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Geochronology and isotopic character...

Ames, Leslie,

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Geochronology and isotopic character of ultrahigh-pressure metamorphism with implications for collision of the Sino-Korean and Yangtze cratons, central China /

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	Geochronology and isotopic character of ultrahigh-pressure metamorphism with implications for collision of the Sino-Korean and Yangtze cratons, central China // Leslie Ames.
作者:	Ames, Leslie,
面頁冊數:	1 electronic resource (129 pages)
附註:	Source: Dissertations Abstracts International, Volume: 57-07, Section: B.
Contained By:	Dissertations Abstracts International57-07B.
標題:	Geology. -
電子資源:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9605822
ISBN:	9798208907634

Geochronology and isotopic character of ultrahigh-pressure metamorphism with implications for collision of the Sino-Korean and Yangtze cratons, central China /
Ames, Leslie,

Geochronology and isotopic character of ultrahigh-pressure metamorphism with implications for collision of the Sino-Korean and Yangtze cratons, central China /Leslie Ames. - 1 electronic resource (129 pages)

Source: Dissertations Abstracts International, Volume: 57-07, Section: B.

The collision zone between the Sino-Korean and Yangtze cratons in central China is marked by subduction-related metamorphic rocks composed of crustal protoliths. These range in metamorphic grade from ultrahigh-pressure eclogite to low-greenschist facies. The paragenesis of the ultrahigh-pressure rocks (coesite and diamond-bearing) indicates subduction to depths greater than $\\sim$120 km as a result of continental collision. Despite extreme metamorphic conditions, zircons have not undergone Pb loss but rather illustrate two periods of growth: crystallization between 700 and 800 Ma and ultrahigh-pressure metamorphism at 218 $\\pm$ 2.5 Ma. Previous studies using regional geology and paleomagnetism have predicted a time-transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture. U-Pb zircon ages of these ultrahigh-pressure metamorphic rocks are 218.4 $\\pm$ 2.5 Ma and 217.1 $\\pm$ 8.7 Ma for the Dabie Mountains and Shandong peninsula, respectively. The similar ages imply that the Tan-Lu fault, which offsets the ultrahigh-pressure metamorphic rocks, is a secondary feature not related to collision or subduction. Biotite $\\rm\\sp{40}Ar/\\sp{39}Ar$ ages from the ultrahigh-pressure rocks of 217 to 190 Ma give an estimate of the duration of retrograde metamorphism (1-30 m.y.). The closure temperature of biotite of $\\sim$300-$350\\sp\\circ\\rm C$ coupled with petrographic data indicate exhumation to mid-crustal levels and relatively cool temperatures within 30 m.y. of peak metamorphic conditions, which requires an appropriately fast exhumation mechanism. Cretaceous plutonism and preliminary fission track data reflect a second stage of exhumation controlled by slower exhumation mechanism(s) than the first stage. Whole rock isotopic data show that both Rb-Sr and U-Pb were open systems during metamorphism but that Sm-Nd probably remained closed. Nd initial isotopes display crustal signatures, indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth, Sm-Nd data in conjunction with U-Pb zircon dating indicate that the ultrahigh-pressure rocks are not classic Yangtze craton basement (2.9 Ga) but that they originally crystallized in a rift environment between $\\sim$700 and 800 Ma.

English

ISBN: 9798208907634Subjects--Topical Terms:

516570
Geology.
Subjects--Index Terms:

subduction

Geochronology and isotopic character of ultrahigh-pressure metamorphism with implications for collision of the Sino-Korean and Yangtze cratons, central China /
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500 $a Source: Dissertations Abstracts International, Volume: 57-07, Section: B.
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502 $b Ph.D. $c University of California, Santa Barbara $d 1995.
520 $a The collision zone between the Sino-Korean and Yangtze cratons in central China is marked by subduction-related metamorphic rocks composed of crustal protoliths. These range in metamorphic grade from ultrahigh-pressure eclogite to low-greenschist facies. The paragenesis of the ultrahigh-pressure rocks (coesite and diamond-bearing) indicates subduction to depths greater than $\\sim$120 km as a result of continental collision. Despite extreme metamorphic conditions, zircons have not undergone Pb loss but rather illustrate two periods of growth: crystallization between 700 and 800 Ma and ultrahigh-pressure metamorphism at 218 $\\pm$ 2.5 Ma. Previous studies using regional geology and paleomagnetism have predicted a time-transgressive collision but age data presented in this study indicate that the collision was approximately coeval along the length of the suture. U-Pb zircon ages of these ultrahigh-pressure metamorphic rocks are 218.4 $\\pm$ 2.5 Ma and 217.1 $\\pm$ 8.7 Ma for the Dabie Mountains and Shandong peninsula, respectively. The similar ages imply that the Tan-Lu fault, which offsets the ultrahigh-pressure metamorphic rocks, is a secondary feature not related to collision or subduction. Biotite $\\rm\\sp{40}Ar/\\sp{39}Ar$ ages from the ultrahigh-pressure rocks of 217 to 190 Ma give an estimate of the duration of retrograde metamorphism (1-30 m.y.). The closure temperature of biotite of $\\sim$300-$350\\sp\\circ\\rm C$ coupled with petrographic data indicate exhumation to mid-crustal levels and relatively cool temperatures within 30 m.y. of peak metamorphic conditions, which requires an appropriately fast exhumation mechanism. Cretaceous plutonism and preliminary fission track data reflect a second stage of exhumation controlled by slower exhumation mechanism(s) than the first stage. Whole rock isotopic data show that both Rb-Sr and U-Pb were open systems during metamorphism but that Sm-Nd probably remained closed. Nd initial isotopes display crustal signatures, indicating that the crust subducted as a coherent slab rather than becoming intercalated with mantle material at depth, Sm-Nd data in conjunction with U-Pb zircon dating indicate that the ultrahigh-pressure rocks are not classic Yangtze craton basement (2.9 Ga) but that they originally crystallized in a rift environment between $\\sim$700 and 800 Ma.
546 $a English
590 $a School code: 0035
650 4 $a Geology. $3 516570
650 4 $a Geochemistry. $3 539092
653 $a subduction
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690 $a 0996
710 2 $a University of California, Santa Barbara. $e degree granting institution. $3 3818149
720 1 $a Tilton, George R. $e degree supervisor.
773 0 $t Dissertations Abstracts International $g 57-07B.
790 $a 0035
791 $a Ph.D.
792 $a 1995
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