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Research Article| January 01, 1971 Precambrian Rocks of the Lake Hopatcong Area, New Jersey DAVIS A YOUNG DAVIS A YOUNG Department of Geology, Washington Square College of Arts and Science, New York University, New York, New York 10003 Search for other works by this author on: GSW Google Scholar Author and Article Information DAVIS A YOUNG Department of Geology, Washington Square College of Arts and Science, New York University, New York, New York 10003 Publisher: Geological Society of America Received: 22 Jun 1970 Revision Received: 18 Aug 1970 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1971, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1971) 82 (1): 143–158. https://doi.org/10.1130/0016-7606(1971)82[143:PROTLH]2.0.CO;2 Article history Received: 22 Jun 1970 Revision Received: 18 Aug 1970 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation DAVIS A YOUNG; Precambrian Rocks of the Lake Hopatcong Area, New Jersey. GSA Bulletin 1971;; 82 (1): 143–158. doi: https://doi.org/10.1130/0016-7606(1971)82[143:PROTLH]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Precambrian rocks near Lake Hopatcong, New Jersey, form a part of the intensely deformed and metamorphosed Reading Prong. The Lake Hopatcong area is divisible into several northeast-trending fault blocks, each of which contains a mappable stratigraphic sequence of paragneisses and granitic or syenitic rocks.The paragneisses generally are well foliated and well layered. They consist chiefly of biotite-feldspar-quartz gneisses and quartz-oligoclase leucogneisses that are interpreted as metamorphosed potassium-rich sandstones and quartz keratophyres, respectively. A thin well-foliated unit of biotite-plagioclase gneiss is thought to be a metamorphosed sill of gabbroic anorthosite.The granitic and syenitic rocks generally form thick, regionally concordant sheets. They are typically foliated and are composed chiefly of microcline microperthite and plagioclase (or mesoperthite), quartz, and iron-rich hornblende and clinopyroxene. These foliated granitic and syenitic rocks are viewed as syntectonic magmatic intrusives. One regionally discordant, unfoliated sheet of clinopyroxene quartz syenite is probably a late tectonic magmatic intrusive.Mineral assemblages in Lake Hopatcong paragneisses may be assigned to the hornblende granulite subfacies of metamorphism. The presence of Ca-bearing mesoperthite in biotite-feldspar-quartz gneiss indicates that metamorphic temperatures exceeded 700° C, and the assemblage garnet-sillimanite-quartz without cordierite indicates that load pressure was greater than 2.5 kb. The rocks have thus probably been buried to depths in excess of 10 km. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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Abstract Lead isotopic compositions were determined for sulphides from Pliocene-Pleistocene gold-bearing veins in the Alpine Schist and from Miocene gold-bearing veins and vein breccias from the Shotover-Macetown area in the northwest Otago Schist belt. The lead isotopic signatures are consistent with derivation of Pb in the vein minerals predominantly from metasedimentary rocks that underlie the region. Differences in Pb isotopic signatures between deposits are interpreted to result from lateral and vertical lithological variability within the source rock mass. The host rocks also contain metabasic rocks with N-MORB, E-MORB or within-plate basalt chemistry. However, the observed Pb isotopic signatures in the gold-bearing veins preclude incorporation of significant amounts of Pb from the metabasites. The Pb isotopic signatures of lamprophyre dikes that were intruded into the Otago Schist coeval with Miocene gold mineralisation are distinctly more radiogenic than those of the hydrothermal veins. Thus, although the lamprophyre dikes were emplaced into similar extensional structural sites to the gold-bearing veins, there was no genetic relationship between lamprophyre dikes and gold mineralisation.
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During the last 10 m.y., the Nanga Parbat Haramosh Massif in the northwestern Himalaya has been intruded by granitic magmas, has undergone high‐grade metamorphism and anatexis, and has been rapidly uplifted and denuded. As part of an ongoing project to understand the relationship between tectonism and petrologic processes, we have undertaken an isotopic study of the massif to determine the importance of hydrothermal activity during this recent metamorphism. Our studies show that both meteoric and magmatic hydrothermal systems have been active over the last 10 m.y. We suggest that the rapid uplift of the massif created a dual hydrothermal system, consisting of a near‐surface flow system dominated by meteoric water and a flow regime at deeper levels dominated by magmatic/metamorphic volatiles. Meteoric fluids derived from glaciers near the summit of Nanga Parbat were driven deep into the massif along the transpressional faults causing δ 18 O and δD depletions in the gneisses and marked oxygen isotopic disequilibrium between mineral pairs from the fault zones. The discharge of these meteoric fluids occurs in active hot springs that are found along the steep faults that border the massif. At deeper levels within the massif, infiltration of low δ 18 O magmatic fluids caused δ 18 O depletions in the gneisses within the migmatite zone. These low δ 18 O fluids were derived from the young (<4 Ma), relatively low δ 18 O granites (∼8‰c) that are found within the core of the massif. Geochronological evidence in the form of fission track and 40 Ar/ 39 Ar cooling ages and U/Pb ages on accessory minerals from the granites and gneisses provide a constraint on the timing of fluid flow in the surface outcrops we examined. Fluid infiltration in the migmatite zone rocks located along the Tato traverse was coeval with metamorphism, granite emplacement, and rapid denudation, in the interval 0.8–3.3 Ma. Finally, we infer from the presence of active hot springs that significant flow systems continue to be active at depth within the central portion of the Nanga Parbat‐Haramosh Massif.
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