Topic
Quartz latite
About: Quartz latite is a research topic. Over the lifetime, 101 publications have been published within this topic receiving 2997 citations.
Papers published on a yearly basis
Papers
TL;DR: Ewart et al. as discussed by the authors inferred that the mafic lavas are derived from the Goboboseb-Messum Centre and the Messum Carter Basalts (MCB) and showed evidence for crystal fractionation, have 'arc-like' trace element signatures, correlated e-SiO, e-Ti/γ and -Ti/Zr.
Abstract: The Goboboseb Mountains and Messum Complex represent a major Cretaceous (132 Ma) bimodal eruptive centre in the southern Etendeka continental flood basalt (CFB) province. The eruptives compris the Awahab Formation and are represented by a lower sequence of mafic lavas, followed by the Goboboseb quartz latite members, the Messum Mountain Basalts, and finally the Springbok quartz latite. The sequence is cut by numerous dolerite dykes, sills and plugs, rare rhyolite, and carbonatite. The mafic lavas comprise two distinct series, which although corresponding broadly to the Etendeka regional low Ti and Zr basalts (LTZ type), are distinguished by Ti/Zr ratios into the LTZ.H (higher Ti/Zr) and LTZ.L (lower Ti/Zr) series. The LTZ.H basalts have no previously described extrusive equivalent in the Etendeka (or Parana) CFB, and consist of magnesian, mildly alkaline to tholeiitic lavas, dominated by oliv + cpx phenocryst assemblages which fractionate (near the surface) to phono-tephrite. They are identified as predominantly mantle plume melts (Tristan-Walvis plume). The LTZ.L lavas are less magnesian, extending to icelandites, are tholeiitic, with cpx ± oliv + pl + Fe-Ti oxide phenocryst assemblages and groundmass pigeonite and subcalcic augite. Stratigraphically, the LTZ.H lavas are interbedded with LTZ.L types in the lower part of the sequence and also occur as dykes. Within the Messum Complex, a remnant early sequence of basalts (Messum Carter Basalts) are in part transitional between the LTZ.L and LTZ.H series. The LTZ.H, and at least some of the LTZ.L lavas are inferred to have been erupted from the Goboboseb-Messum Centre. Chemically, the LTZ.H melts are broadly intermediate between E-MORB and OIB magmas, with higher Ti/Zr Sm/ γb and Ti/γ ratios than the LTZ.L types, which suggest segregation depths between the garnet and spinel peridotite stability fields. The Pb-Nd-Sr isotopic compositions of the LTZ.H eruptives are similar to, but not identical with the modern Tristan plume composition, and the observed variability is attributable to limited lower-crust assimilation and/or Atlantic MORB source mixing. The LTZ.L lavas show evidence for crystal fractionation, have 'arc-like' trace element signatures, correlated e-SiO, e-Ti/γ and -Ti/Zr, e-1/Sr and 1/Nd-e variations, and relatively radiogenic Pb, evolved Sr(e, 58-174) and low Nd(e -6·1 to -9·5) isotopic compositions. Their geochemistry is inferred to be AFC (assimilation-fractional crystallization) controlled, and is modelled by three-component mixing involving mantle plume derived melt, mafic lower crust and silicic mid-upper crust. The voluminous quartz latites (Part II, Ewart et al., 1978) extend these geochemical trends.
187 citations
TL;DR: In this article, high resolution ion microprobe (SHRIMP) UPb zircon analyses from two tuffs and a felsic flow in the middle and upper Belt Supergroup of northwestern Montana significantly refine the age of sedimentation for this very thick (15-20 km) Middle Proterozoic stratigraphic sequence.
Abstract: New sensitive high resolution ion microprobe (SHRIMP) UPb zircon analyses from two tuffs and a felsic flow in the middle and upper Belt Supergroup of northwestern Montana significantly refine the age of sedimentation for this very thick (15-20 km) Middle Proterozoic stratigraphic sequence. In ascending stratigraphic order, the results are (1) 1454 ± 9 Ma for a tuff in the upper part of the Helena Formation at Logan Pass, Glacier National Park; (2) 1443 ± 7 Ma for a regionally restricted porphyritic rhyolite to quartz latite flow of the Purcell Lava in the Yaak River region; and (3) 1401 ± 6 Ma for a tuff in the very thin transition zone between the Bonner Quartzite and Libby Formation, west of the town of Libby. Combining these ages with those previously published by other workers for ca. 1470-Ma sills in the lower Belt in Montana and Canada indicates that all but the uppermost Belt strata (about 1700 m) were deposited over a period of about 70 million years, considerably reducing the time span from long...
