Lithospheric Material Research Articles

The Effect of Using Canva-Based Media Usage on Geography Learning Outcomes of Class X Students at UNPATTI Laboratory High School

This study aims to determine the effect of using Canva digital media on the geography learning outcomes of tenth-grade students on the lithosphere material at UNPATTI Laboratory High School. This research employs an experimental method with a control group and an experimental group design. The research sample consists of 28 students divided into two groups: the control group, which used conventional learning methods, and the experimental group, which used Canva. The results of the independent t-test shown in the table indicate a significant difference between the learning outcomes of the control group and the experimental group. The Levene's Test showed an F value of 0.804 with a significance value (Sig.) of 0.378, indicating that the assumption of equal variances is acceptable. In the t-test for mean comparison, the obtained t value was -2.651 with degrees of freedom (df) of 26 for the assumption of equal variances, and 25.547 for the assumption of unequal variances. The two-sided significance value, which was less than 0.05 (0.013 and 0.014 respectively), indicates a significant difference between the two groups. The mean difference between the two groups was -5.857, showing that the learning outcomes of the control group were significantly lower than those of the experimental group. The results of the independent t-test showed a significant difference between the learning outcomes of the two groups, with the experimental group showing higher learning outcomes. These findings suggest that using Canva as a learning tool can enhance learning outcomes for tenth-grade students on lithosphere material. This study supports the literature stating that interactive technology-based learning approaches can positively impact learning outcomes. Therefore, the use of Canva in learning can be considered an effective strategy to improve educational quality.

Geochemical and temporal evolution of Indian MORB mantle revealed by the Investigator Ridge in the NE Indian Ocean

The Investigator Ridge, located along the prominent Investigator Fracture Zone in the Wharton Basin, northeast Indian Ocean, was chosen to investigate the temporal and geochemical evolution of the Indian upper mantle. We present new 40Ar/39Ar age, as well as major and trace element and Sr-Nd-Pb-Hf isotope data, from a large part of this so far scarcely sampled ridge. The 40Ar/39Ar ages range from 100.0 Ma to 64.1 Ma, and except for the two youngest samples (65.5 and 64.1 Ma) of likely Christmas Island Seamount Province (CHRISP) origin, display decreasing ages along the ridge from south to north. This pattern is consistent with the ages derived from paleomagnetic anomalies on the local oceanic crust that also decrease in age northwards and suggests an origin of the studied rocks at or near the now extinct Wharton spreading center. These ages also provide information about the displacements along the multiple Investigator Fracture Zones indicating large left-lateral as well as right-lateral offsets of the paleo spreading axis. The fracture zone also shows signs of recent tectonic reactivation. The Investigator Ridge samples are derived from a DUPAL-like mantle source similar to present-day Indian MORB. This source contains a depleted mantle type component, an enriched, moderately HIMU-like, component such as common “C” or “FOZO”, and an additional enriched component of recycled subcontinental lithospheric mantle material. In both the Investigator Ridge and CHRISP samples, the trace element and isotope compositions systematically change with age implying a temporal geochemical evolution of the Indian Mantle Domain in this region. It contained higher proportions of subcontinental lithospheric material delaminated during breakup of Gondwana and mixed with depleted upper mantle material in its early phase. With time, the source evolved in the direction of “C” or “FOZO”, which then became the dominant enriched component and is observed in the youngest samples.

UPAYA MENINGKATKAN HASIL BELAJAR KOGNITIF GEOGRAFI SISWA KELAS X MELALUI PENERAPAN SOAL EVALUASI BENTUK URAIAN DI SMAN 61 JAKARTA

This study aims to describe the efforts made through research on the application of evaluation questions in the form of descriptions in order to improve students' cognitive geography learning outcomes. Data collection was carried out for five weeks, from March to May 2023, with a total of 36 students for the experimental class group. The instrument used is a formative test of lithosphere material with 8 questions in the form of descriptions as an instrument applied to the trial application of evaluation questions in the form of descriptions to improve student learning outcomes. The method used in this research is descriptive quantitative, with experimental approach, and a pretest-posttest control group design. Based on the results of data calculation and processing, it was found that the description questions applied to the lithosphere material chapter were able to improve student learning outcomes by 7.28. And based on the data obtained from the research results, it shows that the application of evaluation questions in the form of descriptions is able to increase the percentage of completeness of student learning outcomes compared to the previous chapter, the basics of geography chapter, which uses multiple choice evaluation questions, namely from seventy percent to eighty-six percent, or by sixteen percent.

