Jeofizikkulubu | Geophysics

Jeofizikkulubu | Geophysics

Scroll Down For Interesting Geophysics
Chandra Reveals the Elemental Nature of Cassiopeia A
Where do most of the elements essential for life on Earth come from? The answer: inside the furnaces of stars and the explosions that mark...
Read More
Fluid and metal sources of the Changfagou porphyry copper deposit, southern Jilin Province, NE China: Constraints from fluid inclusions and H-O-S-Pb isotope systematics
The Changfagou copper deposit, a newly discovered porphyry deposit in the southern Jilin Province, NE China, is tectonically located on the northeastern margin of the...
Read More
Archaeologists uneasy as Trump shrinks Bears Ears monument lands
Thousands of ancient Native American sites to lose protections.
Read More
Ancient weakening of Earth’s crust explains unusual intraplate earthquakes
New research reveals that mysterious intraplate seismic zones underwent significant deformation hundreds of millions of years ago.
Read More
Chandra Reveals the Elemental Nature of Cassiopeia A
Where do most of the elements essential for life on Earth come from? The answer: inside the furnaces of stars and the explosions that mark...
Read More
Fluid and metal sources of the Changfagou porphyry copper deposit, southern Jilin Province, NE China: Constraints from fluid inclusions and H-O-S-Pb isotope systematics
The Changfagou copper deposit, a newly discovered porphyry deposit in the southern Jilin Province, NE China, is tectonically located on the northeastern margin of the...
Read More
Archaeologists uneasy as Trump shrinks Bears Ears monument lands
Thousands of ancient Native American sites to lose protections.
Read More
Ancient weakening of Earth’s crust explains unusual intraplate earthquakes
New research reveals that mysterious intraplate seismic zones underwent significant deformation hundreds of millions of years ago.
Read More
Cleaning the interior of container and tank wagon
Nearly all deposits in tankers, containers and tank wagons can be removed by high-pressure water. Conventional cleaning of containers and tanks of all types is...
Read More
Mkango Announces Conditional Acceptance Of Talaxis Transaction By TSX Venture Exchange Subject Only To Shareholder Approval
London / Calgary: December 11, 2017 - Mkango Resources Ltd. (AIM/TSX-V: MKA) (the \'Company\' or \'Mkango\') is pleased to announce that the TSX Venture Exchange...
Read More
Arctic fishing, robot explorers and Chinese medicines
The week in science: 1–7 December 2017.
Read More
Wanted: academics wise to the needs of government
Funders should not support policy-relevant work that treats policy impact as an afterthought, advises Chris Tyler.
Read More

Geochemical characteristics and tectonic setting of the bimodal volcanic rocks in Sepikou region of eastern Tianshan

The Sepikou region is located in the eastern Bogda Mountains of the east Tianshan. The Bogda belt is mainly composed of Carboniferous strata, including the Lower Carboniferous Qijiaojing Formation (C1q), Upper Carboniferous Liushugou Formation (C2l), and Qijiagou Formation (C2qj). Here, we report the petrology, geochemistry, and geochronology of bimodal volcanic rocks from the Upper Carboniferous Liushugou Formation, which is widely distributed in the Sepikou region. The basalts, basaltic andesite, and keratophyre have similar petrochemical characteristics and exhibit the high-Na, low-K characteristics belonging to calc-alkalic rocks. These are characterized by the high abundance of K, Rb, Th, Ba, the depletion of HFSE (Nb, Ta, Zr, and Hf), and the slight depletion of Ti. Chondrite-normalized rare-earth elements (REE) patterns for basalts-keratophyre show right-leaning parallel curve clusters, together with a slight enrichment in light rare-earth elements (LREE) contents and low heavy rare-earth elements (HREE)/LREE ratios. The keratophyre exhibits slightly negative Eu anomalies. Compared with the basalts, the rhyolites have high alkali contents, slightly high ∑REE contents, low heavy rare-earth elements/LREE ratios, negative εSr(t) (−9.1 to −12.0), low 87Sr/86Sr initial ratio, highly positive εNd (t) (+5.3 to +6.4), and low Pb isotope ratios. The fractionated REE patterns with prominent negative Eu anomalies suggest they were chiefly derived from the mantle magma underplated basaltic body remelting from the depleted mantle source. The LA-ICP-MS analysis on zircons from quartz keratophyre and rhyolite yield similar ages of 314.9 ± 1.2 and 314.0 ± 1.1 Ma, respectively, suggest that the major bimodal volcanism took place in the Late Carboniferous epoch. The quartz keratophyre zircons, with the 176Hf/177Hf ratios of 0.282897–0.283097, have highly positive εHf (10.99–19.97) and depleted mantle model ages between 180 and 628 Ma. The mafic rocks were chiefly derived from the depleted mantle with the partial incorporation of crustal components. The bimodal volcanic rocks were formed under a continental rift setting. The rift experienced extension in the early period of the Early Carboniferous and its final closure arose after a late period of the Late Carboniferous.

