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Subproject G1: Thermal and compositional structure of the continental lithosphere in the Central Andes

Research Field: Petrology-Geochemistry, Geophysics

Staff

Working area of the subproject G1

g1_working_area

Fig. 1: Working area of project G1

The currently available and partially complemented information on composition of surface rocks, magmas and xenoliths, as well as geophysical observations will be integrated into an internally consistent quantitative model of composition and temperature in the lithosphere-asthenosphere system of the Central Andes (20-25?S, 65-70?W). For the crust, an already existing crude density model will be refined and extended (18-26 ?S 64-70?W). For the upper mantle, a compositional model will be constructed based on isotopic and chemical characteristics which will distinguish between cratonic and mobile-belt lithosphere. Data on Vp, Vp/Vs, Qp from local source tomography, as well as P-to-S-converted waves will be integrated into an internally consistent model, and inverted for 3-D distribution of temperature and water content in the upper mantle. These composition and temperature distributions will be used to calculate topography of the thermal lithosphere-asthenosphere boundary, rheological properties, gravity field, geoid and dynamic topography, and will be iteratively improved to achieve an optimal fit to geophysical observations. Estimated upper mantle temperatures will be used together with "temperature markers" and surface heat flow to calculate temperature in the crust. Optimal present-day temperature, composition and rheological models will be discussed in relation to the plateau-building process. New seismic data from ongoing and planned seismic/seismological SFB experiments, which will be available by the end of the 2003, will be incorporated into the final model.

Objectives, methods, work plan, and schedule

Objectives

The aim of this project is to integrate information on chemical-mineralogical composition and temperature of the crust and the upper mantle, as derived by both petrological-geochemical studies and interpretation of geophysical observations, into an internally consistent model for the present-day composition and state of the Central Andean lithoshpere. Within this context we will upgrade previous 2-D steady-state thermal models of the Central Andean lithosphere (Springer, 1999) to a 3-D thermal model constrained, in addition to surface heat flow, by P-and S- velocities and Qp structure in the mantle, as well as by existing "temperature markers" in the crust. Methods

To achieve these goals, new inversion techniques are being developed which are able to operate with a large number of observations and constraints from different disciplines containing information on composition and temperature. These techniques are organized into four closely connected themes: composition of the crust, composition of the upper mantle, temperature in the upper mantle, and temperature in the crust.

Composition of the crust

Constraints on composition of the crust and upper mantle are provided by several disciplines. Each of these constraints, in principal, could be used to construct a specific compositional model with its specific strong and weak points. These constraints are:

Direct constraints from the composition of surface rocks, xenoliths and magmas. Models of crustal composition based on these direct constraints (Lucassen et al. 2001) have obvious advantages but suffer from uncertainty of the extrapolation from surface to depth.
P- and S-velocity seismic structure can be converted into composition using both methods of petrophysical modelling (Sobolev and Babeyko 1994) and laboratory experiments statistics (e.g. Christensen and Mooney 1995). This approach has the advantage of depth resolution, but suffers from inaccuracy and inconsistency of different seismic observations and from ambiguous petrophysical interpretation.
Gravity observations can be inverted for density structure and then converted to composition using petrophysical interpretation. The advantage of this approach is the high accuracy of gravity observations, whereas the disadvantages are ambiguous density inversion and an ambiguous petrophysical interpretation.

We will combine all these approaches in our attempt to find a model that satisfies all constraints. We will first add new petrological-geophysical observations (specifying and extending the model of Lucassen et al., submitted a). This will provide a set of major element bulk compositions of rocks expected to be significant components of the lithosphere.

Second, for all these rocks we will calculate equilibrium mineral compositions and densities as well as P- and S- seismic velocities using the petrophysical-modelling technique of Sobolev and Babeyko (1994). Calculated densities and seismic velocities for these rocks will be parameterised using a small number of major compositional parameters such as volume fractions of major rock types. For example, if there are two major rock types A and B (say mafic and felsic) then only one composition-parameter, namely volume fraction of rock-type A (or B) is required; for three major rock types 2 parameters are required, etc.

