Institut für Mineralogie

Timm John Dr. rer. nat.
Institut für Mineralogie WWU Münster Corrensstrasse 24 D-48149 Münster Fon +49 251 83-33404 Fax +49 (0)251 83-38397 email:  timm.john"at"uni-muenster.de  Office: Room 126 Scientific Career Research Publications Links & Downloads

Scientific Career

Positions Held since Jan. 2009: Institut für Mineralogie, Universität Münster. Aug. 2006-Dec. 2008: Senior postdoc position at the centre for Physics of Geological Processes (PGP), Research topics: physical and geochemical consistent numerical solution for reactive fluid flow in rocks under high-pressure / low-temperature conditions, based on field observations. Jan. 2002-Aug. 2006: Postdoctoral Fellow. Research project part of SFB 574 Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanism for Natural Disasters at Kiel University. P-T-t-X and isotopic investigations of subducted fragments of former oceanic lithosphere to understand element and volatile losses in subducting slabs. Nov 2000-Jun. 2001: Visiting scientist at the Zentrallabor für Geochronologie at Mineralogical Institute, University of Münster, Germany. Mar. 1998-Dec. 2001: Research associate, Kiel University, Germany; Dissertation project: petrological, geochemical, and geochronological investigations on high-pressure rocks of Zambia. Feb. 1991-Nov. 1991: Drilling assistant (pratical) in a geological pilot study in Bitterfeld (Germany), Noell Umweltdiensten. Duties included soil sampling with different techniques at different depths and to develop maps about the pollution and hazard potential of the investigated area. Education Dec. 2001: Dr. rer. nat., University of Kiel, Germany, Thesis: Subduction and continental collision in the Lufilian Arc - Zambezi Belt orogen: A petrological, geochemical, and geochronological study of eclogites and whiteschists (Zambia). Feb. 1998: Diplom in Geology, University of Bremen, Germany, Thesis: Metamorphic and geodynamic evolution of the southern Ashanti Belt (SW Ghana), in German; Mapping: Geological mapping of the Palaeozoic / Cenozoic units of the north-western Gulf of Suez (Egypt) in German. Apr. 1994: Diplomvorprüfung in Geology, RWTH Aachen, Germany. Mar. 1998-Dec. 2001: Doctoral student, University of Kiel, Germany. Oct. 1994-Feb. 1998: Student of Geology, University of Bremen, Germany. Apr. 1992-Jul. 1994: Student of Mineralogy and Geology, RWTH Aachen, Germany.

Research

Physical and chemical processes during the dehydration of subducting oceanic lithosphere (reactive fluid flow under high-pressure / low-temperature conditions). During subduction, downgoing plates heat up and their hydrous minerals become progressively unstable and break down to produce water. It is now evident that the released fluids can reach the mantle wedge and cause melting. The most prominent metamorphic reaction occurring in subduction zones is the eclogitization of oceanic crust. It is commonly assumed that the density increase of this reaction makes plate subduction self-sustained. Seismic studies indicate that this transformation happens under non-equilibrium conditions and field evidence points to fluids as a trigger. The details of intra-slab fluid flow are, however, not yet understood. Field evidence points to not yet quantified relationships between reactions, fluid flow, seismicity and mobilization of both major and trace elements. I use a combined field and laboratory based approach to explore the interrelationships of these processes. I investigate how fluids migrate inside slabs (i.e. if fluid migration occurs main ly by distributed porous flow or by channelized fluid flow) and furthermore the interrelation between fluid flow and seismic slip. Reactive fluid flow and transport of so-called fluid-immobile elements. The presence of fluids in Earth's crust results in processes that enable significant element mobilization. Metasomatic changes in rocks due to open system reactive