Ar Component Research Articles

A comparison of mixed frequency approaches for nowcasting Euro area macroeconomic aggregates

In this paper, we focus on the different methods which have been proposed in the literature to date for dealing with mixed-frequency and ragged-edge datasets: bridge equations, mixed-data sampling (MIDAS), and mixed-frequency VAR (MF-VAR) models. We discuss their performances for nowcasting the quarterly growth rate of the Euro area GDP and its components, using a very large set of monthly indicators. We investigate the behaviors of single indicator models, forecast combinations and factor models, in a pseudo real-time framework. MIDAS with an AR component performs quite well, and outperforms MF-VAR at most horizons. Bridge equations perform well overall. Forecast pooling is superior to most of the single indicator models overall. Pooling information using factor models gives even better results. The best results are obtained for the components for which more economically related monthly indicators are available. Nowcasts of GDP components can then be combined to obtain nowcasts for the total GDP growth.

Ar–Ar ages and trapped Ar components in Martian shergottites RBT 04262 and LAR 06319

We made 39Ar–40Ar (Ar–Ar) analyses of whole rock (WR) and mineral samples of two Martian shergottites, RBT 04262 (RBT) and LAR 06319 (LAR), in order to determine their Ar–Ar ages and the 40Ar/36Ar ratios of the trapped Martian Ar they contain. All samples released trapped (excess) 40Ar and 36Ar and suggested Ar–Ar ages older than their formation ages. Because trapped Ar components having different 40Ar/36Ar were released at different extraction temperatures, we utilized only a portion of the data to derive preferred Ar–Ar ages. We obtain Ar–Ar ages of 171±8Ma for RBT plagioclase and 163±13Ma for LAR whole rock. We identify two trapped Ar components. At low temperatures, particularly for plagioclase, Trapped-A with 40Ar/36Ar 285±3 was released, and we believe this is most likely absorbed terrestrial air. At high extraction temperatures, particularly for pyroxene, Trapped-B with 40Ar/36Ar 1813±127 was released. The poikilitic/non-poikilitic texture of RBT and the presence of large pyroxene oikocrysts allowed a clear definition of Trapped-B. This Ar component is Martian, and its isotopic similarity to the Martian atmospheric composition suggests that it may represent Martian atmospheric Ar incorporated into the shergottite melt via crustal rocks. Trapped-B partitioned into pyroxene at a constant molar ratio of K/36ArTr=33.2±9.5×106 for RBT 04262, and 80±21×106 for LAR 06319. Trapped-A mixed in different proportions with Trapped-B could give apparently intermediate trapped 40Ar/36Ar compositions commonly observed in shergottites.

Income Mobility and Welfare

This paper develops a framework for the quantitative analysis of individual income dynamics, mobility and welfare. Individual income is assumed to follow a stochastic process with two (unobserved) components, an i.i.d. component representing measurement error or transitory income shocks and an AR(1) component representing persistent changes in income. We use a tractable consumption-saving model with labor income risk and incomplete markets to relate income dynamics to consumption and welfare, and derive analytical expressions for income mobility and welfare as a function of the various parameters of the underlying income process. The empirical application of our framework using data on individual incomes from Mexico provides striking results. Much of measured income mobility is driven by measurement error or transitory income shocks and therefore (almost) welfare-neutral. A smaller part of measured income mobility is due to either welfare-reducing income risk or welfare-enhancing catching-up of low-income individuals with high-income individuals, both of which have economically significant effects on social welfare. Decomposing mobility into its fundamental components is thus seen to be crucial from the standpoint of welfare evaluation.

Income Mobility and Welfare

This paper develops a framework for the quantitative analysis of individual income dynamics, mobility and welfare. Individual income is assumed to follow a stochastic process with two (unobserved) components, an i.i.d. component representing measurement error or transitory income shocks and an AR(1) component representing persistent changes in income. We use a tractable consumption-saving model with labor income risk and incomplete markets to relate income dynamics to consumption and welfare, and derive analytical expressions for income mobility and welfare as a function of the various parameters of the underlying income process. The empirical application of our framework using data on individual incomes from Mexico provides striking results. Much of measured income mobility is driven by measurement error or transitory income shocks and therefore (almost) welfare-neutral. A smaller part of measured income mobility is due to either welfare-reducing income risk or welfare-enhancing catching-up of low-income individuals with high-income individuals, both of which have economically significant effects on social welfare. Decomposing mobility into its fundamental components is thus seen to be crucial from the standpoint of welfare evaluation.

