Phytoplankton dynamics associated with the monsoon in the Sulu Sea as revealed by pigment signature   总被引：2，自引：0，他引：2  

Meguru Miki  Neelam Ramaiah  Shigenobu Takeda  Ken Furuya 《Journal of Oceanography》2008,64(5):663-673

Phytoplankton dynamics during the northeast monsoon was investigated in the Sulu Sea from algal pigment analysis. We visited the Sulu Sea in February 2000, a mid period of the northeast monsoon, and in November and December 2002, the beginning of the northeast monsoon. SeaWiFS images showed generally low concentrations of surface chlorophyll a (Chl a) during the southwest monsoon and higher concentrations with several peaks during the northeast monsoon. In the beginning of the northeast monsoon, subsurface chlorophyll maxima (SCM) occurred, where vertical variation in class-specific composition as estimated from pigment signatures was prominent. Prochlorococcus, cyanobacteria, prymnesiophytes and crysophytes were important groups above the SCM, and the contribution of cyanobacteria to Chl a became much lower at and below the SCM. Contributions of chlorophytes and prasinophytes to Chl a generally showed maxima near the SCM. This distribution was accompanied by vertical changes in the concentration of photoprotective pigments relative to photosynthetic accessory pigments. During the mid northeast monsoon, the upward supply of nutrients was probably enhanced at some stations due to vertical mixing, and as a consequence diatoms dominated in the upper 100 m water column of these stations, and other eukaryotic flagellates including prymnesiophytes, chrysophytes and cryptophytes were secondary major components of the community. The elevation of Chl a concentration and changes in phytoplankton community during the northeast monsoon likely influence the variation in biological production at higher trophic levels in the Sulu Sea.  相似文献   

苏鲁造山带在朝鲜半岛的延伸:造山带、前寒武纪基底以及古生代沉积盆地的证据与制约   总被引：3，自引：0，他引：3  

翟明国  郭敬辉  李忠  陈代钊  彭澎  李铁胜  张艳斌  侯泉林  樊祺诚  胡波 《高校地质学报》2007,13(3):415-428

苏鲁超高压带是否延伸到朝鲜半岛以及用何种方式延伸,成为很多地质学家注目的科学问题。新的研究成果包括:(1)在朝鲜半岛前寒武纪京畿陆块中,识别出一个含有榴辉岩的变质杂岩(洪城杂岩),榴辉岩透镜体出露于花岗片麻岩中,榴辉岩的锆石SHRIMP年龄是230Ma和～880Ma,围岩片麻岩的年龄约为810～820Ma;(2)朝鲜半岛的3个陆块(狼林、京畿和岭南陆块)具有与华北克拉通相似的岩石组合与演化历史;(3)南北朝鲜两个主要的古生代沉积盆地与华北具有很好的可比性;(4)临津江带和沃川带都不具有碰撞造山带的变质特征。据此提出了地壳拆离与逆冲模式,即华北与扬子陆壳的碰撞带沿朝鲜半岛西缘、大致呈南北走向分布。扬子陆壳俯冲带的深部(超高压部分)未在朝鲜半岛地表出露,下地壳(高压部分)从俯冲带拆离并逆掩到地表(洪城杂岩),以透镜体(岩片)状插入京畿地块的前寒武纪基底杂岩中,没有形成横穿朝鲜半岛的变质(造山)带。临津江带和沃川带有可能是扬子陆块的上地壳,它们从下地壳拆离、逆掩到地表,现在的展布状态是受到中生代构造的控制。  相似文献   

苏鲁超高压变质带仰口蛇纹岩的成因——矿物化学、地球化学和年代学证据     

李强  温珍河  侯方辉  朱晓青  孙军 《地质通报》2016,35(11):1784-1796

通过矿物化学、全岩主微量元素和铂族元素研究,结合锆石年代学判断苏鲁造山带仰口蛇纹岩的原岩成因和演化历史。蛇纹岩中尖晶石经历了多阶段变质;全岩主量元素具有超基性堆晶岩的性质,代表玄武质组分含量的Ca O+Al_2O_3变化于2.0%~5.83%之间;部分不相容微量元素富集;铂族元素中Ir的含量低(0.64×10~(-9)~1.43×10~(-9)),Pd/Ir值高(1.05~3.42)。蛇纹岩中的锆石一部分为新形成的变质成因锆石(年龄平均为230±3Ma),与高压-超高压变质的年代吻合;另一部分可能是在三叠纪变质阶段古老锆石重结晶形成的。由此认为,仰口蛇纹岩的原岩可能为超基性堆晶岩,三叠纪时随着俯冲的扬子板块发生变质,在发生蛇纹石化作用之前经历了熔体/流体的改造。  相似文献   

