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This Thesis deals with the metamorphic and structural development of the La Paz Crystalline Complex (Ortega-Gutierrez 1982), which extends south of the city of La Paz, Baja California Sur, Mexico, to the southern tip of the Baja California peninsula.\nThe results presented are data on the development of structures and metamorphism based on detailed geologic mapping. This includes the succession of metamorphic isograds, pT-paths for structural units and the relation of the two. It allows to explain the development of the crystalline complex in light of the specific tectonic situation.\nThe most important new result is that the whole complex does not make up one distinct tectonostratigraphic terrane, as supposed previously (Sedlock et al. 1993, Gastil 1991, Beck 1991 and references therein), but that the complex is separated by a SSW-NNE striking fault. This fault juxtaposes rocks of different origin and with different metamorphic history. Intrusives in the north-western area are of relatively primitive M-type, in the south-eastern area, intrusives show a higher degree of crustal contamination (Schaaf et al. 2000). The structural work presented here shows that the fault already described in literature as the \u2018La Paz Fault\u2019, but interpreted differently (Aranda-G\xf3mez & P\xe9rez-Venzor 1989, Sedlock et al. 1993, Schaaf et al. 2000) is indeed the structural feature described above. Metamorphic contrast across the fault is minor, but an anticlockwise pT-path could be constructed for the footwall. \nComparison with new results from the northern part of Baja California (Johnson et al. 1999, Schmidt & Paterson 2002, Ortega-Rivera 2003) shows that the La Paz Crystalline Complex is indeed a part of the Peninsular Ranges Batholith (Gastil 1983, 1991). The separation into a western and an eastern part is characteristic for this complex and can be compared to the geochemical, metamorphic and structural characteristics presented here.\nPT-determinations were conducted for the overall low-pressure metamorphism using several methods: construction of petrogenetic grids for metapelitic rocks (Spear et al. 1999, Pattison et al. 2002), different geothermobarometers (e. g. garnet/biotite, Holdaway 2000, GASP, Holdaway 2001) and a relatively new approach to calculate pseudosections through thermodynamically modelled systems with known bulk-composition (Connolly & Petrini 2002, Tinkham et al. 2001). The pseudosections are a very useful graphic tool to represent modelled metamorphic mineral parageneses, which can be easily compared with actual measurements (Microscope, Electron Microprobe).