Model Pembelajaran Kooperatif Tipe Jigsaw Untuk Meningkatkan Hasil Belajar Peserta Didik Kelas X Materi Litosfer Di Sma Swasta Maharani Tahun Ajaran 2022/2023

The problem at Maharani Private High School is that teachers or educators still use conventional methods so that students become passive in class and students' low understanding of the subject of geography, lithosphere material, which still contains many concepts, makes students feel bored, lazy, and this affects the results. learning and obtained by students whose grades do not meet the standard criteria for maximum completeness. The minimum standard for completion criteria (KKM) in geography subjects at Maharani Private High School is 75. This classroom action research aims to 1) find out the application of the jigsaw type cooperative learning model, 2) to find out the development of class X students' learning outcomes regarding lithosphere materials and types of rocks after using a jigsaw type learning model. The method used in this research is classroom action research or PTK using a jigsaw type cooperative learning model for class X students with research subjects of 20 students. The location of this research is Maharani Private High School for the 2022/2023 academic year, Weliman District, Malaka Regency, East Nusa Tenggara Province. This classroom action research was carried out in two cycles consisting of four stages including planning, observation, implementation and reflection. This research data was analyzed qualitatively descriptively. The results of this research show that using the jigsaw type cooperative learning model can improve the learning outcomes of class X SMA students on lithosphere material. The research results obtained for the first cycle of student learning outcomes were 6 students who completed with a percentage of 30% and as many as 14 students who did not complete or 70% of the 20 students, meanwhile, in cycle II the students who completed experienced an increase, namely 19 students. or as many as 95% and 1 student who did not complete or only 5% in cycle II. It can be concluded that using the jigsaw type learning model can significantly improve student learning outcomes in geography subjects on lithosphere material at Maharani Private High School for the 2022/2023 academic year.

Lithospheric deformation revealed by teleseismic phases SKS PKS and SKKS splitting in the NE margin of the Tibetan plateau

The NE margin of the Tibetan plateau influenced by multiple blocks, the regional dynamic model and lithospheric deformation characteristics are still controversial. In this study, 15 years data from permanent broadband seismic stations of the seismic network in the study area were adopted for splitting analyses of teleseismic phases XKS (SKS PKS and SKKS, shortly named XKS) using a grid search method, longer observations provided each station with a large number of clear seismic phases. The results show that the fast wave directions of XKS splitting are oriented toward WNW or NW, with reference to the direction of absolute plate motion, the lithospheric deformation is dominantly driven by the asthenosphere, although there are local variations. On both sides of the Haiyuan fault zone, there is a noticeable variation in lithospheric azimuthal anisotropy, further enhances the possibility that it is an extended boundary of the Tibetan plateau. Rheological anisotropic features on the western side of the Ordos block emphasize the obstruction of the rigid Ordos lithosphere. The crust and mantle seem to be coupled below the Qinling orogen, possibly related to the lateral movement of lithospheric material. However, in the Hexi corridor, there may be layered anisotropy within the lithosphere, which is inferred to relate to the subductions of the Alxa block and the Qilian orogen. The thicker lithosphere on the southern margin of the Alxa block may influence the asthenospheric flow. In addition, anisotropy results at the southeastern edge of the Alxa block and the Yinchuan graben reflect the possibility that the lithosphere may be characterized by a combination of horizontal and vertical movements. These results have greatly improved our understanding of the dynamic models and lithospheric deformation characteristics of the northeastern margin of the Tibetan plateau and adjacent areas.

