排序方式： 共有17条查询结果，搜索用时 31 毫秒
1.
WANG Tao TONG Ying HONG Da-wei JAHN Bor-ming Kovaeh Victor P. HAN Bao-fu WANG Yan-bin 《矿物岩石地球化学通报》2008,27(Z1)
The Central Asia Orogenic Belt is the world's largest Phanerozoic accretionary orogen. The Altai orogen was key to understand the orogeny. Voluminous intrusions occur in the Chinese Altai orogen. 相似文献
2.
3.
4.
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
5.
JAHN BOR-MING; AUVRAY B.; BLAIS S.; CAPDEVILA R.; CORNICHET J.; VIDAL F.; HAMEURT J. 《Journal of Petrology》1980,21(2):201-244
Archean metavolcanic rocks from three greenstone belts (Suomussalmi,Kuhmo and Tipasjärvi) of eastern Finland have been subjectto a detailed geochemical study which leads to a discussionof their petrogenesis and the problem of compositional heterogeneityin the Archean mantle. Lithostratigraphically, the greenstonebelts are roughly divided into a lower and an upper volcanicsequence. Rocks of komatiitic and tholeiitic compositions arerestricted to the lower sequence, while andesitic tuffs, dacite-rhyodacitelavas and minor basalts of alkaline affinity occur in the uppersequence. All rocks from the greenstone belts have been subjectto regional metamorphism of the upper greenschist facies tothe lower garnet amphibolite facies. Consequently, the geochemicaldistinction of original magma types and the discussion of petrogenesishave relied heavily on the abundances of less mobile elements,such as TiO2, rare earth elements (REE), and some transitionmetals (e.g. Ni and Cr). Using all the possible discriminants of major element compositions,we have concluded that two general magmatic series that existin the lower volcanic sequence might be distinguished by theparameter of TiO2 content: the komatiitic series is characterizedby having TiO2 1.0 per cent and the tholeiitic series by 1.0per cent. The general series do not imply that a cogenetic relationshiplinked only by fractional crystallization exists in each series. Several magmatic types could be distinguished by their characteristicREE distribution patterns. In general, the komatiitic rocksshow flat HREE (heavy REE) and flat or depleted LREE (lightREE) patterns; the tholeiitic rocks show fractionated patternswith some degree of LREE enrichment, whilst the acidic rocksdemonstrate highly fractionated patterns with significant HREEdepletion. Model calculations indicate that: (1) the komatiiticand the tholeiitic series have no clear genetic relationship;(2) some basaltic komatiites (MgO < 12 per cent) could havebeen derived by crystal fractionation from a melt of peridotitickomatiite composition (MgO 30 per cent), but others requirevarious degrees of partial melting from the same or differentsource regions to account for their trace element abundances;(3) both partial melting and fractional crystallization haveinterplayed for the production of various rocks within the tholeiiticseries; (4) three different types of source materials are proposedfor all magmas from the lower volcanic sequence. All three typeshave the same initial HREE (about 2x chondrites) but differentLREE (from very depleted to 2x, flat) abundances; (5) volcanicrocks of the upper volcanic sequence must have originated atgreat depths where garnet remains in the residue after partialmelting and melt segregation. The recognition of the strongly LREE-depleted mantle sources,deduced from the REE patterns of peridotitic komatiites fromFinland, Canada and Rhodesia, may suggest that this depletionis a worldwide phenomenon, and that the Archean upper mantleis as heterogeneous in composition as the modern upper mantle.The causal effect of the depletion might be related to the generationof some contemporaneous LREE-enriched tholeiitic rocks, or morelikely, to contemporaneous or previous continental crust formingevents. 相似文献
6.
7.
JUTTA WINSEMANN JAHN J. HORNUNG JANINE MEINSEN ULRICH ASPRION ULRICH POLOM† CHRISTIAN BRANDES MICHAEL BUßMANN CHRISTIAN WEBER 《Sedimentology》2009,56(4):1041-1076
This paper presents a detailed analysis of the high‐resolution facies architecture of the Middle Pleistocene Porta subaqueous ice‐contact fan and delta complex, deposited on the northern margin of glacial Lake Weser (North‐west Germany). A total of 10 sand and gravel pits and more than 100 wells were examined to document the complex facies architecture. The field study was supplemented with a ground‐penetrating radar survey and a shear‐wave seismic survey. All collected sedimentological and geophysical data were integrated into a high‐resolution three‐dimensional geological model for reconstructing the spatial distribution of facies associations. The Porta subaqueous fan and delta complex consist of three fan bodies deposited on a flat lake‐bottom surface at the margin of a retreating ice lobe. The northernmost fan complex is up to 55 m thick, 6·2 km wide and 6·5 km long. The incipient fan deposition is characterized by high‐energy flows of a plane‐wall jet. Very coarse‐grained, highly scoured jet‐efflux deposits with an elongate plan shape indicate a high Froude number, probably >5. These jet‐efflux sediments are deposited in front of a large ～3·2 km long, up to 1·2 km wide, and up to 25 m deep flute‐like scour, indicating the most proximal erosion and bypass area of the jet that widens and deepens with distance downstream to the region of maximum turbulence (approximately five times the conduit diameter). Evidence for subsequent flow splitting is given by the presence of two marginal gravel fan lobes, deposited in front of 1·3 to 2·5 km long flute‐like scours, that are 0·8 to 1 km wide and 7 to 20 m deep. In response to continued aggradation, small jets developed at the periphery of these bar‐like deposits and filled in the low areas adjacent to the original superelevated regions, locally raising the depositional surface and characterized by large‐scale trough cross‐stratified sand and pebbly sand. The incision of an up to 1·2 km wide and up to 35 m deep channel into the evolving fan is attributed to a catastrophic drainage event, probably related to a lake outburst and lake‐level fall in the range of 40 to 60 m. At the mouth of this channel, highly scoured jet‐efflux deposits formed under hydraulic‐jump conditions during flow expansion. Subsequently, Gilbert‐type deltas formed on the truncated fan margin, recording a second lake‐level drop in the range of 30 to 40 m. These catastrophic lake‐level falls were probably caused by rapid ice‐lobe retreat controlled by the convex‐up bottom topography of the ice valley. 相似文献
8.
