Origin and metamorphism of peperite and associated rocks in the Devonian Elwell Formation, northern Sierra Nevada, California

Brooks, Elwood R.; Wood, Michael M.; Garbutt, Phillip L.

doi:10.1130/0016-7606(1982)93<1208:oamopa>2.0.co;2

Cited by 60 publications

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“…However, most peperite described in the literature involves relatively ¢ne-grained sediment (Brooks et al, 1982;White and Busby-Spera, 1987;Hanson, 1991;Hanson andWilson, 1991, 1993;Boulter, 1993;Rawlings, 1993;Mueller et al, 1994;Brooks, 1995;Goto and McPhie, 1996;Hanson and Hargrove, 1999). There are few descriptions involving coarse-grained host sediment (Busby-Spera and Hanson and Wil-son, 1991), perhaps because of di⁄culties in identi¢cation rather than low abundance.…”

Section: Introductionmentioning

confidence: 99%

Characteristics and origin of peperite involving coarse-grained host sediment

Squire

McPhie

2002

Journal of Volcanology and Geothermal Research

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Peperite involving basalt and polymictic volcanic conglomerate occurs in the Pliocene Ba Volcanic Group at Yaqara in northern Viti Levu, Fiji. Because the host sediment is coarse-grained and dominated by basalt clasts, the peperite could be easily overlooked and mistaken for another coarse volcaniclastic facies. However, the presence of groups of basalt clasts that show jigsaw-fit texture, fluidally shaped basalt clasts with complete glassy margins, gradational contacts with adjacent sedimentary facies and the absence of stratification indicate that molten basalt mingled with unconsolidated gravel. Using these criteria, we show that other superficially similar, coarse, polymictic facies with fluidal basalt clasts are not peperite. Both blocky and fluidal basalt clasts occur together in the peperite. The amoeboid basalt clasts in the fluidal peperite result from dismembering of ductile, low-viscosity, relatively hot magma. At this stage, propagating magma lobes were probably insulated from direct contact with the wet sediment by a vapour film. The angular, polyhedral basalt clasts in the blocky peperite indicate brittle disintegration of somewhat cooler, higher-viscosity magma. The presence of jigsaw-fit texture and polyhedral clasts with glassy margins suggest that quench fragmentation of the basalt was important in the formation of the blocky peperite. Although there is no positive evidence for steam explosivity, the presence of steam could be recorded by small quartz-filled cavities that occur within the host sediment. The co-existence of fluidal and blocky basalt clasts is interpreted to reflect successive ductile then brittle fragmentation of intruding magma. The change from fluidal to blocky peperite might have resulted from progressive cooling of the magma during intrusion, and also from the breakdown of fluidisation when the limited supply of fine sediment in the host gravel was exhausted. ß

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Section: Introductionmentioning

confidence: 99%

Characteristics and origin of peperite involving coarse-grained host sediment

Squire

McPhie

2002

Journal of Volcanology and Geothermal Research

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“…14a, b) (e.g. Brooks et al 1982). (5) Thin tendrils of sandstone occupy the joints along the margin of the pyroxene-phyric andesite bodies and an aureole of homogenized sediments occur around these clasts (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…The chilled glassy margin is locally fragmented and dispersed as hyaloclastite in the pumiceous matrix within the pillow-bearing non-stratified polymictic pumicematrix breccia are juvenile clasts. On the basis of facies relationships and textures, we interpret the pillow-bearing non-stratified polymictic pumice-matrix breccia and nonstratified sediment-matrix breccia facies to be peperite (Brooks et al 1982;White et al 2000;Skilling et al 2002) generated as a mingling between an andesite sheet intrusion and coarse volcaniclastic sediments represented by the stratified polymictic pumice-matrix breccia and conglomerate facies. Our interpretation of peperitic mingling of molten andesite with unconsolidated or poorly consolidated, water-saturated, volcaniclastic deposits is supported by: (a) The gradational contacts between the parent intrusion of coherent andesite and pillow-like fluidal andesite clasts (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…One of the studied deposits has been interpreted as peperite and is one of the first occurrences of this kind of facies in the Miocene of the central Andes (e.g., Harris et al 2006). This study also provides opportunities for analysis of the poorly known deposits produced by non-explosive magma-water interaction in andesitic rocks (e.g., Brooks et al 1982;Kano 1989;Hanson 1991). Moreover, the described examples improve our knowledge of the behaviour of magma that interacts with coarse-grained, poorly sorted, and highly permeable sediments (e.g., Squire and McPhie 2002).…”

