Eclogite facies metamorphism of the lithosphere forms dense mineral assemblages at high- (1.6-2.4 GPa) to ultra-high-pressure (>2.4-12 GPa: UHP) conditions that drive slab-pull forces during its ...subduction to lower mantle conditions. The relative densities of mantle and lithospheric components places theoretical limits for the re-exposure, and peak conditions expected, of subducted lithosphere. Exposed eclogite terranes dominated by rock denser than the upper mantle are problematic, as are interpretations of UHP conditions in buoyant rock types. Their subduction and exposure require processes that overcame predicted buoyancy forces. Phase equilibria modelling indicates that depths of 50-60 km (P = 1.4-1.8 GPa) and 85-160 km (P = 2.6-5 GPa) present thresholds for pull force in end-member oceanic and continental lithosphere, respectively. The point of no-return for subducted silicic crustal rocks is between 160 and 260 km (P = 5.5-9 GPa), limiting the likelihood of stishovite-wadeite-K-hollandite-bearing assemblages being preserved in equilibrated assemblages. The subduction of buoyant continental crust requires its anchoring to denser mafic and ultramafic lithosphere in ratios below 1:3 for the continental crust to reach depths of UHP conditions (85-160 km), and above 2:3 for it to reach extreme depths (>160 km). The buoyant escape of continental crust following its detachment from an anchored situation could carry minor proportions of other rocks that are denser than the upper mantle. However, instances of rocks returned from well-beyond these limits require exceptional exhumation dynamics, plausibly coupled with the effects of incomplete metamorphism to retain less dense low-P phases.
Cryptic geochemical indicators of prograde lawsonite breakdown are established in basic and metasedimentary Eocene blueschist and eclogite in New Caledonia utilizing phase equilibria modelling and ...synchrotron X‐ray fluorescence mapping. Lawsonite–epidote‐bearing eclogite has garnet with concentric zones depleted in the LREE and MREE, and clinozoisite with high‐Sr rims, which geochemically record a prograde stage of lawsonite stability. These records persist in eclogite that now lacks lawsonite, and may be used to validate texturally based interpretations for prograde lawsonite stability. The compositional trends depend on extrinsic and intrinsic variables, including bulk rock composition, which determine the rock‐forming and accessory minerals that host Sr and the REEs. Distinct prograde reaction histories are recorded by two eclogite terranes in NE New Caledonia due to subtle distinctions in their protolith whole‐rock compositions.
Uncommonly long‐lived subduction and variable plate geometry along the South American Andean Plate margin resulted in diverse relationships between magmatic flux and extensional and contractional ...deformation, as recorded by the overriding continental plate. Convergence velocities, absolute overriding plate velocities, and subducting slab ages were resolved along the trench from 170 Ma to the present using a recently developed kinematic global plate model to identify any relationship between subduction conditions, deformation style, and magmatic features in the overriding plate. Key correlations reflect the dependence of macroscopic crustal strain style on subduction mechanism and relative plate vectors. Extensional back‐arc basins involving mafic/oceanic crust developed only when the overriding plate velocity of South America was directed away from the trench and the modeled age of the subducting slab was older than 50 Myr. The development of fold and thrust belts, and uplift of major plateaus, was accompanied by trench normal convergence velocities in excess of 4 cm/yr. Parameters investigated in this study revealed no correlation with the timing of major magmatic events, nor was any correlation observed with the structural style of fold and thrust belts.
Key Points
Overriding plate deformation can be related to plate boundary parameters
Plate velocities and subducted slab ages are associated with basin development
Plate velocities are associated with contraction events
Results of biostratigraphic and geochronological investigations in eastern Nagaland and Manipur, NE India, provide new constraints on the tectonic evolution of the western margin of the Burma ...microplate. U/Pb zircon ages indicate that the Naga Hills ophiolite developed in a suprasubduction zone setting as part of an intraoceanic island arc developed during late Early Cretaceous (mid‐Aptian) time and is younger than similar rocks exposed along the Indus‐Yarlung Tsangpo suture zone. Radiolarian microfossils provide Jurassic and Cretaceous age constraints for Tethyan ocean floor sediments that were subducted beneath the forming ophiolite. Timing of the emplacement of these rocks onto the passive margin of eastern India is constrained by Paleocene/Eocene radiolarians in sediments over which the ophiolitic assemblage has been thrust. Previously undated schists and gneisses in the Naga Metamorphics are of Early Ordovician age, and their sedimentary protolith was most likely derived from sources in the south of Western Australian and East Antarctica. After Barrovian‐style metamorphism, these rocks were uplifted and eroded becoming an important source of detritus shed into the Eocene Phokphur Formation. This unit also contains abundant clasts sourced from the disrupted basement of the Naga Hills ophiolite, which it overlies. It also contains Permo‐Triassic‐aged detritus eroded off an enigmatic source that was possibly a continental convergent margin arc system somewhere along the northern margin of Gondwana.