华北克拉通山西省晚石炭世基性岩墙成因：锆石U-Pb年龄、地球化学和Sr-Nd同位素证据 总被引：1，自引：1，他引：0
作为岩石圈伸展拉张背景侵位的特征岩石,基性岩墙群（煌斑岩、辉绿岩和辉绿玢岩等）地质和地球化学研究日益受到地质研究者的关注。研究显示,基性岩墙在全球范围主要分布在美国、加拿大、巴西、澳大利亚和中国等地区,且年代格架主要集中在前寒武纪时期（2.4Ga、2.1Ga、1.8Ga、1.4Ga、1.0Ga）。目前,国内中生代以来基性岩墙群主要出露于华北克拉通、华南、西藏和塔里木盆地。本研究基性岩墙来自山西省大同附近,对于该套岩墙,本文给出了锆石U-Pb定年、地球化学和Sr-Nd同位素证据。LA-ICP-MS锆石U-Pb年龄为293Ma,岩石具有变化较小的主元素变化特征（SiO2=50.78%~51.35%,TiO2=2.16%~2.32%,Al2O3=14.53%~15.08%,Fe2O3=12.42%~12.66%,MnO=0.13%~0.16%,MgO=5.14%~5.35%,CaO=7.93%~8.25%,Na2O=3.52%~3.78%,K2O=1.01%~1.14%和P2O5=0.24%~0.36%）。另外,基性岩墙富集轻稀土元素、大离子侵石元素（Ba,K和Sr）和高场强元素（Nb,Ta和Zr）,亏损Th、Pb和Ti。同时,基性岩墙具有相对一致的（87Sr/86Sr）i比值（0.70422~0.70423）,正的εNd（t）值（5.8~6.1）和变化较小的Nd模式年龄（tDM1=0.67~0.72Ga,tDM2=0.57~0.59Ga）。以上特征表明,基性岩墙来自亏损软流圈地幔的分布熔融作用,岩浆侵位过程中发生了橄榄石、辉石和含Ti相矿物的分离结晶作用,但没有受到地壳物质的混染作用影响。基性岩墙的成因上与华北克拉通和西伯利亚板块碰撞后的拉伸作用有密切联系。 相似文献
9.
桐柏高压变质地体:对桐柏-大别-苏鲁高压/超高压变质带构造框架和俯冲/折返机制的制约 总被引：3，自引：1，他引：2
桐柏造山带位于秦岭造山带和大别-苏鲁造山带之间,是揭示秦岭-桐柏-大别-苏鲁巨型造山带中各地质体之间构造关系及地质演化差异的关键地区。桐柏高压变质地体主要由两个高压岩片(I和II)及其北侧的构造混杂岩带和南侧的蓝片岩-绿片岩带构成。高压岩片I以北、南两条榴辉岩带为代表,构成桐柏山背形构造的两翼,其峰期变质条件分别为530~610℃、1.7~2.0GPa和460~560℃、1.3~1.9GPa。高压岩片II以桐柏杂岩中的变质岩包体为代表,其峰期变质条件推测在<700℃、>1.2GPa的榴辉岩相范围内,而退变质条件为660~700℃、0.80~1.03GPa。U-Pb、Lu-Hf、Rb-Sr和Ar-Ar同位素年代学研究表明,高压岩片I的峰期变质时代为255Ma,冷却至白云母封闭温度的时代为238Ma;而高压岩片II的主期变质作用发生在232~220Ma,作为桐柏杂岩主体的片麻状花岗岩则侵位于140Ma。这说明,高压岩片I和II分属于两个时代不同的俯冲/折返岩片,当高压岩片II被俯冲到地壳深处并经受高压变质时,其上覆的高压岩片I已经折返到中上地壳的水平。这一结果验证了在西大别、东大别和苏鲁地区提出的高压/超高压岩石的穿时(或差异)俯冲/折返模型,同时说明华南大陆地壳最早的俯冲发生在晚二叠世,这也代表华北与华南陆块之间从洋壳俯冲转化为陆壳俯冲的时间。基于桐柏杂岩与北大别杂岩的可比性,认为桐柏高压变质地体相对低温低压的变质环境以及超高压岩石的缺乏缘于华南陆块的俯冲深度向西逐渐变浅,而早白垩世的构造挤出造成了桐柏-大别高压/超高压变质带东宽西窄的构造格局。 相似文献
10.