Rongcheng Ultra-Calcic Garnet Pyroxenite: Its Geochemistry, Origin and Implications for Pre-UHP Tectonics in the Sulu UHP Metamorphic Belt
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摘要: 在苏鲁超高压变质带荣成蓝晶石榴辉岩中, 发现一具有特殊结构和地球化学特征的石榴辉石岩.该石榴辉石岩以包裹体的形式赋存于强烈退变的蓝晶石榴辉岩中.岩相学观测表明该岩石的主要结构为石榴石呈薄带、项链状相互连接的网状结构, 分割由辉石和石榴石、钛铁氧化物等出溶片晶组成的区域.全岩地球化学分析表明, 和邻近的蓝晶石榴辉岩相比, 该岩石具有(1) 相对低的SiO2 (42.5%~43.1%), 异常高的CaO (21.4%~21.9%)和CaO/Al2O3比值(1.46~1.64); (2) 较高的TiO2 (1.77%~1.89%)、V (359~419μg/g)、Nb (~8μg/g)、Y (17.7~23.1μg/g)和Zr (~150μg/g); (3) LREE富集和微弱的Eu负异常; (4) 较低的Cr、Ni和Co.上述地球化学特征表明荣成辉石岩的原岩形成于经过橄榄石分离结晶作用的超基性岩浆或经历了Na和K亏损过程的高钙基性岩浆.这2种过程都要求较高的温压条件, 压力 > 15×105kPa, 温度 > 1300 ℃, 这和荣成辉石岩的原岩的初始稳定条件的温压估算相一致.该研究结果表明在苏鲁超高压变质带中, 一些超高压变质岩的母岩形成于高温部分熔融或岩浆演化作用, 明显不同于大多数榴辉岩或片麻岩的原岩形成环境.Abstract: We report an unusual garnet pyroxenite, as a nodule enclosed within kyanite eclogites from Rongcheng, northeastern Sulu UHP metamorphic belt. Apart from its unusual texture, high degrees of various minerals (garnet, titanite, and Fe-Ti oxides) and solid exsolution within garnet or clinopyroxene, this nodule has unusual major and trace element geochemistry as shown by (1) low SiO2 (42.5%-43.1%), extremely high CaO (21.4%-21.9%), and high CaO/Al2O3 ratio (1.46-1.64); (2) high TiO2 (1.77%-1.89%), Zr (to 150 μg/g), V (359-419 μg/g), Nb (to 8 μg/g), and Y (17.7-23.1 μg/g) contents; (3) LREE-enriched, and nepherine normative; and (4) low Cr, Ni, and Co. Previous study on the mineral chemistry and texture relationships between different generations of minerals has suggested that it was formed as a cumulative clinopyroxene magacryst with high Ca-tschermakite component (31%-34%) from a gabbroic magma at p= (15-22) ×105 kPa, and T > 1 100 ℃. Major and trace element geochemistry on this nodule and its host kyanite eclogite suggest that the precursor of the Rongcheng pyroxenite was derived either from an ultramafic magma highly fractionated by accumulation of olivines or from an ultra-calcic basic magma that had lost some K2O and Na2O. No matter which was responsible for the formation of its precursor, both require a melting event and magma differentiation to occur at a pressure and temperature greater than 15×10-5 kPa and 1 300 ℃, respectively. This contribution suggests that protoliths for some of the eclogites within the Sulu UHP metamorphic belt formed in a tectonic environment distinct from those of Neoproterozoic age.
