Evidence for Early Miocene wrench faulting in the Marlborough Fault System,New Zealand: structural implications

Abstract

In New Zealand, the Marlborough strike-slip faults link the Hikurangi subduction zone to the Alpine fault collision zone. Stratigraphic and structural analysis in the Marlborough region constrain the inception of the current strike-slip tectonics.

Six major Neogene basins are investigated. Their infill is composed of marine and freshwater sediments up to 3 km thick; they are characterised by coarse facies derived from the basins bounding relief, high sedimentation rates and asymmetric geometries. Proposed factors that controlled the basins generation are the initial geometry of the strike-slip faults and the progressive strike-slip motion. Two groups of basins are presented: the early Miocene (23 My) basins were generated under wrench tectonics above releasing-jogs between basement faults. The late Miocene (11 My) basins were initiated by halfgrabens tilted along straighter faults during a transtensive stage. Development of faults during Cretaceous to Oligocene times facilitated the following propagation of wrench tectonics. The Pliocene (5 My) to current increasing convergence has shortened the basins and distorted the Miocene array of faults. This study indicates that the Marlborough Fault System is an old feature that connected part of the Hikurangi margin to the Alpine fault since the subduction and collision initiation. © Elsevier, Paris     

Evolution of an intra‐oceanic island arc during the Late Silurian to Late Devonian,New England Fold Belt

Geochemical studies of volcanic rocks in the Gamilaroi terrane and Calliope Volcanic Assemblage, New England Fold Belt, eastern Australia, indicate that the setting in which these rocks formed changed in both space and time. The Upper Silurian to Middle Devonian basalts of the Gamilaroi terrane show flat to slightly light rare‐earth element (LREE) depleted chondrite normalised patterns, depletion of high field strength elements (HFSE) relative to N‐MORB, low Ti/V and high Ti/Zr ratios, high Ni, Cr and large‐ion lithophile element (LILE) contents, features characteristic of intra‐oceanic island arc basaltic magmas. They are associated with low‐K, less mafic volcanics, showing moderate LREE enrichment, low Nb and Y contents and Rb/Zr ratios. The depletion of HFSE in the basalts indicates that the magmas were derived from a refractory source in a supra‐subduction zone setting. The presence of such a zone implies that the arc was associated with a backarc basin, the location of which was to the west where a wide backarc region existed from the Middle Silurian. This polarity of arc and backarc basin suggests that the subduction zone dipped to the west. In contrast to their older counterparts, Middle to Upper Devonian basalts of the Gamilaroi terrane have MORB‐like chondrite normalised patterns and higher Ti and lower LILE contents. Moreover, they have low Ti/Zr ratios and MORB‐like Ti/V ratios and HFSE contents, features typical of backarc basins. Dolerites of the Gamilaroi terrane also have predominantly backarc basin signatures. These features suggest that both the basalts and dolerites have been emplaced in an extensional environment produced during the rifting of the intra‐oceanic island arc lithosphere. A progressive increase in Ti/V ratios, and TiO₂ and Fe₂O₃ contents at constant MgO, of stratigraphically equivalent basalts, towards the north‐northwest part of the belt, is consistent with either greater extension to the north or melting of a more fertile magma source. By contrast, basalts in the southeast part of the terrane have moderately high Ti/Zr and low Ti/V ratios and in some samples, exhibit depletion of HFSE, compositional features transitional between island arc and backarc basin basalts. The Lower to Middle Devonian mafic rocks in the Calliope Volcanic Assemblage show both LREE enriched and depleted chondrite normalised REE patterns. Further, the majority have high Ti/Zr ratios and low Zr contents as well as relatively high Th contents relative to MORB. These features are common to rocks of Middle Devonian age as well as those of Early Devonian age and are suggestive of eruption in an arc setting. Thus, the data from this study provide new evidence for the evolution of the New England Fold Belt from the Late Silurian to the Late Devonian and reveal a history more complicated than previously reported.     

