南太行山地区中基性侵入岩中角闪石的矿物学及其成因

角闪石作为南太行山地区中基性侵入岩中主要组成矿物,其详细的成因矿物学研究对了解该套岩石的形成机理具有重要意义。电子探针分析表明角闪石的成分变化很大如SiⅣ、AlⅣ和A位置上的Na和K离子,主要为韭闪石、韭闪石质普通角闪石、普通角闪石和阳起石质普通角闪石。且富镁和钙,为钙镁质角闪石。同时,不同岩石类型中的角闪石的组成无显著差异。大颗粒的核心部位形成于深部岩浆房中(18 ~25km),其组成的连续变化主要反映结晶深度的不同。角闪石的成因矿物学研究表明该套岩石不可能来源于华北古老的下地壳,而可能起源于新增生的下地壳和/或壳幔过渡带。     

海南岛晚中生代花岗闪长岩及其包体的锆石U-Pb定年及构造意义

海南岛晚中生代的岩浆活动十分强烈,代表性的岩体有千家岩体、屯昌岩体和保城岩体,岩体岩性为花岗闪长岩,其中包含大量的闪长岩包体。系统的LA-ICP-MS锆石U-Pb定年结果表明,花岗闪长岩及包体均形成于101 Ma,为双峰式侵入岩,由来自地幔的高温基性岩浆注入下地壳较酸性的长英质岩浆,两种岩浆同时上侵冷却形成。它们形成的构造环境为板内拉张环境,指示了海南岛于101 Ma处于强烈的岩石圈减薄阶段,这与晚中生代太平洋板块俯冲引起的弧后拉张有关。     

冀北滦平地区中生代火山岩地层锆石U-Pb测年及启示

在冀北—辽西地区, 冀北的滦平地区是中生代地层最为齐全, 也是唯一的晚中生代沉积作用基本连续的地区.许多研究者认为该地区的土城子组与张家口之间存在着J₃—K₁界线和中生代的构造转换界面.该地区分布的主要中生代地层自下而上依次为髫髻山组、土城子组、张家口组、大北沟组、大店子组和西瓜园组.通过LAICPMS方法的锆石UPb测年, 获得了该地区中生代火山岩地层的年代格架, 即髫髻山组的顶界年龄为(162.8±3.2)Ma, 土城子组形成的主体年代范围是(142.6±1.3)~(136.4±1.9)Ma, 张家口组形成的年代范围是(135.7±1.8)~(135.2±2.3)Ma, 大店子组顶部安山岩的年龄是(131.4±3.7)~(130.2±3.0)Ma.锆石的稀土元素分析表明: 土城子组中锆石的稀土元素特征与张家口组中锆石的特征一致, 而与髫髻山组中的锆石有较大的区别.综合以上分析数据及野外地质特征可以得出以下结论: (1)该地区的土城子组与髫髻山组之间不仅时间间隔较长, 而且二者中火山岩的源区也有较大的区别; 土城子组与张家口组之间不仅时间上基本连续, 而且二者中火山岩的源区也有明显的一致性.这就表明了滦平地区的土城子组与张家口组是同一地质背景下的产物, 即该地区二者之间应不存在J₃—K₁界面和构造转换界面.(2)滦平地区大店子组顶部火山岩在年代上与辽西北票—义县地区的义县组底部、辽西凌源地区的张家口组顶部基本相当.      

Ultrahigh-pressure metamorphism in the forbidden zone: the Xugou garnet peridotite, Sulu terrane, eastern China

The Xugou garnet peridotite body of the southern Sulu ultrahigh‐pressure (UHP) terrane is enclosed in felsic gneiss, bounded by faults, and consists of harzburgite and lenses of garnet clinopyroxenite and eclogite. The peridotite is composed of variable amounts of olivine (Fo₉₁), enstatite (En_92?93), garnet (Alm_20?23Prp_53?58Knr_6?9Grs_12?18), diopside and rare chromite. The ultramafic protolith has a depleted residual mantle composition, indicated by a high‐Mg number, very low CaO, Al₂O₃ and total REE contents compared to primary mantle and other Sulu peridotites. Most garnet (Prp_44?58) clinopyroxenites are foliated. Except for rare kyanite‐bearing eclogitic bands, most eclogites contain a simple assemblage of garnet (Alm_29?34Prp_32?50Grs_15?39) + omphacite (Jd_24?36) + minor rutile. Clinopyroxenite and eclogite exhibit LREE‐depleted and LREE‐enriched patterns, respectively, but both have flat HREE patterns. Normalized La, Sm and Yb contents indicate that both eclogite and garnet clinopyroxenite formed by high‐pressure crystal accumulation (+ variable trapped melt) from melts resulting from two‐stage partial melting of a mantle source. Recrystallized textures and P–T estimates of 780–870 °C, 5–7 GPa and a metamorphic age of 231 ± 11 Ma indicate that both mafic and ultramafic protoliths experienced Triassic UHP metamorphism in the P–T forbidden zone with an extremely low thermal gradient (< 5 °C km^?1), and multistage retrograde recrystallization during exhumation. Develop of prehnite veins in clinopyroxenite, eclogite, felsic blocks and country rock gneiss, and replacements of eclogitic minerals by prehnite, albite, white mica, and K‐feldspar indicate low‐temperature metasomatism.     

