Mineral micro-inclusions as petrogenetic indicator: modern oceanic crust

The project is devoted to the fundamental geological problem of phase composition and behavior of multicomponent crystal matter during changes of physical-chemical conditions. It relies on the potential of mineral structure and phase composition for reconstructing geological processes. Specifically the genesis of solid-phase micro inclusions hosted in rock-forming minerals and their fate in a dynamic geological environment will be addressed using state of the art electron beam micro-analytical techniques. Due to their insignificant geological age (less than 10 Ma), gabbros from Mid-Ocean Ridges are particularly well suited for studying the behavior of micro-inclusions. These gabbros experienced a relatively short geological history with relatively few rock forming events, which are much easier to unravel than the complex petrogenetic history of rocks from geodynamic settings with a long geological history. The genesis and fate of solid-phase micro inclusions hosted in rock-forming minerals of Mid- Atlantic Ridge gabbros at 1330-1335N will be investigated. In particular the genesis and the post formation behavior of the mineral micro-inclusions will be examined in the context of felsic magmatism and hydrothermal alterations affecting the gabbros. The evolution of the microstructural and textural features of the micro-inclusion and their relations to the host phases as well as the chemical characteristics of the mineral micro-inclusions will be correlated with available petrographic and geochemical data. By this, new insights into the information content of mineral micro-inclusions and into the petrogenetic history of Mid-Atlantic Ridge gabbros will be obtained.

The project is devoted to the fundamental geological problem of phase composition and behavior of multicomponent crystal matter during changes of physical-chemical conditions. It relies on the potential of mineral structure and phase composition for reconstructing geological processes. Specifically the genesis of solid-phase micro inclusions hosted in rock-forming minerals and their fate in a dynamic geological environment has been addressed using state of the art electron beam micro-analytical techniques. Due to their young geological age (less than 10 Ma), gabbros from mid-ocean ridges are particularly well suited for studying the behavior of mineral micro-inclusions. These gabbros experienced a relatively short geological history, which is much easier to unravel than the complex petrogenetic evolution of rocks from geodynamic settings with a long geological history. Moreover the mid ocean ridges are crucial for global processes such as plate tectonics and global element cycling, because they continuously produce large amounts of basaltic magmas, which constitute the ocean floor in the form of oceanic basalts and gabbros. The magnetic signatures imprinted into the iron-titanium oxide minerals of the rocks from the ocean floor provide key information on plate tectonics and on the evolution of the Earths magnetic field. Finally, hydrothermally driven enrichment processes along the mid ocean ridges lead to the formation of economically important iron and base-metal deposits.In this study, the genesis and fate of iron-titanium oxide micro inclusions hosted in the rock-forming minerals of Mid-Atlantic Ridge gabbros at 1330-1335N has been investigated. In particular the genesis and the post formation behavior of the mineral micro-inclusions has been examined in the context of felsic magmatism and hydrothermal alterations affecting the gabbros. The evolution of the microstructural and textural features of the micro-inclusion and their relations to the host phases as well as the chemical characteristics of the mineral micro-inclusions have been correlated with available petrographic and geochemical data. By this, new insights could be obtained into the genesis of the mineral micro-inclusions and into the petrogenetic history of Mid-Atlantic Ridge gabbros. According to our findings, the iron-titanium oxide micro inclusions of the gabbros are subject to systematic changes. A first phase is characterized by recrystallization in a closed system without changes in mineral chemical composition. The second phase is represented by high-temperature oxidation, where the necessary oxygen is delivered by the hydrothermal fluid. Finally a massive depletion of iron occurs by dissolution and removal in the hydrothermal fluid. This latter process is a prerequisite for secondary enrichment processes and the formation of ore deposits.