Then we will invert the crustal seismic velocity model for compositional parameters. The seismic velocity structure will be obtained from an improved tomographic model (see below), which will consist of 3-D Vp and Vp/Vs distributions in the crust. At the end of this step we will obtain the 3D distributions of the compositional parameters. In this inversion we will use estimates on the reflectivity coefficients supplied by subproject F3. The updated physical properties of the hydrated rocks will be used from subproject G5.

From the obtained distribution of compositional parameters we will calculate the density field and then gravity anomalies. To calculate the gravity response of our composition model we will use additional information on the depth to the crystalline basement (from geological and seismic data) and on the depth to the Moho (from converted waves study by Yuan et al. 2001). The gravity response of the model will be compared with the observed gravity field (in cooperation with subproject F4) and corrected for large-scale deep heterogeneity (slab, lithosphere-asthenosphere structure). The difference between calculated and observed gravity fields will be analysed and the composition model accordingly corrected.

Composition of the upper mantle

Lower crustal and upper mantle xenolith data yielded the first concrete estimations of temperature and composition of the mantle lithosphere before the onset of the Cenozoic plateau formation (Lucassen et al., 1999c, submitted b). Analytical work on composition of the mantle derived volcanic rocks and of the mantle xenoliths will be largely finished by the end of 2001, but will be completed in the following period. It includes localities from southern Bolivia (ca 18?S) to Salta (ca 26?S) and Cordoba (ca 32?S), the Chilean Coastal Cordillera and down to Patagonia in order to obtain a large-scale picture for the interpretation of mantle lithosphere. We will use classical geochemical methods such as geothermobarometry for xenoliths and whole rock chemical composition, isotopic systems Rb-Sr, Sm-Nd and U-Th-Pb and trace element distribution in minerals (mainly clino- and orthopyroxene, on mineral separates by ICP-MS and in-situ by LA-ICP-MS and ion probe). K-Ar and Ar-Ar data for some of the occurrences of volcanic rocks must be derived in order to establish ages in laboratories of G?ttingen and Salzburg. Chemical modeling will be done using MELTS. Results and data of subproject G2 will be used here.

For a more detailed evaluation of all geochemical data in combination with the geophysical data, an electronic database for use in the SFB GIS system is currently being set up, starting with the petrological-geochemical data compiled by M. Krause.

Using petrophysical modeling techniques (Sobolev and Babeyko 1994), we will calculate densities and seismic velocities for mantle xenoliths from their major element bulk chemical compositions. The updated physical properties of the hydrated rocks will be taken from subproject G5.

Temperature in the upper mantle

Seismic velocities and intrinsic seismic wave attenuation in the upper mantle are more sensitive to temperature variations than to compositional variations (Sobolev et al. 1996, 1997a). Therefore high-resolution tomographic images can be used to estimate temperatures in the mantle (Sobolev et al. 1996, 1997a; Goes et al. 2000). Particularly useful are seismic observations which able to image P-wave, S-wave and attenuation structures simultaneously, because these three fields can then be parameterised as function of temperature (Sobolev et al. 1997a). Comprehensive seismic observations from local earthquakes in the Central Andes contain the data required for these images. Currently, these data are being inverted for Vp, Vp/Vs, and Qp structures (Schurr 2000) using classical methods of unconstrained tomographic inversion. Such methods are particularly useful if no additional information is available. However, in our case there is a wealth of additional information allowing us to put constraints on the inversion to minimise ambiguity of the solution. Because tomographic images are of key importance for this study, we will first experiment with different inversion methods in order to improve the seismic images.

The entire tomographic-inversion region will be subdivided into three depth domains, namely crust, slab, and mantle wedge, which will be differently parameterised. The topography of the crust-mantle boundary will be taken from a converted wave study (Yuan et al. 2001), and the topography of the slab will be taken as envelope of the seismicity localized in the existing tomographic model (Schurr 2000). A similar parameterisation has been implemented and successfully applied to the Japanese subduction zone (Zhao and Hasegawa 1993). We will probably use their computer code, which is readily available. Alternatively, the previously used code of Thurber (1983) could be modified to include velocity discontinuities. When available, we will use relative arrival times and relocations as determined by subproject F3.

