Van Bemmelen Research Articles

Thrusting of a volcanic arc: a new structural model for Java

ABSTRACT Java is part of a volcanic island arc situated in the Indonesian archipelago at the southern margin of the Eurasian Plate. Sundaland continental crust, accreted to Eurasia by the Early Mesozoic, now underlies the shallow seas to the north of Java where there has been considerable petroleum exploration. Java has an apparently simple structure in which the east–west physiographic zones identified by van Bemmelen broadly correspond to structural zones. In the north there is the margin of the Sunda Shelf and, in southern Java, there are Cenozoic volcanic arc rocks produced by spatially and temporally discrete episodes of subduction-related volcanism. Between the Sunda Shelf and the volcanic rocks are Cenozoic depocentres of different ages containing sedimentary and volcanic material derived from north and south. This simplicity is complicated by structures inherited from the oldest period of subduction identified beneath Java, in the Cretaceous, by extension related to development of the volcanic arcs, by extension related to development of the Makassar Straits, by late Cenozoic contraction, and by cross-arc extensional faults which are active today. Based on field observations in different parts of Java, we suggest that major thrusting in southern Java has been overlooked. The thrusting has displaced some of the Early Cenozoic volcanic arc rocks northwards by 50 km or more. We suggest Java can be separated into three distinct structural sectors that broadly correspond to the regions of West, Central and East Java. Central Java displays the deepest structural levels of a series of north-directed thrusts, and Cretaceous basement is exposed; the overthrust volcanic arc has been largely removed by erosion. In West and East Java the overthrust volcanic arc is still preserved. In West Java the arc is now thrust onto the shelf sequences that formed on the Sundaland continental margin. In East Java the volcanic arc is thrust onto a thick volcanic/sedimentary sequence formed north of the arc in a flexural basin due largely to volcanic arc loading. All the components required for a petroleum system are present. This hypothesis is yet to be tested by seismic studies and drilling, but, if correct, there may be unexplored petroleum systems in south Java that are worth investigating.

De ontwikkelingsgeschiedenis van Rein van Bemmelens (1904-1983) undatietheorie: veertig jaar Nederlandse geologie

The development of Rein van Bemmelens ( 1904 - 1983 ) undation theory: Forty years of Dutch geology The Dutch geologist Rein van Bemmelen was the greatest opponent of plate tectonics in the Netherlands. He lived and worked during an important period in the history of earth sciences. He had studied geology when Wegeners theory was introduced and enthusiastically received in the Netherlands and he worked as a geologists during the period in which, after Wegeners theory was rejected in the Netherlands, several Dutch geologists came with their own theories to explain the origin of continents and oceans and in which plate tectonics was introduced in the Netherlands. He had proposed his own theory, the undation theory, at the beginning of the 1930s and kept on developing it during the following years. He continued to do so until his death in 1983. The history of the undation theory thus sheds light on the history of geology in the Netherlands. I will trace the history of geology in the Netherlands using Rein van Bemmelen and his undation theory as a lense.

The Commonly Used cGMP-dependent Protein Kinase Type I (cGKI) Inhibitor Rp-8-Br-PET-cGMPS Can Activate cGKI in Vitro and in Intact Cells

Small-molecule modulators of cGMP signaling are of interest to basic and clinical research. The cGMP-dependent protein kinase type I (cGKI) is presumably a major mediator of cGMP effects, and the cGMP analogue Rp-8-Br-PET-cGMPS (Rp-PET) (chemical name: beta-phenyl-1,N2-etheno-8-bromoguanosine-3',5'-cyclic monophosphorothioate, Rp-isomer) is currently considered one of the most permeable, selective, and potent cGKI inhibitors available for intact cell studies. Here, we have evaluated the properties of Rp-PET using cGKI-expressing and cGKI-deficient primary vascular smooth muscle cells (VSMCs), purified cGKI isozymes, and an engineered cGMP sensor protein. cGKI activity in intact VSMCs was monitored by cGMP/cGKI-stimulated cell growth and phosphorylation of vasodilator-stimulated phosphoprotein. Unexpectedly, Rp-PET (100 microm) did not efficiently antagonize activation of cGKI by the agonist 8-Br-cGMP (100 microm) in intact VSMCs. Moreover, in the absence of 8-Br-cGMP, Rp-PET (100 microm) stimulated cell growth in a cGKIalpha-dependent manner. Kinase assays with purified cGKI isozymes confirmed the previously reported inhibition of the cGMP-stimulated enzyme by Rp-PET in vitro. However, in the absence of the agonist cGMP, Rp-PET partially activated the cGKIalpha isoform. Experiments with a fluorescence resonance energy transfer-based construct harboring the cGMP binding sites of cGKI suggested that binding of Rp-PET induces a conformational change similar to the agonist cGMP. Together, these findings indicate that Rp-PET is a partial cGKIalpha agonist that under certain conditions stimulates rather than inhibits cGKI activity in vitro and in intact cells. Data obtained with Rp-PET as cGKI inhibitor should be interpreted with caution and not be used as sole evidence to dissect the role of cGKI in signaling processes.

