Basement control on dyke distribution in Large Igneous Provinces: Case study of the Karoo triple junction.

Continental flood basalts consist of vast quantities of lava, sills and giant dyke swarms that are associated with continental break-up. The commonly radiating geometry of dyke swarms in these provinces is generally interpreted as the result of the stress regime that affected the lithosphere during the initial stage of continental break-up or as the result of plume impact. On the other hand, structures in the basement may also control dyke orientations, though such control has not previously been documented. In order to test the role of pre-dyke structures, we investigated four major putative Karoo-aged dyke swarms that taken together represent a giant radiating dyke swarm (the so-called "triple-junction") ascribed to the Jurassic Karoo continental flood basalt (> 3x10 6 km2; southern Africa). One of the best tests to discriminate between neoformed and inherited dyke orientation is to detect Precambrian dykes in the Jurassic swarms. Accordingly, we efficiently distinguished between Jurassic and Precambrian dykes using abbreviated low resolution, 40Ar/39Ar incremental heating schedules. Save-Limpopo dyke swarm samples (n = 19) yield either apparent Proterozoic (728-1683 Ma) or Mesozoic (131-179 Ma) integrated ages; the Olifants River swarm (n = 20) includes only Proterozoic (851-1731 Ma) and Archaean (2470-2872 Ma) dykes. The single age obtained on one N-S striking dyke (1464 Ma) suggests that the Lebombo dyke swarm includes Proterozoic dykes in the basement as well. These dates demonstrate the existence of pre-Karoo dykes in these swarms as previously hypothesized without supporting age data.In addition, aeromagnetic and air-photo interpretations indicate that: (1) dyke emplacement was largely controlled by major discontinuities such as the Zimbabwe and Kaapvaal craton boundaries, the orientation of the Limpopo mobile belt, and other pre-dyke structures including shear zones and (2) considering its polygenetic, pre-Mesozoic origin, the Olif ants River dyke swarm cannot be considered part of the Karoo magmatic event.This study, along with previous results obtained on the Okavango dyke swarm, shows that the apparent "triple junction" formed by radiating dyke swarms is not a Jurassic structure; rather, it reflects weakened lithospheric pathways that have controlled dyke orientations over hundreds of millions of years. One consequence is that the "triple-junction" geometry can no longer be unambiguously used as a mantle plume marker as previously proposed, although it does not preclude the possible existence of a mantle plume. More generally, we suggest that most Phanerozoic dyke swarms (including triple junctions) related to continental flood basalts were probably controlled in part by pre-existing lithospheric discontinuities

Schizotypy, childhood trauma and brain morphometry

Background: Childhood trauma confers risk for psychosis and is associated with increased ‘schizotypy’ (a multi-dimensional construct reflecting risk for psychosis in the general population). Structural brain alterations are associated with both childhood trauma and schizotypy, but the potential role of trauma exposure in moderating associations between schizotypy and brain morphology has yet to be determined. Methods: Participants were 160 healthy individuals (mean age: 40.08 years, SD = 13.64, range 18–64; 52.5% female). Childhood trauma exposure was assessed using the Childhood Adversity Questionnaire, and schizotypy was assessed using the Schizotypal Personality Questionnaire. Univariate voxel-based morphometry and multivariate analyses of grey matter volume covariation (GMC; derived from independent component analysis) were performed to determine the main effects of schizotypy, trauma exposure and their interaction on these indices of grey matter volume. Moderation analyses were performed following significant interaction. Results: Levels of schizotypy, in particular the Cognitive-Perceptual and Interpersonal dimensions, were negatively associated with GMC in the striatum, the hippocampus/parahippocampal gyrus, thalamus and insulae. Trauma exposure was negatively associated with GMC of the middle frontal gyrus and parietal lobule, while negatively associated with GMC in the cerebellum. Levels of schizotypy (total scores, and the cognitive-perceptual dimension) were negatively associated with striatal GMC in individuals not exposed to trauma, but not in those exposed to trauma. Conclusions: Schizotypy and childhood trauma were independently associated with changes of grey matter in brain regions critical for cognition and social cognition. In individuals not exposed to trauma, increased schizotypy was associated with decreased striatal and limbic grey matter

