DOI: 10.1016/j.epsl.2020.116646
论文题名: Predominantly recycled carbon in Earth's upper mantle revealed by He-CO2-Ba systematics in ultradepleted ocean ridge basalts
作者: Graham D.W. ; Michael P.J.
刊名: Earth and Planetary Science Letters
ISSN: 0012821X
出版年: 2021
卷: 554 语种: 英语
中文关键词: barium
; carbon
; helium
; mantle
; mid-ocean ridge basalts
英文关键词: Carbon
; Carbon dioxide
; Fourier transform infrared spectroscopy
; Glass
; Helium
; Laser ablation
; Lead alloys
; Lead metallography
; Melting
; Mixing
; Molar ratio
; Neodymium alloys
; Recycling
; Strontium alloys
; Structural geology
; Submarine geology
; Ternary alloys
; Trace elements
; Transform faults
; CO2 concentration
; East Pacific Rise
; FTIR spectroscopy
; Geochemical components
; Heterogeneous mantle
; Laser-ablation-ICP-MS
; Mid ocean ridge basalts
; Recycled materials
; Basalt
; barium
; carbon
; helium
; mantle source
; mid-ocean ridge basalt
; mixing
; partial melting
; trace element
; upper mantle
; East Pacific Rise
; Pacific Ocean
英文摘要: Basalts erupted within intra-transform spreading centers can be valuable probes of geochemical components in Earth's upper mantle, and provide constraints on the proportions of mantle carbon that are juvenile (primordial) vs. tectonically recycled. Here we present new results for submarine basalt glasses, erupted within the Garrett Transform Fault (GTF) and to its north and south along the East Pacific Rise (EPR). Analyses of 3He/4He, and He and CO2 concentrations in vesicles and glass were performed, through a series of crushing and melting experiments plus FTIR spectroscopy. Trace elements were analyzed by laser ablation ICP-MS. The GTF basalts provide further tests for the origin of volatile-undersaturated basalts using CO2/Ba and CO2/Nb systematics. CO2 is highly correlated with Ba and Nb in basalts erupted in the transform domain (n = 13, including 5 undersaturated basalts) and does not show the variability expected from mixing between undegassed and variably degassed melts. Rather, the melts appear to originate from a heterogeneous mantle source that was variably depleted through partial melting, and limited mixing of melts is involved in their generation. The CO2/Ba and CO2/Nb weight ratios of 106 ± 8 and 308 ± 27, respectively, are similar to values determined previously for a global suite of undersaturated mid-ocean ridge basalts (MORBs). The ridge and transform domains have distinct 3He/4He ratios. Along the nearby EPR, 3He/4He = 8.5 - 9.1 RA, while within the Garrett Transform Fault 3He/4He = 9.2 - 10.1 RA. These two basalt populations are also distinct in their Pb-Sr-Nd isotope compositions based on earlier regional studies. The distinct populations result from partial melting of two different mantle source compositions. Melting of depleted mantle containing a small amount (∼1 to 5%) of enriched, ancient heterogeneities occurs beneath the EPR. Melting of ultradepleted mantle (in which the heterogeneities have been removed by earlier melting beneath the EPR) occurs beneath the GTF. This explains the distinction between intra-transform and spreading ridge domains for 3He/4He, if the heterogeneities were enriched in U, Th and He and had low 3He/4He as would be found in tectonically recycled material. The enriched mantle component sampled by the EPR basalts has molar CO2/3He =2×109, and it dominates the CO2/3He ratio generally ascribed to the upper mantle source for mid-ocean ridge basalts. In contrast, the ultradepleted MORB mantle component sampled by the GTF basalts has CO2/3He =3×108 or less. This indicates that most of the carbon in Earth's upper mantle originates from tectonic recycling. © 2020 Elsevier B.V. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/165483
Appears in Collections: 气候变化与战略
There are no files associated with this item.
作者单位: College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, United States; Department of Geosciences, The University of Tulsa, 800 S. Tucker Drive, Tulsa, OK 74104, United States
Recommended Citation:
Graham D.W.,Michael P.J.. Predominantly recycled carbon in Earth's upper mantle revealed by He-CO2-Ba systematics in ultradepleted ocean ridge basalts[J]. Earth and Planetary Science Letters,2021-01-01,554