N2 fixation variability in the oligotrophic Sulu Sea, western equatorial Pacific region over the past 83 kyr     

Keiji Horikawa  Masao Minagawa  Yoshihisa Kato  Masafumi Murayama  Seiya Nagao 《Journal of Oceanography》2006,62(4):427-439

N₂ fixation is an important biological process that adds new nitrogen to oceans and plays a key role in modulating the oceanic nitrate inventory. However, it is not known how, when, and where N₂ fixation rates have varied in response to past climate changes. This study presents a new record of nitrogen isotopic composition (δ¹⁵N) over the last 83 kyr from a sediment core (KH02-4 SUP8) taken in the Sulu Sea in the western equatorial Pacific region; data allow the N₂ fixation variability in the sea to be reconstructed. Sediments, sinking, and suspended particulate organic matter (POM) all have lighter isotopic values compared to the δ¹⁵N values of substrate nitrate (av. 5.8‰) in North Pacific Intermediate Water. These lighter δ¹⁵N values are regarded as reflecting N₂ fixation in the Sulu Sea surface water. A δ¹⁵N mass balance model shows that N₂ fixation rates were significantly enhanced during 54–34 kyr in MIS-3 and MIS-2. It has been speculated that higher interglacial denitrification rates in the Arabian Sea and the eastern tropical Pacific would have markedly decreased the global oceanic N inventory and contributed to the increase in N₂ fixation in oligotrophic regions, but such a model was not revealed by our study. It is possible that changes in N₂ fixation rates in the Sulu Sea were regional response, and accumulation of phosphate in the surface waters due to enhanced monsoon-driven mixing is thought to have stimulated enhancements of N₂ fixation during MIS-3 and MIS-2.  相似文献   

Metamorphic P–T conditions and thermal structure of Chinese Continental Scientific Drilling main hole eclogites: Fe–Mg partitioning thermometer vs. Zr-in-rutile thermometer     

R. Y. ZHANG  Y. IIZUKA  W. G. ERNST  J. G. LIOU  Z.-Q. XU  T. TSUJIMORI  C.-H. LO  B.-M. JAHN 《Journal of Metamorphic Geology》2009,27(9):757-772

Core rocks recovered from the main hole (5158 m deep) of the Chinese Continental Scientific Drilling (CCSD‐MH) project, southern Sulu UHP terrane, east‐central China, consist of eclogites, various gneisses and minor metaperidotite cumulates; this lithological section underwent subduction‐zone UHP metamorphism. Coesite‐bearing eclogites are mainly present between the depths of 100–2000 m, but below 2000 m, mafic eclogites are rare. Selected elements (Zr, Nb, Cr, Fe, Si, Mg, Al & Ti) in rutile from 39 eclogite cores from 100 to 2774 m, and major elements of minerals from representative eclogites were analysed by electron microprobe. Zirconium and Nb concentrations of rutile cluster ～100–400 and 200–700 ppm respectively. However, Zr and Nb contents in rutile from strongly retrograded eclogites show larger variations than those of fresh or less retrograded eclogites, implying that somehow fluid infiltration affected rutile chemistry during retrograde metamorphism. Zr contents in rutile inclusions in garnet and omphacite are slightly lower than those of the matrix rutile, suggesting that the rutile inclusions formed before or close to the peak temperature. The P–T conditions of the CCSD‐MH eclogites were estimated by both Fe–Mg exchange and Zr‐in‐rutile thermometers, as well as by the Grt–Cpx–Phn–Ky geothermobarometer. The maximum temperature range of 700–811 °C calculated at 40 kbar using the Zr‐in‐rutile thermometer is comparable with temperature estimates by the Fe–Mg exchange thermometer. The temperature estimates of eclogites in a ～3000 m thick section define a continuous gradient, and do not show a distinct temperature gap, suggesting that the rocks from 100 to 3000 m depth might belong to a single, large‐scale UHP slab. These data combined with P–T calculations for CCSD‐MH peridotites yield a low geotherm (～5 °C km^?1) for the Triassic subduction zone between the Sino‐Korean and Yangtze cratons; it lies ～30–35 mW m^?2 conductive model geotherm.  相似文献   

