Characterization of single-crystal synthetic diamond for multi-watt continuous-wave Raman lasers

A continuous-wave diamond Raman laser is demonstrated with an output power of 5.1 W at 1217 nm. This Raman laser is intracavity pumped by a side-pumped Nd:YLF rod laser: a 43-fold brightness enhancement between the Nd:YLF and diamond Raman lasers is observed, with the M2 beam propagation factor of the diamond Raman laser measured to be <; 1.2. Although higher output powers are demonstrated in a similar configuration using KGd(WO4)2 (KGW) as the Raman laser material (6.1 W), the brightness enhancement is much lower (2.5 fold) due to the poorer beam quality of the KGW Raman laser (M2 <; 6). The Raman gain coefficient of single-crystal synthetic diamond at a pump wavelength of 1064-nm is also measured: a maximum value of 21±2 cm/GW is returned compared to 5.7±0.5 cm/GW for KGW at the same wavelength

Northeast- or southwest-dipping subduction in the Cretaceous Caribbean gateway?

Most of the Caribbean plate, which currently lies between the American continents, represents a mantle plume-derived 8–20 km thick Cretaceous oceanic plateau that was formed in the Pacific region and moved eastwards. The northern islands of the Caribbean are largely made up of a dismembered island arc that was located along the western entrance to the inter-American region (termed the Great Arc of the Caribbean) in the mid-late Cretaceous. Importantly, the timing of Caribbean lithospheric movement into the inter-American region is controversial, with one hypothesis advocating that it happened in the Hauterivian-Albian (132.9–100.5 Ma), and a second hypothesis proposing the Turonian-Campanian (93.9–72.1 Ma). In order to investigate this problem, island arc rocks are studied on St. John, U.S. Virgin Islands, which are Barremian (127 Ma) to Santonian (83.6 Ma) in age. Immobile trace element and Ndsingle bondHf radiogenic isotope ratios demonstrate that the arc rocks are derived from the partial melting of an Atlantic MORB-like mantle source region that has been variably contaminated with slab-derived fluids composed of continental detritus and slow sediment clay components. We argue that the lack of a mantle plume geochemical signature in the rocks supports the idea that the movement of Caribbean lithosphere into the inter-American region occurred in the late Cretaceous (post-Santonian) due to a subduction polarity reversal caused by collision of the Caribbean oceanic plateau with the Great Arc of the Caribbean

Tectonomagmatic evolution of the Caribbean plate: Insights from igneous rocks on Jamaica

The identification of post-Jurassic arc and plateau rocks in Jamaica has helped constrain the tectonic evolution of the Caribbean plate by identifying when, where and how the different volcanic rocks formed. This research therefore not only evaluates the existing models of Caribbean plate evolution, it also presents for the first time, a detailed gcochcmical and geochronolgical analysis of the igneous rocks on Jamaica. This study has focussed on the igneous rocks of the Blue Mountains, Central, Above Rocks and Benbow Cretaceous Inliers and the Tertiary Wagwater belt. Major and trace element data, Sr, Nd, Pb and Hf isotope analysis and argon radiometric ages have confirmed the presence of a Cretaceous oceanic plateau section within the Blue Mountains inlier and a number of primitive and evolved Cretaceous island arc sequences in the remaining inliers. Rare high-Nb basalts (HNB) and adakites have also been discovered in the Tertiary Wagwater belt. Many elements have been mobilised because of intense tropical weathering, and so the tectonic setting and petrogenesis of most of the analysed samples were interpreted using immobile trace elements which has led to the development of the Co- Th, Th/Zr-La/Yb. Cc/Lu-Sm/Yb, La'Hf-Sm/Y and Th/Hf-Sm/Yb discrimination diagrams. These diagrams have been used to classify the Jamaican volcanic arc rocks and thus identity their extent of fractionation and incompatible trace element enrichment. Immobile trace element and isotope geochemistry has identified at least 5 mantle wedge components and 8 slab components in the Jamaican island arc rocks. Additionally, the Bath-Dunrobin plateau lavas, the adakites and the HNBs represent at least three other chemically distinct source regions. The Bath-Dunrobin plateau lavas are derived from a - 90 Ma heterogeneous mantle plume source region which is distinct from the source regions for other Caribbean oceanic plateau lavas as it contains a larger HIMU component giving it more radiogenic Pb isotope ratios. The adakites have been derived from the combination of complex post-eruptive alteration, partial melting, fractional crystallisation and hybridisation processes. Rather than being related to a melt from a subducting slab, the Jamaican adakites appear to be derived from a melt of lower crustal garnet amphibolite with inter-bedded sedimentary material. The HNBs are derived from a HIMU-type source, which contained garnet and amphibole and so is distinct from the source region of the oceanic plateau. Using the new geochemical and geochronological data, together with the stratigraphic information and temporal location of the Jamaican igneous rocks, it is possible to place Jamaica in the Pacific model of Caribbean plate evolution. From 120- 75 Ma Jamaica formed the northernmost part of the Great Arc of the Antilles and erupted bimodal tholeiitic and calcalkaline magmas, which eventually evolved into calcalkaline and shoshonitic lavas after the collision of the Caribbean oceanic plateau -90 Ma. From -55 Ma Jamaica collided with the Yucatan peninsula and was subsequently tectonically transported to the east by transtensional opening of the Cayman Trough. This extension enabled decompression melting of the underlying asthenosphere to form the HNBs and adakites

Petrogenesis of plagiogranites in the Muslim Bagh Ophiolite, Pakistan: implications for the generation of Archaean continental crust