Seismic data then will be inverted for three independent variables (Vp, Vp/Vs, Qp-as previously) using constraints on seismic velocities in the crust and mantle rocks which follow from petrophysical modelling. The resulting tomographic model (hereafter called MCM- Minimal Constrained Model) will provide a scale for data fit, which could be achieved by independent inversion for P, S and Q structure. We will experiment with the parameterisation (including anisotropic parameterisation in the slab domain) to obtain a maximal fit of the data. We expect that MCM will have significantly higher accuracy than current tomographic models due to more flexible parameterisation and separation of the effects of the slab, crust and rest of the mantle.

In another set of tomographic models (hereafter called SCM-Strongly Constrained Model) we will jointly invert seismic travel times and t* parameters using mineral physics constraints on relations between Vp, Vp/Vs and Qp. In the SCM, temperature and possibly also water content of minerals will be estimated in either a two-step- or a one-step scheme. In the two-step scheme we will first estimate Vp, Vp/Vs and Qp and then invert them for temperature and water content similar to Sobolev et al. (1997a). In the one-step scheme we will invert the data directly for temperature and water content using non-linear parameterisation based on mineral physics, and taking mantle composition from xenolith data. In the SCM, we will also experiment with different parameterisations (including different ways of linearisation of originally non-linear parameterisation) and constraints in order to obtain maximal fit of the seismic observations. In this work we will also use results of seismic scattering analysis by the subproject F3 to separate intrinsic and scattering components of the observed Qp.

Finally, the 3-D temperature model of the mantle will be used to calculate the dynamical topography and geoid by non-Newtonian thermal convection modeling (Sobolev et al. 1997b) using a thermal-convection code by Christensen and Harder (1991). In these calculations we will employ recent estimations of the lithospheric rigidity in the Central Andes (subproject F4). Comparison of the calculated topography and geoid with observations will be used for iterative improvement of the temperature model. Finally, we will obtain 3-D mantle temperatures consistent with seismic, gravity, petrological and mineral physics data and constraints as was achieved in the case of the French Massif Central (Sobolev at al. 1997a,b). From the mantle temperature model we will calculate the topography of the thermal lithosphere-asthenosphere boundary. A subset of this model, namely temperature at Moho, will be then used as boundary condition to calculate temperature in the crust. The final temperature and rheologic model will be provided to the subprojects G2, F1 and F2.

Temperature in the crust

Estimation of temperature in the crust of the Central Andes is problematic for several reasons. First, geothermal models using surface heat flow as input and mantle heat flow as a constraint are only valid for areas reflecting thermal conditions of a lithosphere that has been stabile for several tens of millions of years. Second, even at steady-state, temperatures in a stratified continental crust strongly depend on contrasts in thermal conductivity, its function of temperature, and on the radiogenic heat-production distribution. None of these parameters are well constrained in the Andean lithosphere, with an exception of the oceanic lithosphere of the Nazca Plate. However, possible thermal-parameter distributions can be constrained by the conceptual model of crustal composition. For areas of supposedly transient thermal conditions resulting from tectonic processes, such as crustal underthrusting and/or delamination of lower crust and mantle lithosphere, the lower boundary conditions (e.g. at the crust/mantle/asthenosphere boundary) will be constrained by mantle temperatures derived from seismic tomography. With this constraint it will be possible to localize, for example, the 1250?C-isotherme that was used in the Springer (1999) models. Although, in contrast to the mantle, the seismic velocities in the crust are usually more affected by changes in composition than in temperature, and hence the seismic velocity cannot be inverted directly in a temperature distribution, locally very high temperatures can produce measurable signatures in the seismic structure. Very strong P-to-S conversions at 20 km depth below the APVC and some other regions of the high-plateau (Chmielowski et al. 1999; Yuan et al. 2000) cannot be explained other than by the presence of the high degree partial melts and therefore could be treated as high temperature (>700-800?C) markers in the middle crust. Another, potentially very interesting temperature marker in hot felsic crust is the alpha-beta quartz transition, which is marked by significant decrease of the Vp/Vs ratio at the temperature slightly below transition temperature and strong increase of the Vp/Vs ratio at transition temperature. Other possible temperature markers are very high conductivity domains (partial melt) detected by MT studies, depth to Curie temperature from magnetic data and depth to the crustal seismicity cut-off.

