Sea-floor metamorphism recorded in epidosites from the ca. 1.0 Ga Miaowan ophiolite, Huangling anticline, China

Abstract

The epidosites are interpreted to form in upflow zones at the base of ore-forming oceanic hydrothermal systems that vent as black smokers on the sea floor. This study presents new field, major and trace element, and oxygen isotope data for the recently discovered epidosites in the ca. 1.0 Ga Miaowan (庙湾) ophiolite located near the northern margin of the Yangtze craton. The epidosites occur mainly in the cores of strongly deformed, lensoidal amphibolites. Field observations, major and trace elements and oxygen isotopes suggest that the epidosites were formed by metasomatism of ocean floor basalts, diabase dykes, and gabbros during seafloor hydrothermal alteration.

Keywords

epidosite / hydrothermal alteration / metasomatism / Miaowan ophiolite / Yangtze craton / China

References

[1] Banerjee N. R., Gillis K. M., Muehlenbachs K.. Discovery of Epidosites in a Modern Oceanic Setting, the Tonga Forearc. Geology, 2000, 28(2): 151-154.

[2] Bettison-Varga L., Varga R. J., Schiffman P.. Relation between Ore-Forming Hydrothermal Systems and Extensional Deformation in the Solea Graben Spreading Center, Troodos Ophiolite, Cyprus. Geology, 1992, 20(11): 987-990.

[3] Deng H., Kusky T. M., Wang L., . Discovery of a Sheeted Dike Complex in the Northern Yangtze Craton and Its Implications for Craton Evolution. Journal of Earth Science, 2012, 23(5): 676-695.

[4] Harper G. D., Bowman J. R., Kuhns R.. A Field, Chemical, and Stable Isotope Study of Subseafloor Metamorphism of the Josephine Ophiolite, California-Oregon. Journal of Geophysical Research, 1988, 93(B5): 4625-4656.

[5] Jiang X. F., Peng S. B., Kusky T. M., . Geological Features and Deformational Ages of the Basal Thrust Belt of the Miaowan Ophiolite in the Southern Huangling Anticline and Its Tectonic Implications. Journal of Earth Science, 2012, 23(5): 705-718.

[6] Lu Y. F.. Geokit: A Geochemical Toolkit for Microsoft Excel. Geochimica, 2004, 33(5): 459-464.

[7] Nehlig P., Juteau T., Bendel V., . The Root Zones of Oceanic Hydrothermal Systems: Constraints from the Samail Ophiolite (Oman). Journal of Geophysical Research, 1994, 99(B3): 4703-4713.

[8] Peng S. B., Kusky T. M., Jiang X. F., . Geology, Geochemistry, and Geochronology of the Miaowan Ophiolite, Yangtze Craton: Implications for South China’s Amalgamation History with the Rodinian Supercontinent. Gondwana Research, 2012, 21(2): 577-594.

[9] Polat A., Appel P. W. U., Frei R., . Field and Geochemical Characteristics of the Mesoarchean (∼3 075 Ma) Ivisaartoq Greenstone Belt, Southern West Greenland: Evidence for Seafloor Hydrothermal Alteration in a Supra-Subduction Oceanic Crust. Gondwana Research, 2007, 11(1–2): 69-91.

[10] Richardson C. J., Cann J. R., Richards H. G., . Metal-Depleted Root Zones of the Troodos Ore-Forming Hydrothermal Systems, Cyprus. Earth and Planetary Science Letters, 1987, 84(2–3): 243-253.

[11] Schiffman P., Smith B. M., Varga R. J., . Geometry, Conditions and Timing of Off-Axis Hydrothermal Metamorphism and Ore Deposition in the Solea Graben. Nature, 1987, 325: 423-425.

[12] Schiffman P., Smith B. M.. Petrology and Oxygen Isotope Geochemistry of a Fossil Seawater Hydrothermal System within the Solea Graben, Northern Troodos Ophiolite, Cyprus. Journal of Geophysical Research, 1988, 93(B5): 4612-4624.

[13] Sun, S. S., McDonough, W. F., 1989. Chemical and Isotopic Systematics of Oceanic Basalts: Implications for Mantle Composition and Processes. In: Saunders, A. D., Norry, M. J., eds., Magmatism of the Ocean Basins. Geol. Soc. Spec. Publ., London, 42: 313–345