Relationship between the migration of crustal material, normal faulting, and gneiss domes in the vicinity of the Dinggye region, central part of the Tethys–Himalaya terrane: Insights from the 3-D electrical structure

The Dinggye region, in the central part of the Himalayan orogenic belt, includes the southern part of the Xainza-Dinggye rift and the Mabja Gneiss Dome with leucogranite cores. Previous studies of gneiss domes in this region report the existence of channel flow processes or tectonic exhumation, in addition to partial melting of orogenic mid-crust. However, the relationship between the crustal migration of materials and the north-south-trending normal rifts remains largely unexplored. In this work, we generate a new 3-D electrical resistivity model from an array of magnetotelluric data in the Dinggye region and examine it in addition to other electrical resistivity models to the north and east from previous works. By comparing the geophysical models with available geological and geochemical evidence, we find a clear relationship between the electrical resistivity structure, the presence of gneiss domes, north-south-trending normal rifting, and deep plunging subduction which is related to the source of Helium isotopes (crustal or mantle origin). Overall, the results suggest that the southern migration of lithospheric materials likely contributed to the evolution of the rifts in the Tethys-Himalaya terrane, which also may have been influenced by uplifting and cooling of gneiss domes. The models are consistent with tearing of the Indian lithosphere beneath the Xainza-Dinggye rift and other adjacent rifts. Additionally, the difference in the electrical structure related to the Indian crust along the east-west direction likely results from the exhumation of the continental slab, metamorphism in the Tethys-Himalaya terrane, and southern extrusion of materials in the Lhasa terrane.

Major, trace element and Sr-Nd isotope evidence for a sublithospheric mantle source for the Umkondo large igneous province

The Mesoproterozoic (1.11 Ga) Umkondo large igneous province (LIP) in southern Africa and Antarctica was emplaced in < 5 Myr and is dominated by low-Ti tholeiitic doleritic-gabbroic sills. It is of particular interest because it is the least studied LIP in southern Africa with both sublithospheric and lithospheric mantle sources proposed and it coincides with the early assembly of Rodinia, so it has importance in understanding the nature of magmatism and tectonics in and around the Kalahari craton during the Mesoproterozoic. In this study, we compiled a large database of existing (∼750) and new (∼100) major and trace element data for the Umkondo province, as well as 42 new Sr-Nd isotopic measurements, to provide constraints on its magma sources and geochemical evolution. Major element compositional variations in the low-Ti tholeiites are explained by low-pressure (1 kbar) three-phase fractional crystallisation (olivine, clinopyroxene and plagioclase) of a parent magma with ∼ 10 wt.% MgO in oxidising conditions (QFM + 1). Inverse models show that the low-Ti tholeiitic magmas were derived as residual melts after the crystallization of 12%–33% olivine from primary komatiitic-basaltic magmas (up to ∼ 20 wt.% MgO) in equilibrium with mantle olivine (Fo90). Low Sm/Yb and TiO2/Yb-Nb/Yb indicate that the primary magmas were derived by 2%–20% shallow (40–50 km) partial melting of spinel lherzolite. High Sm/Yb is restricted to dyke swarms and may imply limited magma production from deeper (up to ∼ 70 km) garnet lherzolite-like sources. The low-Ti tholeiites of the Umkondo province are enriched in large ion lithophile elements (Rb-Sr-Cs-K) and depleted in high-field strength elements (Zr-Hf-Nb-Ta), indicating the involvement of crustal material and/or the subcontinental lithospheric mantle. This is supported by covariations in Th/Nb, Nb/Yb, Nb/La and Ce/Sm with generally negative ΔNb. Sr-Nd isotopes lend support to the notion that the Umkondo magmas were derived from depleted and/or enriched sublithospheric mantle sources and subsequently contaminated by enriched lithospheric material during emplacement (initial (at 1.11 Ga) 87Sr/86Sr between 0.704820 and 0.737464 and εNd between −8.9 and +5.3). The Vredefort sills are significant as they display the most depleted Sr-Nd isotopic signatures (average initial 87Sr/86Sr of 0.705342 and average εNd of 0.4) and are the least contaminated magma suite in the Umkondo province. Because of (i) the large volume of low-Ti magmas, (ii) evidence of a primary hot and MgO-rich (komatiitic) magma, and (iii) the short duration of magmatism, we suggest that the Umkondo province was formed by plume-induced melting of the sublithospheric mantle beneath the Kalahari craton in an extensional setting. This contrasts with previous suggestions that the heat source developed in response to the “thermal insulation” of the mantle beneath a thickened Kalahari craton in the absence of a mantle plume. There is further evidence from the elevated Zn/Fe that the sublithospheric mantle was lithologically heterogeneous and consisted of mixed peridotite and pyroxenite domains. There is a general lack of ultramafic cumulates in the low-Ti magma suite that may imply there was deeper ponding and storage of the primary magmas that fractionated large quantities of ultramafic rocks. There is also a paucity of high-Ti rocks in the Umkondo province that may reflect limited direct melting of the lithospheric mantle or that they are simply not as well-preserved in this province compared to the Karoo province. The similar trace element and Sr-Nd isotopic compositions of the Umkondo sills in southern Africa with the Borgmassivet sills in Antarctica support the concept that the Kalahari craton and Grunehogna terrane were adjoined at 1.11 Ga. The timing of the Umkondo province indicates there was localised lithospheric extension and upwelling asthenospheric mantle during a time of dominantly compressional tectonics on Earth at the end of the ‘boring billion’.

