Abstract.A complete Alpine cross section integrates numerous seismic reflection and refraction profiles, across and along strike, with published and new field data. The deepest parts of the profile are constrained by geophysical data only, while structural features at intermediate levels are largely depicted according to the results of three-dimensional models making use of seismic and field geological data. The geometry of the highest structural levels is constrained by classical along-strike projections of field data parallel to the pro-

The Austroalpine and Upper Penninic nappes in eastern Switzerland represent a passive continental margin and the adjacent ocean of Jurassic-Cretaceous age, imbricated by Late Cretaceous-Tertiarv orogenic shortening. Well-preserved, rift-related faults allow reconstruction of the passive margin and ocean-continent transition zone and yield new information on the kinematics of rifting. Rifting evolved from pure-shear stretching to detachment-controlled, asymmetric stretching and resulted in complete exhumation of subcontinental mantle rocks at the sea floor. After precursory normal faulting in the Late Triassic, Jurassic rifting occurred in two phases, During the first rifting phase (Hettangian-Sinemurian), predominantly east-dipping normal faults developed in the upper crust; their dips decreased in the rniddle to lower crust, where they probably graded into anastomosing shear zones in the lower crust and mantle lithosphere. The resulting overall geometry approximated pure-shear stretching. During the second rifting phase (Toarcian-Middle Jurassic), a system of west-dipping detachment faults formed, penetrating the whole lithosphere and accommodating asymmetric extension. During progressive stretching, subcontinental mantle rocks were tectonicallv exhumed and exposed at the sea floor in two areas, represented by the Platta and Malenco nappes (Penninic), The intervening Nlargna and Sella continental nappes are interpreted as an extensional allochthon belonging to the Apulian margin. Finally, a mid-ocean ridge may have formed west of the Margna-Sella allochthon. The Austroalpine realm thus represents the lower-plate margin-and the Briangonnais, the upper-plate marginof the Piemont-Liguria ocean. This scenario is in qualitative agreement with the subsidence histories of the two margins. IZII 'tlnp.I tueruqrElep urctrl eql Jo ,(E,\\el€eiq eqt rPeu (986I '€lrrure d :gg6I '.retelrs puE reSurlteH) ,,]ceJl3 e8pe rrtlrtsosr". eql .Jo esneJäq ulroJ ,(Enr .raplnoqs UrJ A\o't.ll?u E ,{luo pue 'Surqcter1s I€lsnJc Io turloru€ q8rq eqt ot 8urm,o '3ur1;u go SuiuurSeq eql ruor.+ septsqns ut8-ttut eleld-:e,ro1 eqt'lsertuor uI eJueprsqns IeurJeql ,(q pe,uol1o; leplnoqs l.+r-r puoJq r Io uorttrrrJo.' pur: gqdn guuf s ol sppel Suruurq] IelsruJ.]o eJuasgu eql ur araqdsoqtll altur?ru eqt 1o Suruurqt 'uriruru e1e1d-:eddn aq1 ug (g) 'urirelu eteld-"reddn eql uo srncJo sre,{e1 deep Jo uortpunqxr qrns oN 'e1e1d :eddn aql ro le^orrar aq1 o1 enp 'ur8.reur a1u1d-.re.uo1 eqt.;o ued plsrp etp ur.,(1pcruo1cel peunqxe aq,{eu leueleru ellu€ur pu? p1sruo-;e,ro1 (7) 'ueaJo erll p"u:,uo1 Eurddrp eurlcouoiu e 'J'r 'eJnxog purS"reru e ,{q pezt.relJ?lurlJ sr ur8;eu e1e1d-:eddn arp s€eJaql\'ur?;eru e1e1d-re,tro1 eql uo sJnJco ,(1prrd,{1 'upeco eq} pJE,trol osues-Jeeqs e qlr,t\ llnp,J luoulqJ€lep e ,{q paroog 's{colq Irlsn-rr-.reddn pa11r1 ;o "re,(e1 V (l) :(Z 3rg) sur8ruur Sursoddo aqt Io sorntea.] e^rtruusrp 8ur.trol1o; eql ur stlnse.I uJaped srql 'Orf 6t€ d'U9 ^'q.u!tz Utq.sllosaD uopucq.slol rnleN rep Uurpsserl€lletrer :uapunqnsrD ur elJepeqtutlqlue0 r...