USP10: the nexus between nexin and vasopressin

from the time electrophysiological tools became available to renal physiologists, tissues have been bombarded with a variety of hormones and pharmacological compounds to investigate their role in “salt and water transport.” The investigations into the actions of antidiuretic hormone (ADH) on a

Cadmium Trapping in an Epithelial Sodium Channel Pore Mutant

The putative selectivity filter of the epithelial sodium channel (ENaC) comprises a three-residue sequence G/SXS, but it remains uncertain whether the backbone atoms of this sequence or whether their side chains are lining the pore. It has been reported that the S589C mutation in the selectivity filter of alphaENaC renders the channel sensitive to block by externally applied Cd2+; this was interpreted as evidence for Cd2+ coordination with the thiol group of the side chain of alpha589C, pointing toward the pore lumen. Because the alphaS589C mutation alters the monovalent to divalent cation selectivity ratio of ENaC and because internally applied Cd2+ blocks wild-type ENaC with high affinity, we hypothesized that the inhibition of alphaS589C ENaC by Cd2+ results rather from the coordination of this cation with native cysteine residues located in the internal pore of ENaC. We show here that Cd2+ inhibits not only ENaC alphaS589C and alphaS589D but also alphaS589N mutants and that Ca2+ weakly interacts with the S589D mutant. The block of alphaS589C, -D, and -N mutants is characterized by a slow on-rate, is nearly irreversible, is voltage-dependent, and can be prevented by amiloride. The C546S mutation in the second transmembrane helix of gamma subunit in the background of the ENaC alphaS589C, -D, or -N mutants reduces the sensitivity to block by Cd2+ and renders the block rapidly reversible. We conclude therefore that the block by Cd2+ of the alphaS589C, -D, and -N mutants results from the trapping of Cd2+ ions in the internal pore of the channel and involves Cys-546 in the second transmembrane helix of the gammaENaC subunit.

A Conformation Change in the Extracellular Domain that Accompanies Desensitization of Acid-sensing Ion Channel (ASIC) 3

Acid-sensing ion channels (ASICs) are thought to trigger some forms of acid-induced pain and taste, and to contribute to stroke-induced neural damage. After activation by low extracellular pH, different ASICs undergo desensitization on time scales from 0.1 to 10 s. Consistent with a substantial conformation change, desensitization slows dramatically when temperature drops (Askwith, C.C., C.J. Benson, M.J. Welsh, and P.M. Snyder. 2001. PNAS. 98:6459–6463). The nature of this conformation change is unknown, but two studies showed that desensitization rate is altered by mutations on or near the first transmembrane domain (TM1) (Coric, T., P. Zhang, N. Todorovic, and C.M. Canessa. 2003. J. Biol. Chem. 278:45240–45247; Pfister, Y., I. Gautschi, A.-N. Takeda, M. van Bemmelen, S. Kellenberger, and L. Schild. 2006. J. Biol. Chem. 281:11787–11791). Here we show evidence of a specific conformation change associated with desensitization. When mutated from glutamate to cysteine, residue 79, which is some 20 amino acids extracellular to TM1, can be altered by cysteine-modifying reagents when the channel is closed, but not when it is desensitized; thus, desensitization appears to conceal the residue from the extracellular medium. D78 and E79 are a pair of adjacent acidic amino acids that are highly conserved in ASICs yet absent from epithelial Na+ channels, their acid-insensitive relatives. Despite large effects on desensitization by mutations at positions 78 and 79—including a shift to 10-fold lower proton concentration with the E79A mutant—there are not significant effects on activation.

