云南中旬地区两个斑岩铜矿容矿斑岩的地球化学特征——以雪鸡坪和普朗斑岩铜矿床为例

位于义敦岛弧南端的中甸岛弧已成为我国又一重要的斑岩铜矿产地，其中雪鸡坪中型斑岩铜矿床产于西斑岩带，普朗超大型斑岩铜矿床产于东斑岩带。详细对比研究了这两个斑岩铜矿床矿床地质，含矿斑岩的岩石化学、地球化学以及年代学等特征，认为：①两者的元素组成非常相似，如稀土配分形式均为轻稀土元素富集型，亏损重稀土元素和Y，富集Sr、K、Rb、Ba、Th等大离子亲石元素，亏损Nb、Ta、Zr、Hf、置等高场强元素，显示了埃达克岩的地球化学特征，表明它们可能是俯冲的甘孜-理塘洋壳部分熔融的产物，并受到地壳物质的混染；②中甸岛弧的结构及时空演化保持了义敦岛弧的共性，发育完整的沟-弧-盆体系，其中东斑岩带属于外弧，而西斑岩带属于内弧，中斑岩带及零星分布的属都蛇绿混杂岩产于弧间盆地。     

New insight into the crust and upper mantle structure under Alaska

To better understand the seismic structure of the subducting Pacific plate under Alaska, we determined the three-dimensional P-wave velocity structure to a depth of approximately 200 km beneath Alaska using 438,146 P-wave arrival times from 10,900 earthquakes. In this study an irregular grid parameterization was adopted to express the velocity structure under Alaska. The number of grid nodes increases from north to south in the study area so that the spacing between grid nodes is approximately the same in the longitude direction. Our results suggest that the subducting Pacific slab under Alaska can be divided into three different parts based on its geometry and velocity structure. The western part has features similar to those in other subduction zones. In the central part a thick low-velocity zone is imaged at the top of the subducting Pacific slab beneath north of the Kenai Peninsula, which is believed to be most likely the oceanic crust plus an overlying serpentinized zone and the coupled Yakutat terrane subducted with the Pacific slab. In the eastern part, significant high-velocity anomalies are visible to 60–90 km depth, suggesting that the Pacific slab has only subducted down to that depth.     

基于GIS的长输管道定量线路优化研究

长输管道的线路优化是寻求最优路径的过程。以管段间影响线路路由的诸多因素数据为研究对象，建立基于知识库的“管道建设成本模型”，利用基于栅格场的GIS空间分析实现“管道定量线路优化”。     

Rise and fall of the Eastern Great Indonesian arc recorded by the assembly, dispersion and accretion of the Banda Terrane, Timor

New age, petrochemical and structural data indicate that the Banda Terrane is a remnant of a Jurassic to Eocene arc–trench system that formed the eastern part of the Great Indonesian arc. The arc system rifted apart during Eocene to Miocene supra-subduction zone sea floor spreading, which dispersed ridges of Banda Terrane embedded in young oceanic crust as far south as Sumba and Timor. In Timor the Banda Terrane is well exposed as high-level thrust sheets that were detached from the edge of the Banda Sea upper plate and uplifted by collision with the passive margin of NW Australia. The thrust sheets contain a distinctive assemblage of medium grade metamorphic rocks overlain by Cretaceous to Miocene forearc basin deposits. New U/Pb age data presented here indicate igneous zircons are less than 162 Ma with a cluster of ages at 83 Ma and 35 Ma. ⁴⁰Ar/³⁹Ar plateau ages of various mineral phases from metamorphic units all cluster at between 32–38 Ma. These data yield a cooling curve that shows exhumation from around 550 °C to the surface between 36–28 Ma. After this time there is no evidence of metamorphism of the Banda Terrane, including its accretion to the edge of the Australian continental margin during the Pliocene. These data link the Banda Terrane to similar rocks and events documented throughout the eastern edge of the Sunda Shelf and the Banda Sea floor.     

