Abstract
Petrographic investigations and electron microprobe analyses have been performed on a rare aggregate of clinopyroxene megacrysts collected from Cenozoic basalts in Yinfengling, Leizhou Peninsula of South China. The aggregate, composed of several clinopyroxene megacrysts, shows abundant exsolution lamellae of garnet (Grt) and orthopyroxene (Opx), and granular texture. Cr- and Ti-poor spinels are also present in this sample. They occur predominantly as Sp–Opx–Grt clusters (Cr# = 0.025–0.034) at the interspace between different megacrysts, and subordinately as bleb-shaped (Cr# = 0.025–0.034) or thin-lamella crystals (Cr# = 0.006–0.021) in clinopyroxene. Three different assemblages of exsolution are identified, namely (1) Sp (high Cr/Al) and Opx; (2) Grt–Opx; (3) Sp (low Cr/Al) and Opx. In addition, some garnets were likely developed as response to breakdown of the high-Cr/Al Sp. The homogeneous compositions in all constituent minerals and the good agreement between calculated Cpx/Grt partition coefficients (K d’s) for trace elements and reference data strongly suggest a chemical equilibrium among coexisting minerals, probably attained by diffusion after the exsolution. Thermobarometric calculation based on exsolved assemblage yields a temperature of 900 ± 30°C and a pressure of 12 ± 2.2 kbar, corresponding to the present-day thermal gradient in the region. Much higher P–T estimates (T = 1,210 ± 30°C, P = 16.2 ± 3.5 kbar) are obtained for the reconstructed composition of cpx prior to exsolution. The contrast in thermal state before and after the exsolution might reflect the thermal evolution of the lithosphere beneath South China during the Cenozoic.
Similar content being viewed by others
References
Aoki K, Fujimaki H, Kitamura M (1980) Exsolved garnet-bearing pyroxene megacrysts from some south African kimberlites. Lithos 13:269–279
Becker H (1997) Petrological constraints on the cooling history of high-temperature garnet peridotite massifs in lower Austria. Contrib Mineral Petrol 128:272–286
Bertrand P, Mercier J-CC (1985) The mutual solubility of coexisting ortho- and clinopyroxene: toward an absolute geothermometer for natural system? Earth Planet Sci Lett 76:109–122
Brey GP, Köhler T (1990) Geothermobarometry in four-phase lherzolites: II. New thermobarometers, and practical assessment of existing thermobarometers. J Petrol 31:1353–1378
Buseck PR, Nord GL, Veblen DR (1980) Subsolidus phenomena in pyroxenes. In: Prewitt CT (ed) Reviews in mineralogy, pyroxenesm. vol 7. Mineralogical Society of America, Washington, pp 117–211
Clarke DB, Pe-Piper GG (1982) Multiply exsolved clinopyroxene megacrysts from the Frank Smith mine, Cape province, South Africa. Lithos 16:75–84
Desnoyers C (1975) Exsolutions d’amphibole, de grenat et de spinelle dans les pyroxenes de roches ultrabasiques: periodtites et pyroxenolites. Bull Soc Fr Min Cristal 98:65–77
Ellis DJ, Green DH (1979) An experimental study of the effect of Ca upon garnet-clinopyroxene Fe-Mg exchange equilibria. Contrib Mineral Petrol 71:13–22
Fan WM, Menzies MA (1992) The composition of lithospheric mantle in rifting volcanism environment: geochemical evidence from Cenozoic basaltic rocks from Leiqiong area. In: Liu RX (ed) Geochronology and geochemistry of Cenozoic volcanic rocks in China. Seismic Press, Beijing, pp 320–329 (in Chinese)
Field SW, Haggerty SE (1994) Symplectites in upper mantle peridotites: development and implications for the growth of subsolidus garnet, pyroxene and spinel. Contrib Mineral Petrol 118:138–156
Green DH (1966) The origin of “eclogites” from Salt Lake crater, Hawaii. Earth Planet Sci Lett 1:414–420
Griffin WL, Wass SY, Hollis JD (1984) Ultramaffic xenoliths from Bullenmerri and Gnotuk maars, Victoria, Australia: petrology of a sub-continental crust-mantle transition. J Petrol 25:53–87
