Deep CTD Casts in the Challenger Deep,Mariana Trench

On 1 December 1992, CTD (conductivity-temperature-depth profiler) casts were made at three stations in a north-south section of the Challenger Deep to examine temperature and salinity profiles. The station in the Challenger Deep was located at 11°22.78′ N and 142°34.95′ E, and the CTD cast was made down to 11197 db or 10877 m, 7 m above the bottom by reeling out titanium cable of 10980 m length. The southern station was located at 11° 14.19′ N and 142°34.79′ E, 16.1 km from the central station, where water depth is 9012 m. CTD was lowered to 7014 db or 6872 m. The northern station was located at 11°31.47′ N and 142° 35.30′ E, 15.9 km from the central station, and CTD was lowered to 8536 db or 8336 m, 10 m above the bottom. Below the thermocline, potential temperature decreased monotonously down to 7300–7500 db beyond a sill depth between 5500 m and 6000 m, or between 5597 db and 6112 db, of the trench. Potential temperature increased from 7500 db to the bottom at a constant rate of 0.9 m°C/1000 db. Salinity increased down to 6020–6320 db, and then stayed almost constant down to around 9000 db. From 9500 db to the bottom, salinity increased up to 34.703 psu at 11197 db. Potential density referred to 8000 db increased monotonously down to about 6200 db, and it was almost constant from 6500 db to 9500 db. Potential density increased from 9500 db in accordance with the salinity increase. Geostrophic flows were calculated from the CTD data at three stations. Below an adopted reference level of 3000 db, the flow was westward in the north of Challenger Deep and eastward in the south, which suggests a cyclonic circulation over the Challenger Deep. Sound speed in Challenger Deep was estimated from the CTD data, and a relation among readout depth of the sonic depth recorder, true depth, and pressure was examined.     

Bait-attending fauna of the Kermadec Trench, SW Pacific Ocean: Evidence for an ecotone across the abyssal-hadal transition zone

The bait-attending fauna of the abyssal-hadal transition zone of the Kermadec Trench, SW Pacific Ocean (4329-7966 m), was investigated using a baited camera and a trap lander. The abyssal stations (4329-6007 m) revealed a typical scavenging fish community comprising macrourids and synaphobranchid eels, as well as natantian decapods. At the hadal depths of 7199 and 7561 m, the endemic liparid Notoliparis kermadecensis was observed aggregating at the bait reaching surprisingly high numbers of 5 and 13, respectively. A total of 3183 invertebrate samples were collected (mean deployment time=16 h) of which 97.8% were of the order Amphipoda (nine families, 16 species). Ten of the amphipod species represent new distributional records for the Kermadec Trench and the New Zealand Exclusive Economic Zone; this includes the shallowest known record of the endemic hadal amphipod Hirondellea dubia (6000, 6007 m). Using amphipods to statistically examine the compositional change across the abyssal-hadal boundary, an ecotone between depths <6007 and >6890 m was found, indicating that there is an ecologically distinct bait-attending fauna in this trench.     

马里亚纳海沟柱状沉积物稀土地球化学特征及其指示意义

对我国载人潜器"蛟龙号"首次在马里亚纳海沟南部获取的沉积物柱状样(JL7KGC01A)进行了涂片观察、粒度、黏土矿物和稀土元素组成分析。结果表明:沉积物为典型深海黏土沉积。根据沉积物的粒度、黏土组分和稀土元素含量变化以及不同程度的δCe和δEu异常将该沉积物柱状剖面分为明显的上下两个沉积层段,即:1.8~2.41 m段与0.03~1.8 m两个层段。下部层段(1.8~2.41 m)相比上部层段(0.03~1.8 m),沉积物平均粒径较粗,蒙脱石/伊利石比值较高,稀土元素含量低且具有弱的Ce负异常和Eu正异常,表明该段沉积物受到较多的火山物质的影响。结合年代学分析认为研究区沉积物在2.2 Ma发生明显转变,2.2 Ma之前沉积物物源以附近火山物质为主,2.2 Ma之后物源仍以火山物质为主,但陆源物质供应逐渐增加。物源的转变暗示着本区在2.2 Ma之前火山活动较为频繁。     

Tectonic effects of a subducting aseismic ridge: The subduction of the Nazca Ridge at the Peru Trench

