Petrologic perspectives on tectonic evolution of a nascent basin (Okinawa Trough) behind Ryukyu Arc：A review

Okinawa Trough is a back-arc, initial marginal sea basin, located behind the Ryukyu Arc–Trench System. The formation and evolution of the Okinawa Trough is intimately related to the subduction process of the Philippine Sea Plate beneath the Eurasian Plate since the late Miocene. The tectonic evolution of the trough is similar to other active back-arcs, such as the Mariana Trough and southern Lau Basin, all of which are experiencing the initial rifting and subsequent spreading process. This study reviews all petrologic and geochemical data of mafic volcanic lavas from the Okinawa Trough, Ryukyu Arc, and Philippine Sea Plate, combined with geophysical data to indicate the relationship between the subduction sources(input) and arc or back-arc magmas(output) in the Philippine Sea Plate–Ryukyu Arc–Okinawa Trough system(PROS). The results obtained showed that several components were variably involved in the petrogenesis of the Okinawa Trough lavas: sub-continental lithospheric mantle underlying the Eurasian Plate, Indian mid-oceanic ridge basalt(MORB)-type mantle, and Pacific MORB-type mantle. The addition of shallow aqueous fluids and deep hydrous melts from subducted components with the characteristics of Indian MORB-type mantle into the mantle source of lavas variably modifies the primitive mantle wedge beneath the Ryukyu and subcontinental lithospheric mantle(SCLM) beneath the Okinawa Trough. In the northeastern end of the trough and arc, instead of Indian MORB-type mantle, Pacific MORB-type mantle dominates the magma source. Along the strike of the Ryukyu Arc and Okinawa Trough, the systematic variations in trace element ratios and isotopic compositions reflect the first-order effect of variable subduction input on the magma source. In general, petrologic data, combined with geophysical data, imply that the Okinawa Trough is experiencing the "seafloor spreading" process in the southwest segment, "rift propagation" process in the middle segment, and "crustal extension" process in the northeast segment, and a nascent ocean basin occurs in the southwest segment.     

准噶尔盆地南缘西部侏罗—白垩系储层发育特征及分布

通过大量镜下薄片观察,南缘白垩系、侏罗系砂岩总体表现为低成分成熟度、低结构成熟度、较低胶结物含量和较弱溶蚀作用的"三低一弱"特征.西山窑组与八道湾组含煤系砂岩具塑性岩屑与高岭石含量较高,颗粒溶蚀压碎及成岩压实作用较强的"二高二强"特征.储层储集空间类型大致分为粒间孔、粒内孔、胶结物溶蚀及微孔隙等,以原生粒间孔为主.区域上,四棵树凹陷、霍玛吐呼背斜带是南缘侏罗—白垩系油气勘探有利区,齐古断褶带侏罗系由于断裂作用强烈,裂缝发育,对储层性质具改善作用.     

Petrology and provenance of the Toro Negro Formation (Neogene) of the Vinchina broken-foreland basin (Central Andes of Argentina)

Detrital modes of sandstones and conglomerates of the Toro Negro Formation (Late Miocene-early Pliocene) were used to analyze the evolution of the broken-foreland stage of the Vinchina Basin (28°30′–29°00′ S and 68°30′–68°20′ W) of NW Argentina. This basin located in the Western Sierras Pampeanas is bounded to the west by the Precordillera and to the east by the Famatina System. Three sandstone petrofacies: plutonic-metamorphic, volcanic and mixed petrofacies and three conglomerate lithic associations: basement, sedimentary and volcanic lithic associations were recognized, allowing to establish three source areas: Western Sierras Pampeanas (Toro Negro and Umango Ranges), Cordillera Frontal and Precordillera.During the Late Miocene, the Toro Negro Range (to the north) together with the Cordillera Frontal and Precordillera (to the west) were the main sources for depositional sequences I and II (lower member of the Toro Negro Formation). On the contrary, during the latest Miocene-early Pliocene, Depositional Sequence III (upper member) exhibited a progressive increase in the supply from the eastern Precordillera (to the west) with additional material from the Umango Range to the south. Besides, evidence of synchronic volcanism is recorded in the upper part of Depositional Sequence II and the lower part of Depositional Sequence III.The coexistence of the three source areas and the changing distribution patterns due to re-accommodation of sediment dispersal routes demonstrate that the evolution of this type of basin is much more complex than previously envisaged. Therefore, an integrated analysis using different tools (sedimentary facies, paleocurrent measurements, sandstone petrography and conglomerate composition) is needed for a clearer understanding of broken-foreland basins.     