No abstract

The Iberia Abyssal Plain segment of the West Iberia margin was drilled during Ocean Drilling Program Legs 149 and 173 and has been extensively studied geophysically. We present new microstructural investigations and new age data. These, together with observed distribution of upper-and lower-crustal and mantle rocks along the ocean-continent transition suggest the existence of three detachment faults, one of which was previously unrecognized. This information, together with a simple kinematic inversion of the reinterpreted seismic section Lusigal 12, allows discussion of the kinematic evolution of detachment faulting in terms of the temporal sequence of faulting, offset along individual faults, and thinning of the crust during faulting. Our study shows that the detachment structures recognized in the seismic profile became active only during a final stage of rifting when the crust was already considerably thinned to c. 12km. The total amount of extension accommodated by the detachment faults is of the order of 32.6km corresponding to a [3 factor of about two. During rifting, the mode of deformation changed oceanwards. Initial listric faulting led to asymmetric basins, accommodating low amounts of extension, and was followed by a situation in which the footwall was pulled out from underneath a relatively stable hanging wall accommodating high amounts of extension. Deformation along the latter faults resulted in a conveyor-belt type sediment accumulation in which the exhumed footwall rocks were exposed, eroded and redeposited along the same active fault system.

The first evidence for ultrahigh‐pressure (UHP) metamorphism in the Eastern Alps is reported from kyanite eclogites of the Pohorje Mountains in Slovenia. Polycrystalline quartz inclusions surrounded by radial fractures in garnet, omphacite, and kyanite are interpreted to be pseudomorphs after coesite. Abundant quartz rods and needles in omphacite indicate an exsolution from a preexisting supersilicic clinopyroxene that contained a Ca‐Eskola component. Geothermobarometry on the mineral assemblage garnet + omphacite + kyanite + phengite + quartz/or coesite yields peak pressure and temperature conditions of 3.0–3.1 GPa and 760°–825°C, well within the stability field of coesite, thus supporting the microtextural evidence for UHP metamorphism. This records the highest‐pressure conditions of Eo‐Alpine metamorphism during the Cretaceous orogeny in the Alps, implying a very deep subduction of the continental crust to at least 90–100 km depths. The new data are evidence for a regional southeastward increase of peak pressures in the Lower Central Austroalpine, indicating a south‐ to eastward dip of the subduction zone. Subduction was intracontinental; northwestern parts of the Austroalpine (Lower Central Austroalpine) were subducted under southeastern parts (Upper Central Austroalpine). The subduction zone formed in the Early Cretaceous in the northwestern foreland of the Meliata suture after Late Jurassic closure of the Meliata Ocean and the resulting collision, by a forward subduction shift to a Permian rift.

[1] The Rhodope Metamorphic Province in the area around the Mesta Graben (SW Bulgaria) exposes a structurally lower complex, the Pangaion-Pirin Complex of Variscan continental crust and its cover (mostly orthogneiss and marble), and a higher complex, the Rhodope Terrane of mixed oceanic and continental origin with metamorphosed Jurassic arc magmatites. The boundary between the two is the top-to-thesouthwest Nestos Shear Zone. The regional top-tothe-southwest shearing of the two basement complexes is related to the emplacement of the Rhodope Terrane over the Pangaion-Pirin Complex along this shear zone. Syntectonic and posttectonic Alpine intrusions within the basement can provide age limits for the thrusting.

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New evidence for ultrahigh-pressure metamorphism (UHPM) in the Eastern Alps is reported from garnet-bearing ultramafic rocks from the Pohorje Mountains in Slovenia. The garnet peridotites are closely associated with UHP kyanite eclogites. These rocks belong to the Lower Central Austroalpine basement unit of the Eastern Alps, exposed in the proximity of the Periadriatic fault. Ultramafic rocks have experienced a complex metamorphic history. On the basis of petrochemical data, garnet peridotites could have been derived from depleted mantle rocks that were subsequently metasomatized by melts and/or fluids either in the plagioclase-peridotite or the spinel-peridotite field. At least four stages of recrystallization have been identified in the garnet peridotites based on an analysis of reaction textures and mineral compositions. Stage I was most probably a spinel peridotite stage, as inferred from the presence of chromian spinel and aluminous pyroxenes. Stage II is a UHPM stage defined by the assemblage garnet + olivine + low-Al orthopyroxene + clinopyroxene + Cr-spinel. Garnet formed as exsolutions from clinopyroxene, coronas around Cr-spinel, and porphyroblasts. Stage III is a decompression stage, manifested by the formation of kelyphitic rims of high-Al orthopyroxene, aluminous spinel, diopside and pargasitic hornblende replacing garnet. Stage IV is represented by the formation of tremolitic amphibole, chlorite, serpentine and talc. Geothermobarometric calculations using (i) garnet-olivine and garnet-orthopyroxene Fe-Mg exchange thermometers and (ii) the Al-inorthopyroxene barometer indicate that the peak of metamorphism (stage II) occurred at conditions of around 900°C and 4 GPa. These results suggest that garnet peridotites in the Pohorje Mountains experienced UHPM during the Cretaceous orogeny. We propose that UHPM resulted from deep subduction of continental crust, which incorporated mantle peridotites from the upper plate, in an intracontinental subduction zone. Sinking of the overlying mantle and lower crustal wedge into the asthenosphere (slab extraction) caused the main stage of unroofing of the UHP rocks during the Upper Cretaceous. Final exhumation was achieved by Miocene extensional core complex formation.