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The Origin of Nb and Ta Anomalies in...

Spitz, Blake I.

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The Origin of Nb and Ta Anomalies in Recent Ejecta from Turrialba Volcano, Costa Rica.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	The Origin of Nb and Ta Anomalies in Recent Ejecta from Turrialba Volcano, Costa Rica./
作者:	Spitz, Blake I.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
面頁冊數:	154 p.
附註:	Source: Masters Abstracts International, Volume: 82-04.
Contained By:	Masters Abstracts International82-04.
標題:	Geochemistry. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27997810
ISBN:	9798672160931

The Origin of Nb and Ta Anomalies in Recent Ejecta from Turrialba Volcano, Costa Rica.
Spitz, Blake I.

The Origin of Nb and Ta Anomalies in Recent Ejecta from Turrialba Volcano, Costa Rica. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 154 p.

Source: Masters Abstracts International, Volume: 82-04.

Thesis (M.S.)--The University of Iowa, 2020.

This item must not be sold to any third party vendors.

Turrialba Volcano, the southeastern-most volcano in the Central American Volcanic Arc, began erupting explosively in 2010 after 144 years of quiescence. Juvenile volcanic glass fragments were collected from tephra layers associated with this new eruptive phase to investigate the origin of the magmas feeding this system.Major element analyses of these glasses show them to be highly diverse. Mafic glasses are basaltic andesites with a range of TiO2 concentrations. More differentiated glasses have wide-ranging compositions, although most follow a trachyandesite to trachydacite and rhyolite differentiation trend.Trace element analyses of glass shards erupted from 2010-2017 and olivine-hosted melt inclusions erupted in 1884-1886 confirm the presence of parental magmas with calcalkaline (low-Nb) to ocean island basalt-like (high-Nb) signatures in recent ejecta. Four magma endmember types are identified: (1) low La/Nb and Ba/La, (2) High La/Nb, moderate Ba/La, (3) Moderate La/Nb and Ba/La and high Nb/Ta and (4) Low La/Nb and high Ba/La. High-Nb (Endmember 1) glasses are relatively rare and unfractionated, whereas most low-Nb (high La/Nb) glasses at all levels of differentiation have trace element compositions within a field bounded by endmember compositions. For most samples, ratios between more and less fluid mobile incompatible trace elements (e.g. Ba/La) only modestly differ between low- and high-Nb glasses suggesting only a modest difference in input from the subducting slab to generate most of Turrialba's magmas.The Magma Chamber Simulator was used to better understand magma differentiation at Turrialba. Pure crystal fractionation models reproduce differentiation trends for mafic andesites, but fail to produce trends at higher SiO2 contents, showing that Turrialba's magmas cannot be produced through fractional crystallization alone, but require the input of silicic melts of altered volcanic material.It is proposed here that magmas at Turrialba and nearby Irazu are generated by melting of diapirs composed of a melange of altered oceanic crust, chlorite schist and subducted volcaniclastic sediments from the interface of the subducting Cocos plate and overlying mantle wedge. Diapir composition and melting is controlled by where along the slab-wedge interface it rises. The diapir feeding Irazu has a relatively short travel path through the mantle wedge and therefore maintains a relatively low temperature, which results in melting with residual rutile and ilmenite. The inhomogeneous distribution of slab and mantle components in this diapir results in the generation of diverse low-Nb magmas. The deeper forming diapirs feeding Turrialba have less water and a longer travel path through the hot core of the mantle wedge. This results in melts undersaturated in rutile and ilmenite, and lack Nb and Ta anomalies. The diverse resulting magmas mix, fractionate and assimilate hydrothermally altered volcanic rocks in the shallow magma system beneath Turrialba prior to eruption. The rare presence of these high-Nb magmas at Turrialba reflect the thermal structure of the underlying mantle related to its position behind the arc front and above the slab edge.

