Pan Guitang

Post-collisional crustal extension setting and VHMS mineralization in the Jinshajiang orogenic belt, southwestern China

Abstract The Jinshajiang orogenic belt (JOB) of southwestern China, located along the eastern margin of the Himalayan–Tibetan orogen, includes a collage of continental blocks joined by Paleozoic ophiolitic sutures and Permian volcanic arcs. Three major tectonic stages are recognized based on the volcanic–sedimentary sequence and geochemistry of volcanic rocks in the belt. Westward subduction of the Paleozoic Jinshajiang oceanic plate at the end of Permian resulted in the formation of the Chubarong–Dongzhulin intra-oceanic arc and Jamda–Weixi volcanic arc on the eastern margin of the Changdu continental block. Collision between the volcanic arcs and the Yangtze continent block during Early–Middle Triassic caused the closing of the Jinshajiang oceanic basin and the eruption of high-Si and -Al potassic rhyolitic rocks along the Permian volcanic arc. Slab breakoff or mountain-root delamination under this orogenic belt led to post-collisional crustal extension at the end of the Triassic, forming a series of rift basins on this continental margin arc. Significant potential for VHMS deposits occurs in the submarine volcanic districts of the JOB. Mesozoic VHMS deposits occur in the post-collisional extension environment and cluster in the Late Triassic rift basins.

Ages and tectonic significance of the collision-related granite porphyries in the Lhunzhub Basin, Tibet, China

The Paleocene collision-related granite porphyries are identified for the first time along the western margin of the Lhunzhub Basin, Tibet. SHRIMP U-Pb zircon analysis indicates that the granite porphyries were emplaced at 58.7±1.1 Ma (MSWD = 0.79) during the Indo-Asian continental collision. The granite porphyries are peraluminous and high in K, belonging to the calc-alkaline to high-K calc-alkaline series. They are relatively enriched in LILE, Th and LREE and depletion in Ba, Nb, P and Ti, characterized by LREE-enriched patterns with slightly to moderately negative Eu anomalies. These Paleocene granite porphyries are interpreted as the products generated by partial melting of the pre-existing arc crustal rocks caused by the increase of pressures and temperatures during the crustal shortening at the early stages of the Indo-Asian continental collision since 65 Ma. Despite inherited geochemical features and tectonic settings of the arc protoliths, they are significantly different from the volcanic rocks of the Dianzhong Formation within the Linzizong Group and the Miocene granite porphyries in the Gangdise belt.

Introduction to recent advances in regional geological mapping (1:250, 000) and new results from southern Qinghai-Tibet Plateau

A large volume of new geological data has been obtained in the process of new round of geological surveys (at a scale of 1:250, 000) and other geoscientific studies in southern QinghaiTibet Plateau ( Wang et al. 2004). The new results and achievements provide stable bases that are beneficial for understanding the principles governing the geological processes and verifying them in the Qinghai-Tibet Plateau. Significant data on the spatio-temporal distribution of the regional primary junction belts (suture zones) and faults also serve as the base for basic geological information required to establish a workable geotectonic framework for Qinghai-Tibet Plateau. The discovery of high-pressure granulites and lots of data on isotope chronology of Precambrian metamorphic rocks offer new insights to discuss the formation mechanism and exhumation process of the metamorphic basement in the southern Tibet. Findings of new strata and confirmation of already known strata containing abundant fossils provide new evidences to establish a regional stratigraphic system that will be used for geological classification and comparison. Likewise, discovery of some magmatic rock types and isotope-based age data on them enable to reconstruct the process of evolution and also propose a spatiotemporal framework for the magmatic rocks. Newly discovered unconformities and sedimentary facies or the verification of existing ones together with the associated geological information are fundamental for the analysis of sedimentary basin and for the paleogeographic reconstruction of tectonic lithofacies. The results and progresses in Quaternary geological mapping at regional scale and also in studying the neotectonic movements will be useful for deciphering the history of uplift of Plateau, the changes in the paleoenvironments and also the development of lakes in the geological past. Additional progress in finding the relics of ancient human activity, deciphering zoological environments and also studying the geology of regions of touristic importance has been made. These will be definitely valuable for research on zoological environment and ancient human civilization of Qinghai-Tibet Plateau and also for regional economic development. Besides these discoveries, new information on mineralization gained through the regional geological surveys will serve as guidelines for undertaking necessary action to explore and develop the mineral resources and also for appraisal of important metallogenic regions and belts in Qinghai-Tibet Plateau.

Chapter 4 – Songpan-Garze Belt: Fore-Arc Accretion or Back-Arc Collapsing?