Key Points
Naga Metamorphics are of Early Ordovician age, and their protolith was derived from south Western Australian and/or East Antarctic sources
Paleocene/Eocene radiolarians in mélange confirm timing of Naga Hills Ophiolite (Aptian) emplacement onto the east Indian passive margin
The Phokphur Formation contains enigmatic Permo‐Triassic detritus possibly from a continental arc on the northern margin of Gondwana
The metamorphic conditions and mechanisms required to induce foundering in deep arc crust are assessed using an example of representative lower crust in SW New Zealand. Composite plutons of ...Cretaceous monzodiorite and gabbro were emplaced at ~1.2 and 1.8 GPa are parts of the Western Fiordland Orthogneiss (WFO); examples of the plutons are tectonically juxtaposed along a structure that excised ~25 km of crust. The 1.8 GPa Breaksea Orthogneiss includes suitably dense minor components (e.g. eclogite) capable of foundering at peak conditions. As the eclogite facies boundary has a positive dP/dT, cooling from supra-solidus conditions (T > 950 ºC) at high-P should be accompanied by omphacite and garnet growth. However, a high monzodioritic proportion and inefficient metamorphism in the Breaksea Orthogneiss resulted in its positive buoyancy and preservation. Metamorphic inefficiency and compositional relationships in the 1.2 GPa Malaspina Pluton meant it was never likely to have developed densities sufficiently high to founder. These relationships suggest that the deep arc crust must have primarily involved significant igneous accumulation of garnet-clinopyroxene (in proportions >75%). Crustal dismemberment with or without the development of extensional shear zones is proposed to have induced foundering of excised cumulate material at P > 1.2 GPa.
Chemotherapy resistance frequently drives tumour progression. However, the underlying molecular mechanisms are poorly characterized. Epithelial-to-mesenchymal transition has been shown to correlate ...with therapy resistance, but the functional link and signalling pathways remain to be elucidated. Here we report that microRNA-30c, a human breast tumour prognostic marker, has a pivotal role in chemoresistance by a direct targeting of the actin-binding protein twinfilin 1, which promotes epithelial-to-mesenchymal transition. An interleukin-6 family member, interleukin-11 is identified as a secondary target of twinfilin 1 in the microRNA-30c signalling pathway. Expression of microRNA-30c inversely correlates with interleukin-11 expression in primary breast tumours and low interleukin-11 correlates with relapse-free survival in breast cancer patients. Our study demonstrates that microRNA-30c is transcriptionally regulated by GATA3 in breast tumours. Identification of a novel microRNA-mediated pathway that regulates chemoresistance in breast cancer will facilitate the development of novel therapeutic strategies.
Starkly contrasting tectonic reconstructions have been proposed for the Late Cretaceous to mid Eocene (~85–45Ma) evolution of the southwest Pacific, reflecting sparse and ambiguous data. Furthermore, ...uncertainty in the timing of and motion at plate boundaries in the region has led to controversy around how to implement a robust southwest Pacific plate circuit. It is agreed that the southwest Pacific comprised three spreading ridges during this time: in the Southeast Indian Ocean, Tasman Sea and Amundsen Sea. However, one and possibly two other plate boundaries also accommodated relative plate motions: in the West Antarctic Rift System (WARS) and between the Lord Howe Rise (LHR) and Pacific. Relevant geologic and kinematic data from the region are reviewed to better constrain its plate motion history during this period, and determine the time-dependent evolution of the southwest Pacific regional plate circuit. A model of (1) west-dipping subduction and basin opening to the east of the LHR from 85–55Ma, and (2) initiation of northeast-dipping subduction and basin closure east of New Caledonia at ~55Ma is supported. West-dipping subduction and basin opening were not driven by convergence, as has previously been proposed. Our plate circuit analysis suggests that between at least 74Ma and subduction initiation at ~55Ma there was little net relative motion between the Pacific plate and LHR, <20km of convergence with a component of strike-slip motion. Subduction must therefore have been primarily driven by the negative buoyancy of the slab, or perhaps forced trench retreat due to orogenic collapse. We propose that at least two plate boundaries separated the Pacific plate from the LHR during this time, however, as there was little to no motion between these plates then a plate circuit which treats the Pacific plate and LHR as a single plate (“Australian” circuit) will produce similar kinematic results to a circuit which leaves their relative motion unconstrained and treats them as separate plates (“Antarctic” circuit). Prior to 74Ma the reliability of magnetic anomalies from southwest Pacific spreading systems is questionable and it is difficult to properly test alternative plate circuits. After 55Ma we advocate using an Antarctic plate circuit as the Australian plate circuit models that were tested predict significant net compression in the WARS, for which evidence is absent. Our preferred model makes testable predictions, such as burial of an arc beneath the Tonga and Vitiaz ridges, and Late Cretaceous to Eocene slabs in the mantle beneath the southwest Pacific, both of which can be investigated by future work. These predictions are particularly important for testing the earlier 85–55Ma phase of the model, which is largely underpinned by ages and interpretations of South Loyalty Basin crust obducted onto New Caledonia, rather than an extinct arc or arc-related rocks.
Metastasis remains a significant challenge in treating cancer. A better understanding of the molecular mechanisms underlying metastasis is needed to develop more effective treatments. Here, we show ...that human breast tumor biomarker miR-30c regulates invasion by targeting the cytoskeleton network genes encoding twinfilin 1 (TWF1) and vimentin (VIM). Both VIM and TWF1 have been shown to regulate epithelial-to-mesenchymal transition. Similar to TWF1, VIM also regulates F-actin formation, a key component of cellular transition to a more invasive mesenchymal phenotype. To further characterize the role of the TWF1 pathway in breast cancer, we found that IL-11 is an important target of TWF1 that regulates breast cancer cell invasion and STAT3 phosphorylation. The miR-30c-VIM/TWF1 signaling cascade is also associated with clinical outcome in breast cancer patients.
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