Crustal temperatures then can be calculated by some optimal interpolation between temperature values at the Moho or asthenosphere boundary gained from seismic tomographic data (see previous text), the temperature markers, and surface temperature. Furthermore, it will be investigated to which extent this temperature model deviates from previous ones (Springer 1999) and from a refined "Springer model" using variations in thermal rock properties according to the compositional model and to refined lower-boundary conditions. The investigations are aimed at the clarification of the mode of heat transfer, and whether abnormal thermal structure can be reflected by surface heat flow, which would put some time constraint on heat flow.

The new temperature model of the lithosphere-asthenosphere system will be different in the following aspects from the previous model (Springer, 1999).

The new model will be 3-D as opposed to 2-D.
Mantle temperatures in the new model will be constrained by seismic tomography and gravity data, versus the rather arbitrary mantle temperatures assumed previously.
Crustal temperature markers will be used in the new model as additional constraints.
Radiogenic heat production and thermal conductivity in the new model will be constrained by a composition model of the crust.

The temperature model will be correlated with the temperature model obtained on the basis of Curie-temperatures by subproject F4. Crustal temperature markers related to converted wave anomalies and MT anomalies will be used based on the studies and in co-operation with the seismology group (subproject G3) and the MT group (subproject G4) respectively.

Work plan and schedule

Work in the first year will be focused on the collection of additional information and revision of the existing data as well as on methodical aspects of modeling and inversion. In the second year, work on methodical aspects will be mostly finalized and prepared for publication, and preliminary models will be computed. In the last year, final models will be computed and prepared for publication.

Detailed plan

First year, 2002

Supplementary field work to sample localities of mafic volcanic rocks and possible xenoliths in southern Bolivia, northern Chile and northwestern Argentina (exact localities depending on results of analytical work currently being caried out) by F. Lucassen and G. Franz together with project partners in Salta and Antofagasta. The dataset available up to now from the work in 1999-2001 is sufficient for a rough interpretation, but may have to be complemented by additional samples.

Analytical work on these samples will include isotopic determination (Rb-Sr, Sm-Nd, U-Th-Pb) and mineral chemistry, including in-situ determination of trace elements. Complementary field work with diploma students from the Technische Universit?t Berlin in the southern continuation of the mobile belt in connection to the Argentinian Precordillera to sample localities for age determination. The age determinations by R. Becchio (DAAD stipend; supervisor: F. Lucassen) will be made at the GFZ Potsdam.

Publication of results from previous work with M. Escayola and J. Viramonte (Salta) on mantle xenoliths from Sierras de Condores, NW Argentina.

Development of constrained inversion methods of the local-earthquake seismic observations. Constraints will be of two different types: (1) geometric, (2) mineral-physical and petrological constraints on seismic velocities and Q-factors in the mantle (B. Schurr and S. Sobolev in cooperation with G. Asch and A. Rietbrock). Modification of the ray tracing code, calculation of preliminary Minimum Constrained Models (MCM-for definition see above), experiments with parameterization (B. Schurr). B. Schurr will also participate in the seismological experiment of R. Kind and G. Asch (G3).

Compilation of U-Th-K data from chemical analyses made in previous and ongoing SFB subprojects, heat-budget calculation of Brazilian crust (A. F?rster).

