A 5-km-thick reservoir with >380,000 km3 of magma within the ancient Earth's crust

Several recent studies have argued that large, long-lived and molten magma chambers1–10 may not occur in the shallow Earth’s crust11–23. Here we present, however, field-based observations from the Bushveld Complex24 that provide evidence to the contrary. In the eastern part of the complex, the magmatic layering was found to continuously drape across a ~4-km-high sloping step in the chamber floor. Such deposition of magmatic layering implies that the resident melt column was thicker than the stepped relief of the chamber floor. Prolonged internal differentiation within such a thick magma column is further supported by evolutionary trends in crystallization sequence and mineral compositions through the sequence. The resident melt column in the Bushveld chamber during this period is estimated to be >5-km-high in thickness and >380,000 km3 in volume. This amount of magma is three orders of magnitude larger than any known super-eruptions in the Earth’s history25 and is only comparable to the extrusive volumes of some of Earth’s large igneous provinces26. This suggests that super-large, entirely molten and long-lived magma chambers, at least occasionally, occur in the geological history of our planet. Therefore, the classical view of magma chambers as ‘big magma tanks’1–10 remains a viable research concept for some of Earth’s magmatic provinces.

Transgressive nature and chilled margins of the Upper Zone in the western Bushveld Complex, South Africa

ABSTRACT The Upper Zone of the Bushveld Complex has long been known to have formed from a major influx of magma into the chamber that caused large-scale erosion of the chamber floor cumulates. The most dramatic manifestations of this process are two major gap areas (Northern and Southern) in the western Bushveld Complex in which the Upper Zone appears to have eroded away the underlying cumulates down to the very base of the Complex. However, due to almost complete lack of outcrops in the gap areas, no direct field observations have ever been reported to confirm the transgressive nature of the Upper Zone. Here, we present for the first time such observations from the Kameelhoek chromite mine located at the margin of the Northern Gap. In the open pit we have documented several transgressive depressions (up to 40 m in width) in the orthopyroxenite and chromitites of the Lower Critical Zone that are filled in with magnetite gabbro of the Upper Zone. The magnetite gabbro is chilled against the sidewalls of the depressions, forming glassy and fine-grained textured rocks with plagioclase laths arranged in radial clusters. Mineralogically and chemically, the magnetite gabbro correlates with cumulates from the lowermost part of the Upper Zone at its normal position in the complex. Three major points that have emerged from this study are: (1) the Critical Zone has been eroded away by magma that was parental to the Upper Zone, (2) this eroding magma was not the one that initiated formation of the Pyroxenite Marker, but rather the evolved melt that replenished the chamber at some later stage, and (3) the melt was phenocryst-free and likely derived from a deep-seated staging chamber. Our study thus supports a recent notion that even during the formation of the Upper Zone, the Bushveld chamber had still been operating as an open system that was replenished by melts from deeper magma sources.

Frequency of number of roots and root canals of maxillary first premolar teeth.

Objective: To determine the frequency of the number of roots and root canals in a sample of 250 extracted maxillary first premolar teeth of patients visiting Peshawar Dental College and Hospital Khyber Pakhtunkhwa. Study Design: Cross Sectional. Setting: Department of Oral Biology, Peshawar Dental College and Hospital Khyber Pakhtunkhwa. Period: April 2016 to December 2016. Material & Methods: A total of 250 extracted human maxillary first premolars were collected from the Department of Oral & Maxillofacial Surgery, Peshawar Dental College, and Hospital Khyber Pakhtunkhwa. All teeth were visually inspected to count the number of roots. Subsequently, the access cavity was prepared, and pulp extirpated from each tooth. Endodontic explorer was used to locating the canal orifice(s) at the pulp chamber floor. Later the root canal orifices were injected with India ink to stain the canals. After that roots of teeth were sectioned at different levels to note down the number of canals. Data were analyzed using SPSS version 19. The statistical significance of the variations from mean values was considered significant if the p-value was less than 0.05. Results: Out of 250 maxillary first premolar teeth, 44.8% had one root, 40.4% had two separate and 12.8% had two fused roots. Three roots were seen in 2.0% teeth. Two root canals were present in the vast majority (70.4%), whereas one and three root canals were seen in 27.6% and 2.0% teeth, respectively. The correlation between the number of roots and root canals of maxillary first premolar teeth was highly significant. Conclusions: There was a high frequency of maxillary first premolars with two roots and two root canals.

