&nb
sp;The tran
sition from oceanic
subduction to continental colli
sion i
s a key
stage in the evolution of ancient orogen
s. We pre
sent new data for Early Cretaceou
s diorite and
granite porphyry from northecentral Tibet to con
strain the evolution of the BangongeNujiang Tethyan Ocean (BNTO). The diorite
s have moderate SiO2 and high MgO content
s,
similar to high-Mg ande
site
s. Zircon grain
s yield UePb age
s of 128e124 Ma and po
sitive εHf(t) value
s between þ13.2 and þ 16.3, corre
sponding to Hf depleted-mantle model age
s (TDM) of 281e131 Ma. The high-Mg diorite wa
s probably formed by partial melting of hydrou
s mantle wedge flfluxed by
slab-derived flfluid
s in an oceanic
subduction
setting. The
granite porphyrie
s yield zircon UePb age
s of 117e115 Ma and zircon εHf(t) value
s ranging from þ0.1 to þ4.5. Mo
st
sample
s have high SiO2 and Fe2O3T content
s, variable FeOT /MgO and Ga/Al ratio
s, and are depleted in Ba, Sr, P, and Ti,
similar to I- and A-
type granites. The
granite porphyrie
s were mo
st likely derived from partial melting of juvenile dioritic or granodioritic cru
st due to break-off of the BNTO litho
sphere following colli
sion between the Lha
sa and Qiangtang block
s. The Early Cretaceou
s high-Mg diorite and A
type granite porphyry thu
s record the Early Cretaceou
s tran
sition from oceanic
subduction to continental colli
sion along the BangongeNujiang
suture zone (BNSZ).
© 2019 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.