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Key words:
- garnet pyroxenite /
- kyanite eclogite /
- REE /
- Sulu UHP metamorphic belt
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图 1 荣成石榴辉石的采样点附近的地质简图(a)和分析样品的位置关系图(b)
Fig. 1. Geological map showing the location of Rongcheng garnet pyroxenite (a) and the sample locations within the pyroxenite (b) (LR11-4, LR11-7, and RM21-1 to 5)
图 2 荣成石榴辉石岩的主要元素(a)和微量元素(b) 随位置的变化关系
Fig. 2. Diagrams showing selected major (a) and trace element (b) compositions as a function of location within the Rongcheng garnet pyroxenite
图 3 山东荣成蓝晶石榴辉岩和石榴辉石岩的稀土分布模式
Fig. 3. Chondrite normalized REE distribution pattern for the Rongcheng garnet pyroxenite and kyanite eclogites
图 4 大别-苏鲁超高压变质带的石榴辉石岩的CaO含量(a)和CaO/Al2O3 (b) 与MgO之间的关系
数据来源: 大别山据Zhang et al. (2000)、Jahn et al. (2003); 山东日照据Zhang and Liou (2003)、Yang (2006); 荣成-1据Jahn et al. (1996)、Jahn (1998); Sierra Nevada据Ducea and Saleeby (1996)、Douge et al. (1988); 高钙-玄武岩据Medard et al. (2004); 荣成-2据本项研究
Fig. 4. Covariation diagram of CaO (a), CaO/Al2O3 (b) versus MgO in garnet pyroxenites from the Dabie-Sulu UHP metamorphic belt, and Sierra Necada. The island arc type ultra-calcic basaltic lavas are also shown for comparison
表 1 山东荣成石榴辉石岩及附近蓝晶石榴辉岩的主要元素(%)和微量元素(μg/g) 地球化学成分
Table 1. Major (%) and trace element (μg/g) compositions for the Rongcheng garnet pyroxenites and kyanite eclogites
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Bath, M.G., Rudnick, R. L., Horn, I., et al., 2001. Geochemistry of xenolithic eclogites from West Africa, Part Ⅰ : A link between low MgO eclogites and Archean crust formation. Geochimica et Cosmochimica Acta, 65: 1499-1527. doi: 10.1016/S0016-7037(00)00626-8 Barth, M.G., Rudnick, R. L., Horn, I., et al., 2002. Geochemistry of xenolithic eclogites from West Africa, Part Ⅱ : Origins of the high MgO eclogites. Geochim. Cosmochim. Acta, 66: 4325-4345. doi: 10.1016/S0016-7037(02)01004-9 Brenan, J.M., Watson, E.B., 1991. Partitioning of trace elements between olivine and aqueous fluids at high P-Tconditions: Implications for the effect of fluid composition on trace element transport. Earth and Planetary Science Letters, 107: 672-688. doi: 10.1016/0012-821X(91)90110-4 Brenan, J.M., 1993. Partitioning of fluorine and chlorine between apatite and aqueous fluids at high pressure and temperature: Implications for the F and Cl content of high P-T fluids. Earth and Planetary Science Letters, 117: 251-263. doi: 10.1016/0012-821X(93)90131-R Carr, M. J., Rose, W.I., 1984. CENTAM: A data base of Central American volcanic rocks. Journal of Volcanology and Geothermal Research, 33: 239-240. Della-Pasqua, F.N., Varne, R., 1997. Primitive ankaramitic magmas in volcanic arcs: A melt inclusion approach. Canadian Mineralogist, 35: 291-312. Dodge, F.C.W., Lockwood, J.P., Calk, L.C., 1988. Fragments of mantle and crust from beneath the Sierra Nevada batholith: Xenoliths in volcanic pipe near Big Creek, California. GSA Bulletin, 100: 938-947. doi: 10.1130/0016-7606(1988)100<0938:FOTMAC>2.3.CO;2 Ducea, M.N., Saleeby, J.B., 1996. Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry. J. Geophys. Res. , 101: 8229-8244. doi: 10.1029/95JB03452 Green, D. H., Schmidt, M. W., Hibberson, W. O., 2004. Island-arc ankaramites: Primitive melts from fluxed refractory lherzolitic mantle. Journal of Petrology, 45: 391-403. doi: 10.1093/petrology/egg101 Harte, B., Gurney, J. J., 1975. Evolution of clinopyroxene and garnet in an eclogite nodule from the Roberts Victor kimberlite pipe, South Africa. Physics and Chemistry of the Earth, 9: 367-387. doi: 10.1016/0079-1946(75)90029-4 Jahn, B.M., Cornichet, J., Cong, B., et al., 1996. Ultrahigh εNd eclogites from an UHP metamorphic terrane of China. Chemical Geology, 127: 61-79. doi: 10.1016/0009-2541(95)00108-5 Jahn, B.M., Fan, Q., Yang, J.J., et al., 2003. Petrogenesis of the Maowu pyroxenite-eclogite