TY - JOUR
T1 - Nd and Sr isotopic mapping of the Archaean-Proterozoic boundary in southeastern Tanzania using granites as probes for crustal growth
AU - Maboko, M. A.H.
AU - Nakamura, E.
N1 - Funding Information:
We wish to acknowledge technical support provided by Tomoyuki Shibata, Masako Yoshikawa, Akio Mak-ishima and other members of the Pheasant Memorial Laboratory (PML) of the Institute for the Study of the Earth's Interior of Okayama University, Misasa, Japan. MAHM's stay at the PML was made possible by a generous fellowship from the Matsumae International Foundation. Fieldwork in Tanzania was financed by a grant from The Tanzanian Commission for Science and Technology.
PY - 1996/3
Y1 - 1996/3
N2 - Granitoids of two different generations occur across the Archaean-Proterozoic boundary in southeastern Tanzania. The first generation, which is confined to the Archaean Tanzania Craton, yields Rb-Sr whole-rock isochron ages of 2600 Ma and low, mantle-like, initial 87Sr/86Sr ratios (0.702-0.704). These coupled with positive or near-zero ∈Nd values (-0.2 to 2.0) suggest that these granitoids represent juvenile mantle material which was added to the continental crust at about 2600 Ma. The second generation of granitoids intrudes the Palaeoproterozoic Usagaran Belt and is characterised by Rb-Sr whole-rock isochron ages of about 1900 Ma. These granitoids show Sm-Nd crustal formation ages which are 200 to 600 Ma older than their emplacement ages and negative ∈Nd values (-2.2 to -6.2). Mixing calculations suggest that the Proterozoic granitoids may have formed by partial melting of 2000 Ma (Usagaran) mantle-derived material which had incorporated between 15 and 45% of an Archaean component from the adjacent Tanzania Craton.
AB - Granitoids of two different generations occur across the Archaean-Proterozoic boundary in southeastern Tanzania. The first generation, which is confined to the Archaean Tanzania Craton, yields Rb-Sr whole-rock isochron ages of 2600 Ma and low, mantle-like, initial 87Sr/86Sr ratios (0.702-0.704). These coupled with positive or near-zero ∈Nd values (-0.2 to 2.0) suggest that these granitoids represent juvenile mantle material which was added to the continental crust at about 2600 Ma. The second generation of granitoids intrudes the Palaeoproterozoic Usagaran Belt and is characterised by Rb-Sr whole-rock isochron ages of about 1900 Ma. These granitoids show Sm-Nd crustal formation ages which are 200 to 600 Ma older than their emplacement ages and negative ∈Nd values (-2.2 to -6.2). Mixing calculations suggest that the Proterozoic granitoids may have formed by partial melting of 2000 Ma (Usagaran) mantle-derived material which had incorporated between 15 and 45% of an Archaean component from the adjacent Tanzania Craton.
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U2 - 10.1016/0301-9268(95)00048-8
DO - 10.1016/0301-9268(95)00048-8
M3 - Article
AN - SCOPUS:0029730782
SN - 0301-9268
VL - 77
SP - 105
EP - 115
JO - Precambrian Research
JF - Precambrian Research
IS - 1-2
ER -