Tectonic Thermal Event Research Articles

Subduction age of Neo-Tethys oceanic crust in southwest Yunnan, China: Laser micro-area40Ar-39Ar dating

The basic granulite, which is considered to be the MORB based on geochemistry and isotopic characteristics[1], has been discovered recently as the enclaves in the Yingjiang islandarc magmatic suite on the border of Burma and west Yunnan, east of Myitkyina suture in the eastern Burma. The laser micro-area40Ar-39Ar technique is used to date the age of garnet and cliopyroxene that is the result of the early metamorphic event. The isochron outcome is ∼74.4 Ma which is induced to be the age of the suduction event of the Myitkyina oceanic crust on the basis of the Cenozoic lithosphere tectonic evolution, tectonic thermal events and the age of deformation and metamorphism. The discovery of the high-grade or high-pressure metamophic rocks in the island-arc magmatic suite by the way of studying itsP-T-t paths can provide a good way to study the age and process of oceanic crust subduction, slab break-off, metamorphic terrain exhumation and the evolution of paleoocean basin.

The neodymium isotopic characteristic and geological significance of Kuokesu plagioclase amphibolites from the Kuruktag, Xinjiang, China

The plagioclase amphibolites from Kuokesu area, Kuruktag, Xinjiang occur as enclaves embedded in the granodioritic gneiss. In the light of major elements and REE data, the parent rocks of the plagioclase amphibolites belong to weak-alkaline basalts. Their Nd model ages mainly range from 2 832 to 3 075 Ma. The seven plagioclase amphibolites yield a reasonable good isochron age of (828 ±86) Ma(2σ) with INd= 0.510 981 ±82, eNd(t) = −11.5±1.6. Such a case shows the existence of great proportion of the Archaean mafic crustal basement on the Kuokesu area. The strong tectonic-thermal event at about 820 Ma made the Sm-Nd isotope of the metamorphic rocks homogenization. This event would be associated with the Tarim Movement.

Burial History and Kinetic Modeling for Hydrocarbon Generation, Part I: The galo Model

This paper discusses the principles and applications of the GALO computer program, which generates numerical simulations of the evolution of a sedimentary basin. The program calculates variations in the sedimentary bed thickness, predicts the thermal regime in the sedimentary cover or in the basement, and estimates the potential hydrocarbon yield of the source rocks. Alternative methods for determining the magnitude of tectonic subsidence of the basement surface within the framework of a local isostasy model are applied to provide a detailed model of the sequential tectonic-thermal events involved in the development of the basin. The program determines reaction parameters controlling the maturation of the organic matter in source rocks; these parameters are based largely on the hydrocarbon pyrolysis yield data and the stage of maturation of the organic matter entered into the program. Neglecting this stage drastically displaces the reaction spectrum toward higher energies, leading to considerable underestimation of hydrocarbon output.

U-Pb, Rb-Sr isotopic chronology of Jinning granites in the Songpan-Ganze Orogenic Belt and its tectonic significances

A series of Jinning granites are located in the eastern margin of the main part of the Songpan-Ganze Orogenic Belt. The research is focused on Gezong and Donggu granites in the Danba area. From the viewpoint of isotopic chronology, geochemistry and tectonic geology, their formation ages, origins and geneses of source materials, and the influences of Himalayan tectonic thermal events are discussed- It is suggested that they were the products of Jinning tectono-magmatism. The source materials were the poorly matured volcano-sedimentary rocks formed in the middle-late period of the middld-Proterozoic. They represent in fact the basement of the old Yangtze Block. The late Proterozoic erogenic belt of the entire western margin of the Yangtze Block, including the Danba area, should be the key part of the old Yangtze Block.

New evidence for cenozoic resetting of KAr ages in volcanic rocks of the Northern Portion of the Armiralty Bay, King George Island, Antarctica

This paper presents six KAr whole-rock ages of the Znosko Glacier Formation (Cardozo Cove Group) that crops out between Mackellar Inlet (type-area) and Ezcurra Inlet, inner Admiralty Bay, King George Island, Antarctica. Originally attributed to the Upper Mesozoic, a RbSr isochron diagram place the lithostratigraphic unit in the Paleocene (60±5 Ma). The same samples were isotopically analyzed by the KAr method and the calculated ages, which range between 40 and 50 Ma, confirm the effect of an important tectonic-thermal event, responsible for structural deformations and metasomatic alterations in that unit. We discuss the origin of the tectonic event and the related KAr reset on rocks cropping out around Admiralty Bay.

Reconnaissance geochronology of the crystalline basement rocks of the Coastal Cordillera of southern Peru

Granulite-facies gneiss of the Arequipa massif extensively developed along the Coastal Cordillera of southern Peru gives a whole-rock isochron age of 1,811 ± 39 m.y. (λ 87 Rb = 1.47 × 10 −11 yr −1 ) and an initial 87 Sr/ 86 Sr ratio of 0.7086 ± 0.0009. Migmatitic granite within the gneiss is probably of late Precambrian or early Paleozoic age. Mineral ages, both K-Ar and Rb-Sr, from the gneisses and granites are disturbed. Potassium feldspar from the gneiss appears to have been reset by the migmatitization event, whereas mica and potassium feldspar from the migmatitic granite appear to reflect established tectonic-thermal events of Late Devonian and Late Triassic time. In both metamorphic grade and age pattern, these rocks are similar to those of the Trans-Amazonian nucleus of the Guianas, Brazil, Uruguay, and the Buenos Aires province of Argentina. We suggest that the Arequipa massif has always been an integral part of the Trans-Amazonian nucleus and that the Andean belt is ensialic, at least in Peru. The manner in which the structural trends in the Arequipa massif strike into the Pacific Ocean leads to speculation concerning the evolution of the Pacific. Simple rifting, tectonic erosion, and major transcurrent faulting are considered as possible mechanisms to explain the truncation.