Structural feature and its significance of the northernmost segment of the Tertiary Biluoxueshan-Chongshan shear zone, east of the Eastern Himalayan Syntaxis

Abstract

Here we describe ductile, ductile-brittle and brittle deformation styles in the northern segment of the Tertiary Biluoxueshan-Chongshan shear zone lying to the east of the Eastern Himalayan Syntaxis. In the northernmost part of the zone in the vicinity of the Eastern Himalayan Syntaxis, it consists of mylonitic gneiss, granite, and schist. Based on field relations and mineral assemblages, the rocks are classified into gneiss belt in the west limb, including banded gneiss, augen mylonite and migmatite gneiss, and schist belt in the east limb. Except for the massive granite pluton, the other three tectonites are affected by polystage deformation (D1-D4). Fold deformation of the first stage D1 is isoclinal to tight pattern with nearly N-S fold axes and steeply axial planar cleavage S1, which resulted in the local crustal thickening under a contractive setting. D2 overprinted D1 and is characterized by tight folds with steep axes and N-S fold axial planar, which are also characterized by large-scale ductile strike-slip shear foliation S2, parallel to the nearly N-S trending axial planes of D1 and D2. The structural pattern of D2 represents a transpression along the zone. D3 occurred during the late stage of the transpression or post-transpression, producing the NW-SE and NE-SW trending strike-slip faults of the third stage D3. Following the D3 deformation, the zone was exhumed to shallow crustal level where the various tectonites underwent a brittle transtensional deformation D4, combined with one N-S trending strike-slip component and one normal faulting component. Structures and previous geochronologies presented in the paper suggest that the study area is correlated with those in the adjacent tectonic zones, Ailaoshan-Red River shear zone and Gaoligong shear zone in the western Yunnan. It underwent intensive polyphase deformation, namely, crustal thickening, transpression, and transtension, responding to syn-collision and post-collision of India-Eurasia from 65 Ma to current period east of the Eastern Himalayan Syntaxis. Biluoxueshan-Chongshan shear zone, Tertiary, structure, polystage deformation Citation: Zhang B, Zhang J J, Zhong D L, et al. Structural feature and its significance of the northernmost segment of the Tertiary Biluoxueshan-Chongshan shear zone, east of the Eastern Himalayan Syntaxis. Sci China Earth Sci, 2011, 54: 959 -974,

Tectonics and Paleomagnetic Rotation Pattern of Yunnan (24°N–25°N, China): Gaoligong Fault Shear Versus Megablock Drift

“…Although sites Yun24, Yun25, Yun29, and Yun42 are located at less than 2 km from the contact with the mylonites of the Gaoligong fault, a postrotation (i.e., post Oligo‐Miocene) magnetic overprint is excluded (with the possible exception of site Yun42) by the evidence that both the in situ and tilt‐corrected directions are far from the GAD field direction (Figure and Table ). The apparently puzzling lack of a Neogene magnetic overprint for sites adjacent to mylonites is explained considering that the high‐grade rocks were exhumed along an extensional detachment that presumably elided the whole upper crust, juxtaposing high‐grade metamorphic rocks and unmetamorphosed sediments (B. Zhang et al, ).…”

“…The Chongshan shear zone extends for hundreds of kilometers along the Biluoxueshan‐Chongshan Mountains in western Yunnan with a width of ~10 km. The shear zone is divided by a N‐S trending fault into two belts with contrasting metamorphic facies: an eastern low‐grade schist belt and a western high‐grade gneiss belt, considered to be a paired‐metamorphic zone (G. Wang et al, ; B. Zhang et al, ; B. Zhang, Zhang, Zhong, et al, ; R. Zhang et al, ; B. Zhang et al, ). The shear zone formed during the Cenozoic and exhumation (from a depth of approximately 20 km) occurred from late Eocene to Miocene times (Akciz et al, ).…”

“…The Chongshan shear zone shows tectonic deformation starting as early as late Paleocene times (57 Ma), and a shear sense that is inconsistent along its southern and northern branches (B. Zhang, Zhang, Chang, et al, ; B. Zhang et al, , ). Along the northern segment of the zone a dextral displacement exceeding 100 km during the 57–16 Ma age window was reported, while left‐lateral shear has been documented further south (B. Zhang et al, ).…”

New insights into the Cenozoic lateral extrusion of crustal blocks on the southeastern edge of Tibetan Plateau: Evidence from paleomagnetic results from Paleogene sedimentary strata of the Baoshan Terrane

“…However, the CSF mainly underwent left‐lateral strike‐slip shearing in the period from the Oligocene to the middle Miocene. Although the northern segment of the CSF experienced right‐lateral ductile shearing during a short interval (from ~17–16 Ma), it was restricted to a very local scale, and no obvious right‐lateral offset can be observed [ Zhong et al ., ; Wang and Burchfiel , ; Socquet and Pubellier , ; Zhang et al ., ]. This contradiction may be caused by a systematic error in the paleomagnetic data.…”

Petrogenesis of the early Eocene I-type granites in west Yingjiang (SW Yunnan) and its implication for the eastern extension of the Gangdese batholiths

“…The belt is dominated by the Gangdese batholiths and Linzizong volcanic units that have been regarded as major components of the Andean-type convergent margin associated with the northward subduction of the Neotethyan oceanic lithosphere along the YarluZangpo suture (e.g., Allegrè et al, 1984;Searle et al, 1987;Harris et al, 1988a;Jiang et al, 1999;Hodges, 2000;Yin and Harrison, 2000;Aitchison et al, 2002;Mo et al, 2005;Chu et al, 2006;Wen et al, 2008a,b;Lee et al, 2009;Zhu et al, 2009a;Zhang et al, 2010c;Zhu et al, 2011;Guan et al, 2012;Lee et al, 2012;Zhu et al, 2013). However, in the Eastern Himalayan Syntaxis, previous studies have mainly focused on the kinematics and thermogeochronology of the strikeslip faults in the key metamorphic zones involving the Ailaoshan, Chongshan and Gaoligong fault systems (e.g., Tapponnier et al, 1990;Wang and Burchfiel, 1997;Ji et al, 2000a;Socquet and Pubellier, 2005;Searle, 2006;Wang et al, 2006;Song et al, 2010;Zhang et al, 2010aZhang et al, , 2011Zhang et al, , 2012. Little attention has been paid to the petrogenesis of igneous rocks in the metamorphic zones in West Yunnan (SW China) prior to the collision of India with Asia and its relationship with the Gangdese batholiths.…”