Invited commentary

The ARCHeR trial represents an important contribution that provides data regarding the safety and efficacy of the Guidant Acculink and Accunet carotid stent and filter systems and also adds to the growing data pool on the results of carotid stenting in high-risk patients. It is important, however, that the limitations of this study be fully understood. The ARCHeR trial is not a prospective, randomized, controlled trial. It is not a comparative trial at all. It is an industry-sponsored, multi-institutional case registry. This registry was developed in order to accumulate a body of data on the performance of the Guidant products with a major goal of gaining Food and Drug Administration approval. It must be noted that the majority of the coauthors of this paper are either Guidant employees or consultants or receive financial support from Guidant. In order to garner Food and Drug Administration approval, the authors needed to show that the results of treatment with their product were not inferior to the results of standard treatment (carotid endarterectomy; CEA). As a basis for comparison, they used historical controls derived from selected series in the literature. By methods that are difficult to understand, they arrived at a control group (CEA) composite adverse event rate of 14.4%, to which they compare their stenting results (composite adverse event rate of 9.6%). Bias in selection of the series used to determine their control group adverse event rate is evident. The control group even included series of patients undergoing simultaneous coronary artery bypass grafting and CEA, a group in which stroke and mortality rates are high and in which the majority of strokes and deaths are not CEA related. In their appendix, the authors cite many series to support their control group adverse event rate, but they omit several series as well. For example, in 2003, Gasparis et al1Gasparis A.P. Ricotta L. Cuadra S.A. Char D.J. Purtrill W.A. Van Bemmelen P.S. et al.High risk carotid endarterectomy fact or fiction?.J Vasc Surg. 2003; 37: 40-46Abstract Full Text Full Text PDF PubMed Scopus (113) Google Scholar reported on 228 high-risk CEA patients.1Gasparis A.P. Ricotta L. Cuadra S.A. Char D.J. Purtrill W.A. Van Bemmelen P.S. et al.High risk carotid endarterectomy fact or fiction?.J Vasc Surg. 2003; 37: 40-46Abstract Full Text Full Text PDF PubMed Scopus (113) Google Scholar Their definition of high risk was at least as stringent as that used by the ARCHeR team (age >80 years, myocardial infarction in the prior 6 months, New York Heart Association class III or IV angina, Canadian Heart Association (CHA) class III or IV congestive heart failure, steroid- or oxygen-dependent chronic obstructive pulmonary disease, creatinine of 3 mg/dl or greater, contralateral occlusion, carotid reoperation, prior neck irradiation, or high lesion). The 30-day results of CEA in these patients included mortality, myocardial infarction, and stroke rates of 0.4%, 0.9%, and 0.9%, respectively, with a combined stroke/death rate of 1.3%. There are other reports of CEA in high-risk patients that call into question the validity of the ARCHeR authors’ control group adverse event rate.2Reed A.B. Gaccione P. Belkin M. Donaldson M.C. Mannick J.A. Whittemore A.D. et al.Preoperative risk factors for carotid endarterectomy defining the patient at high risk.J Vasc Surg. 2003; 37: 1191-1199Abstract Full Text Full Text PDF PubMed Scopus (113) Google Scholar, 3Ouriel K. Hertzer N.R. Beven E.G. O’Hara P.J. Krajewski L.P. Clair D.G. et al.Preprocedural risk stratification identifying an appropriate population for carotid stenting.J Vasc Surg. 2001; 33: 728-732Abstract Full Text Full Text PDF PubMed Scopus (166) Google Scholar Even if the reader discounts the comparative data in this article, the results are interesting. In symptomatic patients, the 30-day stroke, death, and combined stroke/death rates were 10.9%, 2.2%, and 11.6%, respectively. In asymptomatic patients, the rates were 3.8%, 2.0%, and 5.4%. It should be noted that just as in the CEA trials, the results achieved in ARCHeR by experienced carotid interventionalists in large programs may not be reflective of the results likely to be achieved by less highly selected or experienced interventionalists. The data on durability are also notable. Although the target lesion revascularization rate at 1 year was only 2.2%, fully 26% of patients had 50% to 69% restenosis, and 5% had more than 70% restenosis at 1 year. In the relatively small number of patients followed up for 2 and 3 years, the incidence of 50% to 69% and greater than 70% restenosis did not increase. While the ARCHeR trial contains a wealth of data on the results of carotid stenting with the Guidant products, it does not provide a valid assessment of the relative merits of stenting and CEA in the management of high-risk patients. Definitive assessment of the relative merits of stenting and CEA awaits properly designed and conducted prospective randomized controlled trials.

