Oxygen isotope and chemical studies on the origin of large plagiogranite bodies in northern Oman, and their relationship to the overlying massive sulphide deposits
Published:January 01, 2003
Debra S. Stakes, Hugh P. Taylor, Jr, 2003. "Oxygen isotope and chemical studies on the origin of large plagiogranite bodies in northern Oman, and their relationship to the overlying massive sulphide deposits", Ophiolites in Earth History, Y. Dilek, P. T. Robinson
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The extraordinarily well-preserved and well-exposed Semail ophiolite of northern Oman hosts several large plagiogranite intrusions in proximity to economic copper sulphide deposits of the Lasail mining district. A progression of isotopic, chemical and mineralogical transformations observed within the plagiogranites and high-level gabbros (HLG), and a comparison of these effects with those in the lowermost dykes of the immediately overlying sheeted dyke complex (SDC) tracks the evolution of hydrothermal fluids and the alteration of overlying dykes and pillow lavas during discharge of these fluids on the sea floor. The largest hydrothermal alteration aureoles, and the greatest extent of metamorphic veins and metasomatic replacement features, are found adjacent to the largest high-level plagiogranite bodies, beneath and adjacent to the major ore bodies in northern Oman. The ubiquitous presence of metamorphic actinolitic hornblende, sodic plagioclase, epidote and titanite in metabasalts within the high-temperature alteration zones points to the most likely mineralogical and structural controls on the development and evolution of the hydrothermal fluids. Depleted Cu contents of the adjacent crustal rocks and Cu enrichments above the plagiogranite intrusions demonstrate the redistribution of heavy metals adjacent to the complexes. Field relationships implicate the formation of both the epidosites and plagiogranites in the genesis of the ore deposits. An important process inferred from the field and geochemical data is the assimilation of previously hydrothermally altered basaltic and gabbroic country rocks by stoping into the magma chambers developed near the SDC-gabbro horizon in the ophiolite. We suggest that this process of combined assimilation-fractional crystallization, together with replenishment and recharge by injection and quenching of basaltic magma ‘pillows’ into these plagiogranite magma chambers (i.e. RAFC), plays a major role in the development of these composite intrusions.
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Ophiolites in Earth History
The 32 research papers in this volume examine the mode and nature of igneous, metamorphic, tectonic, sedimentological and biological processes associated with the evolution of ophiolites in Earth’s history. Divided into six sections, the book presents a wealth of new data and syntheses from ophiotites around the world. Introductory chapters review the distribution of ophiolites in space and time and present a synoptic discussion on their importance in Earth history. Papers in the second section present diverse data from Tethyan ophiolites and provide refined geodynamic models for their evolution. The following two sections present case studies documenting magmatic, metamorphic and tectonic processes in ophiolite genesis and hydrothermal and biogenic alteration of fossil oceanic crust. Mechanisms of ophiolite emplacement are explored in Section V with a focus on the Semail massif (Oman). The last section examines the regional occurrence and geodynamic significance of ophiolite belts on different continents. The book reflects the contemporary work of the international community in a most up-to-date treatment of process-oriented questions on the evolution of ophiolites.