Late Mesozoic granitoids of the Dalat zone are of sub-alkaline affinity,
belong to the high-K calc-alkaline series and display features typical
of I-type granites. The Dinhquan suite consists of hornblende-biotite
granodiorites, diorites, and minor granites emplaced at similar to110
My. These rocks have relatively low initial Sr-87/Sr-86 ratios
(0.7049-0.7061) and moderate epsilon(Nd(T)) values (-0.8 to -2.0).
Chondrite-normalized REE patterns are fractionated and have small
negative Eu anomalies (Eu/Eu* = 0.55-0.97). All these characteristics,
combined with low Al2O3/(FeO + MgO + TiO2) and (Na2O + K2O)/(FeO + MgO +
TiO2) ratios and high Mg# values, suggest an origin through dehydration
melting of alkaline mafic lower crustal source rocks. The Cana suite
contains biotite-bearing granites poor in hornblende. The rocks are
96-93 My old in age, having higher initial Sr-87/Sr-86 ratios
(0.7060-0.7064) and nearly constant epsilon(Nd(T)) (- 2.5 to - 2.7)
values. These characteristics, in conjunction with the chemical
signatures and old T-DM model ages, indicate that crustal material
played a very important role in their petrogenesis. The granites are
further characterized by strong negative Eu anomalies (Eu/Eu* =
0.04-0.39) and Sr, suggesting melting with residual plagioclase and/or a
high degree of fractional crystallization. The Deoca suite is made up of
92-88 My old pink porphyritic hornblende-biotite-bearing granodiorites,
monzogranites and diorites. Initial isotopic compositions (Sr-87/Sr-86 =
0.7055-0.7069; epsilon(Nd(T)) = +0-9 to -3.3) and chemical features
suggest derivation by dehydration melting of heterogeneous
metagreywacke-type sources with additional input of mantle-derived
material. Furthermore, the Deoca rocks have concave-upward REE patterns
indicating that amphibole played a dominant and garnet an insignificant
role during magma segregation. (C) 2003 Elsevier Ltd. All rights
reserved.