Familial clustering of birth risk for adverse childhood outcomes

Objective: To identify classes of children exposed to distinct clusters of perinatal and familial risk factors at the time of birth, and examine relationships between class membership and a variety of adverse outcomes in childhood. Design: A prospective longitudinal study of children (and their parents) born between 2002 and 2004 and who have been followed-up until 12–13 years of age. A combination of latent class analysis and logistic regression analyses were used. Results: Adverse developmental, social, and mental health outcomes in early and middle childhood were greatest for children with ‘pervasive familial risk’ (i.e., parental mental illness, parental criminality, and perinatal risk factors) at the time of birth; some associations were stronger among girls. Conclusion: Pervasive exposure to multiple risk factors in the pre- and perinatal period increases the risk of adverse outcomes in childhood. Future interventions should tailor strategies to address unique combinations of adverse risk exposures in vulnerable families

Lithospheric mantle evolution monitored by overlapping large igneous provinces: case study in southern Africa

Most of the studies on the large igneous provinces (LIPs) focus on Phanerozoic times, and in particular, thoserelated to the disruption of Pangea (e.g. CAMP, Karoo, Parana–Etendeka) while Precambrian LIPs (e.g.Ventersdorpf, Fortescue) remain less studied. Although the investigation of Precambrian LIPs is difficultbecause they are relatively poorly preserved, assessment of their geochemical characteristics in parallel withyounger overlapping LIP is fundamental for monitoring the evolution of the mantle composition through time.Recent 40Ar/39Ar dating of the Okavango giant dyke swarm (and related sills) in southern Africa showed that~90% of the dykes were emplaced at 179±1Ma and belong to the Karoo large igneous province whereas ~10% ofdykes yielded Proterozoic ages (~1–1.1 Ga). Here,weprovide newmajor, trace and rare earth elements analysesof the low-Ti Proterozoic Okavango dyke swarm (PODS) that suggest, combined with age data, a cognate originwith the 1.1 Ga Umkondo large igneous province (UIP), southern Africa.The geochemical characteristics of the PODS and UIP basalts are comparable to those of overlapping low-TiKaroo basalts, and suggest that both LIPs were derived from similar enriched mantle sources. A mantle plumeorigin for these LIPs is not easily reconciled with the geochemical dataset and the coincidence of twocompositionally similar mantle plumes acting 900 Myr apart is unlikely. Instead,we propose that the Umkondoand Karoo large igneous provinces monitored the slight evolution of a shallow enriched lithospheric mantlefrom Proterozoic to Jurassic

Karoo and Etendeks flood basalt provinces, southern Africa and the tectonic development of their adjacent margins:

Southern Africa hosts remnants of two continental flood basalt provinces emplaced in association with fragmentation of Gondwana. The earliest is the 183 Ma Karoo Province whose relationship to continental breakup and sea floor spreading is complex. Geochemical stratigraphy, Ar-Ar Dating and palaeomagnetism indicate that Karoo mafic igneous rocks throughout Southern Africa were emplaced over a very short interval at 183 Ma

Interactive effects of polygenic risk and cognitive subtype on brain morphology in schizophrenia spectrum and bipolar disorders

Grey matter volume (GMV) may be associated with polygenic risk for schizophrenia (PRS-SZ) and severe cognitive deficits in people with schizophrenia, schizoaffective disorder (collectively SSD), and bipolar disorder (BD). This study examined the interactive effects of PRS-SZ and cognitive subtypes of SSD and BD in relation to GMV. Two-step cluster analysis was performed on 146 clinical cases (69 SSD and 77 BD) assessed on eight cognitive domains (verbal and visual memory, executive function, processing speed, visual processing, language ability, working memory, and planning). Among them, 55 BD, 51 SSD, and 58 healthy controls (HC), contributed to focal analyses of the relationships between cognitive subtypes, PRS-SZ and their interaction on GMV. Two distinct cognitive subtypes were evident among the combined sample of cases: a ‘cognitive deficit’ group (CD; N = 31, 20SSD/11BD) showed severe impairment across all cognitive indices, and a ‘cognitively spared’ (CS; N = 75; 31SSD/44BD) group showed intermediate cognitive performance that was significantly worse than the HC group but better than the CD subgroup. A cognitive subgroup-by-PRS-SZ interaction was significantly associated with GMV in the left precentral gyrus. Moderation analyses revealed a significant negative relationship between PRS-SZ and GMV in the CD group only. At low and average (but not high) PRS-SZ, larger precentral GMV was evident in the CD group compared to both CS and HC groups, and in the CS group compared to HCs. This study provides evidence for a relationship between regional GMV changes and PRS-SZ in psychosis spectrum cases with cognitive deficits, but not in cases cognitively spared

Cumulative Environmental Risk in Early Life: Associations With Schizotypy in Childhood