High-SiO2 rocks referred to as oceanic plagiogranites are common within the crustal sequences of ophiolites; however, their mode of petrogenesis is controversial with both late-stage fractional crystallization and partial melting models being proposed. Here, we present new whole-rock data from plagiogranitic dyke-like bodies and lenses from the lower and middle sections of the sheeted dyke complex of the Cretaceous Muslim Bagh Ophiolite, northwestern Pakistan. The plagiogranites have similar geochemical signatures that are inconsistent with them being the fractionation products of the mafic units of the Muslim Bagh Ophiolite. However, the plagiogranites all display very low TiO2 contents (<0.4 wt%), implying that they formed by partial melting of mafic rocks. Melt modelling of a crustal gabbro from the Muslim Bagh Ophiolite shows that the trace-element signature of the plagiogranites can be replicated by 5–10% melting of a crustal hornblende gabbro with amphibole as a residual phase, resulting in a concave-up middle rare Earth element pattern. Compositional similarities between the Muslim Bagh Ophiolite plagiogranites and Archaean TTG (trondhjemite–tonalite–granodiorite) has implications for the generation of juvenile Archaean continental crust. As the Muslim Bagh Ophiolite was derived in a supra-subduction zone, it is suggested that some Archaean TTG may have been derived from melting of mafic upper crust in early subduction-like settings. However, due to the small volume of Muslim Bagh Ophiolite plagiogranites, it is inferred that they can be instructive on the petrogenesis of some, but not all, Archaean TTG

1.6 W continuous-wave Raman laser using low-loss synthetic diamond

Low-birefringence (Δn<2x10−6), low-loss (absorption coefficient <0.006cm−1 at 1064nm), single-crystal, synthetic diamond has been exploited in a CW Raman laser. The diamond Raman laser was intracavity pumped within a Nd:YVO4 laser. At the Raman laser wavelength of 1240nm, CW output powers of 1.6W and a slope efficiency with respect to the absorbed diode-laser pump power (at 808nm) of ~18% were measured. In quasi-CW operation, maximum on-time output powers of 2.8W (slope efficiency ~24%) were observed, resulting in an absorbed diode-laser pump power to the Raman laser output power conversion efficiency of 13%

1.4 µm continuous-wave diamond Raman laser

The longest wavelength (~1.4 µm) emitted by a diamond Raman laser pumped by a semiconductor disk laser (SDL) is reported. The output power of the intracavity-pumped Raman laser reached a maximum of 2.3 W with an optical conversion efficiency of 3.4% with respect to the absorbed diode pump power. Narrow Stokes emission (FWHM 40 nm was achieved via rotation of an intracavity birefringent filter that tuned the SDL oscillation wavelength

Chalcophile element processing beneath a continental arc stratovolcano

The chalcophile elements are important both in terms of their economic value and as potential tracers of magmatic processes at convergent margins. However, because of analytical difficulties, comprehensive datasets of chalcophile element concentrations for volcanic rocks are rare. Here, we present analyses of a near complete suite of chalcophile elements (S, Cu, Ag, Se, As, Sb, Sn, W, Mo, Pb, Bi, Tl, Zn, Ga, Co) for volcanic rock samples collected from a typical continental arc stratovolcano in southern Chile (Antuco). Enrichment in Pb, Bi, W, Tl, Sb and As relative to Parental-MORB indicates that these elements have been mobilised from the subducting slab into the sub-arc mantle wedge, in contrast to Cu and Ag. Very low Se concentrations suggest that Se, like S, was lost during co-eruptive degassing of the Antuco magmas. Previous studies on oceanic arcs have demonstrated that as higher fO2 subduction-related magmas ascend through the overlying lithosphere, magnetite fractionation may trigger sulfide fractionation during crystallisation. If such a process is extensive and has a sharp onset, this would result in a plummet in the Cu, Se and Ag contents of the residual melt. At Antuco, although a decrease in the Fe2O3(T) and TiO2 concentrations at ∼55 wt.% SiO2 (∼3 wt.% MgO) indicates magnetite fractionation, this is not associated with a corresponding drop in Cu contents. Instead, we observe a general decrease in Cu and a decrease in Cu/Ag with increasing SiO2 and decreasing MgO. Furthermore, Cu/Ag in the most primitive Antuco rocks are lower than the global MORB array, indicating that the melts were sulfide saturated at an early stage in their crustal evolution. Through modelling fractional crystallisation, we show that only a minor volume (0.5–0.6 vol.%) of fractionating sulfide is needed to produce divergent trends in Cu and Ag, as observed in the Antuco samples. Our results show that sulfide fractionation occurred from an early stage during the crustal evolution of Antuco's magmas. We infer that this was promoted by stalling in the lower crust, which for oxidised magmas at depths >20 km is within the sulfide stability field. However, elevated DyN/YbN of the Antuco magmas compared to oceanic island arc magmas provides an additional, or alternate mechanism to inducing sulfide fractionation in the lower crust prior to ascent, through initial garnet fractionation. Fractional crystallisation within this depth range meant that later magnetite fractionation had only a minor impact on the partitioning behaviour of the chalcophile elements. In contrast, arc magmas transiting thinner crust may not experience sulfide saturation until a later stage in their evolution, induced by magnetite fractionation. Our results imply that convergent margin crustal thickness, and therefore the depth range of magmatic differentiation, determines the dominant control on initial magmatic sulfide saturation and therefore the primary distribution of chalcophile elements. This implies that secondary processes are required to explain the transport and concentration of sulfides and chalcophile elements at shallower crustal levels