Late Mesozoic Exhumation of the Huangling Massif:Constraints on the Evolution of the Middle Yangtze River

Plate subduction leads to complex exhumation processes on continents.The Huangling Massif lies at the northern margin of the South China Block.Whether the Huangling Massif was exhumed as a watershed of the middle reaches of the Paleo-Yangtze River during the Mesozoic remains under debate.We examined the exhumation history of the Huangling Massif based on six granite bedrock samples,using apatite fission track(AFT)and apatite and zircon(U-Th)/He(AHe and ZHe)thermochronology.These samples yielded ages of 157–132 Ma(ZHe),119–106 Ma(AFT),and 114–72 Ma(AHe),respectively.Thermal modeling revealed that three phases of rapid cooling occurred during the Late Jurassic–Early Cretaceous,late Early Cretaceous,and Late Cretaceous.These exhumation processes led to the high topographic relief responsible for the emergence of the Huangling Massif.The integrated of our new data with published sedimentological records suggests that the Huangling Massif might have been the watershed of the middle reaches of the Paleo-Yangtze River since the Cretaceous.At that time,the rivers flowed westward into the Sichuan Basin and eastward into the Jianghan Basin.The subduction of the Pacific Plate beneath the Asian continent in the Mesozoic deeply influenced the geomorphic evolution of the South China Block.

Rare-Element Pegmatites Rocks Rich and Li of the Aïr Massif of the Tchirozerine: Mineralogy and Chemical Composition Agadez Region-Northem Niger

The lithium potential in the Aïr massif is represented by mineral index of spodumene pegmatites and, lepidolite pegmatites. The mineral deposits of lithium occur in cluster or veins that cut the host rock or are located near the contact between the greenstone belt and granitic massif. The evidence of lithium is in the form of clusters or disseminated and stockwerk. Mineralogical characteristics show similarities between the Air Massif pegmatites and indicate the same homogenous source during the magma-generation process. The pegmatite rocks attracted the attention due to their wide exposure and composition, well appearance, and economically hosting of significant rare earth metals such as Sn and W. The mineralogical and petrographical investigations on the eight pegmatites rocks samples observed have a relative similarity, while a little difference in the shapes attributed to the ratio in the pegmatite rocks of the minerals. The occurrence of the kink band indicates the influence of the tectonic processes which affected the Aïr massif after the emplacement of late magmatic or post-magmatic pegmatites by injection into fractured rocks in the upper part of the crust. The Air Massif pegmatite has higher concentrations Li and of all trace elements except Hf and occasionally Zr, Ti, Sn and Mg of for the economic exploration.

Exploratory and Descriptive Study of the Kimberlite Massif of Boya-02 at Eastern Kasai in the Democratic Republic of Congo

The Boya-02 kimberlite was identified at depth by geophysical survey work (a single-probe AM survey in 1997 and a gravity survey in 2006) that De Beers DRC Exploration carried out around anomaly 193/172/0019. This anomaly located approximately 50 km southwest of the town of Mbuji-Mayi in the Kasaï-Oriental Province in the DRC should therefore be the subject of detailed exploration with the aim of better identifying and describing this kimberlite. Thus, through exploratory work and cross-checking of geophysical and geological data, the discovery of this Massif was made by drilling on the aeromagnetic anomaly 193/172/X298. Based on drilling, sampling and laboratory petrographic analysis reports, the Boya-02 kimberlite was classified among highly diluted re-sedimented volcaniclastic kimberlites (KVR), rich in olivine and incidentally in quartz and poor in juvenile substances. This kimberlite represents a deposit of very low economic interest following extremely high dilution. The Boya-02 kimberlite was modeled using ground magnetism data. It is a complex anomaly comprising 2 components with variable amplitude appearing on a subtly magnetized linear detail. The modeled dimensions of two components of this anomaly are 0.32 Ha and 0.2 Ha at depths of 32 m & 14 m for the deposits to the West and the East respectively. Garnet data for the Boya-02 occurrence reports a maximum Pmin value of 49.7 kbar (207 garnets). These data demonstrate the high diamond potential which assumes a conductive cratonic geotherm of 40 mWm2.

