These granulites plot along a secondary isochron, calculated for µ = 9.7, with isotopic evolution between 1.3 and 0.5 Ga, consistent with a whole-rock Pb evolution for the timespan between the average Nd model age and the post-metamorphic closure of feldspar for Pb. Sources of Mesoproterozoic igneous rocks and formation time of the continental crust of the Kokchetav Massif (Northern Kazakhstan). Another reason for the metasediments to fall on an errorchron may be equilibration with seawater Sr during deposition. Histograms of Nd model ages for: (a) Tanzania (29 from this study, Table Ben Othman et al., 1984; Maboko, 1995; Maboko & Nakamura, 1996); (c) East Africa with Madagascar (Ben Othman et al., 1984; Harris et al., 1984; Paquette et al., 1994); (d) Antarctica with the Napier complex in Enderby Land (DePaolo et al., 1982; McCulloch & Black, 1984; Black et al., 1986; Black & McCulloch, 1987), the Rayner complex (Black et al., 1987), the Lützow–Holm complex (Tanaka et al., 1985; Owada et al., 1994; Shiraishi et al., 1995), the Yamato Mts (Zhao et al., 1995), the Sør–Rondane Mts (Shiraishi & Kagami, 1992), and the Heimefrontfjella (Arndt et al., 1991) and Sverdrupfjella (Moyes et al., 1993) from western Dronning Maud Land; (e and f) South India (Drury et al., 1983; Bernard-Griffiths et al., 1987; Peucat et al., 1989, Choudhary et al., 1992; Santosh et al., 1992; Harris et al., 1994; Brandon & Meen, 1995; Jayananda et al., 1995; Unnikrishnan-Warrier et al., 1995; Bhaskar Rao et al., 1996); (g) Sri Lanka (Milisenda et al., 1988,Burton & O'Nions, 1990; Kagami et al., 1990). Major and trace element analyses, including rare earth elements (REE), by X-ray fluorescence (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) for all these samples have been reported by Appel, (1996). 1490-1450 Ma) deposition and orogenesis in a reconstructed orogenic belt, northern New Mexico, USA: Defining the Picuris orogeny. This interpretation is consistent with the data array in the 208Pb/204Pb vs 206Pb/204Pb diagram (Fig. Plagioclase may appear not to dissolve because of the precipitation of CaF2, which mimics the original grains. Continental growth seen through the sedimentary record. Fractionation was corrected by normalizing the isotope ratios to 146Nd/144Nd = 0.7219. and Petrology, Exploration Calculation of corrected Nd model ages uses the following algorithm [after Milisenda et al. A Palaeoproterozoic tectono-magmatic lull as a potential trigger for the supercontinent cycle. In such old and eroded belts, Pb and Nd isotopes supply particularly valuable information on crustal genesis, evolution and terrane amalgamation and can be used to distinguish between old reworked and juvenile crust. Tanzania and Karnataka craton, Tanzania lowland migmatites, Napier complex, Madras, Nilgiri and northern block of South India, Western Nile complex of Uganda), some of which show very narrow age ranges of no more than 400 my (Madras and Nilgiri Block, Tanzania Craton and lowland migmatites) or a near-normal distribution (Napier complex). Most boundaries of these age domains are overprinted by Neoproterozoic (Pan-African) tectonism and metamorphism. This distribution of apparent crustal residence ages suggests that there are at least three age provinces within the orogenic belt, each with its own pre-metamorphic history. Reassessment of continental growth during the accretionary history of the Central Asian Orogenic Belt. Journal of Geophysical Research: Solid Earth. The Sm–Nd and Rb–Sr data are listed in Table 1 and include duplicates for dissolution and mass-spectrometer analyses. Mesoproterozoic-trans-Laurentian magmatism: A synthesis of continent-wide age distributions, new SIMS U–Pb ages, zircon saturation temperatures, and Hf and Nd isotopic compositions. This lithological boundary may coincide with the age province boundary. In the region of post‐Precambrian continental growth, the regions farthest from the Precambrian continental edge are composed of mostly (>85%) of material newly differentiated from the mantle. 7a), which is interpreted as further evidence for a common crustal history of these domains and a boundary between different crustal age domains within the Uluguru Mts. O–H–Sr–Nd isotope constraints on the origin of the Famatinian magmatic arc, NW Argentina. Processes in Geophysics, Atmospheric Four types of crustal domains can be distinguished on the basis of the Nd model ages in this part of Gondwana. Reprint of “Pre-collisional (> 0.5 Ga) complexes of the Olkhon terrane (southern Siberia) as an echo of events in the Central Asian Orogenic Belt”. (1984): TDM = 1/ λ ln (1 + {[0.51316 – (143Nd/144Nd)meas. The age of the Pan-African metamorphic event in Tanzania has now been dated at 615–650 Ma on the basis of U–Pb monazite geochronology from granulites in the Mozambique Belt (Möller et al., 1994; Möller, 1995), consistent with some U–Pb zircon data obtained previously (Coolen et al., 1982; Maboko et al., 1985; Muhongo & Lenoir, 1994). These values represent the most likely depleted mantle composition, because crustal contamination would lower the 143Nd/144Nd values significantly (Goldstein et al., 1984). The Heimefrontfjella and Vijayan complex are the younger (more juvenile?) Final dissolution was achieved with concentrated HF [see also DeWolf & Mezger (1994)]. Characterization of Nd Radiogenic Isotope Signatures in Sediments From the Southwestern Atlantic Margin. (b) Enlargement for samples with low isotope ratios. This view was challenged by Burke et al., (1977), who interpreted the Mozambique Belt as one of the prime examples of collisional belts formed by plate tectonic processes, which involves the formation of new crustal material in a standard Wilson cycle (e.g. Almost all of the Phanerozoic additions occur in areas where there was no preexisting continental basement; Mesozoic magmatic additions account for only about 2% of the crustal mass in the area underlain by Precambrian basement. The compiled data are summarized in a series of histograms (Fig. It furthers the University's objective of excellence in research, scholarship, and education by publishing worldwide, This PDF is available to Subscribers Only. Recent studies on granulites, gneisses and granites from the craton, the Usagaran Belt and the Pan-African belt of Tanzania by Maboko, (1995), and Maboko & Nakamura, (1996) encompass 32 samples and provide an important addition to the database presented here. This trend suggests that the metasediments were derived from an older exposed hinterland and that some, but not necessarily all, igneous material is a juvenile addition to the crust. Information about your device and internet connection, including your IP address, Browsing and search activity while using Verizon Media websites and apps. Calculation of corrected Nd model ages uses the following algorithm [after Milisenda et al. 3). Like the Archean samples, these young samples also follow the S&K evolution curve in the 208Pb/204Pb vs 206Pb/204Pb diagram (Fig. Isotope ratios were measured on a Finnigan MAT 261 mass spectrometer in multi-collector static mode for Sm, Nd and Sr. Therefore only the time-integrated effects are displayed in a conventional isochron diagram (Fig. 2), and is based on the highest εNd value of young mantle-derived rocks. Shackleton, (1967) also proposed that the Mozambique Belt comprises Archean basement and several younger metasedimentary sequences. The evolution of a mid-crustal thermal aureole at Cerro Toro, Sierra de Famatina, NW Argentina. On an expanded scale (Fig. Tracing the history from Rodinia break-up to the Gondwana amalgamation in the Embu Terrane, southern Ribeira Belt, Brazil. (1984). The continental crust is the principal record of conditions on the Earth for the last 4.4 billion years. and you may need to create a new Wiley Online Library account.