Second year, 2003

Further development of the methods of constrained inversion of the local-source seismic observations. Calculation of the final MCM. Calculation of the preliminary, strongly constrained models (SCM-for definition see above) for temperature and composition in the mantle (B. Schurr and S. Sobolev). Calculation of dynamic topography and geoid. (A. Babeyko and S. Sobolev). Iterative improvement of the models by comparison of calculated and observed topography, gravity and geoid (B. Schurr, S. Sobolev in cooperation with F4 and F1). Preparation for publication of a paper on methodology of constrained tomographic inversion (B. Schurr, S. Sobolev). Detailed models of crustal composition with vertical and lateral maximum resolution (F. Lucassen, S. Sobolev, G. Franz); extension of the model to the area south of 26 ?S (R. Becchio, F. Lucassen). Assigning thermal properties (thermal conductivity, radiogenic heat production) to the models of crustal composition (A. F?rster). Composition model of the Andean mantle lithosphere, mapping of large-scale mantle domains by isotopes and mineral chemistry (F. Lucassen). Construction of preliminary crustal thermal models based on heat conduction using temperature at Moho (from preliminary mantle thermal models) as lower boundary condition and using different scenarios on thermal rock properties from compositional models and temperature markers as additional constraints (A. F?rster).

Third year, 2004

Calculation of the final temperature-composition model (publication by whole group). Application of the developed methods to other areas in the Central and Southern Andes where a similar data set will have been built up by 2003 (whole group, in connection with SALT project).

Collaboration with external research groups

Names of important partners in the host countries

Chile:

Antofagasta, H. Wilke

Argentina:

UN Salta, J. Viramonte, M. Escayola, R. Becchio
Comodoro Rivadavia, E. Vietto
Sergemar Buenos Aires, D. Rubielo
Universidad La Plata, C. Rapela

Cooperation with non-SFB teams

B. Pankhurst (UK)

Publications

Literature

Reviewed publications

Babeyko, A.Yu., Sobolev, S.V., Trumbull, R.B., Oncken O., & Lavier L.L. (2002): Numerical models of crustal scale convection and partial melting beneath the Altiplano-Puna plateau. - Earth and Planet. Sci. Letters, 199: 373-388.

EGENHOFF, S. (1999): Response of an Upper Cambrian to Lower Ordovician shelf in southern Bolivia to the switch from an extensional to a compressional regime. - International Association of Sedimentologists, 19th Regional Meeting, 73; Kopenhagen.

EGENHOFF, S. (1999): Entwicklung eines Schelfs beim ?bergang von extensivem zu kompressivem Regime am Beispiel der oberkambrischen bis unterordovizischen Abfolgen in S?dbolivien. - Terra Nostra, 99/4: 48.

EGENHOFF, S., MALETZ, J. & ERDTMANN, B,-D. (1999): Upper Ordovician basin Evolution in southern Bolivia. - In: KRAFT, P. & FATKA, O. (eds.): "QuoVadis Ordovician?". - Acta Universitas Carolinae. Geologica,, v. 43: 131-132.

Franz, G. and F. Lucassen (1999): Comment on the paper Tuncoviscana folded belt in northwestern Argentina : testimony of Late Proterozoic Rodinia fragmentation and pre-Gondwana collisonal episodes" by Omarini et al.. - International Journal Earth Sciences (Geologische Rundschau), : ; . - []

Lucassen F, Escayola M, Franz G, Romer RL, Koch K Isotopic composition of Late Mesozoic mafic rocks from the Andes (23 - 32?S) -Implications for their mantle sources Contributions to Mineralogy and Petrology.. - , : ; . - []

Lucassen R, H.G. Wilke, R. Becchio, J. Viramonte, G.Franz, A. Laber, K., Wemmer, P. Vroon (1999): The Paleozoic basement of the Central Andes (18?-26?S) - the metamorphic view.-. - J. South Am. Earth Sci., : ; . - []

Lucassen, F. & Franz, G. (1994): Arc Related Jurassic Igneous and Meta- Igneous Rocks in the Coastal Cordillera of Northern Chile/Region Antofagasta. - Lithos, 32: 273-298.