Harte B, Gurney JJG (1975) Evolution of clinopyroxene and garnet in an eclogite nodule from the Roberts Victor kimberlite pipe, South Africa. Phys Chem Earth 9:367–387
Harte B, Kirkley MB (1997) Partitioning of trace elements between clinopyroxene and garnet: data from mantle eclogites. Chem Geol 136:1–24
He LJ, Wang KL, Xion LP, Wang JY (2001) Heat flow and thermal history of the South China Sea. Phys Earth Planet Inter 126:211–220
Herzberg C (1978) Pyroxene geothermometry and geobarometry: experimental and thermodynamic evaluation of some subsolidus phases relations involving clinopyroxenes in the system CaO-MgO-Al2O3-SiO2. Geochim Cosmochim Acta 42:945–957
Ho KS, Chen JC, Juang WS (2000) Geochronology and geochemistry of late Cenozoic basalts from the Leiqiong area, souther China. J Asian Earth Sci 18:307–324
Jerde EA, Taylor LA, Crozaz G, Sobolev NV (1993) Exsolution of garnet within clinopyroxene of mantle eclogites: major and trace-element chemistry. Contrib Mineral Petrol 114:148–159
Johnson KTM (1994) Experimental cpx/and garnet/melt partitioning of REE and other trace elements at high pressures: petrogenetic implications. Mineral Mag 58A:454–455
Klemme S, O’Neill HStC (2000) The near-solidus transition from garnet lherzolite to spinel lherzolite. Contrib Mineral Petrol 138:237–248
Krogh EJ (1988) The garnet-clinopyroxene Fe-Mg geothermometer—a reinterpretation of existing experimental data. Contrib Mineral Petrol 99:44–48
Lappin MA, Dawson BD (1975) Two Roberts-Victor cumulate eclogites and their re-equilibration. Phys Chem Earth 9:351–365
Lin CY, Huang XL, Xu YG, Shi LB, Chen XD (2003) Thermal structure and rheology of upper mantle beneath Leizhou Peninsula, Guangdong Province, China. J Trop Oceanogr 22:49–62 (in Chinese with English abstract)
Liu XC, Zhao ZR, Zha Y, Chen J, Liu XH (2003) Pyroxene exsolution in mafic granulites from the Grove Mountains, east Antarctiva: constraints on Pan-African metamorphic conditions. Eur J Mineral 15:55–65
McCallister RH (1978) The coarsening kinetics associated with exsolution in an iron-free clinopyroxene. Contrib Mineral Petrol 65:327–331
Mercier J-CC (1980) Single-pyroxene thermobarometry. Tectonophysics 70:1–37
Mercier J-CC, Nicolas A (1975) Textures and fabrics of upper-mantle peridotites as illustrated by xenoliths from basalts. J Petrol 16:454–487
Nickel HG, Green DH (1985) Empirical geothermobarometry for garnet peridotites and implications for the nature of the lithosphere, kimberlites and diamonds. Earth Planet Sci Lett 73:158–170
Nimis P, Taylor WR (2000) Single clinopyroxene thermobarometry for garnet peridotites. Part I: calibration and testing of a Cr-in-Cpx barometer and an enstatite-in-Cpx thermometer. Contrib Mineral Petrol 139:541–554
Nimis P (1999) Clinopyroxene geobarometry of magmatic rocks. Part 2. Structural geobarometers for basic to acid, tholeiitic and mildly alkaline magmatic systems. Contrib Mineral Petrol 135:62–74
Qi Q, Taylor LA, Zhou XM (1995) Petrology and geochemistry of mantle peridotite xenoliths from SE China. J Petrol 36:55–79
Reiche M, Bautsch H-J (1985) Electron microscopical study of garnet exsolution in orthopyroxene. Phys Chem Mineral 12:29–33
Sautter V, Hart B (1988) Diffusion gradients in an eclogite xenolith from the Roberts Victor kimberlite pipe: 1. Mechanism and evolution of garnet exsolution in Al2O3-rich clinopyroxene. J Petrol 29:1325–1352
Sautter V, Hart B (1990) Diffusion gradients in an eclogite xenolith from the Roberts Victor kimberlite pipe: (2) kinetics and implications for petrogenesis. Contrib Mineral Petrol 105:637–649
Schmickler B, Jacob DE, Foley SF (2004) Eclogite xenoliths from the Kuruman kimberlites, South Africa: geochemical fingerprinting of deep subduction and cumulate processes. Lithos 75:173–207
