U–Pb ages of zircons from Mesozoic intrusive rocks in the Yanbian area, Jilin Province, NE China: Transition of the Paleo-Asian oceanic regime to the circum-Pacific tectonic regime
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Early Triassic
Diorite
Pacific Plate
Continental Margin
Northern continental margin basins in South China Sea are located among Pacific Plate,Indian Plate and Philippine Sea Plate;these plates had different impacts on these basins.The study of the evolution of the three plates and paleo-South China Sea showed that the stress environment had been changed in the late Cretaceous in northern continental margin area.The stress environment was compressional in the Lower Cretaceous and had been changed into extension in the Late Cretaceous.The cause of extensional environment was different since the Late Cretaceous.Extensional environment was caused by stress relaxation of eogenetic orogen in South China continental margin area,by southern subduction of paleo-South China Sea and by rollback of the subducting Pacific slab from the late Cretaceous to the Paleocene,and the early rift basin began to form in continental margin in northern South China Sea.Continued reduction of western subduction rate of Pacific slab and southern subduction of Paleo-South China Sea formed the same stress environment in the Eocene and rift basins formed continually.Southern movement of mantle materials and southern subduction of Paleo-South China Sea formed the extensional environment from the Oligocene to the Early-Miocene and seafloor spreading of South China Sea began in the Early Oligocene.The three plates affected these north continental margin basins in South China Sea together since the Middle Miocene.
Continental Margin
Seafloor Spreading
Pacific Plate
Passive margin
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P. Comin-Chiaramonti and C. B. Gomes (Eds). Alkaline Magmatism in Central-Eastern Paraguay; Relationships with Coeval Magmatism in Brazil. São Paulo (Editora da Universidade de São Paulo) 1996, 458 pp. ISBN 85-314-0326-6. - Volume 62 Issue 5
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Tables S1–S6.
Hang
Pacific Plate
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在北方 Qinling 早古生代的 granitoids 标明日期的锆石 U-Pb 产出 500， 452 和 420 妈的三座年龄山峰。他们能时间地被相关与对在 ca 的超离频压力的变态高压。500 妈，后退在 ca 的 granulite 外形变态。在 ca 的 450 妈和角闪岩外形变态。420 妈分别地。花岗石的 magmatism 的第一个事件被认为源于大陆人碰撞，而 magmatism 的第二和第三个事件被归因于外壳的高举。从高压、超离频压力的变形岩石与地区性的地质的背景和新结果结合了， ca。500 妈 magmatism 作为包括北方中国 Craton 的南部的边缘的在在南方 Qinling microcontinent 和北方 Qinling 带之间的 accretionary 楔的沉积岩石的部分融化的结果被解释。ca。450 妈集中的 magmatism 被归功于到脱水融化深深地以响应平板 breakoff 的变厚的条件的 subducted 大陆人外壳，和在 ca 的最后的 magmatism。420 妈作为到扩展的从收缩的在构造转变期间的部分融化的产品被解释。
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Many geologists have been interested in the Okinawa Trough due to its unique tectonic environment.The magmatism is regarded as one of the key questions in the Okinawa Trough.The advances associated with the magmatism in the trough have been overviewed,including the studies about the characters of the magmatic sources,the processes of the magma melting and evolution and the regularities of melting.Based on these,the difficult questions on this field have been presented and a new idea that using the method of U-series disequilibria to study the magmatism in Okinawa Trough has been brought forward.Meanwhile,some research directions about the study of magmatism in the Okinawa Trough should be paid much attention to in the future,e.g.① the influence of the Philippine subduction slab on the magmatism processes,②the implications of the subducting sediment for the magma,③the controlling factors of the magma melting,④ the link between the magmatism and the seafloor hydrothermal activity.