Cenozoic Plate interaction of the Australia and Philippine Sea Plates: “hit-and-run” tectonics

Recent studies in northwest New Guinea have shown the presence of at least two marginal basins of different age, both of which formed in back-arc settings. The older basin opened between the Middle Jurassic and Early Cretaceous, a remnant of which is now preserved as the New Guinea Ophiolite. Its obduction started at 40 Ma and it was finally emplaced on the Australian margin at 30 Ma. The younger basin was active during the Oligocene to Middle Miocene and was obducted in the Early Pliocene. Studies of the western edge of the Philippine Sea also reveal an important deformation of the Philippine arc in the Oligocene, which hitherto has remained unexplained. Using information from these systems, paleomagnetic results, kinematic reconstructions and geochemistry of the supra-subduction ophiolite, we present a plate model to explain the region's Eo–Oligocene development. We suggest that an extensive portion of oceanic crust extended the Australian Plate a considerable distance north of the Australian Craton. As Australia began its steady 7–8 cm/year northward drift in the Early Eocene, this lithosphere was subducted. Thus, the portion of the Philippine Sea Plate carrying the Taiwan–Philippine Arc to its present site may have actually been in contact with the ophiolite now in New Guinea and obduction led to deformation of the Philippine Sea Plate itself. Neogene Plate kinematics transported the deformed belt in contact with the Sunda block in the Late Miocene and Pliocene. This interpretation has implications for the origin for the Philippine Sea Plate and the potential incorporation of continental fragments against its boundaries.     

A new record and a new ichnospecies of Arachnostega from the Middle Miocene of Egypt

The ichnogenus Arachnostega Bertling, 1992 is recorded for the first time from a bioeroded, coral-rich, Middle Miocene limestone bed in the middle Siwa Escarpment Member (Marmarica Formation) at Siwa Oasis, northern Western Desert of Egypt. These burrowing traces are preserved on the surface of a few internal moulds of bivalves and gastropods. Until now, the ichnogenus Arachnostega included a single ichnospecies, A. gastrochaenae Bertling, 1992. In the material studied herein, two ichnospecies are identified, described, illustrated and compared with other, similar traces. One of these is a new ichnospecies of Arachnostega; this is here named A. siwaensis ichnosp. nov. It is distinguished from A. gastrochaenae in the possession of tunnels that usually branch in a V-pattern; intervals of ramification are longest in the main branch and decrease in second- and third-order branches. Arachnostega traces were produced in a warm, low-energy, shallow-marine (<10?m water depth) environment. Polychaetes are the most likely producers of marine Arachnostega, which are commonly occurred in the same studied bed. This new occurrence is significant in extending the known stratigraphical and geographical ranges of Arachnostega into the Middle Miocene of Egypt.     

雄安新区岩土标准地层序列划分

为统一雄安新区地层序列划分标准,实现雄安新区工程勘察数据的入库、互相调用和综合利用分析,在搜集雄安新区大量工程勘察资料的基础上,综合考虑地质年代、地质成因、沉积序列、地层岩性、物理力学性质等因素,对雄安新区100 m深度范围内的地层进行了统一划分,并对标准地层采用"主层编码+岩性亚层编码+特殊成分编码+工程性质次亚层编码"的形式进行了标准化编码。将雄安新区100 m以浅地层自上而下划分为18个主层,其中冲洪积层及冲湖积层、5个钙质结核层是具有典型特征的标志层,可作为地层划分的重要依据,并根据颗粒粗细对各主层内的亚层进行了分层。雄安新区100 m深度范围内地层序列划分标准的建立,可为勘察单位在雄安新区规范、标准地开展工程地质工作提供借鉴,同时也可满足政府部门对工程地质数据的有效管理与精准服务的需求。     

A new tribe of Galerucinae leaf beetle (Insecta: Coleoptera: Chrysomelidae) from the Upper Cretaceous Taimyr amber

