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From Molecules to Mountain Building: Incorporating Magnesium into Carbonates.

Record Type:	Electronic resources : Monograph/item
Title/Author:	From Molecules to Mountain Building: Incorporating Magnesium into Carbonates.
Author:	Hobbs, Franklin.
Published:	Ann Arbor : ProQuest Dissertations & Theses, 2021
Description:	171 p.
Notes:	Source: Dissertations Abstracts International, Volume: 83-03, Section: B.
Notes:	Advisor: Xu, Huifang;Szlufarska, Izabela.
Contained By:	Dissertations Abstracts International83-03B.
Subject:	Geology.
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28714481
ISBN:	9798535550039

From Molecules to Mountain Building: Incorporating Magnesium into Carbonates.
Hobbs, Franklin.

From Molecules to Mountain Building: Incorporating Magnesium into Carbonates. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 171 p.

Source: Dissertations Abstracts International, Volume: 83-03, Section: B.

Thesis (Ph.D.)--The University of Wisconsin - Madison, 2021.

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

Magnesium incorporation in the carbonate structure is at the heart of the “Dolomite Problem.” Due to a strong magnesium hydration shell, dolomite (CaMg(CO3)2) and magnesite (MgCO3) will not form in the laboratory at sub-40 °C despite super saturation. Yet both dolomite and magnesite are seen throughout geologic time and recent dolomites are found in evaporative environments. This discrepancy is addressed across wide time and lengths scales, from angstroms to kilometers and nanoseconds to thousands of years.This thesis first presents a refined a temperature and pH cycling method to achieve up to 91 mol% MgCO3 of (Mg,Ca)CO3 carbonates without exceeding 40 °C. The experimental conditions ideal for magnesite growth match very well with an evaporative/lagoonal/playa geologic setting: small thermal mass for daily temperature swings, algal mass for pH control, and a solution highly concentrated in Mg2+ with high Mg:Ca ratios. Additionally, this study suggests the inclusion of dissolved silica in the system may play at catalytic role in the development of magnesium-bearing carbonates. To test these hypotheses in a field setting, this thesis explores the hydrology and mineralogy of Deep Springs Lake, a playa setting with primary dolomite precipitation. The central playa sites with the highest sedimentation rates have dissolved silica concentrations close to saturation. Bulk assemblages of core samples contain 20–40% fine grained, partially ordered dolomite along with a 10–20% poorly crystalline or amorphous clay fraction, while TEM imaging finds a co-incident relationship between the fine-grained dolomite and Mg-rich smectite clays. The Mg-rich smectite clays act as a sink for the excess dissolved silica during evaporation. While it has been proposed that the silica molecule could act as a catalyst by disrupting the surficial magnesium hydration barrier, the mechanism is still unknown. Using a molecular dynamics framework verified by ab-initio calculations, this thesis found that while stable configurations of surface silica exist, their presence has no effect on the number of waters coordinated to the surface and no effect on the distance between the water to surface cations. However, the desorption of dissolved silica from the surface increases the local Mg-bound water exchange rate from 0.51 ns–1 to 0.97 ns–1.

ISBN: 9798535550039Subjects--Topical Terms:

196077
Geology.
Subjects--Index Terms:

Deep springs lake

From Molecules to Mountain Building: Incorporating Magnesium into Carbonates.
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300 $a 171 p.
500 $a Source: Dissertations Abstracts International, Volume: 83-03, Section: B.
500 $a Advisor: Xu, Huifang;Szlufarska, Izabela.
502 $a Thesis (Ph.D.)--The University of Wisconsin - Madison, 2021.
506 $a This item must not be sold to any third party vendors.
520 $a Magnesium incorporation in the carbonate structure is at the heart of the “Dolomite Problem.” Due to a strong magnesium hydration shell, dolomite (CaMg(CO3)2) and magnesite (MgCO3) will not form in the laboratory at sub-40 °C despite super saturation. Yet both dolomite and magnesite are seen throughout geologic time and recent dolomites are found in evaporative environments. This discrepancy is addressed across wide time and lengths scales, from angstroms to kilometers and nanoseconds to thousands of years.This thesis first presents a refined a temperature and pH cycling method to achieve up to 91 mol% MgCO3 of (Mg,Ca)CO3 carbonates without exceeding 40 °C. The experimental conditions ideal for magnesite growth match very well with an evaporative/lagoonal/playa geologic setting: small thermal mass for daily temperature swings, algal mass for pH control, and a solution highly concentrated in Mg2+ with high Mg:Ca ratios. Additionally, this study suggests the inclusion of dissolved silica in the system may play at catalytic role in the development of magnesium-bearing carbonates. To test these hypotheses in a field setting, this thesis explores the hydrology and mineralogy of Deep Springs Lake, a playa setting with primary dolomite precipitation. The central playa sites with the highest sedimentation rates have dissolved silica concentrations close to saturation. Bulk assemblages of core samples contain 20–40% fine grained, partially ordered dolomite along with a 10–20% poorly crystalline or amorphous clay fraction, while TEM imaging finds a co-incident relationship between the fine-grained dolomite and Mg-rich smectite clays. The Mg-rich smectite clays act as a sink for the excess dissolved silica during evaporation. While it has been proposed that the silica molecule could act as a catalyst by disrupting the surficial magnesium hydration barrier, the mechanism is still unknown. Using a molecular dynamics framework verified by ab-initio calculations, this thesis found that while stable configurations of surface silica exist, their presence has no effect on the number of waters coordinated to the surface and no effect on the distance between the water to surface cations. However, the desorption of dissolved silica from the surface increases the local Mg-bound water exchange rate from 0.51 ns–1 to 0.97 ns–1.
590 $a School code: 0262.
650 4 $a Geology. $3 196077
650 4 $a Geochemistry. $3 196060
650 4 $a Materials science. $3 221779
650 4 $a Laboratories. $3 220491
650 4 $a Minerals. $3 234145
650 4 $a Sediments. $3 915770
650 4 $a Energy. $3 212397
650 4 $a Scanning electron microscopy. $3 242518
650 4 $a Crystal structure. $3 915771
650 4 $a Transmission electron microscopy. $3 192825
650 4 $a Simulation. $3 915618
650 4 $a Precipitation. $3 915772
650 4 $a Solid solutions. $3 915773
650 4 $a Fourier transforms. $3 915774
650 4 $a Charged particles. $3 915775
650 4 $a Sensors. $3 915776
650 4 $a Carbon dioxide. $3 245464
650 4 $a Seawater. $3 511146
650 4 $a X rays. $3 915777
650 4 $a Magnesium. $3 225498
650 4 $a Carbon cycle. $3 915778
650 4 $a Aperture. $3 915779
650 4 $a Geobiology. $3 188950
650 4 $a Microorganisms. $3 276154
650 4 $a Atoms & subatomic particles. $3 915685
653 $a Deep springs lake
653 $a Dolomite
653 $a Dolomite problem
653 $a Magnesite
653 $a Silica
653 $a Smectite
690 $a 0794
690 $a 0372
690 $a 0996
690 $a 0791
690 $a 0483
710 2 $a The University of Wisconsin - Madison. $b Materials Science. $3 766031
773 0 $t Dissertations Abstracts International $g 83-03B.
790 $a 0262
791 $a Ph.D.
792 $a 2021
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28714481