Trough (economics)
Seafloor Spreading
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Synopis A number of diorite complexes occur within the Channel Islands region, notably on Jersey, Alderney, and particularly Guernsey. Much of northern Guernsey is made up of the largest of these complexes (fig. S1), the Bordeaux diorite. In the north-western part of this diorite, around Chouet, a complicated association of plutonic rocks occurs. Although the field relationships in this area are sometimes difficult to interpret—this is often the case in diorite complexes—three separate groups of rocks may be distinguished within the association: a diorite group; a granodiorite group; and an inhomogeneous suite of rocks (fig. S2). The widespread diorite group consists predominantly of an even-grained diorite, which is relatively homogeneous but which occasionally grades into an acicular diorite, the latter often containing pods and veins of appinite. The granodiorite group is the least common, occurring as bodies which are interpreted as intrusive sheets and bosses within the even-grained diorite, but occurring as angular blocks within the inhomogeneous suite of rocks. The granodiorite invariably contains rounded diorite xenoliths. The inhomogeneous suite consists of a variety of rocks from patchy, dark diorite, through quartz diorite to tonalite. Commonly, these rock types are intimately associated, often showing gradational contacts with each other and frequently with the more basic portions occurring as ‘xenolithic’ material within the more acidic portions. At contacts between the inhomogeneous suite and the even-grained diorite certain features (e.g. lobate margins and pipe-like structures) indicate that the diorite must have been close to its solidus temperature at the time of emplacement of the inhomogeneous suite. The field relationships between the three groups are interpreted as indicating that the diorite group was emplaced first, followed by the granodiorite group, with both of these clearly pre-dating the inhomogeneous suite. Fifty-nine specimens, chosen to give a representative sample of each of the three rock groups, have been analysed for major, minor, and a selection of trace elements and thirteen of these specimens have been analysed for REE . The chemistry of the analysed rocks confirms the division into three groups, with each group showing distinctive characteristics. Furthermore, chemical plots (e.g. Al 2 O 3 , P 2 O 5 , Cr, and Ni v. SiO 2 ) show discontinuities and areas of overlap between each group which cannot be explained within the constraints of a single genetic model relating the three groups to each other. This argument is particularly strong for the relationship between the diorite group, which spans the range 50 to 59% SiO 2 , and the inhomogeneous suite, spanning the range 53 to 68% SiO 2 . In the area of overlap (53 to 59% SiO 2 ) the two groups are geochemically different. Therefore, for a variety of reasons, including emplacement order, the geochemical characteristics of the groups and the lithological inhomogeneity which is associated only with the chemically intermediate members of the association (the inhomogeneous suite), three quite different and genetically unrelated liquids are required to generate the three groups of rocks. The even-grained diorite shows chemical variation (e.g. with increasing SiO 2 , decreasing Al 2 O 3 , MgO, CaO, Sc, V, Cr, and Ni, and increasing Na 2 O, La, Nd, and Y) consistent with amphibole + plagioclase fractionation up to 55% SiO 2 . At 55% SiO 2 several elements show a change of slope (e.g. FeO + Fe 2 O 3 , TiO 2 , Rb, Ba, and Zr) indicating the introduction of biotite as a fractionating phase. Increasing total REE content with increasing SiO 2 throughout the even-grained diorite supports the contention that amphibole is an important fractionating phase. The higher TiO 2 , P 2 O 5 , Sr, La, Ce, Nd, and Y contents and negligible Cr and Ni contents of the acicular diorite suggest an origin by delayed crystallization of volatile-enriched portions of the diorite group magma. The granodiorite group shows little geochemical variation. Members of this group contain detectable amounts of Cr and Ni, unlike virtually all members of the inhomogeneous suite. For this reason, and because of the field relationships, the granodiorite is considered to be genetically unrelated to members of the inhomogeneous suite and a separate liquid is thus required for its genesis. This liquid may have been the fractionated derivative of some other magma (though if this is so the ‘parent’ is entirely unrepresented at the present erosion level) or it may represent a direct crustal melt. Diorite xenoliths within the granodiorite are chemically similar to the even-grained diorite. Despite the lithological complexity of the inhomogeneous suite, its geochemical unity is clearly established in that, for instance, virtually none of the members of the suite (including even the most SiO 2 -poor) contain detectable Cr and Ni. Moreover, geochemical variation within the group is rational (with the possible exceptions of Sr, Zr, and Ba) and may be explained in terms of a crystal fractionation model. However, the fractionation must have acted on a liquid itself unrelated to either the diorite or granodiorite group magmas. An additional complication is that later derivative liquids intrude into and partly digest earlier-formed semi-solids of the suite to produce much of the observed inhomogeneity. The phases which have controlled fractionation within the suite include plagioclase (established petrographically as well as geochemically) and hornblende. The role of apatite is uncertain. The fractionation of hornblende is particularly useful in explaining the change in REE contents within the inhomogeneous suite. Total REE contents increase from the dark diorite to the quartz diorite, but decrease from the quartz diorite to the tonalite with concomitant relative HREE depletion. This is taken to be a reflection of the changing hornblende/liquid partition coefficients for REE with increasing SiO 2 , which are less than one for liquids of basaltic and andesitic composition but greater than one for liquids of dacitic composition.
Diorite
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The igneous petrology of an area near the Long Lake gold mine, Sudbury district. Ontario, is described. The area lies at the contact of a region of folded sediments and one of granite-gneiss. Two rock types, Keweenawan diabase and Long Lake diorite, resulted from the injection of basic magma into the sediments. Later a large granitic batholith invaded the region. Reaction between the magma and the quartz-rich sediments is postulated to account for a border phase of very quartz-rich tonalite. The Long Lake diorite grades into a more acidic phase and this phase is explained as due to emanations from the batholith affecting the diorite and adding silica and soda.
Diorite
Batholith
Quartz monzonite
Country rock
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