Invited commentary

Carotid endarterectomy (CEA) remains a safe and highly efficacious procedure, even in patients considered to be at high risk by conventional standards.1Gasparis A.P. Ricotta L. Cuadra S.A. Char D.J. Purtill W.A. Van Bemmelen P.S. et al.High-risk carotid endarterectomy fact or fiction.J Vasc Surg. 2003; 37: 40-46Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar, 2Mozes G. Sullivan T.M. Torres-Russotto D.R. Bower T.C. Hoskins T.L. Sampaio S.M. et al.Carotid endarterectomy in SAPPHIRE-eligible high-risk patients implications for selecting patients for carotid endarterectomy.J Vasc Surg. 2004; 39: 958-966Abstract Full Text Full Text PDF PubMed Scopus (158) Google Scholar, 3Miller M.T. Comerota A.J. Tzilinis A. Daoud Y. Hammerling J. Carotid endarterectomy in octogenarians does increased age indicate “high risk”?.J Vasc Surg. 2005; 41: 231-237Abstract Full Text Full Text PDF PubMed Scopus (81) Google Scholar The criteria by which a patient with carotid disease is considered to have “unacceptably” high risk for CEA remain in dispute, especially considering that current standards have largely been set by trials evaluating the safety of carotid angioplasty and stenting. Thus, the present study is a most welcome attempt to clarify patient variables that are associated with mortality in patients undergoing CEA. The authors have applied elegant statistics to analyze the potential association of perioperative death and various comorbidities entered as International Classification of Diseases, 9th Revision (ICD-9) codes. The main strength of the study is the huge dataset that included >20,000 patients from a wide range of practice situations extending over 10 years. In addition to identifying specific risk factors for death, the authors have created a weighted index that is both simple and practical. Although timely and intuitive, the study is not flawless. The authors have acknowledged three limitations that are worth emphasizing: First, they did not include system-level factors that have previously been shown to impact outcome, particularly surgeon and hospital volumes. Fortunately, the authors intend to include these variables in their forthcoming prospective study. A second important limitation is the significant potential for coding bias. An analysis of coding trends by individual hospital would be required to evaluate the possible impact of over- or undercoding. Furthermore, the diligence of individual coders may have had an impact on the frequency of individual codes in this study. A third limitation is the reliance on integer ICD-9 codes rather than extended codes with decimal places. For example, code 331 reflected both cerebral degeneration due to cerebrovascular disease (global ischemia) and Alzheimer’s disease—differences that are clinically important. Likewise, code 280 reflected all iron-deficiency anemias, which may have been a marker for other diseases such as malignancy. Thus, the important risk factors identified in this study may be relatively nonspecific. Despite the inherent limitations, this is a powerful study with immediate practical implications. The information may help to decide between CEA and angioplasty/stenting to treat compelling carotid lesions in individual patients, and these data may be useful in defining patients at high risk in ongoing trials. Until the results of the authors’ prospective analysis are known, the index probably represents the best method currently available for stratifying an individual patient’s risk for CEA.

Chapter 13 Structure and structural history

The present structure of Sumatra is dominated by the effects of the current subduction system in which the Indian Plate is being subducted northeastwards beneath the island at a rate of c. 7 cm a 1 . The structure of Sumatra was described by van Bemmelen (1949) and in terms of plate tectonics by Hamilton (1979). The main structural elements of Sumatra and its surrounding region are defined with respect to the Sumatran subduction system (Fig. 13.1). (1) Forearc region, which includes the subduction trench, part of the Sunda Trench extending from Myanmar to eastern Indonesia, the developing accretionary complex, composed of ocean floor materials scraped off the Indian Plate, the forearc ridge which rises above sea level to form the forearc islands, and the forearc basins which lie between the ridge, and the volcanic arc on the mainland of Sumatra (Fig. 13.2). (2) Barisan Mountains and the Sumatran Fault System. The Barisan Mountains are composed of an uplifted basement of Upper Palaeozoic and Mesozoic sedimentary and volcanic rocks, variously metamorphosed, deformed and intruded by granites, overlain by Cenozoic sediments and volcanics, including the products of the volcanoes related to the present subduction system, which form the currently active volcanic arc. The Sumatran Fault system is a complex of dextral strike-slip faults running the whole length of the island through the centre of the Barisan Mountains from NW to SE, with zones of compression and extension, forming areas of uplift and pull apart basins which form grabens along the line of the

