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.

Pearya: a composite terrane with Caledonian affinities in northern Ellesmere Island

Abstract: In Ellesmere Island, the Canadian Shield and Arctic Platform are flanked on the northwest by the lower Paleozoic Franklinian mobile belt, which comprises an unstable shelf (miogeocline) and a deep-water basin, divisible into an inner sedimentary belt and an outer sedimentary–volcanic belt. Both are tied to the shelf by interlocking facies changes, but additional exotic units may be present in the outer belt.Pearya, bordering the deep-water basin on the northwest, is divisible into four successions. Succession I comprises sedimentary and(?) volcanic rocks, deformed, metamorphosed to amphibolite grade, and intruded by granitic plutons at 1.0–1.1 Ga. Succession II consists mainly of platformal sediments (carbonates, quartzite, mudrock), with smaller proportions of mafic and siliceous volcanics, diamictite, and chert ranging in age from Late Proterozoic (Hadrynian) to latest Cambrian or Early Ordovician. Its concealed contact with succession I is tentatively interpreted as an angular unconformity. Succession ...

Tectono-stratigraphic evolution of the Early Proterozoic Wisconsin magmatic terranes of the Penokean Orogen

Abstract: The Early Proterozoic Penokean Orogen developed along the southern margin of the Archean Superior craton. The orogen consists of a northern deformed continental margin prism overlying an Archean basement and a southern assemblage of oceanic arcs, the Wisconsin magmatic terranes. The south-dipping Niagara fault (suture) zone separates the south-facing continental margin from the accreted arc terranes. The suture zone contains a dismembered ophiolite.The Wisconsin magmatic terranes consist of two terranes that are distinguished on the basis of lithology and structure. The northern Pembine–Wausau terrane contains a major succession of tholeiitic and calc-alkaline volcanic rocks deposited in the interval 1860–1889 Ma and a more restricted succession of calc-alkaline volcanic rocks deposited about 1835 – 1845 Ma. Granitoid rocks ranging in age from about 1870 to 1760 Ma intrude the volcanic rocks. The older succession was generated as island arcs and (or) closed back-arc basins above the south-dipping subducti...

Melting of the continental crust: fluid regimes, melting reactions, and source-rock fertility

Abstract: This chapter presents a synthesis of partial melting in Earth’s continental crust. However, rather than simply attempting to synthesize all the data from previous experimental and theoretical studies, the chapter takes a definite scientific position that reflects present understanding of crustal melting. Unless otherwise stated, the term "granitic" is used in the broad sense to denote magma or melt compositions ranging from syenogranite through to tonalite. The word "fertility" is used to denote the relative capacity of a given protolith material to produce granitic partial melt, under the specified physicochemical conditions (mainly P, T, and fO2). The high temperatures that are required to partially melt crustal rocks and form granitic magmas equate with the conditions of upper amphibolite-to granulite-facies metamorphism. This is one important reason for the inferred intimate connection between the production of granulite-facies rocks, the production and withdrawal of partial melts, and the differentiation of the continental crust (see, for example, Fyfe, 1973; Clemens, 1990; Thompson, 1990). Partial melting may occur in response to various intracrustal processes that occur during tectonic thickening and orogenic collapse of the crust (e.g., Patino Douce et al., 1990; Harris & Massey, 1994). However, the thermal requirements of granulite-facies processes generally demand that additional, extra-crustal heat sources be available to drive the reactions. Thermal modeling has demonstrated that thickened crust (with a normal thermal profile) does not reach the temperatures necessary to partially melt (on time scales of up to 100 Myr) unless large amounts of aqueous fluid are also introduced to depths of 20–40km (e.g., England & Thompson, 1984). From the analysis of England and Thompson (1984) it appears that the only exceptions to this general rule would occur where the crust has unusually low thermal conductivity ( 65 mW/m2). Thus, except in some migmatite terranes, production of voluminous, mobile, granitic magma commonly involves advection of mantle heat to the continental crust. The most likely vectors of this heat would be underplated or intraplated mafic magmas. Such under-accretion probably represents the major means by which Earth’s continents have grown in volume since the Archean (e.g., Rudnick, 1990). The only alternative is to postulate that the crust was unusually enriched in heat-producing elements (e.g., Sandiford et al., 1998; McLaren et al., 1999; Chapter 11). This does seem to be the case in a few specific terranes, but is unlikely to be a general feature. In any case, the withdrawal of large volumes of granitic magmas from the deep crust, and their emplacement at higher crustal levels, has two major consequences. The first consequence is that the deep crust will be left in a mafitized, partially dehydrated, residual condition (e.g., Brown & Fyfe, 1970; Fyfe, 1973; Clemens, 1990; Thompson, 1990). To become exposed at the surface, such dense rocks would need to undergo a second major tectonic episode, perhaps temporally unrelated to the original partial-melting event, (e.g., the residual metapelites ("stronalites") of the Ivrea Zone). This necessity may contribute to the relative scarcity of such rocks, in comparison with the abundance of their mobile magmatic counterparts. Delamination and foundering into the mantle may also be the fate of some residual lower crust (e.g., Bohlen, 1991). The second consequence is that the upper crust will become enriched in felsic minerals and heat-producing elements. This is probably the major mechanism for post-Archean and ongoing, large-scale crustal differentiation (Vielzeuf et al., 1990).

