Advances in Crustal MElting

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WHY?


Partial melting of the continental crust is responsible for: i) generating the magmas that ascend through the crust and may extrude with explosive eruptions (with relevant climatic effects); ii) inducing the geochemical differentiation of the continental crust and the refertilization of the mantle wedge; iii) lowering the strength of rocks, with paramount effects on global tectonics and geodynamics.
The project Advances in Crustal MElting (ACME) aims at a better understanding of crustal anatexis processes in nature, and in particular is interested in the recognition and characterization of primary anatectic magmas as they are produced at depth. This information will allow a considerable improvement in the quantification of geochemical balances, melt viscosities, crustal rheology and timescale of processes, and in general can pose essential constraints to geodynamic models of lithosphere evolution.


WHO?


The ACME research group is based at the Department of Geosciences of the University of Padova, and brings together scientists with differentiated expertise in the fields of Earth Sciences, whose research is focused mainly on metamorphic petrology and crustal melting. ACME, led by Prof. Bernardo Cesare, builds on the enthusiasm of early stage researchers in Padova and on a worldwide network of collaborations with experts in crustal petrology.


WHAT?


Our aim is a better understanding of anatectic processes by means of natural examples. Melt inclusion studies of anatectic rocks may provide:

  • Microstructural evidence for partial melting
  • P-T conditions at which anatexis takes place in natural settings
  • Nature of melting reactions
  • Extent of melt-residuum equilibria during anatexis
  • Rates of processes in the partially melted crust
  • Original composition of natural anatectic melts
  • Fluid regime during anatexis

HOW?


We are developing a rigorous analytical approach for the microstructural, geochemical and mineralogical analysis of anatectic rocks and of their inclusions. This involves both traditional methods and cutting-edge techniques. Our approach starts with rigorous microstructural analysis of regular thin sections using a conventional optical microscope in order to identify the samples suitable for a melt inclusion study. In the next step, polished thin or thick sections may be investigated using a scanning electron microscope; phases within the inclusions may be characterized by EDS analysis and compositional maps. Micro-Raman is also very useful to identify the phases within the inclusions (especially in the case of polymorphs) and to evaluate the possible coexistence of fluid inclusions in the same clusters. From a chemical view point, nanogranitoids must be remelted to a homogeneous liquid, in order to reverse the phase changes occurred during cooling after entrapment (i.e. crystallization of daughter phases and fluid exsolution). In this way, we can obtain complete compositional data, including the volatile contents. Based on the size, abundance and microstructural occurrence of the melt inclusions, different setups can be used in the piston cylinder experiments (e.g. single garnet crystals, wafers of garnet, drilled cores of garnet). Once the inclusions have been rehomogenized they can be analyzed in terms of major element composition by electron microprobe. Volatiles such as H2O and CO2 dissolved in the rehomogenized glasses may be quantified using NanoSIMS, and trace elements may be measured with LA-ICPMS.


WHERE?


ACME was or is involved in the characterization of anatectic processes in rocks from different geodynamic settings:

  • Kerala Khondalite Belt, India
  • Athabasca, Canada
  • Ronda, Spain
  • Central Massachusetts, USA
  • Mercaderes - Rio Mayo, Colombia
  • Gruf Complex, Italy
  • Ivrea Zone, Italy
  • Ulten Zone, Italy
  • Barun, Nepal
  • Kaligandaki, Nepal
  • La Galite, Tunisia
  • Dronning Maud Land, Antarctica
  • Rauer Islands, Antarctica
  • Lu╠łtzow-Holm Complex, Antarctica
  • Lanterman, Antarctica
  • Bohemian Massif
  • Limpopo Belt
  • Barberton Belt
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Studied areas by the ACME group.





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