Chapter 12 Metallic mineral deposits

This account concentrates on the the primary metallic mineral deposits and occurrences in Sumatra, in particular the recent discoveries of gold, tin and base metals. The residual and placer deposits are given less emphasis, as no significant discoveries have been made in recent years. The history of mineral exploration and discovery in Indonesia has been reviewed recently by van Leeuwen (1993, 1994), documenting the change in emphasis of mineral-based activities from western to eastern Indonesia since the World War II. These studies bring up-to-date the classic account by van Bemmelen (1949), written when the mineral deposits in western Indonesia, particularly those in Sumatra, were among the better known and prior to 1942, important contributors to the Indonesian economy. The larger mineral deposits in southern Sumatra have been described briefly by Gafoer & Purbo-Hadiwidjoyo (1986), and are referred to in the regional descriptions of the mineral deposits of SE Asia by Hutchison & Taylor (1978) and Hutchison (1996). In wider-ranging reviews the geological setting of gold and base metal deposits in Indonesia have been discussed by Carlile & Mitchell (1994), while those of tin deposits in SE Asia are catalogued by Schwartz et al. (1995). Sumatra has long been known as a source of gold, the name of the island being derived from the Sanscrit word Svarnadvipa , meaning 'Golden Island', dating from the importance of gold deposits to the rulers of the Hindu kingdoms that flourished in Sumatra from the seventh until the eleventh century. The estimated total production of precious

Chapter 8 Tertiary volcanicity

The Centenary of the Netherlands Indies Geological Survey was commemorated by the publication of a synthesis of the geology of Indonesia by van Bemmelen (1949). In his account of the geology of Sumatra van Bemmelen (1949) described three distinct, but continuous, cycles of volcanic activity during the Tertiary and Quaternary: Old Neogene (Late Oligocene-Mid-Miocene); Young Neogene (Mid-Miocene-early in the Quaternary); and Young Quaternary. The first cycle began with the 'Old Andesites', and ended with the Mid-Miocene uplift of the Barisan Mountains. The second cycle commenced with the eruption of basic igneous products and concluded with an acidic phase which coincided with a second episode of uplift of the Barisan Mountains. Subsequently, knowledge of the Tertiary volcanic rocks in Sumatra has been refined as the result of programmes of geological mapping in the early 1970s by the Geological Survey of Indonesia and the United States Geological Survey, and between 1975 and the mid-1990s by the Geological Research and Development Centre, the Directorate of Mineral Resources and the British Geological Survey. Exploration by oil and mineral companies has also provided data concerning the distribution of Tertiary plutonic rocks in the Pre-Tertiary basement and in the Tertiary sedimentary basins, of volcanic units interbedded with sediments. Further contributions to the understanding of Tertiary volcanicity in Sumatra and its forearc islands have been made by academic researchers and post-graduate students from the Institute of Technology, Bandung and the University of London, in collaboration with the Geological Research and Development Centre, LIPI and LEMIGAS, and the

Chapter 9 Quaternary volcanicity

The Quaternary volcanoes along the Sunda and Banda arcs of Indonesia are a well-known example of subduction-related volcanism. Subduction zones are the major sites of crustal recycling on the Earth, and it is the recycling of crustal material into the mantle that contributes to the continuing chemical differentiation of the planet Relatively primitive subduction-related magmas that might be melts of material beneath the volcanic arc, unmodified by postmelting processes, are rare, so that much attention has been dedicated in the last two decades to the study of the isotopic systematics of the most mafic volcanics as a means of identifying their source materials. These suggest that sediments-or fluids derived from the sediments-subducted along the Sunda Trench might have an effect on the composition of the Sunda-Banda arc volcanics. Gasparon & Varne (1998), however, argued that the isotopic signature of mafic volcanics in some sectors of the arc resembles that of Indian Ocean basalts, and that along-arc variations in magma types cannot be accounted for by crustal contamination in the mantle source. Indeed, Gasparon & Varne (1995, 1998) suggested that late-stage (post-melt generation) crustal contamination is the main process responsible for the wide array of volcanics in the Quaternary Sunda arc. The first detailed and comprehensive synthesis of the geology of Indonesia was published by van Bemmelen (1949), and an IAVCEI cataloque of the active volcanoes followed in 1951, compiled by Neumann van Padang (1951). This was later revised and updated by Kusumadinata (1979). These two fundamental publications, rich in information

