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.

The Confirmation of the Neoproterozoic Langshan Group in Inner Mongolia and Its Significance

There is a large Mesoproterozoic rift at the northern margin of North China Craton （NCC）, and one of China＇s most important metallogenic belts, the Langshan-Zhaertai Shan-Bayan Obo mesoproterozoic metallogenic belt is just located in this rift. This metallogenic belt contains some large or ultra-large ore deposits, such as the Bayan Obo iron deposits and ultra-large rare earth deposits, and the large Dongshengmiao Cu-Pb-Zn sulphide deposits.

Formation of the Neoproterozoic Rifting Depression Groups of the Tarim Basin and its Hydrocarbon Potential: Responded to the Initial Opening of the Proto-Tethy Ocean

The largest and superimposed Tarim basin developed on the one of the three bigger craton, Tarim Craton, in China.The early Paleozoic is the heyday of its development and cratonization, and then changes to the different property basin. The reserved sedimentary strata of Neoproterozoicare recognized mainly in the local of outcrops periphery orogenic belts, but drilling core in the basin reveals them seldom. The proto-type of the initial Tarim Basinis always a mystery. The vast desert, hugethickness of sedimentary strata, multiple tectonic movements, and a low quality of deep data are the keys to getting to know him. We comprehensive field outcrops, wells, seismic reflection profiles with higher SNRs and aeromagnetic data, recognized about 20 normal fault-controlled rifting depressions of the Cryogenian and Ediacaran, which scattered throughout the basin, and developed on the Precambrian metamorphic and crystalline basement. The structural framework is clearly different from that of the overlying Phanerozoic. The rifting depressions consist of mainly half grabens, symmetrical troughs and horst-grabens. From the northeast to southwest of the basin, they are divided into three rifting depression groups(RDG)with the WNW, ENE, and NW-trends that are mainly controlled by normal faults. From the Cryogenian to Ediacaran, most of the main inherited faults to active and eventually ceased at the end of the Ediacaran or Early Cambrian, while subsidence centers appeared and migrated eastward along the faults. They formed under the NNESSW oriented and NNW-SSE-oriented extensional paleo-stress fields(relative to the present) during the Neoproterozoic, and were accompanied by clockwise shearing. According to the analysis of the activities of syn-sedimentary faults, filling sediments, magmatic events, and coordination with aeromagnetic anomalies, the tectonic properties of the fault depressions are different and are primarily continental rifts or intra-continental fault-controlled basins. The formation of the rifting depression was associated with the initial opening of the South Altun-West Kunlun Ocean and the South Tianshan Ocean, which were located at the northern and southern margins of the Tarim Block, respectively, in response to the break-up of the Supercontinent Rodinia and the initial opening of the Proto-Tethys Ocean.Inthe RDG developedfluvial, shallow marine and carbonate platform facies, accompanied with multiple phases of magma activities and glaciations during the Cryogenian and Ediacaran. The structural architectures of interfaces between the Neoproterozoic and Cambrian are mainly angular and parallel unconformities in the RDG. Over the parallel unconformities in the RDGs are beneficial for the organic-rich and/or phosphorites of the Yuertus Formation of the Lower Cambrian. The main fault belts of RDGs also controlled the small platform margin and slope break belt of in the Cambrian. The Neoproterozoic and the Lower Cambrian petroleum systems of the basin might be controlled by the RDGs in the initiation of the Tarimcraton.

Geochemistry and Tectonic Settings of Felsic Dykes in the Neoproterozoic Nagar Parkar Igneous Complex, SE Sindh, Pakistan

The Nagar Parkar complex consists of Neoproterozoic igneous and metamorphic rocks dissected by episodic mafic and felsic dykes.The latter can be classified broadly into porphyritic felsic dykes and aplitic felsic dykes(minor)

Chemical Variation of Chromian Spinel Compositions in a Serpentinized Peridotites: Implications for Evolution of the Neoproterozoic Ophiolites

Tectonic setting of the Neoproterozoic ophiolites is poorly understood.Because of extensive serpentinization/metamorphism in the mantle section,accessory chromian spinel has been used as an important geotectonic indicator.