Income Risk, Income Mobility and Welfare

This paper develops a framework for the quantitative analysis of individual income dynamics, mobility and welfare. Individual income is assumed to follow a stochastic process with two (unobserved) components, an i.i.d. component representing measurement error or transitory income shocks and an AR(1) component representing persistent changes in income. We use a tractable consumption-saving model with labor income risk and incomplete markets to relate income dynamics to consumption and welfare, and derive analytical expressions for income mobility and welfare as a function of the various parameters of the underlying income process. The empirical application of our framework using data on individual incomes from Mexico provides striking results. Much of measured income mobility is driven by measurement error or transitory income shocks and therefore (almost) welfare-neutral. A smaller part of measured income mobility is due to either welfare-reducing income risk or welfare-enhancing catching-up of low-income individuals with high-income individuals, both of which have economically significant effects on social welfare. Decomposing mobility into its fundamental components is thus seen to be crucial from the standpoint of welfare evaluation.

40Ar‐39Ar age of Northwest Africa 091: More evidence for a link between L chondrites and fossil meteorites

Abstract—Most40Ar‐39Ar ages of L chondrites record an event at approximately 500 Ma, indicating a large collisional impact at that time. However, there is a spread in ages from 400 to 600 Ma in these meteorites that is greater than the analytical uncertainty. Identification of, and correction for, trapped Ar in a few L chondrites has given an age of 470 ± 6 Ma. This age coincides with Ordivician fossil meteorites that fell to Earth at 467 ± 2 Ma. As these fossil meteorites were originally L chondrites, the apparent conclusion is that a large impact sent a flood of L chondrite material to Earth, while material that remained on the L chondrite parent body was strongly heated and reset. We have reduced40Ar‐39Ar data for Northwest Africa 091 using various techniques that appear in the literature, including identification and subtraction of trapped Ar. These techniques give a range of ages from 455 to 520 Ma, and show the importance of making accurate corrections. By using the most straightforward technique to identify and remove a trapped Ar component (which is neither terrestrial nor primordial), an40Ar‐39Ar age of 475 ± 6 Ma is found for Northwest Africa 091, showing a temporal link to fossil meteorites. In addition, high temperature releases of Northwest Africa 091 contain evidence for a second trapped component, and subtraction of this component indicates a possible second collisional impact at approximately 800 Ma. This earlier age coincides with40Ar‐39Ar ages of some H and L chondrites, and lunar samples.

Income Risk, Income Mobility and Welfare

This paper develops a framework for the quantitative analysis of individual income dynamics, mobility and welfare. Individual income is assumed to follow a stochastic process with two (unobserved) components, an i.i.d. component representing measurement error or transitory income shocks and an AR(1) component representing persistent changes in income. We use a tractable consumption-saving model with labor income risk and incomplete markets to relate income dynamics to consumption and welfare, and derive analytical expressions for income mobility and welfare as a function of the various parameters of the underlying income process. The empirical application of our framework using data on individual incomes from Mexico provides striking results. Much of measured income mobility is driven by measurement error or transitory income shocks and therefore (almost) welfare-neutral. A smaller part of measured income mobility is due to either welfare-reducing income risk or welfare-enhancing catching-up of low-income individuals with high-income individuals, both of which have economically significant effects on social welfare. Decomposing mobility into its fundamental components is thus seen to be crucial from the standpoint of welfare evaluation.

Estimation Methods of the Long Memory Parameter: Monte Carlo Analysis and Application

Since the seminal paper of Granger & Joyeux (1980), the concept of a long memory has focused the attention of many statisticians and econometricians trying to model and measure the persistence of stationary processes. Many methods for estimating d, the long-range dependence parameter, have been suggested since the work of Hurst (1951). They can be summarized in three classes: the heuristic methods, the semi-parametric methods and the maximum likelihood methods. In this paper, we try by simulation, to verify the two main properties of [dcirc]: the consistency and the asymptotic normality. Hence, it is very important for practitioners to compare the performance of the various classes of estimators. The results indicate that only the semi-parametric and the maximum likelihood methods can give good estimators. They also suggest that the AR component of the ARFIMA (1, d, 0) process has an important impact on the properties of the different estimators and that the Whittle method is the best one, since it has the small mean squared error. We finally carry out an empirical application using the monthly seasonally adjusted US Inflation series, in order to illustrate the usefulness of the different estimation methods in the context of using real data.

