Tectono-stratigraphic framework of late Paleoproterozoic to Cambrian
strata of the Quánjí block and its role in the development of northern
Tibet Plateau orogenic collage
Abstract
The Quánjí Block (QB) is a sliver of anomalously old and well-preserved
continental crust embedded within the Paleozoic-Mesozoic tectonic
collage of the northeastern Tibet Plateau. New geological mapping,
stratigraphic logging, and geochronological analysis leads to a refined
understanding of QB’s history from Paleoproterozoic to present.
Deposited atop a largely Paleoproterozoic basement, the Quánjí Group
records rifting and epicratonic cover at 1.7-1.6 Ga. The Xiǎogāolú Group
preserved black shale, ribbon-shaped fossil and the Ediacaran‐Cambrian
glaciation. Ages from Cambrian Olóngbùlǔkè Group samples in open
platform deposits are quite different from ages in underlying units,
with a subdued age groups in the Neoproterozoic (880-815 Ma) ages. The
apparent change in detrital zircon sources coincides with the regionally
expressed Great Unconformity during the Precambrian-Cambrian transition.
The new mapping, stratigraphy, and U-Pb geochronology of QB suggest the
late Paleoproterozoic to Cambrian history of QB has a remarkable
similarity to that of North China Block’s (NCB’s) southern margin, and
indicate that the QB has been displaced dextrally from an initial
location adjacent to NCB. The transform motion occurred in stages
between ca. 350 and 200 Ma.