Neoarchean Magmatic Events in the Western Songnen Massif,Central Asian Orogenic Belt:Timing and Tectonic Significance

Whether a Neoarchean basement existing in the Songnen massif is currently debated.Identification of Archean magmatism from the Songnen Massif is helpful to resolve this issue.Here,we report newly discovered Neoarchean Shanquan pluton in the Western Songnen Massif.These Neoarchean Shanquan pluton are mainly composed of granites that are exposed near the town of Shanquan in Heilongjiang Province.LA-ICP-MS zircon U-Pb dating reveals that the sample 2015TW1 has an upper intercept age of 2801±69 Ma and a weighted mean age of 2708±18 Ma,while samples LJ27QY1 and LJ27QY2 have upper intercept ages of 2677±57 Ma and 2653±18 Ma,and weighted mean ages of 2649±10 Ma and 2653±15 Ma,respectively.This indicates that these granites were formed at~2.7 Ga.Most of the~2.7 Ga zircons have older TDM2 ages of 2762–3326 Ma with positiveεHf(t)values ranging from 0 to 6.4,while a few of the zircons have negativeεHf(t)values ranging from-8.1 to-11.5 and older TDM2 ages varying from 3158 to 3264 Ma.The zircon Hf isotopes indicate that Paleo-Mesoarchean crusts might once existed in the Songnen Massif,and the studied Neoarchean magmas were principally derived from partial melting of these Paleo-Mesoarchean ancient crust.Based on the geochronological spectrum of magmatic and detrital zircons,the Songnen,Erguna,Jiamusi,Bureya massifs may have a common basement prior to the Neoproterozoic and may even be linked with the Triam Craton.

Permian Tectonic Evolution in Southwestern Khanka Massif:Evidence from Zircon U-Pb Chronology,Hf isotope and Geochemistry of Gabbro and Diorite

Laser ablation-inductively coupled plasma mass spectrometry （LA-ICP-MS） zircon U-Pb dating and geochemical data for the Permian gabbros and diorites in the Hunchun area are presented to constrain the regional tectonic evolution in the study area. Zircons from gabbro and diorite are euhedral-subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios （0.26-1.22）, implying their magmatic origin. The dating results indicate that the gabbro and diorite formed in the Early Permian （282-2 Ma） and in the Late Permian （255-3 Ma）, respectively. In addition, the captured zircons with the weighted mean age of 279-4 Ma are also found in the diorite, consistent with the formation age of the gabbro within uncertainty. The gabbros belong chemically to low-K tholeiitic series, and are characterized by low rare earth element （REE） abundances, fiat REE pattern, weak positive Eu anomalies （JEu）, and depletion in high field strength elements （HFSEs, Nb, Ta, and Ti）, similar to the high-aluminum basalts from island arc setting. Initial Hf isotopic ratios of zircons from the gabbro range from ＋7.63 to ＋14.6, suggesting that its primary magma could be mainly derived from partial melting of a depleted lithospheric mantle. The diorites belong to middle K calc-alkaline series. Compared with the gabbros, the diorites have higher REE abundance, weak negative Eu anomalies, and more depletion in HFSEs （Nb, Ta, and Ti）, similar chemically to the volcanic rocks from an active continental margin setting. Initial Hf isotopic ratios and Hf two-stage model ages of zircons from the diorite range from ＋11.22 to ＋14.17 and from 424 to 692 Ma, respectively, suggesting that its primary magma could be mainly derived from partial melting of the Early Paleozoic and/or Neoproterozoic accretted lower crust. Taken together, it is suggested that geochemical variations from the Early Permian gabbros to the Late Permian diorites reveal that the subduction of the Paleo-Asian oceanic plate beneath the Khanka Massif and collision between the arc and continent （Khanka Massif） happened in the late stage of the Late Paleozoic.

2.7 Ga Monzogranite on the Songnen Massif and Its Geological Implications

Objective The formation and evolution of Songnen massif has always been a hot topic,and the presence of Precambrian basement on the Songnen massif is still controversial:(1)Lacking of Pre-Paleozoic dating results,the Precambrian basement on Songnen massif does not extend largely according to the isotopic dating results of core from basement,(2)the existence of gneiss from deep drill holes

Paleoproterozoic Nb-enriched meta-gabbros in the Quanji Massif,NW China:Implications for assembly of the Columbia supercontinent