α1A‐Adrenoceptors mediate contractions to phenylephrine in rabbit penile arteries

Maintained penile erection depends on the absence of alpha-adrenoceptor (alpha-AR) activation and so can be facilitated by alpha-blockers. This study seeks the alpha(1)-AR subtypes involved in order to inform the pro-erectile consequences of subtype selective blockade. Wire myography was used with dorsal (nutritional supply) and cavernous (erectile inflow) penile arteries; standard alpha-AR-selective agonists and antagonists were employed to classify responses. In both penile arteries noradrenaline (NA) and phenylephrine (PE, alpha(1)-AR agonist) caused concentration-dependent contractions. Sensitivity to NA was increased by NA uptake blockers, cocaine (3 microM) and corticosterone (30 microM). PE responses were antagonised by phentolamine (non-selective alpha-AR: dorsal pK(B) 8.00, cavernous 8.33), prazosin (non-subtype-selective alpha(1)-AR: dorsal 8.60, cavernous 8.41) and RS100329 (alpha(1A)-AR selective: dorsal 9.03, cavernous 8.80) but not by BMY7378 (alpha(1D)-AR selective: no effect at 1-100 nM) or Rec15/2615 (alpha(1B)-AR selective: no effect at 1-100 nM). Schild analysis was straightforward in cavernous artery, indicating that PE activates only alpha(1A)-AR. In dorsal artery Schild slopes were low, though alpha(1A)-AR was still indicated. Analysis using UK 14,304 and rauwolscine indicated an alpha(2)-AR component in dorsal artery that may account for low slopes to alpha(1)-AR antagonists. Penile arteries have a predominant, functional alpha(1A)-AR population with little evidence of other alpha(1)-AR subtypes. Dorsal arteries (nutritional supply) also have alpha(2)-ARs. Thus, alpha-AR blockers with affinity for alpha(1A)-AR or alpha(2)-AR would potentially have pro-erectile properties; the combination of these perhaps being most effective. This should inform the design of drugs to assist/avoid penile erection.

Mathematical Model for developing Data-Base System of Environments in Coastal Sea Area 4th Report : Spatial Distribution and AR Component of Water Quality Data

Mathematical Model for developing Data-Base System of Environments in Coastal Sea Area 4th Report : Spatial Distribution and AR Component of Water Quality Data

Noble gases in olivine phenocrysts from drill core samples of the Hawaii Scientific Drilling Project (HSDP) pilot and main holes (Mauna Loa and Mauna Kea, Hawaii)

We have determined concentrations and isotopic compositions of all noble gases in olivine phenocrysts from the Hawaii Scientific Drilling Project (HSDP) drill core, comprising Mauna Loa lavas in the top 247 m and Mauna Kea lavas down to the preliminary depth of 3109 m. Our aim was to describe the long‐term isotopic evolution of noble gases over a significant time fraction of the active life of a major Hawaiian volcano. The He isotopic signature displays a clear temporal trend: 3He/4He ratios increase from MORB‐like 9 RA in the youngest lavas to 15 RA in the Mauna Loa section and from ∼7 RA to ∼12 RA in the subaerial Mauna Kea deposits. They remain close to 12 RA in most of the submarine Mauna Kea samples, except for a few excursions with 3He/4He ratios of up to 21 RA in borehole depths between 2000 and 2600 m. The average 3He/4He ratio of 12 RA is lower than that observed in recent eruptions of Kilauea and Loihi seamount and supports the idea of a concentrically zoned Hawaiian plume [Kurz et al., 1996]. The Ne isotopic signature does not show a temporal evolution. It remains plume‐like (plotting close to the Loihi–Kilauea correlation line in a Ne three‐isotope diagram) over the whole Mauna Kea section in those samples which are not dominated by air‐like Ne. Maximum 20Ne/22Ne and 21Ne/22Ne ratios reach 12.10 ± 0.36 and 0.0360 ± 0.0042, respectively. 40Ar/36Ar ratios vary widely between 360 and ∼3300 in the ≥1000°C release steps due to variable atmospheric contributions. In at least one sample, a 40Ar/36Ar ratio of 14,300 ± 910 demonstrates the presence of a MORB‐like Ar component. Kr and Xe isotopic compositions are atmospheric throughout. We discuss several possibilities on how to explain the isotopic trends of the noble gases and their correlation to other geochemical parameters. Simple admixture of MORB‐like noble gases to the plume component cannot account for the observations. We favor a model involving early melt extraction from the outer plume sections, followed by radiogenic ingrowth and, possibly, some interaction with ambient mantle material.

