Evolution of the Grenada and Tobago basins and implications for arc migration

The tectonic mechanisms controlling how volcanic arcs migrate through space and geologic time within dynamic subduction environments is a fundamental tectonic process that remains poorly understood. This paper presents an integrated stratigraphic and tectonic evolution of Late Cretaceous to Recent volcanic arcs and associated basins in the southeastern Caribbean Sea using seismic reflection data, wide-angle seismic refraction data, well data, and onland geologic data. We propose a new tectonic model for the opening of the Grenada and Tobago basins and the 50-250-km eastward jump of arc volcanism from the Late Cretaceous Aves Ridge to the Miocene to Recent Lesser Antilles arc in the southeast Caribbean based on the mapping of three seismic megasequences. The striking similarity of the half-graben structure of the Grenada and Tobago basins that flank the Lesser Antilles arc, their similar smooth basement character, their similar deep-marine seismic facies, and their similar Paleogene sediment thickness mapped on a regional grid of seismic data suggest that the two basins formed as a single, saucer-shaped, oceanic crust Paleogene forearc basin adjacent to the now dormant Aves Ridge. This single forearc basin continued to extend and widen through flexural subsidence during the early to middle Eocene probably because of slow rollback of the subducting Atlantic oceanic slab. Rollback may have been accelerated by oblique collision of the southern Aves Ridge and southern Lesser Antilles arc with the South American continent. Uplift and growth of the southern Lesser Antilles arc divided the Grenada and Tobago basins by early to middle Miocene time. Inversion of normal faults and uplift effects along both edges of the Lesser Antilles arc are most pronounced in its southern zone of arc collision with the South American continent. The late Miocene to Recent depositional histories of the Grenada and Tobago basins are distinct because of isolation of the Grenada basin by growth and uplift of the Neogene Lesser Antilles volcanic ridge.     

SAR 图像中不同特性条纹噪声的滤除

分析Burst工作模式星载SAR 系统中, 采用全孔径成像算法会产生周期性明暗条纹噪声的原因, 提出一种简单高效的一维频域滤除算法, 并给出包含该操作的改进距离多普勒成像算法流程。对于因雷达系统本身原因而产生的一些非周期不规则条纹噪声进行讨论, 针对此类噪声提出一种二维频域区域滤波的算法。通过对实际星载SAR 数据的处理, 验证算法的有效性。     

Magnetotelluric soundings and crustal architecture at Century mine,northern Australia

Magnetotelluric soundings were obtained along two traverse lines to the north and west of the Century mine in northwest Queensland. The survey was designed to cross the Termite Range Fault, a major structure on the Lawn Hill Platform, and to provide insights into the crustal-scale architecture that may have controlled the location of this world-class zinc deposit. The projected surface trace of the Termite Range Fault is coincident with a major change in resistivity character that extends to a significant depth. A relatively flat-lying, stacked series of resistive/conductive layers occurs on the northeastern side of the fault , while on the southwestern side the resistive/conductive layers are much less evident. The major contrast in resistivity is interpreted as due to a steep northeast-dipping Termite Range Fault that may extend to 20 km depth. To the southwest of the Termite Range Fault, a second major fault, the Riversleigh Lineament, is inferred from geology and gravity data, although there is no corresponding resistivity contrast seen across this fault in the magnetotelluric-derived model. This fault is interpreted as a buried structure, as distinct from the reactivated Termite Range Fault, and the two faults together may have created a wide damage zone (with an associated strike change) in the crust. A regional-scale 3D geological model of the Lawn Hill Platform provides a basis for correlating the resistive/conductive layers with major lithological units in the area. The stacked layers in the 2D resistivity inversion model of the Termite Range Fault hangingwall are reasonably well correlated with lithological units, particularly in the near-surface. A key point is that although similar geological units occur on either side of the Termite Range Fault, the contrasting electrical properties of these units are pronounced and their source is not well constrained; increased carbonaceous material in the Termite Range Fault hangingwall units is implied. In addition, there is a strong gradient in the Bouguer gravity field in the region of the Termite Range Fault and Riversleigh Lineament structures. This gradient provides supporting evidence for a northeast-facing fault structure in the basement and cover architecture. Newly acquired seismic data in the area has yet to be evaluated and compared with the magnetotelluric model. These results demonstrate an important role for magnetotelluric soundings in determining resistivity contrasts relating to the configuration of geological units and the architecture of deep-seated mineralising faults.     