fluid flow often cause surprisingly high solubilities and transport rates of so-called fluid-immobile elements, such as HFSE (high field strength elements, e.g., Th, Nb, Ta, Ti) and the REE (rare earth elements). During metasomatism new minerals form which are more stable under the changing physical and chemical conditions. The associated element transport and mineral growth may finally result in economic ore mineralization. We are currently investigating how titanium, tantalum, and niobium (Ti-Nb-Ta) are mobilized and transported and how Nb-Ta are fractionated, even though they are regarded as geochemical identical twins. Metasomatic processes are also interesting with respect to thorium (Th), because this rather immobile element becomes redistributed and concentrated into accessory minerals, while the host rocks experience infiltration of highly oxidizing fluids. Global chlorine-cycle: halogen concentrations and stable isotopes as tracer for fluid related processes. The large recycling machines, such as subduction zones and spreading centres, are important for element exchange and transport on Earth. Even though the volatile element chlorine represents an important component of the fluids stored in subducting oceanic lithosphere, the behaviour of chlorine within subduction zones and during the formation of magmas in island arc, in plumes or at spreading ridges is not understood yet. This part of my research is mainly emphasised to establish a conservative trace for subduction zone fluids, i.e. halogen ratios and stable chlorine isotopes (delta37Cl), to identify different fluid sources and to quantify fluid-rock interaction and fluid fluxes. Therefore two main topics are currently in investigation, one is to define the Cl-isotopical signal of the main fluid sources of the deeper fluid cycle, i.e. serpentinite and blueschist dehydration; the other is to investigate how conservative the Cl-isotopes behave during fluid flow and fluid-rock in teraction. I will also try to find "fluid-composition-indicative" minerals to use those as a fluid-probe. Evolution of craton margins during continent break up and continental collisions (reconstruction of supercontinents and the break up of Gondwana). Geodynamic processes during orogenesis cause changes in pressure and temperature conditions (P-T conditions), which affect the rocks within an orogen. The reconstruction of the P-T evolution of a metamorphic rock allows to determine the geodynamic causes of metamorphism (e.g., subduction, tectonic thickening, extension during orogenic collapse or rifting, erosion, magmatic underplating). To be able to distinguish between the possible causes for metamorphism and to get a more complete understanding of geodynamic processes the knowledge of the age and the duration of metamorphic events, i.e. the P-T-t path, is essential. My current research is mainly focused on the geodynamic reconstruction of the Neoproterozoic to Cambrian orogens of south central Africa, which are related to the formation of the supercontinent Gondwana. I started to investigate the geodynamic evolution of the Tianshan melange zone (NW China) as a prime example for a cold subduction zone and the cont inetal margin of Ghana as a prime example for rifting processes along oceanic and continental transform margins.

Publications

Reviewed Articles Halama, R., Bebout, G. E., John, T. & Schenk, V. (2010). Nitrogen recycling in subducted oceanic lithosphere: the record in high- and ultra-high pressure metabasltic rocks. Geochimica et Cosmochimica Acta volume 74, 1636-1652. | doi: 10.1016/j.gca.2009.12.003 | Beinlich A., Klemd R., John T., Gao J. (2010). Trace-element mobilization during Ca-metasomatism along a major fluid conduit: eclogitization of blueschist as a consequence of fluid-rock interaction. Geochimica et Cosmochimica Acta 74, 1892-1922. | doi: 10.1016/j.gca.2009.12.011 | Lisker, F. & John, T. (accepted). How