The phlogopite peridotite unit of the Finero Complex is a restitic largest in the Alps. The chromite is magnesian and locally harzburgite that records two metasomatic events. The first event is contains inclusions of Fe-Ni-Cu sulphide and platinum related to the intrusion of basaltic magma, which reacted with the group element minerals (Ferrario & Garuti, 1990). pyroxene of the host harzburgite to produce chromitite pods with dunite Chromitite forms well-defined bodies with modal chrohaloes. It also produced secondary clinopyroxene and amphibole in mite concentrations as high as 75%. The occurrences the harzburgite and enriched harzburgite in Na and the light rare were described by Roggiani (1948), Friedenreich (1956, earth elements. The second metasomatic event is related to the later Forbes et al. (1978) andSaager et al. (1982). intrusion of clinopyroxenitic dykes. During this event, water-richThe petrology of the Finero Complex is poorly unvapour penetrated the harzburgite along fractures and reacted with derstood. One reason is that the phlogopite peridotite, it to form phlogopite, thus enriching the rock in K. Chromitites host which makes up the core of the complex, exhibits anzircons that yield an age for the first metasomatic event of 207•9 + omalous petrographic and geochemical characteristics 1•7/−1•3 Ma, during which time extensional tectonics prevailed in indicative of metasomatism and of a multistage evolution the Southern Alps.

Integration of several geologic lines of evidence reveals the prevalence of a lowland trans-Andean portal communicating western Amazonia and the westernmost Andes from at least middle Miocene until Pliocene times. Volcanism and crustal shortening built up relief in the southernmost Central and Eastern Cordilleras of Colombia, closing this lowland gap. Independent lines of evidence consist first, of field mapping in the Tatacoa Desert with a coverage area of ∼381 km2, 1,165 km of geological contact traces, 164 structural data points, and 3D aerial digital mapping models. This map documents the beginning of southward propagation of the southernmost tip of the Eastern Cordillera’s west-verging, fold-and-thrust belt between ∼12.2 and 13.7 Ma. Second, a compilation of new and published detrital zircon geochronology in middle Miocene strata of the Tatacoa Desert shows three distinctive age populations: middle Miocene, middle Eocene, and Jurassic; the first two sourced west of the Central Cordillera, the latter in the Magdalena Valley. Similar populations with the three distinctive peaks have now been recovered in western Amazonian middle Miocene strata. These observations, along with published molecular and fossil fish data, suggest that by Serravallian times (∼13 Ma), the Northern Andes were separated from the Central Andes at ∼3°N by a fluvial system that flowed into the Amazon Basin through the Tatacoa Desert. This paleogeographic configuration would be similar to a Western Andean, or Marañon Portal. Late Miocene flattening of the subducting Nazca slab caused the eastward migration of the Miocene volcanic arc, so that starting at ∼4 Ma, large composite volcanoes were built up along the axis of today's Central Cordillera, closing this lowland Andean portal and altering the drainage patterns to resemble a modern configuration.

A silicic ignimbrite flare-up episode occurred in the Pannonian Basin during the Miocene, coeval with the synextensional period in the region. It produced important correlation horizons in the regional stratigraphy; however, they lacked precise and accurate geochronology. Here, we used U-Pb (LA-ICP-MS and ID-TIMS) and (U-Th)/He dating of zircons to determine the eruption ages of the youngest stage of this volcanic activity and constrain the longevity of the magma storage in crustal reservoirs. Reliability of the U-Pb data is supported by (U-Th)/He zircon dating and magnetostratigraphic constraints. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2 counter clockwise block rotation and the beginning of a new deformation phase, which structurally characterised the onset of the youngest volcanic and sedimentary phase.

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Laser ablation-inductively coupled plasmamass spectrometry (LA-ICP-MS) was used as a complementary technique to X-ray¯uorescence (XRF), for multi-element analysis of geological samples fused with lithium-tetraborate Li 2 B 4 O 7 . Different calibration strategies using external non-matrix matched reference materials were investigated. Various internal standards were tested, including the use of Li from the¯ux, and the use of the naturally occurring internal standards, Si or Ca. The use of a naturally occurring standard is not as ef®cient as this required a prior analysis of the samples using XRF. The obtained values for the analysis of geological reference materials were compared with consensus literature values, and satisfactory agreement was found. Laser pits, which were formed, had a diameter of 80 mm and 3±5 replicates on each fused disc were measured. The reproducibility of the method was better than 10% for concentrations above 1 mg/g and better than 15% for lower concentrations. The use of Li as the internal standard offers the possibility of multielement determinations in geological samples, which have an unknown composition when the laser ablation analysis is carried out. However, using the calculated stoichiometric composition of the lithium-tetraborate for the calculation of the Li concentration leads to a constant deviation from the recommended values. Therefore, it was necessary to determine the Li concentration within each sample batch using at least one lithium tetraborate fused geological reference material. This resulting Li concentration in the beads was then used for all subsequent samples in a run. Limits of detection, reproducibility, deviation from reference values indicate the potential of LA-ICP-MS for such bulk analysis without matrix matched calibration standards.