“…According to the paleontological evidence, the Triassic coral fauna in the Qiangtang terrane are similar to those of the Songpan‐Ganzi terrane (Bo, Wang, et al, ; Bo, Yao, et al, ). This indicates that the Qiangtang terrane was close to the Songpan‐Ganzi terrane during the Triassic, which resulted in the migration and exchange of the benthonic organisms (Bo, Yao, et al, ).…”
To constrain the relationship between the Qiangtang and Lhasa terranes and the evolution of the Bangong-Nujiang Ocean (BNO), we carried out a paleomagnetic investigation of the Middle Jurassic limestone from the Shuanghu region in the southern Qiangtang terrane. Stepwise thermal demagnetization succeeded in isolating high-temperature characteristic directions by either principal component or great circle fitting analyses. The site-mean direction of the 13 sampling sites was Dg = 334.7°, Ig = 51.2°, kg = 27.9, α 95 = 8.0°(in geographic coordinates) and Ds = 245.2°, Is = 54.1°, ks = 113.9, α 95 = 3.9°(in stratigraphic coordinates). The paleomagnetic data passed both fold and reversal tests. Both rock magnetic and petrographic investigations suggest a primary magnetization. The paleomagnetic results imply that the paleolatitude of the Qiangtang terrane was 34.6 ± 4.6°N (reference site: 32.7°N, 89.4°E) in the Middle Jurassic. Combined with previous reliable paleomagnetic results, it is suggested that the Qiangtang terrane was situated at a stable paleolatitudinal position and did not undergo obvious N-S displacement between the Late Triassic and the Middle Jurassic. Comparison with the paleomagnetic results available for the Lhasa terrane implies that the width of the BNO was 2,600 ± 710 km (23.4°± 6.4°) during the Middle Jurassic. The BNO expanded from the Early to Middle Triassic, reached its maximum width in the Late Triassic, and then shrank until it closed by the Cretaceous.
“…According to the paleontological evidence, the Triassic coral fauna in the Qiangtang terrane are similar to those of the Songpan‐Ganzi terrane (Bo, Wang, et al, ; Bo, Yao, et al, ). This indicates that the Qiangtang terrane was close to the Songpan‐Ganzi terrane during the Triassic, which resulted in the migration and exchange of the benthonic organisms (Bo, Yao, et al, ).…”
To constrain the relationship between the Qiangtang and Lhasa terranes and the evolution of the Bangong-Nujiang Ocean (BNO), we carried out a paleomagnetic investigation of the Middle Jurassic limestone from the Shuanghu region in the southern Qiangtang terrane. Stepwise thermal demagnetization succeeded in isolating high-temperature characteristic directions by either principal component or great circle fitting analyses. The site-mean direction of the 13 sampling sites was Dg = 334.7°, Ig = 51.2°, kg = 27.9, α 95 = 8.0°(in geographic coordinates) and Ds = 245.2°, Is = 54.1°, ks = 113.9, α 95 = 3.9°(in stratigraphic coordinates). The paleomagnetic data passed both fold and reversal tests. Both rock magnetic and petrographic investigations suggest a primary magnetization. The paleomagnetic results imply that the paleolatitude of the Qiangtang terrane was 34.6 ± 4.6°N (reference site: 32.7°N, 89.4°E) in the Middle Jurassic. Combined with previous reliable paleomagnetic results, it is suggested that the Qiangtang terrane was situated at a stable paleolatitudinal position and did not undergo obvious N-S displacement between the Late Triassic and the Middle Jurassic. Comparison with the paleomagnetic results available for the Lhasa terrane implies that the width of the BNO was 2,600 ± 710 km (23.4°± 6.4°) during the Middle Jurassic. The BNO expanded from the Early to Middle Triassic, reached its maximum width in the Late Triassic, and then shrank until it closed by the Cretaceous.
“…Regionally, the revised Wuga Formation correlates with the Rhaetian Quehala Formation of the central BNSZ, a clastic succession. Norian rocks have been described from the central BNSZ (Mailonggang Formation) 12 , the Lhasa Terrane (Mailonggang Formation and Jiangrang Formation) 30 – 33 , and the South Qiangtang Terrane (Riganpeico Formation) 34 where they are made up largely of thick-bedded limestone and dolomite (Fig. 4 ).…”
Section: Discussionmentioning
confidence: 99%
“… Figure 4 The Norian (A) and Rhaetian (B) sediments in the BNSZ, Lhasa Terrane, and South Qiangtang Terrane. ①-Mailonggang section (conodonts) 30 ; ②-Yawa section (conodonts and corals) 32 ; ③-DibuCo section (conodonts) 31 ; ④-NamuCo section (corals) 33 ; ⑤,⑥-sections within the South Qiangtang Terrane (corals) 34 ; ⑦-DaruCo section (corals) 12 ; ⑧-ZhaxicobuCo section (conodonts; this paper); LS Lhasa Terrane, SQ South Qiangtang Terrane, LSSZ LongmuCo-Shuanghu Suture Zone, BNSZ Bangong-Nujiang Suture Zone, IYSZ Indus-Yarlung Zangbo Suture Zone. Red solid lines define boundaries between different tectonic terranes.…”
The Bangong-Nujiang Suture Zone (BNSZ) of Tibet (Xizang) has been interpreted to represent a relic of the Bangong-Nujiang Ocean. However, the existence of this ocean during Triassic time remains a point of contention. A sedimentary succession spanning the Upper Permian through Triassic described from the central BNSZ suggests that the Lhasa and South Qiangtang terranes were contiguous thus negating the existence of a terrane-separating ocean during Triassic time. However, the apparent lack of Triassic deposits in the west BNSZ has called into question the existence of Triassic deposits in the central region of the BNSZ. Our biostratigraphic work in the Wuga Formation of the Gaize area has yielded abundant Norian conodonts thus confirming the existence of Upper Triassic deposits in the west BNSZ. The clastic deposits of the Wuga Formation are herein interpreted to be of Rhaetian age. Moreover, intercalated limestone and chert are termed the Dongnale Formation of Norian age. The Norian to Rhaetian succession can be correlated with strata of the central BNSZ as well as with deposits of the Lhasa Terrane and the South Qiangtang Terrane. Similar stratigraphies among these regions through the Late Triassic suggests a shared depositional setting and that the BNSZ was not an ocean in Norian and Rhaetian time.
“…(b) Geological map of the Gaize-Dongco area (after Kapp et al, 2005;Zeng et al, 2006). Numbered sections (1-12) are from Zeng et al (2016), Li et al (2017), Fan et al (2014Fan et al ( , 2016Fan et al ( , 2018, Peng et al (2015), Chen et al (2006), Chen (2016), andBo et al (2017). (c-d) Updated geologic maps of the Gaize and Dongco areas, respectively.…”
Accretionary wedges are tectonic settings overriding subduction zones and generally show broad structural diversity, which, in first order, is reflected in tectonic accretion or erosion (Clift & Vannucchi, 2004). Therein, the accreted materials can involve variable amounts of oceanic basement or trench-fill sediments, which occur as either coherent units or mélanges (Meneghini et al., 2009). Wedge diversity is further complicated by the fact that mélanges may result from either sedimentary, tectonic or diapiric mechanisms, or a combination thereof (Festa et al., 2012). The nature of the lower plate, including oceanic-basement topography and volume of sediments, exerts a fundamental control on the wedge diversity (Clift & Vannucchi, 2004).
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