Sun Zhen

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  • Article
    The role of magmatism in the thinning and breakup of the South China Sea continental margin: Special Topic: the South China Sea Ocean Drilling
    (Oxford University Press, 2019-08-13) Sun, Zhen ; Lin, Jian ; Qiu, Ning ; Jian, Zhimin ; Wang, PinXian ; Pang, Xiong ; Zheng, Jinyun ; Zhu, Benduo
    Magmatism plays a key role in the process of continental margin breakup and ocean formation. Even in the extremely magma-poor Iberia and Newfoundland margin, studies of field outcrops have shown that syn-rift magmatism had participated in rifting from a very early stage and contributed directly to the rifting process. The final transition from exhumed continental mantle to the ocean formation is also triggered by the accumulation and eruption of magma [1]. Therefore, Atlantic-type passive continental margins are classified into two end-members: magma-poor (non-volcanic) and magma-rich (volcanic). The differences between them lie in whether a large amount of intrusive and extrusive magmatism from the mantle plume/hotspot is involved in the syn-rift and breakup stages. A magma-rich margin [2] should include the following characteristics: (i) a high-velocity lower crust (HVLC) caused by syn-rift mafic magma underplating; (ii) continental crust intruded by abundant sills and dikes; (iii) a large volume of seaward-dipping reflectors (SDRs) caused by flood basalt eruption or tuffs. All other margins are classified as magma-poor margins.
  • Article
    The latest spreading periods of the south china sea: new constraints from macrostructure analysis of IODP expedition 349 cores and geophysical data
    (American Geophysical Union, 2019-08-29) Sun, Zhen ; Ding, Weiwei ; Zhao, Xixi ; Qiu, Ning ; Lin, Jian ; Li, Chun‐Feng
    Macrostructures preserved in deformed rocks are essential for the understanding of their evolution, especially when the deformation is weak and hard to discriminate in regional scale or purely through geophysical data. In order to resolve the inconsistency between NS trending fracture zones and NE oriented spreading fabrics of the South China Sea during the latest spreading stage, we analyzed macrostructures identifiable from the basalt and consolidated sediment samples of the Integrated Ocean Drilling Program (IODP) Sites U1431 and U1433. These two sites are close to the East and Southwest relict spreading ridges and provide critical information on the latest spreading stages. The structures in the basalt of both sites suggest two dominant orientations of NS and NE. At U1431, sediments show mainly WNW trending slickensides, different from that of basalt. At U1433, no structures were found in postspreading sediment. Thus, NE and NS trending structures in basalt are most possibly formed by seafloor spreading. Crosscutting relationship suggests that NE trending structures formed first, followed by NS and finally WNW trending structures. These observations are consistent with geophysical features. Magnetic anomalies and ocean bottom seismometer velocity suggest that the latest relict ridge of the East Subbasin coincides with the EW trending seamount chain. Located between the relict ridges of East and Southwest Subbasins, NS trending Zhongnan‐Liyue Fracture Zone had acted as the latest transform fault. Based on the above evidences, we proposed that the South China Sea may have experienced a short period of NS oriented spreading after earlier SE spreading. These results resolve the previous inconsistencies.
  • Article
    Ages and magnetic structures of the South China Sea constrained by deep tow magnetic surveys and IODP Expedition 349
    (John Wiley & Sons, 2014-12-27) Li, Chun-Feng ; Xu, Xing ; Lin, Jian ; Sun, Zhen ; Zhu, Jian ; Yao, Yongjian ; Zhao, Xixi ; Liu, Qingsong ; Kulhanek, Denise K. ; Wang, Jian ; Song, Taoran ; Zhao, Junfeng ; Qiu, Ning ; Guan, Yongxian ; Zhou, Zhiyuan ; Williams, Trevor ; Bao, Rui ; Briais, Anne ; Brown, Elizabeth A. ; Chen, Yifeng ; Clift, Peter D. ; Colwell, Frederick S. ; Dadd, Kelsie A. ; Ding, Weiwei ; Almeida, Ivan Hernandez ; Huang, Xiao-Long ; Hyun, Sangmin ; Jiang, Tao ; Koppers, Anthony A. P. ; Li, Qianyu ; Liu, Chuanlian ; Liu, Zhifei ; Nagai, Renata H. ; Peleo-Alampay, Alyssa ; Su, Xin ; Tejada, Maria Luisa G. ; Trinh, Hai Son ; Yeh, Yi-Ching ; Zhang, Chuanlun ; Zhang, Fan ; Zhang, Guo-Liang
