Petrology and Geodynamics

Additional information

Current research

Polymineralic inclusions in eclogite-facies metapelites from Tanzania – insights on partial melting and geodynamic processes in a 2 Ga old subduction zone.

 

Characterization of fluid-flow regime and element mobility during metasomatism of the oceanic crust and during deserpentinization proceses (SFB 574).

The Raspas ophiolite complex stands out by high-pressure zoisite veins, associated metasomatized zoisite eclogites and deserpentinized, pseudo-spinifex textured chlorite harzburgites enabling to investigate the fluid-flow regime and element mobility within a subducting oceanic lithosphere at depth of about 60 km. Fluid inclusion studies reveal a homogeneous low-salinity aqueous fluid composition with minor CH4 and CO2 which is in accord with open-system fluid infiltration derived from an external source. Cyclic fluid expulsion during high-pressure deserpentinization  is indicated by oscillatory mineral zoning. Enrichment in LREE, MREE, Pb, Sr, Th and U in the zoisite eclogites and veins indicate mobility of these elements in the metasomatizing fluid. In addition the fluid-mobile trace elements B, Rb, Pb and Sr are found in fluid inclusions. This case study shows that a large range of trace elements is fluid mobile under eclogite-facies conditions and can be transported by channelized fluid flow and high fluid flux into the mantle wedge where arc magmas are generated (Herms et al. 2012).

 

Fluid composition, fluid-flow regime and fluid migration deduced for the oldest subduction-related eclogites.

Fluid inclusion studies on subduction-related 2 Ga eclogites of the Usagaran Complex, Tanzania, indicate an eclogite-facies fluid regime dominated by CO2+N2 with dissolved Ca and Mg components and a saline aqueous fluid. The variable N2 contents of the CO2-dominated fluid inclusions are interpreted as resulting from local fluid inhomogeneity due to in-situ fluid production. This argues against an externally derived fluid flow. Evidence for fluid immiscibility and selective removal of volatiles and dissolved components give rise to the proposel that some of the trace elements remained in the subducted rocks while others migrated towards the mantle wedge (Herms 2002).

 

Fluid evolution of high-pressure granulites (prograde to retrograde stage) constrained by fluid inclusion investigations.

High-pressure granulites from the Uluguru Mts. which are part of the Pan African Belt, represent an exceptional case where fluid inclusion investigations enabled to record the entire fluid evolution from the prograde to the retrograde stage. Fluid inclusion work  further indicated that in metapelites and metabasites the fluid composition has been internally controlled by phase equilibria while a fluid influx was suggested for the shear zones (Herms and Schenk, 1998).

 

Fluid composition and fluid flow during the metamorphic evolution of lower crustal rocks.

In the Serre of Calabria (Italy), representing the deepest part of an exposed Hercynian crust, fluid inclusion investigations have been combined with analyses of the channel fluids in cordierite to characterize the fluid composition during the metamorphic evolution of the lower crustal rocks (Herms and Schenk 1992). Fluid inclusion data enabled to constrain the petrologically deduced P-T path, even for low P-T conditions where mineral reactions are not available, while stable isotopes have been used to get information about fluid movements.

 

Full publication list

 

Abstract

 

 

Conference talks

  • Herms, Petra, Möller, Andreas, Appel, Peter, Raase, Peter, (2015) Polymineralic Inclusions Representing In Situ Melting in Garnet of Eclogite-Facies Metapelites during Uplift and Heating In: ECROFI XXIII (European Current Research on Fluid Inclusions), 27. - 30.06. 2013, Leeds.

  • Herms, Petra, (2013) Polymineralic inclusions associated with CO2 fluid inclusions in garnet of eclogite-facies metapelite – evidence for decompressional melting under CO2 dominated conditions (talk) In: ECROFI XXII (European Current Research on Fluid Inclusions), 04. - 09.06. 2013, Antalya, Turkey.