The first occurrence of the Paleocene Lygistepollenites balmei Zone in the Eastern Highlands region,New South Wales

Sub‐basaltic sediments in the Mt Royal Range area, studied with a view to testing models of the evolution of the Eastern Highlands, have yielded a palynoflora ascribed to the Paleocene Lygistepollenites balmei Zone. The palynofloras come from a core sampling sediment which accumulated when a stream was dammed by basalt. This is the first reported occurrence of a definite Paleocene flora in the Eastern Highlands region. Basalt in the vicinity of the core gave a K‐Ar age of 54.1 ± 0.3 Ma. The discrepancy between the pollen age and the K‐Ar date is considered to be relatively minor.     

Evidence for 1808–1770 Ma bimodal magmatism,sedimentation, high-temperature deformation and metamorphism in the Aileron Province,central Australia

Field relationships and LA-ICP-MS U–Pb geochronology from the Yundurbungu Hills (Aileron Province, central Australia) reveal a record of 1808–1770 Ma bimodal magmatism, sedimentation, high-temperature deformation and metamorphism. Specifically, the data presented here provide the first unequivocal evidence for ca 1774 Ma high-temperature deformation and metamorphism during the 1790–1770 Ma Yambah Event in the southern part of the North Australian Craton. Granitic lithologies were synkinematically emplaced between 1808 and 1770 Ma, with early phases recording D₁ deformation and the youngest phase postdating D₁ deformation. The protolith to a D₁ deformed metasedimentary unit was deposited between 1792 and 1774 Ma, followed by the intrusion and deformation of a composite mafic–felsic magmatic association at ca 1774 Ma. An S₁ migmatitic fabric in the composite mafic–felsic gneiss is truncated by the youngest (ca 1770 Ma) phase of granitic magmatism, constraining the timing of S₁ deformation. A second period of sedimentation appears to post-date D₁ deformation, with deposition occurring sometime after ca 1774 Ma. Subsequent overprinting during the 1590–1550 Ma Chewings Event is recorded by the growth of metamorphic monazite and zircon. This event deformed the ca 1774 Ma S₁ gneissic fabric, producing a composite S₁/S₂ gneissic fabric in early metasedimentary and magmatic lithologies and a simple S₂-only fabric in lithologies that were intruded or deposited after ca 1774 Ma. Consistent with previous work, we suggest that localised high-temperature deformation and bimodal magmatism at ca 1774 Ma in the Yundurbungu Hills is consistent with a back-arc setting linked to prolonged north-directed subduction.     

Lithospheric folding in the southern North Sea: combined effects of Alpine compression and North Atlantic Ocean opening

Late Cretaceous to Palaeogene graben inversion in the southern North Sea is classically related to Alpine compression. Regional deformation analysis of Upper Cretaceous sediments based on seismic and well data reveals the existence of large-scale NW-SE folds. Folding patterns are interpreted as the result of lithospheric buckling during NE-SW shortening. We suggest that graben inversion at the scale of the southern North Sea is only a part of a more general process, involving lithospheric folding. Folding developed in response to two major plate boundary conditions, that is, E-W to NE-SW opening of the Atlantic Ocean constrained to the southeast by N-S Alpine collision. Lithospheric folding might have influenced both the oil generation process and reservoir properties in this area.     

大兴安岭中段五岔沟地区蛤蟆沟林场A型花岗岩年代学、岩石地球化学及构造背景研究

对大兴安岭中部五岔沟镇蛤蟆沟林场花岗岩体研究结果表明,蛤蟆沟林场花岗岩体主要岩性组合为碱长花岗岩、黑云母正长花岗岩、黑云母二长花岗岩和花岗斑岩,其LA-ICP-MS锆石U-Pb测年结果为136.97±0.99Ma、135.85±0.78Ma、126.04±0.48Ma和135.87±0.49Ma,表明其形成时代为早白垩世。岩石主量元素具有富硅、富钾的特征,A/CNK值介于0.997~1.05之间,稀土元素相对富集轻稀土元素、亏损重稀土元素,并具有较为明显的Eu负异常,微量元素相对富集大离子亲石元素和高场强元素,贫Ba、Sr、Ti、P,这些特征表明蛤蟆沟林场花岗岩为铝质A型花岗岩,是中下地壳岩石部分熔融的产物,形成于大陆裂谷或板内构造环境（A1型花岗岩）,代表了伸展的大地构造背景,可能是受到古太平洋俯冲和蒙古鄂霍次克洋闭合的双重影响。     