Lucassen, F. & Franz, G. (1996): Magmatic Arc Metamorphism: Petrology and Temperature History of Metabasic Rocks in the Coastal Cordillera of Northern Chile. - Journal of Metamorphic Geology, 14: 249-265.

Lucassen, F. & Thirlwall, M.F. (1998): Sm-Nd formation ages and mineral ages in metabasites from the Coastal Cordillera, Northern Chile. - Geol. Rundschau.

Lucassen, F. Harmon, R., Franz, G., Romer, R.L., Becchio, R., Siebel, W. (2002): Lead evolution of the Pre-mesozoic crust in the Central Andes (18?-27?): Progressive homogenisation of Pb. - Chemical Geology, 186: 183-197.

Lucassen, F., & Wilke, H.-G. (1998): Paleozoic to Mesozoic metamorphism, magmatism, sedimentation and development of the topographic relief - an active continental margin history?. - , in prep.

Lucassen, F., Becchio, R, Harmon, R. and Franz, G. (1999): A Chaos of lead in the basement of the Central Andes (18?-27?)?. - ISAG 99, : 450-453; G?ttingen. - []

Lucassen, F., Becchio, R., Harmon, R., Kasemann, S., Franz, G., Trumbull, R., Wilke, H.-G., Romer, R.L., Dulski, P. (2001): Composition and density of the continental crust at an active continental margin: the Central Andes between 21 and 27 S. - Tectonophysics, 341: 195-223.

Lucassen, F., Becchio, R., Wilke, H.-G., Franz, G., Viramonte, J. & Wemmerr, K. (1998): The paleozoic basement of the Central Andes (2?-26?S) - the metamorphic view. - GSA Bulletin, submitted.

Lucassen, F., Becchio, R., Wilke, M.F., Thirlwall, H.G., Franz, G., and Wemmer, K. (2000): Proterozoic-Paleozoic development of the basement of the Central Andes (18?-26?) - a mobile belt of the South american craton. - Journal of South American Earth Science, in press.

Lucassen, F., Escayola, M., Romer, R.L., Viramonte, J., Koch, K., Franz, G. (2002): Isotopic composition of Late Mesozoic basic and ultrabasic rocks from the Andes (23-32 S) - implications for the Andean mantle. - Springer Verlag.

Lucassen, F., Escayola, M., Romer, R.L., Viramonte, J. and Franz, G. (1999): Isotopic composition of Late Mesozoic mafic rocks from the Andes (23? - 32?S) - how heterogeneous is the mantle source?. - II SSAGI, : 238-242; Cordoba, Argentina. - []

Lucassen, F., Fowler, C. M. R., Franz, G. (1996): Extension and Magmatic Accretion During the Early and Mid-Mesozoic in the North Chile Coast Range: A Geological and Thermal Model. - Tectonophysics, submitted.

Lucassen, F., Fowler, C.M.R., Franz, G. (1996): Formation of magmatic crust at the Andean continental margin during early Mesozoic: a geological and thermal model of the North Chilean Coast Range. - Tectonophysics, 262: 263-279.

Lucassen, F., Franz, G. (1992): Generation and metamorphism of new crust in magmatic arcs: a case study from northern Chile. - Terra Nova, 4: 41-52.

Lucassen, F., Franz, G. & Laber A. (1999): Permian high pressure rocks - the basement of the Sierra de Lim?n Verde in N-Chile. - J. South Am. Earth Sci., 12: 183-199.

Lucassen, F., Lewerenz, S., Franz, G., Viramonte, J. & Mezger, K. (1999): Metamorphism, isotopic ages and composition of lower crustal granulite xenoliths from the Cretaceous Salta Rift, Argentina. - Contributions to Mineralogy and Petrology, 134: 325- 341; . - []

Lucassen, F., Thirlwall, M.F. (1998): Sm-Nd ages of mafic rocks from the Coastal Cordillera at 24?S, northern Chile. - Geologische Rundschau, 86: 767-774.