Penerapan Model Pembelajaran Inkuiri terhadap Hasil Belajar Siswa pada Mata Pelajaran Geografi

The purpose of this study was to determine how the application of the inquiry learning model to student learning outcomes in Geography subjects at SMA Negeri 5 Halmahera Utara. Non-randomized control group pretest and posttest design were used in the research method, which is a quasi-experimental approach. The findings show the strong influence of the inquiry learning model on student learning outcomes for lithosphere material in the subject of Geography. This shows that the results of the posttest data analysis test using a t-test with a significance threshold of 0.05, where tcount &gt; ttable is 14.91 &gt; 1.76, is significant. Based on observations, the application of the inquiry learning model in the experimental class compared to conventional learning, its application was at a very good level of 93%.

An Approach to Determine of the Formation Stages of Volcanism Using Natural Gamma-Ray Spectrometer from Geophysical Methods (Example of Gölcük Volcanism)

Gölcük Caldera is in the Isparta Angle, which is an interesting tectonic structure in Southwest Anatolia. This caldera is formed as a result of back-arc volcanism associated with the northward subduction zone of the African plate under the Eurasian Plate during the Tertiary. It attracts the attention of many researchers with its tectonic and volcanic structure. In this article, the results of in situ natural gamma radiation measurements made in the caldera are evaluated. In the study, radioactive element (Potassium (%K), Uranium (eU), and Thorium (eTh)) contents of volcanics were measured in situ with the portable gamma-ray spectrometer, which is effectively used in Geophysical Engineering. The changes in natural gamma radiation of alkaline volcanic are presented with maps. When these maps are examined, it is understood that K%, U-ppm and Th-ppm concentrations of Gölcük volcanic are higher than the world average values. The high potassium concentration draws even more attention. The high potassium content indicates that the local volcanic are ultrapotassic and contain lithospheric materials. In addition, since the radioactive element concentration will reflect the magmatic development, the volcanic stages in the region have been tried to be determined. The number of these stages was determined from the curves of the radioactive data from a purely geophysical engineering (numerical) point of view, and the study area was interpreted as consisting of three different phases. This finding is supported by the results of the articles on the aging studies of the samples taken as a result of observations. In addition to these, the ranges of radioactive elements belonging to these stages were determined.

Hot mantle upwelling and Mesozoic mineralization in Southeast China

Our study region is located in the Cathaysia block (CB), Southeast China. The most significant feature of the CB is the widespread Mesozoic magmatism and poly-metallic mineralization. However, there is still no consensus on their genesis and related tectonic processes. In this study, we determine high-resolution (0.3° in the horizontal direction) tomographic images of Vp and Vs and Vp/Vs ratio in the crust and upper mantle using 6773 P-wave and 4526 S-wave travel-time data of teleseismic events recorded by a broadband linear seismic array. The array was deployed by our team in the middle part of the CB, consisting of 81 portable stations with an interval of 5–8 km. Our tomographic results reveal two obvious low-velocity (low-V) zones with high Vp/Vs ratio (high-σ) beneath the Nanling ore belt and the Wuyishan terrane, which may reflect magmatic channels formed by partial melting that may provide heat for metal mineralization. Two high-V anomalies with low-σ are located beneath the western Wuyishan terrane and the eastern CB, which may represent refractory lithosphere or remnants of delaminated lithospheric material caused by underplating of the magma due to the subduction of the paleo-Pacific plate and its following rollback. There exists an anomaly with low-Vp, high-Vs and low-σ at depths of 150–300 km beneath the western Wuyishan terrane, which may be related to the reserved trace of magmatic conduits. On the basis of the tomographic results, we propose a geodynamic model to explain the deep mechanism of mineralization beneath the CB.

