2.8-Ma ash-flow caldera at Chegem River in the northern Caucasus Mountains (Russia), contemporaneous granites, and associated ore deposits

Lipman, Peter W.; Богатиков, О. А.; Tsvetkov, A. A.; Gazis, Carey; Гурбанов, А. Г.; Hon, Ken; Koronovsky, Nikolai V.; Коваленко, В. И.; Marchev, Peter

doi:10.1016/0377-0273(93)90033-n

Cited by 44 publications

(10 citation statements)

References 23 publications

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“…It is difficult to interpret the band of high k sn values north of the topographic crest and east of ~250 km (Figure b) because of significant glaciation in this area [e.g., Gobejishvili et al ., ; Milanovsky , ], the unknown effect on k sn of relatively extensive volcanic deposits in this region from the Elbrus [e.g., Lebedev et al ., ] and Chegem [e.g., Lipman et al ., ] eruptive centers, and the correlations of local maxima in k sn with other lithologic transitions documented here (Figures and b). Steepness values decrease dramatically westward at the west end of the range, consistent with relative low topography and proposed westward decreasing rock uplift rates here [e.g., Vezzoli et al ., ].…”

Section: Discussionmentioning

confidence: 63%

Transition from a singly vergent to doubly vergent wedge in a young orogen: The Greater Caucasus

2014

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The Greater Caucasus Mountains, due to their youth (~5 Ma), provide an opportunity for insight into the early stages of orogen development during continent-continent collision. However, their recent tectonic evolution and first-order architecture remain unclear. Here we investigate the evolution of the orogen by integrating new observations of the fluvial geomorphology and neotectonics of the range with prior work on seismicity, geodetic strain, bedrock geology, and foreland basin structure. We find that the range contains four zones along strike that differ in structural architecture, topography, and first-order tectonic history. In particular, two south directed, singly vergent zones at the western and eastern tips of the orogen are separated by both a central doubly vergent zone that is dominated by north directed deformation and an eastern doubly vergent zone in which south directed thrusting dominates. We hypothesize that the along-strike changes in vergence and locus of deformation reflects different stages in the development of a doubly vergent orogen, with the tips of the range preserving an early, singly vergent form and the center recording a more advanced orogen. The differences between the two doubly vergent zones seem to be driven by the initial stages of collision between the structurally thickened crust of the Greater and Lesser Caucasus orogens, which initiated at~5 Ma.

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Section: Discussionmentioning

confidence: 63%

Transition from a singly vergent to doubly vergent wedge in a young orogen: The Greater Caucasus

2014

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“…Many studies suggest that resurgence via symmetric and asymmetric flexural doming is accommodated by emplacement of shallow plutons (e.g., Kennedy et al, 2012;Nielson & Hulen, 1984;Self et al, 1986;Smith & Bailey, 1968;Steven & Lipman, 1976). Some resurgent calderas also include simple-shear-dominated piston or trapdoor resurgence of a rigid block (e.g., Carlino, 2012;Carlino et al, 2006;de Silva et al, 2015;Lipman, 2000;Lipman et al, 1993Lipman et al, , 1996Orsi et al, 1991Orsi et al, , 1996. In addition, late ring dikes and cone sheets may contribute to caldera resurgence (e.g., Saunders, 2004;Schirnick et al, 1999).…”

Section: Citationmentioning

confidence: 99%

Protracted Multipulse Emplacement of a Postresurgent Pluton: The Case of Platoro Caldera Complex (Southern Rocky Mountain Volcanic Field, Colorado)

Tomek

Gilmer

Petronis

et al. 2019

Geochem Geophys Geosyst

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Many eroded calderas expose associated postcollapse plutons, but detailed fieldwork‐supported studies have rarely focused on the internal structure that can contribute to understanding of emplacement dynamics. The Alamosa River monzonite pluton is a postcollapse intrusion at the Platoro caldera complex that erupted six large ignimbrites between 30.2 and 28.8 Ma in the Southern Rocky Mountains volcanic field. Magnetic fabrics in this intrusion indicate the pulsed emplacement of a vertically extensive pluton. The magmatic pulses are documented by three concentric domains of magnetic foliations elongated in ~NE‐SW direction, corresponding to structural trends at the Platoro caldera complex and preexisting regional structures. As no evidence for deformation of wall rocks and the adjacent resurgent block has been identified, we interpret the Alamosa River pluton as a postresurgent intrusion. The space‐opening process involved magmatic stoping and small‐scale magma wedging. New SHRIMP‐RG U/Pb zircon dates (28.98 ± 0.18, 27.42 ± 0.35, and 27.32 ± 0.38 Ma) suggest a magmatic lifespan of ~1.7 My for the Alamosa River pluton. Our results indicate that postcaldera magmatism includes pulsed and protracted activity from large intracaldera resurgent plutons to smaller postresurgent stocks and sheeted complexes. As demonstrated by the Alamosa River pluton, some intrusions are emplaced shortly after collapse and resurgence, but postcaldera volcano‐plutonic systems may remain active for several million years or more. We also suggest that subvolcanic magma bodies may be assembled incrementally and that the record of early composite magma lenses preserved as magma wedges are later obliterated by convective flowage and crystallization.

