scholarly journals The dynamothermal aureole of the Donqiao ophiolite (northern Tibet)

1997 ◽  
Vol 34 (1) ◽  
pp. 59-65 ◽  
Author(s):  
Mei-Fu Zhou ◽  
John Malpas ◽  
Paul T. Robinson ◽  
Peter H. Reynolds
Keyword(s):  
High Pressure ◽  
Subduction Zone ◽  
Greenschist Facies ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Mineral Paragenesis ◽  
Metasedimentary Rocks ◽  
Northern Tibet ◽  
Suprasubduction Zone ◽  
Ar Geochronology

Metamorphic rocks found at the base of the Jurassic Donqiao ophiolite of northern Tibet are interpreted as a basal dynamothermal aureole produced during obduction of the massif. The rocks form a sequence some 8 m thick, varying from high-grade amphibolites at the contact with overlying harzburgites to greenschist facies metasedimentary rocks lower down. The mineral paragenesis is similar to other such aureoles, and indicates that temperatures in excess of 750 °C may have been reached during metamorphism. The lack of high-pressure minerals suggests that the rocks were produced by subcretion in a relatively shallow dipping subduction zone. Ar–Ar geochronology on amphibole separates provides dates of 175–180 Ma for the displacement of the ophiolite, significantly older than the age of emplacement estimated from stratigraphie relationships. The ophiolite was clearly obducted very soon after its formation in a suprasubduction zone environment.

Geochemical and Nd isotopic constraints for the origin of eclogite protoliths, northern Cordillera: implications for the Paleozoic tectonic evolution of the Yukon-Tanana terrane

1999 ◽  
Vol 36 (10) ◽  
pp. 1697-1709 ◽  
Author(s):  
Robert A Creaser ◽  
Jo-Anne S Goodwin-Bell ◽  
Philippe Erdmer
Keyword(s):  
High Pressure ◽  
Subduction Zone ◽  
Convergent Margins ◽  
Metasedimentary Rocks ◽  
High Pressure Metamorphism ◽  
Distal Edge ◽  
History Of ◽  
Convergent Plate Margin ◽  
Ocean Ridge ◽  
Subduction Zone Magmatism

On the basis of trace-element data, basaltic protoliths for Paleozoic eclogites from the Yukon-Tanana terrane (YTT) have diverse origins. Eclogites from Stewart Lake and the Simpson Range have characteristics of basaltic protoliths generated by subduction-zone magmatism, are hosted by serpentinitic-gabbroic rocks, and record Mississippian high-pressure metamorphism and cooling. In contrast, eclogites from Faro, Ross River, and Last Peak show either within-plate geochemistry or mid-ocean ridge protolith geochemistry with a small subduction component, are hosted by continental metasedimentary rocks of the Nisutlin assemblage, and record Permian high-pressure metamorphism and cooling. We interpret these results to derive from the following tectonic events in the Paleozoic history of the YTT: (1) activity at a Devonian-Mississippian convergent plate margin at the distal edge of North America, with near-contemporaneous subduction-zone magmatism and high-pressure metamorphism; (2) Mississippian rifting of that margin to form the outboard YTT, the Slide Mountain marginal basin, and the Faro, Ross River, and Last Peak eclogite protoliths; and (3) west-dipping subduction of the Slide Mountain Ocean under the outboard YTT in Permian time, to produce the Faro, Ross River, and Last Peak eclogites and Permian arc magmatism throughout the YTT. The basaltic protoliths of the Paleozoic YTT eclogites bear close similarity to those produced in rifted convergent margins, such as the Miocene Japanese arc - back-arc system.

Neotethys closure history of Anatolia: insights from 40 Ar-39 Ar geochronology and P-T estimation in high-pressure metasedimentary rocks

2013 ◽  
Vol 31 (6) ◽  
pp. 585-606 ◽  
Author(s):  
A. Pourteau ◽  
M. Sudo ◽  
O. Candan ◽  
P. Lanari ◽  
O. Vidal ◽  
...  
Keyword(s):  
High Pressure ◽  
Metasedimentary Rocks ◽  
History Of ◽  
Ar Geochronology

Zircon U-Pb and geochemical signatures in high-pressure, low-temperature metamorphic rocks as recorders of subduction zone processes, Sikinos and Ios islands, Greece

2021 ◽  
pp. 120447
Author(s):  
Eirini M. Poulaki ◽  
Daniel F. Stockli ◽  
Megan E. Flansburg ◽  
Michelle L. Gevedon ◽  
Lisa D. Stockli ◽  
...  
Keyword(s):  
High Pressure ◽  
Low Temperature ◽  
Subduction Zone ◽  
Metamorphic Rocks ◽  
Subduction Zone Processes

Two contrasting mineral assemblages in the Meliata blueschists, Western Carpathians, Slovakia

1999 ◽  
Vol 63 (4) ◽  
pp. 489-501 ◽  
Author(s):  
S. W. Faryad ◽  
G. Hoinkes
Keyword(s):  
High Pressure ◽  
Low Pressure ◽  
Greenschist Facies ◽  
Western Carpathians ◽  
Metamorphic Rocks ◽  
Low Grade ◽  
Mineral Assemblages ◽  
Compositional Variations ◽  
Si Content ◽  
End Members

AbstractLow-grade metamorphic rocks from the Meliata unit (Western Carpathians) are characterized by the presence of typical blueschist-facies minerals. In metabasalt, an early low-pressure assemblage (<0.5 GPa at 350°C characterized by muscovite and zoisite, is followed by high-pressure glaucophane, phengite, Na-pyroxene, chlorite, clinozoisite and Al-poor titanite, indicating pressures of >1.2 GPa at 450°C Na-pyroxene shows strong compositional variations between the end-members Jd4–70, Aeg10–49 and Q17–49, respectively. Phengite has high Si content of 3.5 a.p.f.u. The zoisite with Al2Fe (100[Fetot/(−2+Altot+Fetot)]) = 3–5%, is rimmed by clinozoisite, with a maximum of 75% Al2Fe, as well as being enclosed by glaucophane. The occurrence of clinozoisite, rimming zoisite, suggests that the transformation of orthorhombic to monoclinic epidote depends not only on the temperature but also on the pressure. In the studied metabasalt, retrograde phases reflecting greenschist-facies conditions are albite and chlorite. Some neighbouring metabasites may additionally contain actinolite and biotite.