BACKGROUND AND HYPOTHESIS: Psychotic disorders are associated with a growing number of recognized environmental exposures. Cumulative exposure to multiple environmental risk factors in childhood may contribute to the development of different patterns of schizotypy evident in early life. Hypotheses were that distinct profiles of schizotypy would have differential associations with a cumulative score of environmental risk factors. STUDY DESIGN: We prospectively examined the relationship between 19 environmental exposures (which had demonstrated replicated associations with psychosis) measured from the prenatal period through to age 11 years, and 3 profiles of schizotypy in children (mean age = 11.9 years, n = 20 599) that have been established in population data from the New South Wales-Child Development Study. Multinomial logistic regression was used to examine associations between membership in each of 3 schizotypy profiles (true schizotypy, introverted schizotypy, and affective schizotypy) and exposure to a range of 19 environmental risk factors for psychosis (both individually and summed as a cumulative environmental risk score [ERS]), relative to children showing no risk. RESULTS: Almost all environmental factors were associated with at least 1 schizotypy profile. The cumulative ERS was most strongly associated with the true schizotypy profile (OR = 1.61, 95% CI = 1.52-1.70), followed by the affective (OR = 1.33, 95% CI = 1.28-1.38), and introverted (OR = 1.32, 95% CI = 1.28-1.37) schizotypy profiles. CONCLUSIONS: Consistent with the cumulative risk hypothesis, results indicate that an increased number of risk exposures is associated with an increased likelihood of membership in the 3 schizotypy profiles identified in middle childhood, relative to children with no schizotypy profile

Self-harm and suicidal ideation among young people is more often recorded by child protection than health services in an Australian population cohort

Objective: We investigated patterns of service contact for self-harm and suicidal ideation recorded by a range of human service agencies – including health, police and child protection – with specific focus on overlap and sequences of contacts, age of first contact and demographic and intergenerational characteristics associated with different service responses to self-harm. Methods: Participants were 91,597 adolescents for whom multi-agency linked data were available in a longitudinal study of a population cohort in New South Wales, Australia. Self-harm and suicide-related incidents from birth to 18 years of age were derived from emergency department, inpatient hospital admission, mental health ambulatory, child protection and police administrative records. Descriptive statistics and binomial logistic regression were used to examine patterns of service contacts. Results: Child protection services recorded the largest proportion of youth with reported self-harm and suicidal ideation, in which the age of first contact for self-harm was younger relative to other incidents of self-harm recorded by other agencies. Nearly 40% of youth with a health service contact for self-harm also had contact with child protection and/or police services for self-harm. Girls were more likely to access health services for self-harm than boys, but not child protection or police services. Conclusion: Suicide prevention is not solely the responsibility of health services; police and child protection services also respond to a significant proportion of self-harm and suicide-related incidents. High rates of overlap among different services responding to self-harm suggest the need for cross-agency strategies to prevent suicide in young people

Pathways from developmental vulnerabilities in early childhood to schizotypy in middle childhood

Objectives: Childhood disturbances in social, emotional, language, motor and cognitive functioning, and schizotypy have each been implicated as precursors of schizophrenia-spectrum disorders. We investigated whether relationships between early childhood developmental vulnerabilities and childhood schizotypy are mediated by educational underachievement in middle childhood. Methods: Participants were members of a large Australian (n = 19,216) population cohort followed longitudinally. Path analyses were used to model relationships between developmental vulnerabilities at age ~5 years, educational underachievement from ages ~8 to 10 years and three distinct profiles of schizotypy at age ~11 years (true, introverted and affective schizotypy). Results: Early childhood developmental vulnerabilities on five broad domains (related to physical, emotional, social, cognitive and communication development) were associated with schizotypy profiles in middle childhood. Educational underachievement in middle childhood was associated with all schizotypy profiles, but most strongly with the true schizotypy profile (OR = 3.92, 95% CI = 3.12, 4.91). The relationships between schizotypy profiles and early childhood developmental vulnerabilities in ‘language and cognitive skills (school-based)’ and ‘communication skills and general knowledge’ domains were fully mediated by educational underachievement in middle childhood, and the relationships with early childhood ‘physical health and well-being’ and ‘emotional maturity’ domains were partially mediated. Conclusion: Developmental continuity from early childhood developmental vulnerabilities to schizotypy in middle childhood is mediated by educational underachievement in middle childhood. While some domains of early developmental functioning showed differential relationships with distinct schizotypy profiles, these findings support a developmental pathway to schizotypy in which cognitive vulnerability operates from early childhood through to middle childhood