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51.
Oliver E. Jagoutz J.-P. Burg S. Hussain H. Dawood T. Pettke T. Iizuka S. Maruyama 《Contributions to Mineralogy and Petrology》2009,158(6):739-755
We present major and trace element analyses and U–Pb zircon intrusion ages from I-type granitoids sampled along a crustal
transect in the vicinity of the Chilas gabbronorite of the Kohistan paleo-arc. The aim is to investigate the roles of fractional
crystallization of mantle-derived melts and partial melting of lower crustal amphibolites to produce the magmatic upper crust
of an island arc. The analyzed samples span a wide calc-alkaline compositional range (diorite–tonalite–granodiorite–granite)
and have typical subduction-related trace element signatures. Their intrusion ages (75.1 ± 4.5–42.1 ± 4.4 Ma) are younger
than the Chilas Complex (~85 Ma). The new results indicate, in conjunction with literature data, that granitoid formation
in the Kohistan arc was a continuous rather than punctuated process. Field observations and the presence of inherited zircons
indicate the importance of assimilation processes. Field relations, petrographic observations and major and trace element
compositions of the granitoid indicate the importance of amphibole fractionation for their origin. It is concluded that granitoids
in the Kohistan arc are derivative products of mantle derived melts that evolved through amphibole-dominated fractionation
and intra crustal assimilation. 相似文献
52.
Hisashi Asanuma Yusuke Sawaki Shuhei Sakata Hideyuki Obayashi Kazue Suzuki Kouki Kitajima Takafumi Hirata Shigenori Maruyama 《Island Arc》2018,27(4)
Supracrustal rocks around the North Pole Dome area, Western Australia, provide valuable information regarding early records of the evolution of crustal processes, surface environments, and biosphere. Owing to the occurrence of the oldest known microfossils, the successions at the North Pole Dome area have attracted interest from many researchers. The Paleoarchean successions (Warrawoona Group) mainly comprise mafic‐ultramafic greenstones with intercalated cherts and felsic lavas. Age constraints on the sediments have been mainly based on zircon U–Pb geochronology. However, many zircon grains have suffered from metamictization and contain anomalously high contents of common Pb, which makes interpretation of the U–Pb data complicated. In order to provide more convincing chronological constraints, an U–Pb Concordia age is widely accepted as the best estimate. Most zircons separated from two adamellites also suffered from severe metamictization. In our analyses, less metamictized domains were selected using a pre‐ablation technique in conjunction with elemental mapping, and then their U–Pb isotopic compositions were determined with a laser ablation inductively coupled plasma mass spectrometry. Most analyzed domains contained certain amounts of common Pb (204Pb/206Pb > 0.000 1), whereas three and five U–Pb data points with less common Pb (204Pb/206Pb < 0.000 1) were obtained. These U–Pb datasets yielded U–Pb Concordia ages of ca 3 445 Ma and 3 454 Ma, respectively. These ages represent the timing of the adamellite intrusion, and constrain the minimum depositional age of the Warrawoona Group. In addition, a single xenocrystic zircon grain showed a 207Pb/206Pb age of ca 3 545 Ma, supporting the idea that the sialic basement of the Pilbara Craton existed prior to 3 500 Ma. The in situ U–Pb zircon dating combined with the pre‐ablation technique has the potentials to identify non‐metamictized parts and to yield precise and accurate geochronological data even from partially metamictized zircons. 相似文献
53.
54.
Ikawa Hiroki Kuwagata Tsuneo Haginoya Shigenori Ishigooka Yasushi Ono Keisuke Maruyama Atsushi Sakai Hidemitsu Fukuoka Minehiko Yoshimoto Mayumi Ishida Sachinobu Chen Charles P. Hasegawa Toshihiro Watanabe Tsutomu 《Boundary-Layer Meteorology》2021,179(3):447-476
Boundary-Layer Meteorology - Known as the heat-mitigation effect, irrigated rice-paddy fields distribute a large fraction of their received energy to the latent heat during the growing season. The... 相似文献
55.
Seiji Maruyama Keiji Takemura Takafumi Hirata Tohru Yamashita Tohru Danhara 《第四纪科学杂志》2020,35(1-2):66-80
The major and trace element concentrations of volcanic glass shards from visible tephra layers in the SG93 and SG06 cores from Lake Suigetsu, central Japan, were determined by femtosecond laser ablation–inductively coupled plasma–mass spectrometry. The glass-shard analyses, together with the petrographic properties of the tephra samples, allow the Suigetsu tephra layers to be broadly classified into tephras derived from calderas on Kyushu Island, and from Daisen and Sambe volcanoes in the Chugoku district of southwest Japan. The layers correlated with tephras from Kuju caldera and Daisen volcano, and with the younger Sambe tephras, have adakitic elemental features. A Suigetsu tephra sample correlated with the Sambe−Kisuki tephra based on petrographic properties has an elemental pattern similar to that of the Toya tephra from Hokkaido Island, northeast Japan. This match implies that tephras from northeast Japan, as well as Kyushu–Chugoku tephras, are possible correlatives of the Suigetsu tephra layers. Both petrographic properties and major–trace element data of volcanic glass shards are essential for robust tephra correlations, and hierarchical cluster analysis proved additionally useful in statistically evaluating relationships among the tephras. 相似文献
56.