About this title

This volume provides the first comprehensive account of the geology of Sumatra since the masterly synthesis of van Bemmelen (1949). Following the establishment of Geological Survey of Indonesia, after WW II, the whole island has been mapped geologically at the reconnaissance level, with the collaboration of geological surveys of the United States and the United Kingdom. The mapping programme, completed in the mid-1990s, together with supplementary data obtained by academic institutions and petroleum and mineral exploration companies, has resulted in a vast increase in geological information, which is summarized in this volume. The synthesis of structural controls on sedimentation and magmatism during the evolution of Sumatra since the late Paleozoic has provided a background for the formation of economic deposits of metallic minerals, coal, oil and gas. The volume provides a sound basis for future geological research and for the exploration of the energy and mineral resources of the island.

Invited Commentary

Invited Commentary

Permian corals of Timor (Rugosa and Tabulate): history of collection and study

The modern history of collection and study of corals in the Permian strata of Timor began in 1911,with a German expedition (J.Wanner, leader) and a Dutch expedition (H. Molengraaff, leader) to collect Permian and Triassic fossils in the colony of Netherlands Timor, and with a survey by the Swiss geologist F. Weber the same year in Portuguese Timor, the eastern portion of the island. Later expeditions led by Jonker (1916) and Brouwer (1937), both of the Netherlands, greatly increased already huge collections of fossils and additionally, understanding of the island's geology. Monographic studies of these coral collections by Gerth (1921), Koker (1924), Schindewolf (1942), Hehenwarter (1951) and Schouppé & Stacul (1955, 1959) have much enhanced the systematic value of these fossil corals, both Rugosa and Tabulata. Locality information and maps containing collecting localities are somewhat scattered (Wanner 1931, Burck 1923, Marez Oyens 1940, Van Bemmelen 1949), but are summarized here. A list of all valid species names(109 Rugosa, 25 Tabulata) is appended to this paper, with type localities and horizon. Serious problems of nomenclature are avoided in this paper by accepting genus names used in Hill (1981), modified by later systematic studies, such as that of Fedorowski (1986), but some unknown number of names in the list of species are to be synonymized, especially since 31 of them are based on a single specimen (e.g. Niermann 1975). The biostratigraphy of these faunas is uncertain, in great part due to the greatest number of corals having been collected from a tectonic mélange sequence in the Baun to Basleo structural region, and additionally because of the purchase of huge numbers of fossils from the indigenous people of Timor, with accompanying uncertainties regarding locality and horizon data. The coral fauna of Permian age from Timor needs serious restudy to insure its stratigraphic and palaeontologic value, but future study will require new field collection of specimens from the relatively complete stratigraphic sequences in the northern ‘Fatu’ belt of outcrops. The huge numbers of individuals of some coral species provide great opportunities for understanding population structure in these faunas.