    Combined analyses of deep tow magnetic anomalies and International Ocean Discovery Program Expedition 349 cores show that initial seafloor spreading started around 33 Ma in the northeastern South China Sea (SCS), but varied slightly by 1–2 Myr along the northern continent-ocean boundary (COB). A southward ridge jump of ∼20 km occurred around 23.6 Ma in the East Subbasin; this timing also slightly varied along the ridge and was coeval to the onset of seafloor spreading in the Southwest Subbasin, which propagated for about 400 km southwestward from ∼23.6 to ∼21.5 Ma. The terminal age of seafloor spreading is ∼15 Ma in the East Subbasin and ∼16 Ma in the Southwest Subbasin. The full spreading rate in the East Subbasin varied largely from ∼20 to ∼80 km/Myr, but mostly decreased with time except for the period between ∼26.0 Ma and the ridge jump (∼23.6 Ma), within which the rate was the fastest at ∼70 km/Myr on average. The spreading rates are not correlated, in most cases, to magnetic anomaly amplitudes that reflect basement magnetization contrasts. Shipboard magnetic measurements reveal at least one magnetic reversal in the top 100 m of basaltic layers, in addition to large vertical intensity variations. These complexities are caused by late-stage lava flows that are magnetized in a different polarity from the primary basaltic layer emplaced during the main phase of crustal accretion. Deep tow magnetic modeling also reveals this smearing in basement magnetizations by incorporating a contamination coefficient of 0.5, which partly alleviates the problem of assuming a magnetic blocking model of constant thickness and uniform magnetization. The primary contribution to magnetic anomalies of the SCS is not in the top 100 m of the igneous basement.
  • Article
    Continental interior and edge breakup at convergent margins induced by subduction direction reversal: a numerical modeling study applied to the South China Sea margin
    (American Geophysical Union, 2020-10-06) Li, Fucheng ; Sun, Zhen ; Yang, Hongfeng ; Lin, Jian ; Stock, Joann M. ; Zhao, Zhongxiang ; Xu, Hehua ; Sun, Longtao
    The dynamics of continental breakup at convergent margins has been described as the results of backarc opening caused by slab rollback or drag force induced by subduction direction reversal. Although the rollback hypothesis has been intensively studied, our understanding of the consequence of subduction direction reversal remains limited. Using thermo‐mechanical modeling based on constraints from the South China Sea (SCS) region, we investigate how subduction direction reversal controls the breakup of convergent margins. The numerical results show that two distinct breakup modes, namely, continental interior and edge breakup (“edge” refers to continent above the plate boundary interface), may develop depending on the “maturity” of the convergent margin and the age of the oceanic lithosphere. For a slab age of ~15 to ~45 Ma, increasing the duration of subduction promotes the continental interior breakup mode, where a large block of the continental material is separated from the overriding plate. In contrast, the continental edge breakup mode develops when the subduction is a short‐duration event, and in this mode, a wide zone of less continuous continental fragments and tearing of the subducted slab occur. These two modes are consistent with the interior (relic late Mesozoic arc) and edge (relic forearc) rifting characteristics in the western and eastern SCS margin, suggesting that variation in the northwest‐directed subduction duration of the Proto‐SCS might be a reason for the differential breakup locus along the strike of the SCS margin. Besides, a two‐segment trench associated with the northwest‐directed subduction is implied in the present‐day SCS region.
  • Article
    Mantle upwelling beneath the South China Sea and links to surrounding subduction systems
    (Oxford University Press, 2019-08-28) Lin, Jian ; Xu, Yigang ; Sun, Zhen ; Zhou, Zhiyuan
    The evolution of the South China Sea (SCS) is directly linked to the complex subduction systems of the surrounding Pacific, Philippine Sea and Indo-Australian Plates (Fig. 1a). Major advances in the last several years are providing new insights into the SCS-mantle dynamics, through regional seismic imaging of the upper mantle [1,2], unprecedented IODP drilling expeditions (349/367/368/368X) [3–5] that obtained the oceanic basement basalt samples for the first time, geochemical analyses of the SCS-mantle source compositions [6–8] and geodynamic modeling [9,10]. Furthermore, new geological mapping, seismic imaging [11,12] and IODP drilling [13,14] have revealed evidence for significantly greater magma production at the northern SCS rifted margin, in comparison to the magma-poor end-member of the Atlantic rifted margins. This paper provides a new perspective of the SCS-mantle dynamics inspired by new observations and geodynamic modeling. We first highlight new geophysical evidence for a broad region of low-seismic-velocity anomalies in the upper mantle beneath the northern SCS, abundant magmatism during continental breakup and post-seafloor spreading, and geochemical evidence for recycled oceanic components beneath the SCS. We then present new models of layered flows in the mantle beneath the SCS, revealing two modes of plate- and subduction-driven mantle upwelling, including (i) narrow centers of mantle upwelling at shallow depths induced by divergent plate motion at seafloor-spreading centers and (ii) broad zones of mantle upwelling as a result of subduction-induced mantle-return flows at greater depths. These new observations and geodynamic studies suggest strong links between mantle upwelling beneath the SCS and surrounding subducting plates.