Mineral Chemistry of Peridotites from Paleozoic, Mesozoic and Cenozoic Lithosphere: Constraints on Mantle Evolution beneath Eastern China   总被引：24，自引：0，他引：24  

ZHENG  JIANPING; GRIFFIN  WILLIAM L.; O'REILLY  SUZANNE Y.; YANG  JINSUI; LI  TIANFU; ZHANG  MING; ZHANG  RUTH Y.; LIOU  JOHN G. 《Journal of Petrology》2006,47(11):2233-2256

Major- and trace-element data on the constituent minerals ofgarnet peridotite xenoliths hosted in early Paleozoic (457–500Ma) kimberlites and Neogene (16–18 Ma) volcanic rockswithin the North China Craton are compared with those from thepre-pilot hole of the Chinese Continental Scientific DrillingProject (CCSD-PP1) in the tectonically exhumed Triassic (220Ma) Sulu ultrahigh-pressure (UHP) terrane along its southernmargin. P–T estimates for the Paleozoic and Neogene peridotitexenoliths reflect different model geotherms corresponding tosurface heat flows of 40 mW/m² (Paleozoic) and 80 mW/m² (Neogene).Garnet peridotite xenoliths or xenocrysts from the Paleozoickimberlites are strongly depleted, similar to peridotites fromother areas of cratonic mantle, with magnesium olivine (meanFo_92.7), Cr-rich garnet and clinopyroxene with high La/Yb. Garnet(and spinel) peridotite xenoliths hosted in Neogene basaltsare derived from fertile mantle; they have high Al₂O₃ and TiO₂contents, low-Mg-number olivine (mean Fo_89.5), low-Cr garnetand diopside with flat rare earth element (REE) patterns. Thedifferences between the Paleozoic and Neogene xenoliths suggestthat a buoyant refractory lithospheric keel present beneaththe eastern North China Craton in Paleozoic times was at leastpartly replaced by younger, hotter and more fertile lithosphericmantle during Mesozoic–Cenozoic times. Garnet peridotitesfrom the Sulu UHP terrane have less magnesian olivine (Fo_91.5),and lower-Cr garnet than the Paleozoic xenoliths. The diopsideshave low heavy REE (HREE) contents and sinusoidal to light REE(LREE)-enriched REE patterns. These features, and their highMg/Si and low CaO and Al₂O₃ contents, indicate that the CCSD-PP1peridotites represent a moderately refractory mantle protolith.Details of mineral chemistry indicate that this protolith experiencedcomplex metasomatism by asthenosphere-derived melts or fluidsin Mesoproterozoic, and subsolidus re-equilibration involvingfluids/melts derived from the subducted Yangtze continentalcrust during UHP metamorphism in the early Mesozoic. Tectonicextension of the subcontinental lithospheric mantle of the NorthChina Craton and exhumation of the Sulu UHP rocks in the earlyMesozoic induced upwelling of the asthenosphere. Peridotitessampled by the Neogene basalts represent newly formed lithospherederived by cooling of the upwelling asthenospheric mantle inJurassic–Cretaceous and Paleogene time. KEY WORDS: garnet peridotite xenoliths; North China Craton; lithospheric thinning; Sulu UHP terrane; UHP lithosphere evolution; mantle replacement  相似文献   

Isotopic constraints on age and duration of fluid-assisted high-pressure eclogite-facies recrystallization during exhumation of deeply subducted continental crust in the Sulu orogen   总被引：13，自引：1，他引：13  

Z.-F. ZHAO  Y.-F. ZHENG  T.-S. GAO  Y.-B. WU  B. CHEN  F.-K. CHEN  F.-Y. WU 《Journal of Metamorphic Geology》2006,24(8):687-702