内蒙古阿荣旗兴胜岩金矿地质特征及找矿远景

兴胜岩金矿处于大兴安岭中段东西向金银钼成矿带上,位于火山盆地边缘隆起带,火山期后热液活动强烈,构造都很发育,控制着矿（化）体的分布。火山期后次火山岩、花岗斑岩、似斑状花岗闪长岩和闪长岩等岩浆热液活动是重要的成矿热源,成矿与近东西向次级构造有关,矿体产于蚀变破碎带石英脉及蚀变角砾岩中。通过对金矿床地质特征及矿床成因分析,认为构造、岩浆活动在成矿过程中起着重要作用,对大兴安岭中段东坡找矿起到指导作用,明确了本区找矿方向。     

The volcanoes of an oceanic arc from origin to destruction: A case from the northern Luzon Arc

Volcanoes were created, grew, uplifted, became dormant or extinct, and were accreted as part of continents during continuous arc–continent collision. Volcanic rocks in Eastern Taiwan’s Coastal Range (CR) are part of the northern Luzon Arc, an oceanic island arc produced by the subduction of the South China Sea Plate beneath the Philippine Sea Plate. Igneous rocks are characterized by intrusive bodies, lava and pyroclastic flows, and volcaniclastic rocks with minor tephra deposits. Based on volcanic facies associations, Sr–Nd isotopic geochemistry, and the geography of the region, four volcanoes were identified in the CR: Yuemei, Chimei, Chengkuangao, and Tuluanshan. Near-vent facies associations show different degrees of erosion in the volcanic edifices for Chimei, Chengkuangao, and Tuluanshan. Yuemei lacks near-vent rocks, implying that Yuemei’s main volcanic body may have been subducted at the Ryukyu Trench with the northward motion of the Philippine Sea Plate. These data suggest a hypothesis for the evolution of volcanism and geomorphology during arc growth and ensuing arc–continent collision in the northern Luzon Arc, which suggests that these volcanoes were formed from the seafloor, emerging as islands during arc volcanism. They then became dormant or extinct during collision, and finally, were uplifted and accreted by additional collision. The oldest volcano, Yuemei, may have already been subducted into the Ryukyu Trench.     

http://www.sciencedirect.com/science/article/pii/S1674987113000054

Substantial part of the northern margin of Indian plate is subducted beneath the Eurasian plate during the Caenozoic Himalayan orogeny, obscuring older tectonic events in the Lesser Himalaya known to host Proterozoic sedimentary successions and granitic bodies. Tectonostratigraphic units of the Proterozoic Lesser Himalayan sequence (LHS) of Eastern Himalaya, namely the Daling Group in Sikkim and the Bomdila Group in Arunachal Pradesh, provide clues to the nature and extent of Proterozoic passive margin sedimentation, their involvement in pre-Himalayan orogeny and implications for supercontinent reconstruction. The Daling Group, consisting of flaggy quartzite, meta-greywacke and metapelite with minor mafic dyke and sill, and the overlying Buxa Formation with stromatolitic carbonate-quartzite-slate, represent shallow marine, passive margin platformal association. Similar lithostratigraphy and broad depositional framework, and available geochronological data from intrusive granites in Eastern Himalaya indicate strikewise continuity of a shallow marine Paleoproterozoic platformal sequence up to Arunachal Pradesh through Bhutan. Multiple fold sets and tectonic foliations in LHS formed during partial or complete closure of the sea/ocean along the northern margin of Paleoproterozoic India. Such deformation fabrics are absent in the upper Palaeozoic–Mesozoic Gondwana formations in the Lesser Himalaya of Darjeeling-Sikkim indicating influence of older orogeny. Kinematic analysis based on microstructure, and garnet composition suggest Paleoproterozoic deformation and metamorphism of LHS to be distinct from those associated with the foreland propagating thrust systems of the Caenozoic Himalayan collisional belt. Two possibilities are argued here: (1) the low greenschist facies domain in the LHS enveloped the amphibolite to granulite facies domains, which were later tectonically severed; (2) the older deformation and metamorphism relate to a Pacific type accretionary orogen which affected the northern margin of greater India. Better understanding of geodynamic evolution of the northern margin of India in the Paleoproterozoic has additional bearing on more refined model of reconstruction of Columbia.