Neoproterozoic to early Paleozoic tectonic evolution of the Zavkhan terrane of Mongolia: Implications for continental growth in the Central Asian orogenic belt

Abstract

The Zavkhan terrane is a Proterozoic cratonic fragment in southwestern Mongolia that forms the core of the Central Asian orogenic belt. We provide new geologic and U-Pb zircon geochronologic constraints on the Neoproterozoic and early Paleozoic tectonic evolution of the terrane. Orthogneisses dated as ca. 1967 and ca. 839 Ma form the basement and are intruded and overlain by ca. 811-787 Ma arc-volcanic and volcaniclastic rocks that lack a gneissic fabric, suggestive of a mid-Neoproterozoic metamorphic event. Rifting and formation of the Zavkhan ribbon continent occurred from ca. 770-717 Ma and was followed by passive margin sedimentation between 717 and 580 Ma. During the latest Ediacaran to Cambrian, the southern margin of the Zavkhan terrane was reactivated with the obduction of the Lake terrane, slab break-off and reversal, and ca. 509-507 Ma magmatism. Metamorphosed Proterozoic and Cambrian units are cut by undeformed ca. 496 Ma gabbro, providing a tight constraint on the age of Cambrian metamorphism. Late Ordovician to Silurian rifting is marked by bimodal magmatism and deposition in narrow fault-bound basins. Our data indicate that the Zavkhan terrane traveled alone in the Neoproterozoic, collided with the Lake terrane in the late Ediacaran to Cambrian, accreted an unknown crustal block during Cambrian Epoch 2-Epoch 3, and then rifted away in the Ordovician. We suggest the majority of continental growth in Mongolia occurred through the trapping and oroclinal bending of ribbon continents rather than long-lived accretion on the margin of a major craton.

Integrated stratigraphic, geochemical, and paleontological late Ediacaran to early Cambrian records from southwestern Mongolia

“…This data suggest that the bounding Bulnay fault is not as old as suggested in (modified from [Bold et al, 2016a]) and that the Precambrian terranes in Mongolia all may be exotic to Siberia. Furthermore, orogenesis began around these cratonal fragments, which were later trapped between Fig.…”

“…Detrital zircon studies have been minimally incorporated into origination questions of the Proterozoic cratonic fragments of Mongolia except what is discussed in Salnikova et al [2001] from metasediments of the Tuva-Mongolia zone, Bold et al [2016a] from the Zavkhan terrane, and Rojas- Agramonte et al [2011]. Detrital zircon spectra of the Neoproterozoic siliciclastic rocks of the Zavkhan terrane yielded prominent age peaks at 2600-2400, 2100-1950, and 950-700 Ma [Bold et al, 2016a]. Detrital zircon spectra of the same age siliciclastic rocks of the Tuva-Mongolia zone also yielded major age peaks at 2100-1950 and 950-700 Ma (Fig.…”

“…1. A -Simplified map of the Central Asian orogenic belt; B -Simplified terrane map of Mongolia [Bold et al, 2016a]. Proterozoic cratonic fragments are grey.…”

Neoproterozoic‐Early Paleozoic Peri‐Pacific Accretionary Evolution of the Mongolian Collage System: Insights From Geochemical and U‐Pb Zircon Data From the Ordovician Sedimentary Wedge in the Mongolian Altai

“…Indeed, neighboring Neoproterozoic‐early Paleozoic arc‐related complexes of the Lake Zone and its adjacent Zavhan and Baydrag blocks may have provided an important contribution to the studied Ordovician sedimentary basin. It is well documented that the Mongolian Precambrian blocks underwent multiple magmatic and metamorphic events dated at 2.8 Ga to 0.9 Ga (Bold et al, ; Buriánek et al, ; Demoux, Kröner, Badarch, et al, ; Kozakov et al, ; Kröner et al, ). The widely reported Neoproterozoic magmatic rocks correlated with subsequent magmatic event yielded ages of 750–610 Ma (Dijkstra et al, ; Kuzmichev et al, ; Levashova et al, ; Osozawa et al, ; Sal'nikova et al, ).…”

“…They were interpreted as remnants of a major Precambrian continent. They consist of Archean (2.9–1.8 Ga) to early Neoproterozoic gneisses (1.05–0.86 Ga) (Demoux et al, ; Kozakov et al, ; Kröner et al, ), rare Neoproterozoic (812 ± 18 Ma Rb‐Sr age and 785 ± 11 Ma zircon U‐Pb age) tonalitic plutons (Kuzmichev et al, ), and volcanic rocks with zircon U‐Pb ages of 805–770 Ma (Bold et al, ; Levashova et al, ). These basement complexes are overlain by Neoproterozoic to Cambrian passive margin sedimentary succession consisting of pebbly sandstone, marble, quartzite, and diamictite (K‐Ar muscovite age of 699 ± 35 Ma, Badarch et al, ) and limestones (Kröner et al, ; Lindsay et al, ).…”