Genesis and source affinities of heterogeneous ultramafic rocks in the North Kongling Complex, Yangtze craton: Architecture of a Paleoproterozoic accretionary orogen

Ultramafic massifs are minor but meaningful components of orogens because they record the mantle properties and the processes of plate generation, subduction, accretion, and collision, thus providing key information about crust-mantle interaction processes and the evolution of orogens. Here, we present an integrated study of field observations, whole-rock and mineral geochemistry, zircon U-Pb ages, and whole-rock Sm-Nd and Re-Os isotopes for serpentinized harzburgites and olivine pyroxenites from the Paleoproterozoic Shuiyuesi mélange belt, North Kongling Complex, to constrain the tectonic evolution of the Yangtze craton, South China. The serpentinized harzburgites are characterized by enrichment of light rare earth elements (LREEs) and negative εNd(t) (−4.3 to −3.9) values, but they have high olivine Mg# (91.7−93.1) and very low Re contents (&amp;lt;0.09 ppb) and negative γOs(t) (−5.1 to −4.0) values. The Archean Re-Os model ages (TRD = 2.82 Ga) of the harzburgites that have the most depleted Re-Os isotope composition represent estimates for the age of the initial melt extraction. Metasomatic zircons from the serpentinized harzburgites yield a weighted average age of ca. 2.04 Ga, which is interpreted to represent the age of metasomatism during a subduction event. These geochemical and isotopic features and geochronologic results suggest that the protolith of the serpentinized harzburgites in the North Kongling Complex originated as fragments of late Mesoarchean (ca. 2.82 Ga) subcontinental lithospheric mantle and experienced melt/fluid metasomatism in a subarc mantle wedge at 2.04 Ga. The olivine pyroxenites are cumulates, and they are characterized by high MgO, Ni, and Cr contents and depleted to slightly enriched LREEs but depletion in high field strength elements (HFSEs). They have positive εNd(t) (+2.0 to +6.6) values and Paleoproterozoic Nd model ages (2.41−2.05 Ga), suggesting that the olivine pyroxenites were derived from a Paleoproterozoic depleted mantle source. Metamorphic zircons from the olivine pyroxenites indicate subsequent metamorphism at 2.0 Ga, in response to a collision. The olivine pyroxenites together with the metabasites in the Shuiyuesi mélange belt represent the dismembered fragments of oceanic lithosphere that formed in a suprasubduction zone during the Paleoproterozoic. Combined with the Archean and Paleoproterozoic rocks in the North Kongling Complex, it appears that the Mesoarchean subcontinental lithospheric mantle peridotites and Paleoproterozoic ophiolitic rocks were simultaneously accreted during a Paleoproterozoic orogenic event. We further propose that a subduction channel may have played an important role in the architecture of the accretionary orogen, in which both oceanic lithospheric materials and subcontinental lithospheric mantle wedge materials would have been simultaneously scraped off and accreted during slab subduction-accretion.

The Development of Mobile Geography Virtual Laboratory for Rock and Soil Practicum Studies

The concept of concrete lithosphere material has limitations in being verbally stimulated by the teacher, so students have difficulty understanding the material. During the learning process, lithosphere material is rarely carried out in practicum activities due to the lack of media that can involve students directly. This study aims to produce, measure feasibility, and determine the effectiveness of mobile geography virtual laboratory learning media. This research was included in R&amp;D research by adopting a 4-D development model. The results obtained, namely the Mobile Geography Virtual Laboratory media, are feasible and effectively used in rock and soil practicum activities. The results of this research can be an innovative solution for geography learning, especially in adequately supporting the implementation of practicum activities so that students can become more active and independent.

