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991.
准噶尔盆地西北缘车排子地区侏罗系物源及古水流分析 总被引:16,自引:8,他引:16
通过岩石岩屑组分分析、重矿物组分分析、倾角测井、地层厚度分析等方法,对准噶尔盆地西北缘车排子地区侏罗系进行物源及古水流方向分析。岩屑组分分析指示着大致的物源前进方向,重矿物分析明确了物源泄入的主要通道,倾角测井在单井点处对古流向有相当高的表现精度,但这三种方法均存在数据平面覆盖率较低和分布密度差异大的缺陷,而运用地震层位解释所得的地层等厚度图则可以在较大尺度上的二维平面内推测沉积时期的古地形,进而可以推测古流向,但它仅是一种间接预测方法,存在局部古流向预测精度较低的不足。文中综合各种方法,将直接预测方法的高精度和间接方法的高覆盖能力结合起来,对古流向作出较高精度的预测。在古流向研究的基础上建立了冲积扇-辫状河-河泛平原沉积体系的沉积相模式。该模式认为对于水流能量保持能力差的冲积扇,其古流向应该沿短轴陡坡降方向,即大致为SEE方向,而对于水流能量保持能力较强的辫状河来说,其古流向应该沿长轴缓坡降方向,即为SE甚至SSE方向。该模式的提出对于提高地震相-沉积相的转相精度具有一定的指导意义。 相似文献
992.
993.
Takamoto Okudaira Yasutaka Hayasaka Osamu Himeno Koichiro Watanabe Yasuhiro Sakurai Yukiko Ohtomo 《Island Arc》2001,10(2):98-115
Abstract The Ryoke metamorphic belt in south-west Japan consists mainly of I-type granitoids and associated low-pressure/high-temperature metamorphic rocks. In the Yanai district, it has been divided into three structural units: northern, central and southern units. In this study, we measured the Rb–Sr whole-rock–mineral isochron ages and fission-track ages of the gneissose granodiorite in the central structural unit. Four Rb–Sr ages fall in a range of ca 89–87 Ma. The fission-track ages of zircon and apatite are 68.9 ± 2.6 Ma and 57.4 ± 2.5 Ma (1σ error), respectively. Combining the newly obtained ages with previously reported (Th–)U–Pb ages from the same unit, thermochronologic study revealed two distinctive cooling stages; 1) a rapid cooling (> 40°C/Myr) for a period (~7 Myr) soon after the peak metamorphism (~ 95 Ma) and 2) the subsequent slow cooling stage (~ 5°C/Myr) after ca 88 Ma. The first rapid cooling stage corresponds to thermal relaxation of the intruded granodiorite magma and its associated metamorphic rocks, and to the uplift by a displacement along low-angle faults which initiated soon after the intrusion of the magma. Uplift by the later stage deformation having formed large-scale upright folds resulted in progress of the exhumation during the first stage. The average exhumation velocity of the stage is ≥ 2 mm/yr. During the second stage, the rocks were not accompanied by ductile deformation and were exhumed with the rate of 0.1–0.2 mm/yr. The difference in the exhumation velocity between the first and second cooling stages resulted from the difference in the thickness of the crust and in the activity of ductile deformation between the early and later stages of the orogenesis. 相似文献
994.
Kyanite-anthophyllite schist and southwest extension of the Dabie Mountains ultrahigh- to high-pressure belt 总被引:1,自引:1,他引:1
Abstract Kyanite-anthophyllite schist preserves the first record of high pressure in the amphibolite-facies unit of the SW Dabie Mountains, whereas ultrahigh- and high-pressure (UHP and HP) metamorphism has been well documented by the occurrence of coesite, diamond and mafic eclogite in the SE Dabie Mountains. Textural evidence indicates that minerals of the kyanite-anthophyllite schist formed mainly in two stages: (i) garnet + kyanite + antho-phyllite + rutile formed at pressure in excess of 1.2 GPa at T < 650°C; (ii) cordierite±staurolite formed by reaction of anthophyllite + kyanite at P < 0.5 GPa, T∼530°C. Plagioclase and ilmenite replaced garnet and rutile respectively during decompression. In a still later stage, secondary biotite recrystallized, accompanied by sillimanite replacing kyanite, and spinel replacing staurolite. The P-T information suggests that the amphibolite unit in the SW Dabie Mountains is part of the Triassic collision belt between the Sino-Korean and Yangtze cratons. The P-T paths of the UHP eclogite in the eastern Dabie Mountains and the HP kyanite-anthophyllite schist in the SW Dabie Mountains show similar decompression and equivalent late stage Barrovian-style metamorphism. Emplacement of voluminous granitoid at middle crustal levels between 134–118 Ma contributed to the development of the Barrovian-type metamorphism in the Dabie Mountains. 相似文献
995.