Section: Introductionmentioning

confidence: 89%

“…14a, b) (c.f. Brooks et al 1982). The pyroxene-phyric andesite bodies are internally texturally zoned (Fig.…”

Section: Epiclastic Fragmentationmentioning

confidence: 97%

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Non-explosive magma–water interaction in a continental setting: Miocene examples from the Eastern Cordillera (central Andes; NW Argentina)

et al. 2008

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The Middle-Upper Miocene Las Burras-AlmagroEl Toro (BAT) igneous complex within the Eastern Cordillera of the central Andes (∼24°S; NW Argentina) has revealed evidence of non-explosive interaction of andesitic magma with water or wet clastic sediments in a continental setting, including peperite generation. We describe and interpret lithofacies and emplacement mechanisms in three case studies. The Las Cuevas member (11.8 Ma) comprises facies related to: (i) andesite extruded in a subaqueous setting and generating lobe-hyaloclastite lava; and (ii) marginal parts of subaerial andesite lava dome(s) in contact with surface water, comprising fluidal lava lobes, hyaloclastite, and juvenile clasts with glassy rims. The Lampazar member (7.8 Ma) is represented by a syn-volcanic andesite intrusion and related peperite that formed within unconsolidated, water-saturated, coarse-grained volcaniclastic conglomerate and breccia. The andesite intrusion is finger-shaped and grades into intrusive pillows. Pillows are up to 2 m wide, tightly packed near the intrusion fingers, and gradually become dispersed in the host sediment ≥50 m from the parent intrusion. The Almagro A member (7.2 Ma) shows evidence of mingling between water-saturated, coarsegrained, volcaniclastic alluvial breccia and intruding andesite magma. The resulting intrusive pillows are characterized by ellipsoidal and tubular shape and concentric structure. The high-level penetration of magma in this coarse sediment was unconfined and irregular. Magma was detached in apophyses and lobes with sharp contacts and fluidal shapes, and without quench fragmentation and formation of a hyaloclastite envelope. The presence of peperite and magma-water contact facies in the BAT volcanic sequence indicates the possible availability of water in the system between 11-7 Ma and suggests a depositional setting in this part of the foreland basin of the central Andes characterized by an overall topographically low coastal floodplain that included extensive wetlands.

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Carbonate melting and peperite formation at the intrusive contact between large mafic dykes and clastic sediments of the upper Palaeozoic Saint‐Jules Formation, New‐Carlisle, Quebec

et al. 2005

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The base of an upper Palaeozoic graben-fill in eastern Canada was affected by mafic dyke intrusions shortly after deposition, resulting in the formation of peperite. Complex magma-sediment interactions occurred as the melts mingled with the wet and poorly consolidated clastic material of this sedimentary basin, which is separated from underlying rocks by the Acadian unconformity (Middle Devonian). As a result of these interactions, the mafic rocks are strongly oxidized, albitized and autobrecciated near and above the unconformity, where blocky juvenile clasts of mafic glass and porphyritic basalt have mingled with molten or fluidized sediments of the upper Palaeozoic Saint-Jules Formation, forming a peperite zone several metres thick. In contrast to most peperite occurrences, the New-Carlisle peperites are associated with the tip of dykes rather than with the sides of sills or dykes. We argue that more heat can be concentrated above a dyke than above a sill, as the former provides a more efficient and focused pathway for heated waters to invade the poorly consolidated host sediments. Superheated groundwaters that issued from the sides of the dykes appear to have promoted melting of carbonate components in calcareous sedimentary rock clasts of the Saint-Jules Formation, locally generating carbonate melts that contributed to the mingling of juvenile and sedimentary clasts in the peperite.

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Origin and metamorphism of peperite and associated rocks in the Devonian Elwell Formation, northern Sierra Nevada, California

Cited by 60 publications

References 0 publications

Characteristics and origin of peperite involving coarse-grained host sediment

Characteristics and origin of peperite involving coarse-grained host sediment

Non-explosive magma–water interaction in a continental setting: Miocene examples from the Eastern Cordillera (central Andes; NW Argentina)

Carbonate melting and peperite formation at the intrusive contact between large mafic dykes and clastic sediments of the upper Palaeozoic Saint‐Jules Formation, New‐Carlisle, Quebec

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