Diverse models have been proposed for the role of the Tarim Craton within the Paleoproterozoic Columbia supercontinent assembly. Here we report a suite of-1.71 Ga Nb-enriched meta-gabbro lenses in the eastern Quanji Massif, within the Tarim Craton in NW China. The meta-gabbroic rocks have Nb contents of 11.5-16.4 ppm with Nb/La ratios varying from 0.84 to 1.02((Nb/La)_N = 0.81-0.98) and Nb/U ratios from 38.0 to 47.2. They show low SiO_2(45.1-48.5 wt.%) and MgO(5.96-6.81 wt.%) and Mg#(Mg# = Mg/(Mg + Fe) = 43.5-47.7), high FeO^t(13.0-15.7 wt.%) and moderate Ti02(1.70-2.51 wt.%).with tholeiitic affinities. These rocks possess low fractionated REE patterns without obvious Eu anomalies(Eu/Eu~* = 0.87-1.02). Their primitive mantle-normalized elements patterns display significant Zr-Hf troughs, positive Nb anomalies, weak negative Ti and P anomalies, and high contents of Rb and Ba,resembling Nb-enriched basalts generated in arc-related tectonic settings. Their arc-like geochemical signatures together with whole rock εNd(t) values of 0.4-2.1 and corresponding old T_(DM)(2.22-2.37 Ga)as well as(^(143)Nd/^(144)Nd)_t and(^(87)Sr/^(86)Sr)t(t = 1712 Ma) values of 0.5104-0.5105 and 0.7030-0.7058,respectively, suggest that their precursor magma originated from mantle wedge peridotite metasomatised by subduction-derived melts. The results from our study reveal subduction along the eastern periphery of the Tarim Craton and marginal outgrowth continuing to ~1.7 Ga within the Columbia supercontinent.

New Zircon U-Pb Geochronology of the Post-kinematic Granitic Plutons in the Diancang Shan Metamorphic Massif along the Ailao Shan-Red River Shear Zone and Its Geological Implications

The Ailao Shan-Red River fault zone is the boundary between the Yangtze block to the northeast and the Indochina block to the southwest.It is an important tectonic zone due to its role in the southeastward extrusion of the Indochina block during and subsequent to the Indian-Eurasian collision.Diancang Shan（DCS） high-grade metamorphic complex,located at the northwest extension along the Ailao Shan-Red River（ASRR） shear zone,is a representative metamorphic complex of the ASRR tectonic belt.Structural and microstructural analysis of sheared rocks in the high-grade metamorphic rocks reveals that they are coherent with solid-state high-temperature ductile deformation,which is attributed to left-lateral shearing along the ASRR shear zone.New LA-ICP-MS zircon U-Pb geochronological and microstructural studies of the post-kinematic granitic plutons provide a straightforward time constraint on the termination ductile left-lateral shearing and exhumation of the metamorphic massif in the ASRR shear zone.It is suggested that the left-lateral shearing along the ASRR shear zone ended at ca.21 Ma at relative lower-temperature or decreasing temperature conditions.During or after the emplacement of the young dikes at ca.21 Ma,rapid brittle deformation event occurred,which makes the DCS massif start fast uplift/exhumation and cooling to a shallow crustal level.

Age and geochemistry of the Neoproterozoic granitoids in the the Songnen–Zhangguangcai Range Massif, NE China: Petrogenesis and tectonic implications

