New Early Cretaceous palaeomagnetic and geochronological results from the far western Lhasa terrane: Contributions to the Lhasa-Qiangtang collision

Weiwei Bian,Huaichun Wu,Shihong Zhang,Haiyan Li,Feng Gao,Tianshui Yang,Jingjie Jin,Yiming Ma

doi:10.1038/s41598-017-16482-3

Abstract

To better constrain the Lhasa-Qiangtang collision, a combined palaeomagnetic and geochronological study of the far western Lhasa terrane was conducted on the Duoai Formation lava flows (~113–116 Ma), as well as on the Early Cretaceous Jiega Formation limestone. Following detailed rock magnetic, petrographical, and palaeomagnetic experiments, characteristic remanent magnetisation directions were successfully isolated from most samples using principal component analysis. The tilt-corrected direction groups yielded a palaeopole at 69.1°N, 319.8°E with A95 = 4.8° (N = 19). A primary origin for the magnetisation is consistent with positive fold tests. Our results from the Early Cretaceous units, combined with published palaeomagnetic data obtained from Cretaceous strata from the Lhasa and western Qiangtang terranes, show that these two terranes had already collided by the Early Cretaceous, the Lhasa terrane had a relatively east-west alignment, and it remained at a relatively stable palaeolatitude during the entire Cretaceous. Comparing the Cretaceous palaeolatitude calculated for the western Lhasa terrane with those from Eurasia and Mongolia suggests a latitudinal convergence of ~1400 ± 290 km and ~1800 ± 300 km, respectively, since the Early Cretaceous.

Highlights

The Tibetan Plateau, known as the Earth’s third pole, is a complex amalgamation of several continental fragments that include, from south to north, the Himalaya, Lhasa, Qiangtang, Songpan-Ganzi, and Kunlun-Qaidam blocks (Fig. 1a)
The large palaeolatitude discrepancy may be attributed to several factors: (1) lower palaeolatitudes, observed from sedimentary rocks, may partly result from compaction-induced inclination shallowing[28]; (2) some volcanic palaeomagnetic datasets originated from analyses of too few lava flows to average palaeosecular variation[15,16], or from stacks of lava flows whose attitudes were not accurately measured; (3) some palaeomagnetic datasets were from only a few sites that may be unreliable
Rhyolites of the Langjiu Fm are mapped as part of the Early Cretaceous Zenong Group (I44C004002), our sensitive high-resolution ion micro-probe (SHRIMP) zircon U-Pb age calculations indicate eruption at 22.6 ± 0.9 Ma and 24.2 ± 0.4 Ma30

Summary

Introduction

The Tibetan Plateau, known as the Earth’s third pole, is a complex amalgamation of several continental fragments that include, from south to north, the Himalaya, Lhasa, Qiangtang, Songpan-Ganzi, and Kunlun-Qaidam blocks (Fig. 1a) These continental fragments have gradually accreted to the stable Asian continent since the Early Palaeozoic[1], and the record of their plate motions, collisions, and subsequent deformation plays a key role in understanding the formation and evolution of the Tibetan Plateau[2,3]. We collected 62 cores from six sites (ZZ1–ZZ6) in the Early Cretaceous Jiega Fm limestone in section B (32°9.3′–32°9.4′N, 80°47.7′–80°47.8′E), located ~40 km southeast of the town of Zuozuo, with the goal of performing a regional fold test (Supplementary Fig. S1g). Two fresh block samples were collected from the bottom (ZN1) and top (ZN21) sites of section A for zircon U-Pb geochronology

Methods

Results

Discussion

Conclusion