Lavas, domes and subvolcanic bodies

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1 Lavas, domes and subvolcanic bodies Christoph Breitkreuz, TU Bergakademie Freiberg Lascar, Chile Ropy surface of a pahoehoe lava SiO 2 -poor lavapahoehoe = low viscosity lava with smooth, sometimes ropy surface Aa = high viscosity lava with blocky (autobrecciated) top, sides, front and base Lava tube Difference in viscosity: T and microlith content Krafla, Islandia Hornito (with trolls)

2 Mt. Shasta, N California Intermediate Lavas: High aspect ratio (height / length) Steep front and sides Sometimes with levees Lluillaillaco, N Chile/NW Argentina

3 Andesitic lava, columnar jointing Crater wall of Crater Lake, Oregon

4 Basaltic lava, Iceland Devil s Post pile, E California Hochsimmer lava flow, Eifel, W Germany

5 S Slovakia, Neogene Thickening of flood lava flows by inflation Fig. 5.2 Schematic cross sections of emplacement of a generic inflating pahoehoe sheet flow. Vertical scale varies from 1-5 m for Hawaiian flows to 5-50 m for the CRB Flows (CRB = Columbia River Basalt). (a) Flow arrives as a small, slow-moving, lobe of molten lava held inside a stretchable, chilled viscoelastic skin with brittle crust on top. Bubbles are initially trapped in both the upper and basal crusts. (b) Continued injection of lava into the lobe results in inflation (lifting of the upper crust) and new breakouts. During inflation, bubbles rising from the fluid core become trapped in the viscoelastic mush at the base of the upper crust, forming horizontal vesicular zones. The growth of the lower crust, in which pipe vesicles develop, is much slower. Relatively rapid cooling and motion during inflation results in irregular jointing in the upper crust. (c) After stagnation, diapirs of vesicular residuum form vertical cylinders and horizontal sheets within the crystallizing lava core. Slow cooling of the stationary liquid core forms more regular joints. (d) Emplacement history of flow is preserved in vesicle distribution and jointing pattern of frozen lava (From Self et al. 1997). Faciesanalysis of continental floodlava provinces Excerpts of figs. 6 and 7 from Single & Jerram (2004)

6 Single & Jerram 2004, JGS Flood lava Facies: Single & Jerram 2004: JGS, Jerram et al. 2002, GSA S.P. 362 See also Jerram & Widowson 2005, Lithos SiO 2 -rich lavas, domes and subvolcanic bodies Magmatic bodies emplaced as a coherent fluid SiO 2 -rich domes: a) unstable Mt. Pelee, 1902/3

7 Mt. St. Helens, Washington (USA) : 34 dacitic domes destroyed during explosive eruptions Pyroclastic flow (Type Merapi) resulting from the partial or complete, gravitative or explosive collapse of a lava front or a dome Merapi, Indonesia Santiaguito, Guatemala Continuous to episodic extrusion and episodic gravitational collapse of a lava front Harris et al. 2002

8 SiO 2 -rich lavas and domes: b) stable Glass Mtn., California Chao coulée, Neogene, Chile: 14 km, thickness 400 m Meidob Hills, Sudan 4 km Mesa lava forms on horizontal surface 4 km

9 Espesor (m) Espesor (m) aspect ratio Orton ,2 0,6 1,0 Volumen (km³) During continuous extrusion the thickness of a lava is limited: collapse under its own weight Continuous growth Fink et al SiO 2 -rich lava flows and lava domes PhD project Marion Geißler (Paulick & Breitkreuz 2005)

10 Textures that form during the emplacement of SiO 2 -rich lavas Landnamalaugar, Iceland Flow foliation, type open flower Effusive vent with creases Fig. 5.5 Schematic diagram showing development of foliation attitudes in vent area of dome. (1) Viscous dome emplaced. Shallow surface fractures develop. (2) Fractures nearest center deepen preferentially. (3) Fractures propagate inward as lava spreads laterally, causing most of upper surface to become a fracture surface. (4) Later stage of growth. Flows have developed. Most of flow still capped by fracture surface. Compression during flow forms surface folds. Flow stratigraphy not indicated. (5) Detail of vent area showing uplift and outward rotation of blocks as lava continues to rise (From Fink 1983). Vesiculation (second boiling)