A 1987 survey of the offshore Peru forearc using the SeaMARC II seafloor mapping system reveals that subduction of the Nazca Ridge has resulted in uplift of the lowermost forearc by as much as 1500 m. This uplift is seen in the varied depths of two forearc terraces opposite the subducting ridge. Uplift of the forearc has caused fracturing, minor surficial slumping, and increased erosion through small canyons and gullies. Oblique trending linear features on the forearc may be faults with a strike-slip component of motion caused by the oblique subduction of the Nazca Ridge. The trench in the zone of ridge subduction is nearly linear, with no re-entrant in the forearc due to subduction of the Nazca Ridge. Compressional deformation of the forearc due to subduction of the ridge is relatively minor, suggesting that the gently sloping Nazca Ridge is able to slide beneath the forearc without significantly deforming it. The structure of the forearc is similar to that revealed by other SeaMARC II surveys to the north, consisting of: 1) a narrow zone (10 to 15 km across) of accreted material making up the lower forearc; 2) a chaotic middle forearc; 3) outcropping consolidated material and draping sediment on the upper forearc; and 4) the smooth, sedimented forearc shelf.The subducting Nazca plate and the Nazca Ridge are fractured by subduction-induced faults with offsets of up to 500 m. Normal faulting is dominant and begins about 50 km from the trench axis, increasing in frequency and offset toward the trench. These faults are predominantly trench-parallel. Reverse faults become more common in the deepest portion of the trench and often form at slight angles to the trench axis.Intrusive and extrusive volcanic areas on the Nazca plate appear to have formed well after the seafloor was created at the ridge crest. Many of the areas show evidence of current scour and are cut by faulting, however, indicating that they formed before the seafloor entered the zone of subduction-induced faulting.     

马里亚纳海沟万米级水文观测研究

深渊观测是开展深渊科学研究的前提。文章介绍了2020年7月"东方红3"船在马里亚纳海沟"挑战者深渊"附近完成的一次海洋调查。基于船载温盐深综合剖面测量系统获取的万米级剖面数据,分析全海深的温盐性质,并依据Thorpe尺度方法和细尺度参数化方法,进一步估算不同深度层的湍动能耗散率。结果表明:"挑战者深渊"的深层海水十分稳定, 3 000—5 000 dbar的温盐特征与下层绕极水相同;受弱层结背景下的内潮影响, 5 000—8 000 m的耗散率显著提升。本次调查获取的万米级水文剖面为马里亚纳海沟的深渊探索提供了数据方面的支撑。     

陕西勉略宁三角区基本地质组成及演化

陕西勉略宁三角区发育４大套不同构造背景下所形成的岩石组合，表明区内经历了晚太古结晶基底与早中元古浅变质火山岩过渡基底形成、晚元古一早古生代扬子大陆边缘演化、勉略海槽演化及陆内造山４个大的复杂演化阶段，最终形成今日之基本构造格局与地质面貌．     

马里亚纳海沟水深探测及“挑战者深渊”海底地形特征

"海洋六号"综合调查船先后于2011、2012年,利用EM122多波束测深系统在马里亚纳海沟最深海域"挑战者深渊"进行了全覆盖水深测量,获得了区域内详细的海底地形资料,揭示了马里亚纳海沟在区内呈近东西向延伸以及海沟两侧斜坡地形迥异、不对称的特点,南北两侧不同的地形地貌特征反映了马里亚纳海沟形成过程中两侧不同的次生构造活动影响。"挑战者深渊"区内有西部、中部和东部3个洼地,其中,西部洼地较深,其中心位置(142°12.14'E,11° 19.92'N)水深10 917 m,是马里亚纳海沟的最深点。     

海山的倾斜俯冲对上覆板块变形的影响

伴随洋壳的俯冲,驼伏其上的海山会导致上覆板块的强烈变形.为解释该构造变形特征,本文运用物理模拟实验的方法,着重分析海山的斜向俯冲对上覆板块变形的影响,并将模拟结果与正向俯冲过程进行对比.实验结果显示:海山开始进入俯冲,前缘楔体的增生会被阻止,同时楔体被抬升并出现脱顶构造,未被海山破坏的楔体会出现后冲断层的激活,后冲断层轴平行于海山的俯冲方向.海山进一步俯冲,突起项部发育一系列张扭性质的微断裂和走滑性质的共轭断裂,尾随突起之后的楔体由于重力会产生正断层系统.比起正向俯冲,斜向俯冲过程中所产生的后逆冲体、海山两侧的叠瓦状逆冲推覆构造都出现不对称分布,断裂和微断裂束的走向不规则散开,后冲断层的轴向及海山俯冲过后在楔体上产生的凹槽的轨迹都不断斜向迁移,且凹槽两侧的地势不一致等.最后利用文中的物理模拟结果,很好的解释了马尼拉海沟中段俯冲构造的构造特征,同时对其他俯冲大陆边缘的构造解释具有指导意义.