much denudation at the Ghana transform margin? - A review of the offshore apatite fission track record. Earth Surface Processes and Landforms. John, T., Scherer, E.E., Schenk, V., Herms, P., Halama, R. & Garbe-Schönberg, D. (2010). Subducted seamounts in an eclogite-facies ophiolite sequence: The Andean Raspas Complex, SW Ecuado. Contributions to Mineralogy and Petrology, 159, 265-284. | doi:10.1007/s00410-009-0427-0 | Adamuszek, M., John, T., Dabrowski, M., Podladchikov, Y.Y. & Gertisser, R. (2009). Assimilation and diffusion during xenolith-magma interaction: A case study of the Variscan Karkonosze granite, Bohemian Massif. Mineralogy and Petrology, 97, 203-222. | doi:10.1007/s00710-009-0088-8 | John, T., Medvedev, S., Rüpke, L.H., Podladchikov, Y., Andersen, T.B. & Austrheim, H. (2009). Generation of intermediate-depth earthquakes by self-localizing thermal runaway. Nature Geoscience, 2, 137-140. | doi: 10.1038/NGEO419 | Schmidt, A., Weyer, S., John, T. & Brey, G.P. (2009). HFSE systematics of rutile-bearing eclogites: New insights into subduction zone processes and implications for the Earth's HFSE budget. Geochimica et Cosmochimica Acta, 73, 455-468. | doi: 10.1016/j.gca.2008.10.028 | van der Straaten, F., Schenk, V., John, T. & Gao, J. (2008). Blueschist-facies rehydration of eclogites: implications for subduction channel fluid-rock interaction from the Tianshan, NW China. Chemical Geology, 255, 195-219. | doi: 10.1016/j.chemgeo.2008.06.037 | Iyer, K., Austrheim, H., John, T. & Jamtveit, B. (2008). Serpentinization of the oceanic lithosphere and some geochemical consequences: Constraints from the Leka Ophiolite Complex, Norway. Chemical Geology, 249, 66-90. | doi: 10.1016/j.chemgeo.2007.12.005 | John, T., Klemd, R., Gao, J. & Garbe-Schönberg, D. (2008). Trace-element mobilization in slabs due to non steady-state fluid-rock interaction: constraints from an eclogite-facies transport vein in blueschist (Tianshan, China). Lithos, 103, 1-24. | doi: 10.1016/j.lithos.2007.09.005 | Gao, J., John, T., Klemd, R. & Xiong, X. (2007). Mobilization of Ti-Nb-Ta during subduction: evidence from rutile-bearing dehydration segregations and veins hosted in eclogite, Tianshan, NW China. Geochimica et Cosmochimica Acta, 71, 4974-4996. | doi: 10.1016/j.gca.2007.07.027 | Zack, T. & John, T. (2007). An evaluation of reactive fluid flow and trace-element mobility in subducting slabs. Chemical Geology, 239, 199-216. | doi: 10.1016/j.chemgeo.2006.10.020 | John, T. & Schenk, V. (2006). Interrelations between intermediate-depth earthquakes and fluid flow within subducting oceanic plates: constraints from eclogite-facies pseudotachylytes. Geology, 34, 557-560. | doi: 10.1130/G22411A.1 | John, T., Scherer, E., Haase, K. & Schenk, V. (2004). Trace element fractionation during fluid-induced eclogitization in a subducting slab: trace element and Lu-Hf / Sm-Nd isotope systematics. Earth and Planetary Science Letters, 227, 441-456. | doi: 10.1016/j.epsl.2004.09.009 | John, T., Schenk, V., Mezger, K. & Tembo, F. (2004). Timing and P-T evolution of whiteschist metamorphism in the Lufilian Arc-Zambesi Belt orogen (Zambia): implications to the Gondwana assembly. The Journal of Geology, 112, 71-90. John, T. & Schenk, V. (2003). Partial eclogitisation of gabbroic rocks in a late Precambrian subduction zone (Zambia): prograde metamorphism triggered by fluid infiltration. Contributions to Mineralogy and Petrology, 146, 174-191. | doi: 10.1007/s00410-003-0492-8 | John, T., Schenk, V., Haase, K., Scherer, E. & Tembo, F. (2003). Evidence for a Neoproterozoic ocean in south central Africa from MORB-type geochemical signatures and P-T estimates of Zambian eclogites. Geology, 31, 243-246. | doi: 10.1130/0091-7613(2003)031<0243:efanoi>2.0.CO;2 | John, T., Klemd, R., Hirdes, W. & Loh, G., (1999). The metamorphic evolution of the Paleoproterozoic (Birimian) volcanic Ashanti belt (Ghana, West Africa). Precambrian