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“…Hence, we refer to the porphyry as a resurgent intrusion. Resurgent intrusions are exposed at eroded calderas elsewhere, such as the Lake City (Lipman, 1976b), Grizzly Peak (Fridrich et al, 1991), Turkey Creek (du Bray and Pallister, 1991), Chegem (Lipman et al, 1993), and Caetano (John et al, 2008) calderas. Compaction foliation of intra caldera tuff would be expected to dip steeply away from contacts with a resurgent intrusion, but we have not visited a suffi cient number of appropriate outcrops of Middle Fork intracaldera tuff to test this hypothesis.…”

Section: Granite Porphyrymentioning

confidence: 99%

The Late Cretaceous Middle Fork caldera, its resurgent intrusion, and enduring landscape stability in east-central Alaska

et al. 2014

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Dissected caldera structures expose thick intracaldera tuff and, uncommonly, co genetic shallow plutons, while remnants of correlative outfl ow tuffs deposited on the preeruption ground surface record elements of ancient landscapes. The Middle Fork caldera encompasses a 10 km × 20 km area of rhyolite welded tuff and granite porphyry in eastcentral Alaska, ~100 km west of the Yukon border. Intracaldera tuff is at least 850 m thick. The K-feldspar megacrystic granite porphyry is exposed over much of a 7 km × 12 km area having 650 m of relief within the western part of the caldera fi ll. Sensitive high-resolution ion microprobe with reverse geometry (SHRIMP-RG) analyses of zircon from intracaldera tuff, granite porphyry, and outfl ow tuff yield U-Pb ages of 70.0 ± 1.2, 69.7 ± 1.2, and 71.1 ± 0.5 Ma (95% confidence), respectively. An aeromagnetic survey indicates that the tuff is reversely magnetized, and, therefore, that the caldera-forming eruption occurred in the C31r geomagnetic polarity chron. The tuff and porphyry have arc geochemical signatures and a limited range in SiO 2 of 69 to 72 wt%. Although their phenocrysts differ in size and abundance, similar quartz + K-feldspar + plagioclase + biotite mineralogy, whole-rock geochemistry, and analytically indistinguishable ages indicate that the tuff and porphyry were comagmatic. Resorption of phenocrysts in tuff and porphyry suggests that these magmas formed by thermal rejuvenation of near-solidus or solidifi ed crystal mush. A rare magmatic enclave (54% SiO 2 , arc geochemical signature) in the porphyry may be similar to parental magma and provides evidence of mafi c magma and thermal input.The Middle Fork is a relatively well preserved caldera within a broad region of Paleozoic metamorphic rocks and Mesozoic plutons bounded by northeast-trending faults. In the relatively downdropped and less deeply exhumed crustal blocks, Cretaceous-Early Tertiary silicic volcanic rocks attest to long-term stability of the landscape. Within the Middle Fork caldera, the granite porphyry is interpreted to have been exposed by erosion of thick intracaldera tuff from an asymmetric resurgent dome. The Middle Fork of the North Fork of the Fortymile River incised an arcuate valley into and around the caldera fi ll on the west and north and may have cut down from within an original caldera moat. The 70 Ma land surface is preserved beneath proximal outfl ow tuff at the west margin of the caldera structure and beneath welded outfl ow tuff 16-23 km east-southeast of the caldera in a paleovalley. Within ~50 km of the Middle Fork caldera are 14 examples of Late Cretaceous (?)-Tertiary felsic volcanic and hypabyssal intrusive rocks that range in area from <1 km 2 to ~100 km 2 . Rhyolite dome clusters north and northwest of the caldera occupy tectonic basins associated with northeast-trending faults and are relatively little eroded. Lava of a latite complex, 12-19 km northeast of the caldera, apparently fl owed into the paleovalley of the Middle Fork of the North Fork of the Fortymile River. To...

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2.8-Ma ash-flow caldera at Chegem River in the northern Caucasus Mountains (Russia), contemporaneous granites, and associated ore deposits

Cited by 44 publications

References 23 publications

Transition from a singly vergent to doubly vergent wedge in a young orogen: The Greater Caucasus

Transition from a singly vergent to doubly vergent wedge in a young orogen: The Greater Caucasus

Protracted Multipulse Emplacement of a Postresurgent Pluton: The Case of Platoro Caldera Complex (Southern Rocky Mountain Volcanic Field, Colorado)

The Late Cretaceous Middle Fork caldera, its resurgent intrusion, and enduring landscape stability in east-central Alaska

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