Geological-Structural Map of the Orobic and Porcile
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8° 16° A EA 10°0'0''E ALPS A C.ma Desenigo M. Canale Quaternary covers 46° A cSA 9°55'0'' E W 9°45'0'' E Insubric Fault 9°35'0'' E MF MF Bergell Bergell Triangia Tertiary Intrusives IT GEOLOGICAL-STRUCTURAL MAP OF Southern Alps: AL Ardenno IF Sondrio 46°10'0'' N Sedimentary covers Y Adamello Sondrio 42° ( Valtellina Carbonate ( Dazio Allochthonous Units THE OROBIC AND PORCILE THRUST JUNCTION, T. IF ( ( PT Upper Triassic Units V Valtellina Morbegno alle del Livrio Servino and Carniola di T. ( V e ( Gallinera( al T Bovegno 38° cil T. ( ( artano Por ( , CENTRAL SOUTHERN ALPS (N ITALY) ) Verrucano Lombardo , , M. Vespolo V Orobic T. ( ( Orobic( ) ) V al Gerola al al Gerola al V ( ( ( , al Cervia ( ) CE-A ( Ponteranica conglomerate ( V ( ( ) al Madre P.zo Meriggio , ( 46°0'0''N ( TC-A ) Collio volcanics and ( ( ) , ( PT O-A ( volcaniclastic sediments ( , ) P.zo Campaggio ( ( , B - Valcanale F 46°5'0'' N ( Valtorta .( ( ( Southern Alps: Basement ( ( ( ( ( Mica schists PAOLO D’ADDA and STEFANO ZANCHETTA ( (Edolo schists Auct) e ( ( ( ( Giudicarie belt M. Tartano , ( PT M. Toro ) ( ( MA-A ) ) Two mica gneiss ( ( ) ( , , , Gerola C. Stella Clusone Fault ) P.zo Rotondo , Auct. C M. Aga P.zo del (Morbegno Gneiss ) ) ( , ( ( Mib ( o ) Diavolo G , OT OT Leucocratic gneiss ( M. Verrobbio P. San Marco Foppolo ( ( ) Gonfolite Group (Gneiss del Corno Stella Auct) ( ( ( ( , ( ,) ) ( OT TC-A , ( ( Granitoid gneiss ( Tertiary magmatic ( ( ( M. Pegherolo , ,) ) rocks N Austroalpine domain ) , ) ( ) Department of Earth and Environmental Sciences, ,) , ,, ( ,( P.zo di Trona ), ) , , ) ) , ( ) ) Lombardian Flysch (LC) Carona ) , , Tonale unit , )) ) , , Mezzoldo M Cabianca N ) , , )) , ), , O-A University of Milano Bicocca )) , , , ) ) ) Jurassic to Lower Cretaceous , Branzi ), ) ) , , 46°0'0'' N Campo-Languard complex ,) Bergamo( A' ,) ) ) ), ) successions TC-A ( ( ( ( ( , , , ( ) ,) , Upper Triassic successions Piazzatorre Bernina unit ( ) Antiforms ( ( Gromo 0 10 20 km Lake Garda Val Torta Margna unit Lower to Middle Triassic Valtorta al Brembana Thrusts ( V ( successions Back-thrusts Orobic anticlines 0 2,5 5 km ©Journal of Maps 2014 corresponding author: [email protected] ( B Milano A'' ( (Permian to Lower Triassic) ( ( Variscan basement Modified after Zanchetta et al., 2011. IF: Insubric fault; MF: Mortirolo Fault; O-A: Orobic Anticline; OT: Orobic Thrust; A ( ( PT: Porcile Thrust; TC-A: Trabuchello-Cabianca Anticline. 1550000 1551000 1552000 1553000 80 43 D B 47 5101000 Quaternary cover 1:10.000 scale 44 Undifferentiated glacial 55 Talus cones and debris flows. 58 deposits. Undifferentiated talus Rock glaciers. deposits. Original mapping fieldwork by: 68 55 62 60 64 P. D’Adda and S. Zanchetta, 2009-2010 55 48 45 48 Permian - Triassic cover 35 A Original field mapping at 1: 5000 scale Carniola di Bovegno: yellow vacuolar dolomitic limestones and dolostones 55 with lensenses of grey to green marls and clay (OLENEKIAN-ANISIAN). 