Search

The tectonic evolution of the Paleo‐Jinshajiang Ocean, and in particular the time of its closure, is debated. Here we present new constraints on the evolution of this region from an integrated paleomagnetic and geochronologic study of the Late Triassic Batang Group volcanic rocks in Qamdo, Eastern Qiangtang Terrane (EQT). Two zircon U‐Pb ages indicate that the volcanic rocks erupted at ∼227–222 Ma. New paleomagnetic results yield a robust Late Triassic paleopole of 57.6°N, 176.4°E (A95 = 7.8°), corresponding to a paleolatitude of 32.5 ± 7.8°N for the study area. Integrated with other lines of paleomagnetic and geological evidence, we show that the northward drift of the EQT placed it at the same paleolatitude as the Tarim Block by ∼227–222 Ma, which suggests that the Paleo‐Jinshajiang Ocean in the Qamdo region closed before that time, and likely around ∼230 Ma. Plain Language Summary: The closure of the Paleo‐Jinshajiang Ocean, which was one of the most important ancient oceans of Asia, closed when the Qiangtang Terrane (QT) collided with the terranes now located to the north of it. However, the evolution of this ocean, and especially the timing of its closure, are still debated. The drift history of the QT is a key to understanding the evolution of the Paleo‐Jinshajiang Ocean. We present here new constraints on the evolution of this region from an integrated paleomagnetic and zircon U‐Pb geochronologic study of Late Triassic volcanic rocks in Qamdo, Eastern QT. Two zircon U‐Pb geochronologic results indicate that the volcanic rocks erupted at ∼227–222 Ma. New paleomagnetic results yield a robust Late Triassic paleopole of 57.6°N and 176.4°E, and indicate that the study area was then located at a paleolatitude of 32.5 ± 7.8°N. In integrating these data with other lines of evidence, we show that a northward drift of the EQT since the early Permian brought it to the same paleolatitude as the Tarim Block by ∼227–222 Ma. This implies that the closure of the Paleo‐Jinshajiang Ocean in the Qamdo region occurred before 227–222 Ma, and likely around ∼230 Ma. Key Points: Volcanic rocks of the Late Triassic Batang Group are dated by U‐Pb on zircon to ∼227–222 MaPaleomagnetic data from these rocks yield a robust Late Triassic paleopole of 57.6°N, 176.4°E(A95 = 7.8°)Closure of the Paleo‐Jinshajiang Ocean occurred before 227–222 Ma, and likely around ∼230 Ma [ABSTRACT FROM AUTHOR]

The impact of strong (weak) intraseasonal oscillation (ISO) over South China Sea (SCS) and South Asia (SA) in summer on the SCS and SA summer monsoon and the summer rainfall in Eastern China are studied by using the NCEP-NCAR analysis data and the rainfall data of 160 stations in China from 1961 to 2010. It is found that the impacts are significantly different in different months of summer. The study shows that in June and July cyclonic (anticyclonic) atmospheric circulation over SCS and SA corresponds to strong (weak) ISO over SCS. In August, however, strong (weak) ISO over SCS still corresponds to cyclonic (anticyclonic) atmospheric circulation over SA. In June and August cyclonic (anticyclonic) atmospheric circulation over South Asia corresponds to strong (weak) ISO over SA while a strong (weak) ISO corresponds to anticyclonic (cyclonic) atmospheric circulation over SA in July. Besides, in June the strong (weak) ISO over SA corresponds to cyclonic (anticyclonic) atmospheric circulation over SCS, while in July and August the atmospheric circulation is in the same phase regardless of whether the ISO over SA is strong or weak. The impacts of the strong (weak) ISO over SCS on the rainfall of eastern China are similar in June and July, which favors less (more) rainfall in Yangtze-Huaihe Rivers basin but sufficient (deficient) rainfall in the south of Yangtze River. However, the impacts are not so apparent in August. In South Asia, the strong (weak) ISO in July results in less (more) rainfall in the south of Yangtze River but sufficient (deficient) rainfall in Yangtze-Huaihe Rivers basin. The influence on the rainfall in eastern China in June and August is not as significant as in July. [ABSTRACT FROM AUTHOR]