The Songnen–Zhangguangcai Range Massif(SZRM)is located in the eastern Central Asian Orogenic Belt and crops out over an extensive part of NE China.The massif was originally thought to contain numerous Precambrian terranes(e.g.,Xingdong,Dongfengshan,Yimianpo and Zhangguangcailing groups).However,more recent zircon U–Pb dating indicates that the majority of these so-called Precambrian sedimentary and igneous rocks actually formed during either the Paleozoic or Mesozoic and contain only minor Precambrian components(Wang et al.,2014).The presence of Neoproterozoic and Paleoproterozoic detrital zircons with magmatic origins from and Paleozoic units of the SZRM indicating that this area occurs Proterozoic magmatism(Wang et al.,2014),whereas no Proterozoic magmastism has been found.Recently,Pei et al.(2007)reported the ca.1800Ma magmastism,as evidenced by the data of exploration drillholes in the southern Songliao basin.However,an alternative view is that the basement within the SZRM is predominantly Phanerozoic,as evidenced by the presence of Paleozoic fossils and comparatively rare geochronological data(Guo and Liu,1985;Wu et al.,2011),meaning that the ca.1800 Ma rocks in this area may be a tectonically emplaced slice of the North China Craton(Zhang et al.,2005).All of this means that the age and nature of the SZRM basement,and whether this area records Neoproterozoic magmatism,remain unclear.This study presents new geochronological,whole-rock geochemical,and zircon Hf isotopic data for early Proterozoic granitoids within the eastern margin of the SZRM of NE China.These data provide insights into the Neoproterozoic tectonic setting of the SZRM and the links between this magmatism and the evolution of the Rodinia supercontinent.The zircon U–Pb dating indicates that the Neoproterozoic magmatism within the SZRM can be subdivided into two stages:(1)a^917–911 Ma suite of syenogranites and monzogranites,and(2)an^841 Ma suite of granodiorites.The 917–911 Ma granitoids contain high concentrations of Si O2(67.89–71.18 wt.%),K2O(4.24–6.91 wt.%),and Al2O3(14.89–16.14 wt.%),and low concentrations of TFe2O3(1.63–3.70 wt.%)and Mg O(0.53–0.88 wt.%).They are enriched in the light rare earth elements(LREE)and the light ion lithophile elements(LILE),are depleted in the heavy REE(HREE)and the heavy field strength elements(HFSE;e.g.,Nb,Ta,and Ti),and have slightly positive Eu anomalies,indicating they are geochemically similar to high-K adakitic rocks.They have zirconεHf(t)values and TDM2 ages from–4.4 to+1.5and from 1915 Ma to 1592 Ma,respectively,suggesting they were derived from a primary magma generated by the partial melting of ancient thickened lower crustal material.In comparison,the 841 Ma granodiorites contain relatively low concentrations of Al2O3(14.50–14.58 wt.%)and K2O(3.27–3.29 wt.%),relatively high concentrations of TFe2O3(3.78–3.81 wt.%)and the HREE,have negative Eu anomalies,and have zirconεHf(t)values and TDM2ages from–4.7 to+1.0 and from 1875 to 1559 Ma,respectively.These granodiorites formed from a primary magma generated by the partial melting of ancient crustal material.The^917–911 Ma magmatism within the SZRM is inferred to have formed in an orogenic setting,whereas the^841 Ma magmatism formed in an anorogenic setting related to either a post-orogenic tectonic event or the onset of Neoproterozoic continental rifting.It is proposed that the microcontinental massifs within the SZRM formed during or following the final stage of assembly of Rodinia before rifting away from the Tarim Craton in response to Rodinia breakup.

ANISOTROPIC FEATURE OF QIANGTANG MASSIF TEXTURE

Qiangtang Massif is located in the hinterland of Qinghai—Tibet plateau, which belong to the mid\|east section of Tethys Tectonic Domain.1 Features of the whole texture and structure of Qiangtang massif By synthetic analysis of gravity,magnetic field,MT,seismic surveying,etc. Geophysical data, the massif, lied in the tectonic setting and geodynamic setting mingled by the south,north tectonic belts, have the features of massif,basin and tectonic belt three forming an organic whole,multi\|degree coupling in plane and section with division of region in south\|north trend,division of block\|fault in east\|west trend,division of sphere\|layer in vertical direction. (1) Belting in south\|north trend: Qiangtang massif could be divided into four units from north to south, that is north edge doming zone, west part doming area,Qiangtang Basin and south edge doming zone. Qiangtang Basin also can be divided into four tectonic units—north Qiangtang down\|warping region, middle downing zone, south Qiangtang down\|warping and east part slope region. The near east\|west trend tectonic zones are well developed. There is aero\|magnetic anomaly distributed in belting with east\|west trend but also concentrated in section. Gravity anomaly is high in the south\|west part and low in the northeast part. Inter\|crust low resistance layer alternately distributed with high and low belting of sou th\|north trend in plane.

Sequence of Ductile Shear Zones in UHP Metamorphic Province with in Dabie Massif,China

Structural studies in the Dabie massif show that distribution of strain is extremely heterogeneous and illustrates the pattern of deformation partitioning in the ultra high pressure (UHP) metamorphic province on all scales. Based on the field structural analysis along with microstructural observation, at least five widespread episodes of ductile shear zone systems are identified by using geometric, kinematic and rheological indicators and they constitute a shear zone sequence in the UHP metamorphic province within the Dabie massif (DM), China. Each shear zone system, for example, the UHP eclogite facies shear zone system in the sequence, exhibits its own features including geometric styles, mineral assemblages, metamorphic pt conditions and deformation regimes during the formation of such shear zone system. Detailed macro and micro scopical features of different episodes of the shear zones are given with respect to mechanism of strain localization and deformation partitioning. The tectonic significance during the creation and exhumation of the UHP metamorphic rocks is evaluated briefly, as well. It is argued that the ductile shear zones in the UHP metamorphic province play an important role in the Dabie mountain building geodynamic process.

