Terra Nova, 23, 257–263, 2011 Abstract New apatite (U‐Th)/He and fission‐track data from the Nevado–Filábride complex in the Sierra Nevada of southern Spain are used to constrain the Neogene exhumation history. Apatite (U‐Th)/He ages are close to fission‐track ages in western Sierra Nevada indicating that rapid cooling occurred at 8–6 Ma, consistent with exhumation due to extension along the Mecina Fault. The western Sierra de los Filabres cooled rapidly at c. 12 Ma, while the central Sierra de los Filabres experienced less rapid cooling at 8 Ma. The age distribution in the Sierra de los Filabres can be explained by exhumation due to flexural uplift to the south‐west of the footwall of the Mecina Fault. The lower cooling rates in the central Sierra de los Filabres suggest that folding and erosion were the main exhumation processes during the Late Tortonian. Terra Nova, 00, 1–7, 2011

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24HRTEM textural evidence shows that clay minerals in the Tinguiririca geothermal 25 field (Andean Cordillera, central Chile) are the result of direct alteration of former 26 volcanic glass and minerals by hydrothermal fluids at similar temperatures to the 27 present day. They show the classical pattern of diagenetic transformation from 28 * Corresponding author. Tel.: +56-2-29784539; Fax: +56-2-26963050 E-mail address: mvazquez@ing.uchile.cl (M.Vázquez) 2 smectite at the top to illite at the bottom, with the progressive formation of 1 corrensite and chlorite. The high fluid/rock ratio, disposability of necessary 2 cations and absence of previous detrital phyllosilicates allow the consideration of 3 this area as a natural laboratory to establish the extreme ideal conditions for very 4 low-T reactions. Transformations from smectite to R1 illite-smectite (I-S) and from 5 these to R3 mixed-layers occur respectively at 80-120ºC and 125-180ºC. In spite 6 of ideal genetic conditions, the new-formed minerals show all the defective 7 character and lack of textural and chemical equilibrium previously described in 8 the literature for diagenetic and hydrothermal low-temperature assemblages. 9Chemistry of smectite-illite phases evolves basically through a diminution of the 10 pyrophyllitic component toward a theoretical muscovite (Si 4+ +☐ -> Al 3+ +K + ). 11However, a second chemical vector (Si 4+ +Mg 2+ -> Al 3+ +Al 3+ ), that is, decreasing 12 of the tschermack component, also contributes to the evolution toward the less 13Si-more Al rich muscovite in relation to the original smectite. Residual Mg (and 14 Fe) from the latter reaction is consumed in the genesis of chloritic phases.