Long-term changes in distribution and chemistry of middle Miocene to Quaternary volcanism in the Chokai-Kurikoma area across the Northeast Japan Arc

Abstract To understand the characteristics of long‐term spatial and temporal variation in volcanism within a volcanic arc undergoing constant subduction since the cessation of back‐arc opening, a detailed investigation of middle Miocene to Quaternary volcanism was carried out within the Chokai‐Kurikoma area of the Northeast Japan Arc. This study involved a survey of available literature, with new K–Ar and fission track dating, and chemical analyses. Since 14 Ma, volcanism has occurred within the Chokai‐Kurikoma area in specific areas with a ‘branch‐like’ pattern, showing an east–west trend. This is in marked contrast to the widespread distribution of volcanism with a north–south trend in the 20–14 Ma period. The east–west‐ trending ‘branches’ are characterized by regular intervals (50–100 km) of magmatism along the arc. These branches since 14 Ma are remarkably discrepant to the general northwest–southeast or north‐northeast–south‐southwest direction of the crustal structures that have controlled Neogene to Quaternary tectonic movements in northeast Japan. In addition, evidence indicating clustering and focusing of volcanism into smaller regions since 14 Ma was verified. Comparison of the distribution and chemistry of volcanic rocks for three principal volcanic stages (11–8, 6–3 and 2–0 Ma) revealed that widely but sparsely distributed volcanic rocks had almost the same level of alkali and incompatible element concentrations throughout the area (with the exception of Zr) in the 11–8 Ma stage. However, through the 6–3 Ma stage to the 2–0 Ma stage, the concentration level in the back‐arc cluster increased, while that in the volcanic front cluster remained almost constant. Therefore, the degree of partial melting has decreased, most likely with a simultaneous increase in the depth of magma segregation within the back‐arc zone, whereas within the volcanic front zone, the conditions of magma generation have changed little over the three stages. In conclusion, the evolution of the thermal structure within the mantle wedge across the arc since 14 Ma has reduced the extent of ascending mantle diapirs into smaller fields. This has resulted in the tendency for the distribution of volcanism to become localized and concentrated into more specific areas in the form of clusters from the late Miocene to Quaternary.     

Sequence stratigraphy, structural style, and age of deformation of the Malaita accretionary prism (Solomon arc–Ontong Java Plateau convergent zone)

Possibilities for the fate of oceanic plateaus at subduction zones range from complete subduction of the plateau beneath the arc to complete plateau–arc accretion and resulting collisional orogenesis. Deep penetration, multi-channel seismic reflection (MCS) data from the northern flank of the Solomon Islands reveal the sequence stratigraphy, structural style, and age of deformation of an accretionary prism formed during late Neogene (5–0 Ma) convergence between the 33-km-thick crust of the Ontong Java oceanic plateau and the 15-km-thick Solomon island arc. Correlation of MCS data with the satellite-derived, free-air gravity field defines the tectonic boundaries and internal structure of the 800-km-long, 140-km-wide accretionary prism. We name this prism the “Malaita accretionary prism” or “MAP” after Malaita, the largest and best-studied island exposure of the accretionary prism in the Solomon Islands. MCS data, gravity data, and stratigraphic correlations to islands and ODP sites on the Ontong Java Plateau (OJP) reveal that the offshore MAP is composed of folded and thrust faulted sedimentary rocks and upper crystalline crust offscraped from the Solomon the subducting Ontong Java Plateau (Pacific plate) and transferred to the Solomon arc. With the exception of an upper, sequence of Quaternary? island-derived terrigenous sediments, the deformed stratigraphy of the MAP is identical to that of the incoming Ontong Java Plateau in the North Solomon trench.We divide the MAP into four distinct, folded and thrust fault-bounded structural domains interpreted to have formed by diachronous, southeast-to-northwest, and highly oblique entry of the Ontong Java Plateau into a former trench now marked by the Kia–Kaipito–Korigole (KKK) left-lateral strike-slip fault zone along the suture between the Solomon arc and the MAP. The structural style within each of the four structural domains consists of a parallel series of three to four fault propagation folds formed by the seaward propagation of thrust faults roughly parallel to sub-horizontal layering in the upper crystalline part of the OJP. Thrust fault offsets, spacing between thrusts, and the amplitude of related fault propagation folds progressively decrease to the west in the youngest zone of active MAP accretion (Choiseul structural domain). Surficial faulting and folding in the most recently deformed, northwestern domain show active accretion of greater than 1 km of sedimentary rock and 6 km, or about 20%, of the upper crystalline part of the OJP. The eastern MAP (Malaita and Ulawa domains) underwent an earlier, similar style of partial plateau accretion. A pre-late Pliocene age of accretion (3.4 Ma) is constrained by an onshore and offshore major angular unconformity separating Pliocene reefal limestone and conglomerate from folded and faulted pelagic limestone of Cretaceous to Miocene age. The lower 80% of the Ontong Java Plateau crust beneath the MAP thrust decollement appears unfaulted and unfolded and is continuous with a southwestward-dipping subducted slab of presumably denser plateau material beneath most of the MAP, and is traceable to depths >200 km in the mantle beneath the Solomon Islands.     