Fluid availability during high‐grade metamorphism is a critical factor in dictating petrological, geochemical and isotopic reequilibration between metamorphic minerals, with fluid‐absent metamorphism commonly resulting in neither zircon growth/recrystallization for U‐Pb dating nor Sm‐Nd isotopic resetting for isochron dating. While peak ultra‐high pressure (UHP) metamorphism is characterized by fluid immobility, high‐pressure (HP) eclogite‐facies recrystallization during exhumation is expected to take place in the presence of fluid. A multichronological study of UHP eclogite from the Sulu orogen of China indicates zircon growth at 216 ± 3 Ma as well as mineral Sm‐Nd and Rb‐Sr reequilibration at 216 ± 5 Ma, which are uniformly younger than UHP metamorphic ages of 231 ± 4 to 227 ± 2 Ma as dated by the SHRIMP U‐Pb method for coesite‐bearing domains of zircon. O isotope reequilibration was achieved between the Sm‐Nd and Rb‐Sr isochron minerals, but Hf isotopes were not homogenized between different grains of zircon. The HP eclogite‐facies recrystallization is also evident from petrography. Thus this process occurred during exhumation with fluid availability from decompression dehydration of hydrous minerals and the exsolution of hydroxyl from nominally anhydrous minerals. This provides significant amounts of internally derived fluid for extensive retrogression within the UHP metamorphosed slabs. Based on available experimental diffusion data, the consistent reequilibration of U‐Pb, Sm‐Nd, Rb‐Sr and O isotope systems in the eclogite minerals demonstrates that time‐scale for the HP eclogite‐facies recrystallization is c. 1.9–9.3 Myr or less. This provides a maximum estimate for duration of the fluid‐facilitated process in the HP eclogite‐facies regime during the exhumation of deeply subducted continental crust.  相似文献   

青龙山榴辉岩的退变质显微结构及相关的物质迁移——南苏鲁榴辉岩退变质过程中流体活动的证据   总被引：3，自引：0，他引：3  

杨天南徐文华  陈方远 《岩石矿物学杂志》2004,23(3):236-252

对南苏鲁青龙山榴辉岩的扫描电子显微镜及光学显微镜的详细观察表明，其峰期矿物组合为石榴石 绿辉石Ⅰ 蓝晶石 金红石( 柯石英)，基本无含水矿物，并被第二期矿物(或组合)逐步替代，形成后成合晶或冠状体假像，即：绿辉石Ⅰ→绿辉石Ⅱ 钠长石 铁氧化物后成合晶，金红石→金红石 钛铁矿，蓝晶石→钠云母。第二期矿物又被第三期矿物(组合)替代：绿辉石Ⅱ( 钠长石 铁氧化物)→角闪石( 斜长石 铁氧化物)，石榴石→韭闪石 铁氧化物。绿帘石与石英是最晚期流体沿微裂隙活动的产物。详细的矿物成分分析及成分迁移估算结果显示，早期后成合晶的形成过程产生多余的Fe、Mg、Na，但消耗部分Ca、Si。产生的Mg、Fe迁移到石榴石边部，引发石榴石内部的(Mg，Fe)／Ca交换，在石榴石颗粒中形成向边部Ca降低、Mg和Fe升高的成分环带。交代产生的Ca被后成合晶消耗，而后成合晶产生的Na被替代蓝晶石的钠云母消耗。在退变质作用晚期，更多流体进入榴辉岩，引发流体渗滤交代反应，无水的早期后成合晶被含水后成合晶(角闪石 斜长石 铁氧化物)替代，同时在石榴石边部形成角闪石 少量铁氧化物反应边。成分迁移估算显示，上述两个过程的成分变化具有一定程度的耦合性。矿物反应曲线、THERMOCALC计算确定的P-T轨迹显示，青龙山榴辉岩的退变质过程主要发生在高压条件(低地温梯度)下，明显不同于北苏鲁地区榴辉岩。这种热演化特点的差异暗示南北苏鲁超高压变质块体可能具有不同的回返历史。  相似文献   

U–Pb zircon ages and Sr-Nd-Pb isotopic compositions for Permian–Jurassic plutons in the Ogcheon belt and Ryeongnam massif, Korea: Tectonic implications and correlation with the China Qinling–Dabie belt and the Japan Hida belt     

