Geochemistry and Petrology of Mid-Tertiary Ash Flow Tuffs from the Sierra El Virulento Area, Eastern Chihuahua, Mexico

Moll, E.J.

doi:10.1002/9781118782057.ch11

Cited by 2 publications

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References 31 publications

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“…It is well known that variations in bulk‐rock Sr isotopes are thought to reflect combinations of hydrothermal alteration, crustal contamination, and variable source compositions (Beard, ; Davies & Halliday, ; Hildreth & Fierstein, ; Johnson, ; Johnson, Lipman, & Czamanske, ; Mikoshiba, Kanisawa, Matsuhisa, & Togashi, ; Moll, ). In this case, Sr‐rich plagioclases from the shoshonitic samples show low and uniform 87 Sr/ 86 Sr ratios (0.7036–0.7040), consistent with the whole‐rock Sr‐isotope compositions ( 87 Sr/ 86 Sr = 0.7037–0.7039), and this phenomenon could rule out the possibility of significant crustal contamination.…”

Section: Discussionmentioning

confidence: 99%

Petrogenesis of Cenozoic shoshonitic rocks in Fiji: Constraints from mineral and whole‐rock geochemistry

Sun

Wang

et al. 2017

Geological Journal

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This paper reports mineral and whole‐rock geochemical data (major and trace elements, Sr–Nd isotopes, and in situ plagioclase Sr‐isotope analysis) for Cenozoic volcanic rocks from Sabeto, NW Fiji, with the aim of constraining the origin of Cenozoic shoshonitic rocks found throughout Fiji. The most mafic shoshonitic lavas (absarokites) exhibit porphyritic textures and massive structure with phenocrysts of olivine (Fo = 76–78), clinopyroxene (Mg# = 73.9–80.0), and plagioclase (An = 71.9–92.1). Major element geochemical data include SiO2 = 47.31–48.46 wt%, MgO = 4.20–5.76 wt%, Mg# = 49–51, Al2O3 = 17.64–18.93 wt%, and (Na2O + K2O) = 5.12–7.01 wt%. The trace element geochemistry is typically arc like, with enrichment in the large ion lithophile elements (LILEs), the light rare earth elements (LREEs), and P, along with depletion in the heavy rare earth elements (HREEs) and high‐field‐strength elements (HFSEs; e.g., Nb, Ta, Zr, Hf, and Ti). Whole‐rock (87Sr/86Sr)i ratios and εNd(t) values vary from 0.7037 to 0.7039 and from +7.62 to +8.45, respectively. The former is near equal to the 87Sr/86Sr ratios of plagioclase phenocrysts (0.7034–07039). Based on these geochemical data and the results of previous studies, we propose that the Sabeto shoshonitic primary magma was derived from partial melting of the depleted lithospheric mantle, modified by subduction‐related fluids. The thermobarometric calculation indicates that the P–T conditions of Fiji shoshonitic magma chamber are ~1100 °C and ~2.8 GPa (~90 km depth), with an average H2O fraction of ~6 wt%. In addition, the shoshonitic melts experienced fractional crystallization of clinopyroxene, olivine, and plagioclase during magma evolution. These volcanic rocks formed in an extensional setting following collision of the Vitiaz arc and the Ontong Java Plateau during the Pliocene.

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Section: Discussionmentioning

confidence: 99%

Petrogenesis of Cenozoic shoshonitic rocks in Fiji: Constraints from mineral and whole‐rock geochemistry

Sun

Wang

et al. 2017

Geological Journal

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“…3.7) definitely represents titanomagnetites from a silicic volcanic source, with the three titanomagnetite analyses from a silicic tuff plotting in this field. 'Comnariilon,'of Vdlq4g, $titro.fci,t'lfllfy iilnrimg Ex'traotflon (v.a[ue* -tt a Titanomagnetite analyses comparable to those presented here have been reported from k.own dacitic and rhyolitic tuffs (ronn 1970;Moll 1981;Froggatt 1982:' Westgat€ et at. 1985.…”

Section: Sourcesupporting

confidence: 72%

Paleomagnetic Studies of the Late Miocene Mangapoike River Section, Northern Hawke's Bay, New Zealand