The Puesto Piris Formation: Evidence of basin-development in the North Patagonian Massif during crustal extension associated with Gondwana breakup

The Marifil Volcanic Complex, exposed in the eastern North Patagonian Massif, Argentina, includes up to 550 m of red conglomerates, sandstones, black siltstones, limestones, and reworked tuff of the Puesto Piris Formation. The basal part of this unit, which was deposited in high-gradient topographic relief, is composed of conglomerates and sandstones with thin layers of reworked tuffs. The lithofacies associations of the basal part indicate that the depositional mechanisms were mantled and gravitational flows.The middle part of the unit consists of fine sandstones, limestones, and black siltstones that were deposited in low-energy fluvial and lacustrine environments. The outcrops are located along the NEe SW direction and the major thickest units represented by limestones and siltstones, occur near the southeastern border of this NEeS W depocenter. Since the rhyolitic and trachytic lava flows and tuffs of the Marifil Volcanic Complex are interbedded with the sedimentary sequences of the Puesto Piris Formation,both units are coeval. Zircon Ue Pb age was obtained for a trachytic lava flow(193.4 ±3.1 Ma) suggesting that sedimentation and volcanism are Sinemurian. This extensional episode was recorded in the eastern,western, and southwestern sectors of the North Patagonian Massif, and is possibly associated with the Gondwana supercontinent breakup.

Kalaymyo Peridotite Massif in the Indo-Myanmar Ranges(Western Myanmar): Its Mineralogy and Petrology

Mesozoic ophiolites crop out discontinuously in the Indo-Myanmar Ranges in NE India and Myanmar,and represent the remnants of the Neotethyan oceanic lithosphere(Sengupta et al.,1990;Mitchell,1993).These ophiolites in the Indo-Myanmar Ranges are the southern continuation of the Neotethyan ophiolites occurring along the Yarlung Zangbo Suture Zone(YZSZ)in southern Tibet farther northwest(Mitchell,1993;Fareeduddin and Dilek,2015),as indicated by their coeval crystallization ages and geochemical compositions(Yang et al.,2012;Liu et al.,2016).The Kalaymyo ophiolite is located in the central part of the eastern Indo-Myanmar Ranges(Fig.1).composition of these ophiolites from the central Tibetan Plateau(CTP)is dominated by MORBs and minor OIBs and a distinct lack of IATs and BONs,which is inconsistent with most ophiolites worldwide(Robinson and Zhou,2008;Zhang et al.,2008).But the generation and tectonic nature of these ophiolites are still controversial.*The Kalaymyo peridotites consist mainly of harzburgites,which show typical porphyroclastic or coarse-grained equigranular textures.They are composed ofolivine(Fo=89.8–90.5),orthopyroxene(En86-91Wo1-4Fs8-10;Mg#=89.6–91.9),clinopyroxene(En46-49Wo47-50Fs3-5;Mg#=90.9–93.6)and spinel(Mg#=67.1–78.9;Cr#=13.5–31.5),and have relatively homogeneous whole-rock compositions with Mg#s of90.1–90.8 and Si O2(41.5–43.65 wt.%),Al2O3(1.66–2.66wt.%)and Ca O(1.45–2.67 wt.%)contents.TheydisplayLightRareEarthElement(LREE)-depleted chondrite-normalized REE patterns with(La/Yb)CN=0.04–0.21 and(Gd/Yb)CN=0.40–0.84,and show a slight enrichment from Pr to La with(La/Pr)CN in the range of 0.98–2.36.The Kalaymyo peridotites are characterized by Pd-enriched chondrite-normalized PGE patterns with superchondritic(Pd/Ir)CN ratios(1.15–2.36).Their calculated oxygen fugacities range between QFM–0.57 and QFM+0.90.These mineralogical and geochemical features collectively suggest that the Kalaymyo peridotites represent residual upper mantle rocks after low to moderate degrees(5–15%)of partial melting at a mid-ocean-ridge(MOR)environment.The observed enrichment in LREE and Pd was a result of their reactions with enriched MORB-like melts,percolating through these already depleted,residual peridotites.The Kalaymyo and other ophiolites in the Indo-Myanmar Ranges hence represent mid-ocean ridge(MOR)–type Tethyan oceanic lithosphere derived from a downgoing plate and accreted into a westward migrating subduction–accretion system along the eastern margin of India.