Cheong-Bin Kim  Ho-Wan Chang  Andrew Turek 《Island Arc》2003,12(4):366-382

Abstract The Ogcheon fold belt and the Ryeongnam massif in the Korean Peninsula are made up of Precambrian igneous and sedimentary rocks that have been metamorphosed, tectonically deformed and extensively intruded by mafic to felsic plutonic rocks of Permian to Jurassic age. In the present study, we report seven new U–Pb zircon ages and Sr‐Nd‐Pb isotopic data for Permian to Jurassic plutons in the Ogcheon belt and the Ryeongnam massif. In the Ogcheon belt, these are: the Cheongsan porphyritic granite (217 ± 3.1 My), the Baegrog foliated granodiorite (206.4 ± 3.6 My), the Sani granite (178.8 ± 2.9 My) and the Yeonggwang foliated granite (173.0 ± 1.7 My). For the Ryeongnam massif, we report on the Yeongdeog foliated granodiorite (252.2 ± 2.9 My), the Sancheong gabbro (203.8 ± 3.3 My) and the Baegseogri foliated granodiorite (177.8 ± 2.4 My). All of these ages are lower concordia intercepts; the upper concordia intercepts indicate derivation from a Precambrian protolith. Sr, Nd and Pb isotopes also reveal that much of the Permian–Jurassic (252–173 Ma) plutonism in Korea was generated by recycling of Precambrian rocks. These new ages, together with other published zircon ages indicate that the plutonism in the Ogcheon fold belt is coeval with that in the Ryeongnam massif, but based on the Sr‐Nd‐Pb isotopic evidence, they are not cogenetic. In addition, zircon ages provide information on the movement along the Honam shear zone, which cuts across the whole Korean Peninsula and along most of its length provides the boundary between the Ogcheon fold belt and the Ryeongnam massif. It has a prolonged history of movement and deformation and appears to have been active from the Precambrian through to the Mesozoic, from before 1924 Ma to at least 180 Ma. The Permian–Jurassic igneous and tectonic activity in Korea is a manifestation of the more extensive orogenic activities that affected the East Asian continent at that time. In China, ultra high‐pressure rocks of the Qinling–Dabie belt formed between 210 and 230 Ma as result of the collision between the South China block and the North China block. In central Japan, corresponding plutonic activity is dated as 175 to 231 Ma. The absence of ultra high‐pressure rocks in Korea and Japan precludes a simple extension of the Qinling–Dabie belt eastwards; however, the effects of the continental collision eastwards are apparent from the igneous and tectonic activity.  相似文献   

苏鲁地体超高压和退变质时代的厘定:来自片麻岩锆石微区SHRIMP U-Pb定年的证据   总被引：31，自引：16，他引：31       下载免费PDF全文

刘福来  许志琴  宋彪 《地质学报》2003,77(2):229-237

锆石微区矿物包体的激光拉曼和阴极发光测试以及相应的SHRIMP U-Pb定年结果表明,苏鲁地体片麻岩锆石微区记录了十分复杂的年代学信息。其中副片麻岩锆石核部记录了345～743 Ma的继承性锆石年龄,标志着原岩碎屑锆石来源的复杂性;含柯石英的锆石微区记录了220～234 Ma的超高压变质年龄;而含石英包体的边部则记录了202～219 Ma的退变质年龄。正片麻岩继承性锆石核部所记录的年龄为574～680 Ma,表明原岩锆石曾经历了部分Pb丢失,原岩的形成年龄应大于680 Ma;含柯石英锆石微区所记录的超高压变质年龄为224～242 Ma;而锆石边部所记录的退变质年龄为209～219 Ma。两类片麻岩锆石微区所隐藏的超高压变质和退变质年龄信息十分相近,平均值分别为229±4Ma和211±4Ma,标志着苏鲁地体超高压变质时代应为印支期,相应的构造抬升速率约5.6 km/Ma。该项成果不仅确定了苏鲁地体超高压变质和退变质时代,而且对于深入探讨苏鲁地体快速折返过程中的动力学机制有着重要的科学意义。  相似文献