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Breaking Established Boundaries in I...

Schaub, Douglas Richard,

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Breaking Established Boundaries in Igneous Petrology /

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Breaking Established Boundaries in Igneous Petrology // Douglas Richard Schaub.
作者:	Schaub, Douglas Richard,
面頁冊數:	1 electronic resource (88 pages)
附註:	Source: Dissertations Abstracts International, Volume: 86-08, Section: B.
Contained By:	Dissertations Abstracts International86-08B.
標題:	Geology. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31767210
ISBN:	9798304917742

Breaking Established Boundaries in Igneous Petrology /
Schaub, Douglas Richard,

Breaking Established Boundaries in Igneous Petrology /Douglas Richard Schaub. - 1 electronic resource (88 pages)

Source: Dissertations Abstracts International, Volume: 86-08, Section: B.

Revisiting fundamental assumptions can provide an avenue for solving apparently intractable problems. Application of this principle to two systems within the field of igneous petrology (mid-ocean ridge magmatism, magmatic gas exsolution and vapor deposition) has yielded several unexpected and groundbreaking results. The first work presented here explores complexities in the origin of mid-ocean ridge basalts (MORB). Numerous studies have identified that simple decompression melting of fertile peridotite followed by shallow level fractionation of the olivine tholeiite magma cannot fully account for the compositional features of MORB. Further work has made it increasingly clear that the abundant xenocrysts of forsteritic olivine and anorthitic plagioclase hosted in many MORB samples, and the process of their incorporation from conduit walls by the ascending olivine tholeiite, must play an integral role in MORB generation. Studies of xenocryst melt inclusions indicate a complex history of melting and crystallization within the conduit prior to xenocryst incorporation into MORB, including the formation of melt and spinel by incongruent melting of olivine and plagioclase. What has remained unclear is how the high temperatures presumed necessary to induce melting of highly refractory olivine and plagioclase could be attained. Experimental work presented here demonstrates that, contrary to the prevailing understanding, melting of anorthitic plagioclase in the presence of olivine is governed by a negative azeotropic topology rather than a classic melting loop. This induces a substantial reduction of solidus temperatures relative to expected values in the range An85-100 at pressures of 0.5-1.0 GPa, enabling refractory troctolitic cumulates to melt under lower crustal conditions. This result is consistent with textural and compositional observations of MORB xenocrysts, xenocryst-hosted melt inclusions, and host rock characteristics. A second challenging problem in petrology is constraining the trace element budget of magmatic gas, which is difficult to impossible to measure directly. This thesis presents the first effort to investigate the trace element contents of magmatic gas associated with topaz formation by use of single-crystal synchrotron microbeam X-ray techniques on picogram quantities of trace elements (some never previously measured at these concentrations) in vapor-deposited topaz crystals. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis were combined to determine that As5+ and Ge4+ substitute for Si in the topaz tetrahedral site, while Mn3+, Fe3+, Ga3+, and Ti4+ are incorporated into the octahedral site. Quantified X-ray fluorescence (XRF) measurements on two crystals from the same locality revealed variable As, Fe, Ga, and Ti contents, indicating an undersaturated source gas with a shifting composition over the course of topaz deposition. Identical Ge contents suggest a buffering effect on Ge in the gas, possibly due to co-precipitation of another Ge-bearing phase such as quartz. Very low Mn content in the topaz crystals does not appear to reflect the abundance of Mn in the gas (coexisting bixbyite indicates saturation); rather the combined structural and compositional observations suggests a Jahn-Teller inhibitory effect on the substitution of Mn for Al in topaz.

English

ISBN: 9798304917742Subjects--Topical Terms:

516570
Geology.
Subjects--Index Terms:

Igneous petrology

Breaking Established Boundaries in Igneous Petrology /
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650 4 $a Geochemistry. $3 539092
650 4 $a Petrology. $3 535210
653 $a Igneous petrology
653 $a Magmatic gas
653 $a Mid-ocean ridge basalt
653 $a Plagioclase
653 $a Topaz
653 $a Trace element
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690 $a 0996
690 $a 0584
710 2 $a State University of New York at Stony Brook. $b Geosciences. $e degree granting institution. $3 3814523
720 1 $a Nekvasil, Hanna $e degree supervisor.
720 1 $a Hurowitz, Joel $e degree supervisor.
773 0 $t Dissertations Abstracts International $g 86-08B.
790 $a 0771
791 $a Ph.D.
792 $a 2024
856 4 0 $u https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=31767210