ISBN: 9798672160931Subjects--Topical Terms:

539092
Geochemistry.
Subjects--Index Terms:

Volcanology

The Origin of Nb and Ta Anomalies in Recent Ejecta from Turrialba Volcano, Costa Rica.
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245 1 4 $a The Origin of Nb and Ta Anomalies in Recent Ejecta from Turrialba Volcano, Costa Rica.
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300 $a 154 p.
500 $a Source: Masters Abstracts International, Volume: 82-04.
500 $a Advisor: Reagan, Mark K.
502 $a Thesis (M.S.)--The University of Iowa, 2020.
506 $a This item must not be sold to any third party vendors.
520 $a Turrialba Volcano, the southeastern-most volcano in the Central American Volcanic Arc, began erupting explosively in 2010 after 144 years of quiescence. Juvenile volcanic glass fragments were collected from tephra layers associated with this new eruptive phase to investigate the origin of the magmas feeding this system.Major element analyses of these glasses show them to be highly diverse. Mafic glasses are basaltic andesites with a range of TiO2 concentrations. More differentiated glasses have wide-ranging compositions, although most follow a trachyandesite to trachydacite and rhyolite differentiation trend.Trace element analyses of glass shards erupted from 2010-2017 and olivine-hosted melt inclusions erupted in 1884-1886 confirm the presence of parental magmas with calcalkaline (low-Nb) to ocean island basalt-like (high-Nb) signatures in recent ejecta. Four magma endmember types are identified: (1) low La/Nb and Ba/La, (2) High La/Nb, moderate Ba/La, (3) Moderate La/Nb and Ba/La and high Nb/Ta and (4) Low La/Nb and high Ba/La. High-Nb (Endmember 1) glasses are relatively rare and unfractionated, whereas most low-Nb (high La/Nb) glasses at all levels of differentiation have trace element compositions within a field bounded by endmember compositions. For most samples, ratios between more and less fluid mobile incompatible trace elements (e.g. Ba/La) only modestly differ between low- and high-Nb glasses suggesting only a modest difference in input from the subducting slab to generate most of Turrialba's magmas.The Magma Chamber Simulator was used to better understand magma differentiation at Turrialba. Pure crystal fractionation models reproduce differentiation trends for mafic andesites, but fail to produce trends at higher SiO2 contents, showing that Turrialba's magmas cannot be produced through fractional crystallization alone, but require the input of silicic melts of altered volcanic material.It is proposed here that magmas at Turrialba and nearby Irazu are generated by melting of diapirs composed of a melange of altered oceanic crust, chlorite schist and subducted volcaniclastic sediments from the interface of the subducting Cocos plate and overlying mantle wedge. Diapir composition and melting is controlled by where along the slab-wedge interface it rises. The diapir feeding Irazu has a relatively short travel path through the mantle wedge and therefore maintains a relatively low temperature, which results in melting with residual rutile and ilmenite. The inhomogeneous distribution of slab and mantle components in this diapir results in the generation of diverse low-Nb magmas. The deeper forming diapirs feeding Turrialba have less water and a longer travel path through the hot core of the mantle wedge. This results in melts undersaturated in rutile and ilmenite, and lack Nb and Ta anomalies. The diverse resulting magmas mix, fractionate and assimilate hydrothermally altered volcanic rocks in the shallow magma system beneath Turrialba prior to eruption. The rare presence of these high-Nb magmas at Turrialba reflect the thermal structure of the underlying mantle related to its position behind the arc front and above the slab edge.
590 $a School code: 0096.
650 4 $a Geochemistry. $3 539092
650 4 $a Geology. $3 516570
650 4 $a Thermodynamics. $3 517304
650 4 $a Environmental education. $3 528212
653 $a Volcanology
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653 $a Central American Volcanic Arc
653 $a Eruptive phase
653 $a Mafic glasses
653 $a Basaltic andesites
653 $a Magma Chamber Simulator
653 $a Costa Rica
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710 2 $a The University of Iowa. $b Geoscience. $3 2093005
773 0 $t Masters Abstracts International $g 82-04.
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792 $a 2020
793 $a English
856 4 0 $u https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27997810