Sen G, Jones RE (1988) Exsolved silicate and oxide phases from clinopyroxenes in a single Hawaiian xenolith: implications for oxidation state of the Hawaiian upper mantle. Geology 16:69–72
Sun S-s, McDonough WF (1989) Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders AD, Norry MJ (eds) Magmatism in the Ocean Basins. Geological Society, London, pp 313–345
Walter M, Katsura T, Kubo A, Shinmei T, Nishikawa O, Ito E, Lesher C, Funakoshi K (2002) Spinel-garnet lherzolite transition in system CaO-MgO-Al2O3-SiO2 revisited: an in situ X-ray study. Geochim Cosmochim Acta 66:2109–2121
Weinbruch S, Styrsa V, Müller WF (2003) Exsolution and coarsening in iron-free clinopyroxene during isothermal annealing. Geochim Cosmochim Acta 67:5071–5082
Wells PRA (1977) Pyroxene thermometry in simple and complex systems. Contrib Mineral Petrol 62:129–139
Wood BJ (1974) Solubility of alumina in orthopyroxene coexisting with garnet. Contrib Mineral Petrol 46:1–15
Xu WL, Liu XC, Wang QH, Lin JQ, Wang DY (2004) Garnet exsolution in garnet clinopyroxenite and clinopyroxenite xenoliths in early Cretaceous intrusions from the Xuzhou region, eastern China. Mineral Mag 68:443–453
Xu XS, O’Reilly SY, Zhou XM, Griffin WL (1996) A xenolith-derived geotherm and the crust-mantle boundary at Qilin, southeastern China. Lithos 38:41–62
Xu YF, Zhu ZH, Wen Q, Wen G, Pu ZH (1999) Clay mineral, chemical characteristics and environmental record of the multi-stage laterite at Yingfengling section, Leizhou Peninsula. Geochimica 28:281–288 (in Chinese with English abstract)
Xu YG, Sun M, Yan W, Liu Y, Huang XL, Chen XM (2002) Xenolith evidence for polybaric melting and stratification of the upper mantle beneath South China. J Asian Earth Sci 20:937–954
Yu JH, O’Reilly SY, Griffin WL, Xu X, Zhang M, Zhou X (2003) The thermal state and composition of the lithospheric mantle beneath the Leizhou Penisula South China. J Volcanol Geotherm Res 122:165–189
Zack T, Foley SF, Jenner GA (1997) A consistent partition coefficient set for clinopyroxene, amphibole and garnet from laser ablation microprobe analysis of garnet pyroxenites from Kakanui, New Zealand. Neues Jahrb Mineral Abhirchen 172:23–41
Zhang RY, Liou JG (2003) Clinopyroxenite from the Sulu ultrahigh-pressure terrane, eastern China: origin and evolution of garnet exsolution in clinopyroxene. Am Mineral 88:1591–1600
Acknowledgments
We gratefully acknowledge the constructive comments of L. Taylor, S. Tappe, and an anonymous reviewer, which helped improve the manuscript. Dr. Y.S. Liu is thanked for his kind help during the LA-ICP-MS analyses and Dr. X.C. Liu for helpful discussions on the initial draft. The financial supports from the China National Science Foundation (40421303, 40202009, 40673038, and 49925308) and the Chinese Academy of Sciences (KZCX2-101, KZCX2-209, the Bairen Project) are gratefully acknowledged. This represents part of a collaborative research program of the Guangzhou Institute of Geochemistry, Chinese Academy of Sciences and the Department of Geosciences, National Taiwan University.
Author information
Authors and Affiliations
Corresponding author
Additional information
Communicated by J. Hoefs.
Electronic supplementary material
Below is the link to the electronic supplementary material.
Rights and permissions
About this article
Cite this article
Huang, XL., Xu, YG., Lo, CH. et al. Exsolution lamellae in a clinopyroxene megacryst aggregate from Cenozoic basalt, Leizhou Peninsula, South China: petrography and chemical evolution. Contrib Mineral Petrol 154, 691–705 (2007). https://doi.org/10.1007/s00410-007-0218-4
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00410-007-0218-4