Geochemical, zircon U–Pb–Hf, and whole-rock Sr–Nd isotopic study of Late Jurassic Sanming A-type granite in the Wuyi area, Fujian province, Southeast China

The Sanming pluton is the only Late Jurassic A-type granitic intrusion in the Wuyi area, west Fujian Province, Southeast China, and its formation has important implications for our understanding of the tectonic evolution of the region. The U–Pb ages of 157 ± 1 Ma and 159 ± 1.1 Ma were obtained for the pluton by zircon LA–ICP–MS analysis, which is interpreted to be the crystallization age of the Sanming pluton (i.e., Late Jurassic). The pluton has the geochemical characteristics of A-type granite, such as high K2O+Na2O contents (average 7.703 wt%), FeOT/(FeOT + MgO) ratios (average 0.85), and high 10,000 Ga/Al values and Zr + Nb + Ce + Y (380–446.1 ppm, average 419.2 ppm) contents, but relatively low CaO, Sr, and Eu contents. Zircon saturation temperatures range from 875 °C to 890 °C, also similar to other A-type granites. The (87Sr/86Sr)i ratios (0.707368–0.71102) and εNd(t) and εHf(t) values (−5.54 to −6.09, and −6.93 to −1.07, respectively), the 2-stage Nd model ages of 1.50–1.55 Ga, and 2-stage Hf model ages of 1.25–1.62 Ga, suggest the pluton was derived by extensive fractionation of melts containing both mantle materials and Mesoproterozoic crustal components. The Sanming A-type granitic pluton is younger than adakitic rocks in the region (162 Ma), suggesting a localized transition from compressional to intraplate extensional tectonics at 162–159 Ma, with mantle-derived material playing a crucial role in the formation of A-type granites in the Wuyi Mountain area. This tectonic transition is explained by localized rollback of the subducting Pacific plate.

Mineralogical characteristic of ductile–brittle shear zone in the Baguamiao gold deposit, Shaanxi Province: Implication for gold mineralization

The Baguamiao gold deposit in Fengxian County of Shaanxi Province is located in Fengtai polymetallic ore concentration area in the orogenic belt of West Qinling Mountain. It is a typical gold deposit under the control of brittle–ductile shear zone. The progressive deformation of brittle–ductile shear zone has been found to be closely associated with gold enrichment: the gold-bearing sulphides pyrrhotite and pyrite are distributed along blastobedding S0 in the undeformed area, they are developed along phyllitic foliation S1 (//S0) in the slightly deformed area, along mylonitic foliation (S2#S0), or S–C foliation in the highly deformed area, and they are enriched along rheological quartz vein (S2–L) and joint quartz vein (S3) in the highly deformed and the tectonic fluid area. Researches based on electron microprobe analysis and mineral–structure–geochemistry indicate that the characteristic metamorphic mineral assemblage of the brittle–ductile shear zone is albite–biotite–sericite–chlorite–quartz–ankerite, with diagenetic and metallogenic temperatures and pressures spanning from 350 to 450 °C and from 0.12 to 0.31 GPa, respectively. In addition, greenschist facies in intermediate temperature and intermediate and low-pressure environment is the metamorphic facies of shear zone in main period. A reconstruction of the palaeotemperature history, based on the biotite and chlorite compositional geothermometer, revealed an intermediate-temperature phase, a high-temperature phase, and a high-temperature critical phase. Biotitization tends to develop towards an oxidation phase, while chloritization is characterized by development towards a reduction phase, indicating large-scale gold enrichment and mineralization were accompanied by strong redox reactions in the ore-forming fluid.

A review of the Early Mesozoic granitoids in the Qinling Orogen: Implication for gold metallogeny

The Qinling Orogen is located between the North China and South China blocks, and considered to form by the multiple accretionary processes, being also characterized by development of voluminous magmatic intrusions as well as abundant mineral resources. Here we compile the geological, geochemical and geochronological data of the Early Mesozoic granitoids from the Qingling Orogen and attempt to constrain the Early Mesozoic tectonic evolution and mechanism of gold mineralization in this region. The Early Mesozoic granitoids are most widespread in the Qinling Orogen, especially in western part, and can be classified into S-, I-, I-A-types, with the I-type constituting the major variety. The isotopic ages of the three types granitoids are 200–222 Ma, 185–248 Ma, 210–227 Ma, respectively, indicating overlapping ages with a wide span of I-type granitoids. The S-, I-, I-A-type granitoids show obvious zonation characteristics, that is the S-type granitoids only occurred in southern South Qinling Belt, the I-type granitoids are most widespread in the western Qinling Orogen, and the I-A-type granitoids are mainly exposed in the North Qinling Belt. The S-type granitoids crystallized at relatively low temperature (800–850 °C) and deep-crustal level (ca. 8 kb) and derived mainly from partial melting of a clay-poor psammitic source. The I-type granitoids formed at high temperature (>925 °C) and pressures above the garnet-in phase boundary (>1.2 GPa) and derived from greywackes and partially igneous source. Moreover, the I-A-type granitoids probably derived from distinct sources with sufficient interaction, or common origin but underwent different degrees of crustal contamination, and generated at high temperatures (ca. 950 °C) and low pressures (1.0–0.2 GPa) conditions. These features indicate the Qinling Orogen experienced subduction, syn-collisional, and post-collisional during the Early Mesozoic, and also suggest the S-, I-, I-A-types granitoids underwent an episodic growth documenting the tectonic regime switchover at this stage. The gold deposits in the western Qinling Orogen can be classified as orogenic, Carlin-type, and Carlin-like gold deposits with the formation age of Late Triassic. The orogenic and Carlin-type gold deposits have no genetic relation to granitic magmatism, but the Carlin-like gold deposits is related to the synchronous magmatism. Combined with regional geology and metallogenic systems, we suggest that the multi-stage Qinling Orogenesis resulted in the formation of the Early Mesozoic S-, I-, I-A-type granitoids and different types of gold deposits with some characteristic differences.