Rb-Sr and Sm-Nd Mineral Isochron Ages of the Metamorphic Rocks in the Namaqualand Metamorphic Complex, South Africa

2002 ◽  
Vol 5 (4) ◽  
pp. 771-779 ◽  
Author(s):  
M. Yuhara ◽  
T. Miyazaki ◽  
J. Ishioka ◽  
S. Suzuki ◽  
H. Kagami ◽  
...  
Keyword(s):  
South Africa ◽  
Metamorphic Rocks ◽  
Metamorphic Complex ◽  
Mineral Isochron

scholarly journals The tectonic significance of the Early Cretaceous forearc-metamorphic assemblage in south-central Alaska based on detrital zircon U–Pb dating of sedimentary protoliths

2015 ◽  
Vol 52 (12) ◽  
pp. 1182-1190 ◽  
Author(s):  
Amanda Labrado ◽  
Terry L. Pavlis ◽  
Jeffrey M. Amato ◽  
Erik M. Day
Keyword(s):  
Early Cretaceous ◽  
Detrital Zircon ◽  
Early Jurassic ◽  
Ductile Deformation ◽  
Metamorphic Rocks ◽  
Accretionary Complex ◽  
Metamorphic Complex ◽  
Metasedimentary Rocks ◽  
South Central ◽  
Detrital Zircon Ages

A complex array of faulted arc rocks and variably metamorphosed forearc accretionary complex rocks form a mappable arc–forearc boundary in southern Alaska known as the Border Ranges fault (BRF). We use detrital U–Pb zircon dating of metasedimentary rocks within the Knik River terrane in the western Chugach Mountains to show that a belt of Early Cretaceous amphibolite-facies metamorphic rocks along the BRF was formed when older mélange rocks of the Chugach accretionary complex were reworked in a sinistral-oblique thrust reactivation of the BRF during a period of forearc plutonism. The metamorphic subterrane of the Knik River terrane has a maximum depositional age (MDA) of 156.5 ± 1.5 Ma and a detrital zircon age spectrum that is indistinguishable from the Potter Creek assemblage of the Chugach accretionary complex, supporting correlation of these units. These ages contrast strongly with new and existing data that show Triassic to earliest Jurassic detrital zircon ages from metamorphic screens in the plutonic subterrane of the Knik River terrane, a fragmented Early Jurassic plutonic assemblage generally interpreted as the basement of the Peninsular terrane. Based on these findings, we propose the following new terminology for the Knik River terrane: (1) “Carpenter Creek metamorphic complex” for the Early Cretaceous “metamorphic subterrane”, (2) “western Chugach trondhjemite suite” for the Early Cretaceous forearc plutons within the belt, (3) “Friday Creek assemblage” for a transitional mélange unit that contains blocks of the Carpenter Creek complex in a chert–argillite matrix, and (4) “Knik River metamorphic complex” in reference to metamorphic rocks engulfed by Early Jurassic plutons of the Peninsular terrane that represent the roots of the Talkeetna arc. The correlation of the Carpenter Creek metamorphic complex with the Chugach mélange indicates that the trace of the BRF lies ∼1–5 km north of the map trace shown on geologic maps, although, like other segments of the BRF, this boundary is blurred by local complexities within the BRF system. Ductile deformation of the mélange is sufficiently intense that few vestiges of its original mélange fabric exist, suggesting the scarcity of rocks described as mélange in the cores of many orogens may result from misidentification of rocks that have been intensely overprinted by younger, ductile deformation.

Timing of subduction zone metamorphism during the formation and emplacement of Troodos and Baer–Bassit ophiolites: insights from 40Ar–39Ar geochronology

2007 ◽  
Vol 144 (5) ◽  
pp. 797-810 ◽  
Author(s):  
GAVIN HEUNG-NGAI CHAN ◽  
JOHN MALPAS ◽  
COSTAS XENOPHONTOS ◽  
CHING-HUA LO
Keyword(s):  
Subduction Zone ◽  
Late Cretaceous ◽  
Accretionary Prism ◽  
Passive Margin ◽  
Metamorphic Rocks ◽  
Metamorphic Complex ◽  
Troodos Ophiolite ◽  
Crustal Thinning ◽  
Step Heating ◽  
Short Time

The Troodos ophiolite in Cyprus and Baer–Bassit ophiolite in Syria together form part of the Tethyan ophiolite belt. They were generated in a supra-subduction zone setting in Late Cretaceous times. As with many of the ophiolite occurrences in this belt, the sequences are closely associated with tectonic ‘coloured mélange’ zones, which contain, among a variety of lithologies, metre- to kilometre-size blocks of metamorphic rocks. Precise 40Ar–39Ar laser step-heating experiments performed on four amphibolites from SW Cyprus and six from NW Syria, yield plateau ages ranging from 75.7±0.3 Ma to 88.9±0.8 Ma in Cyprus and 71.7±0.5 to 88.4±0.4 Ma in Syria. The older limits of these time spans are coeval with the age of the formation of the associated ophiolites. Unlike other metamorphic sole rocks which seem to form in relatively short time spans, these metamorphic rocks found in Cyprus and Syria are interpreted to have formed in Late Cretaceous times by accretion below the overriding Troodos and Baer–Bassit crust for a period of 15–18 Ma. The metamorphic complexes were exhumed by extension and crustal thinning associated with subduction roll-back and the rotation of the overriding plate until the cessation of subduction in Maastrichtian times. In Cyprus, the exhumed metamorphic complex was incorporated into an accretionary prism constructed primarily of the collapsed Mamonia passive margin sequence intercalated with rocks of the Troodos ophiolite during plate collision in the Maastrichtian. Concomitantly, in Syria, the Baer–Bassit ophiolite and subcreted metamorphic complex were emplaced onto the Arabian passive margin and fragmented into blocks and knockers, forming the Baer–Bassit mélange.