Control of Interior Sources on Time-Bound Characteristics of Mineralization in Southwest Yangtze Massif

Strata bound ore deposits of Au, Ag, Hg, Sb, As, Sn, Pb and Zn in southwest Yangtze massif are concentrated in Cambrian, Devonian, Upper Permian to Lower Triassic and rarely in other horizons, showing a strong time bound feature. The metallogenic elements are highly enriched in these host strata and limited in other horizons. Isotope researches indicate that the metallogenic elements in the ore deposits mainly come from the host strata. The studies of trace elements in the host mudstone show lower w (Th)/ w (Sc), w (Th)/ w (U) ratios, higher mafic elements (such as Cr, Ni, Co) mass fractions than the average values of the same kind of rocks in the upper crust and the research area. The chondrite normalized REE patterns of mudstone in the host strata are quite different from the common mudstones and shales with relatively steep HREE slopes (relatively high w (Tb) n/ w (Yb) n ratios, between 1.48 and 2.00) and no or slightly negative Eu anomalies (high δ (Eu) ratios, between 0.79 and 0.89). The NASC normalized REE patterns of siliceous rocks in the host strata show the HREE enrichment (the w (La) n/ w (Yb) n ratios are less than 1), a little Eu positive anomalies and Ce depletion with high abundances of As, Se, Sb and Ba elements, which shows the hydrothermal deposit features. The NASC normalized REE patterns of the mudstone in the host strata are very similar to those of the hydrothermal siliceous rocks and to those of the tuffs and basalts except the higher total REE mass fractions. All of these geochemical characteristics suggest the existence of interior sources pouring into basin when the host strata were deposited. The research of basin evolution also indicates that the host strata were deposited in the pulling apart periods. It can be realized from these facts that the degree of enrichment and deficiency of the elements in the normal depositional strata is very limited, and it is only the particular horizons corresponding to the particular periods of the earth ’s evolution that can be the significant source beds because only in these unusual horizons can be highly enriched metallogenic elements. The interior sources corresponding to the pulling apart of basin evolution may be the main cause to make the mineralization of the strata bound ore deposits in southwest Yangtze massif take on time bound characteristics.

Modeling of deformation processes in rock massif in the vicinity of underground goafs considering the formation of discontinuity zones

The construction of mechanical-mathematical model and numerical method for the deformation processes of rock massifs with goafs and underground structures is very complex and also important task in modern rock mechanics.In this study,the mechanical-mathematical model is developed for rock massif in vicinity of underground goafs considering the internal block-layered structure of the rock massif.A new constitutive model is introduced in this study to describe the negative Poisson’s ratio for the lock-layered structure.Two types of defining equations systems for studying the state of a rock massif taking into account the block-layered structure are described.Finally,several examples are given using the present mechanical-mathematical model.

Detrital Zircon U-Pb Geochronology of the Xilin Group: Constraints for the Early Paleozoic Tectonic Evolution of the Songliao Massif

