世代的矿物演化,世代Ⅰ为单斜辉石+棕绿色普通角闪石+斜长石+石英+钛铁矿,世代Ⅱ为蓝绿色普通角闪石+斜长石+石榴子石,世代Ⅲ为阳起石+钠长石+黝帘石。世代Ⅰ指示其峰期变质达高角闪岩相条件。角闪斜长辉石岩的锆石全部为浑圆状多晶面晶体,其CL图像具高温变质结晶特征。LA-ICPMS技术测定获得上交点U-Pb年龄为(1 913±38)Ma(MSWD=0.15),指示峰期变质发生在古元古代末。研究表明,全吉地块中区域性分布的古元古代早期的二长花岗片麻岩与达肯大坂岩群在响应全球Columbia超大陆汇聚事件中一起发生了区域变质作用。

柴达木盆地北缘全吉群红藻山组凝灰岩锆石U-Pb年龄及其地质意义

全吉群是不整合于柴达木北缘全吉（欧龙布鲁克）地块变质基底之上的第一套盖层型沉积,目前多数研究者认为其时代大体为新元古代晚期。本文在柴北缘全吉山的全吉群红藻山组建组剖面上,对位于该组下部的两层凝灰岩开展了LA-MC-ICPMS锆石U-Pb同位素定年研究,获得其岩浆锆石的U-Pb同位素年龄分别为（1 640±15）Ma和（1 646±20）Ma,标定了红藻山组的形成年龄,为柴北缘中新元古界年代地层的重新厘定与划分,提供了新的、直接的年代学约束,具有重要的科学意义。首先,这一新进展表明,在柴北缘地区,传统的全吉群红藻山组以下各组的时代,并非一直以来的＂新元古代晚期南华纪—震旦纪（埃迪卡拉纪）＂,而应属于国内的中元古代长城纪、国际上的古元古代固结纪（Statherian,1 800～1 600Ma）晚期;其次,根据当前定年并结合新近在红藻山组与上覆地层之间发现有古风化壳及区域性不整合、全吉群上部发育有埃迪卡拉纪化石及冰碛砾岩等证据,本文进一步确认,柴北缘全吉群在红藻山组与其上覆黑土山组等地层单位之间其实存在着相当长时间的地层缺失,传统的＂全吉群＂应予解体。由此并参考已有资料,本文认为,早先代表柴达木地块形成的＂全吉运动＂并不能与华南的＂晋宁运动＂对比,而应与华北的＂吕梁运动＂相当,全吉地块乃至整个柴达木及周边地区的中、新元古代地质演化历史及其大地构造亲缘属性等,都应重新予以考虑。

柴达木地块北缘全吉地块钾长石浅粒岩碎屑锆石LA-ICP-MSU-Pb定年——对达肯大坂岩群时代的约束

为查明全吉地块基底中达肯大坂岩群的最大沉积年龄,用LA-ICP-MS技术测定了钾长石浅粒岩中的锆石U-Pb年龄。CL图像和Th/U比值指示这些锆石均为岩浆成因的锆石。36个测点207Pb/206Pb年龄变化范围为2094～2280Ma,其中年龄谐和度高于90%的30个测点的207Pb/206Pb年龄相对概率密度曲线呈单峰分布特征,峰值年龄为2190Ma左右。结合全吉地块最早一期变质事件的年龄,钾长石浅粒岩原岩碎屑和所在的达肯大坂岩群的沉积年龄范围被约束在1.95～2.19Ga之间。本研究表明,前人在侵入于达肯大坂岩群的伟晶岩脉中获得的约2.42Ga年龄的锆石应捕获于围岩,属于继承性岩浆碎屑成因,该类锆石年龄不能用来约束达肯大坂岩群原岩的最小沉积年龄。

青海都兰东北部哈莉哈德山花岗片麻岩LA-ICP-MS锆石U-Pb年龄及构造意义

青海都兰东北部哈莉哈德山花岗片麻岩原岩为具有S-型花岗岩特征的酸性侵入岩。来自该片麻岩的20粒锆石的LA-ICP-MS U-Pb年龄测定表明,该片麻岩的原岩花岗岩岩浆于约950Ma侵位结晶,岩浆物源源区存在中—新元古代的物质成分。正确甄别哈莉哈德山花岗片麻岩的变质围岩是否隶属于全吉地块的达肯大坂岩群,是理解全吉地块与柴达木地块在新元古代时期构造演化关系的关键。