Publisher Summary Songpan–Garze belt is a back-arc basin from the Late Paleozoic to Early Mesozoic. This belt is not a giant fore-arc accretional subduction complex but an abyssal fill in a back-arc basin. This basin started to be of existence by rifting on the western continental margin of the Pan Cathaysia during the Devonian and became a back-arc basin by seafloor spreading. Thus the chapter deals with the fore-arc accretion and back-arc subduction. The three margins surrounding this “triangular” basin have their own tectonic dynamic properties. The eastern margin started as the western passive continental margin of the Yangtze block and then changed into a foreland basin related to the North China block and the Qiangtang block during the middle to late Triassic. Because of the westward oblique subduction of the Yangtze block, two subduction melanges—the South Kunlun melange in the north and the Hoh Xil–Garze–Litang melange in the south—were formed on both north and south sides of this basin at almost the same period. The stratigraphic sequences and sedimentological characteristics indicate that the main body of the Bayan Har Basin is composed of Triassic flysch sediments deposited in a foreland basin during the Triassic.Publisher Summary Songpan–Garze belt is a back-arc basin from the Late Paleozoic to Early Mesozoic. This belt is not a giant fore-arc accretional subduction complex but an abyssal fill in a back-arc basin. This basin started to be of existence by rifting on the western continental margin of the Pan Cathaysia during the Devonian and became a back-arc basin by seafloor spreading. Thus the chapter deals with the fore-arc accretion and back-arc subduction. The three margins surrounding this “triangular” basin have their own tectonic dynamic properties. The eastern margin started as the western passive continental margin of the Yangtze block and then changed into a foreland basin related to the North China block and the Qiangtang block during the middle to late Triassic. Because of the westward oblique subduction of the Yangtze block, two subduction melanges—the South Kunlun melange in the north and the Hoh Xil–Garze–Litang melange in the south—were formed on both north and south sides of this basin at almost the same period. The stratigraphic sequences and sedimentological characteristics indicate that the main body of the Bayan Har Basin is composed of Triassic flysch sediments deposited in a foreland basin during the Triassic.

Songpan-Garze Belt

Publisher Summary Songpan–Garze belt is a back-arc basin from the Late Paleozoic to Early Mesozoic. This belt is not a giant fore-arc accretional subduction complex but an abyssal fill in a back-arc basin. This basin started to be of existence by rifting on the western continental margin of the Pan Cathaysia during the Devonian and became a back-arc basin by seafloor spreading. Thus the chapter deals with the fore-arc accretion and back-arc subduction. The three margins surrounding this “triangular” basin have their own tectonic dynamic properties. The eastern margin started as the western passive continental margin of the Yangtze block and then changed into a foreland basin related to the North China block and the Qiangtang block during the middle to late Triassic. Because of the westward oblique subduction of the Yangtze block, two subduction melanges—the South Kunlun melange in the north and the Hoh Xil–Garze–Litang melange in the south—were formed on both north and south sides of this basin at almost the same period. The stratigraphic sequences and sedimentological characteristics indicate that the main body of the Bayan Har Basin is composed of Triassic flysch sediments deposited in a foreland basin during the Triassic.Publisher Summary Songpan–Garze belt is a back-arc basin from the Late Paleozoic to Early Mesozoic. This belt is not a giant fore-arc accretional subduction complex but an abyssal fill in a back-arc basin. This basin started to be of existence by rifting on the western continental margin of the Pan Cathaysia during the Devonian and became a back-arc basin by seafloor spreading. Thus the chapter deals with the fore-arc accretion and back-arc subduction. The three margins surrounding this “triangular” basin have their own tectonic dynamic properties. The eastern margin started as the western passive continental margin of the Yangtze block and then changed into a foreland basin related to the North China block and the Qiangtang block during the middle to late Triassic. Because of the westward oblique subduction of the Yangtze block, two subduction melanges—the South Kunlun melange in the north and the Hoh Xil–Garze–Litang melange in the south—were formed on both north and south sides of this basin at almost the same period. The stratigraphic sequences and sedimentological characteristics indicate that the main body of the Bayan Har Basin is composed of Triassic flysch sediments deposited in a foreland basin during the Triassic.

Songpan-Garze Belt: Fore-Arc Accretion or Back-Arc Collapsing?

Publisher Summary Songpan–Garze belt is a back-arc basin from the Late Paleozoic to Early Mesozoic. This belt is not a giant fore-arc accretional subduction complex but an abyssal fill in a back-arc basin. This basin started to be of existence by rifting on the western continental margin of the Pan Cathaysia during the Devonian and became a back-arc basin by seafloor spreading. Thus the chapter deals with the fore-arc accretion and back-arc subduction. The three margins surrounding this “triangular” basin have their own tectonic dynamic properties. The eastern margin started as the western passive continental margin of the Yangtze block and then changed into a foreland basin related to the North China block and the Qiangtang block during the middle to late Triassic. Because of the westward oblique subduction of the Yangtze block, two subduction melanges—the South Kunlun melange in the north and the Hoh Xil–Garze–Litang melange in the south—were formed on both north and south sides of this basin at almost the same period. The stratigraphic sequences and sedimentological characteristics indicate that the main body of the Bayan Har Basin is composed of Triassic flysch sediments deposited in a foreland basin during the Triassic.Publisher Summary Songpan–Garze belt is a back-arc basin from the Late Paleozoic to Early Mesozoic. This belt is not a giant fore-arc accretional subduction complex but an abyssal fill in a back-arc basin. This basin started to be of existence by rifting on the western continental margin of the Pan Cathaysia during the Devonian and became a back-arc basin by seafloor spreading. Thus the chapter deals with the fore-arc accretion and back-arc subduction. The three margins surrounding this “triangular” basin have their own tectonic dynamic properties. The eastern margin started as the western passive continental margin of the Yangtze block and then changed into a foreland basin related to the North China block and the Qiangtang block during the middle to late Triassic. Because of the westward oblique subduction of the Yangtze block, two subduction melanges—the South Kunlun melange in the north and the Hoh Xil–Garze–Litang melange in the south—were formed on both north and south sides of this basin at almost the same period. The stratigraphic sequences and sedimentological characteristics indicate that the main body of the Bayan Har Basin is composed of Triassic flysch sediments deposited in a foreland basin during the Triassic.