Prevalence of Second Mesio-Buccal (Mb2) Canal in Permanent Maxillary First Molar

Objective: The aim of this study is to determine the prevalence of second mesio-buccal canal in permanent maxillary first molars. Study Design: Cross sectional study. Place and Duration: Dr Ishrat ul Ebad Khan Institute of Oral Health Sciences, Karachi during the period from February 2020 to January 2021 Patients and Methods: Three hundred and fifty cases of both genders were presented in this study. Patients were aged between 18-60years. Patients’ detailed demographics including age, sex and body mass index were recorded after taking written consent. Local anesthesia was given for isolation of rubber dam. The pulp chamber floor was clearly visualized and the access cavity was ready. The location of the MB2 channel in three phases was done. Complete data was analyzed by SPSS 22.0 version. Results: Mean age of the patients were 30.14±17.47 years with mean BMI 25.61±8.25 kg/m2. Among 350 cases, Majority of the patients 225 (64.3%) were male while the rest 125 (35.7%) were females. Majority of the patients were from age group 20-30 years and less patients were between 51-60 years old. Frequency of second mesiobuccal canal was found in 280 (80%) patients. Conclusion: We concluded in this study that prevalence of MB2 channel was reported in 80% in the initially permanent maxillary molars. Most MB2 canal apertures are distal from the main MB channel and most MB2 apertures are palatal. Key words: Permanent maxillary first molar, MB2 canals, Frequency

Management of Intracanal Separated File Fragment in a Four-Rooted Mandibular Third Molar

The success of endodontic therapy is attributed to complete arbitration of the bound entities concealed within the complexity and absolute disinfection of the root canal system, thus, deeming it mandatory to effectively negotiate and overcome the challenges posed by obstruction, either iatrogenic or anatomic. To achieve this, considerable depth of knowledge and expertise with reference to variations in root canal morphology and clinical mishap management is substantially as important as developing fine observation skills in conjunction with an appropriate armamentarium and a keen sense of determination, thereby enhancing one’s clinical acumen by several folds. In the present case, following rubber dam isolation, the temporary restoration was removed, and the remaining carious dentin was excavated. Endodontic access cavity was refined and explored with a DG-16 probe, following which three separate canal orifices were identified in the pulp chamber floor (mesiobuccal, mesiolingual, and distal). On further observation under a surgical operating microscope and continuous exploration with the DG-16 probe, a fourth canal was found in the mesial aspect of the tooth (middle mesial). With instrumentation, it was confirmed that a fractured object was indeed present at the apical third of the mesiolingual root of tooth 38. Bypassing of the fractured fragment was initiated with a size 10 SS K-file coupled with copious irrigation with 3% sodium hypochlorite. In the present case report, four distinct canals comprising 3 mesial and 1 distal canal were recognized, and the fractured instrument in one of the canals was bypassed successfully.

Chromitite layers require the existence of large, long-lived, and entirely molten magma chambers

An emerging and increasingly pervasive school of thought is that large, long-lived and largely molten magma chambers are transient to non-existent in Earth’s history1–13. These ideas attempt to supplant the classical paradigm of the ‘big magma tank’ chambers in which the melt differentiates, is replenished, and occasionally feeds the overlying volcanoes14–23. The stratiform chromitites in the Bushveld Complex – the largest magmatic body in the Earth’s crust24 – however, offers strong contest to this shifting concept. Several chromitites in this complex occur as layers up to 2 metres in thickness and more than 400 kilometres in lateral extent, implying that chromitite-forming events were chamber-wide phenomena24–27. Field relations and microtextural data, specifically the relationship of 3D coordination number and grain size, indicate that the chromitites grew as a 3D framework of touching chromite grains directly at the chamber floor from a melt saturated in chromite only28–30. Mass-balance estimates dictate that a 1 to 4 km thick column of this melt26,31,32 is required to form each of these chromitite layers. Therefore, an enormous volume of melt (>1,00,000 km3)24,25 must have been involved in the generation of all the Bushveld chromitite layers, with half of this melt being expelled from the magma chamber24,26. We therefore argue that the very existence of thick and laterally extensive chromitite layers in the Bushveld and other layered intrusions strongly buttress the classical paradigm of ‘big magma tank’ chambers.

