Terrane

About: Terrane is a research topic. Over the lifetime, 11025 publications have been published within this topic receiving 442596 citations. The topic is also known as: tectonostratigraphic terrane.

Petrochemical constraints for dual origin of garnet peridotites from the Dabie‐Sulu UHP terrane, eastern‐central China

Abstract: Garnet peridotites occur as lenses, blocks or layers within granulite–amphibolite facies gneiss in the Dabie-Sulu ultra-high-pressure (UHP) terrane and contain coesite-bearing eclogite. Two distinct types of garnet peridotite were identified based on mode of occurrence and petrochemical characteristics. Type A mantle-derived peridotites originated from either: (1) the mantle wedge above a subduction zone, (2) the footwall mantle of the subducted slab, or (3) were ancient mantle fragments emplaced at crustal depths prior to UHP metamorphism, whereas type B crustal peridotite and pyroxenite are a portion of mafic–ultramafic complexes that were intruded into the continental crust as magmas prior to subduction. Most type A peridotites were derived from a depleted mantle and exhibit petrochemical characteristics of mantle rocks; however, Sr and Nd isotope compositions of some peridotites have been modified by crustal contamination during subduction and/or exhumation. Type B peridotite and pyroxenite show cumulate structure, and some have experienced crustal metasomatism and contamination documented by high 87Sr/86Sr ratios (0.707–0.708), low eNd(t) values (−6 to −9) and low δ18O values of minerals (+2.92 to +4.52). Garnet peridotites of both types experienced multi-stage recrystallization; some of them record prograde histories. High-P–T estimates (760–970 °C and 4.0–6.5±0.2 GPa) of peak metamorphism indicate that both mantle-derived and crustal ultramafic rocks were subducted to profound depths >100 km (the deepest may be ≥180–200 km) and experienced UHP metamorphism in a subduction zone with an extremely low geothermal gradient of <5 °C km−1.

Paleoplate tectonics between Cathaysia and Angaraland in inner Mongolia of China

Abstract: On the basis of recent investigations in southern Inner Mongolia the authors consider that there are two Proterozoic rifts of E–W trend in the northern margin of the North China Platform. The Zhaertay Group and Baiyun'ebo Group of closed lagoon facies or neritic facies were deposited respectively in the two rifts. The lead isotopic dating of carbonaceous limestone from the middle sequence of Baiyun'ebo Group yields an age of 1500 Ma. Along the rifts a series of alkaline volcanics and intrusions is scattered in the Yinshan Mountains and Yanshan Mountains. To the north of the rifts, four ophiolite belts and at least five accreted terranes of various ages have been recognized in the Paleozoic orogenic zone. The presence of the ophiolite suites and these accreted suspect terranes in Inner Mongolia indicates that probably there was an open ocean between Siberia and North China in Paleozoic times, when repeated subduction of the oceanic crust had occurred along both continental margins. The suture line between Cathaysia and Angaraland extends from Linxi to Solon Obo. In the late Permian, epicontinental mountain systems of the two converging continents collided with each other. From the analysis of the tectonic evolution of Inner Mongolia and adjacent areas we conclude that the evolution of the southern margin of the Siberian Platform is approximately the same as the history of activity of the trench-arc-basin system in the eastern Asian epicontinental areas during Mesozoic and Cenozoic times but the northern margin of the North China Platform is similar in evolution to the Cordilleran system in western North America.

Formation and Evolution of Granite Magmas During Crustal Reworking: the Significance of Diatexites

Abstract: (Taylor & McLennan, 1985), the physical processes inA continuous section through reworked Archaean crust records the volved, particularly how granite magma is formed, remain generation of granitic magma and its subsequent development in the controversial (Miller et al., 1988; White & Chappell, Opatica subprovince in the Canadian shield. There, the transition 1990). A partially melted source can form a granitic from palaeosome to granite was a closed-system process through magma only if large volumes of melt are separated from intermediate stages of patch migmatite and diatexite. The average most of their residuum. Understanding this process is degree of partial melting was less than 30%, but the melt crucial to determining how crustal recycling and differfraction was redistributed within individual diatexite layers during entiation occurs. For example, melt–residuum separation deformation. Regions that lost melt became residual diatexites could be a nearly perfect, single-stage process at the enriched in TiO2, FeOT, MgO, CaO, Sc, Cr, Co, Sr, rare earth site of partial melting, as described for leucosomes in elements (REE) and high field strength elements (HSFE). Melt metatexite migmatites (Wickham, 1987a; Sawyer, 1991, accumulated to create diatexite magmas enriched in large ion 1994; Brown et al., 1995). Alternatively, the separation lithophile elements (LILE), but contaminated with residuum macould be an imperfect, multi-stage process that yields a terial. Such diatexite magmas are parental to granites found at magma with a large residual component, as is observed higher crustal levels in the terrane. Flow of the diatexite magma in in diatexite migmatites (Bea, 1991; Greenfield et al., response to deformation separated some of its residuum into schlieren. 1996; Sawyer, 1996). The metatexite model necessarily Parautochthonous plutons were created where ascending granitic produces leucocratic, residuum-free granites, such as magma locally ponded below impermeable layers and structures. those described by Le Fort (1981) and Montel et al. Magma left the anatectic region in dykes and lost its remaining residuum as it crystallized. Consequently, the allochthonous granite (1991), and maximizes the geochemical signature of magmas that rose through 20 km of crust to feed the highest level crustal differentiation. In contrast, the diatexite model plutons in this region are highly fractionated and essentially free of can produce residuum-rich granites, and so reduce the residuum. geochemical effect of crustal differentiation, as Chappell (1996) noted. How anatectic magmas formed in the deeper crust evolve to the granitic magmas emplaced in the upper crust is also poorly known, because few crustal sections