意大利亚平宁地区第三纪中新世“Calcaria Lucina”冷泉碳酸盐岩中结晶扇的沉积岩石学及地球化学特征

结晶扇是冷泉碳酸盐岩的一种标志性沉积构造,主要由文石或重晶石等矿物呈放射状聚集形成。意大利亚平宁地区的第三纪中新统广泛发育冷泉碳酸盐岩,其中"Calcari a Lucina"冷泉碳酸盐岩中发育有典型的结晶扇。结晶扇主要由放射状文石聚集形成,含少量的方解石,具有明显的生长纹层。文石纹层的δ13CPDB为-37.9‰~-53.5‰,δ18OPDB为+2.4‰~+6.0‰,相邻文石纹层之间的δ13CPDB和δ18OPDB值差别明显,可能是与碳和氧的来源及流体渗漏速度有关。全岩稀土元素总量很低,w(REE)为0.23×10-6,页岩标准化模式具有明显的Ce负异常,显示结晶扇形成于氧化环境。     

川南须家河组第四段TONSTEINS的岩石地化特征

对四川南部上三叠统须家河组第４段（Ｔ３ｘｊ＾４）中的５层ＴＯＮＳＴＥＩＮＳ做了较详细的岩石学、地球化学研究。结果表明,它们都是同沉积的酸性火山灰,在泥炭沼泽环境下,经过水解和后期成岩作用,转变成质地较纯的高岭石粘土岩。ＴＯＮＳＴＥＩＮＳ的岩石结构类型较简单,以致密型和团粒－致密型为主,结晶型较少。同层ＴＯＮＳＴＥＩＮ的岩石结构的某些亲石元素含量及组合关系在较大范围内保持稳定,并具有显著的标志性;Ｔ     

库鲁克塔格地区火山岩的岩浆过程与源区组成

在新疆库鲁克塔格地区的震旦纪和寒武纪沉积岩地层中,分布有四层火山岩。它们分别产出于早震旦世的贝义西组、晚震旦世的扎摩克提组和水泉组以及早寒武芤的西山布拉克组。其中,西山布拉克组和水泉组火山岩均属碱性玄武岩系列;扎摩克提组火山岩分属碱性玄武岩系列和拉斑玄武岩系列;贝义西组火山岩具有明显的双峰式组合特征,大部分属碱性火山岩。它们的多元素配分曲线均同板内玄武岩的大隆起特征。斜长石的分离结晶作用导致少部分     

PETROLOGIC AND GEOCHRONOLOGIC STUDIES OF THE KONGUR SHAN DETACHMENT SYSTEM, CENTRAL PAMIR

PETROLOGIC AND GEOCHRONOLOGIC STUDIES     

Petrology of nepheline syenite gneiss from Amazonian Brazil

Nepheline syenite gneiss is exposed in three localities near the village of Boca Nova (47·04′W, 1°51′S) in northeastern Pará, Brazil. Isotopic and chemical evidence for an igneous premetamorphic history include: (1) bulk compositions which plot in the Q–Ne–Ks system on a peralkaline fractionation curve; (2) bulk compositions which fall on the Hviddal igneous trend in the SiO₂–Al₂O₃–Na₂O + K₂O molecular diagram; (3) an average K/Rb ratio identical to the average for nepheline syenites of the Khibina massif; (4) K/Rb ratios which lie on the ideal igneous fractionation curve; (5) Nb(Ta) contents far in excess of average crustal abundance; and (6) a low Sr₈₇/Sr⁸⁶ value (0·7034) characteristic of mantle derivation. Post-kinematic lit-par-lit injections, discordant veins, and concordant pods of leucocratic nepheline–alkali feldspar pegmatite partially replaced the metamorphic assemblage and destroyed any microscopic equilibrium texture that may have been present. The final disequilibrium assemblage consists of Fe-rich biotite and two generations each of sodic plagioclase, microcline, and nepheline. Some minor metasomatic chemical effects may be present in the rocks but a case for nephelinization of crustal rocks cannot be documented. Field, petrographic, and chemical constraints indicate that the Boca Nova gneiss is an early-stage migmatite formed by anatexis of metamorphosed igneous nepheline syenite or its volcanic equivalent. Regional metamorphism and partial melting opened the Rb-Sr system so that the whole-rock Rb/Sr isochron age of 724 m.y. has no unambiguous interpretation. A K/Ar age of 580 ± 10 m.y. from biotite denning the metamorphic foliation is regarded as a minimum date for the regional metamorphism and anatexis. No other alkaline rocks of comparable age are known in the Sao Luis Craton.