Contending with space–time interaction in the spatial prediction of pollution: Vancouver's hourly ambient PM10 field

AbstractIn this article we describe an approach for predicting average hourly concentrations of ambient PM10 in Vancouver. We know our solution also applies to hourly ozone fields and believe it may be quite generally applicable. We use a hierarchical Bayesian approach. At the primary level we model the logarithmic field as a trend model plus Gaussian stochastic residual. That trend model depends on hourly meteorological predictors and is common to all sites. The stochastic component consists of a 24‐hour vector response that we model as a multivariate AR(3) temporal process with common spatial parameters. Removing the trend and AR structure leaves ‘whitened’ time series of vector series. With this approach (as opposed to using 24 separate univariate time series models), there is little loss of spatial correlation in these residuals compared with that in just the detrended residuals (prior to removing the AR component). Moreover our multivariate approach enables predictions for any given hour to ‘borrow strength’ through its correlation with adjoining hours. On this basis we develop a spatial predictive distribution for these residuals at unmonitored sites. By transforming the predicted residuals back to the original data scales we can impute Vancouver's hourly PM10 field. Copyright © 2002 John Wiley & Sons, Ltd.

Constraints on the age and halogen composition of mantle fluids in Siberian coated diamonds

Extension of the Ar–Ar stepped heating technique has been used to characterise the Ar, halogen (Cl, Br, I), Ca and K components in seven coated diamonds from the Aikhal kimberlite, Siberia. At least three components have been identified with different Ar isotope compositions. The major component is characterised by high 40Ar/ 36Ar >11 000 and constant 40Ar*/Cl (527±22×10 −6), Br/Cl (1.74±0.18×10 −3) and I/Cl (22.0±3.4×10 −6) indicative of a mantle fluid phase. This component is widespread in coated diamonds having been previously reported in samples from Africa and Canada. Estimates of halogen abundances in the sub-continental mantle, based on data from African and Siberian coated diamonds, are 3 ppm Cl, 11 ppb Br and 0.4 ppb I. These low abundances, which are in good agreement with values derived for the depleted asthenospheric mantle derived from MORB data, imply that the upper mantle is >90% degassed of its halogens. A second Ar component in coated stones is most simply understood by in situ decay of 40K and is consistent with the coat-forming event occurring close to the time of host kimberlite eruption 350–380 Ma ago. A third Ar component has a low 40Ar/ 36Ar ratio (∼300), is unassociated with release of K or halogens, and is most likely to be atmospheric blank.

A Time-Series Model of Stock Returns with a Positive Short-Term Correlation and a Negative Long-Term Correlation

We study portfolio stock return behavior that exhibits both a positive autocorrelation over short horizons and a negative autocorrelation over long horizons. These autocorrelations are more significant in small size portfolios. Among various forms of temporary components in stock prices, an AR(2) component is the simplest model compatible with this pattern of returns, which yields an ARMA(2,2) model of stock returns. We show that the significance of this model is that it requires the presence of feedback trading, which is a form of irrational trades, and the market's slow adjustment to the market fundamentals, which is consistent with recent modelings of stock prices. We find that the variation of the temporary component becomes greater as the firm size gets smaller. This implies that the deviation from the market fundamentals is larger in small size portfolios than in large size portfolios.