body from the UHP metamorphic terrane of Dabieshan: Chemical and isotopic constraints. Lithos, 70: 243-267. doi: 10.1016/S0024-4937(03)00101-4 Jahn, B.M., 1998. Geochemical and isotopic characteristics of UHP eclogites of the Dabie orogen: Implications for continental subduction and collisional tectonics. In: Hacker, B., Liou, J.G., eds., When continents collide: Geodynamics and geochemistry of ultrahigh-pressure rocks. Kluwer Academic Publishers, Dordrecht, the Netherlands, 203-239. Kamenetsky, V.S., Crawford, A.J., Eggins, S., et al., 1997. Phenocrysts and melt inclusion chemistry of near-axis seamounts, Valu Fa Ridge, Lau Basin: Insight into mantle wedge melting and the addition of subduction components. Earth Planet. Sci. Lett. , 151: 205-223. doi: 10.1016/S0012-821X(97)81849-3 Kamenetsky, V.S., Eggins, S.M., Crawford, A.J., et al., 1998. Calcic melt inclusions in primitive olivine at 43°N: Evidence for melt-rock reaction/melting involving clinopyroxene-rich lithologies during MORB generation. Earth Planet. Sci. Lett. , 160: 115-132. doi: 10.1016/S0012-821X(98)00090-9 Kato, T., Enami, M., Zhai, M., 1997. Ultra-high-pressure(UHP)marble and eclogite in the Su-Lu UHP terrane, eastern China. Journal of Metamorphic Geology, 15: 169-182. doi: 10.1111/j.1525-1314.1997.00013.x Lee, C.T.A., Leeman, W.P., Canil, D., et al., 2005. Similar V/Sc systematics in MORB and Arc basalts: Implication for the oxygen fugacities of their mantle source region. Journal of Petrology, 46: 2313-2336. doi: 10.1093/petrology/egi056 Liang, F.H., Zeng, L.S., Chen, J., et al., 2006. Discovery of apatite with copper-bearing pyrrhotite exsolution in an eclogite from Rongcheng, eastern Shandong Province. Acta Petrologica Sinica, 22(2): 433-438(in Chinese with English abstract). Liu, F.L., Xu, Z.Q., Katayama, I., et al., 2001. Mineral in clusions in zircon of para- and orthogneiss from prepilot drillhole CCSD-PP1, Chinese Continental Scientific Drilling Project. Lithos, 59: 199-215. doi: 10.1016/S0024-4937(01)00064-0 McKay, G.A., 1992. Partitioning of rare earth elements between major silicate minerals and basaltic melts. Review in Mineralogy, 21: 45-77. Massonne, H. J., Bautsch, H. J., 2002. An unusual garnet pyroxenite from the Granulitgebirge, Germany: Origin in the transition zone(> 400 km depths)or in a shallower upper mantle region. International Geological Review, 44: 779-796. doi: 10.2747/0020-6814.44.9.779 Medard, E., Schmidt, M. W., Schiano, P., 2004. Liquidus surfaces of ultracalcic primitive melts: Formation conditions and sources. Contrib. Mineral. Petrol. , 148: 201-215. doi: 10.1007/s00410-004-0591-1 Meen, J.K., Eggler, D.H., Ayers, J.C., 1989. Experimental evidence for very low solubility of rare earth elements in CO2-rich fluids at mantle conditions. Nature, 340: 301-303. doi: 10.1038/340301a0 Nakamura, D., Hirajima, T., 2000. Granulite-facies overprinting of ultrahigh pressure metamorphic rocks, northeastern Su-Lu region, eastern China. Journal of Petrology, 41: 563-582. doi: 10.1093/petrology/41.4.563 Schiano, P., Eiler, J.M., Hutcheon, I.D., et al., 2000. Primitive CaO-rich, silica-undersaturated melts in island arcs: Evidence for the involvement of clinopyroxene-rich lithologies in the petrogenesis of arc magmas. Geochemistry, Geophysics, Geosystems 1, Paper number 1999G000032. Schmidt, M.W., Green, D.H., Hibberson, W.O., 2004. Ultracalcic magmas generated from Ca-depleted mantle: An experimental study on the origin of ankaramites. Journal of Petrology, 45: 531-554. doi: 10.1093/petrology/egg093 Sigurdsson, I. A., Steinthorsson, S., Gronvold, K., 2000. Calcium-rich melt inclusions in Cr-spinels from Borgarhraun, northern Iceland. Earth and Planetary Science Letters, 183: 15-26. doi: 10.1016/S0012-821X(00)00269-7 Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: Implication for mantle composition and processes. In: Saunders, A., Norry, M., eds., Magatism in the ocean basins. Geological Society London Special Publication, 42: 313-345. Tang, J., Zheng, Y.F., Wu, Y.B., et al., 2004. Zircon U-Pb ages and oxygen isotopes of high-grade metamorphic rocks in the eastern part of the Shandong Peninsula. Acta Perologica Sinica, 20(5): 1039-1062(in Chinese with English abstract). Wallis, S.R., Ishiwatari, A., Hirajima, T., et al., 1997. Occurrence and field relationships of ultrahigh pressure metagranitoid and coesite eclogite in the Sulu terrane, eastern China. Journal of the Geological Society, London, 154: 45-54. doi: 10.1144/gsjgs.154.1.0045 Wang, Q., Ishiwatari, A., Zhao, Z., et al., 1994. Coesite bearing granulite retrograded from eclogite in Weihai, eastern China. European Journal of Mineralogy, 5: 141-152. Yang, J.J., 1991. Eclogites, garnet, pyroxenites and related ultrabasics in Shandong and north Jiangsu of east China. Geological Publishing House, Beijing, 26-52(in Chinese). Yang, J.J., 2006. Ca-rich garnet-clinopyroxene rocks at Hujialin in the Su-Lu terrane(eastern China): Deeply subducted arc cumulates. Journal of Petrology(in press). Yang, J.S., Xu, Z.Q., Wu, C.L., et al., 2002. SHRIMP U-Pb dating on coesite-bearing zircon: Evidence for Indosinian ultrahigh-pressure metamorphism in Sulu, east China. Acta Geological Sinica, 76: 354-371(in Chinese with English abstract). Yang, T.N., Zeng, L.S., Liou, J.G., 2005. Mineral evolution of a garnet-pyroxenite nodule within eclogite, eastern Sulu ultrahigh-pressure metamorphic terrane, East China. Journal of Metamorphic Geology, 23: 667-680. doi: 10.1111/j.1525-1314.2005.00602.x Yang, T.N., Xu, Z.Q., Leech, M., 2004. Mass balance during retrogression of eclogite-facies minerals in the Rongcheng eclogite, eastern Sulu ultrahigh-pressure terrane, China. American Mineralogist, 89: 1525-1532. doi: 10.2138/am-2004-1022 Ye, K., Cong, B.L., Ye, D.N., 2000. The possible subduction of continental material to depths greater than 200km. Nature, 407: 734-736. doi: 10.1038/35037566 Zeng, L.S., Zhang, Z.M., Liu, F.L., et al., 2006. V/Sc as a new tool to fingerprint the magmatic differentiation processes in the formation of the protoliths for the CCSD eclogites. Acta Petrologica Sinica, 22(7)(in Chinese with English abstract, in press). Zhang, R.Y., Liou, J.G., Yang, J.S., et al., 2000. Petro chemical constrains for dual origin of garnet peridotites from the Dabie-Sulu UHP terrane, eastern-central China. Journal of Metamorphic Geology, 18: 149-166. doi: 10.1046/j.1525-1314.2000.00248.x Zhang, R.Y., Liou, J.G., 2003. Clinopyroxenite from the Sulu ultrahigh-pressure terrene, eastern China: Origin and evolution of garnet exsolution in clinopyroxene. American Mineralogist, 88: 1591-1600. doi: 10.2138/am-2003-1022 Zhang, R. Y., Liou, J. G., Ernst, W. G., 1995. Ultrahigh pressure metamorphism and decompressional P-T paths of eclogites and country rocks from Weihai, eastern China. The Island Arc, 4: 293-309. doi: 10.1111/j.1440-1738.1995.tb00151.x Zhang, R.Y., Zhai, S.M., Fei, Y.W., et al., 2003. Titanium solubility in coexisting garnet and clinopyroxene at very high pressure: The significance of exsolved rutile in garnet. Earth and Planetary Science Letters, 216: 591-601. doi: 10.1016/S0012-821X(03)00551-X 梁凤华, 曾令森, 陈晶, 等, 2006. 胶东荣成榴辉岩中含铜磁黄铁矿出溶结构的磷灰石的发现及其意义. 岩石学报, 22(2): 433-438. https://www.cnki.com.cn/Article/CJFDTOTAL-YSXB200602015.htm 唐俊, 郑永飞, 吴元保, 等, 2004. 胶东地块东部变质岩锆石U-Pb定年和氧同位素研究. 岩石学报, 20(5): 1039-1062. https://www.cnki.com.cn/Article/CJFDTOTAL-YSXB200405004.htm 杨建军, 1991. 中国东部山东和江苏北部的榴辉岩、辉石岩和有关的超基性岩. 北京: 地质出版社, 26-52. 杨经绥, 许志琴, 吴才来, 等, 2002. 含柯石英锆石的SHRIMP U-Pb定年: 胶东印支期超高压变质作用的证据. 地质学报, 76(3): 354-371. doi: 10.3321/j.issn:0001-5717.2002.03.008 曾令森, 张泽明, 刘福来, 等, 2006. V/Sc比值——可透视榴辉岩变质作用并指示基性岩浆作用的一种新的地球化学工具: 在CCSD主孔榴辉岩中的应用. 岩石学报, 22(7)(待刊). -
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