DOI: 10.1016/j.earscirev.2020.103165
论文题名: Evolution of textures, crystal size distributions and growth rates of plagioclase, clinopyroxene and spinel crystallized at variable cooling rates from a mid-ocean ridge basaltic melt
作者: Giuliani L. ; Iezzi G. ; Vetere F. ; Behrens H. ; Mollo S. ; Cauti F. ; Ventura G. ; Scarlato P.
刊名: Earth Science Reviews
ISSN: 00128252
出版年: 2020
卷: 204 语种: 英语
中文关键词: Cooling rate
; Crystal growth rate
; Crystal texture
; CSD
; MORB
; Solidification
英文关键词: clinopyroxene
; cooling
; crystal structure
; experimental mineralogy
; experimental study
; growth rate
; melt
; mid-ocean ridge basalt
; plagioclase
; size distribution
; solidification
; texture
英文摘要: Mid-ocean ridge basalts (MORBs) are the most abundant eruptive tholeiitic products on Earth. Many experiments have been performed to investigate the solidification of basalts but under limited thermal ranges of cooling (ΔTc) and cooling rates (ΔT/Δt). We analyze the experimental charges solidified from previous studies: the BIR1A basalt from USGS was solidified using ΔT/Δt of 1, 7, 60, 180, 1800 and 9000 °C/h, in the ΔTc between 1300 and 800 °C, at atmospheric conditions. The previous studies allowed determining the glass-forming ability (GFA) of sub-alkaline silicate liquids, but do not give information on their textures. Here, we quantify the evolution of sizes, shapes, number of crystals per area (#/A), CSDs and growth rates (Gs) of plg (plagioclase), cpx (clinopyroxene) and sp. (spinel). Textures were investigated by image analysis on thousands of crystals and are one of the most complete datasets ever obtained from laboratory studies: they reflect rapid, intermediate and sluggish cooled parts of MORB from liquidus to solidus. Faceted plg grows only at ΔT/Δt ≤ 60 °C/h, while cpx and sp. became dendritic at ΔT/Δt between 60 and 180 °C/h. As ΔT/Δt increase, crystal size ranges decrease from 1000 to 10 μm at 1 °C/h to 100–1 at 60 °C/h μm for plg, from 400 to 8 μm at 1 °C/h to 25–0.5 μm at 1800 °C/h μm for cpx, and from 90 to 6 μm at 1 °C/h to 6–0.5 at 1800 °C/h μm, for sp. The #/A increases with increasing ΔT/Δt, except for cpx between 60 and 180 °C/h. As ΔT/Δt increases, CSDs of plg, cpx and sp increase their slopes (m) and population densities per size (n0), reduce the size ranges and tend to be log-linear. At low ΔT/Δt, CSDs are composed of several log-linear segments, which slopes are related to different pulses of crystal nucleation, and subsequent growth by coarsening. The CSDs parameters (slope, m, and nucleation density per size, n0) linearly scale each other and both are highly correlated with ΔT/Δt. Maximum (Gmax) and average (GCSD) growth rates are computed respectively by averaged major axis (Lmax) of the five longest crystals and by the m of CSDs. Both the Gs are a function of experimental time (t) and increase with the increasing of ΔT/Δt, changing up to two orders of magnitude. The Gmax of cpx is correlated with m and n0 and can be used in natural MORB to retrieve either ΔT/Δt and Gmax. The plg and cpx crystals with sizes between 0.1 and 1 mm are abundant in the experimental charges obtained at low ΔT/Δt. In volcanic rocks, these crystal sizes are generally considered representative of intra-telluric conditions (phenocrysts and microphenocrysts). Our data demonstrate that crystals with mm-sizes may also grow in syn-to-post-depositional conditions. The continuous evolution of textures in response to ΔT/Δt variations implies that kinetic effects can fully capture the solidification of MORBs. As a result, the widely accepted assumption that phenocrysts represent the products of evolution processes in volcanic conduits or magma reservoirs could be not valid for some basaltic lavas. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/166090
Appears in Collections: 气候变化与战略
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作者单位: Dipartimento di Ingegneria & Geologia (InGeO), Università G. D'Annunzio di Chieti-Pescara, Via dei Vestini 31, Chieti, 66100, Italy; Istituto Nazionale di Geofisica e Vulcanologia, INGV, Via di Vigna Murata 605, Roma, 00143, Italy; Dipartimento di Fisica & Geologia, Università degli studi di Perugia, Piazza dell'Università 1, Perugia, 06123, Italy; Institute for Mineralogy, Leibniz University of Hannover, Callinstrasse 3, Hannover, D-30167, Germany; Dipartimento di Scienze della Terra, Sapienza Università di Roma, Piazzale A. Moro 5, Roma, 00185, Italy
Recommended Citation:
Giuliani L.,Iezzi G.,Vetere F.,et al. Evolution of textures, crystal size distributions and growth rates of plagioclase, clinopyroxene and spinel crystallized at variable cooling rates from a mid-ocean ridge basaltic melt[J]. Earth Science Reviews,2020-01-01,204