Research, 98, 11-30. | doi: 10.1016/S0301-9268(99)00024-8 | John, T., Klemd, R., Hirdes, W., Loh, G. (1998). The metamorphic evolution of the Paleoproterozoic (Birimian) gold-bearing Ashanti volcanic belt, West Africa. Zeitschrift für Angewandte Geologie, 44, 108-110. | full text | Short Publications and Reports Gaidies, F. & John, T. (2009). Conditions and processes during metamorphic and igneous petrogenesis. Mineralogy and Petrology, 97, 145-147. John, T. (2009). Mapping movements in the deep - backstory. Nature Geoscience, 2, E2. John, T., Rickers, K., Schenk, V. & Wilke, M. (2003). Calculation of trace element partition coefficients for variable P-T conditions on the basis of precise thermobarometry due to micro-XANES. HASYLAB-Report, 936. Schenk, V., Raase, P. & John, T. (2003). Metamorphic devolatilization and element losses in paleo-subduction zones. Sonderforschungsbereich 574 (Progress report), Report on subproject C1, 277-292. Invited Talks John, T. (2007). Reactive fluid flow in slabs - a metamorphic view on the origin of the slab component. Goldschmidt conference, Geochimica et Cosmochimica Acta. John, T., Austrheim, H., Schmid, D.W., Rüpke, L. & Podladchikov Y. (2007). Interplay of deformation, fluid infiltration and eclogitization. Goldschmidt conference, Geochimica et Cosmochimica Acta. John, T. (2007). Reactive fluid flow in slabs - a metamorphic view on the origin of the slab component. MARGINS and SFB-574 Workshop to Integrate Subduction Factory and Seismogenic Zone Studies in Central America, Abstract volume. Halama, R., John, T., Schenk, V., McDonough, W.F. & Rudnick, R.L. (2007). Li isotope fractionation in the subducted slab Ð a case study from the Raspas complex, Ecuador. Goldschmidt conference, Geochimica et Cosmochimica Acta. Zack, T. & John, T. (2006). Channelization and reactive fluid flow in subducting slabs. Geochimica et Cosmochimica Acta, 70, A728. Klemd, R., Gao, J. & John, T. (2006). Trace element-enriched fluids released during slab dehydration: implications for oceanic slab - mantle wedge transfer. Geochimica et Cosmochimica Acta, 70, A323. John, T. & Schenk, V. (2005). Interrelations between Intermediate-Depth Earthquakes and Fluid Flow in subducting Oceanic Plates. EGU conference, Geophysical Research Abstracts, 7, EGU05-A-02218. John, T., Scherer, E., Haase, K. & Schenk, V. (2005). Does fluid-induced eclogitization of slab crust generate arc signatures? Goldschmidt conference, Geochimica et Cosmochimica Acta, 69, A650. Gao, J., John, T. & Klemd, R. (2005). Partial dehydration of blueschist: insights into the slab-wedge transfer. Goldschmidt conference, Geochimica et Cosmochimica Acta, 69, A653. Conference Abstracts John, T., Layne, G.D., & Haase, K.M. (2008). The chlorine isotopic composition of mantle endmebers. IGC33 abstract volume, EID05402L. John, T., Podladchikov, Y., Beinlich, A. & Klemd, R. (2008). Drying porosity waves: add fluids to dry up. IGC33 abstract volume , MPN03709L. John, T., Layne, G.D., & Haase, K.M. (2008). The chlorine isotope signature of mantle endmebers. Geochimica et Cosmochimica Acta, 71A434 John, T., Podladchikov, Y., Beinlich, A. & Klemd, R. (2008). Drying porosity waves: add fluids to dry up. Geophysical Research Abstracts , 10, EGU2008-A-08117. John, T., Vrijmoed, J.C., van der Straaten, F., Podladchikov, Y. & Jamtveit, B. (2008). Hydration of eclogite at the slab-wedge interface: an example of fluid infiltration into a swelling system. Geophysical Research Abstracts , 10, EGU2008-A-08191. John, T., Rüpke, L.H., Medvedev, S., Podladchikov, Y. & Andersen, T.B. (2007). Spontaneous thermal run-away as an earthquake mechanism at elevated pressure: insights from petrology and numerical analysis. Eos Transactions AGU , Fall Meet. Suppl., Abstract DI51A-0282. John, T., Rüpke, L., Medvedev, S., Austrheim, H., Podladchikov, Y., Andersen, T.B. & Braeck S. (2007). About deformation, reactions, and