Possibly diamond-bearing mantle peridotites and podiform chromitites in the Luobusa and Donqiao ophiolites, Tibet

1993 ◽  
Vol 30 (8) ◽  
pp. 1650-1659 ◽  
Author(s):  
Wen-Ji Bai ◽  
Mei-Fu Zhou ◽  
Paul T. Robinson
Keyword(s):  
High Pressure ◽  
Subduction Zone ◽  
Suture Zone ◽  
Ultramafic Rocks ◽  
Eurasian Plate ◽  
Southern Tibet ◽  
Suprasubduction Zone ◽  
Mantle Peridotites ◽  
Podiform Chromitites ◽  
Reducing Environment

The Luobusa ophiolite of the Yarlung–Zangbo (southern Tibet) suture zone and the Donqiao ophiolite of the Bangong–Nujiang (northern Tibet) suture zone are allochthonous bodies that contain possibly diamond-bearing mantle peridotites and podiform chromitites. The mantle sections in both massifs consist chiefly of harzburgite and diopside-bearing harzburgite with abundant lenses of dunite and chromitite. These ultramafic rocks are more strongly depleted than typical abyssal peridotites and their whole-rock and mineral chemistries suggest formation above a subduction zone. An unusual mineral association (diamond, SiC, graphite, native chromium, Ni–Fe alloy, Cr2+-bearing chromite), indicating a high-pressure, reducing environment, occurs in both the peridotites and chromitites. We suggest that these ophiolites were generated originally in a suprasubduction zone environment and were later carried deep into the mantle along a second subduction zone, at which time the diamonds and other high-pressure minerals were formed. It is not yet clear whether the diamonds formed by high-pressure metamorphism of the oceanic crust or by crystallization from mantle melts, but their occurrence in chromitites and harzburgites suggests a metamorphic origin. During the collision of India with the Eurasian plate, the mantle sections were tectonically emplaced at shallow crustal levels rapidly enough to preserve the diamonds.

Coeval plutonism and metamorphism in a latest Oligocene metamorphic core complex in northwest Turkey

2000 ◽  
Vol 137 (5) ◽  
pp. 495-516 ◽  
Author(s):  
ARAL I. OKAY ◽  
MUHARREM SATIR
Keyword(s):  
Subduction Zone ◽  
Shear Zone ◽  
Metamorphic Core Complex ◽  
Metamorphic Rocks ◽  
High Grade ◽  
Core Complex ◽  
The Core ◽  
The North ◽  
Shear Sense ◽  
Metamorphic Core

A metamorphic core complex of latest Oligocene age crops out in the Kazdağ mountain range in northwest Turkey. The footwall of the core complex consists of gneiss, amphibolite and marble metamorphosed at 5 ± 1 kbar and 640° ± 50 °C. The average muscovite and biotite Rb/Sr ages from the gneisses are 19 Ma and 22 Ma, respectively, and imply high temperature metamorphism during latest Oligocene times. The hangingwall is made up of an unmetamorphosed Lower Tertiary oceanic accretionary melange with Upper Cretaceous eclogite lenses. The hangingwall and footwall are separated by an extensional ductile shear zone, two kilometres thick. Mylonites and underlying high-grade metamorphic rocks show a N-trending mineral lineation with the structural fabrics indicating down-dip, top-to-the-north shear sense. The shear zone, the accretionary melange and the high-grade metamorphic rocks are cut by an undeformed granitoid with a 21 Ma Rb/Sr biotite age, analytically indistinguishable from the Rb/Sr biotite ages in the surrounding footwall gneisses. The estimated pressure of the metamorphism, and that of the granitoid emplacement, indicate that the high-grade metamorphic rocks were rapidly exhumed at ∼ 24 Ma from a depth of ∼ 14 km to ∼ 7 km by activity along the shear zone. The subsequent exhumation of the metamorphic rocks to the surface occurred during Pliocene–Quaternary times in a transpressive ridge between two overstepping fault segments of the North Anatolian Fault zone. The high-grade metamorphic rocks of the Kazdağ range are surrounded by voluminous calc-alkaline volcanic and plutonic rocks of Late Oligocene–Early Miocene age, which formed above the northward-dipping Hellenic subduction zone. The magmatic arc setting of the core complex and stratigraphic evidence for subdued topography in northwest Turkey prior to the onset of extension suggest that the latest Oligocene regional extension was primarily related to the roll-back of the subduction zone rather than to the gravitational collapse.

DO HIGH-GRADE BLOCKS RECORD THE COOLING OF THE FRANCISCAN SUBDUCTION ZONE?

2019 ◽  
Author(s):  
Howard W. Day ◽  
◽  
Sean R. Mulcahy ◽  
Jesslyn K. Starnes ◽  
Francisco E. Apen
Keyword(s):  
Subduction Zone ◽  
High Grade
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