DOI: 10.1016/j.tecto.2021.229011
论文题名: The São Francisco cratonic root beneath the Neoproterozoic Brasilia belt (Brazil): Petrophysical data from kimberlite xenoliths
作者: Fernandes P.R. ; Tommasi A. ; Vauchez A. ; Neves S.P. ; Nannini F.
刊名: Tectonophysics
ISSN: 00401951
出版年: 2021
卷: 816 语种: 英语
中文关键词: Annealing
; Craton
; Deformation
; Mantle
; Melt-rock reaction
; Metasomatism
; Olivine
; Seismic anisotropy
; Seismic velocities
英文关键词: Belts
; Garnets
; Mica
; Olivine
; Seismic waves
; Seismology
; Shear waves
; Volcanic rocks
; Crystallographic preferred orientations
; Equilibrium conditions
; Equilibrium temperatures
; Lithospheric mantle
; Mineral composition
; Petrophysical datum
; Petrostructural analysis
; Seismological data
; Microstructure
英文摘要: Petrostructural analysis of 31 mantle xenoliths from three kimberlitic pipes intruding the Neoproterozoic Brasilia belt close to the southwestern margin of the São Francisco craton (SFC) reveals microstructures and compositions similar to those observed in cratonic roots worldwide. (1) The spinel-peridotites sampling the upper section of the lithospheric mantle have dominantly refractory modal and mineral compositions, whereas garnet-peridotites sampling the deep lithospheric mantle have more fertile compositions, consistent with those observed in cratonic roots worldwide. (2) The spinel-peridotites present a variation in microstructure from coarse-granular to coarse-porphyroclastic, but similar olivine crystallographic preferred orientations (CPO). (3) The garnet-peridotites have fine-porphyroclastic microstructures. (4) Many coarse-porphyroclastic spinel-peridotites display Fe-enrichment in olivine and pyroxenes, often associated with Ti-enrichment in pyroxenes or spinel and occurrence of modal phlogopite. (5) Equilibrium temperatures and pressures of garnet-peridotites are consistent with a cratonic geotherm, but equilibrium conditions of spinel-peridotites require a warmer geotherm. We interpret these observations as indicating that the xenoliths sample the SFC mantle root, which extends beneath the Brasilia belt, but was modified by reactive transport of the magmas forming the Alto Parnaiba Igneous Province (APIP) between 120 and 90 Ma. The APIP magmatism resulted in heterogeneous modal metasomatism, Fe enrichment, development of coarse-porphyroclastic microstructures in spinel peridotites and fine-porphyroclastic microstructures in garnet-peridotites, and moderate heating of the cratonic mantle root. These changes may produce a decrease in seismic velocities explaining the local weak negative anomaly observed in the lithospheric mantle beneath the APIP, which contrasts with the positive velocity anomalies characterizing the SFC mantle root in P-wave tomography models. However, reactive magma transport did not erase the olivine CPO. Comparison of the average seismic properties of the xenoliths with seismological data implies dominantly subhorizontal fossil flow directions and a non-negligible contribution of the cratonic root to teleseismic S-waves splitting. © 2021 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/170805
Appears in Collections: 气候变化与战略
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作者单位: Serviço Geológico do Brasil (CPRM), Brazil; Géosciences Montpellier, CNRS & Université de Montpellier, France; Instituto de Geociências, Universidade Federal de Pernambuco (UFPE), Brazil; Universidade Federal de Uberlândia (UFU), Brazil
Recommended Citation:
Fernandes P.R.,Tommasi A.,Vauchez A.,et al. The São Francisco cratonic root beneath the Neoproterozoic Brasilia belt (Brazil): Petrophysical data from kimberlite xenoliths[J]. Tectonophysics,2021-01-01,816