Gravitational collapse of the continental crust: definition, regimes and modes

[Ann. Soc. Geol. Belge Bull. 64 (1965) 95–123] The concept of gravitational collapse has fundamentally improved our understanding of orogenic processes. This concept has its roots in pioneers' works, such as those of Jeffreys, van Bemmelen, Bucher and Ramberg, who were among the first to recognise the importance of gravity in the evolution of mountain belts. The development of this concept slowed down during the late 1960s and the 1970s before reemerging in the 1980s. Gravitational collapse corresponds to the decay of lateral contrast in gravitational potential energy that builds up during lithospheric deformation. When the forces that support this anomaly (i.e., tectonic forces and the strength of both the deformed and surrounding lithosphere) decrease, the gravitational potential anomaly may relax. Depending on the sign of the anomaly, two fundamental regimes of gravitational collapse can be defined. During divergent gravitational collapse, an excess in gravitational potential energy drives crustal material away from the deformed lithosphere. Divergent collapse is the regime that may affect the thickened crust. In contrast, during convergent gravitational collapse, a deficit in gravitational potential energy drives crustal material towards the deformed lithosphere. This regime can be expected to occur following thinning of the continental crust. For each regime, two end-member modes of collapse with contrasted characteristics are defined depending on the behaviour of the lithosphere surrounding the deformed domain. When the surrounding lithosphere is fixed (fixed-boundary collapse), collapse occurs through a transfer of gravitational potential energy from the elevated regions towards the low lands. This transfer is accommodated by a combination of gravitational sliding of the brittle crust and horizontal spread of the lower crust. In orogenic domains, fixed-boundary divergent collapse implies the lateral growth of the orogenic domain at the expense of the surrounding lithosphere. In contrast, when the surrounding lithosphere is free to move (free-boundary divergent collapse), the thickened crust is homogeneously thinned without transfer of gravitational potential energy towards the forelands.

The Plio–Quaternary Ambon arc, Eastern Indonesia

Plio–Quaternary lavas and granites have been collected from Ambon, Seram, Kelang, Haruku, Saparua, Ambelau and Banda Api islands, Eastern Indonesia. They include low-K calc-alkaline basalts, andesites, dacites and rhyolites and high-K calc-alkaline andesites, dacites, rhyolites and granites. All these rocks present the usual chemical characteristics of island-arc magmas. The high-K suite of Ambon is mostly represented by cordierite-bearing dacites (known as ambonites) and granites. Low-K and high-K magmas were emplaced in neighbouring islands or even in the same island (Ambon), often concomitantly, during two magmatic pulses at 5–3.2 Ma and 2.3–1 Ma, respectively. We propose that the low-K suite results from the evolution of basaltic magmas derived from mantle melting above the Western Irian Jaya plate which subducts along the Seram trough. Intermediate and acidic rocks of the high-K suite (e.g. ambonites) are thought to derive from low-K mafic magmas through massive assimilation of the Seram–Ambon continental crust, as originally proposed by Van Bemmelen in 1949. The timing of magmatic events and the geochemical features of the studied lavas are clearly different from those of the southern part of the Banda arc, in which the low-K suite is lacking. In agreement with earlier seismic evidence for two different slabs subducting beneath the Seram–Ambon continental block and beneath the southern Banda arc (from Wetar to Manuk), respectively, we propose to recognise a new Plio–Quaternary island arc, i.e. the Ambon arc, extending west–east from Ambelau to the Banda Archipelago active low-K volcanoes through Kelang, southwestern Seram, Ambon, Haruku and Saparua.

Petrogenesis of the Toba Tuffs, Sumatra, Indonesia

During the past 1.2 my, at least 3400 km3 of magma have been erupted in four ash flow tuff units from the Toba Caldera Complex. This activity culminated at 74 ka with the fourth eruption, which produced 2800 km3 of magma and formed the 100 km × 30 km caldera visible today. A relatively homogeneous two-pyroxene dacite was erupted during the first phase of activity. Magma erupted during each successive eruption was compositionally zoned, generally ranging from rhyodacite to rhyolite. The youngest three tuff deposits contain up to 40 wt % crystals of quartz, sanidine, plagioclase, biotite, and amphibole. Minor minerals are magnetite, ilmenite, allanite, zircon, fayalite, and orthopyroxene; inclusions of apatite and pyrrhotite are common. Extensive fractional crystallization in double-diffusive convecting magma bodies is suggested for creation of the compositional variation. Although similar in composition and mineralogy, the tuffs can be distinguished by subtle variations in their mineral, whole-rock, and glass compositions. Intensive parameter determinations suggest that much of the crystallization of the quartz-bearing tuffs occurred between 700 and 760°C at depths of 10 km. Water pressure estimates indicate that Ptot > PH2O; thus volatile oversaturation probably did not initiate the eruptions. Individual pumice blocks and fiamme collected from the youngest three units record simultaneous eruption across compositional boundaries. Low-energy ring fracture eruptions resulted in dense welding of all units except for the top of the youngest unit, and thick accumulations of rhyodacitic magma in the collapsing calderas.

