scholarly journals Major and trace element chemistry and D/H, 18O/16O, 87Sr/86Sr and 143Nd/144Nd ratios of rocks from the spreading center of the Okinawa Trough, a marginal back-arc basin.

1991 ◽  
Vol 25 (2) ◽  
pp. 121-136 ◽  
Author(s):  
Hiroji Honma ◽  
Minoru Kusakabe ◽  
Hiroo Kagami ◽  
Shigeru Iizumi ◽  
Hitoshi Sakai ◽  
...  
Keyword(s):  
Trace Element ◽  
Okinawa Trough ◽  
Spreading Center ◽  
Trace Element Chemistry ◽  
Element Chemistry ◽  
The Okinawa Trough ◽  
Back Arc

scholarly journals A Decade of Global Navigation Satellite System/Acoustic Measurements of Back-Arc Spreading in the Southwestern Okinawa Trough

2021 ◽  
Vol 9 ◽  
Author(s):  
Horng-Yue Chen ◽  
Ryoya Ikuta ◽  
Ya-Ju Hsu ◽  
Toshiaki Tsujii ◽  
Masataka Ando ◽  
...  
Keyword(s):  
Time Series ◽  
Surface Deformation ◽  
Okinawa Trough ◽  
Spreading Center ◽  
Integrated Analysis ◽  
Plate Boundaries ◽  
Velocity Change ◽  
Upward Migration ◽  
The Okinawa Trough ◽  
Back Arc

Long-term seafloor geodetic measurements are important for constraining submarine crustal deformation near plate boundaries. Here we present an integrated analysis of a decade of GNSS/acoustic data collected at a site 60 km to the east of northeast Taiwan near the axis of the Okinawa Trough back-arc basin. We obtained a time-series of horizontal and vertical positions based on 18 measurements from 2009 to 2019. These data reveal a southeastward movement at a rate of 43 ± 5 mm/yr since 2012 with respect to the Yangtze Plate. The horizontal motion can be explained by the clockwise rotation of the Yonaguni Block and northern Central Range. In addition, the vertical displacement of the transponder array shows rapid subsidence of 22 ± 9 mm/yr from 2012 to 2019. The fast subsidence rate and negative free-air gravity anomaly in this region indicate that crustal thinning is compensated mainly by surface deformation rather than upward migration of the Moho. Taking into account the offset in 2012 owing to the replacement of the transponder array, the horizontal position time series of our site are best explained by two linear lines with a slope change in July 2013. The timing of the velocity change coincides broadly with a change in the nearby seismicity rate and dike intrusion 150 km away from the site. Our results highlight the potential of seafloor geodesy in assessing temporal changes in deformation near the spreading center of the Okinawa Trough, which cannot be one using data from onland GNSS stations.

Mineralogical Constraints on the Magma Mixing Beneath the Iheya Graben, an Active Back-Arc Spreading Centre of the Okinawa Trough

2020 ◽  
Author(s):  
Yu-Xiang Zhang ◽  
Zhi-Gang Zeng ◽  
Glenn Gaetani ◽  
Le Zhang ◽  
Zhi-Qing Lai
Keyword(s):  
Trace Element ◽  
Major Element ◽  
Magma Mixing ◽  
Okinawa Trough ◽  
Nd Isotope ◽  
Magma Plumbing System ◽  
The Okinawa Trough ◽  
Back Arc ◽  
Magma Plumbing

Abstract The Iheya Graben is a back-arc spreading centre in the middle part of the Okinawa Trough. It is also located in the centre of an anomalous volcanic zone (volcanic arc migration phenomenon, or VAMP) and is characterized by bimodal volcanism, unusually high heat flow and active hydrothermal circulation. The subvolcanic magma plumbing system and the magmatic processes related to the formation of rare erupted intermediate lavas in this area remain uncertain. In this study, we conducted systematic mineralogical analyses (in situ major element, trace element and Sr isotopes) and whole rock geochemical analyses (major element, trace element and Sr–Nd isotopes) on an andesite (T5-2; type C andesite) and a rhyolite (C11; type 2 rhyolite), and present evidence for magma mixing in the origins of these lavas. Andesite T5-2 contains a mafic mineral assemblage and a silicic mineral assemblage, which are derived from a basaltic melt and a type 2 rhyolitic melt, respectively. A 4:6 mixture of basalt and type 2 rhyolite from the Iheya Graben reproduces the whole-rock major element, trace element, and Sr–Nd isotope compositions of T5-2. Rhyolite C11 contains a group of disequilibrium minerals that crystallized from a less evolved rhyolitic melt with relatively more enriched Sr–Nd isotope compositions, suggesting mixing of this melt with a more evolved and isotopically more depleted rhyolitic melt. This mixing process could produce a series of rhyolitic melts with a negative correlation between SiO2 concentrations and 87Sr/86Sr ratios (or a positive correlation for 143Nd/144Nd ratios), which are recorded by the whole group of type 2 rhyolites. The results from mineral-based thermobarometers suggest that the premixing storage temperatures of the basaltic and rhyolitic melts are ∼1100 °C and 870–900 °C, respectively. The hybrid andesitic melt has temperatures of ∼950 to ∼980 °C. The magma storage pressures are not well constrained, ranging from ∼400 MPa to ∼100 MPa. We show that magma mixing plays a significant role in the origins of diverse volcanism in the middle Okinawa Trough; more specifically, two of the three types of andesites (types B and C) and one of the two types of rhyolites (type 2) are associated with magma mixing. We thus propose a complex magma plumbing system with multichamber magma storage and frequent magma mixing beneath the Iheya Graben.

TRACE ELEMENT CHEMISTRY OF EMERALDS

2018 ◽  
Author(s):  
Casey Beaudoin ◽  
◽  
G. Nelson Eby
Keyword(s):  
Trace Element ◽  
Trace Element Chemistry ◽  
Element Chemistry

Chemical variation of clinopyroxene phenocrysts from the trachybasaltic lavas of Mount Etna, Sicily

1980 ◽  
Vol 43 (330) ◽  
pp. 765-770 ◽  
Author(s):  
A. M. Duncan ◽  
R. M. F. Preston
Keyword(s):  
Trace Element ◽  
Mount Etna ◽  
Chemical Variation ◽  
Etna Volcano ◽  
Trace Element Chemistry ◽  
Sector Zoning ◽  
Steady Decrease ◽  
Element Chemistry

SummaryThe chemical variation of clinopyroxene phenocrysts from the trachybasaltic lavas of Etna volcano is described. The phenocrysts show a limited, but distinct trend in chemical variation from calcic-augite in the hawaiites to augite in the benmoreites. The trend of this variation is unusual, being one of Mg-enrichment with differentiation of the magma. Ca shows a steady decrease in the clinopyroxenes from the hawaiites to the benmoreites. Na, however, shows little chemical variation in the pyroxenes. The trace element chemistry is briefly examined. The clinopyroxenes show well-developed oscillatory and sector zoning. The basal {11} sectors are enriched in Si and Mg and depleted in Ti, Al, and Fe relative to the {100}, {110}, and {010} prism sectors.

Geochemistry of the 1989–1990 eruption of redoubt volcano: Part I. Whole-rock major- and trace-element chemistry

1994 ◽  
Vol 62 (1-4) ◽  
pp. 429-452 ◽  
Author(s):  
Christopher J. Nye ◽  
Samuel E. Swanson ◽  
Victoria F. Avery ◽  
Thomas P. Miller
Keyword(s):  
Trace Element ◽  
Trace Element Chemistry ◽  
Element Chemistry
Sign in / Sign up

Export Citation Format

Share Document