174 citations
TL;DR: The bimodal NW Etendeka province of Namibia is located at the continental end of the Tristan plume trace in coastal Namibia as mentioned in this paper, and consists of a high-Ti (Khumib type) and three low-Ti basalt (Tafelberg, Kuidas and Esmeralda types) suites.
Abstract: The bimodal NW Etendeka province is located at the continental end of the Tristan plume trace in coastal Namibia. It comprises a high-Ti (Khumib type) and three low-Ti basalt (Tafelberg, Kuidas and Esmeralda types) suites, with, at stratigraphically higher level, interstratified high-Ti latites (three units) and quartz latites (five units), and one low-Ti quartz latite. Khumib basalts are enriched in high field strength elements and light rare earth elements relative to low-Ti types and exhibit trace element affinities with Tristan da Cunha lavas. The unradiogenic Pb-206/Pb-204 ratios of Khumib basalts are distinctive, most plotting to the left of the 132 Ma Geochron, together with elevated Pb-207/Pb-204 ratios, and Sr-Nd isotopic compositions plotting in the lower Nd-143/Nd-144 part of mantle array (EM1-like). The low-Ti basalts have less coherent trace element patterns and variable, radiogenic initial Sr (similar to0.707-0.717) and Pb isotope compositions, implying crustal contamination. Four samples, however, have less radiogenic Pb and Sr that we suggest approximate their uncontaminated source. All basalt types, but particularly the low-Ti types, contain samples with trace element characteristics (e.g. Nb/Nb-*) suggesting metasediment input, considered source-related. Radiogenic isotope compositions of these samples require long-term isolation of the source in the mantle and depletions (relative to unmodified sediment) in certain elements (e.g. Cs, Pb, U), which are possibly subduction-related. A geodynamic model is proposed in which the emerging Tristan plume entrained subducted material in the Transition Zone region, and further entrained asthenosphere during plume head expansion. Mixing calculations suggest that the main features of the Etendeka basalt types can be explained without sub-continental lithospheric mantle input. Crustal contamination is evident in most low-Ti basalts, but is distinct from the incorporation of a metasedimentary source component at mantle depths.
170 citations
TL;DR: In this paper, a detailed examination of the Awahab Formation reveals an additional disconformity, which separates olivine-phyric basalts from basalt/basaltic andesites, marking out a shield volcanic feature which is concentrated in an area to the SE of the Huab River near to the Doros igneous centre.
152 citations
TL;DR: In the Jemez volcanic field, the dominant erupted lithology was dacite, which appears to have been generated by mixing of magmas whose compositions are approximated by earlier andesites and high-silica rhyolites.
Abstract: Over 100 radiometric dates and recent detailed geologic mapping allow some refinements of the stratigraphic relations of major units and generalization of temporal lithologic variations in the Jemez volcanic field. Volcanism had begun in the area by about 16.5 Ma with episodic eruptions of alkaline basalts. By 13 Ma, alkaline volcanism had been replaced with eruptions of more voluminous olivine tholeiite. High-silica rhyolite, derived from melts of lower crust, also was erupting by about 13 Ma. Basalt and high-silica rhyolite continued to be erupted until about 7 and 6 Ma, respectively, but effusions of dominantly andesitic differentiates of basalt that began as early as about 12 Ma volumetrically overshadowed all other eruptive products between 10 and 7 Ma. From 7 to 3 Ma the dominant erupted lithology was dacite, which appears to have been generated by mixing of magmas whose compositions are approximated by earlier andesites and high-silica rhyolites. Less than 4–3 Ma volcanism was dominated by eruption of rhyolitic tuffs. Field relations, geochemistry, and dates specifically indicate the following with regards to stratigraphie relations: (1) distinctions among basalt of Chamisa Mesa, Paliza Canyon Formation basalts, and Lobato Basalt for other than geographic reasons are artificial; basaltic volcanism was continuous in volcanic field from >13 to 7 Ma, (2) Canovas Canyon and Bearhead rhyolites form a continuum of high-silica rhyolite volcanism from >13 to 6 Ma, (3) hypabyssal and volcanic rocks of the Cochiti mining district probably represent the exhumed interior of a Keres Group volcano(s), (4) temporal overlaps exist among the major stratigraphie groups which may imply some genetic relations, and (5) the Tewa Group formation Cerro Rubio Quartz Latite may more appropriately be considered part of the Tschicoma Formation of the Polvadera Group. Preliminary analysis of hydrothermal alteration in the context of the volcanic stratigraphy suggests at least three distinct hydrothermal events have occurred in the volcanic field's history.
147 citations
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| Year | Papers |
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| 2016 | 2 |
| 2015 | 1 |
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| 2012 | 2 |
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