辽东中生代晚期和古近纪玄武岩及深源捕虏晶--对岩石圈地幔性质的制约

辽东地区玄武岩的K-Ar定年结果表明,曲家屯玄武岩形成于晚白垩世,K-Ar年龄为81．58±2．46Ma;乱石山子玄武岩形成于古近纪,K-Ar年龄为58．36±1．64Ma。本区玄武岩含有丰富的橄榄石、单斜辉石和角闪石捕虏晶。乱石山子玄武岩中橄榄石捕虏晶的Mg^#值（79．5-88．5之间,平均值为84）较曲家屯玄武岩中橄榄石捕虏晶Mg^#值（77．0～79．8之间,平均值为78．4）偏高;单斜辉石捕虏晶为透辉石,其从核部到边部的Mg^#等变化趋势与橄榄石类似;斜方辉石捕虏晶为占铜辉石,其Mg^#值介于85．2-87．6之间,平均值为86．4。捕虏晶发育的环状裂隙、扭折带、矿物成分环带以及捕虏晶与主岩Mg^#值之间的不平衡均暗示它们为玄武质岩浆上升捕获的早期岩浆晶出矿物的堆晶体。玄武岩的岩石地球化学分析结果表明：（1）它们属于碱性系列,为碱性玄武岩,曲家屯玄武岩较乱石山子玄武岩贫硅、镁,富钙、铝,它们均具有原始岩浆的特征;（2）二者具有相似的稀土元素配分模式,但曲家屯玄武岩轻稀土元素总量更高,且轻重稀土元素分离程度高;（3）二者具有相似的Sr-Nd同位素组成,Isr和εNd（t）值分别介于0．7039～0．7045和＋1．60～＋3．69,反映了亏损的岩石圈地幔特征。     

大别-胶南高压地体变质杂岩中流体包裹体特征和形成的热动力条件

在中国陆内南北板块之间古缝合线内大别-胶南高压地体中。分布着一套变质程度不一的杂岩系,我们将其划分出三期高峰变质作用形成的不同性质变形变质岩相带,并阐述了各自所代表的矿物流体包裹体特征,计算出它们形成时的温度、压力、氧逸度、差异应力等热动力参数,为揭示地体变形变质环境和构造演化特点,提供了可靠(?)数值根据。     

塔里木盆地库车坳陷中生代盆地性状及成因分析

库车坳陷充填有厚约4000~5000 m(局部最大厚度可达6000 m)的中生界陆相地层。地面特征和地震资料表明,库车坳陷北部地区中生界与下伏强烈变形、变质的古生界呈角度不整合接触,南部地区中生界与下伏寒武系-奥陶系呈平行不整合或微角度不整合接触。按照地层厚度趋势推测的中生界在山前地带有强烈的剥蚀,沉积厚度轴线位于南天山晚古生代造山楔之上,显示库车坳陷中生代盆地是上叠在塔里木克拉通北部边缘隆起和南天山晚古生代造山楔过渡带上的拗陷盆地。三叠纪-侏罗纪沉降-沉积中心向后陆(造山带)迁移,早白垩世向前陆迁移,且盆地同沉积期区域规模的断裂活动不明显,据此推测晚古生代造山作用后的岩石圈热作用及地壳均衡作用是中生代盆地沉降的主控动力学因素。     