Rb–Sr Geochronology of the Hida metamorphic belt, Japan

1970 ◽  
Vol 7 (6) ◽  
pp. 1383-1401 ◽  
Author(s):  
K. Shibata ◽  
T. Nozawa ◽  
R. K. Wanless
Keyword(s):  
Granitic Rocks ◽  
Metamorphic Event ◽  
Crystalline Schist ◽  
Metamorphic Rocks ◽  
Schist Belt ◽  
Metamorphic Belt ◽  
Early Mesozoic ◽  
Mineral Isochron ◽  
Middle Paleozoic ◽  
Later Phase

Rb–Sr whole-rock and mineral isochron ages have been determined for metamorphic and granitic rocks of the Hida metamorphic belt. The results indicate that an extensive metamorphic event together with plutonic activity took place within the belt during the latest Paleozoic – early Mesozoic period. The older ages of 220–250 m.y. represent an earlier phase of the metamorphism, whereas the younger ages of 170–180 m.y. represent a later phase. The Funatsu granitic rocks yielded a whole-rock isochron age of 176 m.y. with an initial 87Sr/86Sr ratio of 0.7056. This age is believed to indicate the time of original emplacement, and the rocks are considered to represent late-kinematic intrusion in the Hida belt.Some information on the middle Paleozoic metamorphism in the Hida Mountains was obtained from the isochron study. The whole-rock isochron age of 412 m.y. for the metamorphic rocks of the Fujibashi area may be considered, although not confirmed, to indicate the time of older metamorphism. The Omi Schist of the Circum–Hida crystalline schist belt, which belongs to the glaucophanitic type of metamorphism, gave a mineral isochron age of 350 m.y. thereby providing evidence of mid-Paleozoic metamorphism.The initial 87Sr/88Sr ratios for the whole-rock samples of the Hida metamorphic belt are found to be generally low, i.e. 0.705–0.708. This is especially so for the metamorphic rocks from the northern part of the belt where the lowest values were found.

scholarly journals Supplemental Material: Crustal material recycling induced by subduction erosion and subduction-channel exhumation: A case study of central Tibet (western China) based on P-T-t paths of the eclogite-bearing Baqing metamorphic complex

2020 ◽  
Author(s):  
Xin Jin ◽  
Yu-Xiu Zhang ◽  
Kai-Jun Zhang ◽  
et al.
Keyword(s):  
Western China ◽  
Metamorphic Rocks ◽  
Crustal Material ◽  
Metamorphic Complex ◽  
Subduction Channel ◽  
Material Recycling ◽  
Subduction Erosion ◽  
Mineral Compositions ◽  
Central Tibet

Compositional mapping images of one garnet, Triassic paleo-geographic facies of Qiangtang, summarized published Paleozoic and Proterozoic ages in Tibetan Plateau and Himalaya, mineral compositions, and chronology data of the Baqing metamorphic rocks.

Lithostratigraphy of the Mesoproterozoic Windpoort Granite (Spektakel Suite), western Namaqualand, South Africa

2019 ◽  
Vol 122 (2) ◽  
pp. 249-256
Author(s):  
C.H. de Beer ◽  
P.H. Macey
Keyword(s):  
South Africa ◽  
Alkali Feldspar ◽  
Metamorphic Rocks ◽  
Leucocratic Granite

AbstractThe Windpoort Granite is a porphyritic, leucocratic granite belonging to the Spektakel Suite, a group of late- to post-tectonic granites intruded into the orthogneisses and supracrustal metamorphic rocks in western Namaqualand. Like other granites of this type, it is devoid of penetrative tectonic foliation, at most displaying a magmatic foliation parallel to the boundaries of the intrusion. Its main characteristic setting it apart from other Spektakel Suite granites in western Namaqualand is its tightly packed arrangement of small stubby alkali feldspar phenocrysts. Its U-Pb LA-ICPMS age of 1087 ± 11 Ma agrees with the age of other Spektakel Suite granites showing similar field relationships. It classifies geochemically as a highly potassic monzogranite with more evolved compositions than all other plutons of the Spektakel Suite.

DEFORMATIONS AND THE SEQUENCE OF THE STRUCTURES FORMATION IN THE NORTHERN PART OF THE ZONE OF DEVELOPMENT OF MAKSUTOVO METAMORPHIC COMPLEX (SOUTHERN URALS)

2018 ◽  
pp. 17-26
Author(s):  
B. G. Golionko ◽  
A. V. Ryazantsev
Keyword(s):  
Structural Evolution ◽  
Southern Urals ◽  
Strike Slip ◽  
Metamorphic Rocks ◽  
Metamorphic Complex ◽  
The Third ◽  
Deformation Stage ◽  
Third Stage ◽  
Western Border ◽  
Definition Of

Composition and structural evolution of the Maksutovo metamorphic complex in the its northern part has been examined. The early folds 77) plunging in the SE direction have been established to be developed only in the rocks of the Maksutovo metamorphic complex. The problem of the definition of the geodynamic nature of the 7Л deformation stage, marked by the folds 77), has not been solved yet. Tectonic inclusions of the metamorphic rocks adjacent to the western border of the Main Uralian Thrust without traces of 7Л deformation stage must not be considered as parts of the Maksutovo metamorphic complex. 7Л1 deformation stage expressed in formation of thrusts and 77. west vergent folds is connected with late Paleozoic continental collision. The third stage of deformation 7JIII is marked by development of 77) folds with steep hinges associated with post collision strike slip movements

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