抚顺东部地区紫苏花岗质岩石形成于晚太古宙,以包体形式产于黑云长英质片麻岩中。许多特征均说明,它并非由紫苏北岗质岩浆直接结晶形成的,而是源岩在部分熔融与分凝过程中产生的残留相、后经麻粒岩相变质作用及构造变形改造所致的再造岩石。 相似文献
996.
湘中南区昔日的棋子桥期包含了:(1)茅冲组常滨岸碎屑岩;(2)沙河组近滨台盆泥灰岩相;(3)棋子桥组开阔台地灰岩相;(4)黄公塘组局限台地云岩相4个岩石地层单位类型,笔者研究表明,以上各岩相类型分别与沉各型磷矿、黄铁矿和砂岩铜矿以及层控制铅锌,黄铁矿床密切有关,因而对其进行探讨具有害观找矿指导意义。 相似文献
997.
根据西成矿田中泥盆统安家岔组和西汉水组具有多旋回性的特点,运用马尔科夫链分析法对其进行沉积相的划分,总结出中泥盆世处于海洋环境,并可划分为4个相带:陆缘碎屑岩相带、碳酸盐台地相带、台地边缘相带及浅海陆棚碎屑岩相带,进一步分为11个相和22个亚相。 相似文献
998.
滇东早奥陶世阿莫里坎砂岩相沉积 总被引:2,自引:2,他引:2
根据沉积特征、大化石、遗迹化石及微体化石等诸方面证据,认为滇东早奥陶世地层属于广泛分布于西南欧、北非、中东及纽芬兰东部的阿莫里坎砂岩相沉积。 相似文献
999.
An extended episode of early Mesoproterozoic metamorphic fluid flow in the Reynolds Range,central Australia* 总被引:1,自引:0,他引:1
ABSTRACT The products of metamorphic fluid flow are preserved in zones within the marbles and metamorphosed semipelites of the Upper Calcsilicate Unit in the granulite portion of the Late Palaeoproterozoic Reynolds Range Group, northern Arunta Block, central Australia. The zones of retrogression, characterized by minerals such as wollastonite, grossular and clinohumite, local resetting of oxygen isotopic compositions and local major element metasomatism, were channelways for water-rich fluids derived from granulite facies metapelites. U–Th–Pb isotopic ages measured by the SHRIMP ion microprobe on zircon and monazite from a granulite facies semipelite, an early semiconcordant aluminous quartz-rich fluid-flow segregation and a late discordant quartz-rich segregation record some of the extended thermal history of the area. Zircon cores from the semipelite show its likely protolith to be an igneous rock 1812 ± 11 Ma old, itself derived from a source containing zircon as old as 2.2 Ga. Low-Th/U overgrowths on the zircon grew during granulite facies metamorphism at 1594 ± 6 Ma. Monazite cooled to its blocking temperature at 1576 ± 8 Ma. Zircon cores from the semiconcordant segregation are dominantly >2.3 Ga old, indicating that the source of the fluids was not the particular metamorphosed semipelite studied. Two generations of low-Th/U overgrowths on the zircon give indistinguishable ages for the older and younger of 1589 ± 8 and 1582 ± 8 Ma, respectively. The monazite age is the same, 1576 ± 12 Ma. Zircon from the late discordant segregation gave 1568 ± 4 Ma. Fluid flow occurred for at least 18 ± 3 (σ) Ma and ended 26 ± 3 (σ) Ma after the peak of metamorphism, suggesting a very slow cooling rate of ~3°C Ma–1. The last regional high-grade metamorphism in the Reynolds Range occurred at ~1.6 Ga, not ~1.78 Ga as previously thought. The high-grade event at ~1.78 Ga is a separate event that affected only the basement to the Reynolds Range Group. 相似文献
1000.
南天山库勒湖变质岩系的构造变形特征 总被引:1,自引:0,他引:1
库勒湖变质岩系以断片形式出现于南天山造山带中,出露宽度约3.5km。主要由层状大理岩、黑云母石英片岩、糜棱岩化大理岩和碳质灰岩组成。黑云母石英片岩的Rb-Sr全岩等时线年龄为606.3±4.39Ma,薄层碳质岩中产晚元古代的疑源类化右和微古植物碎片,如黑色六面膜片Brocholaminarianigrita等。该套前寒武系发育有4期变形:第1期变形发生于606.3Ma左右,形成矿物的生长线理和片理、大理岩;第2期变形形成于370~335.51Ma,为变质岩系的主变形期,表现为拉伸线理、流劈理及韧性剪切带的形成;第3期变形成生于259Ma左右。以发育开阔褶皱,平卧、翻卷褶皱及拉伸线理的褶皱为特征;第4期变形主要为脆-塑性变形,可能发生于146Ma左右,发育有脆性道冲断层、破劈理和引曳褶皱。这4期变形反映了南天山造山带中的构造演化热事件。 相似文献