  • Article
    The South China Sea is not a mini-Atlantic: plate-edge rifting vs intra-plate rifting
    (Oxford University Press, 2019-09-12) Wang, Pinxian ; Huang, Chi-Yue ; Lin, Jian ; Jian, Zhimin ; Sun, Zhen ; Zhao, Minghui
    The South China Sea, as ‘a non-volcanic passive margin basin’ in the Pacific, has often been considered as a small-scale analogue of the Atlantic. The recent ocean drilling in the northern South China Sea margin found, however, that the Iberian model of non-volcanic rifted margin from the Atlantic does not apply to the South China Sea. In this paper, we review a variety of rifted basins and propose to discriminate two types of rifting basins: plate-edge type such as the South China Sea and intra-plate type like the Atlantic. They not only differ from each other in structure, formation process, lifespan and geographic size, but also occur at different stages of the Wilson cycle. The intra-plate rifting occurred in the Mesozoic and gave rise to large oceans, whereas the plate-edge rifting took place mainly in the mid-Cenozoic, with three-quarters of the basins concentrated in the Western Pacific. As a member of the Western Pacific system of marginal seas, the South China Sea should be studied not in isolation on its origin and evolution, but in a systematic context to include also its neighboring counterparts.
  • Article
    Seismic stratigraphy of the central South China Sea basin and implications for neotectonics
    (John Wiley & Sons, 2015-03-16) Li, Chun-Feng ; Li, Jiabiao ; Ding, Weiwei ; Franke, Dieter ; Yao, Yongjian ; Shi, Hesheng ; Pang, Xiong ; Cao, Ying ; Lin, Jian ; Kulhanek, Denise K. ; Williams, Trevor ; Bao, Rui ; Briais, Anne ; Brown, Elizabeth A. ; Chen, Yifeng ; Clift, Peter D. ; Colwell, Frederick S. ; Dadd, Kelsie A. ; Hernandez-Almeida, Ivan ; Huang, Xiao-Long ; Hyun, Sangmin ; Jiang, Tao ; Koppers, Anthony A. P. ; Li, Qianyu ; Liu, Chuanlian ; Liu, Qingsong ; Liu, Zhifei ; Nagai, Renata H. ; Peleo-Alampay, Alyssa ; Su, Xin ; Sun, Zhen ; Tejada, Maria Luisa G. ; Trinh, Hai Son ; Yeh, Yi-Ching ; Zhang, Chuanlun ; Zhang, Fan ; Zhang, Guo-Liang ; Zhao, Xixi
    Coring/logging data and physical property measurements from International Ocean Discovery Program Expedition 349 are integrated with, and correlated to, reflection seismic data to map seismic sequence boundaries and facies of the central basin and neighboring regions of the South China Sea. First-order sequence boundaries are interpreted, which are Oligocene/Miocene, middle Miocene/late Miocene, Miocene/Pliocene, and Pliocene/Pleistocene boundaries. A characteristic early Pleistocene strong reflector is also identified, which marks the top of extensive carbonate-rich deposition in the southern East and Southwest Subbasins. The fossil spreading ridge and the boundary between the East and Southwest Subbasins acted as major sedimentary barriers, across which seismic facies changes sharply and cannot be easily correlated. The sharp seismic facies change along the Miocene-Pliocene boundary indicates that a dramatic regional tectonostratigraphic event occurred at about 5 Ma, coeval with the onsets of uplift of Taiwan and accelerated subsidence and transgression in the northern margin. The depocenter or the area of the highest sedimentation rate switched from the northern East Subbasin during the Miocene to the Southwest Subbasin and the area close to the fossil ridge in the southern East Subbasin in the Pleistocene. The most active faulting and vertical uplifting now occur in the southern East Subbasin, caused most likely by the active and fastest subduction/obduction in the southern segment of the Manila Trench and the collision between the northeast Palawan and the Luzon arc. Timing of magmatic intrusions and seamounts constrained by seismic stratigraphy in the central basin varies and does not show temporal pulsing in their activities.