Eclogite from the Subducted Lower Crust of the Yangtze Plate within the Luotian Dome and its Geological Implication
-
摘要: 在“罗田穹隆”中发现了下地壳俯冲成因榴辉岩.榴辉岩呈透镜状或板状产于含石榴子石条带状片麻岩中.新鲜的榴辉岩主要由石榴子石、绿辉石、金红石等组成, 含少量退变质的角闪石、斜长石、紫苏辉石、透辉石、(钛) 磁铁矿和石英等.研究区榴辉岩以保留早期麻粒岩相变质矿物残留体以及经受晚期麻粒岩相和角闪岩相退变为特征, 指示它们由扬子镁铁质下地壳麻粒岩相岩石俯冲到深部发生变质并形成榴辉岩, 然后折返至下地壳发生麻粒岩相退变, 由于麻粒岩相退变质阶段仅以后成合晶形式出现, 因而它们可能在下地壳停留时间不长, 就又进一步被构造抬升至中上地壳而发生角闪岩相退变.大别山造山带乃至扬子板块北缘现今缺乏厚层镁铁质下地壳, 它们也很少出露地表, 推测这些俯冲的镁铁质下地壳可能已拆离再循环进入地幔.从而为“罗田穹隆”的形成和演化以及大别山高压-超高压岩石的形成与折返机制等研究提供了关键性的岩石学证据Abstract: The eclogite produced from the subducted mafic lower crust of the Yangtze continental plate is a new finding within the Luotian dome in northern Dabie Mountains. The eclogites occur as lens in garnet-bearing banded gneisses. The mineral assemblage of the eclogite is garnet, omphacite, rutile and quartz; secondary minerals are hornblende, plagioclase, hypersthene, diopside and ilmenite. The eclogites from the Luotian dome have typical characteristics with relics of earlier hypersthene and plagioclase minerals of granulite-facies and latter overprinting of granulite-facies. No aqueous mineral formed during peak metamorphism may be related to their protoliths, which come from the lower crust. Petrologic evidence suggests that the eclogites studied were produced from the mafic lower crust of the Yangtze continent and suffered from granulite- and amphibolite-facies retrogressive metamorphism. At present, mafic rocks from the lower crust in the Dabie Mountains or even in the northern Yangtze plate have been scarce, which may be delaminated and recycled into underlying convecting mantle. These provide key petrologic evidence for formation and evolution of the Luotian dome, and formation and exhumation processes and uplift of high-grade metamorphic rocks such as eclogite in the northern Dabie Mountains.
-
Key words:
- eclogite /
- granulite-facies /
- lower crust /
- Luotian dome /
- northern Dabie Mountains
-
图 1 大别山造山带地质简图(据徐树桐等, 2002修改)
Ⅰ.变质复理石; Ⅱ-1.北部杂岩带; Ⅱ-2.苏家河变质带; Ⅲ.南部超高压变质带; Ⅳ.“冷”榴辉岩带; Ⅴ.大别杂岩; Ⅵ.宿松变质带
Fig. 1. Schematic geological map of the Dabie Mountains orogen
图 2 “罗田穹隆”中榴辉岩的显微照片
a.石榴子石中绿辉石包体及其两期退变后成合晶, 样品号LT10;b.石榴子石中绿辉石、金红石和石英包体, 样品号LT8-1; c.含针状石英出溶体的钠质透辉石有角闪石退变边, 样品号LT8-1;d.含针状石英出溶体的钠质透辉石有紫苏辉石退变边, 样品号LT8-1; e.石榴子石中早期紫苏辉石+斜长石矿物包体组合以及麻粒岩相(Hy2+Pl+Di) 和角闪岩相(Hb+Pl) 退变质矿物组合, 样品号LT3;f.含紫苏辉石+斜长石包体的锆石的背散射图像, 样品号LT10;Gt.石榴子石; Omp.绿辉石; Ru.金红石; Zir.锆石; Pl.斜长石; Qtz.石英; Hy1.早期紫苏辉石; Hy2.晚期紫苏辉石; Sy1.由晚期紫苏辉石+透辉石+斜长石组成的麻粒岩相退变后成合晶; Sy2.由角闪石+斜长石+磁铁矿组成的角闪岩相后成合晶.除e照片的视域宽度为0.2 mm外, 其余照片的视域宽度均为3 mm.