The Xilin Group, composed of the Chenming, Laodaomiaogou, Qianshan and Wuxingzhen formations, is one of the Early Paleozoic terranes in the eastern Songliao Massif, mainly consisting of thick layers of fine clastic and carbonate rocks. This study presents LA-ICP-MS zircon U-Pb geochronological data for the Laodaomiaogou and Qianshan formations, further constraining their provenance and the Early Paleozoic tectonic evolution of the Songliao Massif on the eastern Central Asian Orogenic Belt. Most zircons from the Laodaomiaogou and Qianshan formations show magmatic oscillatory zoning and high Th/U ratios(0.26–2.41). Zircon U-Pb dating results indicate that the detrital zircons from the silty mudstone of the Laodaomiaogou Formation yield peak ages of 634 Ma, 775 Ma, 820 Ma, 880 Ma and 927 Ma, as well as multi-episodic Archean to Paleoproterozoic and Mesoproterozoic ages(1405–643 Ma), implying its deposition time is younger than ~634 Ma. Furthermore, the occurrence of Early Cambrian fossils indicates that the Laodaomiaogou Formation was deposited during the late stage of the Early Cambrian(~514 Ma). The zircons from the K-bentonite of the Qianshan Formation show four peak ages of 444 Ma, 471 Ma, 489 Ma and 518 Ma and the youngest age peak of 444 ± 4 Ma(n = 6) indicates that the Qianshan Formation was deposited during the Late Ordovician. In addition, the peak ages of the detrital zircons in the silty mudstone of the Qianshan Formation are 472 Ma and 498 Ma, as well as two other concordant points with;Pb/;Pb apparent ages of 1824 Ma and 1985 Ma. The dating results in this study, together with published data, indicate the absence of Pan-African magmatic events in the Songliao Massif prior to the initial deposition of the Xilin Group, in contrast to those distributed widely in the Jiamusi Massif. Taken together, we conclude that the depositional provenance of the Laodaomiaogou and Qianshan formations was derived from the Songliao Massif. Furthermore, the characteristics of the detrital zircon age composition and rock associations indicate that the Laodaomiaogou Formation formed in a passive continental margin environment, in contrast to the Qianshan Formation, which formed in an active continental margin environment. The above results also imply that the Songliao and Jiamusi massifs might not have collided before the Late Ordovician.

Thermodynamic modeling and elemental migration for the early stage of rodingitization:An example from the Xialu massif of the Xigaze ophiolite,southern Tibet

The analysis of early stage rodingite from the ultramafic rocks of the Xialu Massif in the Xigaze Ophiolite,Tibet,in China shows that the rodingitization involved continuous changes in fluid composition during different stages of subduction.The early stage prehnite-bearing rodingite was produced at low pressures and temperatures along extensional fractures.Samples of rodingite were collected along a profile from the center to the margin of a rodingitized intrusive igneous rock(^10 m×30 m),and they record wide variations in bulk composition,mineralogy,and texture.The mineral assemblages,from center to margin,vary from(1)relics of primary clinopyroxene(Cpx_(r))and primary amphibole(Amp_(r))+newly formed late amphibole(Act)+primary plagioclase(Pl_(r))+clinozoisite+prehnite+albite+chlorite+titanite+ilmenite(R1 rodingite),through(2)relics of primary clinopyroxene(Cpx_(r))+newly formed late clinopyroxene(Cpx_(n))+primary and late amphiboles(Amp_(r)+Act)+clinozoisite+prehnite+albite+chlorite+titanite(R2 rodingite),to(3)newly formed late clinopyroxene(Cpx_(n))and amphibole(Act)+clinozoisite+prehnite+albite+chlorite+titanite(R3 rodingite).As a result of the metasomatic process of rodingitization,the content of CaO in the whole rock chemical composition from R1 to R3 increases,SiO_(2) decreases,and Na_(2)O+K_(2)O is almost completely removed.Massbalance diagrams show enrichments in large ion lithophile elements such as Rb,Cs,Ba,and Pb as well as Ni during rodingitization.The central part of the rodingitized intrusion(R1 rodingite)was only slightly affected by metasomatism.On the other hand,the contents of the rare earth elements(REEs),high field strength elements(HFSEs;e.g.Zr,Nb,Ta,Hf,and Y),and some highly compatible elements such as Cr and Sc decreased slightly during rodingitization.Thermodynamic modeling based on equilibrium mineral assemblages indicates that the rodingite of the Xialu Massif formed in an H_(2)O-saturated,CO_(2)-rich environment.The estimated conditions of metamorphism were-281-323℃and 0.4-3.9 kbar,representing the subgreenschist facies.In this environment,REEs and HFSEs were soluble in the fluids and partly removed.Moreover,these prehnite rodingites formed in a progressively reducing and less alkaline environment,as indicated by decreases in f(O_(2))and bulk-rock Fe^(3+)/Fe^(2+) ratios,and the records of fluidΔpH from the center to the margin of the studied rodingitized intrusion.