Adsorption and desorption kinetics of diflubenzuron and fenitrothion in two different boreal forest soils

Adsorption and desorption of two insecticides, diflubenzuron (DFB) and fenitrothion (FEN), were studied by batch equilibrium method under laboratory conditions (pH 5.5, 20°C), using an organic soil (soil 1) and a silty clay loam soil (soil 2), collected from a boreal forest in northern Ontario, Canada. Adsorption parameters were calculated using the linear, Freundlich and Langmuir equations. Maximum amount adsorbed and the time required for maximum adsorption of DFB were 88 μg/g and 18 h (soil 1), and 73 μg/g and 24 h (soil 2), respectively. Corresponding values for FEN were 92 μg/g (soil 1) and 81 μg/g (soil 2), and maximum adsorption time for both soils was 30 h. DFB was more strongly adsorbed to both soils compared to FEN, however between the two soils, soil 1 showed stronger affinity for the chemicals than soil 2. The KD, KF and n values corroborated these findings. The Langmuir model showed deviation, probably due to heterogeneity of the soil surface and multi‐layer adsorption. Desorption studies showed, after six consecutive washes, that the adsorbed DFB was firmly retained by the soil matrix and only about 16 to 27% was desorbed. However, the desorption of FEN in the soils, under similar conditions, was higher and ranged from 38 to 49%. The soil parameters, KOC and KOM, were determined using the KD and the measured %OC (organic carbon) and %OM (organic matter) values. Moreover, KOC was calculated (KOC(calc)), using the KOM and the van Bemmelen factor. Reasonably good agreement was found between the measured KOC and the KOC(calc) value. Combining the average values of Koc and T1/2 (half‐life in soil), the groundwater ubiquity score (GUS) was computed to estimate the mobility of these two insecticides in the forest soil. The GUS values indicated that both insecticides could be considered as non‐leachers.

Duplex Doppler ultrasonography was accurate in determining 60% or greater carotid artery stenosis

DiagnosisMay 1, 1996Duplex Doppler ultrasonography was accurate in determining 60% or greater carotid artery stenosisGregory L. Moneta, MDGregory L. Moneta, MDOregon Health Sciences University, Portland, Oregon, USA (G.L.M.)Search for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/ACPJC-1996-124-3-075 SectionsAboutFull Text ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinkedInRedditEmail Source CitationCarpenter JP, Lexa FJ, Davis JT. Determination of sixty percent or greater carotid artery stenosis by duplex Doppler ultrasonography. J Vasc Surg. 1995 Dec;22:697-705. https://pubmed.ncbi.nlm.nih.gov/8523604References1 Moneta GL, Edwards JM, Chitwood RW, et al. Correlation of North American Symptomatic Carotid Endarterectomy Trial (NASCET) angiographic definition of 70% to 99% internal carotid artery stenosis with duplex scanning. J Vasc Surg. 1993;17:152-9. Google Scholar2 Faught WE, Mattos MA, van Bemmelen PS, et al. Color-flow duplex scanning of carotid arteries: new velocity criteria based on receiver operator characteristic analysis for threshold stenoses used in the symptomatic and asymptomatic carotid trials. J Vasc Surg. 1994;19:818-28. Google Scholar3 Moneta GL, Edwards JM, Papanicolaou G, et al. Screening for asymptomatic internal carotid artery stenosis: duplex criteria for discriminating 60% to 99% stenosis. J Vasc Surg. 1995:21:989-94. Google Scholar4 Moore WS, Ziomek S, Quinones-Baldrich WJ, et al. Can clinical evaluation and noninvasive testing substitute for arteriography in the evaluation of carotid artery disease? Ann Surg. 1988;208:91-94. Google Scholar5 Daigle RJ, Stavros AT, Lee RM. J Vasc Tech. 1990;14:206-13. Google Scholar Author, Article, and Disclosure InformationAffiliations: Oregon Health Sciences University, Portland, Oregon, USA (G.L.M.) PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetails May 1, 1996Volume 124, Issue 3Page: 75KeywordsAngiographyAtherosclerosisCarotid arteriesCarotid endarterectomyCommon carotid arteriesMorbidityQuality improvementSpecificityStenosisStrokeUltrasound imaging ePublished: 9 March 2020 Issue Published: May 1, 1996 Copyright & PermissionsCopyright © 1996 by American College of Physicians. All Rights Reserved.Loading ...