fluids: combining petrology and modelling to better understand deeper earthquakes. Geophysical Research Abstracts, 9, EGU2007-A-11588. John, T. (2006). A metamorphic view on earthquakes and fluid pathways in subducting oceanic plates. Eos Trans. AGU, Fall Meet. Suppl., Abstract V31C-0600. John, T., Klemd, R. Gao, J. & Garbe-Schönberg, D. (2006). Reactive fluid flow and trace-element mobilization in slabs: insights from dehydrating blueschist. Geochimica et Cosmochimica Acta, 70, A653. John, T. & Schenk, V. (2006). A metamorphic view on earthquakes and fluid pathways in subducting oceanic plates. Geophysical Research Abstracts, 8, EGU06-A-08912. John, T., Klemd, R., Gao, J. & Garbe-Schönberg, C-D. (2006). Trace-element mobilities due to reactive fluid flow: insights from dehydrating blueschists (Tianshan, China). Geophysical Research Abstracts, 8, EGU06-A-07863. John, T., Scherer, E., Haase, K. & Schenk, V. (2005). Does fluid-induced eclogitization of oceanic crust generate arc signatures? Geophysical Research Abstracts, 7, EGU05-A-02227. John, T. & Schenk, V. (2005). Interrelations between Intermediate-Depth Earthquakes and Fluid Flow in subducting Oceanic Plates. Geochimica et Cosmochimica Acta 69, A654. John, T. & Schenk, V. (2004). Does fluid-induced eclogitization of subducted lower oceanic crust produce the slab component of arcs? Eos Trans. AGU, 85 (47), Fall Meet. Suppl., Abstract V31A-1427. John, T. & Schenk, V. (2004). Eclogitic frictional melts in subducted oceanic crust: are intermediate depth earthquakes causing pathways for channelized fluid flow? Beihefte zum European Journal of Mineralogy, 16, 59. John, T., Scherer, E., Haase, K. & Schenk, V. (2004). Does fluid-induced eclogitisation of subducted lower oceanic crust produce the slab component of arcs? Beihefte zum European Journal of Mineralogy, 16, 60. John, T., Scherer, E., Haase, K. & Schenk, V. (2004). Is the slab component in arc magmas produced by fluid-induced eclogitisation of subducted lower oceanic crust? Geochimica et Cosmochimica Acta, 68, A601. John, T., Scherer, E., Haase, K. & Schenk, V. (2003). Is LREE fractionation in eclogites due to dehydration of underlying serpentinite? Beihefte zum European Journal of Mineralogy, 15, 93. John, T., Scherer, E., Haase, K. & Schenk, V. (2003). LREE fractionation in MORB-type eclogites due to fluid induced eclogitisation of gabbroic rocks: evidence from trace element, Lu-Hf, and Sm-Nd isotope systematics. West Norway Eclogite Field Symposium, Abstract volume. John, T., Schenk, V., Scherer, E., Haase, K., Mezger, K. & Tembo, F. (2002). Subduction and continental collision in the Lufilian Arc-Zambesi Belt orogen (Zambia): implications to the Gondwana assembly. 19th Colloquium on African Geology, El Jadida, Morocco, Abstract volume, p. 188. John, T., Scherer, E., Schenk, V., & Mezger, K. (2001). Evidence for a Neoproterozoic ocean in south central Africa from Lu-Hf ages and P-T estimates of MORB-type eclogites Zambia). Beihefte zum European Journal of Mineralogy, 13, 88. John, T., Schenk, V., Mezger, K. & Tembo, F. (2001). Reaction histories of partially eclogitised MORB-type gabbros from a Neoproterozoic subduction zone (Zambia). EUG XI, Journal of Conference Abstract, 6, 431. John, T., Schenk, V. & Tembo, F. (2000). MORB-type geochemical signatures of eclogites from central Zambia: evidence for a Precambrian suture-zone. 18th Colloquium on African Geology, Graz, Journal of African Earth Sciences, 30, 4A. John, T., Schenk, V. & Tembo, F. (1999). The metamorphic evolution and U/Pb dating of monazites of the southern Irumide Belt, SE-Zambia. Abstract Volume IGCP Conference Zambia, 7 John, T., Klemd, R. & Hirdes, W. (1999). Metamorphism and its relation to gold mineralization in the Paleoproterozoic Birimian volcanic Ashanti belt (Ghana, West Africa). Beihefte zum European Journal of Mineralogy 11, 112

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