Paleocene–Miocene topographic and tectonic evolution of the northern central Andean plateau, southern Peru

The Paleocene–Miocene sedimentary successions along the Western Cordillera – Altiplano Plateau margin in southern Peru record the growth history of the northern Altiplano Plateau and the development of the foreland basin system. We evaluate the paleoelevation history of the northern Altiplano Plateau for the period of primary upper crustal shortening (i.e., Paleocene–Miocene) to determine the amount of shortening-related surface uplift. We provide new apatite fission-track and tuff zircon U–Pb ages to add to the existing age models of the strata. We further calculate the first-order approximation of paleoelevations of these formations from paleo-meteoric water δ18Omw values reconstructed from authigenic carbonate δ18Oc. The calculations show that surface elevations increased by more than 1 km along with the basin development from backbulge and foredeep to wedge-top and hinterland basins. The calculated paleoelevation of 1.8–2.4 km at the end of contractional deformation during the late Miocene indicates that a rapid surface uplift of more than 1.5 km is required to attain the modern high elevations. It is further inferred that this post-late Miocene surface uplift was probably associated with the lower crustal flow and ensuing convective removal of lower lithosphere materials.

Remnants of the amalgamation of the east and west Cathaysia blocks revealed by a short-period dense nodal array

The Cathaysia block located at the southeast South China block (SCB) is considered formed by the amalgamation of the east and west Cathaysia blocks along the Gaoyao–Huilai and Zhenghe–Dapu deep faults (here referred as GHF and ZDF, respectively). Although the extension of the ZDF to the northeast, which represents the amalgamation of the two sub-blocks has been confirmed, the development of the GHF to the southwest remains to be verified. To better constrain the detailed deep structure beneath the southwest Cathaysia, which hold great significance for revealing the evolution of the SCB, a linear seismic array with 331 nodal geophones was deployed across the Sanshui basin (SSB). Combining with the regional 10 permanent stations (PA), we obtained two profiles with teleseismic P-wave receiver function stacking. The most obvious feature in our results is the ascending Moho towards the coastal area, which is consistent with the passive margin continental and extensional tectonic setting. The stacking profile from the dense nodal array (DNA) shows that the Moho is offset beneath the transition zone of the Nanling orogeny and SSB. We deduce that this offset may be casued by the deep extension of the GHF, which represents the remnants of the amalgamation of the Cathaysia block. From the other evidences, we infer that the widespread and early erupted felsic magmas in the SSB may have resulted from lithospheric materials that were squeezed out to the surface. The relative higher Bouguer gravity and heat flow support the consolidation of magmas and the residual warm state in the shallow crustal scale beneath the SSB. The sporadic basaltic magmas in the middle SSB may have a close relation to deep extension of the GHF, which serves as a channel for upwelling hot materials.

Slip distribution and block rotation of the Indo-South China region inferred from GNSS analyses

Indo-South China lying between the Indian Plate and the rigid South China Block is characterized by intense crustal deformation with severe seismic hazards. How deformation is partitioned through slip on various structural features provides key insights into understanding the regional geodynamic processes. Based on the up-to-date GPS velocity data together with the existing active tectonic, seismological, and geophysical data, we find that the relative motion between India and South China is mainly accommodated by two parts: ∼47 mm/yr dextral slip and 15–18 mm/yr contraction to the west of the Shan Plateau, and ∼ 10 mm/yr sinistral slip and ∼ 10 mm/yr extension to the east of it. The Burmese Range takes up ∼ 22 mm/yr dextral slip and 10–13 mm/yr contraction, while the Sagaing Fault accommodates ∼ 18 mm/yr dextral slip and 5–6 mm/yr contraction. The Shan Plateau Shear Zone absorbs ∼ 8 mm/yr dextral slip and 5–6 mm/yr extension. The Chuandian Terrane from east of the Red River Fault to the Xiaojiang Fault manifests 8–10 mm/yr sinistral slip and 5–6 mm/yr extension. The block motion inversion reveals that the clockwise rotation and deformation are caused by the northeastward motion of the India Plate and the clockwise lithospheric flow around the Eastern Himalayan Syntaxis. The Shan Plateau Shear Zone may be a newly formed dextral shear zone at depth of the middle and lower crust, driving the sinistral slip and extension along the ENE-trending faults in upper crustal level. The Shan Plateau Shear Zone might have replaced the Red River Fault as the western boundary to cause the southeastward coherent movement of the Chuandian Terrane. The complex pattern of active tectonic deformation in the region results from interactions among hyper-oblique subduction beneath the Burmese Range, clockwise rotation of lithospheric material around the Eastern Himalayan Syntaxis, and the apparently rigid Sundaland Block separating the two systems in between.