Crustal Age Domains and the Evolution of the Continental Crust in the Mozambique Belt of Tanzania: Combined Sm–Nd, Rb–Sr, and Pb–Pb Isotopic Evidence

Abstract: African reworking. Eclogite-facies metapelites of the Early Prot- Mozambique Belt; Sr‐Nd‐Pb isotopes erozoic Usagaran Belt likewise exhibit Archean Nd model ages, but higher Pb isotopic ratios are consistent with last recrystallization of feldspar at 2 Ga. Granulites with Nd model ages from 1 to 1·5 Ga only occur in NE Tanzania; because of their restricted range INTRODUCTION in Pb isotopic composition they are interpreted as juvenile additions The study of ancient high-grade gneiss belts provides during late Proterozoic time. Granulites of the W Uluguru Mts important insights into the dynamics of deep-seated orohave Nd model ages between 2·1 and 2·6 Ga, and highly variable genic processes that often cannot be observed in modern feldspar Pb isotope composition indicating possible derivation from active orogenic belts because most of these expose only cratonic and/or Usagaran material, reworked and mixed with a the upper brittle parts of the continental crust. In such old small proportion of younger Proterozoic material during the Pan- and eroded belts, Pb and Nd isotopes supply particularly African orogeny. This could indicate the suture zone between a valuable information on crustal genesis, evolution and western Archean‐Proterozoic continental mass and juvenile arc- terrane amalgamation and can be used to distinguish terranes docking on from the east during subduction of the Mo- between old reworked and juvenile crust. zambique Ocean. The combined isotope data provide strong evidence This study combines Nd and Sr isotope systematics of that parts of the East African crust grew by lateral accretion of whole rocks and Pb isotopes from leached feldspars Early and Mid Proterozoic segments onto an Archean nucleus. to investigate the assembly and crustal history of the However, the Neoproterozoic (Pan-African) orogeny not only led to Proterozoic, polymetamorphic Mozambique Belt. The diVerent chemical properties of the elements determine addition of new crust in the NE of Tanzania, but also reworked

Geochemical, age, and isotopic constraints on the location of the Sino–Korean/Yangtze Suture and evolution of the Northern Dabie Complex, east central China

Abstract: The Northern Dabie Complex in east central China lies between the Sino‐Korean plate to the north and the Yangtze plate to the south. The Northern Dabie Complex has been variously proposed to represent a Paleozoic magmatic arc on the Sino‐Korean plate, an exhumed piece of subducted Yangtze plate crust, or crust produced almost entirely by Cretaceous extension-related magmatism. Trace element compositions of Northern Dabie Complex orthogneisses and granites show arc signatures similar to those of ultra-high-pressure rocks in the central Dabie, but no mineralogical evidence of ultra-high-pressure metamorphism is present in the samples investigated here. Field relationships, textures, major and trace element compositions, and ion microprobe U-Pb zircon protolith crystallization ages reveal three distinct types of gneiss: diorite gneiss xenoliths (770 6 26 Ma, 95% confidence limit), those within first-genation highly deformed migmatitic grey gneisses (747 6 14 Ma), and those cross-cut by secondgeneration Cretaceous weakly foliated felsic gneisses (127 6 4 Ma). Unfoliated Cretaceous granites (117 6 11 Ma, monazite Th-Pb age 5 117 6 1 Ma) intrude secondgeneration gneisses. Cretaceous second† Corresponding author e-mail: john.c.ayers@ vanderbilt.edu. generation gneisses and granites yield zircon inheritance ages of ca. 2 Ga, 700‐800 Ma, and (rarely) 227‐271 Ma, indicating that the Northern Dabie Complex is not simply a Cretaceous extensional terrane. The 700‐800 Ma zircon ages are similar to those of granitic gneisses from the central ultra-highpressure zone (698 6 47 Ma) and are characteristic of the Yangtze craton. «Nd values suggest that Cretaceous rocks in the Northern Dabie Complex formed by partial melting of basement with very low «Nd and not by melting of first-generation or diorite gneisses. Nd-depleted mantle model ages are consistent with the time of formation of the Yangtze craton at 1.4‐2.5 Ga. The Northern Dabie Complex is interpreted to be an extension of the Yangtze craton that was unaffected by ultra-high-pressure metamorphism. The Sino‐Korean/Yangtze suture must lie to the north of the Northern Dabie Complex.