11 Finely vesicular pumice, FVP (Fink 1983) Coarsely vesicular pumice, CVP (Fink 1983) Fig. 5.8 Schematic diagram showing simultaneous rise of coarse pumice diapirs and inward propagation of fractures. Fracture axis corresponds to former anticlinal and lies axis parallel to flow direction (From Fink 1983).. Density inversion may result in diapirism Fink 1983 Little Glass Mtns, California

12 Fragmentation in phreatic dykes Brittle to ductile deformation Hematitisation by phreatic fluids Lavas may contain lithic clasts! Lassen Peak, California: lava dacítica Textures that form during emplacement of subvolcanic bodies Sill

13 Cerro Blanco Volcanic Complex, Jurassic, N Chile, Bretschneider 2004 Brittle fragmentation of the sediments, ductile intrusion and fragmentation of the dyke Cenozoic sill complex, Isle of Skye Saucer-shaped sills in the Karroo basin, South Africa Elliott et al. 1999, Stor(?e)y & Kyle 1997, Elliott & Fleming 2004: Ferrar-super sill-dyke province, Verbindung mit Karroo: Saucer shape sill: Google: E31 57, S26 17 Und GSSP 234

14 Late Paleozoic Sill Complex on the Flechtingen-Roßlau Block Awdankiewicz et al Basaltic sill with peperitic margins emplaced into wet, unconsolidated volcanoclastic deposits; Sag hegy, Neogene, Hungary G.K. Gilbert, 1877 Simple laccolith with a central conduit, types piston to chrismas tree (Corry 1988) Capverdian Islands

15 Henry Mtns. Lakkoliths, Utah Fliess Halle Volcanic Complex Level of erosion cupula bowl Flow foliation, type onion Intrusive-extrusive complexes Permian, Saar-Nahe Basin, W Germany (Lorenz & Haneke 2004) With late explosive activity Type Merapi

16 Laccolith complex with many conduits: A) Donnersberg Type Emplacement in the same level ( baloons in a box ) Breitkreuz & Mock 2004 Donnersberg Laccolith Complex, Saar-Nahe Basin, W Germany Laccolith complex with many conduits: B) Halle Type Emplacement in different levels Breitkreuz & Mock 2004 Halle Volcanic Complex, Late Carboniferous - Permian, E Germany 3D exposure due to intense coal and uranium exploration Halle Volcanic Complex

17 Östlicher HVK: Kontakte zwischen Lava, Sill, Lakkolith und Klastiten Mock et al Mock et al. in 2005 Type Donnersberg, Type Halle Level of neutral bouyancy How to distinguish the different types of lavas, domes and subvolcanic bodies? 1. Textures of the top margin Deformed or liquified sediment vs. Infiltration textures Peperites, brecciation Contact metamorphic halos 2. Concept Core vs. Carapace Facies Texturzonierung in einer SiO 2 -reichen Lava comminuted vitrophyre autobreccia (top) carapace flow front core 0-30 % of total thickness carapace basal breccia obsidian (dense vitrophyre) partially devitrified obsidian talus vesicle-rich obsidian (pumiceous vitrophyre) completely recrystallized (crystalline lava) * given that the cooling unit resembles the depositional one

18 * given that the cooling unit resembles the depositional one Texturzonierung in einer SiO 2 -reichen Lava comminuted vitrophyre autobrecciation vesiculation inhomogeneous domains of crystallisation autobreccia (top) carapace core 0-30 % of total thickness basal breccia carapace obsidian (dense vitrophyre) flow front talus vesicle-rich obsidian (pumiceous vitrophyre) partially devitrified obsidian completely recrystallized (crystalline lava) Homogeneous groundmass, completely recrystallized Texturzonierung in einer SiO 2-reichen Lava comminuted vitrophyre Texturas de matríz autobreccia (top) carapace flow front core 0-30 % of total thickness carapace basal breccia obsidian (dense vitrophyre) partially devitrified obsidian talus vesicle-rich obsidian (pumiceous vitrophyre) completely recrystallized (crystalline lava) * given that the cooling unit resembles the depositional one Thickness relation between carapace and core facies Manley & Fink 1987 Carapace Facies: 70 to 100% of the total thickness Carapace facies: some decimeters to meters

19 Thank you!