新疆北部古地磁研究

通过和布克赛尔、克拉玛依、玛纳斯—乌鲁木齐地区泥盆纪到白垩纪古地磁研究,主要取得以下结果:(1)首次建立了准噶尔西北缘及南缘石炭纪—白垩纪古地磁极移曲线,由石炭纪到二叠纪的古地磁极位置基本在同一区间,说明该时期这些地区为一个统一的构造单元,而其古地磁极明显与塔里木、哈萨克斯坦、西伯利亚地块存在着差异。(2)该地区侏罗纪及白垩纪古地磁结果与塔里木地块结果一致,侏罗纪乌鲁木齐与和布克赛尔磁偏角相差30°左右,说明和布克赛尔地区相对乌鲁木齐地区逆时针旋转了30°左右,晚古生代以后曾发生过南向移动,而侏罗、白垩纪以来均向北发生了相当规模的北向运动,并发生了相对旋转,目前东、西准噶尔的构造格局可能就是由于局部相对旋转造成的。(3)中国大陆在早二叠世还不是一个联合的整体,而是以相互分离的独立块体分布于45°N—15°S的古特提斯洋中。(4)该地区二叠纪的磁偏角为165°—168°,而塔里木为218°,哈萨克斯坦为229°,说明存在35°—55°的逆时针旋转,这个旋转可能是由于西部推覆构造造成的。如果将西准噶尔超基性岩带顺时针旋转35°—55°后,东准噶尔超基性岩带、西准噶尔超基性岩带和斋桑泊—鲁布佐夫斯克超基性岩带应在同一构造带上。(5)该地区晚古生代古纬度变化不明显,位于30°—45     

Metamorphism of the Amdo metamorphic complex,Tibet: implications for the Jurassic tectonic evolution of the Bangong suture zone

Tibet consists of several terranes that progressively collided with the southern margin of Asia during the Mesozoic following the closure of intervening ocean basins. This Mesozoic amalgamation history, as well as the extent to which it may have contributed to crustal thickening prior to the Cenozoic Indo‐Asia collision, remains poorly constrained and strongly debated. Here, we present a metamorphic petrological and U‐Pb zircon geochronological study of the Amdo metamorphic complex, one of the few exposures of high‐grade metamorphic rocks in central Tibet, located along the Bangong suture between the Qiangtang terrane to the north and the Lhasa terrane to the south. U‐Pb ages of metamorphic zircon in gneiss constrain the timing of peak metamorphism at c. 178 Ma, prior to the Early Cretaceous collision between the two terranes. Peak P–T conditions of gneiss within the metamorphic complex are constrained by conventional as well as multi‐equilibrium (THERMOCALC v.3.21 and v.3.33) geothermobarometry of two samples of garnet‐amphibolite. Whereas THERMOCALC v.3.21 yields similar results as conventional geothermobarometry, THERMOCALC v. 3.33 yields dramatically lower pressures, mostly due to the change in the amphibole activity model used. Using THERMOCALC v.3.21, the two garnet‐amphibolite samples yield similar P–T conditions of 0.83 ± 0.06 GPa at 646 ± 33 °C and 0.97 ± 0.06 GPa at 704 ± 35 °C. Plagioclase coronas on the garnet‐amphibolite sample with lower peak P–T conditions indicate a period of isothermal decompression. Additional geothermometry on two garnet‐free amphibolites yielded similar temperatures of 700–750 °C and suggests similar P–T conditions across most of the complex. However, two exposures of garnet‐kyanite schist located along the southern edge of the metamorphic complex yielded slightly lower peak conditions of 0.75–0.85 GPa and 550–610 °C. Petrographic and field relations suggest the difference in metamorphic grade between the schist and gneiss is due to an intervening thrust fault. The existence of the thrust fault indicates that at least part of the exhumation of the complex was due to contractional deformation, possibly during the Lhasa‐Qiangtang collision. Our P–T–t results indicate the occurrence of a significant Early Jurassic tectonothermal event along the southern, active margin of the Qiangtang terrane that deeply buried the Amdo rocks. We suggest that the metamorphism is a result of arc‐related tectonism that may have been regionally extensive along the southern Qiangtang terrane; geological records of this tectonism may be rarely exposed along strike because of a lack of exhumation or subsequent depositional and structural burial.     

长江中下游中生代岩浆岩及铜铁成矿带的深部构造背景

地球物理和中、新生代幔源岩浆岩同位素地球化学研究表明华北和华南陆块的深部岩石圈地缝合线较地表地缝合线南移。在郯庐断裂带以东南移至南京一镇江一线，并从南京往西呈南西走向延伸至桐城一带；在郯庐断裂带以西的大剐山区，深部地缝合线至少南移至岳西以南。这一贴近长江中下游的深部地缝合线，有可能在郯庐断裂系早白垩世发生大规模左行走滑作用下而导致引张，从而诱发了地幔上隆和大规模岩浆事件及铜铁成矿作用。