Effect of Aspect on Climate Variation in Mountain Ranges of Shennongjia Massif, Central China

The aim of this study was to better understand the mechanisms of regional climate variation in mountain ranges with contrasting aspects as mediated by changes in global climate. It may help predict trends of vegetation variations in native ecosystems in natural reserves. As measures of climate response, temperature and precipitation data from the north, east, and south-facing mountain ranges of Shennongjia Massif in the coldest and hottest months(January and July), different seasons(spring, summer, autumn, and winter) and each year were analyzed from a long-term dataset(1960 to 2003) to tested variations characteristics, temporal and spatial quantitative relationships of climates. The results showed that the average seasonal temperatures and precipitation in the north, east, and south aspects of the mountain ranges changed at different rates. The average seasonal temperatures change rate ranges in the north, east, and south-facing mountain ranges were from –0.0210℃/yr to 0.0143℃/yr, –0.0166℃/yr to 0.0311℃/yr, and –0.0290 ℃/yr to 0.0084℃/yr, respectively, and seasonal precipitation variation magnitude were from –1.4940 mm/yr to 0.6217 mm/yr, –1.6833 mm/yr to 2.6182 mm/yr, and –0.8567 mm/yr to 1.4077 mm/yr, respectively. The climates variation trend among the three mountain ranges were different in magnitude and direction, showing a complicated change of the climates in mountain ranges and some inconsistency with general trends in global climate change. The climate variations were significantly different and positively correlated cross mountain ranges, revealing that aspects significantly affected on climate variations and these variations resulted from a larger air circulation system, which were sensitive to global climate change. We conclude that location and terrain of aspect are the main factors affecting differences in climate variation among the mountain ranges with contrasting aspects.

Speleological Investigation of the Largest Limestone Massif in Georgia (Caucasus)

Georgia is home to multiple, widespread limestone massifs with well-developed karst areas and their associated landscape features found throughout the country. Due to geological, geomorphological, and speleological characteristics of the limestone massifs in Georgia, there are developments in classical karst processes and landforms, which contain very impressive karst features, such as dolines, caves, calcite depositions and others. For example, in Georgia, the world’s deepest caves are found, such as: Krubera-2197 m;Sarma-1830 m;Pantyukhina-1508;Ilyukhina-1275 m;Kuibyshev-1110 m, and others. Of these, Krubera Cave is currently the deepest in the world. The goal of this work is to present speleological investigation of Muradi Cave, which is developed in Racha limestone massif. Muradi Cave is unique as the fact that it contains almost all types and subtypes of speleothems and sediments recorded nowadays in the caves of the Caucasus region, and the mineral aggregates found in Muradi Cave are rare for the caves of the Caucasus region. Unlike many of the hypogene caves in the region, Murdai Cave is formed from a more traditional mechanism of speleogenesis, but the influence of tectonic activity and complex hydrologic regimes led to the development of speleothems and passage morphology less common in the region and likely from hypogenic overprinting. The primary objectives of this study of Muradi Cave included undertaking important investigation in this country, to better understand the speleogenetic processes.

Petrology and Geochemistry of Basement Complex Rocks in Okom-Ita Area, Oban Massif, Southeastern Nigeria

The determination of the mineralogical composition of rocks that underlie Okom-Ita area, in Oban Massif became necessary for the interpretation of the petrogenesis and protoliths of rocks in the area. Twelve representative rock samples were selected for thin section petrography and bulk rock geochemical analysis. The results reveal that the dominant intrusive rocks in Okom-Ita area are pegmatites, quartz veins and dolerites emplaced within gneisses, schists and phyllites host rocks. The quartz veins and pegmatites are leucocratic consisting predominantly of quartz, plagioclase and subordinate amount of Muscovites. The dolerite is dark grey, fine to medium grained and texturally ophitic and consists dominantly of pyroxenes, olivine and opaques. Three varieties of gneisses were recognized: feldspathic, banded and biotite gneisses. The gneisses, schists, and phyllites are dominated by SiO2 in the range of (60% - 75%). The rocks exhibit higher molecular concentration {Al2O3 > (CaO + Na2O + K2O)}, high alkali concentration with Na2O > K2O, high Al2O3 to alkali ratios and low TiO2, CaO and MgO concentrations. These distribution trends suggest a compensation for the high silica and alumina concentrations and support a granitic protolith for the pegmatites and their host gneisses and schists. The dolerites and amphibolites are impoverished in SiO2, but relatively enriched in lime and alkali oxides. Plots in the AFM, TiO2-K2O-P2O5 and Na2O/Al2O3-K2O/Al2O3 diagrams show that the pegmatite was derived from calc-alkaline magmatic source, while the dolerite was derived from tholeiitic basalt magma.