Wright¹

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<p>The Mangapoike River section (38.9 degrees S, 177.6 degrees E), on the eastern limb of the Wairoa Syncline, northern Hawke's Bay, is a thick (> 4000 m) and well exposed sequence of Waiauan to Waipipian sediments in which foraminiferal and radiolarian biostratigraphy and silicic tuff lithostratigraphy are well known. An Early Pliocene magnetostratigraphy has been determined by Kennett and Watkins (1974). The present study extends the magnetostratigraphy to the Middle -Late Miocene, and establishes a late Miocene to Early Pliocene 3000 m magnetostratigraphic reference column for New Zealand. The only identifiable remanence carrying magnetic mineral in the Mangapoike sediments is titanomagnetite. Its chemistry does not vary with grain size. Oxidation of the titanomagnetite is deuteric, and thus pre-depositional. Fluctuations of titanomagnetite concentration between 10-3 to 10-4 wt percent are the main influence on the variation of NRM intensity. Viscous magnetisations characterised by both the alignment of NRM directions in a general present day field direction and remanence decay and aquisition over laboratory time were recognised in 85 percent of the 1204 paleomagnetic specimens. Secondary magnetisations were removed by thermal demagnetisation at temperatures varying between 200 degrees C and 320 degrees C. AF demagnetisation was not effective in removing viscous magnetisations, even at peak alternating fields of 35 mT, since the coercivities of the primary and secondary magnetisations overlap completely. The random relationship between the degree of bioturbation and in-site dispersion at individual sites indicates the magnetisation is acquired after bioturbation, and thus is a post-depositional detrital magnetisation. The time lag between deposition and acquisition of the magnetisation is approximately 1000 yrs. Six normal (MN1 - MN6) and seven reversed (MR1 - MR7) polarity magnetozones are identified within the late Miocene at Mangapoike. Only one normal magnetozone (MN6) is recognised in the stratigraphic interval equivalent to that from which Kennett and Watkins (1974) reported two normal zones (C1 and C2). MN6 is correlated to C2. C1 is inferred to be an uncleaned normal overprint. The magnetozones are correlated to Chrons 11 to 4, which implies an average sedimentation rate of 64 cm/1000 yrs. The previously known Miocene - Pliocene 3 degrees angular unconformity at Mangapoike (Hornibrook 1977) represents the period from 6.3 Ma to at least 5.41 Ma. A previously unrecognised unconformity from at least 6.86 to at least 6.42 Ma is postulated, based on the preferred magnetostratigraphic interpretation. The presence of the unconformity is supported by radiolarian and benthic foraminiferal biostratigraphy. Three distinct lithological events at Mangapoike, based both on the synchroneity with deep-sea benthic delta 18O records and unconformities of the Vail-curve, are inferred to result from glacioeustatism. At Mangapoike, the Waiauan - Tongaporutuan boundary, as defined by the incoming of Bolivinita cf pohana, has a magnetostratigraphic age of 10.3 Ma. Both the LAD of Loxostomum truncatum and the FAD of Bolivinita cf pohana are less than 42,000 yrs. younger than the late Waiauan glacioeustatic event. The Waiauan - Tongaporutuan boundary is thus postulated to result from glacioeustatism. Glacioeustatism may also explain the excellent age correlation between the base of the Tongaporutuan and the base of the Tortonian stratotype. Correlation of the late Miocene and early Pliocene magnetostratigraphies and biostratigraphies of on-shore New Zealand with either of the magnetostratigraphic interpretations of DSDP Site 594 results in an unacceptably high diachroneity of some planktic taxa of 1.8 Ma over 3.6 degrees of latitude. Of four possiblities to resolve the anomaly, incorrect magnetostratigraphic correlations at Site 594 is the most likely. The previously determined age of 6.2 Ma for the LAD of Globoquadrina dehiscens in New Zealand is erroneous. A magnetostratigraphic age for the LAD of G. dehiscens at Mangapoike is 9.2 Ma. This age is not an extinction date for the taxon throughout New Zealand, and the LAD may well be erratic and diachronous within New Zealand. The Wairoa Syncline, a forearc basin within the Hikurangi margin, has a rotation rate as determined from declination directions, of 7-8 degrees /Ma for the last 5 Ma. Of this less than 1.5 degrees /Ma is due to apparent polar wander of the Australian plate. Extrapolation of this rate towards the present is consistent with a present day rotation rate of 7 degrees /Ma derived from strain analysis of geodetic data. Prior to 10 Ma the rate of tectonic rotation is poorly constrained and may vary between 3 degrees /Ma and 0 degrees /Ma. The change in the rate of rotation of the Wairoa Syncline around 5 Ma is probably related to a marked change in regional tectonic regime involving opening and spreading to the north of New Zealand and compression and shortening to the south.</p>

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Geochemistry and Petrology of Mid-Tertiary Ash Flow Tuffs from the Sierra El Virulento Area, Eastern Chihuahua, Mexico

Cited by 2 publications

References 31 publications

Petrogenesis of Cenozoic shoshonitic rocks in Fiji: Constraints from mineral and whole‐rock geochemistry

Petrogenesis of Cenozoic shoshonitic rocks in Fiji: Constraints from mineral and whole‐rock geochemistry

Paleomagnetic Studies of the Late Miocene Mangapoike River Section, Northern Hawke's Bay, New Zealand

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