The copper–gold and gold deposits of the Neoproterozoic Mara Rosa magmatic arc, central Brazil

Mineral exploration in the Neoproterozoic Goiás Magmatic Arc, central Brazil, dates back to the beginning of the 1970s. The Goiás Magmatic Arc extends for more than 1000 km in the western and northern parts of Goiás, into Tocantins, and disappears under the Phanerozoic Parnaíba Basin. Two main areas of Neoproterozoic juvenile crust, the Arenópolis and the Mara Rosa arcs, are identified. They lie in the southern and northern sectors of the Goiás Arc, respectively, and are relatively well studied.The Goiás Magmatic Arc dominantly comprises tonalitic/dioritic orthogneisses and narrow NNE-striking volcano-sedimentary belts. Recent U–Pb zircon data indicate crystallization of the tonalite protoliths in two main episodes: the older between ca. 890 and 790 Ma and the younger at 670–600 Ma. Nd isotopic data indicate the very primitive nature of the original magmas, with T_DM model ages mostly within the interval between 0.9 and 1.0 Ga and _Nd(T) values between +3.0 and +4.6. In the Chapada–Mara Rosa area, the supracrustal rocks form three individual NNE belts, known as the eastern, central and western belts, separated from each other by metatonalites/metadiorites.Gold and Cu–Au deposits of the Mara Rosa area occur in four main associations: (i) Au–Ag–Ba (e.g., Zacarias), which are interpreted as stratiform, disseminated volcanogenic deposits, (ii) Cu–Au (e.g., Chapada) which has been interpreted either as volcanogenic or as a porphyry-type deposit, (iii) Au-only deposits (e.g., Posse), interpreted as an epigenetic disseminated deposit controlled by a mesozonal shear zone and (iv) Au–Cu–Bi (e.g., the Mundinho occurrence), which are considered as vein-type deposits controlled by magnetite-rich diorites.The gold and Cu–Au deposits located within the Goiás Magmatic Arc can be spatially and temporally related to the magmatic evolution of a collisional belt or, in other words, to an orogenic gold deposit model. These models are based on the continuous evolution of collisional plates, which can be subdivided into four stages with distinct magmatic characteristics: (i) subduction stage, (ii) syntectonic collisional magmatism stage, (iii) post-tectonic collisional magmatism stage and (iv) post-orogenic extension stage.     

视距归弧法放样圆曲线

本文介绍了视距归弧法放样圆曲线，并对精度作了分析，说明了该方法的应用范围及优点。     

Focal mechanism and modern stress field along the Burmese Arc and its vicinity

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The 1957 great Aleutian earthquake

The 9 March 1957 Aleutian earthquake has been estimated as the third largest earthquake this century and has the longest aftershock zone of any earthquake ever recorded—1200 km. However, due to a lack of high-quality seismic data, the actual source parameters for this earthquake have been poorly determined. We have examined all the available waveform data to determine the seismic moment, rupture area, and slip distribution. These data include body, surface and tsunami waves. Using body waves, we have estimated the duration of significant moment release as 4 min. From surface wave analysis, we have determined that significant moment release occurred only in the western half of the aftershock zone and that the best estimate for the seismic moment is 50–100×10²⁰ Nm. Using the tsunami waveforms, we estimated the source area of the 1957 tsunami by backward propagation. The tsunami source area is smaller than the aftershock zone and is about 850 km long. This does not include the Unalaska Island area in the eastern end of the aftershock zone, making this area a possible seismic gap and a possible site of a future large or great earthquake. We also inverted the tsunami waveforms for the slip distribution. Slip on the 1957 rupture zone was highest in the western half near the epicenter. Little slip occurred in the eastern half. The moment is estimated as 88×10²⁰ Nm, orM _w =8.6, making it the seventh largest earthquake during the period 1900 to 1993. We also compare the 1957 earthquake to the 1986 Andreanof Islands earthquake, which occurred within a segment of the 1957 rupture area. The 1986 earthquake represents a rerupturing of the major 1957 asperity.