Радиоизотопные исследования позднекайнозойских вулканических пород Азии и Северной Америки: источники вулканизма глобального, регионального и локального значения

Of global importance are sources of Late Cenozoic volcanic rocks, indicated by fast and slow anomalies of the lower mantle: ASITA, SOPITA, AFITA, and NAITA. ASITA characterizes the LOMU–ELMU protomantle melt anomalies of the lower mantle high velocity skeleton of Asia during the early mantle geodynamic epoch. SOPITA and AFITA are marked by the HIMU plume component, which was generated in the low-velocity lower mantle of the South Pacific and Africa during the middle mantle geodynamic epoch, about 2 Ga. NAITA denotes processes of generation of the North American high-velocity lower-mantle anomaly in the late geodynamic epoch. Of regional importance are sub-lithospheric sources that are characterized by a common geochemical structure of volcanic rocks of large volcanic regions, formed due to the evolution of homogeneous proto-mantle deep reservoirs. An example is sources of the Wulanhada-Hannuoba and Abaga-Dariganga volcanic regions, marking the spatial transition from the LOMU proto-mantle reservoir of the former to the ELMU one of the latter. Local sources of volcanoes are displayed in limited volumes of melts from the heterogeneous lithosphere. An example is sources of the Wudalianchi volcanic field, on which, at first, in the time interval of 2.5–0.8 Ma, the material of the Laoshantou and Gelaqiu sources with a common age of 1.88 Ga occurred, and then, during the spatial-temporal evolution of volcanism in the last 0.6 Ma, the material from these sources was mixed with a younger lithospheric material.

The nature and origin of cratons constrained by their surface geology

AbstractCratons, defined by their resistance to deformation, are guardians of crustal and lithospheric material over billion-year time scales. Archean and Proterozoic rocks can be found in many places on earth, but not all of them represent cratonic areas. Some of these old terrains, inappropriately termed “cratons” by some, have been parts of mobile belts and have experienced widespread deformations in response to mantle-plume-generated thermal weakening, uplift and consequent extension and/or various plate boundary deformations well into the Phanerozoic.It is a common misconception that cratons consist only of metamorphosed crystalline rocks at their surface, as shown by the indiscriminate designation of them by many as “shields.” Our compilation shows that this conviction is not completely true. Some recent models argue that craton formation results from crustal thickening caused by shortening and subsequent removal of the upper crust by erosion. This process would expose a high-grade metamorphic crust at the surface, but greenschist-grade metamorphic rocks and even unmetamorphosed supracrustal sedimentary rocks are widespread on some cratonic surfaces today, showing that craton formation does not require total removal of the upper crust. Instead, the granulitization of the roots of arcs may have been responsible for weighing down the collided and thickened pieces and keeping their top surfaces usually near sea level.In this study, we review the nature and origin of cratons on four well-studied examples. The Superior Province (the Canadian Shield), the Barberton Mountain (Kaapvaal province, South Africa), and the Yilgarn province (Western Australia) show the diversity of rocks with different origin and metamorphic degree at their surface. These fairly extensive examples are chosen because they are typical. It would have been impractical to review the entire extant cratonic surfaces on earth today. We chose the inappropriately named North China “Craton” to discuss the requirements to be classified as a craton.

Laramide structure of southeastern Arizona: Role of basement-cored uplifts in shallow-angle subduction

AbstractLaramide reverse faults in southeastern Arizona commonly are obscured by mid- to late Cenozoic extension and subsequent cover, resulting in debate about their configuration and origin. A new mid-Cenozoic paleogeologic map depicts the structural configuration before extension, and new structural reconstructions characterize Laramide shortening in terms of structural style, magnitude, evolution, and timing.Reverse faults restore to moderate to high angles, are associated with fault-propagation folds, and involve significant basement and thus constitute thick-skinned deformation. The paleogeologic map suggests several major basement-cored block uplifts, many of which are newly identified. The largest uplifts may measure 150 km along strike, similar to those in the classic Laramide province of Wyoming and Colorado. Estimated shortening across the central study area is 14% or 23 km, whereas it is only 5% (9 km) to the north and 11% (12 km) to the south. Shortening by this mechanism is inadequate to explain previous estimates of crustal thickening in the region (∼50–60 km). Therefore, magmatic underplating, lower-crustal flow, or underplating of trench sediments and lithospheric material also may have contributed to thickening. Shortening largely occurred from 86 Ma to 64 Ma and possibly as late as 53 Ma, with initiation being younger to the northeast or north. Integration with data from southwestern New Mexico implies complex geometry for the subducting flat slab. Finally, reverse faults generally do not appear to have reactivated older faults, as previously suggested, primarily because reverse faults have associated fault-propagation folds in rocks that predate supposed reactivated structures.