Magmatic karst reveals dynamics of crystallization and differentiation in basaltic magma chambers

An understanding of magma chamber dynamics relies on answering three important yet highly controversial questions: where, why, and how magma chambers crystallize and differentiate. Here we report on a new natural phenomenon—the undercut-embayed chamber floor in the Bushveld Complex—which allows us to address these questions. The undercut-embayed floor is produced by magmatic karstification (i.e. erosion by dissolution) of the underlying cumulates by replenishing magmas that form basal flows on the chamber floor. This results in a few metres thick three-dimensional framework of spatially interconnected erosional remnants that separate the floor cumulates from the overlying resident melt. The basal flow in this environment is effectively cooled through the floor, inducing heterogeneous nucleation and in situ growth against much of its three-dimensional framework. The solidification front thus propagates in multiple directions from the surfaces of erosional remnants. Fractional crystallization may occur within this environment by convective removal of a compositional boundary layer from in situ growing crystals and is remarkably efficient even in very confined spaces. We propose that the way magma crystallizes and differentiates in the undercut-embayed chamber floor is likely common for the evolution of many basaltic magma chambers.

Root and canal specific features of maxillary first molars with fused roots

Background / Aim. Maxillary first molars are one of the most challenging teeth for endodontic therapy. There are certain disparities in number of roots and canals, and canal inter-relationship within the same root, particularly in those with fused roots. The aim was to evaluate ex vivo features of roots, root canals and canal walls in maxillary first molars with fused roots. Methods. Sixty-four extracted maxillary first molars with fused roots were included for cone-beam computed tomographic and microscopic studies. Tooth dimensions at the level of pulp chamber floor, number, location and distance between orifices, number and canal morphology, canal wall thickness, and features of apical foramina were examined and measured. Results. Incidence of maxillary first molars with root fusion was 17.5%, of which 60.0% was palatal fused to disto-buccal root. At the level of pulp chamber floor bucco-palatal dimension was significantly larger with 10.4 mm than mesio-distal with 7.0 mm. Four canal orifices were detected in 65.6%, with the shortest distance of 1.95 mm between mb1 and mb2. In fused roots most frequently were two or three canals strongly correlating to the number of major apical foramina. No fusion of canals was found in fused roots. The thinnest canal wall in mesio-buccal and disto-buccal fused root was mesial with 1.25 mm, and distal with 1.31 mm, while for the palatal root the thinnest was palatal wall with 1.97 mm. Conclusion. The most frequent type of fusion was between palatal and disto-buccal root. Bucco-palatal dimension at the level of pulp chamber floor was significantly larger than mesio-distal, with the shortest inter-orifice distance between mb1 and mb2 orifice. Number of canals was either two or three, strongly coinciding with the number of major apical foramina. There was no fusion of the canals in fused roots. The thinnest canal wall was either mesial or distal.

Significance of the Coronal Pulp Chamber Floor Anatomy in the Human Dentition: A Narrative Review

In root canal treatment, the foundation on which all surgical procedures are performed is a thorough knowledge of the anatomy of the pulp chamber and the root canal system. The endodontic triad comprises biomechanical preparation, microbial control and complete obturation of the root canal space. Knowledge of the pulp chamber floor anatomy is important in locating the numbers and orifices of root canals present within the tooth being root canal treated. This is particularly important while treating teeth that are heavily restored, mal-positioned, or calcified. The current review attempts to explain the complex anatomy of the pulp chamber floor and its significance in root canal treatment. CPD/Clinical Relevance: To allow the location of all root canal orifices in the pulp chamber and to perform successful root canal treatment, knowledge of pulp chamber floor anatomy is essential. The clinician should consider that, as the external morphology of the tooth varies in individuals, so does the internal morphology.