The new tribe Taimyralticini trib. nov., new genus Taimyraltica gen. nov. and new species Taimyraltica calcarata sp. nov. (Coleoptera: Chrysomelidae: Galerucinae) are described from Upper Cretaceous (Santonian) Taimyr amber of northern Siberia (Yantardakh locality). The new genus shares characters with genera of the tribe Alticini (small size, transverse antebasal groove on pronotum, regular punctate-striate elytra) and the Galerucini (narrow, non-swollen metafemora). A possible apomorphy of the new genus and tribe is a large and acute metatibial spur, erect and oriented transversely to the longitudinal axis of tibia. This character state is unknown in recent and fossil genera of Galerucinae. Early evolution and divergence of leaf beetles are discussed, and a Jurassic and Early Cretaceous subfamily radiation is proposed. Fossil galerucines are reviewed. The oldest Phyllotreta is recorded from the lower Miocene of Izarra (Spain). Our findings show an extreme rarity of Phytophaga in Taimyr amber from Yantardakh. Absence of Phytophaga was recorded earlier at Obeschayuschiy (Santonian-Campanian of the Magadan Region) and compared with their much larger share in Khetana (north of Khabarovsk Krai); we find nearly the same differences between Taimyr amber from Yantardakh and Canadian amber. In Obeschayuschiy this appears due to the Mesophytic character of the flora. It is assumed that the Santonian amber gymnosperm forest of the Khatanga Basin had the same character.     

Two new glaphyrids (Coleoptera,Scarabaeoidea) from the Jehol Biota,China

Two new species, Cretohypna puncta sp. nov. and Cretohypna robusta sp. nov., of Glaphyridae are described and illustrated. These fossils were collected from the Jehol Biota, Lower Cretaceous Yixian Formation of Liutiaogou Village in Ningcheng, Inner Mongolia, China. Up to date, 18 fossil species in 6 genera of Glaphyridae have been reported, among which ten species are from China. Respective keys to the Mesozoic genera of Glaphyridae and to species of Cretohypna Yan, Nikolajev & Ren, 2012 are provided. This is the first report of spiracles in fossil Glaphyridae leading to a hypothesis that the character of the 7th abdominal spiracles present in pleural membrane is a plesiomorphy for Glaphyridae.     

Paleomagnetism of the Carboniferous Rouchel Block,Tamworth Belt,and pole path revision for the New England Orogen,eastern Australia

Structural, magnetic and gravity trends of the southern New England Orogen (SNEO) indicate four oroclinal structures, none conclusively confirmed paleomagnetically. Curved structures of the Tamworth Belt (TB)—a continental forearc exposed across six tectono-stratigraphic blocks with interlinked Carboniferous stratigraphies and extensive ignimbritic rocks known to retain primary magnetisations despite prevalent overprinting—are prospective to oroclinal testing through comparison of Carboniferous pole paths for individual blocks. Pole paths (a) have been established for the Rocky Creek and Werrie blocks (northwestern/western TB), (b) are described herein for the Rouchel Block (southwestern TB), and (c) are forthcoming for the Gresford and Myall blocks (southern/southeastern TB). The Rouchel path derives from detailed paleomagnetic, rock magnetic and magnetic fabric studies. Thermal, alternating field and liquid nitrogen demagnetisations show a low-temperature overprint, attributed to late Oligocene weathering, and high-temperature (HT) primary and overprint components in both magnetite and hematite carriers, showing slight, systematic, directional differences with hematite providing the better cleaned site poles. Seven primary mean-site poles of Tournaisian and mainly Visean age and three overprint poles show six positive fold tests, five at 95% or higher confidence levels. Two dispersed groupings of intermediate (IT) and HT overprint site poles of Permian and Permo-Triassic age are attributed to early and late phases in oroclinal evolution of the SNEO. HT and IT/HT overprint site poles of mid-Carboniferous age are attributed to Variscan Australia–Asia convergence. Individual pole paths for the Rocky Creek, Werrie and Rouchel blocks show no noticeable rotation between them, indicating primary curvature for the southwestern TB. Their integrated SNEO pole path establishes a reference frame for determining rotations of the southern and southeastern TB.     

地下建筑物浮力探讨及其设计应用

简要介绍了地下结构浮力方面的一些新的比较有说服力的研究成果,结合这些研究成果及现场实际的部分粘结预应力抗拔桩荷载试验结果,对抗拔桩进行了优化设计,降低了抗浮投入。