全吉地块莫河片麻岩原岩侵位年龄的再研究

莫河片麻岩位于全吉地块东段,其原岩为花岗闪长质-二长花岗质侵入体。前人对该片麻岩的锆石年龄测定结果相差约120Ma。在野外详细地质观察基础上重新采集样品,用LA-ICP-MS法重新测定了15颗岩浆成因锆石的U-Pb年龄,结果得上交点年龄为(2 394±31)Ma(2$)(MSWD=0.82)。由于锆石也受到变质变形作用的强烈改造,认为该年龄可能更接近于该片麻岩原岩的侵位年龄。新的定年结果表明,全吉地块存在近2.4Ga的花岗岩类侵入活动。

柴达木盆地北缘全吉地块东端变基性岩体LA-ICP-MS锆石U-Pb年龄:中元古代陆块裂解的证据

全吉地块东端古元古代二长花岗片麻岩中普遍发育变质的基性岩体,它们的形成时代、变质作用时代和对地块基底构造演化的指示意义尚不清楚。应用LA-ICP-MS技术测定其中的一个变基性岩体的锆石U-Pb年龄,获得的10个测点数据显示,锆石受到热事件的强烈改造而发生严重铅丢失,但拟合的不一致线仍给出相关性较好的上交点年龄1712Ma±47Ma和下交点年龄472Ma±29Ma,MSWD=1.4。这表明,变质基性岩的原岩形成于中元古代早期,是全吉地块在古元古代末期汇入Columbia超大陆之后于中元古代早期初始裂解而侵位的基性岩体。这些基性岩体在早古生代卷入了柴北缘碰撞带而发生角闪岩相变质作用,并受到构造肢解。

青海刚察泉吉地区中酸性侵入岩年代学特征及其意义

青海刚察泉吉地区中酸性侵入岩发育,为了进一步查明侵入岩的特征、侵入时代和形成环境,对其进行了地质学、岩石地球化学及年代学研究.LA-ICP-MS锆石U-Pb定年结果表明,研究区中酸性侵入岩侵位年龄主要集中在430-455 Ma,指示岩体为晚奥陶世-早志留世,指示两个期次岩浆产物,侵位于巴龙贡噶尔组的花岗闪长岩测年结果显示锆石206Pb/238U值为444±11 Ma,指示该花岗闪长岩体的侵位时代属晚奥陶世,因此限定了巴龙贡噶尔组（Sb） 时代上限应该早于晚奥陶世.从岩石地球化学特征来看,花岗岩类表现为富钾、准铝-过铝质,富集大离子亲石元素Rb、K 和Ba,亏损高场强元素Nb、Ti和P,具弱铕负异常;闪长岩类表现为富钾、准铝质、铕负异常特征不明显.从形成环境来看,研究区中酸性侵入岩均具有大陆碰撞环境的特征.结合区域地质构造环境及前人研究成果,研究区侵入岩是俯冲-碰撞环境下晚奥陶世-早志留世的加里东期产物.

柴北缘构造带深部岩石的LA-ICP-MS锆石U-Pb年龄及微量元素研究:对全吉地块基底演化的启示

通过LA-ICP-MS方法对柴北缘全吉地块基底的斜长角闪岩和花岗闪长岩进行了锆石U-Pb年代学及锆石微区微量元素的研究。斜长角闪岩中的岩浆锆石上交点年龄为2 396±26 Ma,代表了锆石结晶的年龄,下交点为905±140 Ma,代表了锆石发生铅丢失事件的年龄。其岩浆锆石具有U/Yb较高(0.1~1),Hf值较低(<10 000×10^(-6)),U值较低(<150×10^(-6))的特点,显示其岩浆源区与富集地幔密切相关。在锆石微量元素判别图解中数据主要落在陆弧区和洋岛区,指示其形成的构造环境为弧后盆地。花岗闪长岩中岩浆锆石的加权平均年龄为484±21 Ma,岩浆锆石具有U/Yb较高(>1)和U值较高(平均值为640×10^(-6))的特点,显示岩浆源区为典型陆壳。锆石微量元素判别图解显示其形成于陆弧。研究结果表明,全吉地块基底除前寒武纪岩石外,还包含早古生代的岩石组合。全吉地块基底内部岩石组合与形成时代的复杂性,与全吉地块经历的多次洋壳俯冲、陆陆碰撞密切相关。