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Late Miocene movement within the Himalayan Main Central Thrust shear zone, Sikkim, north-east India 总被引：7，自引：0，他引：7
E. J. Catlos C. S. Dubey T. M. Harrison M. A. Edwards 《Journal of Metamorphic Geology》2004,22(3):207-226
In the Sikkim region of north‐east India, the Main Central Thrust (MCT) juxtaposes high‐grade gneisses of the Greater Himalayan Crystallines over lower‐grade slates, phyllites and schists of the Lesser Himalaya Formation. Inverted metamorphism characterizes rocks that immediately underlie the thrust, and the large‐scale South Tibet Detachment System (STDS) bounds the northern side of the Greater Himalayan Crystallines. In situ Th–Pb monazite ages indicate that the MCT shear zone in the Sikkim region was active at c. 22, 14–15 and 12–10 Ma, whereas zircon and monazite ages from a slightly deformed horizon of a High Himalayan leucogranite within the STDS suggest normal slip activity at c. 17 and 14–15 Ma. Although average monazite ages decrease towards structurally lower levels of the MCT shear zone, individual results do not follow a progressive younging pattern. Lesser Himalaya sample KBP1062A records monazite crystallization from 11.5 ± 0.2 to 12.2 ± 0.1 Ma and peak conditions of 610 ± 25 °C and 7.5 ± 0.5 kbar, whereas, in the MCT shear zone rock CHG14103, monazite crystallized from 13.8 ± 0.5 to 11.9 ± 0.3 Ma at lower grade conditions of 525 ± 25 °C and 6 ± 1 kbar. The P–T–t results indicate that the shear zone experienced a complicated slip history, and have implications for the understanding of mid‐crustal extrusion and the role of out‐of‐sequence thrusts in convergent plate tectonic settings. 相似文献
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西藏羊八井热田地热流体成因及演化的惰性气体制约 总被引：4，自引：5，他引：4
地热流体中惰性气体的相对丰度和同位素组成，不仅可以揭露热田的热源性质，而且还能够揭示深，浅层地热流体的内在联系和演化过程等。在西藏羊八井热田的地热气体中，已检测出大量的^4He组分，3He/^4He值是大气的0．087－0．259倍，表明深部地壳物质的局部熔融为热田提供能量，浅层地热流体的3He/4He 值自西北向东南呈降低趋势，与热储温度的变化相一致，反映出侧向运移时补充了更多的壳源氦，热田北区深层地热流体具有稍高的3He/4He值，是浅层地热流体的母源，气体中氪和氙的相对丰度具有大气降水成因的特征，结合现有的实际资料，建立了热田地热流体的概念模型。 相似文献
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The SE Pacific stock of Patagonian grenadier (Macruronus magellanicus) showed evidence of an abrupt reduction in recruitment after 2000. This drop exceeded expectations from changes in the spawning stock biomass (SSB), indicating a change in the stock-recruitment relationship (S-R). We evaluated whether variability in recruitment could be explained by concurrent changes in three environmental indices: sea-surface temperature anomaly (SSTA); southern oscillation index (SOI); and latitudinal position of the west wind drift bifurcation (WWDL). Continuous and discrete effects of these indices were tested as covariates in linear log-log and non-linear Ricker's S-R models. Discrete effects represented regime shifts detected in SSTA (1998), SOI (1998) and WWDL (1995). While SSTA was the only continuous variable found to be significant, the discrete 1998 regime shift supported the most informative model. The best Ricker's model considered a discrete intercept change in the same year: 1998. Although a spurious correlation between SSTA and S-R changes is possible, SSTA may be reflecting major physical or biological changes relevant to M. magellanicus juveniles in the SE Pacific. 相似文献
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Elizabeth J. Catlos Kathryn Huber Timothy A. Shin 《International Journal of Earth Sciences》2013,102(8):2175-2198