45 60 Servino: well bedded quartz sandstones with green to light green pelites 42 and minor yellow to green marls. Bedding is often involved in E-W trending Digital Version by: folds, and cataclastic layers are common near the tectonic boundary with the 58 65 75 overthrusted metamorphic basement (INDUAN-OLENEKIAN). P. D’Adda and S. Zanchetta 75 Verrucano Lombardo: red to brown continental conglomerates and 65 78 breccias with lenses of red sandstones and pelites. Clasts are millimetric to centimetric and consist of quartz, red volcanites and volcanoclastites and minor metapelites. They derived from the erosion of the Lower Permian 70 volcanics (Collio Fm) and metamorphic basement of the Southern Alps Topographic base: CTR Regione Lombardia 60 (LATE PERMIAN). 48 22 Coordinate system: Gauss Boaga (Monte Mario 1) Cabianca Volcanite (Collio vulcanico auct.): red to brown volcanic and 40 volcaniclastic deposits, with minor alternating sandstone and siltstones (EARLY PERMIAN). 45 45 Basal Conglomerate: dark green to grey breccias and sandstones derived from the erosion of the metamorphic southalpine basement . Clasts are 32 45 65 millimetric to centimetric and consist of quarzites, metapelites and minor 47 metagranitoids. Souh of Cima dei Siltri a N-dipping cataclastic foliation strongly overprintsh the original texture (EARLY PERMIAN). 58 20 72 82 82 48 Southalpine crystalline basement 55 75 38 35 74 5100000 62 65 5100000 38 Pre-Alpine dikes: dark coloured and very fine grained porphyrites, with 78 65 75 45 plagioclase, biotite, amphibole (±quartz). A slight S2 foliation is observable 78 where an isoorientation of amphibole and biotite occur. Contacts with coutry 42 32 rocks are sharp and folded by D3. 56 70 55 55 68 Amphibolites: with amphibole, plagioclase 42 52 40 24 35 18 32 (±quartz±garnet±biotite±chlorite). The S2 foliation is defined by 85 35 compositional layering or by shape preferred orientation of amphibole. 38 68 65 Granitoid gneiss (Ortogneiss del Monte Fioraro, Auct.): granitoid gneiss 45 68 72 52 18 40 with K-feldspar porphyroclasts. The typical mineralogy is given by K-feldspar, quartz, plagioclase, muscovite, biotite (±garnet±titanite±chlorite). The 43 45 55 48 regional foliation (S2) is defined by isoorientation of phyllosilicates.S2 is 38 62 locally crenulated and folded by D3. The contacts with micashists are folded 55 by D3 N-dipping folds. 44 68 70 50 65 18 Leucocratic gneiss (Gneiss Chiari del Corno Stella, Auct.): medium to coarse grained ortogneiss, white to light-gray in outcrop. Quartz, albite, 55 54 54 54 plagioclase, muscovite, biotite (±chlorite±tourmaline) and millimetric to 65 centimetric porphyroclasts of K-feldspar. These rocks form elongated bodies 20 55 along the Porcile fault and occur also along a secondary plane related with 30 32 18 34 44 the Orobic Thrust, NE of Cima dei Siltri. In the study area the S2 foliation is 68 60 25 almost completely overprinted by cataclastic deformation. 55 38 37 35 62 85 50 Two-mica gneiss: fine to medium grained paragneiss with quartz, 65 58 44 62 35 52 65 plagioclase, biotite, muscovite (±garnet±chlorite). They are always 68 interleaved with micaschists displaying transitional contacts with them. Two- 38 66 85 mica gneiss crop out only in the footwall of the Porcile line, near the fault 40 62 38 38 64 plane. D3 folds only slightly affect the S2 foliation, which is in turn 65 reactivated and overprinted by a N-dipping cataclastic foliation within the fault zone. 50 45 40 Mica schists: fine to medium grained micaschists, gray to dark- gray in outcrop. The typical mineralogy is made of muscovite, quartz, plagioclase, 52 48 biotite (±garnet±staurolite±clorite). The pervasive schistosity (S2) is defined 72 by the shape preferred orientation of phillosilicates. Quartz lenses can often 34 be observed. Garnet and biotite are partially replaced by chlorite indicating 65 retrograde metamorphism. 