Fig. 2. Micro photographs of the eclogites from the Luotian dome in the Dabie Mountains
表 1 “罗田穹隆”中榴辉岩代表性矿物的电子探针分析
Table 1. Electro-probe analyses of major minerals from the eclogites in the Luotian dome
表 2 榴辉岩锆石中代表性矿物包体及一个具成分环带石榴子石的电子探针分析
Table 2. Electro-probe analyses of major mineral inclusions in zircon and a zoned garnet from the eclogites in the Luotian dome
-
[1] Blundy, J.D., Holland, T.J.B., 1990. Calcic amphibole equilibria and a new amphibole-plagioclase geothermometer. Contrib. Mineral. Petrol. , 104 : 208-224. doi: 10.1007/BF00306444 [2] Ellis, D.J., Green, D.H., 1979. An experimental study of the effect of Caupon garnet-clinopyroxene Fe-Mg exchange equilibration. Contrib. Mineral. Petrol. , 71: 13-22. doi: 10.1007/BF00371878 [3] Krogh, E. J., 1988. The garnet-clinopyroxene Fe-Mg geothermometer—A reinterpretation of existing experimental data. Contrib. Mineral. Petrol. , 99 : 44-48. doi: 10.1007/BF00399364 [4] Li, S. G., Huang, F., Zhou, H. Y., et al., 2001. U-Pb compositions of the ultrahigh pressure metamorphic (UHPM) rocks from Shuanghe and gneisses from northern Dabie zone in the Dabie Mountains, central China: Constraint on the exhumation mechanism of UHPM rocks. Chinese Science Bulletin, 31 : 977 -984 (in Chinese). [5] Li, S. G., Yang, W., 2002. Decoupling of surface and subsurface sutures in the Dabie orogen and a continent-collisional lithospheric-wedging model: Sr-Nd-Pb isotopic evidences of Mesozoic igneous rocks in eastern China. Chinese Science Bulletin, 47: 1898-1905 (in Chinese). doi: 10.1360/csb2002-47-24-1898 [6] Liu, Y. C., Li, S. G., Xu, S. T., et al., 2000. U-Pb zircon ages of the eclogite and to nalitic gneiss from the northern Dabie Mountains, China and multi-overgrowths of metamorphic zircons. Geological Journal of China Universities, 6(3): 417-423 (in Chinese with English abstract). [7] Liu, Y. C., Li, S. G., Xu, S. T., et al., 2001a. Sm-Nd dating of eclogites from northern Dabie Mountains and its constrains on the timing of granulite-facies retrogression. Geochimica, 30(1) : 79-87 (in Chinese with English abstract). [8] Liu, Y. C., Xu, S. T., Li, S. G., et al., 2001b. Distribution and metamorphic P-T condition of the eclogites from the mafic-ultramafic belt in the northern part of the Dabie Mountains. Acta Geologica Sinica, 75(3) : 385-395 (in Chinese with English abstract). [9] Liu, Y. C., Xu, S. T., Li, S. G., et al., 2000. Eclogites from the northern Dabie Mountains, eastern China: Geochemical characteristics, Sr-Nd isotopic compositions and tectonic implications. Science in China (Series D), 43 (suppl. ) : 178-188. [10] Raheim, A., Green, D. H., 1974. Experimental determination of the temperature and pressure dependence of the Fe-Mg partition coefficient for coexisting garnet and clinopyroxene. Contrib. Mineral. Petrol. , 48 : 179-203. doi: 10.1007/BF00383355 [11] Schmidt, M. W., 1990. Amphibole composition in tonalite as a function of pressure: An experimental calibration of the Alin-hornblende barometer. Contrib. Mineral. Petrol. , 110 : 304-310. [12] Tsai, ChinHo, Liu, J. G., 2000. Eclogite-facies