40Ar-39Ar geochronometry of pseudotachylytes by vacuum encapsulation: North Cascade Mountains, Washington, USA

To determine a reliable means of dating pseudotachylytes, we obtained total gas ages, plateau ages and argon-retention ages on samples from the North Cascade Mountains, Washington. Quartz ampoule vacuum-encapsulation analysis of small grains (a few milligrams) from six samples allowed evaluation of 39 Ar loss through recoil during irradiation, and laser ablation on four samples allowed textural control. In microlitic samples, recoil-loss 39 Ar ranges from 0.2% to 8.4%. The “total gas” ages incorporating this 39 Ar are inconsistent, but retention ages are much more internally consistent, and within analytical error they match or nearly match plateau ages from most of the microlitic samples at 54–55 Ma. Samples analyzed by laser ablation suggest one episode of faulting and pseudotachylyte formation at 55–59 Ma, and an earlier episode at ca. 80 Ma. The partly glassy pseudotachylyte yielded laser-ablation, total gas, and retention ages of ca. 65 Ma. The microlitic pseudotachylytes indicate formation close to 55 Ma, with possible older faulting and pseudotachylyte formation at ca. 81–84 Ma. The good consistency among the retention ages, the laser ages with highest precision, and especially the plateau dates, combined with the ages falling within the anticipated time span, provides confidence in the geologic reality of the ages. Nevertheless, it is clear that large clasts and crystal fragments within these particular veins did not completely degas or may have an anomalous inherited radiogenic 40 Ar component.

On the characterization of VBR MPEG streams

We present a comprehensive model for variable-bit-rate MPEG video streams. This model captures the bit-rate variations at multiple time scales. Long-term variations are captured by incorporating scene changes, which are most noticeable in the fluctuations of I frames. The size of an I frame is modeled by the sum of two random components: a scene-related component and an AR(2) component that accounts for the fluctuations within a scene. Two random processes of i.i.d. rvs are used to model the sizes of P and B frames, respectively. The complete model is then obtained by intermixing the three sub-models according to a given GOP pattern. It is shown that the composite model exhibits long-range dependence (LRD) in the sense that its autocorrelation function is non-summable. The LRD behavior is caused by the repetitive GOP pattern which induces periodic cross-correlations between different types of frames. Using standard statistical methods, we successfully fit our model to several empirical video traces. We then study the queueing performance for video traffic at a statistical multiplexer. The results show that the model is sufficiently accurate in predicting the queueing performance for real video streams.

Excess 40Ar in biotite and hornblende from the Noril'sk 1 intrusion, Siberia: implications for the age of the Siberian Traps

The Siberian Traps represent the largest known Phanerozoic manifestation of continental flood volcanism. The general agreement is now that the volcanism was of short duration (∼ 1 m.y.) and was synchronous with the Permian-Triassic boundary. Discrepancies between different geochronologic results prevent rigorous evaluation of the age and duration of magmatism. Several alkalic mafic intrusions associated with the Siberian Traps represent subvolcanic feeders for the Trap lavas. The Noril'sk 1 intrusion is intruded into the earliest flows and is chemically and isotopically related to stratigraphically overlying flows. Biotites from the Noril'sk 1 intrusion have previously yielded 40Ar 39Ar plateau dates (254-251 Ma) that are significantly older than seemingly reliable 40Ar 39Ar plateau dates (250-247 Ma) on plagioclase and whole-rock samples from Trap basalts that are geologically constrained to be older than the intrusion. Possible explanations of this discrepancy include: (1) plagioclase and whole-rock samples are anomalously young due to 40Ar loss via alteration or episodic outgassing, and/or (2) the biotites contain excess 40Ar. Detailed laser heating 40Ar 39Ar analysis of six individual grains of biotite in a total of 214 steps yield data that permit characterization of multiple components of Ar through isotope correlation patterns. An isochron age of 250.1 ± 1.5 Ma (2σ) and an excess Ar component with 40Ar 36Ar = 565 ± 39 , are obtained by regression of the 115 highest temperature steps. Step heating of a bulk hornblende sample also reveals excess Ar, with 40Ar 36Ar = 327 ± 10 and an isochron age of 249.3 ± 1.6 Ma. Neglecting uncertainties in the ages of neutron fluence monitors, the two dates just overlap at 2σ, but are distinctly younger than the previous mean plateau date (253.9 ± 1.6 Ma) for biotite. The different initial 40Ar 36Ar for the two phases is interpreted as reflecting the evolution of an initial lower mantle composition towards increasing crustal contamination.