80 Symbols 40 45 45 5099000 5099000 Bedding Traces of S2 foliation Overturned bedding Traces of mylonitic foliation 47 30 S2 foliation Traces of syncline axial surfaces Axes of D3 folds Traces of anticline axial surfaces 32 55 52 45 60 L3 mineralogical lineation Faults 40 56 Axial surfaces to D3a folds Inferred faults 55 52 Axes of D3 folds 60 85 b Thrusts 60 Cataclastic foliation Inferred thrusts Cataclastic shear zones 48 58 Landslides 30 85 Traces of geological cross-sections 38 A’ 45 1552000 1553000 33 32 55 65 62 N 0 500 1000 m 45 B’ N Cima dei Siltri (2179 m) S Cross section A-A’ 1550000 1549000 1551000 2250 Orobic thrust S. Simone Pass N 2500 Mt. Fioraro (2428 m) Porcile Thrust Cross section B-B’ 2000 Pizzo delle Segade (2160 m) S 2000 Orobic Thrust BASEMENT OROBIC THRUST PORCILE THRUST Stereographic projections of structural data are all equal (hangingwall in the San Marco Pass area) (hanging wall NW of M. Rotondo) A2 (28) A3 (46) A2 (25) A3 (28) area and projected to the lower hemisphere. N N N N S2 (73) PA3 (45) S2 (85) PA3 (30) Stereographic projections of structural data (foliation, fold W E W E W E W E elements and lineation) have been realized with Monte Arete OpenStereo (Grohmann, C.H. and Campanha, G.A.C., Laghi di Porcile PT PT Monte Toro C N S N S 2010. OpenStereo: open source, cross-platform software 2500 OT 2500 OT: Orobic Thrust Cà San Marco S S S S OT OT for structural geology analysis. Presented at the AGU A2 (22) (basement in the footwall W of M. Rotondo) A3 (29) 2000 N S SEDIMENTARY COVER N N 2000 2000 PT: Porcile Thrust S2 (79) PA3 (21) fold axes 2010 Fall Meeting, San Francisco, CA.). SP1 and SP2 axial planes 1500 cleavage 1500 1500 Fault slip data sets have been projected with the software W E W E 1000 1000 1000 Trace of main thrust surfaces of Angelier (1984). 500 500 500 Pseudotachylytes S S 0 1 km 0 1 km 0 1 km sl section A-A' sl section B-B' sl section C-C' a b PERMO-MESOZOIC COVERS SOUTHERN ALPS BASEMENT 1500 V AL V C 2000 AL V Esino Limestone Quartz veins with Fe-ores MADRE M. Vitalengo AL LUNGA 2406 m 2000 2000 Angolo Limestone Mica schists and quartz-mica schists M. Gavet B CER Mylonitic foliation OROBIC THRUST Mylonitic foliation PORCILE THRUST OLIGOCENE (?) re-activation 2318 m (basement, hangingwall) (basement, hangingwall) Carniola di Dextral faults Sinistral faults Two-mica gneisses Bovegno VIA Sponda Camoscera 0 2000 0 Servino Ortogneiss and amphibolic gneiss PT 2446 m Verrucano Mylonitic quartz-feldspar gneisses P.zo Scala 45 Lombardo 2340 m 45 B.ta dei Lupi Ponteranica Leucocratic gneiss ("Corno dip angle P.so di Tartano 90 90 dip angle Conglomerate Stella gneiss") M. Cadelle Laghi di 2483 m Collio Formation Porcile Reverse faults with striations Reverse faults with striations Basal 2000 (thrust fault zone and cover in the footwall) 0 (thrust fault zone) 0 M. Fioraro strike kinematics Conglomerate 2000 M.