Magmatic evolution of Low-Ti lavas in the southern Paraná-Etendeka Large Igneous Province

The southern section of the Paraná-Etendeka large igneous province exposes a sequence of heterogeneous Low-Ti lava packages that range compositionally from olivine tholeiites to rhyolites. The recent advances in the volcanic stratigraphy provide a high-resolution framework that constrains the spatial and temporal evolution of the lava sequence. The stratigraphy is formed by Low-Ti lavas, separated in four volcanic units, namely: Torres, Vale do Sol, Palmas and Esmeralda. Our data shows that individual volcanic units can be separated chemically and represent distinct batches of magma. The composition of erupted lavas is mostly controlled by a complex interplay between source composition and crystallization (±assimilation) within the crust. The magmatic plumbing system evolved gradually from the onset, towards the climax and waning phase of magmatism. LIP onset is composed by more primitive (MgO > 5%) pahoehoe basalt lava flows of the Torres Formation. These low-volume eruptions were fed by a poorly connected magmatic plumbing system focused within the lower crust. Geochemical evidence suggests that the parental basalts of Torres Formation were derived from picritic primary magmas that have evolved by fractional crystallization and assimilation of enriched lithospheric materials. The main phase of magmatism is formed by thick (>20 m), tabular, crystal-poor lavas with evolved composition, including the basaltic andesite of the Vale do Sol Formation and silicic rocks of the Palmas Formation. These large volume eruptions were formed by extensive fractional crystallization (+assimilation) of precursor basaltic magmas and directly fed by shallow magma chambers within the upper crust. The waning phase of magmatism, recorded in the Esmeralda Formation basalts-basaltic andesite, is marked by low-volume Hawaiian-like eruptions of compound lava flows at the surface and the retraction of the magmatic plumbing system at depth. These lavas also mark a shift towards more primitive (asthenospheric) compositions and the shallowing of mantle melting, reflecting the progressive extension of lithosphere during magmatism. For the Low-Ti lava sequence of the Paraná-Etendeka, the surface expression and composition of lava fields are directly controlled by crystallization (+assimilation) processes, and these petrological processes can account for broad geochemical variations within large igneous provinces.

Do the 85°E Ridge and Conrad Rise form a hotspot track crossing the Indian Ocean?

Age-progressive volcanic chains are generally considered as surface expressions of deep-rooted mantle plumes, whereas non-age progressive volcanic groups or solitary volcanic edifices are generally attributed to shallow sources. The Buried Hills, Partly Buried Hills, Afanasy Nikitin Rise and newly discovered Southern Seamount Chain, located between the Kerguelen and Reunion hotspot tracks in the Indian Ocean, form the curved and discontinuous 85°E volcanic track. With the exception of the Afanasy Nikitin Rise, characterized by the most enriched mantle one (EMI) compositions in an ocean basin, no other parts of this volcanic track have been previously sampled. Although some models favor a hotspot origin for the 85°E Ridge track associated with the Crozet, Marion or Conrad Rise plumes, its origin remains highly controversial. We report new 40Ar/39Ar age and geochemical (major, trace element and Sr-Nd-Pb-Hf isotope) data from the 85°E Ridge. Our age data display a progression of decreasing ages (82–66 Ma) from the north to south, suggesting formation by a relatively stationary sub-lithospheric melt anomaly. The geochemistry of the 85°E Ridge can be explained by mixing of Indian-type plume material with Indian mid-ocean-ridge basalt (MORB) and detached continental lithospheric (mantle and/or lower crustal) material in the upper mantle. Plate reconstructions demonstrate that the southern portion of the 85°E Ridge and Conrad Rise could be derived from the Conrad Rise hotspot/plume. A weak, pulsating mantle plume could explain the weak morphological expression and intermittent nature of this hotspot track, compared to the Reunion and Kerguelen tracks.