Magmatism and continental break-up in the South Atlantic: high precision 40Ar- 39Ar geochronology

A detailed Ar Ar study of the Paraná-Etendeka continental flood basalts (CFB) has been undertaken using laser spot analysis. Data provide information not only on the age of the samples but also on the variability of the non-radiogenic Ar component and state of alteration. The results indicate the Paraná-Etendeka CFB were erupted over 10 million years between 137 and 127 Ma providing a minimum overall eruption rate of ∼ 0.1 km 3 yr −1. This is an order of magnitude less than that previously proposed for this, the Deccan and Siberian CFB provinces but it is similar to estimates for Hawaii, Iceland and the Columbia River CFB. In detail, the new Ar Ar analyses indicate that magmatism within the Paraná-Etendeka province migrated from NW to SE prior to and during the opening of the South Atlantic, providing an explanation for the asymmetry of the CFB lavas about the South Atlantic. Moreover, chemically defined magma types were erupted at different times in different places, and so within the Paranáthey may not be used as reliable chronostratigraphic units. Rather, such magmatic units may reflect the extent of compositionally distinct source regions in the uppermost mantle, and indicate that partial melting took place over a wide area under the ParanáBasin. The NW-SE migration of the onset of magmatism might be interpreted as a plume trace, but the inferred rate of movement is 3 times faster than that inferred from subsequent magmatism on the Rio Grande Rise. It is argued that the onset of magmatism reflected extensional tectonics normal to the Ponta Grossa dyke swarm. Given that magmatism preceded the main phase of rifting, and that extension across the Ponta Grossa was moderate, current plume models have difficulty in predicting sufficient melting within the asthenosphere.

Conditioning of a distributed ion pump

A conditioning procedure using N 2 or Ar gas is applied to a distributed ion pump (DIP) of the TRISTAN accumulation ring. Effectiveness and problems of conditioning are experimentally investigated. Only a slight effect is observed in the N 2 gas conditioning due to the great pressure difference along the beam duct, so that a uniform conditioning cannot be achieved. The Ar gas conditioning, on the other hand, well activates the DIP. Pumping speeds near the design value, ⋍80 l s −1 per meter at pressures ⋍ 1×10 −6 Pa , are obtained. The Ar component, however, increases after baking by more than a factor of 3 within 280 h. This increase makes it difficult to apply Ar gas conditioning to an accelerator ring.

40Ar 39Ar chronology of Variscan tectono-metamorphic events in an exhumed crustal nappe: the Monts du Lyonnais complex (Massif Central, France)

The Monts du Lyonnais metamorphic complex is part of the high-grade nappes of the Massif Central, France. Retrogression of metamorphic conditions occurred synchronously with evolution of deformation from penetrative thrust structures at high- T conditions (stage P 1–2, 700±50°C) to strike-slip ductile shear at lower P- T conditions (stage P 3, T⩽600°C). This evolution distinguishes progressive exhumation and cooling of this previously buried Variscan segment. In this study, 40Ar 39Ar chronologic investigations are addressed to representative samples of each tectono-metamorphic stage associated with the exhumation of the nappe. The two mineral generations yield indistinguishable dates of 350-340 Ma which are interpreted as post-metamorphic cooling ages. However, the minerals which crystallized during the late intra-continental stage P 3 yield concordant plateau dates, while the minerals which grew during the P 1–2 stage and escaped later retrogressive deformation systematically display disturbed age spectra. These heterogeneous profiles could result from the presence of a minor excess Ar component, incorporated at the time of the P 3 event, when intense deformation took place under decreasing metamorphic temperature and synkinematic granite emplaced along ductile wrench faults. This tectono-metamorphic event could have been responsible for a local redistribution of Ar from the deformed rock volumes into the less or not deformed ones, or for a redistribution of Ar at the grain scale. In the Monts du Lyonnais complex, the effects of intense deformation and dynamic crystallization were probably associated with retrograde cooling to control the contrasting behaviour of the two mineral generations. As a regional consequence, these radiometric data imply that complete retrogression of the Monts du Lyonnais complex was achieved 340 Ma ago. The sharp cluster of ages obtained for the amphiboles, muscovites and biotites used in this study suggests relatively rapid cooling (at least 50°C Ma −1) of the complex after attainment of metamorphic conditions associated with the P 3 event. The younger values of 325-315 and 250 Ma produced by K-feldspar and plagioclase, respectively, may reflect that: (1) the metamorphic complex experienced slow cooling (at most 10°C Ma −1) between 325 and 315 Ma ago; and (2) a late, weak thermal event (<200°C) occurred 250 Ma ago.