relics and inferred ultrahigh-pressure metamorphism in the North Dabie complex, central China. American Mineralogist, 85: 1-8. doi: 10.2138/am-2000-0101 [13] Wei, C. J., Shan, Z., Zhang, L., et al., 1998. Determination and geological significance of the eclogites from the northern Dabie Mountains, central China. Chinese Science Bulletin, 43: 253-256. [14] Wells, R. A., 1977. Pyroxene thermometry in simple and complex systems. Contrib. Mineral. Petrol. , 62: 129-139. doi: 10.1007/BF00372872 [15] Wood, B. J., 1974. The solubility of alumina in orthopyroxene coexisting with garnet. Contrib. Mineral. Petrol. , 46 : 1-15. doi: 10.1007/BF00377989 [16] Wood, B. J., Banno, S., 1973. Garnet-orthopyroxene and orthopyroxene-clinopyroxene relationship in simple and complex systems. Contrib. Mineral. Petrol. , 42: 109-124. doi: 10.1007/BF00371501 [17] Xiao, Y., Hoefs, J., vandenKerkhof, A. M., et al., 2001. Geochemical constraints of the eclogite and granulite facies metamorphism as recognized in the Raobazhai complex from North Dabie Shan, China. J. Metamorphic Geol., 19: 3-19. doi: 10.1046/j.1525-1314.2001.00290.x [18] Xu, S. T., Liu, Y. C., Jiang, L. L., et al., 2002. Architecture and kinematics of the Dabie Mountains orogen. University of Science and Technology of China Press, Hefei, 1-133(in Chinese with English abstract). [19] Xu, S. T., Liu, Y. C., Su, W., et al., 2000. Discovery of the eclogite and its petrography in the northern Dabie Mountain. Chinese Science Bulletin, 45(3) : 273-278. doi: 10.1007/BF02884690 [20] Zhang, H. F., Gao, S., Zhang, B. R., et al., 2001. Pb isotopic study on crustal structure of Dabie Mountains, central China. Geochimica, 30(4) : 395-401 (in Chinese with English abstract). [21] Zhang, Z. M., Zhong, Z. Q., You, Z. D., et al., 2000. Granulite-facies retrograde metamorphism of garnet pyroxenite in Muzidian, northern Dabie Mountains. Earth Science―Journal of China University of Geosciences, 25(3) : 295-301 (in Chinese with English abstract). [22] 李曙光, 黄方, 周红英, 等, 2001. 大别山双河超高压变质岩及北部片麻岩的U -Pb同位素组成———对超高压岩石折返机制的制约. 科学通报, 31: 977-984. doi: 10.3321/j.issn:0023-074X.2001.12.002 [23] 李曙光, 杨蔚, 2002. 大别造山带深部地缝合线与地表地缝合线的解耦及大陆碰撞岩石圈楔入模型: 中生代幔源岩浆岩Sr-Nd-Pb同位素证据. 科学通报, 47: 1898-1905. doi: 10.3321/j.issn:0023-074X.2002.24.013 [24] 刘贻灿, 李曙光, 徐树桐, 等, 2000. 大别山北部榴辉岩和英云闪长质片麻岩锆石U -Pb年龄及多期变质增生. 高校地质学报, 6 (3): 417-423. doi: 10.3969/j.issn.1006-7493.2000.03.007 [25] 刘贻灿, 李曙光, 徐树桐, 等, 2001a. 大别山北部榴辉岩的Sm-Nd年龄测定及其对麻粒岩相退变质时间的制约. 地球化学, 30 (1): 79-87. https://www.cnki.com.cn/Article/CJFDTOTAL-DQHX200101009.htm [26] 刘贻灿, 徐树桐, 李曙光, 等, 2001b. 大别山北部镁铁-超镁铁质岩带中榴辉岩的分布与变质温压条件. 地质学报, 75 (3): 385-395. https://www.cnki.com.cn/Article/CJFDTOTAL-DZXE200103017.htm [27] 徐树桐, 刘贻灿, 江来利, 等, 2002. 大别山造山带的构造几何学和运动学. 合肥: 中国科学技术大学出版社, 1-133. [28] 张宏飞, 高山, 张本仁, 等, 2001. 大别山地壳结构的Pb同位素地球化学示踪. 地球化学, 30: 395-401. doi: 10.3321/j.issn:0379-1726.2001.04.014 [29] 张泽明, 钟增球, 游振东, 等, 2000. 北大别木子店石榴辉石岩的麻粒岩相退变质作用. 地球科学———中国地质大学学报, 25 (3): 295-301. https://www.cnki.com.cn/Article/CJFDTOTAL-DQKX200003014.htm -
下载:
点击查看大图
图(2) / 表(2)
计量
- 文章访问数: 3502
- HTML全文浏览量: 120
- PDF下载量: 12
- 被引次数: 0