Located in the eastern Pontides of the Sakarya Zone in north-central Turkey, the Tokat Massif records the closure of both the Paleo-Tethyan (Karakaya Complex) and Neo-Tethyan ocean basins. Meta-igneous samples collected from the region were studied to determine their sources and ages. We find significant geochemical differences between metagabbros of the Karakaya and Neo-Tethyan units in terms of their trace elements: Neo-Tethyan rocks are consistent with generation in an island arc setting, whereas Karakaya assemblages were likely generated in an oceanic spreading-center environment. Karakaya metagabbros also contain glaucophane, consistent with subduction subsequent to formation. Small (2–50 μm) zircon and baddeleyite grains from four Karakaya metagabbros were dated in thin section using an ion microprobe. The results demonstrate the reliability of the method to directly constrain the tectonomagmatic history of these types of assemblages. The rocks yield Late Permian/Early Triassic 238U/206Pb crystallization ages of 258 ± 14 Ma (±1σ, zircon) and 254 ± 8 Ma (±1σ, baddeleyite) and an Early Cretaceous minimum metamorphic age of 137 ± 8 Ma (±1σ, zircon). Some zircon grains and baddeleyite grains with zircon overgrowths yield Early to Middle Jurassic ages. Here we present a model in which metamorphism and deformation in this region occurred during northward subduction and closure of a Paleo-Tethyan ocean basin and accretion of the Karakaya units to the Laurasian continental margin. This was followed by the onset of closure of the Neo-Tethys during the Campanian-Paleocene and accretion of island arc units to the Tokat region. 相似文献
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T. Mark Harrison Marty Grove Oscar M. Lovera E. J. Catlos Jessica D&#x;Andrea 《Journal of Asian Earth Sciences》1999,17(5-6)
The key to comprehending the tectonic evolution of the Himalaya is to understand the relationships between large-scale faulting, anatexis, and inverted metamorphism. The great number and variety of mechanisms that have been proposed to explain some or all of these features reflects the fact that fundamental constraints on such models have been slow in coming. Recent developments, most notably in geophysical imaging and geochronology, have been key to coalescing the results of varied Himalayan investigations into constraints with which to test proposed evolutionary models. These models fall into four general types: (1) the inverted metamorphic sequences within the footwall of the Himalayan thrust and adjacent hanging wall anatexis are spatially and temporally related by thrusting; (2) thrusting results from anatexis; (3) anatexis results from normal faulting; and (4) apparent inverted metamorphism in the footwall of the Himalayan thrust is produced by underplating of right-way-up metamorphic sequences. We review a number of models and find that many are inconsistent with available constraints, most notably the recognition that the exposed crustal melts and inverted metamorphic sequences not temporally related. The generalization that appears to best explain the observed distribution of crustal melts and inverted metamorphic sequences is that, due to specific petrological and tectonic controls, episodic magmatism and out-of-sequence thrusting developed during continuous convergence juxtaposing allochthonous igneous and metamorphic rocks. This coincidental juxtaposition has proven to be something of a red herring, unduly influencing attention toward finding a causal relationship between anatexis and inverted metamorphism. 相似文献
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准噶尔盆地南缘新生代构造特征及其与砂岩型铀矿成矿作用初析 总被引：5，自引：0，他引：5
准噶尔盆地南缘盆山结合部中新生界沉积巨厚,新生代变形强烈,是研究新盆山耦合的理想场所,也是我国砂岩型铀矿找矿的远景区段。本文在综合前人资料和野外观测分析基础上,根据新生代构造活动特征,将准噶尔盆地南缘划分为博格达山前和西部断褶带两个构造分区,博格达山前以强烈的逆冲推覆为特征,发育多条活动的逆冲推覆断裂; 乌鲁木齐以西至乌苏南的西部断褶带则发育三-四排的褶皱-逆冲断裂构造带。对采自博格达山前逆冲推覆断裂带内的方解石和断层泥,利用电子自旋共振测年手段,推测博格达山前的富康-吉木萨尔断裂带和北三台断裂带分别在0.7~1Ma和0.25Ma期间,经历了一期重要的逆冲推覆作用。结合盆地南缘砂岩型铀矿的展布规律及其成矿条件的分析,探讨了新生代构造运动对砂岩型铀矿成矿的控制作用,认为西部断褶带的第一排构造带具有较好的成矿前景,而博格达山前由于新生代构造活动强烈而相对成矿不利,为此提出了准噶尔盆地南缘砂岩型铀矿成矿“构造优先权”的构造控矿模式,进而指出了区域找矿的优选区段。 相似文献