The making and breaking of supercontinents: Some speculations based on superplumes, super downwelling and the role of tectosphere 总被引:13,自引:7,他引:6
The mechanisms of formation and disruption of supercontinents have been topics of debate. Based on the Y-shaped topology, we identify two major types of subduction zones on the globe: the Circum-Pacific subduction zone and the Tethyan subduction zone. We propose that the process of formation of supercontinents is controlled by super downwelling that develops through double-sided subduction zones as seen in the present day western Pacific, and also as endorsed by both geologic history and P-wave whole mantle tomography. The super-downwelling swallows all material like a black hole in the outer space, pulling together continents into a tight assembly. The fate of supercontinents is dictated by superplumes (super-upwelling) which break apart the continental assemblies. We evaluate the configuration of major supercontinents through Earth history and propose the tectonic framework leading to the future supercontinent Amasia 250 million years from present, with the present day Western Pacific region as its frontier. We propose that the tectosphere which functions as the buoyant keel of continental crust plays a crucial role in the supercontinental cycle, including continental fragmentation, dispersion and amalgamation. The continental crust is generally very thin, only about one tenth of the thickness of the tectosphere. If the rigidity and buoyancy is derived from the tectosphere, with the granitic upper crust playing only a negligible role, then supercontinent cycle may reflect the dispersion and amalgamation of the tectosphere. Therefore, supercontinent cycle may correspond to super-tectosphere cycle. 相似文献
57.
A speculation on the structure of the D″ layer: The growth of anti-crust at the core–mantle boundary through the subduction history of the Earth 总被引:1,自引:1,他引:0
The growth curve of the continental crust shows that large amounts of continental crust formed in the early part of the Earth history are missing. In order to test a hypothesis that the former crust was subducted to the deep mantle, we performed phase assemblage analysis in the systems of mid-oceanic ridge basalt (MORB), anorthosite, and tonalite–trondhjemite–granite (TTG) down to the core–mantle boundary (CMB) conditions. Results show that all these materials can be subducted to the CMB leading to the development of a compositional layering in the D″ layer. We speculate that there could be five layers of FeO-enriched melt from partial melting of MORB, MORB crust, anorthosite, TTG, and slab or mantle peridotite in ascending order. Although the polymorphic transformation of perovskite to post-perovskite in (Mg,Fe)SiO3 may explain the seismic discontinuity at the top of the D″ layer (D″ discontinuity), the effects of solid solution on the sharpness of the transformation suggest that the compositional layering is more plausible for the origin of the D″ discontinuity. The D″ layer can be an “anti-crust” made up mostly of TTG + anorthosite derived from the former continental crust. Tectonic style of the anti-crust at the CMB is similar to that at the surface. At both places, chemically distinct layers are density stratified and are also characterized by the processes of accretion, magmatism, and metasomatism. 相似文献
58.
A prograde pressure–temperature (P–T) path is estimated for pelitic schists from the latest Precambrian Kokchetav ultrahigh-pressure massif, Kazakhstan, using compositional zoning and mineral inclusions in coarse-grained and inclusion-rich garnets. Ti-bearing inclusions are abundant in garnet and display a zonal distribution. Ilmenite occurs in the inner-core, where most of it makes a composite inclusion with rutile, whereas monomineralic rutile occurs in the outer-core to mantle domains. In the rim region both ilmenite and rutile are present, although in small amounts. Application of the ilmenite-garnet thermometer yields a systematic temperature increase towards rim from 500 to 750 °C. The pressure-sensitive reaction: 3 Fe-Ilm (in Ilm) + Ky + 2 Qtz = 3 Rt + Alm (in Grt) yielded pressures of 1.2–1.3 GPa for the outer-core inclusions.A petrogenetic grid in the K2O–CaO–FeO–MgO–Al2O3–SiO2–H2O model system was used to estimate the equilibrium compositions of the garnet. The change of the grossular component along the model P–T path expected from the forward modelling is close to the observed compositional profile of the outer-core to rim domains. No constraint is available from thermobarometry in the inner-core; however, the forward modelling of garnet zoning provides information on the early stage of the P–T path during the garnet growth.The estimated P–T path is counter-clockwise in the prograde stage with a steep bend at around 700 °C and 1.2–1.5 GPa. This is similar to the metamorphic P–T gradient of the Kokchetav massif. This result contrasts markedly with the traditional clockwise P–T path in many collisional metamorphic terranes, and is regarded to represent a subduction geotherm at the Precambrian–Cambrian boundary. The P–T path proposed in this study also supports the models for the recovery of the “snowball Earth” from late-Proterozoic glaciation through effect of water in the solid Earth mantle. 相似文献
59.
60.
Izu-Bonin arc subduction under the Honshu island, Japan: Evidence from geological and seismological aspect 总被引:1,自引:1,他引:0
Shinji Yamamoto Junichi Nakajima Akira Hasegawa Shigenori Maruyama 《Gondwana Research》2009,16(3-4):572-580
The Izu-Bonin intra-oceanic arc with 20–35 km thick continental crust is being subducted under the Honshu, presumably since 17 Ma. Tomographic image clearly demonstrates that the whole Izu-Bonin arc is subducting under the Honshu arc. Geologic cross section and the thickness of continental crust do not support the accretion of thick crust in spite of the continued subduction over 17 Ma. 相似文献