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Ca/Sr and 87Sr/86Sr geochemistry of disseminated calcite in Himalayan silicate rocks from Nanga Parbat: Influence on river-water chemistry

2000; Geological Society of America; Volume: 28; Issue: 5 Linguagem: Inglês

10.1130/0091-7613(2000)28 2.0.co;2

1943-2682

Andrew D. Jacobson, Joel D. Blum,

Geological and Geochemical Analysis

Research Article| May 01, 2000 Ca/Sr and 87Sr/86Sr geochemistry of disseminated calcite in Himalayan silicate rocks from Nanga Parbat: Influence on river-water chemistry Andrew D. Jacobson; Andrew D. Jacobson 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Search for other works by this author on: GSW Google Scholar Joel D. Blum Joel D. Blum 1Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA Search for other works by this author on: GSW Google Scholar Geology (2000) 28 (5): 463–466. https://doi.org/10.1130/0091-7613(2000)28 2.0.CO;2 Article history received: 30 Nov 1999 rev-recd: 22 Feb 2000 accepted: 29 Feb 2000 first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Andrew D. Jacobson, Joel D. Blum; Ca/Sr and 87Sr/86Sr geochemistry of disseminated calcite in Himalayan silicate rocks from Nanga Parbat: Influence on river-water chemistry. Geology 2000;; 28 (5): 463–466. doi: https://doi.org/10.1130/0091-7613(2000)28 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 SocietyGeology Search Advanced Search Abstract Trace amounts of disseminated calcite were identified in gneiss, schist, and granite bedrock sampled from the Raikhot watershed and other locations within the Nanga Parbat massif of northern Pakistan. The calcite grains occur interstitially within individual silicate minerals, at grain boundaries, and as fracture fillings that transect the mineralogic fabric of the rock. Disseminated calcite composes is ≤ 0.29 wt% of silicate rocks sampled in the Raikhot watershed and has Ca/Sr (µmol/nmol) and 87Sr/86Sr ratios that range from 0.878 to 5.33 and from 0.794 039 to 0.930 619, respectively. Elsewhere in the Nanga Parbat region, disseminated calcite composes ≤ 3.6 wt% of the silicate rock samples and has Ca/Sr (µmol/nmol) and 87Sr/86Sr ratios that range from 0.535 to 3.33 and from 0.715 757 to 0.771 244, respectively. For all samples, the 87Sr/86Sr ratios of disseminated calcite are similar to the 87Sr/86Sr ratios measured in the silicate host rock. Within the partially glaciated Raikhot watershed, the rapid weathering of disseminated calcite with high Ca/Sr and 87Sr/86Sr ratios has a strong influence on the chemical composition of stream water and exceeds contributions from silicate mineral dissolution. Comparisons of disseminated calcite compositions with source-water chemistry throughout the Himalaya suggest that disseminated calcite may be a more important component of Himalayan silicate rocks than previously recognized. Therefore, calculations relating the Sr isotope geochemistry of Himalayan rivers to atmospheric CO2 consumption should consider this widespread and compositionally variable carbonate end member. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.