Lucassen, R, Franz, G., Thirlwall, M. F. and Mezger K. (1999): Crustal recycling of metamorphic basement: Late Paleozoic granites of the Chilean Coast Range and Precordillera at -22oS. - Journal of Petrology, 40: 1527- 1551; . - []

Publikationen in Tagungsbänden

Egenhoff, S.O., M?ller, J., Malez, J., & Erdtmann, B.D. (1997): Basin development of an Ordovician back-arc basin in southern Bolivia. - Canadian Soc. Of Petroleum Geologists (CSPG) - Soc. Of Economic Paleontologists and Mineralogists (SEPM) Joint Convention, Calgary, Canada, Abstracts: 88.

Lucassen F., Lewerenz S., Schilling F., Franz G., Viramonte J. (1996): Cretaceous xenoliths from the lower crust and upper mantle - Provincia de Salta, Argentina. - Terra Nostra, 8: 89 (Lateinamerika-Kolloquium 1996).

Lucassen F., Schilling F., Franz G. (1994): Numerische Modellierung von magmatischer Akkretion in einem Extensionsregime: Entwicklung der K?stenkordillere Nordchiles im fr?hen bis mittleren Mesozoikum. - Terra Nostra, 2: 51.

Lucassen, F. & Franz, G. (1997): Crustal recycling of metamorphic basement: late Proterozoic granites of the Chilean Coast Range and Precordillea at ~ 22?S. - VIII Congr. Geol. Chil., Actas, II: 1344-1348.

Lucassen, F., Becchio, R., Franz, G., Trumbull, R., Kramer, W. and Wilke, H.-G. (1998): Metamorphism and composition of the Central Andean crust through time. 3rd Andean Geoscience Workshop, University of Plymouth, 16th June 1998. - , : ; .

Lucassen, F., Franz, G. & Fowler, C.M.R. (1993): Arc Related Igneous and Meta- igneous Rocks in the Coastal Cordillera of Northern Chile: Continuous Replacement of the Crust?. - Second International Symposium on Andean Geodynamics ISAG, Oxford (UK).

Lucassen, F., Franz, G. & Laber, A. (1994): Geology and Petrology of Metamorphic Rocks from the Preandean Basement of Northern Chile, 18?-24? S. - VII? Congreso Geol. Chileno, Concepci?n, Chile, Actas I: 96-100; Concepci?n.

Lucassen, F., Franz, G. & Laber, A. (1994): Geology and Petrology of Metamorphic Rocks from the Preandean Basement of Northern Chile, 18?-24? S. - Lateinamerika Kolloquium; T?bingen.

Lucassen, F., Schilling, F. R., Franz, G. (1994): Numerical Modelling of Magmatic Accretion in an Extensional Regime: Early to Mid-Mesozoic Development of the North Chilean Coast Range. - Terra Nostra, 2: a10.

Lucassen, F., Wilke, H.G., Viramonte, J., Becchio, R., Franz, G., Laber, A., Wemmer, K. (1996): The metamophic basement of the Central Andes (18?-26?S) - did terranes arrive during Paleozoic?. - Terra Nostra (15. Geowiss. Lateinamerika Koll.), 8/96: 90; Hamburg.

Lucassen, F., Wilke, H.G., Viramonte, J., Becchio, R., Franz, G., Laber, A., Wemmer, K., Vroon (1996): The Paleozoic basement of the Central Andes (18?-26?S): a metamorphic view. - 3rd International Symposium on Andean Geodynamics, St. Malo - Frankreich, ORSTOM (eds.): Troisi?me symposium international sur la G?odynamique andine (ISAG), St Malo: 779-782.

Qualifikationsarbeiten (Habilitationsschriften, Promotionen, Diplomarbeiten) und interne Berichte

Schnurr, W. (2001): Zur Geochemie und Genese neogener und quart?rer felsischer Vulkanite in den s?dlichen Zentralanden (25?-27?S und 67?-69?W). - Berl. Geowiss. Abh. Reihe A, 211.