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Elizabeth J. Catlos Enrique Reyes Michael Brookfield Daniel F. Stockli 《International Geology Review》2017,59(8):919-945
The Menghai batholith (Yunnan Province, China) is the southern extension of the ~370 km long Lincang granite body that syntectonically intruded the collisional zone between Gondwana (Baoshan block) and Laurasia (Simao block) terranes during closure of the Palaeo-Tethyan Ocean. Eight Menghai granodiorites were analysed across an ~45 km E–W transect from the pluton’s central region to eastern perimeter. Each rock was imaged in cathodoluminescence and geochemically analysed for major and trace elements. A minimum 30 zircons per sample were dated using laser ablation inductively coupled plasma–mass spectrometry. Samples are peraluminous to strongly peraluminous, magnesian, calcic or calc-alkalic granodiorites. Trace element suggest a high pressure (12–15 kbar) low clay source with >20–30% volume interaction with basalt. Crustal anatexis was likely related to post-collisional lithosphere delamination and upwelling of hot asthenosphere, forming large-volume melts. Zircon ages (207Pb–206Pb and 238U–206Pb) range from 3234 ± 42 to 171.7 ± 5.4 Ma (±2σ). Inherited zircon ages include the Palaeoarchaean–Neoarchaean (average 2938 ± 27 Ma, n = 8 ages), Lüliang (2254 ± 38 Ma, n = 7), Changcheng–Jixianian (1274 ± 47 Ma, n = 33), Qinbaikou (963 ± 29 Ma, n = 7), Nanhua (787 ± 24 Ma, n = 7), Sinian (595.4 ± 12.2 Ma, n = 14), Qilian (452.2 ± 8.7 Ma, n = 24) and Tienshan (358.9 ± 12.4 Ma, n = 5). The presence of these ages decrease from the batholith’s central portion (>50% ages) to eastern perimeter (2–16% ages), as the rocks appear progressively metamorphosed. The distribution of U/Th ratio suggests inherited zircons are Carboniferous (317.6 ± 5.7 Ma) and older and crystallization ages span the Permian to Early Jurassic. The average and youngest zircon age per sample decreases from the centre of the batholith to its eastern perimeter, from 226.8 ± 8.8 and 210.7 ± 3.3 to 211.8 ± 5.7 and 171.0 ± 5.4 Ma, respectively. If recorded by syntectonic zircon crystallization, collision and closure of a branch of the Palaeo-Tethyan Ocean occurred here over an ~100 million years time period from the Permian (281.0 ± 13.0 Ma) to Jurassic (171.5 ± 5.4 Ma). 相似文献
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The Menderes Massif experienced polyphase deformation, but distinguishing Pan-African events from Alpine tectono-metamorphic evolution, and discriminating Eocene–Oligocene shortening from recent extension remain controversial. To address this, monazite in garnet-bearing rocks from the massifs Gordes, Central, and Cine sections were dated in thin section (in situ) using the Th–Pb ion microprobe method. Cambro–Ordovician monazite inclusions in Cine and Central Menderes Massif garnets are ~450 m.y. older than matrix grains. Monazites in reaction with allanite from the Kuzey Detachment, which bounds the northern edge of the Central Menderes Massif, are 17±5 Ma and 4.5±1.0 Ma. The Pliocene result shows that dating of monazite can record the time of extension. The Kuzey Detachment might have exhumed rocks a lateral distance of ~53 km at a rapid rate of ~12 mm/year assuming the present ~20° ramp dip, Pliocene monazite crystallization at ~450°C, and a geothermal gradient of ~25°C/km. Assuming an angle of 60°, the rate decreases to ~5 mm/year, with the detachment surface at ~21 km depth in the Pliocene. Two Gordes Massif monazites show a similar allanite–monazite reaction relationship and are 29.6±1.1 Ma and 27.9±1.0 Ma, suggesting that the Cenozoic extension in the Gordes Massif, and possibly the entire Menderes Massif, might have begun in the Late Oligocene. 相似文献